Sunday, June 16, 2013

Alleviation of genotoxic effects of cyclophosphamide using encapsulation into liposomes in the absence or presence of vitamin C.


 2012 Mar;31(1):85-91. doi: 10.4149/gpb_2012_009.


Cyclophosphamide (CP) is a widely used anticancer and immunosuppressant that induces oxidative stress. To ameliorate the side effects resulted from CP treatment, liposomes were tested as an efficient drug delivery system with or without vitamin C as an antioxidant. CP resulted in clastogenic and cytotoxic effects that significantly increased for the total chromosomal aberrations as well as the numerical ones in the CP group (150.8 and 6, respectively) than the control group (6.6 and 0.0) as mean values at p < 0.05. Micronucleus assay showed a significant increased micronucleated polychromatic erythrocytes percentage (MNPCEs% = 11.7%) and a significant decrease of polychromatic to normochromatic erythrocytes ratio (0.551) when compared to the group treated with liposomised CP and vitamin C (3.44%; 0.795, respectively) at p < 0.05. Also, the total glutathione S-transferase activity as a body antioxidant enzyme was decreased from 52.2 in the control to 16.09 nmol/min/mg protein in CP group at p < 0.05, while the highly significant amelioration results were observed in the liposomised vitamin C and CP group (40.88 nmol/min/mg protein). Our findings support the potential use of CP in a liposomal formulation doped with vitamin C to diminish the potential side effects of the agent.

Thermally induced conformational changes in horseradish peroxidase

David G. Pina1 et al.
Eur. J. Biochem. 268, 120-126 (2001), FEBS 2001

REACTIVE OXYGEN SPECIES: Metabolism, Oxidative Stress, and Signal Transduction

Klaus Apel and Heribert Hirt

Annu. Rev. Plant Biol. 2004. 55:373–99

Several reactive oxygen species (ROS) are continuously produced in plants as byproducts of aerobic metabolism. Depending on the nature of the ROS species, some are highly toxic and rapidly detoxified by various cellular enzymatic and nonenzymatic mechanisms. Whereas plants are surfeited with mechanisms to combat increased ROS levels during abiotic stress conditions, in other circumstances plants appear to purposefully generate ROS as signaling molecules to control various processes including pathogen defense, programmed cell death, and stomatal behavior. This review describes the mechanisms of ROS generation and removal in plants during development and under biotic and abiotic stress conditions. New insights into the complexity and roles that ROS play in plants have come from genetic analyses of ROS detoxifying and signaling mutants. Considering recent ROS-induced genomewide expression analyses, the possible functions and mechanisms for ROS sensing and signaling in plants are compared with those in animals and yeast.

Free radicals and antioxidants in normal physiological functions and human disease

Marian Valko, Dieter Leibfritz, Jan Moncol, Mark T.D. Cronin, Milan Mazur, Joshua Telser

The International Journal of Biochemistry & Cell Biology 39 (2007) 44–84

Reactive oxygen species (ROS) and reactive nitrogen species (RNS, e.g. nitric oxide, NO•) are well recognised for playing a dual role as both deleterious and beneficial species. ROS and RNS are normally generated by tightly regulated enzymes, such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. Overproduction of ROS (arising either from mitochondrial electron transport chain or excessive stimulation of NAD(P)H) results in oxidative stress, a deleterious process that can be an important mediator of damage to cell structures, including lipids and membranes, proteins, andDNA. In contrast, beneficial effects ofROS/RNS (e.g. superoxide radical and nitric oxide) occur at low/moderate concentrations and involve physiological roles in cellular responses to noxia, as for example in defence against infectious agents, in the function of a number of cellular signalling pathways, and the induction of a mitogenic response. Ironically, various ROS-mediated actions in fact protect cells against ROS-induced oxidative stress and re-establish or maintain “redox balance” termed also “redox homeostasis”. The “two-faced” character of ROS is clearly substantiated. For example, a growing body of evidence shows that ROS within cells act as secondary messengers in intracellular signalling cascades which induce and maintain the oncogenic phenotype of cancer cells, however, ROS can also induce cellular senescence and apoptosis and can therefore function as anti-tumourigenic species. This review will describe the: (i) chemistry and biochemistry of ROS/RNS and sources of free radical generation; (ii) damage to DNA, to proteins, and to lipids by free radicals; (iii) role of antioxidants (e.g. glutathione) in the maintenance of cellular “redox homeostasis”; (iv) overview of ROS-induced signaling pathways; (v) role of ROS in redox regulation of normal physiological functions, as well as (vi) role of ROS in pathophysiological implications of altered redox regulation (human diseases and ageing). Attention is focussed on the ROS/RNS-linked pathogenesis of cancer, cardiovascular disease, atherosclerosis, hypertension, ischemia/reperfusion injury, diabetes mellitus, neurodegenerative diseases (Alzheimer’s disease and Parkinson’s disease), rheumatoid arthritis, and ageing. Topics of current debate are also reviewed such as the question whether excessive formation of free radicals is a primary cause or a downstream consequence of tissue injury.

Lipopolysaccharide Identification with Functionalized Polydiacetylene Liposome Sensors

Marianne Rangin and Amit Basu
J. AM. CHEM. SOC. 2004, 126, 5038-50


Tuesday, June 4, 2013

Polydiacetylene Liposome Microarray Toward Influenza A Virus Detection: Effect of Target Size on Turn-On Signaling

  1. Sungbaek Seo1
  2. Jiseok Lee1
  3. Eun-Jin Choi2
  4. Eun-Ju Kim2
  5. Jae-Young Song2,
  6. Jinsang Kim3,*
Volume 34Issue 9pages 743–748May 14, 2013


Target size effect on the sensory signaling intensity of polydiacetylene (PDA) liposome microarrays was systematically investigated. Influenza A virus M1 peptide and M1 antibody were selected as a probe–target pair. While red fluorescence from the PDA liposome microarrays was observed when the larger M1 antibody was used as a target, when the same M1 antibody was used as a probe to detect the smaller M1 peptide sensory signal did not appear. The results reveal that the intensity of the PDA sensory signal is mainly related to the steric repulsion between probe–target complexes not the strength of the probe–target binding force. Based on this finding, we devised a PDA sensory system that directly detects influenza A whole virus as a larger target, and confirmed the target size effect on the signaling efficiency of PDA.

A Light-Actuated Nanovalve Derived from a Channel Protein

Armagan Kocer, Martin Walko, Wim Meijberg, Ben L. Feringa

29 JULY 2005 VOL 309 SCIENCE, pp.755

Toward the realization of nanoscale device control, we report a molecular valve embedded in a membrane that can be opened by illumination with longwavelength ultraviolet (366 nanometers) light and then resealed by visible irradiation. The valve consists of a channel protein, the mechanosensitive channel of large conductance (MscL) from Escherichia coli, modified by attachment of synthetic compounds that undergo light-induced charge separation to reversibly open and close a 3-nanometer pore. The system is compatible with a classical encapsulation system, the liposome, and external photochemical control over transport through the channel is achieved.

Sunday, June 2, 2013

Shape and Size of a Nonionic Surfactant Micelle. Triton X-100 in Aqueous Solution

H. Hasko Paradies

J. Phys. Chem. 1980, 84, 599-607

Phase Separation of Polymerized Mixed Liposomes: Analysis of Release Behavior of Entrapped Molecules with Skeletonization

Shinji Takeoka, Hiromi Sakai, Hiroyuki Ohno,+ and Eishun Tsuchida'

Macromolecules 1991,24, 1279-1283

The mixed liposomes, composed of a polymerizable lipid, 1,2-bis(2,4-octadecadienoyl)-snglycero-3-phosphorylcholine(D ODPC), and nonpolymerizable membrane constituents, DPPC, cholesterol, and sodium didodecyl phosphate, were prepared by an extrusion method. After polymerization, onpolymerizable constituents were removed to obtain the polymerized framework of the liposome (the skeletonized liposome). The release of small molecules from the skeletonized liposomes through resulting holes was analyzed. A 5(6)-carboxyfluorescein (CF) and saccharides with various molecular weights were applied as release molecules. The molecular weight of dextran, whose retention ratio in the skeletonized liposomes is 5096, relates to the apparent size of the holes, i.e., the apparent domain size of the phase separation of a polymerized mixed liposome. The size of the holes increases with an increase in the mole fraction of nonpolymerizable lipids. This also depends on the polymerization temperature and the structure of nonpolymerizable lipids.

Thermodynamics of micelle formation and surface chemical behavior of p-tert-Octylphenoxyethylene Ether (TritonX-100) in Aqueous Medium

J. Surface Sci. Technol., Vol 17, no.1-2, pp.1-15, 2001

LIPOSOMES OF CONTROLLABLE SIZE IN THE RANGE OF 40 TO 180 nm BY DEFINED DIALYSIS OF LIPID/DETERGENT MIXED MICELLES

OTMAR ZUMBUEHL and HANS GEORG WEDER

Biochimica et Biophysica Acta, 640 (1981) 252-262

Liposomes, in the size range of 40--180 nm, are formed when lipid and additives are solubllized with detergent, yielding defined mixed micelles, and the detergent is subsequently removed by controlled dialysis. Their most important properties are that they are indeed unilamellar with usefully large encapsulated volumes and are homogeneous in size. Liposomes have been formed from both natural and synthetic phospholipids with cholesterol and charged molecules added. This relatively simple technique may be particularly useful for encapsulating drugs, enzymes and other macromolecules and in studies of reconstitution of membrane proteins.

Saturday, May 25, 2013

Direct formation of mixed micelles in the solubilization of phospholipid liposomes by Triton X-100

FEBS Letters 426 (1998) 314-318

The vesicle to micelle transition which results in the interaction of the Triton X-100 surfactant with phosphatidylcholine vesicles was studied by means of dynamic light scattering (at different reading angles) and by freeze-fracture electron microscopy techniques. Vesicle solubilization was produced by the direct formation of mixed micelles without the formation of complex intermediate aggregates. Thus, vesicle to micelle transformation was mainly governed by the progressive formation of mixed micelles within the bilayer. A subsequent separation of these micelles from the liposome surface (vesicle perforation by the formation of surfactant-stabilized holes on the vesicle surface) led to a complete solubilization of liposomes.

Temperature Dependence of Triton X-100 Micelle Size and Hydration

Kiril Streletzky and George D. J. Phillies
Langmuir 1996,11, 42-47

Quasi-elastic light scattering spectroscopy was used to measure the mutual diffusion coefficient, D of Triton X-100 micelles in aqueous solution and the translational diffusion coefficient, D, of mesoscopic probes in the same solutions. We apply conventional hydrodynamic treatments of diffision under the assumption that Triton X-100 minimal micelles are adequately represented as hard spheres. Dm and D, measured at a series of surfactant concentrations are used to infer the micelle radius, am, aggregation number, N, and degree of hydration, 6, for temperatures 10 5 T 5 50 "C. As T is increased toward the cloud point, am and N increase, the increase in N being especially dramatic above 40 "C, 6 at first increases but then tends to saturate with increasing T.

The Size, Shape, and Hydration of Nonionic Surfactant Micelles. Triton X-100

Robert J. Robson and Edward A. Dennis
The Journal of Physical Chemistry, Vol. 81, No. 11, 1977

Calculations of the size, shape, and hydration of micelles composed of the nonionic surfactant Triton X-100 were performed based on molecular weight and intrinsic viscosity data. Geometrical considerations show that if the hydrophobic core as well as the whole micelle is spherical, then its structure cannot contain the distinctpolar and apolar regions that are classically assumed for micelles. On the other hand, ellipsoids of revolution would be consistent with a classical micellar structure and an oblate rather than a prolate ellipsoid would be most consistent with intrinsic viscosity measurements and volume calculations.

Thermodynamic and Structural Studies of Triton X-100 Micelles in Ethylene Glycol-Water Mixed Solvents

C. Carnero Ruiz, J. A. Molina-Bolfvar, and J. Aguiar
Langmuir 2001, 17, 6831-6840

Micellar properties of p-tert-octyl-phenoxy (9.5) polyethylene ether (Triton X-100) in aqueous mixtures of ethylene glycol (EG) were determined using such techniques as surface tension, static and dynamic light scattering, and fluorescence spectroscopy. Thermodynamics of micellization was obtained from the temperature dependence of critical micelle concentration values. The differences in the Gibbs energies of micellization of Triton X-100 between water and binary solvent systems were calculated to evaluate the influence of cosolvent on the micellization process. From this study, it can be concluded that the structurebreaking ability of EG and its interaction with the oxyethylene groups of the surfactant are dominating factors in the micellization process. Thermodynamics of adsorption of the solution-air interface was also evaluated. It was found that the surface activity of the surfactant decreases slightly with increasing concentration of EG at a given temperature. By a combination of static and dynamic light scattering measurements, a reduction of the micelle size was observed, mainly due to a decrease of the micellar aggregation number, whereas the micellar solvation was not substantially modified in magnitude with EG addition. However, the change of the surface area per headgroup of the surfactant suggested an alteration in the nature of its solvation layer, produced probably by a certain participation of cosolvent in the micellar solvation layer. This point was corroborated from the fluorescence polarization studies of several luminescent probes, including coumarin 6, merocyanine 540, and rhodamine B. These experiments revealed a slight increase of the micellar microviscosity. Finally, the proposed mechanism was also supported by the increase observed in the cloud point of Triton X-100, induced by the EG addition.

Friday, May 17, 2013

Protection and Promotion of UV Radiation-Induced Liposome Leakage via DNA-Directed Assembly with Gold Nanoparticles

Neeshma Dave and Juewen Liu

Adv. Mater. 2011, 23, 3182–3186

Mind over myocardium

Shailaja Neelakantan
S16 | NATURE | VOL 493 | 31 JANUARY 2013
Mental factors beyond stress trigger physiological changes that can cause heart disease.

A Promising Drug Controlled-Release System Based on Diacetylene/ Phospholipid Polymerized Vesicles

Caixin Guo, Shaoqin Liu, Chang Jiang, Wenyuan Li, and Zhifei Dai
Langmuir 2009, 25(22), 13114–13119


A novel polymerized vesicular carrier loaded with paclitaxel was developed by introducing the ultraviolet (UV) crosslinkable 10,12-pentacosadiynoic acid (PCDA) into bilayered phospholipid vesicles with the purpose of improving the physicochemical stability as well as the controlled-release property of liposomes. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) results revealed the enhanced stability of PCDA-polymerized vesicles against Triton X-100. In particular, alteration in PCDA/phospholipids ratios and UV-irradiation time can modulate the cumulative paclitaxel released. For instance, vesicles composed of phospholipids only released 98.0(2.1% of paclitaxel within 24 h. Over the same time period, 72.0 ( 5.8%, 43.9 ( 6.5%, and 20.1 ( 5.4% of paclitaxel was released from polymerized PCDA/phospholipid vesicles at molar ratios of 1:3, 1:1, and 3:1, respectively. Likewise, by increasing the UV-irradiation time from 20 to 40 min, the cumulative release of paclitaxel from polymerized  CDA/phospholipid vesicles at molar ratio of 1:1 decreased from 90.5 ( 3.7% to 37.6 ( 2.3% over a time period of experimental observation of 24 h. The influences of vesicle composition (i.e., PCDA/phospholipids ratio) and UV-irradiation time on the release rates of paclitaxel were further examined by finite element (FE) analyzed using Abaqus. Our results demonstrate that novel polymerized vesicles capable of regulating the release of anticancer drugs such as paclitaxel have been developed.

Liposome−Quantum Dot Complexes Enable Multiplexed Detection of Attomolar DNAs without Target Amplification

Juan Zhou, Qiang-xin Wang, and Chun-yang Zhang
J. Am. Chem. Soc. 2013, 135, 2056−2059


Sensitive detection of DNA usually relies on target amplification approaches such as polymerase chain reaction and rolling circle amplification. Here we describe a new approach for sensitive detection of lowabundance DNA using liposome−quantum dot (QD) complexes and single-particle detection techniques. This assay allows for detection of single-stranded DNA at attomolar concentrations without the involvement of target amplification. Importantly, this strategy can be employed for simultaneous detection of multiple DNA targets.

Saturday, May 11, 2013

Interaction of Ionic Surfactants with Cornea-Mimicking Anionic Liposomes

Chhavi Gupta, Andrew K. Daechsel, and Anuj Chauhan
Langmuir 2011, 27, 10840–10846


The interaction of surface-active molecules with lipid bilayers is ubiquitous both in biological systems and also in several technological applications.Here we explore the interaction of ionic surfactants with liposomes whose composition mimics the ocular epithelia. In this study, liposomes with a composition mimicking ocular epithelia are loaded with calcein dye above the self-quenching concentration. The liposomes are then exposed to surfactants, and the rate of dye leaked from the liposomes due to the interaction of surfactants is measured. Both cationic and anionic surfactants at various concentrations and ionic strengths are explored. Results show that the liposome bilayer permeability to the dye increases on exposure to the surfactants, leading to the release of the dye trapped in the core. However, the dye release stops after a finite time, suggesting a transient increase in permeability followed by healing. The leakage profiles exhibit two different timescales for the cationic surfactant but only one timescale for the anionic surfactant. The total dye leakage increases with surfactant concentration, and at a given concentration, the dye leakage is significantly higher for the cationic surfactants. The timescale for the healing decreases with increasing surfactant concentration, and increasing ionic strength increases the dye leakage for the anionic surfactant. These results show that the surfactant binding to the lipid bilayer increases the permeability while the bilayers heal likely because of the surfactant jump from the outer to the inner leaflet and/or rearrangement into tighter aggregates.

Shrink-Wrap Vesicles

Shelly M. Fujikawa, Irene A. Chen, and Jack W. Szostak
Langmuir 2005, 21, 12124-12129


We describe a simple approach to the controlled removal of molecules from the membrane of large unilamellar vesicles made of fatty acids. Such vesicles shrink dramatically upon mixing with micelles composed of a mixture of fatty acid and a phospholipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)), as fatty acid molecules leave the vesicle membrane and accumulate within the mixed micelles. Vesicle shrinkage was confirmed by dynamic light scattering, fluorescence recovery after photobleaching of labeled vesicles, and fluorescence resonance energy transfer between lipid dyes incorporated into the vesicle membrane. Most of the encapsulated impermeable solute is retained during shrinkage, becoming concentrated by a factor of at least 50-fold in the final small vesicles. This unprecedented combination of vesicle shrinkage with retention of contents allows for the preparation of small vesicles containing high solute concentrations, and may find applications in liposomal drug delivery.

On Effective Leadership


MANY HAVE PONDERED WHY SOME NATIONS ARE MUCH MORE SUCCESSFUL THAN OTHERS. IS THE central factor an abundance of natural resources, wise traditional systems of governance, or the absence of serious confl icts? Or does a nation thrive merely as the result of a series of historical accidents? I believe that a primary determinant of success, often neglected, is how the leaders of its major institutions,* governmental and nongovernmental, are selected; how they in turn choose their deputies; and under what incentives they must operate. The incentives part is perhaps the easiest to describe. To achieve anything of great importance takes time, but in an increasingly rapid-paced world of quarterly reports and sound bites, leaders often become hamstrung by short-term goals. And in large public organizations such as government agencies, leaders need to resist the inevitable pressures from employees to expand the responsibilities and budget of their particular division, even when other parts of the government (or society) are more qualifi ed to meet a goal. A core assumption here is that the leaders are qualifi ed to lead. In a merit-based society, the selection of the most qualifi ed person for each position of responsibility, independent of personal connections, background, sex, or age, has the obvious advantage of placing critical decision-making into capable hands. Much less obvious is the confounding fact that oustanding “A” individuals commonly have the selfconfidence and discrimination needed to hire A, and whenever possible, A-plus, deputies below them. Conversely, when a poorly qualified person is selected as a leader, the oppposite occurs. Feeling insecure, such B individuals will hire only B-minus or C deputies, giving rise to a propagating chain of mediocrity that degrades the entire institution. When serving as president of the U.S. National Academy of Sciences (NAS), I befriended a very wise NAS Foreign Associate from Nigeria, Dr. Akin Mabogunje, who wrote an autobiography on the occasion of his 80th birthday.† In the final chapter, he describes the deplorable situation in his country created by “ascriptive rights”: rights that “just depend on being able to assert that one belongs to a group or part of the country to be able to lay claim to positions of authority or power.” As he starkly states: “The first consequence of putting unqualified individuals in important positions is their failure to grasp the nature of the opportunity being given to them to excel. Lacking the requisite mental capacity to cope with the challenges of the leadership position, they invariably turn their attention inward to weed out those whose presence reminds them of their own inadequacies. The mission of the institutions is thus lost in the pervasive fear of victimization for diligence. Any attempt at pursuing excellence at work is seen as a way of showing off the weakness of management and is punished rather than rewarded. In no time, the institution is manned by individuals who are willing to kowtow to the whims and caprices of the so-called managers or heads.” I have seen the tragic consequences of the situation Mabogunje describes repeated over and over in nations around the world, from important U.S. institutions such as large school districts to international organizations associated with the United Nations. But I have also witnessed the opposite: the flourishing of institutions in which the deputies outshine the boss. This is why my advice to managers is to aim at hiring people who, at least in some respects, appear to be more talented than you are. This requires honest humility. But only in this way can a leader hope to achieve his or her goals.
It is only through a meritocracy in which leaders encourage creativity from outstanding subordinates and are primarily rewarded for long-term, rather than short-term achievements that a nation—and the world—can expect to meet the many challenges that lie before us.

– Bruce Alberts

A study on the interactions of surfactants with phospholipid/ polydiacetylene vesicles in aqueous solutions

Colloids and Surfaces A: Physicochem. Eng. Aspects 257–258 (2005) 25–30
Yan-Lei Su, Jin-Ru Li, Long Jiang


Abstract: A colorimetric method for studying the interactions of surfactants with lipid vesicles, formed from dimyristoylphosphatidycholine (DMPC) and polymerized 10,12-pentacosadiynoic acid (PCDA), in aqueous solutions was reported. The electrostatic interaction and hydrophobic interaction play a key role in the interaction of the mixed lipid vesicles with surfactant. The hydrophobic interaction results in the insertion of the alkyl chain of surfactants into the hydrophobic domain of the vesicles. The insertion perturbs the conformation of the polymerized PCDA backbone in the mixed vesicles, which induces the chromatic response. The value of chromatic response induced by the addition of surfactants was found to correlate with the DMPC content in the vesicles; an increase of DMPC content would enhance the interaction of surfactants with the mixed vesicles. 

Sunday, April 21, 2013

How Do Amphiphiles Form Ion-Conducting Channels in Membranes? Lessons from Linear Oligoesters


THOMAS M. FYLES

ACCOUNTS OF CHEMICAL RESEARCH

The X-ray crystal structures of biological ion channels are exquisitely complex, but not all natural products capable of forming ion-conducting channels are equally elaborate. Examples such as the peptides gramicidin or alamethicin or the polyene antibiotics amphotericin and nystatin clearly form well-defined channels without requiring a massive protein superstructure. These molecules form the starting point for a supramolecular chemistry challenge: how to create synthetic compounds and systems that catalyze the translocation of ionic species across bilayer membranes mimicking naturally occurring channels. Over the past three decades, supramolecular chemists have developed numerous examples of systems with transport rates and efficiencies that rival natural channels. As the field developed, researchers discovered many compounds that are functional for ion transport but bear very little resemblance to any imagined architectures of ion channels. We and others have followed these lead compounds extensively in a quest to focus on the mechanisms such simple compounds use to achieve their function. These compounds show all the hallmarks of ion channels including high activity, ion specificity, regular time-dependent conductance changes, and in some cases higher-order phenomena such as voltage-dependent activity.

Saturday, April 20, 2013

Comparative Properties and Methods Of Preparation Of Lipid Vesicles (Liposomes)

Francis Szoka, Jr and Demetrios Papahadjopoulos
Ann. Rev. Biophys. Bioeng. 1980. 9:467-508


In this review we point out the salient points in vesicle preparation and the relative advantages of each type of vesicle. Our aim is to acquaint the reader with the pitfalls in liposome preparations, the lipid compositions that can be used, methods of preparation, size distributions of the resulting vesicles, efficiencies of encapsulation of the aqueous space, and methods to characterize the resulting vesicles.

Time-resolved nonlinear fluorescence spectroscopy using femtosecond multiphoton excitation and single-photon timing detection

Andreas Volkmer, David A Hatrick and David J S Birch
Meas. Sci. Technol. 8 (1997) 1339–1349. Printed in the UK



Abstract: We have developed a time-correlated single-photon timing nonlinear fluorometer for recording the fluorescence decay times and rotational correlation times of molecular probes using 120 fs regeneratively amplified Ti:Sapphire laser excitation via simultaneous non-resonant absorption of two or more near infrared photons. A microchannel plate photomultiplier giving 70 ps impulse response is used for detection. Studies on 1,6-diphenylhexatriene, rhodamine 6G and p-terphenyl in propylene glycol demonstrate two- and three-photon induced fluorescence characteristics. The radiative properties for one- and multiphoton excitation were found to be identical. However, the time-zero anisotropy observed for multiphoton excitation was larger than for one-photon excitation, indicating an increased degree of orientation of excited molecules after multiphoton absorption. The results reveal the potential of multiphoton-induced fluorescence anisotropy in the study of the structure and dynamics of microheterogeneous systems (i.e. biomembranes, porous matrices etc) by selecting the excitation wavelength and class of probe molecule.

Friday, April 19, 2013

Bilayer heating in magnetite nanoparticle–liposome dispersions via fluorescence anisotropy


Geoffrey D. Bothun, Matthew R. Preiss
Journal of Colloid and Interface Science 357 (2011) 70–74


Temperature measurements have been made within magnetite (Fe3O4) nanoparticle–liposome dispersions subjected to electromagnetic field at radiofrequency (RF) heating based on the fluorescence anisotropy of diphenylhexatriene (DPH) embedded within the bilayer. Incorporating cholesterol within dipalmitoylphosphatidylcholine (DPPC) bilayers broadened the anisotropy window associated with lipid melting. Cryogenic transmission electron microscopy showed that the dispersions contained magnetoliposomes with nanoparticle aggregates at both low and high encapsulation densities. RF heating results demonstrated the ability to measure the temperature of the ML bilayer with on/off RF cycles using DPH anisotropy. These measurements reflected the temperature of the bulk aqueous phase, which is consistent with previous work showing rapid heat dissipation from a nanoparticle surface during RF heating and a negligible difference between surface and bulk temperature.

Saturday, April 13, 2013

Mixed Micellization of Dimeric (Gemini) Surfactants and Conventional Surfactants


R. G. Alargova, I. I. Kochijashky, M. L. Sierra, K. Kwetkat, and R. Zana
Journal of Colloid and Interface Science 235, 119–129 (2001)


The aqueous solutions of mixtures of various conventional surfactants and dimeric anionic and cationic surfactants have been investigated by electrical conductivity, spectrofluorometry, and time-resolved fluorescence quenching to determine the critical micelle concentrations and the micelle aggregation numbers in these mixtures. The following systems have been investigated: 12- 2-12/DTAB, 12-2-12/C12E6, 12-2-12/C12E8, 12-3-12/C12E8, Dim3/ C12E8, and Dim4/C12E8 (12-2-12 and 12-3-12Ddimethylene-1,2- and trimethylene-1,3-bis(dodecyldimethylammonium bromide), respectively; C12E6 and C12E8 Dhexa- and octaethyleneglycol monododecylethers, respectively; Dim3 and Dim4Danionic dimeric surfactants of the disodium sulfonate type, Scheme 1; DTABD dodecyltrimethylammonium bromide). For the sake of comparison the conventional surfactant mixtures DTAB/C12E8 and SDS/C12E8 (SDSDsodium dodecylsulfate) have also been investigated (reference systems). Synergism in micelle formation (presence of a minimum in the cmc vs composition plot) has been observed for the Dim4/C12E8 mixture but not for other dimeric surfactant/nonionic surfactant mixtures investigated. The aggregation numbers of the mixed reference systems DTAB/C12E8 and SDS/C12E8 vary monotonously with composition from the value of the aggregation number of the pure C12E8 to that of the pure ionic component. In contrast, the aggregation number of the dimeric surfactant/C12E8 mixtures goes through a minimum at a low value of the dimeric surfactant mole fraction. This minimum does not appear to be correlated to the existence of synergism in micelle formation. The initial decrease of the aggregation number of the nonionic surfactant upon addition of ionic surfactant, up to a mole fraction of ionic surfactant of about 0.2 (in equivalent per total equivalent), depends little on the nature the surfactant, whether conventional or dimeric. The results also show that the microviscosity of the systems containing dimeric surfactants is larger than that of the reference systems.

Vesicle-to-Micelle Transformation in System Containing Dimeric Surfactants

B.K. Paul, N. Guchhait
J. Colloid Interface Sci., 363 (2011), pp. 529–539

Insolubility of lipids in Triton X-100: physical origin and relationship to sphingolipid/cholesterol membrane domains (rafts)


Erwin London, Deborah A. Brown
Biochimica et Biophysica Acta 1508 (2000) 182-195


The insolubility of lipids in detergents is a useful method for probing the structure of biological membranes. Insolubility in detergents like Triton X-100 is observed in lipid bilayers that exist in physical states in which lipid packing is tight. The Triton X-100-insoluble lipid fraction obtained after detergent extraction of eukaryotic cells is composed of detergent-insoluble membranes rich in sphingolipids and cholesterol. These insoluble membranes appear to arise from sphingolipid- and cholesterol-rich membrane domains (rafts) in the tightly packed liquid ordered state. Because the degree of lipid insolubility depends on the stability of lipid-lipid interactions relative to lipid-detergent interactions, the quantitative relationship between rafts and detergent-insoluble membranes is complex, and can depend on lipid composition, detergent and  temperature. Nevertheless, when used conservatively detergent insolubility is an invaluable tool for studying cellular rafts and characterizing their composition. ß 2000 Elsevier Science B.V. All rights reserved.


Friday, April 12, 2013

Sunday, April 7, 2013

Lipopolysaccharide Identification with Functionalized Polydiacetylene Liposome Sensors

Marianne Rangin and Amit Basu

J. AM. CHEM. SOC. 2004, 126, 5038-5039


Lipopolysaccharides (LPS) are complex glycolipids embedded within the outer membrane of Gram negative bacteria.1 Each cell contains over 2 million copies of LPS.1b LPS consists of a conserved lipidated disaccharide, known as Lipid A, which is attached to a core oligosaccharide fragment. The core region is extended by additional glycosylation to provide the O-specific antigen or polysaccharide region. The identity of these terminal sugars vary for different bacterial species and serotypes. Sensors which are capable of detecting and identifying different types of LPS can be used to develop devices for bacterial diagnostics.

Friday, April 5, 2013

A high-throughput fluorescence polarization anisotropy assay for the 70N domain of replication protein A

Souza-Fagundes EMFrank AOFeldkamp MDDorset DCChazin WJRossanese OWOlejniczak ETFesik SW.

Anal Biochem. 2012 Feb 15;421(2):742-9. doi: 10.1016/j.ab.2011.11.025. Epub 2011 Dec 1.

Replication protein A (RPA) interacts with multiple checkpoint proteins and promotes signaling through the ATR kinase, a key regulator of checkpoint pathways in the mammalian response to DNA damage. In cancer cells, increased DNA repair activity contributes to resistance to chemotherapy. Therefore, small molecules that block binding of checkpoint proteins to RPA may inhibit the DNA damage response and, thus, sensitize cancer cells to DNA-damaging agents. Here we report on the development of a homogeneous, high-throughput fluorescence polarization assay for identifying compounds that block the critical protein-protein interaction site in the basic cleft of the 70N domain of RPA (RPA70N). A fluorescein isothiocyanate (FITC)-labeled peptide derived from the ATR cofactor, ATRIP, was used as a probe in the binding assay. The ability of the assay to accurately detect relevant ligands was confirmed using peptides derived from ATRIP, RAD9, MRE11, and p53. The assay was validated for use in high-throughput screening using the Spectrum collection of 2000 compounds. The FPA assay was performed with a Z' factor of ≥ 0.76 in a 384-well format and identified several compounds capable of inhibiting the RPA70N binding interface.

Thursday, April 4, 2013

Production of reactive oxygen species in endothelial cells under different pulsatile shear stresses and glucose concentrations

L. K. Chin, J. Q. Yu, Y. Fu, T. Yu, A. Q. Liua and K. Q. Luo

Lab Chip, 2011, 11, 1856


A hemodynamic Lab-on-a-chip system was developed in this study. This system has two unique features: (1) it consists of a microfluidic network with an array of endothelial cell seeding sites for testing them under multiple conditions, and (2) the flow rate and the frequency of the culture medium in the microchannel are controlled by a pulsation free pump to mimic the flow profile of the blood in the blood vessel under different physiological conditions. The investigated physiological conditions were: (1) the resting condition in a normal shear stress of 15 dyne cm 2 with a normal heart rate of 70 bpm, (2) an exhaustive exercise condition with a high shear stress of 30 dyne cm 2 and a fast heart rate of 140 bpm, and (3) a constant high shear stress of 30 dyne cm 2. Two chemical conditions were investigated (10 mM and 20 mM glucose) to mimic hyperglycemic conditions in diabetes patients. The effects of various shear stresses either alone or in combination with different glucose concentrations on endothelial cells were examined using the developed hemodynamic Lab-on-a-chip system by assessing two parameters. One is the intracellular level of reactive oxygen species (ROS) determined by a fluorescent probe, H2DCFDA. Another is the mitochondrial morphology revealed with a fluorescent dye, MitoTracker Green FM. The results showed that ROS level was elevated nearly 4-fold after 60 min of exhaustive exercise. We found that the pulsatile nature of the fluid was the determination factor for causing ROS generation in the cells as almost no increase of ROS was detected in the constant shear stress condition. Similarly, much higher level of ROS was detected when 10 mM glucose was applied to the cells under normal or high pulsatile shear stresses compared with under a static condition. These results suggest that it is necessary to use pulsatile shear stress to represent the physiological conditions of the blood flow, and demonstrate the advantage of utilizing this newly developed hemodynamic Lab on-a-chip system over the conventional non-pulsatile system in the future shear stress related studies.

Monday, April 1, 2013

Evaluation of the Probe 2‘,7‘-Dichiorofluorescin as an Indicator of Reactive Oxygen Species Formation and Oxidative Stress

Carl P. LeBel, Harry Ischiropoulos, and Stephen C. Bondy

Chem. Res. Toxicol. 1992, 5, 227-231


The use of dichlorofluorescin (DCFH) as a measure of reactive oxygen species was studied in aqueous media. Hydrogen peroxide oxidized DCFH to fluorescent dichlorofluorescein (DCF), and the oxidation was amplified by the addition of ferrous iron. Hydrogen peroxide-induced DCF formation in the presence of ferrous iron was completely inhibited by deferoxamine and partially inhibited by ethylenediaminetetraacetic acid, but was augmented by diethylenetriaminepentaacetic acid. Iron-peroxide-induced oxidation of DCFH was partially inhibited by catalase but not by horseradish peroxidase. Nonchelated iron-peroxide oxidation of DCFH was partially inhibited by several hydroxyl radical scavengers, but was independent of the scavenger concentration, and this suggests that free hydroxyl radical is not involved in the oxidation of DCFH in this system. Superoxide anion did not directly oxidize DCFH. Data suggest that H2O2-Fe2+-derived oxidant is mainly responsible for the nonenzymatic oxidation of DCFH. In addition, peroxidase alone and oxidants formed during the reduction of H202 by peroxidase oxidize DCFH. Since DCFH oxidation may be derived from several reactive intermediates, interpretation of specific reactive oxygen species involved in biological systems should be approached with caution. However, DCFH remains an attractive probe as an overall index of oxidative stress in toxicological phenomena.

Saturday, March 30, 2013

The oxidation of glucose and related compounds by glucose oxidase from Aspergillus Niger


Pazur J.H., Kleppe K.

Biochemistry. 1964, 3, 578-83.

Synthesis, Characterization, and Long-Term Stability of Hollow Polymer Nanocapsules with Nanometer-Thin Walls

Dergunov, S. A., K. Kesterson, et al. (2010).

Macromolecules (Washington, DC, U. S.) 43(18): 7785-7792.

Hollow polymer nanocapsules are produced by the polymn. within hydrophobic interior of lipid bilayers that act as temporary self-assembled scaffolds. Pore-forming templates are co-dissolved with monomers in the bilayers to create pores with controlled size and chem. environment. Polymn. was monitored with UV spectroscopy and dynamic light scattering. High-resoln. magic angle spinning NMR characterization provided detailed structural information about nanocapsules. Spherical shape was confirmed by electron microscopy. Medium-sized mols. can be entrapped within porous nanocapsules. No release of encapsulated mols. was obsd. within 240 days. 

Ultrasonic gene and drug delivery using eLiposomes


Marjan Javadi, William G. Pitt, Christopher M. Tracy, Jeffery R. Barrow, Barry M. Willardson, Jonathan M. Hartley, Naakaii H. Tsosie

Journal of Controlled Release 167 (2013) 92–100


eLiposomes are liposomes encapsulating emulsions and therapeutics for targeted delivery. By applying ultrasoundto eLiposomes, emulsion droplets can transform from liquid to gas and rupture the lipid bilayer of the eLiposome to release a drug or plasmid. In this study, perfluoropentane (PFC5) emulsions were encapsulated inside folated eLiposomes carrying a model drug (calcein) or a model GFP plasmid to examine the effects of a folate ligand, PFC5 emulsion and various ultrasonic acoustic parameters in drug delivery and gene transfection into HeLa cells.
Confocal microscopy was used to quantify drug delivery and the level of plasmid transfection into HeLa cells. The results showed that drug delivery or transfection was minimal without incorporation of internal PFC5 emulsions and folate ligand on the eLiposome surface. It was also shown that application of ultrasound greatly enhanced the drug delivery and plasmid transfection. Delivery of these therapeutics appears to be to the cytosol, indicating that the expansion of the emulsion droplets disrupted both the eLiposomes and the
endosomes.

Wednesday, March 27, 2013

Investigating Ligand−Receptor Interactions at Bilayer Surface Using Electronic Absorption Spectroscopy and Fluorescence Resonance Energy Transfer

Navneet Dogra, Xuelian Li, and Punit Kohli

dx.doi.org/10.1021/la300724z | Langmuir 2012, 28, 12989−12998


We investigate interactions between receptors and ligands at bilayer surface of polydiacetylene (PDA) liposomal nanoparticles using changes in electronic absorption spectroscopy and fluorescence resonance energy transfer (FRET). We study the effect of mode of linkage (covalent versus noncovalent) between the receptor and liposome bilayer. We also examine the effect of size-dependent interactions between liposome and analyte through electronic absorption and FRET responses. Glucose (receptor) molecules were either covalently or noncovalently attached at the bilayer of nanoparticles, and they provided selectivity for molecular interactions between glucose and glycoprotein ligands of E. coli. These interactions induced stress on conjugated PDA chain which resulted in changes (blue to red) in the absorption spectrum of PDA. The changes in electronic absorbance also led to changes in FRET efficiency between conjugated PDA chains (acceptor) and fluorophores (Sulphorhodamine-101) (donor) attached to the bilayer surface. Interestingly, we did not find significant differences in UV−vis and FRET responses for covalently and noncovalently bound glucose to liposomes following their interactions with E. coli. We attributed these results to close proximity of glucose receptor molecules to the liposome bilayer surface such that induced stress were similar in both the cases. We also found that PDA emission from direct excitation mechanism was ∼2−10 times larger than that of the FRET-based response. These differences in emission signals were attributed to three major reasons: nonspecific interactions between E. coli and liposomes, size differences between analyte and liposomes, and a much higher PDA concentration with respect to sulforhodamine (SR-101). We have proposed a model to explain our experimental observations. Our fundamental studies reported here will help in enhancing our knowledge regarding interactions involved between soft particles at molecular levels.

Tuesday, March 26, 2013

Polydiacetylene Liposomes Functionalized with Sialic Acid Bind and Colorimetrically Detect Influenza Virus

JACS:, 1995, 117, 829-830


Anke Reichert, Jon 0. Nagy, Wayne Spevak, and Deborah Charych*


Cell membranes are remarkable structures from a materials science point of view. These highly organized, self-assembled structures provide indispensable functions for cells such as molecular recognition, pumping, gating, energy conversion, and signal transduction.The design of “smart” materials based on membrane structures with specific functional properties is an emerging field of study! We have prepared synthetic, polymerizable liposomes that resemble the organization and functionalization of cell membranes and have employed them as simple colorimetric sensors. The liposomes were designed to specifically bind to influenza virus particles and, in addition, report the binding event by undergoing a visible color change. In effect, these molecular assemblies mimic cell surface molecular recognition as well as signal transduction.

Monday, March 25, 2013

Effect of inorganic positive ions on the adsorption of surfactant Triton X-100 at quartz/solution interface


Volume 51Issue 10pp 918-927






The electrode-separated piezoelectric sensor (ESPS), an improved setup of quartz crystal microbalance (QCM), has been employed to investigate the adsorption behavior of nonionic surfactant Triton X-100 at the hydrophilic quartz-solution interface in mineralized water medium in situ, which contained CaCl2 0.01 mol·L−1, MgCl2 0.01 mol·L−1, NaCl 0.35 mol·L−1. In a large scale of surfactant concentration, t effects of Ca2+, Mg2+ and Na+ on the adsorption isotherm and kinetics are obviously different. In aqueous solution containing NaCl only, adsorption of Triton X-100 on quartz-solution interface is promoted, both adsorption rate and adsorption amount increase. While in mineralized water medium, multivalent positive ions Ca2+ and Mg2+ are firmly adsorbed on quartz-solution interface, result in the increasing of adsorption rate and adsorption amount at low concentration of surfactant and the peculiar desorption of surfactant at high concentration of Triton X-100. The results got by solution depletion method are in good agreement with which obtained by ESPS. The “bridge” and “separate” effect of inorganic positive ions on the adsorption and desorption mechanism of Triton X-100 at the quartz-solution interface is discussed with molecular dynamics simulations (MD), flame atomic absorption spectrometry (FAAS) and atomic force microscopy (AFM) methods.

Saturday, March 23, 2013

Synergistic Effect of Electric Field and Ultrasound on Transdermal Transport




Volume 13Issue 4pp 633-638


Near-Infrared Luminescence of Lanthanide Calcein and Lanthanide Dipicolinate Complexes Doped into a Silica-PEG Hybrid Material

Kris Driesen, Rik Van Deun, Christiane Go¨rller-Walrand, and Koen Binnemans*

Chem. Mater. 2004, 16, 1531-1535


The near-infrared luminescence of lanthanide complexes of 4′,5′-bis[N,N bis(carboxymethyl)aminomethyl]fluorescein (calcein) and pyridine-2,6-dicarboxylic acid (dipicolinic acid, dpa) doped in a hybrid sol-gel material was investigated. The silica-poly(ethylene glycol) (silica-PEG) inorganic-organic materials were prepared at a neutral pH. The lanthanide ions are well shielded from the environment by the calcein and dpa ligands, and the complexes are stable in the sol-gel matrix after preparation. The dysprosium and neodymium dipicolinate complexes showed near-infrared luminescence (NIR-luminescence) by direct excitation to the 4f-levels. The ytterbium dipicolinate complex doped in the sol-gel showed NIR-luminescence by excitation of the ligand in the UV region. All other tested lanthanide ions (Ln ) Pr, Sm, Er, Ho) did not show luminescence. Neodymium and ytterbium complexes with calcein show intense NIR-luminescence when the ligand is excited by visible light. The corresponding erbium complex doped in the silica-PEG matrix also showed NIR-luminescence at 1525 nm. No NIR-luminescence could be detected for the other lanthanide complexes doped in the matrix (Ln ) Pr, Sm, Dy, Ho).

Sunday, March 17, 2013

Porous nanocapsules with "invisible" walls.

Pinkhassik, E. (2010).
Pacifichem 2010, International Chemical Congress of Pacific Basin Societies, Honolulu, HI, United States, December 15-20, 2010
We use lipid bilayers as supramol. self-assembled scaffolds for directed assembly of functional nanomaterials. Recently, we reported a simple method for controlling size, chem. environment, and d. of nanopores spanning nanometer-thin membranes. These membranes are characterized by tunable mol. wt. cut-off, extremely fast mass transfer, and long-term structural stability. Vesicle-templates polymer nanocapsules can retain medium-sized mols. such as pH-sensitive indicator dyes while providing uninhibited access for small mols. to the capsule interior. Nanocapsules showed no cytotoxicity. In one application, we use nanocapsules for targeted delivery of radiog. contrast agents and therapeutic agents to osteoarthritic lesions. In another application, we entrap catalysts within nanocapsules to combine high efficiency of homogeneous catalysts with ease of sepn. from reaction products.

Wednesday, March 13, 2013

Chemical and enzymic intermediates in the peroxidation of o-dianisidine by horseradish peroxidase. 2. Evidence for a substrate radical-enzyme complex and its reaction with nucleophiles.

Claiborne, A. and I. Fridovich (1979).
Biochemistry 18(11): 2329-2335.

Abstract:
Changes in the optical absorption spectrum of horseradish peroxidase during the oxidn. of o-dianisidine at pH 7.5 reveal an intermediate distinct from the previously described compds. I and II. The rate of decay of this new complex appeared to be rate limiting for the catalytic cycle in this pH range, since imidazole, which augments the catalytic reaction, also enhanced the rate of decay of this complex. Nitrogenous compds. reportedly unable to ligate to hemes, such as 2-methylimidazole and benzimidazole, were nevertheless capable of augmenting the peroxidase-catalyzed rate of oxidn. of o-dianisidine. The activity of nitrogenous compds., in this regard, appeared to be a function of their nucleophilicity and was sensitive to steric factors but relatively free of a deuterium solvent isotope effect. It is suggested that the nucleophile-responsive intermediate is an enzyme-dianisidine radical complex and that abstraction of the 2nd electron from the bound radical is facilitated by binding of nitrogenous nucleophiles. 

Chemical and enzymic intermediates in the peroxidation of o-dianisidine by horseradish peroxidase. 1. Spectral properties of the products of dianisidine oxidation.

Claiborne, A. and I. Fridovich (1979).
Biochemistry 18(11): 2324-2329.

Abstract:
Studies of the optical spectra of the products formed during peroxidn. of o-dianisidine by horseradish peroxidase (HRP) indicate at least 3 distinct species. At pH 3.7 and 4°, peroxidn. of dianisidine at low concns. yields the free dianisidine quinonediimine (the 2-equiv oxidized form) with λmax 452 and 514 nm. At higher concns., the 1st detectable product is not the free quinonediimine but an intermol. complex (meriquinone or charge-transfer complex) consisting of quinonediimine and parental diamine. This complex is freely reversible and is sensitive to simple diln. or acidification, either of which restores the spectrum of the free quinonediimine. Furthermore, at near-neutral pH, the quinonediimine appears to undergo irreversible self-coupling yielding yet a different optical spectrum presumably characteristic of the bisazobiphenyl structure proposed by K. M. Moller and P. Ottolenghi (1966). Butylated hydroxyanisole was shown to react in the presence of peroxidase-H2O2 and dianisidine to yield a spectrum (λmax 575 nm) nearly identical with that obtained when Gibbs' reagent (2,6-dichloroquinone-4-chloroimide) was incubated with butylated hydroxyanisole, thus suggesting that the free quinonediimine itself couples with the phenolic antioxidant. Finally, continuous-flow EPR studies of dianisidine oxidn. both with HRP-H2O2 and with ceric sulfate were unable to detect any free dianisidine semiquinone radical in the steady state; it is concluded that oxidn. of dianisidine occurs in a rapid 2-electron process in both the HRP-H2O2 and Ce(IV) systems

Tuesday, March 12, 2013

Directed assembly of sub-nanometer thin organic materials with programmed-size nanopores


Delia C. Danila, L. Todd Banner, Evguenia J. Karimova, Lyudmila Tsurkan, Xinyan Wang, and
Eugene Pinkhassik

Angew. Chem. Int. Ed. 2008, 47, 7036 –7039

Abstract:

Nanocolander: Sub-nanometer thin organic materials with uniform imprinted pores are formed by controlled polymerization within temporary self-assembled scaffolds. Pores are measured by a colored size-probe retention assay. A nanocapsule with no pores retains yellow, red, and blue probes and is colored brown; 0.8 nm pores lead to release of yellow probes, while capsules with 1.3 nm pores only retain blue probes.

Friday, March 8, 2013

Liposome−Quantum Dot Complexes Enable Multiplexed Detection of Attomolar DNAs without Target Amplification


Juan Zhou, Qiang-xin Wang, and Chun-yang Zhang

dx.doi.org/10.1021/ja3110329 |J. Am. Chem. Soc. 2013, 135, 2056−2059


Sensitive detection of DNA usually relies on target amplification approaches such as polymerase
chain reaction and rolling circle amplification. Here we describe a new approach for sensitive detection of low abundance DNA using liposome−quantum dot (QD) complexes and single-particle detection techniques. This assay allows for detection of single-stranded DNA at attomolar concentrations without the involvement of target amplification. Importantly, this strategy can be employed for simultaneous detection of multiple DNA targets.

Functionalization of Imprinted Nanopores in Nanometer-Thin Organic Materials

Sergey A. Dergunov and Eugene Pinkhassik

DOI: 10.1002/anie.200803261

Introduction:


Recently, we described a method for creating nanometer-thin organic materials with nanopores of programmed size. Control of pore geometry and mass transfer has been
identified as key to advances in DNA-sequencing devices, microreactors, molecular electronics, and drug-delivery devices. Nanocapsules with selective permeability have gained considerable attention in biomedical applications. Controlling the chemical environment of nanopores is critical for realizing the full potential of nanometer-thin porous materials.[7] Herein, we describe an efficient method for creating uniform nanopores with a programmed chemical environment and demonstrate the successful quatitative conversion of functional groups in the nanopores.

Integrated Nanoreactor Systems: Triggering the Release and Mixing of Compounds Inside Single Vesicles


Pierre-Yves Bolinger, Dimitrios Stamou, and Horst Vogel*
LCPPM, Swiss Federal Institute of Technology Lausanne, CH-1015 Lausanne, Switzerland


Introduction: Lipid vesicles constitute nanocontainer systems ideally suited for the isolation, preservation, transport, and localization of few1 or single2 molecules. Their ultrasmall dimensions (minimal diameters of 20 nm) allow unparalleled reduction of confined volumes to the zeptoliter range (1 zL ) 10-21 L). The availability of lipids
with variations in the hydrocarbon chains and the polar headgroups permits in addition the optimal design of a container that is tight and inert to the reactants and products of many biochemical processes like protein expression,3 enzymatic reactions,4 or mRNA transcription5 to mention a few. The potential of these systems for miniaturization and bionanotechnology was nevertheless realized only after single vesicles were extracted from the ensemble and addressed as individuals, either by means of micromanipulation6 or by directed assembly on patterned surfaces.1,7 Here we present a method that allows the on-demand release and mixing of soluble compounds stored in the interior of individual vesicular nanoreactors.

Synthesis of Bilayer-Coated Nanogels by Selective Cross-Linking of Monomers inside Liposomes


Joris P. Schillemans, Frits M. Flesch, Wim E. Hennink, and Cornelus F. van Nostrum*

Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences (UIPS),
Utrecht UniVersity, P.O. Box 80.082, 3508 TB Utrecht, The Netherlands


ABSTRACT: In this study, bilayer-coated polyacrylamide hydrogel nanoparticles were prepared by photoinitiated polymerization of acrylamide (AA) and bis(acrylamide) (BA) in the inner compartment of liposomes. The liposomes were formed in AA/BA solutions from lipid/Triton X-100 (TX100) mixed micelles by adsorption of TX100 to Bio-Beads SM2 and were studied by dynamic light scattering and transmission electron microscopy. The hydrodynamic diameters of the liposomes were 100 nm with low polydispersity. Addition of ascorbic acid before photopolymerization prevented macroscopic hydrogel formation by inhibition of free-radical polymerization of nonencapsulated monomers. Bare nanogel particles were finally obtained by removal of the lipid bilayer. As opposed to the commonly used dilution method, this convenient and versatile method of nanogel synthesis will allow incorporation of membrane proteins in the bilayer and the use of monomers that readily pass the lipid membrane.

Sunday, March 3, 2013

Determination of Pore Sizes and Relative Porosity in Porous Nanoshell Architectures Using Dextran Retention with Single Monomer Resolution and Proton Permeation

Authors:
Thusitha P. Muhandiramlage, Zhiliang Cheng, David L. Roberts, John P. Keogh, Henry K. Hall, Jr. and Craig A. Aspinwall
Abstract:

Unilamellar phospholipid vesicles prepared using the polymerizable lipid bis-sorbylphosphatidylcholine (bis-SorbPC) yield three-dimensional nanoarchitectures that are highly permeable to small molecules. The resulting porous phospholipid nanoshells (PPNs) are potentially useful for a range of biomedical applications including nanosensors and nanodelivery vehicles for cellular assays and manipulations. The uniformity and size distribution of the pores, key properties for sensor design and utilization, have not previously been reported. Fluorophore-assisted carbohydrate electrophoresis (FACE) was utilized to assess the nominal molecular weight cutoff limit (NMCL) of the PPN via analysis of retained dextran with single monomer resolution. The NMCL of PPNs prepared from pure bis-SorbPC was equivalent to a 1800 Da linear dextran, corresponding to a maximum pore diameter of 2.6 nm. Further investigation of PPNs prepared using binary mixtures of bis-SorbPC and dioleoylphosphatidylcholine (DOPC) revealed a similar NMCL when the bis-SorbPC content exceeded 30 mol %, whereas different size-dependent permeation was observed below this composition. Below 30 mol % bis-SorbPC, dextran retention provided insufficient mass resolution (162 Da) to observe porosity on the experimental time scale; however, proton permeability showed a marked enhancement for bis-SorbPC ≥ 10 mol %. Combined, these data suggest that the NMCL for native pores in bis-SorbPC PPNs results from an inherent property within the lipid assembly that can be partially disrupted by dilution of bis-SorbPC below a critical value for domain formation. Additionally, the analytical method described herein should prove useful for the challenging task of elucidating porosity in a range of three-dimensional nanomaterials