Saturday, May 11, 2013

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.