George M. Whitesides

Bio: George M. Whitesides is an academic researcher from Harvard University. The author has contributed to research in topics: Microcontact printing & Self-assembled monolayer. The author has an hindex of 240, co-authored 1739 publications receiving 269833 citations. Previous affiliations of George M. Whitesides include University of California, Davis & University of Texas at Austin.

Rates of thiol-disulfide interchange reactions involving proteins and kinetic measurements of thiol pKa values

Abstract: Bronsted coefficients have been determined for the rates of thiol-disulfide interchange between low molecular weight thiols and the disulfide groups of four native or modified proteins: DNase (beta nuc congruent to 0.36), lysozyme (beta nuc congruent to 0.55), adenylate kinase(SSCH3)2 (beta nuc congruent to 0.65), and papain(SSCH3) (beta nuc congruent to 0.45). These values are similar to those observed for reductions of oxidized glutathione and Ellman's reagent by a similar set of thiols (beta nuc congruent to 0.5). Glutathione is anomalously slow in reduction of certain protein disulfide groups: although this effect may in part reflect steric hinderance to attack by the relatively large glutathione molecule at disulfides shielded by protein tertiary structure, other (presently undefined) factors appear also to be important, at least in the case of DNase. The rates of reduction of several disulfide derivatives of papain(SSR) by DTT were determined. These data provide estimates of the Bronsted coefficient for the "central" thiol in thiol-disulfide interchange: these estimates fall in the range beta c congruent to -0.25 to -0.43. Rates of reduction of protein disulfide moieties were analyzed by using a Bronsted equation developed previously [Szajewski, R. P., & Whitesides, G. M. (1980) J. Am. Chem. Soc. 102, 2011] to yield pKa values for the participating thiol moieties: in particular, for papain, pKa(Cys-25) = 8.4 at pH 9 and pKa (Cys-25) = 4.1 at pH 6. The thiols of the structurally essential cysteine group of lysozyme seem to have pKa congruent to 11. The advantages and disadvantages of this method for estimating thiol pKa values are discussed.

Wetting of functionalized polyethylene film having ionizable organic acids and bases at the polymer-water interface: relations between functional group polarity, extent of ionization, and contact angle with water

Abstract: : This paper examines the wetting by water of low density polyethylene film modified at the polymer water (air) interface by introduction of polar organic functional groups (carboxylic acids, amines, and others). Water/polymer contact angles were determined for each of these interfaces; for interfaces containing acidic or basic functional groups, the contact angle was determined as a function of the pH. The observed contact angle was related to the hydrophilicity of these functional groups: as the hydrophilicity (as measured by Hansch pi parameters) increased up to a certain point, the contact angle decreased. Beyond that point, increased hydrophilicity had little additional influence on the contact angle. The result is interpreted in terms of water adsorbed on the polar interfacial functional groups: extensive hydration of interfacial groups having large negative pi parameters moderates their effective hydrophilicity. Keywords: Polyethylene, Wettability, Ionization, Acids, Bases, Monolayers, Gold.

Directional control of cell motility through focal adhesion positioning and spatial control of Rac activation

Abstract: Local physical interactions between cells and extracellular matrix (ECM) influence directional cell motility that is critical for tissue development, wound repair, and cancer metastasis. Here we test the possibility that the precise spatial positioning of focal adhesions governs the direction in which cells spread and move. NIH 3T3 cells were cultured on circular or linear ECM islands, which were created using a microcontact printing technique and were 1 μm wide and of various lengths (1 to 8 μm) and separated by 1 to 4.5 μm wide nonadhesive barrier regions. Cells could be driven proactively to spread and move in particular directions by altering either the interisland spacing or the shape of similar-sized ECM islands. Immunofluorescence microscopy confirmed that focal adhesions assembled preferentially above the ECM islands, with the greatest staining intensity being observed at adhesion sites along the cell periphery. Rac-FRET analysis of living cells revealed that Rac became activated within 2 min afte...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

Large-scale pattern growth of graphene films for stretchable transparent electrodes

Abstract: Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.

Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites

Abstract: Multilayer films of organic compounds on solid surfaces have been studied for more than 60 years because they allow fabrication of multicomposite molecular assemblies of tailored architecture. However, both the Langmuir-Blodgett technique and chemisorption from solution can be used only with certain classes of molecules. An alternative approach—fabrication of multilayers by consecutive adsorption of polyanions and polycations—is far more general and has been extended to other materials such as proteins or colloids. Because polymers are typically flexible molecules, the resulting superlattice architectures are somewhat fuzzy structures, but the absence of crystallinity in these films is expected to be beneficial for many potential applications.