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.

Hierarchically ordered oxides

Abstract: Porous silica, niobia, and titania with three-dimensional structures patterned over multiple length scales were prepared by combining micromolding, polystyrene sphere templating, and cooperative assembly of inorganic sol-gel species with amphiphilic triblock copolymers. The resulting materials show hierarchical ordering over several discrete and tunable length scales ranging from 10 nanometers to several micrometers. The respective ordered structures can be independently modified by choosing different mold patterns, latex spheres, and block copolymers. The examples presented demonstrate the compositional and structural diversities that are possible with this simple approach.

Neutrophil chemotaxis in linear and complex gradients of interleukin-8 formed in a microfabricated device

Abstract: Although a wealth of knowledge about chemotaxis has accumulated in the past 40 years, these studies have been hampered by the inability of researchers to generate simple linear gradients instantaneously and to maintain them at steady state. Here we describe a device microfabricated by soft lithography and consisting of a network of microfluidic channels that can generate spatially and temporally controlled gradients of chemotactic factors. When human neutrophils are positioned within a microchannel, their migration in simple and complex interleukin-8 (IL-8) gradients can be tested. The cells exhibit strong directional migration toward increasing concentrations of IL-8 in linear gradients. Neutrophil migration halts abruptly when cells encounter a sudden drop in the chemoattractant concentration to zero ("cliff" gradient). When neutrophils are challenged with a gradual increase and decrease in chemoattractant ("hill" gradient), however, the cells traverse the crest of maximum concentration and migrate further before reversing direction. The technique described in this paper provides a robust method to investigate migratory cells under a variety of conditions not accessible to study by earlier techniques.

Noncovalent Synthesis: Using Physical-Organic Chemistry To Make Aggregates

Abstract: A molecule is usually understood to be a stable collection of atoms connected bv a continuous network of covalent bonds. The develipment of methods for constructing these networks has been a central occupation of organic chemistry, and the success of these methods has made possible the power, elegance, and utility of modern organic synthesis. The preparations of vitamin B12,l palytoxin,2 calicheamicin,3 and other complex secondary metabolites illustrate the extraordinary sophistication of this field. This type of synthesis-which we refer to as covalent synthesis, in the absence of a better termcontinues to expand its capabilities, but it may be understandably difficult to provide very large and structurally complex molecules quickly and economically by using it.4 Organic chemistry has always taken much of its inspiration and motivation from Nature. As biological molecules-especially large molecules having complex tertiary structures such as proteins, DNA, and RNA-have become central concerns of organic chemistry, noncovalent interactions have moved toward the center of attention. Although biological macromolecules are largely composed of Covalent bonds, the networks of these bonds are not always continuous, and many important structures-including multimeric proteins and DNA itself-are "aggregates" and not simply "molecules". Many biological molecules and aggregates derive much of their unique structure and function from noncovalent interactions: that is, from

Using self-assembled monolayers to understand the interactions of man-made surfaces with proteins and cells.

Abstract: Self-assembled monolayers (SAMs) formed on the adsorption of long-chain alkanethiols to the surface of gold or alkylsilanes to hydroxylated surfaces are well-ordered organic surfaces that permit control over the properties of the interface at the molecular scale. The ability to present molecules, peptides, and proteins at the interface make SAMs especially useful for fundamental studies of protein adsorption and cell adhesion. Microcontact printing is a simple technique that can pattern the formation of SAMs in the plane of the monolayer with dimensions on the micron scale. The convenience and broad application offered by SAMs and microcontact printing make this combination of techniques useful for studying a variety of fundamental phenomena in biointerfacial science.

Formation of monolayers by the coadsorption of thiols on gold: variation in the head group, tail group, and solvent

Abstract: Long-chain alkanethiols, HS(CH2)nX, adsorb from solution onto gold and form oriented. ordered monolayers. Monolayers exposing more than one functional group at the surface can be generated by coadsorption of t*'o or more thiols from solution. In general, the ratio of the concentration of the t\r'o components in a mixed monolayer is not the same as in solution but reflects the relative solubilities of the components in solution and interactions between the tail groups, X, in the monolayers. Multicomponent monolayers do not phase-segregate into single-component domains large enough to influence the contact angle (a few tens of angstroms across) and also do not act as ideal two.dimensional solutions. In the two-component system HS(CH2)J/HS(CH2)"CH3 in ethanol, where X is a polar tail group such as CH2OH or CN, adsorption of the polar component is particularly disfavored at low concentrations of the polar component in the monolayer. These isotherms may arise from poor solvation of the polar tail groups in the quasi-two-dimensional alkane solution provided by the methyl tail groups. From dilute solutions in alkanes, adsorption of HS(CH2)r9CH2OH is strongly preferred over HS(CHz)roCHr, probably due to the stabilization afforded by intramonolayer hydrogen bonds between the hydroxyl tail groups. The wettability of mixed monolayers is not linear in the composition of the surface. (n a surface comprised of a polar and a nonpolar component, the polar component is more hydrophilic when its concentration in the monolayer is low than when the monolayer is composed largely of the polar component.

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.