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.

Poly[ethynylene(3-n-butyl-2,5-thiophenediyl)-ethynylene]: A Soluble Polymer Containing Diacetylene Units and its Conversion to a Highly Cross-Linked Organic Solid

Abstract: We are engaged in a program directed at the synthesis and study of highly cross-linked organic solids. Our approach has been to prepare low molecular weight polymers and oligomers consisting of aromatic moities l inked by diacetylene units, to cross-link the diacetylenic units thermally, and to examine the properties of the resulting solids. Our init ial efforts were directed toward the preparat ion of monomers having as high a rat io of carbon to hydrogen as possible. t '2 Al though this apprt ,ach vieldecl mater ia ls wi th interest ing propert ies (high Young's modulus, hardness, and thermal stabil ity) the oligomericT polymeric intermediates had poor solubility and high cure energies (in some cases exceeding 500 J/g); these values of cure energy made the preparation of Iarge pieces diff icult. We chose to introduce an alkyl group into the aromatic portion of the monomer to increase the solubil itv and to lower the cure energy of the polymer derived from it. This paper reports our results of a study of polyIeth1'nvlene(3-n-butyl-2,5-thiophenediyl)ethynylenel and related oligomers and polymers: preparation of these diacetylenic oligomers and polymers in soluble form, conversion of the oligomers to hypercross-linked3 organic solids with high carbon content, and characterization of these solids. An accompanying paper by Rutherford and Stil le describes related work.a Our studies demonstrate that the properties o f p o l y I e t h y n y l e n e ( 3 n b u t y l 2 , 5 t h i o p h e n e d i y l ) ethynylenel derived from the oxidative coupling of 3-nbutyl-2,5-diethynylthiophene (1) can be controlled by the addition of 2-ethynylthiophene (2)5'6 as an end-capping agent. We have also prepared 2,3,5-triethynylthiophene (3) and carried out the oxidative copolymerization of 1, 2, and 3 in a 10:1:1 molar ratio to investigate the properties of a diacetylene network7 polymer.

Eliminating positively charged lysine epsilon-NH3+ groups on the surface of carbonic anhydrase has no significant influence on its folding from sodium dodecyl sulfate.

Abstract: This study compares the folding of two polypeptidesbovine carbonic anhydrase (BCA) and peracetylated BCA (BCA-Ac18)having the same sequence of amino acids but differing by 18 formal units of charge, from a solution containing denaturing concentrations of sodium dodecyl sulfate (SDS). Acetylation of BCA with acetic anhydride converts all 18 lysine-e-NH3+ groups to lysine-e-NHCOCH3 groups and generates BCA-Ac18. Both BCA and BCA-Ac18 are catalytically active, and circular dichroism spectroscopy (CD) suggests that they have similar secondary and tertiary structures. SDS at concentrations above ∼10 mM denatured both proteins. When the SDS was removed by dialysis, both proteins were regenerated in native form. This study suggests that large differences in the net charge of the polypeptide have no significant influence on the structure, the ability to refold, or the rate of refolding of this protein from solutions containing SDS. This study reinforces the idea that charged residues on the surface of BCA do not ...

Using covalent dimers of human carbonic anhydrase II to model bivalency in immunoglobulins.

Abstract: This paper describes the development of a new bivalent system comprising synthetic dimers of carbonic anhydrase linked chemically through thiol groups of cysteine residues introduced by site-directed mutagenesis. These com- pounds serve asmodels withwhich tostudytheinteractionofbivalentproteins with ligands presented at the surface of mixed self-assembled monolayers (SAMs). Monovalent carbonic anhydrase (CA) binds to benzenesulfonamide ligands pre- sented on the surface of the SAM with Kd surf = 89 nM. The synthetic bivalent proteins—inspired by the structure of immunoglobulins—bind bivalently to the sulfonamide-functionalized SAMs with low nanomolar avidities (Kd avidity,surf =1 � 3 nM); this difference represents a ∼50-fold enhancementofbivalentovermonovalentassociation.ThepaperdescribesdimersofCAhaving(i)differentlengthsofthecovalent linker that joined the two proteins and (ii) different points of attachment of the linker to the protein (either near the active site (C133) or distal to the active site (C185)). Comparison of the thermodynamics of their interactions with SAMs presenting arylsulfonamidegroupsdemonstratedthatvaryingthelengthofthelinkerbetweenthemoleculesofCAhadvirtuallynoeffectonthe rate of association, or on the avidity of these dimers with ligand-presenting surfaces. Varying the point of attachment of the linker betweenmonomericCA'salso had almost noeffectonthe avidity ofthe dimers, although changingthe point ofattachment affected the rates of binding and unbinding. These observations indicate that the avidities of these bivalent proteins, and by inference the avidities of structurally similar bivalent proteins such as IgG, are unexpectedly insensitive to the structure of the linker connecting them.

Magnetic Levitation as a Platform for Competitive Protein−Ligand Binding Assays

Abstract: This paper describes a method based on magnetic levitation (MagLev) that is capable of indirectly measuring the binding of unlabeled ligands to unlabeled protein. We demonstrate this method by measuring the affinity of unlabeled bovine carbonic anhydrase (BCA) for a variety of ligands (most of which are benzene sulfonamide derivatives). This method utilizes porous gel beads that are functionalized with a common aryl sulfonamide ligand. The beads are incubated with BCA and allowed to reach an equilibrium state in which the majority of the immobilized ligands are bound to BCA. Since the beads are less dense than the protein, protein binding to the bead increases the overall density of the bead. This change in density can be monitored using MagLev. Transferring the beads to a solution containing no protein creates a situation where net protein efflux from the bead is thermodynamically favorable. The rate at which protein leaves the bead for the solution can be calculated from the rate at which the levitation height of the bead changes. If another small molecule ligand of BCA is dissolved in the solution, the rate of protein efflux is accelerated significantly. This paper develops a reaction-diffusion (RD) model to explain both this observation, and the physical-organic chemistry that underlies it. Using this model, we calculate the dissociation constants of several unlabeled ligands from BCA, using plots of levitation height versus time. Notably, although this method requires no electricity, and only a single piece of inexpensive equipment, it can measure accurately the binding of unlabeled proteins to small molecules over a wide range of dissociation constants (K(d) values within the range from ~10 nM to 100 μM are measured easily). Assays performed using this method generally can be completed within a relatively short time period (20 min-2 h). A deficiency of this system is that it is not, in its present form, applicable to proteins with molecular weight greater than approximately 65 kDa.

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.