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.

Mechanism of thermal decomposition of dibutylbis(triphenylphosphine)platinum(II)

Abstract: The thermal decomposition of di-n-butylbis(triphenylphosphine)platinum(Il) (l) in methylene chloride to n-butane, l-butene, and a complex of platinum(0) is proposed to take place by an intramolecular process involving an init ial dissociation of I equiv of triphenylphosphine from 1 to yield a three-coordinate intermediate 5, elimination of platinum hydride from one butyl group of 5 with concomitant ransfer of the resulting l-butene to the vacant coordination site, several cycles composed of rapid addition of platinum hydride to the coordinated butene and subsequent rapid reelimination of platinum hydride from the resulting butylplatinum complexes, and a final reductive elimination of n-butane from an intermediate having both hydride and butyl moieties bonded to platinum. Three significant conclusions concerning the mechanism of thermal decomposition of t have emerged lrom this study. First a vacant coordination site on platinum is a prerequisite for thermal decomposition under the conditions studied. Second, the identity of the rate-l imiting step for the overall decomposition reaction depends upon the concentration of triphenylphosphine added to the solution: in the absence of added triphenyiphosphine, the rate-l imiting step is the dissociation of I to 5; in the presence of ca. I equiv of added triphenylphoiphine, the rate-limiting step is the reductive elimination of butane. Third, the olefins participating in the platinum hydride addition-elimination sequence are coordinated in the intermediate platinum Complexes ufficiently firmly that they do not exchange with 1-butene free in solution. f nformat ion concerning the mechanisms of thermal r decomposi t ion of a lkyl der ivat ives of t ransi t ion metals is pert inent both to theoret ical d iscussions of the electronic structure of carbon-metal c bonds and pract ical appl icat ions of t ransi t ion metal organometal l ic compounds in organic synthesis and catalysis. ( l ) Supported' in part by The Nat ional Science Foundat ion, Grants GP-7266 and GP-142,17. (?) Nat ional Inst i tutes of Heal th Predoctoral Fel low, 1967-196g: E. B. Herschberg Fel low, 1966-1967. (3) Nat ional Inst i tutes of Heal th Predoctoral Fel low. 1967-1970, Journal ol'the Anterican Chemical Societ;' I 94:15 I Jult ' 26, 1972 Mechanisms involving both the homolytic scission of carbon-metal a bonds and the 6 elimination of metal hydrides have been proposed for these thermal decomposi t ions;{ '5 however, the lat ter course has been established as the more common for-n-alkyl derivatives (4) M. S. Kharasch and O. Reinmuth. \"Gr ignard React ions of Nonmetal l ic SubstancEs,\" Prent ice Hal l , New York, N. Y. , 1954, Chapter 5. (5) Reviews: (a) G. E. Coates, M. L. H. Creen, and K. Wadc, \"Organometal l ic Compounds,\" Vol . 2, 3rd ed, Methuen and Co., London, 1968, Chapter 7; (b) G. W. Parshal l and J. J. Mrowca, Adcan. Organometal . Chem.,7,157 (1968): (c) F. A. Cotton, Chem. Reo., 52 , 557 (1955) ; (d ) I . I . K r i t skaya , Usp . Kh im. ,35 , 167 (1966) . of platinum(Il),u rhodiur,n(I),7 and copper(I),E by ideniif ication of metal hydrides as products of the decompositions, and for derivatives of other metals by less direct techniques.s'e The nature of the factors determining both the rate of metal hydride elimination in the thermal decompositions of these classes of compounds and the reversibi l i ty of th is el iminat ion are unknown. The work reported in th is paper deals wi th an examinat ion of the mechanism of thermal decomposition of crs-di-n-butylbis(triphenylphosphine)platinum(Il) (1), a representative alkyl derivative of a dE transition metal ion, whose physical properties make it amenable to detailed mechanistic examination. The purpose of this study was to substantiate a pathway for itreimat decomposition of 1 involving platinum hydride elimination and to provide detail to the steps surrounding this elimination.

Formation and Reaction of Interchain Carboxylic Anhydride Groups on Self-Assembled Monolayers on Gold

Abstract: This paper demonstrates a new method for the synthesis of mixed self-assembled monolayers (mixed SAMs) by reaction of a reactive intermediatean interchain carboxylic anhydridewith alkylamines. The interchain anhydride was prepared in high yield from a SAM of 16-mercaptohexadecanoic acid (HS(CH2)15COOH) on gold by treatment with trifluoroacetic anhydride. Alkylamines reacted cleanly with the interchain anhydride to generate a mixed SAM, which comprised a mixture of acids and amides in approximately 1:1 ratio on the surface. The SAMs of the interchain anhydride and the mixed SAM were characterized using polarized infrared external reflectance spectroscopy, X-ray photoelectron spectroscopy, contact angle, and ellipsometry. Control of the wettability of the SAMs was demonstrated by allowing the interchain anhydride to react with alkylamines having different alkyl groups; this model system gave wetting data consistent with earlier studies of mixed monolayers and verified the ability of this method to manipulat...

Prototyping of Masks, Masters, and Stamps/Molds for Soft Lithography Using an Office Printer and Photographic Reduction

Abstract: This paper describes a practical method for the fabrication of photomasks, masters, and stamps/molds used in soft lithography that minimizes the need for specialized equipment. In this method, CAD files are first printed onto paper using an office printer with resolution of 600 dots/in. Photographic reduction of these printed patterns transfers the images onto 35-mm film or microfiche. These photographic films can be used, after development, as photomasks in 1:1 contact photolithography. With the resulting photoresist masters, it is straightforward to fabricate poly(dimethylsiloxane) (PDMS) stamps/molds for soft lithography. This process can generate microstructures as small as 15 microm; the overall time to go from CAD file to PDMS stamp is 4-24 h. Although access to equipment-spin coater and ultraviolet exposure tool-normally found in the clean room is still required, the cost of the photomask itself is small, and the time required to go from concept to device is short. A comparison between this method and all other methods that generate film-type photomasks has been performed using test patterns of lines, squares, and circles. Three microstructures have also been fabricated to demonstrate the utility of this method in practical applications.

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.