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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.


Papers
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Journal ArticleDOI
TL;DR: In this paper, computer-generated patterned hydrophobic films are produced on hydrophilic glass substrates by a microcontact "stamp" printing technique, where the silicone elastomeric stamp (inked with C18H37SiCl3) contacts the hyrophilic surface.

62 citations

Journal ArticleDOI
TL;DR: The values of charge and electrophoretic mobility of a protein are changed upon acylation of its α- and Lys e-NH3+ groups, leading to resolved charge ladders of proteins that have values of MW > 50 kD that differ incrementally in the number of residues modified.
Abstract: The values of charge and electrophoretic mobility of a protein are changed upon acylation of its α- and Lys e-NH3+ groups. Partial acylation of the amino groups of a protein results in a set of derivatives that is often resolved by capillary electrophoresis into a set of distinct peaksthe “rungs” of a protein charge ladderthat differ incrementally in the number of residues modified. Proteins that have values of MW 50 kD form broad unresolved peaks. Resolved charge ladders of proteins that have values of MW > 50 kD may be formed using acylating agents that introduce several charges upon acylation of each of their Lys e-NH3+ groups. As an example, l-lactate dehydrogenase (MW = 147 kD) does not form a resolved charge ladder when modified with acetic anhydride. When it is acylated with either 1,2,4-benzenetricarboxylic anhydride, 3, or 1,2,4,5-benzenetetracarboxylic dianhydride, 4,...

62 citations

Journal ArticleDOI
TL;DR: The chemoenzymatic synthesis provided convenient access to glucosaminigpnosphate and N-acetylgluiosamine&phosphatc (GlcNAc-GP) in )lGmmol quantities and the chemical synthesis proceeded through five steps in an overall yield of 15% from pentaacetvlgluco.
Abstract: practical chemoenzymatic and chemical routes to uridine 5'-diphospho-N'acetylglucosamine (UDP-GlcNAc) on r !ruscale have been developed. The chemoenzymatic synthesis provided convenient access to glucosaminigpnosphate and N-acetylgluiosamine&phosphatc (GlcNAc-GP) in )lGmmol quantities. The condensation betweenblcNAc-6-P and UTi, was catalyzed by readily available crude enzyme extracts from dried cells of the ieit Co\"aida utitis and afforde d a LTVo yield of UDP-GlcNAc from GlcNAc-6-P. The otherwise straightforward .h.-*n y-\"tic sequence was hampered by the need to punfy the product from the final complex reaction mixture. The chemical synthesis of UDP-GlcNAc proceeded through five steps in an overall yield of 15% from pentaacetvlgluco.\"-i.,. with the selective formation of tetraacetylglucosamine-a-1-phosphate as the key reaction.

62 citations

Journal ArticleDOI
TL;DR: It is concluded that the transfer of ions between the contacting surfaces is the most common mechanism for charge separation when organic materials are involved, and this study demonstrates the wealth of quantitative information it can provide as a tool for studying the atomic/molecular mechanisms of contact electrification.
Abstract: Here we describe a study of the charging and discharging of solids in a system comprising a metal sphere that rolls across an electrically insulating plate. There are two kinetically distinct processes: 1) charging at a constant rate; 2) abrupt discharging, when the potential difference between sphere and surface reaches a critical value determined by the dielectric strength of air. This work has two objectives: 1) to develop a procedure for examining the rate of charging and discharging as a function of a range of relevant variables; 2) to use this information to test the hypotheses that charge separation involved ions and that discharge of the potential produced involved a breakdown of air. In published work, we have described this system; this study demonstrates the wealth of quantitative information it can provide as a tool for studying the atomic/molecular mechanisms of contact electrification. These mechanisms are relevant to processes ranging from lightning to xerography, and are a subject of active controversy. Three mechanisms appear to contribute to contact electrification: 1) ion transfer between surfaces having mobile ions, 2) partitioning of ions from adsorbed water onto the surfaces of non-ionic insulators, and 3) electron transfer between conductors and semiconductors (materials with mobile electrons and well-defined Fermi surfaces). We have concluded—in agreement with a hypothesis by Diaz —that the transfer of ions between the contacting surfaces is the most common mechanism for charge separation when organic materials are involved. The data we present here are consistent with contact charging by the slow transfer of ions, interrupted by episodic, rapid discharge events involving ionized plasmas when the difference in electrical potential between the surfaces exceeds the breakdown limit of air. These experiments used the rolling sphere tool (RST, Figure 1) developed by Grzybowski et al. We investigated contact electrification between stainless steel spheres (d= 3.2 mm) and three different surfaces (relative humidity, RH = 20–25 %, T 22 8C, w = 80 rpm). The Supporting Information contains the experimental procedures we followed for preparing the insulating surfaces: 1) glass (a 1.0 mm thick, 76 mm diameter wafer of low-alkali glass); 2) glass silanized with N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride; 3) glass silanized with 3-(trihydroxysilyl)-1-propane-sulfonic acid. When the sphere was far (more than ca. 2.5 cm) from the electrode (width 5 mm, 0.2 radians), the electrometer reported only the charge on the portion of the insulator (the glass plate) to which the electrode coupled (Qw). When the sphere passed over the electrode, the electrometer registered a peak in the charge, the height of which was the sum (Qs+w) of the charges that the electrode sensed on the sphere (Qs) and Qw. Figure 2a shows the charge the electrometer recorded for one revolution of the sphere. The fullwidth at half-maximum of the peak was about 0.63 radians. Figure 2b shows a representative plot of the complex pattern of charge (Q, in picocoulomb, pC: 1 pC = 6.2 ; 10 elementary charges) the electrometer reported as the sphere rolled on a glass wafer. When the sphere was directly over the electrode, the electrometer measured a fraction of the charge on the sphere (80–90 %; see the Supporting Information). Qw (grey dot-dash guidelines) and Qs+w (black dashed guidelines) increased linearly with time. Sharp discontinuities— discharge events through air—interrupted the charging. Subtracting Qw from Qs+w gave Qs—the charge that the electrometer sensed on the rolling sphere alone—as a function of time (Figure 2c). We have observed qualitatively similar behavior on a variety of materials, including organic polymers; we will detail these experiments in a full paper. The polarity of charge separation was invariant when a steel sphere (positive) rolled on a clean glass wafer (negative) (Figure 3a). When the sphere rolled on a surface with bound Figure 1. Illustration of the “rolling sphere tool” to measure the kinetics of contact electrification between rolling stainless steel spheres and insulating surfaces. The Supporting Information contains additional graphical representations.

62 citations

Patent
Enoch Kim1, Younan Xia1, Milan Mrksich1, Jane Jackman1, George M. Whitesides1 
14 Mar 1997
TL;DR: In this article, a method for patterning chemically or biochemically active agents on a substrate surface has been proposed, which involves providing a micromold having a contoured surface including indentations defining a pattern and forming, on the substrate surface, a chemically or bio-active agent or fluid precursor of a structure on the surface.
Abstract: Techniques for patterning chemically or biochemically active agents on a substrate surface involve providing a micromold having a contoured surface including indentations defining a pattern and forming, on a substrate surface, a chemically or biochemically active agent or fluid precursor of a structure on the surface. A chemically or biochemically active agent or fluid precursor also can be transferred from indentations in an applicator to a substrate surface. The substrate surface can be planar or non-planar. Fluid precursors of polymeric structures, inorganic ceramics and salts, and the like can be employed to form patterned polymeric articles, inorganic salts and ceramics, etc. at the surface. The articles, according to one aspect, are formed in a pattern including a portion having a lateral dimension of less than about 1 millimeter. Smaller dimensions can be achieved. The indentation pattern of the applicator can be used to transfer separate, distinct chemically or biochemically active agents or fluid precursors to separate, isolated regions of a substrate surface. The invention provides for inexpensive and simple synthesis of a combinatorial chemical or biochemical library.

62 citations


Cited by
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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
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 …

33,785 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组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�ly.
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。

18,940 citations

Journal ArticleDOI
TL;DR: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols used xiii 1.
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

14,171 citations

Journal ArticleDOI
05 Feb 2009-Nature
TL;DR: The direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers is reported, and two different methods of patterning the films and transferring them to arbitrary substrates are presented, implying that the quality of graphene grown by chemical vapours is as high as mechanically cleaved graphene.
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.

10,033 citations

Journal ArticleDOI
29 Aug 1997-Science
TL;DR: In this article, a general approach for multilayers by consecutive adsorption of polyanions and polycations has been proposed and has been extended to other materials such as proteins or colloids.
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.

9,593 citations