Showing papers by "George M. Whitesides published in 1993"

Features of gold having micrometer to centimeter dimensions can be formed through a combination of stamping with an elastomeric stamp and an alkanethiol ‘‘ink’’ followed by chemical etching

Abstract: This letter describes a technique that can be used to produce well‐defined features of gold. The technique involves patterning of a self‐assembled monolayer (SAM) on a gold substrate using an elastomer stamp (fabricated either from a phenol‐formaldehyde polymer or polydimethylsiloxane), followed by selective etching in an aqueous, basic solution of cyanide ion and dissolved dioxygen (1M KOH, 0.1 M KCN). Electrically conductive structures of gold with dimensions as small as 1 μm have been produced using this procedure. Once a rubber stamp is fabricated, patterning and etching of gold substrates is straightforward. This method is convenient, does not require routine access to clean rooms and photolithographic equipment, and can be used to produce multiple copies of a pattern.

Adsorption of proteins onto surfaces containing end-attached oligo(ethylene oxide): a model system using self-assembled monolayers

Abstract: This paper reports a study of the adsorption of four proteins-fibrinogen, lysozyme, pyruvate kinase, and RNAse A-to self-assembled monolayers (SAMs) on gold. The SAMs examined were derived from thiols of the structure HS(CH 2 ) 10 R, where R was CH 3 , CH 2 OH, and oligo(ethylene oxide). Monolayers that contained a sufficiently large mole fraction of alkanethiolate groups terminated in oligo(ethylene oxide) chains resisted the kinetically irreversible, nonspecific adsorption of all four proteins. Longer chains of oligo(ethylene oxide) were resistant at lower mole fractions in the monolayer. Resistance to the adsorption of proteins increased with the length of the oligo(ethylene oxide) chain: the smallest mole fraction of chains that prevented adsorption was proportional to n -0.4 , where n represents the number of ethylene oxide units per chain

Formation of microstamped patterns on surfaces and derivative articles

Abstract: A method of patterning a material surface is provided in which an elastomeric stamp having a stamping surface is coated with a self-assembled monolayer forming species having a functional group selected to bind to a particular material, and the stamping surface is placed against a surface of material and is removed to leave a self-assembled monolayer of the species according to the stamping surface pattern of the stamp. Additional stamping steps may be subsequently effected to produce any of a variety of SAM patterns on the surface. Additionally, portions of the material surface that are not coated with a stamped SAM pattern may be filled in with another SAM-forming species. Alternately, portions that are not covered by a SAM layer may be etched or plated. Additionally, an optical switch and other optical devices and elements are provided, comprising articles similar to the inventive stamp.

Convenient methods for patterning the adhesion of mammalian cells to surfaces using self-assembled monolayers of alkanethiolates on gold

Abstract: We describe two convenient and flexible methods for controlling the attachment and spreading of mammalian cells on solid surfaces using patterned, self-assembled monolayers (SAMs). These patterned surfaces were easily formed by the serial adsorption of two or more c.r-substituted alkanethiols (HS(CHz)\"R) on gold.3'a These methods enable patterns to be formed with dimensions down to I pm and permit the examination of controlled adhesion of populations of cells and of individual cells and cellular processes. Previously, several methods have been used to pattern substrates for cell growth in the study of cell adhesion and motility.s The ability to form patterns with dimensions comparable to those of cells, exposing well-defined functional groups, will be useful in studying the physical-organic hemistry of cell attachment and growth: partitioning of proteins on adsorption onto surfaces from media; correlation of proteins adsorbed with attachment; influences of local environment on cellular spreading. We examined adherent cell lines (RBL and Pl9).6 These cells were plated onto SAMs patterned into areas in which the exposed groups R promoted (or inhibited) attachment of cells. SAMs terminated with the oligo(ethylene glycol) group (R = (OCH2CH2)6OH, EG6OH) uniformly prevented attachment of cells, as they resist adsorption of proteins;7 other functional groups promoted attachment of cells to different extents. The high resistance to adhesion provided by the EG6OH-terminated SAMs allowed us to study differential attachment in both complex (containing fetal bovine serum) and minimal (protein and serumfree) media. The patterning of the attachment of cells in cultures has been accomplished by patterning the deposition of metalss and by patterning alkylsiloxane monolayers by optical,E'e UV,r0 and plasma lithography.ll These methods are useful, but they have

Molecular self-assembly through hydrogen bonding : supramolecular aggregates based on the cyanuric acid.melamine lattice

Abstract: Reaction of the tris(melamine) derivatives hubMr (CnHr- 1,3,5-(CONHC6H4- 3-N(9ryrCnHo-4-C (CHr)r)COC6- H,-2-NHC.,Nr(NHr )(NHCHTCHTC(CHr) r)-5-Brl.) and flexM. (CoHr-1,3,5 (CO:(CHr),OCOC6H I-2-NHCTN)(NH2)( N- HCHTCHT(CU,lrltJ with R,CA (neohexyl isocyanuiate) and R"CA (3,3,3-triphenylpropyt isocy-anurate) in CHClr, respectively, yields ,truiturali.r- well-defined supramoleculir aggregates hubMq(R'CA)3 and flexM3(R"CA)3. These structures were characterized using ,H NMR, rlC NMR, and UV spectroscopy, gel permeation chromatography, and vapor pressure osmometry. flexM, is a confor-mationally flexible analog of hubM.,. The greater degree of preorganization that is built into the molecular structure of hubM3 compaied to flexM., ttiuk.r hubMr(R'Cn)i a more stable aggregate than flexMr(R"CA)r. These self- assembling structuies arethe first step in a program to design, synthesize. and develop methods to characterize supramolecular

Imaging of features on surfaces by condensation figures

Abstract: Condensation of a vapor to a liquid on a cold surface that is not wet completely by this liquid leads to the formation of an array of droplets. If the surface is heterogeneous in its physical properties (especially its interfacial free energy), the patterns of these arrays reflect this heterogeneity. The distribution of droplets of water (condensation figures or CFs) observed by optical microscopy on a surface can be correlated with the molecular structure of that surface. The substrates used to investigate the formation and morphology of the CFs were patterned, self-assembled monolayers of different alkanethiolates on gold and of alkyl siloxanes on glass. Analysis of CFs is a valuable nondestructive technique for characterizing heterogeneities in surfaces.

Fabrication and imaging of two-dimensional patterns of proteins adsorbed on self-assembled monolayers by scanning electron microscopy

Abstract: This paper describes methods for controlling both the concentration and spatial distribution of proteins adsorbed onto patterned, self-assembled monolayers (SAMs). Patterned SAMs were formed by the serial chemisorption of two or more ω-functionalized alkanethiols (HS(CH 2 ) n R) on gold. Several techniques (microwriting, micromachining, stamping, and UV microlithography) were used to fabricate the patterned SAMs. The most useful systems of patterned SAMs for studying the adsorption of proteins are those in which spatially-defined areas that resist protein adsorption are formed from oligo(ethylene glycol)-terminated thiols (e.g., R=(OCH 2 CH 2 ) 6 OH) and other areas that allowprotein adsorption are formed from thiols terminated by nonpolar (R=CH 3 ) and ionic (R=CO 2 - , PO 3 H - , 2-imidazolo) groups

Equilibrium constants for thiol-disulfide interchange reactions: a coherent, corrected set

Abstract: Equilibrium constants (K eq ) for the thiol-disulfide interchange reactions between dithiothreitol (DTT) and lipoic acid (14.2±0.7), lipoic acid (Lip) and mercaptoethanol (13.3 M±1.0 M), and mercaptoethanol (ME) and glutathione (GSH or GSSG) (1.20±0.10) were measured in D 2 O at pD 7.0 by 1 H NMR spectroscopy. Two of these equilibrium constants [DTT and Lip (21..±0.9), and Lip and ME (8.6±0.7)] were also measured in D 2 O/CD 3 OD

Monolayers on disordered substrates: self-assembly of alkyltrichlorosilanes on surface-modified polyethylene and poly(dimethylsiloxane)

Abstract: Self-assembled monolayers (SAMs) have been formed on disordered, polymeric substrates. On polyethylene (PE), preparation of the SAM entailed three steps: oxidation of the surface of the PE with an oxygen plasma; formation of a silicate layer anchored to the oxidized surface by reaction with SiCL; formation of an aikylsiloxane surface layer by adsorption of alkyltrichlorosilanes from the vapor phase, and reaction with SiOH groups (and adsorbed water) on the surface of the silicate layer. On poly(dimethylsiloxane) (PDMS), plasma oxidation produced a surface silicate layer that could be used for subsequent adsorption of an alkylsiloxane layer without additional steps. The wettability of these SAMs is similar to that of comparable SAMs formed by adsorption onto better defined substrates (silicon wafers and gold). Reaction of SAMs on PE or PDMS bearing terminal vinyl groups with an aqueous permanganate/periodate solution produced surfaces bearing carboxylic acid moieties.

Interchange between monolayers on gold formed from unsymmetrical disulfides and solutions of thiols: evidence for sulfur-sulfur bond cleavage by gold metal

Abstract: Chemisorption of alkanethiols, RSH, or dialkyl disulfides, RSSR, on gold gives ordered monolayers-l-S SAMs (self-assembled monolayers) formed from either precursor are believed to comprise the sattte species on the gold surface-gold(I) alkyl thiolate (RS-Aus+ on these predominately Au(111) surfaces) adsorbed epitaxially on the gold(0) substrate-but the only direct experimental eviderrce supporting this belief is the observation of indistinguishable S(2p) binding energies for both systems measured by X-ray photoelectron spectroscopy (XPS).0'z The objective of the work described in this paper was to compare the reactivity of the surface organosuHur species generated from alkanethiols and dialkyl disulfides in a iype of reaction we expected to be senstive to details of bonding to the surface-interchange of these surface organosulfur species with thiols or disulfides in solution. This study examined the reactivity of species formed on gold from an unsymmetrical disulfide LgSSMd (HO(CH21tr55(CHtsCFs; LB = long chain; Md = medium chain). We wanted to address two questions (Scheme I): (1) Are both halves of LgSSMd incorporated in the SAM to the same extent when a solution of this disufide is allowed to react with a bare gold surface? Is the snr\"e result observed on a surface already covered with an alkyl thiolate? (2) Do the hypothesized surface species, LgS-AuI and MdS-AuI, behave as independent entities in their reactions with species in solution, or are their reactivities

Use of affinity capillary electrophoresis to determine kinetic and equilibrium constants for binding of arylsulfonamides to bovine carbonic anhydrase

Abstract: Affinity capillary electrophoresis (ACE) provides a new approach to studying protein-ligand interactions. The basis for ACE is the change in the electrophoretic mobility of the protein when it forms a complex with its ligand. This binding interaction can be quantified directly for charged ligands or indirectly for neutral ligands in competition with a previously characterized charged ligand. Determination of kinetic and equilibrium constants using ACE relies only on the changes in the migration time and shape (but not the area) of the peak due to protein. Simulation of the protein mobility under conditions of ACE suggests that the experimentally obtained electropherograms can be explained in terms of few variables: on and off rates (and thus, binding constant), concentration of the ligand(s), and relative mobilities of the protein and its complex(es).

Tin- and indium-mediated allylation in aqueous media : application to unprotected carbohydrates

Abstract: The convenient and efficient indium- and tin-mediated allylation method for extending the carbon chain of unprotected carbohydrates is illustrated by preparation of 4-6 and 9-10. Various 2-deoxyaldoses can be synthesized by the allylation of aldoses. Indium-mediated reactions between ethyl 2-(bromomethyl)acrylate and aldoses provide access to 2-keto-3-deoxyulosonic acids. These reactions are diastereoselective; the major product contains a threo relationship between the newly generated hydroryl group and the C-2 hydroxyl group of the starting carbohydrate. Results obtained from reactions involving authentic organotin and organoindium reagents and from the corresponding heterogeneous reactions are similar

Molecular Self-Assembly through Hydrogen Bonding: Aggregation of Five Molecules To Form a Discrete Supramolecular Structure

Abstract: This article describes reactions of the trivalent melamine derivatives C6H3-1,3,5-(CONHC6H4-3-N(CH2C6H4- 4-C(CHi)3)COC6H3-2-(NHCrN3(NH2XNHCH2CH2C(CH3)3))-5-Brl, (hubM3) and (CH3),COC(O)NHCICH2O(CHz)r- SCH2C(O)NHC6H4-2-NHC3N3(NH2)(NH(CH2)2C(CH3)r)1, (trisMr) with the bivalent isocyanurate derivatives CuHz- l,5.(CH(CH)2|z-2 ,4.(cH,ffi(o))z( benzCA,)andc4o-2 '5-(cH(cH3)2)?-3 '4-(cH,ffi6( NHC(O)12 (furanCA2) in CHCI3 to afford a series of supramolecular aggregates containing 2 equiv of the tris melamine and 3 equiv of the bis cyanurate (2 + 3 complexes). These cornplexes consist of two parallel hydrogen-bonded lattices that incorporate 36 hydrogen bonds. The structures have been characterized by 'H NMR, r3C NMR, and UV spectroscopies, gel permeation chromatography, and vapor pressure osmometry. These techniques demonstrate that the 2 * 3 aggregates in CHCI3 solution are stable and structurally well-defined. hubM3 is more rigid than trisM3. This difference in rigidity is used to probe the relationship between the molecular structure of the trivalent melamine derivative and the geometry and stability of the resulting aggregate. (hubMr):(benzCA2)3 and (hubM3)2(furanCA2)3 each seem to exist in one isomeric form; (trisM3)2(benzCA2), and (trisM3)2(furanCA2)3 are both mixtures of isomers (due, probably, to the relative flexibility of the arms of trisMr).

Using affinity capillary electrophoresis to identify the peptide in a peptide library that binds most tightly to vancomycin

Abstract: This paper describes a procedure, based on competitive binding, for identifying tight-binding ligand(s) for a receptor in mixtures of equimolar ligand candidates using affinity capillary electrophoresis (ACE). Vancomycin and a small library of 32 peptides were used as a model system to illustrate the procedure. This procedure should be applicable to peptide mixtures of greater complexity than the one used here, as well as to mixtures of nonpeptidic compounds. Limits and limitations to the procedure are described

Catalytic activity of native enzymes during capillary electrophoresis: an enzymic microreactor

Abstract: This work evaluates the use of a plug of enzyme, migrating in an electrophoresis capillary under nondenaturing conditions, to convert substrate (which may be injected onto the capillary as a separate plug or included in the electrophoresis buffer) to product. This concept is demonstrated using two systems: the irreversible oridation of glucose-6-phosphate (glc-6-P) to 6-phosphogluconate using glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) and either NAD or NADP as cofactor, and the reversible conversion of ethanol to acetaldehyde using yeast alcohol dehydrogenase (YADH, EC 1.1.1.1) and NAD(H) as cofactor

Indium-mediated allylations of unprotected carbohydrates in aqueous media: a short synthesis of sialic acid

Abstract: _ !t] (a) Sche,uer, R. Adu. Carbohydr. Chem. Biochem.lg82, 40, 191. (!) !!a\\gmor!,,S.!. A,nnz .R eu. I mmu,na l. lgt4, 30 7, 560. (c) Ravindranath, \\4. H.; H-iSq, H, H.; Cooper, E. L.; Paulson, J. C. J. BioI. Chern. tg}l, 260', 8850. (d) Paulson, J. C. In Interactions of Animal Viruses with CeIt Surface Re^ceptors;Cgry,8.M., Ed.; Academic Press: New york, 1g8b; p 1q1.. (e)Savage, D. C.In Effect on Host Animals of Bacteria Adherini to Epithelial Surfaces; Savage, D. C., Fletcher, M., Eds.; plenum press-: New_Yor-k, 1985;p 43?. (f) Shibuya, N.; Goldstein, I. J.; Broekaert, W. F.; Nsimba-Lubaki, M.; Peeters, B.; Peumans, W. J. J. Biot. Chern.Igg1262,1596. _ (2) Wiegandt, H. ln Glycoliprds; Wiegandt, H., Ed.; Elsevier: New York,1985; Vol. 10, p 199. _ (!) {a) Magn-aniJ L.;Nilsson, B.; Brockhaus, M.; Zopf, D.; Steplewski, !.; Koprowsk_i, I! Ginsburg,V .Cancer Res. lgEg, 43, b4g8. (b) Kannagi, !_.; lukushi, Y.; Tachikawa, T.; Noda, A.; Shin, S.; Shigeta, K.; Hiraiila, N.; Fukuda, Y.; Inamoto, T.; Hakamori, S.; Imura, H. eancer i?es. lgE6. 46,26L9. (c) Danishefsky, S. J.;Koseki, K.; Griffith, D. A.; Gervay, J.; Petcrson, J. M.; McDonald, F. E.; Oriyama,T. J. Am. Chem. Soc. iggZ, 114,833L. (d) Ichikawa, Y.;Lin, Y. C.; Dumag, D.P.; Shen, G. J.; GarciaJunceda, E.; Williams,-M. A.; Bayer, R.; Ketchem. C.; Walker, L. E.; Paulson, J. C.; Wong, C. H. J. Am. Chem. Soc. lgg2, 114,9289.' _ (4) Horowi!2, M. I.; Pigman, W. The Glycoconjugotes; Academic Prese: New York, 1977-1985; Vole 1-4. _ (S) (9) Pqulson, J. C.; Rogers, G. N.; Carroll, S. M.; Higa, H. H.; Pritchett, !.; Milka, G.; Sabesan, S. Rrre Appl. Chem. 1984,56, ?9?. (bi Wiley, D. C.; Skehel, J. J-. Annu. Reu. Bioiienr. lgE?, B6b. (c) Weis, W.; Brown, .f.-H.; Cusack, S.; Paulson, J. C.; Skehel, J. J.; Wiley, D. C. Nature lggS, 333;426. (d) von ltzstein, M.; Wu, W.Y.; Kak, G. B.; Pegg, M. S.; Dyason, J^. p.; Jin, B-;_Phan, T. V.; Smythe, M. L.; White, H. F-.; Oliver, S. W.; Qol_man-, P.N!,; Varghese, J. N.; Ryan, D. M.; Woods, J. M.; Bettrelt, R. C.; Holhlg, V.J.; Cameron, J. M.; Penn, C. R. Nature lgg3, J6J, LLg. (6) DeNinno, M. P. Synthesis 1991, 583. _ (7) (a)_ Chao, L. C.; Rieke, R. D. J. Org. Chem. 1976, 40, 2259. (b) Petrier, C.; Einhorn, J.; Luche, J. L. Tetrahedron Lett. lg}5, 26, L4/tg. (c) Einhorn, C.; I,!che, J. L. J. Organomet. Chem. lg}7, J2i, tZ?. (d) Araki, !_.; I_to, H.; Butsu-gan,Y. J. Org. Chem.lg88, 5J, 1881. (e) Araiti, S.; Ito, H; BqtsuCgn,_Y. Synth. Commun.lg88, 18, 4bB. (f) Wu, S.; Huang, B_.; Gao, X. Synth. Comrnun.1990,20, L279. (S) Li, C. J.; ittait, t. ti. Tetrahedron Lett. 1991, 32, 7017.

Damage to trifluoroacetamido-terminated organic self-assembled monolayers (SAMs) on aluminum, titanium, copper and gold by aluminum K.alpha. x-rays is due principally to electrons

Abstract: This paper models damage induced by monochromatized Al Kα X-rays to organic thin films using self-assembled monolayers supported on Al, Ti, Cu, and Au. An X-ray photoelectron spectrometer is used both to conduct the X-ray irradiation and to analyze the damage. In all cases these monolayers comprised a trifluoroacetimido (CF 3 CONH-) group bound to the substrate through an undecyl tether to either a chemisorbed thiolate or carboxylate. This work extends a previous study of using trifluoroacetoxy-terminated SAMs on Au and Si. We find the X-ray-induced damage to the CF 3 CONH-terminated SAM is first order in the loss of fluorine

Neuraminidase-resistant hemagglutination inhibitors: acrylamide copolymers containing a C-glycoside of N-acetylneuraminic acid.

Abstract: Copolymers consisting of a polyacrylamide backbone with side chains terminated in C-glycosidic analogs of N-acetylneuraminic acid were synthesized by free radical copolymerization of alpha-2-C-[3-[[2-(N-acryloylamino)ethyl]thio]propyl]-N- acetylneuraminic acid (5) with acrylamide. Unlike natural and synthetic polyvalent materials that contain N-acetylneuraminic acid in O-glycosidic form, these C-glycosidic copolymers resist neuraminidase-catalyzed cleavage of the neuraminic acid residue from the copolymer backbone. Examination of these C-glycosidic copolymers in a hemagglutination inhibition assay indicated that they are as effective in vitro as polyvalent O-glycosidic copolymers in inhibiting agglutination of erythrocytes by influenza virus. The minimum value of the inhibition constant, calculated on the basis of the concentration of Neu5Ac groups in solution, is Ki(HAI) approximately 10(-7) M for both copolymers. The inhibitory potency of the C-glycoside-based copolymers becomes more significant at lower concentrations of Neu5Ac moieties in solution than does the inhibitory potency of the O-glycoside-based copolymer.

Synthesis of dithiols as reducing agents for disulfides in neutral aqueous solution and comparison of reduction potentials

Abstract: Several dithiols have been prepared that are useful for the reduction of disulfides in aqueous solution. The reduction potential of these dithiols have been determined from the measurement of the equilibrium constant of thiol/disulfide interchange with oxidized dithiothreitol using a 1 H NMR assay. The values of pK a of some of the dithiols mere measured to estimate their rate of reduction of disulfides

Synthesis, characterization, and thermodynamic analysis of a 1 + 1 self-assembling structure based on the cyanuric acid.cntdot.melamine lattice

Abstract: This article describes the reaction of the trivalent melamine derivative C 6 H 3 -1,3,5-[CO 2 (CH 2 ) 4 OCOC 6 H 4 -2-NH- C 3 N 3 (NH 2 )(NHCH 2 CH 2 C(CH 3 ) 3 )] 3 (homoflexM 3 , h-flexM 3 ) with the trivalent isocyanurate derivative C 6 H 3 -1,3,5-[CONHC 6 H 4 -3-N((CH 2 ) 17 CH 3 )COC 6 H 3 -2-NC(O)NHC(O)NHC(O)-5-O(CH 2 ) 17 CH 3 ] 3 (hubCA 3 ) in CHCl 3 to afford a structurally well-defined 1+1 supramolecular aggregate h-flexM 3 .hubCA 3 .This structure is held together by a network of 18 hydrogen bonds and is one of the most stable nonbiological supramolecular aggregates synthesized to date.The structure was characterized by 1 H NMR and UV spectroscopies, gel permeation chromotography ,and vapor pressure osmometry.The exchange reaction between h-flexM 3 .hubCA 3 and h-flexM' 3 (a close structural analog of h-flexM 3 ) was monitored by 1 H NMR spectroscopy.This exchange reaction appeared to occur by dissociation; the reaction was first-order in h-flexM 3 .hubCA 3 and zero-order in h-flexM' 3 .The transition-state parameters for the axchange reaction were calculated by following the exchange process at several temperatures.

Diastereoselectivity (enantioselectivity) of aldol condensations catalyzed by rabbit muscle aldolase at C-2 of RCHOHCHO if R has an appropriately placed negatively charged group

Abstract: D-Fructose 1,6-bis(phosphate) aldolase from rabbit muscle (RAMA, E.C. 4. 1.2. 13) catalyzes the aldol condensation between dihydroxyacetone phosphate (DHAP) and various aldehydes; the products are ketosugars with 3(S),4(R) stereochemistry. When racemic α-hydroxy aldehydes are condensed with DHAP, two diastereomeric products are formed. Tits paper demonstrates that RAMA can kinetically resolve α-hydroxy aldehydes with a negative charge removed four or five atoms from the aldehydic center

Affinity Electrophoresis in Multisectional Polyacrylamide Slab Gels Is a Useful and Convenient Technique for Measuring Binding Constants of Aryl Sulfonamides to Bovine Carbonic Anhydrase B

Abstract: This paper describes convenient preparations of heterogeneous multisectional polyacrylamide slab gels and the protocols that use these gels to measure protein-ligand binding constants [using bovine carbonic anhydrase B (CAB) as a model system]. Unlike procedures for affinity electrophoresis using tube gels, all binding information concerning protein-ligand interactions was encoded in a single multisectional gel: the procedure involving for measuring binding constants required no postelectrophoresis manipulation of gels. Use of these types of gels improves the accuracy of affinity gel electrophoresis (AGE) by providing reliable internal protein standards. Binding constants measured by AGE agree with those determined in homogeneous solution by spectrophotometric measurements. This technique has been used to investigate the influence of the length of the spacer separating the ligand and the polyacrylamide backbone on the binding constants. Dissociation constants obtained using the affinity gels approach the values measured in free solution, when the spacer is sufficiently long (> or = 18 A); affinity ligands having short spacers give high apparent dissociation constants.

Organized molecular assemblies

Abstract: Self-assembled monolayers (SAMs) are part of a class of organized molccular assemblies (OMAs) that represent a major new theme in condensed-matter science. The character- istics of SAMs and a summary of research recommendations are first presented in an executive summary. After introducing the definitions and characteristics of OMAs in which Langmuir-Blodgett (LB) films are compared with SAMs, the opportunities for scientific study. technological applications of SAMs. and limitations to transf-erring scientific understandin-e into technology are discussed. The discussion of SAMs includes the scientific opportunities in condensed-matter science. heteroepitaxy. and nanostructurest the technolo-sical applications in fuel cells. photoelectrochemistry. polymer/ metal (oxirle) interfaces, and thin-film. multilayer. solar collectors; and the lirnitations of stability. monolayer-substrate interactions. and mechanical stability for the transf'er of science into technology. Afier providing an overview and discussing potential payoffs from research, the needs and opportu- nities are summarized fbr tribology. fuel cells, photovoltaic cells, electrochromic windows. surface contamination, selectivity, and lbulin-e in membrane separations. biosurfaces. sensors. and corrosion.