Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SAM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,549 records · Page 86Linked to original sources
PubMed1999

Differential display and cloning of the hippocampal gene mRNas in senescence accelerated mouse.

Identification of genes that are specifically expressed in the hippocampus of senescence accelerated mouse (SAM) is important for understanding the molecular basis of the pathological changes in the brain and of the deterioration of learning and memory in SAM-prone/8 (SAMP8), a substrain of SAM. The differential display technique was applied to compare mRNAs expression between SAMP8 and SAM-resistance 1 (SAMR1), another substrain of SAM. Complementary DNA fragments corresponding to several apparently differentially expressed mRNAs were recovered and sequenced. Six differentially expressed cDNA bands were identified. Sequence analyses demonstrated that W4 and W5 cDNA fragments corresponded to unknown genes. W1 and W6 showed 66.1 and 62.3% homology to rat GTP-exchange protein (eIF-2B) and rat phospholipase D, respectively, while W2 and W3 showed 89.2 and 90.8% homology to human bullous pemphigoid antigen and human glucogen debranching enzyme isoform 1/2/3/4/6, respectively. The results suggested that these genes are closely related to the malfunction of the brain in SAM.

Aging↗
PubMed2002

Surface modification of an organosilane self-assembled monolayer on silicon substrates using atomic force microscopy: scanning probe electrochemistry toward nanolithography.

Organosilane self-assembled monolayers (SAMs) have been applied to resist materials for nanolithography based on scanning probe microscopy. An organosilane SAM was prepared on Si substrates from a precursor, that is octadecyltrimethoxysilane. Using an atomic force microscope with a conductive probe, current was injected from the probe into the SAM-covered Si substrate so that the SAM was locally degraded at the probe-contacting point. Nanoscale patterns drawn on the SAM was clearly imaged by lateral force microscopy. The patterning could be conducted in air while, in vacuum at the order of 10(-6) Torr, no detectable patterns were fabricated. The presence of adsorbed water at the probe/sample junction was confirmed to be crucial for the patterning of the SAM/Si. Its mechanism was, thus, ascribed to electrochemical reactions of both the SAM and Si with adsorbed water.

Journal Article↗
PubMed2002

A facilitated electron transfer of copper--zinc superoxide dismutase (SOD) based on a cysteine-bridged SOD electrode.

The direct electrochemical redox reaction of bovine erythrocyte copper--zinc superoxide dismutase (Cu(2)Zn(2)SOD) was clearly observed at a gold electrode modified with a self-assembled monolayer (SAM) of cysteine in phosphate buffer solution containing SOD, although its reaction could not be observed at the bare electrode. In this case, SOD was found to be stably confined on the SAM of cysteine and the redox response could be observed even when the cysteine-SAM electrode used in the SOD solution was transferred to the pure electrolyte solution containing no SOD, suggesting the permanent binding of SOD via the SAM of cysteine on the electrode surface. The electrode reaction of the SOD confined on the cysteine-SAM electrode was found to be quasi-reversible with the formal potential of 65 +/- 3 mV vs. Ag/AgCl and its kinetic parameters were estimated: the electron transfer rate constant k(s) is 1.2 +/- 0.2 s(-1) and the anodic (alpha(a)) and cathodic (alpha(c)) transfer coefficients are 0.39 +/- 0.02 and 0.61 +/- 0.02, respectively. The assignment of the redox peak of SOD at the cysteine-SAM modified electrode could be sufficiently carried out using the native SOD (Cu(2)Zn(2)SOD), its Cu- or Zn-free derivatives (E(2)Zn(2)SOD and Cu(2)E(2)SOD, E designates an empty site) and the SOD reconstituted from E(2)Zn(2)SOD and Cu(2+). The Cu complex moiety, the active site for the enzymatic dismutation of the superoxide ion, was characterized to be also the electroactive site of SOD. In addition, we found that the SOD confined on the electrode can be expected to possess its inherent enzymatic activity for dismutation of the superoxide ion.

Aminobutyrates↗
PubMed2000

Synthesis and characterisation of a new class of stable S-adenosyl-L-methionine salts.

S-adenosyl-L-methionine (SAM) is an important metabolic intermediate that serves as a donor of methyl and aminopropyl groups to a variety of acceptor molecules. The molecule in vitro is unstable both in solution and in crystalline form undergoing irreversible conversion to 5'-methyltioadenosine (MTA) and homoserine lactone. Since this form of instability seems to be prevented in the cell of the living organism by bonds with macromolecules, we designed and developed a novel class of salts of SAM with large size anions to improve the stability of the sulfonium compound outside the cell. For this purpose we synthesised and characterised by NMR and IR spectroscopy anions consisting of amidic derivatives of taurine with fatty acids. Stability studies performed with the new SAM salts indicate that SAM becomes much more stable when it interacts with large size anions and in fact, more than 84% of the SAM is recovered after 36 months in lyophilized samples. The high stability of the new products widens the possibility of new therapeutic applications of SAM in human therapy.

Anions↗
PubMed1987

Stress-induced activation of the sympathetic nervous system.

Discrepancies between perceptions of internal or external circumstances and innate or acquired expectations lead to patterned stress responses involving several homeostatic systems, of which the sympathoadrenomedullary system (SAMS) is one. Severe, generalized threats such as hypoglycaemia, hypoxia, haemorrhage, circulatory collapse, and fight/flight situations elicit generalized SAMS activation, including cardiac stimulation, splanchnic, cutaneous, and renal vasoconstriction, and usually preserved skeletal muscle blood flow. Patterned sympathetic neural responses, resulting in redistribution of blood volume or changes in glandular activity, occur during orthostasis, exercise, altered environmental temperature, the postprandial state, and performance of attention-requiring tasks. In all these situations, SAMS activity is co-ordinated with that of the parasympathetic nervous system, the pituitary-adrenocortical system, and probably several neuropeptide systems. Although acute stress-induced SAMS activation can be a health hazard, the role of chronically repeated, stress-induced SAMS activation in the development of cardiovascular disease remains unclear. Benzodiazepines, beta-adrenoceptor blockers, and alpha 2-adrenoceptor agonists can attenuate effects of stress-induced SAMS activation, but pressor responses often are maintained.

Animals↗
PubMed2002

Neurite outgrowths of neurons on patterned self-assembled monolayers.

The effects of specific chemical functionalities on the neurite outgrowths of embryonic chick dorsal root ganglia (DRG) neurons and PC12h cells were investigated using a set of chemically functionalized surfaces prepared by self-assembled monolayers (SAMs) of alkanethiolates with R = NH2, COOH, and CH3 on patterned gold surfaces. The numbers of neurons with neurite outgrowths were compared in the course of a two-week cultivation period. Neurons with neurite outgrowths were observed predominantly on a patterned SAM of long-chain alkanethiolates with amino groups. After about two weeks, the neurons detached from the patterned SAM. However, the activity of beta-galactosidase immobilized via a patterned SAM did not decrease over a 13-d period, reflecting the long-term stability of the SAM. Therefore, the neurons became detached upon cell death. These results demonstrate that the patterned SAM of 11-amino-1-undecanethiolate is a scaffold suitable for making cell chips.

Journal Article↗
PubMed2000

Low-energy ion--surface reactions of pyrazine with two classes of self-assembled monolayers: influence of alkyl chain orientation

Collisions of pyrazine with two classes of self-assembled monolayer (SAM) films are employed to determine whether surface confinement and the resulting alkyl chain orientation, influences low-energy ion-surface reactions. SAM films formed from n-alkanethiols (CH3(CH2)n-S-Au, n = 14-17) and 4-(4-alkoxyphenylbenzenethiols (4-(4-CH3(CH2)mOC6H4)-C6H4-S-Au, m = 14-17) chemisorbed onto Au (111) substrates are known to exhibit a chain-length-dependent odd-even effect that places the terminal C-C bond into different orientations. Ion-surface collisions (20 eV) of pyrazine molecular ion (M = m/z 80) with these surfaces yield reaction product ions corresponding to the addition of hydrogen atoms ([M + H]+ = m/z 81) and methyl groups ([M + CH3]+ = m/z 95) from the surface to the probe ion. Differences in the relative abundance of the reaction product ions are measured as a function of chain length for both classes of SAM film. SAM films with odd chain lengths (n, m = 14 and 16) have a consistently higher abundance of H addition product ions than SAM films with even chain lengths (n, m = 15 and 17). Alternating reactivity is also observed for the addition of CH3, with methyl addition occurring more readily on even-chain-length films. The variations are consistent with the well-characterized orientation differences known to exist for films of this type. Specifically, odd-chain-length films are oriented such that the last C-C bond is more parallel to the plane of the surface than it is for even-chain-length films. The critical element of the parallel orientation is that it leaves, on average, one hydrogen atom on the terminal methyl and both hydrogen atoms on the first underlying methylene in more reactive positions compared to even chain lengths. Conversely, the trend in the relative abundance of CH3 addition indicates that the orientation produced by an even-chain-length film, with the last C-C bond more perpendicular to the surface, allows the probe ion better access to the methyl carbon. Reflection absorption IR spectroscopy (RAIRS) data independently confirm the orientational disposition of the films. The RAIRS data show that the odd-even effect is less dramatic for the n-alkanethiols when compared to 4-(4-alkoxyphenyl)benzenethiols. A smaller difference in ion-surface reactivity is measured for n-alkanethiols, demonstrating that ion-surface reactions can distinguish subtle differences in average orientation. In short, we report that the extent of ion-surface reactions of pyrazine ion with two classes of SAM films is directed by the spatial orientation of the surface-confined species that participate in the reaction.

Journal Article↗
PubMed2001

Development of an electrochemical immunosensor for direct detection of interferon-gamma at the attomolar level.

An electrochemical immunosensor for direct detection of the 15.5-kDa protein interferon-gamma (IFN-gamma) at attomolar level has been developed. Self-assembled monolayers (SAMs) of cysteine or acetylcysteine are formed on electropolished polycrystalline Au electrodes. IFN-gamma adsorbs physically to each of these SAMs. With injections of 100 mM KCl, IFN-gamma can be removed in the flow without damaging the acetylcysteine SAM. However, the cysteine SAM is affected by these KCl injections. In an on-line procedure in the flow, a specific antibody (MD-2) against IFN-gamma is covalently attached following carbodiimide/succinimide activation of the SAM. The activation of the carboxylic groups, attachment of MD-2, and deactivation of the remaining succinimide groups with ethanolamine are monitored impedimetrically at a frequency of 113 Hz, a potential of +0.2 V versus SCE, and an ac modulation amplitude of 10 mV. Plots of the real (Z') and imaginary (Z") component of the impedance versus time provide the information to control these processes. In the thermostated setup (23.0 degrees C), samples of unlabeled IFN-gamma (in phosphate buffer pH 7.4) are injected and the binding with immobilized MD-2 is monitored with ac impedance or potential-step methods. While the chronoamperometric results are rather poor, the ac impedance approach provides unsurpassed detection limits, as low as 0.02 fg mL-1 (approximately 1 aM) IFN-gamma. From a calibration curve (i.e. Z" versus the amount injected), recorded by multiple 50-microL injections of 2 pg mL(-1) of IFN-gamma, a dynamic range of 0-12 pg mL(-1) could be derived. However, when nonspecific adsorption is taken into account, which has been found to be largely reduced through injections of 100 mM KCl, a much smaller dynamic range of 0-0.14 fg mL(-1) remains. The immunosensor can be regenerated by using a sequence of potential pulses in the flow by which the SAM with attached MD-2 and bound IFN-gamma is completely removed. When the developed procedures described above are repeated, the response of the immunosensor is reproducible within 10%.

Acetylcysteine↗
PubMed2003

Scanning tunneling microscopy with chemically modified gold tips: in situ reestablishment of chemical contrast.

A method was developed for the reestablishment of chemical contrast in STM images obtained with chemically modified gold tips. Such tips display selective chemical contrast, which allows the selective imaging of specific species on the sample surface. Chemically modified STM tips can be fabricated by forming a self-assembled monolayer (SAM) on an electrochemically etched gold tip. One difficulty with this method thus far has been the relatively short lifetime of SAM-treated tips. The method described here utilizes the brief application of a high bias voltage between the sample and the tip to cause SAM molecules to reoccupy the tip apex, thereby allowing the tips to display selective chemical contrast in imaging. These treatments consist of applying a +1.9-V sample bias for 0.5-10 min under tunneling conditions. The usable lifetime of SAM-modified tips could be increased by more than 2 orders of magnitude, from hours to at least a month, dramatically increasing the efficiency of using SAM-modified gold tips. SAM molecules can also be removed from the tip apex by application of a negative sample bias (-2.0 V for 0.5-10 min) making it possible to alternate between conventional STM images and STM images with chemically enhanced contrasts.

Journal Article↗
PubMed2005

Characterization of ligand-functionalized microcantilevers for metal ion sensing.

A sensor for metal cations is demonstrated using single and binary mixtures of different thiolated ligands as self-assembled monolayers (SAMs) functionalized on silicon microcantilevers (MCs) with gold nanostructured surfaces. Binding of charged metal ions to the active surface of a cantilever induces an apparent surface stress, thereby causing static bending of the MC that is detected in this work by a beam-bending technique. A MC response mechanism based on changes in surface charge is discussed. The monodentated ligands arranged as SAMs on the MC surface are not expected to fully satisfy the coordination sphere of the detected metals. This leads to lower binding constants than would be expected for chelating ligands, but reversible responses. The modest binding constants are compensated in terms of the magnitudes of responses by the inherent higher sensitivity of the nanostructured approach as opposed to more traditional smooth surface MCs. Response characteristics are optimized in terms of SAM formation time, concentration of ligand solution, and pH of working buffer solution. Limits of detection for the tested mono-, di-, and trivalent metal ions are in low to submicromolar range. The results indicated that shapes and magnitudes of response profiles are characteristics of the metal ions and type of SAM. The response factors for a given SAM with the tested metal ions, or for a given metal with the tested SAMs, varied by roughly 1 order of magnitude. While the observed selectivity is not large, it is anticipated that sufficient ionic recognition contrast is available for selective metal ion identification when differentially functionalized arrays of MCs (different ligands on different cantilevers in the array) are used in conjunction with pattern recognition techniques.

Biosensing Techniques↗
PubMed2006

Carbohydrate-protein interactions by "clicked" carbohydrate self-assembled monolayers.

A Huisgen 1,3-dipolar cycloaddition "click chemistry" was employed to immobilize azido sugars (mannose, lactose, alpha-Gal) to fabricate carbohydrate self-assembled monolayers (SAMs) on gold. This fabrication was based on preformed SAM templates incorporated with alkyne terminal groups, which could further anchor the azido sugars to form well-packed, stable, and rigid sugar SAMs. The clicked mannose, lactose, and alpha-Gal trisaccharide SAMs were used in the analysis of specific carbohydrate-protein interactions (i.e., mannose-Con A; ECL-lactose, alpha-Gal-anti-Gal). The apparent affinity constant of Con A binding to mannose was (8.7 +/- 2.8) x 10(5) and (3.9 +/- 0.2) x 10(6) M(-1) measured by QCM and SPR, respectively. The apparent affinity constants of lactose binding with ECL and alpha-Gal binding with polyclonal anti-Gal antibody were determined to be (4.6 +/- 2.4) x 10(6) and (6.7 +/- 3.3) x 10(6) M(-1), respectively by QCM. SPR, QCM, AFM, and electrochemistry studies confirmed that the carbohydrate SAM sensors maintained the specificity to their corresponding lectins and nonspecific adsorption on the clicked carbohydrate surface was negligible. This study showed that the clicked carbohydrate SAMs in concert with nonlabel QCM or SPR offered a potent platform for high-throughput characterization of carbohydrate-protein interactions. Such a combination should complement other methods such as ITC and ELISA in a favorable manner and provide insightful knowledge for the corresponding complex glycobiological processes.

Carbohydrates↗
PubMed1999

A strategy for the generation of surfaces presenting ligands for studies of binding based on an active ester as a common reactive intermediate: a surface plasmon resonance study.

This paper describes the immobilization of ten proteins and two low-molecular-weight ligands on mixed self-assembled monolayers (SAMs) of alkanethiolates on gold generated from the tri(ethylene glycol)-terminated thiol 1 (HS(CH2)11(OCH2CH2)3OH) (chi(1) = 1.0-0.0) and the longer, carboxylic acid-terminated thiol2(HS(CH2)11(OCH2-CH2)6OCH2CO2H) (chi(2) = 0.0-1.0). The immobilization was achieved by a two-step procedure: generation of reactive N-hydroxysuccinimidyl esters from the carboxylic acid groups of 2 in the SAM and coupling of these groups with amines on the protein or ligand. Because this method involves a common reactive intermediate that is easily prepared, it provides a convenient method for attaching ligands to SAMs for studies using surface plasmon resonance spectroscopy (and, in principle, other bioanalytical methods that use derivatized SAMs on gold, silver, and other surfaces). These SAMs were resistant to nonspecific adsorption of proteins having a wide range of molecular weights and isoelectric points. The pH of the coupling buffer, the concentration of protein, the ionic strength of the solution of protein, and the molecular weight of the protein all influenced the amount of the protein that was immobilized. For the proteins investigated in detail--carbonic anhydrase and lysozyme--the highest quantities of immobilized proteins were obtained when using a low ionic strength solution at a value of pH approximately one unit below the isoelectric point (pI) of the protein, at a concentration of approximately 0.5 mg mL-1. Comparisons of the kinetic and thermodynamic constants describing binding of carbonic anhydrase and vancomycin to immobilized benzenesulfonamide and N-alpha-Ac-Lys-D-Ala-D-Ala groups, respectively, on mixed SAMs (by methods described in this paper) and in the carboxymethyl dextran matrix of commercially available substrates yielded (for these systems) essentially indistinguishable values of Kd, koff, and kon.

Adsorption↗
PubMedDate not supplied

Self-assembled monolayers with latent aldehydes for protein immobilization.

Aldehyde functions are widely used for immobilization of biomolecules on glass surfaces but have found little attention for biofunctionalization of self-assembled monolayers (SAMs) on gold, due to interference between thiol and aldehyde functions. This problem was recently solved by synthesis of an alkanethiol that carried a vicinal diol group [Jang et al. (2003) Nano Lett. 3, 691-694]. The latter served as a latent aldehyde function that was unmasked by short exposure of the vicinal diol-terminated SAM to aqueous periodate. However, the synthesis of the new vicinal diol-terminated alkane thiol was time-consuming and had an overall yield of approximately 3.5%. In the present study, a general modular strategy was introduced by which SAM components with vicinal diol functions were rapidly synthesized with high yield: this was accomplished by amide bond formation between a SAM-forming carboxylic acid (exemplified by lipoic acid and 16-mercaptohexadecanoic acid) with 3-aminopropane-1,2-diol, using suitable protecting groups. The disulfide or free thiol group afforded SAM formation on gold and, after periodate oxidation of the vicinal diol functions, proteins were covalently bound via their lysine residues. At 1 mg/mL protein concentration, complete surface coverage was reached within minutes. No further protein was bound by nonspecific adsorption, but cognate proteins were specifically bound with high capacity. Pyrogallol-O-hexadecanoic acid and 10-undecenoic acid were also coupled with 3-aminopropane-1,2-diol by amide bond formation, thereby producing latent aldehyde-containing SAM components for metal oxides and hydrogen-terminated silicon, respectively, to show the general usefulness of the new synthetic design.

Aldehydes↗
PubMed2004

Conserved and nonconserved residues in the substrate binding site of 7,8-diaminopelargonic acid synthase from Escherichia coli are essential for catalysis.

The vitamin B(6)-dependent enzyme 7,8-diaminopelargonic acid (DAPA) synthase catalyzes the antepenultimate step in the synthesis of biotin, the transfer of the alpha-amino group of S-adenosyl-l-methionine (SAM) to 7-keto-8-aminopelargonic acid (KAPA) to form DAPA. The Y17F, Y144F, and D147N mutations in the active site were constructed independently. The k(max)/K(m)(app) values for the half-reaction with DAPA of the Y17F and Y144F mutants are reduced by 1300- and 2900-fold, respectively, compared to the WT enzyme. Crystallographic analyses of these mutants do not show significant changes in the structure of the active site. The kinetic deficiencies, together with a structural model of the enzyme-PLP/DAPA Michaelis complex, point to a role of these two residues in recognition of the DAPA/KAPA substrates and in catalysis. The k(max)/K(m)(app) values for the half-reaction with SAM are similar to that of the WT enzyme, showing that the two tyrosine residues are not involved in this half-reaction. Mutations of the conserved Arg253 uniquely affect the SAM kinetics, thus establishing this position as part of the SAM binding site. The D147N mutant is catalytically inactive in both half-reactions. The structure of this mutant exhibits significant changes in the active site, indicating that this residue plays an important structural role. Of the four residues examined, only Tyr144 and Arg253 are strictly conserved in the available amino acid sequences of DAPA synthases. This enzyme thus provides an illustrative example that active site residues essential for catalysis are not necessarily conserved, i.e., that during evolution alternative solutions for efficient catalysis by the same enzyme arose. Decarboxylated SAM [S-adenosyl-(5')-3-methylthiopropylamine] reacts nearly as well as SAM and cannot be eliminated as a putative in vivo amino donor.

Alanine↗
PubMed2002

Charge transport through self-assembled monolayers of compounds of interest in molecular electronics.

The electrical properties of self-assembled monolayers (SAMs) on metal surfaces have been explored for a series of molecules to address the relation between the behavior of a molecule and its structure. We probed interfacial electron transfer processes, particularly those involving unoccupied states, of SAMs of thiolates or arylates on Au by using shear force-based scanning probe microscopy (SPM) combined with current-voltage (i-V) and current-distance (i-d) measurements. The i-V curves of hexadecanethiol in the low bias regime were symmetric around 0 V and the current increased exponentially with V at high bias voltage. Different than hexadecanethiol, reversible peak-shaped i-V characteristics were obtained for most of the nitro-based oligo(phenylene ethynylene) SAMs studied here, indicating that part of the conduction mechanism of these junctions involved resonance tunneling. These reversible peaked i-V curves, often described as a negative differential resistance (NDR) effect of the junction, can be used to define a threshold tip bias, V(TH), for resonant conduction. We also found that for all of the SAMs studied here, the current decreased with increasing distance, d, between tip and substrate. The attenuation factor beta of hexadecanethiol was high, ranging from 1.3 to 1.4 A(-1), and was nearly independent of the tip bias. The beta-values for nitro-based molecules were low and depended strongly on the tip bias, ranging from 0.15 A(-1) for tetranitro oligo(phenylene ethynylene) thiol, VII, to 0.50 A(-1) for dinitro oligo(phenylene) thiol, VI, at a -3.0 V tip bias. Both the V(TH) and beta values of these nitro-based SAMs were also strongly dependent on the structures of the molecules, e.g. the number of electroactive substituent groups on the central benzene, the molecular wire backbone, the anchoring linkage, and the headgroup. We also observed charge storage on nitro-based molecules. For a SAM of the dintro compound, V, approximately 25% of charge collected in the negative scan is stored in the molecules and can be collected at positive voltages. A possible mechanism involving lateral electron hopping is proposed to explain this phenomenon.

Journal Article↗
PubMed2005

The reaction of tetrakis(dimethylamido)titanium with self-assembled alkyltrichlorosilane monolayers possessing -OH, -NH2, and -CH3 terminal groups.

The reactions of tetrakis(dimethylamido)titanium, Ti[N(CH(3))(2)](4), with alkyltrichlorosilane self-assembled monolayers (SAMs) terminated by -OH, -NH(2), and -CH(3) groups have been investigated with X-ray photoelectron spectroscopy (XPS). For comparison, a chemically oxidized Si surface, which serves as the starting point for formation of the SAMs, has also been investigated. In this work, we examined the kinetics of adsorption, the spatial extent, and stoichiometry of the reaction. Chemically oxidized Si has been found to be the most reactive surface examined here, followed by the -OH, -NH(2), and -CH(3) terminated SAMs, in that order. On all surfaces, the reaction of Ti[N(CH(3))(2)](4) was relatively facile, as evidenced by a rather weak dependence of the initial reaction probability on substrate temperature (T(s) = -50 to 110 degrees C), and adsorption could be described by first-order Langmuirian kinetics. The use of angle-resolved XPS demonstrated clearly that the anomalous reactivity of the -CH(3) terminated SAM could be attributed to reaction of Ti[N(CH(3))(2)](4) at the SAM/SiO(2) interface. Reaction on the -NH(2) terminated SAM proved to be the "cleanest", where essentially all of the reactivity could be associated with the terminal amine group. In this case, we found that approximately one Ti[N(CH(3))(2)](4) adsorbed per two SAM molecules. On all surfaces, there was significant loss of the N(CH(3))(2) ligand, particularly at high substrate temperatures, T(s) = 110 degrees C. These results show for the first time that it is possible to attach a transition metal coordination complex from the vapor phase to a surface with an appropriately functionalized self-assembled monolayer.

Journal Article↗
PubMed2006

Self-assembled monolayers on Pt(111): molecular packing structure and strain effects observed by scanning tunneling microscopy.

Self-assembled monolayers (SAMs) of octanethiol and benzeneethanethiol were deposited on clean Pt(111) surfaces in ultrahigh vacuum (UHV). Highly resolved images of these SAMs produced by an in situ scanning tunneling microscope (STM) showed that both systems organize into a super-structure mosaic of domains of locally ordered, closely packed molecules. Analysis of the STM images indicated a (square root 3 x square root 3)R30 degrees unit cell for the octanethiol SAMs and a 4(square root 3 x square root 3)R30 degrees periodicity based on 2 x 2 basic molecular packing for the benzeneethanethiol SAMs under the coverage conditions investigated. SAMs on Pt(111) exhibited differences in molecular packing and a lower density of disordered regions than SAMs on Au(111). Electron transport measurements were performed using scanning tunneling spectroscopy. Benzeneethanethiol/Pt(111) junctions exhibited a higher conductance than octanethiol/Pt(111) junctions.

Journal Article↗
PubMed2005

Thermo-kinetics study of laser-induced desorption of self-assembled monolayers from gold: case of laser micropatterning.

Laser-induced desorption of self-assembled monolayers (SAMs) from gold surfaces within context of the direct laser patterning methodology was investigated through combining results of a heat diffusion thermal model with desorption kinetics of alkanethiol SAMs. It was found that contrast plots of experimental scanning electron microscopy (SEM) images, which are correlated to surface coverage of SAMs desorbed after laser irradiation, agreed with the theoretically predicted surface composition of SAMs. The surface composition of SAM was then interpreted in terms of the wetting property of the resulting surface. The effect of incident laser beam power and size on the final spatial coverage of SAMs on the surface and feature sizes was investigated both experimentally and by modeling. Theoretical modeling and experimental evidence showed that the resulting feature sizes are wider when the surface is heated by a laser of higher power. Increasing the laser beam size results in broadening of feature sizes. Considering the correlation of the theoretical and experimental results, we concluded that the feature sizes are controllable in a predictable way (using the presented thermal-kinetics model) through varying laser beam power and beam size.

Journal Article↗