Size-dependent adsorption of 1,4-phenylenediisocyanide onto gold nanoparticle surfaces

Adsorption of 1,4-phenylenediisocyanide (PDI) has been studied for different-sized gold nanoparticles with mean diameters of 6, 14, 23, 40, 57, and 97 nm using UV-vis absorption spectroscopy and surface-enhanced Raman scattering (SERS). The SERS enhancement was found to be relatively weak for 6-nm particles due to less aggregation between PDI and gold particles. Concentration-dependent SERS spectra show that PDI was assumed to bridge two different gold particles at low concentrations of PDI, but as the concentration was increased, the bridge appeared to be broken, and PDI bonded to the gold particle only via one of its two isocyanide groups. For the 57- and 97-nm particles, however, the nu(NC)(free) stretching band in the SERS spectrum almost disappeared, even at a high bulk concentration of PDI, differently from the case of the smaller sizes (14, 23, and 40 nm). The 57- and 97-nm particles appeared to cross-link through the pendent isocyanide group even at a high bulk concentration. UV-vis absorption spectra indicated that PDI appeared to aggregate more extensively with increasing size in agreement with Raman data. Our result shows an example that the adsorption scheme of an aromatic diisocyanide may be varied depending on particle size as well as the bulk concentration.     

Hydrogen storage properties of isocyanide-stabilized palladium nanoparticles

Monodispersed palladium nanoparticles protected with n-octyl isocyanide were prepared, and their hydrogen absorption behavior was evaluated. The formation of the nanoparticles has been confirmed by means of 1H NMR and elemental analysis. Fourier transform infrared (FT-IR) showed that three distinct bands (2156, 1964, and 1611 cm(-1)) assigned to mono-, double-, and triple-bridged isocyanide ligands on the palladium surface. The average diameter of the particles was estimated to be 2.1 +/- 0.7 nm from observation by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) analysis revealed that the particles contained Pd(0) with little amounts of Pd(II) or Pd(IV), in sharp contrast to the thiol- or phosphine-stabilized palladium nanoparticles. The absorption and desorption of hydrogen were reversible, and the reactions were much faster for the nanoparticles than for the bulk palladium metal, whereas the storage capacity was almost the same, 0.6 wt %.     

金纳米粒子组装体系中偶联单分子层膜结构的SERS光谱表征与分析

通过分子自组装方法制备4,4′-二硫联吡啶(PySSPy)单分子膜修饰的金电极. 利用所形成的对巯基吡啶自组装单分子膜(SAMs)作为偶联层进行金纳米粒子有序膜的组装. 对该纳米粒子组装体系进行Raman光谱测定, 得到了具有良好信噪比的对巯基吡啶单分子膜的表面增强拉曼散射(SERS)光谱. 在此基础上, 进一步采用电化学现场SERS光谱技术研究了该纳米粒子组装体系的SERS光谱随电位变化的规律. 在该体系稳定的电位范围内表征对巯基吡啶单分子膜的特征谱峰1011与1093 cm^-1、1575与1610 cm^-1以及1206与1215 cm^-1这三对谱峰其强度随着所施加电位的改变呈现出明显的规律性. 分析表明, 偶联单分子层中吡啶环芳香性随着所施加电位的改变而有规律地变化是SERS光谱特征改变的内在原因.     

Combined STM and FTIR characterization of terphenylalkanethiol monolayers on Au(111): effect of alkyl chain length and deposition temperature

Self-assembled monolayers (SAMs) of 4,4'-terphenyl-substituted alkanethiols C6H5(C6H4)2(CH2)n-SH (TPn, n = 1-6) on Au (111) substrates were studied using scanning tunneling microscopy (STM) and infrared reflection absorption spectroscopy (IRRAS). When the SAMs were prepared at room temperature (RT, 298 K), TPn films (except TP2) exhibit an odd-even effect regarding both molecular orientation and packing density. For all investigated films, STM data reveals the presence of a large degree of lateral order. In the case of odd-numbered TPns, the films revealed a (2 square root(3) x square root(3))R30 degree molecular arrangement. For the even-numbered TP4 and TP6 SAMs, a c(5 square root(3) x 3) rectangular unit cell was found. The packing density for the even-numbered TPn SAMs is 25% lower than that for the odd-numbered TPn SAMs. When the SAMs were prepared at 333 K, the even-numbered SAMs were found to form structures with a significantly lower packing density. In the case of TP2, instead of the (2 square root(3) x square root(3))R30 degree structure formed at room temperature, a c(5 square root(3) x 3) structure was observed. For TP6 SAMs, the room-temperature c(5 square root(3) x 3) structure was replaced by a (6 square root(3) x 2 square root(3))R30 degree structure.     

Self-assembled monolayers derived from a double-chained monothiol having chemically dissimilar chains

The structure and conformation of self-assembled monolayers (SAMs) derived from the adsorption of a specifically designed double-chained partially fluorinated thiol having the formula 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-heptadecafluoro -2-tetradecylnona-decane-1-thiol ( 2) onto the surface of evaporated gold were examined by ellipsometry, contact angle goniometry, polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). The results were compared to those of SAMs generated from normal hexadecanethiol ( 1) and a structurally related single-chained partially fluorinated thiol having the formula 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-heptadecafluorononadecane-1-thiol ( 3). Collectively, the studies demonstrate that the double-chained adsorbate 2 forms SAMs on gold in which the alkyl chains are less densely packed and less conformationally ordered than those in the SAMs derived from each of the single-chained adsorbates. Furthermore, the fluorocarbon moieties in the SAMs derived from 2 are more tilted from the surface normal than those in the SAMs derived from 3. The low values of contact angle hysteresis suggest, however, that the double-chained adsorbate 2 generates homogeneous monolayer films on the surface of gold.     

Efficient photocurrent generation by self-assembled monolayers composed of 3 10-helical peptides carrying linearly spaced naphthyl groups at the side chains

Self-assembled monolayers (SAMs) were prepared on a gold substrate from a 310-helical peptide carrying three naphthyl groups at the side chain (SSN3B) or from the reference peptides carrying no or one naphthyl group. The 310-helical conformation of SSN3B in solution was confirmed by 1H NMR spectroscopy and geometry optimization. Cyclic voltammetry and infrared absorption-reflection spectroscopy showed vertical molecular orientation and a well-packed structure in the SSN3B SAM. Anodic photocurrent was successfully generated by the SSN3B SAM in the presence of triethanolamine, and the current intensity was found to be much larger than those by the other SAMs from peptides carrying one naphthyl group. It was therefore concluded that the linearly spaced naphthyl groups along the helical axis act as photosensitizer and electron-hopping site to promote photocurrent generation remarkably.     

SERS and RAIR for Molecular Structure of Phenylazonaphthalene-terminated Self-Assembled Monolayer

Aromatic azo-based SAMs are attractive because of their possibilities for fabrication of data storage molecular devices1-2. The system of azobenzene-based alkylthiol on gold is one of the most intensive studies, which has a highly ordered and closely packed structure. The dense packing, however, limits the electroactivity of azobenzene. Therefore, another kind of aromatic azo molecule, phenylazonaphthalene, is considered as a substitute.. The SAMs of 10-[4-(4-phenylazo)naphth-1-oxyl]-1-d…     

Planar-chiral metal complexes comprised of square-planar metal and achiral tetradentate ligands: design, optical resolution, and thermodynamics

Planar-chiral palladium complexes {[[N,N'-[1,4-butanediylbis(oxy-7,1-naphthalenediyl)]bis(2-pyridinecarboxamidato)](2-)-κN(1),κN(1)',κN(2),κN(2)']palladium (PdL(4)) and [[2,2'-[1,4-butanediylbis[[(oxy-7,1-naphthalenediyl)imino]methyl]]dipyrrolato](2-)-κN(1),κN(1)',κN(2),κN(2)']palladium (PdL(5))} were synthesized from achiral tetradentate ligands N,N'-[1,4-butanediylbis(oxy-7,1-naphthalenediyl)]bis(2-pyridinecarboxamide) (H(2)L(4)) and N,N'-bis[(1H-pyrrol-2-yl)methylidene]-7,7'-(1,4-butanediyldioxy)bis(1-naphthalenamine) (H(2)L(5)) bearing two dissymmetric bidentate units at both ends and a Pd(II) ion, respectively. The palladium complexes were crystallized in the monoclinic space group P2(1)/n with the unit cell parameters a = 16.5464(6) ?, b = 11.3534(4) ?, c = 17.6697(7) ?, β = 115.5300(10)°, and Z = 4 for PdL(4) and a = 17.2271(8) ?, b = 10.1016(5) ?, c = 17.9361(9) ?, β = 105.6310(10)°, and Z = 4 for PdL(5). The planar-chiral structures of PdL(4) and PdL(5) were confirmed by single-crystal X-ray analyses, resulting in the fact that the crystals were racemic mixtures. The racemic mixtures were successfully resolved by using chiral high-performance liquid-chromatography techniques. Racemizations of the complexes were found to be drastically dependent on the arrangement of the charged or uncharged metal-binding N atoms of the ligands.     

Supramolecular incorporation of fullerenes on gold surfaces: comparison of C60 incorporation by self-assembled monolayers of different calix[n]arene (n = 4, 6, 8) derivatives

[reaction: see text] Two new calix[6]arene derivatives 3 and 4 in a 1,4-anti conformation and one calix[8]arene derivative 5 were synthesized. SAMs of calix[n]arene (n = 4, 6, 8) derivatives 1-5 were formed on gold bead electrodes. Cyclic voltammetry with Ru(NH3)6(3+/2+) as a redox probe, together with impedance spectroscopy and reductive desorption, indicates that SAMs of 5 have a higher coverage than those of 3 and 4 due to the presence of hydrogen bonding and possibly its conformation. Noncovalent immobilization of C60 on gold surfaces was achieved with SAMs of calix[8]arene derivative 5 but not with those of 1-4.     

Self-assembly, characterization, and chemical stability of isocyanide-bound molecular wire monolayers on gold and palladium surfaces

Self-assembled monolayers (SAMs) of the isocyano derivative of 4,4'-di(phenylene-ethynylene)benzene (1), a member of the "OPE" family of "molecular wires" of current interest in molecular electronics, have been prepared on smooth, {111} textured films of Au and Pd. For assembly in oxygen-free environments with freshly deposited metal surfaces, infrared reflection spectroscopy (IRS) indicates the molecules assume a tilted structure with average tilt angles of 18-24 degrees from the surface normal. The combination of IRS, X-ray photoelectron spectroscopy, and density functional theory calculations all support a single sigma-type bond of the -NC group to the Au surface and a sigma/pi-type of bond to the Pd surface. Both SAMs show significant chemical instability when exposed to typical ambient conditions. In the case of the Au SAM, even a few hours storage in air results in significant oxidation of the -NC moieties to -NCO (isocyanate) with an accompanying decrease in surface chemical bonding, as evidenced by a significant increase in instability toward dissolution in solvent. In the case of the Pd SAM, similar air exposure does not result in incorporation of oxygen or loss of solvent resistance but rather results in a chemically altered interface which is attributed to polymerization of the -NC moieties to quasi-2D poly(imine) structures. Conductance probe atomic force microscope measurements show the conductance of the degraded Pd SAMs can diminish by approximately 2 orders of magnitude, an indication that the SAM-Pd electrical contact has severely degraded. These results underscore the importance of careful control of the assembly procedures for aromatic isocyanide SAMs, particularly for applications in molecular electronics where the molecule-electrode junction is critical to the operational characteristics of the device.     

Influence of alkyl chain length on the structure of dialkyldithiophosphinic Acid self-assembled monolayers on gold

We report the formation and characterization of self-assembled monolayers (SAMs) based on dialkyldithiophosphinic acid adsorbates {[CH(3)(CH(2))(n)](2)P(S)SH (n = 5, 9, 11, 13, 15)} on gold substrates. SAMs were characterized using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, contact angle measurements, and electrochemical impedance spectroscopy. Data show that there is a roughly 60:40 mixture of bidentate and monodentate adsorbates in each of these SAMs. The presence of monodentate adsorbates is due to the numerous and deep grain boundaries of the underlying gold substrate, which disrupt chelation. Comparing the characterization data of dialkyldithiophosphinic acid SAMs with those of analogous n-alkanethiolate SAMs shows that both SAMs follow a similar trend: The alkyl chains become increasingly organized and crystalline with increasing alkyl chain length. The alkyl groups of dialkyldithiophosphinic acid SAMs, however, are generally less densely packed than those of n-alkanethiolate SAMs. For short alkyl chains (hexyl, decyl, and dodecyl), the significantly lower packing densities cause the alkyl chains to be liquid-like and disorganized. Long-chain dialkyldithiophosphinic acid SAMs are only slightly less crystalline than analogous n-alkanethiolate SAMs.     

Hemoglobin on phosphonic acid terminated self-assembled monolayers at a gold electrode: immobilization, direct electrochemistry, and electrocatalysis

Phosphonic acid (--PO(3)H(2)) terminated self-assembled monolayers (SAMs) on a gold surface were used as a functional interface to immobilize hemoglobin (Hb). In situ surface-enhanced infrared absorption spectroscopy (SEIRAS) measurements show that Hb immobilization is a sluggish process due to formation of multilayer Hb structures on the PO(3)H(2)-terminated SAMs, as revealed by ellipsometry, atomic force microscopy (AFM), and cyclic voltammetry (CV). In the multilayered Hb film, the innermost Hb molecules can directly exchange electrons with the electrode, whereas Hb beyond this layer communicates electronically with the electrode via protein-protein electron exchange. In addition, electrochemical measurements indicate that immobilization of Hb on the PO(3)H(2)-terminated SAMs is not driven by the electrostatic interaction, but likely by hydrogen-bonding interaction. The immobilized Hb molecules show excellent bioelectrocatalytic activity towards hydrogen peroxide, that is, the PO(3)H(2)-terminated SAMs are promising for construction of third-generation biosensors.     

Synthesis and structural characterization of glucopyranosylamide films on gold

Self-assembled monolayers (SAMs) of glucose derivatives on gold have been prepared from alpha- and beta-glucopyranosylamide derivatives. The glucosyl conjugates were synthesized stereoselectively via the in situ generation of glucosyl isoxazolines followed by treatment with thiopyridyl esters. The resulting film structures were characterized by atomic force microscopy, reflection Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The experimental data indicated that alpha- or beta-linked glucopyranosylamide derivatives with free hydroxyl groups attach to gold via the thiol linker. Both derivatives form monolayer films with high packing densities--comparable to those typically observed for alkanethiol monolayers on gold. Acetate analogues of these conjugates do not form SAMs on gold; they form multilayered films under identical deposition conditions.     

Synthesis and self-assembling properties on gold of 2-methyl-1,4-naphthoquinone derivatives containing ω-mercaptoalkylalkanoate groups

The synthesis of a series of 2-methyl-1,4-naphthoquinone (2-MeNQ) derivatives containing surface active ω-mercaptoalkylalkanoate groups with 5-12 atoms in the side-chains is reported. The compounds form stable self-assembled monolayers (SAMs) on gold. The complete reduction of the terminal 2-MeNQ group in the SAMs was confirmed by in situ Fourier-transform surface-enhanced Raman spectroscopy (FT-SERS). The basic electrochemical properties of the monolayers were determined by cyclic voltammetry (CV).     

Self-assembled monolayers of alkanethiolates on palladium are good etch resists

This paper describes microcontact printing (muCP) of long-chain alkanethiolates on palladium, followed by solution-phase etching with an iron(III)-based etchant, to make patterned structures. The commonly used soft-lithographic procedure for fabricating microstructures-muCP of SAMs on gold-has three shortcomings: a significant surface density of pinhole defects, substantial edge roughness, and incompatibility with processes used in CMOS fabrication. Microcontact printing on palladium gives fewer defects and smaller edge roughness than on gold, and is compatible with CMOS. The mechanism by which etch-resistant patterns are formed is different for palladium and gold. The Pd/S interfacial layer formed by the reaction of palladium films with sulfur-containing compounds provides good resistance to etches independently of the barrier to access the surface provided by the film of (CH2)n groups in the long-chain SAMs. This barrier is the basis of the etch resistance of SAMs on gold, but only supplements the etch resistance of the sulfur-containing interfacial layer on palladium. Characterization of the SAM formed from hexadecanethiol on palladium is described.     

Sub-monolayer assemblies of octanethiol and octadecylthiol at gold electrodes for the direct analysis of 4,4'-oxydianiline in wastewaters and shoe-dyeing samples

Self-assembled monolayers (SAMs) of di-n-octadecyldisulphide (C(18)) and n-octanethiol (C(8)) were prepared on gold electrodes. From the studies carried out by cyclic voltammetry and square wave voltammetry, it was observed that the electrochemical behaviour of 4,4'-oxydianiline on these electrodes is affected by the length chain of the alkanethiol. After the optimization of all the variables involved in the electrochemical response of 4,4'-oxydianiline by square wave voltammetry employing the modified electrodes, it is possible the determination of 4,4'-oxydianiline with a detection limit of 0.04microg/mL (C(18)) and 0.06microg/mL (C(8)) and determination limits of 0.12 and 0.22microg/mL, respectively. The calculated Er (%)(n=10) and R.S.D.(%)(n=10) values were minor than 2.2% and 3.7%. The proposed methods were successfully applied to the analysis of oxydianiline in wastewater and shoe-dyeing samples.     

Binding property and structure of aromatic isocyanide self‐assembly monolayers on Ag and Au surfaces

The binding property of p‐biphenyl isocyanide self‐assembled monolayers (SAMs) on Au and Ag was investigated by temperature‐dependent surface‐enhanced Raman spectroscopy (SERS). p‐Biphenyl isocyanide was found to desorb on Ag at a low temperature of ～393 K whereas it appeared to remain enduring at a high temperature of ～453 K for Au. Structures of p‐biphenyl isocyanide SAMs on Au and Ag flat films were checked by means of near‐edge x‐ray absorption fine structure spectroscopy (NEXAFS) at the two different normal (90° ) and grazing (20° ) angles of the incident x‐ray beam. Our results suggested that the SAMs prepared by p‐biphenyl isocyanide should have a relatively disordered structure even at room temperature on both Au and Ag, as indicated from an insubstantial change in NEXAFS spectra at the two different angles from those of p‐biphenyl thiolate and p‐biphenyl methanethiolate. The weakness of the isocyanide–metal bond in comparison with the sulphur–metal bond may result in both low surface coverage and orientational disorder. A density functional theory calculation method was employed to attempt to explain the difference in stability for phenyl isocyanide on Ag and Au surfaces. Our calculation result yielded a lower binding energy of phenyl isocyanide on Ag than that on Au, consistent with the temperature‐dependent Raman results. Copyright © 2005 John Wiley & Sons, Ltd.     

界面可控硫醇SAMs纳米金修饰金电极的电化学行为研究

在裸金电极上自组装不同比例的4,4’-二甲基联苯硫醇(MTP)和硫辛酸(TA)混合液,形成自组装膜(MTP+TA/Au SAMs),再修饰纳米金,制得纳米金混合巯基修饰金电极(AuNPs/MTP+TA/Au)。研究了纳米金混合巯基修饰金电极的电化学行为和阻抗行为,结果表明电极表面pH值的改变对电极表面的电子转移有重要影响。对葡萄糖传感器的制备条件、测定条件、抗干扰能力等进行了讨论,结果表明修饰电极的微结构和微环境有必要进一步研究。     

Self-assembled monolayers of peptide nucleic acids on gold surfaces: a spectroscopic study

We have characterized self-assembled monolayers (SAMs) of thiol-derivatized peptide nucleic acid (PNA) chains adsorbed on gold surfaces by using reflection absorption infrared spectroscopy (RAIRS) and X-ray photoemission spectroscopy (XPS) techniques. We have found that the molecular orientation of PNAs strongly depends on surface coverage. At low coverage, PNA chains lie flat on the surface, while at high coverage, PNA molecules realign their molecular axes with the surface normal and form SAMs without the need of co-immobilization of spacers or other adjuvant molecules. The change in the molecular orientation has been studied by infrared spectroscopy and it has been confirmed by atomic force microscopy (AFM). PNA immobilization has been followed by analyzing the N(1s) XPS core-level peak. We show that the fine line shape of the N(1s) core-level peak at optimal concentration for biosensing is due to a chemical shift. A combination of the above-mentioned techniques allow us to affirm that the structure of the SAMs is stabilized by molecule-molecule interactions through noncomplementary adjacent nucleic bases.     

An anionic In(III)-based metal-organic framework with Lewis basic sites for the selective adsorption and separation of organic cationic dyes

An In(Ⅲ)-based metal-organic framework (BUT-29) can selectively absorb cationic dyes in DMF even in the presence of other organic dyes, and has the higher adsorption capacity.