Monolayers Of Derivatives Research Articles

Ion recognition at the interface of self-assembled monolayers (SAMs) of bis-thioctic ester derivatives of oligo(ethyleneglycols).

Self-assembled monolayers (SAMs) of bis-thioctic ester derivatives of oligoethylene glycols were prepared. When the number of (-CH2-CH2-O-)n units in these podands was either five or six, the corresponding SAMs showed ion binding properties and selectivities similar to those exhibited by 15-crown-5 or 18-crown-6 in aqueous solution, respectively. Impedance data for the SAMs as a function of metal ion concentrations were fitted by using a Langmuir isotherm to determine the association constants (Ka) with the different ions. The SAM derived from the n = 5 compound is selective for Na+ while that with n = 6 is selective for K+. Results presented here confirm the formation of ion recognition domains during self-assembly of acyclic polyethylene glycol derivatives on gold surfaces; this suggests that surface-confined pseudocrown ether structures are formed.

Ion Recognition at the Interface of Self-Assembled Monolayers (SAMs) of Bis-Thioctic Ester Derivatives of Oligo(ethyleneglycols)

Ion Recognition at the Interface of Self-Assembled Monolayers (SAMs) of Bis-Thioctic Ester Derivatives of Oligo(ethyleneglycols)

Dynamics in physisorbed monolayers of 5-alkoxy-isophthalic acid derivatives at the liquid/solid interface investigated by scanning tunneling microscopy

Monolayers of isophthalic acid derivatives at the liquid/solid interface have been studied with scanning tunneling microscopy (STM). We have investigated the dynamics related to the phenomenon of solvent co-deposition, which was previously observed by our research group when using octan-1-ol or undecan-1-ol as solvents for 5-alkoxy-isophthalic acid derivatives. This solvent co-deposition has now been visualized in real-time (two frames per second) for the first time. Dynamics of individual molecules were investigated in mixtures of semi-fluorinated molecules with video-STM. The specific contrast arising from fluorine atoms in STM images allows us to use this functionality as a probe to analyze the data obtained for the mixtures under investigation. Upon imaging the same region of a monolayer for a period of time we observed that non-fluorinated molecules progressively substitute the fluorinated molecules. These findings illustrate the metastable equilibrium that exists at the liquid/solid interface, between the physisorbed molecules and the supernatant solution.

Langmuir-Blodgett films of cellulose ethers containing carbazole

Spread monolayers of cellulose derivatives containing side chain carbazole chromophores are investigated. Structural parameters, such as side chain length and the degree of carbazole substitution, are systematically varied. At lower carbazole content, surface pressure-area isotherms exhibit a liquid analogous phase at molecular areas similar to those observed for cellulose alkyl ethers. A characteristic constant pressure plateau is also evident. As the carbazole content is increased, isotherms shift to lower molecular areas, implying the close parallel packing of chromophore units in the monolayers. An increase in carbazole content also provokes an increase in surface pressure, as well as changes in isotherm shape. For monolayers that show an isotherm plateau, the equilibrium transition surface pressure is found to decrease with increasing temperature. Relatively small positive enthalpy and entropy changes are calculated for the transition. These values are consistent with the identification of the phase transition as bilayer formation. Monolayer transfer to solid substrates was attempted for all samples. Transfer ratios close to unity can be achieved by the optimisation of transfer conditions. Because of the differences in isotherm shape, derivatives with higher carbazole content are transferred at low surface pressure (5 mN·m–1), while (dodecyl)3.0 cellulose and samples of lower carbazole content are transferred at 12 mN·m–1.

Self-Assembled Monolayers of Heme Derivatives on a Gold Surface

Abstract Thiolated heme derivatives were synthesized and their self-assembly behaviors on gold surfaces together with that of native heme were studied. The kinetics of this adsorption and the thickness of the formed monolayer were investigated by surface plasmon resonance spectroscopy. Native heme shows a different adsorption behavior compared to that of the synthesized derivatives. Though the heme derivatives were found to form monolayers, native heme formed only irregular aggregates on gold surfaces. IR spectroscopy was used to reveal the molecular structure of the adsorbates in the vicinity of the peptide linkage in the heme molecules on the gold surfaces. UV spectroscopy was employed to determine the tilt angle of the porphyrin rings relative to the gold surface normal. Cyclic voltammograms and potential-modulated UV-vis reflectance spectra of heme derivatives were observed in order to estimate the adsorbed amount and the redox behaviors of heme derivatives on gold surfaces.

Photochemical Behavior of Diolefinic Compounds with Amide Bonds: Relationship between Molecular Environment and Reaction Kinetics in the Monolayers

Photopolymerization has been conducted successfully in the Langmuir and Langmuir-Blodgett monolayers of p-phenylenediacrylic acid derivatives. We have evaluated the mutual relationship between the reaction-induced monolayer structural change and the dependence of the reaction kinetics on the monolayer structure.

Interfacial Properties of Substituted Fulleropyrrolidines on the Water Surface

A series of novel substituted fulleropyrrolidines have been synthesized and characterized. A correlation between the substituent structure and the spreading behavior at the air−water interface has been proposed through the systematic study of their Langmuir films. This evidences that only some derivatives are suitable to form true monolayers at the air-water interface, because of the strong π−π intermolecular attractive forces among C60 spheres. The factors that influence the nature of the floating layers on the water subphase have been identified. At last, tuneable parameters for the preparation of real and stable monolayers of fullerene derivatives have been proposed.

Self-assembled monolayers containing biphenyl derivatives as challenge for nc-AFM

Mixed self-assembled monolayers (SAMs) of biphenylmethanethiol derivatives with CH 3 and COOH terminal groups and those of 1-decanethiol and a biphenylmethanethiol derivative with a CH 3 or a COOH terminal group were prepared on Au(111) surfaces. The resulting mixed SAMs were imaged by scanning tunneling microscopy (STM). These mixed SAMs can be used to study chemical force microscopy (CFM) by noncontact atomic force microscopy (nc-AFM). Namely, the CH 3 and COOH terminal groups of the SAMs can be recognized by different surface interactions with a surface functional group on a gold-coated AFM tip derivatized with the same thiol compound with a CH 3 or a COOH terminal group. The present result also suggests that these SAMs can be used to study CFM using nc-AFM with simultaneous tunneling current measurement. By this method, for example, a molecular location of a biphenylmethanethiol derivative with a COOH terminal group in an alkanethiol matrix observed by nc-AFM can be confirmed by the tunneling current measurement due to lower tunneling barrier height of the biphenylmethanethiol than that of the alkanethiol derivative.

Self-assembled monolayers of bis-thioctic ester derivatives of oligoethyleneglycols: remarkable selectivity for K+/Na+ recognition

Bis-thioctic ester terminated derivatives of oligoethylene glycols form extremely stable self-assembled monlayers (SAMs) on gold electrodes and these can recognize K+ selectively over Na+, as measured by cyclic voltammetry and impedance spectroscopy.

Formation and Novel Functions of Self-assembled Monolayers of Thiol Derivatives

Formation and Novel Functions of Self-assembled Monolayers of Thiol Derivatives

Scanning tunneling microscopy investigation of tricycloquinazoline liquid crystals on gold

Self-assembled monolayers (SAMs) of hexaalkylthioether derivatives of tricycloquinazoline (TCQ) on Au(111) and tungsten diselenide (WSe 2) were investigated by scanning tunneling microscopy (STM). The Au(111) surfaces were found to be etched by the thioether containing solutions. Corroded surfaces which are similar to gold surfaces that were coated with SAMs of thiols or disulfides were revealed by STM. Atomic adsorption spectroscopy proved that an amount of gold that corresponds to ca. 30% of a monolayer was dissolved in the assembly solutions. On gold, the aromatic cores of the molecules were found to be in face-on orientation. The alkyl substituents were in most cases folded upwards and shielding the aromatic cores. Only after long immersion times were crystalline areas observed locally, in which the alkyl chains were lying flat on the gold surface. On WSe 2 mono- and multilayers of TCQ molecules in face-on orientation could be imaged by STM. The observed columnar structures displayed long-range order.

Structural differences in self-assembled monolayers of anthraquinone derivatives on silver and gold electrodes studied by cyclic voltammetry and in situ SERS spectroscopy

Self-assembled monolayers (SAMs) of 1-anthraquinonylbutylsulfide (1-AQS) and 2-anthraquinonylbutylsulfide (2-AQS) on silver and gold electrodes were investigated by cyclic voltammetry and in situ surface enhanced Raman spectroscopy (SERS). A reversible redox wave was observed for 1-AQS and the redox potential shifted ca. −30 and −60 mV pH −1 at silver and gold electrodes, respectively, in the pH region 5–9. On silver electrodes, the electrochemical properties of 1-AQS were similar to those of 2-AQS. In addition, the Raman spectrum of 1-AQS powder is very similar in intensity and peak positions to that of 2-AQS powder. However, in situ SERS measurements showed that the 1-AQS molecule was tilted relative to the silver surface normal and no change in its orientation took place between oxidized and reduced forms. The oxidized 2-AQS molecule was shown to be adsorbed perpendicular to the silver surface, but on reduction at −0.6 V the orientation of the anthraquinone plane changed. On gold electrodes, no clear SERS spectrum was obtained for the SAM of 1-AQS, suggesting a flat orientation of the anthraquinone plane relative to the electrode surface. SERS spectra of 2-AQS on the gold surfaces gave clear spectra, suggesting a perpendicular orientation of the anthraquinone plane relative to the gold surface independent of the applied potential. These differences in orientation are ascribed to the position of the butylsulfide moiety on the anthraquinone ring at gold and silver electrodes.

Electrochemistry of Langmuir–Blodgett and self-assembled monolayers of pyrrole derivatives

We prepared bis( ω-(N-pyrrolyl)- n-undecyl)disulfide (BPUS) self-assembled (SA) monolayers and octadecylpyrrole (ODP) Langmuir–Blodgett (LB) monolayers in order to understand electrochemical properties of pyrrole derivatives. This study shows that the monolayers are not electrochemically oxidized to form polypyrrole. Instead, we propose the pyrrole monolayers form dimers and/or ketone type degradation products upon oxidation. If the monolayer is exposed to the laboratory ambient, then the SA monolayer is decomposed and removed from the surface during the electrochemical measurement. However, the LB monolayer was not. The transfer efficiency of the LB monolayer was approximately 7–10% that of the SA monolayer.

Langmuir–Blodgett films of azocrown ethers on electrodes — voltammetric recognition of isomers

Abstract Monolayers of amphiphilic derivatives of crown ethers bearing electroactive azo groups in the macrocycle were transferred from the air ∣ water interface onto indium–tin oxide (ITO) or thin mercury film electrodes (TMFE) using the Langmuir–Blodgett technique. Differences in the electrochemical reversibility of the systems observed on these two electrodes were explained by different orientation of the azocrown molecules on the hydrophobic (TMFE) and hydrophilic (ITO) electrode surfaces. The electrochemical studies of the monolayer modified electrodes proved that the organization of the monolayer and the redox properties of the azocrown molecules depend on the geometry around the NN moiety. Voltammetry allowed Z - and E -isomers of the azocrowns to be recognized and their isomerization processes in monolayers to be followed. The effects of pH and of the alkali metal cations on the stability of the isomers were studied. Isomerization to the more stable E -isomer was hindered in alkaline solutions and under these conditions well separated reduction peaks of the E - and Z -isomers were obtained.

Electrochemical and Spectroscopic Characterization of Self-Assembled Monolayers of Unsymmetrical Ferrocenyl Dialkyl Sulfide Derivatives on Gold

Electrochemical and Spectroscopic Characterization of Self-Assembled Monolayers of Unsymmetrical Ferrocenyl Dialkyl Sulfide Derivatives on Gold

Remarkably stable self-assembled monolayers of new crown-ether annelated tetrathiafulvalene derivatives and their cation recognition properties†

Bis-thioctic ester derivatives of crown-ether annelated tetrathiafulvalenes (TTFs) form extremely stable self-assembled monolayers (SAMs) on gold electrodes and can recognize alkali metal ions by cyclic voltammetry.

Interfacial photochemistry: fundamental and applications

Abstract

Stable monolayers of fullerene derivatives

Two new fullerene derivatives 1a and 1b, form robust Langmuir monolayers at the air–water interface, that transfer onto substrates by Langmuir–Blodgett (LB) or Langmuir–Schaefer (LS) techniques. The measured molecular areas (105 Å 2 for 1a dropped from a deuterochloform solution at 20°C) reach those expected for a true monolayer of C 60 at the air–water interface. An STM image of an LS film of 1a on HOPG shows considerable order.

Study of Langmuir monolayers of crown-ether C 60 derivatives and their interaction with different subphase ions

The Langmuir monolayers of two crown-ether C 60 derivatives with different crown size (18-crown-6, and 15-crown-5) were studied by surface spectrophotometry and Brewster angle microscopy. The surface pressure–area ( π– A) isotherms of the C 60 derivatives on pure water and different subphase ions were obtained. The limiting area of the isotherms depends on both the crown size and the presence of subphase ions. The larger crown size gave the larger limiting area of the isotherm. The addition of K +, Ba 2+ or NH 4 + to the subphase stabilized the monolayers and increased the limiting areas of the monolayer. Brewster angle microscopy shows different aggregation properties of crown-ether C 60 derivative monolayers on pure water compared with those on K +, Ba 2+ or NH 4 + subphases.

Self-Assembled Carbohydrate Monolayers: Formation and Surface Selective Molecular Recognition

The formation of self-assembled monolayers (SAMs) of representative thiocarbohydrate derivatives onto a gold surface has been investigated to build an artificial carbohydrate scaffold to mimic non-bonded molecular recognition phenomena. Three types of carbohydrate SAMs were formulated from (i) 1-β-d-thioglucose (1), (ii) 1-β-d-thioglucose tetraacetate (2), and (iii) 2-mercaptoethyl α-d-mannopyranoside (3). Subsequently, each SAM was spectroscopically characterized by reflection-absorption infrared spectroscopy (RAIRS). Deprotection of the acylated carbohydrate SAM was achieved in situ, indicating that chemical transformation may be performed without disruption of the sulfurgold bond. With the mannose derivative, in which the carbohydrate moiety was separated from the gold surface by the spacer unit OCH2CH2SH, it was possible to demonstrate that such a carbohydrate SAM was able to interact selectively with a specific carbohydrate binding protein, i.e., concanavalin A (Con A). Exposure of the mannose derive...