Monolayers Of Derivatives Research Articles

Enantioselective recognition of calix[4]arene derivatives bearing chiral bicyclic guanidinium for d/ l-phenylalanine zwitterions at the air–water interface

Monolayers of the amphiphilic calixarene derivatives (BSGC, MSGC and MGC) bearing chiral bicyclic guanidinium on the surface of pure water and of aqueous subphases containing l-phenylalanine or d-phenylalanine ( l/ d-Phe) were studied by film balance measurements. LB films deposited from the monolayers on the three kinds of subphases were investigated by circular dichroism spectra (CD). All the results indicate that BSGC, MSGC and MGC can form stable monolayers on these subphases. Moreover, BSGC (with two chiral bicyclic guanidinium units) can enantioselectively recognize l-aromatic amino acid and its enantioselectivity for l-Phe is better than MSGC (with one chiral bicyclic guanidinium unit) at the air–water interface, and the enantioselectivity of MGC (without hydrophobic silylether group at the arm of the chiral bicyclic guanidinium unit) for l-Phe is higher than MSGC (with hydrophobic silylether group). Therefore their enantioselectivities for l-Phe depend on the molecular structures.

Interaction of monolayers of calix649resorcinarene derivatives with copper ions in the aqueous subphase

Stable monolayers of novel amphiphilic calix[4]resorcinarene derivates at the air–water interface were prepared. Their interactions with copper ions from the aqueous subphase were investigated by measuring surface pressure–area and surface potential–area isotherms, as well as by Brewster angle microscopy. Theoretical aspects of interpreting the dependence of the surface pressure on the bulk copper ions concentration were discussed. The interaction of copper ions with calix[4]resorcinarene derivates was interpreted in terms of Gibbs–Shishkovsky adsorption equation.

Enantioselective recognition of calix649arene derivatives bearing chiral bicyclic guanidinium for /-phenylalanine zwitterions at the air?water interface

Monolayers of the amphiphilic calixarene derivatives (BSGC, MSGC and MGC) bearing chiral bicyclic guanidinium on the surface of pure water and of aqueous subphases containing l -phenylalanine or d -phenylalanine ( l / d- Phe) were studied by film balance measurements. LB films deposited from the monolayers on the three kinds of subphases were investigated by circular dichroism spectra (CD). All the results indicate that BSGC, MSGC and MGC can form stable monolayers on these subphases. Moreover, BSGC (with two chiral bicyclic guanidinium units) can enantioselectively recognize l -aromatic amino acid and its enantioselectivity for l -Phe is better than MSGC (with one chiral bicyclic guanidinium unit) at the air–water interface, and the enantioselectivity of MGC (without hydrophobic silylether group at the arm of the chiral bicyclic guanidinium unit) for l -Phe is higher than MSGC (with hydrophobic silylether group). Therefore their enantioselectivities for l -Phe depend on the molecular structures.

Determining the Self-Assembling and Redox Process of a Viologen Monolayer by Electrochemical Quartz Crystal Microbalance

Electrochemical and quartz crystal microbalance (EQCM) methods are used to probe the redox behavior of self-assembled monolayers of viologen derivatives with long alkyl chains and disulfide or thiol groups that provide for attachment to gold electrodes. The EQCM measurements revealed that cations exit and enter the viologen monolayer during reduction and oxidation, respectively. In this study, the self-assembly process of viologen was monitored using resonant frequency (ΔF) and resonant resistance (ΔR). The QCM measurements indicated a mass adsorption for viologen assembling on the gold surface with a frequency change of approximately 135 Hz and calculated its surface coverage (Γ) to be 3.5273×10-9 mol/cm2. Also, a reversible redox process was observed and analyzed with an ionic interaction at the viologen/solution interface using ΔF.

Monolayers of reactive cellulose derivatives

AbstractFunctional cellulose derivatives are very versatile materials for the creation of mono‐ and multilayer systems. Hydrophobic alkyl and trimethylsilyl celluloses form highly ordered Langmuir‐Blodgett multilayers on hydrophobic substrates. Cellulose thiosulfates and methyl thio ethers were self‐assembled on gold and silver surfaces to form hydrophilic monolayers. Cellulose layer systems are capable for chemical transformations under conservation of the structural order. They are suitable platforms for the investigation of molecular recognition at surfaces and the construction of sensor devices. Both biological ligands, e.g. biotin, and enzymes, e.g. horse radish peroxidase, could be attached to cellulose under conservation of their biological function.

Selective Adsorption of Copper Phthalocyanine Atop Functionalized Organic Monolayers

We report the observation of site-selective adsorption of copper phthalocyanine (CuPc) atop organic surfaces. The organic surfaces consist of monolayers of various alkane derivatives (stearic acid, 1-octadecano,l and 1-iodooctadecane) adsorbed on the surface of highly oriented pyrolytic graphite (HOPG). Our scanning tunneling microscopy (STM) studies show that the alkane derivatives form templates, which can provide different adsorption sites for the CuPc. The observed selective adsorption behavior is attributed to a dominating preference of the CuPc for adsorption on the hydrocarbon-chain portions of the supporting layers. We also discuss the results of molecular mechanics simulations, which support the STM observations.

Study on hydrolytic kinetics of Langmuir monolayers of biodegradable polylactide derivatives

The rate of hydrolysis of Langmuir monolayer films of biodegradable polylactide (PLA) derivates was investigated at the air/water interface. The present study investigated such parameters as surface pressure, pH, and time. The hydrolysis of polyester monolayers depended strongly on the subphase pH, the concentration of active ions. Under the conditions studied here, polymer monolayers showed faster rates of hydrolysis when they were exposed to a basic subphase rather than they did when exposed to acidic or neutral subphases. By increasing the concentration of the degradation medium, the hydrolytic rate ofdl-PLA monolayers was accelerated (accelerating effect). In addition, the basic hydrolysis of modified PLA with small amounts of hydrophilic (benzyloxycarbonyl) methyl morpholine-2,5-dione or glycolide was much faster than that of the PLA homopolymer.

Light Emission from Organic Molecules on Metal Substrates Induced by Tunneling Currents

Tunneling currents in a scanning tunneling microscope were used to induce light emission by positioning either a gold-coated W tip on the surface of a porphyrin molecular monolayer on Cu(100) or a pure W tip on the surface of a perinone derivative monolayer on Au(100). The emission spectra from the surfaces of both molecules are dominated by the plasmon-mediated emission from substrates. Molecular fluorescence is completely quenched by the metal substrate. The organic molecules act as a spacer to modify the tip-induced plasmon modes, enhance the intensity of the plasmon-mediated emission, and cause blue shift of the spectra.

A model study of artificial linker system using self-assembled calix[4]arene derivative monolayers for protein immobilization

The attachment of biomolecules, in particular proteins, onto solid supports is fundamental in the development of advanced biosensors, biochips, bioreactors, and many diagnostic techniques. In addition, the effective investigation of biomolecular structure and function with chip-based modern instruments often requires effective attachment of the biomolecule to a substrate. For this reason, it is very important to construct well-characterized linker system that can immobilize protein efficiently. Here, we investigate the formation of self-assembled monolayers (SAMs) with calix[4]arene ethylester and carboxylic acid derivatives that can serve as a model system for protein immobilization at solid surfaces. The calix[4]arene derivative monolayers were formed on Au surface and carefully characterized by atomic force microscopy (AFM), Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS) and surface plasmon resonance (SPR). Immobilization process of protein using bovine serum albumin (BSA) on the artificial linker layer was measured by SPR. The surface concentration of BSA was calculated by simulation of experimental SPR data. The surface concentration of BSA on the carboxylic acid form was higher than that of the ethylester. These results can help in modeling and understanding of protein immobilization on the linker layer.

Surface plasmon resonance spectroscopic study of UV-addressable phenylalanine sensing based on a self-assembled spirooxazine derivative monolayer

Light-addressable compounds are very interesting due to the possibilities of their practical use such as optical switches and memories or variable transmission materials. For example, transportation of phenylalanine across liposomal bilayers mediated by a photoresponsive carrier like spirooxazine through electrostatic interaction between phenylalanine and spirooxazine derivative. Thus, the spirooxazine is expected to form a UV-addressable phenylalanine sensing interface. In this study, we prepared phenylalanine sensing interface of a spirooxazine derivative by self-assembly technique and evaluated interaction between a spirooxazine moiety and phenylalanine with a surface plasmon resonance (SPR). The refractive index change of monolayer caused by interaction between a spirooxazine derivative and phenylalanine led to the SPR angle shifts upon UV irradiation. The SPR angle shift increased with increasing the concentration of phenylalanine solution. These results indicated that the spirooxazine derivative self-assembled monolayer (SAM) has an application potential for UV-addressable phenylalanine sensing.

PBN Derived Amphiphilic Spin-Traps. I/Synthesis and Study of Their Miscibility with Polyunsaturated Phospholipids

The synthesis of new amphiphilic α-phenyl-N-tert-butylnitrone (PBN) derivatives bearing two hydrocarbon tails with 17 carbon atoms (compound A17) or 11 carbon atoms (compound B11) is reported. The amphiphilic and morphological properties of these potential antioxidant compounds were investigated at the air−water interface. The analyses were conducted using Langmuir film balance and Brewster angle microscopy. As it is possible to obtain pressure−area (π−A) isotherms from pure A17 and B11, this means that they can form stable monomolecular films at the air−water interface. Monolayers of pure PBN derivatives exhibited different interface behavior. Indeed, along with compression, the B11 monolayer showed only a liquid-expanded phase and the A17 monolayer showed a liquid-condensed phase. Brewster angle microscopy showed the presence of condensed domains within the A17 monolayer. The lateral interactions of these compounds with the polyunsaturated phospholipids, 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLoPC) and 1,2-dilinoleoyl-sn-glycero-3-phosphoethanolamine (DLoPE), were evaluated by analysis of π−A isotherms and excess free energy of mixing. Each PBN derivative was miscible with DLoPC or DLoPE and formed nonideal mixed monolayers at the air−water interface. Only the A17 molecules exhibited favorable interactions at high surface pressures (over 20 mN/m) with both DLoPC and DLoPE, however. Under these conditions, A17 should be a better antioxidant than B11.

尿素頭部を有したアゾベンゼン誘導体単分子膜の充填状態の湿度応答性

尿素を有したアゾベンゼン誘導体の尿素部位とアゾベンゼン部位をつなぐスペーサー長を系統的に変化させた化合物 (n-3, 4, 5, 6, 7) を新規に合成した. これら誘導体のLangmuir-Blodgett単分子膜を作製し, 紫外可視吸収スペクトル測定により, その湿度応答性について, 基板特性および化合物の構造を変化させて評価を行った. 親水性基板ではスペーサー長の長い化合物の膜は規則的な湿度応答を示し, 短くなるに従いその応答は不規則になるか, まったく応答を示さなくなった. 親水基板と疎水基板を用いた際の比較から, 基板表面への水分子の吸脱着が, 膜分子の会合状態を可逆的に変化させるものと解釈できる.

Cis-trans Driven organized reorientation of an azobenzene derivative monolayer at the liquid/graphite interface

An azobenzene derivative, 2-hydroxy-4,4′-dihexyloxyazobenzene, in which a hydroxy group is introduced at the 2-position of the phenyl ring, forms an ordered monolayer at the liquid/graphite interface. Upon light irradiation, this monolayer can undergo a reversible cis-trans driven cooperative reorientation as observed by scanning tunneling microscopy.

An Electrochemical Study of the SAMs of 6-Mercaptopurine (6MP) at Hg and Au(111) Electrodes in Alkaline Media

A study of the reductive desorption process of 6MP-coated Hg and Au(111) electrodes in alkaline media has been carried out by means of such electrochemical techniques as cyclic voltammetry, chronoamperometry, and capacity−potential curves. The cyclic voltammograms show a single reduction peak whose peak potentials are strongly dependent on the nature of the substrate, Hg and Au(111) in this study. The full widths at half-maximum (fwhm) for Hg and Au(111) electrodes respectively are 19 and 21 mV at a scan rate of 0.1 V/s. These values are generally indicative of the existence of strong lateral interactions between molecules.The chronoamperometric curves have been recorded by single potential step experiments from a potential where the monolayer is stable to different final values within the range of potential where the monolayer is being desorbed. The curve shapes resemble those of systems that follow nucleation and growth mechanisms in the formation or dissolution of two-dimensional layers. In fact, the curve analysis using the nucleation and growth model of etching centers which was carried out in this report is actually in agreement with a mechanism of this kind for the dissolution of the 6MP monolayer at Hg and Au(111) electrodes. This study compares the properties of the 6MP monolayer at the two substrates Hg and Au(111) as well as with other thiol derivative monolayers.

Base-pair mapping by chemical force microscopy on nucleobase self-assembled monolayers

Self-assembled monolayers (SAMs) of double-chain disulfide derivatives of nucleobases (adenine and thymine) were formed on Au substrates in order to measure complementary hydrogen bonding by chemical force microscopy at the interfaces. Surface plasmon resonance measurements indicated that the formation of the nucleobase SAMs on Au surface was completed within 80 min. To measure adhesion force by atomic force microscopy (AFM), Au-coated AFM tips were modified with the nucleobase SAMs, too. SAM-modified Au substrates micro-patterned on quartz substrates were prepared for adhesion force mapping. The adhesion force between the complementary nucleobases is larger than that of the non-complementary combination. Electrochemical detection using a redox-intercalator was demonstrated for hybridization of single-stranded polynucleic acid with the nucleobase SAMs modified on Au electrodes.

A Study on the Styrylpyridunium Derivative Monolayer at the Air/Water Interface

Trans and cis forms of N-alkyl-4-styrylpyridinium derivatives (C n SP, n=4, 8, 12, 16) were successfully synthesized and purified. The derivatives of styrylpyridinium cause photoisomerization when they illuminated with UV light. The pressure-area isotherms of C n SP and their derivative were studied on the effect of alkyl chain length. The photoisomerization of C n SP monolayers at the air/water interface was indirectly studied by measuring surface potential change with photoirradiation on the water surface. The characteristics of C n SP were furthermore studied with surface pressure-area isotherm, Brewster Angle Microscopy (BAM) and optical diffraction efficiency.

A Study on the Styrylpyridunium Derivative Monolayer at the Air/Water Interface

Trans and cis forms of N-alkyl-4-styrylpyridinium derivatives (C n SP, n=4, 8, 12, 16) were successfully synthesized and purified. The derivatives of styrylpyridinium cause photoisomerization when they illuminated with UV light. The pressure-area isotherms of C n SP and their derivative were studied on the effect of alkyl chain length. The photoisomerization of C n SP monolayers at the air/water interface was indirectly studied by measuring surface potential change with photoirradiation on the water surface. The characteristics of C n SP were furthermore studied with surface pressure-area isotherm, Brewster Angle Microscopy (BAM) and optical diffraction efficiency.

Highly cohesive monolayers of lipid derivatives of colchicine: a dynamics study

Monolayers of lipid derivatives of colchicine spread at the air–water interface reach the thermodynamic equilibrium over an abnormally long period of time. Dynamics of this equilibration and the behavior of the film during compression–decompression cycles are observed by fluorescence microscopy. The thermodynamically disfavored structures observed are unrelated to previously described unusual shapes in the liquid expanded-gas coexistence regions. The relation between the cholesterol-like effect of the colchicinoid moiety, its propensity to dimerize, and the high viscosity of the monolayer are discussed.

Dissociation of Surface Functional Groups and Preferential Adsorption of Ions on Self-Assembled Monolayers Assessed by Streaming Potential and Streaming Current Measurements

The interfacial charge formation of self-assembled monolayers (SAMs) of thiol derivatives on gold was investigated by streaming potential and streaming current measurements in aqueous electrolyte solutions. All experiments were performed at a slit channel formed by two parallel sample plates. For the first time, ζ potentials of planar SAM−solution interfaces were determined experimentally. Surface pK values were calculated from the pH dependence of the ζ potential. Monolayers carrying ω-carboxylic moieties show a shift of the pK toward the alkaline direction as compared to the carboxy-terminated alkanethiol molecules in solution. Contact angle titrations using a captive bubble method confirmed the dissociation behavior of monolayers with acidic groups. Monolayers of methyl-terminated thiols exhibit ζ potential−pH plots that account for unsymmetrical ion adsorption. Models of the electric double layer are discussed to describe the interface between self-assembled monolayers and electrolyte solutions. Two c...

Adsorption of poly(N-ethyl-4-vinyl pyridinium bromide) onto langmuir-blodgett films built up from amphiphilic polymers

The interaction of a strong cationic polyelectrolyte, poly(N-ethyl-4-vinyl pyridinium bromide), with Langmuir-Blodgett (LB) films built up from four monolayers of amphiphilic derivatives of the alternating copolymers of maleic acid and alkenes (one of the monolayers was formed by the amphiphilic copolymer containing pyrenyl groups as fluorescent labels) was examined. Transformations of absorbance spectra and quenching of fluorescence of the LB films were detected after their contact with aqueous solutions of the cationic polyelectrolyte. These changes were attributed to the adsorption of poly(N-ethyl-4-vinyl pyridinium bromide) onto such films. The efficiency of this process was found to be rather sensitive to the variations in pH of the surrounding medium: adsorption of the cationic polyelectrolyte onto the LB films was pronounced in basic media while it became rather weak in acidic media.