Monolayers Of Derivatives Research Articles

ChemInform Abstract: 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.

Structure of the interface between water and self-assembled monolayers of neutral, anionic and cationic alkane thiols

Molecular dynamics simulations of self-assembled monolayers (SAMs) of alkanethiol derivatives interfaced with water reveal the structure of the interface and show how it influences the properties of water. Three SAMs of different character (neutral, anionic and cationic) are compared: 6-hexanethiol, 11-mercaptoundecanoic acid and 11-amino-1-undecanethiol. The simulation captures phenomena such as the hydrophobic gap, local increase of the density of water near the interface and ordering of water into layers.

Self-Assembled Monolayers of α-Cyclodextrin Derivatives on Gold and Their Host−Guest Behavior

Various sulfur-modified alpha-cyclodextrin (alpha-CD) derivatives formed ordered monolayers on gold surfaces as confirmed by water contact angle goniometry, electrochemistry, X-ray photoelectron spectroscopy, and atomic force microscopy measurements. Self-assembled monolayers (SAMs) of the adsorbates showed high polarity, uniform monolayer arrangement, and low charge transfer resistance. Electrochemical capacitance measurements were used to determine the binding affinity of aliphatic carboxylic acid salts with four, six, and eight carbon atoms. The nonmethylated cyclodextrin host-guest pairs showed 1-2 orders of magnitude higher binding constants on surfaces than in solution.

Nanometric Layers for Direct, Signal-On, Selective, and Sensitive Electrochemical Detection of Oligonucleotides Hybridization

We report a signal-on, reagentless electrochemical DNA biosensor, based on an electroactive self-assembled naphthoquinone derivative (JUG(thio)) monolayer. This system achieves highly sensitive (approximately 300 pM) and selective signal-on detection. Before hybridization, the single strand can interact with JUG(thio) and slow down the redox reaction. When the complementary target is added, the formation of the double helix eliminates the single strand/JUG(thio) interactions and the JUG(thio) redox rate, and hence the current increase.

Langmuir–Blodgett films incorporating molecular wire candidates of ester-substituted oligo(phenylene–ethynylene) derivatives

Langmuir and Langmuir–Blodgett (LB) films of two “wire-like” oligo(phenylene–ethynylene) methyl ester derivatives, namely methyl-4-[(4″-(nonyloxyphenylethynyl)-4′-(phenylethynyl)]-benzoate and methyl-4-[(4″-hexadecyloxyphenylethynyl)-4′-(phenylethynyl]-benzoate (abbreviated as C9BPEB and C16BPEB), have been prepared and characterized. Surface pressure isotherms for both materials have been obtained, with C9BPEB showing more expanded monolayers. An analysis of the reflection spectra of monolayer films at the air–water interface suggests the formation of H-aggregates, and supports an organizational model in which tilt angles of C16BPEB and C9BPEB molecules with respect to the water surface are approximately 70° and 60°, respectively. The sequential transfer of monolayers of these BPEB ester derivatives onto solid substrates results in a Z-type deposition in the case of C9BPEB and Y-type for C16BPEB. The current–voltage ( I– V) characteristics of LB monolayers are relatively symmetrical for both films, with the asymmetric contacts more evident in the I– V C16BPEB characteristics.

Electroactive Self-Assembled Monolayers on Gold via Bipodal Dithiazepane Anchoring Groups

Novel dithiazepane-functionalized ferrocenyl-phenylethynyl oligomers 1 and 2 have been synthesized. Self-assembled monolayers (SAMs) of these ferrocene derivatives have been studied by X-ray photoelectron spectroscopy, ellipsometry, and cyclic voltammetry. It has been shown by XPS that monolayers of the dithiazepane-anchored molecules on gold electrodes contain gold-thiolate species. Cyclic voltammetry of the SAMs were characteristic of stable electroactive monolayers even for single-component SAMs of 1 and 2, with the more ideal responses recorded for the two-component SAMs diluted with undecanethiol. The small variation in peak splittings at progressively higher scan rates in these SAMs makes dithiazepane-bridged redox species promising candidates for further studies on molecular wires with bipodal anchoring.

Scanning conductive probe microscopy of thiophen molecules incorporated into chemically adsorbed monolayer

We will describe a technique for acquiring the current-voltage characteristics of a metal-molecule-metal probe junction in the lateral direction using a conducting probe atomic force microscopy (CP-AFM) technique. To conduct a repetitive experiment efficiently, we have utilized the current imaging mode of the CP-AFM system. We have prepared a chemically adsorbed monolayer (CAM) of 3-{6-{11-(Trichlorosilyl)undecanoyl}hexyl} thiophene (TEN) on a glass substrate. The samples with the electric path were prepared by a chemical adsorption technique with TEN on a glass substrate, followed by an electro-oxidative polymerization with pure water. The conductivity of a polythiophene derivative monolayer was investigated for its application as a wire. The corresponding I-V curves have exhibited stability and are steep in current.

Surface plasmon resonance spectroscopic chiral discrimination using self-assembled leucine derivative monolayer

Pirkle-type chiral stationary phases (CSPs) showed excellent enantiomeric separation for amino acid derivatives by forming energetically different two transient diastereomeric π–π donor–acceptor complexes with two enantiomers. A CSP derived from N-(3,5-dinitrobenzoyl) leucine with a thiol ending group for immobilization on Au was synthesized and self-assembled on Au surface as chiral sensing layer. The monolayer characterized by spectroscopic and microscopic methods such as AFM, FTIR reflection absorption spectroscopy (FTIR-RAS) and cyclic voltammetry (CV). The enantiospecific detection onto CSP of the leucine derivative was studied by surface plasmon resonance (SPR). ( S)-CSP SAM showed high chiral differential detection for ( S)-analyte in a range of 1.0 × 10 −9 to 1.0 × 10 −4 M. In combination with the SPR method, the leucine derivative monolayer provided a reliable and simple experimental platform for enantiospecific detection.

Monolayers of the lipid derivatives of isoniazid at the air/water interface and the formation of self-assembled nanostructures in water

Isoniazid (INH, isonicotinic acid hydrazide) is one of the most commonly used anti-tubercular drugs. However, resistance of Mycobacterium tuberculosis strains to anti-mycobacterial agents including INH is an increasing problem worldwide. Development of new anti-mycobacterial agents thus has attracted attention. Five lipid derivatives of INH were prepared in this study. They formed monolayers at the air/water interface, and some nanostructures with different morphologies were obtained through molecular self-assembly in water. The derivatives included one fatty acyl derivative containing a 12-C hydrocarbon-long chain ( 1), three fatty alcohol derivatives with a succinyl as spacer and an 8, 12 or 16-C hydrocarbon-long chain ( 2, 3 and 4), and one tetrahydro-2 H-1,3,5-thiadiazine-2-thione (THTT) derivative containing a 12-C hydrocarbon-long chain ( 5). The surface pressure–area isotherms depended on the volume and configuration of heads and the length of tails of derivatives. Compound 2 had a relatively large head and a short tail, easily standing uprightly at the interface. Under a certain surface pressure, the linear polar head groups of 3 could be partly squeezed out and insert into subphase because the length of heads were comparable to the one of tails. The very long tails of 4 always maintained above the interface and led to a high collapse pressure. Compound 5 possessed an extended and large head consisting of the THTT and INH groups so that the relatively short tails tilted at the interface and difficultly contact with each other. The THTT rings might be partly squeezed out and enter into air under a certain surface pressure. The self-assembly behaviours of derivatives in water depended on the molecular configuration and agreed with the corresponding monolayer behaviours. The flexible and medium-long tails ( 1 and 3) led to the derivatives to form nanoscale vesicles, though the short or very long tails did not ( 2 and 4). Interestingly, intermolecular hydrogen bonding could occur between the molecules of 5, and improve the derivative forming helical nanofibres other than vesicles. The molecular self-assembly of INH's lipid derivatives was explored in details in this study. The formation mechanisms of self-assembled nanostructures were analyzed. Various types of self-assembled nanostructures were obtained and the formation mechanisms were analyzed. The relationship between the self-assembly and the molecular configuration of amphiphilic derivatives was also revealed. The lipid derivatives of INH show promising anti- Mycobacterium action because the amphiphilic prodrugs allow for better penetration of the bacterial cells. The self-assembled nanostructures may likely be the potential self-assembled drug delivery systems for tuberculosis therapy.

Structure Formation in Bis(terpyridine) Derivative Adlayers: Molecule−Substrate versus Molecule−Molecule Interactions

The influence of the substrate and the deposition conditions-vapor deposition versus deposition from solution-on the structures formed upon self-assembly of deposited bis(terpyridine) derivative (2,4'-BTP) monolayers on different hexagonal substrates, including highly oriented pyrolytic graphite (HOPG), Au(111), and (111)-oriented Ag thin films, was investigated by high-resolution scanning tunneling microscopy and by model calculations of the intermolecular energies and the lateral corrugation of the substrate-adsorbate interaction. Similar quasi-quadratic network structures with almost the same lattice constants obtained on all substrates are essentially identical to the optimum configuration expected from an optimization of the adlayer structure with C-H...N-type bridging bonds as a structure-determining factor, which underlines a key role of the intermolecular interactions in adlayer order. Slight distortions from the optimum values to form commensurate adlayer structures on the metal substrates and the preferential orientation of the adlayer with respect to the substrate are attributed to the substrate-adsorbate interactions, specifically, the lateral corrugation in the substrate-adsorbate interaction upon lateral displacement and rotation of the adsorbed BTP molecules. The fact that similar adlayer structures are obtained on HOPG under ultrahigh vacuum conditions (solid|gas interface) and on HOPG in trichlorobenzene (solid|liquid interface) indicates that the intermolecular interactions are not severely affected by the solvent.

Monolayers of triaroylbenzene derivatives

Monolayers of triaroylbenzene derivatives bearing three octyl groups projecting away from the molecular core and terminated by hydroxyl, carboxylic acid, and methyl ester groups have been studied using surface pressure isotherm measurements and Brewster angle microscopy. The octyl derivative lacking a terminal hydrophilic group forms a monolayer of limited stability. The derivatives with hydrophilic end-groups on the octyl chains form stable monolayers. A reorientation at the water surface under compression from a ‘face-on’ to a distorted ‘edge-on’ arrangement appears likely. At intermediate molecular areas, a phase transition occurs and aggregate formation is observed. Studies of mixtures with methyl stearate exhibit a contrast inversion between the background phase and immiscible domains of methyl stearate supporting the concept of a reorientation of the triaroylbenzene derivatives during compression.

A novel fullerene lipoic acid derivative: Synthesis and preparation of self-assembled monolayers on gold

Synthesis and preparation of self-assembled monolayers of a novel fullerene lipoic acid derivative on gold are reported. The presence of densely packed SAMs was confirmed by ellipsometry and cyclic voltammetry. The electrochemical response of the modified electrode in organic media exhibits the first two redox peaks characteristic of the extended π-electron system of fullerene. C 60 surface coverage (1.4 × 10 −10 mol cm −2) has been electrochemically determined by the redox process of the adsorbed fullerene moiety and by reductive desorption of the SAM in strong alkaline solution. Electrochemical data indicate that all four sulphur atoms are involved in the self-assembly process, providing an increase of SAM stability in comparison to mono or di-thiolated appended molecules. Visualisation of discrete fullerene molecules by scanning tunnelling microscopy supplied further evidence for gold modification and molecular distribution on the surface. Mixed monolayers of hexanethiol and fullerene derivatives in a proportion of 1:2 have been also studied with the purpose of controlling the amount and distribution of fullerene units on the gold surface.

Structures and Stability of Ferrocene Derivative Monolayers on Ag(110): Scanning Tunneling Microscopy Study

A scanning tunneling microscopy (STM) study of an unsaturated long-chain-bridged diferrocene, Fc(CH2)6HCCH(CH2)6Fc (u-diFc, Fc = ferrocenyl), on Ag(110) reveals three ordered molecular phases, α, β, and β‘. It is found that the α and the β phase are predominant on the ordered structures with the Fc group neighboring to the center of the hydrocarbon chain in the former phase but with the Fc group arranging into a row-like structure in the latter phase. High-resolution STM images also show that the β‘ structure is analogous to the β phase but is not well-defined and exhibits the zigzag shape because of the variable distance between two neighboring molecular rows and molecular arrangement shifted along the molecular row. Interestingly, the irreversible phase transition from α to β‘ has been observed in the recorded regions by using the real-time STM. On the basis of the experimental results, three molecular models are provided, and the stability of these three structures has been investigated as well.

Formation and Characterization of Self-Assembled Phenylboronic Acid Derivative Monolayers toward Developing Monosaccaride Sensing-Interface

We designed and synthesized phenylboronic acid as a molecular recognitionmodel system for saccharide detection. The phenylboronic acid derivatives that haveboronic acid moiety are well known to interact with saccharides in aqueous solution; thus,they can be applied to a functional interface of saccharide sensing through the formation ofself-assembled monolayer (SAM). In this study, self-assembled phenylboronic acidderivative monolayers were formed on Au surface and carefully characterized by atomicforce microscopy (AFM), Fourier transform infrared reflection absorption spectroscopy(FTIR-RAS), surface enhanced Raman spectroscopy (SERS), and surface electrochemicalmeasurements. The saccharide sensing application was investigated using surface plasmonresonance (SPR) spectroscopy. The phenylboronic acid monolayers showed goodsensitivity of monosaccharide sensing even at the low concentration range (1.0 × 10-12 M).The SPR angle shift derived from interaction between phenylboronic acid andmonosaccharide was increased with increasing the alkyl spacer length of synthesizedphenylboronic acid derivatives.

Surface Plasmon Spectroscopic Detection of Saxitoxin

For the surface-optoelectronic study of Saxitoxin sensing, we fabricated self-assembled calix[4]arene derivative monolayers as the recognition-functional interfaces ona gold surface. An interaction study between Saxitoxin and calix[4]arene derivativemonolayers were performed using surface plasmon resonance (SPR) spectroscopy. Amongthree calix[4]arene derivatives, calix[4]arene crown ether SAM showed the highestsensitivity to Saxitoxin. The detection limit of this system is three orders of magnitudelower than that of the mouse bioassay which is the current benchmark for Saxitoxindetection.

Molecular self-assembly of conducting polymer by Conducting Probe Technique in Atomic Force Microscope

A polypyrrole derivative monolayer was investigated for the application as a wire. First, a pyrrole derivative monolayer was prepared by chemically adsorbing (self-assembling) monolayer (CAM) of 6-pyrrolylhexyl-12,12,12-trichloro-12- siladodecanoate (PEN) on a glass substrate. Then, the monolayer was polymerized in the presence of pure water by electrooxidation. The surface characterization of the molecular interaction was investigated by measuring the properties of CAMs attached to the glass substrate in the lateral direction. We formed PEN having polypyrrolyl groups, using Pt-patterned electrodes on glass surfaces and measured the conductance under a small bias voltage, using a conductive cantilever of atomic force microscopy (AFM). The polypyrrole derivative monolayer thus synthesized was covalently bonded to the glass substrate and showed conductivity as high as 3.05..103 S/cm after electro-oxidized. The method of preparing a conductive polymer monolayer by the combining chemical adsorption and electro-oxidation leads to a lot molecular wire to perpendicular to the Pt electrodes, and it is one of the key technologies for molecular devices.

(Bio)functional surface structural design of substrate materials based on self-assembled monolayers from aminocellulose derivatives and amino(organo)polysiloxanes

Practical procedures according to the self-assembling principle are used to modify a number of substrate materials such as glass, silicon, gold, metals/oxides, polymers (e.g. polystyrene), implant materials (polydimethylsiloxane, polyhydroxyethylmethacrylate, polymethylacrylate, poly- l-lactate) for a wide range of (bio)functional applications based on self-assembled monolayers of structural-designed derivatives of a novel aminocellulose type with varying (bio)functional surface properties and special amino(organo)polysiloxanes. By microcontact printing, lateral structural patterns are stamped onto the substrate material surfaces in the form of monolayer composites of aminocellulose chains and amino(organo)polysiloxanes.

Odd–even effect and metal induced structural convergence in self-assembled monolayers of bipyridine derivatives

Scanning tunneling microscopy (STM) observations reveal that bipyridine derivatives which exhibit various two-dimensional structures due to the odd-even chain length effect are converged into a lamellar structure upon metal coordination.

A STUDY ON THE SURFACE CHARACTERISTIC OF THE VIOLOGEN SELF-ASSEMBLED MONOLAYERS USING QCA AND STM

Viologen has been extensively investigated in the paper because their well-behaved electro-chemistry has led to their use in a variety of thesises, including the electron acceptor for the electric charge delivery mediation of the devices. The self-assembled monolayers of alkane derivatives with sulfur containing head groups on gold substrates have been widely examined recently, since the binding between S atoms and Au surface is strong. We could know it was formed monolayer onto quartz crystal microbalance (QCM) surface by self-assembly method from resonant frequency shift using quartz crystal analyzer (QCA). The measured frequency shift were about 408 Hz by VC 8 SH . From this value, we calculated that the mass adsorbed VC 8 SH were about 432 ng. The EQCM measurements revealed that anions exit and enter the viologen monolayer during reduction and oxidation, respectively. We also use the scanning tunneling microscopy (STM) for manipulating the surface on a nanometer scale to form nanostructures.

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.