Photophysics of self-assembled monolayers of a π-conjugated quinquethiophene derivative

The photophysics of fully and partially covered self-assembled monolayers (SAMs) of a quinquethiophene (5T) derivative have been investigated. The monolayers behave as H-aggregates. The fluorescence of fully covered SAMs is weak and red-shifted, and the extinction is blue-shifted as compared to that of single molecules. The fluorescence of partially covered SAMs is dominated by that of single molecules on the surface. The extinction spectra are similar for fully and partially covered monolayers, which show that even the smallest islands are H-aggregates. The extinction spectra furthermore closely resemble those for 5T single crystals, which demonstrates that in oligothiophene crystals the intermolecular interactions within one layer molecules are stronger than the interlayer electronic coupling.     

Ac voltammetric and square wave voltammetric study of the self-assembled monolayers of thiol-functionalized viologen derivative

Electroactive self-assembled monolayers (SAMs) containing viologeu group are formed through the adsorption of thiol-functionalized viologen compound CH3(CH2)9V2+(CH2)8SH,where V2+ is N,N'-diaIkylbipyridinium (i.e.a viologen group),onto gold electrodes from methanol/water solution and its electrochemical behavior is investigated by Ac voltammetry and square wave voltam-metry,which have the high sensitivity against background charging.The viologen SAM formed is a sub-monolayer and the normal potentials corresponding to the two successive one-electron transfer processes of the active centers (viologen) are-360 mV and-750 mV (vs.Ag/AgCl) in 0.1mol/L phosphate buffer solutions (pH 6.96) respectively,and the standard electron transfer rate constant is 9.0s-1 The electrochemical behavior of this SAM in various solutions has been preliminarily discussed.     

Molecular recognition of a self-assembled monolayer of a polydithiocarbamate derivative of β-cyclodextrin on silver

The synthesis and molecular recognition properties of a new sulfur containing β-cyclodextrin (β-CD) derivative chemisorbed on a silver surface are described. Hepta-6-amino-6-deoxy-β-CD was allowed to react with CS₂ in the presence of ammonia to give a mixture of partially substituted dithiocarbamate derivatives with an average degree of substitution of 4.5. A modified silver electrode with this derivative is capable of discriminating between the three positional isomers of nitrobenzoate ion and nitrophenol, as determined by cyclic voltammetry. Only the meta- and para-isomers give a signal corresponding to the reduction of the nitro group. This is attributed to the different orientations of the nitro group with respect to the silver surface after inclusion in the CD cavity. Experiments in the presence of cyclohexanol showed a decrease in signal intensity of the meta- and para-isomers which is associated with the competitive complexation of this guest, suggesting that the electroactive probe is complexed to the cavity.     

Characterization of self-assembled monolayers of thiols on Au(111)

Self-assembled monolayers (SAMs) of n-butanethiol, n-dodecanethiol and their equimolar mixture on Au(111) were prepared and characterized by ellipsometry, contact angle measurement, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results revealed that these SAMs are oriented ultrathin films with the thickness of nanometer scale, and the SAMs were influenced by the molecular chain length, the lattice orientation and cleanliness of the substrates. The surface of the longer chain SAM is hydrophobic. The thicknesses of three SAMs of n-butanethiol, n-dodecanethiol and their mixture revealed by ellipsometry and XPS are about 0.59 - 0.67nm, 1.60- 1.69 nm and 1.23 - 1.32nm, respectively. AFM images further demonstrated that the SAM formed by the mixture has some microdomains with two different thicknesses.     

Synthesis and structural characterization of a barium coordination polymer based on a μ2-monoatomic bridging 4-nitrobenzoate

Abstract

The synthesis, spectral characterization, crystal structure and properties of [Ba(H₂O)₂(NMF)₂(4-nba)₂], 1 (NMF = N-methylformamide; 4-nba = 4-nitrobenzoate), are reported. ¹H and ¹³C NMR spectral data reveal the presence of NMF in 1. A strong band at 1660?cm^?1 in the infrared spectrum indicates the binding of amide oxygen to Ba(II) which is confirmed by the single crystal structure. The unique Ba(II) in 1 situated on a mirror plane exhibits nine coordination and is bonded to two symmetry related monodentate terminal NMF ligands via the amide oxygen, and a terminal aqua ligand. The μ₂-monoatomic bridging binding mode of each of a crystallographically independent 4-nba ligand and a unique water ligand link the Ba(II) cations into an infinite chain extending along a, leading to the formation of a 1D coordination polymer with Ba···Ba separations of 4.2522(3) Å. In the chain, the {BaO₉} polyhedra are linked in a face sharing fashion. Thermal decomposition of 1 results in the formation of BaCO₃ residue. A comparative study of the structural chemistry of several barium coordination polymers is described.     

Synthesis and characterization of biodegradable polymer： Poly （ethene maleic acid ester-co-D,L-lactide acid）

A novel biodegradable polymer--poly （ethene maleic acid ester-co-D,L-lactide acid） was synthesized by copolymerizing lactide and prepolymer, which was prepared by the condensation of maleic anhydride and glycol, using p-toluene sulphonic acid as a catalyst, attempting to improve the hydrophilicity, increase flexibility and modulate the degradation rate. FTIR,^1H NMR, MALLS and DSC were employed to characterize these polymers.     

Formation of self-assembled monolayers of π-conjugated molecules on TiO2 surfaces by thermal grafting of aryl and benzyl halides

We demonstrate the formation of molecular monolayers of π-conjugated organic molecules on nanocrystalline TiO(2) surfaces through the thermal grafting of benzyl and aryl halides. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were used to characterize the reactivity of aryl and benzyl chlorides, bromides, and iodides with TiO(2) surfaces, along with controls consisting of nonhalogenated compounds. Our results show that benzyl and aryl halides follow a similar reactivity trend (I > Br > Cl > H). While the ability to graft benzyl halides is consistent with the well-known Williamson ether synthesis, the grafting of aryl halides has no similar precedent. The unique reactivity of the TiO(2) surface is demonstrated using nuclear magnetic resonance spectroscopy to compare the surface reactions with the liquid-phase interactions of benzyl and aryl iodides with tert-butanol and -butoxide anion. While the aryl iodides show no detectable reactivity with a tert-butanol/tert-butoxide mixture, they react with TiO(2) within 2 h at 50 °C. Atomic force microscopy studies show that grafting of 4-iodo-1-(trifluoromethyl)benzene onto the rutile TiO(2)(110) surface leads to a very uniform, homogeneous molecular layer with a thickness of ～0.45 nm, demonstrating formation of a self-terminating molecular monolayer. Thermal grafting of aryl iodides provides a facile route to link π-conjugated molecules to TiO(2) surfaces with the shortest possible linkage between the conjugated electron system and the TiO(2).     

Electrochemical characterization of cationic surfactants’ adsorption on a disturbed n-alkanethiolate self-assembled monolayer-modified polycrystalline gold electrode

The adsorption of cetyltrimethylammonium bromide (CTAB) on disturbed n-alkanethiolate self-assembled monolayers (SAMs) was investigated by electrochemical methods with potassium ferricyanide [K₃Fe(CN)₆] as a probe. Compared with the completely restrained signal at ordinary compact n-alkanethiolate SAMs, the electrochemical response of K₃Fe(CN)₆ at the disturbed n-alkanethiolate SAMs was partly restored and became progressively reversible in the presence of increasing concentrations of CTAB, which was employed to characterize the adsorption of cationic surfactants on hydrophobic SAMs. The effect of CTAB concentration on electrochemical impedance spectroscopy (EIS) plots indicated that CTAB experienced two different types of adsorptive behavior at the disturbed n-alkanethiolate SAMs: monomer adsorption at low concentrations below 1×10^–6 M and monolayer adsorption at CTAB concentrations above 1×10^–5 M. The adsorption of a series of cationic surfactants with similar structures to CTAB on disturbed n-alkanethiolate SAMs was also explored. These surfactants had similar adsorptive behavior and showed nearly linear adsorption characteristics with the length of their hydrophobic tails.     

Label-free and sensitive impedimetric nanosensor for the detection of cocaine based on a supramolecular complexation with β-cyclodextrin,immobilized on a nanostructured polymer film

Cocaine, a powerful addictive stimulant drug, has a variety of adverse effects on the body, thus its sensitive detection is very important. Here, we report on a simple, label-free, and sensitive impedimetric sensor for determination of cocaine based on its affinity to form an inclusion complex with β-cyclodextrin (β-CD). First, we prepared nanostructured poly N-acetylaniline film via electropolymerization of its monomer on a glassy carbon electrode (PNAANI/GC), subsequently overoxidized it, and conjugated β-CD to the polymer backbone. The designed and synthesized nanostructured PNAANI film serves a dual function in the sensor: on one hand, it maintains a high effective surface area on a geometrically small electrode that significantly enhances the number of β-CD molecules immobilized on the electrode; on the other hand, it provides an upright-oriented β-CD conjugation to the polymer backbone, thus all the β-CD receptors are actively involved in responding to the target. Sensitivity of the sensor was further enhanced by preconcentration of cocaine on the modified electrode surface. We attributed the changes in the interfacial charge transfer resistance (R _ct) of the electrode to cocaine concentration. Under optimized condition (pH 7.4, 5-min accumulation at an open circuit voltage), the sensor responded to cocaine concentration in the range of 100 nM–1.0 mM with a detection limit of 50 nM. Selectivity of the sensor for cocaine relative to some potential inferring compounds was also investigated, and the results were promising. The proposed approach exhibited an extended dynamic range, low detection limit, good sensitivity, and a desirable selectivity, which provides an efficient application prospect for on-field cocaine sensing.     

Comparative study of the electrosynthesis and characterization of films made from 1,1′-binaphthyl and 2-methoxynaphthalene

Oligomers of 2-methoxynaphthalene and 1,1-binaphthyl were electrochemically synthesized by cyclic voltammetry (CV) in 0.1 M tetrabutylammonium hexafluorophosphate–nitrobenzene (TBAPF₆–NB). The redox characterization of the films was studied in monomer-free 0.1 M TBAPF₆–NB and 0.1 M tetrabutylammonium hexafluorophosphate–acetonitrile (TBAPF₆–ACN) solutions. The electrochemical response from the anodic charging (p-doping) of an oligo(1,1-binaphthyl) film in both solvents consists of a continously increasing current without a well-defined oxidation peak. Upon discharging the film a distinct reduction peak can be seen. The p-doping response of an oligo(2-methoxynaphthalene) film in both solvents consists of a prepeak followed by a plateau until the new electrochemical process starts. On the reverse scan two poorly resolved reduction peaks which merge into a broad cathodic peak as the scan rate increases can be observed. The cathodic charging and discharging (n-doping) response of 2-methoxynaphthalene film in 0.1 M TBAPF₆–ACN consists of a broad and well-defined redox peak. The structures of the film were studied by Raman and Fourier transform infrared spectroscopy (FTIR). Both techniques provide complementary vibrational information on the coupling of the starting materials studied. The morphologies of the electrosynthesized films were studied by scanning electron microscopy (SEM). The influence of the two substituents, the methoxy and naphthyl groups, on the electrosynthesis properties of the naphthalene molecule was studied.     

Molecular dynamics simulations of low-ordered alzheimer β-amyloid oligomers from dimer to hexamer on self-assembled monolayers

Accumulation of small soluble oligomers of amyloid-β (Aβ) in the human brain is thought to play an important pathological role in Alzheimer's disease. The interaction of these Aβ oligomers with cell membrane and other artificial surfaces is important for the understanding of Aβ aggregation and toxicity mechanisms. Here, we present a series of exploratory molecular dynamics (MD) simulations to study the early adsorption and conformational change of Aβ oligomers from dimer to hexamer on three different self-assembled monolayers (SAMs) terminated with CH(3), OH, and COOH groups. Within the time scale of MD simulations, the conformation, orientation, and adsorption of Aβ oligomers on the SAMs is determined by complex interplay among the size of Aβ oligomers, the surface chemistry of the SAMs, and the structure and dynamics of interfacial waters. Energetic analysis of Aβ adsorption on the SAMs reveals that Aβ adsorption on the SAMs is a net outcome of different competitions between dominant hydrophobic Aβ-CH(3)-SAM interactions and weak CH(3)-SAM-water interactions, between dominant electrostatic Aβ-COOH-SAM interactions and strong COOH-SAM-water interactions, and between comparable hydrophobic and electrostatic Aβ-OH-SAM interactions and strong OH-SAM-water interactions. Atomic force microscopy images also confirm that all of three SAMs can induce the adsorption and polymerization of Aβ oligomers. Structural analysis of Aβ oligomers on the SAMs shows a dramatic increase in structural stability and β-sheet content from dimer to trimer, suggesting that Aβ trimer could act as seeds for Aβ polymerization on the SAMs. This work provides atomic-level understanding of Aβ peptides at interface.     

Poly-N-benzylaniline prepared in perchloric acid——a new soluble semiconducting polymer

Chemical or electrochemical oxidation of N-benzylaniline in perehloric acid solution yieldsa highly colored polymer——poly-N-benzylaniline (PBAn).The polymer has good solubility in a num-ber of organic solvents in either acid or base form.At room temperature,conductivity measurementson pressed pellets of the acid form PBAn give a conductivity of 9.3×10~(-6) S·cm~(-1).The soluble polymerwas analyzed using a variety of common experimental techniques including UV-vis,IR,NMR,ESRspectroscopy,elemental analysis and electrochemieal analysis.All experimental results showed thatPBAn has a structure similar to polyaniline with the elimination of some benzyl groups.     

Growing kinetics and structural characterization of oxide film formed on La-doped Co-40Cr alloy

The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000℃ in air by thermal-gravity analysis (TGA). Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM)) were used to examine the oxidized film's morphology and the structure after oxidation. Secondary ion mass spectrum (SIMS) method was used to examine the binding energy change of chromium caused by La-doping and its in?uence on formation of Cr2O3 film. Laser Raman spectrum was used to examine the tress changes within oxidized films. It was found that lanthanum implantation remarkably reduced the isothermal oxidizing rate of Co-40Cr and improved the anti-cracking and anti-spalling properties of Cr2O3 film. The reasons were that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide, increased the high temperature plasticity of oxidized film. Lanthanum mainly existed in the outer surface of Cr2O3 film in the forms of fine La2O3 and LaCrO3 spinel particles.     

Synthesis,characterization and luminescence properties of a coordination polymer based on self-assembly of PrIII with inorganic–organic hybrid bridging ligands

A new coordination polymer having the formula [Pr(μ ₅-S₂O₃)(μ ₄-tp)_0.5(H₂O)] _n (1) (S₂O₃ = thiosulfate dianion; tp = terephthalate dianions) was obtained by in situ reaction of Pr₂(SO₄)₃ · 6H₂O with H₂tp ligands under solvothermal conditions (H₂O/ethanol). The coordination polymer obtained was characterized by elemental analysis, FT-IR, thermogravimetry (TG), fluorescent spectra and single crystal X-ray diffraction analysis. The most intriguing structural feature is that the complex exhibits a 3D open framework resulting from bridge-linking coordination between ligands and praseodymium ions. Additionally, 1 has characteristic emission spectra of Pr^III with good fluorescence properties. This is the first coordination polymer based on thiosulfate/terephthalate ligands and a rare earth metal and has an unprecedented pentadentate-bridge-linking coordination mode of the thiosulfate group.     

Utilization of a spiropyran derivative in a polymeric film optode for selective fluorescent sensing of zinc ion

Spiropyrans are the most studied families of func- tional materials due to their reversible structural con- version in response to external optical, chemical, and thermal stimulation[1]. Irradiation with ultraviolet light causes formation of an extended π-conjugation open form (merocyanine form) by heterolytic cleavage of the C (spiro)-O bond, which generates an intense ab- sorption in the visible region. Under the irradiating of visible light, the opened form will come back to the closed spi…     

Synthesis and characterization of novel β-amino acid derivatives

In the work discussed in this paper, novel β-amino acid derivatives were prepared by Michael addition between 3-substituted-2-propenic acid and hydrazine hydrate. The optimum reaction conditions were determined by analyzing the effects of the ratio of the starting materials, temperature, and reaction time. The conclusions were: reaction temperature 80 °C, reaction time 8 h, n (3-substituted-2-propenic acid)/n (hydrazine hydrate) = 1:15. Products were characterized by measurement of melting point, elemental analysis, and IR and ¹H NMR spectroscopy.     

Aqueous processing of graphene–polymer hybrid thin film nano-composites and gels

Research into the structure, properties and applications of graphene has moved at a tremendous pace over the past few years. This review describes one aspect of this research, that of the incorporation of graphene particles with a range of polymers to create novel hybrid materials with increased functionality such as improved conductance, increased strength and introduced biocompatibility or cytotoxicity. This review focuses on dispersing graphene in polymer matrices, both insulating and conducting. Additionally, a brief discussion of carbon based platelet production methods is given in order to provide context on the subsequent use of this family of materials such as graphene, graphene oxide (GO) and reduced graphene oxide (rGO) incorporated into polymeric thin films.     

Standing up versus looping over: controlling the geometry of self-assembled monolayers of α,ω-diynes on gold

It is shown that self-assembled monolayers (SAMs) composed of α,ω-diynes on gold have different structures depending on the concentration of molecules used to make the SAM. Evidence for both hairpinned and standing-up molecules is provided. This behavior is in contrast to SAMs of α,ω-dithiols on gold, which generally form SAMs with only the straight conformation. The looped SAMs composed of α,ω-diynes offer a less densely packed and thus somewhat accessible surface that may be useful when the underlying surface is used as an electrode. Furthermore, biasing the structure of the molecules in the SAM between looped and standing-up may be useful in the design of dynamic surfaces.