Changes in spectral features with varying mole fractions of anisaldehyde in binary mixtures

Raman and IR spectra of neat anisaldehyde (4‐methoxybenzaldehyde (4MeOBz)) and its binary mixtures (in polar and nonpolar solvents) with varying mole fraction of 4MeOBz were investigated. The concentration dependence of the wavenumber position and line width (full width at half maximum, FWHM) was analyzed to study the interaction of the solute vibrational modes with the microscopic solvent environment. The wavenumbers of Raman modes of 4MeOBz, namely, the carbonyl stretching, aldehydic δ (C H) and ring‐breathing modes, showed a linear variation in the peak position for varying concentrations of 4MeOBz in the different solvents. The dependence of Raman line width with concentration of 4MeOBz of these modes was also taken into account. The solute–solvent interaction is stronger in 2‐propanol and acetonitrile because of the formation of hydrogen bonds between them, whereas in benzene the interaction is too weak to affect the Raman modes. The modes, ν (CO) in 2‐propanol and aldehydic δ (C H) in acetonitrile, gave a Gaussian‐type line width variation, which was explained by the concentration fluctuation model, and the linear variation of the line widths was also interpreted by solute–solvent interactions. IR spectra were taken for these binary mixtures, which also give further support to these data. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of various acylating agents directly from carboxylic acids

Abstract

A straightforward synthesis of acylating reagents such as Weinreb and MAP amides from aromatic, aliphatic carboxylic acids, and amino acids using PPh₃/NBS combination is described. A chemo-selective modification of the carboxylic acid group into Weinreb amide in the presence of more reactive aldehydes and ketones is presented. All reactions were performed at ambient temperature under air using undried commercial grade solvent. Furthermore, the present methodology could be performed at a gram scale under inert-free reaction conditions. In addition, 7-azaindoline amide auxiliary (used for catalytic asymmetric aldol- and Mannich-type reactions), which behaves like Weinreb amide is also synthesized under similar reaction conditions.     

Adsorption dynamics of water on Pt{110}-(1 x 2)

The dynamics of H(2)O adsorption on Pt{110}-(1 x 2) is studied using supersonic molecular beam and temperature programed desorption techniques. The sticking probabilities are measured using the King and Wells method at a surface temperature of 165 K. The absolute initial sticking probability s(0) of H(2)O is 0.54+/-0.03 for an incident kinetic energy of 27 kJmol. However, an unusual molecular beam flux dependence on s(0) is also found. At low water coverage (theta<1), the sticking probability is independent of coverage due either to diffusion in an extrinsic precursor state formed above bilayer islands or to incorporation into the islands. We define theta=1 as the water coverage when the dissociative sticking probability of D(2) on a surface predosed with water has dropped to zero. The slow falling H(2)O sticking probability at theta>1 results from compression of the bilayer and the formation of multilayers. Temperature programed desorption of water shows fractional order kinetics consistent with hydrogen-bonded islands on the surface. A remarkable dependence of the initial sticking probability on the translational (1-27 kJ/mol) and internal energies of water is observed: s(0) is found to be essentially a step function of translational energy, increasing fivefold at a threshold energy of 5 kJ/mol. The threshold migrates to higher energies with increasing nozzle temperature (300-700 K). We conclude that both rotational state and rotational alignment of the water molecules in the seeded supersonic expansion are implicated in dictating the adsorption process.     

Redox switching of polyoxometalate-methylene blue-based layer-by-layer films

Iron-substituted crown-type polyoxometalate (POM) [P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)](20-) has been successfully immobilized onto glassy carbon electrode surfaces by means of the layer-by-layer (LBL) technique employing the cationic redox active dye, methylene blue (MB). The constructed multilayers exhibit pH-dependent redox activity for both the anionic POM and the cationic dye moieties, which is in good agreement with their solution behavior. The films have been characterized by alternating current impedance, atomic force microscopy, and X-ray photoelectron spectroscopy, whereby the nature of the outer layer within the assemblies was found to have an effect upon the film's behavior. Preliminary investigations show that the POM dye-based films show electrocatalytic ability toward the reduction of hydrogen peroxide, however, only when there is an outer anionic POM layer.     

Binary mixture of p‐methylbenzaldehyde with polar and nonpolar solvents

In this work, a combined theoretical and experimental study of binary mixture of liquid p‐methylbenzaldehyde (PMBz) is reported using ab initio calculations as well as Raman and IR spectroscopies. The purpose of this study was twofold: firstly, to describe the interaction of PMBz in terms of bonding energies and preferred geometries; and secondly, to characterize the spectroscopic effects on the vibrational modes of PMBz in the binary mixture of different polar and nonpolar solvents. The three vibrational modes, namely, carbonyl stretching, ν(C CH₃) and aldehydic (C H) vibrations have been analyzed in all the three solvents in different concentrations. The dependence of Raman linewidth on the concentration of PMBz of these modes was also taken into account. By analyzing the peak position and linewidth of these modes, it is seen that the solute–solvent interaction is stronger in BuOH and 1,2 dichloroethane (DCE) because of the hydrogen‐bonding interaction between these molecules. The formation of C H···O hydrogen bonds in liquid p‐methylbenzaldehyde is also investigated by Gaussian fitting. The ab initio calculations suggest several possible dimer configurations. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of UV irradiation on stabilized collagen: role of chromium(III)

Research on the effect of UV radiation on stabilized collagen is an area of potential interest owing to the fact that collagen is an important biomaterial finding immense use in various fields. In this present study, effect of UV irradiation on collagen stabilized using chromium(III) has been studied. The physical and optical properties affected by UV irradiation have been detailed. Viscosity measurements have shown that chromium(III) treated collagen has better stability against UV radiation than native collagen. Circular dichroic studies indicate that increase in concentration of chromium(III) does not affect the conformation of collagen however, the duration of irradiation has profound impact on the conformation of collagen. The fluorescence intensity of native collagen has been found to decrease more than that of chromium(III) treated collagen. The difference absorption spectra also shows that chromium(III) treatment brings about more stability to collagen against UV irradiation.     

Diammonium μ-oxobis[trichloroferrate(III)] salts. Crystal and molecular structure of bis(benzyldimethylphenylammonium) μ-oxobis(trichloroferrate)

Several alkyl-, aralkyl-, and aryl-substituted diammonium-oxobis[trichloroferrate(III)] salts, of potential interest as model compounds for the study of certain electrophysical and biological processes, are synthesized via the corresponding tetrachloroferrate(III) salts and are characterized by IR and Raman spectroscopy. A structure analysis is performed on the representative bis(benzyldimethylphenylammonium)-oxobis(trichloroferrate). The (tetracoordinate) iron atoms in the oxo-bridged dinuclear anion of the salt each possess an ever so slightly distorted tetrahedral ligand environment; the bridge geometry [Fe-O distances 1.757(5) and 1.775(5) Å, Fe-O-Fe angle 147.7(3)°] compares well with that of other salts containing the [Cl₃Fe-O-FeCl₃]^2- anion. Crystallographic Data:a=26.392(5) Å,b=14.015(3) Å,c=9.638(2) Å,=92.65(2)°, andZ=4; space groupP2₁/n.R(F)=0.070,R _W (F)=0.078 for 4447 observed reflections.     

Transition metal ion-substituted polyoxometalates entrapped in polypyrrole as an electrochemical sensor for hydrogen peroxide

A conducting polymer was used for the immobilization of various transition metal ion-substituted Dawson-type polyoxometalates (POMs) onto glassy carbon electrodes. Voltammetric responses of films of different thicknesses were stable within the pH domain 2-7 and reveal redox processes associated with the conducting polymer, the entrapped POMs and incorporated metal ions. The resulting POM doped polypyrrole films were found to be extremely stable towards redox switching between the various redox states associated with the incorporated POM. An amperometric sensor for hydrogen peroxide detection based upon the POM doped polymer films was investigated. The detection limits were 0.3 and 0.6 μM, for the Cu(2+)- and Fe(3+)-substituted POM-doped polypyrrole films respectively, with a linear region from 0.1 up to 2 mM H(2)O(2). Surface characterization of the polymer films was carried out using atomic force microscopy, X-ray photoelectron spectroscopy and scanning electron microscopy.     

Photophysical properties of hydroxylated amphiphilic poly(p-phenylene)s

A homologous series of polyhydroxylated poly(p-phenylene)s with different alkoxy groups (C6PPPOH, C12PPPOH, and C18PPPOH) were synthesized with use of the Suzuki polycondensation reaction. Comparative studies of the structure correlation between their photophysical properties and film morphology is described. The absorption and emission spectra of polymers in solution and thin films showed similar features indicating that the electronic properties in solution were retained in the film state. Compared to the polymer with the short alkoxy chains (C6PPPOH), the polymers with long alkoxy groups (C12PPPOH and C18PPPOH) showed improved film forming properties with continuous and smooth film morphology. The absorption properties of the C12PPPOH showed an enhanced effective conjugation length and high quantum yield implying planarization of the backbone through alkoxy chain packing (C12H25O-) and potential hydrogen bonds. No overlap in the absorption and emission spectra was observed, which indicated minimized excimer formation or excitation energy transfer in the films. Time-resolved fluorescence measurements showed that the decay times increased from 43 ps (C6PPPOH) to 78 ps (C12PPPOH) and 99 ps (C18PPPOH). Electrochemical studies were performed for all polymers and the observed oxidation potential for C6PPPOH was higher than that of C12PPPOH and C18PPPOH. In addition, the C12PPPOH has the lowest band gap of DeltaE = 2.59 eV when compared to the 3.1 (C6PPPOH) and 2.61 eV (C18PPPOH) gaps. The optical band gaps estimated from the absorption onset of the polymers are significantly higher than those obtained from electrochemical data. C12PPPOH was chosen for investigating the charge carrier mobility by the time-of-flight (TOF) technique. The observed results also showed negative field dependent values of the drift mobility for the polymer C12PPPOH.