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Circular dichroism (CD) spectroscopy has been used extensively for the investigation of the conformation and configuration of chiral molecules, but its use for evaluating the mode of self-assembly in soft materials has been limited. Herein, we report a protocol for the study of such materials by electronic circular dichroism (CD) spectroscopy using commercial/benchtop instruments and synchrotron radiation (SR) using the B23 beamline available at Diamond Light Source. The use of B23 beamtime for SRCD was advantageous due to the unique enhanced spatial resolution achieved because of its highly collimated and small beamlight cross-section (ca 250 μm) and higher photon flux in the far UV region (175-250 nm) enhancing the signal-to-noise ratio relative to benchtop CD instruments. A set of low molecular weight (LMW) hydrogelators, comprising two Fmoc-protected enantiomeric monosaccharides and one Fmoc-dipeptide (Fmoc-FF) were studied. The research focused on the optimization of sample preparation and handling, which then enabled the characterisation of sample conformational homogeneity and thermal stability. CD spectroscopy, in combination with other spectroscopic techniques and microscopy, will allow a better insight into the self-assembly of chiral building blocks into higher order structural architectures.

UV--visible (UV-vis) absorption spectroscopy is widely used as a primary means of assaying concentrations and in characterizing the kinetics of reactions and chemical processes; it is ubiquitously used for chromatographic detection. Although currently somewhat less widely used as a first means of structural analysis, compared to spectroscopies such as nuclear magnetic resonance, it remains pre-eminent for a wide range of specialist areas, especially those involving distinctive chromophoric compounds such as dyes, indicators, and filters. Its ability to probe the electronic states of molecules also ensures its wide use for detailed physical studies. The focus of this article is on the qualitative and quantitative application of UV-vis spectroscopy to organic compounds and practical guidance for the preparation of samples, interpretation of spectra, and understanding of the variables that can occur or be utilized. Typical spectral data for representative classes of compound are indicated and discussed.

This study investigated the development of a novel approach to surface characterisation of drug polymorphism and the extension of the capabilities of this method to perform ‘real time’ in situ measurements. This was achieved using diffuse reflectance visible spectroscopy (DRV spectroscopy) and dye deposition, using the pH sensitive dye, thymol blue (TB). Two polymorphs, SFN-β and SFN-γ, of the drug substance sulfanilamide (SFN) were examined. The interaction of adsorbed dye with polymorphs showed different behavior, and thus reported different DRV spectra. Consideration of the acid/base properties of the morphological forms of the drug molecule provided a rationalization of the mechanism of differential coloration by indicator dyes. The kinetics of the polymorphic transformation of sulfanilamide polymorphs was monitored using treatment with TB dye and DRV spectroscopy. The thermally-induced transformation fitted a first-order solid-state kinetic model (R2 = 0.992), giving a rate constant of 2.43 x 10−2 s−1.

There are currently no techniques that allow facile on-line determination between amorphous and crystalline material. Herein, a new colorimetric method, perichromism, has been developed to distinguish between amorphous and crystalline material, based on diffuse reflection ultraviolet–visible (UV-visible) spectroscopy. A probe molecule, phenol red, at 0.1% w/w concentration was added to sucrose and dissolved in water. The solution was freeze-dried, which resulted in an amorphous excipient with the probe molecule incorporated in an intimate mixture. The samples were then stored at a selected controlled temperature and relative humidity to allow control of crystallization of the sucrose. The amorphous or crystalline nature of each sample, both with and without the addition of the phenol red probe molecule, was monitored through X-ray diffraction, differential scanning calorimetry, and Raman spectroscopy. It was found that sucrose remained amorphous when stored in an atmosphere with a relative humidity below 32%; above this level, crystallization occurred. It was found that the presence of the probe molecule did not alter the extent of crystallinity of sucrose. Analysis of the samples containing the phenol red probe by diffuse reflection spectroscopy revealed that spectra could be classified into two groups depending on the λmax. Furthermore, correlation of the diffuse reflection spectra with X-ray diffraction and differential scanning calorimetry data showed that sucrose was amorphous in one group and crystalline in the other group, thereby revealing that diffuse reflection spectroscopy can, when phenol red is used as a probe molecule, quickly and easily determine whether sucrose is crystalline or amorphous.

Transient absorption spectroscopy (TAS) has been employed to identify the spectra of photogenerated electrons and holes on WO3. WO3 is a widely studied photoanode for the oxidation of water, and by measuring the decay of photoholes on the milliseconds to seconds time scale in the presence of an electron scavenger, we provide a lower limit for the required lifetime of holes for water oxidation on WO3. The rate of electron/hole recombination on WO3 has also been examined at a range of excitation intensities and is found to be nonlinear with excitation intensity.

FeVO 4 was synthesised using a low temperature, aqueous precipitation reaction. The material prepared directly from this synthesis was found to be predominantly amorphous and required a thermal treatment. The resultant material was characterised using XRD, FT-IR, Raman spectroscopy and magnetic susceptibility measurements. Materials annealed above 600 °C were found to consist mainly of FeVO 4 , although traces of hematite were found following annealing at higher temperatures. Diffuse-reflectance UV spectroscopy and subsequent Tauc plots revealed a band gap of ca . 2.00 eV corresponding to an indirect transition. Photocurrent–voltage characteristics recorded under simulated solar illumination indicate that photocurrents are sensitive to annealing temperature and the number of layers deposited on an electrode surface.

Structures of the [M(bpy)3]2+ complexes (M = Fe and Ru) have been calculated at the B3-LYP/DZVP level. IR and Raman spectra were calculated using the optimised geometries, employing a scaled quantum chemical force field, and compared with an earlier normal coordinate analysis of [Ru(bpy)3]2+ which was based upon experimental data alone, and the use of a simplified model. The results of the calculations provide a highly satisfactory fit to the experimental data and the normal coordinate analyses, in terms of potential energy distributions, allow a detailed understanding of the vibrational spectra of both complexes. Evidence is presented for Jahn-Teller distortion in the 1E MLCT excited state.

The absorption spectra. cyclic voltammetry and spectroelectrochemistry of [Ni(II)DPTAA] and [Co(II)DPTAA] (DPTAA = 6,13-diphenyldibenzo[b,i][1,4,8,11] tetraaza[14]annulene) complexes in DMF are reported in detail. The ligand oxidation is observed for [Ni(II)DPTAA] at +0.70 V vs. SCE whereas Ni2(+/+) occurs at - 1.60 V. For [Co(II)DPTAA], a ligand oxidation redox couple is seen at +0.56 V while the Co2+/+ and Co2+/3+ redox couples appear at -1.21 and +0.24 V, respectively. All observed redox couples are assigned to reversible one-electron processes on account of peak separations and scan-rate dependency. These processes were further investigated by spectroelectrochemistry for [Co(II)DPTAA]. For [Co(II)DPTAA], axial ligation of pyridine was found to shift the Co2+/3+ redox couple more negative. while the ligand oxidation was shifted to more positive potentials. From a spectrophotometric titration of [Co(II)DPTAA] with pyridine an equilibrium constant, K-f, was determined for the binding of pyridine to [Co(II)DPTAA]. This was found to be 10.2 dm(3) mol(-1), slightly lower than that of [Co(II)TAA], indicating the influence of the phenyl groups. From this value and shifts in the Co2+/3+ redox couple upon ligation, an equilibrium constant for the binding of pyridine to [Co(III)DPTAA], K'(f), was found to be 5.06 x 10(6) dm(3) mol(-1). (c) 2007 Elsevier B.V. All rights reserved.

Recently, responsive surfaces have attracted attention due to their potential applications. Reported research have studied the deposition of environmentally responsive particles on different surfaces, qualitatively tested their response to environmental conditions and studied their possible applications. In this work, novel fluorescent temperature-sensitive nanoparticles were synthesized using a surfactant free emulsion polymerization technique: poly(N-isopropylacrylamide-co-5% vinyl cinnamate) (p(NIPAM)5%VC). The new particles were characterized using dynamic light scattering and fluorescence spectroscopy. A novel sensitive method for the quantitative analysis of p(NIPAM) 5% VC using fluorescence spectroscopy was developed to determine the concentration of nanoparticle dispersions. This was further used to quantitatively determine the mass of nanoparticles deposited per unit area of glass pre-treated with acid, glass pre-treated with base, quartz, stainless steel, gold and teflon at 25 °C and 60 °C. Factors affecting the adsorption/desorption of the nanoparticles were studied, including the effect of substrate surface charge, surface roughness (using atomic force microscopy, AFM), hydrophilicity/hydrophobicity and the temperature at which the adsorption/desorption experiments were carried out. The results show that the effect of surface charge is the most significant, followed by that of surface roughness and temperature. Meanwhile, the influence of the hydrophobicity/hydrophilicity of the surface on the adsorption/desorption of nanoparticles appears to be far less significant than the previously mentioned factors.

UV--visible (UV-vis) absorption spectroscopy is widely used as a primary means of assaying concentrations and in characterizing the kinetics of reactions and chemical processes; it is ubiquitously used for chromatographic detection. Although currently somewhat less widely used as a first means of structural analysis, compared to spectroscopies such as nuclear magnetic resonance, it remains pre-eminent for a wide range of specialist areas, especially those involving distinctive chromophoric compounds such as dyes, indicators, and filters. Its ability to probe the electronic states of molecules also ensures its wide use for detailed physical studies. The focus of this article is on the qualitative and quantitative application of UV-vis spectroscopy to organic compounds and practical guidance for the preparation of samples, interpretation of spectra, and understanding of the variables that can occur or be utilized. Typical spectral data for representative classes of compound are indicated and discussed.

Sugar amino acids and their oligomers, known as carbopeptoids, are commonly studied as foldamers. However, study of their conformational preference is often challenging when the adopted conformations are extended and/or disordered. This study is the first to explore the disordered nature of such carbopeptoids by utilizing a family of 2,5-trans carbopeptoids. An array of spectroscopic techniques has been used to investigate the conformational preference of these carbopeptoids. However, using this data alone it has not been possible to assign conformational preference as an ordered extended conformation or as a disordered family of closely related conformations. Computational methods need to be employed to achieve reliable interpretation of the spectroscopic data. Chirality, 2008. © 2008 Wiley-Liss, Inc.