Geochemical characterisation of Antarctic soils and lacustrine sediments from Terra Nova Bay

In Terra Nova Bay region (northern Victoria Land, Antarctica), the interactions among soil, meltwater and lakes are poorly understood with regard to the physicochemical transformations that occur when solid materials are exchanged among them. In order to ascertain the natural dynamics of several elements, namely Al, As, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Ti and Zn, as well as the perturbations by human activities and/or global contamination, soils and sediments from four catchments (Tarn Flat, Edmonson Point, Inexpressible Island and Northern Foothills) were studied.To accomplish the above mentioned objectives, the particle-size distribution and mineralogical composition, as well as the total C, H and N contents and the total concentrations of the investigated elements were determined. Finally in order to assess metal mobility, the modified BCR three-step sequential extraction procedure was applied to the samples and the partitioning of five metals, namely Cr, Fe, Mn, Pb and Zn, into different fractions was determined.Lithology and topography are the main factors that differentiate the physicochemical characteristics of the soils and sediments investigated. The lacustrine sediments and the soils sampled around the lakes showed a similar mineralogical and chemical composition, as evidence that rock- and soil-weathering processes occur primarily during the warm summer periods, when the lakes are partially ice-free. Nevertheless the presence of chlorite in these systems indicated that chemical weathering has taken place even in these extreme conditions. In general, the geochemical composition of soils and sediments in this Antarctic area seems to be influenced mainly by the nature of the bedrock and by the input of sea-spray, and, to a lesser degree, by mechanical and chemical weathering as well as by biological processes; no evidence of a local or global anthropogenic contamination was found.     

Raman spectroscopic studies of terthiophenes for molecular electronics

The effect of thiol and selenol functionalization on the vibrational spectra and photochemical stability of terthiophene based molecular wires was investigated using surface-enhanced Raman scattering (SERS). The molecules were found to exhibit markedly different properties at the silver surface of the SERS substrate, despite having almost identical Raman spectra in solution and in the solid state. In contrast to terthiophene (3T), the bisthiolterthiophene (T3) and biselenol-terthiophene (Se3) molecules were stable against photoinduced structural changes when adsorbed to the metal surface at low concentrations. This indicates that the strong bonds to the silver surface, via S or Se terminal atoms, leads to a rapid decay of photoexcited states. Comparison with ab initio calculations shows that both T3 and Se3 bind with only one of the functional groups to the Ag surface.     

A review of Fourier-transform Raman spectroscopic studies on polymers

The published work on the FT-Raman spectra of polymers other than elastomers is reviewed and assessed. Experimental techniques, including sampling procedures, measurements at elevated temperatures and microscope accessories are considered first, followed by the scope for quantitative measurements. The survey of published work on polymers is arranged into the subdivisions hydrocarbon polymers, polyamides and polyimides, poly(aryl ether ketone) and poly(aryl ether ether ketone) and the corresponding sulphones, halogenated polymers, highly conjugated polymers, various other polymers, polymerization kinetic studies and thin polymer films.     

Resonance Raman spectroscopic studies of hydroperoxo-myoglobin at cryogenic temperatures

In agreement with previous reports (Gasyna, Z. FEBS Lett. 1979, 106, 213-218 and Leibl, W.; Nitschke, W.; Huettermann, J. Biochim. Biophys. Acta 1986, 870, 20-30) radiolytically reduced samples of oxygenated myoglobin at cryogenic temperatures have been shown by optical absorption and EPR studies to produce directly the peroxo-bound myoglobin at 77 K. Annealing to temperatures near 185 K induces proton transfer, resulting in the formation of the hydroperoxo heme derivative. Resonance Raman studies of the annealed samples has permitted, for the first time, the direct observation of the key nu(Fe-O) stretching mode of the physiologically important Fe-OOH fragment of this ubiquitous intermediate. The assignment of this mode to a feature appearing at 617 cm(-1) is strongly supported by documentation of a 25 cm(-1) shift to lower energy upon substitution with (18)O(2) and by a 5 cm(-1) shift to lower energy for samples prepared in solutions of deuterated solvent.     

Surface-enhanced Raman spectroscopic studies of coactivator-associated arginine methyltransferase 1

We report, for the first time, the surface-enhanced Raman spectra of an important enzyme, coactivator-associated arginine methyltransferase 1 (CARM1), involved in various biological activities such as tumor suppressor function and stem cell differentiation. We have employed surface-enhanced Raman scattering (SERS) to obtain insight into the structural details of CARM1 by adsorbing it to silver (Ag) nanoparticles. The enzyme retains its activity even after its adsorption onto Ag nanoparticles. We observe strong SERS modes arising from amide vibrations and aromatic ring amino acids. The SERS spectra revealed amide I bands at 1637 cm(-1) and 1666 cm(-1), which arise as a result of the alpha helix of the protein and the polypeptide backbone vibration of a random coil, respectively. In order to confirm the amide vibrations, we have performed SERS on deuterated CARM1, which exhibits a clear red shift in amide band positions. The SERS spectra may provide useful information, which could be harnessed to study the functional interactions of CARM1 with small molecule modulators.     

Raman spectroscopic and DSC studies of diglycine-perchlorate (DGPCl)

Single crystals of diglycine perchlorate (DGPCl) and deuterated diglycine perchlorate (DDGPCl) are synthesized and studied using differential scanning calorimetry (DSC) and Raman spectroscopy. DSC data indicated that both DGPCl and DDGPCl undergo a reversible first-order phase transition (solid-solid) at −11.5 °C and −9.3 °C, respectively. The Raman spectra of DGPCl and DDGPCl obtained at ambient temperature are analyzed to infer on the strength of hydrogen bonding in this compound relative to the parent compounds. The occurrence of NH stretching frequency at higher value in DGPCl in comparison with glycine suggests presence of a weak N–H?O hydrogen bond in DGPCl than in glycine. The lower isotropic melting temperature of DGPCl as compared to that of glycine is understood on the basis of the relative strength of hydrogen bonding in these compounds.     

Infrared and Raman spectroscopic studies of glasses with NASICON-type chemistry

Structures of NASICON glasses of the general formula AB₂(PO₄)₃, where A = Li, Na or K and B = Fe, Ga, Ti, V or Nb, have been investigated using vibrational (IR and Raman) spectroscopies. Phosphate species appear to establish an equilibrium via a disproportionation reaction involving a dynamical bond-switching mechanism where both charge and bonds are conserved. B ions in the system acquire different coordinations to oxygens. Alkali ions cause absorptions due to cage vibrations. All the observed spectroscopic features are consistent with speciation involving disproportionation reactions.     

Infrared and Raman spectroscopic studies of l-valine l-valinium perchlorate monohydrate

FT-IR and FT-Raman spectra were recorded and analyzed for l-valine l-valinium perchlorate monohydrate crystals. The wave number assignments have been made for the functional groups, viz. COOH, COO(-), --[NH(3)](+), C--(CH(3))(2), C--C--N and C--H. One of the two amino acid residues remains in the zwitterionic form while the other residue exists in the cationic form. The symmetry of the ClO(4)(-) anion has been found to be lowered corresponding to ClO(2) group. The hydrogen bonds that prevail between amino acid residues, perchlorate anion and water molecule influence the wave numbers of several stretching and deformation modes to deviate from the expected values.     

Raman spectroscopic detection of biomolecular markers from Antarctic materials: evaluation for putative Martian habitats

The vital UV-protective and photosynthetic pigments of cyanobacteria and lichens (microbial symbioses) that dominate primary production in Antarctic desert ecosystems auto-fluoresce at short-wavelengths. A long wavelength (1064 nm) near infra-red laser has been used for non-intrusive Raman spectroscopic analysis of their ecologically significant compounds. There is now much interest in the construction of portable Raman systems for the analysis of cyanobacterial and lichen communities in the field; to this extent, Raman spectra obtained with laboratory-based systems operating at wavelengths of 852 and 1064 nm have been evaluated for potential fieldwork applications of miniaturised units. Selected test specimens of the cyanobacterial Nostoc commune, epilithic lichens Acarospora chlorophana, Xanthoria elegans and Caloplaca saxicola and the endolithic Chroococcidiopsis from Antarctic sites have been examined in the present study. Although some organisms gave useable Raman spectra with short-wavelength lasers, 1064 nm was the only excitation that was consistently excellent for all organisms. We conclude that a 1064 nm Raman spectrometer, miniaturised using an InGaAs detector, is the optimal instrument for in situ studies of pigmented communities at the limits of life on Earth. This has practical potential for the quest for biomolecules residual from any former surface or subsurface life on Mars.     

Fourier transform Raman spectroscopic studies on sterically hindered aryl dichalcogenides

The Fourier transform Raman spectra of trisubstituted aryl dichalcogenides (2,4,6-R₃C₆E)₂ (R = Me, Prⁱ, Bu^t; E = Se, Te) in the region 600-100 cm⁻¹ are reported. Contrary to expectations, the ν(E-E) stretching frequencies increase slightly with increasing steric bulk of the aryl substituents but are less substituent-dependent than in previously reported examples.     

Raman spectroscopic studies of the cure of dicyclopentadiene (DCPD)

The cure of polydicyclopentadiene conducted by ring-opening metathesis polymerisation in the presence of a Grubbs catalyst was studied using non-invasive Raman spectroscopy. The spectra of the monomer precursor and polymerised product were fully characterised and all stages of polymerisation monitored. Because of the monomer's high reactivity, the cure process is adaptable to reaction injection moulding and reactive rotational moulding. The viscosity of the dicyclopentadiene undergoes a rapid change at the beginning of the polymerisation process and it is critical that the induction time of the viscosity increase is determined and controlled for successful manufacturing. The results from this work show non-invasive Raman spectroscopic monitoring to be an effective method for monitoring the degree of cure, paving the way for possible implementation of the technique as a method of real-time analysis for control and optimisation during reactive processing. Agreement is shown between Raman measurements and ultrasonic time of flight data acquired during the initial induction period of the curing process.     

Infrared and Raman spectroscopic studies of mesogens with a cyanobicyclohexyl skeleton

The i.r. spectra of three cyanobicyclohexyls with three, four and seven carbon atoms in a linear side chain were investigated. Dichroic spectra of the compounds oriented between KBr plates were obtained for the crystalline, smectic and nematic phases. Raman spectra of the crystalline and isotropic phases and of the solutions were recorded to support the i.r. data.It was assumed that the cyclohexyl rings are predominantly in the ee-conformation, but the rings are relatively free to rotate relative to each other. The conformation of the hydrocarbon chains vary upon melting, but no significant changes occur when going from one liquid phase to another. In the molecule with a three-membered carbon chain the all trans chain was the only conformation found. The all trans conformation was preferred in the liquid crystalline state of the molecules having four and seven carbons in the side chains compared with the conformations found in solution at the same temperature.     

Raman spectroscopic studies of CO2 laser-irradiated human dental enamel.

While the effects of carbon dioxide (CO2) laser radiation on the physical properties of human dental enamel are well characterized, little is known regarding laser-induced chemical changes. In this study, enamel was exposed to CO2 laser radiation to induce fusion and recrystallization, and the Raman spectra recorded using both dispersive and Fourier-transformed (FT) Raman spectroscopy. Spectra were compared to a heart-treated specimen of hydroxyapatite (HAP) and enamel. Laser irradiation induced chemical changes which differed from those induced by heat treatment. Comparing the Raman spectra of lased enamel to HAP and tricalcium phosphate (TCP), it is evident that CO2 laser irradiation of enamel causes the partial conversion of HAP to TCP. The effect of laser irradiation is not merely a simple local heating effect as previously thought, since simple heating of enamel leads to the formation of both TCP and Ca(OH)2, while laser treatment of enamel results in the formation of TCP but not Ca(OH)2.     

The cytidinium—cytidine complex: infrared and Raman spectroscopic studies

Using IR and Raman spectra, it is shown that the sytidinium cation hydrogen bonds to cytidine to form a stable 1:1 complex, in both aqueous solution (pH ~ 3.3) and as a solid. The spectra indicate that the proton is located asymmetrically in the NH?N bond of the complex, on the vibrational time scale, in both solution and the solid. The perdeuterated systems were also examined; their spectra support these conclusions.     

Raman and FTIR spectroscopic studies of copolymers of methyl methacrylate with butadiene

The comprehensive characterization by Raman and IR spectroscopy of the products of the free-radically initiated copolymerization of methyl methacrylate with 1,3-butadiene is reported. Raman spectroscopy has been used to determine quantitatively the microstructure of the polymerized 1,3-butadiene units in the copolymers.     

Combined Fourier transform infrared and Raman spectroscopic studies of some carbonyl-diphosphine-indenyl-iron cations

The Fourier transform infrared and Raman spectra of the cations [η⁵-C₉H₇Fe(CO)_n dppa]⁺ (n = 1, 2; dppa=bisdiphenylphosphinoalkane, where alkane=methane, ethane, butane, hexane and octane) and [{η⁵-C₉H₇Fe(CO)₂}₂-μ-dppa]²⁺ indicate that the alkyl chain lengths have effects on the structures of the bidentate cations resulting in increased back-donation to carbonyl groups as the chain length increases. In contrast the alkyl chain lengths have no similar effects in the unidentate mononuclear and bridged cations.     

Surface enhanced Raman spectroscopic studies of 1H-indazole on silver sols.

The SER spectra of 1H-indazole adsorbed on silver hydrosol were recorded in the 1800-100 cm(-1) and in the 3200-2800 cm(-1) regions. The SERS data were interpreted on the basis of previous vibrational assignments, with the help of the results of DFT calculations carried out using the 6-31G** basis. From the comparison of SER and normal Raman spectra it can be deduced that 1H-indazole is non-dissociatively adsorbed on metal surface and that it interacts with silver sol via nitrogen atoms and ring pi-system. The molecular plane assumes a tilted orientation with respect to the silver surface. The effect of varying the concentration of adsorbate was also evaluated. The observed changes of the relative intensities of some enhanced bands suggest that the molecule assumes a more tilted orientation upon lowering the concentration of the adsorbate.     

Fourier transform Raman spectroscopic studies of a novel wood pulp bleaching system

The use of near-infrared (NIR) Fourier transform (FT) Raman spectroscopy for the study of lignocellulosic materials is discussed. An application utilizing NIR FT-Raman spectroscopy to study a novel chlorine-free process for the bleaching of wood pulps is presented in detail. The new process, still under development, entails the oxidation of residual lignin in wood pulps by vanadium-substituted polyoxometalates, and reoxidation of the reduced polyoxometalates by chlorine-free oxidants such as air, dioxygen, peroxides or ozone. Results from FT-Raman measurements of polyoxometalate-treated pulps are compared with those from chemical, spectroscopic and optical techniques commonly used in the pulp and paper industry.     

Raman spectroscopic studies on single supersaturated droplets of sodium and magnesium acetate

Raman spectroscopy was used to study structural changes, in particular, the formation of contact-ion pairs in supersaturated aqueous NaCH(3)COO and Mg(CH(3)COO)(2) droplets at ambient temperatures. The single droplets levitated in an electrodynamic balance (EDB), lost water, and became supersaturated when the relative humidity (RH) decreased. For NaCH(3)COO droplet the water-to-solute molar ratio (WSR) was 3.87 without solidification when water molecules were not enough to fill in the first hydration layer of Na(+), in favor of the formation of contact-ion pairs. However, the symmetric stretching vibration band (nu(3) mode) of free -COO(-) constantly appeared at 1416 cm(-1), and no spectroscopic information related to monodentate, bidentate, or bridge bidentate contact-ion pairs was observed due to the weak interactions between the Na(+) and acetate ion. On the other hand, the band of methyl deformation blue shifted from 1352 to 1370 cm(-1) (at RH = 34.2%, WSR = 2.43), corresponding to the solidification process of a novel metastable phase in the highly supersaturated solutions. With further decreasing RH, a small amount of supersaturated solution still existed and was proposed to be hermetically covered by the metastable phase of the particle. In contrast, the interaction between Mg(2+) and acetate ion is much stronger. When WSR decreased from 21.67 to 2.58 for the Mg(CH(3)COO)(2) droplet, the band of C-C-symmetric stretching (nu(4) mode) had a blue shift from 936 to 947 cm(-1). The intensity of the two new shoulders (approximately 1456 and approximately 1443 cm(-1)) of the nu(3) band of free -COO(-) at 1420 cm(-1) increased with the decrease of WSR. These changes were attributed to the formation of contact-ion pairs with bidentate structures. In particular, the small frequency difference between the shoulder at approximately 1443 cm(-1) and the nu(3) band of the free -COO(-) group (approximately 1420 cm(-1)) was proposed to be related to the formation of a chain structure based on the contact-ion pairs of bridge bidentate. The continuous formation of various contact-ion pairs started at higher WSR value (WSR = 15.5) greatly reduced the hygroscopic properties of Mg(CH(3)COO)(2) droplet, so that the WSR of Mg(CH(3)COO)(2) droplets was even lower than that of NaCH(3)COO in the RH range of 40-60%.