Isomer discrimination of polycyclic aromatic hydrocarbons in the Murchison meteorite by resonant ionization

We have used two-color resonant two-photon ionization (2C-R2PI) mass spectrometry to discriminate between isomers of polycyclic aromatic hydrocarbons in the Murchison meteorite. We measured the 2C-R2PI spectra of chrysene and triphenylene seeded in a supersonic jet by laser desorption. Since each isomer differs in its R2PI spectrum, we can distinguish between isomers using wavelength dependent ionization and mass spectrometry. We found both chrysene and triphenylene in sublimates from carbonaceous residue obtained by acid demineralization of the Murchison meteorite. Their R2PI mass spectra show only the molecular ion, even though these samples contain a complex inventory of organic molecules.     

On the origin of the Murchison meteorite phosphonates. Implications for pre-biotic chemistry

Ab initio calculations, combined with experimental studies on the anaerobic hydrolysis of phosphaalkynes under thermal and photochemical conditions suggest a potential, exogenous source of reduced oxidation state phosphorus for the early Earth.     

The squaric acid aggregate in mordenite investigated by Raman spectroscopy

A more detailed investigation of the squaric acid aggregate within mordenite was undertaken with the use of Raman spectroscopy. The previous reported investigation was limited to the carbonyl stretching region in the IR. In the present work the entire region from 500 to 2000 cm(-1) was investigated, revealing rather substantial vibrational shifts of the oxocarbon ring modes in the aggregate. Comparison of such shifts with those observed for the squaric acid (H2Sq)/4,4'-bipyridine (Bipy) charge transfer (CT) complex reveals that the interaction is much stronger in the aggregate, a clear effect of the restrict geometry. On the other hand, the shifts observed for the CO stretching modes are rather modest. The comparison of the ring modes present in the Raman spectra of squaric acid, potassium hydrogen squarate, potassium squarate, H2Sq/Bipy and squaric acid aggregate in mordenite strongly suggests that in the latter hydrogen bonded species are present.     

Thermal stability of aripiprazole monohydrate investigated by Raman spectroscopy

Aripiprazole (7-[4-[4-(2,3-dichlorophenyl)-1-piperazinyl]butoxy]-3,4-dihydrocarbostyril) is a well-known antipsychotic oral drug, whose molecular structure makes it suitable for polymorphism. Several crystalline structures were reported in the literature including anhydrate, hydrate and solvate modifications. It was observed that aripiprazole monohydrate exhibits a complex dehydration dynamics which was not completely elucidated. In this work the dehydration process of the aripiprazole hydrate was investigated by using Raman scattering, hot-stage microscopy and differential scanning calorimetry. The temperature evolution of the Raman spectra was analyzed through the multivariate statistical method of principal component analysis. Our results support that the dehydration process of aripiprazole is divided into two steps. First a diffusion-controlled loss of water followed by a fast nucleation and crystallization of the anhydrous form.     

On the characterization of disordered and heterogeneous carbonaceous materials by Raman spectroscopy

The applicability of Raman spectroscopy to characterize disordered and heterogeneous carbonaceous materials (CM) is discussed, by considering both natural and synthetic CM. First, different analytical mismatches during the measurement are discussed and technical indications are provided in order to eliminate them. Second, the accuracy and relevance of the different parameters obtained by the decomposition of spectra by conventional fitting procedure, is reviewed. Lastly, a new Raman technique (Raman area mode microspectroscopy) giving an homogeneous repartition of power within a large laser beam is presented, this technique being powerful to study strongly heterogeneous CM and/or photosensitive samples.     

Li ion diffusion in LiAlO2 investigated by Raman spectroscopy

The temperature dependence of Li ions behavior of γ-LiAlO₂ has been studied from 78 to 873 K. On heating, the Li ions underwent positional disordering along the structural channels, with the Li ions related modes at 220, 366 and 400 cm⁻¹ broadening and weakening dramatically. An anomalous maximum in the bandwidths of the Li ions related modes is observed. It should be apparent that there are at least two distinct thermally activated processes. A model suggested by Andrade and Porto is used to describe the linewidth of a phonon.     

The effect of carbonaceous materials on faradaic and charging current contribution in carbon paste electrodes investigated by chemometrics methods

Journal of Solid State Electrochemistry - Different carbon paste electrodes were prepared from carbonaceous materials including multi-walled carbon nanotubes (functionalized and pristine form),...     

Measurement of the carbonaceous component in the Milan urban particulate matter

The carbonaceous component in the Milan urban particulate matter, i.e. the two components black carbon (BC) and organic carbon (OC), has been measured by means of a thermogravimetric analyzer combined with an infrared spectrophotometer (TGA/FT-IR). While black carbon may be considered a primary pollutant, organic carbon includes both primary emissions and secondary organic aerosols. Since carbonaceous aerosol (including a small quantity of inorganic carbon, too) makes up roughly from 25% to 50% of the average annual PM 2.5 mass concentration, a deeper understanding of this component is required. The TGA/FT-IR technique, employed for the first time to our knowledge for the quantification of the particulate matter carbonaceous component, allows, thought the results here presented are preliminary, to assess the two components BC and OC in a simple way especially if compared with the methods reported in the literature. The total carbon (TC) determinations performed by TGA/FT-IR on Milan urban particulate matter are in good agreement with the results obtained by a total organic carbon (TOC) analyzer operating directly on the solid sample.     

Role of hydration in the phase transition of polypeptides investigated by NMR and Raman spectroscopy

NMR, Raman spectroscopy and ab initio quantum-chemical calculations have been employed to investigate the role of the hydration water in the inverse temperature transition of elastin-derived biopolymers represented by poly(Gly-Val-Gly-Val-Pro) and poly(Ala-Val-Gly-Val-Pro). Temperature and concentration dependences of the Raman spectra measured for water solutions of polymers and of a low-molecular-weight model have been correlated with the vibrational frequencies calculated at the DFT (B3LYP) and MP2 levels for the peptide segment surrounded by a growing number of water molecules. The results indicate strong hydration before the transition that, in addition to water hydrogen-bonded to amide groups, includes hydrophobic hydration of non-polar groups by a dynamic cluster of several water molecules. According to ¹H longitudinal and transverse relaxation of HOD signals in D₂O solutions, the number of water molecules motionally correlated with the polymer is about 4 per one amino acid residue.     

Photodissociation dynamics of the ethoxy radical investigated by photofragment coincidence imaging

The photodissociation dynamics of the ethoxy radical (CH3CH2O) have been studied at energies from 5.17 to 5.96 eV using photofragment coincidence imaging. The upper state of the electronic transition excited at these energies is assigned to the C2A'state on the basis of electronic structure calculations. Fragment mass distributions show two photodissociation channels, OH + C2H4 and CH3 + CH2O. The presence of an additional photodissociation channel, identified as D + C2D4O, is revealed in time-of-flight distributions from the photodissociation of CD3CD2O. The product branching ratios and fragment translational energy distributions for all of the observed mass channels are nonstatistical. Moreover, the significant yield of OH + C2H4 product suggests that the mechanism for this channel involves isomerization on the excited-state surface. Photodissociation at a much lower yield is seen following excitation at 3.91 eV, corresponding to a vibronic band of the B2A' <-- X2A' transition.     

Source apportionment of atmospheric carbonaceous particulate matter based on the radiocarbon

A method was established to quantitatively estimate sources of atmospheric carbonaceous matter, using a combination of radiocarbon technology, linear regression of organic carbon (OC) -K⁺ and elemental carbon (EC) tracer method. Fractional contributions of fossil fuels, biomass burning, biogenic secondary organic carbon (BSOC) and soil dust to the atmospheric size-resolved carbonaceous matters in Shanghai suburb were estimated using this new method. The fossil carbon contributed most of the OC in particles smaller than 0.49 μm, and its fraction decreased with the increase of particle size. Biomass burning contributed 17–28 % to the OC. The BSOC contributed comparable proportions to the OC in particles smaller than 3.0 μm with the biomass burning, but larger in the particles lager than 3.0 μm. The soil dust contributed least fraction to the OC of each size with a proportion of 2–13 %. The biomass burning and fossil sources shared comparable fraction of the EC in all size range.     

Nitrogen-doped pyrogenic carbonaceous matter facilitates azo dye decolorization by sulfide: The important role of graphitic nitrogen

Pyrogenic carbonaceous matter(PCM) catalyzes azo dye decolorization by sulfide, but the nitrogen doping catalytic mechanisms are poorly understood. In this study, we found that stagnate time of azo dye methyl orange(MO) decolorization was reduced to 0.54-18.28 min in the presence of various nitrogen-doped graphenes(NGs), remarkably lower compared to graphene itself. Particularly, graphitic nitrogen played a critical role in NGs-catalyzed MO decolorization by sulfide. Gas chromatography-mass spec...     

Nucleic acid and protein structures and interactions in viruses investigated by laser Raman spectroscopy

Raman spectroscopy may be profitably exploited to determine details of protein and nucleic acid structures and their mutual interactions in viruses and gene regulatory complexes. Present applications use data obtained from model nucleic acid crystals, fibers and solutions to reveal preferred backbone and nucleoside conformations for different morphological states of DNA and RNA in plant (TMV, BDMV) and bacterial viruses (P22, Pfl, Xf, Pf3, fd, Ifl, IKe). Interpretation of the results is enhanced by deconvolution methods which, in favorable cases, permit quantitative conclusions regarding macromolecular structures. Both equilibrium and dynamic Raman applications are described.     

The adsorption of rifampicin on gold or silver surfaces mediated by 2-mercaptoethanol investigated by surface-enhanced Raman scattering spectroscopy

In this work the adsorption of the antibiotic rifampicin (RP) on the surface of gold (AuNP) or silver nanoparticles (AgNP) was investigated using both surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) spectroscopies. Such spectra were obtained in the absence and presence of the surface modifier 2-mercaptoethanol (ME) using excitations by laser radiations of 532, 632.8 and 1064 nm wavelengths. The use of different conditions under the presence of ME led to changes in the spectral pattern ascribed to the influence of resonance Raman (RR) effect and distinct chemical interactions of RP with the metallic surfaces. The sensibility of the chromophoric moiety, i.e. a <pi>-conjugated orbital, to the adsorption geometries, which can be controlled by surface modifiers, impacts the RR effect. Theoretical models involving RP and metal atoms were obtained from Density Functional Theory (DFT) calculations, and used for supporting the vibrational assignment.     

Influence of crystal size on the electron–phonon coupling in ZnO nanocrystals investigated by Raman spectroscopy

We have synthesized ZnO nanocrystals of different sizes (25–41 nm) using the sol–gel method and characterized them using different techniques such as: transmission electron microscopy (TEM) and X-ray diffraction (XRD). Raman spectra of different sizes of ZnO nanocrystals were recorded at two excitation wavelengths, 514 and 647 nm, in the spectral range 300–1200 cm⁻¹. The vibrational modes were assigned on the basis of group theory analysis. The influence of mean crystallite size on the strength of the electron–phonon coupling is experimentally estimated by the variation of relative intensities of second order Raman band and the first order Raman band for ZnO nanocrystals of different sizes. We found that the intensity ratio of the 2E₂ and 1E₂ Raman bands decreases almost linearly for both excitation wavelengths with decreasing crystallite size, which reveals that the Fröhlich interaction plays a dominant role in the electron–phonon coupling of the ZnO nanocrystals.     

Organic matter in onshore cretaceous chalks and its variations,investigated by pyrolysis-mass spectrometry

Organic matter from twelve onshore Cretaceous chalks, present in amounts of about 0.002–0.1% by weight, was extracted in the form of humic acids. Curie-point pyrolysis-mass spectrometry, with factor analysis of the spectra, disclosed three principal modes of variation in the organic composition, as reflected by well-defined homologous groups of products. The principal of these factors was closely similar to a previously found soil factor and was characterized by well-defined groups of aromatic hydrocarbon products. Comparisons with infrared spectra and elemental composition suggest that it corresponds to early diagenetic alteration, probably involving microbial activity in the original sediments. A second factor, characterized by products of lignin and porphyrin origin, represents a contribution from terrestrial plant sources. This, however, is negligible in all but two of the samples. The third factor, characterized by amino acid products, is likely to reflect the contribution of marine organisms, particularly plankton, to the original organic sediment.     

The binding and correlation effects in carbon dioxide as investigated by gas X-ray diffraction

The X-ray scattering intensities of gaseous carbon dioxide have been measured by the enerey-dispersive method. Comparison of the measured intensities with theoretical calculations by the Hartree-Fock independent-atom model revealed the binding effect in the small-s region, which is largely consistent with theoretical predictions based on the molecular Hartree-Fock wavefunction.     

Reversible phase transformation of MnO2 nanosheets in an electrochemical capacitor investigated by in situ Raman spectroscopy

The reversible phase transformation is reported from hexagonal to monoclinic structure responding to the intercalation/deintercalation of Na(+) between MnO(2) nanosheets upon potential cycling in aqueous electrolyte via an in situ Raman technique. This structural evolution will influence the Na(+) diffusion process in MnO(2) nanosheets and cause phase retention during the self-discharge process.