Raman spectroscopic analysis of minerals and organic molecules of relevance to astrobiology.

Characteristic geological features and hydrated minerals recently found on the surface of Mars by the NASA planetary rovers Spirit and Opportunity suggest that a possible biosphere could have once existed there. Analytical instrumentation protocols for the unequivocal detection of biomarkers in suitable geological matrices are critical for future unmanned explorations, including the forthcoming ESA-ExoMars mission scheduled for 2018. Raman spectroscopy is currently a part of the Pasteur instrumentation suite of the ExoMars mission scheduled for 2018 for the remote detection of extant or extinct life signatures in the Martian surface and subsurface. Terrestrial analogues of Martian sites have been identified, and the biogeological modifications incurred as a result of extremophilic survival activity have been studied. Polyaromatic hydrocarbons (PAHs) are recognised as a class of degradation product that occur from biological processes terrestrially. In this work, various concentrations of polyaromatic hydrocarbons in matrices of gypsum, calcite and quartz have been investigated by Raman microspectrometry to determine the lowest detectable organic levels. The studies are conceived in simulation of their potential PAHs identification in geobiological conditions in Martian scenarios. Two laser source wavelengths, namely, 785 and 633 nm, were adopted to excite Raman spectra from the PAHs, which represent degraded carbons and therefore potentially provide a key bimolecular marker of ancient life.

Identification of a new co-crystal of salicylic acid and benzamide of pharmaceutical relevance.

Raman spectroscopy, X-ray powder diffraction/X-ray crystallography and differential scanning calorimetry have been used to study the phenomenon of co-crystal formation in stoichiometric mixtures of salicylic acid with benzamide. Raman spectroscopy was particularly useful for the characterization of the products and was used to determine the nature of the interactions in the co-crystals. It was observed that little change in the vibrational modes associated with the phenyl groups of the respective reactants took place upon co-crystal formation, but changes in intensities of the vibrational modes associated with the amide and the carboxylic acid groups were observed upon co-crystal formation. Several new vibrational bands were identified in the co-crystal which were not manifested in the physical mixture of both components and could be used as diagnostic features of co-crystal formation.

Vibrational spectroscopic study of fluticasone propionate.

Fluticasone propionate is a synthetic glucocorticoid with potent anti-inflammatory activity that has been used effectively in the treatment of chronic asthma. The present work reports a vibrational spectroscopic study of fluticasone propionate and gives proposed molecular assignments on the basis of ab initio calculations using BLYP density functional theory with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation. Several spectral features and band intensities are explained. This study generated a library of information that can be employed to aid the process monitoring of fluticasone propionate.

Vibrational spectroscopic study of terbutaline hemisulphate.

The Raman spectrum of terbutaline hemisulphate is reported for the first time, and molecular assignments are proposed on the basis of ab initio BLYP DFT calculations with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation; these predictions compare favourably with the observed vibrational spectra. Comparison with previously published infrared data explains several spectral features. The results from this study provide data that can be used for the preparative process monitoring of terbutaline hemisulphate, an important beta(2) agonist drug in various dosage forms and its interaction with excipients and other components.

Vibrational spectroscopic and ultrasound analysis for in-process characterization of high-density polyethylene/polypropylene blends during melt extrusion.

Spectroscopic techniques such as Raman, mid-infrared (MIR), and near-infrared (NIR) have become indispensable analytical tools for rapid chemical quality control and process monitoring. This paper presents the application of in-line Fourier transform near-infrared (FT-NIR) spectroscopy, Raman spectroscopy, and ultrasound transit time measurements for in-line monitoring of the composition of a series of high-density polyethylene (HDPE)/polypropylene (PP) blends during single-screw extrusion. Melt composition was determined by employing univariate analysis of the ultrasound transit time data and partial least squares (PLS) multivariate analysis of the data from both spectroscopic techniques. Each analytical technique was determined to be highly sensitive to changes in melt composition, allowing accurate prediction of blend content to within +/- 1% w/w (1sigma) during monitoring under fixed extrusion conditions. FT-NIR was determined to be the most sensitive of the three techniques to changes in melt composition. A four-factor PLS model of the NIR blend spectra allowed determination of melt content with a standard prediction error of +/- 0.30% w/w (1sigma). However, the NIR transmission probes employed for analysis were invasive into the melt stream, whereas the single probes adopted for Raman and ultrasound analysis were noninvasive, making these two techniques more versatile. All three measurement techniques were robust to the high temperatures and pressures experienced during melt extrusion, demonstrating each system's suitability for process monitoring and control.

Raman spectra of biomarkers of relevance to analytical astrobiological exploration: hopanoids, sterols and steranes.

The aim of this work is to investigate the viability and potential of three groups of organic compounds as biomarkers in a future robotic analytical exploration of Mars. The three compounds have been identified as suitable candidates for potential biomarkers for extant or extinct life from the terrestrial fossil record. The three groups of compound were all similar in structure, being either tetra- or penta-cyclic compounds. The limits of detection for a sample were also tested to estimate what concentrations it would still be amenable to Raman spectroscopic investigation. This was investigated using both solid mixtures and liquid solutions. The spectra of these compounds are characterised so that they can be added to the Raman database for future Mars missions. This involved identifying functional group characteristics, assigning peaks for each individual sample and characteristic features which would categorise the samples.

The effect of laser wavelength on the Raman Spectra of phenanthrene, chrysene, and tetracene: implications for extra-terrestrial detection of polyaromatic hydrocarbons.

Raman spectroscopy, with visible laser (514 and 633 nm) and near infrared (785 and 1064 nm) excitation, has been used to obtain high quality spectra of phenanthrene, chrysene, and tetracene. Samples with dimensions from a minimum size of 10 microm have been analyzed utilizing a Raman microprobe fitted with a charge-coupled device (CCD) array detector and a FT-Raman instrument. Fluorescence is observed for samples using visible 514, 633 and near infrared 785 nm excitation but most of the samples can be measured with a near infrared 1064 nm Nd:YAG laser.

In situ monitoring of pH titration by Raman spectroscopy.

Molecular speciation of organic compounds in solution is essential for the understanding of ionic complexation. The Raman technique was chosen because it allows the identification of compounds in different states, and it can give information about the molecular geometry from the analysis of the vibrational spectra. The effect of pH on organic compounds can give information about the ionisation of molecule species. In this study the ionisation steps of salicylic acid and paracetamol have been studied by means of potentiometry coupled with Raman spectroscopy at 30.0 degrees C in a solution of ionic strength 0.96moldm(-3) (KNO(3)) and 0.04moldm(-3) (HNO(3)). The protonation and deprotonation behaviour of the molecules were studied in different pH regions. The abundance of the three different species in the Raman spectra of aqueous salicylic acid have been identified satisfactorily, characterised, and determined by numeric treatment of the data using a multiwavelength curve-fitting program and confirmed with the observed spectral information.

An experimental and computational study on the epimeric contribution to the infrared spectrum of budesonide.

Budesonide is a mixture of 22R and 22S epimers. The epimeric content of budesonide was reported in both British and European pharmacopoeias to be within the range of 60-49/40-51 for R and S epimers, respectively. In this work, contribution of the two epimers to the overall infrared spectrum of budesonide has been investigated by quantum chemical calculations.

Vibrational spectroscopic study of salbutamol hemisulphate.

Salbutamol hemisulphate is a relatively selective beta(2)-adrenergic agonist and is used as a bronchodilator. In this work, we present a detailed vibrational spectroscopic investigation of salbutamol hemisulphate using mid-infrared and near-infrared Fourier-transform (NIR-FT) Raman spectroscopies. These data are supported by quantum chemical calculations, which allow us to characterise the vibrational spectra of this compound reasonably. As such, this study could be viable for examining the way in which this drug interacts with its target molecules.

Computational and vibrational spectroscopic studies of ipratropium bromide.

In this study, ipratropium bromide is investigated using vibrational spectroscopy and quantum chemical calculations. The structure of ipratropium bromide was optimised using density functional theory calculations and the geometry optimisation has been carried out on two conformations with and without intramolecular hydrogen bonding. Infrared and Raman spectra were calculated from the optimised structures. Many modes in the calculated spectra could be matched with the experimental spectra and a description of the modes is given. By analysis of the theoretical vibrational modes, it is shown that ipratropium bromide specimens are likely to be a mixture of the two conformations with and without intramolecular hydrogen bonding. In addition, several spectral features and band intensities in the CH and OH stretching regions are explained. Quantum mechanical calculations allowed improved understanding of ipratropium bromide and its vibrational spectra.