Article

Outdoor use of mobile Raman spectrometers to study the solutions and ices of amino acids

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  • Ministry of Interior – Directorate General of the Fire Rescue Service CR,
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Abstract

Selected amino acids (glycine, alanine, and threonine) were analysed in the form of water solutions, mixtures of these amino acids in solution, as well as their respective ices using two hand-held instruments under outdoor and winter mountain conditions. The hand-held instruments featured 785 and 532nm excitations; the latter being one of the first using this wavelength on the market. The changes to the Raman spectra of the solutions and ices are discussed in relationship to the degree of ambiguity of the detection of the amino acids within the mixtures. The hand-held instruments were able to detect two amino acids out of the three in solution. The results showed that the hand-held instruments provide sufficient quality spectra when analysing ices prepared from the solutions; however, an unambiguous detection of these amino acids within mixtures still remains a challenge.

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... Although amino acids represent a valuable testing target, e.g., for mobile Raman instruments potentially applicable to planet exploration [20,21], the spectra are collected and examined using powder samples or crystalline samples from dried aqueous solutions. However, this process is unrealistic for real detection situations and analytical purposes where amino acid coating layers play a major role. ...
Article
The Raman spectra of 20 proteinogenic amino acids were recorded in the solution, glass phase (as drop coating deposition Raman (DCDR) samples) and crystalline forms in the wide spectral range of 200–3200 cm− 1. The most apparent spectral differences between the Raman spectra of the crystalline forms, glass phases and aqueous solutions of amino acids were briefly discussed and described in the frame of published works. The possible density dependencies of spectral bands were noted. In some cases, a strong influence of the sample density, as well as of the organization of the water envelope, was observed. The most apparent changes were observed for Ser and Thr. Nevertheless, for the majority of amino acids, the DCDR sample form is an intermediate between the solution and crystalline forms. In contrast, aromatic amino acids have only a small sensitivity to the form of the sample. Our reference set of Raman spectra is useful for revealing discrepancies between the SERS and solid/solution spectra of amino acids. We also found that some previously published Raman spectra of polycrystalline samples resemble glassy state rather than crystalline spectra. Therefore, this reference set of spectra will find application in every branch of Raman spectroscopy where the spectra of biomolecules are collected from coatings.
... Additionally, small, light, and portable spectrometers can be applied directly under field conditions, which is not feasible with other analytical techniques. Raman spectroscopy has been evaluated for the detection of compounds at low temperatures, and miniaturized Raman spectrometers with 785 nm lasers have been used to investigate mixtures of amino acids in mineral matrices at about -10°C and complex mixtures of amino acids in water ice even in small quantities (Culka et al., 2014c). ...
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... These instruments that feature excitation sources of the most often used wavelengths (such as 1064, 785 and 532 nm) have previously proved to be quite useful in the fields of geology and astrobiology; the geological applications tested have included analyses of rockforming [18,19] and organic [20] minerals, as well as carbonaceous material from an Ordovician stromatolite [21]. Biomarker detection in Alpine winter conditions [22][23][24] studies involving handheld instrumentation with astrobiological applications for the icy worlds of Europa and Titan. All the studies listed above used an excitation wavelength of 785 nm. ...
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In this study the possibility to detect biomarkers in experimentally prepared evaporitic matrices using a portable Raman instrument was estimated. Testing of the instrument was carried-out under the Alpine conditions outdoors at a low ambient temperature of -10 °C and at an altitude of 2860 m (Pitztal, Austria). Amino acids glycine and l-alanine, nucleo bases thymine and adenine, and metabolite urea were the organics mixed with gypsum powder. In this step it was shown that portable Raman spectroscopic instrumentation is capable of detecting biomarkers in complex samples in a host geological matrix. Such detection is possible even when the laser beam was focussed through the gypsum crystals 3-9 mm thick. For exobiology areas, this is an important fact, because life and/or related biomolecules are likely to be found in cavities under the surface of partially transparent evaporitic minerals that provide them a shelter from the hostile surrounding environment. For influencing the intensity of Raman bands the thickness of covering crystals is not as important as is the actual concentration of the biomarkers. This work and similar experiments serve for better evaluation of Raman spectroscopy as a method for future planetary exploration mission adoption.
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Handheld Raman spectrometers (Ahura First Defender XL, Inspector Raman DeltaNu) permit the recording of acceptable and good quality spectra of a large majority of minerals outdoors and on outcrops. Raman spectra of minerals in the current study were obtained using instruments equipped with 785 nm diode lasers. Repetitive measurements carried out under an identical instrumental setup confirmed the reliability of the tested Raman spectrometers. Raman bands are found at correct wavenumber positions within ±3 cm(-1) compared to reference values in the literature. Taking into account several limitations such as the spatial resolution and problems with metallic and black and green minerals handheld Raman spectrometers equipped with 785 nm diode lasers can be applied successfully for the detection of minerals from the majority of classes of the mineralogical system. For the detection of biomarkers and biomolecules using Raman spectroscopy, e.g. for exobiological applications, the near infrared excitation can be considered as a preferred excitation. Areas of potential applications of the actual instruments include all kind of common geoscience work outdoors. Modified Raman systems can be proposed for studies of superficial or subsurface targets for Mars or Lunar investigations.
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The detection of relatively low concentrations of the biomarkers in experimentally prepared evaporitic matrices using a portable Raman instrument (Ahura First Defender XL equipped with a 785 nm diode laser and fixed frontal probe) under Alpine conditions was tested. The instrument was able to detect nucleobases thymine (1673 and 984 cm(-1)) and adenine (722 and 536 cm(-1)) at concentrations of 1 wt% in the gypsum matrix outdoors at a low ambient temperature of -10°C and at an altitude of 2860 m(Pitztal, Austria). Amino acids glycine (1324 and 892 cm(-1)) and alanine (1357 and 851 cm(-1)) were unambiguously detected at 10 wt%. The main Raman features: strong, medium and partially weak intensity bands were observed in good agreement with the reference spectra for individual compounds (with a spectral resolution 7-10 cm(-1)) in the wavenumber range 200-1800 cm(-1). In the qualitative part of the experiment it was established that the portable instrument is able to detect the components in the mixture of three biomarkers (glycine, alanine and mellitic acid) and two evaporitic minerals unambiguously. It also detected the majority of the six similar amino acids in the mixture with gypsum and epsomite evaporitic minerals. The results obtained here demonstrate the possibility of a miniaturised Raman spectrometer to be able to cope with the various exobiologically related tasks that can be expected in the future planetary surface exploration missions. Within the payload designed by ESA and NASA for future missions, Raman spectroscopy will represent a unique research instrument.
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Raman spectra of 13 amino acids: L-alanine, β-alanine, L-asparagine, L-aspartic acid, L-glutamic acid, L-glutamine, glycine, L-methionine, L-proline, L-serine, L-threonine, L-tryptophan and L-tyrosine were acquired outdoors using two portable Raman instruments from the Ahura and Delta Nu manufacturers, both with 785 nm laser excitation. Both instruments provide quality Raman spectra with nevertheless a variable dependence upon the prevailing experimental conditions. The data acquired in these experiments will inform the selection of suitable Raman spectrometers for the in-field detection of biomolecules of relevance to the search for life signatures spectroscopically in terrestrial extreme environments and in extraterrestrial exploration, especially of planetary surfaces and subsurfaces using robotic instrumentation.
Article
The zwitterionic forms of the two simplest alpha-amino acids, glycine and l-alanine, in aqueous solution and the solid state have been modeled by DFT calculations. Calculations of the structures in the solid state, using PW91 or PBE functionals, are in good agreement with the reported crystal structures, and the vibrational spectra computed at the optimized geometries provide a good fit to the observed IR and Raman spectra in the solid state. DFT calculations of the structures and vibrational spectra of the zwitterions in aqueous solution at the B3-LYP/cc-pVDZ level were found to require both explicit and implicit solvation models. Explicit solvation was modeled by inclusion of five hydrogen-bonded water molecules attached to each of the five possible hydrogen-bonding sites in the zwitterion and the integration equation formalism polarizable continuum model (IEF-PCM) was employed, providing a satisfactory fit to observed IR and Raman spectra. Band assignments are reported in terms of potential-energy distributions, which differ in some respects to those previously reported for glycine and l-alanine.
Article
The broad objective of this research was to better understand the physical chemistry of freeze drying of the system glycine/water, with emphasis on the role of polymorphism of glycine on freezing and freeze-drying behavior. Frozen solutions of glycine were characterized by differential scanning calorimetry (DSC) and by freeze-dry microscopy. Cooling rates ranged from 0.1 degrees C/min to quench-cooling by immersing samples in liquid nitrogen. During slow cooling, only a beta-glycine/ice eutectic mixture is formed, melting at -3.60 degrees C. For quench-frozen solutions, the low-temperature thermal behavior is more complex. A complex glass transition region is observed on the DSC thermogram, with midpoint temperatures at about -73 degrees C and -60 degrees C, as well as two separate crystallization exotherms. Use of very low heating rates in the DSC experiment allows resolution of four separate endotherms in the temperature range just below the melting of ice. The experimental data support the conclusion that these endotherms arise from melting of the beta-glycine/ice eutectic mixture at -3.6 degrees C, dissolution of crystals of alpha-glycine at -2.85 degrees C, and melting of the gamma-glycine/ice eutectic mixture at -2.70 degrees C. One of the endotherms could not be characterized because of inadequate resolution from the beta-glycine/ice eutectic melting endotherm. Freeze-dried solids were characterized by X-ray powder diffraction after annealing under conditions established by the DSC and freeze-dry microscopy experiments. Annealing at controlled temperatures in the melting region prior to recooling the system was useful not only in interpreting the complex DSC thermogram, but also in controlling the glycine polymorph resulting from freeze drying.
Article
The analysis of inelastic incoherent neutron scattering spectra (IINS), infrared and Raman spectra obtained for deuterated and normal samples of L-threonine, made it possible to identify the majority of vibration modes due to particular molecular groups and to separate modes due to hydrogen bond vibrations in the crystals. Optimization of geometries for the zwitterion form was done using ab initio Hartree-Fock (HF) levels. Calculations of normal modes and force fields was done and used as basis for an assignment of the spectral features.
Article
The analysis of precious artefacts and antiquities demands care in order to minimise the risk of accidental damage during measurement. Mobile fibre-optic-based Raman instruments offer a means to avoid destructive sampling and eliminate the need to transport artefacts for spectrochemical analysis. In this work we present a new mobile instrument developed and optimised for the in situ Raman investigation of objects of art and antiquities. The instrument is controlled by a portable computer. Selected mounts cover many types of artefacts. Newly written software routines organise spectra together with measurement parameters and facilitate calibration of the instrument. The present paper describes this new Raman instrument and discusses some challenges in the transition from a laboratory environment to in situ investigations in museums.
Article
The structure and hydrogen bonding of water in an aqueous solution of various alpha,omega-amino acids were analyzed using the contours of the OH stretching in the polarized Raman spectra. From the relative intensity of the collective band (C value) corresponding to a long-range coupling of the OH stretching in the aqueous amino acid solutions, the number of hydrogen bonds disrupted due to the presence of one amino acid molecule (N(corr) value) was evaluated. The N(corr) value for glycine was slightly positive, whereas with an increase in the number of methylene groups between ammonium and carboxylate groups, the N(corr) value gradually increased. These results suggest that the species with proximal anionic and cationic groups do not disturb the hydrogen-bonded network structure of water significantly, probably due to the counteraction of the electrostatic hydration effect attributable to the anionic and cationic groups.
Article
A key process in the development of new drugs is elucidation of the interaction between the drug molecule and the target protein. Such knowledge then makes it possible to make systematic structural modifications of the drug molecule to optimize the interaction. Many analytical techniques can be applied to proteins in solution such as circular dichroism, ultraviolet, and fluorescence spectroscopy but these all have limitations. In this paper, we investigate the feasibility of using relatively simple, visible light Raman spectroscopic methods to investigate amino acids and related biopolymers.
Article
The infrared and Raman spectra of glycine molecule has been studied in spectral region 400-4000 cm(-1) in solid form as well as in water. The vibrational frequencies for the fundamental modes of the glycine in neutral and its zwitterionic form have also been calculated using AM1 semiempirical method as well as ab initio method with minimal basis set. The reliability of the minimal basis set and AM1 method with higher basis sets, for IR spectra of the neutral glycine conformers were examined. We find that the 6-21G basis set calculation yields structural parameters, rotational constant and dipole moment of glycine conformers, which are very similar to those obtained from extended basis set calculation as well as experimental values. IR frequencies for glycine conformer I are also calculated in water using SCRF=PCM model and compared with experimental values. A comparison between calculated frequencies for neutral glycine, and its zwitterionic form with observed IR and Raman bands have been made. The total energies for gas phase glycine and its zwitterionic form along with those of hydrated forms were also calculated. It is found from the calculations that in the gas phase neutral glycine is more stable as compared to its zwitterionic form.
Article
Raman spectroscopy is proposed as a valuable analytical technique for planetary exploration because it is sensitive to organic and inorganic compounds and able to unambiguously identify key spectral markers in a mixture of biological and geological components; furthermore, sample manipulation is not required and any size of sample can be studied without chemical or mechanical pretreatment. NASA and ESA are considering the adoption of miniaturised Raman spectrometers for inclusion in suites of analytical instrumentation to be placed on robotic landers on Mars in the near future to search for extinct or extant life signals. In this paper we review the advantages and limitations of Raman spectroscopy for the analysis of complex specimens with relevance to the detection of bio- and geomarkers in extremophilic organisms which are considered to be terrestrial analogues of possible extraterrestial life that could have developed on planetary surfaces.
Article
In this work, we present the absorption spectra and molar coefficients of all 20 amino acids in aqueous solutions down to 500 cm(-1). The spectral region between 1200 and 500 cm(-1) was yet disregarded for protein infrared spectroscopy, mainly due to the strong H(2)O absorption. Absorption spectra were obtained mainly for physiological relevant pH region. Intense bands for aromatic amino acids, histidine and such with OH group could clearly be identified throughout the given spectral region. For sulfur-containing amino acids cysteine and methionine some strong bands besides the weak carbon-sulfur stretching vibration was shown. Effects of aqueous solution environment, pH, protonation states were discussed, together with previously reported data from theoretical approaches. With this complete set of spectral information application to proteins in the whole mid infrared region could be described precise and the potential of the lower spectral region to study typical cofactor ligands like histidine, shown.