Raman and infrared spectra of the all-trans, 7-cis, 9-cis, 13-cis and 15-cis isomers of β-carotene: Key bands distinguishing stretched or terminal-bent configurations form central-bent configurations

Raman and infrared spectra in the region of 1800-150 cm⁻¹ were recorded for a set of cis-trans isomers of d̃-carotene, i.e. the all-trans, 7-cis, 9-cis, 13-cis and 15-cis isomers. Spectral comparison revealed Raman and infrared key bands which (1) distinguish stretched or terminal-bent configurations (all-trans, 7-cis and 9-cis) from central-bent configurations (13-cis and 15-cis), and (2) distinguish unmethylated 7-cis and 15-cis configuratios. Keybands (1) include Raman bands at 1160 and 1140 cm⁻¹ and infrared bands at 825 and 775 cm⁻¹ (the intensity varies with the position of the cis-bend) Key bands (2) include Raman bands at 1274 and 962 cm⁻¹ and an infrared band at 741 cm⁻¹ (characteristic of the 7-cis configuration), and also a Raman band at 1247 cm⁻¹ and an infrared band at 775 cm⁻¹ (characteristic of the 15-cis configuration). The normal modes for the key bands were determined by a set of normal coordinate calculations for the isomeric configurations of a simplified model of d̃-carotene. The key bands were mainly related to the C H in-plane bendings, coupled with the CC or C C stretching, or to the C H out-of-plane wagging vibrations, some of which coupled with the CC torsion.     

Vibrational spectroscopic studies of the structure of di‐amino acid peptides. Part II: cyclo(L‐Asp‐L‐Asp) in the solid state and in aqueous solution

Solid‐state protonated and N,O‐deuterated Fourier transform infrared (IR) and Raman scattering spectra together with the protonated and deuterated Raman spectra in aqueous solution of the cyclic di‐amino acid peptide cyclo(L ‐Asp‐L ‐Asp) are reported. Vibrational band assignments have been made on the basis of comparisons with previously cited literature values for diketopiperazine (DKP) derivatives and normal coordinate analyses for both the protonated and deuterated species based upon DFT calculations at the B3‐LYP/cc‐pVDZ level of the isolated molecule in the gas phase. The calculated minimum energy structure for cyclo(L ‐Asp‐L ‐Asp), assuming C₂ symmetry, predicts a boat conformation for the DKP ring with both the two L ‐aspartyl side chains being folded slightly above the ring. The CO stretching vibrations have been assigned for the side‐chain carboxylic acid group (e.g. at 1693 and 1670 cm⁻¹ in the Raman spectrum) and the cis amide I bands (e.g. at 1660 cm⁻¹ in the Raman spectrum). The presence of two bands for the carboxylic acid CO stretching modes in the solid‐state Raman spectrum can be accounted for by factor group splitting of the two nonequivalent molecules in a crystallographic unit cell. The cis amide II band is observed at 1489 cm⁻¹ in the solid‐state Raman spectrum, which is in agreement with results for cyclic di‐amino acid peptide molecules examined previously in the solid state, where the DKP ring adopts a boat conformation. Additionally, it also appears that as the molecular mass of the substituent on the C^α atom is increased, the amide II band wavenumber decreases to below 1500 cm⁻¹; this may be a consequence of increased strain on the DKP ring. The cis amide II Raman band is characterized by its relatively small deuterium shift (29 cm⁻¹), which indicates that this band has a smaller N H bending contribution than the trans amide II vibrational band observed for linear peptides. Copyright © 2009 John Wiley & Sons, Ltd.     

IR/Raman spectroscopy and DFT calculations of cyclic di‐amino acid peptides. Part III: comparison of solid state and solution structures of cyclo(L‐Ser‐L‐Ser)

B3‐LYP/cc‐pVDZ calculations of the gas‐phase structure and vibrational spectra of the isolated molecule cyclo(L ‐Ser‐L ‐Ser), a cyclic di‐amino acid peptide (CDAP), were carried out by assuming C₂ symmetry. It is predicted that the minimum‐energy structure is a boat conformation for the diketopiperazine (DKP) ring with both L ‐seryl side chains being folded slightly above the ring. An additional structure of higher energy (15.16 kJ mol⁻¹) has been calculated for a DKP ring with a planar geometry, although in this case two fundamental vibrations have been calculated with imaginary wavenumbers. The reported X‐ray crystallographic structure of cyclo(L ‐Ser‐L ‐Ser), shows that the DKP ring displays a near‐planar conformation, with both the two L ‐seryl side chains being folded above the ring. It is hypothesized that the crystal packing forces constrain the DKP ring in a planar conformation and it is probable that the lower energy boat conformation may prevail in the aqueous environment. Raman scattering and Fourier‐transform infrared (FT‐IR) spectra of solid state and aqueous solution samples of cyclo(L ‐Ser‐L ‐Ser) are reported and discussed. Vibrational band assignments have been made on the basis of comparisons with the calculated vibrational spectra and band wavenumber shifts upon deuteration of labile protons. The experimental Raman and IR results for solid‐state samples show characteristic amide I vibrations which are split (Raman: 1661 and 1687 cm⁻¹, IR: 1666 and 1680 cm⁻¹), possibly due to interactions between molecules in a crystallographic unit cell. The cis amide I band is differentiated by its deuterium shift of ∼30 cm⁻¹, which is larger than that previously reported for trans amide I deuterium shifts. A cis amide II mode has been assigned to a Raman band located at 1520 cm⁻¹. The occurrence of this cis amide II mode at a wavenumber above 1500 cm⁻¹ concurs with results of previously examined CDAP molecules with low molecular weight substituents on the C^α atoms, and is also indicative of a relatively unstrained DKP ring. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman and infrared spectra,conformational stability,vibrational assignment,barriers to internal rotation and ab initio calculations of but-2-enoyl chloride

The Raman (3500–10 cm⁻¹) and infrared (3200–50 cm⁻¹) spectra were recorded for the fluid and solid phases of but-2-enoyl chloride (crotonyl chloride), trans-CH₃CHCHCClO, where the methyl group is trans to the CClO group, and a complete vibrational assignment is proposed. These data were interpreted on the basis that the s-trans (anti) form (two double bonds oriented trans to one another) is the most stable form in the fluid phases and the only conformer remaining in the solid state. The asymmetric torsional fundamental of the more stable s-trans and the higher energy s-cis (syn) form were observed at 97.5 and 86.9 cm⁻¹, respectively. From these data the asymmetric potential function governing the internal rotation about the C C bond was determined. The potential coefficients are V₁ = −111 ± 2, V₂ = 1860 ± 48, V₃ = 6 ± 2, V₄, = −43 ± 24 and V₆ = −22 ± 6. The s-trans to s-cis and s-cis to s-trans barriers were determined to be 1890 and 1785 cm⁻¹, respectively, with an enthalpy difference between the conformers of 105 ± 52 cm⁻¹ [300 ± 149 cal mol⁻¹ (1 cal = 4.184 J)]. Similarly, the barrier governing internal rotation of the CH₃ group for the s-trans conformer was also determined to be 912 ± 30 (2.61 ± 0.09 kcal mol⁻¹) from the torsional fundamental observed in the far-infared spectrum of the gas. All these data were compared with the corresponding quantities obtained from ab initio Hartree–Fock gradient calculations employing the RHF/3–21G*, RHF/6–31G* and/or MP2/6–31G* basis sets. These results were compared with the corresponding quantities for some similar molecules.     

Vibrational spectra and crystal structure of the di‐amino acid peptide cyclo(L‐Met‐L‐Met): comparison of experimental data and DFT calculations

Experimental Raman and FT‐IR spectra of solid‐state non‐deuterated and N‐deuterated samples of cyclo(L ‐Met‐L ‐Met) are reported and discussed. The Raman and FT‐IR results show characteristic amide I vibrations (Raman: 1649 cm⁻¹, infrared: 1675 cm⁻¹) for molecules exhibiting a cis amide conformation. A Raman band, assigned to the cis amide II vibrational mode, is observed at ∼1493 cm⁻¹ but no IR band is observed in this region. Cyclo(L ‐Met‐L ‐Met) crystallises in the triclinic space group P1 with one molecule per unit cell. The overall shape of the diketopiperazine (DKP) ring displays a (slightly distorted) boat conformation. The crystal packing employs two strong hydrogen bonds, which traverse the entire crystal via translational repeats. B3‐LYP/cc‐pVDZ calculations of the structure of the molecule predict a boat conformation for the DKP ring, in agreement with the experimentally determined X‐ray structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal micro‐Raman spectroscopic study of polymorphic transformation of famotidine under different compression pressures

The objective of this study was to investigate the effect of pressure and/or temperature on the polymorphic transformation of famotidine from form B to form A by using a thermal confocal Raman microspectroscopy. A compact with a wide transparent zone in the center and an opaque zone surrounding it was prepared by compressing a conical mass of famotidine form B. Two unique Raman peaks at 2897 and 2920 cm⁻¹ for famotidine forms B and A, respectively, were used as markers. The result indicates that the opaque zone in each compact was composed of famotidine from B, and it did not undergo any polymorphic transformation by preparing with higher compression pressure and/or by heating. The Raman peak intensity ratio of the 2920 cm⁻¹ and 2897 cm⁻¹ bands markedly increased starting from 120 °C for the transparent zone prepared by compressing with 19.61 × 10⁴ kPa pressure, but increased from 100 °C with 49.03 × 10⁴ kPa pressure, indicating the occurrence of thermally induced polymorphic transformation of famotidine from form B to form A. However, the transparent zone prepared by 9.81 × 10⁴ kPa compression pressure retained the same Raman spectrum as that of the famotidine form B, revealing that the thermally induced polymorphic transformation of famotidine was dependent on the pressure applied. There was no polymorphic transformation of famotidine in the transparent zone when it was prepared by a higher compression pressure at a lower temperature or by a lower pressure at a higher temperature. The combined effect of compression and temperature was found to accelerate the polymorphic transformation from form B to form A in the transparent zone of famotidine. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman microspectroscopic mapping or thermal system used to investigate milling‐induced solid‐state conversion of famotidine polymorphs

Confocal Raman microspectroscopy was used to nondestructively determine the polymorphic conversion of famotidine in the course of the milling process. A mapping system was applied to assess the blending uniformity of each polymorphic component in the milled mixture. Raman microspectroscopy combined with a thermal analyzer was also used to investigate the synergistic co‐effects of milling and heating on the polymorphic conversion of famotidine polymorphs. Famotidine has two polymorphs, forms A and B, the raw material of famotidine used was proved to be of form B. The Raman peak intensity ratio of the 2920 cm⁻¹ band for form A and 2897 cm⁻¹ band for form B was used to act as an indicator to evaluate the polymorphic conversion of famotidine form B to form A after different milling courses. The results indicate that the peak intensity at 2897 cm⁻¹ gradually decreased with the milling time, whereas the peak intensity at 2920 cm⁻¹ slowly enlarged, suggesting the polymorphic conversion of famotidine from form B to form A. The longer milling process might strongly induce and promote this polymorphic conversion of famotidine. Both polymorphic forms of famotidine were found to be well uniformly distributed within the milled samples due to their smaller varieties by using the Raman microscopic mapping system. The temperature effect could synergistically accelerate the polymorphic conversion of famotidine from form B to form A in the milled sample. The thermal‐dependent critical temperature for sharply enhancing the content of famotidine form A in each milled sample was also identified. Copyright © 2007 John Wiley & Sons, Ltd.     

Lipid organization and stratum corneum thickness determined in vivo in human skin analyzing lipid–keratin peak (2820–3030 cm−1) using confocal Raman microscopy

While the intercellular lipid structure of the stratum corneum (SC) plays an important role in the skin barrier function, the depth‐dependent profile of the intercellular lipids contributes decisively to deepen the understanding of the skin barrier function, drug penetration, development of skin diseases and their medication. The depth‐dependent profile of the lipids' chemico‐physical properties, such as the solid–fluid phase transition and the order–disorder transition, can exclusively be measured in human skin in vivo by means of confocal Raman microscopy. In the present paper, the lipid–keratin peak (2820–3030 cm⁻¹) was investigated. The lipid‐related Raman peaks centered at 2850 cm⁻¹ and 2880 cm⁻¹ were deconvoluted using Gaussian functions and investigated for their depth‐dependent shape and positional changes. Different fitting procedures show that even an additional Gaussian function cannot be used to fully characterize the lipid's polymethylene chains around 2880 cm⁻¹, which justifies the introduction of the sharpness of the peak centered near 2880 cm⁻¹. The results show that the 2880 cm⁻¹ peak sharpness might be used for determining the SC thickness. The concentration of the lipids with long‐chain carbon backbone (free fatty acids and ceramides) semi‐quantitatively decreases from 10 µm to 20 µm (SC thickness is 19.8 µm). The maximum position and broadness of the Gaussian peak centered at 2850 cm⁻¹ show that near the surface and in the deeper layers of the SC, the state of the lipids is more fluid and disordered compared to the medium layers of the SC. Copyright © 2016 John Wiley & Sons, Ltd.     

Visible,near‐infrared,and ultraviolet laser‐excited Raman spectroscopy of the monocytes/macrophages (U937) cells

Raman spectra of the monocytes were recorded with laser excitation at 532, 785, 830, and 244 nm. The measurements of the Raman spectra of monocytes excited with visible, near‐infrared (NIR), and ultraviolet (UV) lasers lad to the following conclusions. (1) The Raman peak pattern of the monocytes can be easily distinguished from those of HeLa and yeast cells; (2) Positions of the Raman peaks of the dried cell are in coincidence with those of the monocytes in a culture cell media. However, the relative intensities of the peaks are changed: the peak centered around 1045 cm⁻¹ is strongly intensified. (3) Raman spectra of the dead monocytes are similar to those of living cells with only one exception: the Raman peak centered around 1004 cm⁻¹ associated with breathing mode of phenylalanine is strongly intensified. The Raman spectra of monocytes excited with 244‐nm UV laser were measured on cells in a cell culture medium. A peak centered at 1485 cm⁻¹ dominates the UV Raman spectra of monocytes. The ratio I₁₅₇₄/I₁₆₁₃ for monocytes is found to be around 0.71. This number reflects the ratio between proteins and DNA content inside a cell and it is found to be twice as high as that of E. coli and 5 times as high as that of gram‐positive bacteria. Copyright © 2009 John Wiley & Sons, Ltd.     

Qualitative analysis of desi ghee,edible oils,and spreads using Raman spectroscopy

Keeping in view the importance of dietary fats in modulating disease risk, a study was planned to compare edible oils, spreads, and desi ghee based on fatty acid composition through Raman spectroscopy. The double bonds in unsaturated oils tend to react more with oxygen causing oxidative stress in living cells; therefore, the excessive use of processed vegetable oils may pose risk for human health. In the spectral analysis, Raman peaks at 1063 and 1127 cm⁻¹ represent out‐of‐phase and in‐phase aliphatic C C stretch for saturated fatty acids. The peak at 1300 cm⁻¹, labeled for alkane, decreases with increase in the double bond contents (unsaturation). Further, the Raman peak at 1655 cm⁻¹ showed a monotonic increase as a function of unsaturation. The double bond contents in the Raman spectra from 1650–1657 cm⁻¹ represent unsaturated fatty acids that changes during the synthesis of spreads and banaspati ghee. Desi ghee, extracted from cow and buffalo milk, showed distinctive Raman peaks at 1650 and 1655 cm⁻¹, which originates because of isomers of conjugated linoleic acid. These Raman shifts differentiated desi ghee from other artificially produced banaspati ghee, spreads, and oils. Conjugated linoleic acid has proved to be anti‐carcinogenic, anti‐inflammatory, and anti‐allergic properties; therefore, the limited use of desi ghee may reduce the risk of cardiac diseases. Principal component analysis has been applied on the Raman spectra that clearly differentiated desi ghee, mono‐unsaturated extra virgin olive oil, and extra virgin olive oil spread from other oils, oil mixtures, spreads, and ghee. In addition, principal component analysis has been blindly applied successfully on 13 unknown samples to classify them with reference to the known ghee sample. Copyright © 2016 John Wiley & Sons, Ltd.     

Raman fingerprint of the interaction of K+ with the COO− group of zwitterionic alanine

The interaction of K⁺ with the zwitterionic form of alanine (ZAla) is investigated using Raman spectroscopy and density functional theory calculations. The Raman spectra of an aqueous solution of Ala and its mixture with KOH at different molar concentrations [ZAla + xKOH, x = 1–5 M] have been recorded in the spectral region 400–1800 cm⁻¹. The wavenumber position of the band at ~529 cm⁻¹ shows a red shift of 14 cm⁻¹, while the Raman band at ~634 cm⁻¹ shows a blue shift of 10 cm⁻¹ with the increasing x from 1 to 5 M. The intensity ratio I₆₃₄/I₅₂₉ is increased with increasing x, and it could be because of the increase in concentration of the [ZAla + K⁺] complex in the solution. The new Raman band appeared at ~1079 cm⁻¹ in the Raman spectra of [ZAla + xKOH, x = 1–5] complex. To determine the most probable site for the interaction of K⁺ with ZAla, the structures of ZAla and the [ZAla + K⁺] were optimized at B3LYP/6‐311++G(d,p) level of theory. The electrostatic potential calculation carried out for ZAla reveals that the maximum density of electron is lying over COO⁻, and therefore, COO⁻ would be the most probable site for the interaction of K⁺ with ZAla. The theoretically calculated Raman spectra of ZAla, [ZAla + K⁺] and the [ZAla⁻ + K⁺] are in good agreement with experimentally observed Raman spectra. Thus, the Raman bands at ~529, 634, and 1079 cm⁻¹ may be used as the Raman fingerprint for the interaction of K⁺ with COO⁻ of the ZAla and ZAla⁻. Copyright © 2015 John Wiley & Sons, Ltd.     

Spectroscopic analysis of a dye–mineral composite–a Raman and FT‐IR study

In this investigation, we address the question of how organic thioindigo binds to inorganic palygorskite to form a pigment similar to Maya Blue. We also address how such binding, if it occurs, might be affected by varying the proportion of dye relative to that of the mineral, and by varying the length of heating time used in preparation of the pigment. In addition to samples of palygorskite and thioindigo both alone, four synthetic pigment samples were prepared; two samples of 8 wt.% dye, one heated at 170 °C for 3 h and one at 170 °C for 9 h, and two samples of 16 wt.% dye, one heated at 170 °C for 3 h and one at 170 °C for 9 h. All samples were examined using Fourier transform‐infrared (FT‐IR) and FT‐Raman spectroscopy. For the pigment samples, FT‐IR peaks at 1627 cm⁻¹ are attributed to a downshifted CO stretching mode of thioindigo due to dye–clay interaction. This interpretation is corroborated by FT‐Raman CO peaks with 14 cm⁻¹ shifts to lower wavenumber for the pigment relative to thioindigo alone. Additional Raman scattering between 550 cm⁻¹ and 650 cm⁻¹ also suggests dye–clay interaction through metal–oxygen bonding. We are thus led to the possibility of mostly hydrogen bonding between silanol and carbonyl at lower dye concentration, with a predominance of metal–oxygen bonding at higher dye concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

Phosphate and amide III mapping in sialoliths with Raman microspectroscopy

Sialoliths, a cause of the salivary gland infection, are reported to be composed of inorganic and organic substances. However, the precise mechanism of sialolith formation remains unclear. The purpose of this report is to elucidate this mechanism by analyzing the precise distribution of phosphate (an inorganic substance) and amide III (an organic substance) in sialoliths by using Raman microspectroscopy. Sialoliths from the submandibular gland duct were analyzed by this form of observation and by a scanning electron microscope (SEM) equipped with an energy‐dispersive X‐ray spectroscope (EDX). In Raman microspectroscopy we analyzed the spectral peak of the phosphate (PO₄³⁻) symmetric stretching vibrational mode (υ₁) at 960 cm⁻¹ and that of amide III at 1265 cm⁻¹ to demonstrate the mapping of an image of these elements showing a semiquantitative distribution of phosphate and amide III in the sialoliths. It was found that phosphate and amide III were concentrated at the center of the sialoliths, and the phosphate distribution in the sialoliths showed concentric laminations. These results indicated the possibility that the sialoliths originated from a nidus of organic materials and progressively grew by the deposition of layers of organic and inorganic materials. Copyright © 2008 John Wiley & Sons, Ltd.     

Time‐lapse Raman imaging of single live lymphocytes

We present time‐lapse Raman imaging (TLRI) of living cells as a new approach in label‐free chemical imaging through non‐electronic resonant, spontaneous Raman microspectroscopy. Raman hyperspectral datacubes of individual live peripheral blood lymphocytes were successively acquired. The Raman imaging time per voxel, with a volume of 0.3 fl, was 100 ms and the total image time of a 32 × 32 pixels image was less than 2 min. Multiple images of an individual cell have been obtained. A full series of TLRI images typically resulted in more than 1.6 million data points per image. We analyzed the datasets using hierarchical cluster analysis. A fingerprint of molecular changes was observed before the cell was blebbing. The molecular fingerprint was related to a gradual disappearance of the Raman signal from carotenoids. Concomitant changes occurred in the C H stretch high wavenumber region, presumably due to a change in the protein and lipid environment of carotenoids. These changes were smaller than 5% of the total signal at 2937 cm⁻¹. We hypothesize that the lipid environment of the carotenoids changes as a result of the photophysics in the carotenoid molecules. The detectability of carotenoids was shown to be 2.3 µMper voxel, which corresponds to 415 molecules. TLRI enables high‐speed chemical imaging not only in the intense high wavenumber region of the Raman spectrum, but particularly in the more informative fingerprint region between 500 and 1800 cm⁻¹. Copyright © 2010 John Wiley & Sons, Ltd.     

Conformational stability from Raman spectra,r0 structural parameters,and vibrational assignment of methylcyclohexane

The Raman spectra (3500–50 cm⁻¹) of the liquid and solid methylcyclohexane and the infrared spectra of the gas and solid methylcyclohexane have been recorded. The Raman band at 754 cm⁻¹ in the liquid has been confidently assigned to the less stable axial conformer and its intensity was recorded as a function of temperature from 25 to −95 °C. By the utilization of 15 different temperatures, the enthalpy difference between the more stable chair‐equatorial conformer and the chair‐axial form was determined to be 712 ± 71 cm⁻¹ (8.50 ± 0.84 kJ/mol). The ab initio predicted value of 710 cm⁻¹ (8.50 kJ/mol) from the MP2(full)/6‐311G(2d,2p) calculations with and without diffuse functions is in excellent agreement. The harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational wavenumbers have been obtained for both conformers from MP2(full)/6‐31G(d) ab initio calculations. With two scaling factors of 0.88 for the C‐H stretches and 0.9 for the remaining ones, the fundamental wavenumbers have been predicted and along with the depolarization values and infrared band contours (B‐type for A″ modes) a complete vibrational assignment has been made for the chair‐equatorial conformer. Predicted r₀ structural parameters have been provided from adjusted parameters from ab initio MP2(full)/6‐311+G(d,p) calculations. The results are discussed and compared with the corresponding properties of some similar molecules. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman microspectroscopic evidence that dry‐fixing preserves the temporal pattern of non‐specific differentiation in live human embryonic stem cells

Raman microspectroscopy allows the classification of populations of human embryonic stem cells (hESCs) in different stages of differentiation based on the relative intensities of certain amino acid and nucleic acid bands. Here, we report the results of a comparative study of the Raman spectra of live cells versus cells killed and fixed by rapid desiccation, focusing on the ratio of intensities at 757 cm⁻¹ (tryptophan) and 784 cm⁻¹ (DNA and RNA). We observe that the same temporal pattern emerges over a 3‐week time course in both sample types. This suggests that prolonged observations of dry‐fixed cells can yield high signal‐to‐noise chemical images that cannot be obtained from colonies of living cells where the time scale of significant biological changes are comparable to the time scale of the measurement. This permits, for example, comparison of the spatial distributions of cells at different stages of differentiation within the same colonies. Copyright © 2010 John Wiley & Sons, Ltd.     

New SERS feature of β‐carotene: consequences for quantitative SERS analysis

While recording SERS spectra of pure β‐carotene at sub‐micromole concentrations for reference purpose, we discovered an unusual spectral response never reported before. In pre‐resonance conditions with the 532‐nm line, SERS of β‐carotene with AgNPs exhibits among the strong υ(CC) mode at 1512 cm⁻¹ unshifted from normal Raman spectrum, additional strong bands at 1649, 1575 and 1387 cm⁻¹ as well as other medium bands not observed in the Raman spectrum of the crystalline powder. Such behavior is explained in terms of selection rules relaxation upon cyclohexene terminal rings of the β‐carotene interaction with the NP surface. AFM images of the SERS system suggested dimers and trimers clustering of the nanoparticles with adsorbed β‐carotene. In light of the new SERS feature the consequences in correct interpretation of the SERS imaging from complex biosystems containing carotenoids are discussed. Relative intensity ratio of the β‐carotene band at 1512 cm⁻¹ and water against concentration allowed a reliable SERS calibration curve for 50 to 500 nmol l⁻¹ concentration range and provided quantitative SERS assessment of the carotenoid content in the sea urchin (Paracentrotus lividus) gonads extracts. Copyright © 2015 John Wiley & Sons, Ltd.     

A vibrational spectroscopic investigation of rhodanine and its derivatives in the solid state

Raman and infrared spectra are reported for rhodanine, 3‐aminorhodanine and 3‐methylrhodanine in the solid state. Comparisons of the spectra of non‐deuterated/deuterated species facilitate discrimination of the bands associated with N H, NH₂, CH₂ and CH₃ vibrations. DFT calculations of structures and vibrational spectra of isolated gas‐phase molecules, at the B3‐LYP/cc‐pVTZ and B3‐PW91/cc‐pVTZ level, enable normal coordinate analyses in terms of potential energy distributions for each vibrational normal mode. The cis amide I mode of rhodanine is associated with bands at ∼1713 and 1779 cm⁻¹, whereas a Raman and IR band at ∼1457 cm⁻¹ is assigned to the amide II mode. The thioamide II and III modes of rhodanine, 3‐aminorhodanine and 3‐methylrhodanine are observed at 1176 and 1066/1078; 1158 and 1044; 1107 and 984 cm⁻¹ in the Raman and at 1187 and 1083; 1179 and 1074; 1116 and 983 cm⁻¹ in the IR spectra, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermo‐Raman spectroscopy of synthetic nesquehonite — implication for the geosequestration of greenhouse gases

Pure nesquehonite (MgCO₃·3H₂O)/Mg(HCO₃)(OH)·2H₂O was synthesised and characterised by a combination of thermo‐Raman spectroscopy and thermogravimetry with evolved gas analysis. Thermo‐Raman spectroscopy shows an intense band at 1098 cm⁻¹, which shifts to 1105 cm⁻¹ at 450 °C, assigned to the ν₁CO₃²⁻ symmetric stretching mode. Two bands at 1419 and 1509 cm⁻¹ assigned to the ν₃ antisymmetric stretching mode shift to 1434 and 1504 cm⁻¹ at 175 °C. Two new peaks at 1385 and 1405 cm⁻¹ observed at temperatures higher than 175 °C are assigned to the antisymmetric stretching modes of the (HCO₃)⁻ units. Throughout all the thermo‐Raman spectra, a band at 3550 cm⁻¹ is attributed to the stretching vibration of OH units. Raman bands at 3124, 3295 and 3423 cm⁻¹ are assigned to water stretching vibrations. The intensity of these bands is lost by 175 °C. The Raman spectra were in harmony with the thermal analysis data. This research has defined the thermal stability of one of the hydrous carbonates, namely nesquehonite. Thermo‐Raman spectroscopy enables the thermal stability of the mineral nesquehonite to be defined, and, further, the changes in the formula of nesquehonite with temperature change can be defined. Indeed, Raman spectroscopy enables the formula of nesquehonite to be better defined as Mg(OH)(HCO₃)·2H₂O. Copyright © 2008 John Wiley & Sons, Ltd.     

OctTES/TEOS system for hybrid coatings: real‐time monitoring of the hydrolysis and condensation by Raman spectroscopy

The hybrid organic–inorganic system Tetra‐ethyl‐ortho‐silicate functionalized with Octyl‐triethoxy‐silane, studied as protective coating for the preservation of historical glasses from the environmental weathering agents, has been characterized by Raman spectroscopy by monitoring the sol‐gel reactions over time through characteristic features in the spectrum. In particular, for the hydrolysis reaction the disappearance of the 653 cm⁻¹ (Si‐O symmetric breathing) and 810 cm⁻¹ (CH₂ rocking in Si‐alkoxides) peaks and the growth of the 710 cm⁻¹ band, because of hydrolyzed alkyl‐silane, and of the 881 cm⁻¹ peak (ethanol C–C symmetric stretching) have been checked. Moreover, the condensation reaction can be tracked by the disappearance of the two main peaks of the alcohols at 816 and 881 cm⁻¹, going along with the growth of the broad band between 250 and 500 cm⁻¹ (Si–O–Si symmetric bending) and of the feature at 840 cm⁻¹ (Si–O–Si stretching). At the end of the condensation process the Raman spectrum still displays spectral bands unique to the alkyl chain in Octyl‐triethoxy‐silane, in the 1330–1450 cm⁻¹ and 2725–3000 cm⁻¹ ranges. Copyright © 2016 John Wiley & Sons, Ltd.