Molecular mechanism of gelation upon the addition of water to a solution of poly(acrylonitrile) in dimethylsulfoxide

The solidification of a solution of poly(acrylonitrile) (PAN) in dimethylsulfoxide (DMSO) upon introduction of water into the solution is studied by Raman spectroscopy. In the absence of water, DMSO molecules are found to produce dipole-dipole bonds with PAN molecules. Upon the introduction of water, DMSO molecules produce hydrogen bonds with it and bands at 1005 and 1015 cm⁻¹ appear in the Raman spectrum, which are assigned to the valence vibrations of S=O bonds involved in the hydrogen bonds. Simultaneously, water molecules produce hydrogen bonds with PAN molecules: R-C≡N...H-O-H...N≡C-R, where R is the carbon skeleton of a PAN molecule. Accordingly, a band at 2250 cm⁻¹ arises in the Raman spectrum, which is assigned to the valence vibrations of C≡N bonds producing hydrogen bonds with a water molecule. When the water content is low and the DMSO concentration is high, the length of the hydrogen bonds varies in wide limits and the band at 2250 cm⁻¹ is wide. As the water content rises, DMSO molecules come out of PAN, the variation of the hydrogen bond length in it decreases (the band at 2250 cm⁻¹ narrows), and a high-viscosity system (gel) arises that consists of PAN molecules bonded to water molecules via “equally strong” hydrogen bonds.     

IR spectroscopic manifestations of hydration of poly(diphenyl sulfophthalide) during its storage

IR spectroscopy measurements show that films of poly(diphenyl sulfophthalide) (PDSP), a cardo polymer, interact with atmospheric moisture during storage at room conditions. A total of 15 absorption bands were isolated in spectra of PDSP hydrated during storage, which belong to sorbed water and hydrolysis products. A number of absorption bands (within 1500–1800 cm⁻¹ and 980–1100 cm⁻¹) were obtained by subtracting the spectrum of the film after heating from that of the initial hydrated film. At least six individual bands in the region of the O-H bond stretching vibration were isolated by decomposing a broad complex band (3700–2000 cm⁻¹) into Gaussian components. The isolated bands were tentatively assigned based on the available literature data and quantum-chemical calculations of the characteristics of a number of complexes of a diphenyl sulfophthalide model compound with water molecules. The IR spectra and energies of the hydrogen bonds formed were calculated at the B3LYP/6-311G(d, p) level. In particular, the absorption bands at 1010 and 1079 cm⁻¹ were assigned to the symmetric stretching vibrations of the S=O bonds in the −SO₃⁻ anion, the 1062-cm⁻¹ absorption band, to ν(C-OH), and the absorption bands at 3646, 3586, and 3475 cm⁻¹, to complexes of water with sulfophthalide cycles of the polymer. After a long storage, PDSP largely transforms into a polymeric oxonium salt, and its spectrum becomes similar to that of a polymeric salt prepared by alkaline hydrolysis. A general mechanism of the interaction of PDSP with water is proposed, according to which the hydrolysis of the sulfophthalide cycles (SPC) by sorbed water yields new hydrophilic groups, sulfoacid, and hydroxyl groups. A further sorption of water by the sulfoacid results in its ionization and the formation of various hydroxonium forms. Sorption and hydrolysis are reversible processes: water is desorbed and the SPC is recovered when the polymer is heated to 100–150°C, as can be judged from an increase in the intensity of the S=O bond vibrations of the sulfophthalide cycle at 1352 and 1192 cm⁻¹. The possibility of using strongly hydrated PDSP for manufacturing proton-conducting membranes is discussed.     

Raman spectra of various polymorphs of isotactic polypropylene

The Raman spectra of the α, γ, and smectic modifications of isotactic polypropylene (PP) are studied. The most significant spectral differences are observed in the frequency range around 2960 cm⁻¹ for the spectral doublet assigned to the asymmetric stretching vibrations of the CH₃ groups and in the frequency range around 800 cm⁻¹, which is used for analysis of the phase composition of isotactic PP. It is demonstrated that the peak positions and relative intensities of the doublet assigned to the asymmetric stretching vibrations of the CH₃ groups can be used to identify the polymorph modifications of isotactic PP.     

A study of the molecular structure of DL-serine with the method of low-temperature IR spectroscopy

Use of low-temperature IR spectroscopy in studies of compounds with a developed system of hydrogen bonds such as DL-serine revealed a complete set of vibrational frequencies. The region of manifestation of stretching vibrations of OH groups involved in the formation of strong hydrogen bonds was found. It is shown experimentally that in a crystal some of the molecules of SL-serine exist in the nonionized form. On the basis of analysis of experimental data, frequency ranges of stretching deformation and torsional vibrations of NH ₃ ⁺ , COO⁻, and OH groups were determined more accurately. It is found that in the crystals there exist molecules of DL-serine with different spatial orientation of NH ₃ ⁺ COO⁻, and COH groups. It is shown that conformational diversity of molecular structures is also preserved at T=18 K. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 864–868, November–December, 1998.     

Raman spectroscopy of hydrogen‐arsenate group (AsO3OH) in solid‐state compounds: copper mineral phase geminite Cu(AsO3OH)·H2O from different geological environments

The participation of hydrogen‐arsenate group (AsO₃OH)²⁻ in solid‐state compounds may serve as a model example for explaining and clarifying the behaviour of As and other elements during weathering processes in natural environment. The mineral geminite, a hydrated hydrogen‐arsenate mineral of ideal formula Cu(AsO₃OH)·H₂O, has been studied by Raman and infrared spectroscopies. Two samples of geminite of different origin were investigated and the spectra proved quite similar. In the Raman spectra of geminite, six bands are observed at 741, 812, 836, 851, 859 and 885 cm⁻¹ (Salsigne, France), and 743, 813, 843, 853, 871 and 885 cm⁻¹ (Jáchymov, Czech Republic). The band at 851/853 cm⁻¹ is assigned to the ν₁ (AsO₃OH)²⁻ symmetric stretching mode; the other bands are assigned to the ν₃ (AsO₃OH)²⁻ split triply degenerate antisymmetric stretching mode. Raman bands at 309, 333, 345 and 364/310, 333 and 345 cm⁻¹ are attributed to the ν₂ (AsO₃OH)²⁻ bending mode, and a set of higher wavenumber bands (in the range 400–500 cm⁻¹) is assigned to the ν₄ (AsO₃OH)²⁻ split triply degenerate bending mode. A very complex set of overlapping bands is observed in both the Raman and infrared spectra. Raman bands are observed at 2289, 2433, 2737, 2855, 3235, 3377, 3449 and 3521/2288, 2438, 2814, 3152, 3314, 3448 and 3521 cm⁻¹. Two Raman bands at 2289 and 2433/2288 and 2438 cm⁻¹ are ascribed to the strong hydrogen bonded water molecules. The Raman bands at 3235, 3305 and 3377/3152 and 3314 cm⁻¹ may be assigned to the ν OH stretching vibrations of water molecules. Two bands at 3449 and 3521/3448 and 3521 cm⁻¹ are assigned to the OH stretching vibrations of the (AsO₃OH)²⁻ units. The lengths of the O H···O hydrogen bonds vary in the range 2.60–2.94 Å (Raman) and 2.61–3.07 Å (infrared). Two Raman and infrared bands in the region of the bending vibrations of the water molecules prove that structurally non‐equivalent water molecules are present in the crystal structure of geminite. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the antimonate mineral bottinoite Ni[Sb2(OH)12]·6H2O and in comparison with brandholzite Mg[Sb5+2(OH)12]·6H2O

Raman spectroscopy was used to study the mineral bottinoite and a comparison with the Raman spectra of brandholzite was made. An intense sharp Raman band at 618 cm⁻¹ is attributed to the SbO symmetric stretching mode. The low intensity band at 735 cm⁻¹ is ascribed to the SbO antisymmetric stretching vibration. Low intensity Raman bands were found at 501, 516 and 578 cm⁻¹. Four Raman bands observed at 1045, 1080, 1111 and 1163 cm⁻¹ are assigned to δ SbOH deformation modes. A complex pattern resulting from the overlapping band of the water and hydroxyl units is observed. Raman bands are observed at 3223, 3228, 3368, 3291, 3458 and 3510 cm⁻¹. The first two Raman bands are assigned to water stretching vibrations. The two higher wavenumber Raman bands observed at 3466 and 3552 cm⁻¹ and two infrared bands at 3434 and 3565 cm⁻¹ are assigned to the stretching vibrations of the hydroxyl units. Observed Raman and infrared bands are connected with O H···O hydrogen bonds and their lengths 2.72, 2.79, 2.86, 2.88 and 3.0 Å (Raman) and 2.73, 2.83 and 3.07 Å (infrared). Copyright © 2010 John Wiley & Sons, Ltd.     

Fluorescent properties and spontaneous Raman spectroscopy of new ketocyanine probes in organic solvents

We have used fluorescence spectroscopy and spontaneous Raman spectroscopy to study the characteristics of two ketocyanine dyes: 2,5-di[(E)-1-(4-diethylaminophenyl)methylidene]-1-cyclopentanone (CPET) and 2-[(E)-1-(4-diethylaminophenyl)methylidene]-5-{(E)-1-[4-(4,7,10,13-tetraoxa-1-azacyclopentadecalin) phenyl]methylidene}-1-cyclopentanone (CPMR) in organic solvents. The position of their electronic spectra depends strongly on the polarity of the solvent. We measured the dipole moments of the dyes in the equilibrium ground state and the Franck-Condon excited state. In mixtures of neutral nonpolar toluene with aprotic polar dimethylsulfoxide, we observe inhomogeneous broadening of the electronic spectra for the indicated compounds, due to fluctuations in solution of the intermolecular interaction energy. The time-resolved characteristics of fluorescence obtained suggest formation of an intermolecular hydrogen bond between the dye and the surrounding medium in a toluene-ethanol mixture. We measured the Raman spectra of CPET and CPMR in different organic solvents. The most intense lines in the 1582–1591 cm⁻¹ region can be assigned to stretching of the phenyl rings of the molecules; the lines in the 831–842 cm⁻¹ region can be assigned to a cyclopentanone ring mode; the lines at 1186–1195 cm⁻¹ can be assigned to stretching of the =C-C-bond of the phenyl ring and rocking of the H atoms of the phenyl ring. We have observed that the position and width of the lines for the stretching vibrations of the ketocyanines depend substantially on the polarity of the surrounding medium. The studied dyes can be used as probes for studying different biological systems by site-selective laser spectroscopy and Raman spectroscopy. The fact that these two methods can be used simultaneously for diagnostics of biosystems is an important advantage of ketocyanine dyes compared with other known probes. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 763–769, November–December, 2006.     

Conductivity of solutions of poly(acrylonitrile) in dimethyl sulfoxide

The conductivity of solutions of poly(acrylonitrile) (PAN) in dimethyl sulfoxide (DMSO) is studied. Using the Raman spectroscopy method, it is found that PAN causes associates of DMSO molecules to dissociate into free molecules, as a result of which the conductivity of the solution grows. Simultaneously, PAN molecules hamper the rotation of DMSO molecules, which decreases the conductivity. There exists a critical concentration of PAN (≈5.4 vol. %) at which the rotation of DMSO molecules is hindered to the greatest extent and the conductivity drops by an order of magnitude.     

Raman spectroscopic study of the uranyl carbonate mineral zellerite

Raman and infrared spectra of the uranyl mineral zellerite, Ca[(UO₂)(CO₃)₂(H₂O)₂]·3H₂O, were measured and tentatively interpreted. U O bond in uranyl and O H···O hydrogen bonds were calculated from the vibrational spectra. The presence of structurally nonequivalent water molecules in the crystal structure of zellerite was inferred. A proposed chemical formula of zellerite is supported. Raman bands at 3514, 3375 and 2945 cm⁻¹and broad infrared bands at 3513, 3396 and 3326 cm⁻¹ are related to the ν OH stretching vibrations of hydrogen‐bonded water molecules. Observed wavenumbers of these vibrations prove that in fact hydrogen bonds participate in the crystal structure of zellerite. The presence of two bands at 1618 and 1681 cm⁻¹ proves structurally distinct and nonequivalent water molecules in the crystal structure of zellerite. Copyright © 2008 John Wiley & Sons, Ltd.     

Magneto-Raman scattering inp-type indium antimonide

We report for the first time stimulated magneto-Raman scattering inp-type InSb. Two different Raman scattering processes were observed. The first one has a Raman shift of about 2cm⁻¹/kG and is observed at magnetic fields up to 30kG. The other one is observable only at high magnetic fields above 30kG and shows Raman shifts between 1.2cm⁻¹ and 3.0cm⁻¹ with a tuning rate of about 0.2cm⁻¹/kG. The first process can be interpreted either as spin-flip Raman scattering by photo-excited electrons in the conduction band or as Raman scattering by holes in the valence band involving transitions from heavy to light hole states. The other Raman shift observed seems to occur on account of transitions between the heavy hole ladders.     

Fluorescence excitation spectra of jet-cooled carbazole complexes with monohydric alcohols

We have analyzed the fluorescence excitation spectra of carbazole complexes with a single molecule of methyl, deuterated methyl, ethyl, and propyl (1-propanol and 2-propanol) alcohols, cooled in a supersonic jet. We have determined the shifts in the fluorescence excitation spectra of the complexes relative to the frequency of the purely electronic transition of unbound carbazole. They occur as a result of formation of hydrogen bonds between the N-H group of the carbazole and the OH group of the alcohols. The frequencies of stretching vibrations of the hydrogen bonds with different alcohols vary within the range 150–157 cm⁻¹, while the frequencies of the bending vibrations vary in the range 21–22.9 cm⁻¹. From the shape of the rotational contours of the bands for the purely electronic and vibronic transitions of the complexes, we determined that they belonged to rotational conformers. We calculated the equilibrium configurations of the complexes in the ground state. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 756–760, November–December, 2007.     

Theoretical Interpretation of the Vibrational Spectra of Carboxylic-Acid Dimers in the High-Frequency Range

An anharmonic band shift in the vibrational spectra of carboxylic-acid dimers is estimated on the basis of ab initio quantum calculations of anharmonic force constants. The implementation of ab initio quantum calculations taking into account the anharmonic nature of vibrations is connected with the choice of the atomic basis in the framework of a specific quantum method. All these factors together with the exclusion principle for bands in the infrared and Raman scattering spectra allow identification of the position of the bands of valence vibrations of CH bonds in the range of 2500–3500 cm^–1. The results of model calculations give reason to assert that the fundamental vibrations of the carboxylic fragment are the characteristic frequency and vibrational mode and, for OH bonds, also the characteristic intensity. Small doublet splitting and the exclusion principle for frequencies allow identification of the valence vibrations of CH bonds.     

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.     

Raman spectra of potassium, rubidium, and thallium hydrogen phthalates

The polarized Fourier-transform Raman spectra of oriented single crystals of K, Rb, and Tl hydrogen phthalates, as well as of deuterated potassium hydrogen phthalate, are studied in the range 50–3300 cm^?1 in different scattering geometries. The frequencies of internal vibrations in the spectra of these compounds are assigned to vibrations of the orthophenylene and carboxyl groups. The replacement of K with Rb or Tl leads to an insignificant low-frequency shift of vibrations. A multiband structure of OH(D) stretching vibrations is observed in the range 1900–2800 cm^?1 in the spectra of all hydrogen phthalates, which is caused by Fermi-resonance interactions. A number of additional bands are observed in the spectrum of deuterated potassium hydrogen phthalate, which indicates that deuterium atoms partially replace hydrogen atoms in both the orthophenylene and the carboxyl groups.     

Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO₃OH)· 2H₂O. The mineral is characterised by an intense Raman band at 865 cm⁻¹ assigned to the ν₁ (AsO₃)²⁻ symmetric stretching mode. The equivalent IR band is found at 864 cm⁻¹. The low‐intensity Raman bands in the range from 844 to 886 cm⁻¹ provide evidence for ν₃ (AsO₃) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm⁻¹ region are attributed to ν₂ and ν₄ (AsO₃) bending modes. Prominent Raman bands at around 3187 cm⁻¹ are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm⁻¹ to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO₃OH)²⁻ units. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the antimonate mineral brandholzite Mg[Sb2(OH)12]·6H2O

Raman spectra of brandholzite Mg[Sb₂(OH)₁₂]·6H₂O were studied, complemented with infrared spectra, and related to the structure of the mineral. An intense Raman sharp band at 618 cm⁻¹ is attributed to the SbO symmetric stretching mode. The low‐intensity band at 730 cm⁻¹ is ascribed to the SbO antisymmetric stretching vibration. Low‐intensity Raman bands were found at 503, 526 and 578 cm⁻¹. Corresponding infrared bands were observed at 527, 600, 637, 693, 741 and 788 cm⁻¹. Four Raman bands observed at 1043, 1092, 1160 and 1189 cm⁻¹ and eight infrared bands at 963, 1027, 1055, 1075, 1108, 1128, 1156 and 1196 cm⁻¹ are assigned to δ SbOH deformation modes. A complex pattern resulting from the overlapping band of the water and hydroxyl units is observed. Raman bands are observed at 3240, 3383, 3466, 3483 and 3552 cm⁻¹; infrared bands at 3248, 3434 and 3565 cm⁻¹. The Raman bands at 3240 and 3383 cm⁻¹ and the infrared band at 3248 cm⁻¹ are assigned to water‐stretching vibrations. The two higher wavenumber Raman bands observed at 3466 and 3552 cm⁻¹ and two infrared bands at 3434 and 3565 cm⁻¹ are assigned to the stretching vibrations of the hydroxyl units. Observed Raman and infrared bands in the OH stretching region are associated with O‐H···O hydrogen bonds and their lengths 2.72, 2.79, 2.86, 2.88 and 3.0 Å (Raman) and 2.73, 2.83 and 3.07 Å (infrared). Copyright © 2009 John Wiley & Sons, Ltd.     

Raman Spectrum of Vanadium-Zirconia Yellow Pigment

Monoclinic vanadium-zirconia yellow pigments were prepared by gelling mixtures of zirconium n-propoxide and vanadyl acetylacetone. The nature of interactions between the host ion and the foreign cation in the vanadium-zirconia pigment was investigated in order to contribute to a better understanding of the origin of this pigmenting system using Raman scattering measurements. The Raman spectra of powdered samples of the vanadium-zirconia pigment recorded between 100 and 1400 cm^?1 show the peaks at 991, 701, and 403 cm^?1 assigned to the asymmetric and symmetric stretching and bending vibrations of the V⁴⁺ = O bonds, respectively. The assignment of these peaks was discussed by comparison with Raman spectra of vanadium oxides and on the basis of V-O bond distances deduced from the Hardcastle and Wachs equation and from the valence state of the vanadium cation calculated by Brown in the valence sum rule. This suggests that the V⁴⁺ cations replace Zr⁴⁺ in sevenfold coordinated site in the monoclinic zirconia structure. The V⁴⁺ cation allowing the d-d electronic transition is related to the origin of the lemon yellow coloration.     

Polarized Raman spectroscopy study of NiSi film grown on Si(001) substrate

We report on the growth of NiSi film on Si(001) substrate with an orientation of NiSi[200]//Si[001]. Polarized Raman spectroscopy was used to assign the symmetry of the NiSi Raman peaks. Raman peaks at 213 cm⁻¹, 295 cm⁻¹, and 367 cm⁻¹ are assigned to be A _g symmetry and peaks at 196 cm⁻¹, and 254 cm⁻¹ are B _3g symmetry.     

Laser Raman and infra-red spectra of biomolecule: 5-aminouracil

Laser Raman (200–4000 cm⁻¹) and IR (200–4000 cm⁻¹) spectra of 5-aminouracil were recorded in the region 200–4000 cm⁻¹. Assuming a planar geometry and C_s point group symmetry, it has been possible to assign all the 36 (25a′ + 11a″) normal modes of vibration for the first time. The two NH bonds of the NH₂ group appear to be equivalent as the NH₂ stretching frequencies satisfy the empirical relation proposed for the two equivalent NH bonds of the NH₂ group. The two NH₂ stretching frequencies are distinctly separated from the CH/NH ring stretching frequencies. A strong and sharp IR band at 3360 cm⁻¹ could be identified as the anti-symmetric NH₂ mode whereas the band at 3290 cm⁻¹ with smaller density could be identified as the symmetric NH₂ stretching mode. All other bands have also been assigned different fundamentals/overtones/combinations.      

Vibrational Spectroscopic Characterization of the Arsenate Mineral Barahonaite: Implications for the Molecular Structure

The mineral barahonaite is in all probability a member of the smolianinovite group. The mineral is an arsenate mineral formed as a secondary mineral in the oxidized zone of sulphide deposits. We have studied the barahonaite mineral using a combination of Raman and infrared spectroscopy. The mineral is characterized by a series of Raman bands at 863 cm^?1 with low wavenumber shoulders at 802 and 828 cm^?1. These bands are assigned to the arsenate and hydrogen arsenate stretching vibrations. The infrared spectrum shows a broad spectral profile. Two Raman bands at 506 and 529 cm^?1 are assigned to the triply degenerate arsenate bending vibration (F ₂, ν₄), and the Raman bands at 325, 360, and 399 cm^?1 are attributed to the arsenate ν₂ bending vibration. Raman and infrared bands in the 2500–3800 cm^?1 spectral range are assigned to water and hydroxyl stretching vibrations. The application of Raman spectroscopy to study the structure of barahonaite is better than infrared spectroscopy, probably because of the much higher spatial resolution.