Experimental and ab initio DFT calculated Raman spectrum of Sudan I,a red dye

The red dye Sudan I was investigated by Raman spectroscopy using different excitation wavelengths (1064, 532 and 244 nm). A calculation of the Raman spectrum based on quantum mechanical ab initio density functional theory (DFT) was made using the RB3LYP method with the 3‐21G and 6‐311 + G(d,p) basis sets. The vibrations in the region 1600–1000 cm⁻¹ were found to comprise various mixed modes including in‐plane stretching and bending of various C C, N N, C N and C O bonds and angles in the molecule. Below ∼900 cm⁻¹, the out‐of‐plane bending modes were dominant. The central hydrazo chromophore of the Sudan I molecule was involved in the majority of the vibrations through NN and C N stretching and various bending modes. Low‐intensity bands in the lower wavenumber range (at about 721, 616, 463 and 218 cm⁻¹) were selectively enhanced by the resonance Raman effect when using the 532 nm excitation line. Comparison was made with other azo dyes in the literature on natural, abundant plant pigments. The results show that there is a possibility in foodstuff analysis to distinguish Sudan I from other dyes by using Raman spectroscopy with more than one laser wavelength for resonance enhancement of the different bands Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental and theoretical studies on corals. I. Toward understanding the origin of color in precious red corals from Raman and IR spectroscopies and DFT calculations

An attempt to explain the origin of the vivid red color in precious pink and red corals was undertaken. Raman and IR spectroscopies were applied to characterize white, pink and red corals. The position of the Raman signal near 1500 cm⁻¹ of some corals and pearls was associated by several authors with the presence of the mixture of all‐trans‐polyenic pigments, containing 6–16 conjugated CC bonds or β‐carotenoids. This hypothesis was examined theoretically by performing extensive B3LYP‐DFT calculations of vibrational spectra of the model polyenic compounds. The B3LYP/6‐311++G** predicted positions of the dominating Raman mode depend on the number of CC units (Cn parameter) and can be accurately predicted for larger systems from a simple nonlinear fit. The DFT‐predicted Raman activities of these modes are extremely sensitive to Cn, and sharply increase with the number of double bonds. This implies a presence of only—two to three polyenes differing slightly in the number of CC units as the source of color in pink and red corals. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of reddish pigments in octocorals by Raman spectroscopy

The nature of the pigments in octocorals has been investigated by Raman spectroscopy, where laser excitation at 632.8 and 1064 nm were used to characterize the colored components present in the skeleton of the exotic pink‐yellow soft coral Chromonephthea braziliensis, the reddish purple sea fan Leptogorgia punicea and the endemic deep violet red Leptogorgia violacea from the southeastern coast of Brazil. The observed positions of two major Raman bands at ca 1500 cm⁻¹ [ν(CC)] and 1130 [ν(C C)] for all specimens strongly suggest the presence of a mixtureof conjugated polyenes belonging to a class of compounds named parrodienes. The hemiketal steroidal feeding deterrent, 23‐keto‐cladiellin‐A, isolated from C. braziliensis was identified in the crude extracts by the Raman analysis using 1064 nm excitation. The observation of the most important vibrational bands of this compound can be useful in future investigations to monitor its presence in crude extracts of C. braziliensis and or other species. Copyright © 2010 John Wiley & Sons, Ltd.     

Differential Raman cross section of dimethyl sulfide

Biogenic sulfur compounds such as dimethyl sulfide (DMS) are important contributors to the global carbon cycle. The differential Raman cross section of DMS relative to the nitrogen fundamental, σ_DMS, has been measured at several excitation wavelengths in order to assess the applicability of Raman spectroscopy for the direct quantitative measurement of this compound. At 488 nm, σ_DMS for the ν₆ carbon–sulfur stretching mode was found to be 4.9 ± 1.6, while for the ν₂ carbon–hydrogen stretching mode it was 2.8 ± 0.9. Using, KrF laser excitation, values for σ_DMS could be measured simultaneously at two excitation wavelengths, 248.32 and 248.69 nm. The average values of σ_DMS for 248‐nm excitation based on measurements at these two excitation wavelengths were 3.5 ± 1.4 for the carbon–sulfur stretching mode and 4.6 ± 0.6 for the carbon–hydrogen stretching mode. The results indicate that no significant resonance enhancement of σ_DMS for either mode occurs, although they show some slight enhancement of the cross section for the ν₂ band (C H stretching mode). It was concluded that the measured values of σ_DMS are high enough to allow the quantitative detection of DMS at the millimolar level. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectral investigations on the binary system (acetic acid N,N‐dimethyl formamide)

Raman spectra of acetic acid (AA), N,N‐dimethyl formamide (DMF) and their binary mixtures with varying mole fraction of the AA were recorded in the region 300–1750 cm⁻¹ to investigate the formation of self‐associated dimer and hydrogen‐bonded complexes in a mixed system. The observed spectral features of the CO stretching mode suggest the formation of self‐association with a smaller aggregation size, and also indicate the presence of repulsive interactions between AA and DMF. The existence of two kinds of AA molecules (free and complex) is elucidated from the splitting of the OC O deformation mode. The intermolecular hydrogen‐bond formation and the possibility of attractive interaction between AA and DMF are also examined from the observed spectral features in the CCO symmetric stretching mode of AA, and CN symmetric stretching mode of DMF. Copyright © 2006 John Wiley & Sons, Ltd.     

Experimental and computational studies on the solvation of lithium tetrafluorobrate in dimethyl sulfoxide

Solvation structures of the lithium cation and tetrafluorobrate anion in dimethyl sulfoxide (DMSO) were investigated by Raman spectroscopy and ab initio calculations at various salt concentrations. The SO and C S stretching bands were used to monitor the structural change of the solvation shell. It has been shown that the solvation number of Li⁺, calculated by the changes in intensities of the C S asymmetric and symmetric stretching bands, is consistent with the value predicted by ab initio calculations. The wavenumber shift of the C H stretching band is suggested to be the result of the anion solvation and the dissociation of the associated DMSO molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

淡水养殖珍珠中有机物的激光共振拉曼光谱分析

采用3个不同的激发波长λ=514,633和785 nm对淡水养殖珍珠进行了较为系统的原位拉曼光谱研究,且与相同条件下测定的苹果蜗牛卵壳拉曼光谱进行对比,结果表明:(1)珍珠中所探测到的有机物拉曼峰频率色散明显,推测为聚乙炔类物质,而非前人所认为的类胡萝卜素;(2)苹果蜗牛卵壳中有机物为典型的类胡萝卜素,当λ变化时其拉曼峰基本无频率色散现象;(3)根据拉曼峰位置推测珍珠中聚乙炔类物质共轭C=C双键的数目约为10和16,蜗牛卵壳中类胡萝卜素的共轭C=C双键的数目约为13.     

Probing the structure and Franck–Condon region of protochlorophyllide a through analysis of the Raman and resonance Raman spectra

The structure and Franck–Condon region of protochlorophyllide a, a precursor in the biosynthesis of chlorophyll and substrate of the light‐regulated enzyme protochlorophyllide oxidoreductase (POR), were investigated by Raman and resonance Raman (RR) spectroscopy. The spectroscopic results are compared to the spectra of the structurally closely related porphyrin model compound magnesium octaethylporphyrin (MgOEP), and interpreted on the basis of density functional theory (DFT) calculations. It is shown that the electronic properties of the two porphyrin macrocycles are affected by different vibrational coupling modes, resulting in a higher absorption cross section of protochlorophyllide a in the visible spectral region. Furthermore, a comparison of the Fourier transform (FT)‐Raman and RR spectra of protochlorophyllide a indicates the modes that are resonantly enhanced upon excitation. Based on vibrational normal mode calculations, these modes include C C ring‐breathing and CC stretching vibrations of the porphyrin macrocycle. In particular, the strong band at 1703 cm⁻¹ can be attributed to the CO carbonyl vibration of the cyclopentanone ring, which is attached in conjugation to the π‐electron path of the porphyrin ring system. The enhancement of that mode upon electronically resonant excitation is discussed in the light of the reaction model suggested for the photoreduction of protochlorophyllide a in the POR. Copyright © 2009 John Wiley & Sons, Ltd.     

NIR‐FT Raman,FT‐IR and surface‐enhanced Raman scattering spectra,with theoretical simulations on chloramphenicol

Chloramphenicol (CLM), originally derived from the bacterium Streptomyces venezuelae, is an inhibitor of bacterial ribosomal peptidyl transferase activity. The near infrared Fourier transform (NIR‐FT) Raman, surface‐enhanced Raman spectroscopy (SERS) and Fourier transform infrared (FT‐IR) spectral analyses of CLM, a potential antibacterial drug for the treatment of typhoid fever, were carried out along with density functional computations. The vibrational spectral analysis reveals that the CH₂ asymmetric and symmetric stretching modes are shifted to higher wavenumbers than the computed values, owing to the electronic effects resulting from induction of methylene group with the adjacent electronegative atom. The lowering of CO stretching wavenumber is due to the presence of the strong electronegative atom, nitrogen, attached to the carbonyl carbon, causing large degree of molecular π‐electron delocalization and redistribution of electrons, which weakens the CO bond. The absence of a C H stretching vibration and the observed C H out‐of‐plane bending modes suggest that the CLM molecule may be adsorbed in a flat orientation with respect to the silver surface. Copyright © 2008 John Wiley & Sons, Ltd.     

Resonance Raman intensity analysisof the excited‐state photochemical dynamicsof dimethyl 1,3‐dithiole‐2‐thione‐4,5‐dicarboxylate in the A‐band absorption

Dimethyl 1,3‐dithiole‐2‐thione‐4,5‐dicarboxylate (DDTD) was synthesized and characterized using NMR, Fourier transform (FT)‐Raman, Fourier transform‐infrared (FT‐IR) and UV spectroscopies. Resonance Raman spectra (RRs) were obtained with 341.5, 354.7 and 368.9 nm excitation wavelengths and density functional calculations were carried out to elucidate the π (S C S) →π* (S C S) electronic transitions and the RRs of DDTD in cyclohexane solution. The RRs indicate that the Franck–Condon region photo dynamics have a multidimensional character with motion predominantly along the CS stretch and the C S symmetric stretch modes in the five‐member heterocycle. A preliminary resonance Raman intensity analysis was carried out and the results for DDTD were compared with previously reported results for 1,3‐dithiole‐2‐thione (DTT). Differences and similarities of the spectra in terms of molecular symmetry and electron density are also discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Modeling red coral (Corallium rubrum) and African snail (Helixia aspersa) shell pigments: Raman spectroscopy versus DFT studies

Pigments from red coral (Corallium rubrum) and African snail (Helixia aspersa) shell were studied non‐invasively using Raman spectroscopy with 1064‐nm laser beam. The two observed bands because of organic pigments confined in biomineralized CaCO₃ matrix at about 1500 and 1100 cm⁻¹ were assigned to ν(CC) and ν(C―C), respectively. Both signals originate from polyene(s) of largely unknown structure, containing several conjugated CC bonds. The small peak at 1016 cm⁻¹ in the Raman spectrum of coral pigment was assigned to in‐plane ―CH₃ rocking or structural deformation of polyene chain because of spatial confinement in the mineral matrix. The organic pigments in red coral and snail shell were present in inorganic matrix containing aragonite (shell) and calcite (coral). In addition, using Raman spectroscopy, it was observed that aragonite was replaced by calcite as result of healing damaged parts of snail shell. This is an important finding which indicates a great potential of nondestructive Raman spectroscopy instead of X‐ray technique, as a diagnostic tool in environmental studies. To support analysis of the observed Raman spectra detailed calculations using density functional theory (DFT with B3LYP and BLYP density functionals) on structure and vibrations of model all‐trans polyenes were undertaken. DFT calculated CC and C―C stretching frequencies for all‐trans polyenes containing from 2 to 14 CC units were compared with the observed ν(CC) and ν(C―C) band positions of the studied coral and shell. Individual correction factors were used to better match theoretical wavenumbers with observed band positions in red coral and African snail. It was concluded that all‐trans polyene pigments of red coral and dark parts of African snail shell contain 11–12 and 14 CC double bond units, respectively. However, Raman spectroscopy cannot produce any clear information on the presence and nature of the end‐chain substituents in the studied pigments. Copyright © 2016 John Wiley & Sons, Ltd.     

Concentration‐dependent frequency shifts of the CS stretching modes in ethylene trithiocarbonate studied by Raman spectroscopy

Resonant with the CS π → π* electronic transition, the intensity of CS stretching and its overtone have been greatly enhanced in the 488‐ and 319‐nm excited resonance Raman spectra. The isotropic and anisotropic parts of the Raman spectra of CS stretching modes of ethylene trithiocarbonate (ET) at different concentrations have been analyzed in order to study the noncoincidence effect (NCE). In neat ET, the experimentally measured values of noncoincidence Δυ_nc are ~4.60 cm⁻¹ for the CS stretching modes, which reduce to 1.30 cm⁻¹ at the mole fraction χ_m (ET) = 0.13. Both the isotropic and anisotropic peak frequencies of CS stretching were found to shift to higher wavenumber when the concentrations are diluted, while the value of Δυ_nc goes on decreasing upon dilution. The absolute Raman cross section of carbonyl stretching was also measured, and their behavior was unusual (first increasing and then decreasing with the decrease of concentration). The experimental result shows that there may exist self‐association in the high concentration, and the main NCE mechanism may be due to the transition dipole–transition dipole coupling between the ET molecules. Copyright © 2015 John Wiley & Sons, Ltd.     

Resonance Raman spectra and excited state structural dynamics of ethylene trithiocarbonate in the A‐ and B‐band absorptions

A‐ and B‐band resonance Raman spectra were acquired for ethylene trithiocarbonate in cyclohexane solution. The results indicate that the S₃ state structural dynamics is mostly along vibrational motions of the CS stretch υ₁₁, while the S₄ state one has motions mainly via the S C S symmetric stretch υ₁₈, CS stretch υ₁₁, and the H C H rock + S C S antisymmetric stretch υ14 reaction coordinates. The very different excited state structural dynamics were briefly discussed in terms of vibronic couplings using local symmetry point group. Copyright © 2009 John Wiley & Sons, Ltd.     

IR,Raman and SERS spectra of 5‐sulphosalicylic acid dihydrate

IR, Raman and surface‐enhanced Raman scattering (SERS) spectra of 5‐sulphosalicylic acid were recorded and analysed. The vibrational wavenumbers were computed by density functional theoretical (DFT) method using B3LYP/6–31G* basis. The bands due to the stretching modes CO, C S and SO₂ are intense in the SERS spectrum. The C H stretching mode also appears in the SERS spectrum. The molecule is found to adsorb through both the carboxyl and sulphonyl groups. A possible tilted orientation of the molecule is suggested. Copyright © 2006 John Wiley & Sons, Ltd.     

Resonance Raman spectroscopy and theoretical study on the photodissociation dynamics of formanilide in S3 state

Resonance Raman spectra were obtained for formanilide (FA) in acetonitrile solution with 239.5‐ and 245.9‐nm excitation wavelengths in resonance with the S₃ state, and density functional theory (DFT) was used to elucidate the electronic transitions and resonance Raman spectra of FA. The spectra indicate that, in the Franck–Condon region, photodissociation dynamics has a multidimensional character with the motions mainly along the CO stretching υ₈, the ring CC stretch υ₉, the NH wag and ring CCH in‐plane bend υ₁₁, the NH wag and ring CCH in‐plane bend υ₁₂, ring CC stretch and ring CCH in‐plane bend υ₁₆, the NH wag and ring CCH in‐plane bend υ₁₇, the ring CCH in‐plane bend υ₁₈, and the ring trigonal bend υ₂₄. The excited‐state dynamics of the S₃ state is discussed, and the results are compared with those previously reported for benzamide (BA) to examine the N‐ or C‐terminal‐substituted aromatic effect of the peptide bond. Copyright © 2010 John Wiley & Sons, Ltd.     

彩色珍珠致色成分的拉曼光谱研究

对多种彩色珍珠样品进行了可见光光谱和拉曼光谱测试,研究了珍珠致色成分的种类及其与颜色的关系。研究结果表明：(1) 彩色淡水珍珠和海水珍珠样品均会在1 121～1 132和1 506～1 524 cm-1范围出现强峰,该特征峰归属于多烯化合物的C—C和CC伸缩振动;(2) 随着珍珠颜色的加深,样品位于1 117～1 132,1 502～1 524和2 000～3 500 cm-1范围的峰逐渐增强,特征峰所代表的有机质与珍珠颜色有关;(3) 深紫色淡水珍珠和深橘红色海水珍珠样品在1 475～1 575 cm-1范围的包络峰可分成8～10个次级峰,计算可知多烯化合物CC双键数目分别为N=9～27和N=7～27。珍珠中不同种类和含量的多烯化合物,可能是彩色珍珠的致色原因。     

Excited‐state structural dynamics and vibronic coupling of 1,3‐dithiole‐2‐thione—resonance Raman spectroscopy and density functional theory calculation study

1,3‐Dithiole‐2‐thione (DTT) was synthesized and characterized using NMR, FT‐Raman, FT‐IR, UV spectroscopies. Resonance Raman spectra (RRs) were obtained with 341.5, 354.7 and 368.9 nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the RRs of DTT in cyclohexane solution. The RRs indicate that the Franck‐Condon region photodynamics is predominantly along the CS stretch+ H‐CC‐H scissor υ₄, accompanied by the H‐CC‐H scissor υ₃, S‐C‐S symmetric stretch υ₆, CC stretch υ₂, and overtone of the non‐totally symmetric SC‐S2 out‐of‐plane deformation 2υ₁₁. The excited‐state dynamics and the force constant of CS stretch calculated by the RRs were discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectroscopic and thermal studies on the inclusion of trans‐cinnamic acid and a number of its hydroxyl‐derivatives with α, β and γ‐cyclodextrins molecules

The inclusion compounds of α‐, β‐ and γ‐cyclodextrins (α‐CD, β‐CD and γ‐CD) with trans‐cinnamic acid (t‐CIA), 3‐hydroxy‐trans‐cinnamic acid (t‐3OHCIA), 4‐hydroxy‐trans‐cinnamic acid (t‐4OHCIA) and 3,4‐dihydroxy‐trans‐cinnamic acid (t‐3,4OHCIA) were prepared and characterized, in the solid state, by means of thermogravimetry and Raman spectroscopy. The effects of the inclusion process on the guest molecules and on the hydrogen bond interactions of the guest were studied by monitoring sensitive vibrational modes, such as CO, CC and ring C H stretching modes. By combining Raman and TG data with ab initio calculations and information from CSD database on similar compounds, inclusion geometries for the different compounds are proposed. The size of the host cavity and the maximization of host/guest hydrogen‐bonding contacts appear to be the main factors determining the inclusion geometries. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrochemical functionalisation of SWNTs with poly(3,4‐ethylenedioxythiophene) evidenced by anti‐Stokes/Stokes Raman spectroscopy

The capability of anti‐Stokes/Stokes Raman spectroscopy to evaluate chemical interactions at the interface of a conducting polymer/carbon nanotubes is demonstrated. Electrochemical polymerisation of the monomer 3,4‐ethylenedioxythiophene (EDOT) on a Au support covered with a single‐walled carbon nanotube (SWNT) film immersed in a LiClO₄/CH₃CN solution was carried out. At the resonant optical excitation, which occurs when the energy of the exciting light coincides with the energy of an electronic transition, poly(3,4‐ethylenedioxythiophene) (PEDOT) deposited electrochemically as a thin film of nanometric thickness on a rough Au support presents an abnormally intense anti‐Stokes Raman spectrum. The additional increase in Raman intensity in the anti‐Stokes branch observed when PEDOT is deposited on SWNTs is interpreted as resulting from the excitation of plasmons in the metallic nanotubes. A covalent functionalisation of SWNTs with PEDOT both in un‐doped and doped states takes place when the electropolymerisation of EDOT, with stopping at +1.6 V versus Ag/Ag⁺, is performed on a SWNT film deposited on a Au plate. The presence of PEDOT covalently functionalised SWNTs is rationalised by (1) a downshift by a few wavenumbers of the polymer Raman line associated with the symmetric C C stretching mode and (2) an upshift of the radial breathing modes of SWNTs, both variations revealing an interaction between SWNTs and the conjugated polymer. Raman studies performed at different excitation wavelengths indicate that the resonant optical excitation is the key condition to observe the abnormal anti‐Stokes Raman effect. Copyright © 2010 John Wiley & Sons, Ltd.     

Carotenes and carotenoids in natural biological samples: a Raman spectroscopic analysis

Raman spectroscopic studies of a range of naturally occurring carotenoids in over 50 specimens of plant tissue and a range of standard extracts have been undertaken, and the characteristic bands of CC and C C stretching and C CH bending have been recorded. Comparison of the spectroscopic data with the chemical assignment of the carotenoids from chemical extraction of the plant tissues reveals that there is a problem in the interpretation of the spectroscopic data which can be attributed to significant wavenumber shifts, particularly in the CC stretching band wavenumber, for carotenoids in the organic tissues arising from molecular interactions between the carotenoid and its host matrix. The simple identification of carotenoids in biological tissues on the basis of comparison with the standard spectra of extracted material must be made with caution; the progressive shift in wavenumber of the CC stretching band in the conjugated polyene chain of carotenoids with the number of CC groups, and hence the identification of the carotenoid, cannot be unambiguously interpreted for the range of materials studied here. Copyright © 2009 John Wiley & Sons, Ltd.