Complete Assignment Of Bands Research Articles

Towards the critical understanding of selected vibrational features in biologically important dicyano aromatic conjugated molecules: Importance of electron donating/withdrawal groups and geometry associated with dicyano group.

The Raman spectra of a series of synthesized DC molecules (benzylidene malononitrile derivatives) with different electron donating (EDG) and electron withdrawing (EWG) group have been presented and analyzed with DFT calculated spectra. In particular, different functional groups effect on cyano stretching (∼2200 cm-1), phenyl ring breathing and alkenic double bond stretch which often appears mixed up (1475-1650 cm-1) are studied systematically for several aromatic conjugated DC derivatives. Interestingly, symmetric stretching frequency of the DC compounds having two CN groups at geminal position appears at higher wavenumber (by 11-15 cm-1) compared to their corresponding asymmetric stretch frequency. Angle (between dicyano group) dependent theoretical study indicates that the relative appearance of cyano symmetric/anti-symmetric stretching frequency depends on whether dicyano groups are at the geminal or vicinal position and the angle between them. Complete band assignments of observed Raman frequencies have been performed by potential energy distributions (PEDs) available in GAR2PED software. Our results will help to understand the vibrational feature of this important class of compounds in biological medium when used as probe.

Raman and surface enhanced Raman scattering of a black dyed silk

The Raman and surface enhanced Raman scattering (SERS) spectra of a black dyed silk sample (BDS) were registered. The spectral analysis was performed on the basis of Raman and SERS spectral data of isolated samples of Bombyx mori silk fibroin, its motif peptide component (GAGAGS) and the synthetic reactive black 5 dye (RB5). The macro FT‐Raman spectrum of the silk sample is consistent with a silk II‐Cp crystalline fraction of Bombyx mori silk fibroin; the SERS spectrum is highly consistent with conformational modifications of the fibroin due to the interactions with the Ag nanoparticles. The GAGAGS peptide sequence dominates the Raman spectrum of the silk. The SERS spectrum of the peptide suggests a random coil conformation imposed by the surface interaction; the serine residue in the new conformation is exposed to the surface. Quantum chemical calculations for a model of the GAGAGS–Ag surface predict a nearly extended conformation at the Ag surface. The Raman spectrum of the dye was analysed, and a complete band assignment was proposed; it was not possible to propose a preferential orientation or organization of the molecule on the metal surface. Quantum chemical calculations for a model of the dye interacting with a silver surface predict a rather coplanar orientation of the RB5 on the Ag metal surface. The Raman spectrum of the BDS sample is dominated by signals from the dye; the general spectral behaviour indicates that the dye mainly interacts with the silk through the sulphone (–SO2–) and sulphonate (–SO2–O–) groups. Besides the presence of dye signals, mainly ascribed to the sulphone and sulphonate bands, the SERS spectrum of the BDS sample also displays bands belonging to the amino acids alanine, glycine, serine and particularly tyrosine. Copyright © 2013 John Wiley & Sons, Ltd.

Far infrared spectra of solid state aliphatic amino acids in different protonation states

Far infrared spectra of zwitterionic, cationic, and anionic forms of aliphatic amino acids in solid state have been studied experimentally. Measurements were done on glycine, L-alanine, L-valine, L-leucine, and L-isoleucine powder samples and film samples obtained from dried solutions prepared at pH ranging from 1 to 13. Solid state density functional theory calculations were also performed, and detailed potential energy distributions were obtained from normal mode results. A good correspondence between experimental and simulated spectra was achieved and this allowed us to propose an almost complete band assignment for the far infrared spectra of zwitterionic forms. In the 700-50 cm(-1) range, three regions were identified, each corresponding to a characteristic set of normal modes. A first region between 700 and 450 cm(-1) mainly contained the carboxylate bending, rocking, and wagging modes as well as the ammonium torsional mode. The 450-250 cm(-1) region was representative of backbone and sidechain skeletal bending modes. At last, the low wavenumber zone, below 250 cm(-1), was characteristic of carboxylate and skeletal torsional modes and of lattice modes. Assignments are also proposed for glycine cationic and anionic forms, but could not be obtained for all aliphatic amino acids due to the lack of structural data. This work is intended to provide fundamental information for the understanding of peptides vibrational properties.

Tetrahydroxy-p-benzoquinone as a Source of Polydentate O-Donor Ligands. Synthesis, Crystal Structure, and Magnetic Properties of the [Cu(bpy)(dhmal)]2Dimer and the Two-Dimensional [{SiW12O40}{Cu2(bpy)2(H2O)(ox)}2]·16H2O Inorganic−Metalorganic Hybrid

The use of tetrahydroxy-p-benzoquinone as a slow source of dihydroxymalonato and oxalato ligands led to the isolation under open-air mild reaction conditions of five different compounds, two of them prepared for the first time: [Cu(bpy)(dhmal)]2 (1) and [{SiW12O40}{Cu2(bpy)2(H2O)(ox)}2].16H2O (5) (bpy, 2,2'-bipyridine; dhmal, dihydroxymalonate; ox, oxalate). A possible mechanism for the oxidation of the benzoquinone to give the croconate dianion, which undergoes further ring-opening oxidation to decompose into dihydroxymalonate and oxalate, is proposed. All compounds have been characterized by elemental analysis, thermogravimetry, infrared spectroscopy, and powder X-ray diffraction. Single-crystal X-ray diffraction, electron paramagnetic resonance, and magnetic susceptibility measurements have been performed for compounds 1 and 5. A complete band assignment of the experimental FT-IR spectra is given through comparison with the ones calculated using density functional theory (DFT). The neutral dimer 1 constitutes the first structurally characterized example of a transition metal-dhmal complex, and it contains two copper atoms bridged by two dihydroxymalonato ligands acting in a mu2-kappa3O,O',O":kappa1O coordination fashion, so that an equatorial-axial Cu2(mu2-O)2 rhomboid core is formed. On the other hand, the inorganic-metalorganic hybrid compound 5 shows a two-dimensional arrangement of Keggin polyanions linked by one of the Cu atoms of the oxalate cationic dimers to give layers parallel to the (10) plane, the remaining ox-Cu-bpy fragments acting as interlamellar separators. In both cases, magnetic and EPR results are discussed with respect to the crystal structure of the compounds and, for compound 1, also with respect to DFT calculations of the exchange coupling constant.

Studies of metal isotope and deuteration effects in vibrational spectra of palladium(II) complex with histamine

AbstractVibrational spectra of the palladium(II) complex with histamine were studied within the density functional theory (DFT) formalism. In addition, frequency shifts due to N‐deuteration and isotopic Pd104 on Pd110 replacement were determined theoretically and compared with those measured. All spectra were supplemented by the potential energy distribution analysis. The theoretical results were applied to the complete band assignment of newly and previously measured spectra. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

FT-Raman spectroscopy and density functional theory studies on silica-supported rhodium complexes

FT-Raman spectra of catalytically active rhodium complexes with various olefinic and various anionic ligands were recorded in benzene solution. Immobilization of these complexes on a SiO 2-surface yielded heterogeneous catalysts, which were investigated. Activation with SiCl 4 or TiCl 4 improved the catalytic activity. Therefore the FT-Raman spectroscopic investigations were also extended to this case. On the basis of density functional theory calculations a complete band assignment has been performed for the acetylacetonato complex [Rh(acac)(C 2H 4) 2].

Spectroscopic Study of [Fe2(O2)(OBz)2{HB(pz‘)3}2]: Nature of the μ-1,2 Peroxide−Fe(III) Bond and Its Possible Relevance to O2Activation by Non-Heme Iron Enzymes

Spectroscopic and theoretical studies of a binuclear cis μ-1,2 peroxide-bridged Fe(III) complex, [Fe2(O2)(OBz)2{HB(pz‘)3}2], where HB(pz‘)3 represents hydrotris(3,5-diisopropyl-1-pyrazolyl)borate and OBz is benzoate, are presented and discussed. It is shown that the high O−O stretching frequency of 876 cm-1 does not reflect a strong O−O bond (kO-O = 3.1 mdyn/Å) but rather results from substantial mechanical coupling between the Fe−O and O−O stretch motions. The coupling strength in μ-1,2 peroxide-bridged complexes is mainly determined by the metal−O−O bond angle, and this angle is larger in the three structurally characterized Fe−peroxide dimers than in related Cu and Co dimers due to a strong π-bonding interaction in the former. Using absorption, magnetic circular dichroism, and resonance Raman spectroscopies we can identify four peroxide-to-Fe charge transfer (CT) transitions contributing to the optical absorption spectrum below 35 000 cm-1. These transitions give rise to two similarly intense bands centered at ∼14 600 and 26 200 cm-1 (ε ∼ 3800 M-1 cm-1) and to weaker features at 12 500 cm-1 (∼400 M-1 cm-1) and 24 650 cm-1 (∼1600 M-1 cm-1). A complete band assignment based on the experimental data and assisted by density functional calculations is presented and provides significant insight into Fe−peroxide bonding. From a quantitative analysis of the optical absorption and resonance Raman data within the framework of time-dependent theory of electronic spectroscopy it follows that the π contribution to the peroxide → Fe charge donation amounts to 50−65%. The σ contribution, however, is smaller than in the well-characterized trans μ-1,2 peroxide-bridged Cu(II) dimer, and the charge on peroxide is thus similar in the two complexes, suggesting that the bridging peroxide in [Fe2(O2)(OBz)2{HB(pz‘)3}2] has a rather basic/nucleophilic character. The mechanistic implications of these results for the conversion of the putative cis μ-1,2 peroxide-bridged diiron(III) intermediate (P or Hperoxo) of methane monooxygenase to a high-valent diiron(IV)−oxo species are discussed.

A far infrared and theoretical ab initio vibrational study of fluorosulfonic acid as monomer and cyclic dimer

Geometrical parameters and wavenumbers of the normal modes of vibration of fluorosulfonic acid (FSO 2OH) and its cyclic dimer were calculated using ab initio methods. The vibrational results were adjusted by means of scaled force fields to the complete band assignments reported in the literature for the monomer molecule and to the partial assignments known for the dimer. Besides, a description of the H-bond or intermonomer modes was obtained. The far infrared spectrum of the gaseous substance revealed a new band, due to one of the last mentioned modes.

Raman and infrared spectra of trichloromethanesulphenyl chloride (CCl3SCl)

AbstractThe infrared and Raman spectra of CCL3SCl have been thoroughly investigated and as results a complete assignment of bands and point group C1 for the molecule are proposed.

Spectres Raman de Résonance de Dérivés Parasubstitués de l' Azobenzène

AbstractResonance Raman spectra of twenty parasubstituted azobenzene derivatives are compared, enabling a more complete assignment of bands to be made. Since all the spectra are rather similar, the various ring substituents are not resonance Raman active, and all the observed bands can be assigned to vibrational modes of the aromatic rings and to the azo group itself. Frequency shifts in the PhN stretching region are opposite to those expected based on delocalization along the PhNNPh moiety. From the complexity of band pattern around the NN stretching region and from the above described frequency shifts, several types of vibrational coupling are evident. On the basis of the band assignments, some useful conclusions can be reached for interpreting the observed spectral changes when azobenzene derivatives are used as chromophore probes in biochemical system studies.

The infrared spectra (3500-140 cm?1) of the 2,2'-bipyridine, 2-aminomethylpyridine and ethylenediamine adducts and the sodium tris-compounds of cobalt(II), nickel(II) and zinc(II) acetylacetonates

The M(acac)2B and NaM(acac)3 complexes (M = Coll, Nill orZnll; acac=acetylacetonateanion; B=2,2′=bipyridine, 2-aminomethylpyridine or ethylenediamine) have been prepared and their i.r. spectra determined over the 3500-140 cm−1 range. Complete band assignments have been made on a comparative basis, with the effects of ligand substitution and metal ion substitution being considered. Bands in the i.r. spectra of the complexes which are associated with 2,2′-bipyridine, 2-aminomethylpyridine and ethylenediamine arc in excellent agreement with values previously established for these ligand and metal-ligand vibrations, in related complexes. Band assignments for acetylacetonate anion and metal-acetylacetonate vibrations substantiate those made in certain of the previously published papers. The method of assignment adopted has allowed the complete assignment of bands in the i.r. spectra of the metal complexes.

Vibrational Assignments of Organosilanetriols. II. Crystalline Phenylsilanetriol and Phenylsilanetriol-D3

Fourier transform infrared spectra (3800 to 450 cm−1) and laser Raman spectra (4000 to 0 cm−1) of crystalline phenylsilanetriol and phenylsilanetriol-d3, and liquid state phenylsilanetriol and phenylsilanetriol-d3are first reported. Complete band assignments are attempted. All vibrational modes of the SiOH group except for the SiC torsional mode, including the SiOH in-plane and out-of-plane bending modes, are observed. In addition to the phenylsilanetriols, infrared and laser Raman spectra of crystalline diphenylsilanediol and triphenylsilanol are also studied to aid the band assignments.

Vibrational Assignments of Organosilanetriols. I. Vinylsilanetriol and Vinylsilanetriol-D3in Aqueous Solutions

Infrared and laser Raman spectra of vinylsilanetriol and vinylsilanetriol-d3in H2O and D2O, respectively, are reported. Complete band assignments of the silanetriol group are discussed. In addition, band assignments of the vinyl group are reexamined. Most of the related bands to silanol are very broad or weak in intensity except for the SiO stretching modes which are potentially of use for structural analysis of silane coupling agents in the presence of glass surfaces.

The photoelectron spectra of some heterocyclic compounds which contain N, O, Cl and Br

The photoelectron spectra of 19 heterocyclic compounds, several of which are germicidal agents, containing N, O, Cl and Br have been investigated. Complete band assignments have been made for the lone-pair regions of the spectra for future reference in structure/biological-activity correlations. A detailed comparison of the carbonyl-oxygen lone-pair splitting patterns in the spectra indicates that succinimide is skeletally planar, while N-chlorosuccinimide and N-bromosuccinimide are substantially nonplanar in the gas phase.

Spectres infrarouges de 4000 à 40 cm− des composés de coordination de l'éther méthylique avec les halogénures de magnésium

Abstract Six compounds of the formula MgX 2 nMe 2 O (H 6 or D 6 ) have been prepared. Their infrared spectra are reported (4000–40 cm −1 ) and a complete assignment of bands is made. Coordination effects on the methyl stretching and skeletal vibrations of donors are discussed. The analysis suggests tetracoordination of magnesium and existence of oxygen bridges in 1-1 complexes. Approximate Mg-O and Mg-Br stretching force constants have been calculated in 1–2 complexes.