Structural and spectroscopic analysis of dipeptide <Emphasis Type="SmallCaps">l</Emphasis>-methionyl-glycine and its hydrochloride

Dipeptide l-methionyl-glycine (Met-Gly) hydrochloride was characterized structurally by means of solid-state linear polarized IR (IR-LD) spectroscopy of oriented samples as colloidal suspension in nematic liquid crystal. Quantum chemical ab initio calculations and vibrational analysis support the experimental data. ¹H and ¹³C nuclear magnetic resonance (NMR) data, mass spectrometry (ESI-MS and FAB-MS) techniques, thermogravimetry (TGV), and differential scanning calorimetry (DSC) method were employed as well. The experimental and theoretical data of hydrochloride salt were compared with analogous data of the neutral dipeptide with the aim to explain the role of intermolecular hydrogen bonding on the conformational behavior and spectroscopic properties of the compound studied.     

Investigation of silicate mineral sanidine by vibrational and NMR spectroscopic methods

Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrational (IR and Raman), EPR and NMR spectroscopic techniques. The principal reflections occurring at the d-spacings, 3.2892, 3.2431, 2.9022 and 2.6041 Å confirm the presence of sanidine structure in the mineral. Sanidine shows five prominent characteristic infrared absorption bands in the region 1200–950, 770–720, 590–540 and 650–640 cm⁻¹. The Raman spectrum shows the strongest band at 512 cm⁻¹ characteristic of the feldspar structure, which contains four membered rings of tetrahedra. The UV–vis–NIR absorption spectrum had strong absorption features at 6757, 5780 and 5181 cm⁻¹ due to the combination of fundamental OH– stretching. The bands at 11236 and 8196 cm⁻¹and the strong, well-defined band at (30303 cm⁻¹ attest the presence of Fe²⁺ and Fe³⁺, respectively, in the sample. The signals at g = 4.3 and 3.7 are interpreted in terms of Fe³⁺ at two distinct tetrahedral positions Tl and T2 of the monoclinic crystal structure The ²⁹Si NMR spectrum shows two peaks at −97 and −101 ppm corresponding to T2 and T1, respectively, and one peak in ²⁷Al NMR for Al(IV).     

Polymorphism of phenylpyruvic acid studied by IR, Raman and solid state C NMR spectroscopy

Polymorphs I and II of phenylpyruvic acid are obtained as mixtures of both crystal forms or relatively pure crystals, from different solvents. Polymorph I is more stable than polymorph II at room temperature. Spectral characteristics of these polymorphs are discussed on the basis of IR, Raman and solid state ¹³C NMR spectra. Also, the assignment of the IR features observed in the 1600–1700 cm⁻¹ region is re-investigated by referring to the spectra of heavy-atom substituted derivatives. It is suggested that the C=O stretching band is split by the crystal field for both polymorphs.     

Identification Des Produits De La Reduction Electrochimique d'Un Nouvel Antiinflammatoire: Le Piroxicam

Abstract

The electrochemical reduction of piroxicam has been investigated on a mercury pool in acidic and alcaline media.

After exhaustive electrolysis, the extraction followed by chromatographic separation of the reaction products gives the reduced compounds which have been identified by spectroscopic techniques. From the analysis of the NMR ¹H, ¹³C and IR spectra and the results of our preceding electrochemical investigation, the polarographic behaviour of piroxicam has been elucidated. The process occurs by the irreversible reduction of the double bond of the enol function over the total pH range investigated. However, in alkaline and highly acidic solutions, a preceding two-electron step occurs, giving rise to the opening of the thiazine ring.     

Raman and infrared spectroscopic investigation of contact ion pair formation in aqueous cadmium sulfate solutions

Raman and IR data for aqueous CdSO₄ and (NH₄)₂SO₄ solutions have been recorded over broad concentration and temperature ranges. Whereas the v₁-SO ₄ ^2– band profile is symmetrical in (NH₄)₂SO₄ solutions, in CdSO₄ solutions a shoulder appears on the high frequency side which increases in intensity with increasing concentration and temperature. The molar scattering coefficient of the v₁-SO ₄ ^2– band is the same for all forms of sulfate in (NH₄)₂SO₄ and CdSO₄ solutions and is independent of temperature up to 99°C. The high frequency shoulder is attributed to the formation of a contact ion pair [Cd²⁺OSO ₃ ^2– ] (11 associate). Also the v₃-SO ₄ ^2– antisymmetric stretching mode shows a splitting in the CdSO₄ solution. Further spectroscopic evidence for contact ion pair formation is provided by IR spectroscopy. No higher associates or anionic complexes are required to interpret the spectroscopic data. The degree of association has been measured as a function of concentration and temperature. The thermodynamic association constant, K_A=0.15±0.05 kg-mol^–1 at 25°C is estimated from the Raman data by an extrapolation procedure by taking account of the activity coefficients. Values are reported for the activity coefficient of the ion pair. From the Raman temperature dependence studies, the enthalpy of formation for the contact ion pair is estimated to be 10±1 kJ-mol^–1.     

Gould-Jacobs reaction of 6-amino-2,3-diphenylquinoxaline

Summary Catalytic hydrogenation of 2,3-diphenyl-6-nitroquinoxaline led to the corresponding amine1 which in turn afforded products3a-i on reaction with alkoxymethylene derivatives2a-i. Thermal cyclization of3b and3f yielded substituted pyrazinoquinolones5b and5f, respectively. Optimal conditions for the successful hydrolysis of ester5b were found. The structures of all products were deduced from their IR, UV,¹H, and¹³C NMR spectroscopic data.Dedicated to Prof.F. Sauter on the occasion of his 65th birthday     

Synthesis and VT-NMR studies of cationic hydride platinum clusters

The synthesis of three trinuclear platinum hydrides [Pt₃(L-L)₃(H)₃]⁺ (L-L = 1,2-bis(diphenylphosphino)ethane, dppe, l; 1-diphenylphosphino-2-diphenylarsinoethane, dppae. 2; 1,2-bis(diphenylarsino)ethane, dpae, 3) is reported. The complexes were characterized by IR, FAB-MS, and NMR (¹H,³¹P and¹⁹⁵Pt) spectroscopic techniques. The fast exchange of the hydride ligands, observed at ambient temperature, is frozen out at low temperature. The low-temperature¹H and³¹P NMR spectra are consistent with an open array of Pt atoms in the clusters, in keeping with a 16-electron configuration on each platinum atom. Two of the hydride ligands are terminally bonded to two metal centers, whereas the third one is µ₃-coordinated, interacting more tightly with the unique platinum atom.     

The Structure of Gallium in Strongly Alkaline,Highly Concentrated Gallate Solutions—a Raman and <Superscript>71</Superscript>Ga-NMR Spectroscopic Study

Highly concentrated alkaline gallate solutions with 0.23≤[Ga(III)]_T≤2.32 mol⋅dm⁻³ and 1≤[NaOH]_T≤15 mol⋅dm⁻³ have been prepared and investigated by Raman and ⁷¹Ga-NMR spectroscopy. Both the Raman and ⁷¹Ga-NMR spectra are consistent with the presence of only one Ga-bearing species in these solutions, the tetrahedral hydroxocomplex, Ga(OH)₄⁻. Contact ion pairs were found to cause variations in the Raman and ⁷¹Ga-NMR parameters that are at the edge of detectability. Other species that have been claimed to exist in the literature, like higher hydroxo complexes (i.e., Ga(OH)₆³⁻) or the μ-oxo-bridged dimer (i.e., (OH)₃Ga-O-(OH)₃²⁻), were not detected by these spectroscopic techniques. If such solution species exist at all, their concentrations are below the detection limit of Raman and ⁷¹Ga-NMR spectroscopy. The behavior of gallium appears to be very similar to that of aluminium under identical conditions, except that the dimeric species detected in aluminate solutions is undetectable in analogous gallates.     

An Au(III) complex of glycyl- S -serine: a linear polarized IR and 1H- and 13C-NMR investigation

The structure of a mononuclear Au(III) complex of the dipeptide glycyl-S-serine (Gly-Ser) has been predicted using solid-state linear dichroic IR (IR-LD) spectroscopy, based on an orientation technique in a nematic liquid crystal suspension. Results are compared with data from ¹H- and ¹³C-NMR, MS, elemental analysis, thermogravimetry and differential scanning calorimetry. The metal ion is coordinated as a tridentate through NH₂, N (from deprotonated amide) and O (COO^?) groups to form [Au(C₅H₉N₂O₄)Cl], with the fourth position of the square-planar coordination sphere being completed by a Cl^? ion.     

Synthesis and spectral characterization of some complexes of platinum(II) containing η-methyleugenol

Several complexes of the formula trans-[Pt(Meug)(Am)Cl₂], Meug: methyleugenol (4-allyl-1,2-dimethoxybenzene), a η²-coordinated olefin, and Am: ammine, methylamine, diethylamine, o-toluidine, m-toluidine, p-toluidine, o-anisidine, m-anisidine and p-anisidine have been prepared. UV, IR, Raman, ¹H NMR, ¹³C NMR and 2D NMR spectra of the complexes were recorded and analyzed.     

Phosphate Derivatives of Natural Lactones. I. Synthesis of Novel Isoalantolactone Dialkylphosphonates

Novel isoalantolactone dialkylphosphonates were synthesized in 70-87% yields by reacting this eudesmanolide with dialkylphosphites. Their structures were proved by spectral analysis using IR, PMR, ¹³C and ³¹P NMR, and two-dimensional ¹H-¹H (COSY) spectroscopy. The reaction of isoalantolactone with dialkylphosphites is highly stereoselective.     

Phosphate Derivatives of Natural Lactones. II. Synthesis of Novel Dialkylphosphonates of Arteannuin B

Novel dialkylphosphonates of arteannuin B were synthesized in 45-47% yields by reaction of this cadinanolide with dialkylphosphites. Their structures were established using IR, PMR, ¹³C and ³¹P NMR spectroscopy, and two-dimensional ¹H-¹H NMR (COSY) spectroscopy. The reaction of arteannuin B and dialkylphosphites is highly stereoselective.     

Revised vibrational band assignments for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile based on ab initio, DFT and normal coordinate calculations

In the present study, a systematic vibrational spectroscopic investigation for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile (TFB), aided by electronic structure calculations has been carried out. The electronic structure calculations – ab initio (RHF) and hybrid density functional methods (B3LYP) – have been performed with 6-31G* basis set. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization ratios and Raman activities have been computed. The results of the calculations have been used to simulate IR and Raman spectra for TFB that showed excellent agreement with the observed spectra. Potential energy distribution (PED) and normal mode analysis have also been performed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed. A complete assignment of the observed spectra has been proposed.     

Tris(dimethylamino)phosphine Selenide Complexes of Cadmium(II): Synthesis and Multinuclear (31P, 77Se,and 113Cd) NMR Characterization in Solution

The complexes CdL₄(ClO₄)₂ (1), CdL₂(NO₃)₂ (2), and CdL₂Cl₂ (3) (L = (Me₂N)₃P(Se)) have been prepared and characterized by elemental analysis, conductivity measurements, IR, and multinuclear (³¹P, ⁷⁷Se, and ¹¹³Cd) NMR spectroscopy. ³¹P and ⁷⁷Se NMR data were informative of changes associated with complex formation. The structure of the prepared complexes was further confirmed in solution by their ¹¹³Cd NMR spectra, which show a quintuplet for the perchlorate complex and a triplet for each of the nitrate and chloride complexes due, respectively, to coupling with four and two equivalent phosphorus atoms, consistent with a four coordinate tetrahedral geometry for the cadmium center. The NMR data are discussed and compared with those reported for related complexes.     

Tin(IV) Tetrachloride Complexes with Bis-(Dialkylamino)phosphoryl Fluoride: A Multinuclear (119Sn, 31P, 19F,and 1H) NMR Characterization in Solution

The two octahedral complexes SnCl₄·2(O)PF(NR₂)₂ (R = Me or Et) were prepared from reaction of SnCl₄ with the ligand (R₂N)₂P(O)F in anhydrous CHCl₃. The new adducts have been characterized by elemental analysis, IR, and multinuclear (¹¹⁹Sn, ³¹P, ¹⁹F, and ¹H) NMR spectroscopy. The NMR data show that the adducts exist in solution as a mixture of cis and trans isomers with markedly different proportions. When compared with previously described hexamethylphosphoramide (HMPA) and trimethylphosphate (TMPA) analogues, our results indicate that the cis isomer is the predominant species in solution. Low temperature ³¹P and ¹¹⁹Sn NMR spectra show that the compounds partially dissociate in dichloromethane.     

Phosphorus Derivatives of Natural Lactones. Synthesis of New Grosshemin Dialkylphosphonates

New phosphorus-containing derivatives of grosshemin were synthesized in 68-70% yield by reacting this guaianolide with dialkylphosphites. Their structures were established by IR, PMR, ¹³C NMR, and ³¹P NMR spectroscopies and two-dimensional ¹H-¹H NMR spectroscopy (COSY). The reaction of grosshemin with dialkylphosphites was found to be highly stereoselective.     

Beryllium(II) Complexes with Bis(dimethylamino)phosphorylfluoride: A Multinuclear NMR (31P, 19F,and 9Be) Characterization in Solution

Complexes of beryllium chloride and nitrate with (Me₂N)₂P(O)F were characterized in solution by multinuclear NMR spectroscopy and in some cases by IR spectroscopy and conductimetry. ³¹P and ¹⁹F NMR spectra were informative of changes associated with complex formation revealing resonances consistent with different species in solution and suggest an equilibrium between these species in both beryllium derivatives. These compounds show narrow lines in the solution ⁹Be NMR spectra, indicative of a highly symmetric environment for beryllium. The presence of the different species was more pronounced in beryllium chloride complexes. The results are compared to those reported in the literature for hexamethylphosphoramide (HMPA).     

Synthesis, molecular conformation, vibrational and electronic transition, isometric chemical shift, polarizability and hyperpolarizability analysis of 3-(4-methoxy-phenyl)-2-(4-nitro-phenyl)-acrylonitrile: a combined experimental and theoretical analysis

This work presents the synthesis and characterization of a novel compound, 3-(4-Methoxy-phenyl)-2-(4-nitro-phenyl)-acrylonitrile (abbreviated as 3-(4MP)-2-(4-NP)-AN, C₁₆H₁₂N₂O₃). The spectroscopic properties of the compound were examined by FT-IR, UV–vis and NMR (¹H and ¹³C) techniques. FT-IR spectrum in solid state was observed in the region 4000–400 cm⁻¹. The UV–vis absorption spectrum of the compound which dissolved in chloroform was recorded in the range of 200–800 nm. The ¹H and ¹³C NMR spectra were recorded in CDCl₃ solution. To determine lowest-energy molecular conformation of the title molecule, the selected torsion angle is varied every 10° and molecular energy profile is calculated from 0° to 360°. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP/6-31G(d,p) basis set. The dipole moment, linear polarizability and first hyperpolarizability values were also computed using the same basis set. A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The HOMO and LUMO analysis were used to elucidate information regarding charge transfer within the molecule. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR spectrum. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. Comparison of the calculated frequencies, NMR chemical shifts, absorption wavelengths with the experimental values revealed that DFT and TD-DFT method produce good results. The linear polarizabilities and first hyperpolarizabilities of the studied molecule indicate that the title compound can be used as a good nonlinear optical material. The thermodynamic properties of the studied compound at different temperatures were calculated, revealing the correlations between standard heat capacity, standard entropy, standard enthalpy changes and temperatures.     

Gold(III)pentafluorophenylarylazoimidazole: Synthesis and spectral (H, C, COSY, HMQC NMR) characterisation

Reaction of [Au^III(C₆F₅)₃(tht)] with RaaiR′ in dichloromethane medium leads to [Au^III(C₆F₅)₃ (RaaiR′)] [RaaiR′=p-R-C₆H₄-N=N-C₃H₂-NN-l-R′, (1-3), R = H (a), Me (b), Cl (c) and R′= Me (1), CH₂CH₃ (2), CH₂Ph (3), tht is tetrahydrothiophen]. The nine new complexes are characterised by ES/MS as well as FAB, IR and multinuclear NMR (¹H,¹³C,¹⁹F) spectroscopic studies. In addition to dimensional NMR studies as¹H,¹H COSY and¹H¹³C HMQC permit complete assignment of the complexes in the solution phase.     

Amino-substituted gem-diphosphonic acids: structures of complexes with divalent metal cations in aqueous solutions

A comparative study of complexation of acids R₂N(CH₂)_nCR"(PO₃H₂)₂ (R = H or Me; R" = OH or H; n = 1 or 2) with the Ca²⁺, Mg²⁺, Zn²⁺, and Cu²⁺ cations in aqueous solutions was carried out by vibrational (IR and Raman) and electronic spectroscopy using the data of ESR spectroscopy and conformational analysis (molecular mechanics). The MOPCPO chelate ring is formed in all ML and MHL complexes. The involvement of the N atom in coordination was found only in the Cu²⁺ complexes and is determined by the structure of the ligand. The relationship between the stability constants and the structures of the complexes in aqueous solutions is analyzed.