Theoretical and experimental study of the inelastic neutron scattering spectra of β-5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one

The inelastic neutron scattering (INS) spectra of β-5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (β-NTO) are presented to 1400 cm⁻¹. The β-NTO vibrational frequencies observed differ considerably from the -NTO vibrational frequencies and normal mode frequency calculations for the isolated molecule. The INS spectrum contains detail unobserved in the previous IR studies, including combinations and overtones of the phonon and internal modes of β-NTO. The INS spectra are compared with periodic DFT calculations to show that the periodic DFT results correctly predict the solid-state molecular vibrational frequencies.     

A density functional derived vibrational force field for β-ionone Use of the ultraviolet resonance Raman intensities to check the vibrational analysis accuracy

In the present article we aim to determine an accurate and transferable molecular force field for β-ionone in order to perform molecular dynamics calculations on the retinal isomers. For β-ionone, a force field is derived from calculations using the Density Functional Theory (DFT). The force constants expressed in the internal coordinate space were scaled fitting theoretical to experimental vibrational wavenumbers. The validity of the force field was checked using a comparison between calculated and observed resonance Raman intensities obtained from the A-term part (Franck–Condon) of the scattering tensor.     

Spatial structure of β-substituted alkoxyvinyl trifluoromethyl ketones

Spatial structure of six β-substituted enones, with common structure R₁O–CR₂CH–COCF₃, were R₁ = C₂H₅, R₂ = H (ETBO); R₁ = R₂ = CH₃ (TMPO); R₁ = C₂H₅, R₂ = C₆H₅ (ETPO); R₁ = C₂H₅, R₂ = 4- O₂NC₆H₄ (ETNO); R₁ = C₂H₅, R₂ = C(CH₃)₃ (ETDO) were investigated by ¹H and ¹⁹F NMR, infrared spectroscopy and AM1 calculations. NMR spectra revealed that enones (MBO), (ETBO) and (TMPO) are exclusively (3E) isomers, whereas in (ETPO), (ETNO) and especially in (ETDO) the percentage of (3Z) isomers is significant and depends on the nature of solvents. Conformational behaviour of studied enones are determined by the rotation around of CC double bond, C–C and C–O single bonds (correspondingly trifluoroacetyl and alkoxy groups), and (EZZ) conformer being the most stable in all cases. IR spectra revealed that with the exception of (ETDO) (EZZ) conformer is most populated in all cases. Bulky substituents like phenyl or tert-butyl group at β-position of enone result in the equilibrium mainly between (EZZ) and (ZZZ) forms, whereas β-hydrogen and β-methyl substituents determine the equilibrium between (EZZ) and (EEZ) or (EZE) conformers.     

Vibrational spectroscopic detection of H-bonded β- and γ-turns in cyclic peptides and glycopeptides

The conformation of N-glycoproteins and N-glycopeptides has been the subject of many spectroscopic studies over the past decades. However, except for some preliminary data, no detailed study on the vibrational spectroscopy of glycosylated peptides has been published until recently.

This paper reports FTIR spectroscopic properties in DMSO and TFE of the N-glycosylated cyclic peptides cyclo[Gly-Pro-Xxx(GlcNAc)-Gly-δ-Ava] 3a and 3b in comparison with data on the non-glycosylated parent peptides cyclo(Gly-Pro-Xxx-Gly-δ-Ava) 2a and 2b [a, Xxx = Asn; b, Xxx = Gln; δ-Ava = NH-(CH₂)₄-CO] and N-acetyl 2-acetamido-2-deoxy-β- -gluco pyranosylamine (GlcNAc-NHAc, 4). The assignment of amide I band frequencies to conformation is based on ROESY experiments and determination of the temperature coefficients in DMSO-d₆ solution. (For the synthesis and NMR characterization of 2a and 3a see Ref. [19].)

Cyclic peptides are expected to adopt folded (β- and/or γ-turn) conformations which may be fixed by intramolecular H-bonding(s). A comparison of the temperature coefficients of the NH protons and amide I band frequencies and intensities suggests that in DMSO there is no significant difference in the backbone conformation and H-bond system of the N-glycosylated models and their parent cyclic peptides. The common feature of the backbone conformation of models 2 and 3 is the predominance of a 1 ← 4 (C₁₀) H-bonded type II β-turn encompassing Pro-Xxx or Pro-Xxx(GlcNAc), respectively. The ROESY connectivities in the Asn(GlcNAc) model (3a) have not been found to reflect intramolecular H-bondings between the peptide and the sugar.

The unique feature of the FTIR spectra in DMSO of the cyclic models is the lack or weakness of low-frequency (< 1640 cm⁻¹) amide I component bands. In TFE the amide I region of the FTIR spectra shows an increased number of components below 1650 cm⁻¹ reflecting a mixture of open and H-bonded β- and γ-turn conformers.

Because of its destabilizing effect upon γ-turns and other weakly H-bonded structures, DMSO decreases the number of backbone conformers. DMSO also destroys side-chain-backbone H-bondings of type C₇, C₆ or C₈. Possible ‘glyco’ C₇ H-bondings in GlcNAc-NHAc (4) or in glycopeptides 3a and 3b cannot resist the effect of DMSO either.

The FTIR data in TFE of models 2–4 suggest that the acceptor amide group of strong C₇ H-bondings in peptides and glycopeptides absorbs at 1630 ± 5 cm⁻¹ and that of bifurcated H-bondings between 1600–1620 cm⁻¹.     

Vapour phase chemistry of oxovanadium iv β-diketonates

A series of fluorinated and one non-fluorinated β-diketonate complexes of oxovanadium IV have been prepared, their gas phase IR spectra examined, vapour pressures determined and their vapour phase thermal decomposition investigated. Decomposition of the fluorinated complexes occurred according to the overall reaction scheme VO(β-diket)₂»VOF₂ + Furanone. The furanones C₅HF₅O₂, C₅H₄F₂O₂ and C₈H₁₀F₂O₂ were isolated and identified. The non-fluorinated complex gave the parent diketone and a vanadium oxide as its principal products.     

Controversy about β-tricalcium phosphate

The calcium phosphate which corresponds to the formula Ca₃(PO)₄ · nH₂O (2<n<3) was isolated from solutions with Ca/P molar ratio 0.2 and pH 7. The compound was characterised by chemical and thermogravimetric analyses, Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction. The FTIR spectra were compared with spectra of β-tricalcium phosphate (β-TCP) in the atlases for analysis of urinary calculi and other literature data.     

An improved synthetic method and vibrational study of (pentamethylcyclopentadienyl) dicarbonylrhenium dihalides (η-C5Me5)Re(CO)2X2 (X = C1, Br and I)

An improved synthetic method has been found for the preparation of the pentamethylcyclopentadienyl rhenium dicarbonyldihalide complexes. From the reaction of (η⁵-C₅Me₅)Re(CO)₃ with Br₂ or I₂ in THF-H₂O a mixture of cis and trans isomers of (η⁵-C₅Me₅)Re(CO)₂X₂ X = Br and I is formed. On the other hand, the reaction of [(η⁵-C₅Me₅)Re(CO)₃C1][SbC1₆] in water gives the cis-(η⁵-C₅Me₅)Re(CO)₂C1₂ complex. The solid IR spectra of the dicarbonyldihalide complexes are recorded and an assignment of the normal modes in terms of local symmetry is suggested by comparison with those observed in analogous molecules. A normal coordinate analysis performed using a modified general valence force field and considering simplified models, confirms most of the experimental assignments. The set of valence force constants reflects the structure of the isomers under study.     

Update of the anharmonic force field parameters of the ozone molecule

A new set of spectroscopic constants of the ¹⁶O₃ molecule (ω_i, x_ij, y_ijk, γ^DD, _i^X, β_ij^X,…), which determine vibrational dependence of band centres and rotational parameters, is derived from recent accurate analysis of high-resolution experimental ro-vibrational spectra through the theoretical approach based on second-order perturbation expansions in normal coordinates accounting for Darling–Dennison resonance interactions. These values are used to update empirical values of anharmonic coefficients (k_ijl, k_ijlm) of the potential function expansion in normal coordinates. Quadratic f_rr, f_r, f_rr′, f as well as cubic f_rst and quartic f_rstl force constants in internal (bond lengths, bond angle) coordinates are also derived. A detailed discussion is devoted to the accuracy of parameter determination for each of four steps of calculations. It is emphasised that the conventional method based on the inversion of formulae of the perturbation theory gives the largest uncertainties at the last step of calculations: the determination of the anharmonic force field in internal coordinates.     

Structure cristalline et conformation en solution aqueuse de la carnosine (β-alanyl-L-histidine)

Carnosine (β-alanyl-L-histidine) is a biologically active molecule involved in muscular metabolism. It crystallises in the C; space group with a = 24.725 Å b = 5,427 Å c = 8,004 Å β = 100,2° (Z = 4)

In the crystal, acid and basic groups are engaged in hydrogen bonds whose strength is evaluated through IR frequencies. Molecular conformation in the solid state is defined by τ₁ = /t-177° τ₂ = −38° φ = −96° ψ = +131° χ₁ = 181° χ₂₁ = 62°

NMR study of carnosine in aqueous solution indicates that rotation about CH₂-CH₂ is free and that the other angles take the following values: Ø −150° or −90° and X₁ = 165° or 315°. Infrared and Raman spectra suggest that τ₂ undergoes small changes when going from crystal to solution while ψ is close to +150°.     

Normal coordinate and infrared band intensities of trichloronitromethane and trichloroacetate ions

Laser Raman and IR spectra in the region 50–3000 cm⁻¹ for trichloronitromethane and trichloroacetate ions were recorded. All observed vibrational bands have been assigned to normal modes. Normal coordinate analyses of these molecules have been carried out in the valence force-field approximation. A set of force constants was obtained leading to good agreement between observed and calculated frequencies. The relative displacements of the atoms resulting from normal coordinate calculations were used to compute the IR band intensity of each mode by the CNDO/2-MO procedure. The intensity calculations confirmed the assignments and supported the calculated force constants.     

Vibrational spectra, conformations, ab initio calculations and vibrational assignments of 3-pentyn-2-ol

The infrared spectra of 3-pentyn-2-ol, CH₃CCCH(OH)CH₃, have been recorded as a vapour and liquid at ambient temperature, as a solid at 78 K in the 4000–50 cm⁻¹ range and isolated in an argon matrix at ca. 5 K. Infrared spectra of the solid phase at 78 K were obtained before and after annealing to temperatures of 120 and 130 K. The IR spectra of the solid were quite similar to that of the liquid.

Raman spectra of the liquid were recorded at room temperature and at various temperatures between 295 and 153 K. Spectra of an amorphous and annealed solid were recorded at 78 K. In the variable temperature Raman spectra, some bands changed in relative intensity and were interpreted in terms of conformational equilibria between the three possible conformers. Complete assignments were made for all the bands of the most stable conformer in which OH is oriented anti to C₁(a_Me). From various bands assigned to a second conformer in which OH is oriented anti to H_gem(a_H), the conformational enthalpy differences was found to be between 0.4 and 0.8 kJ mol⁻¹. The highest energy conformer with OH anti to C₃(a_C) was not detected.

Quantum-chemical calculations have been carried out at the MP2 and B3LYP levels with a variety of basis sets. Except for small basis set calculations for which the a_H conformer had slightly lower energy, all the calculations revealed that a_Me was the low energy conformer. The B3LYP/cc-pVTZ calculations suggested the a_Me conformer as more stable by 0.8 and 8.3 kJ mol⁻¹ relative to a_H an a_C, respectively. Vibrational wavenumbers and infrared and Raman band intensities for two of the three conformers are reported from B3LYP/cc-pVTZ calculations.     

EPR study of selected gadolinium complexes: β-diketonates and polycarboxylates

The gadolinium chelates with: acetylacetone—Gd(acac)₃ · 3H₂O, thenoyltrifluoroacetone—Gd(TTA)₃ · 2H₂O, benzoylacetone—Gd(BAC)₃ · 2H_2O, ethylenediaminetetraacetate Gd(EDTA) and diglycolate Gd(DGA)₃ have been chosen for EPR study (X band). The EPR spectra of these complexes were obtained in the form of badly separated signals and thus were difficult to interpret. In order to improve the spectra resolution a computer analysis based on Fourier transform was applied. This analysis permitted a considerable increase in resolution of the spectra and revealed the fine structure of Gd³⁺ ion in the condensed phase.     

Calculation of CO(XΣ) + 0(P) recombination chemiluminescence spectrum

Relative emission spectra for the bent to linear, CO₂(¹B₂)---CO₂(X¹Σ⁺_g) transitions have been calculated using the model: harmonic oscillator, symmetric-top wavefunctions and energy levels for CO₂(¹B₂); first-orer Fermi resonance vibrational wavefunctions and energy levels for CO₂(X¹Σ⁺_g); a Boltzmann distribution of vibrational and rotational states in CO₂(¹B₂); and a constant electronic transition moment. With the literature CO₂(¹B₂) molecular structure, spectra calculated using this model show characteristics similar to the low-temperature chemiluminescence from the combination of atomic oxygen and carbon monoxide. The calculated spectra account for experimental band positions to wavelengths of 570 nm and the weak dependence of the spectra on temperature over the range 206–353 K. The latter result was obtained from a CO₂(¹B₂) bending fundamental of 600 cm⁻¹. The calculated spectra also show a violet-shift in intensity and an attenuated band structure at higher temperatures. The magnitude of these effects depends on the CO₂(¹B₂) force constants and not on the CO₂(¹B₂) molecular structure.     

Crystallographic analysis of atomic structures and the phenomenological mechanism of crystallization

A theoretical study of the structure and vibrational spectrum of methyl-β-D-glucopyranoside is performed with allowance for the hydrogen bond effect on them. At the density functional theory level with the use of the B3LYP functional in the 6–31G(d) basis set the structural dynamic models of a free molecule of methyl-β-D-glucopyranoside and its simplest complexes with hydrogen bonding in the form of dimers with different structures are constructed. Energies are minimized; structures, electro optical parameters, force constants, and normal vibrational frequencies in the harmonic approximation and their intensities in IR spectra are calculated; the hydrogen bond energy is estimated. Based on the calculation, the conclusions are drawn about the structure of the methyl-β-D-glucopyranoside sample, the formation and interpretation of its IR spectrum, and the possibilities of the used density functional theory method.     

Synthesis, structural characterization and ab initio calculation of dipyridyltetraazathiapentalene: a highly conjugative polycyclic molecule with hypervalent N–S–N bond

A highly conjugative polyheterocyclic compound, tetraazathiapentalene fused with pyridine rings, was synthesized by reacting 2-aminopyridine with carbon disulfide. The single crystal X-ray determination reveals that the molecule crystallizes in monoclinic space group C2/c, with the following unit cell dimensions: a=11.062(2), b=9.030(1), c=20.898(5) Å, β=102.98(1)°, V=2034.00(3) Å³, Z=8, and that a hypervalent N–S–N bond exists in the molecule. Ab initio calculations predict its IR and ¹H NMR spectra that are coincident with the experimental ones and reveal the bonding nature of the hypervalent N–S–N bond and the electronic structure of the molecule.     

Pure vibrational raman spectra of some simple molecular crystals: γ-O2, O2 in hcp ar, β-N2

Resolved spectra of the pure vibrational Raman scattering in single oriented crystals of -γ-O₂, 6% O₂ in hcp ar, and β-N₂ are reported. Two components of different width were observed in γ-O₂, while a single, very narrow (0.027 cm⁻¹) line was observed in β-N₂.     

Polarised vibrational spectra of KH2PO3 single crystal

Polarised IR and Raman spectra for KH₂PO₃ single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO₃ groups.

The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions.     

Vibrational spectrum of [(CD3)3S]I and normal coordinate calculations for [(CH3)3S] and [(CD3)3S] cations

IR (4000-30 cm⁻¹) and Raman (4000-0 cm⁻) spectra of [(CD₃)₃S]I have been observed, together with those of [(CH₃)₃S]I. By assuming a C_3v molecular symmetry for the cations [(CH₃)₃S]⁺ and [(CD₃)₃S]⁺, all the active fundamentals of [(CD₃)₃s]⁺ have been assigned and normal coordinate calculations have been carried out by a symmetry force field for [(CH₃)₃S]⁺ and [(CD₃)₃S]⁺. The strength of the S---C and C---H bonds in the compound has been compared with that in dimethyl sulfide by using their valence stretching force constants.     

β-Ga2O3∶Cr3+近红外长余辉纳米颗粒的制备及发光性能

以三乙二醇为表面配体, 利用沉淀法制备了β-Ga₂O₃∶Cr³⁺近红外(NIR)长余辉纳米颗粒. 考察了反应条件对β-Ga₂O₃∶Cr³⁺的发光性能和晶体结构的影响, 并初步探讨了其NIR余辉发光机理. 结果表明, 当溶液的pH值为7, 煅烧温度为700 ℃时, 可获得高纯度的β-Ga₂O₃∶Cr³⁺纳米颗粒, 其平均粒径为30 nm, 最大余辉发射波长可调控为750 nm, NIR余辉发光时间长于384 h. 本方法得到的β-Ga₂O₃∶Cr³⁺长余辉纳米颗粒不仅尺寸小, 而且NIR余辉时间长, 发射波长可调控, 在低背景噪音的深组织活体成像中具有潜在的应用前景.     

Interaction between β-cyclodextrin and ionic liquids in aqueous solutions investigated by a competitive method using a substituted 3H-indole probe

We report herein the interaction of three kinds of ionic liquids, i.e., 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF₄) and 1-butyl-3-methylimidazolium chloride (bmimCl) with β-cyclodextrin (β-CD) using 2-(p-aminophenyl)-3,3-dimethyl-5-carboethyoxy-3H-indole (1) as a fluorescent probe through a competitive method. The formation of the 1:1 (guest:host) inclusion complex was suggested and the association constants at different temperatures were estimated, from which the thermodynamic parameters ΔG^Θ, ΔH^Θ and ΔS^Θ were also obtained. The negative entropy and enthalpy changes indicated that the formation of above inclusion complexes was entropically unfavorable and enthalpy-driven. Conductivity measurements were also employed to study above systems. The results showed agreement with those based on the competitive method. Furthermore, through NMR, the location of anions in the system of ILs and β-CD was investigated. We suggested that the anion was accommodated to a great extent by the cavity forming ion pair with imidazolium cation which was totally in the cavity of β-CD. The above work demonstrated that molecule 1 is a very sensitive fluorescence probe for studying the interaction of a non-fluorescent guest with cyclodextrins.