(1)H-(17)O nuclear-quadrupole double-resonance study of hydrogen disorder in 2-nitrobenzoic acid

Temperature dependence of (17)O nuclear quadrupole resonance frequencies was measured in solid 2-nitrobenzoic acid by a (1)H-(17)O nuclear quadrupole double resonance technique. The experimental results show the presence of a fast exchange of hydrogen atoms between two nonequivalent positions within the O-H ellipsis O hydrogen bonds. The hydrogen disorder is ascribed to concerted jumps of two hydrogen atoms within the hydrogen bonds connecting two molecules in a dimer. The energy difference DeltaE of the two hydrogen configurations is equal to DeltaE = 60 meV = 5.8 kJ/mol. The dipole structure of the (17)O NQR lines from the C-O-H oxygen positions was also measured at -100 degrees C and at room temperature. The orientation of the principal axes of the electric field gradient tensor with respect to the O-H bond and the sign of the quadrupole coupling constant were determined. The oxygen-hydrogen distance R(O-H), as determined from the dipole structure of the (17)O NQR lines is at -100 degrees C equal to 0.099 nm. At room temperature we observe a longer distance, R(O-H) = 0.101 nm, in agreement with the hydrogen intrabond exchange.     

Temperature dependence of79BrNQR frequency in cadmium strontium,barium, zinc,magnesium and nickel bromates

The⁷⁹Br quadrupole resonance in cadmium, strontium, barium, zinc, magnesium and nickel bromates is studied in the range 77 to 305 K. The temperature dependence of the resonance frequencies in these systems has been analysed on the basis of the torsional motion of the BrO ₃ ⁻ groups. The torsional frequency and its temperature behaviour have been analysed.     

The effects of stoichiometry and structure on the dynamic torsional properties of a cured epoxy resin system

The dynamic torsional characteristics of a difunctional, bisphenol-A-type epoxy resin cured with different amounts of metaphenylene diamine, using two cure cycles, were determined in torsion at four frequencies between ?150° and 200°C. Besides two prominent relaxations, α and β, a third broad, but not very intense, relaxation has been shown to be present in all samples in the intermediate temperature range and has been designated the α transition. An analysis of the data on the temperature and frequency dependence of these relaxations allows some insight into their possible molecular origins. The torsional moduli were found to be related to the molecular packing, as reflected in their densities.     

Application of polymer-bound 4-(bromomethyl)-3-nitrobenzoic acid for synthesis of trisubstituted 1,4-benzodiazepine-2,3-diones

A method utilizing polymer-bound 4-(bromomethyl)-3-nitrobenzoic acid as a key precursor leading to 1,4-benzodiazepin-2,3-dionescaffold is described. It involves afour-step sequence including nucleophilic displacement,acylation, simultaneous reduction-cyclization and alkylation,providing rapid access to the title compounds in excellent yieldand purity.     

A field-cycling NMR investigation of resonant spin-lattice relaxation features arising from tunnelling methyl groups

(1)H nuclear spin-lattice relaxation has been investigated in sodium acetate trihydrate and sorbic acid using field-cycling NMR in the solid state. The relaxation is dominated by the reorientation of the methyl groups. Resonant features arising from coherent tunnelling are observed in both the magnetic field dependence of the spin lattice relaxation rate, T(1)(-1)(B(z)) and in the inverse temperature dependence, T(1)(-1)(1/T). The two systems have different barrier heights and tunnelling frequencies, providing different perspectives on the tunnel resonance phenomena. The magnetic field dependence enables different spectral density components to be separately investigated and in the carboxylic acid, sorbic acid, concerted proton transfer in the hydrogen bonds is also identified at low field and low temperature. The methyl hindering barriers and the correlation times characterising the reorientational dynamics has been accurately determined in both materials.     

Pulsed excitation of luminescence in dihydrated oxalic acid

Luminescence has been excited by an a.c. electric field in oxalic acid dihydrate at temperatures 273, 283 and 293 K. The voltage and frequency dependence of the emitted light flux has been studied. The brightness (B) has been observed to increase with voltage (V_rms) and frequency (v). The relation b = b₀ exp(-b/V^{$\text{1}\text{2}$_rms)} describes the voltage dependence of brightness quite accurately at frequencies greater than 500 Hz. The brightness wave forms at different voltages and frequencies of the applied field have also been studied. One primary and one secondary peak have been observed in each half cycle of the applied sinusoidal voltage.     

Rotational tunnelling and methyl group reorientation in Sn(CH3)4 by inelastic neutron scattering and nuclear magnetic resonance

Tunnelling frequencies, torsional excitations and spin-lattice relaxation times have been measured at various temperatures in tetramethyltin using INS and NMR techniques. All the results can be explained in terms of the molecular and crystal structure which establishes the existence of two types of non-equivalent methyl groups in the ratio 3∶1. The more frequent CH₃(1) groups show a tunnel splitting of 13.3 μeV and a torsional excitation of 13.2 meV in the ground state, and an activation energy of 1.9 kJ/mol. The corresponding values for CH₃(2) are 1.72 μeV, 17.7 meV and 3.4 kJ/mol, respectively. Rotational potentials have been derived using tabulated eigenvalues. The experiment confirms the theory of Hewson on the temperature dependence of tunnelling states.     

Structural,optical, thermal and mechanical characterization of an organic nonlinear optical material: 4-methyl-3-nitrobenzoic acid single crystal

Organic single crystals of 4-methyl-3-nitrobenzoic acid (4M3N) have been grown by slow evaporation solution growth technique at room temperature. The single crystal X-ray diffraction study reveals that 4M3N crystallizes in monoclinic system with space group P21/n. The crystalline perfection of the crystal was analyzed by high resolution X-ray diffraction (HRXRD) measurements. The functional groups present in 4M3N have been identified from FT-IR and FT-Raman spectra. The lower cut-off wavelength of 4M3N is found to be 404 nm and the optical band gap is calculated as 2.91 eV. The refractive index shows normal behavior with wavelength. The physio chemical changes, decomposition and stability of the 4M3N compound were established by TG-DTA studies. Vickers microhardness measurement concludes that 4M3N belongs to soft material (n=2.5) category. The LDT value is found to be higher than that of KDP and some of the important organic NLO materials. The third order nonlinear refractive index and nonlinear absorption coefficient of the 4M3N have been measured by Z-scan studies. The imaginary and real parts of the third-order susceptibility values were determined as Im χ³=9.129×10⁻¹¹ esu and Re χ³=1.4034×10⁻⁹ esu respectively. The dislocation density was calculated to be 3.0448×10⁶ cm⁻² which indicates the quality of the crystal.     

Rotational, internal rotational, and translational motion of acetic acid and dimethyl sulfoxide in their liquid mixture (with some results for DMSO dissolved in MeOH)

The proton magnetic relaxation rate of DMSO in the mixture 33.3 mole % DMSO + 66.7 mole % CD₃COOD has been measured in the temperature range 3.5 < 1000/T < 6.0 K and at six frequencies 6 < ν < 144 MHz. The intramolecular relaxation rate was determined by the aid of the isotopic substitution technique. The rotational correlation time of “the molecule” and the time constant of the internal motion have been extracted from these experimental results. The corresponding measurements were also performed on DMSO in the solvent CD₃OD (71 mole %) where no internal motion effect appeared in the temperature dependence of the relaxation rate. Furthermore, proton relaxation rates of the acetic acid methyl group and deuteron relaxation rates of the acid methyl and OD group are reported. Again, the data are given in the temperature range as above and for a number of frequencies. Rotational time correlation functions g(t) for the axid molecule are derived. Finally we present experimental results for the self-diffusion coefficients of both mixture partners DMSO and AcH and of DMSO in the solvent MeOH.     

On possibility of a structural transition in the vicinity of the melting point in liquid copper

The temperature dependence of the kinematic viscosity of liquid copper has been studied by the method of torsional vibrations during heating and cooling within the temperature range 1080–1500°C. A reversible structural transition was discovered in the vicinity of 1170°C. This transition manifests itself in a jumpwise change of viscosity and the activation energy of viscous flow at this temperature.     

Relation between the photoreaction of p-nitrobenzoic acid onto silver-coated filters and the surface roughness, as detected by SERS and AFM

The SERS of p-nitrobenzoic acid has been first obtained in Ag hydrosol and compared with those deriving from filtration of colloidal silver. The roughness of the Ag-coated filters has been examined by AFM measurements and related to the SERS enhancement. The addition of chloride anions to the colloidal suspension strongly increases the surface roughness of the solid metal substrates and activates the photoreaction of the adsorbate by irradiation with green laser light.     

Effect of temperature on IR-absorption of diphenyl

In this work, the temperature dependence of the intensities of the IR absorption bands corresponding to the fundamental vibrations, overtones and combination frequencies of diphenyl is presented. A thorough discussion of the interpretation of the fundamental modes of vibration has been made on the basis of the temperature dependence of the intensities of these absorption bands.The structure of the diphenyl molecule has been the subject of numerous investigations. Despite a considerable amount of work on the Raman(1), IR(3,4,5) and ultraviolet (2) spectra, the assignment of the fundamental frequencies has not yet been established with certainty, Some assistance can be obtained from the temperature dependence of the IR spectrum of this material.     

Degradation of 4-chloro 2-aminophenol using combined strategies based on ultrasound,photolysis and ozone

The present work investigates the degradation of 4-chloro 2-aminophenol (4C2AP), a highly toxic organic compound, using ultrasonic reactors and combination of ultrasound with photolysis and ozonation for the first time. Two types of ultrasonic reactors viz. ultrasonic horn and ultrasonic bath operating at frequency of 20 kHz and 36 kHz respectively have been used in the work. The effect of initial pH, temperature and power dissipation of the ultrasonic horn on the degradation rate has been investigated. The established optimum parameters of initial pH as 6 (natural pH of the aqueous solution) and temperature as 30 ± 2 °C were then used in the degradation studies using the combined approaches. Kinetic study revealed that degradation of 4C2AP followed first order kinetics for all the treatment approaches investigated in the present work. It has been established that US + UV + O₃ combined process was the most promising method giving maximum degradation of 4C2AP in both ultrasonic horn (complete removal) and bath (89.9%) with synergistic index as 1.98 and 1.29 respectively. The cavitational yield of ultrasonic bath was found to be eighteen times higher as compared to ultrasonic horn implying that configurations with higher overall areas of transducers would be better selection for large scale treatment. Overall, the work has clearly demonstrated that combined approaches could synergistically remove the toxic pollutant (4C2AP).     

The millimeter wave rotational spectrum of lactic acid

The results of a comprehensive investigation of the rotational spectrum of lactic acid over the frequency region 171-318 GHz are reported. Some supersonic expansion measurements at 8-16 GHz have also been made. A complete set of octic level constants in the asymmetric rotor Hamiltonian has been determined for the ground vibrational state from a fit to over 1000 measured transition frequencies. Spectroscopic constants have also been determined for the first five excited states of the low frequency, 60 cm⁻¹, torsional vibrational mode, and for four other vibrationally excited states. Vibrational states become rather crowded above 200 cm⁻¹, with seven different states only in the next 100 cm⁻¹, and almost all of the measured states in this energy region show evidence of perturbations. The analysis was carried out with the newly developed AABS software package for Assignment and Analysis of Broadband Spectra.     

Chain dynamics in the low-temperature phases of lipid membranes by electron spin-echo spectroscopy

Spin-echo decays of spin-labelled phospholipids have been recorded to study the chain dynamics in the low-temperature phases of dipalmitoyl phosphatidylcholine membranes with and without 50 mol% cholesterol. The phase-memory relaxation time, T(2M), depends on the position of spin-labelling in the sn-2 chain, and on the presence of cholesterol. A biphasic temperature dependence of T(2M) is obtained over the range 150-270 K. Echo-detected field-swept absorption EPR spectra were recorded as a function of the echo delay time, tau. The echo-detected EPR lineshapes show a strong dependence on tau, revealing anisotropic phase relaxation arising from torsional chain motions. Cholesterol has a large effect on torsional oscillations about the chain long axis. Small-amplitude chain motions in the low-temperature phases may be important for cryopreservation of membranes.     

Nuclear magnetic resonance studies of surface interactions between trifluoromethanesulfonic acid and silica

The nature of the interaction between trifluoromethanesulfonic acid (triflic acid) and the surface groups of silica as a support has been investigated by¹H and¹⁹F-NMR studies. The¹⁹F-NMR spin-lattice relaxation time (T ₁) dependence on temperature suggests that the dominant relaxation mechanism for¹⁹F is a combination of spin-rotation (SR) interactions, one of which seems to be quenched by cage-like structures. This mechanism is activated by the treatment followed to stabilize the acid on silica. Hydrogen proton relaxation seems instead to be driven by dipolar interactions and the formation of hydrogen bridges. Activation energies have been estimated for various cases, assuming an Arrhenius-type temperature dependence for the correlation times of molecular motion. A linear dependence of¹H chemical shift on inverse temperature was also found, which is interpreted as thermal weakening of hydrogen bonding. The results support the conclusion that the stability of triflic acid on silica is due to the formation of strong hydrogen bridges between the sulfonic groups of triflic acid and the silica surface hydroxyls, provided a network structure similar to that observed for pure acid is obtained in which strong interactions between acid molecules occur. The acid seems to be organized as solid-like “drops” on the silica surface, which accounts for the long residence time on the silica surface.     

Electrical conductivity and dielectric properties of sulfamic acid doped polyaniline

The temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε″) is studied for different samples of polyaniline (PANI), doped with different concentration of sulfamic acid in the frequency range (10–100 kHz) and temperature range (300–400 K). The dc conductivity has also been measured to see the effect of sulfamic acid and the conduction mechanism has been explained by the propagation of polaron through a conjugated polymer chain due to shifting of double bonds (alternation), which gives rise to electrical conduction.     

Viscosity of In100 − xSbx molten alloys in the vicinity of equiatomic composition

The viscosity of In–Sb liquid alloys has been measured in the vicinity of equiatomic concentration (40–60 at.% Sb). The measurements were carried out by a torsional oscillation viscometer. Temperature dependence of viscosity coefficient shows the Arrhenius like behavior with anomalous increase near the melting temperature. It is shown that viscosity isotherms reveal a sharp maximum at equiatomic composition, which becomes smoother with temperature increase.     

Torsional vibrations of a shaft with non-uniform cross section

A solution is presented for the equation governing the propagation of torsional waves in shafts with variable cross sections. The solution permits one to treat several types of profiles, and in particular to compute the natural frequencies of an axisymmetrical shaft with various kinds of end conditions. Computed frequencies for three kinds of end conditions are compared with those of an equivalent cylindrical shaft, particularly with respect to the dependence on the geometrical characteristics.     

Heat generation in a torsional spring subjected to sinusoidal oscillations

The effect of thermomechanical coupling in a viscoelastic hollow cylinder subjected to sinusoidal shear stresses or shear displacements has been studied. The problem is a simple model of torsional springs made of rubberlike materials. The material is assumed to be thermorheologically simple. A non-linear boundary value problem is formulated for the almost steady mechanical oscillation coupled with a slowly varying temperature distribution. The wave motion is analyzed by the well-known WKB approximation. Corresponding temperature distributions are calculated numerically by iterative procedures. Although the applied stress and applied displacement are small, significant temperature rises are found. Different stress and temperature distributions are compared for various frequencies.