Quantum‐Chemical Investigation of Hydrogen Bonds in Porphin

Using the DFT Becke–Lee–Yang–Parr exchangecorrelation threeparametric functional (B3LYP), we have calculated the geometry, the electron density distribution, and the vibration frequencies for pyrrole, porphin, and their 13 analogs with a regularly varying structure. It is shown that the determining role in the change in the frequencies of stretching and outofplane deformation vibrations of porphin compared to pyrrole is played by intramolecular hydrogen bonds at the porphyrin macroring center. We have separately considered and compared with the data for porphin complexes of pyrrole with different intermolecular hydrogen bonds: with an aromatic ring (NH··· cluster formed by the pyrrole selfaggregation in the liquid state) and an unshared electron pair (NH···OH₂ and NH···NC₄H₄ clusters). The degree of participation of the NH group in the hydrogen bonds increases in the series NH··· cluster, porphin, NH···OH₂ and NH···NC₄H₄ clusters.     

Relationship between Hansen Solubility Parameters and Lewis Acid–Base Parameters of Polymers

Hansen solubility parameters and Lewis acid–base parameters are two groups of parameters that are used to characterize solvents, polymers, and the interactions between polymer matrix and additives. Although their definitions are very different, they can well explain the interactions in polymer composites. Therefore, some relations should exist between them. In this paper, the Lewis acid–base parameters of three polymers (PET, PS, and PVA) were measured by IGC technique. Including five other polymers (PE, PMMA, PC, PVC, and PVDF), the relationship between total Lewis acid–base intensity (K _a+K _b) and total polar intensity (δ² _p+δ² _h) of the eight kinds of polymers are discussed, where δ_p and δ_h are the polar components of the Hansen parameters. It is found that these polymers are all Lewis base polymers according to the values of K _b/K _a. Generally, a polymer with a larger (K _a+K _b) value possesses a higher (δ² _p+δ² _h) value.     

A Preliminary Study of the Relationship between Lewis Acid–Base Parameters and Structure of Polymers

Acid–base theory is an important method to describe the interaction between materials. The inverse gas chromatography (IGC) technique can be used to measure the surface Lewis acid–base parameters of materials. Compared with the solubility parameter method, the merit of the IGC technique is that it can give the surface acid–base properties of many undissolvable materials, such as inorganic materials, metal‐oxides, and thermosetting polymers. In this paper, six polymers are chosen to discuss the rationality of their Lewis acid–base parameters from the molecular structure viewpoint. Compared with some small molecules, the values of these polymers are reasonable. However, endowing each group with a set of acid–base parameters is impossible at this stage because of the lack of sufficient data. Thus more characterization work is needed to develop the IGC method.     

Group VI Dinuclear Oxo Metal Complexes of Salicylideneimine‐2‐anisole Schiff Base

Interaction of the Schiff base salicylideneimine‐2‐anisole (salanH) with Cr(CO)₆ yielded the dicarbonyl derivative Cr₂O₂(CO)₂(salan)₂. The dinuclear oxo complex M₂O₄(salan)₂, M?Mo and W, was isolated from the reaction of M(CO)₆ with salanH. Elemental, spectroscopic and magnetic studies of the reported complexes allowed structures to be proposed. The thermal properties of the complexes were investigated by thermogravimetry.     

Fluorescence Quenching of UVITEX‐OB by Aniline in Alcohols and Alkanes

Fluorescence quenching of UVITEX‐OB [2,5‐thiophenediylbis(5‐tert‐butyl‐1,3‐benzoxazole)] by aniline in different polar and nonpolar solvents was examined at room temperature by steady‐state fluorescence measurements. Positive deviations from the nonlinear Stern–Volmer plots were observed in most of the solvents indicating the extent of quenching to be large. The quencher concentration dependence data were analyzed using ground‐state complex and sphere of action static quenching models in order to interpret the results. The magnitudes of the quenching rate parameters suggest that a sphere of action static quenching model is expected to describe the data most accurately. Also, the results are suggestive of both static and dynamic quenching processes being responsible for the observed positive deviation in the Stern–Volmer plot. Experimental results are described by an equation derived using the finite sink approximation model, which allows the evaluation of diffusion‐limited interaction and the estimation of encounter distance and mutual diffusion coefficient independently.     

Intramolecular Hydrogen Bond in Steroid 5‐Hydroxy‐6‐Ketones and 5‐Hydroxy‐6‐Ketoximes of the Stigmastane Series

The intramolecular hydrogen bond in steroid 5hydroxy6ketones and 5hydroxy6ketoximes of the stigmastane series has been investigated by the method of IR spectroscopy. It is shown that 5hydroxy groups in cisA/Bsteroids are linked by the intramolecular hydrogen bond with polar substituents at C₃ and C₆. These hydrogen bonds are lacking in corresponding transA/Bsteroids. According to the IR spectra, intramolecular associates of polymer type are formed in 5hydroxy6hydroxyminosteroids.     

Equation of state for technetium from X‐ray diffraction and first-principle calculations

The ambient temperature equation of state (EoS) of technetium metal has been measured by X-ray diffraction. The metal was compressed using a diamond anvil cell and using a 4:1 methanol-ethanol pressure transmitting medium. The maximum pressure achieved, as determined from the gold pressureEquation of state for technetium from X-ray diffraction and first-principle calculations scale, was 67 GPa. The compression data shows that the HCP phase of technetium is stable up to 67 GPa. The compression curve of technetium was also calculated using first-principles total-energy calculations. Utilizing a number of fitting strategies to compare the experimental and theoretical data it is determined that the Vinet equation of state with an ambient isothermal bulk modulus of B_0T=288 GPa and a first pressure derivative of B′=5.9(2) best represent the compression behavior of technetium metal.     

Spectroscopic and Conductance Studies of New Transition Metal Complexes with a Schiff Base Derived from 4‐Methoxybenzaldehyde and 1,2‐bis(p‐Aminophenoxy)ethane

Four new metal complexes of Cu(II), Ni(II), Zn(II) and Co(III) with Schiff base derived from 4‐methoxybenzaldehyde and 1,2‐bis(p‐aminophenoxy)ethane have been prepared and characterized by magnetic susceptibility, conductance measurements, elemental analyses, UV–Vis, ¹H NMR and IR spectra studies. The magnetic and spectroscopic data indicate an octahedral geometry for the six‐coordinate complexes. The ligand was used for complexation studies. Stability constants were measured by means of a conductometric method. Furthermore, the stability constants for complexation between ZnCl₂, Cu(NO₃)₂ and AgNO₃ salts and ligand (L) in 80% dioxane–water and pure methanol were determined from conductance measurements. In 80% dioxane–water, he stability constants (log Ke) increase inversely with the crystal radii in the order Ag(I) < Zn(II) < Cu(II).     

High‐Resolution Submillimeter Wave Spectroscopy of Hydrogen Sulphide with Heterodyne Spectrometer

A submillimeter heterodyne spectrometer using continuous wave optically pumped molecular laser as local oscillator and Schottky diode as mixer was developed at Physical Research Laboratory, Ahmedabad (India) for quantitative spectroscopy of polyatomic molecules in laboratory. The experimental details of spectrometer and its application to study of molecular line parameters are presented. In particular line strength, collision line width (self and foreign) of H₂S 5_5,05_4,1 transition¹(579.799 GHz) have been measured. Air molecules have been used as foreign (perturbing) molecules taking Earths atmosphere into consideration².     

Solvent Dependence of Tautomeric Equilibria of 1‐(o‐Substituted Phenyl)Barbituric and ‐2‐Thiobarbituric Acid Derivatives

Abstract

The enolisation tendencies of 1‐(o‐substituted phenyl)barbituric and ‐2‐thiobarbituric acid derivatives have been studied by observing the behaviour of the compounds in different solvents by ¹H and ¹³C NMR. It has been found that the enolisation tendencies of the thiobarbituric acid derivatives observed in polar solvents are greater than those of the barbituric acid derivatives. The ratio of keto–enol tautomers of thiobarbituric acid derivatives in DMSO and in DMF has been calculated.     

Possible Explanation of the Negative Values of m_ve~2Obtained from the β-Spectrum Shape Analyses

By comparing the results obtained using the same experimental data of CIAE but different theoretical formula fits it is pointed out that the negative value of mv2 is most likely stemmed from inaccuracy of the theoretical formula of the β-spectrum.     

CNDO/2 Calculations for Hydroxy Stretching Bands of Intramolecular Hydrogen Bonds in cis−Cyclohexane-1,3-Diol and cis−3-Aminocyclohexanol

CNDO/2 calculations are used to predict the hydroxy stretching frequency and intensity of the intramolecular hydrogen bonds in the title compounds. The predictions are compared with experimental data.     

Rayleigh Scattering Experiment for the Measurement of Hydrogen Cluster Size

The hydrogen clusters are produced at liquid nitrogen temperature in a supersonic adiabatic expansion of moderate backing pressure gases into vacuum through a Laval nozzle and their averaged size are measured by Rayleigh scattering. The average cluster size N^-c is about 250 hydrogen atoms at a backing pressure 1.0 MPa in these measurements.     

Calculation of the Tautomeric Properties of 3‐Formyl‐Tetrinic Acid by the ab initio and DFT Methods

We have carried out a nonempirical quantumchemical calculation with full optimization of the geometry of all theoretically possible tautomeric forms of 3formyltetrinic acid (FTRA) according to the Møller–Plesset secondorder perturbation theory with the use of a 6–31G(d) double zeta basis set. The correlation corrections to the total energy of molecules for optimized geometric configurations were calculated in the 631G(d,p) basis. All the possible tautomeric forms of FTRA and the harmonic vibrational frequencies were also calculated within the density functional theory (DFT) with the use of the Perdew–Burke–Ernzerhof (PBE) functional in a threeexponent basis. It is shown that FTRA in vapors (in the perfect gas approximation) exists in the form of a mixture of three enol forms, among which two exoforms predominate. The frequencies and forms of normal vibrations for each cisenol tautomer in the region of vibrations of ketogroups and double bonds differ widely, which permits identification of the tautomers present in the mixture. The possible mechanisms of enolenol transformations of 3acyltetrinic acids are discussed.     

To the Problem of the Water Transparency Bandwidth (1.8–11.2 eV) and Hydrogen Bonds

It is experimentally detected the gravity center of theOHband of Raman scattering (RS) of picosecond pulses in water shifts by ~40 cm^?1 (~0.005 eV) to the high-frequency wing due to shortening the time of observation of the hydrogen bond restructuring in comparison with RS of nanosecond pulses. It was shown that declarative negation of hydrogen bonds and the introduction of the water transparency window half-width (5 eV) or (11.2 eV as seen in Fig. 1 of the paper by V. G. Artemov [Bulletin of the Lebedev Physics Institute 42, 187-191 (2015)] should be regarded as incorrect. These values multiply exceed the well known half-width in the range of 650–360 nm (~1.8 eV [1] which is defined by the fundamental absorption region and OH stretching vibration band overtones from the side of UV and IR regions, respectively.     

Infrared Study (3700 - 3000 cm−1) of Hydrogen Bonds Involving Triphenyl Derivatives of Group V Elements

The hydrogen bonded complexes between hydroxylic derivatives and nitrogen bases have been extensively studied by infrared spectrometry but very few experimental results are available for bases involving other elements of group V. Some thermodynamic or spectroscopic data have however been reported for the interaction between alcohol derivatives or phenol and trialkyl- or triphenylphosphine derivatives^1–5 but the electron donor ability of the other compounds is not clearly established especially in the case of phenyl derivatives who have n-and π-electron-donor centers. In this case, the properties of the hydrogen bond can be investigated as a useful tool for the evaluation of the donor properties of the heteroatom and the nature of his interaction with the π ring system⁶. In this work, we have determined the thermodynamic constants and the frequency shifts of the ν_OH stretching vibration of hydrogen bonded complexes involving phenol derivatives and triphenylarsine. The influence of the acidity of the phenol molecules on the properties of the complexes is discussed. Some additional data are reported for complexes involving Ph₃X derivatives (X = N,P,Sb) and discussed as a function of the ionization potential of the heteroatom and the π-ring electrons.     

Flow‐Injection Chemiluminescence Study of Luminol–Hydrogen Peroxide–Carbendazim System

Abstract

A new flow‐injection chemiluminescence (CL) method is described for the determination of carbendazim. The method is based on the CL reaction of luminol and hydrogen peroxide (H₂O₂). Carbendazim can greatly enhance the chemiluminescence intensity in sodium hydroxide–sodium dihydrogen phosphate (NaOH–NaH₂PO₄) medium (pH=12.6). Under the optimum conditions, the linear range for the determination of carbendazim is 2.00×10^?8 to 2.00×10^?6 g mL^?1 with a detection limit (S/N=3) of 7.24×10^?9 g mL^?1. The relative standard deviation is 1.8% for 1.0×10^?7 g mL^?1 carbendazim (n=8). The proposed method has been applied to the determination of carbendazim in tap‐water samples. Furthermore, the possible enhanced CL mechanism is discussed by examining the CL spectra and fluorescence spectra.     

A 2-Hydroxy-1-naphthaldehyde Schiff Base for Turn‐on Fluorescence Detection of Zn2+ Based on PET Mechanism

Journal of Fluorescence - Zinc ion is closely related to human health. Its content in human body is small, while the effect is large. However, it is not the more the better, must be in a scientific...