The energetics of the isomeric anthrols

We report the results of geometry optimized MP2(FULL)/6-31G(d) quantum chemical calculations with zero-point vibrational energies and thermal corrections of the isomeric 1-, 2- and 9-anthrols and the tautomeric anthrone. We find that 1- and 2-anthrols have nearly the same enthalpy of formation and are some 6?kJ?mol^?1 more stable than their 9-isomer in accord with intuition based on steric hindrance. We find that anthrone is more stable than 9-anthrol by 13.7 ± 6.4?kJ?mol^?1, in satisfactory agreement with the value of 23 ± 8?kJ?mol^?1 suggested elsewhere by experiment and its associated analysis.     

Reversibility of 1D Cellular Automata with Periodic Boundary over Finite Fields $\pmb{ {\mathbb{Z}}}_{p}$

The reversibility problem for linear cellular automata with null boundary defined by a rule matrix in the form of a pentadiagonal matrix was studied recently over the binary field ℤ₂ (del Rey and Rodriguez Sánchez in Appl. Math. Comput., 2011, doi:). In this paper, we study one-dimensional linear cellular automata with periodic boundary conditions over any finite field ℤ _p . For any given p≥2, we show that the reversibility problem can be reduced to solving a recurrence relation depending on the number of cells and the coefficients of the local rules defining the one-dimensional linear cellular automata. More specifically, for any given values (from any fixed field ℤ _p ) of the coefficients of the local rules, we outline a computer algorithm determining the recurrence relation which can be solved by testing reversibility of the cellular automaton for some finite number of cells. As an example, we give the full criteria for the reversibility of the one-dimensional linear cellular automata over the fields ℤ₂ and ℤ₃.     

一维几率性细胞自动机演化的临界相变现象分析

本文用实位置空间重整化群方法对一类特殊的一维几率性细胞自动机演化的动力学方程进行了处理,得到该细胞自动机的演化存在相变,其临界点几率参数值为P₀=0,P₁=P₂=0.5,临界动力学指数z=2,并获得了大量的计算机实验资料。     

On the law of entropy increase of some cellular automata on Zd

We consider some time-reversible cellular automata on thed-dimensional integral latticeZ ^d and study their time evolution properties. We show first that a Boltzmann-type entropy can be defined which is not less than its initial value for initial States which have no spatial correlation. For monotonic increase of the entropies for such initial States we need an additional condition which we call renewality. Under the renewality condition entropy is monotonic nondecreasing. We give some examples of cellular automata which satisfy the renewality condition     

Investigation of ionization equilibria of L-aspartic and L-glutamic acids in water at a microscopic level by DFT method

The pK_a values of different dissociable groups of L-Aspartic and L-Glutamic acids in vacuo and in aqueous medium over a wide pH range have been estimated by DFT/B3LYP/6-31G(d) and 6-31G++(d,p) methods. For both the amino acids discrete water molecules (n?=?0, 3 and 6) have been used to get the first hydration sphere. Starting from a low pH, all possible tautomers resulting from each dissociation step are assumed to exist in a cyclic equilibrium. The structures of the species involved in the dissociation and tautomerization processes have been optimized in vacuo and also in aqueous medium considering H-bonded water molecules under the PCM formalism. For obtaining pK_a in aqueous medium the difference in Gibbs energy of the clusters H₃O⁺.mH₂O and (H₂O) _m+1 (m?=?an integer) is necessary and has been evaluated from computed literature data. Calculations reveal that in vacuo the neutral or less charged species predominate but in aqueous medium the zwitterionic or more chargeable forms contribute appreciably. The Gibbs energy changes for the microscopic cyclic equilibria have been estimated theoretically. These lead to overall (macroscopic) pK_a values for the ionization steps which are in good agreement with available experimental data for both the amino acids.     

Theoretical study on the static and dynamic first-order hyperpolarisabilities of adenine tautomers

Static and dynamic electronic and vibrational first-order hyperpolarisabilities (β) of the lowest energy neutral adenine tautomers (amine forms A7 and A9) were obtained in gaseous and aqueous phases by using Hartree–Fock, Møller–Plesset second-order and fourth-order perturbation theory (MP2 and MP4-SDQ) and conventional and long-range corrected density functional theory methods with the Dunning's correlation-consistent cc-pVDZ, aug-cc-pVDZ, aug-cc-pVTZ and d-aug-cc-pVDZ basis sets. Frequency-dependent properties were calculated at the characteristic wavelength of the Nd:YAG laser (1064 nm) for the second harmonic generation and electro-optical Pockels effect nonlinear optical processes. Solvent effects were introduced under the polarised continuum model approximation. The electronic β^e values of the investigated isomers are noticeably affected by the theoretical level, basis set and solvation. In vacuum, the static and dynamic β^e values of A9 are greater than the corresponding data of A7, whereas the contribution of the solvent significantly enhances the hyperpolarisabilities of the A7 tautomer, resulting in β^e(A9)/β^e(A7) ratios between 0.5 and 0.6. The vibrational hyperpolarisabilities of the adenine tautomers are quite close to each other.     

Fluorescence Titration of Some Purines Determination of Lowest Excited-State Ionization Constants

Abstract

Excited-state ionization equilibria of 6-methyl purine and xanthine were investigated in a wide range of pH.

6-Methyl purine is known to have two ionization equilibria in its ground-state. It was found that it had one more ionization equilibrium in strongly acidic region. In the excited state, four ionization equilibria were observed. The pK? values of three of them were determined by means of fluorescence titration.

In the case of xanthine, there exist three ground-state equilibria. In the excited-state, four equilibria were observed. The pK? values of two of them were determined by means of fluorescence titration.     

Bioenergetics control by light: laser effects on a human-cell line (EUE) and yeast cells

Summary Short-time effects due to low-power, low-energy (HeNe and GaAs) laser irradiation were studied in two cellular systems: an embryonal-human-cell line (EUE) and yeast cells (Saccharomyces cerevisiae). In EUE cells ?short-term effect? as chemical-energy transduction in cytoskeletal aggregation was evaluated. In yeast cells the glycolitic CO₂ production was taken as an index of redox decarboxylative processes, while adenylnucleotides were tested to evaluated the ATP and adenylate energy charge (AEC) modification. In both cellular systems effects enhanced by laser irradiation were found. A theoretical approach (based on cellular automata) is hinted accounting for the ponderomotive forces induced by the electromagentic field. In memory of the late Prof. L. Bolognani. Also at INFM (Istituto Nazionale di Fisica della Materia)     

Evaluation of Ph and granite/hot water interaction under geothermal conditions

Abstract

The in-situ laboratory measurement of pH in a granite-hot water reaction system has been undertaken under flowing conditions. The calculation of fluid pH and multi-component chemical equilibria in the granite-hot water reaction system was made, using the calculation program SOLVEQ92. In this study, the chemical equilibrium relationship of granite and hot water interaction was also deduced using the some program. The measurement of in-situ pH in the granite-hot water reaction system was undertaken in the temperature and pressure range of 100–250°C and 20MPa respectively. The in-situ pH value shows good agreement with the pH calculation value with regard to multi-component chemical equilibria. As a result of this work, it is reasonable to suggest that the pH of reservoir fluids in geothermal system can be readily estimated by use of the SOLVEQ92 calculation program, which provides a ‘calculated’ pH value.     

On the Anomalous Absorption Spectra of Amino- and Hydroxy-Substituted Anthracenes

It has been known for some time that the longest wavelength absorption band of anthracene arises from the transversely polarized ¹L_a ← ¹A absorptive transition (1). The angular momentum forbidden ¹L_b ← ¹A transition, which is invariably at least ten-fold weaker than the former transition in the acenes has been predicted, on theoretical grounds, to be submerged in the ¹L_a ← ¹A absorption envelope (2). That the ¹L_b ← ¹A transition of anthracene does not lie much higher in energy than the ¹L_a ← ¹A transition was demonstrated by Baba and Suzuki (3) who proved that although the long-wavelength absorption band of 1-anthrol originated from the ¹L_a ← ¹A absorption, as anticipated, the long-wavelength absorption bands of 2-anthrol and its conjugate anion originated from the admixture of charge-transfer from the β-hydroxy group into the longitudinally polarized ¹A ← ¹L_b transition of anthracene.     

Towards an easy carbon dioxide reduction in aqueous solution

Abstract

The homogeneous hydrogenation of carbon dioxide into formate anion has been investigated in aqueous solution, using water soluble ruthenium(1I)-phosphine (meta-monosulphonated triphenylphosphine, TPPMS; and 1,3,5-triaza-7-phosphaadamantane, PTA) complexes as catalysts. These reactions take place in amine free medium under mild conditions, bicarbonate anion is more active than carbon dioxide in the reduction. The initial turnover frequenc of the reduction increases with increasing H₂ pressure, as it was observed in situ by C and 'H NMR spectroscopy. High pressure FT-IR were used to find evidence for the formation of the catalytically active ruthenium hydride species.     

Tetrafluoroberrylate(2) Ions as Hydrogen-Bond Proton Acceptors: Quantum Chemical Considerations

Abstract

The experimentally observed lower proton acceptor ability of the tetrafluorober-rylate(2-) anion, compared to that of the sulphate(2-) and selenate(2-) anions, was explained on the basis of various quantum chemical approaches. The geometries of the above-mentioned XY₄ ² anions were fully optimised at the ab initio HF SCF and MP2 levels of theory, as well as within the DFT (BLYP and B3LYP) approach, using the 6-311+G? and LANL2DZ basis sets. The 6-311++G(3df,3pd) basis set was also used within the DFT BLYP approach. The molecular charge distribution was partitioned among the atomic centers using the Mulliken as well as the natural population analysis. All levels of theory (both with and without inclusion of the electron correlation effects), regardless of the basis set employed, predict lower (by absolute value) atomic charge on the fluorine atom in the tetra-ftuoroberrylate(2-) anion than that on oxygen atoms in sulphate(2-) and selenate(2-) anions. The quantum chemical predictions are fully in line with the spec-troscopically observed order of the proton acceptor abilities in these anions.     

Tautomer contributions to the near UV spectrum of guanine: towards a refined picture for the spectroscopy of purine molecules

By using depopulation laser techniques, like IR-UV population labeling coupled to mass-selected R2PI detection, we confirm that four tautomers are responsible for the near UV spectroscopy (310-280 nm) of guanine: two enol and two keto forms, each pair having a 7NH and a 9NH form. Besides the UV spectroscopy of each tautomer, additional information on the excited state nature and dynamics is obtained from fluorescence studies. In particular, the quenching of fluorescence beyond 285 nm, the existence of a background absorption, as well as the existence of a strongly red-shifted component in the fluorescence emission provides evidence for a strong electronic mixing in the excited state together with an efficient non-radiative process. The details of these features are found to be tautomer-dependent. Comparison of the present results with literature data on other purine molecules, like adenine or 9-substituted guanines, enables us to propose a new insight on the spectroscopy and dynamics of the purine molecules. First, a large variability of the tautomer distribution in the gas phase is found within the purine family, in particular a molecular change, as simple as a 9-methylation on guanine, can reduce the tautomer distribution to a single species (enol form). Since the absorption spectrum is tautomer-dependent as well as substituent-dependent, it turns out that the tautomer population is one of the major parameters that control the overall shape of the UV spectrum. Second, the excited state model, often evoked in the literature, which involves electronic coupling between excited states of different natures, namely ππ^* and nπ^* states, might account for the present fluorescence measurements on guanine, providing an extensive excited state electronic mixing is assumed for these systems. Received 24 June 2002 Published online 13 September 2002     

钼、钒的单一及混合溶液中离子存在形态的拉曼光谱研究

利用拉曼光谱研究了钼、钒单一及混合溶液在pH=10.0~1.0时的离子分布行为. 钼、钒离子在存在形式上存在着差异：当pH=9.0~7.5时钒主要以(VO₃)_n^n-形式存在,而钼主要为MoO₄^2-. 这一差异是目前现有的许多钼钒分离方法的基本原理. 通过将混合溶液体系的拉曼光谱与单一体系进行对比,分析得出了混合体系中离子的存在形式. 当pH低于6.5时,部分V-O-V基团中的V原子会被Mo原子取代,从而形成了钼钒杂多酸离子. 当pH=6.0~2.0时,钒主要以十聚钒酸盐形式存在;当pH=2.0~1.0时,混合溶液中的钼主要以具有七钼酸盐结构的杂多酸离子存在,而在相同pH的单一溶液中,钼的存在形式主要为Mo₈O₂₆^4-和Mo₃₆O₁₁₂^8-.     

Nitrogen isotope fractionation factors (α) measured and estimated from the volatilisation of ammonia from water at pH 9.2 and pH 8.5

ABSTRACT

This paper examines the nitrogen isotope fractionation factors (α) associated with the volatilisation of ammonia from water under controlled conditions at two pH values (8.5 and 9.2). This experiment assumed the continuous removal of ammonia at a single purge rate of 10?mL air min^?1. The fractionation resulting from the removal of total ammonia from the water into an acid trap was named the observed isotope fractionation factor (α_obs), and it was measured as 1.019 (±0.0025) at pH 8.5 and 1.030 (±0.0025) at pH 9.2. The observed isotope fractionation factor includes the equilibrium isotope fractionation factor (α_eq) and the kinetic isotope fractionation factor (α_kin), each one mathematically derived from the experimental data. The equilibrium and kinetic isotope fractionation factors were estimated as α_eq?=?1.036 (±0.0014) and α_kin?=?1.050 (±0.003), respectively. Our results are compared to other previously measured and estimated fractionation factors.     

Relative equilibria of D2H + and H2D+

Relative equilibria of molecules are classical trajectories corresponding to steady rotations about stationary axes during which the shape of the molecule does not change. They can be used to explain and predict features of quantum spectra at high values of the total angular momentum J in much the same way that absolute equilibria are used at low J. This paper gives a classification of the symmetry types of relative equilibria of AB₂ molecules and computes the relative equilibria bifurcation diagrams and normal mode frequencies for D₂H⁺ and H₂D⁺. These are then fed into a harmonic quantization procedure to produce a number of predictions concerning the structures of energy level clusters and their rearrangements as J increases. In particular the formation of doublet pairs is predicted for H₂D⁺ from J ≈ 26.     

Substituent effect on the electrochemical behaviour of some ortho-substituted (aryl)(2-nitrobenzo[ b ]thiophen-3-yl)amines. A combined experimental and computational study

The reduction potential values of the title compounds (1Ar,o) have been evaluated by cyclic voltammetry at a platinum electrode in the presence of 0.1?M N(Et)₄BF₄ in DMSO. Compounds 1Ar,o give reversible reduction peaks. The ortho-substituent affects their values basically by electronic effects (good LFER have been observed). The peculiar behaviour of (2′-hydroxyphenyl)(2-nitrobenzo[b]thiophen-3-yl)amine 1Ar,o(i) (showing two quasi reversible systems of peaks) has been explained on the basis of the special effect of the 2′-hydroxy substituent, which is able to assist a proton transfer through a network of hydrogen bonds involving the amine nitrogen atom (proton shuttle). This behaviour is unexpected in anhydrous DMSO and has similarities with the reaction features observed in water. The above hypothesis has been confirmed by quantum-mechanical DFT calculations carried out on 1Ar,o(i). In this theoretical investigation all the possible species, that can form as a consequence of two mono-electron reduction processes and the relevant various chemical transformations involving the intermediate species, have been carefully investigated.     

Determination of 13C/12C-Ratios in Rumen Produced Methane and CO2 of Cows,Sheep and Camels

Abstract

Naturally produced methane shows different δ¹³C-values with respect to its origin, e.g., geological or biological. Methane-production of ruminants is considered to be the dominant source from the animal kingdom. Isotopic values of rumen methane—given in literature—range between ?80‰ and -50‰ and are related to feed composition and also sampling techniques. Keeping cows, camels and sheep under identical feed conditions and sampling rumen gases via implanted fistulae we compared δ_PDB ¹³C-values of methane and CO₂ between the species. Referring to mean values obtained from 4 or 5 samples at different times of 11 animals (n = 47) we calculated δ_PDB ¹³C-medians resulting in small but not significant differences within and significant differences between the species for CO₂ and methane. The δ_PDB ¹³C-differences between methane and CO₂ were statistically equal within and also between the species. Therefore a linear regression of methane values on CO₂ is appropriate and leads to: δ_PDB ¹³C(methane)‰ = 1,57 * δ_PDB ¹³C(CO₂)‰-47‰ with a correlation coefficient of r = 0,87.     

IR Study on Aqueous Solution Behavior of D-Cycloserine

IR spectra were measured for an antitubercular agent, D-cycloserine (CS), and the hydrolyzate, β-aminooxy-D-alanine (AOA) and the dimer, cis-3, 6-bis(aminooxymethyl)-2, 5-piperadinedione (CS-dimer) at various pHs in aqueous solutions. Molecular species existing in the ionic equilibria were characterized by the pH dependence of the spectra. Band assignments were carried out by reference to the spectra of D₂0 solutions and those of related compounds. Spontaneous transformation of CS to CS-dimer was observed by the IR spectra for the neutral aqueous solution. The spectral evidence suggested that the non-ionic form of CS plays a key role in the dimerization process.