Assignment of a perturbation in the FT-ICLAS spectrum of 12C2H2 around 12 709.5 cm−1

The vibrational state perturbing the J = 17 and 18 rotational states of the zero-order v ₁ + 3v ₃ state of ¹²C₂H₂ is assigned to the state with vibrational energy predicted at G _ν = 12 685.1 cm^?1 using the cluster model (El Idrissi, M. I., Liévin, J., Campargue, A. and Herman, M., 1999, J. chem. Phys., 110, 2074). The assignment is discussed also in terms of the very special pressure shift behaviour demonstrated previously for absorption lines reaching these levels (Herregodts, F., Hepp, M., Hurtmans, D., Vander Auwera, J. and Herman, M., 1999, J. chem. Phys., 111, 7961). The experimental information arising from a set-up newly running at ULB, called FT-ICLAS brings decisive information in the assignment process. This set-up is described briefly.     

Reflections on Ernest Roy Davidson: the UW years 1962–1984

In the following research acetylation as an unexplored factor in the anomeric effect in carbohydrate chemistry has been examined. Crystallographic data for methyl glycosides and their acetates have been compared and discussed. Some of the methyl glycosides form hydrogen bonding with the participation of acetal oxygen atoms. This seems to have the most significant influence on the structural diagnostic parameters for anomeric effect.

Abbreviations: Me-α-Glc: methyl α-D-glucopyranoside; Me-β-Glc: methyl β-D-glucopyranoside; Me-α-Gal: methyl α-D-galactopyranoside; Me-β-Gal: methyl β-D-galactopyranoside; Me-α-Man: methyl α-D-mannopyranoside; Me-β-Man: methyl β-D-mannopyranoside; Ac-Me-α-Glc: methyl 2,3,4,6-tetra-O-acetyl-α-D-glucopyranoside; Ac-Me-β-Glc: methyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside; Ac-Me-α-Gal: methyl 2,3,4,6-tetra-O-acetyl-α-D-galactopyranoside; Ac-Me-β-Gal: methyl 2,3,4,6-tetra-O-acetyl-β-D-galactopyranoside; Ac-Me-α-Man: methyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranoside; Ac-Me-β-Man: methyl 2,3,4,6-tetra-O-acetyl-β-D-mannopyranoside; GIPAW (Gauge Including Projector Augmented Waves) calculations: a DFT based method used for calculating nuclear magnetic resonance parameters; CP/MAS NMR: cross-polarisation (CP) magic angle spinning (MAS) NMR spectroscopy; δ_ss: chemical shift in ¹³C CP/MAS NMR spectrum; δ_t: theoretical chemical shift: as derived from GIPAW DFT; dis: distorted multiplet in ¹H NMR spectrum.     

Synthesis of deuterium-labelled halogen derivatives of L-tryptophan catalysed by tryptophanase

The isotopomers of halogen derivatives of l-tryptophan (l-Trp) (4′-F-, 7′-F-, 5′-Cl- and 7′-Br-l-Trp), specifically labelled with deuterium in α-position of the side chain, were obtained by enzymatic coupling of the corresponding halogenated derivatives of indole with S-methyl-l-cysteine in ²H₂O, catalysed by enzyme tryptophanase (EC 4.1.99.1). The positional deuterium enrichment of the resulting tryptophan derivatives was controlled using ¹H NMR. In accordance with the mechanism of the lyase reaction, a 100% deuterium labelling was observed in the α-position; the chemical yields were between 23 and 51%. Furthermore, β-F-l-alanine, synthesized from β-F-pyruvic acid by the l-alanine dehydrogenase reaction, has been tested as a coupling agent to obtain the halogenated deuterium-labelled derivatives of l-Trp. The chemical yield (～30%) corresponded to that as observed with S-methyl-l-cysteine but the deuterium label was only 63%, probably due to the use of a not completely deuterated incubation medium.     

The correlation of molecular orientation in liquid water by neutron and X-ray scattering

The neutron diffraction structure factor for heavy water at 22°c has been measured for momentum transfers, ?Q, up to a Q of 13 å ^-1. The results have been interpreted by abstracting the molecular structure effects as far as possible and using models for the correlation of orientation of pairs of molecules ranging from completely uncorrelated orientation to that for adjacent molecules in ice I. Neither these nor any of the popular models for the structure of water, nor a non-hydrogen bonded model, fit the neutron diffraction data over the whole range of Q. Nevertheless, information about the molecular-centres structure factor is obtained, especially for Q up to about 3 å ^-1.

The method of analysis is generalized and applied to x-ray diffraction data and in particular to x-ray data for liquid water. It is shown that this method of analysis has some advantages over the conventional one. The effect of correlation of molecular orientation is less than that of molecular structure on x-ray scattering by water and rather more extensive information is obtained for the molecular-centres structure factor than from neutron data—if the conventional assumption of atomic electron clouds is accepted.

A comparison of the x-ray and neutron scattering data for liquid heavy water shows that the two sets of data are reasonably consistent for any of the usual models for water, except for the region of Q between 3 and 5 å ^-1. The molecular-centres structure factor of water has a weak double humped first maximum with peaks at 2·0 å ^-1 and 2·9å ^-1, probably followed by a damped oscillation. This contrasts with atomic liquids but is similar to that found in liquid carbon tetrachloride. The structure of liquid water is not, therefore, necessarily unique or unusual.     

The absorption spectrum of 12C2D2 in the 10000–12500 cm−1 spectral region

The absorption spectrum of dideuteroacetylene has been recorded by intracavity laser absorption spectroscopy (ICLAS) in the 10 200–12 500cm^?1 spectral region. Among 25 absorption bands of ¹²C₂D₂ rotationally analysed in this spectral region, 17 are newly observed. They include one II_u-Σ⁺ _g and thirteen Σ⁺ _u-Σ⁺ _g bands starting from the vibrational ground state and eleven hot bands from the V ₄ = 1 and V ₅ = 1 lower states. The rotational structure of two excited levels is affected by a strongly J-dependent interaction with a perturber which induces intensity transfer to extra lines. The coupling is identified as a I-resonance interaction with δ_u dark states and the vibrational assignment of the perturbers is discussed. Two Σ-Σ bands of the ¹²C¹³ CD₂ species, present in natural abundance in the sample, could also be identified and rotationally analysed. Most of the corresponding excited vibrational levels of ¹²C₂D₂ were unambiguously assigned using the polyad model [Herman, M., el idrissi, M. I., Pisarchik, A., Campargue, A., Gaillot, A.-C., Biennier, L., di lonardo, G. and Fusina, L., 1998, J. chem. Phys., 108, 1377] which allows vibrational energies and B _V rotational constants to be predicted. In particular the previously highlighted 1/244 anharmonic resonance is confirmed by energy and intensity features in several {(V ₁, V ₂, V ₃, V ₄ = 0, V ₅ = 0),(V ₁ ?1, V ₂ + 1, V ₃ V ₄ = 2, V ₅ = 0)} dyads. Significant deviations between predicted and experimental energy levels are observed for a few levels and discussed.     

Spectrophotometric Studies of the Energy Consumed During Oxidative Degradation of D-Fructose

ABSTRACT

Mechanistic investigation of the oxidative degradation of d-fructose (D-Fruc) has been studied by spectrophotometric technique. Molecular mechanics (MM +) calculations suggest that the potential energy (PE/kcal mol^?1) of the d-fruc (opening structure) is at least three (3.71) times more stable than the PE of the cycling structure of the same matrix. The oxidation constant (K _ox) of the anionic form of the d-Fruc (Fruc-NaOH) is about seven times greater than that of the protonated form (Fruc-H₂SO₄). Therefore, the anionic form is more highly oxidizable than is the cationic form of this matrix. The limit of detection can be as low as 18 ppm (mg L^?1) of d-Fruc. This is about 60 times lower than the blood sugar level (BSL) or 100 times lower than that reported previously. The proposed procedure was applied successfully for the oxidation of D-Fruc in uni-fructose powder. The anionic form of D-Fruc (Fruc-NaOH) has the ability to store energy about 744.72 kJ g^?1 h at 608 nm in a condensed lightweight form. Kinetic parameters of the oxidative degradation of the anionic form of D-Fruc at different concentration were deduced. A number of models were used to evaluate the kinetic parameters. The mechanism of the degradation of D-Fruc is explained on the basis of kinetic parameters.     

The equilibrium geometry of the SC3H radical: an ab initio study

The SC₃H radical is known by experiment to have a linear equilibrium structure, but even rather high-level ab initio computations give a bent equilibrium geometry. A theoretical study of the SCCCH radical has been carried out in order to analyse the influence of several factors in the computed equilibrium structure. Quadratic configuration interaction QCISD(T) and restricted coupled cluster RCCSD(T) computations have been performed in combination with large basis sets. Spin-orbit effects have been taken into account through the Breit-Pauli Hamiltonian using multi-configuration SCF and configuration interaction wavefunctions. Our final results indicate that the equilibrium structure must be linear, in agreement with the experimental studies [McCarthy, M. C., Vrtilek, J. M., Gottlieb, C. A., Wang, W., and Thaddeus, P., 1994, Astrophys. J., 431, L127; Hirahara, Y., Ohshima, Y, and Endo, Y, 1994, J. chem. Phys., 101, 7342]. Both spin-orbit and electron correlation effects appear to be of comparable importance, but an adequate computation of the correlation energy has been much more difficult and has ultimately required basis set extrapolations.     

Thermodynamic properties of clathrates: I. The heat capacity and entropy of argon in the argon quinol clathrates

Measurements have been made of the heat capacity C_p from ～ 13°k to ～ 273°k of five clathrates of argon and β-quinol. The argon content ranged from ～ 20 per cent to ～ 80 per cent of the maximum possible amount. Over much of the temperature range studied, C_p proved to be a linear function of the argon content, but from 13°k to 20°k, and from 50°k to 100°k the relation between C_p and argon content is obscure, and may, in fact, be non-linear. Estimates have been made of the contribution to C_p made by a mole of argon in the temperature region where C_p is a linear function of composition, and these experimental values have been compared with those calculated according to the theory of J. H. van der Waals, which is based on the cell model of Lennard-Jones and Devonshire. The agreement between theory and experiment is satisfactory.     

Singlet–triplet transitions in three-atomic molecules studied by time-dependent MCSCF and density functional theory

Singlet–triplet transition moments and phosphorescence lifetimes have been calculated for the three-atomic molecules HCN, O₃, H₂O, H₂S, GeF₂, GeCl₂ and GeBr₂ by time-dependent density functional theory (DFT) utilizing quadratic response functions in order to qualify DFT which recently has become available for studies of this kind [TUNELL, I., Rinkevivius, Z., VAHTRAS, O., SALEK, P., HELGAKER, T., and ÅGREN, H., 2003, J. chem. phys., 119, 11024]. Comparison with ab initio and experimental data indicates that DFT exhibit results of similar quality as explicitly correlated methods which indicates that it indeed is a viable approach for singlet–triplet transitions. O₃ provides an intriguing example in that a systematic investigation of the singlet–triplet transition moment of its Wulf band indicates a clear advantage of the DFT technique despite the multiconfigurational character of the electronic structure of this molecule. The electronic spin–spin coupling and the hyperfine nuclear coupling constants have also been calculated in order to further characterize the triplet state in the spectra of the investigated systems.     

Enzymatic synthesis of some 15N-labelled l-amino acids

Our group has developed a stereospecific enzymatic method, which is very efficient for the in vitro synthesis of l-[¹⁵N]serine, l-[¹⁵N]methionine and l-[¹⁵N]glutamic acid. These amino acids were prepared from the corresponding α -ketoacids in the suitable enzymatic systems. The bacterial NAD-dependent amino acid dehydrogenases alanin dehydrogenase, leucin dehydrogenase and glutamate dehydrogenase were used as catalysts. Glucose dehydrogenase was used for the regeneration of NADH and ¹⁵NH₄Cl as isotopically labelled material at 99 at.% ¹⁵N. All reactions are inexpensive and easy to perform on a synthetically useful scale (1-10g) giving high yields of l-amino acids. The ¹⁵N isotope content was determined by mass spectrometry.     

The McConnell equation for E.S.R. spectra of symmetrical diazanaphthalenes

Electron spin resonance spectra of the six symmetrical diazanaphthalene anions in N,N-dimethylformamide have been measured. The anions were generated within the microwave cavity by electro-reduction of the parent compound. The McConnell equation a _H = Q _CC ^H ρ C has been tested for the diazanaphthalenes with ρ C values calculated by the Hückel method and by the Pariser-Parr-Pople S.C.F. method with variable resonance integrals.     

Isotope effects in the tyrosinase catalysed hydroxylation of l-tyrosine methyl derivatives

To investigate isotope effects in the hydroxylation of [3′,5′-²H₂]-α-methyl- and [3′,5′-²H₂]-N-methyl-l-tyrosine, they were synthesised using acid catalysed isotope exchange at high temperature. The kinetic and solvent deuterium isotope effects on V_max and V_max/K_m parameters of tyrosinase in its action on methylated derivatives of l-tyrosine were determined using the non-competitive spectrophotometric method. Lineweaver–Burk plots were used to consider the inhibition type of O-methyl-l-tyrosine, revealing that it is an uncompetitive inhibitor of tyrosinase.     

Calculation of the indirect nuclear spin-spin coupling constant of the hydrogen molecule by the truncated matrix sum method

The hydrogen molecule coupling constant has been calculated from the second-order perturbation theory summation expression of Ramsey, truncated after the first few terms. The most accurate available wave functions, those of the James-Coolidge type, give a value for the coupling constant of circa 163 hz compared with the experimental value of 278 hz. Values of the largest discrete term (the first term) calculated from various approximate wave functions vary widely. In particular, the calculation analogous to the usual molecular orbital calculation gives a value of 726 hz for the first term (compared with 199 hz calculated from James-Coolidge type wave functions).     

Free radicals in pyrimidines: E.S.R. of a γ-irradiated single crystal of 5-nitrouracil

Free radicals are observed in γ-irradiated single crystals of 5-nitrouracil with the unpaired electron showing hyperfine interaction with one nitrogen atom. The principal values of hyperfine coupling are A_x = 22·5 g, A_y = 25·2 g, and A_z = 40·0 g, and the principal values of the spectroscopic splitting factor are g_u = 2·0117, g_v = 2·0064 and g_w = 2·0027. The relationship of the directions of the corresponding principal axes to the molecular orientations show that the unpaired electron must be located in an sp ² orbital on either N₍₁₎ or N₍₅₎. Considerations of the mechanism of radical formation and comparison to radiation damage in other molecules make the N₍₁₎ location seem more probable. The π interaction of the nitro group on C₍₅₎ evidently prevents the formulation of free radicals with the unpaired electron on C₍₅₎. That carbon atom is the most common location of unpaired electron density in other pyrimidine free radicals.     

Ro-vibrational spectra of C2H2 based on variational nuclear motion calculations

A published ab initio-based potential energy surface and newly constructed dipole moment surface of acetylene have been used to compute vibrational band intensities. The line intensity calculations employed the variational nuclear motion code WAVR4 for computation of wave functions and energy levels, and a newly developed code DIPOLE4 for computation of dipole transitions. Owing to the high computational cost of J > 0 transitions using direct variational methods only J = 0 and J = 1 states and transitions have been computed variationally. The intensities of J > 1 transitions were extrapolated from J = 0 and J = 1 using Hönl–London coefficients. The resulting effective rotational constants B and transition intensities are compared with experimental data for the (3ν₄ + ν₅) combination band, the ν₃ and the ν₅ fundamental band. The prospects of using this procedure for extensive calculations of a hot line list, important for cool stars and extrasolar planets are discussed.     

Real figure of two-dimensional spin-echo NMR spectra for a homonuclear two-spin system in rotating solids

Two-dimensional (2D) spin-echo NMR experiments have been carried out on polycrystalline [2,3-¹³C₂]-alanine under magic-angle sample spinning (MAS) conditions, so that two unusual resonance lines emerged along the F₁ axis (Kuwahara, D., Nakai, T., Ashida, J., and Miyajima, S., 1999, Chem. Phys. Lett., 305, 35). To examine the spectral structure observed in the F₁ direction more closely the 2D NMR experiment was undertaken using a sufficiently small t_l increment, yielding many more resonance lines on a spectrum sliced along the F₁ axis. The line distribution had a very unique and interesting structure. To elucidate the line positions theoretically, the signal for the 2D spin-echo experiment performed with any t₁ increment was calculated analytically for a homonuclear two-spin-1/2 system undergoing MAS. Virtually six resonance lines (exactly 12 resonance lines) occurred on a spectrum sliced along the F₁ axis. In addition, it was demonstrated that the intensities of some resonance lines were largely dependent on the dipolar interaction.     

A re-examination of the I.R. spectrum of dinitrogen trioxide

Assuming a planar geometry of C _s symmetry and using a Urey-Bradley potential field, the force constants of dinitrogen trioxide have been re-determined within the formalism of Wilson's G-F matrix method. The outcome of the present investigation suggests a new set of force constants some of which are drastically (～ 50 per cent) different than those previously reported. Furthermore, since the i.r. frequencies used in the present investigation were obtained both in the solid state and at low temperatures, the mean amplitudes of thermal vibrations of both ¹⁴N₂O₃ and ¹⁵N₂O₃ are given at 77°k. Finally, it is suggested that more isotopic i.r. data is necessary to ascertain unequivocably the geometry of dinitrogen trioxide.     

50 years at the forefront of Physics

Mathemtical Techniques and Physical Applications. By J. Killingbeck and G. H. A. Cole. (Amdemic Press, 1971.) [Pp. xiv + 715.] £7£00. Scope: Textbook; reference. Level: Postgraduate; undergraduate.

Group Theory in Solid-state Physics. By H. W Streitwolf (Macdonald, 1971.) [Pp. 248.] £5·00. Scope: Textbook. Level: Postgraduate.

Statistical Physics. By Ya. P. Terletskii. (North-Holland, 1971.) [Pp xv+279.] $6·30. Scope: Textbook. Level: Postgraduate; undergraduate.

Ubsersichtsbeiträge zur Gasdynamik. Edited by E. Leiter and J. Zierep. (Springer-Verlag, 1971.) [Pp. 386.1 $40·70. Scope: Treatise. Level: Specialist/postgraduate.

Classical Theory of Particles and Melds. Vol. I and Vol. II. By K. H. Ruei. (University Press, Taiwan, Republic of China, 1971.) [Pp.: Vol. I, xxiii + 359; Vol. II, xxvi + 424.] Scope: Textbook. Level: Postgraduate; undergraduate.

Topics in Mathematical Physics. Vol. II: Spectral Theory and Wave Processes. By M. Sh. Birman. (Consultants Bureau, 1971.) [Pp. v + 121.] $14·00. Scope: Treatise. Level: For specialists only.

An Introduction to the Theory of Electromagnetic Waves. By A. C. Hewson. (Longman, 1971.) [Pp. viii+ 115.] £ 1·60. Scope: Textbook. Level: Undergraduate.

Modern Physics and Quantum Mechanics. By Elmer E. Anderson. (W. B. Saunders Co. Ltd., 1971.) [Pp. xi+430.] £6·20. Scope: Textbook. Level: Undergraduate.

Polarized Light and Optical Measurement. By Clarke and Grainqer. (Pergamon Press, 1971.) [Pp. viii+ 187.] £3·50 ($9·50.). Scope: Treatise. Level: Specialist/postgraduate.

Phenomena in Ionized Gases 1971. Edited by R. N. Franklin. (Donald Parsons, 1971.) [Pp. xl+450.] £12·00.

Technology Today. Edited by Edward de Bono. (Routledge &; Kegan Paul Press, 1971.) [Pp. xii+ 144.] Cloth edition £1·75; Paperback 50p. Scope: Survey. Level: General reader.

Diffusion Data. No. 1. Edited by DR. F. H. Wohlbier. (Trans Tech Publications, 1971.) [Pp. 289.] Scope: Library (reference). Level: Specialist/postgraduate.     

Improved one-centre wave functions for the hydrogen and methane molecules

Corrections are made to the Joy-Parr hydrogen and the Saturno-Parr methane one-centre wave functions and the functions are accurately reminimized with respect to the energy. The electronic wave functions and total molecular energies are obtained for various internuclear distances and the equilibrium internuclear distance and the breathing force constant determined. Three methods for calculating the force constant are given and compared. The equilibrium bond length for hydrogen is found to be 1·38 a.u. (experimental, 1·40 a.u.) and the force constant 6·33 md/å (experimental, 5·75 md/å). For methane the equilibrium C-H distance is found to be 2·014 a.u. (experimental, 2·05 a.u. and the force constant 25·8 md/å (experimental, 23·5 md/å). The total computed molecular energies for the equilibrium configurations of hydrogen and methane are -1·1605 a.u. (experimental, -1·175 a.u.) and -39·8444 a.u. (experimental, -40·51 a.u.) respectively.     

Potential energy surfaces for the Walden inversion reaction

A semi-empirical valence bond calculation of potential surfaces for the gas phase reaction between methyl bromide and chloride ion is described. The system is treated in a four participant electron approximation with precautions to include the effects of orthogonalization to the core electrons not involved in bond formation during reaction. The core is taken to include the methyl group as a single fragment whose valence state energy is determined by hybridization at the carbon atom. The qualitative features of the surface are confirmed by a less extensive CNDO calculation.

The lowest potential surface is found to have a central dip, the minimum energy being 0·98 ev below the energy of the reaction products when the C-Cl distance is 3·60 a.u., the C-Br distance 4·11 a.u., and the H-C-Br angle 86°. Analogy with classical two-body scattering suggests that at incident energies of less than 2 ev, the reaction cross section is of the order of 10(1 + 1/E) å ², where E, the initial energy of relative motion, is in ev.