Numerical solutions to the time-dependent Bloch equations revisited

The purpose of this study was to demonstrate a simple and fast method for solving the time-dependent Bloch equations. First, the time-dependent Bloch equations were reduced to a homogeneous linear differential equation, and then a simple equation was derived to solve it using a matrix operation. The validity of this method was investigated by comparing with the analytical solutions in the case of constant radiofrequency irradiation. There was a good agreement between them, indicating the validity of this method. As a further example, this method was applied to the time-dependent Bloch equations in the two-pool exchange model for chemical exchange saturation transfer (CEST) or amide proton transfer (APT) magnetic resonance imaging (MRI), and the Z-spectra and asymmetry spectra were calculated from their solutions. They were also calculated using the fourth/fifth-order Runge-Kutta-Fehlberg (RKF) method for comparison. There was also a good agreement between them, and this method was much faster than the RKF method. In conclusion, this method will be useful for analyzing the complex CEST or APT contrast mechanism and/or investigating the optimal conditions for CEST or APT MRI.     

Phosgene‐free synthesis of polypeptides: Useful synthesis for hydrophobic polypeptides through polycondensation of activated urethane derivatives of α‐amino acids

We report a useful synthetic method of polypeptides using a series of urethane derivative of α‐amino acids (l ‐leucine, l ‐phenylalanine, l ‐valine, l ‐alanine, l ‐isoleucine, l ‐methionine), which are readily synthesized by N‐carbamoylation of tetrabutylammonium salts of α‐amino acids with diphenyl carbonate. Heating these urethane derivatives in N,N‐dimethylacetamide in the presence of n‐butylamine successfully gave the corresponding polypeptides with well‐defined structures through polycondensation with the elimination of phenol and CO₂. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry investigation showed that the resulting polypeptides had an n‐BuNH₂‐incorporated initiating end and an amino group at propagating end. These results strongly indicated that primary amines served as an initiator in this polycondensation system. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3726–3731     

Analytical Hartree–Fock wave functions for the atoms Cs to Lr

 Analytical approximations to Hartree–Fock wave functions are constructed using Slater-type functions for the ground states of all 49 neutral atoms from Cs (Z=55) to Lr (Z=103). The current compilation is more extensive and more accurate than previous ones. The wave functions are available upon request from the authors or from the Web page http://www.unb.ca/chem/ajit/download.htm on the Internet. Received: 6 December 1999 / Accepted: 29 February 2000 / Published online: 12 May 2000     

Charge and radial correlations in helium and helium-like atoms

Summary For two-electron atoms, the method of a variable exponent, which treats the orbital exponent (or effective nuclear charge) of an electron as an explicit function of the radial coordinate of the other electron, is studied. The method is shown to improve the energy and other electronic properties remarkably. An incorporation of the variable exponent into the Kellner approximation for He, for example, gives the energy –2.872 606 1 a.u., which is lower than the original Kellner energy by 0.024 949 8 a.u. and exceeds the Hartree-Fock limit energy by 0.010 926 1 a.u. The improvement due to the variable exponent originates from the inclusion of the charge and radial correlations. Applications of the method to the Eckart and Hylleraas approximations are also presented.     

Influences of product gases on the kinetics of thermal decomposition of synthetic malachite evaluated by controlled rate evolved gas analysis coupled with thermogravimetry

An instrument of controlled rate evolved gas analysis (CREGA) coupled with TG‐DTA was constructed for analyzing the influences of product gases on the kinetics and mechanism of the thermal decomposition of solids that produce more than one gaseous products at the same stage of reaction. The thermal decomposition of synthetic malachite, Cu₂(OH)₂CO₃, was subjected to the measurements of CREGA‐TG under controlled concentrations of H₂O and CO₂ in the reaction atmosphere with taking account of self‐generated H₂O and CO₂ during the course of reaction. By a series of CREGA‐TG measurements carried out under various atmospheric conditions, it was reconfirmed that the reaction is accelerated and decelerated by the effects of atmospheric H₂O and CO₂, respectively. From the kinetic analysis of the CREGA‐TG curves and results of high temperature X‐ray diffraction measurements under various reaction atmospheres, it was revealed that the anomalous effects of atmospheric H₂O on the reactivity and on the reaction rate of the thermal decomposition of synthetic malachite appear at the early stage of the reaction. Usefulness of the CREGA‐TG technique for measuring the kinetic rate data for the thermal decomposition of solids was demonstrated in the present study, by emphasizing the importance of quantitative control of self‐generated reaction atmosphere. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 346–354, 2005     

Stereoselective reactions. XVIII. Synthesis and cytotoxicity of the demethyl derivatives of steganes

Demethyl derivatives of steganes and deoxypodorhizon, 3, 4, 6, 7, 9, 10, 12, 13, 18, 23, were prepared by the selective demethylation of the methoxy group of steganes and deoxypodorhizon, 2, 5, 8, 11, 22. The cytotoxicity of these derivatives was evaluated against KB cell and was found not to exceed that of the parent steganes. 4-Demethyldeoxypodorhizon (18) was found to show more potent cytotoxicity than deoxypodorhizon.     

Demonstration of laser-frequency upshift by electron-density modulations in a plasma wakefield

In a plasma wake wave generated by a high power laser, modulations of the electron density take the shape of paraboloidal dense shells, moving almost at the speed of light. A counterpropagating laser pulse is partially reflected from the shells, acting as relativistic flying mirrors, producing a time-compressed frequency-multiplied pulse due to the double Doppler effect. The counterpropagating laser pulse reflection from the plasma wake wave accompanied by its frequency multiplication (with a factor from 50 to 114) was detected in our experiment.     

Vibronic Structures in Absorption and Fluorescence Spectra of Firefly Oxyluciferin in Aqueous Solutions

To elucidate the factors determining the spectral shapes and widths of the absorption and fluorescence spectra for keto and enol oxyluciferin and their conjugate bases in aqueous solutions, the intensities of vibronic transitions between their ground and first electronic excited states were calculated for the first time via estimation of the vibrational Franck–Condon factors. The major normal modes, overtones and combination tones in absorption and fluorescence spectra are similar for all species. The theoretical full widths at half maximum of absorption spectra are 0.4–0.7 eV and those for the fluorescence spectra are 0.4–0.5 eV, except for phenolate‐keto that exhibits exceptionally sharp peak widths due to the dominance of the 0–0′ or 0′–0 band. These spectral shapes and widths explain many relevant features of the experimentally observed spectra.     

Acid-induced conformational alteration of cis-preferential aromatic amides bearing N-methyl-N-(2-pyridyl) moiety

A series of cis-preferential aromatic N-methyl amides was designed and synthesized, and acid-induced conformational alteration of these compounds was investigated by means of NMR measurements in solution and X-ray crystal structure analysis. Compounds with a terminal N-methyl-N-(2-pyridyl) amide unit showed acid-induced conformational change from cis to trans, while those with a terminal N-methyl-2-pyridinecarboxamide unit showed a change of the carbonyl orientation from anti to syn with retention of cis conformation.     

Phenomenological kinetics of the thermal decomposition of sodium hydrogencarbonate

Aiming to find rigorous understanding and novel features for their potential applications, the physico-geometrical kinetics of the thermal decomposition of sodium hydrogencarbonate (SHC) was investigated by focusing on the phenomenological events taking place on a single crystalline particle during the course of the reaction. The overall kinetics evaluated by systematic measurements of the kinetic rate data by thermogravimetry under carefully controlled conditions were interpreted in association with the morphological studies on the precursory reaction, mechanism of surface reaction, structure of the surface product layer, diffusion path of evolved gases, crystal growth of the solid product, and so on. The precursory reaction was identified as the decomposition of impurity, taking place at the boundary between the surface of the SHC crystal and the adhesive small SHC particles deposited on the surface. In flowing dry N(2), the thermal decomposition of SHC proceeds by two-dimensional shrinkage of the reaction interface controlled by chemical reaction with the apparent activation energy of about 100 kJ mol(-1), after rapid completion of the surface reaction and formation of porous surface product layer. Atmospheric CO(2) and water vapor influence differently on the overall kinetics of the thermal decomposition of SHC. Added gas phase of CO(2) slightly inhibits the overall rate because of the increasing contribution of the surface reaction. Under higher water vapor pressure, the physico-geometrical mechanism of the surface reaction changes drastically, indicating the preliminary reformation of reactant surface and the formation of needle crystals of solid product on the surface. The mechanistic change and extended contribution of the surface reaction result in the deceleration of the surface reaction and acceleration of the established reaction.