The role of the doubly excited configurations in the π-electronic structure of the croconate anion

The electronic structure of the croconate anion is investigated by the semi-empirical VESCF method with CI including up to the doubly excited configurations. The effect of the doubly excited configuration is quite large in the lowest singlet state which turns out to be a ground state, while the calculation including only singly excited configurations produces a triplet ground state. The calculated first transition energy (¹ A₁ ¹ E₁) is in fair agreement with the observed value. The interpretation of the transition moment in case that the doubly excited configurations are included is also discussed.

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Zusammenfassung Die Elektronenstruktur des Croconat-Anions wurde mit der halbempirischen VESCF-Methode mit Konfigurationswechselwirkung, die bis zu zweifach angeregte Konfigurationen einschloß, untersucht. Der Einfluß der zweifach angeregten Konfigurationen ist im niedrigsten Singulettzustand, der sich als Grundzustand herausstellt, sehr stark. Schließt die Rechnung hingegen nur einfach angeregte Konfigurationen ein, so erhält man einen Tripletgrundzustand. Die berechnete erste Übergangsenergie (¹ A₁ ¹ E₁ stimmt gut mit dem beobachteten Wert überein. Ebenso wird die Interpretation des Übergangsmomentes für den Fall, daß auch zweifach angeregte Konfigurationen berücksichtigt werden, diskutiert.

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Resumé La structure électronique de l'anion croconique est étudieé par la méthode VESCF semi-empirique avec IC, configurations diexcitées comprises. L'effet des configurations diexcitées est très important sur l'état singulet le plus has qui est un état fundamental, alors que si l'on ne tient compte que des configurations monoexcitées on obtient un état fundamental triplet. La premiére énergie de transition calculée (¹ A₁ ¹ E₁ est en bon accord avec la valeur observee. Le moment de transition est interprété dans les cas où l'on tient compte des configurations diexcitées.

     

Synthesis and polymerization of 4-o-vinylbenzyl-2,2,6,6-tetramethylpiperidine

Some hindered amine polymers containing 2,2,6,6-tetramethylpiperidine structure were synthesized. A new monomer, 4-O-vinylbenzyl-2,2,6,6-tetramethylpiperidine, was homopolymerized and copolymerized with some vinyl monomers in the presence of AIBN as an initiator. The obtained amine polymers were oxidized with hydrogen peroxide to obtain the polymers having nitroxyl radical moiety.     

Model networks of end-linked polydimethylsiloxane chains

Summary Elastomeric networks of high extensibility were prepared by end-linking mixtures of vinyl-terminated polydimethylsiloxane chains having molecular weights of approximately 600 and 11,000 g mol^–1, with silanes chosen to give junction functionalities ranging from 3 to 8. The resulting bimodal networks were studied in elongation, at 25 °C, to their rupture points, and in swelling equilibrium in benzene at room temperature. The elongation moduli [f ^*] were found to be in satisfactory agreement with previous results obtained by end-linking hydroxyl-terminated polydimethylsiloxane chains. Values of [f ^*] at low and moderate deformations gave relatively low values of the ratio of elasticity constants 2C ₂/2C ₁, which is a measure of the extent to which the elongation changes from approximately affine to nonaffine as the elongation increases. The low values obtained for this ratio are presumably due to diminished interpenetration of configurational domains in the case of very short chains. In spite of its small magnitude, 2C ₂/2C ₁ does show some decrease with increase in , as predicted by the recent molecular theory of rubberlike elasticity developed by Flory. The swelling equilibrium results were also found to be in satisfactory agreement with theory. The elongation moduli increased significantly at high elongations, and the values of the elongation at which the upturn was first discernible were very nearly independent of , This is consistent with the interpretation of this anomalous behaviour in terms of limited chain extensibility. The maximum extensibility generally decreased somewhat with increase in and this caused a decrease in both the ultimate strength and the toughness of the elastomer, as measured by the energy required for rupture.     

The crystal structures of α- and β-CdUO4

The structural parameters of α- and β-CdUO₄ crystals are determined by X-ray powder diffraction technique. α-CdUO₄ is rhombohedral and cell parameters are a = 6.233(3) Å and α = 36.12(5)°. β-CdUO₄ crystallizes in a C-centered orthorhombic cell with a = 7.023(4), b = 6.849(3), c = 3.514 (2) Å. The space groups are $\text{R}\text{3}\text{m}$ for α-CdUO₄ and Cmmm for β-CdUO₄. α-CdUO₄: 1U in (000), 1Cd in ($\text{1}\text{2}\text{1}\text{2}\text{1}\text{2}$), 2O(1) in ±(uuu), 2O(2) in ±(vvv); u = 0.113, v = 0.350, Z = 1. β-CdUO₄: 2U in ($\text{000;}\text{1}\text{2}\text{1}\text{2}\text{0}$), 2Cd in ($\text{1}\text{2}\text{0}\text{1}\text{2}\text{; 0}\text{1}\text{2}\text{,}\text{1}\text{2}$), 4O(1) in ($\text{0, ±y, 0;}\text{1}\text{2}\text{,}\text{1}\text{2}\text{±y, 0}$), 4O(2) in ($\text{±x, 0,}\text{1}\text{2}\text{;}\text{1}\text{2}\text{±x,}\text{1}\text{2}\text{,}\text{1}\text{2}$); x = 0.159, y = 0.278, Z = 2. β-CdUO₄ contains collinear uranyl UO²⁺₂ groups with a UO(1) distance of 1.91 Å, located either along or parallel to the c axis whereas the UO(1) bond length in α-CdUO₄ is 1.98 Å which is longer than the usual uranyl bond length.     

Characterization of magnetic nanoparticles modified with thiol functionalized PAMAM dendron for DNA recovery

Magnetic nanoparticles (MNPs) modified with the thiol functionalized polyamidoamine (PAMAM) dendron were synthesized to estimate their DNA recovery capabilities. Aminosilane-modified MNPs and MNPs surrounded by a phospholipid (distearoylphosphatidylethanolamine (DSPE)) bilayer were used as core particles. Cystamine-core PAMAM dendrimers were reduced by dithiothreitol to dendron thiols and chemically conjugated to the core particles. Characterization of the synthesis revealed an increase of the surface amine charge from generation 1 (G1) to G6, starting with an aminosilane initiator. Particle size distribution analysis indicated that G6 PAMAM-modified MNPs exhibited monodispersity in an aqueous solution. G6 PAMAM-MNPs and G6 PAMAM-PE-MNPs synthesized by the proposed method have equivalent DNA recovery abilities to PAMAM-MNPs prepared by the conventional divergent synthesis method. In optimized conditions, 96% of λDNA was recovered using G6 PAMAM-PE-MNPs. Therefore, the method for preparing PAMAM-MNPs and PAMAM-PE-MNPs proposed in this study will be a novel approach for producing DNA carriers for efficient DNA purification by magnetic separation.     

The Academic Career and Accomplishments of Professor Ding Xiaxi

Professor Ding has attributed systematically and creatively in numerous fields of mathematical sciences. His great contributions include nearly 100 publications, among which there are over 90 academical papers, 4 monographs, and 3 pop-scientific books. He is among the first generation of mathematicians brought up by the new China. As a promising young man, he was selected for further study in the Institute of Mathematics in 1951 after college years. In the newly established institute, he had the opportunity of working under the guidance of Professor Hua Luogeng.