Explicitly correlated multireference configuration interaction with multiple reference functions: avoided crossings and conical intersections

We develop an explicitly correlated multireference configuration interaction method (MRCI-F12) with multiple reference functions. It can be routinely applied to nearly degenerate molecular electronic structures near conical intersections and avoided crossings, where the reference functions are strongly mixed in the correlated wave function. This work is a generalization of the MRCI-F12 method for electronic ground states, reported earlier by Shiozaki et al. [J. Chem. Phys. 134, 034113 (2011)]. The so-called F12b approximation is used to arrive at computationally efficient formulas. The doubly external part of the wave function is expanded in terms of internally contracted configurations generated from all the reference functions. In addition, we introduce a singles correction to the CASSCF reference energies, which is applicable to multi-state calculations. As examples, we present numerical results for the avoided crossing of LiF, excited states of ozone, and the H(2)?+?OH (A(2)Σ(+)) reaction.     

A stereocontrolled formal total synthesis of (±)-thienamycin

The stereocontrolled synthesis of a key intermediate 20 for the preparation of (±)-thienamycin 1 is described. The key steps in the synthesis are the formation of the β-lactam ring by cyclization of the amide 5 via a complete S_N2 mechanism, and the stereospecific conversion of the azetidinone 5 to the amide (trans-11) which have the correct relative configurations at three contiguous chiral centres. The mechanism of the conversion of the azetidinone 16E to the N-free azetidinone 17 and the selenide compound 18 is presumed.     

Efficiency in the loading of a sodium magneto-optical trap from alkali metal dispensers

We study the loading of sodium atoms into a magneto-optical trap from current-controlled sodium metal dispensers. Contrary to what was previously reported [V. Wippel, C. Binder, W. Huber, L. Windholz, M. Allegrini, F. Fuso, E. Arimondo, Eur. Phys. J. D 17 (2001) 285] we demonstrate a significantly higher number of trapped atoms that make Na dispensers a feasible source of atoms for cold-atom studies. The inherent rise in pressure that naturally arises from metal dispensers as they are heated to release atoms is partially controlled by placing the metal dispensers near the pumping port where an ion pump is connected. We also study the effects of placing the sodium dispensers at different distances from the main vacuum chamber where the atoms are trapped and the effectiveness of using a Zeeman slower to cool the atoms as they emerge from the dispensers. We observe trapping of up to 1.9 × 10⁸ atoms, which is significantly higher by almost three orders of magnitude than previously reported experiments.     

Photophysical properties and photocatalytic activities of bismuth molybdates under visible light irradiation

Aurivillius structure Bi(2)MoO(6) (BG: 2.70 eV) that is a low-temperature phase showed an intense absorption band in the visible light region and photocatalytic activity for O(2) evolution from an aqueous silver nitrate solution under visible light irradiation, among various bismuth molybdates (Bi(2)MoO(6), Bi(2)Mo(2)O(9), and Bi(2)Mo(3)O(12)) synthesized by solid-state and reflux reactions. Bi(2)Mo(3)O(12) (BG: 2.88 eV) also showed photocatalytic activity for O(2) evolution under full-arc irradiation of a Xe lamp (lambda > 300 nm). The photocatalytic activity of the Aurivillius structure Bi(2)MoO(6) prepared by the reflux method was dependent on the annealing temperature after the preparation. The crystallinity was the important factor for the activity. Calculation by the density functional method indicated that the conduction band of Aurivillius structure Bi(2)MoO(6) was made up of Mo 4d orbitals. It turned out that the visible-light absorption of this photocatalyst was due to the transition from the valence band consisting of O 2p orbitals to the conduction band. The corner-sharing structure of the MoO(6) octahedra contributed to the visible light response and the photocatalytic performance because excitation energy and/or photogenerated electron and hole pairs began to migrate easily in the Aurivillius structure.     

Disubstituted 1,6-methano[10]annulene derivatives for use in organic light-emitting diodes

Bis(carbazolylphenyl) and bis(diphenylaminophenyl) derivatives of 1,6-methano[10]annulene, which is luminescent material and contains seven-membered rings, are synthesized. The bis(phenylcarbazole) derivative 3 have high melting point and glass transition temperature. Electroluminescence characteristics of organic light-emitting diodes using these methano[10]annulenes were investigated.     

Sub‐Bandgap Excitation‐Induced Electron Injection from CdSe Quantum Dots to TiO2 in a Directly Coupled System

We show that the sub‐bandgap excitation of a directly coupled CdSe quantum dot (QD)–TiO₂ system induces electron injection from CdSe levels to the conduction band of TiO₂, leading to spectral extension of the light response. We anticipate that this study presents a useful guideline for improving the conversion efficiency of QD‐sensitized solar cells.     

Absolute structure, biosynthesis, and anti-microtubule activity of phomopsidin, isolated from a marine-derived fungus Phomopsis sp.

The absolute configuration of phomopsidin, a marine-derived fungal metabolite from Phomopsis sp. isolated at Pohnpei, was determined by the exciton chirality method as 6S, 7S, 8S, 11S, 12R, and 15R. The biosynthetic study using ¹³C-labeled precursors revealed the origin of all carbon atoms in phomopsidin, which was built by nine acetates and three methyl groups from l-methionine. Inhibitory activities of phomopsidin and its Me ester derivative against microtubule assembly were examined together with the structurally related compounds MK8383, solanapyrones, and tanzawaic acids. Phomopsidin and its (16Z)-isomer (MK8383) showed anti-microtubule activity at IC₅₀ of 5.7 and 8.0 μM, respectively, while the Me ester and other compounds were not active at 100 μM.     

Cleavage and some modifications of the 7-amide group of the cephamycins

The cleavage and some modifications of the 7-amide group of cephamycins are described. Cephamycin derivatives 16b, c which were synthesized from the naturally occurring cephamycin C (16a) were converted to the corresponding oxamic acid derivatives 17a, e respectively by the reaction with oxalyl chloride and successive treatment with water. The reaction of the oxamic acid 17a with diphenylcarbodiimide gave 7-aminocephamycinoic acid (7-ACMA) benzhydryl ester (21a) which was further converted to cefoxitin (21c). These compounds 17a, b, c, d, e, f thus obtained from cephamycin C appear to be favorable intermediates for the syntheses of cephamycin analogues such as cefmetazole (28c).     

A new synthesis of dienone lactones using a combination of hypervalent iodine(III) reagent and heteropoly acid

The oxidation of non-phenolic alkanoic acid derivatives to oxygen heterocycles was investigated; a new oxidative route to dienone lactones has been developed using a combination of hypervalent iodine(III) reagent, phenyliodine(III) bis(trifluoroacetate)(PIFA), and heteropoly acid (HPA).