Polymorphism of 1,2-Bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene and Photochromic Reactivity of the Single Crystals

Four polymorphic crystals were obtained by recrystallization of 1,2-bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene (1 a) from hexane. All crystals underwent photochromic reactions upon alternate irradiation with ultraviolet (lambda=370 nm) and visible light (lambda>500 nm). The photocyclization quantum yields were found to be close to unity irrespective of the crystal types, while the photocycloreversion quantum yields were different as much as four times depending on the conformation of the closed-ring isomers in the crystals.     

Diastereoselective conjugate addition of 1-(α,β-unsaturated acyl)hydantoin with nucleophiles

A diastereomeric conjugate addition of dialkylaluminum chloride to 1-(α,β-unsaturated acyl)hydantoin provided the corresponding alkyl adduct with inducted chirality in the β-position. Treatment of 1-(α,β-unsaturated acyl)hydantoin with Gilman reagent in the presence of Lewis acid also gave the same product. In this reaction, diethylaluminum chloride was the most effective Lewis acid and the absolute configuration of the major adduct at the β-position of acyl group depended on the kinds of existing metals.     

Bimodal Size Distribution of Gold Nanoparticles under Picosecond Laser Pulses

The evolution of size distributions of gold nanoparticles under pulsed laser irradiation (Nd:YAG, lambda = 355 nm, pulse width 30 ps) was carefully observed by transmission electron microscopy. Interestingly, the initial monomodal size distribution of gold nanoparticles turned into a bimodal one, with two peaks in the number of particles, one at 6 nm and the other at 16-24 nm. The sizes for small particles depended very little on the irradiated laser energy. This change is attributed to laser-induced size reduction of the initial gold nanoparticles followed by the formation of small particles. In our analysis, we extracted a characteristic value for the size-reduction rate per one pulse and revealed that laser-induced size reduction of gold nanoparticles occurred even below the boiling point. When laser energy is insufficient for the boiling of particles, formation of gold vapor around liquid gold drops is thought to cause the phenomenon. With enough laser energy for the boiling, the formation of gold vapor around and inside liquid gold drops is responsible for the phenomenon. We also observed particles with gold strings after one pulse irradiation with a laser energy of 43 mJ cm(-2) pulse(-1), which is sufficient energy for the boiling. It is considered that such particles with gold strings are formed by the projection of gaseous gold from liquid gold drops with some volume of liquid gold around the bubble. On the basis of comparison with previous work, picosecond laser pulses are thought to be the most efficient way to cause laser-induced size reduction of gold nanoparticles.     

Simultaneous determination of tungsten and molybdenum in sea water by catalytic current polarography after preconcentration on a resin column

The simultaneous determination of tungsten and molybdenum in sea water is based on preconcentration by column extraction with 7-(1-vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol (Kelex- 100) resin, and measurement of the polarographic catalytic currents obtained in a solution of chlorate, benzilic acid and 2-methyl-8-quinolinol. When the concentration factor is 50, the detection limits are 2.4 pM for tungsten and 17 pM for molybdenum (for a signal-to-noise ratio of 3). The precision of the determination is ca. 10% for 67 pM tungsten and ca. 5% for 106 nM molybdenum in sea water (n=4). Results for sea water and other natural waters are presented.     

Pi-extended o-quinoidal tropone derivatives: experimental and theoretical studies of naphtho[2,3-c]tropone and anthro[2,3-c]tropone

pi-Extended o-quinoidal tropone derivatives, naphtho[2,3-c]tropone (3) and anthro[2,3-c]tropone (4), have been investigated theoretically as well as experimentally. The geometrical optimization of 3,4 and related compounds at the B3LYP level employing 6-31G* basis set as well as the GIAO calculations at the RHF level employing the 6-31+G* basis set have been performed to evaluate the contributions of the polarized resonance forms to these molecules. The GIAO calculated NICS(1) values indicate that the aromaticities of the tropone rings of o-quinoidal 3 and 4 are significantly increased as compared with that of parent tropone (1) at the expense of the fused benzenoid rings, consistent with the significant electronic polarization of these molecules in the ground state. On the other hand, the fusion of a benzene or naphthalene ring to the 2,3- or 4,5-position of tropone leads to diminution of aromaticity in the resulting tropone moiety. Experimentally, irradiation of 6,7-(2',3'-naphtho)bicyclo[3.2.0]hepta-3,6-dien-2-one (10) in a rigid glass at -196 degrees C leads to the formation of, which exhibits a characteristic UV-Vis absorption extending to 700 nm and undergoes rapid [pi 12 + pi 14] dimerization upon thawing the glass. In contrast, 6,7-(2',3'-anthro)bicyclo[3.2.0]hepta-3,6-dien-2-one (11) showed no sign of isomerization to 4 under the same reaction conditions.     

Multiple Pentafluorophenylation of 2,2,3,3,5,6,6‐Heptafluoro‐3,6‐dihydro‐2H‐1,4‐oxazine with an Organosilicon Reagent: NMR and DFT Structural Analysis of Oligo(perfluoroaryl) Compounds

The reagent Me₃Si(C₆F₅) was used for the preparation of a series of perfluorinated, pentafluorophenyl‐substituted 3,6‐dihydro‐2H‐1,4‐oxazines ( 2 – 8 ), which, otherwise, would be very difficult to synthesize. Multiple pentafluorophenylation occurred not only on the heterocyclic ring of the starting compound 1 (Scheme), but also in para position of the introduced C₆F₅ substituent(s) leading to compounds with one to three nonafluorobiphenyl (C₁₂F₉) substituents. While the tris(pentafluorophenyl)‐substituted compound 3 could be isolated as the sole product by stoichiometric control of the reagent, the higher‐substituted compounds 5 – 8 could only be obtained as mixtures. The structures of the oligo(perfluoroaryl) compounds were confirmed by ¹⁹F‐ and ¹³C‐NMR, MS, and/or X‐ray crystallography. DFT simulations of the ¹⁹F‐ and ¹³C‐NMR chemical shifts were performed at the B3LYP‐GIAO/6‐31++G(d,p) level for geometries optimized by the B3LYP/6‐31G(d) level, a technique that proved to be very useful to accomplish full NMR assignment of these complex products.     

Inhibitory activities of novel pyrimidine derivatives on the contact hypersensitivity reaction

In order to obtain novel topically applied anti-inflammatory compounds containing an inexpensive anti-oxidative moiety without chirality, we synthesized compound 2c derivatives having a di-tert-butylphenol moiety, and evaluated by topical administration their anti-inflammatory potentials on picryl chloride-(PC) induced contact hypersensitivity reaction (CHR) in mice. In the course of our structure-activity relationship (SAR) studies on the pyrimidine or the anti-oxidative moiety and the linker between them, the most potent compounds (10, 11) were obtained by the insertion of a C2 unit in compound 2c. The potencies of these compounds were 2-fold greater than that of 1. Compounds 10 and 11 were considered to be useful lead compounds having inexpensive anti-oxidative moieties without chirality.     

Synthesis, structures, and solution behavior of di- and trinuclear titanium(IV)--cyclophosphato complexes

The reaction of the cyclotetraphosphate ion (P(4)O(12)(4)(-)) with [CpTiCl(3)] (Cp = eta(5)-C(5)Me(5)) gives [(CpTi)(2)(P(4)O(12))(2)](2)(-) where the P(4)O(12) ligands adopt a saddle conformation, while that with [(CpTiCl)(3)(mu-O)(3)] leads to [(CpTi)(3)(mu-O)(3)(P(4)O(12))](-) containing a crown form P(4)O(12) ligand; both products feature their unique cage structures. On the other hand, the reactions of the cyclotriphosphate ion (P(3)O(9)(3)(-)) with [(CpTiCl(2))(2)(mu-O)] and [(CpTiCl)(3)(mu-O)(3)] afford [(CpTi)(2)(mu-O)(P(3)O(9))(2)](2)(-) and [(CpTi)(3)(mu-O)(3)Cl(P(3)O(9))](-), respectively, and in both cases the P(3)O(9) ligands bridge two titanium centers with an eta(2):eta(1) mode.     

A little theorem of the bigℳ in interior point algorithms

When we apply interior point algorithms to various problems including linear programs, convex quadratic programs, convex programs and complementarity problems, we often embed an original problem to be solved in an artificial problem having a known interior feasible solution from which we start the algorithm. The artificial problem involves a constant (or constants) which we need to choose large enough to ensure the equivalence between the artificial problem and the original problem. Theoretically, we can always assign a positive number of the order O(2 ^L ) to in linear cases, whereL denotes the input size of the problem. Practically, however, such a large number is impossible to implement on computers. If we choose too large, we may have numerical instability and/or computational inefficiency, while the artificial problem with not large enough will never lead to any solution of the original problem. To solve this difficulty, this paper presents a little theorem of the big, which will enable us to find whether is not large enough, and to update during the iterations of the algorithm even if we start with a smaller. Applications of the theorem are given to a polynomial-time potential reduction algorithm for positive semi-definite linear complementarity problems, and to an artificial self-dual linear program which has a close relation with the primal—dual interior point algorithm using Lustig's limiting feasible direction vector.