The reductive amination of aldehydes and ketones by catalytic use of dibutylchlorotin hydride complex

The reductive amination of aldehydes or ketones using Ph(2)SiH(2) or PhSiH(3) has been effectively promoted by the direct use of Bu(2)SnClH-pyridine N-oxide as a catalyst; this method has advantages in terms of its mild conditions and wide application to various carbonyls and amines, including aliphatic examples.     

High-throughput sodium dodecyl sulfate polyacrylamide gel electrophoresis by linking conventional gel plates with automated liquid handler via Gel Adaptor

The automation of SDS-PAGE required substantial investment. To lower this barrier, we devised a cost-effective, simple, and general method where samples are loaded on SDS-PAGE gels held by a newly devised "Gel Adaptor" on a general automated liquid handler. In this method, the liquid handler loads samples on the SDS-PAGE gels held at an angle of 80 degrees on the Gel Adaptor so that the samples can be vertically loaded on the narrow paths of the wells of the slanted gels. This method allows the automated liquid handler to load 144 samples on SDS-PAGE gels in approximately 10 min, greatly reducing the time and cost for high-throughput SDS-PAGE analyses.     

2D hydrogen-bonded square-grid coordination networks with a substitution-active metal site

Reported here is the preparation and property of 2D coordination networks composed of rodlike ligands with ethylene glycol side chains (1). Two 2D coordination networks, [[Co(1)2(H2O)2](NO3)2.1.5H2O]n and [[Ni(1)2(H(2)O)2](NO3)2.1.5H2O]n, have been synthesized and characterized by single-crystal X-ray diffraction, TG, DSC, UV-vis spectroscopy, and magnetic measurements. The structural analyses clarified that infinite 1D hydrogen-bond arrays composed of ethylene glycol chains contribute to the stabilization of 2D coordination frameworks, keeping the environment of substitution-active metal sites unchanged. They are more stable than a similar square-grid coordination network that does not possess an ethylene glycol chain on the ligand. We also succeeded in the direct observation of a reversible apical-ligand-exchange reaction at the cobalt(II) and nickel(II) ions in a single-crystal-to-single-crystal fashion because of the considerable stability as well as moderate flexibility of the framework. The cobalt-containing coordination network crystal showed chromic behavior depending on temperatures. Crystallographic and spectroscopic studies revealed that the color change of the crystal was attributed to the ligand-exchange process between H2O and a NO3 anion on the cobalt metal. Magnetic measurements indicated weak antiferromagnetic nearest-neighbor spin coupling between cobalt(II) ions.     

Enhancing the superconducting transition temperature of CeRh 1-x IrxIn5 due to the strong-coupling effects of antiferromagnetic spin fluctuations: an 115In nuclear quadrupole resonance study

We report on systematic evolutions of antiferromagnetic (AFM) spin fluctuations and unconventional superconductivity (SC) in heavy-fermion (HF) compounds CeRh(1-x)Ir(x)In(5) via an (115)In nuclear-quadrupole-resonance experiment. The nuclear spin-lattice relaxation rate 1/T(1) has revealed the marked development of AFM spin fluctuations as approaching an AFM ordered state. Concomitantly, the superconducting transition temperature T(c) and the energy gap Delta0 increase drastically from T(c)= 0.4K and 2Delta0/k(B)T(c)=5 in CeIrIn(5) up to T(c) =1.2K and 2Delta0/k(B)T(c) =8.3 in CeRh(0.3)Ir(0.7)In5 , respectively. The present work suggests that the AFM spin fluctuations in close proximity to the AFM quantum critical point are indeed responsible for the strong-coupling unconventional SC in HF compounds.     

Assembly state of catalytic modules as chiral switches in asymmetric Strecker amino acid synthesis

Self-assembled chiral polymetallic complexes often demonstrate novel properties as asymmetric catalysts. We report the three-dimensional structures of two such asymmetric catalysts (crystals A and B) for Strecker alpha,alpha-disubstituted amino acid synthesis. These complexes are constructed via assembly of the same chiral modules derived from d-glucose, but their assembly modes differ. The enantioselectivity in the Strecker reaction was dramatically switched, depending on which assembly mode was used: the catalyst generated in situ whose structure is represented by crystal B, or by crystal A. These findings provide insight into the functional importance of higher-order structures of an artificial catalyst.     

Intermolecular [4 + 2] cycloaddition of o-quinodimethanes derived from ene-bis(sulfinylallenes)

Intermolecular [4 + 2] cycloaddition of o-quinodimethanes, prepared in situ from ene-bis(propargyl alcohols) and benzenesulfenyl chloride via ene-bis(sulfinylallene) formation, was investigated. Benzene-bridged bis(propargyl alcohols) reacted with both electron-deficient and electron-rich olefins to give the corresponding [4 + 2] cycloadducts. Ethylene-bridged bis(propargyl alcohols) underwent similar cycloaddition with electron-deficient olefins. Construction of some heterocycles based on the newly developed sequential reaction is also described.     

Antitumor enediyne chromoprotein C-1027: mechanistic investigation of the chromophore-mediated self-decomposition pathway

C-1027 is an extremely potent antitumor agent that causes double-stranded DNA cleavages. It is a unique small molecule-protein complex composed of a highly reactive enediyne chromophore, which upon binding reacts with its target molecule DNA through radical-mediated hydrogen abstraction and an apoprotein that encapsulates the chromophore serving as its carrier to reach DNA. Although C-1027 has favorable properties as an effective drug delivery system, it slowly self-decomposes due to the reactivity of the chromophore toward the apoprotein. Understanding how the C-1027 destroys itself may enable design of its analogues that overcome this limitation. In this paper, mechanistic insights into the self-reactivity of C-1027 that facilitates its own decomposition are described. We provide evidence that the formation of the Gly96 radical, which promotes the oxidative protein scission and the subsequent chromophore release, is the major pathway for the self-decomposition of C-1027. On the basis of the newly isolated products of the self-decomposition, we propose that the apoprotein effectively protects two different structural elements of the chromophore that are essential for its biological activity: the nine-membered enediyne moiety (necessary for DNA cleavage) and the benzoxazine moiety (necessary for DNA intercalation). Using an engineered apoprotein analogue kinetically more stable toward the chromophore radical, we show that enhanced overall properties can be achieved for the natural C-1027 with respect to stability and antitumor activities. The results present the first example of a rationally designed C-1027 analogue reported to display superior in vitro antitumor activity to the natural C-1027. Our findings may have implications for design of proteins that can stably encapsulate highly reactive small molecules.     

Mixed La-Li heterobimetallic complexes for tertiary nitroaldol resolution

A kinetic resolution of tertiary nitroaldols derived from simple ketones is described. Mixed BINOL/biphenol La-Li heterobimetallic complexes gave the best selectivity in retro-nitroaldol reactions of racemic tertiary nitroaldols. By using a mixture of La-Li3-(1a)3 complex (LLB 2a) and La-Li3-(1b)3 (LLB* 2b) complex in a ratio of 2/1, chiral tertiary nitroaldols were obtained in 80-97% ee and 30-47% recovery yield.     

Direct crystallographic observation of a coordinatively unsaturated transition-metal complex in situ generated within a self-assembled cage

In situ crystallographic observation of an extremely labile coordinatively unsaturated transition-metal complex, Cp'Mn(CO)2 (Cp' = methylcyclopentadienyl), was achieved by generating and trapping it within the confined cavity of a self-assembled cage in the crystalline state at a low temperature. The labile target Cp'Mn(CO)2 was formed by the photodissociation of the CO ligand from stable Cp'Mn(CO)3, which was accommodated within the cavity of the coordination cage. Being trapped in the cage at a low temperature, Cp'Mn(CO)2 showed sufficient stability to be analyzed by X-ray crystallography. The diffraction study revealed that the 16-electron unsaturated Mn complex adopted a pyramidal geometry rather than a planar geometry.     

Efficient vibrational relaxation of O2(X 3sigma(g)-, nu = 8) by collisions with CF4

A laser flash photolysis-laser-induced fluorescence (LIF) technique has been employed to study the relaxation kinetics of vibrationally excited O2(X 3sigma(g)-. The time-resolved LIF excited B 3sigma(u)(-)-X 3sigma(g)- system has been recorded and analyzed by the integrated-profiles method. The rate coefficient for vibrational relaxation of O2(X 3sigma(g)-, nu = 8) by collisions with CF(4), [1.4 +/- 0.3(2sigma)] x 10(-11) cm3 molecule(-1) s(-1), indicates that CF4 is an efficient relaxant of O2(X 3sigma(g)- and that the propensity rule for O2 relaxation suggested by Mack et al. (J. A. Mack, K. Mikulecky and A. M. Wodtke, J. Chem. Phys., 1996, 105, 4105) has been observed experimentally.