Colorimetric and fluorometric sensing of the Lewis acidity of a metal ion by metal-ion complexation of imidazo[1,2-a]pyrazin-3(7H)-ones

Metal-ion complexation of 7-benzylimidazo[1,2-a]pyrazin-3(7H)-one derivative (2) with Li⁺, Mg²⁺, Ca²⁺, Ba²⁺, Sc³⁺, and La³⁺ in acetonitrile resulted in successive modulations of its UV/vis absorption and fluorescence spectroscopic properties. This result indicates that 2 can be used as a colorimetric and fluorometric sensor of the Lewis acidity of a metal ion in aprotic solutions. The hypothesis that the metal-ion complex has a O10(imidazopyrazinone)-metal ion bond was supported by X-ray crystallographic analysis and quantum chemical calculations for a Li⁺ complex of 7-methylimidazo[1,2-a]pyrazin-3(7H)-one derivative (1).     

Supramolecular steric effects as the means of making reactive carbon radicals persistent. Quantitative characterization of the external surface of MFI zeolites through a persistent radical probe and a langmuir adsorption isotherm

The photochemistry of tetraphenylacetone (1) adsorbed on the external surface of a MFI zeolite (the sodium form of LZ-105) has been investigated in combination with computational chemistry, surface area measurements, EPR analysis, and classical adsorption isotherms. All of the methods are consistent with a supramolecular structural model in which 1 is first adsorbed strongly through intercalation of a single benzene ring into a hole on the LZ-105 external surface (site I) followed by a weaker binding to the external framework between the holes (site II) until a monolayer of 1 is formed. From both computational and surface area measurements, it is estimated that the site I holes on the external surface will be filled at ca. 0.3-0.5 wt %/wt loading of 1/LZ-105, which corresponds to 6.5 x 10(18) (ca. 10(-)(5) mol) of holes or molecules of 1 adsorbed in holes per gram of zeolite. The supramolecular composition of ca. 0.3-0.5% of 1 on LZ-105 characterizes a "break point" for the photochemistry and the EPR measurements, since it represents the value for saturation of the site I holes with 1. These conclusions are supported quantitatively by experimental isotherms of the adsorption of 1 on LZ-105. Photolysis of 1 intercalated in the site I holes causes fragmentation into two isomeric supramolecular diphenylmethyl (DPM) radicals, one (DMP)(in) which is adsorbed into the internal surface and becomes strongly persistent (half-life of many weeks) and the other (DMP)(ex) which diffuses on the external surface and rapidly dimerizes (less than a few minutes) to produce the radical-radical combination product tetraphenylethane (2). Photolysis of 1 adsorbed on the solid external surface produces two supramolecularly equivalent DPM radicals (DMP)(ex) that diffuse on the external surface and rapidly dimerize to produce 2, and do not produce persistent DPM radicals.     

Synthesis of thermosensitive polymer/mesoporous silica composite and its temperature dependence of anion exchange property

An anion exchanger consisting of amino-functionalized MCM-41 type mesoporous silica coated with temperature-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM), was synthesized in this study. The structure of this composite was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and elemental analysis. The XRD pattern showed that the synthesized composite had the ordered hexagonal structure and the interplanar spacing, d(100), was around 40?. The amount of surface-grafted thermosensitive polymer was estimated to be about 0.8wt.% by elemental analysis. The adsorption-desorption behavior of methyl orange in this synthesized material depended on the temperature of aqueous solution: at 25°C, the reversible adsorption-desorption of methyl orange was repeated with changing pH of the solution; at 40°C, the methyl orange was not adsorbed and desorbed independent of pH of the solution.     

Determination of the double-bond position in hexadecenols by mass spectrometry without prior chemical modification

Fourteen isomers of chemically unmodified hexadecenol were analysed by two types of quadrupole mass spectrometer, coupled with a gas chromatograph, for the location of the double-bond position. A series of spectra were interpreted in terms of mass spectral patterns on a fuzzy classification, in which the intensity ratios of six diagnostic pairs of the predominant ions were preferred in devising similarity indices. The accuracy of the method in the location of double-bond position was confirmed by testing with other series of spectra.     

Theoretical study of the double Renner effect for A2Pi MgNC/MgCN: higher excited rovibrational states

The authors report here the implementation of a newly developed, highly efficient matrix diagonalization routine in the DR program [T. E. Odaka et al., J. Mol. Struct. 795, 14 (2006)]. The DR program solves the rovibronic Schrodinger equation for a triatomic molecule with a double Renner effect, i.e., with two accessible linear arrangements of the nuclei at which the electronic energy is doubly degenerate. With the new routines, the authors can extend the DR calculations of rovibronic energies for A 2Pi MgNC/MgCN by considering a much larger set of rovibronic states, in particular, states at higher J values, than the authors were able to access previously.     

Cooperative motions of protein and hydration water molecules: molecular dynamics study of scytalone dehydratase

Two molecular dynamics (MD) simulations totaling 25 ns of simulation time of monomeric scytalone dehydratase (SD) were performed. The enzyme has a ligand-binding pocket containing a cone-shaped alpha+beta barrel, and the C-terminal region covers the binding pocket. Our simulations clarified the difference in protein dynamics and conformation between the liganded protein and the unliganded protein. The liganded protein held the ligand molecule tightly and the initial structure was maintained during the simulation. The unliganded protein, on the other hand, fluctuated dynamically and its structure changed largely from the initial structure. In the equilibrium state, the binding pocket was fully solvated by opening of the C-terminal region, and the protein dynamics was connected with hydration water molecules entry into and release from the binding pocket. In addition, the cooperative motions of the unliganded protein and the hydration water molecules produced the path through the protein interior for ligand binding.     

In Situ Processing of Nano Crystalline Oxide Particles/Polymer Hybrid

Nano sized crystalline particles/polymer hybrids were synthesized form designed metal-organic precursors. The newly developed method is composed of the synthesis of organic matrix by polymerization and the in situ nucleation and growth of crystalline oxide particles in the organic matrix below 100°C. The design of metal-organic precursor modified with polymerizable ligand and the selection of reaction conditions does influence the size and crystallinity of ceramic particles in organic matrix. The nano-sized magnetic particle/polymer hybrid exhibits the interesting feature of superparamagnetism and quantum size effect. The crystalline particles of BaTiO₃/, PbTiO₃/, and KNbO₃/polymer hybrids behave to be dielectric and show the typical electro-rheological behavior.     

A novel synthesis of 2,3‐dihydro‐1H‐thieno[3,4‐b]pyrroles via ring transformation of cyclic sulfonium ylides by titanium(IV) chloride‐triethylamine system

A series of cyclic sulfonium ylides 4a‐h reacted with titanium( IV ) chloride in the presence of triethyl‐amine to give the corresponding fused 2,3‐dihydro‐1H‐thieno[3,4‐b]pyrroles 5a‐h , via a ring opening and recyclization. In contrast, treatment of compounds 4a, 4b, 4e and 4f with titanium(IV) chloride, triethy‐lamine and dimethylamine hydrochloride gave the corresponding thiophenes 6a, 6b, 6e and 6f . Furthermore, compounds 6a and 6b easily underwent cyclization with sodium hydride to afford the corresponding 5a and 5b .     

alpha-Aminoallylation of aldehydes with ammonia: stereoselective synthesis of homoallylic primary amines

Three-component reactions of aldehydes, ammonia, and allylboronates were found to provide homoallylic primary amines in high yields with high chemo- and stereoselectivities. A two-step, one-pot, stereoselective synthesis of an uncommon alpha-amino acid, alloisoleucine, was achieved utilizing this reaction.