An instability condition for the Hartree–Fock solution of the infinite one‐dimensional system with two‐crossing bands. I. Singlet‐instability check of metallic carbon nanotube

An instability condition is derived for the Hartree–Fock solution so that it can be applied to the system in which the highest occupied and the lowest unoccupied bands cross at the in‐between point in the Brillouin zone. The instability check developed here is further applied to a metallic single‐walled carbon nanotube having the two‐crossing bands toward prediction of its instability. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 574–582, 2000     

Dielectric study of the alpha and beta processes in supercooled ethylene glycol oligomer-water mixtures

Broadband dielectric measurements for 65 wt % ethylene glycol oligomer (EGO)-water mixtures with one to six repeat units of EGO molecules were performed in the frequency range of 10 microHz-10 GHz and the temperature range of 128-298 K. In the case of the water-EGO mixtures with one and two repeat units of the EGO molecule (small EGO), the shape of the dielectric loss peak of the primary process is asymmetrical about the logarithm of the frequency of maximum loss above the crossover temperature, T(C). The asymmetric process continues to the alpha process at a low frequency, and an additional beta process appears in the frequency range higher than that of the alpha process below T(C). In contrast, the water-EGO mixtures with three or more repeat units of the EGO molecule (large EGO) show a broad and symmetrical loss peak of the primary process above T(C). The symmetric process continues to the beta process, and an additional alpha process appears in the frequency range lower than that of the beta process below T(C). These different scenarios of the alpha-beta separation related to the shape of the loss peak above T(C) are a result of the difference in the cooperative motion of water and solute molecules. The solute and water molecules move cooperatively in the small EGO-water mixtures above T(C), and this cooperative motion leads to the asymmetric loss peak above T(C) and the alpha process below T(C). For the large EGO-water mixtures, the spatially restricted motion of water confined by solute molecules leads to the symmetric loss peak above T(C) and the beta process below T(C).     

A practical procedure for the synthesis of multifunctional aldehydes through the Fukuyama reduction and elucidation of the reaction site and mechanism

A highly efficient heterogeneous Pd/C catalyst D1 was found to effect the reduction of thiol esters 1 to the corresponding aldehydes 2 with such a low catalyst loading as 0.5-1.0 mol %. The chemical properties of the Pd/C catalysts together with the XRF analysis reveal that the reduction is most likely to proceed on the solid surface of the Pd/C catalyst rather than in the solution phase outside the pores. A reaction mechanism through oxidative addition of Pd to the thiol esters 1 was postulated by detection of the oxidative addition intermediate by React IR analysis. A practical purification of 2 was accomplished by conversion to water-soluble bisulfite adducts 7.     

Synthesis of well-defined chain-end- and in-chain-functionalized polystyrenes with a definite number of benzyl chloride moieties and D-glucose residues

Novel well-defined chain-end- and in-chain-functionalized polystyrenes with six, eight, twelve, and sixteen benzyl chloride moieties and with four and eight D-glucose residues have been successfully synthesized by developing the methodology based on living anionic polymerization of using new functionalized agents derived from functionalized 1,1-diphenylethylene (DPE) derivatives. They are 1,10-dichloro-4,4-7,7-tetra(3-methoxymethylphenyl)decane, its iodide derivative, the dianion prepared from 1,1-bis(3-methoxymethylphenyl)ethylene and potassium naphthalenide, and 1,1-bis[3′,5′-bis(1,2:5,6-di-O-isopropylidene-α-D-glucofuranose-3-oxymethyl)phenyl]ethylene. The developed methodology involves diverse modes of reactions of polystyryllithium with new functionalized agents and either the subsequent transformation reaction with BCl₃ into benzyl chloride moieties or acid-hydrolysis to regenerate D-glucose residues. The resulting chain-multi-functionalized polystyrenes were precisely controlled with respect to chain length and quantitatively functionalized within experimental errors.     

Fluorination of alcohols and diols with a novel fluorous deoxy-fluorination reagent

We prepared a novel fluorous deoxy-fluorination reagent N,N-diethyl-α,α-difluoro-[3,5-bis(1H,1H,2H,2H-perfluorodecyl)benzyl]amine (1b) from 3,5-diiodobenzoic acid (3b) via N,N-diethyl-3,5-bis(1H,1H,2H,2H-perfluorodecyl)benzamide (2b) in four steps and used it for the fluorination of alcohols and diols. After the fluorination reactions, the isolation of the products and recovery of 2b was performed by extraction with a fluorous/organic solvent system.     

Radical-mediated stannylation of vinyl sulfones: access to novel 4′-modified neplanocin A analogues

Synthesis of 4′-substituted (halogeno, phenyl, ethynyl, and cyano) neplanocin A analogues was carried out. A cyclopentenol derivative having a vinylstannane structure was designed as key-intermediate in this study, which was prepared based on radical-mediated sulfur-extrusive stannylation. The resulting stannylated cyclopentenol 15 was successfully condensed with 6-chloropurine through the Mitsunobu reaction, leading to the carbocyclic nucleoside 20. Compound 20 was converted to its adenine counterpart 21 by treatment with NH₃/MeOH, during which the 4′-stannyl group remained intact. The title compounds were prepared by using 21 or the 4′-iodo derivative (22) mostly through the Stille reaction.     

Dynamic light‐scattering measurement of sieving polymer solutions for protein separation on SDS CE

We evaluated the mesh size and homogeneity of polymer network by dynamic light scattering and discussed the relationship between the physical properties of polymer network and the protein separation behavior by capillary polymer electrophoresis. We compared three kinds of sieving polymers in solutions with a wide range of molecular weights and concentrations: polyacrylamide and polyethylene oxide as flexible polymers, and hydroxyethyl cellulose as a semiflexible polymer. We found that the mobility of protein was dominated primarily by the mesh size ξ, irrespective of the type of sieving polymers, and the peak spacing between protein peaks increased drastically in the range of ξ<10 nm, where the mobility also decreased. And the peak widths were dependent on the molecular species of sieving polymers and their homogeneity of polymer network. We proposed that a polymer network with a homogenous mesh size of less than 10 nm is the best sieving medium for separation of the proteins in the molecular weight range 14 300–97 200 Da from the view point of the resolution in protein separation.     

Fixation of Atmospheric Nitrogen: Synthesis of Heterocycles with Atmospheric Nitrogen as the Nitrogen Source

Dry air is the source of molecular nitrogen for reactions with TiL₄, Li, and TMSCl (L = Cl, OiPr; TMS = trimethylsilyl). The nitrogen–titanium complexes thus prepared can be used to synthesize indoles, pyrroles, and lactams from carbonyl compounds. Applying this method to 1 provides access to 2 , the key compound in the synthesis of (±)-lycopodine.     

Electronic Structure of Cu(II) Complexes with N,N′-Disalicylidene-1,2-cyclohexanediamine and N,N′-Disalicylidenetrimethylenediamine

Summary.  The electronic absorption and X-ray photoelectron spectra of N,N′-disalicylidenetrimethylenediaminatocopper(II) ([Cu(saltn)]) and N,N′-disalicylidene-trans-1,2-cyclohexanediaminatocopper(II) ([Cu(salchx)]) were measured. From these results and from informations derived from MO calculations the electronic structure of the complexes was clarified. Each electronic absorption band which can be assigned to the ππ^ast; or ML/LMCT transition of [Cu(saltn)] or [Cu(salchx)] observed in the wavelength region of 450–200 nm appears at the almost same frequency as the corresponding band of N,N′-disalicylideneethylenediaminatocopper(II) ([Cu(salen)]) in solution. The LLCT bands (the intramolecular CT band between two π-electronic systems separated by saturated hydrocarbon chains such as ) also appear at nearly the same positions (ca. 245 nm) for [Cu(salchx)], [Cu(saltn)], and [Cu(salen)]. The locations of the dd transition and the intensity of the ML/LMCT transition of [Cu(saltn)] are significantly different from those of [Cu(salen)] and [Cu(salchx)]. These differences may arise from the strengths of the interaction between metal and ligand. Received August 21, 2001. Accepted (revised) October 20, 2001