The Electronic Structure of Azuleno[1,2,3-cd]phenalene and Azuleno[5,6,7-cd]phenalene,a Comparison

The photoelectron (PE.) spectra of azuleno[l, 2, 3-cd]phenalene ( 1 ) and azuleno- [5,6,7-cd]phenalene( 2 ) have been recorded. The first five bands of both compounds could be assigned to transitions corresponding to removal of electrons from 4a₂, 6b₁, 5b₁, 3a₂ and 4b_l orbitals. This assignment is based mainly on a comparison between the observed ionization potentials and orbital energies calculated in a HMO and a PPP model. The UV./VIS. polarized absorption spectrum of 1 in the region 10000–45000 cm^?1 has been measured by means of the stretched film technique. The measurements were performed in polyethylene sheets at 77°K. Several bands could be assigned to π* ← π transitions calculated by a PPP-CI method. A comparison between the electronic structures of 1 and 2 is made by means of a simple HMO diagram.     

Solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes under high-speed vibration milling

The solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes (RCHO) 2a-e under high-speed vibration milling (HSVM) conditions have been investigated. Fulleropyrrolidines 4a-e (C₆₀(CH₂N(CH₃)CHR), R=H (4a), C₆H₅ (4b), p-NO₂-C₆H₄ (4c), p-CH₃O-C₆H₄ (4d), p-(CH₃)₂N-C₆H₄ (4e)) were obtained in moderate yields from reactions of C₆₀ with aldehydes 2a-e and N-methylglycine (Prato reaction). In all these solvent-free reactions, 4a was found to be formed besides 4b-e, indicating that fullerenes can react with N-substituted glycines in the absence of aldehyde to give fulleropyrrolidines. For this novel reaction, a possible reaction mechanism involving an electron transfer process has been proposed. Intrigued by this observation, the dependence of the yield on the reagent ratio for the reaction of C₆₀ with paraformaldehyde and/or N-methylglycine was examined to search the optimal conditions. The reaction of C₇₀ with paraformaldehyde and/or N-methylglycine under HSVM conditions was also studied and was found to give the positional isomers of [70]fulleropyrrolidines.     

Blue myoglobin reconstituted with an iron porphycene shows extremely high oxygen affinity

Myoglobin will be a good scaffold for engineering a function into proteins. To modulate the physiological function of myoglobin, almost all approaches have been demonstrated by site-directed mutagenesis, however, there are few studies which show a significant improvement in the function. In contrast, we focused on the replacement of heme in the protein with an artificial prosthetic group. Recently, we prepared a novel myoglobin reconstituted with an iron porphycene as a structural isomer of mesoheme. The bluish colored reconstituted myoglobin is relatively stable and the deoxymyoglobin reversibly binds ligands. Interestingly, the O2 affinity of the reconstituted myoglobin, 1.1 x 109 M-1, is a significant 1,400-fold higher than that of the native myoglobin. Furthermore, the unfavorable autoxidation kinetics show 7-fold decrease in rate for the reconstituted myoglobin relative to the native myoglobin, indicating the stable oxy-form against autoxidation. The net results come from the slow dissociation of the O2 ligand in the reconstituted myoglobin, koff = 0.11 s-1, because of the formation of strong hydrogen bond between His64 and negatively charged dioxygen. The present study indicates that the replacement of native heme with an artificially created prosthetic group will give us a unique function into a hemoprotein.     

Two New Spermidine Alkaloids from Chisocheton weinlandii

The investigation of the MeOH extract of the leaves of Chisocheton weinlandii Harms (Meliaceae) revealed two new open‐chain spermidine alkaloids, chisitine 1 ( 1 ) and chisitine 2 ( 2 ). Their structures were elucidated by NMR spectroscopy, tandem‐mass spectrometry, and independant syntheses (Scheme 3). Detailed MS/MS fragmentation pathways are discussed for both compounds based on H/D exchange and ¹⁸O‐labeling experiments (Schemes 1 and 2).     

Cation recognition on a fullerene-based macrocycle

Heterocyclic orifices in cage-opened fullerene derivatives are regarded as potential ligands toward metals or ions, being reminiscent of truncated fullerenes as a hypothetical class of macrocycles with spherical π-conjugation. Among a number of cage-opened examples reported thus far, the coordination ability and dynamic behavior in solution still remained unclear due to difficulties in structural determination with multiple coordination sites on the macrocycles. Herein, we present the detailed solution dynamics of a cage-opened C₆₀ derivative bearing a diketo bis(hemiketal) moiety in the presence of alkali metal ions. The NMR spectroscopy disclosed the coordination behavior which is identified as a two-step process with a 1 : 2 stoichiometry. Upon coordination to the Li⁺ ion, the macrocycle largely varies its properties, i.e., increased absorption coefficients in the visible region due to weakly-allowed charge transfer transitions as well as the inner potential field from neutral to positive by the charge delocalization along with the spherical π-surface. The Li⁺-complexes formed in situ underwent unprecedented selective dehydroxyhydrogenation under high-pressure conditions. These findings would facilitate further studies on fullerene-based macrocycles as metal sensors, bulky ligands in organic reactions, and ion carriers in batteries and biosystems.

A fullerene-based Lewis-basic macrocyclic ligand underwent complexation with alkali-metal ions in 1 : 1 and 1 : 2 fashions, resulting in considerable perturbation to absorption properties as well as the potential surface inside the cage.     

Multiple fluorescence spectra and stable encapsulation of 7-hydroxy-4-methylcoumarin and rhodamine 6g in silicate glasses by the sol-gel method

7-Hydroxy-4-methylcoumarin(4-methylumbelliferone, HMC) and Rhodamine 6G(R6G) were encapsulated into silicate polymeric glass prepared by the sol-gel method under acidic, basic, and neutral conditions from tetraethyl orthosilicate. The fluorescence spectra of these molecules encapsulated into the xerogel state depend on the used catalysts. Three types of fluorescence emissions having peak wavelengths of ca. 390 nm, 470 nm, and 550 run, respectively, were observed simultaneously in the xerogel state composed of HMC and R6G which were prepared by acid catalysts. The encapsulated HMC remains stable for more than one year in the prepared xerogel. The results open the way to the development of simultaneous three-band laser emissions. The observation of the fluorescence spectrum of HMC is useful for a molecular level photophysical probe elucidating the structural changes oftetraethyl orthosilicate during sol to gel to xerogel transitions.     

High-performance liquid chromatographic identification of disaccharides generated from heparan sulphate isomers using heparitinases

Specific heparan sulphate-lyases, heparitinases I and II, were used to identify unsaturated disaccharide constituents generated from heterogeneous heparan sulphate isomers. All determinations were made using high-performance liquid chromatography with a column containing a sulphonized styrene-divinylbenzene copolymer. Unsaturated disaccharides generated from variously sulphated heparan sulphate isomers after simultaneous digestion with heparitinases I and II facilitated separation of the individual disaccharides, based on sulphate groups at the specific position of the uronic acid and glucosamine residues. The simultaneous digestion with heparitinases I and II produces unsaturated disaccharides from heparan sulphate isomers with the structure of 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-amino-deoxy-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-aminodeoxy-6-O-sulpho-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-6-O-sulpho-D-glucose, 4-deoxy-2-O-sulpho-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-amino-2-deoxy-6-O-sulpho-D-glucose and 4-deoxy-2-O-sulpho-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-6-O-sulpho-D-glucose.     

A facile synthesis of [1,2,4]triazino[3,2-f]purines and [1,2,4]triazepino[3,2-f]purines

[1,2,4]Triazino[3,2-f]purines 3a-e and [1,2,4]triazepino[3,2-f]purine 5 were synthesized by the reaction of 7,8-diamino-1,3-dimethylxanthine 1 with diketones such as glyoxal, diacetyl, dibenzoyl, pyruvic aldehyde dimethyl acetal, phenylglyoxal or acetylacetone in acetic acid in the presence of boric acid or polyphosphoric acid.     

An analysis of the through-bond interaction using the localized molecular orbitals—IV: Long-range proton hyperfine coupling in exo- and endo-hydrogens in bicyclo[2.1.1]hex-5-yl radical

The INDO calculations were performed on bicyclo[2.1.1]hex-5-yl radical. From these calculations, it was confirmed that the hyperfine coupling constants depend largely on the geometry of the α hydrogen. The localized MO's were obtained from the canonical MO's calculated by using the INDO method. With the use of the localized MO's thus obtained, the variation in the hyperfine coupling constants at the 6exo- and 6endo-protons in this radical was explained in terms of the through-bond and/or the through-space interactions according to the procedure which we proposed previously. That is by the procedure we can selectively pick up a particular interaction between the specified localized MO's. The hyperfine coupling constant in this radical can be expressed by the summation of several interaction terms. The difference in the hyperfine spin coupling constants of the H_6exo and H_6endo in the radical now concerned has been attempted to explain using MO coefficients of the occupied orbitals.