Size and shape of soil humic acids estimated by viscosity and molecular weight

Ultrafiltration fractions of three soil humic acids were characterized by viscometry and high performance size-exclusion chromatography (HPSEC) in order to estimate shapes and hydrodynamic sizes. Intrinsic viscosities under given solute/solvent/temperature conditions were obtained by extrapolating the concentration dependence of reduced viscosities to zero concentration. Molecular mass (weight average molecular weight (M (w)) and number average molecular weight (M (n))) and hydrodynamic radius (R(H)) were determined by HPSEC using pullulan as calibrant. Values of M (w) and M (n) ranged from 15 to 118 x 10(3) and from 9 to 50 x 10(3) (g mol(-1)), respectively. Polydispersity, as indicated by M (w)/M (n), increased with increasing filter size from 1.5 to 2.4. The hydrodynamic radii (R(H)) ranged between 2.2 and 6.4 nm. For each humic acid, M (w) and [eta] were related. Mark-Houwink coefficients calculated on the basis of the M (w)-[eta] relationships suggested restricted flexible chains for two of the humic acids and a branched structure for the third humic acid. Those structures probably behave as hydrated sphere colloids in a good solvent. Hydrodynamic radii of fractions calculated from [eta] using Einstein's equation, which is applicable to hydrated sphere colloids, ranged from 2.2 to 7.1 nm. These dimensions are fit to the size of nanospaces on and between clay minerals and micropores in soil particle aggregates. On the other hand, the good agreement of R(H) values obtained by applying Einstein's equation with those directly determined by HPSEC suggests that pullulan is a suitable calibrant for estimation of molecular mass and size of humic acids by HPSEC.     

Synthesis of two possible diastereomers of reticulatain-1

A convergent synthesis of two possible diastereomers of reticulatain-1 (1a and 1b) was accomplished. Comparison of the specific optical rotations of 1a and 1b did not allow for the strict determination of the absolute configuration. However, bis-(R)-MTPA esters of 1a and 1b showed a clear difference in chemical shifts in the ¹H NMR spectra. If the bis-(R)-MTPA ester of natural reticulatain-1 (1) is available, the absolute configuration of 1 will be determined. Inhibitory action of these compounds was examined with bovine heart mitochondrial complex I. Both compounds showed almost the same activity.     

Role of iron and copper in particulate methane monooxygenase of Methylosinus trichosporium OB3b

The role of iron and copper in particulate methane monooxygenase (pMMO) of Methylosinus trichosporium OB3b is described, and an overview of the enzyme's properties is presented. The pMMO from M. trichosporium OB3b was solubilized in the detergent n-dodecyl--D-maltoside and purified by chromatographic techniques. The enzyme consists of 0.9 iron atoms and 12.8 copper atoms per molecule. The iron site in pMMO may be mononuclear non-heme iron. Copper exists as either copper ion coupled to four nitrogen atoms and/or trinuclear copper cluster wherein copper ions are ferromagnetically coupled.     

Three new triterpene saponins from the seeds of Aesculus chinensis

Three new triterpenoid saponins were isolated from the seeds of Aesculus chinensis, and characterized as 22-tigloylprotoaescigenin 3-O-[beta-D-glucopyranosyl (1-->2)] [beta-D-glucopyranosyl (1-->4)]-beta-D-glucopyranosiduronic acid (escin IVg, 1), 22-angeloylprotoaescigenin 3-O-[beta-D-glucopyranosyl (1-->2)] [beta-D-glucopyranosyl (1-->4)]-beta-D-glucopyranosiduronic acid (escin IVh, 2) and 16-angeloyl-21-acetylprotoaescigenin 3-O-[beta-D-glucopyranosyl (1-->2)] [beta-D-glucopyranosyl (1-->4)]-beta-D-glucopyranosiduronic acid (escin VIb, 3), together with two known compounds, escin IIIa (4) and desacylescin 1 (5). Their structures were established on the basis of spectroscopic and chemical evidence.     

Bioactive constituents of Chinese natural medicines. VII. Inhibitors of degranulation in RBL-2H3 cells and absolute stereostructures of three new diarylheptanoid glycosides from the bark of Myrica rubra

Three new diarylheptanoid glycosides, named (+)-S-myricanol 5-0-beta-D-glucopyranoside, myricanene A 5-O-alpha-L-arabinofuranosyl(1-->6)-beta-D-glucopyranoside, and myricanene B 5-0-alpha-L-arabinofuranosyl(1-->6)-beta-D-glucopyranoside, were isolated from the bark of Chinese Myrica rubra, together with twenty known compounds. The absolute stereostructures of the new diarylheptanoid glycosides were elucidated on the basis of chemical and physicochemical evidence, including the application of the modified Mosher's method. The inhibitory effects of isolated constituents on the release of beta-hexosaminidase from RBL-2H3 cells were examined, and several diarylheptanoids, myricanol, (+)-S-myricanol, myricanone, and myricanenes A and B, and a flavonol, myricetin, were found to show the inhibitory activity.     

1,2,4-Triazoles. V. Nuclear magnetic resonance study of N-Methyl derivatives of 1,2,4-triazoles

The chemical shifts of the N-methyl protons of a number of N-methylated-1,2,4-triazoles were studied. Substitution of methyl and methylthio groups in position 3 causes upfield shifts of the N-methyl signals, while substitution of α-pyridyl, γ-pyridyl, and phenyl groups causes downfield shifts. In 3,5-disubstituted 1,2,4-triazoles, substituents in positions 3 and 5 have additive effects on the chemical shifts of N-methyl groups, so that the chemical shifts of the N-methyl groups of such compounds can be calculated. In this way, it was possible to assign the peaks of mixtures of N-monomethylated derivatives obtained by methylation of 1,2,4-triazoles.     

Biotransformation of phorbol by human intestinal bacteria

Anaerobic incubation of phorbol (1) from Croton tiglium with human intestinal bacteria afforded five metabolites: isophorbol (2), deoxyphorbol (3), 4beta,9alpha,20-trihydroxy-13,15-seco-1,6,15-tigliatriene-3,13-dione (4), 4beta,9alpha,20-trihydroxy-15,16,17-trinor-1,6-tigliadiene-3,13-dione (5) and 4beta,9a,20-trihydroxy-14(13-->12)-abeo-12alphaH-1,6-tigliadiene-3,13-dione (6). All these metabolites (2-6) were identified and characterized by spectroscopic means, including two-dimensional (2D)-NMR. Nine defined strains from the human intestine showed an ability to transform 1 to these metabolites.     

Unique commercial applications of the sol-gel process in Japan

Two unique commercial applications of the sol-gel process in Japan are presented. One application involves alkoxide-derived nanometer-sized silica particles used in the final polishing of silicon wafers for the fabrication of integrated circuits. The particles are cocoon-like in shape and have almost replaced conventional abrasives because of the advantages over spherical particles of similar size in terms of obtaining high polishing efficiency for good surface finish. The other application concerns the treatment of paper with an alkoxide solution for water repellent and oil resistance properties, which leads to new products for disposable tableware or cooking ware for microwave oven use.     

Stepwise photocleavage of C-O bonds of bis(substituted-methyl)naphthalenes with stepwise excitation by two-color two-laser and three-color three-laser irradiations

Stepwise photocleavage of naphthylmethyl-oxygen (C-O) bonds of mono(substituted-methyl)naphthalenes [1- and 2-ROCH2Np, R = 4-benzoylphenyl (BP), phenyl (Ph), and methyl (CH3)] and bis(substituted-methyl)naphthalenes [1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np, R = BP and Ph] was observed to give the naphthylmethyl radicals (NpCH2* or ROCH2NpCH2*) in almost 100% yield with two-step or three-step excitation by the two-color two-laser or three-color three-laser irradiation, respectively, at room temperature. The C-O bond cleavage quantum yields of 1-PhOCH2Np, 2-PhOCH2Np, 1,8-(PhOCH2)2Np, and 1,4-(PhOCH2)2Np were higher than those of 1-BPOCH2Np, 2-BPOCH2Np, 1,8-(BPOCH2)2Np, and 1,4-(BPOCH2)2Np. No C-O bond cleavage occurred from 1,8-(HOCH2)2Np and 2-CH3OCH2Np in the higher triplet excited state (T(n)). The experimental results show that the C-O bond cleavage was determined not only by the position of the substituents on Np but also by the type of the substituents. The C-O bond cleavage of 1-ROCH2Np was more efficient than that of 2-ROCH2Np. In the case of 1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np (R = BP and Ph), the first C-O bond cleavage from the T(n) states occurred to give ROCH2-substituted naphthylmethyl radicals (1,8- and 1,4-ROCH2NpCH2*) when the T1 states, generated with the 308-nm first laser irradiation, were excited using the 430-nm second laser. The second C-O bond cleavage occurred when 1,8- and 1,4-ROCH2NpCH2* in the ground state [1,8- and 1,4-ROCH2NpCH2*(D0)] were excited to the excited states [1,8- and 1,4-ROCH2NpCH2*(D(n))] using the third 355-nm laser during the three-color three-laser flash photolysis at room temperature. It was revealed that acenaphthene was produced as the final product during the stepwise C-O bond cleavages of 1,8-(BPOCH2)2Np and 1,8-(PhOCH2)2Np. This is a successful example of stepwise cleavage of two equivalent C-O bonds in a molecule using the three-color three-laser photolysis method.     

A highly effective asymmetric synthesis of α-hydroxy acids by alkylation of chiral n-(benzyloxyacetyl)-trans-2,5-bis(methoxymethoxymethyl)pyrrolidine

Alkylation of lithiated $\text{N}$-(benzyloxyacetyl)-$\text{trans}$-2,5-bis(mehtoxyymethoxymethyl)- pyrrolidine proceeded with high stereoselectivity (≥96% de) and subsequent transformations of the alkylated products gave synthetically useful α-benzyloxy acids or α-hydroxy acids of high enantiomeric purity.