A new iridoid glycoside with nerve growth factor-potentiating activity,gelsemiol 6'-trans-caffeoyl-1-glucoside,from Verbena littoralis

A new iridoid glycoside, gelsemiol 6'-trans-caffeoyl-1-glucoside (1), was isolated from Verbena littoralis, together with four known phenylethanoid glycosides, acteoside (2), 2'-acetylacteoside (3), jionoside (4), and isoverbascoside (5). Their structures were elucidated by spectral data. Compound 1 showed weak enhancement of nerve growth factor (NGF)-mediated neurite outgrowth from PC12D cells.     

Brevisamide: an unprecedented monocyclic ether alkaloid from the dinoflagellate Karenia brevis that provides a potential model for ladder-frame initiation

The dinoflagellate Karenia brevis is known for the production of brevetoxins, a family of polycyclic ether toxins, as well as their antagonist brevenal. Further examination of organic extracts of K. brevis has uncovered yet another unprecedented cyclic ether alkaloid named brevisamide. This report describes the structure elucidation of brevisamide based on detailed MS and NMR spectral analysis, and the importance of this new compound in shedding light on the biogenesis of fused polyethers is discussed.     

Light-harvesting supramolecular porphyrin macrocycle accommodating a fullerene-tripodal ligand

Trisporphyrinatozinc(II) (1-Zn) with imidazolyl groups at both ends of the porphyrin self-assembles exclusively into a light-harvesting cyclic trimer (N-(1-Zn)(3)) through complementary coordination of imidazolyl to zinc(II). Because only the two terminal porphyrins in 1-Zn are employed in ring formation, macrocycle N-(1-Zn)(3) leaves three uncoordinated porphyrinatozinc(II) groups as a scaffold that can accommodate ligands into the central pore. A pyridyl tripodal ligand with an appended fullerene connected through an amide linkage (C(60)-Tripod) was synthesized by coupling tripodal ligand 3 with pyrrolidine-modified fullerene, and this ligand was incorporated into N-(1-Zn)(3). The binding constant for C(60)-Tripod in benzonitrile reached the order of 10(8) M(-1). This value is ten times larger than those of pyridyl tetrapodal ligand 2 and tripodal ligand 3. This behavior suggests that the fullerene moiety contributes to enhance the binding of C(60)-Tripod in N-(1-Zn)(3). The fluorescence of N-(1-Zn)(3) was almost completely quenched (approximately 97 %) by complexation with C(60)-Tripod, without any indication of the formation of charge-separated species or a triplet excited state of either porphyrin or fullerene in the transient absorption spectra. These observations are explained by the idea that the fullerene moiety of C(60)-Tripod is in direct contact with the porphyrin planes of N-(1-Zn)(3) through fullerene-porphyrin pi-pi interactions. Thus, C(60)-Tripod is accommodated in N-(1-Zn)(3) with a pi-pi interaction and two pyridyl coordinations. The cooperative interaction achieves a sufficiently high affinity for quantitative and specific introduction of one equivalent of tripodal guest into the antenna ring, even under dilute conditions ( approximately 10(-7) M) in polar solvents such as benzonitrile. Additionally, complete fluorescence quenching of N-(1-Zn)(3) when accommodating C(60)-Tripod demonstrates that all of the excitation energy collected by the nine porphyrins migrates rapidly over the macrocycle and then converges efficiently on the fullerene moiety by electron transfer.     

Synergic extraction of lanthanoids(III) with thenoyl trifluoroacetone and terpyridine

The synergic extraction of trivalent lanthanoids (Ln: La, Nd, Sm, Eu, Yb and Lu) with 2-thenoyltrifluoroacetone (Htta) and 2,26, 2-terpyridine (tpy) into benzene has been studied. The partition coefficient (P_s) of tpy was obtained experimentally in order to calculate the equilibrium concentration of tpy in the organic phase. From the slope analysis, it was shown that these lanthanoids were extracted as Ln(tta)₃(tpy). The adduct formation constant (_s,1) and the synergic extraction constant were obtained for each lanthanoid. The (_s,1) decreases with increasing atomic number of lanthanoids and the trend of (_s,1) is compared with that for bidentate and unidentate heterocyclic amines.     

Indirect spectrophotometric determination of chromium in aqueous samples with a novel chromogen ferene-TM

Summary An analytical procedure for the indirect determination of chromium at theg level in aqueous samples has been developed. It involves the use of a novel chromogen 3-(2-pyridyl)-5,6 bis(5-(2 furyl disulfonic acid))-1,2,4-triazine disodium salt (Ferene-TM), which forms an intensely blue tris chelate with iron(II) that absorbs at 593 nm with a molar absorptivity of 35,500 1 cm^–1 mol^–1. In an acidic system (pH1.0) chromium(VI) is reduced to chromium(III) in the presence of an excess of iron(II), which in turn decreases the absorption of the tris iron(II)-ferene-TM complex. The differential absorption data show a linear relationship for chromium(VI) in 0.01–1.0 ppm range. Many common cations and anions in micro concentration range do not influence the analytical response.

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Indirekte spektrophotometrische Bestimmung von Chrom in wärigen Lösungen mit dem neuen Farbreagens Ferene-TM

Zusammenfassung Ein Verfahren zur indirekten Bestimmung vong-Mengen Chrom in wäßrigen Proben wurde ausgearbeitet. Es beruht auf der Verwendung eines neuen Farbreagens 3-(2-Pyridyl)-5,6-bis(5-(2-furyldisulfonsäure))-1,2,4-triazin-dinatrium (Ferene-TM). Dieses bildet mit Fe(II) ein intensiv blau gefärbtes Tris-Chelat, das bei 493 nm eine molare Absorptivität von 35500 l· cm^–1·mol^–1 zeigt. Chrom(VI) wird bei pH 1,0 zu Cr(III) in Gegenwart eines Überschusses an Fe(II) reduziert, so daß die Absorption des erwähnten Tris-Chelates herabgesetzt wird. Die Absorptionswerte zeigen für 0,01 bis 1,0 ppm Cr(VI) ein lineares Verhältnis. Viele übliche Kationen und Anionen beeinflussen in Mikromengen das analytische Ergebnis nicht.

     

Synthesis of bipyridylene-bridged bisporphyrin by nickel-mediated coupling reaction: ON-OFF control of cofacial porphyrin unit by reversible complexation.

Novel bipyridylene-bridged bisporphyrin 1a, in which two porphyrin units were attached directly to symmetrical 4,4'-positions of the 2,2'-bipyridyl group, was synthesized by a nickel(0)-mediated homocoupling reaction of 5,10,15-tris(n-heptyl)-20-(2'-bromo-4'-pyridyl)porphyrinatozinc (3a) in 58% yield. Spatial geometries of two porphyrins in 1a were regulated by reversible complexation of the bipyridyl part with PdCl(2). Thus, the addition of 2.2 equiv of palladium chloride to 1a converted the freely rotating conformation to the cofacial bisporphyrin 2a. The subsequent addition of 4,4'-dimethyl-2,2'-bipyridine 9 regenerated the initial bisporphyrin 1a.     

Depth profiles of potassium and its isotope ratio (40K/K) in several forest soils

Depth profiles potassium and its isotope ratio (⁴⁰K/K) were investigated in several forest soils from different geological and climatic backgrounds. The ratio was found not to be constant (0.0117%) but varied appreciably from 0.0085% to 0.0167% among different soils. Possible factors affecting variability of ⁴⁰K/K values were considered by a multivariate factor analysis which suggested that aqueous parameters like humidity and pH might be a controlling factor in the surface soils. The amount (and probably chemical forms) of iron oxide may be another one influencing ⁴⁰K/K values in mineral components at deeper portions.     

Artificial ion channels showing rectified current behavior.

Voltage-dependent artificial ion channels 3 and 4 were synthesized. Two cholic acid derivatives were connected through a m-xylylene dicarbamate unit at 3-hydroxyl groups. Asymmetries were introduced by terminal hydrophilic groups, carboxylic acid and phosphoric acid for 3 and hydroxyl and carboxylic acid for 4. Under basic conditions, these headgroups in 3 and 4 are expected to be dissociate into -1/-2 (pH 8.2) and 0/-1 (pH 7.2), respectively. Single ion channel properties were examined by a planar bilayer lipid membrane method under symmetrical 500 mM KCl at pH 8.2 or 7.2. When 3 and 4 were introduced into the bilayer membrane under application of positive voltage (a positive-shift method), the current values at positive applied voltage were larger than the corresponding ones at the negative applied voltage. The current-voltage plots were fitted by curves through a zero point to show clear rectification properties. The direction of rectification could be controlled by positive- or negative-shift methods. Vectorial alignment of terminal headgroup charges by the voltage-shift incorporation is essential for giving voltage-dependent rectified ion channels.     

Micelle formation of a cationic surfactant in the presence of 1,n-alkanediol and the miscibility of alcohols in micelles

Micelle formation of dodecyltrimethylammonium bromide (DTAB) was examined in the presence of α,ω-alkanediols applying conductivity measurements. Octanediol and hexanediol promoted the formation of mixed micelles of DTAB and the alcohol, but butanediol interfered with micellization. Analysis of the critical micelle concentration (cmc) based on the lattice model for mixed solution with the Bragg–Williams approximation indicated an unfavorable interaction between alcohol and water and a favorable interaction between the alcohol and surfactant, with the exception of butanediol. The exchange energy between alcohol and water was 0.5kT higher for alkanediol (C_2n(OH)₂) than for the corresponding regular alcohol (C_nOH), which is believed to have resulted from the smaller mixing entropy for the alkanediol than for the corresponding regular alcohol. It was inferred from the analysis that the cmc increase for C₄(OH)₂ was caused by favorable interaction with water but unfavorable interaction with the micellar surfactant.     

A supramolecular photosynthetic triad of slipped cofacial porphyrin dimer, ferrocene, and fullerene

A supramolecular triad consisting of self-assembled imidazolyl-zinc-porphyrin dimer, ferrocene, and fullerene was successfully constructed, resulting in long-lived charge separated species after efficient photoinduced electron transfer and charge shift reactions.