Formation,Expansion, and Interconversion of Metallarings in a Sulfur‐Bridged AuICoIII Coordination System

A novel Au^ICo^III coordination system that is derived from the newly prepared [Co(D ‐nmp)₂]⁻ ( 1 ⁻; D ‐nmp=N‐methyl‐D ‐penicillaminate) and a gold(I) precursor Au^I is reported. Complex 1 ⁻ acts as a sulfur‐donating metallaligand and reacts with the gold(I) precursor to give [Au₂Co₂(D ‐nmp)₄] ( 2 ), which has an eight‐membered Au^I₂Co^III₂ metallaring. Treatment of 2 with [Au₂(dppe)₂]²⁺ (dppe=1,2‐bis(diphenylphosphino)ethane) leads to the formation of [Au₄Co₂(dppe)₂(D ‐nmp)₄]²⁺ ( 3 ²⁺), which consists of an 18‐membered Au^I₄Co^III₂ metallaring that accommodates a tetrahedral anion (BF₄⁻, ClO₄⁻, ReO₄⁻). In solution, the metallaring structure of 3 ²⁺ is readily interconvertible with the nine‐membered Au^I₂Co^III metallaring structure of [Au₂Co(dppe)(D ‐nmp)₂]⁺ ( 4 ⁺); this process depends on external factors, such as solvent, concentration, and nature of the counteranion. These results reveal the lability of the Au S and Au P bonds, which is essential for metallaring expansion and contraction.     

Magnetotransport in simple metals. An exactly soluble model

The magnetoconductivity tensors of a metal with a weakly anisotropic Fermi surface are determined from analytic solutions to the Boltzmann equation without any restrictions on the magnitude of the cyclotron frequency compared to the collision rate. Results are given for both a two- and a three-dimensional model, the former being analytically simpler to handle. The Hall coefficient and magnetoresistance are obtained as functions of the magnetic field, and we show by explicit calculation how the thermoelectric coefficients at high magnetic fields are determined by the thermodynamic entropy.     

Constituents and antimicrobial activity of the essential oils from flower, leaf and stem of Helichrysum armenium

The chemical constituents from the flower, leaf and stem of Helichrysum armenium DC. (Asteraceae) growing in Iran were obtained by hydrodistillation and analyzed by GC and GC/MS. The oil of flower was characterized by higher amount of limonene (21.2%), alpha-cadinol (18.2%), borneol (11.9%), delta-cadinene (9.0%), bornyl acetate (8.0%) and alpha-humulene (7.3%). Twenty one constituents representing 96.2% of the chromatographical leaf oil were identified of which limonene (29.2%), alpha-pinene (14.4%), caryophyllene oxide (6.5%), alpha-gurjunene (6.3%), bornyl acetate (5.5%) and torreyol (5.2%) were the major components. The main components of the stem oil were limonene (23.6%), alpha-pinene (13.4%), spathulenol (6.4%), alpha-gurjunene (6.3%), caryophyllene oxide (5.3%), bornyl acetate (5.2%), beta-cubebene (4.8%) and delta-cadinene (4.3%). The composition of the oils is different, although the most abundant components are identical in leaf oil (96.2%). The antimicrobial effect of flower, leaf and stem essential oils from Helichrysum armenium was studied according to the agar diffusion cup method. The essential oils had a moderate effect on the Gram-positive and Gram-negative bacteria and had a substantial fungicidal effect on the fungi under study.     

Facile synthesis of 8-benzoylthio-2,6-methano-3-benzazocines and 3-benzoylthiomorphinans having small-ring substituents

Synthesis of 3-cyclopropylmethyl-, 3-cyclobutylmethyl-, and 3-methyl-8-benzoylthio-2,6-methano-3-benzazocines (1j-l) was performed by regio-selective chlorosulfonation of non-narcotic 8-deoxy derivatives (1a-c) followed by reduction and benzoylation. 3-Benzoylthiomorphinans (2h-j) were also obtained by the same method. Compounds having small-ring substituents (1k, 1l, 2i, 2j) were found to be weak but pure mu- and delta-opioid antagonists. The analgetic activity of 1k was almost equal to that of pentazocine.     

Enzymic method for the spectrophotometric determination of aspartame in beverages

A sensitive spectrophotometric method for the determination of aspartame in beverages is described. The method involves the enzymic conversion of aspartame into formaldehyde by the alpha-chymotrypsin-alcohol oxidase system, followed by the formation of a chromophore with 4-aminopent-3-en-2-one. The calibration graph was linear in the range 2.0-30.0 micrograms ml-1 of aspartame. Many common ingredients of beverages do not interfere with the proposed method. The method was applied to the determination of the aspartame content of various real samples, and the results obtained were compared with those given by high-performance liquid chromatography.     

Surface Aggregation of Candida albicans on Glass in the Absence and Presence of Adhering Streptococcus gordonii in a Parallel-Plate Flow Chamber: A Surface Thermodynamical Analysis Based on Acid-Base Interactions

Adhesive interactions between yeasts and bacteria are important in the maintenance of infectious mixed biofilms on natural and biomaterial surfaces in the human body. In this study, the extended DLVO (Derjaguin-Landau-Verwey-Overbeek) approach has been applied to explain adhesive interactions between C. albicans ATCC 10261 and S. gordonii NCTC 7869 adhering on glass. Contact angles with different liquids and the zeta potentials of both the yeasts and bacteria were determined and their adhesive interactions were measured in a parallel-plate flow chamber.Streptococci were first allowed to adhere to the bottom glass plate of the flow chamber to different seeding densities, and subsequently deposition of yeasts was monitored with an image analysis system, yielding the degree of initial surface aggregation of the adhering yeasts and their spatial arrangement in a stationary end point. Irrespective of growth temperature, the yeast cells appeared uncharged in TNMC buffer, but yeasts grown at 37 degrees C were intrinsically more hydrophilic and had an increased electron-donating character than cells grown at 30 degrees C. All yeasts showed surface aggregation due to attractive Lifshitz-van der Waals forces. In addition, acid-base interactions between yeasts, yeasts and the glass substratum, and yeasts and the streptococci were attractive for yeasts grown at 30 degrees C, but yeasts grown at 37 degrees C only had favorable acid-base interactions with the bacteria, explaining the positive relationship between the surface coverage of the glass by streptococci and the surface aggregation of the yeasts. Copyright 1999 Academic Press.