Combinatorial synthesis, reversed-phase and normal-phase high-performance liquid chromatography elution data and liquid chromatography/positive atmospheric pressure chemical ionization tandem mass spectra of methoxylated and glycosylated resveratrol analogues

Analyses of methoxylated and glycosylated stilbenes remain scarce in the literature because of the commercial unavailability of these compounds. Here a library of 22 compounds was synthesized by combinatorial chemistry. Their elution profiles were compared on three different columns (C18, C8, and silica) with those of seven commercial resveratrol analogues and two viniferins. The spectra recorded by liquid chromatography/positive atmospheric pressure chemical ionization tandem mass spectrometry (LC-APCI(+)-MS/MS) are discussed and recommendations made for easier identification of new stilbenes.     

Use of headspace solid-phase microextraction for the quantification of poly(3-hydroxybutyrate) in microbial cells

Biopolymers such as poly(hydroxyalkanoates) (PHAs) have received much attention due to their physico-chemical properties, biodegradability, and biocompatibility that make them good candidates for industrial and medical applications. Produced by some microorganisms PHAs accumulate within the cells of these organisms. The optimization of microbial processes to produce PHAs at a lower cost requires rapid and accurate techniques for quantification of the biopolymer in biomass. The present study describes a method based on solid-phase microextraction (SPME) coupled to gas chromatography (GC) for the determination of poly(3-hydroxybutyrate) (PHB) in Alcaligenes latus cells. First PHB was depolymerized by either methanolic or hydrolytic digestion into methyl 3-hydroxybutyrate (Me-3-HB) or crotonic acid (CA), respectively. The resulting analytes were then subjected to analysis by headspace SPME/GC with flame ionization detection (FID). The two depolymerization/SPME/GC-FID methods were optimized and applied to the analysis of PHB in bacterial biomass harvested from a fermentation process that uses A. latus. Results were compared with those obtained using GC-FID analysis of MeOH/CHCl(3) digested samples. Excellent agreement was found between the three methods but the two SPME-based methods were environmentally friendly and easier to perform.     

Heterogeneous Ziegler‐Natta Catalyst Based on Neodymium for the Stereospecific Polymerization of Butadiene

The synthesis of a series of neodymium complexes supported on modified silica is reported. In an initial step the silanol groups were masked by a Lewis acid (BCl₃, AlCl₃, TiCl₄, ZrCl₄, SnCl₄, SbCl₅, HfCl₄), and then a soluble arene complex Nd(η⁶‐C₆H₅Me)(AlCl₄)₃ formed in situ was reacted with the modified silica. The supported complexes are active and highly stereospecific for butadiene polymerization; 1,4‐cis insertion is superior by 99%. The catalyst based on a treatment of silica with BCl₃ is the most efficient.     

Unprecedented Biodegradable Cellulose-Derived Polyesters with Pendant Citronellol Moieties: From Monomer Synthesis to Enzymatic Degradation

Levoglucosenone (LGO) is a cellulose-derived molecule that is present commercially on a multi-ton/year scale. Taking advantage of the α,β-conjugated ketone of LGO, a new citronellol-containing 5-membered lactone (HBO-citro) was synthesized through a one-pot two-step pathway involving oxa-Michael addition and Baeyer-Villiger oxidation. The solvent-free treatment of HBO-citro with NaBH₄ at room temperature led to the full reduction of the lactone moiety which gave a novel fully renewable triol monomer having a citronellol side chain (Triol-citro). Noticeably, by simply changing the reducing agent, temperature and reaction duration, the partial reduction of HBO-citro can be achieved to yield a mixture of 5- and 6-membered Lactol-citro molecules. Triol-citro was chosen to prepare functional renewable polyesters having citronellol pendant chains via polycondensation reactions with diacyl chlorides having different chain lengths. Good thermal stability (T_d5% up to 170 °C) and low glass transition temperatures (as low as −42 °C) were registered for the polyesters obtained. The polymers were then hydrolyzed using a commercial lipase from Thermomyces lanuginosus (Lipopan^® 50 BG) to assess their biodegradability. A higher degradation profile was found for the polyesters prepared using co-monomers (acyl chlorides) having longer chain lengths. This is likely due to the decreased steric hindrance around the ester bonds which allowed enhanced accessibility of the enzyme.     

2,2,3,3,11,11,12,12-Octamethyl-1,4,7,10,13-pentaoxacyclohexadecane: improved synthesis and crystal structure with NaSCN

An efficient synthesis of 2,2,3,3,11,11,12,12-octamethyl-1,4,7,10,13-pentaoxacyclohexadecane (1, OM16C5) is described, which affords over an order of magnitude improvement in yield over the previously reported method. The first X-ray crystal structure of 1, as a complex with NaSCN, is also reported.     

Preparative isolation of pseudolaric acids A and B,and their glucosides from the root bark of Pseudolarix kaempferi using high‐speed counter‐current chromatography

In order to provide the chemical markers for the quality control of herbal medicines, four diterpenoids, pseudolaric acids A and B (PAA and PAB), and their glucosides were isolated from the methanol extract of the Chinese herb Pseudolarix kaempferi using high‐speed counter‐current chromatography (HSCCC). The diphase solvent system was n‐hexane/EtOAc/MeOH/H₂O which was used at two ratios (5:5:5:5 and 1:9:4:6 by volume) in the separation of pseudolaric acids and their glycosides, respectively. As a result, PAA (14 mg), PAB (129 mg), PAA‐O‐β‐D ‐glucopyranoside (8 mg, PAAG), and PAB‐O‐β‐D ‐glucopyranoside (42 mg, PABG) were obtained from 0.5 g of the crude extract. Their purities were determined to be above 97% by HPLC analysis. Their chemical structures were confirmed by ¹H and ¹³C NMR analysis or HPLC comparison with the reference compounds.     

Sorption of Sr(II) and Eu(III) onto pyrite under different redox potential conditions

Understanding sorption processes is fundamental for the prediction of radionuclide migration in the surroundings of a deep geological disposal of high-level nuclear wastes. Pyrite (FeS2) is a mineral phase often present as inclusions in temperate soils. Moreover, it constitutes an indirect corrosion product of steel, a containment material that is candidate to confine radionuclides in deep geological disposals. The present study was thus initiated to determine the capacity of pyrite to immobilize Sr(II) and Eu(III). An air oxidized pyrite and a freshly acid-washed (non-oxidized) pyrite were used in background electrolytes of varying reducing-oxidizing ability (NaCl, NH3OHCl, and NaClO4) to study the sorption of both cationic species. The sorptive capacity of pyrite appeared directly correlated to the oxidation of the surface. Non-oxidized pyrite had nearly no affinity for the studied cations whereas Sr(II) and Eu(III) species were significantly retained by oxidized pyrite surface. Using the surface complexation theory, sorption mechanisms were modeled with the Fiteql v3.2 and the Jchess 2.0 codes. Sorption of both Sr and Eu was well fitted, assuming hydroxylated species as the major surface species. This study demonstrates that not only the components of a barrier but also the redox conditions and specifications should be well characterized to predict transport of contaminants in the surrounding of a nuclear wastes disposal.     

Copper(II) Triflate Catalyzed Amination of 1,3-Dicarbonyl Compounds

A method to prepare α,α-acyl amino acid derivatives efficiently by Cu(OTf)(2) +1,10-phenanthroline (1,10-phen)-catalyzed amination of 1,3-dicarbonyl compounds with PhI?NSO(2) Ar is described. The mechanism is thought to initially involve aziridination of the enolic form of the substrate, formed in situ through coordination to the Lewis acidic metal catalyst, by the putative copper-nitrene/imido species generated from the reaction of the metal catalyst with the iminoiodane source. Subsequent ring opening of the resultant aziridinol adduct under the Lewis acidic conditions then provided the α-aminated product. The utility of this method was exemplified by the enantioselective synthesis of a precursor of 3-styryl-2-benzoyl-L-alanine.     

Organometallic early lanthanide clusters: syntheses and X-ray structures of new monocyclopentadienyl complexes

The reaction of Ln(BH(4))(3)(THF)(3) or LnCl(3)(THF)(3) with 1 equiv of KCp*' ligand (Cp' = C(5)Me(4)n-Pr) afforded the new monocyclopentadienyl complexes Cp*'LnX(2)(THF)(n) (X = BH(4), Ln = Sm, n = 1, 1a, Ln = Nd, n = 2, 1b; X = Cl, Ln = Sm, n = 1, 3a) and [Cp*'LnX(2)](n') (X = BH(4), n' = 6, Ln = Sm, 2a, Ln = Nd, 2b; X = Cl, Ln = Nd, 4b). All these compounds were characterized by elemental analysis and (1)H NMR. Crystals of mixed borohydrido/chloro-bridged [Cp*'(6)Ln(6)(BH(4))(12-x))Cl(x)(THF)(n')] (x = 10, n' = 4, Ln = Sm, 2a', Ln = Nd, 2b'; x = 5, n = 2, Ln = Sm, 2a' ') were also isolated. Compounds 2a, 2b, 2a', 2b', and 2a' were structurally characterized; they all exhibit a hexameric structure in the solid state containing the [Cp*(3)Ln(3)X(5)(THF)] building block. The easy clustering of THF adducts first isolated is illustrative of the well-known bridging ability of the BH(4) group. Hexameric 2a was found to be unstable in the presence of THF vapors; this may be correlated to the opening of unsymmetrical borohydride bridges observed in the molecular structure.