From solution-phase to solid-phase enyne metathesis: crossover in the relative performance of two commonly used ruthenium pre-catalysts

A crossover in the ability of two distinct ruthenium-based metathesis pre-catalysts to effect the synthesis of dialkenylboronic esters in solution and on the solid-phase was observed. Specifically, while the Grubbs 2nd generation pre-catalyst 3 affords a greater degree of conversion to product than the Hoveyda-Grubbs pre-catalyst 2 in a solution-phase enyne-metathesis reaction, this trend is reversed in the solid-phase variant. Systematic investigation showed this trend to be general, regardless of variations in the homoallylic alcohol and alkynylboronic ester components of the reaction, as well as in the type of solid support employed. Experiments to determine a mechanistic hypothesis for this trend highlighted the significance of the ruthenium remaining bound to the substrate after metathetic rearrangement and found the presence of phosphine ligand to be detrimental to the success of the solid-phase reaction. Therefore, these results suggest an expanded role for phosphine-free pre-catalysts, such as 2, in challenging solid-phase metathesis reactions.     

Determination of triclosan in foodstuffs

A reverse-phase high-performance liquid chromatographic (RP-HPLC) method coupled with an ultraviolet detector was developed to determine triclosan which had migrated into foodstuffs from packaging materials. The method includes extraction with hexane, followed by evaporation to dryness and residue re-dissolution in ACN 90%. Chromatographic separation was performed with a Kromasil 100 C18 column (15 cm x 0.4 cm ID, 5 microm particle size) at 30 degrees C and using ACN and water as mobile phases. Regarding recoveries, good results (higher than 83% and lower than 112%) were obtained for the three representative food matrixes selected (orange juice, chicken breast meat, and Gouda cheese).     

Direct Electrochemistry of Cytochrome c on EDTA-ZrO2 Organic-inorganic Hybrid Film Modified ElectrodesState Key Laborator3.＂ of Chemo／Biosensing and Chemometrics, Hunan Universit3; Changsha. Hunan 410082. China

A composite film of ethylenediamine tetraacetic acid (EDTA)‐ZrO₂ organic‐inorganic hybrid was prepared based on the chelation between Zr(IV) and EDTA. The direct electrochemical behavior of cytochrome c (cyt. c) at the hybrid film modified glassy carbon electrodes was investigated. The immobilized EDTA can promote the redox of heme in horse heart cyt. c which gives rise to a pair of reversible redox peaks with a formal potential of 40 mV (vs. SCE). The peak current increased linearly with the increase of cyt. c concentration in the range of 1.6 × 10^?6—8.0 × 10^?5 mol·L^?1 with the correlation coefficient of 0.996. Further investigation shows that metal ions can impede the electron transfer of cyt. c. The impediment capability of metal ions depends on their coordination capability with EDTA and their valence number.     

Preparation and thermosensitivity of naturally occurring polypeptide poly(gamma-glutamic acid) derivatives modified by propyl groups

Poly(gamma-glutamic acid) (gamma-PGA) is a biosynthetic polymer, and the carboxyl groups are able to undergo a chemical modification. In this study, poly(alpha-propyl gamma-glutamate) (gamma-PGA propylate) was synthesized by the esterification of these carboxyl groups to yield a thermosensitive and biodegradable polymer. In aqueous solution, the gamma-PGA propylate can impart thermosensitivity by controlling the hydrophobic-hydrophilic balance of the gamma-PGA polymeric chains.     

Adrenaline recognition in water

Host molecule 1 displays a high affinity in water towards catecholamines and especially related structures such as beta-blockers with extended aromatic pi-faces (up to 7x10(3) M(-1) for each single complexation step or 5x10(7) M(-2) for both steps). The amphiphilic structural design leads to an extensive self-association of host molecules through their aromatic flanks. Above a cmc (critical micelle concentration) of 3x10(-4) M, host 1 forms micelles that produce a favorable microenvironment for hydrophobic interactions with the included guest molecules. Electrostatic attraction of the ammonium alcohol by the phosphonate anions is thus combined with hydrophobic contributions between the aromatic moieties. Ionic hydrogen bonds with polar OH or NH groups of the guest enforce the non-covalent interactions, and finally lead to increased specificity. Both its affinity and its selectivity towards adrenergic receptor substrates are greatly enhanced if the receptor molecule 1 is transferred from water into a lipid monolayer. Catecholamines and beta-blockers lead to drastically different effects at concentrations approaching the micromolar regime. Especially beta-blockers with minute structural changes can be easily distinguished from each other. In both cases, extensive hydrophobic interactions with a self-associated and/or self-organized microenvironment are largely responsible for the observed high efficiency and specificity.     

A comparative study of various computational approaches in calculating the structure of pyridoxal 5'-phosphate (PLP)-dependent beta-lyase protein. The importance of protein environment

Various computational approaches, using molecular mechanics (Amber), semiempirical (AM1), density functional (B3LYP), and various ONIOM methods, have been comparatively investigated for the structure of Escherichia coli NifS CsdB protein. The structure of the entire monomer containing 407 amino acid residues and 579 surrounding water molecules has been optimized. The full geometry optimization in the "active site-only" approach (including only active site atoms) has been found to give the largest root-mean-square (RMS) deviation from the X-ray structure; a much better agreement has been achieved by keeping the atoms leading to the backbones of some amino acids frozen in their positions in the X-ray structure. The best agreement has been attained by including the surrounding protein in the calculations using the two-layer ONIOM (B3LYP:Amber) approach. The results presented in this study conclusively demonstrate the importance of the protein/active-site interaction on the active-site structure of the enzyme. The present theoretical study represents the largest system studied at the ONIOM level to date, containing 7992 atoms, including 84 atoms in the QM region and rest in the MM region.     

Helical poly(3-methyl-4-vinylpyridine)/amino acid complexes: preparation, characterization, and biocompatibility

Helical poly(3-methyl-4-vinylpyridine) (P3M4VP)/amino acid complexes have been prepared via acid-base reaction of the achiral polymer with D and L amino acids: alanine, leucine, valine, serine and phenylalanine. The circular dichroism (CD) spectra of P3M4VP/D- and L-alanine complexes in CH(3)OH/H(2)O show opposing (near mirror image) Cotton effect signals at 278.4, 274.8 and 270.8 nm, indicating the formation of enantiomeric secondary structures. The formation of the enantiomeric structures is supported by observed [alpha](D)(25) values of -3.0 and +3.0 for the P3M4VP/D-alanine and P3M4VP/L-alanine complexes, respectively. The preparation of helical P3M4VP/amino acid complexes has been carried out in CH(3)OH and H(2)O at pH 1.8 and 2.7. The intensities of the Cotton effect signals were good. For example, for the P3M4VP/L-alanine complexes in CH(3)OH/H(2)O and H(2)O (pH 1.8), the second Cotton effect signal around 275-277 nm show [theta;] values of 49 980 and 79 210 deg . cm(2) . dmol(-1), respectively. The formation of the helical secondary structure is rapid. The acid-base reaction between P3M4VP and L-alanine in CH(3)OH/H(2)O, in 10 min, show a CD spectrum with Cotton effect signals at 274 and 272 nm with [theta] values of 27,000 deg . cm(2) . dmol(-1) and -36,000 deg . cm(2) . dmol(-1), respectively. P3M4VP permits ready conformational reorientation on complexation with amino acids, but once the helical P3M4VP/amino acid complexes are formed, it is stable at room temperature. P3M4VP is not compatible with HeLa ovarian cancer cells, but the helical P3M4VP/amino acid complexes are compatible with HeLa cells. The complexes minimally interfere with the adhesion and growth of HeLa cells on complex surfaces. Helical poly(3-methyl-4-vinylpyridine)/D- and L-alanine complexes support the attachment and growth of HeLa cells. The micrographs shows HeLa cells after three days: left panel: on P3M4VP/L-alanine complex; right panel: on P3M4VP/D-alanine complex.     

Spectroscopic Study on Interaction of β-Cyclodextrin with Triprolidine Hydrochloride

The complexation of triprolidine hydrochloride （TRP） and β-cyclodextrin （β-CD） in deuterium oxide was investigated by 400 MHz 1^H NMR spectroscopy. The 800 MHz 2D ROESY data revealed that two 1 ：1 and one 2 ： 1 β-CD-TRP inclusion complexes were formed. Both aromatic moieties （p-tolyl and pyridyl ring） has entered into the β-CD cavity, confirming the existence of two different equilibria for 1 ： 1 inclusion complexes in which p-tolyl ring of the guest is more tightly held by the host cavity. The ROE intermolecular interactions provided the plausible structures of these 1 ： 1 and 2 ： 1 stoichiometric inclusion complexes of β-CD-triprolidine hydrochloride in solu- tion.     

Two-dimensional double-quantum 2H NMR spectroscopy in the solid state under OMAS conditions: correlating 2H chemical shifts with quasistatic line shapes.

Solid-state 2H NMR spectroscopy is a well-established and versatile method to study molecular orientation and dynamics in selectively deuterated samples. Herein, we introduce a 2D 2H double-quantum (DQ) NMR experiment performed under fast magic-angle spinning with a slight offset of the magic angle (OMAS). The experiment combines 2H chemical-shift resolution with DQ-filtered quasistatic 2H line shapes. In this way, it is possible to separate 2H resonances and to independently determine 2H quadrupole couplings at multiple sites. While 2H chemical shifts are resolved in the 2H DQ dimension, the quadrupole parameters can be obtained from characteristic line shapes which are reintroduced in the second dimension by the magic-angle offset. The 2D 2H DQ OMAS experiment is demonstrated on L-histidine which was deuterated at multiple sites by recrystallisation from D2O.     

Feasibility of a liquid-phase microextraction sample clean-up and liquid chromatographic/mass spectrometric screening method for selected anabolic steroid glucuronides in biological samples

Anabolic androgenic steroids (AAS) are metabolized extensively in the human body, resulting mainly in the formation of glucuronide conjugates. Current detection methods for AAS are based on gas chromatographic/mass spectrometric (GC/MS) analysis of the hydrolyzed steroid aglycones. These analyses require laborious sample preparation steps and are therefore time consuming. Our interest was to develop a rapid and straightforward method for intact steroid glucuronides in biological samples, using liquid-phase microextraction (LPME) sample clean-up and concentration method combined with liquid chromatographic/tandem mass spectrometric (LC/MS/MS) analysis. The applicability of LPME was optimized for 13 steroid glucuronides, and compared with conventional liquid-liquid extraction (LLE) and solid-phase extraction (SPE) procedures. An LC/MS/MS method was developed for the quantitative detection of AAS glucuronides, using a deuterium-labeled steroid glucuronide as the internal standard. LPME, owing to its high specificity, was shown to be better suited than conventional LLE and SPE for the clean-up of urinary AAS glucuronides. The LPME/LC/MS/MS method was fast and reliable, offering acceptable reproducibility and linearity with detection limits in the range 2-20 ng ml(-1) for most of the selected AAS glucuronides. The method was successfully applied to in vitro metabolic studies, and also tested with an authentic forensic urine sample. For a urine matrix the method still has some unsolved problems with specificity, which should be overcome before the method can be reliably used for doping analysis, but still offering additional and complementary data for current GC/MS analyses.