Study of the synthesis of poly(isobutylene-b-amide-11) by polycondensation α,ω-dianhydride oligoisobutylene with α,ω-diamino oligoamide-11. II. Synthesis of the block copolymers by reaction in solution

Several di-, tri- or multiblock poly(isobutylene-b-amide-11)s are prepared by reaction of α-mono or α,ω-dianhydride oligoisobutylenes with α-mono or α,ω-diamino oligoamides, in o-dichorobenzene at 140°C. They are characterized mainly by ¹H- and ¹³C-NMR spectroscopy and GPC, using the trifluoroacetylation technique. Their thermal differential chromatograms are reported and analyzed.     

Simultaneous speciation of mercury and butyltin compounds in natural waters and snow by propylation and species-specific isotope dilution mass spectrometry analysis

A robust method has been developed for simultaneous determination of mercury and butyltin compounds in aqueous samples. This method is capable of providing accurate results for analyte concentrations in the picogram per liter to nanogram per liter range. The simultaneous determination of the mercury and tin compounds is achieved by species-specific isotope dilution, derivatization, and gas chromatography–inductively coupled plasma mass spectrometer (GC–ICP–MS). In derivatization by ethylation and propylation, reaction conditions such as pH and the effect of chloride were carefully studied. Ethylation was found to be more sensitive to matrix effects, especially for mercury compounds. Propylation was thus the preferred derivatization method for simultaneous determination of organomercury and organotin compounds in environmental samples. The analytical method is highly accurate and precise, with RSD values of 1 and 3% for analyte concentrations in the picogram per liter to nanogram per liter range. By use of cleaning procedures and SIDMS blank measurements, detection limits in the range 10–60 pg L^–1 were achieved; these are suitable for determination of background levels of these contaminants in environmental samples. This was demonstrated by using the method for analysis of real snow and seawater samples. This work illustrates the great advantage of species-specific isotope dilution for the validation of an analytical speciation method—the possibility of overcoming species transformations and non-quantitative recovery. Analysis time is saved by use of the simultaneous method, because of the use of a single sample-preparation procedure and one analysis.     

Preparation of amphiphilic polyisobutylenes-b-polyethylenamines by mannich reaction. I. Synthesis and characterization of α-phenololigoisobutylenes

The cationic polymerization of isobutylene initiated by 4-(2-hydroxy-2-propyl)phenol/BCl₃ system results mainly in α-phenol-ω-chlorooligoisobutylene; however p-(2-chloro-2,4-dimethyl-4-pentyl)phenol is present in all cases. α-Methyl-ω-chlorooligoisobutylene is formed only when the temperature is below?50°C; it results from initiation by the phenol/BCl₃ system. Thermal dehydrochlorination of α-phenol-ω-chlorooligoisobutylene is quantitative and leads to a mixture of isomeric ω-unsaturated oligoisobutylenes. α-Methyl-ω-phenololigoisobutylene is prepared by the Friedel—Crafts reaction between industrial unsaturated oligoisobutylene and phenol in the presence of SnCl₄ at ?30°C; the reaction is quantitative between ?50 and ?30°C degradation takes place. © 1993 John Wiley & Sons, Inc.     

Underpotential deposition of hydrogen on benzene-modified Pt(111) in aqueous H2SO4

The Pt(111) electrode is modified by an overlayer of C6H6 (ads) upon its cycling in the 0.05-0.80 V range in aq H2SO4 + 1 mM C6H6. The C6H6 (ads) overlayer significantly changes the underpotential-deposited H (H(UPD)) and anion adsorption, and cyclic-voltammetry (CV) profiles show a sharp cathodic peak and an asymmetric anodic one in the 0.05-0.80 V potential range. The C6H6 (ads) layer blocks the (bi)sulfate adsorption but facilitates the adsorption of one monolayer of H(UPD). Cycling of the benzene-modified Pt(111) in benzene-free aq 0.05 H2SO4 from 0.05 to 0.80 V results in a partial desorption of C6H6 (ads) and in a partial recovery of the CV profile characteristic of an unmodified Pt(111). The peak potential of the cathodic and anodic feature is independent of the scan rate, s (10 < or = s < or = 100 mV s(-1)), and the peak current density increases linearly with an increase of the scan rate. Temperature variation modifies the peak potential and current density but does not affect the charge density of the cathodic or anodic feature. Temperature-dependent studies allow us to determine the thermodynamic state function for the H(UPD) adsorption and desorption. Delta G degrees(ads)(H(UPD))assumes values from -4 to -12 kJ mol(-1), while has values from 9 to 14 kJ mol(-1). The values of delta Delta G degrees (delta Delta G degrees = delat Delta G degrees(ads) + delta Delta D degrees(des)) decrease almost linearly from 6 kJ mol(-1) at theta(H(UPD) --> 0 to 0 kJ mol(-1) at theta(H(UPD) --> 1. The nonzero values of delta Delta G degrees testify that the adsorbing and desorbing H(UPD) adatoms interact with an energetically different substrate. The lateral interactions changed from repulsive (omega = 29 kJ mol(-1) at theta(H(UPD) --> 0) to attractive (omega = -28 kJ mol(-1) at theta(H(UPD) --> 1) as the H(UPD) coverage increases. The values of delta S degrees(ads)(H(UPD)) increase from 19 to 56 J K(-1) mol(-1), while those of delta S degrees(des)(H(UPD)) decrease from 45 to -30 J K(-1) mol(-1) with an increase of H(UPD) coverage. The values of delta H degrees(des)(H(UPD)) and delta H degrees(des)(H(UPD)) vary from 0 to 27 kJ mol(-1). The Pt(111)-H(UPD) surface bond energy at the benzene-modified Pt(111) electrode falls in the 191-218 kJ mol(-1) range and is weaker than in the case of the unmodified Pt(111) electrode in the same electrolyte.     

Designed helical peptides inhibit an intramembrane protease

gamma-Secretase cleaves the transmembrane domain of the amyloid precursor protein, a process implicated in the pathogenesis of Alzheimer's disease, and this enzyme is a founding member of an emerging class of intramembrane proteases. Modeling and mutagenesis suggest a helical conformation for the substrate transmembrane domain upon initial interaction with the protease. Moreover, biochemical evidence supports the presence of an initial docking site for substrate on gamma-secretase that is distinct from the active site, a property predicted to be generally true of intramembrane proteases. Here we show that short peptides designed to adopt a helical conformation in solution are inhibitors of gamma-secretase in both cells and enzyme preparations. Helical peptides with all d-amino acids are the most potent inhibitors and represent potential therapeutic leads. Subtle modifications that disrupt helicity also substantially reduce potency, suggesting that this conformation is critical for effective inhibition. Fluorescence lifetime imaging in intact cells demonstrates that helical peptides disrupt binding between substrate and protease, whereas an active site-directed inhibitor does not. These findings are consistent with helical peptides interacting with the initial substrate docking site of gamma-secretase, suggesting a general strategy for the development of potent and specific inhibitors of intramembrane proteases.     

The formylation of the upper-rims of thiacalixarenes: synthesis of the first tetra-formylated and the first meta-substituted thiacalix[4]arenes

The conventional Gross reaction for the formylation of the tetrapropoxythiacalix[4]arene using TiCl₄ affords the 18-(chloromethyl)-28-hydroxy-25,26,27-tripropoxythiacalix[4]arene substituted in the meta-position of the macrocycle. The p-tetraformyl-tetrapropoxythiacalix[4]arene, which is an interesting intermediate to the upper-rims functionalization of thiacalixarenes, was prepared with a very good yield using BuLi and N-formylpiperidine.     

qNMR for profiling the production of fungal secondary metabolites

Analysis of complex mixtures is a common challenge in natural products research. Quantitative nuclear magnetic resonance spectroscopy offers analysis of complex mixtures at early stages and with benefits that are orthogonal to more common methods of quantitation, including ultraviolet absorption spectroscopy and mass spectrometry. Several experiments were conducted to construct a methodology for use in analysis of extracts of fungal cultures. A broadly applicable method was sought for analysis of both pure and complex samples through use of an externally calibrated method. This method has the benefit of not contaminating valuable samples with the calibrant, and it passed scrutiny for line fitting and reproducibility. The method was implemented to measure the yield of griseofulvin and dechlorogriseofulvin from three fungal isolates. An isolate of Xylaria cubensis (coded MSX48662) was found to biosynthesize griseofulvin in the greatest yield, 149 ± 8 mg per fermentation, and was selected for further supply experiments. Copyright © 2016 John Wiley & Sons, Ltd.     

Rheological Behavior and Non-enzymatic Degradation of a Sulfated Galactan from Halymenia durvillei (Halymeniales, Rhodophyta)

The rheological behavior of a sulfated galactan extracted from Halymenia durvillei, a red seaweed collected in the coastal waters of a small island of Madagascar (Nosy-be in Indian Ocean), was investigated in dilute and semi-dilute solutions. In dilute solution with NaCl at 0.3?M, the polysaccharide adopted a coil conformation whereas, at higher concentrations, the polymer had the behavior of shear-thinning fluid, typical of polymer with high molar mass or semi-rigid conformation. Degradations of this lambda carrageenan-like, using radical depolymerization, and high-pressure homogenization led to several samples of various and controlled molar masses. The measure of their intrinsic viscosities permitted the determination of the relationship of Mark?CHouwink?CSakurada.     

Highly efficient metal‐free organic catalysts to design new Environmentally‐friendly starch‐based blends

A one‐step process is reported to directly synthesize blends of poly(trimethylene carbonate) (PTMC) with a modified granular starch. Trimethylene Carbonate (TMC) ring‐opening polymerization is performed in the presence of native starch particles in bulk conditions at 150 °C and the efficiency of metal‐free organic catalysts (TBD and phosphazene superbases P1‐t‐Oct, P2‐t‐bu, and P4‐t‐bu) are investigated to replace the organo‐metallic stannous octanoate initiator. TMC monomer is successively converted into PTMC and the robustness of organic catalysts is highlighted with significant activities at very low concentrations (<100 ppm), where stannous octanoate is inefficient. Reactivity of starch toward TMC ROP is deeply investigated by NMR techniques and a starch‐graft‐PTMC is indirectly evidenced. Starch substitution degree reaches 0.9% indicating that PTMC grafting only occurs at the surface of swollen granular starch. PTMC graft length from the starch surface remained low in the range 2–12 and model ROP reactions highlight the role of TMC hydrolysis on PTMC graft length. Despite low PTMC grafts, a fine dispersion of intact starch particles into the PTMC matrix is evidenced. Consequently, metal‐free organic catalysts at low concentrations are promising candidates for synthesizing blends of PTMC with high loadings of surface‐modified starch (32% by weight) in 2 min within a one‐step process. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 493–503