Thermal stability of acrylonitrile/chlorosulphonated polyethylene rubber blend

The properties of chlorosulphonated polyethylene (CSM) rubber, acrylonitrile rubber (NBR) and their blend (50/50 w/w) were studied. Fourier transform infrared (FTIR) studies supported that CSM/NBR rubber blend is self curable, when cross-linking takes place between acrylonitrile groups of NBR and –SO₂Cl groups or in situ generated allyl chloride moieties of CSM. The thermal stability of vulcanizates was analyzed in nitrogen by thermogravimetry. It was found that the initial degradation temperature of elastomer based on CSM rubber is lower than of pure NBR rubber. By adding NBR to CSM rubbers, the degradation temperature of crosslinked material increased, indicating higher thermal stability. The activation energy for the degradation are determined using the Arrhenius equation The activation energies for the rubber blends are higher than for elastomers based on pure rubbers. It was found that the mass loss of the blends at any temperature was between those of the pure rubbers. The differential scanning calorimetry (DSC) was used for the glass transition temperature determination. It is estimated thermodynamic immiscibility of NBR/CSM blend based on noticed two different glass transition temperatures, corresponding to CSM and NBR rubbers.     

Integrated Oxidative Folding of Cysteine/Selenocysteine Containing Peptides: Improving Chemical Synthesis of Conotoxins

Building bridges : The use of diselenide and selectively (¹⁵N/¹³C)‐labeled disulfide bridges is combined to give improvements in oxidative folding and disulfide mapping. Conotoxin analogues, each with a pair of selenocysteines (Sec) and labeled cysteines (see scheme, red), exhibited significantly improved folding and the labeled cysteines allow correctly folded species to be rapidly identified by NMR spectroscopy.

     

An application of second-order UV-derivative spectrophotometry for study of solvolysis of a novel fluocinolone acetonide ester

A novel topical corticosteroid FA-21-PhP, 2-phenoxypropionate ester of fluocinolone acetonide, has been synthesized in order to investigate the possibility of decreasing systemic side effects. In this study model system for in vitro solvolytic reaction of FA-21-PhP has been analyzed in ethanol/water (90:10, v/v) with excess of sodium hydrogen carbonate. The selected conditions have been used as in vitro model for activation of corticosteroid C-21 ester prodrug. The second-order derivative spectrophotometric method (DS) using zero-crossing technique was developed for monitoring ternary mixture of solvolysis. Fluocinolone acetonide (FA) as a solvolyte was determined in the mixture in the concentration range 0.062–0.312 mM using amplitude ²D_274.96. Experimentally determined LOD value was 0.0295 mM. The accuracy of proposed DS method was confirmed with HPLC referent method. Peak area of parent ester FA-21-PhP was used for solvolysis monitoring to ensure the initial stage of changes. Linear relationship in HPLC assay for parent ester was obtained in the concentration range 0.054–0.54 mM, with experimentally determined LOD value of 0.0041 mM. Investigated solvolytic reaction in the presence of excess of NaHCO₃ proceeded via a pseudo-first-order kinetic with significant correlation coefficients 0.9891 and 0.9997 for DS and HPLC, respectively. The values of solvolysis rate constant calculated according to DS and HPLC methods are in good accordance 0.038 and 0.043 h^?1, respectively.     

Interaction of quinapril anion with cationic surfactant micelles of cetyltrimethylammonium bromide

In this study, the interaction of the anion of quinapril (QUIN), angiotensin converting enzyme (ACE) inhibitor, with cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated. The effect of cationic micelles on the spectroscopic and acid-base properties of QUIN was studied at pH 8. The binding of QUIN anion to CTAB micelles implied a shift in drug acidity constant (pK(a)(water)-pK(a)(micelle)=1.39) proving the great affinity of negatively charged QUIN ion for the positively charged CTAB micelle surface. The strong dependence of the partition coefficient K(x) on QUIN concentration, obtained by using pseudo-phase model, is consistent with an adsorption-like phenomenon. From the dependence of differential absorbance at lambda=272 nm on CTAB concentration, by using mathematical model that treats the solubilization of QUIN anion as its binding to specific sites in the micelles (Langmuir adsorption isotherm), the binding constant K(b)=(2.3+/-0.4)x10(3) mol(-1)dm(3) was obtained. QUIN-CTAB binding constant was also calculated from micellar liquid chromatography (MLC) and this method was found to be not accurate enough for its determination.     

Bioactive,Elastic, and Biodegradable Emulsion Electrospun DegraPol Tube Delivering PDGF‐BB for Tendon Rupture Repair

Healing of tendon ruptures represents a major challenge in musculoskeletal injuries and combinations of biomaterials with biological factors are suggested as viable option for improved healing. The standard approach of repair by conventional suture leads to incomplete healing or rerupture. Here, a new elastic type of DegraPol® (DP), a polyester urethane, is explored as a delivery device for platelet‐derived growth factor—BB (PDGF‐BB) to promote tendon healing. Using emulsion electrospinning as an easy method for incorporation of biomolecules within polymers, DegraPol® supports loading and release of PDGF‐BB. Morphological, mechanical and delivery device properties of the bioactive DP scaffolds, as well as differences arising due to different electrospinning parameters are studied. Emulsion electrospun DP scaffolds result in thinner fibers than pure DP scaffolds and experience decreased strain at break [%], but high enough for successful surgeon handling. PDGF‐BB is released in a sustained manner from emulsion electrospun DP, but not completely, with still large amount of it being inside the polymeric fibers after 30 d. In vitro studies show that the bioactive scaffolds promote tenocyte proliferation in serum free and serum⁺ conditions, demonstrating the potential of this surgeon‐friendly bioactive delivery device to be used for tendon repair.

     

3-Aryl-4-Isoquinolinone Derivatives An Efficient Oxidative Preparation

A comparative study of the oxidation of 3-aryl-4-hydroxytetrahydroisoquinolines has been carried out. A modification of the Jones conditions turn out to be the best methodology for the regioselective preparation of target 4-isoquinolinone derivatives.     

A combination of tandem amine-exchange/heterocyclization and biaryl coupling reactions for the straightforward preparation of phenanthro[9,10-d]pyrazoles

The tandem amine-exchange/heterocyclization of enaminoketones is successfully applied to the regioselective preparation of a series of new 4,5-diarylpyrazoles by reaction of phenylhydrazine and several 3-N,N-(dimethylamino)-1,2-diarylpropenones. The comparison of a vast array of biaryl coupling procedures provides general, complementary approaches to new phenanthro[9,10-d]pyrazoles. The most efficient procedures for this final step in the construction of the tetracyclic system are based on a Stille-type tandem stannylation-biaryl coupling of o,o'-dihalogenated diarylpyrazoles and an hypervalent iodine-mediated nonphenolic oxidative coupling of nonhalogenated precursors.     

Revisiting the Ullmann-ether reaction: a concise and amenable synthesis of novel dibenzoxepino[4,5-d]pyrazoles by intramolecular etheration of 4,5-(o,o'-halohydroxy)arylpyrazoles

A concise synthesis of a series of novel dibenzoxepino[4,5-d]pyrazoles was accomplished by implementation of an intramolecular Ullmann-ether reaction on o,o'-halohydroxy-4,5-diarylpyrazoles mediated by CuBr.DMS. An alternative useful approach based on the palladium-catalyzed biaryl-ether linkage formation (Buchwald-Hartwig reaction) was also successfully applied, offering limitations with regard to the steric demand of the substituents. The synthesis of the key o,o'-halohydroxy-4,5-diarylpyrazole intermediates proceeds through the construction of the heterocyclic ring by a tandem amine-exchange/heterocyclization sequence of 3-N,N-(dimethylamino)-1,2-diarylpropenones with phenylhydrazine followed by basic hydrolysis for deprotection. The enamino ketone precursors were conveniently prepared from the corresponding O-sulfonyloxy and O-benzoyloxy ortho-substituted 1,2-diarylethanones, starting from inexpensive salicylaldehyde or phenylacetic derivatives. Preliminary binding affinity experiments against peripheral and central nervous system receptors have been done with negative results.