Hydrolytic Cleavage Research Articles

Synthesis, Spectroscopic, Antibacterial, Antioxidant, DNA Binding and Cleavage, Molecular Docking Studies of Ni(II) and Cu(II) Complexes of S and N Donor Schiff Base Ligands

Binary metal complexes of the ligands (L), H3FPT and H3FP4MT with Ni(II) and Cu(II) metal ions (M) were synthesized and characterized by different spectral and analytical techniques. Among these complexes, Ni(II)- H3FPT complex was found to be polymeric. The ligands and their complexes inhibited the growth of gram positive and gram negative bacterial strains to a moderate extent. The antioxidant nature of ligands and complexes was also established. Intercalative mode of binding of the complexes with calf thymus (CT) DNA was proposed from electronic absorption titrations, fluorescence quenching studies and viscosity measurements. The complexes showed hydrolytic cleavage of plasmid pBR322. Docking studies of metal complexes with DNA revealed that the complexes of H3FP4MT are more active than H3FPT.

A heterotrinuclear bioinspired coordination complex capable of binding to DNA and emulation of nuclease activity

The investigation of compounds capable of strongly and selectively interacting with DNA comprises a field of research in constant development. In this work, we demonstrate that a trinuclear coordination complex based on a dinuclear Fe(III)Zn(II) core designed for biomimicry of the hydrolytic enzyme kidney bean purple acid phosphatase, containing an additional pendant arm coordinating a Pd(II) ion, has the ability to interact with DNA and to promote its hydrolytic cleavage. These results were found through analysis of plasmid DNA interaction and cleavage by the trinuclear complex 1 and its derivatives 2 and 3, in addition to the analysis of alteration in the DNA structure in the presence of the complexes through circular dichroism and DNA footprinting techniques. The suggested covalent interaction of the palladium-containing complex with DNA was analysed using an electrophoretic mobility assay, circular dichroism, high resolution gel separation techniques and kinetic analysis. This is a new and promising metal complex targeted to nucleic acids and acting in two separate ways: strong DNA interaction and hydrolytic cleavage.

Pyridine substituted BODIPYs: synthesis, characterization and cholinesterease, α-glucosidase inhibitory, DNA hydrolytic cleavage effects

In this study, the synthesis of new monostyryl (BDPY-2) and distyryl BODIPY dyes (BDPY-4, BDPY-5) containing pyridine groups has been reported for the first time. The acetylcholinesterase from Electrophorus electricus (AChE), butyrylcholinesterase from equine serum (BuChE), α-glucosidase from Saccharomyces cerevisiae and DNA hydrolytic cleavage actions of BDPY-2, BDPY-4, BDPY-5 were investigated using various techniques. The results indicated that the compounds had varying inhibition properties against AChE, BuChE, and α-glucosidase. BDPY-4 was the most potent compound on AChE with IC50 of 54.78 ± 4.51 µM, and Lineweaver–Burk plots indicated that the compound is bound to a site other than the active site as a noncompetitive inhibitor. The compound-protein binding experiment showed that BDPY-4 changed the microenvironment around AChE. On the other hand, the compounds showed lower α-glucosidase inhibition than the positive control. The DNA hydrolytic cleavage effects were not observed on supercoiled plasmid DNA in the presence of the compounds as compared to negative controls. These findings suggested that BDPY-4 might be a promising compound to treat Alzheimer’s diseases.

Instantaneous Degelling Thermoresponsive Hydrogel.

Responsive polymeric hydrogels have found wide application in the clinic as injectable, biocompatible, and biodegradable materials capable of controlled release of therapeutics. In this article, we introduce a thermoresponsive polymer hydrogel bearing covalent disulfide bonds. The cold aqueous polymer solution forms a hydrogel upon heating to physiological temperatures and undergoes slow degradation by hydrolytic cleavage of ester bonds. The disulfide functionality allows for immediate reductive cleavage of the redox-sensitive bond embedded within the polymer structure, affording the option of instantaneous hydrogel collapse. Poly(ethylene glycol)-b-poly(lactic acid)-S-S-poly(lactic acid)-b-poly(ethylene glycol) (PEG-PLA-SS-PLA-PEG) copolymer was synthesized by grafting PEG to PLA-SS-PLA via urethane linkages. The aqueous solution of the resultant copolymer was a free-flowing solution at ambient temperatures and formed a hydrogel above 32 °C. The immediate collapsibility of the hydrogel was displayed via reaction with NaBH4 as a relatively strong reducing agent, yet stability was displayed even in glutathione solution, in which the polymer degraded slowly by hydrolytic degradation. The polymeric hydrogel is capable of either long-term or immediate degradation and thus represents an attractive candidate as a biocompatible material for the controlled release of drugs.

Metallonucleases encompassing curcumin, 2-aminobenzothiazole and o-phenylenediamine: a search for new metallonucleases

A few novelmetallonucleases were synthesized from curcumin derived Schiff base incorporating 2-aminobenzothiazoleand o-phenylenediamine. By characterization, these complexes were found to have 1:1:1 stoichiometry [M:L:o-Ph]. They were inferred to be electrolytic in nature in accordance to the values of molar conductance. From the spectral data the proposed geometry of all the complexes was deduced to be square planar. The complexes were screened against a few pathogens for their antimicrobial activities which reveal that they are efficient antimicrobial activity than the free ligands. The interactions of CT-DNA were studied by UV spectrophotometric, viscosity and cyclic voltammetric techniques. The complexes with higher values of Kb are optional to have greater DNA binding propensity. They have potent interaction with the CT-DNA and hence they are proficient DNA cleavable linkers due to their importance in biotechnology and drug design. Furthermore, the copper(II) complex exhibits efficient DNA cleavage with supercoiled pBR322 involving hydrolytic cleavage pathway.

Abstract MP213: Activation Of Biosynthetic Pathways Regulates Cardiomyocyte Cell Cycle Induction In Human Cardiomyocyte

Induction of cardiomyocyte proliferation is a promising therapeutic approach to treat heart failure. Several studies have identified metabolism as an important regulator of myocyte proliferation; however, the changes in metabolism during cardiomyocyte division remain unclear. Here, we use ectopic expression of cyclin B1, Cyclin D1, CDK1, and CDK4 (termed 4F) as a tool for understanding how metabolism influences cardiomyocyte proliferation. Mature hiPS-CMs stimulated to proliferate by 4F expression showed significant downregulation of oxidative phosphorylation genes, decreased glucose oxidation, and upregulation of genes that regulate biosynthetic pathways of glucose metabolism such as those involved in NAD(P) + synthesis ( NAMPT, NADK1, NNT ), the hexosamine biosynthetic pathway (HBP) and protein O-GlcNAcylation ( GFPT1 , OGT, OGA ), and the serine biosynthesis pathway (SBP; PHGDH , PSAT1 , SHMT2 ). In 4F-expressing hiPSC-CMs, stable isotope tracing indicated higher enrichment of glucose-derived 13 C in pentose phosphate intermediates, UDP-hexose, phospholipid precursors, NAD + , pyrimidines, UDP-HexNAc, and products of the serine biosynthesis pathway and one-carbon metabolism, suggesting that cell cycle induction activates biosynthetic pathways in cardiomyocytes. Knocking down nicotinamide phosphoribosyltransferase (NAMPT), a critical enzyme in the NAD + salvage pathway, 2 days before 4F overexpression significantly inhibited cell cycle progression in 4F-transduced hiPS-CMs. OGA overexpression, which catalyzes the hydrolytic cleavage of O-GlcNAc from post-transitionally modified proteins, completely abolished 4F-mediated cell cycle induction. Furthermore, NCT503, an inhibitor of the rate-limiting step in the serine biosynthesis pathway, abolished 4F-mediated increases in cell cycle markers. In a gain-of-function approach, we overexpressed phosphoenolpyruvate carboxykinase 2 (PCK2), which can drive carbon from the Krebs cycle to the glycolytic intermediate pool. PCK2 overexpression significantly augmented 4F-mediated cell cycle entry. These findings suggest that a metabolic shift from catabolic to anabolic activity is a critical step for cardiomyocyte cell cycle entry and is required to facilitate proliferation.

Indicators of acidity and methods of its neutralization during preventive conservation and restoration of architectural graphics

The purpose of the article is to analyze the impact of pH of the paper on the state of preservation, to describe the main methods of neutralization of acidity in the implementation of restoration and conservation measures for the preservation of architectural graphics. To indicate the need to monitor the pH state when preserving paper-based collections. Methodology. To analyze the art, methods of systematization, comparison, and generalization to determine and describe the optimal techniques and experience for the preservation of collections of architectural graphics on a paper basis. The scientific novelty consists in a comprehensive study of the relationship between pH and the state of preservation of architectural graphics and methods of neutralization of the acidity in the process of conservation and restoration. Conclusions. It is established that the acidity is due to the parameters of paper production, due to natural aging processes, air pollution, adsorption of acid impurities in the paper, storage conditions, a technique using certain pigments, and so on. It is necessary to monitor the acidity when implementing preventive conservation measures as it is an important indicator of physico-chemical changes in the paper. Acidity accelerates the process of hydrolytic cleavage of cellulose molecules and is one of the reasons for the loss of paper-based collections. A large number of monuments requires conservation and restoration measures to neutralize the pH. Existing methods of stabilization and buffering of acidity are effective, but the search for new, easier to implement, cheaper solutions is ongoing. The new methods can have a longer effect and can be widely used in collections.

Hydrolysis-Driven Viscoelastic Transition in Triblock Copolyether Hydrogels with Acetal Pendants.

While the hydrolytic cleavage of ester groups is widely exploited in degradable hydrogels, the scission in the midst of chain backbones can bring dramatic changes in the mechanical properties of the hydrogels. However, the predictive design of the mechanical profile of the hydrogels is a complex task, mainly due to the randomness of the location of chain scission. To overcome this challenge, we herein present degradable ABA triblock poly(ethylene oxide)-based hydrogels containing an A-block bearing acetal pendant, which provides systematically tunable mechano-temporal properties of the hydrogels. In particular, hydrophobic endocyclic tetrahydropyranyl or exocyclic 1-(cyclohexyloxy)ethyl acetal pendants are gradually cleaved by acidic hydrolysis, leading to the gel-to-sol transition at room temperature. Most importantly, a series of dynamic mechanical analyses coupled with ex situ NMR spectroscopy revealed that the hydrolysis rate can be orthogonally and precisely tuned by changing the chemical structure and hydrophobicity of acetal pendants. This study provides a platform for the development of versatile degradable hydrogels in a highly controllable manner.

In vitro DNA binding, pBR322 cleavage and molecular docking studies of 1,2-diaminobenzene, dichloro glycyl glycinate tin(IV) and zirconium(IV) complexes

De novo design and synthesis of complexes 1,2-diaminobenzene, dichloro glycyl glycinate tin(IV) and zirconium(IV), 1 and 2 as molecular drug entities were carried out. The structure elucidation of 1 and 2 was done by analytical techniques and spectroscopic methods viz. IR, UV–vis, 1H, 13C, 119Sn NMR, ESI–Mass and XRD techniques. In vitro DNA binding studies of 1 and 2 by various biophysical techniques viz electronic absorption, emission spectroscopy and circular dichroism measurements were carried out to evaluate their potential to act as chemotherapeutic candidates; furthermore, cleavage studies with pBR322plasmid DNA and computer-aided molecular docking studies were also done to study the mechanistic pathway and mode of binding at the molecular level. The observed results revealed that complex 1 exhibited greater DNA binding propensity in contrast to complex 2 primarily via electrostatic binding mode. The pBR322 DNA cleavage studies of both the complexes revealed the hydrolytic cleavage mechanism and DNA minor groove binding, which was ascertained by molecular docking studies of the drug candidate. Communicated by Ramaswamy H. Sarma

Arginine Modulates Carbapenem Deactivation by OXA-24/40 in Acinetobacter baumannii

The resistance of Gram-negative bacteria to β-lactam antibiotics stems mainly from β-lactamase proteins that hydrolytically deactivate the β-lactams. Of particular concern are the β-lactamases that can deactivate a class of β-lactams known as carbapenems. Carbapenems are among the few anti-infectives that can treat multi-drug resistant bacterial infections. Revealing the mechanisms of their deactivation by β-lactamases is a necessary step for preserving their therapeutic value. Here, we present NMR investigations of OXA-24/40, a carbapenem-hydrolyzing Class D β-lactamase (CHDL) expressed in the gram-negative pathogen, Acinetobacter baumannii. Using rapid data acquisition methods, we were able to study the “real-time” deactivation of the carbapenem known as doripenem by OXA-24/40. Our results indicate that OXA-24/40 has two deactivation mechanisms: canonical hydrolytic cleavage, and a distinct mechanism that produces a β-lactone product that has weak affinity for the OXA-24/40 active site. The mechanisms issue from distinct active site environments poised either for hydrolysis or β-lactone formation. Mutagenesis reveals that R261, a conserved active site arginine, stabilizes the active site environment enabling β-lactone formation. Our results have implications not only for OXA-24/40, but the larger family of CHDLs now challenging clinical settings on a global scale.

Synthesis and biological activity of N6-mannopyranosyladenines

In this work, potentially bioactive condensation products of adenine with D-mannose and 6-deoxy-L-mannose (L-rhamnose) were synthesized in water and ethanol solutions. According to FTIR spectroscopy and elemental analysis, mono-N6-glycosylated adenines were isolated from water systems in satisfactory yields, while ethanol solutions contained mixtures of N6 and N9-products, as well as complexes of the latter with copper ions. A detailed analysis of the vibrational spectra of N6-glycosyladenines confirmed the structure of carbohydrate fragments in the form of pyranose rings, while some part of the product was obtained in the form of deoxyaminoketosis. N-rhamnosyladenine was formed with a more than double yield because of a higher stability of rhamnose with regard to side reactions. The reflection spectra of model solutions of glycosyladenines, recorded 4 days after preparation, showed no bands characteristic of free adenine in the range of 1250-1110 cm-1, which indicates a sufficient resistance of the synthesized products towards hydrolytic cleavage under experimental conditions. The conducted biotesting of the isolated products on wheat seeds (Triticum aestivum L.) showed an increase in the content of chlorophylls in seedlings for both mannosilade-nines compared to the control. A decrease in the concentration of synthesized products in germination solutions from 0.1 to 0.001% led to an increase in the accumulation of photosynthetic pigments, while this effect was more pronounced for rhamnosyladenine. The latter can be connected with the structural features of car-bohydrate fragments, in particular, the differences in the hydroxylation degree of glucoside fragments. Future research will investigate the mechanisms of transformation and action of N6-substituted adenines.

Fabrication and Characterization of Saffron Stamen Aqueous Extract Controlled Release System as Potential Topical Treatment of Thermal Burn Wounds

AbstractIn our study, we aimed the preparation of Saffron stamen aqueous extract (SSAE) loaded chitosan nanoparticles (CNPs) to be used topically for thermal burns. First, biological activity tests such as DNA binding, DNA cleavage and antibacterial activity were performed to determine the effectiveness of SSAE to be encapsulated. Additionally, a genotoxicity test was performed for the reliability of SSAE. Ionic gelation method was used for encapsulation, and SSAE‐loaded CNPs were obtained. Average particle size, zeta potential, polydispersity index (PdI), morphology, and releasing kinetics of the SSAE‐loaded CNPs and blank CNPs were determined. DNA binding showed that SSAE interacted with DNA electrostatically. It was determined that all doses of SSAE used in hydrolytic and oxidative DNA cleavage experiments cleave DNA. As a result of the Ames / Salmonella test, it was found that 1,25 mg SSAE was not genotoxic. Then, this concentration was used in nanoparticle synthesis. As a result of DLS analysis, it was determined that SSAE‐loaded CNPs have an average size of 57.61±1.234 nm, 0.175±0.008 PdI, and +14±0.755 mV zeta potential. Encapsulation efficiency and loading capacity of SSAE‐loaded CNPs calculated as 71.76 % and 2,64 % respectively. As a result of releasing kinetics, it was determined that 79.54 % of SSAE was released after 168 hours. Antibacterial results revealed that SSAE loaded CNPs were more effective against bacteria than blank SSAE.

Combining Multiplex Fluorescence in situ Hybridization with Fluorescent Immunohistochemistry on Fresh Frozen or Fixed Mouse Brain Sections.

Fluorescent in situ hybridization (FISH) is a molecular technique that identifies the presence and spatial distribution of specific RNA transcripts within cells. Neurochemical phenotyping of functionally identified neurons usually requires concurrent labelling with multiple antibodies (targeting protein) using immunohistochemistry (IHC) and optimization of in situ hybridization (targeting RNA), in tandem. A "neurochemical signature" to characterize particular neurons may be achieved however complicating factors include the need to verify FISH and IHC targets before combining the methods, and the limited number of RNAs and proteins that may be targeted simultaneously within the same tissue section. Here we describe a protocol, using both fresh frozen and fixed mouse brain preparations, which detects multiple mRNAs and proteins in the same brain section using RNAscope FISH followed by fluorescence immunostaining, respectively. We use the combined method to describe the expression pattern of low abundance mRNAs (e.g., galanin receptor 1) and high abundance mRNAs (e.g., glycine transporter 2), in immunohistochemically identified brainstem nuclei. Key considerations for protein labelling downstream of the FISH assay extend beyond tissue preparation and optimization of FISH probe labelling. For example, we found that antibody binding and labelling specificity can be detrimentally affected by the protease step within the FISH probe assay. Proteases catalyze hydrolytic cleavage of peptide bonds, facilitating FISH probe entry into cells, however they may also digest the protein targeted by the subsequent IHC assay, producing off target binding. The subcellular location of the targeted protein is another factor contributing to IHC success following FISH probe assay. We observed IHC specificity to be retained when the targeted protein is membrane bound, whereas IHC targeting cytoplasmic protein required extensive troubleshooting. Finally, we found handling of slide-mounted fixed frozen tissue more challenging than fresh frozen tissue, however IHC quality was overall better with fixed frozen tissue, when combined with RNAscope.

Enzymatically triggered graphene oxide released from multifunctional carriers boosts anti-pathogenic properties for promising wound-healing applications

Spurred by recent progress in biomaterials and therapeutics, stimulus-responsive strategies that deliver an active substance in temporal-, spatial-, and dose-controlled fashions have become achievable. Implementation of such strategies necessitates the use of bio-safe materials that are sensitive to a specific pathological incitement or that, in response to a precise stimulus, undergo hydrolytic cleavage or a change in biomolecular conformation. An innovative design of polymeric stimulus-responsive systems should controllably release a drug or degrade the drug carrier in response to specific lesion enzymes. Wound healing is a great challenge due to various hidden factors such as pathogenic infections, neurovascular diseases, excessive exudates, lack of an effective therapeutic delivery system, low cell proliferation, and cell migration. In addition, long-term use of antibiotics in chronic wound management can result in side effects and antimicrobial resistance. Novel treatments with antibacterial pharmaceuticals thus vitally need to be developed. Recently, graphene and graphene family members have emerged as shining stars among biomaterials for wound-healing applications due to their excellent bioactive properties, which can overcome limitations of current wound dressings and fulfill wound-healing requirements. Herein, we developed a feasible approach to impregnate graphene oxide (GO) into genipin-crosslinked gelatin (3GO) hydrogels to enzymatically control GO release. The developed hydrogels were characterized by chemical, physical, morphological, and cellular analyses. The results proved that the 3GO1 hydrogel is biocompatible and significantly enhanced the mechanical strength by encapsulating GO. Moreover, the rate of GO release depended on the crosslinking degree and environmental enzyme levels. Enzymatically released GO displayed uniform dispersity, retained its antibacterial activities against Staphylococcus aureus and Pseudomonas aeruginosa through sharp edges and wrapping mechanisms, and promoted human fibroblast migration. This multifunctional hydrogel we developed with antibacterial efficacy is suitable for future application as wound dressings.

Gas Chromatography-Mass Spectrometry Analysis of Agricultural Residues using Indigenous Laccase producing Fungi (Albifimbria viridis) as Herbicides

Background and Objective: Discarded as wastes, parts of the agricultural products can be used for feed productivity as well as management of animal feed production. Production of various products is possible using appropriate processing. The objective of the present study was to use laccase of Albifimbria viridis in degradation of agricultural residues and to produce compounds with herbicide properties. Material and Methods: The fungi were isolated from agricultural soils. The isolates were identified using morphological detection and PCR amplification of the internal transcribed spacer. Supernatants were collected from semi-solid cultures and laccase activity was assessed using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) substrate. This was carried out using n-hexane and degradation of the agricultural residues was investigated using gas chromatography-mass spectrometry. Results and Conclusion: Growth of the fungal isolate in culture media with tannic acid was studied using scanning electron microscopy. In total, the isolate produced 50 U ml-1 laccase. Gas chromatography-mass spectrometry analyses revealed production of oxime, methoxy-phenyl and 2-cyclopenten-1-one for tannic acids, o-guaiacol, tetradecane, hexadecane, octadecane, octadecanoic acid, hexadecanoic acid and benzene, 1,3-bis(1,1-dimethylethyl) for sorghum seeds and 2-acetyl-5-methylfuran, phenol, 2-methoxy and benzene, 1,2-dimethoxy for wheat straw during fungal growth (0.73 mg ml-1). Results have shown that the laccase enzyme produced from Albifimbria viridis native strain is capable of hydrolytic cleavage of chemical pollutants from agricultural wastes for herbicide bioremediation. Conflict of interest: The authors declare no conflict of interest.

Ag(I) Complexes of Imine Derivatives of Unexpected 2-Thiophenemethylamine Homo-Coupling and Bis-(E)-N-(furan-2-ylmethyl)-1-(quinolin-2-yl)methanimine

Imines are fundamental organic compounds used as synthetic intermediates and as ligands in coordination chemistry. They are also found to be important pharmacophores in various bioactive compounds. In this report, two Schiff bases were prepared using the traditional condensation of 4-pyridinecarboxaldehyde with 2-thiophenemethylamine and 2-quinolinecarboxaldehyde with furfurylamine to form (E)-1-(pyridin-4-yl)-N-(thiophen-2-ylmethyl)methanimine (L1) and (E)-N-(furan-2-ylmethyl)-1-(quinolin-2-yl)methanimine (L2) respectively. L1 and L2 were complexed with silver perchlorate in 2:1 [M:L] stoichiometry to obtain complexes 1 and 2, respectively. The crystal structures of 1 and 2 were unequivocally determined by single-crystal X-ray diffraction analysis. The resulting structures revealed 2 to be a four-coordinate as expected. In contrast, an unexpected chemoselective hydrolytic cleavage of one mole of the (CH=N) imine ligands occurred in complex 2 and, further, the amines (thiophenemethylamine) homo-coupled to form a new imine ligand derivative in situ (L1a) before coordinating to the Ag(I) center along with L1. This observation described an alternative synthetic route to be explored to synthesize a diverse range of imine derivatives, which involves the Ag(I)-promoted homo-coupling of amines. Herein, the crystal structures of Ag(I) complexes of pyridinyl [Ag(L1)(L1a)]ClO4 (1) and quinolinyl [Ag(L2)2]ClO4 (2) Schiff bases are presented.

Exploiting diol reactivity for the access to unprecedented low molecular weight curdlan sulfate polysaccharides

Curdlan is a bacterial sourced polysaccharide, consisting of a linear backbone of β-1 → 3-linked glucose (Glc) units. The high interest in pharmaceutical applications of curdlan and derivatives thereof is fueling the study of multi-step sequences for regioselective modifications of its structure. Here we have developed semi-synthetic sequences based on a regioselective protection-sulfation-deprotection approach, allowing the access to some, new, low molecular weight curdlan polysaccharide derivatives with unprecedented sulfation patterns. Three different semi-synthetic schemes were investigated, all relying upon the installation of a cyclic benzylidene protecting group on Glc O-4,6-diols, followed by either direct sulfation and deprotection, or some additional steps – including a hydrolytic or oxidative cleavage of the benzylidene rings – prior to sulfation and deprotection. The six obtained polysaccharides were subjected to a detailed structural characterization by 2D-NMR analysis, revealing that some of them showed the majority of Glc units along the polymeric backbone decorated by unprecedented sulfation motifs.

Conjugation of haloalkane dehalogenase DhaA with arabinogalactan to increase its stability

Haloalkane dehalogenase DhaA can catalyze the hydrolytic cleavage of carbonhalogen bonds, along with production of the corresponding alcohol, a proton and a halide. However, DhaA suffers from poor environmental tolerance, such as sensitivity to high temperature, low pH and hypersaline. Arabinogalactan (AG) is a hydrophilic polysaccharide with highly branched long chains. DhaA was conjugated with AG to improve the environmental stability of DhaA in the present study. Each DhaA was averagely conjugated with 4∼5 AG molecules. Conjugation of AG essentially maintained the enzymatic activity of DhaA (91.4 %) without apparent structural alteration. The hydration layer formed by AG could reduce the solvent accessible area of DhaA and slow the protonation process, thereby improving the pH and high salt stability of DhaA. In particular, the remaining activities of the conjugate (AG-DhaA) were 35.3 % after treatment at pH4.0 for 1 h, and 80.8 % in 1 M NaCl after treatment for 16 h. As compared with DhaA, AG-DhaA showed slightly different kinetic parameters (K M of 1.90 μmol/L and k cat of 2.60 s -1).

C21, C22 pregnane glycosides and cytotoxic C27 spriostanol steroids from Asparagus cochinchinesis

A preliminary chemical investigation on 70% MeOH extract of the roots of Asparagus cochinchinensis resulted in the isolation of nine steroids. These isolates comprised of four new C21 (1–4) and one new pregnane (5) glycosides, and four known C27 (6–9) spirostanol steroids. Their structures were identified via analysis of the spectroscopic data and the results of hydrolytic cleavage. The cytotoxic activities of the compounds were tested toward the human tumor cell line Hela (cervical cancer), and compounds 7 and 8 displayed moderate activity with IC50 values of 35.5 and 39.6 μM, respectively.

Chemical and physical interactions of regenerated cellulose yarns and isocyanate-based matrix systems

In the development of structural composites based on regenerated cellulose filaments, the physical and chemical interactions at the fibre-matrix interphase need to be fully understood. In the present study, continuous yarns and filaments of viscose (rayon) were treated with either polymeric diphenylmethane diisocyanate (pMDI) or a pMDI-based hardener for polyurethane resins. The effect of isocyanate treatment on mechanical yarn properties was evaluated in tensile tests. A significant decrease in tensile modulus, tensile force and elongation at break was found for treated samples. As revealed by size exclusion chromatography, isocyanate treatment resulted in a significantly reduced molecular weight of cellulose, presumably owing to hydrolytic cleavage caused by hydrochloric acid occurring as an impurity in pMDI. Yarn twist, fibre moisture content and, most significantly, the chemical composition of the isocyanate matrix were identified as critical process parameters strongly affecting the extent of reduction in mechanical performance. To cope with the problem of degradative reactions an additional step using calcium carbonate to trap hydrogen ions is proposed.