Green biocomposites of chitosan dispersed in natural rubber matrices,and their urea controlled-release application

A green biocomposite comprising chitosan dispersed in partially cross-linked natural rubber matricesd was prepared. The starting materials and biocomposites were characterized by means of Fourier transform–infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Chitosan was found well dispersed in partially cross-linked natural rubber matrices indicating that natural rubber latex is successfully stabilized by sodium dodecyl sulfate. The swelling study of the biocomposites was carried out in several solvents. The biocomposites were used for the controlled-release of urea. The release behavior was found consistent, controlled, and prolonged over a period of 72 h. The Korsmeyer–Peppas model was applied to the experimental data and the possible release mechanism was found Fickian diffusion, which indicates that the polymer relaxation time is much greater than the characteristic solvent diffusion time.     

Asymmetric Synthesis of β, γ-β-Hydroxyl-γ-butyrolactones

Chiral β-hydroxyl-γ-butyrolactones have attracted substantial interest in recent years due to their presence inmany strongly active natural products having antitumor, fungicidal, anti-inflammatory activity, and their use as important precursors in natural product synthesis. [1] In the course of the total synthesis of the natural product Tuxpano lide ,[2] we found a concise and efficient strategy on the stereocontrolled synthesis of β-hydroxyl-γ-butyrolactonederivatives from cheap and achiral starting material.     

An unusual mode of DNA duplex association: Watson-Crick interaction of all-purine deoxyribonucleic acids

Nucleic acid duplexes associating through purine-purine base pairing have been constructed and characterized in a remarkable demonstration of nucleic acids with mixed sequence and a natural backbone in an alternative duplex structure. The antiparallel deoxyribose all-purine duplexes associate specifically through Watson-Crick pairing, violating the nucleobase size-complementarity pairing convention found in Nature. Sequence-specific recognition displayed by these structures makes the duplexes suitable, in principle, for information storage and replication fundamental to molecular evolution in all living organisms. All-purine duplexes can be formed through association of purines found in natural ribonucleosides. Key to the formation of these duplexes is the N(3)-H tautomer of isoguanine, preferred in the duplex, but not in aqueous solution. The duplexes have relevance to evolution of the modern genetic code and can be used for molecular recognition of natural nucleic acids.     

Diffusion and permeability of aldehydes into blends of natural rubber and chemically modified low molecular weight natural rubber

Low molecular weight natural rubber (LMWNR) obtained from natural rubber (NR) by depolymerization of natural rubber latex (NRL) was modified by epoxidation to 35% epoxide level to yield epoxidized low molecular weight natural rubber (ELMWNR). The ELMWNR was in turn modified in a solution of thioglycollic acid (TGA) (0.5 mol phr) to yield a product of 20% conversion of its initial LMWNR epoxide. Blends of NR with LMWNR, ELMWNR and epoxidized low molecular weight natural rubber thioglycollic acid (ELWMNR‐TGA) adduct were made. The mixes were vulcanized at 150°C for 20 min before determining the system parameters (n and k), the sorption (S), diffusion (D) and permeability (P) of the vulcanizates in acetaldehyde and formaldehyde solutions at three different temperatures (25, 40 and 60°C) for a period of 90 days. The sorption, diffusion and permeability of the vulcanizates were found to be temperature dependent. The vulcanizates containing ELMWNR were found not to be easily penetrated by both acetaldehyde and formaldehyde when compared with base mix A that is vulcanizates with only NR. The reaction system was found not to be spontaneous but dependent on the activation energies. Copyright © 2005 John Wiley & Sons, Ltd.     

Alternative donor substrates for inverting and retaining glycosyltransferases

By the use of glycosyl donors containing aromatic leaving groups linked with opposite anomeric configurations compared to those of the natural donor substrates, an inverting (Cst II) and a retaining (LgtC) glycosyltransferase were found to catalyse glycosylation reactions of natural acceptor substrates in the presence of the corresponding nucleotide.     

Effect of non‐rubber components on the mechanical properties of natural rubber

Effect of the nanomatrix structure on mechanical properties of natural rubber was investigated in relation to the strain‐induced crystallization. Structure of natural rubber was analyzed through Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction measurement and transmission electron microscopy. The nanomatrix of the non‐rubber components was found to be inevitably formed in natural rubber, in which natural rubber particles linking to fatty acids were dispersed in the nanomatrix of the proteins and phospholipids. The nanomatrix disappeared after deproteinization of natural rubber with urea. Tensile strength and modulus of natural rubber were reduced by removal of the fatty acids and the proteins, which resulted in disappearance of the nanomatrix structure. The effect of fatty acids on the crystallization of natural rubber in small particles as a dispersoid was proved by tensile test of blend of natural rubber and styrene butadiene rubber. Copyright © 2016 John Wiley & Sons, Ltd.     

Structure and Biosynthesis of Myxofacyclines: Unique Myxobacterial Polyketides Featuring Varing and Rare Heterocycles[]**

A metabolome-guided screening approach in the novel myxobacterium Corallococcus sp. MCy9072 resulted in the isolation of the unprecedented natural product myxofacycline A, which features a rare isoxazole substructure. Identification and genomic investigation of additional producers alongside targeted gene inactivation experiments and heterologous expression of the corresponding biosynthetic gene cluster in the host Myxococcus xanthus DK1622 confirmed a noncanonical megaenzyme complex as the biosynthetic origin of myxofacycline A. Induced expression of the respective genes led to significantly increased production titers enabling the identification of six further members of the myxofacycline natural product family. Whereas myxofacyclines A–D display an isoxazole substructure, intriguingly myxofacyclines E and F were found to contain 4-pyrimidinole, a heterocycle unprecedented in natural products. Lastly, myxofacycline G features another rare 1,2-dihydropyrol-3-one moiety. In addition to a full structure elucidation, we report the underlying biosynthetic machinery and present a rationale for the formation of all myxofacyclines. Unexpectedly, an extraordinary polyketide synthase-nonribosomal peptide synthetase hybrid was found to produce all three types of heterocycle in these natural products.     

Size-expanded DNA bases: an ab initio study of their structural and electronic properties

The size-expanded DNA bases, xA, xC, xG, and xT, are benzo-homologue forms of the natural DNA bases; i.e., their structure can be seen as the fusion of a natural base and a benzene ring. Recently, a variety of DNAs, known as xDNAs, have been synthesized in which size-expanded and natural bases are paired. In this paper we use second-order M?ller-Plesset perturbation theory and density functional theory to investigate the structural and electronic properties of xA, xC, xG, and xT and their natural counterparts. We find that whereas natural and size-expanded bases have both nonplanar amino groups the latter have also nonplanar aromatic rings. When density functional theory is used to investigate the electronic properties of size-expanded and natural bases, it is found that the HOMO-LUMO gap of the size-expanded bases is smaller than that of the natural bases. Also, xG should be easier to oxidize than G.     

Vanadium Chloroperoxidases: The Missing Link in the Formation of Chlorinated Compounds and Chloroform in the Terrestrial Environment?

It is well established that the majority of chlorinated organic substances found in the terrestrial environment are produced naturally. The presence of these compounds in soils is not limited to a single ecosystem. Natural chlorination is also a widespread phenomenon in grasslands and agricultural soils typical for unforested areas. These chlorinated compounds are formed from chlorination of natural organic matter consisting of very complex chemical structures, such as lignin. Chlorination of several lignin model compounds results in the intermediate formation of trichloroacetyl‐containing compounds, which are also found in soils. These decay, in general, through a haloform‐type reaction mechanism to CHCl₃. Upon release into the atmosphere, CHCl₃ will produce chlorine radicals through photolysis, which will, in turn, lead to natural depletion of ozone. There is evidence that fungal chloroperoxidases able to produce HOCl are involved in the chlorination of natural organic matter. The objective of this review is to clarify the role and source of the various chloroperoxidases involved in the natural formation of CHCl₃.     

Use of sodium tetraethylborate for the analysis of trimethyllead species in artificial rainwater and a natural road dust sample

Several artificial rainwater samples and a natural sample of road dust have been analysed for trimethyllead under the aegis of a European Union Measurement and Testing (Bureau of Community Reference — BCR) intercomparison exercise, using a new and simplified purge and trap ethylation technique. Levels of trimethyllead found have been similar to those reported at lower levels from the natural environment. The method has been successful in the presence of excess amounts of inorganic lead, even for organic lead levels one tenth of those recently reported for the natural environment.     

Antianoxic action and active constituents of evodiae fructus

In order to develop new drugs from natural products, constituents of natural medicines were examined for their effectiveness in the KCN-induced anoxia model in mice. Methanol extract from a Chinese medicine, evodia (fruits of Evodia rutaecarpa Benth. or E. officinalis Dode), had a significant effect in the KCN-induced anoxia model in mice and therefore the active constituents were further examined. The results indicated that the antianoxic action of evodia was found in the fraction containing evodiamine. Further analysis of the active constituent indicated that evodiamine and rutaecarpine, indole-alkaloids found in large amounts in the Chinese medicine evodia, were mainly responsible for the antianoxic action.     

Effect of natural gas usage on indoor radon levels

Effect of natural gas usage on indoor radon concentrations were investigated in dwellings in four counties of ?zmir municipality using LR-115 Type II cellulose nitrate films. The dwellings were separated two groups: natural gas user and non-user. Indoor radon levels were found higher in natural gas using dwellings. Also, indoor radon levels were evaluated in terms of concentrations and annual effective dose. Indoor radon concentrations were found between 22.8 and 707.8 Bq m^?3 and highest concentrations were determined in kitchen in third floor of Bornova dwellings. Indoor radon concentrations in kitchens were found higher than the living rooms. On the other hand, opposite results obtained for annual effective dose, because of very short occupancy period of the kitchens.     

Synthesis of a New Isoflavone: 7,8,4′-Trihydroxyisoflavone

Isoflavones have been found a wide range of applications as natural antioxidants being suggested in diet as a gents responsible for the prevention of coronary diseases, breast and prostate cancer. [1] Most of the isoflavones have been isolated from natural sources and their simple structural features lead to the development of many synthetic methods. [2] Here we synthesized a new trihydroxyisoflavone.     

An evaluation of ion chromatography for the analysis of organic anions in natural rubber latex serum

An ion chromatograph was purchased for the determination of anions in natural rubber latex serum.Ion-exclusion chromatography was found to be suitable for both qualitative and quantitative analysis of mixtures of organic anions. Using this technique it has proved possible to produce a method capable of determining a wide range of organic anions in natural rubber latex serum on a routine basis.     

Natural Polymer Characterization

Summary : A review about the characterization of natural polymers is given, describing the polymers found in Nature, methods to distinguish natural from syntheticpolymers, and what modern Polymer Science can learn from Nature     

Preorganized bis-zinc phosphodiester cleavage catalysts possessing natural ligands: a lesson pertinent to bimetallic artificial enzymes

Two preorganized bis-zinc receptors (2 and 3) were synthesized wherein the metals were ligated with ligands present in natural phosphodiesterases: imidazoles and carboxylates. The intrametallic distance is near 4.5 A, that found in natural nucleases and other successful artificial nucleases. With only two imidazoles (2), the zinc binding affinities were not high enough to achieve cooperativity. Yet, with a third ligand, a carboxylate (3), cooperativity was found in the cleavage of HPNPP. The preorganization of 3 was achieved using a "steric gearing" strategy. The enhancement was 80-fold for cooperation between the two metals relative to a mono-metallic analogue (5). However, there was no observable enhancement in the hydrolysis of RNA using 3 relative to 5. Therefore, we conclude that placing two zinc atoms that are ligated with natural ligands at the appropriate distance for catalysis is not sufficient to enhance the cleavage of RNA, but is successful for activated RNA substrate mimics.     

Conformation of glycomimetics in the free and protein-bound state: structural and binding features of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man

The conformational properties of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man in solution have been carefully analyzed by a combination of NMR spectroscopy and time-averaged restrained molecular dynamics. It has been found that both the alpha-1,3- and the alpha-1,6-glycosidic linkages show a major conformational averaging. Unusual Phi ca. 60 degrees orientations for both Phi torsion angles are found. Moreover, a major conformational distinction between the natural compound and the glycomimetic affects to the behavior of the omega(16) torsion angle around the alpha-1 --> 6-linkage. Despite this increased flexibility, the C-glycosyl analogue is recognized by three mannose binding lectins, as shown by NMR (line broadening, TR-NOE, and STD) and surface plasmon resonance (SPR) methods. Moreover, a process of conformational selection takes place, so that these lectins probably bind the glycomimetic similarly to the way they recognize the natural analogue. Depending upon the architecture and extension of the binding site of the lectin, loss or gain of binding affinity with respect to the natural analogue is found.     

Thermal behaviour of montmorillonite pillared with different metal oxides

Natural montmorillonite was pillared by various polyhydroxy cations. The resulting pillared layer clays (PILCs) were characterized by X-ray fluorescence, X-ray diffraction (XRD) and infrared (IR) spectroscopies. The thermal behaviour of Al-PILC was investigated in detail by a combonation of XRD, derivatography IR spectroscopy and a comparison to natural montmorillonite is given. It was found that thermal stability of Al-PILC is lower than that of natural montmorillonite. However, heat treatment in the stability region results in significant sintering of natural montmorillonite, while the interlayer spacing of Al-PILC is hardly affected.     

Kinetic Aspect of Thermal Decomposition of Natural Phosphate and its Kerogen. Influence of heating rate and mineral matter

The natural phosphate and its demineralization products from Moroccan deposit were pyrolysed in a thermogravimetric analyser (TG) to examine the influence of the heating rate and mineral matter on their thermal decomposition. The heating rates investigated in the TG were 5–100°C min⁻¹ to final temperature of 1200°C. The integral method was used in the analysis of the TG to determine the kinetic parameters. It has been found that for the natural phosphate and corresponding kerogen analysed in the TG, the increase of the heating rate shifts the maximum rate loss to higher temperature. A first order reaction was found to be adequate for pyrolysis in the range 150–600°C which was attributed to kerogen decomposition. In addition, the results indicate that the removal of mineral matter affected the kinetic parameters found for kerogen in the natural phosphate. This revised version was published online in August 2006 with corrections to the Cover Date.     

A stereoselective, Sm(II)-mediated approach to decorated cis-hydrindanes: synthetic studies on faurinone and pleuromutilin

The cis-hydrindane motif is found in a number of natural products that display important biological activity. A flexible, stereoselective approach to the framework has been developed that features highly diastereoselective, SmI(2)-mediated cyclisations. The strategy has been exploited in the first synthesis of the proposed structure of faurinone and an approach to the skeleton of the antibacterial natural product, pleuromutilin.