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1.
Enzymatic oxidation of ferulic acid catalyzed by oxidases (laccase and peroxidase) was carried out. Ferulic acid was shown to be subjected to oxidative processes leading to the formation of oligomeric and polymeric structures. The polymer formation takes place due to the formation of CAr-CAr- and CAr-O-CAr-bonds, as well as due to reactions of opening of the propane chain double bond. Different dynamic conditions of the enzymatic reactions were used to study the effects of conditions on the biosynthesis in vitro of some dehydropolymers: the method of dropwise mixing (endwise polymers) and a single addition (bulk polymers). The chemical structures of the resulting compounds were examined by the methods of IR, 1H NMR, and 13C NMR spectroscopy. Differences in the quantitative ratio of structural fragments in a polymer cause changes in its thermal characteristics.  相似文献   

2.
A study of the direct preparation of hollow polymer nanocapsules which composed of the biocompatible and biodegradable polymers, polysaccharide and polylactic acid (PLA), was presented. By the dialysis of a DMSO solution of cholesterol-modified dextran (Chol-Dex) and poly(d,l-lactic acid) against water, hollow polymer nanocapsules with a highly stable structure and relatively narrow size distribution were obtained. The formation mechanism and the effects of various factors such as PLA molecular weight and the weight ratio of Chol-Dex to PLA on the formation of hollow polymer nanocapsules were investigated by SEM, TEM and 1H NMR analysis. The results showed that hollow capsules were obtained when the weight ratio of Chol-Dex to PLA was between 3:1 and 1:1, and when PLA of molecular weights greater than 360 Da were used. The hollow capsules with a sandwich shell structure derived from deposition of PLA and some amphiphilic polysaccharide on the internal interface of the polysaccharide-coated aggregates, which were formed through phase separation during the initial phase of the dialysis. This novel approach to hollow polymer nanocapsule formation represents a rare example of the self-assembly of two biocompatible polymers into nanometer-scale objects with interesting structures, shapes and morphology through a simple assembly process.  相似文献   

3.
Chitosan dissolved in acetic acid reacted with glutaraldehyde solution, ranging in concentration from 0.10 to 25.0 x 10(-2) mol dm3. The modified polymers were characterized by means of carbon, hydrogen and nitrogen elemental analysis, scanning electron microscopy, X-ray diffractometry, 13C nuclear magnetic resonance (NMR), infrared and Raman spectroscopies. The uptake of metallic cations in aqueous medium was checked through copper. The obtained data from 13C NMR, infrared and Raman spectroscopies evidenced the formation of an ethylenic double bond in the chitosan glutaraldehyde interaction. These data suggest that free pendant amine groups of chitosan polymer interact with the aldehydic group of the glutaraldehyde to form stable imine bonds, due to the resonance established with adjacent double ethylenic bonds. The crosslinking is formed by the nonuniform length of chains and by terminal unities. The crosslinking formation can involve two chitosan unities belonging, or not, to the same polymeric chain. The sequence of reactions was established for a chitosan:glutaraldehyde molar proportion of 1:20. The degree of crystallinity and particle size decreased as the amount of glutaraldehyde was increased in the polymer. Physical and chemical properties are not just affected for the chitosan glutaraldehyde reaction, but are also affected strongly by the dissolution of the natural chitosan.  相似文献   

4.
To evaluate the effects of different gamma irradiation doses on PEGd,lPLA and PEG-PLGA multiblock copolymers. The behaviour of the multiblock copolymers to irradiation was compared to that of PLA, PLGA polymers. PEGd,lPLA, PEG-PLGA, PLA and PLGA polymers were irradiated by using a 60Co irradiation source at 5, 15, 25 and 50 kGy total dose. Characterization was performed on all samples before and after irradiation, by nuclear magnetic resonance (NMR), infrared absorption spectrophotometry (FTIR) and gel permeation chromatography (GPC). The effect of gamma irradiation on polymer stability was also evaluated. Results of NMR and FTIR suggest an increase in -OH and -COOH groups, attributed to scission reactions induced by irradiation treatment. Data of GPC analysis showed that the weight average molecular weight (Mw) of polymer samples decreased with increasing irradiation dose. The extent of Mw degradation expressed as percentage of Mw reduction was more prominent for polymers with high molecular weight as PEGd,lPLA and PLA. The dominant effect of gamma-irradiation on both polymer samples was chain scission. The multiblock copolymer PEGd,lPLA presented higher sensitivity to irradiation treatment with respect to PLA, likely due to the presence of PEG in the matrix. The effect of gamma irradiation continues over a much longer period of time after gamma irradiation has been performed. It is suggested that the material reacts with oxygen to form peroxyl free radicals, which may further undergo degradation reactions during storage after irradiation.  相似文献   

5.
The reactions of EX3 (E = Ga, In, Tl, X = Br or Cl) with pyrazine and pyrazine, 2-carboxylic acid (pyzca-H) affords a series of one-dimensional ladder polymers, [EX3(pyz)] (E = Ga, In, Tl, X = Cl, Br) and the zigzag polymer [InBr2(OH2)2(pyzca)]. These polymers are prepared in high yield through a facile synthesis. The structures of each were characterized in the solid state by single crystal X-ray analysis, infrared spectroscopy and where possible NMR. Experimental results reveal how stability of the one-dimensional polymer increases from gallium to thallium, from the air-sensitive gallium polymer to the aqueous preparation and air-stable products of indium and thallium.  相似文献   

6.
Structures of the anionic polymers of streptomycetes Streptomyces fulvissimus VKM Ac-994(T), Streptomyces longispororuber VKM Ac-1735(T), Streptomyces aureoveticillatus VKM Ac-48(T) and Streptomyces spectabilis INA 00606 belonging to the phenetic cluster 'S. fulvissimus' were investigated by chemical and NMR spectroscopic methods. A teichoic acid from the cell wall of S. spectabilis INA 00606 was studied in more detail, and this was shown to represent 1,3-poly(glycerol phosphate) substituted with glucosamine (alpha-D-GlcNAc) and L-glutamic acid (non-stoichiometric substitution). For the first time, glutamic acid is identified as an acyl substituent in teichoic acids of streptomycetes. The polymer chain is built of the following fragments: Cell walls of other streptomycetes of the phenocluster under study contain 1,3-poly(glycerol phosphates) with glucosamine as a glycosyl substituent at O-2 of the glycerol phosphate units and L-glutamic acid and lysine as O-2 acyl substituents. Not all amino sugar residues in the polymers of these strains are N-acetylated, and the content of the glucosamine and lysine residues in the polymers of different strains is not the same. Despite certain quantitative differences in the structures of the polymers, one may consider streptomycetes of the phenocluster 'S. fulvissimus' as closely related microorganisms, the details of the structures serving as additional criteria for the determination of the species status of a strain under study.  相似文献   

7.
Azobenzene-modified poly(l-glutamic acid) (AZOPLGA) polymers with 22 and 35 mol % of azo chromophores in the side chains have been synthesized by condensing 4-methoxy-4'-aminoazobenzene and poly(l-glutamic acid). These polymers have been characterized by NMR, FT-IR, and UV-visible spectroscopic techniques. The conformational features of the polymer backbone chains in the films that were cast from the polymer solutions prepared in different solvents have been investigated by circular dichroism spectroscopy. Experimental data suggested that the thermal cis-trans relaxation and photoinduced birefringence, which are related to the azo chromophores in the side chains of polymer, are not affected by the conformations of polymer backbones. However, the modulations of the surface relief gratings, the result of photoinduced mass transport process, recorded on these polymers are sensitive to polymer main chain conformation, as well as the degree of functionalization.  相似文献   

8.
Molecularly imprinted polymers are highly stable and can be sterilised, making them ideal for use in biotransformation process. In this communication, we describe a novel application of molecularly imprinted polymers in an enzymatic reaction. The enzymatic condensation of Z-L-aspartic acid with L-phenylalanine methyl ester to give Z-L-Asp-L-Phe-OMe (Z-aspartame) was chosen as a model system to evaluate the applicability of using molecularly imprinted polymers to facilitate product formation. When the product-imprinted polymer is present, a considerable increase (40%) in product yield is obtained. Besides their use to enhance product yields, as demonstrated here, we suggest that imprinted polymers may also find use in the continuous removal of toxic compounds during biochemical reactions.  相似文献   

9.
A new class of diblock copolymers was synthesized from biodegradable poly(lactic acid) and poly(ethylene glycol)minus signmonoamine. These polymers were activated by covalently attaching linkers such as disuccinimidyl tartrate or disuccinimidyl succinate to the hydrophilic polymer chain. The polymers were characterized by (1)H NMR spectroscopy, (13)C NMR spectroscopy and gel permeation chromatography (GPC). These investigations indicated that the polymers were obtained with the correct composition, in high purities, and the expected molecular weight. By using dyes containing primary amine groups such as 5-aminoeosin as model substrates, it was possible to show that the polymers are able to bind such compounds covalently. The diblock copolymers were developed to suppress unspecific protein adsorption and allow the binding of bioactive molecules by instant surface modification. The polymers are intended to be used for tissue engineering applications where surface immobilized cell adhesion peptides or growth factors are needed to control cell behavior.  相似文献   

10.
BACKGROUND: The theoretical state diagram for semi-flexible macromolecules such as DNA predicts that a tightly wound toroid can be a stable structure. Experimentally, toroids roughly 100 nm in diameter are routinely observed for DNA in the presence of multivalent cations at low DNA concentration. Theory also predicts toroids can form between non-DNA semi-flexible polymers and multivalent counterions. This phenomenon provides a means to co-package DNA with functionalized anionic polymers to create gene delivery systems. METHODS AND RESULTS: We show using electron microscopy that non-DNA polymers (polylysine, polyglutamic acid, and dextran sulfate) form toroids when mixed with multi- or polyvalent ions of opposite charge. The non-DNA toroids are similar in diameter to ones made with DNA. The results using dextran sulfate, a semi-flexible polymer, are explained by current theory. However, theory predicts that high flexibility in polypeptides should discourage their incorporation into stable toroids. To explain these latter observations we propose that charge neutralization facilitates secondary structure formation, which confers stiffness, thereby allowing stable toroids for the polypeptides studied. We measured the secondary structure of the toroid-forming polypeptides using circular dichroism (CD). The CD spectrum indicates the polypeptides undergo transitions from non-ordered structures (random coil) to ordered secondary structures (either alpha-helix or beta-sheet) upon charge neutralization which supports the hypothesis. The type of secondary structure is dependent on the type of multivalent counterion used to form the toroids. Formation of the polypeptide toroids confers resistance to heat denaturation of the resulting polypeptide secondary structure. The CD spectrum of DNA in a toroid also is changed from that of uncomplexed DNA, but all of the counterions used to form DNA toroids created structures with similar CD spectra in the DNA region (250-290 nm). CONCLUSIONS: The toroid structure obtained using DNA is observed in other semi-flexible non-DNA polymers such as dextran sulfate, and also in flexible polymers such as polylysine and polyglutamic acid upon charge neutralization with multivalent counterions. In the flexible polymers we propose that this phenomenon is due to induction of secondary structure upon charge neutralization, which decreases polymer flexibility, i.e. increases polymer stiffness, to enable toroid formation. These results have significant implications for the co-assembly of non-DNA anionic polymers with DNA to create nanoscopic gene carriers.  相似文献   

11.
Summary Production of poly(3-hydroxybutyric acid) [P(3HB)] by Rhodopseudomonas palustris SP5212 isolated in this laboratory has been optimized under phototrophic microaerophilic conditions. Cells grown in malate medium accumulated 7.7% (w/w) P(3HB) of cellular dry weight at the early stationary phase of growth. The accumulated P(3HB) however, attained 15% (w/w) of cellular dry weight when acetate (1.0%, w/v) was used as the sole carbon source under nitrogen-limiting conditions. Synthesis and accumulation of polymer was favoured by sulphate-free conditions and at a phosphate concentration sub-optimal for growth. The polymer content of cells was increased drastically (34% of cellular dry weight) when the acetate containing medium was supplemented with n-alkanoic acids. Compositional analysis by H1 NMR revealed that these accumulated polymers were composed of 3-hydroxybutyric acid and 3-hydroxyvaleric acid (3HV). The contents of 3HV in these copolymers ranged from 14 to 38 mol%.  相似文献   

12.
Polyphosphazene polyacids show potential as immunostimulating compounds and materials for microencapsulation. Their synthesis requires multistep chemical transition from a hydrolytically unstable macromolecular precursor, poly(dichlorophosphazene), to a water-soluble polyelectrolyte. Insufficient synthetic control in these reactions can lead to molecular weight variations and formation of macromolecules with "structural defects" resulting in significant variations in polymer performance. Simple and reproducible "one pot-one solvent" method is reported for the preparation of polyphosphazene polyacids-poly[di(carboxylatophenoxy)phosphazene] and its copolymers. Molecular weight characteristics and polymer compositions were studied as a function of reaction parameters. Macromolecular byproducts, incompletely substituted polymers containing hydroxyl groups and partially deprotected polymers containing propyl ester functionalities, were synthesized and characterized. It was demonstrated, that the presence of such groups can affect polymer characteristics, such as hydrolytic degradation profiles, immunostimulating activity, and microsphere forming properties. In vivo studies showed that the immunostimulating activity of polyphosphazene polyacids correlates with the content of acid functionalities in the polymer.  相似文献   

13.
Rotary shadowing/electron microscopy of chondroitin 6-sulphate (CS6) and 4-sulphate (CS4) showed that the former, but not the latter, aggregated to mesh works. Preparations made from salt (ammonium acetate) solutions showed enhanced aggregation. Computer modelling, using molecular mechanics and dynamics, was applied to secondary structures (twofold helices) derived from NMR studies, to determine geometric and energetic constraints on duplex and higher-aggregate formation. The calculations suggested that chondroitin, CS6 and undersulphated CS4 could form duplexes, while CS4 could not, thus bridging the gap between atomic dimensions (NMR) and high polymer scale (electron microscopy). Calculations suggested that water structure helped to stabilise the twofold helix. It is proposed that the twofold helical, flat, tape-like molecules aggregate via hydrophobic bonding between the very extensive hydrophobic patches (9 CH units) repeated on alternating sides of the polymers. The negative charge of the polyanions opposes aggregate formation. Calculations showed that duplexes were formed with decreasing stability as the charge density increased, and as the charge was concentrated towards the centre line of the polymer (i.e. in CS4). The unsulphated polymer chondroitin could form duplexes and higher aggregates as readily as hyaluronan. Hyaluronan was calculated to form stable heteroduplexes with CS6 and CS4. The frequency and positioning of the sulphate-ester group within the polymer thus determines whether the molecule participates in duplex formation.  相似文献   

14.
Three nitrophenol isomer-imprinted polymers were prepared under the same conditions using 4-vinylpyridine as a functional monomer. Different recognition capacities for template molecules were observed for the three polymers. Another imprinting system with stronger acidity than nitrophenol isomers, 2-hydroxybenzoic acid (salicylic acid) and 4-hydroxybenzoic acid, was imprinted using 4-vinylpyridine or acrylamide as functional monomer respectively. Both 4-hydroxybenzoic acid-imprinted polymers using the two monomers showed recognition ability for the template molecule. However, when acrylamide was chosen as functional monomer, the salicylic acid-imprinted polymer showed very weak recognition for the template molecule, whereas strong recognition ability of the resultant polymer for salicylic acid was observed with 4-vinylpyridine as functional monomer. It seems that the structure and acidity of template molecules is responsible for the difference in recognition, by influencing the formation and strength of interaction between template molecule and functional monomer during the imprinting process. An understanding of the mechanism of molecular imprinting and molecular recognition of MIPs will help to predict the selectivity of MIPs on the basis of template molecule properties.  相似文献   

15.
Statistical and block copolymers based on poly(2-hydroxyethyl methacrylate) (PHEMA) and poly[oligo(ethylene glycol) methylether methacrylate] (POEGMEMA) were modified with 4-pentenoic anhydride or 4-oxo-4-(prop-2-ynyloxy)butanoic anhydride to generate polymers with pendant vinyl or acetylene, respectively. Subsequent thiol-ene or thiol-yne reaction with thioglycolic acid or 2-mercaptosuccinic acid leads to polymers with carboxylate functionalities, which were conjugated with cisplatin (cis-diamminedichloroplatinum(II) (CDDP)) to generate a drug carrier for Pt-drugs. Only the polymers modified with 2-mercaptosuccinic acid resulted in the formation of soluble well-defined polymers with gel formation being prevented. Due to the hydrophobicity of the drug, the block copolymers took on amphiphilic character leading to micelle formation. The micelles were in addition crosslinked to further stabilize their structure. Pt-containing statistical copolymer, micelles, and crosslinked micelles were then tested regarding their cellular uptake by the A549 lung cancer cell line to show a superior uptake of crosslinked micelles. However, due to the better Pt release of the statistical copolymer, the highest cytotoxicity was observed with this type of polymer architecture.  相似文献   

16.
《Biophysical journal》2022,121(15):2873-2881
Molecular interactions and reactions in living cells occur with high background concentrations of organic compounds including proteins. Uncharged water-soluble polymers are commonly used cosolutes in studies on molecular crowding, and most studies argue about the effects of intracellular crowding based on results obtained using polymer cosolutes. Further investigations using protein crowders and organic cations are important in understanding the effects of cellular environments on nucleic acids with negatively charged surfaces. We assessed the effects of using model globular proteins, serum proteins, histone proteins, structurally flexible polypeptides, di- and polyamines, and uncharged polymers. Thermal stability analysis of DNA oligonucleotide structures revealed that unlike conventional polymer cosolutes, basic globular proteins (lysozyme and cytochrome c) at high concentrations stabilized long internal and bulge loop structures but not fully matched duplexes. The selective stabilization of long loop structures suggests preferential binding to unpaired nucleotides in loops through weak electrostatic interactions. Furthermore, the ability of the proteins to stabilize the loop structures was enhanced under macromolecular crowding conditions. Remarkably, the effects of basic proteins on the stability of fully matched duplexes were dissimilar to those of basic amino-acid-rich polypeptides and polyamines. This study provides new insights into the interaction of nucleic acid structures with organic cations.  相似文献   

17.
Dai S  Li Z 《Biomacromolecules》2008,9(7):1883-1893
Enzymatic modification of a microbial polyester was achieved by the ring-opening polymerization of epsilon-caprolactone (CL) with low-molecular weight telechelic hydroxylated poly[( R)-3-hydroxybutyrate] (PHB-diol) as initiator and Novozym 435 (immobilized Candida antarctica Lipase B) as catalyst in anhydrous 1,4-dioxane or toluene. The ring-opening polymerization was investigated at different conditions with two different types of PHB-diols: PHB-diol(P), containing a primary OH and a secondary OH end groups, and PHB-diol(M), consisting of 91% PHB-diol(P) and 9% PHB-diol containing two secondary OH end groups. The reactions were followed by GPC analyses of the resulting polymers at different time points, and the optimal conditions were established to be 70 degrees C at a weight ratio of CL/enzyme/solvent of 8:1:24. The ring-opening polymerization of CL with PHB-diol(M) (Mn of 2380, NMR) at the molar ratio of 50:1 under the optimal conditions in 1,4-dioxane gave the corresponding poly[HB(56 wt %)-co-CL(44 wt %)] with Mn (NMR) of 3900 in 66% yield. Polymerization of CL and PHB-diol(P) ( Mn of 2010, NMR) at the same condition in toluene gave the corresponding poly[HB(28 wt %)-co-CL(72 wt %)] with Mn (NMR) of 7100 in 86% yield. Both polymers were characterized by (1)H and (13)C NMR and IR analyses as di-block copolyesters containing a PHB block with a secondary OH end group and a poly(epsilon-caprolactone) (PCL) block with a primary OH end group. NMR analyses and control experiments suggested no formation of random copolymers and no change of the PHB block during the reaction. The enzymatic ring-opening polymerization was selectively initiated by the primary OH group of PHB-diol, whereas the secondary OH group remained as an end group in the final polymers. The thermal properties of the di-block poly(HB-co-CL)s were analyzed by DSC, with excellent T g values for the elastomer domain: poly[HB(56 wt %)- co-CL(44 wt %)] with M n (NMR) of 3900 demonstrated a T g of -57 degrees C, Tm of 145, 123, and 53 degrees C; and poly[HB(28wt%)-co-CL(72wt%)] with Mn (NMR) of 7100 gave a Tg of -60 degrees C, Tm of 147 and 50 degrees C. Thus, the selective enzymatic ring-opening polymerization with PHB-diol as macro-initiator provides a new method for the preparation of PHB-based block copolymers as biomaterials with good thermoplastic properties and novel structures containing functional end groups.  相似文献   

18.
Three beta-cyclodextrin (polymers 1-3) and a starch-based (polymer 4) polymers were synthesized using hexamethylene diisocyanate (HMDI) as a cross-linking agent in dry dimethylformamide and used as a sorbent for the removal of some selected azo dyes from aqueous solutions. The cross-linked polymers were characterized by Fourier transform infrared spectroscopy, thermogravimetric and differential scanning calorimetric analysis. Results of sorption showed that cyclodextrin and starch based polymers can be effectively used as a sorbent for the removal of anionic azo dyes. The Influence of the amide groups and the chemical structure of azo dyes are also studied. Results of sorption experiments showed that these adsorbent exhibited high sorption capacities toward Direct Violent 51 (80% for polymer 1, 69% for polymer 2, 70% for polymer 3 and 78% for polymer 4). The sorption capacity of dyes on the polymers was dependent on the presence of sulfonate groups of the anionic dyes. In order to explain the results an adsorption mechanism mainly physical adsorption and interactions such as hydrogen bonding, ion-exchange due to the nature of the polymer network and the formation of an inclusion complex due to the beta-CD molecules through host-guest interaction is proposed.  相似文献   

19.
The cell wall of Streptomyces sp. VKM An-2534, the causative agent of common scab in potato tubers, which does not synthesize thaxtomin and is phylogenetically close to phytopathogen Streptomyces setonii sp. ATCC 25497, contains two anionic carbohydrate-containing polymers. The major polymer is teichuronic acid, whose repeating unit is disaccharide --> 4)-beta-D-ManpNAc3NAcyA-(1 --> 3)-alpha-D-GalpNAc-(1-->, where Acy is a residue of acetic or L-glutamic acid. The polymer of such structure has been found in Gram-positive bacteria for the first time. The minor polymer is teichoic acid [1,5-poly(ribitol phosphate)], in which a part of the ribitol residues are glycosylated at C4 with beta-D-Glcp and, probably, with beta-D-GlcpNAc and some residues are O-acylated with Lys residues. The structures were proved by chemical and NMR spectroscopic methods. It is likely that the presence of acidic polysaccharides on the surface of the phytopathogenic streptomycete is necessary for its attachment to the host plant.  相似文献   

20.
In the development of sugar-linked synthetic polymers as biodegradable polymers, it is imperative to know the variety of polymer structures formed by the reaction of a multi-functional sugar molecule with the functionalized synthetic polymer on which the sugar is to be anchored. Enzymes produced by the microorganisms causing the polymer to biodegrade can be sensitive to the particular type of sugar hydroxyl utilized (such as anomeric, primary, or secondary hydroxyl group) for getting anchored to the polymer. In this paper, we present synthesis of regio-specific ester derivatives of glucose with anhydride, functionalized polymers, i.e., ester formation specifically with the anomeric, primary or secondary hydroxyls of glucose. Characterization of these different esters groups was done using FTIR spectroscopy; each ester peak was further deconvoluted to yield its different components. For this purpose, we studied the reactions of d-glucose, 6-O-trityl glucose, methyl glucoside, 1,2-5,6-diisopropylidene-d-glucose, and 1,2,3,4-tetraacetyl-d-glucose with maleic anhydride functionalized polystyrene (PSMAH). In this study, the primary hydroxyl of glucose was found to be even more reactive than the anomeric hydroxyl. The peaks at 1716, 1725, and 1729–1737 cm−1 were assigned to the ester carbonyl of the anomeric, primary, and secondary hydroxyls of glucose (C2, C3, and C4), respectively. An attempt was made to quantify the extent to which the different polymer structures are formed in a particular reaction by taking ratios of non-variable reference peaks (polystyrene peak at 1493 cm−1) and variable peaks caused by the reaction (the residual anhydride carbonyl at 1780 cm−1).  相似文献   

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