Dendronized hydroxypropyl cellulose: synthesis and characterization of biobased nanoobjects

Dendronized polymers containing a cellulose backbone have been synthesized with the aim of producing complex molecules with versatile functionalization possibilites and high molecular weight from biobased starting materials. The dendronized polymers were built by attaching premade acetonide-protected 2,2-bis(methylol)propionic acid functional dendrons of generation one to three to a hydroxypropyl cellulose backbone. Deprotection or functionalization of the end groups of the first generation dendronized polymer to hydroxyl groups and long alkyl chains was performed, respectively. The chemical structures of the dendronized polymers were confirmed through analysis using (1)H NMR and FT-IR spectroscopies. From SEC analysis, the dendronized polymers were found to have an increasing polystyrene-equivalent molecular weight up to the second generation ( M n = 50 kg mol (-1)), whereas the polystyrene-equivalent molecular weight for the third generation was lower than for the second, although the same grafting density was obtained from (1)H NMR spectroscopy for the second and third generations. Tapping-mode atomic force microscopy was used to characterize the properties of the dendronized polymers in the dry state, exploring both the effect of the polar substrate mica and the less polar substrate highly oriented pyrolytic graphite (HOPG). It was found that the molecules were in the size range of tens of nanometers and that they were apt to undertake a more elongated conformation on the HOPG surfaces when long alkyl chains were attached as the dendron end-groups.     

Partial molar volumes of some alpha-amino acids in aqueous sodium acetate solutions at 308.15 K

The apparent molar volumes V(2,phi) have been determined for glycine, DL-alpha-alanine, DL-alpha-amino-n-butyric acid, DL-valine and DL-leucine in aqueous solutions of 0.5, 1.0, 1.5 and 2.0 mol kg(-1) sodium acetate by density measurements at 308.15 K. These data have been used to derive the infinite dilution apparent molar volumes V(0)(2,phi) for the amino acids in aqueous sodium acetate solutions and the standard volumes of transfer, Delta(t)V(0), of the amino acids from water to aqueous sodium acetate solutions. It has been observed that both V(0)(2,phi) and Delta(t)V(0) vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids. These linear correlations have been utilized to estimate the contributions of the charged end groups (NH(3)(+), COO(-)), CH(2) group and other alkyl chains of the amino acids to V(0)(2,phi) and Delta(t)V(0). The results show that V(0)(2,phi) values for (NH(3)(+), COO(-)) groups increase with sodium acetate concentration, and those for CH(2) are almost constant over the studied sodium acetate concentration range. The transfer volume increases and the hydration number of the amino acids decreases with increasing electrolyte concentrations. These facts indicate that strong interactions occur between the ions of sodium acetate and the charged centers of the amino acids. The volumetric interaction parameters of the amino acids with sodium acetate were calculated in water. The pair interaction parameters are found to be positive and decreased with increasing alkyl chain length of the amino acids, suggesting that sodium acetate has a stronger dehydration effect on amino acids which have longer hydrophobic alkyl chains. These phenomena are discussed by means of the co-sphere overlap model.     

Enantioselective chromatography of alkyl derivatives of 5-ethyl-5-phenyl-2-thiobarbituric acid studied by semiempirical AM1 method

Complexation of alkyl derivatives of 5-ethyl-5-phenyl-2-thiobarbituric acid (2-thiophenobarbital) enantiomers by beta-cyclodextrin was investigated by the AM1 method. The inclusion complexes of beta-cyclodextrin with neutral and anionic forms of these enantiomers have been modeled and energetically optimized. The chiral discrimination of enantiomers was analyzed in terms of differences in the interaction energies. The calculated interaction energies between each enantiomer of the investigated 2-thiobarbiturates and beta-cyclodextrin confirm the ability of beta-cyclodextrin to act as a mobile phase additive in reversed-phase HPLC to separate enantiomers by liquid chromatography and rationalize their order of elution.     

Galactose-substituted alginate 2: conformational aspects

Galactose moieties have been introduced on the uronic groups of alginates from different sources via an N-glycosidic bond, thus affecting the net charge on the polymer chain. The modified polymers have been analyzed by means of viscosity and of high-performance size-exclusion chromatography combined with refractive index multiple angle laser light scattering (HPSEC-RI-MALLS) measurements. The latter technique enabled us to determine the molecular weight of the modified polymers, proving that the synthetic procedure did not affect the chemical integrity of the chain. The intrinsic viscosity and the radius of gyration data showed that the hydrodynamic properties of the polymer chain varied with the degree and the pattern of substitution. In the presence of a relatively low galactose content (up to 19%), a decrease of the hydrodynamic dimensions of the coil was experienced, while on increasing the degree of substitution (especially on GG diads) a re-extension of the chain was discovered. Measurements of intrinsic viscosity at different values of the degree of dissociation have demonstrated that this effect cannot be solely explained by the reduction of the charge density of the polymer. Rather, it implies the occurrence of conformational changes of the chain that are specific to the chemical nature of the site of substitution. These data have been supported by the values of the persistence length of the natural and modified polymers obtained with the Doty-Benoit equation. The chiro-optical properties of the modified polymers studied by means of circular dichroism (CD) spectroscopy confirmed that conformational variations occurred to the polymeric chain upon introduction of galactose residues.     

NMR and CD studies on the interaction of Alzheimer beta-amyloid peptide (12-28) with beta-cyclodextrin

Polymerization of the amyloid beta-peptide (Abeta) has been identified as a major feature of the pathogenesis of Alzheimer's disease (AD). Inhibition of the formation of these toxic polymers of Abeta has emerged as an approach for developing therapeutics for AD. NMR and CD spectra were used to investigate the interaction between cyclodextrin and Abeta(12-28) peptide, which was reported to be an important region for forming amyloid fibrils. CD spectral analyses show that of the alpha-, beta- and gamma-cyclodextrins only beta-cyclodextrin inhibits the aggregation of Abeta(12-28) at pH 5.0. Analysis of the one-dimensional proton NMR spectra of Abeta(12-28) and the mixture of Abeta(12-28) with beta-cyclodextrin clearly indicates that there are chemical shift changes in the aromatic ring of Phe19 and the methyl groups of Val18 in the peptide. The NOESY spectra show cross-peaks between H-3 and H-5 of beta-cyclodextrin and the aromatic protons of Phe19 and Phe20. These chemical shift differences and NOEs demonstrate that there is an interaction between Abeta(12-28) and beta-cyclodextrin. Analysis of the cross-peak intensity in the NOESY spectra reveals that the aromatic rings of Phe19 and 20 are generally inserted into beta-cyclodextrin at the broad side and are oriented toward the narrow side of the cavity.     

Inclusion complexation behavior of dyestuff guest molecules by a bridged bis(cyclomaltoheptaose)[bis(beta-cyclodextrin)] with a pyromellitic acid diamide tether

A novel bridged bis(beta-cyclodextrin) with a pyromellitic acid 2,5-diamide tether (2) has been synthesized by reaction of 6(I)-(2-aminoethyleneamino)-6-deoxycyclomaltoheptaose [mono 6-(2-aminoethyleneamino)-6-deoxy-beta-cyclodextrin] with 1,2,4,5-benzenetetracarboxylic dianhydride. Its inclusion complexation behavior with some representative dyestuffs, i.e., Acridine Red (AR), Rhodamine B (RhB), Neutral Red (NR), Brilliant Green (BG), was studied by using UV-absorption, fluorescence, and 2D NMR spectroscopy. Fluorescence titrations have been performed at 25 degrees C in pH 7.2 buffer solution to calculate the binding constants of resulting complexes. These results obtained indicated that bis(beta-cyclodextrin) 2 exhibits the strongly enhanced binding ability with all dye molecules examined compared with natural cyclodextrins. The binding modes of 2 with dye molecules have been deduced by 2D NMR experiments to establish the correlations between molecular conformations and binding constants of inclusion complexation. It is found that the improved binding ability and molecular selectivity of 2 could be attributed to double-cavity cooperative inclusion interaction and the size/shape matching between the host and guest.     

Capillary electrophoresis analysis of poly(ethylene glycol) and ligand-modified polylysine gene delivery vectors

Cationic polymers including polylysine (PLL) and polyethylenimine are being widely tested as gene delivery vectors in various gene therapy applications. In many cases, the polymers were further modified by hydrophilic polymer grafting or ligand conjugation, which had been shown to greatly affect the vector stability, delivery efficiency and specificity. The characterization of modified polycation is particularly critical for quality control and vector development. Here several different separation modes using capillary electrophoresis for the analytical characterization of the modified polymers are described. PLL molecules were grafted with poly(ethylene glycol) (PEG) chain or conjugated with epidermal growth factor and analyzed under various analytical conditions. Poly(N,N'-dimethylacrylamide)-coated capillary was used to analyze the modified PLL to reduce the interaction between the samples and the capillary wall. PLLs containing different numbers of conjugated ligands were well separated with the coating method but, for PLL-g-PEG, the separation was poor under the same conditions. A method using low buffer pH and hydroxypropylmethyl cellulose additive was developed. These methods are useful to characterize various polycations and important for the quality control and application of potential gene delivery vectors.     

Effects of alkyl chain lengths of gallates upon enzymatic wool functionalisation

The covalent grafting of alkyl gallates on wool through a laccase catalysed reaction in 80/20 (v/v, %) aqueous–ethanol mixture provided in a one-step process a multifunctional textile material with antioxidant, antibacterial and water repellent properties. Gallic acid and its alkyl esters ethyl, propyl, octyl and dodecyl gallate have been enzymatically grafted on wool fibres in order to study the effect of alkyl chain length on wool functional modification. The capacity of laccase to oxidise these phenolic compounds in an aqueous–organic medium has been verified by electrochemical techniques. The increase of CH₂, CH₃ groups in the FTIR spectra, together with the XPS analysis of the enzymatically modified fabrics confirmed the covalent grafting of ester gallates on wool. The result obtained in this work for antibacterial, water repellent as well as antioxidant properties show that the length of the alkyl chain of gallates molecule play an important role on wool functionalisation.     

Creating a unique environment for selecting reactive enzymes with DNA: 'Sticky' binding of oligocation-grafted polymers to DNA

To provide colloidally stable polyplexes formed between pDNA and cationic polymers, cationic polymers have been modified with hydrophilic polymers to form a hydrophilic shell. Block copolymers of cationic and hydrophilic polymers and cationic polymers grafted with hydrophilic polymers are representative designs of such polymers. Here, we report a new design of cationic polymers and oligocationic peptide-grafted polymers. We synthesized 15 kinds of graft copolymers by varying the number of cationic charges of the peptides and their grafting density. We found that graft copolymers with less cationic peptides and less grafting density formed colloidally stable polyplexes. Interestingly, the less cationic graft copolymers bind to excess amounts of pDNA. We also found that the graft copolymers showed selectivity toward reactive enzymes affording the reaction of pDNA with nucleases, while suppressing both the replication of DNA by DNA polymerase and gene expression. The suppression of the replication and expression is considered to result from the high capacity of the graft copolymers for binding with pDNA. The polynucleotides produced by DNA polymerase or RNA polymerase would be captured by the graft copolymers to impede these enzymatic reactions.     

Antibacterial polypropylene via surface-initiated atom transfer radical polymerization

Polypropylene (PP) coated by a non-leachable biocide was prepared by chemically attaching poly(quaternary ammonium) (PQA) to the surface of PP. The well-defined poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), a precursor of PQA, was grown from the surface of PP via atom transfer radical polymerization (ATRP). The tertiary ammine groups in PDMAEMA were consequently converted to QA in the presence of ethyl bromide. Successful surface modification was confirmed by ATR-FTIR, contact angle measurement, and an antibacterial activity test against Escherichia coli (E. coli). The biocidal activity of the resultant surfaces depends on the amount of the grafted polymers (the number of available quaternary ammonium units). With the same grafting density, the surface grafted with relatively high MW polymers (M(n) > 10,000 g/mol) showed almost 100% killing efficiency (killing all of the input E. coli (2.9 x 10(5)) in the shaking test), whereas a low biocidal activity (85%) was observed for the surface grafted with shorter PQA chains (M(n) = 1,500 g/mol).     

壳聚糖-g-N.羧甲基-二(2-苯并眯唑)-1,2-乙二醇的制备及其性能

以2-溴乙酸、壳聚糖、二（2-苯并咪唑）-1,2-乙二醇为原料,利用接枝作用将化学修饰后的小分子药物二（2-苯并咪唑）-1,2-乙二醇连接在天然高分子壳聚糖（CTS）上。并以。HNMR,IR,热分析及XRD等方法对其结构进行表征并研究接枝聚合物的理化性质。本文采用络合滴定法测定了接枝聚合物对一系列重金属离子的吸附作用;采用震荡法进行悬菌定量杀菌实验;还以经典的静态失重法研究了合成的聚合物在腐蚀介质中对N80钢片腐蚀的抑制作用。结果表明：小分子药物-（2-苯并咪唑）-1,2-乙二醇在接枝到天然高分子壳聚糖后热稳定性提高,在酸中具有良好的溶解度,对金属离子吸附能力在一个较宽温度范围内得以保持;同时增强了抑菌力,降低了最小抑菌浓度;利用BBIE与CTS韵协同作用提高了聚合物对金属腐蚀的抑制能力。     

Synthesis and characterisation of new types of side chain cholesteryl polymers

A series of cholesterol derivatives have been synthesised via the alkylation reaction of the 3-hydroxyl group with the aliphatic bromide compounds with different chain lengths, namely 3β-alkyloxy-cholesterol. The double bond between the C5 and C6 positions in these cholesterol derivatives was oxidised into epoxy, followed by an epoxy-ring-opening reaction with the treatment with acrylic acid, resulting in a series of 3β-alkyloxy-5α-hydroxy-6β-acryloyloxycholesterol, C(n)OCh (n=1, 2, 4, 6, 8, 10, 12), The acrylate group is connected to the C6 position, which is confirmed by the single crystal structure analysis. The corresponding polymers, PC(n)OCh, were prepared via free radical polymerisation. The structure of monomers and the resulting polymers were characterised with nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). The thermal properties of PC(n)OCh were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). To determine the secondary structure of polymers, circular dichroism (CD) spectra were performed. It was found that not all monomers produce high-molecular-weight polymers because of steric hindrance. However, all polymers have a helical structure, which can be enhanced by increasing the alkoxy chain length. In addition, increasing the alkoxy chain length decreases the glass transition temperature and increases the decomposition temperature of the polymers.     

In-cage and out-of-cage combinations of benzylic radical pairs in the glassy and melted states of poly(alkyl methacrylate)s

Norrish type 1 reactions of 1-(4-methylphenyl)-3-phenyl-2-propanone (ACOB(1)) have been used to probe structural and morphological properties of a series of poly(alkyl methacrylate)s (PAMAs, where the alkyl is ethyl, butyl, isobutyl, cyclohexyl, and hexadecyl) below and above their glass transition (or melting) temperatures. The PAMAs investigated cover a wide range of glass transition temperatures and structure types. The ratio of in-cage to the sum of in-cage and out-of-cage recombinations of the triplet benzylic radical-pairs generated upon irradiation of ACOB(1) (F(c)) have been calculated from relative photoproduct yields at different temperatures and are compared with the free hole volumes within the polymers as calculated from positronium annihilation lifetime spectroscopy. Laser flash photolysis experiments to follow the growth and decay of the radicals have also been conducted in order to correlate the steady-state irradiation results with the radical pair recombination processes (i.e., in-cage and out-of-cage). The changes in F(c) as a function of PAMA type and phase (temperature) can be correlated with chain relaxation rates and the nature of the polymer side chains, but not hole free volumes. These results are compared with those from our previous work, conducted in polyethylenes with differing degrees of crystallinity, where hole free volume was the primary factor in controlling F(c).     

Modification of Okra mucilage with acrylamide: Synthesis, characterization and swelling behavior

In the present communication, the synthesis and characterization of Okra mucilage, a food grade and water-soluble polysaccharide, based-materials are described. Okra mucilage has been modified by grafting acrylamide (AAm) for developing the new green polymeric materials of specialty applications. Grafting has been done under N₂ atmosphere using redox initiator and hydrogels were prepared by using N,N-methylenebisacrylamide (NN-MBAAm) as crosslinker. The effect of monomer concentration, initiator concentration, reaction time and temperature in terms of grafting efficiency (%GE), percent grafting (PG) and percent gel (%G) has been investigated. The grafted polymers and hydrogels were characterized by SEM, XRD and FTIR techniques to study various structural aspects. The swelling behavior of the crosslinked polymeric material has also been studied as a function of time, temperature and pH. The application area of these polymers is varied from biomaterials to the wastewater treatment.     

Novel redox surfactants and their interactions with glucose oxidase of Aspergillus niger

A number of novel redox surfactants (based on mixed bipyridine/dipyridylamine complexes of osmium (II) where the dipyridylamine ligands bears a saturated C(8), C(10), C(12), C(14), or C(16) alkyl chain) were synthesized and characterized electrochemically and biochemically as mediators for glucose oxidase (EC 1.1.3.4, GOD) of Aspergillus niger. These compounds exhibited critical micelle concentrations (CMCs) in phosphate-buffered saline solution (pH 7.4) in the range 10(-4) 10 10(-3) M, the value decreasing with increasing chain length. Dependence of a number of properties (speed of mediation, redox potential, denaturing action on the enzyme, adsorption on an electrode surface) on the length of the mediator alkyl chain was observed. The presence of an alkyl chain decreased the rate of mediation relative to otherwise similar nonsurfactant mediators, and the longer alkyl chain, the slower the rate of mediation. For each compound, mediation above the CMC was about tenfold slower than that observed below the CMC. However, for the cases of mediator absorbed on an electrode surface with GOD, longer chains give increased physisorption of mixed micelles of enzyme and mediator. The compounds were incidentally found to inhibit the glucose oxidase activity of GOD in a complex manner; inhibition increased with increasing chain length and the deactivation, for any given compound, was more pronounced below the CMC than above. Glucose oxidase activity assays and study of the action of surfactants and mediators on the fluorescent properties of carboxy-fluorescein-labeled GOD led to the consideration of a model for redox surfactant-GOD interaction where three mechanisms may operate: first, a selective interaction of mediators with the GOD active site; second, a nondenaturing association of short-chain (相似文献   

Synthesis and characterization of 2,3-di-O-alkylated amyloses: hydrophobic substitution destabilizes helical conformation

Amylose was selectively alkylated in the 2,3-O position of each anhydroglucose unit after trityl protection of the 6-OH groups. Alkyl iodides of varying chain length (C(2), C(5), C(8)) were coupled to amylose, and degrees of substitution (DSs) were varied between 0.3 and 1.8, as assessed by NMR analysis. Increasing amounts of methyl groups per anhydroglucose unit increased solubility in nonaqueous media, while at the same time reducing the ability of modified amylose to form a complex with iodine. The tendency to form inclusion complexes with the surfactant N-dodecyl pyridinium bromide decreased in the order beta-cyclodextrin > amylose approximately solubilized starch, indicating that the frozen macrocycle of beta-cyclodextrin was the most efficient inclusion host. Introduction of the bulky trityl group abolished the helical amylose conformation, which is not readily reassumed in the presence of hydrophobic substitution of the C2 and C3 positions. These results indicated that a polar outer surface is necessary but not sufficient for the formation of a stable amylose helix.     

Regioselectivity of enzymatic modification of poly(methyl acrylate)

Enzymes are potentially useful catalysts for polymerization as well as modification of polymers. While lipases have been used previously for polymerization reactions, they have not been used for modification of polymers. In this report, lipases were used to determine regioselective modification of ester functions in a telomer of poly(methyl acrylate). The influence of chain length on the extent of transesterification of methyl acrylate telomers of DP(n) 6-50 was studied by examining the relationship between the extents of enzymic modification to other telomerization parameters. The regioselectivity was observed when the average DP(n) of telomers is in a range of 6-22. At a higher DP(n) (>22), however, the average number of reacting ester functions per telomer strongly deviated from the theoretically predicted value. This phenomenon was suspected as a result of steric hindrance caused by folding of longer telomer chains. To verify this hypothesis, acrylate telomers at a DP(n) ranging from 10 to 42 were synthesized using a shorter telogen, i.e., 2,2'-ethanedithiol. The transesterification of these telomers showed a deviation in a degree of conversion when DP(n) was greater than 10, possibly indicating the inhibition caused by steric hindrance. Therefore, regioselective modification of acrylic polymers, which is difficult to achieve by conventional chemical methods, may be accomplished enzymatically.     

Fluorometric studies on inclusion complexation of L/D-tryptophan by beta-cyclodextrin 6-O-pyridinecarboxylates

Novel beta-cyclodextrin (beta-CD) derivatives, bearing a nicotinic or isonicotinic moiety, have been synthesized by a convenient method in 21 and 25% yields, respectively. The stability constants (K) and Gibbs free energy changes (-DeltaG degrees ) for the inclusion complexation of beta-cyclodextrin 6-O-mono(3-pyridinecarboxylate) (1), 6-O-mono(4-pyridinecarboxylate) (2), and 6-O-monobenzoate (3) with L- and D-tryptophan have been determined by spectrofluorome try in aqueous buffer solution (pH = 7.20) at 25.0 degrees C. All of the modifications dramatically enhanced the original K for beta-CD by a factor of 30-280 and interestingly switched the original enantiomer preference for L- to D-tryptophan, thus affording the inverted enantio-selectivities of K(L)/K(D) = 2.5 for beta-CD and K(D)/K(L) = 1.2-2.1 for the modified CDs 1-3. These results are discussed from the viewpoints of the size-fit and geometrical complementary relationship between the host and guest.     

Effect of Alkylsilyl Side‐Chain Structure on Photovoltaic Properties of Conjugated Polymer Donors

Side‐chain engineering is an important strategy for optimizing photovoltaic properties of organic photovoltaic materials. In this work, the effect of alkylsilyl side‐chain structure on the photovoltaic properties of medium bandgap conjugated polymer donors is studied by synthesizing four new polymers J70 , J72 , J73 , and J74 on the basis of highly efficient polymer donor J71 by changing alkyl substituents of the alkylsilyl side chains of the polymers. And the photovoltaic properties of the five polymers are studied by fabricating polymer solar cells (PSCs) with the polymers as donor and an n‐type organic semiconductor (n‐OS) m‐ITIC as acceptor. It is found that the shorter and linear alkylsilyl side chain could afford ordered molecular packing, stronger absorption coefficient, higher charge carrier mobility, thus results in higher J_sc and fill factor values in the corresponding PSCs. While the polymers with longer or branched alkyl substituents in the trialkylsilyl group show lower‐lying highest occupied molecular orbital energy levels which leads to higher V_oc of the PSCs. The PSCs based on J70 :m‐ITIC and J71 :m‐ITIC achieve power conversion efficiency (PCE) of 11.62 and 12.05%, respectively, which are among the top values of the PSCs reported in the literatures so far.