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21.
In this paper, the charge storage performance of electrospun poly(ethylene terephthalate) (PET) mats with high specific surface area was evaluated in comparison to that of PET film electrets. Corona discharge method was used to charge the electrospun PET mats and PET films. The surface potential decay measurements revealed that the corona charged РЕТ mats had higher initial values for the normalized surface potential compared to the РЕТ electret films. A tendency for stabilization of the electret charge to one and the same value for all charged samples (mats and films) after the 50th day was observed. The peaks at 90 °C in the thermally stimulated current (TSC) spectra of uncharged and charged in corona discharge electrospun PET mats were observed and attributed to a relaxation of the separated space charges, the dipole disorientation or injected charges within the bulk. It was found that the value of the storage charge in a corona charged electrospun PET mats was higher than that in PET mats prepared by electrospinning. 相似文献
22.
Fibrous poly(L-lactide) (PLLA) and bicomponent PLLA/poly(ethylene glycol) mats were prepared by electrospinning and then were coated with chitosan. The presence of chitosan coating was proved by scanning electron microscopy and by fluorescence microscopy. On contact with blood, the chitosan coating led to changes in erythrocyte shape and in their aggregation. The haemostatic activity of the mats increased with increasing chitosan content. Microbiological studies against Staphylococcus aureus revealed that the chitosan coating imparts antibacterial activity to the hybrid mats. The combined haemostatic and antibacterial activities render these novel materials suitable for wound-healing applications. 相似文献
23.
Kalin Kalinov Milena Ignatova Nevena Manolova Iliya Rashkov Nadya Markova Denitsa Momekova 《Colloid and polymer science》2014,292(11):2899-2912
Polyelectrolyte complexes (PECs) were prepared from N,N,N-trimethylchitosan iodide (TMCh) of different molar mass and a weak polyacid-poly(acrylic acid) (PAA) or a strong polyacid-poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS). The quaternization of the amino groups of chitosan enabled the formation of water-insoluble PECs in a broad pH range—from 3 to 12 and from 1 to 12 for TMCh/PAA and TMCh/PAMPS, respectively. Whereas the stoichiometry of the TMCh/PAA complex was pH dependant, the stoichiometry of the TMCh/PAMPS complex did not depend on pH. The stoichiometry and the yield of the complexes were influenced by the molar mass of TMCh. PEC nanoparticles were produced by mixing dilute solutions of the oppositely charged polyelectrolytes as revealed by dynamic light scattering analyses. The size of the particles was in the range of 135–924 nm and depended on the polyelectrolyte molar mass, the initial polyelectrolyte concentration, and the molar fraction of the TMCh units. Microbiological screening against Staphylococcus aureus and Escherichia coli revealed that PECs between TMCh and PAA or PAMPS have a good antibacterial effect, which is more slowly pronounced than that of the starting TMCh of different molar mass. 相似文献
24.
Fathi H. Assaleh Aleksandar D. Marinković Jasmina B. Nikolić Saša Ž. Drmanić Danijela Brković Nevena Prlainović Bratislav Ž. Jovanović 《国际化学动力学杂志》2016,48(7):367-378
Linear free energy relationships (LFER) were applied to the kinetic data for the reaction of 5‐substituted orotic acids, series 1 , with diazodiphenylmethane (DDM) in N,N–dimethylformamide and compared with results obtained for 2‐substituted benzoic acids, series 2 . The correlation analysis of the kinetic data with σ substituent parameters was carried out using SSP (single substituent parameter) methods. From the sign and value of proportinality constant ρ, lower sensitivity to the substituent effect was obtained in series 1 , 0.876, than in the series 2 , 1.877. Evaluation of substituent “ortho‐effect” was performed using the Charton model, which includes the steric substituent parameter, and Fujita and Nishioka's model, which describes the total ortho‐effect as contribution of ordinary polar effect, the ortho‐steric and ortho‐polar effects. Results of correlations, obtained by using the Charton model, showed highest contribution of the polar effect, 0.861 vs. 2.101, whereas the steric effect is of lowest significance, 0.117 vs. 0.055, for series 1 and 2 , respectively. Also, a low negative value of coefficient with the steric effect, –0.08, obtained from the Fujita–Nishioka model indicated low steric effect, influencing a decrease of the reaction rate in series 1 . The structural and substituent effects were also studied by using the density functional theory method, and together with kinetic data, it gave a better insight into the influence of the effect of both geometry and substituent on the π?electron density shift induced reactivity of investigated acids. 相似文献
25.
26.
Nevena Milčić Dr. Višnja Stepanić Dr. Ivo Crnolatac Prof. Zvjezdana Findrik Blažević Dr. Zlatko Brkljača Dr. Maja Majerić Elenkov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(56):e202201923
Although the application of organic solvents in biocatalysis is well explored, in-depth understanding of the interactions of solvent with proteins, in particular oligomeric ones, is still scant. Understanding these interactions is essential in tailoring enzymes for industrially relevant catalysis in nonaqueous media. In our study, the homotetrameric enzyme halohydrin dehalogenase (HHDH) from Agrobacterium radiobacter AD1 (HheC) was investigated, as a model system, in DMSO/water solvent mixtures. DMSO, the most commonly used co-solvent for biocatalytic transformations, was found to act as a mixed-type inhibitor with a prevalent competitive contribution. Even 5 % (v/v) DMSO inhibits the activity of HheC by half. Molecular dynamics (MD) simulations showed that DMSO keeps close to Ser-Tyr catalytic residues forming alternate H-bonds with them. Stability measurements paired with differential scanning calorimetry, dynamic light scattering methods and MD studies revealed that HheC maintains its structural integrity with as much as 30 % (v/v) DMSO. 相似文献
27.
Rosica Mincheva François Bougard Dilyana Paneva Magali Vachaudez Charles‐André Fustin Jean‐François Gohy Nevena Manolova Iliya Rashkov Philippe Dubois 《Journal of polymer science. Part A, Polymer chemistry》2009,47(8):2105-2117
For the first time, the polyelectrolyte complex (PEC) formation tool was used for preparation of core‐shell nanoparticles form the natural polyampholyte N‐carboxyethylchitosan (CECh) and weak polycationic (protonated) polyoxyethylene‐b‐poly[2‐(dimethyl‐amino)ethyl methacrylate] (POE‐b‐PDMAEMA) diblock copolymers. The performed dynamic light scattering analyses revealed that nanoparticles with a PEC core and a POE shell could be formed at mixing ratio between the oppositely charged groups equal to 1/1 depending on CECh molar mass, polymerization degree of PDMAEMA block and ionic strength. The results were confirmed by the performed AFM and cryo‐TEM analyses. When high molar mass CECh was used, core‐shell nanoparticles were obtained with the diblock copolymer of the shortest PDMAEMA block at ionic strength (I) of 0.01. At ionic strength value close to the physiological one (I = 0.1) secondary aggregation occurred. Spherical nanoparticles at I = 0.1 were obtained upon lowering the CECh molar mass. Depending on the polymer partners and medium parameters the size of the obtained particles varied from 60 to 600 nm. The X‐ray photoelectron spectra evidenced the hydrophilic POE‐block shell—coacervate CECh/PDMAEMA‐block core structure. The nanoparticles are stable in a rather narrow pH range around 7.0, thus revealing the high pH‐sensitivity of the obtained core‐shell particles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2105–2117, 2009 相似文献
28.
Milena Ignatova Zhanina Petkova Nevena Manolova Nadya Markova Iliya Rashkov 《Macromolecular bioscience》2012,12(1):104-115
In order to impart antibacterial properties to microfibrous electrospun materials from styrene/maleic anhydride copolymers, quaternized chitosan derivatives (QCh) containing alkyl substituents of different chain lengths are covalently attached to the mats. A complete inhibition of the growth of bacteria, S. aureus (Gram‐positive) and E. coli (Gram‐negative), for a contact time of 30–120 min or a decrease of the bacterial titer by 2–3 log units is observed depending on the quaternization degree, the chain length of the alkyl substituent, and the molar mass of QCh. The modified mats are also effective in suppressing the adhesion of pathogenic S. aureus bacteria.
29.
We prove that the supercritical one-dimensional contact process survives in certain wedge-like space-time regions, and that
when it survives it couples with the unrestricted contact process started from its upper invariant measure. As an application
we show that a type of weak coexistence is possible in the nearest-neighbor “grass-bushes-trees” successional model introduced
in Durrett and Swindle (Stoch. Proc. Appl. 37:19–31, 1991). 相似文献
30.
Reaction of salicylaldehydes with tetraethyl ester of methylenebisphosphonic acid, under Knoevenagel reaction conditions, gives the corresponding 1,2-benzoxaphosphorin-3-phosphonates 5 in good yields. The [3+2] regio- and stereoselective cycloaddition of 5a and 5b with ethyl diazoacetate gives two P-4 epimers of the corresponding pyrazoline bisphosphonate tetraethyl esters 9 and 10. Analogously, ethyl diazoacetate reacts with 1 and 2 to give the expected pyrazolines 6-8. The structures of the new compounds are revealed and confirmed by analytical, spectroscopic data and X-ray crystallographic analysis. 相似文献