Regioselective synthesis and biological activity of oxidized chitosan derivatives

Oxidized chitosan derivatives with various degrees of oxidation (DS, 0.1–1.0) were prepared by the treatment of chitosan with CrO₃/aq HClO₄ or by the oxidation of ­3‐O‐ and N‐protected chitosan with 30% aq H₂O₂/Na₂WO₄ followed by 3‐O‐ and N‐deprotection. The oxidized products were then N‐acetylated with Ac₂O in order to improve their water‐solubility. Although the oxidized chitosan derivative of DS 0.28 and the degree of N‐acetylation of chitosan (DA) 38% was insoluble in the pH 3–8 region, that of DS 0.26 and DA 76% was soluble in the neutral pH range. The newly‐prepared acetylated and oxidized chitosan derivatives were found to suppress the chemiluminescence response of inflammatory cells such as canine polymorphonuclear cells (PMNs). Analysis by the surface plasmon resonance method revealed that the bind and release behavior of PMNs to acetylated oxidized chitosan derivatives was similar to that against carboxymethylated chitosan derivatives. The amount of water‐soluble chitosan derivative bound to cytokine IL‐8 was found to be affected by the structural and electronic features of the chitosan substituents in the chitosan chain. Copyright © 2003 John Wiley & Sons, Ltd.     

Epitaxial single crystal surface patterning and study of physical and chemical environmental effects on crystal growth

For designing the responsive polymer brushes, and tuning the local and chemical surface responses to the external stimuli, the epitaxial single crystals were patterned by combination of bared surfaces of poly(ethylene glycol) (PEG) substrate, polymer homo-brushes constructed from poly(ethylene glycol)-b-polystyrene (PEG-b-PS) as well as poly(ethylene glycol)-b-poly(methyl methacrylate) (PEG-b-PMMA), and PEG-b-PS/PEG-b-PMMA mixed-brush channels. To achieve this target, various single crystals and epitaxial structures grown from dilute solutions through self-seeding approach were utilized as seeds to fabricate the next channels. The characteristics and morphologies of different channels were detectable by atomic force microscopy (AFM). The influence of chemical (solvent quality and interaction of substrate with different brushes) and physical (presence of brushes from another type in their vicinity) environments on crystallization was studied. Due to the effect of chemical environment, the PS brushes hampered the growth of PEG crystals at M _n ^PS?=?10,000 g/mol. However, the PMMA brushes allowed PEG crystals to grow completely at M _n ^PMMA =13,100 g/mol, and indicated their hindrance at higher molecular weights (here, M _n ^PMMA?=?17,100 g/mol). It was feasible to neutralize the mentioned hindrance through fabricating the channels with brushes having the highest hindrance (M _n ^PS?=?14,800 g/mol and M _n ^PMMA?=?17,100 g/mol), and altering the physical environment from homo- to mixed-brush morphology. The characteristics (thickness, tethering density, and domain size) of developed channels from a certain material, in all arrangements and in various channels were in good agreement with those of corresponding non-epitaxial single crystals grown under the same conditions.     

Regioselectively Modified Cellulose and Chitosan Derivatives for Mono- and Multilayer Surface Coatings of Hemocompatible Biomaterials

In this study different synthetic strategies were developed and applied to introduce solely or in combination heparin/heparansulfate-like functional groups such as N-sulfo, O-sulfo, N-acetyl, and N-carboxymethyl groups into chitosan and cellulose with highest possible regioselectivity and completeness and defined distribution along the polymer chain. Completely substituted 6-amino-6-deoxycellulose and related derivatives were prepared from tosylcellulose (DS 2.02; C₆ 1.0) by nucleophilic substitution with azido groups only in the 6-position at 50 °C with subsequent reduction to amino groups and completely removing tosyl groups in the 2,3-position. 2,6-Di-O-sulfocellulose was prepared using the reactivity difference between C-2, C-6 and C-3 of cellulose. The reactivity difference between amino groups and hydroxyl groups was used to prepare various N-substituted derivatives. Partially 2,6-di-O-sulfated cellulose was obtained from trimethylsilylcellulose by the insertion of sulfurtrioxide into the Si–O ether linkage. Partially 3-O-sulfocellulose was synthesized by protecting C-2 and C-6 with trifluoroacetyl groups. A copper–chitosan complex was used to synthesize 6-O-sulfochitosan with a DS of 1.0 at C-6 and various partially 6-O-desulfonated products are possible. Using the phthalimido group to increase the solubility of chitosan in DMF, the regioselectivity of 3-O-sulfo groups was improved by regioselective 6-O-desulfonation of nearly complete 3,6-O-disulfochitosan. The platelet adhesion properties of immobilized regioselectively modified water-soluble derivatives on membranes have been tested in vitro. Some regioselectively modified chitosan and cellulose derivatives are potential candidates for the surface coatings of biomaterials if the regioselective reactions are somewhat further optimized.     

Order of Reactivity of OH/NH Groups of Glucosamine Hydrochloride and N-Acetyl Glucosamine Toward Benzylation Using NaH/BnBr in DMF

The order of reactivity of OH and NH groups of glucosamine hydrochloride (GlcNH₂^.HCl) and N-acetyl glucosamine (GlcNAc) toward benzylation with NaH/BnBr in DMF was investigated. For GlcNH₂^.HCl, benzyl groups were introduced in the order of N-Bn > N-Bn₂ > 1-O-Bn > 6-O-Bn > 4-O-Bn > 3-O-Bn; for GlcNAc, benzyl groups were introduced in the order of 1-O-Bn > 6-O-Bn > 4-O-Bn > 3-O-Bn > N-Bn. A range of partially benzylated 2-N,N′-dibenzyl glucopyranosides and GlcNAc derivatives were obtained in a single step.     

Synthesis and cell activity of novel galactosylated chitosan as a gene carrier

It is important for gene carrier to transport DNA into target cells. Although viral vectors are very efficient gene-transfer vehicles, significant drawbacks limit their applications. Chitosan (CS) has been researched widely as a non-viral vector. However, the low cell specificity and low transfection efficiency of chitosan need to be overcome. In order to conquer the drawback of chitosan, the present paper is concerned with the synthesis of novel galactosylated chitosan (GC) through etherization of chitosan and galactose in THF using BF₃·OEt₂ as promoter. The final product was characterized and confirmed by FT-IR and ¹H NMR. The degree of O-substitution (DS) of chitosan by galactose was measured to be 10.38% using anthrone-sulfuric acid colorimetric method. The mean particle diameter and average zeta potential of the GC/DNA complex were 350 nm and +22.1 mV, respectively. The GC/DNA nanoparticle was tested to transfect HEK293 cells, and the viability of HEK293 cells was not affected by the GC/DNA nanoparticle compared to that of the control.     

Synthesis and self-assembly of poly(ethylene glycol)-block-poly(N-3-(methylthio)propyl glycine) and their oxidation-sensitive polymersomes

Amphiphilic block copolymers poly(ethylene glycol)-block-poly(N-3-(methylthio)propyl glycine) (PEG-b-PMeSPG) were synthesized via ring-opening polymerization of N-3-(methylthio)propyl glycine N-thiocarboxyanhydride (MeSPG-NTA) initiated by amino-terminated PEG. The self-assemblies of three PEG-b-PMeSPG copolymers with different PMeSPG block lengths were first prepared by nanoprecipitation method using THF and DMF, respectively, as the organic solvent, and their morphologies were studied by Cryo-EM and DLS. To prepare polymersomes loaded with glucose oxidase (GOx), double emulsion method followed by extrusion treatment was employed. The oxidation-responsive disruption of polymersomes was achieved upon the introduction of glucose because of the oxidants generated in-situ by GOx/glucose.     

Preparation and characterization of magnetic Co0.5Zn0.5Fe2O4-chitosan nanoparticles as surfactants in oilfield

Chitosan nanoparticles with magnetic properties can be potentially used as separation materials in adsorption of oil for enhanced oil recovery. Different from the traditional surfactants, the novel magnetic Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles are of excellent biodegradation and a high level of controllability. The Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles with core-shell structure were prepared successfully. The image of transmission electron microscope and the scanning electron microscopy showed that the cubic-shape magnetic Co_0.5Zn_0.5Fe₂O₄-particles were encapsulated by the spherical chitosan nanoparticles. The size of the Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles was below 100 nm. The saturated magnetization of the Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles could reach 80 emu g^?1 and showed the characteristics of superparamagnetism at the same time. The evaluation on the interfacial properties of the product demonstrated that the interfacial tension between crude oil and water could be reduce to ultra-low values (to about 10^?3 mN m^?1) when the magnetic Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticle was used in several blocks in Shengli Oilfield without other additives. Meanwhile, the magnetic Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles possessed good salt-resisting capacity.     

Preparation of benzoylchitosans and their chiroptical properties in dilute solutions

Two benzoyl substituted chitosan derivatives, 3,6‐O‐dibenzoylchitosan (DBC) and 2‐N‐3,6‐O‐tribenzoylchitosan (TBC), were prepared, and their optical activities in organic solvent were investigated by circular dichroism (CD). For TBC, two splitting bands (a negative one at 288 nm and a positive one at 274 nm) corresponding to the ¹L_b transition of the benzoyl group were observed in chloroform and dichloromethane, while only a negative CD band was recorded in N, N‐dimethylformamide (DMF). These results indicated that the transition moments of benzoyl groups were orderly arranged along the helical polymer chain when TBC was dissolved in a solvent with low polarity, but the same ordered structure did not appear in a polar solvent of DMF. For DBC, only negative CD signals corresponding to the ¹L_b transition of the benzoyl group were observed, regardless of the solvent property, which indicated that the chromophores were not arranged in an ordered fashion with appropriate geometry to interact with one another to induce bi‐signate CD signals. Adding methanol or DMF to the solution of TBC/chloroform resulted in a progressive decrease of the intensity of the positive split band at 274 nm. The intensity of the positive band was weakened upon heating a solution of TBC/chloroform from 20 to 60 °C. The results suggested that the ordered arrangement of the chromophores in the TBC system was dependent on solvent and sensitive to temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4107–4115, 2004     

Effect of solvent in radical polymerization of butadiene 1-carboxylic acid

The radical polymerization and copolymerization of butadiene 1-carboxylic acid (Bu-1-Acid) were studied in a variety of the electron-donor solvents such as dimethylformamide (DMF), tetrahydrofuran (THF), methyl ethyl ketone (MEK), acetonitrile (ACN), and benzene (BZ) using AIBN as an initiator at 50°C. Under these conditions, the polymerization rate of Bu-1-Acid increased in the order, DMF < THF < MEK < ACN < BZ in the various solvents. In copolymerization with styrene [M₂] and acrylonitrile [M₂], the monomer reactivity ratio r₁ increased and r₂ decreased in the same order. Moreover, it was found that Alfrey-Price Q-e value of Bu-1-Acid increased depending on solvent in the order DMF < THF < MEK < ACN < BZ. These variations were correlated to the electron-donating power (Δvcm^?) of the solvents used and are discussed on the basis of the solvation of Bu-1-Acid into the solvent. Also, it was found that the microstructures of these polymers were always trans-1,4 and did not change with the solvent used.     

Iron complexes of the Schiff base ligand bis(2,5-dihydroxyacetophenone) ethylenediamine

Summary Iron complexes of the tetradentate ligand, bis(2,5-dihydroxyacetophenone) ethylenediamine, and a fifth anionic ligand have been prepared and characterized by spectroscopic techniques. E.p.r. studies of the X-band frozen DMF solution reveal the presence of a broad, g ca. 4.0, signal with weak features at lower fields. The complexes exhibit a broad visible band with _max in the 550–605 nm range which is assigned to the phenolate Fe charge transfer transition. The LMCT band energy varies with the anionic ligand, namely, N ₃ ^- > Bz^- > HCOO^- > Cl^- > ClO ₄ ^- (Bz^- = benzimidazole anion), similar to the behaviour of dioxygenases and proteins containing tyrosine coordinated to iron.     

Remarkable pH-responsive Microfiltration Membrane from Well-defined PS-b-PDEAEMA Copolymers by ATRP Method

This work presented a detailed study on pH-responsive self-supporting microfiltration membranes via the non-solvent-induced phase separation (NIPS) process from mixtures of THF and DMF. The well-defined pH-responsive polymers polystyrene-block-poly (N,N-diethylaminoethyl methacrylate) (PS-b-PDEAEMA) were synthesized via atom transfer radical polymerization (ATRP) evidenced by ¹H-NMR and GPC studies. Two amphiphilic diblock copolymers were used, St₇₁-b-DEAEMA₃₁ and St₇₁-b-DEAEMA₈₂. The influence of pH value in the coagulation bath, the solvent composition, the “open-time” before immersion into the coagulation bath and the polymer composition onto the membrane morphology were investigated, and flux values obtained for the different membrane systems were compared. The SEM images and polarized optical microscopy revealed that the size and the number of pores in the membranes were larger along with the decreasing THF content and “open time”. For the copolymer with the longer PDEAEMA block, St₇₁-b-DEAEMA₈₂, the flux values were lower than that of St₇₁-b-DEAEMA₃₁ under different “open time”, which meant that the total area of the pores in the membranes was smaller, respectively. The optimum preparation conditions for microfiltration membrane were as follows: the polymer was St₇₁-b-DEAEMA₈₂, the “open time” was 20s, the non-solvent bath was the pH = 2 distilled water, and the solvent composition was 25% THF and 75% DMF. Both polymers were shown to form self-supporting membrane systems that were able to react onto pH stimuli in terms of water flux.     

H‐shaped (ABCDE type) quintopolymer via click reaction [3 + 2] strategy

H‐shaped quintopolymer containing different five blocks: poly(ε‐caprolactone) (PCL), polystyrene (PS), poly(ethylene glycol) (PEG), and poly(methyl methacrylate) (PMMA) as side chains and poly(tert‐butyl acrylate) (PtBA) as a main chain was simply prepared from a click reaction between azide end‐functionalized PCL‐PS‐PtBA 3‐miktoarm star terpolymer and PEG–PMMA‐block copolymer with alkyne at the junction point, using Cu(I)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as a catalyst in DMF at room temperature for 20 h. The H‐shaped quintopolymer was obtained with a number–average molecular weight (M_n) around 32,000 and low polydispersity index (M_w/M_n) 1.20 as determined by GPC analysis in THF using PS standards. The click reaction efficiency was calculated to have 60% from ¹H NMR spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4459–4468, 2008     

A Novel Keggin Units-Supported Complex: Synthesis,Characterization and Crystal Structure of [(CH3)2NH2]6[Cu(DMF)4(GeW12O40)2] · 2DMF

A novel hybrid compound, [(CH₃)₂NH₂]₆[Cu(DMF)₄(GeW₁₂O₄₀ ^4-)₂] [sdot] 2DMF, has been synthesized from H₄GeW₁₂O₄₀ [sdot] n H₂O, CuCl₂ and N, N -dimethylformamide (DMF) in aqueous solution and characterized by elemental analysis, UV and IR spectra. Single crystal X-ray structure analysis shows that the crystal consists of a α-Keggin heteropolyanion-supported anion [Cu(DMF)₄(GeW₁₂O₄₀ ^4-)₂], two free N, N-dimethylformamide molecules, six protonated dimethylamine (DMA) molecules, and that the coordinating atoms of DMF are the oxygen atoms of C=O group. Thermal analysis indicates that the thermal stability of the GeW₁₂O₄₀ ^4- anion in the title compound is stronger than that in acid.     

MnSb2O6-chitosan nanocomposite: An efficient catalyst for the synthesis of coumarins via Pechmann reaction

In this work, MnSb₂O₆-chitosan nanocomposites were synthesized and have been employed in Pechmann condensation for the synthesis of coumarin derivatives. MnSb₂O₆-chitosan nanocomposites were characterized by Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) techniques. The particles of MnSb₂O₆-chitosan have uniform spheres with sizes that are less than 100 nm. Simplicity, easy work-up, and short reaction times are advantages of this reaction. Also, we evaluated the antibacterial activity for some of the products, and the result showed significant pharmaceutical activities as antibacterial reagents against Staphylococcus aureus and Escherichia coli.     

Confined crystallization,melting behavior and morphology in PEG-b-PLA diblock copolymers: Amorphous versus crystalline PLA

In diblock copolymers, the constraining effects of different stereochemical structure of high-T_m block on crystallization and melting behaviors of other constituent are supposed to be different. In this work, PEG-b-PDLLA and PEG-b-PLLA were synthesized, and crystallization kinetics, crystalline structure, melting behaviors of PEG blocks and morphology development in these systems were evaluated. Compared to those connected to PLLA, PEG-b-PDLLA exhibited lower crystallization rates, implying that connectivity of amorphous chain exerted more pronounced effect on crystallization rate of PEG than that of steric hindrance of PLLA crystallites. While all PEG-b-PDLLA samples showed a single endothermic peak during heating process, multiple melting peaks were observed in PEG-b-PLLA associated with composition, crystallization temperature and cooling rate of PLLA. A lamellar structure was formed by the crystallization of PEG in all PEG-b-PDLLA, however, when PEG-b-PLLA crystallized at room temperature directly, unexpected results occurred: lamellar for diblock copolymers with 31.5 and 48.0 wt% PLA or cylindrical structure for the diblock copolymers with 56.1 and 63.8 wt% PLA. Depending on composition, PEG-b-PLLA created one or two types of lamellar stacks after sequential crystallization of PLLA and PEG. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 455–465     

Aggregation Behavior of Poly(ethylene glycol)-block-poly (γ-benzyl L-glutamate)-graft-poly(ethylene glycol) Copolymer and its Blends with Poly(γ-benzyl L-glutamate) Homopolymer in Mixed Solvents

Poly(ethylene glycol)-block-poly(γ-benzyl L-glutamate)-graft-poly(ethylene glycol) (PEG-b-PBLG-g-PEG) copolymer was synthesized by the ester exchange reaction of PBLG-block-PEG copolymer with mPEG. The self-association behaviors of PEG-b-PBLG-g-PEG and its blends with PBLG homopolymer in the mixtures of ethanol and dimethylformamide (DMF) were investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), and viscometry. Effects of the introduction of PBLG homopolymer, the grafting ratio, and the DMF content on the self-association behaviors of PEG-b-PBLG-g-PEG copolymer in the mixtures of ethanol and DMF were mainly researched. It was revealed that PEG-b-PBLG-g-PEG copolymer could self-assemble to form polymeric micelles with a core-shell structure in various shapes from different preparation conditions. The critical micelle concentration (CMC) and the average particle diameter of the micelles formed by PEG-b-PBLG-g-PEG copolymer in the mixed solvents also changed with different preparation conditions.     

Cellulose/chitosan hybrid nanofibers from electrospinning of their ester derivatives

A facile approach has been established to generate cellulose/chitosan hybrid nanofibers with full range of compositions by electrospinning of their ester derivatives, cellulose acetate (CA) and dibutyryl chitin (DBC), followed by alkaline hydrolysis to cellulose (Cell) and chitosan (CS). DBC was synthesized by acid-catalyzed acylation of chitin (CHI) with butyric anhydride and the newly formed butyl groups on C3 and C6 were confirmed by FT-IR and ¹HNMR. DBC had robust solubility in acetone, DMAc, DMF, ethanol, and acetic acid, all except ethanol were also solvents for CA, allowing mixing of these ester derivatives. Fiber formation by electrospinning of either DBC or CA alone and together in these common solvents and their mixtures were studied. The 1/1 acetone/acetic acid was found to be the optimal solvent system to generate fibers from either DBC or CA as well as their mixtures at all CA/DBC ratios, resulting in hybrid fibers with diameters ranging from 30 to 350 nm. DBC and CA were well mixed and showed no phase separate in the hybrid fibers. Alkaline hydrolysis (NaOH) of the equal mass CA/DBC nanofibers regenerated Cell and CHI readily via O-deacylation, then proceeded to further deacetylate CHI to CS via N-deacetylation at higher alkaline concentrations and/or temperatures. Under conditions studied, hydrolysis with 5N NaOH at 100 °C for 3 h was optimal to regenerate cellulose/chitosan hybrid nanofibers.     

A Zn(II) luminescent complex with a Schiff base ligand: solution,computational and solid state studies

Abstract

A new mononuclear complex of zinc(II), [Zn(HL)₂]?2DMF (H₂L = (E)-N′-((E)-(hydroxyimino)butan-2-ylidene)salicyloylhydrazide, DMF = N,N-dimethylformamide), was prepared and characterized. Single-crystal X-ray crystallography revealed a six-coordinate zinc(II) surrounded by nitrogen of the oxime function and oxygen and distal nitrogens of the acylhydrazone group. This entity also exists in solution as demonstrated by ¹H-NMR and potentiometric titrations. The computational analysis showed that the molecular orbitals involved in the main electronic transitions of the complex species in solution are centered on the ligand with negligible contribution of the metal ion. The photophysical properties of the complex were evaluated in solution and in the solid state. Luminescence studies showed that the solid has a strong emission at 550 nm with a large Stokes shift with respect to absorption. The solid state fluorescence emission is ascribed to ligand-centered and/or ligand-to-ligand charge transfer transitions, following the DFT results in solution. A comparison with a previously reported mononuclear [Zn(HL)₂] allowed the investigation of the influence of DMF molecules in the structural packing and the luminescence properties.     

Electrochemical Properties of Superoxide Ion in Aprotic Media

The electrochemical response of the oxygen/superoxide ion (O₂/O ₂ ^.- ) couple at glassy carbon electrode in N,N-dimethylformamide (DMF) is investigated by cyclic voltammetry. The electrode reaction mechanisms of superoxide ion with hydroquinone and ethyl acetate are discussed in detail. The macroscale generation of superoxide ion is carried out by means of controlled-potential electrolysis. The UV spectrum of superoxide ion in DMF, obtained for the first time, exhibits a single absorption band with _max at 273 nm within 190–500 nm.     

Organocatalyzed Trifluoromethylation of Ketones and Sulfonyl Fluorides by Fluoroform under a Superbase System

Fluoroform (HCF₃, HFC-23) is a side product in the manufacture of polytetrafluoroethylene (Teflon). Despite its attractive properties, taming HCF₃ for trifluoromethylation is quite problematic owing to its low acidity and the lability of the naked trifluoromethyl carbanion generated from HCF₃. Herein we report the organic-superbase-catalyzed trifluoromethylation of ketones and arylsulfonyl fluorides by HCF₃. The reactions were carried out by using a newly developed “superbase organocatalyst system” consisting of catalytic amounts of P₄-tBu and N(SiMe₃)₃. A series of aryl and alkyl ketones were converted into the corresponding α-trifluoromethyl carbinols in good yields under the organocatalysis conditions in THF. The superbase organocatalytic system can also be applied to the trifluoromethylation of arylsulfonyl fluorides for biologically important aryl triflones in THF or DMF in good yields. Protonated P₄-tBu, H[P₄-tBu]⁺, is suggested to be crucial for the catalytic process. This new catalytic methodology using HCF₃ is expected to expand the range of synthetic applications of trifluoromethylation.