Physiological activities of chitosan and N‐trimethyl chitosan chloride in U937 and 3T3‐L1 cells

Chitosan (CH) is a biopolymer with biocompatible, biodegradable, and bioactive properties. N,N,N‐trimethyl chitosan chloride (TMC) is a quaternized form of CH that is highly cationic and more water soluble than unmodified CH. The physiological activities of CHs with different molecular weights (M_w) and degrees of TMCs quaternization were investigated in U937 and 3T3‐L1 cell lines. ¹H‐NMR spectrometry and size exclusion chromatography were used for characterization of the biopolymers. The half inhibition concentration (IC₅₀) of DPPH‐radical‐scavenging activity was below 0.9 mg/m with quaternized CHs. The IC₅₀ values of chitooligosaccharides, low‐ and medium‐molecular‐weight CHs were 8.4, 10.9, and 13.9 mg/ml, respectively. High‐molecular‐weight CHs and TMCs showed apoptotic activity on U937 cells. T41, a TMC of 549 kDa with a 41% degree of quaternization (DQ), yielded 30.7% apoptotic cell death in U937 at 20 µg/ml and effectively repressed cell differentiation and triglyceride accumulation in 3T3‐L1. Depolymerized CHs reduced triglyceride accumulation but also caused cell differentiation. TMCs showed repressor activity to both cell differentiation and triglyceride accumulation. Increasing the molecular weight of CHs and TMCs generally resulted in increased physiological activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Methylation of Chitosan with Iodomethane: Effect of Reaction Conditions on Chemoselectivity and Degree of Substitution

N,N,N‐trimethylchitosan (TMC) was prepared by reacting purified chitosan with iodomethane, in the presence of sodium hydroxide, water and sodium iodide, at room temperature. The reaction medium was N‐methyl‐2‐pyrrolidone. Different samples of TMC were obtained by adding to the reaction medium a fixed volume (5.5 mL) of aqueous NaOH solutions at different concentrations (15, 20, 30 and 40 wt.‐%) and carrying out the reactions for 9 or 24 h. The features observed in the ¹H and ¹³C NMR spectra of these chitosan derivatives, in respect of the chemical shift, number and relative intensity of the signals, depended strongly on the excess of NaOH and H₃CI added to the reaction medium, but when the lowest excess was employed, the characteristics of the derivative were not affected by the reaction time to the same extent. The average degree of quaternization of these N‐methylated derivatives of chitosan ranged from 10.5% to 44.8%, according to the reaction conditions. Increasing the excess of NaOH, in reactions carried out for 9 h, resulted in TMC samples with progressively higher content of trimethylated sites however, the reaction yields were correspondingly lower and O‐alkylation was favored in these cases.

¹H NMR spectrum of sample [A_X]^24h dissolved in D₂O (C_p = 10 g/L).     

Polyelectrolyte complexes of chitosan/heparin and <Emphasis Type="Italic">N,N,N-</Emphasis>trimethyl chitosan/heparin obtained at different pH: I. Preparation,characterization, and controlled release of heparin

Chitosan and N,N,N-trimethyl chitosan (TMC) were treated with heparin (HP) to produce polyelectrolyte complexes (PECs). The structures of PECs were characterized by Fourier transform infrared and CP-MAS ¹³C NMR spectroscopies. A thermal stability of TMC/HP complex was evaluated by thermogravimetric analyses, and morphology was investigated by SEM images. The ratio between the carbons bonded to noncharged nitrogen atoms (CΦ) and the carbons bonded to positively charged nitrogen atoms (Cω) in TMC was calculated through of the degree quaternization (DQ), being the DQ obtained through ¹H NMR data. Experiments of controlled release of HP were performed in distilled water at pH ∼7, using methylene blue/heparin system as solute. The release profiles of HP from TMC/HP complex are quite different each other. The value of CΦ/Cω ratio was used for explaining such an effect. The CΦ/Cω ratio tends to be constantly (∼0.69) as high as the pH of medium in which the PEC of TMC/HP was obtained. The change of CΦ/Cω ratio on the pH was also considered to explain the improvement of thermal stability of PEC2 with increase of pH. Data show that PEC of TMC/HP formed at pH 8 is a promising material for uses in oral site-specific HP release systems.     

Synthesis and properties evaluation of quaternized polyurethanes as antibacterial adhesives

We present new side‐chain quaternized polyurethanes as antibacterial adhesives made by polyaddition polymerization followed by quaternization for different time intervals. The degree of quaternization of N‐diol units in the polymer is changed from 13.6 to 99.0 mol % (almost complete) for tuning the antibacterial action (leaching/contact type) and studying effect on adhesive strength. The degree of quaternization of about 26 mol % provided the nonleaching antibacterial effect with adhesive strength more than 60 N cm^?2 on aluminum and glass substrates. The increase in the degree of quaternization enhanced polymer polarity shifting nonleaching (contact type) antibacterial behavior to the leaching type but maintaining the high adhesive strengths. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 752–757     

Poly(N,N‐diethylacrylamide) microspheres by dispersion polymerization

Poly(N,N‐diethylacrylamide)‐based microspheres were prepared by ammonium persulfate (APS)‐initiated and poly(vinylpyrrolidone) (PVP)‐stabilized dispersion polymerization. The effects of various polymerization parameters, including concentration of N,N′‐methylenebisacrylamide (MBAAm) crosslinker, monomer, initiator, stabilizer and polymerization temperature on their properties were elucidated. The hydrogel microspheres were described in terms of their size and size distribution and morphological and temperature‐induced swelling properties. While scanning electron microscopy was used to characterize the morphology of the microspheres, the temperature sensitivity of the microspheres was demonstrated by dynamic light scattering. The hydrodynamic particle diameter decreased sharply as the temperature reached a critical temperature ～ 30 °C. A decrease in the particle size was observed with increasing concentration of both the APS initiator and the PVP stabilizer. The microspheres crosslinked with 2–15 wt % of MBAAm had a fairly narrow size distribution. It was found that the higher the content of the crosslinking agent, the lower the swelling ratio. High concentration of the crosslinker gave unstable dispersions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6263–6271, 2008     

Rapid Acquisition of 14N Solid‐State NMR Spectra with Broadband Cross Polarization

Nitrogen is an element of utmost importance in chemistry, biology and materials science. Of its two NMR‐active isotopes, ¹⁴N and ¹⁵N, solid‐state NMR (SSNMR) experiments are rarely conducted upon the former, due to its low gyromagnetic ratio (γ) and broad powder patterns arising from first‐order quadrupolar interactions. In this work, we propose a methodology for the rapid acquisition of high quality ¹⁴N SSNMR spectra that is easy to implement, and can be used for a variety of nitrogen‐containing systems. We demonstrate that it is possible to dramatically enhance ¹⁴N NMR signals in spectra of stationary, polycrystalline samples (i.e., amino acids and active pharmaceutical ingredients) by means of broadband cross polarization (CP) from abundant nuclei (e.g., ¹H). The BR oadband A diabatic IN version C ross‐ P olarization ( BRAIN–CP ) pulse sequence is combined with other elements for efficient acquisition of ultra‐wideline SSNMR spectra, including W ideband U niform‐ R ate S mooth‐ T runcation ( WURST ) pulses for broadband refocusing, C arr– P urcell M eiboom– G ill ( CPMG ) echo trains for T₂‐driven S/N enhancement, and frequency‐stepped acquisitions. The feasibility of utilizing the BRAIN–CP/WURST–CPMG sequence is tested for ¹⁴N, with special consideration given to (i) spin‐locking integer spin nuclei and maintaining adiabatic polarization transfer, and (ii) the effects of broadband polarization transfer on the overlapping satellite transition patterns. The BRAIN–CP experiments are shown to provide increases in signal‐to‐noise ranging from four to ten times and reductions of experimental times from one to two orders of magnitude compared to analogous experiments where ¹⁴N nuclei are directly excited. Furthermore, patterns acquired with this method are generally more uniform than those acquired with direct excitation methods. We also discuss the proposed method and its potential for probing a variety of chemically distinct nitrogen environments.     

Thermosensitive superabsorbents based on poly(N,N-diethylacrylamide-co-sodium acrylate)

A series of poly(N,N-diethylacrylamide-co-sodium acrylate) with a degree of crosslinking of 1 mol%have been prepared as thermosensitive superabsorbents for water.The critical swelling temperatures or the volume phase transition temperature(VPTT) and the water absorption capacity of the polymers can be modulated by varying the amount of sodium acrylate(0-60 mol%) in the copolymers.The water absorption and swelling properties of the different hydrogels have been studied as function of temperature.The crosslinked copolymers can absorb large amounts of water at ambient temperatures and dehydrate at higher temperatures with relative ease,making the absorbent materials thermally responsive and thus reusable.The water absorption capacity of the copolymers depends on the pH of the media as the acrylate monomer has a higher water absorption in its deprotonated state.Added urea in the media raises and sharpens the VPTT values of the copolymers containing sodium acrylate.     

Biodegradable and pH-sensitive hydrogels: Synthesis by crosslinking of N,N-dimethylacrylamide copolymer precursors

Novel pH-sensitive hydrogels containing azoaromatic crosslinks were synthesized by the crosslinking of polymeric precursors. First, a reactive polymeric precursor was synthesized by copolymerization of N,N-dimethylacrylamide, N-tert-butylacrylamide, acrylic acid, and N-methacryloylglycylglycine p-nitrophenyl ester. The hydrogel was prepared in the second step by the reaction of the polymeric precursor with N,N′-(ω-aminocaproyl)-4,4′-diaminoazobenzene. The hydrogels were characterized by the network structure, (that is, content of crosslinks, unreacted pendent groups, and cycles), the equilibrium swelling ratio as a function of pH, modulus of elasticity in compression, and the degradability in vitro. The results obtained indicated that the hydrogel network structure strongly depends on the reaction conditions such as polymer concentration, and the ratio of the reactive groups during the crosslinking reaction. The swelling and mechanical properties of hydrogels can be controlled by the modification of polymer backbone structure and/or the crosslinking density. The rates of hydrogel degradation depended on their degree of swelling. The higher the degree of swelling, the higher the degradability. The properties of the hydrogels suggest that they have a potential as carriers for colon-specific drug delivery. © 1994 John Wiley & Sons, Inc.     

N-(4-苯甲酰苯基)衣康酰亚胺与甲基丙烯酸-N,N-二甲氨基乙酯组成的可聚合光氧化还原体系引发的丙烯腈光聚合

Ｎ （４ 苯甲酰苯基）衣康酰亚胺与甲基丙烯酸 Ｎ，Ｎ 二甲氨基乙酯组成的可聚合光氧化还原体系引发的丙烯腈光聚合高青雨杨更须崔元臣张福莲张举贤（河南大学化学化工学院开封４７５００１）李福绵（北京大学化学系北京１００８７１）关键词Ｎ （４ 苯甲酰苯基）...     

二(桥-氯)-二[氯-(N,N,N''''-三苄基乙二胺)铜(Ⅱ)]的晶体结构

0 IntroductionThe copperdim er,bis(μ鄄hydroxo)鄄bis[chloro(N,N,N',N'鄄tetram ethylethylenediam ine) copper髤] chloride(Cu(OH )Cl·TM EDA),prepared from N,N,N',N'鄄tetram鄄ethylethylenediam ine (TM EDA) and CuCl, exhibitedexcellentcatalytic activity for t     

EFFECT OF N,N,N’,N’-TETRAALKYL TEREPHTHALAMIDE ON NON-ISOTHERMAL CRYSTALLIZATION KINETICS OF POLYPROPYLENE

The effect of N,N,N＇,N＇-tetraalkyl terephthalamide （TATA） on the non-isothermal crystallization and melting characteristics ofpolypropylene （PP） was studied. The addition of TATA can lead to the formation ofβ-crystal PP. With the increase in TATA concentration the degree of crystallinity for β-crystal PP increased significantly, and that for a-crystal PP decreased, which indicated that TATA effectively induced the formation of β-crystal PP. WAXD also revealed the existence of β-crystal PP after the introduction of TATA into PP. PP containing TATA crystallized at a temperature range of 5-10℃ higher than that of pure PP, and the half-crystallization time （t1/2） and Avrami exponent （n） of PP at the same cooling rate were decreased by the addition of TATA, indicating that TATA influenced the crystallization rate and crystallization growth mode of PP. The rate constant of crystallization of PP containing TATA （Zc） was larger than that of pure PP, which further indicated that the crystallization of PP was accelerated by the addition of TATA.     

Novel Crosslinked Alkaline Exchange Membranes Based on Poly(phthalazinone ether ketone) for Anion Exchange Membrane Fuel Cell Applications

Novel crosslinked anion exchange membranes based on poly(phthalazinone ether ketone) (PPEK) were successfully prepared through chloromethylation, quaternization, membrane casting and OH‐ ionic exchange reaction from the quaternized PPEK (QPPEK) membrane. The quaternization was performed with N‐methylimidazolium (MIm) as ammonium agent and tetramethylethylenediamine (TMEDA) as crosslinking agent. The ion‐exchange capacity, swelling ratio (SR), water uptake (WU), and ionic conductivity of the QPPEK alkaline membranes have been systematically investigated. The results showed that QPPEK membranes have a high hydroxide conductivity and very low SR. For the QPPEK‐4 alkaline membrane with ion‐exchange capacity (IEC) 2.63 mmol/g, the WU was 35.8%, and the hydroxide conductivity was 0.028 S/cm at 30 °C and 0.032 S/cm at 70 °C, while its SR was only 7.6%. The thermal properties of the QPPEK alkaline membrane and CMPPEK were characterized using thermo‐gravimetric analysis measurements in a nitrogen atmosphere. The alkaline resistance of membrane QPPEK ?4 was also briefly investigated in 6 M KOH at 60 °C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1632–1638     

New,strong cationic hydrogels: Preparation of N,N,N′,N′‐tetraallyl piperazinium dibromide and its copolymers with N,N‐diallyl morpholinium bromide

N,N,N′,N′‐tetraallyl piperazinium dibromide (TAP) has been prepared in high yields by quaternization of N,N′‐diallyl piperazine with allyl bromide. Herein, we have described preparation of nonhydrolysable, strong, cationic hydrogels by copolymerization of TAP with N,N‐diallyl morpholinium bromide (DAM) in the presence of t‐butyl hydroperoxide as initiator in aqueous solutions. Because the monomer and crosslinker involved consist of quaternary amine functions, these hydrogels are fully cationic and do not carry hydrolysable groups. Contrary to expectations, the quaternary amine hydrogels presented do not show any super absorbency, instead dry gel particles in water undergo spontaneous disintegration with an audible bursting of the particles due to instantaneous, high osmotic pressure. Whereas, in KBr or HBr solutions, the swellings are relatively slow. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1006–1013, 2000     

Improved Synthesis of N,N′‐Disuccinimidyl Carbonate using α‐Pinene as Acid Scavenger

An improved synthesis of N,N′‐disuccinimidyl carbonate (DSC) is described where α‐pinene is utilized as an efficient scavenger of HCl liberated during the reaction of N‐hydroxysuccinimide with triphosgene in THF. The α‐pinene hydrochloride formed is soluble in THF and gives very pure DSC in good yields.     

Position-specific 15N isotope analysis in organic molecules: A high-precision 15N NMR method to determine the intramolecular 15N isotope composition and fractionation at natural abundance

The position-specific ¹⁵N isotope content in organic molecules, at natural abundance, is for the first time determined by using a quantitative methodology based on ¹⁵N Nuclear Magnetic Resonance (NMR) spectrometry. ¹⁵N NMR spectra are obtained by using an adiabatic “Full-Spectrum” INEPT sequence in order to make possible ¹⁵N NMR experiments with a high signal-to-noise ratio (>500), to reach a precision with a standard deviation below 1‰ (0.1%). This level of precision is required for observing small changes in ¹⁵N content associated to ¹⁵N isotope effects. As an illustration, the measurement of an isotopic enrichment factor ε for each ¹⁵N isotopomer is presented for 1-methylimidazole induced during a separation process on a silica column. The precision expressed as the long-term repeatability of the methodology is good enough to evaluate small changes in the ¹⁵N isotope contents for a given isotopomer. As observed for ¹³C, inverse and normal ¹⁵N isotope effects occur concomitantly, giving access to new information on the origin of the ¹⁵N isotope effects, not detectable by other techniques such as isotope ratio measured by Mass Spectrometry for which bulk (average) values are obtained.     

Highly efficient metal‐free organic catalysts to design new Environmentally‐friendly starch‐based blends

A one‐step process is reported to directly synthesize blends of poly(trimethylene carbonate) (PTMC) with a modified granular starch. Trimethylene Carbonate (TMC) ring‐opening polymerization is performed in the presence of native starch particles in bulk conditions at 150 °C and the efficiency of metal‐free organic catalysts (TBD and phosphazene superbases P1‐t‐Oct, P2‐t‐bu, and P4‐t‐bu) are investigated to replace the organo‐metallic stannous octanoate initiator. TMC monomer is successively converted into PTMC and the robustness of organic catalysts is highlighted with significant activities at very low concentrations (<100 ppm), where stannous octanoate is inefficient. Reactivity of starch toward TMC ROP is deeply investigated by NMR techniques and a starch‐graft‐PTMC is indirectly evidenced. Starch substitution degree reaches 0.9% indicating that PTMC grafting only occurs at the surface of swollen granular starch. PTMC graft length from the starch surface remained low in the range 2–12 and model ROP reactions highlight the role of TMC hydrolysis on PTMC graft length. Despite low PTMC grafts, a fine dispersion of intact starch particles into the PTMC matrix is evidenced. Consequently, metal‐free organic catalysts at low concentrations are promising candidates for synthesizing blends of PTMC with high loadings of surface‐modified starch (32% by weight) in 2 min within a one‐step process. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 493–503     

Effects of entropy on the gas-phase pyrolysis of ethyl N,N-dimethylcarbamate

In this study, we examined the gas-phase pyrolysis of ethyl N,N-dimethylcarbamate theoretically at various theoretical levels. The reaction consists of a two-step mechanism, with N,N-dimethylcarbamic acid and ethylene as reaction intermediates. In the first step, the reaction proceeds via a six-membered cyclic transition state (TS), which is more favorable than that via a four-membered cyclic TS. Here, the contribution of entropy to the overall potential energy surface was found to play an important role in determining the rate-limiting step, which was found to be the second step when viewed in terms of the enthalpy of activation (DeltaH(not equal)), but the first step when entropy changes (-TDeltaS(not equal)) were considered. These results are consistent with experimental findings. Moreover, the experimental activation entropy can be reproduced by using the hindered rotor approximation, which converts some low vibration frequencies that correspond to internal rotational modes into hindered rotors.     

Resilient Amorphous Networks Prepared by Photo‐Crosslinking High‐Molecular‐Weight D,L‐Lactide and Trimethylene Carbonate Macromers: Mechanical Properties and Shape‐Memory Behavior

Tough networks are prepared by photo‐crosslinking high‐molecular‐weight DLLA and TMC macromers. These amorphous networks exhibit tunable thermal and mechanical properties and have excellent shape‐memory features. Variation of the monomer ratio allows adjustment of T_g between approximately ?13 and +51 °C. The elastic moduli at room temperature can be varied between 4.5 and 2730 MPa. The crosslinks allow the networks to return to their original shape after deformation. 60:40 DLLA:TMC networks have T_g values between room temperature and body temperature, with mechanical properties at body temperature close to soft tissues. Several medical devices are prepared from these networks.

     

Synthesis of thermosensitive hydrogels from acryloyloxyethyl trialkyl phosphonium chloride–N‐isopropylacrylamide–N,N′‐methylenebisacrylamide terpolymers and their temperature dependence of water absorption

Thermosensitive polymer hydrogels were prepared by the copolymerization of three kinds of acryloyloxyethyl trialkyl phosphonium chlorides (AETRs) with alkyl chains of different lengths, with N‐isopropyl acrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm). The water content of the AETR–NIPAAm–MBAAm terpolymers obtained at molar ratios of the crosslinking agent greater than 2 decreased with increasing temperature and decreased sharply around 35 °C. However, the water contents of the AETR–NIPAAm–MBAAm (X/100/1) terpolymers obtained at a molar ratio of 1 of the crosslinking agent increased once with increasing temperature and then decreased from 3 to around 40 °C. The water contents of the AETR–NIPAAm–MBAAm (3/100/1 or 2) terpolymers decreased with the increasing length of alkyl chains in phosphonium groups in the terpolymers. The water contents of the AETR–NIPAAm–MBAAm terpolymers increased by the addition of a small amount of urea and then decreased with increasing urea concentration. However, the water contents decreased abruptly with the addition of NaCl. The AETR–NIPAAm–MBAAm terpolymers exhibited high adsorption for sodium dodecylbenzene sulfonate but no adsorption for sodium benzene sulfonate. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1505–1514, 2001     

Conformational analysis of N,N,N‐Trimethyl‐(3,3‐dimethylbutyl)ammonium iodide by NMR spectroscopy: a sterically hindered trans‐standard

A predominantly trans‐1,2‐disubstituted ethane system – N,N,N‐trimethyl‐(3,3‐dimethylbutyl)ammonium iodide – is of particular interest for conformational analysis, because it contains both an organic and a highly polar substituent, making it soluble and thus applicable to study in a large variety of solvents. The fraction of the trans conformer of this molecule in a wide range of protic and aprotic solvents was determined by the nuclear magnetic resonance proton couplings to be approximately 90%, in contrast to the previously assumed 100%. The consistently strong preference of the trans conformation should establish N,N,N‐trimethyl‐(3,3‐dimethylbutyl)ammonium iodide as a possibly useful ‘trans‐standard’ in conformational analysis, much more so than 1,2‐ditert‐butylethane, which has a poor solubility in many solvents. Copyright © 2013 John Wiley & Sons, Ltd.