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1.
Chitosan was chemically modified to produce quaternary ammonium salts in order to improve its antimicrobial activity and physicochemical properties. Quaternization of N-alkyl chitosan derivatives was carried out using alkyl iodide to elaborate water-soluble cationic polyelectrolytes ( N, N, N-trimethylchitosan, TMC). TMC was characterized by (1)H NMR spectroscopy; the quaternization degree was determined from (1)H NMR spectra and by titration of iodide ion. The antibacterial activity of hydroxypropylcellulose (HPC) films or coatings associated with chitosan or TMC as biocide was evaluated against the growth of Listeria monocytogenes and Salmonella typhimurium. The HPC-chitosan and HPC-TMC coatings exhibited a total inhibition on solid medium of both bacterial strains. Experiments conducted in liquid medium showed that the inhibitory activity against the growth of Listeria innocua was improved after chemical modification. Moreover, physicochemical properties of films were evaluated to determine their potential for food applications. The addition of the antibacterial agents showed a significant impact on the moisture barrier and mechanical properties of HPC films.  相似文献   

2.
Chitosan was modified by coupling with linolenic acid through the 1-ethyl-3-(3-dimethylaminopropyyl)carbodiimide-mediated reaction. The degree of substitution was measured by 1H NMR, and it was 1.8%, i.e., 1.8 linolenic acids group per 100 anhydroglucose units. The critical aggregation concentration (CAC) of the self-aggregate of hydrophobically modified chitosan was determined by measuring the fluorescence intensity of the pyrene as a fluorescent probe. The CAC value in phosphate-buffered saline (PBS) solution (pH 7.4) was 5 x 10(-2) mg/mL. The average particle size of self-aggregates of hydrophobically modified chitosan in PBS solution (pH 7.4) was 210.8 nm with a unimodal size distribution ranging from 100 to 500 nm. A transmission electron microscopy study showed that the formation of near spherical shape nanoparticles had enough structural integrity. The loading ability of hydrophobically modified chitosan (LA-chitosan) was investigated by using bovine serum albumin (BSA) as a model protein. Self-aggregated nanoparticles exhibited an increased loading capacity (19.85 +/- 0.04 to 37.57 +/- 0.25%) with an increasing concentration of BSA (0.1-0.5 mg/mL).  相似文献   

3.
The long-term storage of soil organic matter (SOM) in forest soils is still poorly understood. In this study, particle size fractionation in combination with accelerator mass spectroscopy (AMS) and solid state 13C nuclear magnetic resonance (NMR) spectroscopy was applied to investigate organic carbon (OC) stabilisation in Cambisol and Luvisol profiles under spruce (Picea abies) and beech (Fagus sylvatica L.) forests. In most samples, OC was preferentially associated with <2 μm fractions. Throughout soil profiles the contribution of OC in the clay fraction to the total OC increased from 27%-53% in A horizons to 44-86% in E, B and EB horizons. The 200-2000 μm fractions from all sites and all depths showed a percentage of modern C (pmC)>100. They were enriched in 14C owing to high inputs of recent material from leaves and roots. Clearly less active material was associated with <2 and 2-20 μm fractions. This demonstrated that the particle size fractionation procedure applied to our study was capable to isolate a young OC fraction in all samples. The pmC values were strongly decreasing with depth but the decrease was much more pronounced in the fine fractions. The <2 and 2-20 μm fractions of B, E and EB horizons revealed radiocarbon ages between 512 and 4745 years before present which indicated that the SOM in those horizons was little affected by the recent vegetation. The major components of labile and stable SOM pools in topsoils and subsoils were always O/N-alkyl C (28-53%) and alkyl C (14-48%) compounds. NMR spectra of bulk soils and particle size fractions indicated that high alkyl C and O/N-alkyl C proportions throughout the soil profile are typical of Cambisols and Luvisols which were not subjected to regular burning. A relation between radiocarbon age and chemical composition throughout soil profiles was not observed. This suggests that the long-term stabilisation of SOM is mainly controlled by the existence of various mechanisms of protection offered by the soil matrix and soil minerals but not by the chemical structure of SOM itself.  相似文献   

4.
A series of amiphiphilic cellulose-based graft copolymers (MCC-g-PLA) with various molecular factors were synthesized in ionic liquid BmimCl and characterized by FT-IR, (1)H NMR, (13)C NMR, XRD, and TGA. Their solubility in a variety of solvents was compared. The prepared MCC-g-PLA copolymers can self-assemble into spherical nanomicelles (10-50 nm) in aqueous solution. The self-assembly behaviors of the MCC-g-PLA copolymers were systematically investigated by fluorescence probe. Furthermore, the hydrophobic antitumor drug paclitaxel (PTX) was successfully encapsulated into the MCC-g-PLA micelles. The drug encapsulation efficiency and loading content were found to be as high as 89.30% (w/w) and 4.97%, respectively. Results in this study not only suggest a promising cellulose-based antitumor drug carrier but also provide information for property-directed synthesis of the cellulose graft PLA copolymers.  相似文献   

5.
O-Carboxymethyl chitosan (O-CMCs) and N-((2-hydroxy-3-N,N-dimethylhexadecylammonium)propyl)chitosan chloride (N-CQCs) were synthesized for nonalcoholic fatty liver disease (NAFLD) treatment. The weight-average weight and substitution degree of O-CMCs and N-CQCs were 6.5 × 10(4) and 0.72 and 7.9 × 10(4) and 0.21, respectively. O-CMCs was negatively charged with a zeta-potential value of -31.82 mV, whereas that of N-CQCs was +36.1 mV, and both showed low cytotoxcity. Serum lipid level and liver fat accumulation were reduced with chitosan and its two derivatives. Furthermore, mRNA and protein expression assay of hepatic lipid metabolism enzymes and low-density lipoprotein receptor (LDL-R) were observed by RT-PCR and Western blot. Results showed that N-CQCs exhibited a more evident desired effect than chitosan and O-CMCs, indicating that amphiphilicity, solubility, and surface charge of chitosan and its two derivatives played roles in the expression of hepatic lipid metabolism enzymes and LDL-R. Therefore, dietary supplementation of O-CMCs and N-CQCs can alleviate the high fat diet induced aberrations related to NAFLD by their antilipidemic property.  相似文献   

6.
We compared the quantitative responses of liquid-state (LS) and solid-state (CPMAS) 13C-NMR spectroscopy of four different soil humic substances. The intensities of signals for the alkyl carbons (0–40 ppm) were significantly larger in CPMAS than in LS spectra. This difference is in agreement with the pseudo-micellar model of the conformational nature of humic substances. By this view, the hydrophobic interactions holding together the heterogeneous molecules of humic micelles inhibit the molecular motions of the alkyl carbons, thereby enhancing the spin-lattice relaxation times and consequently lowering the sensitivity of liquid-state NMR. Conversely, regardless of their position in the humic conformation, a better estimation of the number of alkyl carbons can be obtained by CPMAS-NMR because of the cross-polarization of hydrogen nuclei in CH2 and CH3 groups. The intensity of the 40–110 ppm region is also slightly lower in LS than in CPMAS-NMR spectra, despite the hydrophilicity of the oxidized and peptidic carbons resonating in this chemical shift interval. Their molecular motion may also be reduced by either the formation of intra- and inter-molecular hydrogen bondings due to poorly acidic hydroxyl groups of saccharides, or the degree of conformational rigidity that a pseudo-micellar arrangement confers even to hydrophilic domains. The higher content of aromatic carbons (110–160 ppm) found in the LS spectra was attributed partly to the high degree of substitution of the aromatic ring that slows down cross-polarization in CPMAS experiments and partly to the relative overestimation of this region by LS-NMR due to a lack of signal in the aliphatic interval. The slightly lower content of carboxyl carbons estimated in CPMAS spectra as compared to LS spectra was also attributed to slow cross-polarization. This work shows that the combined use of both NMR techniques is profitable in conformational analysis of humic substances and of dissolved organic matter in general.  相似文献   

7.
Homogeneous modification of cellulose, isolated with 10% KOH from delignified sugarcane bagasse, was performed in room-temperature ionic liquid 1-allyl-3-methylinidazolium chloride with phthalic anhydride in the absence of catalyst. The results showed the degree of substitution of phthalated cellulosic derivatives, ranging from 0.10 to 0.73, increased with the increment of reaction temperature, reaction time, and the molar ratio of phthalic anhydride/anhydroglucose units in cellulose under the conditions given. The products were characterized by FT-IR and solid-state CP/MAS 13C NMR spectroscopy as well as thermal analysis, and the results revealed that the phthalation reaction at C-6, C-2, and C-3 positions of the cellulose all occurred. The thermal stability of the phthalated cellulose was found to decrease upon chemical modification. However, this thermal stability of the phthalated cellulose over 200 degrees C is rather satisfactory.  相似文献   

8.
Oil-in-water emulsions containing cationic droplets stabilized by lecithin-chitosan membranes were produced using a two-stage process. A primary emulsion was prepared by homogenizing 5 wt % corn oil with 95 wt % aqueous solution (1 wt % lecithin, 100 mM acetic acid, pH 3.0) using a high-pressure valve homogenizer. This emulsion was diluted with aqueous chitosan solutions to form secondary emulsions with varying compositions: 1 wt % corn oil, 0.2 wt % lecithin, 100 mM acetic acid, and 0-0.04 wt % chitosan (pH 3.0). The particle size distribution, particle charge, and creaming stability of the primary and secondary emulsions were measured. The electrical charge on the droplets increased from -49 to +54 mV as the chitosan concentration was increased from 0 to 0.04 wt %, which indicated that chitosan adsorbed to the droplet surfaces. The mean particle diameter of the emulsions increased dramatically and the emulsions became unstable to creaming when the chitosan concentration exceeded 0.008 wt %, which was attributed to charge neutralization and bridging flocculation effects. Sonication, blending, or homogenization could be used to disrupt flocs formed in secondary emulsions containing droplets with high positive charges, leading to the production of emulsions with relatively small particle diameters (approximately 1 microm). These emulsions had good stability to droplet aggregation at low pH (< or =5) and ionic strengths (<500 mM). The interfacial engineering technology utilized in this study could lead to the creation of food emulsions with improved stability to environmental stresses.  相似文献   

9.
N-heterocyclic derivatives of 2,4-dihydroxybenzcarbothioamide were synthesized from sulfinylbis(2,4-dihydroxybenzenethioyl) and commercially available heterocyclic amines. The composition and chemical structures were confirmed by IR, (1)H NMR, EI-MS, and elemental analysis. For the estimation of potential activity in vitro the MIC values against 15 strains of dermatophytes, yeasts, and molds were determined. The strongest fungistatic potency was found for N-5'-(3'-oxobenzfurylidyne)-2,4-dihydroxybenzcarbothioamide in relation to all tested dermatophyte strains with MIC = 0.48-0.98 microg/mL. On the basis of the spectroscopic data the influence of N-heterocyclic substitution on antimycotic activity is discussed.  相似文献   

10.
The composition of functional light soil organic matter pools of arable Cambisols with a gradient in clay content was investigated. Soil texture differences originate from increasing loess admixture to the parent material (coarse‐grained tertiary sediments). Using density fractionation in combination with ultrasonic dispersion, two types of particulate organic matter (POM) were obtained: (1) free POM and (2) POM occluded in soil aggregates. Both POM fractions were analyzed by elemental analysis (C, N) and CPMAS 13C NMR spectroscopy. With increasing clay content the amount of organic carbon stored in the occluded POM fraction increased considerably, whereas the amounts of free POM were not related to the soil clay content. With increasing soil clay contents increasing proportions of O‐alkyl C and decreasing proportions of aryl C were found for both POM fractions. The occluded POM fraction showed a higher degree of degradation as indicated by lower amounts in O‐alkyl carbon. A lower degree of POM degradation was associated with higher clay contents. Higher soil clay contents promoted the conservation of POM with a low degree of alteration. This effect of soil texture was found to be highly significant when the aryl C : O‐alkyl C ratio was used as indicator for POM decomposition rather than the alkyl C : O‐alkyl C ratio.  相似文献   

11.
Target compounds 8 were obtained by the reaction of alkyl 2-cyano-3,3-dimethylthioacrylate or cyarylamide (7a-7e) and alpha-aminobenzylphosphonate (5a-5e) under reflux condition using ethanol as solvent. Their structures were clearly verified by spectroscopic data (IR and 1H, 13C, and 31P NMR) and elemental analysis. These compounds were shown to be antivirally active in the bioassay. It was found that title compounds 8d and 8e had the same inactivation effect against tobacco mosaic virus (EC 50 = 55.5 and 55.3 microg/mL) as the commercial product ningnanmycin (EC 50 = 50.9 microg/mL). To the best of our knowledge, this is the first report on the synthesis and antiviral activity of cyanoacrylate derivatives containing an alpha-aminophosphonate moiety.  相似文献   

12.
The molecular composition of humic acids (HA) extracted from compost at increasing maturity stages was determined by off-line TMAH-thermochemolysis-GC-MS, in combination with solid-state nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies. While spectroscopy measurements followed the bulk changes, thermochemolysis provided a detailed molecular variation of HA composition. Both thermochemolysis and spectroscopy indicated that polysaccharides, alkyl, cyclic, and aromatic compounds were the predominant components of HA, the stable fraction of compost. NMR dipolar dephasing (DD) experiments confirmed that HA extracts contained lignin in lower amount than its oxidized degradation products. The progressive compost maturity was reflected in HA extracts by a decrease of carbohydrate content and a selective preservation of hydrophobic alkyl molecules, such as medium- and long-chain fatty acids, aliphatic alcohols, linear hydrocarbons, and plant polyester derivatives, like long-chain alkyl dicarboxylic acids, and ω-hydroxyacids. Spectroscopy results showed a concomitant entrapment in HA of biolabile compounds, such as peptidic moieties. The wide range of identified lipid components and plant biomarkers may represent useful tools to trace origin, quality, and transformation of amended compost in soil ecosystems.  相似文献   

13.
Waxy maize starch was chemically modified to varying benzylation levels and the degree of benzylation substitution was measured using a nuclear magnetic resonance (NMR) method. Fourier Transform (FT) Raman spectra of the chemically modified starches were acquired and aromatic C=C stretch Raman bands characteristic of the benzylation modification were used to derive a calibration curve for the Raman intensity of these marker bands versus the degree of benzylation substitution. The best‐fit linear regression to the plotted data gave a linear correlation coefficient of 0.997. The FT‐Raman technique provides a fast, nondestructive method for the measurement of the degree of benzylation substitution of modified waxy maize starches and should be applicable for use with benzylated starches from other botanical sources.  相似文献   

14.
Four flavonol glycosides were isolated from an extract of sea buckthorn pomace (Hippopha? rhamnoides) by Sephadex LH-20 gel chromatography and semipreparative HPLC. Their structures were elucidated by hydrolysis studies, ESI-MS(n), UV, and (1)H and (13)C NMR spectroscopy. The occurrence of the major flavonol glycoside kaempferol 3-O-beta-sophoroside-7-O-alpha-rhamnoside in sea buckthorn is described here for the first time. A further 21 flavonol glycosides of Sephadex LH-20 fractions of sea buckthorn pomace were characterized by HPLC-DAD-ESI-MS. The characteristic MS-MS and MS(3) fragmentation pattern of flavonol glycosides previously identified in sea buckthorn juice and of flavonol glycosides identified by NMR spectroscopy gave valuable indications for their identification. The results demonstrate that loss of the sugar moiety from C-7 of the aglycon is more favored than fission of the glycosidic linkage at the C-3 position. Thus, most of the compounds identified were 7-rhamnosides of isorhamnetin, kaempferol, and quercetin, which exhibit different substitution patterns at the C-3 position, mainly glucosides, rutinosides, and sophorosides. In addition, numerous flavonol glycosides were detected lacking a sugar moiety at C-7. Finally, eight flavonol derivatives were identified that are acylated by hydroxybenzoic or hydoxycinnamic acids.  相似文献   

15.
An explanation as to how casein micelles dissociate when heated in the presence of ethanol is presented. Dissociation of casein micelles in milk-ethanol mixtures was studied using (1)H NMR, and the effects of addition of CaCl(2), NaCl, or EDTA or alteration of milk pH on this dissociation were studied. It is proposed that at low temperatures, ethanol reduces the solvent quality of milk serum, but above a critical temperature (approximately 30 degrees C in a 35% ethanol solution), ethanol enhances solvent quality and dissociates the casein micelles. Ethanol reduced protein hydrophobicity and increased the pK(a) value of phosphoserine, effects that are likely to be significant in the dissociating effect of ethanol at elevated temperatures.  相似文献   

16.
This study provides insight into the relevance of the chemical functional groups of soil organic matter (aromatic, paraffinic, O‐alkyl, carboxyl and carbonyl carbon), as determined by CPMAS 13C NMR, on adsorption processes. Batch adsorption experiments with eight naphthalene derivatives were conducted with soils from a long‐term field experiment and model sorbents. Although the adsorption of some derivatives was mainly affected by the paraffinic organic carbon content in soil, the relation between the C‐distribution and adsorption was complex. This casts doubt on the use of such NMR data to estimate sorption behaviour. Additionally, sorption experiments were performed with six model sorbents representing typical soil components. Considerable adsorption of naphthalene derivatives was observed for montmorillonite and lignin; the smallest values were for kaolinite and cellulose. A quantum chemical approach was used to calculate a local polarity parameter as a molecular property of the naphthalene derivatives. This parameter was correlated with the logarithm of the adsorption coefficients, logKd. Here, clear trends were observed for three of the model sorbents (kaolinite, montmorillonite and lignin).  相似文献   

17.
Soils from A horizons of Eutrochrepts under spruce forest (Sf), mixed deciduous forest (Df), permanent grassland (Gp), and arable rotation (Ar) were fractionated into clay- (<2 μm), silt-(2–20 μm) and sand- (20–2000 μm) sized separates. 13C NMR spectroscopy was used to compare SOM composition across size separates and between land-use regimes. CPMAS 13C NMR spectroscopy showed that the intensity of signals assigned to carbohydrates (representing most O-alkyl C) and lignin (phenolic and methoxyl C) declined with decreasing particle size. Concurrently, alkyl C and C-substitution of aromatic C increased in the order sand, silt, clay. The amount of alkyl C correlated well with microbial resynthesis of carbohydrates. Solution 13C NMR spectra suggested that humic acids (HA) extracted from the size separates were richer in carboxyl C and aromatic C than the bulk size separates. Also HA reflected increasing percentage of alkyl C with decreasing particle size. O-alkyl C were lower in silt HA than in clay HA whereas aromatic C tended to peak in silt HA. These results suggested that sand-sized separates were enriched in plant residues (primary resources) whereas clay-sized separates were dominated by products of microbial resynthesis (secondary resources). Silt was rich in selectively preserved and microbially transformed primary resources. 13C NMR spectroscopy showed only small differences in SOM composition between land-use regimes, except that silt and silt HA from Ar were richer in aromatic C than those from the other plots. But enrichment factors (E= content in fraction/content in whole soil) revealed differences in the distribution of C species across the size separates. Relatively high Earomatic (0.9) and Eo-alkyl (1.0) for sand from Gp indicated high amounts of plant residues, probably due to intense rhizodeposition and to occlusion of plant debris within aggregates. Low Earomatic (0.3) and Eo-alkyl (0.3) for sand from Ar suggested depletion of primary resources, which could be attributed to disintegration of soil aggregates upon cultivation. A pronounced enrichment of alkyl C in Ar clay-sized separates (Ealkyl= 3.1) suggested large amounts of microbial carbon. Microbial products attached to clay surfaces by a variety of physico-chemical bondings appeared more stable against mineralization induced by cultivation than plant residues sequestered in aggregates.  相似文献   

18.
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19.
A novel, fast, and straightforward procedure is presented for the characterization of starch (the largest energy component in food) and modified starches (such as octenyl succinic anhydride (OSA)-modified starches used as a dispersing agent in the food industry). The method uses (1)H NMR to measure the degree of branching and also, for modified starches, the degree of chemical substitution. The substrate is dissolved in dimethyl-d(6) sulfoxide; addition of a very low amount of deuterated trifluoroacetic acid (d(1)-TFA) to the medium gives rise to a shift to high frequency of the exchangeable protons of the starch hydroxyl groups, leading to a clear and well-defined (1)H NMR spectrum, which provides an improved way to determine the degrees of both branching and chemical substitution. Measurements of the size and molecular weight distributions by multiple-detector size exclusion chromatography show that degradation by TFA does not affect the accuracy of the method.  相似文献   

20.
In this paper we report the application of NMR spectroscopy and Raman spectroscopy to determine the degree of maleate substitution in maleinated starches. Five kinds of maleinated starches were investigated and calibration sets were constructed to derive linear regression equations that may be used to predict the degree of maleate substitution for starch samples with unknown amounts of chemical modification. The calibration sets reported have very high linearity (r > 0.99) for both the NMR and Raman methods. The NMR and Raman calibration sets allow fast and nondestructive measurement of the degree of maleate substitution for different starches with little need of sample preparation.  相似文献   

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