Rapid esterification of wheat straw hemicelluloses induced by microwave irradiation

Esterification of wheat straw hemicelluloses with acetyl chloride, propionyl chloride, n-octanoyl chloride, lauroyl chloride, palmitoyl chloride, stearoyl chloride, and oleoyl chloride, respectively, using N-bromosuccinimide (NBS) as a catalyst was achieved in DMF/LICl medium by microwave irradiation. The effects of various acyl chlorides and the molar ratios of xylose units in hemicelluloses/acyl chloride on the degree of substitution (DS) were investigated and DS reached up to 1.34 by a few minutes. ¹³C NMR studies showed that the esterification occurred preferentially at the C-3 and C-2 positions. On the other hand, microwave irradiation brought a partial degradation of the polymer, and therefore resulted in a slight decrease in thermal stability of the hemicellulosic derivatives in comparison with conventional heating technique.     

The use of N,N'-diallylaldardiamides as cross-linkers in xylan derivatives-based hydrogels

N,N′-Diallylaldardiamides (DA) were synthesized from galactaric, xylaric, and arabinaric acids, and used as cross-linkers together with xylan (X) derivatives to create new bio-based hydrogels. Birch pulp extracted xylan was derivatized to different degrees of substitution of 1-allyloxy-2-hydroxy-propyl (A) groups combined with 1-butyloxy-2-hydroxy-propyl (B) and/or hydroxypropyl (HP) groups. The hydrogels were prepared in water solution by UV induced free-radical cross-linking polymerization of derivatized xylan polymers without DA cross-linker (xylan derivative hydrogel) or in the presence of 1 or 5 wt % of DA cross-linker (DA hydrogel). Commercially available cross-linker (+)-N,N′-diallyltartardiamide (DAT) was also used. The degree of substitution (DS) of A, B, and HP groups in xylan derivatives was analyzed according to ¹H NMR spectra. The DS values for the cross-linkable A groups of the derivatized xylans were 0.4 (HPX-A), 0.2 (HPX-BA), and 0.4 (X-BA). The hydrogels were examined with FT-IR and elemental analysis which proved the cross-linking successful. Water absorption of the hydrogels was examined in deionized water. Swelling degrees up to 350% were observed. The swollen morphology of the hydrogels was assessed by scanning electron microscopy (SEM). The presence of cross-linkers in DA hydrogels had only a small impact on the water absorbency when compared to xylan derivative hydrogels but a more uniform pore structure was achieved.     

Homogeneous modification of cellulose with succinic anhydride in ionic liquid using 4-dimethylaminopyridine as a catalyst

Cellulose, extracted from sugarcane bagasse, was successfully succinylated in ionic liquid 1-buty-3-methylimidazolium (BMIMCl) using 4-dimethylaminopyridine (DMAP) as a catalyst. Parameters investigated included the mass ratio of DMAP/succinic anhydride in a range from 0% to 15%, reaction time (from 30 to 120 min), reaction temperature (from 60 to 110 °C). The succinylated cellulosic derivatives had a degree of substitution (DS) ranging from 0.24 to 2.34. It was found that the DS of succinylated cellulosic derivatives using DMAP as a catalyst was higher than that without any catalyst under the same reaction conditions. The products were characterized by FT-IR, solid-state CP/MAS ¹³C NMR, and thermal analysis. FT-IR and solid-state CP/MAS ¹³C NMR spectra showed that succinoylation occurred at C-6, C-2 and C-3 positions. The thermal stability of the succinylated cellulose decreased upon chemical modification.     

Simultaneous determination of dimethylamphetamine and its metabolites in rat hair by gas chromatography–mass spectrometry

In order to study the disposition of dimethylamphetamine (DMAP) and its metabolites, DMAP N-oxide, methamphetamine (MA) and amphetamine (AP), from plasma to hair in rats, a simultaneous determination method for these compounds in biological samples using gas chromatography–mass spectrometry with selected ion monitoring (GC–MS-SIM) was developed. As DMAP N-oxide partially degrades to DMAP and MA during GC–MS analysis, it was necessary to avoid conditions which co-extract the N-oxide in the sample preparation so as to assure no contribution of artifactual products from DMAP N-oxide in the detection of the other compounds. For confirmation of the satisfactory separation of DMAP N-oxide from the others, the internal standards used for quantification were labeled with different numbers of deuterium atoms. Determination of unchanged DMAP was performed without any derivatization, that of DMAP N-oxide was carried out after conversion into trifluoroacetyl-MA by reaction with trifluoroacetic anhydride, and MA and AP were quantified after trifluoroacetyl-derivatization.After intraperitoneal administration of DMAP HCl to pigmented hairy rats (5 mg kg⁻¹ day⁻¹, 10 days, n=3), concentrations of DMAP and its metabolites in urine, plasma and hair were measured by GC–MS-SIM. The area under the concentration versus time curves (AUCs) of DMAP, DMAP N-oxide, MA and AP in the plasma were 397.2±97.5, 279.7±68.3, 18.4±1.2 and 15.9±2.2 μg min ml⁻¹, while their concentrations in the hair newly grown for 4 weeks after administration were 4.82±0.67. 0.45±0.09, 3.25±0.36 and 0.89±0.05 ng mg⁻¹, respectively. This fact suggested that the incorporation tendency of DMAP N-oxide from plasma into hair was distinctly low in comparison with the other compounds.     

Regioselective silylation of N-phthaloylchitosan with TBDMS and TBDPS groups

N-Phthaloylchitosan represents a key intermediate for the regioselective modification of chitosan in organic media. Chemoselective protection of primary alcohols on N-phthaloylchitosan was achieved with tert-butyldimethylsilyl (TBDMS) and tert-butyldiphenylsilyl (TBDPS) groups in imidazole/DMF and DMAP/pyridine. Influence of experimental conditions such as solvent, choice of base, stoichiometry, temperature, and time of reaction was studied regarding the degree of substitution (ds) of silyl groups. TBDMS groups allow higher ds than TBDPS groups. Higher reaction temperatures in different conditions led to lower ds and incomplete substitution. However, regioselective silylation of N-phthaloylchitosan was realized with ds up to 0.92 at room temperature. Silylated derivatives were characterized by elemental analysis, IR, and CP/MAS 13C NMR spectroscopies.     

Rapid homogeneous lauroylation of wheat straw hemicelluloses under mild conditions

Hemicellulose-based hydrophobic biomaterials with degrees of substitution ranging from 0.46 to 1.54 were synthesized under mild conditions in homogeneous media (N,N-dimethylformamide-lithium chloride) by reacting the native wheat straw hemicellulosic polymers with lauroyl chloride using 4-dimethylaminopyridine as a catalyst. Other catalysts such as N-bromosuccinimide, N-methyl pyrrolidine, N-methyl pyrrolidinone, and pyridine were also investigated. Under optimum reaction conditions (2 equiv of lauroyl chloride and triethylamine per hydroxyl group, 5% 4-dimethylaminopyridine, 40 °C, 35 min), a high DS value of 1.54 was obtained. The biomaterials were characterized by FT-IR spectroscopy and ¹³C NMR spectroscopy as well as by thermal analysis. The results showed that the lauroylation occurred preferably at the C-3 hydroxyl group of β-d-Xylp units in the hemicelluloses, and the thermal stability of the hydrophobic polymers increased by esterification.     

Synthesis of iminoalditol and N-alkyl iminoalditol derivatives of ribopyranosides

Iminoalditol analogs of ribopyranosides were prepared by reduction of a vinylogous urethane intermediate formed from methyl 2-C-(5-O-methanesulfonyl-β-d-ribofuranosyl)acetate (1) by treatment with sodium azide in DMF at reflux. The N-alkylated analogs were synthesized either by N-alkylation of the corresponding parent iminoaldithol or, more efficiently, from the product of the reaction of 1 with various alkylamines. The latter process involves an S_N2 substitution at C-5 by the amine followed by an intramolecular hetero-Michael reaction under basic conditions. The ‘aglycon’ of the iminoalditol was also modified through amidation and esterification.     

Succinoylation of sago starch in the N,N-dimethylacetamide/lithium chloride system

The modification reaction of sago starch with succinic anhydride (SA) using pyridine (PY) and/or 4-dimethyaminopyridine (DMAP) as catalyst and N,N-dimethylacetamide (DMA)/lithium chloride (LiCl) system as solvent was studied. A series of succinylated starch derivatives were prepared with a degree of substitution (DS) ranging from 0.14 to 1.54. The structure of the resulting polymers determined by means of ¹³C NMR spectroscopy indicated that substitution preferably occurs at the C₂ and C₆ hydroxyl groups. The thermal stability of the material was decreased by chemical modification. Effects of reactant molar ratio, reaction time, and the concentrations of DMAP and LiCl on the reaction efficiency are discussed.     

Acetylation and characterization of xylan from hardwood kraft pulp

Alkaline treatment of eucalyptus hardwood kraft pulp with 10% NaOH yielded 6-8% xylan. The acetylation of the extracted xylan was carried in DMAC/LiCl/pyridine system to obtain a series of xylan acetates with different degrees of substitution (DS). Structure elucidation of xylan and xylan acetate was obtained by ¹H and ¹³C NMR spectroscopy and other homonuclear and heteronuclear 2D-NMR techniques. Inverse-gated ¹³C NMR was employed to determine the DS of xylan acetate. Furthermore, results also revealed equal reactivities at the C-2 and C-3 positions of xylan towards acetylation. Thermal stability, solubility behavior and nanofiber formation of xylan acetate were influenced by its DS values. The mechanical properties of xylan acetate propionate were also investigated.     

Structure and antioxidant activities of sulfated guar gum: homogeneous reaction using DMAP/DCC catalyst

It was essential to understand the chemical structure of polysaccharides for further research and biochemical or medical application of this natural biopolymer. In the present study, sulfated derivatives of guar gum with high degree of sulfation (DS) were synthesized using 4-dimethylaminopyridine (DMAP)/dimethylcyclohexylcarbodiimide (DCC) as catalyst in homogeneous conditions. The effects of the ratio of chlorosulfuric acid to pyridine, the content of catalyst and reaction temperature were investigated. Results of FT-IR, (1)H and (13)C NMR indicated that C-6 substitution was predominant in sulfated polysaccharide. In the sulfation reaction, a sharp decrease in M(W) was observed. The enhanced antioxidant activities of sulfated polysaccharides were not a function of a single factor but a combination of high DS and low molecule weight.     

Preparation and application of sulfated xylan as a flocculant for dye solution

The main purpose of this study is to explore the sulfation of xylan to produce an anionic flocculant, sulfated xylan, for removing ethyl violet dye from simulated dye solutions. In this work, xylan was sulfated with chlorosulfonic acid in N, N‐dimethylformamide solvent and the reaction conditions were optimized using a response surface methodology. It was observed that the maximum degree of substitution of 1.1 was obtained for sulfated xylan under the conditions of 3.71 chlorosulfonic acid/xylan molar ratio, 70°C and 7 h reaction time. The resulting sulfated xylan had a charge density of ?3.12 mmol/g and molecular weight (M_w) of 22,300 g/mol. Furthermore, elemental and thermogravimetric analyses, Fourier transform infrared spectroscopy and proton nuclear magnetic resonance (¹H‐NMR) confirmed the sulfation of xylan. The application of sulfated xylan as a flocculant for decolorizing the simulated ethyl violet dye wastewater was studied. The results indicated that 97% of dye was removed from 50 mg/L dye solution at the sulfated concentration of 175 mg/L and pH 9, but unmodified xylan was ineffective in flocculating and removing dye segments. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:529–536, 2018     

Enzymatic modification of cassava starch by bacterial lipase

Enzymatic modification of starch using long chain fatty acid makes it thermoplastic suitable for a myriad of industrial applications. An industrial lipase preparation produced by Burkholderia cepacia (lipase PS) was used for modification of cassava starch with two acyl donors, lauric acid and palmitic acid. Reactions performed with palmitic acid by liquid-state and microwave esterification gave a degree of substitution (DS) of 62.08% (DS 1.45) and 42.06% (DS 0.98), respectively. Thermogravimetric analysis showed that onset of decomposition is at a higher temperature (above 600°C) for modified starch than the unmodified starch (280°C). Modified starch showed reduction in α-amylase digestibility compared to native starch (76.5–18%). Swelling power lowered for modified starch as esterification renders starch more hydrophobic, making it suitable for biomedical applications as materials for bone fixation and replacements, carriers for controlled release of drugs and bioactive agents. Thus enzymatic esterification is ecofriendly.     

Preparation and Application of Carboxymethyl Yam (Dioscorea esculenta) Starch

Yam (Dioscorea esculenta) starch was modified by carboxymethylation. The effect of reaction parameters, amount of sodium hydroxide (NaOH), amount of sodium monochloroacetate (SMCA), and reaction time on the degree of substitution (DS) of carboxymethyl yam starch (CMS), was studied using the Box–Behnken experimental design. Physicochemical and potency to be a tablet disintegrant of CMS were evaluated. CMS with DS in the range of 0.08–0.19 were obtained. The results from regression analysis indicated that the most important factor in controlling DS was the amount of NaOH followed by SMCA content and reaction time. However, high concentration of NaOH and SMCA lowered the DS. The optimal conditions to achieve the highest DS (0.19) were found to be at molar ratios of NaOH and SMCA to anhydroglucose unit of 1.80 and 2.35, respectively, and with the reaction time of 4.8 h. The swelling power and viscosity of CMS increased with an increase in the degree of modification. CMS showed satisfying tablet disintegrant properties. The tablets containing 1.0–4.0 % CMS disintegrated faster than 5 min. Hence carboxymethyl yam starch can be used as an excellent tablet disintegrant in low concentration.     

Cellulose esters from waste cotton fabric via conventional and microwave heating

The esterification of cellulose from waste cotton fabric in a N,N-dimethylacetamide/lithium chloride solvent system was carried out using different types of fatty acid chloride including butyryl chloride, capryloyl chloride, and lauroyl chloride as esterifying agents, and N,N-dimethyl 1-4-aminopyridine as a catalyst under conventional and microwave activation. Microwave esterification was performed under 2.45 GHz with power varying from 90 to 450 W. The optimum conditions for esterification of cotton cellulose with various esterifying agents were investigated in terms of reaction time and temperature to attain appropriate %weight increase and degree of substitution of esterified-cellulose. The degree of substitution, functional group and chemical structure, and thermal stability of cellulose ester powder were characterized by ¹H NMR, FTIR, and TGA/SDTA analysis. Morphologies, crystallinity, and solubility of modified cellulose by two different heating methods were compared.     

Preparation of chitin butyrate by using phosphoryl mixed anhydride system

Acylation of chitin with butyric acid was performed in the presence of trifluoroacetic anhydride/phosphoric acid mediated system. The products were characterized by ¹H NMR and FT-IR spectroscopy and their solubility was tested in different organic solvents. Inclusion of butyric acid moieties into the parent molecule was confirmed from the ¹H NMR and FT-IR spectra. FT-IR analysis revealed that the degree of acid substitution (DS) of the products was in a range of 1.9–2.38, which increased with increasing the amounts of butyric acid added to the reaction system. Degree of N-deacetylation (DD) of the products, as determined by ¹H NMR was between 54.2% and 65.6%. The products with DS >2.0 were soluble in dimethyl sulfoxide, N,N-dimethylformamide, tetrahydrofuran, methanol, acetone, chloroform, and acetic acid.     

Selectivity and stability of alkaline protease AL-89 in hydrophilic solvents

The alkaline protease from Bacillus pseudofirmus strain AL-89 used vinyl fatty acid esters of increasing chain length from C10 to C18 equally well as substrates for esterification of sucrose in a reaction mixture of DMF and DMSO (1:1, v/v). The synthesized esters were purified and characterized by NMR and nano-electron spray MS. As evaluated by the initial reaction rates, the primary site of substitution of sucrose was at the C-2 position with the C-3 and C-3′ as secondary substitution sites. The enzyme catalysed the formation of 3-O-acyl sucrose from 2-O-acyl sucrose. The investigation did not reveal if the 3′-O-acyl sucrose was formed the same way. The synthesis of the 2-O-esters showed the characteristics of kinetically controlled reactions, whereas the formation of the 3-O- and 3′-O-esters showed the characteristics of equilibrium controlled reactions. The enzyme catalysed process was effected by initial water content, substrate molar ratio and reaction temperature. Under the reaction conditions of 0% initial water content, a molar ratio of sucrose to vinyl stearate of 1:1.5 and 70 °C an initial formation rate of 13.5, 2.9 and 2.1 μmol min⁻¹ was achieved for 2-O-, 3-O- and 3′-O-stearoyl sucrose respectively with a specific initial synthesis rate of 2-O-stearoyl sucrose of 0.27 μmol min⁻¹ mg⁻¹ biocatalyst. In the absence of substrates the enzyme proved to be more stable in DMF than in water and DMSO at 50 °C. Mixing DMF with DMSO 1:1 (v/v) increased the stability and the half-life was found equal to that in water. In the presence of substrates a residual activity of 40% was observed after 24 h of incubation in the 1:1 (v/v) mixture of DMF and DMSO at 70 °C.     

Preparation of graft polypeptide binding bleomycin derivative

The esterification of carboxyl groups in poly-(l-glutamic acid) and atelo-collagen was carried out using N-hydroxysuccinimide and dicyclohexylcarbodiimide as coupling reagents in dimethylformamide (DMF) and/or dimethylsulphoxide (DMSO). The succinimide ester of polypeptide was allowed to react with the amino group of pepleomycin and then 2-aminoethanol in DMF and DMSO mixture. The graft polypeptide binding pepleomycin molecule is able to release the drug moiety during the biodegration of backbone polypeptides.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-<Emphasis Type="Italic">Z</Emphasis>, <Emphasis Type="Italic">N</Emphasis>′-Formyl α-Amino Acid Derived Gem-Diamines

A variety of N-carbobenzoxy, N′-formyl gem-diaminoalkyl derivatives have been obtained through Goldsmith-Wick reaction of Z-α-amino acid/peptide acid derived isocyanates with 96% HCOOH in presence of 4-dimethylaminopyridine (DMAP) as catalyst. The reaction proceeds to completion within 2–4 h and results in good yields of the products isolated as stable solids.     

Phosphorylated modification and in vitro antioxidant activity of Radix Hedysari polysaccharide

Phosphorylated modification of a polysaccharide obtained from Radix Hedysari (RHP) was studied. Three phosphorylated polysaccharides (RHPP) with variable degrees of substitution (DS(p)) were obtained with 4-dimethylaminopyridine (DMAP) and N, N' Dicyclocarbodiimide (DCC) as catalyst. The structures of RHPP were characterized by FT-IR spectra and (13)C NMR spectra. Depending on different reaction time, RHPP showed different DS(p) ranging from 0.30 to 0.66, and different Mw ranging from 86.6 to 89.7?KDa. Compared with RHP, RHPP exhibited superior antioxidant activities in vitro, which indicated that phosphorylated modification could enhance antioxidant activities of RHP. Furthermore, it was obvious that the DS(p) had a significant effect on the antioxidant activity.     

Bacterial growth on N,N-dimethylformamide: implications for the biotreatment of industrial wastewater

The degradation of N,N-dimethylformamide (DMF) by bacterial consortia was investigated under aerobic, fermentative and nitrate-reducing conditions and a variety of salt concentrations (0.2%, 4% and 7% NaCl w/v) and pH values (5 and 7). Optimization of degradation conditions was studied to provide information and recommendations for large-scale biological treatment processes. Under aerobic conditions, mineralization of DMF (200 mg l⁻¹, 2.7 mM) was achieved under all combinations of salinity and pH. The rate of bacterial growth decreased with increasing salinity. Changes in the salt concentration and pH still resulted in mineralization and unchanged yield of bacterial cells. At 0.2% NaCl and either pH 5 or 7, growth occurred on DMF in the range 0.2–1 g l⁻¹. However, cell yield decreased with increasing concentrations of DMF. Under conditions of 0.2% NaCl, pH 7 and 4% NaCl, pH 5, growth on DMF at 5 g l⁻¹ resulted in the production of an intermediate that was detected using gas chromatography (GC). It is proposed that the intermediate was dimethylamine, and its persistence in growth media was attributed to suppressed growth as a result of an increase in pH. A culture capable of degrading DMF under nitrate-reducing conditions was obtained at 0.2% NaCl and pH 7, but not at more saline and acidic conditions. Growth and degradation of DMF were considerably slower under these conditions compared with aerobic conditions. Fermentative degradation of DMF was not observed. Journal of Industrial Microbiology & Biotechnology (2000) 25, 8–16. Received 14 July 1999/ Accepted in revised form 30 March 2000