Presence Of Free Hydroxyl Groups Research Articles

Chitosan Dissolution in [BMIM]Cl Ionic Liquid: An Optimisation and Bacterial Ecotoxicity Study

Chitosan is formed from chitin deacetylation, but its insolubility remains challenging for industrial applications. An alternative would be employing Ionic Liquids (ILs) as a potential green solvent to dissolve chitosan. Hence, this research aims to study the optimum conditions of chitosan-[BMIM]Cl dissolution using Response Surface Methodology (RSM) and evaluate the ecotoxicity of chitosan-[BMIM]Cl mixture against Gram-positive and Gram-negative bacteria. Chitosan was obtained from heterogenous N-deacetylation of chitin using 50% sodium hydroxide solution at 100°C for 2.5 h. Chitosan dissolution in [BMIM]Cl was optimised using Central Composite Design (CCD) via RSM based on three independent factors: temperature, initial chitosan loading and dissolution time. Ecotoxicity of chitosan-[BMIM]Cl was evaluated using broth microdilution test against Escherichia coli and Staphylococcus aureus. Chitosan with a degree of deacetylation (DD) of 83.42% was obtained after three successive alkali treatments. Fourier Transform Infrared Spectroscopy (FTIR) revealed the presence of free hydroxyl groups, additional amino groups, and reduced C=O and C-H stretch intensity, indicating successful chitin deacetylation. The regression model for chitosan dissolution in [BMIM]Cl was significant (p < 0.05) with a non-significant lack of fit (p > 0.05). The optimised conditions to dissolve chitosan in [BMIM]Cl was 130°C, 1 wt. % and 72 h with a mean relative error of 1.78% and RMSE of 5.0496 wt. %. The toxicity of 10 wt. % chitosan-[BMIM]Cl mixture was “relatively harmless” (EC50 > 1000 mg/L) with an EC50 value of 3.1 wt. % for Escherichia coli and 3.2 wt. % for Staphylococcus aureus.

Nickel Catalyzed Alkylation of Oxindoles with Alkyl Alcohols

AbstractHerein, a simple and efficient nickel‐catalyzed C‐3‐selective alkylation of 2‐oxindoles using primary alkyl and allylic alcohols have been demonstrated. The catalytic protocol enables transformations in the presence of free hydroxyl group, amine, cycloalkanes, olefins, and lactam including more challenging C2‐C4 alcohols, citronellol and oleic acid derived alcohol in up to 96 % yield. Initial mechanistic studies and deuterium labelling experiments were performed. Synthetic modulations of the lactam enabled new routes for the synthesis of C‐3‐substituted indoles, indolines, and un‐symmetric urea derivatives.

Biflavonoids from the roots of Rhus ruspolii and evaluations of their antioxidant activities

ABSTRACT. Biflavonoids are C-C or C-O-C linked flavonoid dimers with highly restricted presence in plant species. They are extensively reported to possess interesting pharmacological properties. The chromatographic fractionation and purification of CH2Cl2/MeOH (1:1) extract of the root of Rhus ruspolli led to the isolation of a new biflavonoid (1) along with four other known biflavonoids (2-5). The structure of the compounds were identified based on the analysis of NMR spectroscopic and mass spectrometric data and also in comparison with reported literature data. Compounds 2-5 were assayed for their antioxidant activity using DPPH and displayed potent in vitro antioxidant activities. The percentage radical scavenging activities were 78.32, 68.90, 93.22 and 92.00 for compounds 2-5, respectively. The highest activity was observed for compound 4 and 5 with IC50 values of 7.90 and 8.40, respectively, which are even greater than that of ascorbic acid (IC50 9.90). The high antioxidant activity of the compounds could be due to the presence of free hydroxyl groups in the flavonoids. The antioxidant activities of these compounds support the traditional uses of the plant in treatment of wound, ectoparasite and as antibacteria and indicates the potential use of these compounds as drug lead candidates.
 
 KEY WORDS: Rhus ruspolii, Roots, Biflavonoids, Chalcones, Antioxidant activity
 Bull. Chem. Soc. Ethiop. 2022, 36(3), 667-674. 
 DOI: https://dx.doi.org/10.4314/bcse.v36i3.15 

Silica nanocomposite based hydrophobic functionality on jute textiles

Cellulosic fibres have hydrophilic property due to the presence of free hydroxyl groups; however, surface functionalization can be used to develop water repellent textiles. Jute is a lignocellulosic fibre and mainly utilised for sacking and hessian due to its stiffness nature. Works on the development of water repellent jute textiles are limited. Work has been carried by applying silica nano sol cum water repellent functional finishing on a bleached jute fabric by pad→dry→cure method. The physical, chemical, morphological, functional, handle and mechanical properties of control and nanocomposite finished jute fabrics were evaluated. Results revealed that silica nanocomposite finished jute fabric has attained the desirable hydrophobic functionality with 138.6° water contact angle, 17° sliding angle and 10.3° water contact angle hysteresis with semi-durable washing durability.

Effect of boric acid on poly vinyl alcohol- tannin blend and its application as water-based wood adhesive

ABSTRACT The work presented here focusses on developing adhesive by blending tannin and polyvinyl alcohol (PVA) in water. To furthermore enhance the properties crosslinking is carried by using boric acid at varying concentrations. Presence of free hydroxyl groups in PVA and tannin acts as a site for crosslinking reaction. The empty p orbital of trivalent boron atom attracts nucleophilic hydroxyl groups of PVA and tannin, hence are expected to form crosslinks. The interaction of boric acid with the blend was confirmed by FTIR spectra studies. The acidic pH favoured the reaction and its effects were observed by increase in viscosity and glass transition temperature (Tg). Films cased with the crosslinked blend demonstrated less hydrophilic behaviour from water contact angle test also increment in pencil hardness value and stress-bearing capacity. Adhesive performance properties like wet tack and time-dependent tensile lap shear strength on softwood and hardwood specimens were evaluated. The crosslinking-enhanced cohesion by reducing the free volumes between the chains and due to this, enhancement in tensile strength on bonded wood substrates was observed. Overall, it was found that the adhesive prepared by crosslinking PVA/tannin blend with boric acid is suitable for wood adhesive application.

STUDY ON MOISTURE-CUR ED POLYURETHANE AS UNDERCOATING LAYER FOR METALLIZATION

In this work a technique of metallizing substrate via electroless plating using moisture-cured polyurethane (MCPU) system as the undercoat is presented. MCPU prepolymer was prepared by mixing polyethylene glycol divinyl ether and diphenylmethane-4, 4’-diisocyanate in 1:1 ratio. The effects of etching time as well as curing period on the surface characteristic of MCPU undercoating were investigated. Contact angle measurements, FTIR and SEM were employed to study the changes on the surface of the treated MCPU undercoatsprior to electroless nickel plating. Electroless plating was performed using nickel bath and visual inspection was performed after completing the electroless plating cycles. Relative increase in wettability of the treated MCPU was observed. The surface became hydrophilic after subjecting to mild etching for 1 minute. SEM analysis revealed different pitted structures on the treated MCPU that were cured at different periods. FTIR analysis of the treated MCPU showed some chemical changes marked by the presence of free hydroxyl group and decrease of CH (methylene), urethane C=O, urethane amide and ether peaks. FTIR also showed the sign of further NCO reaction, which indicates by the decrease of NCO peak and increase of NH and urea C=O peaks. The standard pull-off testing method (ASTM D 4541) was employed to evaluate the adhesion strength of nickel deposits coated on MCPU undercoating layer.The test results revealed that curing period and etching time influence the adhesion performance.The results also show that at a selected curing period, prolong etching time will decrease the adhesion strength. Meanwhile prolong curing period will improve the adhesion strength.

Development of Anti-bacterial PVA/Starch Based Hydrogel Membrane for Wound Dressing

Wound infection is the primary challenge in the wound care management. To facilitate patients, the health care sector is trying to use the modern technology in the field of wound management. Various cellular processes and biological environments are intertwined in the process of wound repair. The compulsion for the modern dressing is not only to cover the wound but also to facilitate the healing rate of wound. In this research, the hydrogel membranes were prepared by crosslinking poly vinyl alcohol (PVA) with starch by using glutaraldehyde. Turmeric was added as an anti-bacterial agent. 0.5 g of turmeric showed the highest anti-bacterial activity among different turmeric contents used. For physical and mechanical characterization, the hydrogel membrane without turmeric (neat hydrogel) and 0.5 g were selected. FTIR of both hydrogel membranes confirmed the presence of free hydroxyl groups. Moreover, hydrogel membrane containing turmeric resulted stronger hydrogen bond interaction. Mechanical analysis of hydrogel membrane revealed sufficient strength to be used as wound dressing. The SEM images evolved that both hydrogel membranes were dense in nature. The swelling behavior values were greater than 100% for both hydrogel membranes. The water vapor transmission rate for 0.5 g turmeric hydrogel membrane was 52.85 g/m2h.

Positions of the Glycans in Molluscan Hemocyanin, Determined by Fluorescence Spectroscopy

Molluscan hemocyanins are glycoproteins with different quaternary and carbohydrate structures. It was suggested that the carbohydrate chains of some Hcs are involved in their antiviral and antitumor effect, as well in the organization of the quaternary structure of the molecules. Using a well-known complex for saccharide sensing, positions and access to the carbohydrate chains in the native hemocyanins from Rapana venosa (RvH) and Helix lucorum (HlH) and also their structural subunits (RvH1, RvH2 and βcHlH) and functional units (FUs) were analysed by fluorescence spectroscopy and circular dichroism. Almost no effect was observed in the fluorescence emission after titration of the complex with native RvH and HlH due to lack of free hydroxyl groups which are buried in the didecameric form of the molecules. Titration with the structural subunits βcHlH and RvH2, increasing of the emission indicates the presence of free hydroxyl groups compared to the native molecules. Complex titration with the structural subunit βc-HlH of H. lucorum Hcs leads to a 2.5 fold increase in fluorescence intensity. However, the highest emission was measured after titration of the complex with FU βcHlH-g. The result was explained by the structural model of βcHlH-g showing the putative position of the glycans on the surface of the molecule. The results of the fluorescent measurements are in good correlation with those of the circular dichroism data, applied to analyse the effect of titration on the secondary structure of the native molecules and functional units. The results also support our previously made suggestion that the N-linked oligosaccharide trees are involved in the quaternary organization of molluscan Hcs.

In Vitro Schistosomicidal Activity of Balsaminol F and Karavilagenin C

Five cucurbitane-type triterpenes (1-5), previously isolated from the African medicinal plant Momordica balsamina, along with five ester derivatives (6-10) of karavilagenin C (2), were evaluated for their potential schistosomicidal activity against Schistosoma mansoni adult worms. The natural compounds were isolated from the ethyl acetate-soluble fraction of the methanol extract of the aerial parts of M. balsamina. In a preliminary study, a significant schistosomicidal activity was observed for both the crude methanol extract and the ethyl acetate fraction. The compounds responsible for the activity were found to be balsaminol F (1) and karavilagenin C (2) with LC50 values of 14.7 ± 1.5 and 28.9 ± 1.8 µM, respectively, after 24 h of incubation (positive control praziquantel, LC₅₀ = 1.2 ± 0.1 µM). Both compounds (1, 2), at 10-50 µM, induced significant reductions in the motor activity of the worms and significantly decreased the egg production. Furthermore, they were able (at 10-100 µM) to separate the adult worm pairs into male and female after 24 h. Compounds 3-5, bearing a sugar moiety as a substituent, and the acylated derivatives of karavilagenin C (6-10) were inactive, suggesting that the presence of free hydroxyl groups in the tetracyclic skeleton might be important for the activity. A correlation between activity and the molecular volume/weight of compounds was also found.

Direct Chemical Method for Preparing 2,3-Epoxyamides Using Sodium Chlorite

A direct method for preparing 2,3-epoxyamides from tertiary allylamines via a tandem C-H oxidation/double bond epoxidation using sodium chlorite is reported. Apparently, the reaction course consists of two steps: (i) allylic oxidation of the starting allylamine to corresponding unsaturated allylamide with sodium chlorite followed by (ii) epoxidation of the allylamide to the 2,3-epoxyamide mediated by hypochlorite ion, which is formed in situ by reduction of sodium chlorite. The reaction conditions tolerate the presence of free hydroxyl groups and typical functional groups such as TBS, aryl, alkyl, allyl, acetyl, and benzyl groups; however, when an activated aromatic ring (e.g., sesamol) is present in the substrate, the use of a scavenger is necessary.

Critical re-investigation of the alditol acetate method for analysis of substituent distribution in methyl cellulose

The alditol acetate method is a common procedure for sugar analysis, also applied to determine the substituent distribution in monomer units of polysaccharide ethers like methyl cellulose by gas liquid chromatography. Consisting of several preparation and work-up steps this procedure is both time consuming and prone to side reactions that promote discrimination of single constituents, especially when no peralkylation step is performed prior to hydrolysis. As a consequence results scatter in dependence on individual treatment and conditions. In the context of this work these critical points were overcome by strict but simplified work-up procedures and using acid instead of alkaline catalyzed acetylation. Under the acidic conditions the tedious removal of borate is no longer necessary and a reduced time requirement was achieved as well as good reproducibility. Comparison with independent reference methods excluded a systematic error of the method and confirmed the results obtained. Without peralkylation, i.e. in the presence of free hydroxyl groups, another fast modification of the method using DMSO as solvent, no removal of borate, and 1-methylimidazole as catalyst for acetylation was found to produce a systematic error.

ChemInform Abstract: Facile Amide Bond Formation from Carboxylic Acids and Isocyanates.

AbstractThe reaction is compatible with a wide range of electron‐deficient aryl isocyanates and aliphatic and aromatic acids and tolerates the presence of free hydroxyl groups, Fmoc‐ and Boc‐protected amino acids, heteroaromatic isocyanates and heteroaromatic acids.

Study on Moisture-Cured Polyurethane as Undercoating Layer for Metallization

In this work a technique of metallizing substrate via electroless plating using moisture-cured polyurethane (MCPU) system as the undercoat is presented. MCPU prepolymer was prepared by mixing polyethylene glycol divinyl ether and diphenylmethane-4, 4’-diisocyanate in 1:1 ratio. The effects of etching time as well as curing period on the surface characteristic of MCPU undercoating were investigated. Contact angle measurements, FTIR and SEM were employed to study the changes on the surface of the treated MCPU undercoatsprior to electroless nickel plating. Electroless plating was performed using nickel bath and visual inspection was performed after completing the electroless plating cycles. Relative increase in wettability of the treated MCPU was observed. The surface became hydrophilic after subjecting to mild etching for 1 minute. SEM analysis revealed different pitted structures on the treated MCPU that were cured at different periods. FTIR analysis of the treated MCPU showed some chemical changes marked by the presence of free hydroxyl group and decrease of CH (methylene), urethane C=O, urethane amide and ether peaks. FTIR also showed the sign of further NCO reaction, which indicates by the decrease of NCO peak and increase of NH and urea C=O peaks. The standard pull-off testing method (ASTM D 4541) was employed to evaluate the adhesion strength of nickel deposits coated on MCPU undercoating layer.The test results revealed that curing period and etching time influence the adhesion performance.The results also show that at a selected curing period, prolong etching time will decrease the adhesion strength. Meanwhile prolong curing period will improve the adhesion strength.

Synthesis of proline derivatives of bile acids and their evaluation as organocatalysts in the asymmetric direct aldol reaction

A new family of bile acid derived organocatalysts was obtained by linking l- or d-proline to amino derivatives of cholic and deoxycholic acids, which were used to promote the asymmetric direct aldol reaction between acetone and 4-nitrobenzaldehyde. Both the activity and enantioselectivity of the organocatalytic systems were dependent not only on the position of the proline moiety on the cholestanic backbone and its absolute configuration, but also on the presence of free hydroxyl group on the steroidal skeleton. The cholic acid derivative bearing a d-prolinamide moiety at the 12-position and free hydroxyl groups at the 3- and 7-positions emerged as the best organocatalytic system giving complete conversion of the substrate, even when using only 2% of catalyst loading and ee up to 80%.

Anxiolytic Effect of Natural Galphimines from Galphimia glauca and their Chemical Derivatives

The anxiolytic effects of galphimine B (1), galphimine A (2), and galphimine E (3), natural nor-secofriedelanes isolated from Galphimia glauca, as well as derivatives obtained by acetylation (4), hydrogenation of the C-1/C-2 double bond (5), basic hydrolysis followed by hydrogenation of the C-1/C-2 double bond (6), and deacetylation (7) of galphimine E (3), were evaluated on ICR mice exposed to the elevated plus-maze test. This study also included the evaluation of a galphimines-rich fraction (GRF) with a known concentration of 1-3, obtained from the dry leaves of G. glauca. Intraperitoneal administration of 15 mg/kg of 1, 2, 6, and GRF (1 h before testing) caused an anxiolytic-like effect in the animals, increasing significantly (p <0.001) the percentage of time of permanence and the number of crossings toward the open arms of the plus-maze. No activity was detected after administration of compounds 3, 4, 5, and 7. These results showed that GRF had activity similar to the most active pure galphimines (1 and 2) and that, like for the spasmolytic activity previously reported, the main determining factor responsible for the anxiolytic activity of the compounds was the presence of free hydroxyl groups at C-4, C-6, and C-7 and the presence of the double bond in the A ring.

Synthesis of Novel 3,4‐Dihydropyrimidinones on Water Soluble Solid Support Catalyzed by Indium Triflate.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of novel 3,4‐dihydropyrimidinones on water soluble solid support catalyzed by indium triflate

AbstractSyntheses of several new 3,4‐dihydropyrimidinones (DHPMs) on sodium sulfate solid support have been reported. The microwave enhanced rapid synthesis of the title compounds yielded a good percentage of the DHPMs. The catalytic activity of indium triflate enables to prepare a wide range of DHPMs. Syntheses of 2‐hydroxyphenyl, 2‐hydroxy‐4‐methoxyphenyl pendant groups on DHPMs scaffold are advantages of the present method, which are rather prone towards cyclization and the presence of free hydroxyl groups on the phenyl ring is confirmed via D2O exchange study. The mechanism of the reaction is expected to proceed via absorption of substrates on the solid support followed by promotion of the reaction by In(OTf)3 coupled with microwave irradiation.

3′,4′-Dihydroxyflavonol reduces infarct size and injury associated with myocardial ischaemia and reperfusion in sheep

3′,4′-Dihydroxyflavonol reduces infarct size and injury associated with myocardial ischaemia and reperfusion in sheep

Synthesis and Characterization of Segmented Hydrosoluble Poly(Tartaraide)s

Segmented poly(tartaramide)s were prepared by polycondensation of monodispersed α,ω-diaminooligo(ethyleneglycol)s, with oligomerization degree included between 2 and 6, with two optically active dialkyl tartrates. The diamines were obtained from the relevant commercial glycols using a modified Gabriel synthesis. The polycondensations were performed in methanol at 55°C with triethylamine as catalyst. By this route, optically active poly(tartaramide)s, with oligomerization degree in the 4-10 range, were obtained in fairly high yields. Solubility and thermal properties of the polycondensation products were found to be related to the length of the oligo(oxyethylene) segment and to the presence of free hydroxyl groups.

PVC containing hydroxyl groups: I. Synthesis, characterization, properties and crosslinking

A detailed characterization of hydroxylated poly(vinyl chloride) (PVC), obtained by modification of PVC with p-mercaptobenzyl alcohol and its crosslinked homologues, is described. The selective character of the modification with respect to the thiol group and the presence of free hydroxyl groups in the polymer is shown using 1H-NMR. The stereoselectivity of the reaction is provided from 13C-NMR. The presence of physical interactions in the system by hydrogen bonding is deduced from light scattering measurements and analysis of the thermal and mechanical properties. The critical concentration of hydroxyl groups required in the chains in order to form an efficient physical network is determined to be about 4%. Chemical networks are obtained by reaction of hexamethylene diisocyanate with the hydroxyl groups present in the polymer, and the process is followed by IR spectroscopy.