Phenylcoumarins from Ochrocarpus Siamensis

Two new phenylcoumarins, 6-butyryl-5-hydroxy-4-phenylseselin and 6-butyryl-5,7-dihydroxy-8-(3,3dimethylallyl)-4-phenyleoumarin, were isolated from the flowers of Ochrocarpus siamensis.     

Antibacterial activity of quaternary ammonium chitosan containing mono or disaccharide moieties: Preparation and characterization

The 9 quaternary ammonium chitosans containing monosaccharides or disaccharides moieties were successfully synthesized by reductive N-alkylation then quaternized by N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride (Quat-188). The chemical structures of quaternary ammonium chitosan derivatives were characterized by ATR-FTIR and ¹H NMR spectroscopy. The degree of N-substitution (DS) and the degree of quaternization (DQ) were determined by ¹H NMR spectroscopic method. It was found that the DS was in the range of 12–40% while the DQ was in the range of 90–97%. The results indicated that the O-alkylation was occured in this condition. Moreover, all quaternary ammonium chitosan derivatives were highly water-soluble at acidic, basic, and neutral pH. Minimum inhibitory concentration (MIC) antibacterial studies of these materials were carried out on Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria compared to quaternary ammonium N-octyl and N-benzyl chitosan derivatives. The quaternary ammonium mono and disaccharide chitosan derivatives showed very high MIC values which were in the range of 32 to >256 μg/mL against both bacteria. Also it was found that the antibacterial activity decreased with increasing the DS. This was due to the increased hydrophilicity of mono and disaccharide moieties. On the other hand, the low MIC values (8–32 μg/mL) were obviously observed when the DS of quaternary ammonium N-octyl and N-benzyl chitosan derivatives was lower than 18%. The results showed that the presence of hydrophobic moiety such as the N-benzyl group enhanced the antibacterial activity compared to the hydrophilic moiety against both bacteria.     

Synthesis and characterization of N-aryl chitosan derivatives

Selective N-arylation of chitosan was performed via a Schiff bases formed by the reaction between the 2-amino group of glucosamine residue of chitosan with an aromatic aldehyde under acidic condition followed by reduction of the Schiff base intermediate with sodium cyanoborohydride (Borch reduction). Aromatic aldehydes bearing either an electron donating or electron withdrawing substituent were used. The chemical structures and thermal properties of the N-aryl chitosans were characterized by FT-IR, (1)H NMR, (13)C NMR, TGA, and DSC. The extent of N-substitution (ES) was influenced by the molar ratio of the aldehyde to the glucosamine residue of chitosan, the reaction time and the substituent on the aromatic ring. Lower ESs resulted from N-arylation using an aldehyde with an electron donating substituent. A linear relationship between the targeted ES and the ES obtained was observed when aldehydes bearing electron withdrawing substituents were employed.     

Synthesis of methylated chitosan containing aromatic moieties: Chemoselectivity and effect on molecular weight

N-Arylated chitosans were synthesized via Schiff bases formed by the reaction between the primary amino group of chitosan with aromatic aldehydes followed by reduction of the Schiff base intermediates with sodium cyanoborohydride. Treatment of chitosan containing N,N-dimethylaminobenzyl and N-pyridylmethyl substituents with iodomethane under basic conditions led to quaternized N-(4-N,N-dimethylaminobenzyl) chitosan and quaternized N-(4-pyridylmethyl) chitosan. Methylation occurred at either N,N-dimethylaminobenzyl and N-pyridylmethyl groups before the residual primary amino groups of chitosan GlcN units were substituted. The total degree of quaternization of each chitosan varied depending on the extent of N-substitution (ES) and the sodium hydroxide concentration used in methylation. Increasing ES increased the total degree of quaternization but reduced attack at the GlcN units. N,N-dimethylation and N-methylation at the primary amino group of chitosan decreased at higher ES’s. Higher total degrees of quaternization and degrees of O-methylation resulted when higher concentrations of sodium hydroxide were used. The molecular weight of chitosan before and after methylation was determined by gel permeation chromatography under mild acidic condition. The methylation of the N,N-dimethylaminobenzyl derivative with iodomethane was accompanied by numerous backbone cleavages and a concomitant reduction in the molecular weight of the methylated product was observed. The antibacterial activity of water-soluble methylated chitosan derivatives was determined using Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria; minimum inhibitory concentrations (MIC) of these derivatives ranged from 32 to 128 μg/mL. The presence of the N,N-dimethylaminobenzyl and N-pyridylmethyl substituents on chitosan backbone after methylation did not enhance the antibacterial activity against S. aureus. However, N-(4-N,N-dimethylaminobenzyl) chitosan with degree of quaternization at the aromatic substituent and the primary amino group of chitosan of 17% and 16–30%, respectively, exhibited a slightly increased antibacterial activity against E. coli.     

Occupational hazard exposures and health risks at wooden toys industry in Southern Thailand

Abstract

The paper aims to examine occupational hazard exposures and health risks in wooden toys processing industry in the Southern Thailand. A walk-through survey was conducted as well as environmental and personal dust sampling measurements were performed during June 2015–January 2016. A cross-sectional study was conducted among 704 workers. Environmental and personal noise and wood dust samplings (NIOSH method 0500 and 0600) were conducted. The workers were exposed to wood dust at levels of 0.4581?mg/m³ for total dust (SD = 0.4391) and 1.111?mg/m³ for respirable dust (SD = 0.3450), respectively. The pulmonary defects among male had higher prevalence than female the (OR = 1.49; 95%CI = 0.97–2.29). Aged group <25 years old had significant lower than aged group >40 years old for almost twice (OR = 0.48). Male workers were significantly at lower risk for noise-induced hearing loss (NIHL) than females (OR = 0.54; 95%CI = 0.34–0.84). This study provides evidence that pulmonary defects among aged group <25 years old had significant lower than aged group >40 years old (p?=?.026). Male workers were significantly at lower risk for NIHL than females (p?=?.006).