Concentrations Of N-bromosuccinimide Research Articles

Kinetic, Thermodynamic and Structural Studies of Native and N-Bromosuccinimide-Modified Mushroom Tyrosinase

Background: Mushroom tyrosinase (MT) as a metalloenzyme is a good model for mechanistic studies of melanogenesis. To recognize the mechanism of MT action, it is important to investigate its inhibition, activation, mutation, and modification properties. Objectives: In this study, the chemical modification of MT tryptophan residues was carried out by using N-bromosuccinimide (NBS) and then, the activity, stability, and structure of the native and modified enzymes were compared. Methods: Chemical modification of MT tryptophan residues was accomplished by enzyme incubation with different concentrations of NBS. The relative activity of native and modified MT was investigated through catecholase enzyme reaction in presence of dihydroxyphenylalanine (L-Dopa) as substrate. Thermodynamic parameters including standard Gibbs free energy change (∆G25°C) and Melting temperature (Tm) were obtained from thermal denaturation of the native and modified enzymes. The circular dichroism and intrinsic fluorescence techniques were used to study secondary and tertiary structure of MT, respectively. All experiments were conducted in 2015 in biophysical laboratory of Qazvin University of Medical Sciences and Islamic Azad University, Science and Research Branch, Tehran. Results: The relative activity reduced from 100% for native enzyme to 10%, 7.9%, and 6.4% for modified MT with different NBS of concentrations 2, 10, and 20 mM, respectively. Thermal instability of modified enzyme was confirmed by decreased Tm and ∆G25°C values after modification. In accordance with kinetic and thermodynamic results, the lower stability of modified MT was observed from the changes occurred on its secondary and tertiary structures. Conclusions: Chemical modification of tryptophan residues with NBS reduces the activity and stability of MT simultaneously with its structural change. Thus, this study emphasizes the crucial role of tryptophan residues in the structure-function relationship of MT enzyme.

N-Bromosuccinimide (NBS) – an efficient catalyst for acetylation of wood

Abstract Solvent-free acetylation of rubberwood (Hevea brasiliensis Müll.Arg) with acetic anhydride (Ac2O) and by means of N-bromosuccinimide (NBS) as catalyst was carried out in an oil bath at 105°C and 120°C. The effect of catalyst concentration, temperature, and reaction time was studied. The extent of acetylation was measured by determining the weight percent gain (WPG), and the acetylated wood was characterized by FTIR-ATR, CP/MAS 13C NMR, and XRD spectroscopy. The presence of NBS in concentrations between 1.0% and 3.0% elevated the acetylation rate to a great extent. WPG increased from 8.1% without catalyst to 22.1% for 2% NBS concentration after 60 min reaction at 120°C. Similarly, after 60-min reaction time at 105°C, WPG with 3% NBS concentration was 19.0% compared to 7.6% with un-catalyzed reaction under the same reaction conditions. The effect of microwave heating (MWh) on the NBS-catalyzed acetylation was also investigated. A significant level of modification was achieved within a few minutes of MWh. The hydrophobic properties and dimensional stability of the acetylated wood were elevated. NBS was found to be an effective catalyst for wood acetylation.

Desenvolvimento de materiais adsorventes de óleos a partir de resíduos do beneficiamento do café e sua aplicação na ração para aves

O objetivo deste trabalho foi modificar quimicamente resíduos do beneficiamento do café (pergaminho), visando a obtenção de um produto mais hidrofóbico, testá-lo quanto ao seu poder adsorvente de óleo e utilizá-lo em formulações de rações para aves. Os resíduos foram analisados quanto a sua composição química-bromatológica e, posteriormente, acetilados com anidrido acético usando diferentes concentrações de N-bromossuccinimida, a temperatura de 120°C por 4 horas. A análise dos resíduos indicou altos teores de fibras. A acetilação possibilitou ganho de massa em todas as amostras estudadas. Nos testes de adsorção de óleo verificou-se aumento significativo na retenção de óleo dos materiais modificados, comprovando a hidrofobização. O material acetilado e com certa quantidade de óleo adsorvida foi chamado de OSoL (óleo sólido) sendo avaliado o seu valor nutricional em rações para aves, substituindo o óleo de soja. Nos ensaios metabólicos adotou-se o método de alimentação forcada, sendo determinados os valores de energia metabolizável verdadeira, energia metabolizável verdadeira corrigida para nitrogênio, coeficiente de digestibilidade da matéria seca, coeficiente de digestibilidade da proteína bruta e coeficiente de metabolizibilidade da energia metabolizável. Os tratamentos mostraram-se semelhantes estatisticamente, sendo, portanto, viável a inclusão do OSoL nas rações animais.

Crystal growth and dielectric, mechanical, electrical and ferroelectric characterization of n-bromo succinimide doped triglycine sulphate crystals

Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at ambient temperature by the slow evaporation technique. An aqueous solution containing 1–20 mol% of n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on morphology and crystal properties was investigated. The cell parameters of the doped crystal were determined by the powder X-ray diffraction technique. The dielectric constant of NBS doped TGS crystal was calculated along the ferroelectric direction over the temperature range of 30–60 °C. The dielectric constant of NBSTGS crystals decrease with the increase in NBS concentration and considerable shift in the phase transition temperature ( T C) towards the higher temperature observed. Pyroelectric studies on doped TGS were carried out to determine the pyroelectric coefficient. The emergence of internal bias field due to doping was studied by collecting P– E hysteresis data. Temperature dependence of DC conductivity of the doped crystals was studied and gradual increase in the conductivity with the increase of dopant concentration was observed. The activation energy (Δ E) calculated was found to be lower in both the ferroelectric and the paraelectric phases for doped crystals compared to that of pure TGS. The micro-hardness studies were carried out at room temperature on thin plates cut perpendicular to the b-axis. Less doped TGS crystals show higher hardness values compared to pure TGS. Piezoelectric measurements were also carried out on 010 plates of doped TGS crystals at room temperature.

Spectrofluorimetric Determination of Acetaminophen with N-Bromosuccinimide

A simple, sensitive, and selective method for determination of acetaminophen based on its oxidation using N-bromosuccinimide (NBS) to produce a highly fluorescent product. Optimization of reaction variables was carried out concerning NBS concentration, pH, temperature, reaction time, and stability time. Under optimal analytical conditions, the fluorescent intensity was measured at lambda emission. 442 nm (excitation at lambda 330 nm). The linearity range is 120-800 ng/mL with lower detection limit of 33.6 ng/mL acetaminophen. The method was applied successfully to the determination of the compound in pharmaceutical preparations, with average recovery of 100.3 +/- 2%. The method was also applied successfully to the determination of the drug in spiked plasma samples, with an average recovery of 101.2 +/- 1%. Interference effects of some compounds, present in combination with acetaminophen, were studied and the tolerance limits of these compounds were determined.

Oleoylation of sugarcane bagasse hemicelluloses using N‐bromosuccinimide as a catalyst

AbstractConditions for the preparation of esters of sugarcane bagasse hemicelluloses with oleoyl chloride using N‐bromosuccinimide (NBS) as a catalyst in the N,N‐dimethylformamide/lithium chloride system under mild conditions were studied comparatively. The oleoylation was followed in terms of yield and degree of substitution (DS). The parameters optimised included oleoyl chloride concentration as the molar ratio of oleoyl chloride/anhydroxylose units in native hemicelluloses (1:1–8:1), NBS concentration (0.5–3.0%), reaction time (20–100 min) and reaction temperature (30–100 °C). Results were also compared with those for other catalysts such as H2SO4 and four tertiary amine catalysts, pyridine, 4‐dimethylaminopyridine, N‐methyl pyrrolidine and N‐methyl pyrrolidinone. An oleoyl chloride/hemicellulose molar ratio of 3:1 was found to be necessary for the reaction to proceed smoothly and to yield a product with a low DS. The new materials were characterised by FT‐IR and 1H and 13C NMR spectroscopies as well as thermal analysis. The thermal stability of the oleoylated hemicelluloses decreased slightly upon chemical modification, but no significant further decrease in thermal stability was observed for DS ≥ 0.29. Copyright © 2004 Society of Chemical Industry

Analysis and Characterization of Acetylated Sugarcane Bagasse Hemicelluloses

ABSTRACT Acetylation of sugarcane bagasse hemicelluloses with acetic anhydride using N-bromosuccinimide (NBS) as a catalyst in N,N-dimethylformamide/lithium chloride system under mild conditions was comparatively studied. The yield and the degree of substitution (DS) ranged from 68.2% and 0.37 to 78.6% and 0.82 as a function of experiment conditions. It was found that the yield and DS increased with N-bromosuccinimide concentration between 0.5 and 1.0%, reaction temperature from 18 to 80°C, and reaction time between 2 and 4 h. In comparison, other catalysts such as H2SO4 and four tertiary amine catalysts, pyridine, 4-dimethylaminopyridine, N-methyl pyrrolidine, and N-methyl pyrrolidinone, were also investigated. The results showed that NBS can be used as a novel and effective catalyst for acetylation of hemicelluloses under extremely mild reaction conditions. The new polymeric products were characterized by FT-IR, 13C NMR spectroscopy, and thermal analysis. The thermal stability of the material was increased by chemical modification.

A convenient acetylation of sugarcane bagasse using NBS as a catalyst for the preparation of oil sorption-active materials

The esterification of sugarcane bagasse with acetic anhydride using N-bromosuccinimide (NBS) as a catalyst under mild conditions in a solvent free system has been investigated. The extent of acetylation was measured by weight percent gain, which increased with an increment of reaction temperature (30–120°C) and time (0.5–72.0 h) and NBS concentration from 0.5 to 1.5%. In comparison with four tertiary amine catalysts (4-dimethylamino pyridine, pyridine, N-methyl pyrrolidine, and N-methyl pyrrolidinone) and one acidic catalyst (0.5% H2SO4), N-Bromosuccinimide was found to be the most effective and inexpensive catalyst for acetylation of hydroxyl groups in the cell walls of bagasse under mild reaction conditions. At a concentration of 1.5% of the NBS catalyst in acetic anhydride, a weight percent gain of 22.3% was achieved at 80°C for 2 h. FT-IR and CP-MAS 13C-NMR studies produced evidence for acetylation. More importantly, the acetylation substantially increased hydrophobic properties of the bagasse. The oil sorption capacity of the acetylated bagasse (18.8 g machine oil/g of bagasse fibre at room temperature), obtained at 80°C for 2 h, was approximately 1.9 times higher than those of the commercial synthetic oil sorbents such as polypropylene fibres. Cyclic sorption/desorption studies showed that a simple squeezing operation was sufficient to remove most of the oil absorbed on the fibre and the sorbents can be used several times. These novel oil sorption-active materials could be used to substitute those of non-biodegradable materials in oil spill cleanup.

An essential tryptophan residue of green crab (Syclla Serrata) alkaline phosphatase

The tryptophan residues in green crab (scylla serrata) alkaline phosphatase (EC 3.1.3.1) have been modified by N-bromosuccinimide (NBS). The modification of five tryptophan residues leads to complete loss of enzymatic activity. With the increase of NBS concentration, both the absorption at 278 nm and the fluorescence emission intensity at 335 nm of the modified enzyme decreased markedly indicating the modification of tryptophan residues. Quantitative treatment of the data (Tsou, Sci. Sinica 1962, 11, 1535-1558) shows that among the tryptophan residues modified, one is essential for its catalytic activity. The presence of the substrate markedly protects the modification of tryptophan residues as well as the inactivation, suggesting that the essential tryptophan residue is situated at the active site of this enzyme.

GTP binding to elongation factor eEF-2 unmasks a tryptophan residue required for biological activity.

Elongation factor eEF-2 from rat liver, which contains 7 tryptophan residues, was treated with increasing concentrations of N-bromosuccinimide (NBS) under conditions in which these residues were oxidized specifically. The reagent produced a characteristic lowering in both the absorbance at 280 nm and the intrinsic fluorescence at 332 nm of the factor. Fluorometric titration of tryptophans and correlation to eEF-2 residual activity on GTP hydrolysis and polyphenylalanine synthesis showed that modification of the two most reactive tryptophans completely inactivated the factor. These residues were identified as Trp343 and Trp221 after cleavage of the protein with cyanogen bromide, separation of the fragments by reversed-phase high-pressure liquid chromatography, and N-terminal sequencing of the two fragments which exhibited a decreased absorbance in the NBS-treated protein. Oxidation of the most reactive residue, Trp343, did not induce significant decrease of activity of the factor or of its ability to interact with GTP or GDP. On the contrary, oxidation of Trp221 inactivated the factor, whose residual fluorescence was still partly quenched by GDP but no longer by GTP. Preincubation of eEF-2 with GDP protected Trp221 against NBS oxidation and prevented concomitant inactivation of the factor, whereas preincubation of eEF-2 with GTP increased the sensitivity of the same Trp221 residue to the reagent. Our results show for the first time that Trp221, which is conserved and belongs to a well preserved domain in eukaryotic cells and archaebacteria, plays an essential part in the catalytic activity of eEF-2. They strongly suggest that GTP induces a conformational change of the protein which unmasks this residue, whereas GDP stabilizes a conformation which makes this residue much less accessible.