Studies of the chemoenzymatic modification of cellulosic pulps by the laccase-TEMPO system

Holzforschung ◽  
2011 ◽  
Vol 65 (4) ◽  
Author(s):  
Ilabahen Patel ◽  
Roland Ludwig ◽  
Dietmar Haltrich ◽  
Thomas Rosenau ◽  
Antje Potthast
Keyword(s):  
Sodium Citrate ◽  
Similar Reaction ◽  
Carbonyl Groups ◽  
Citrate Buffer ◽  
Hydroxymethyl Group ◽  
Mediator System ◽  
Sodium Citrate Buffer ◽  
Reaction Proceeds ◽  
Aldehyde Groups ◽  
Aqueous Conditions

Abstract The chemoenzymatic modification of cellulosic pulps by the laccase-mediator system (LMS) consisting of laccase (EC 1.10.3.2) and the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) has been investigated. The reaction proceeds under mild aqueous conditions (sodium citrate buffer pH 6, 30°C) and introduces primarily aldehyde groups into cellulose so that carboxyl groups amount to one-third to one-fifth of the carbonyl groups only. LMS treatment caused uniform oxidation of the material, also in the high-molecular weight area, which is a non-typical behavior compared to other chemical oxidations of cellulose. Treatment of the pulp only with TEMPO or only with laccase caused no changes whatsoever, whereas treatment with the TEMPO-derived oxoammonium ion (in the absence of laccase) introduced carbonyl groups into the pulp, but no carboxyls. This chemoenzymatic approach was compared to the well-known chemical approach by means of TEMPO and hypohalite. Both approaches yielded comparable distributions of functional groups at the low oxidation degrees studied, indicating a similar reaction mechanism with the TEMPO-derived oxoammonium ion being the actual oxidant. The laccase is able to generate this oxoammonium ion, which in turn oxidized the 6-hydroxymethyl group into the corresponding aldehyde.

Sodium citrate buffer

2009 ◽  
Vol 2009 (12) ◽  
pp. pdb.rec12040-pdb.rec12040
Keyword(s):  
Sodium Citrate ◽  
Citrate Buffer ◽  
Sodium Citrate Buffer

scholarly journals Wells–Dawson phosphotungstates as mushroom tyrosinase inhibitors: a speciation study

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Raphael Lampl ◽  
Joscha Breibeck ◽  
Nadiia I. Gumerova ◽  
Mathea Sophia Galanski ◽  
Annette Rompel
Keyword(s):  
Inhibitory Activity ◽  
Sodium Citrate ◽  
Structural Integrity ◽  
Inhibitory Effect ◽  
Moderate Activity ◽  
Citrate Buffer ◽  
Speciation Study ◽  
Protonated Forms ◽  
Sodium Citrate Buffer ◽  
Low Charge

AbstractIn order to elucidate the active polyoxotungstate (POT) species that inhibit fungal polyphenol oxidase (AbPPO4) in sodium citrate buffer at pH 6.8, four Wells–Dawson phosphotungstates [α/β-PV2WVI18O62]6− (intact form), [α2-PV2WVI17O61]10− (monolacunary), [PV2WVI15O56]12− (trilacunary) and [H2PV2WVI12O48]12− (hexalacunary) were investigated. The speciation of the POT solutions under the dopachrome assay (50 mM Na-citrate buffer, pH 6.8; L-3,4−dihydroxyphenylalanine as a substrate) conditions were determined by 183W-NMR, 31P-NMR spectroscopy and mass spectrometry. The intact Wells–Dawson POT [α/β-PV2WVI18O62]6− shows partial (~ 69%) disintegration into the monolacunary [α2-PV2WVI17O61]10− anion with moderate activity (Ki = 9.7 mM). The monolacunary [α2-PV2WVI17O61]10− retains its structural integrity and exhibits the strongest inhibition of AbPPO4 (Ki = 6.5 mM). The trilacunary POT [PV2WVI15O56]12− rearranges to the more stable monolacunary [α2-PV2WVI17O61]10− (~ 62%) accompanied by release of free phosphates and shows the weakest inhibition (Ki = 13.6 mM). The hexalacunary anion [H2PV2WVI12O48]12− undergoes time-dependent hydrolysis resulting in a mixture of [H2PV2WVI12O48]12−, [PV8WVI48O184]40−, [PV2WVI19O69(H2O)]14− and [α2-PV2WVI17O61]10− which together leads to comparable inhibitory activity (Ki = 7.5 mM) after 48 h. For the solutions of [α/β-PV2WVI18O62]6−, [α2-PV2WVI17O61]10− and [PV2WVI15O56]12− the inhibitory activity is correlated to the degree of their rearrangement to [α2-PV2WVI17O61]10−. The rearrangement of hexalacunary [H2PV2WVI12O48]12− into at least four POTs with a negligible amount of monolacunary anion interferes with the correlation of activity to the degree of their rearrangement to [α2-PV2WVI17O61]10−. The good inhibitory effect of the Wells–Dawson [α2-PV2WVI17O61]10− anion is explained by the low charge density of its protonated forms Hx[α2-PV2WVI17O61](10−x)− (x = 3 or 4) at pH 6.8.

Absorption of sulfur dioxide in citric acid-sodium citrate buffer solutions

1987 ◽  
Vol 26 (7) ◽  
pp. 1291-1296 ◽  
Author(s):  
Binay K. Dutta ◽  
Ranjan K. Basu ◽  
Amit Pandit ◽  
Parthasarathi Ray
Keyword(s):  
Citric Acid ◽  
Sulfur Dioxide ◽  
Sodium Citrate ◽  
Citrate Buffer ◽  
Buffer Solutions ◽  
Sodium Citrate Buffer

scholarly journals Use of Micellar Delivery Systems to Enhance Curcumin’s Stability and Microbial Photoinactivation Capacity

Foods ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 1777
Author(s):  
Victor Ryu ◽  
Silvette Ruiz-Ramirez ◽  
Piyanan Chuesiang ◽  
Lynne A. McLandsborough ◽  
David Julian McClements ◽  
...  
Keyword(s):  
Antimicrobial Activity ◽  
Sodium Citrate ◽  
Effective Interaction ◽  
Tween 80 ◽  
Citrate Buffer ◽  
Surfactant Micelles ◽  
Gram Positive Bacteria ◽  
Surfactant Solutions ◽  
Sodium Citrate Buffer ◽  
Water Dispersibility

Microbial photoinactivation using ultraviolet (UV) or visible light can be enhanced by photosensitizers. This study assessed the efficacy of encapsulating a food-grade photosensitizer (curcumin) in surfactant micelles on its water dispersibility, chemical stability, and antimicrobial activity. Stock curcumin-surfactant solutions were prepared with Surfynol 465 (S465) or Tween 80 (T80) (5 mM sodium citrate buffer). The antimicrobial activity of curcumin-loaded surfactant solutions was determined by monitoring the inactivation of Escherichia coli O157: H7 and Listeria innocua after 5-min irradiation with UV-A light (λ = 365 nm). The solutions mixed with the bacterial suspensions contained 1 µM curcumin and each surfactant below, near, and above their critical micelle concentrations (CMCs). The addition of surfactants at any level to the curcumin solution enhanced its dispersibility, stability, and efficacy as a photosensitizer, thereby enhancing its antimicrobial activity. Gram-positive bacteria were more susceptible than Gram-negative bacteria when curcumin-loaded micelles were used against them. The photoinactivation efficacy of curcumin-surfactant solutions depended on the pH of the solution (low > high), surfactant type (S465 > T80), and the amount of surfactant present (below CMC ≥ near CMC > above CMC = unencapsulated curcumin). This result suggests that excessive partitioning of curcumin into micelles reduced its ability to interact with microbial cells. Synergistic antimicrobial activity was observed when S465 was present below or near the CMC with curcumin at pH 3.5, which could be attributed to a more effective interaction of the photosensitizer with the cell membranes as supported by the fluorescence lifetime micrographs. The use of a micelle-based delivery system facilitates adsorption and generation of reactive oxygen species in the immediate environment of the microbial cell, enhancing photoinactivation.

Fracturing and adhesion behavior of hydroxyapatite formed by a citric acid and sodium citrate buffer system

2016 ◽  
Vol 58 (2) ◽  
pp. 140-145 ◽  
Author(s):  
İbrahim Aydin ◽  
Hakan Çetinel ◽  
Ahmet Pasinli ◽  
Mithat Yuksel
Keyword(s):  
Citric Acid ◽  
Sodium Citrate ◽  
Buffer System ◽  
Citrate Buffer ◽  
Adhesion Behavior ◽  
Sodium Citrate Buffer
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