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Hindered phenol

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https://www.readbyqxmd.com/read/28004081/determination-of-the-activity-signature-of-key-carbohydrate-metabolism-enzymes-in-phenolic-rich-grapevine-tissues
#1
Elizabeth Covington Dunn, Thomas Roitsch, Marina Dermastia
Physiological studies in plants often require enzyme extraction from tissues containing high concentrations of phenols and polyphenols. Unless removed or neutralized, such compounds may hinder extraction, inactivate enzymes, and interfere with enzyme detection. The following protocol for activity assays for enzymes of primary carbohydrate metabolism, while based on our recently published one for quantitative measurement of activities using coupled spectrophotometric assays in a 96-well format, is tailored to the complexities of phenolic- and anthocyanin-rich extracts from grapevine leaf...
December 2016: Acta Chimica Slovenica
https://www.readbyqxmd.com/read/27959520/copper-catalyzed-sp-3-c-h-etherification-with-acyl-protected-phenols
#2
Tolani K Salvador, Charles H Arnett, Subrata Kundu, Nicholas G Sapiezynski, Jeffery A Bertke, Mahdi Raghibi Boroujeni, Timothy H Warren
A variety of acyl protected phenols AcOAr participate in sp(3) C-H etherification of substrates R-H to give alkyl aryl ethers R-OAr employing (t)BuOO(t)Bu as oxidant with copper(I) β-diketiminato catalysts [Cu(I)]. Although 1°, 2°, and 3° C-H bonds may be functionalized, selectivity studies reveal a preference for the construction of hindered, 3° C-OAr bonds. Mechanistic studies indicate that β-diketiminato copper(II) phenolates [Cu(II)]-OAr play a key role in this C-O bond forming reaction, formed via transesterification of AcOAr with [Cu(II)]-O(t)Bu intermediates generated upon reaction of [Cu(I)] with (t)BuOO(t)Bu...
December 28, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27872660/improvement-of-catalytic-performance-of-lignin-peroxidase-for-the-enhanced-degradation-of-lignocellulose-biomass-based-on-the-imbedded-electron-relay-in-long-range-electron-transfer-route
#3
Le Thanh Mai Pham, Su Jin Kim, Yong Hwan Kim
BACKGROUND: Although lignin peroxidase is claimed as a key enzyme in enzyme-catalyzed lignin degradation, in vitro enzymatic degradation of lignin was not easily observed in lab-scale experiments. It implies that other factors may hinder the enzymatic degradation of lignin. Irreversible interaction between phenolic compound and lignin peroxidase was hypothesized when active enzyme could not be recovered after the reaction with degradation product (guaiacol) of lignin phenolic dimer. RESULTS: In the study of lignin peroxidase isozyme H8 from white-rot fungi Phanerochaete chrysosporium (LiPH8), W251 site was revealed to make the covalent coupling with one moiety of monolignolic radical (guaiacol radical) by LC-MS/MS analysis...
2016: Biotechnology for Biofuels
https://www.readbyqxmd.com/read/27860031/efficient-coupling-reaction-of-quinone-monoacetal-with-phenols-leading-to-phenol-biaryls
#4
Tohru Kamitanaka, Koji Morimoto, Kohei Tsuboshima, Daichi Koseki, Hitoho Takamuro, Toshifumi Dohi, Yasuyuki Kita
A simple and efficient synthesis of phenol biaryls by the cross-couplings of quinone monoacetals (QMAs) and phenols is reported. The Brønsted acid catalytic system in 1,1,1,3,3,3-hexafluoro-2-propanol was found to be particularly efficient for this transformation. This reaction can be extended to the synthesis of various phenol biaryls, including sterically hindered biaryls, with yields ranging from 58 to 90 % under mild reaction conditions and in a highly regiospecific manner.
December 12, 2016: Angewandte Chemie
https://www.readbyqxmd.com/read/27804193/organocatalytic-enantioselective-synthesis-of-cyclohexadienone-containing-hindered-spirocyclic-ethers-through-an-oxidative-dearomatization-oxa-michael-addition-sequence
#5
Reddy Rajasekhar Reddy, Satish Sonbarao Gudup, Prasanta Ghorai
An unprecedented enantioselective oxa-Michael reaction of α-tertiary alcohols using cinchona-alkaloid-based chiral bifunctional squaramide catalysts is reported. An oxidative dearomatization of phenol followed by an enantioselective oxa-Michael addition sequence provided a broad array of chiral sterically hindered tetrahydrofurans and tetrahydropyrans attached to a cyclohexadienone moiety in spiro fashion. In general, good yields and excellent enantioselectivities (up to 99 %) were observed. The chiral oxo-cycles obtained have easily been transformed into chromans without disturbing the enantioselectivity...
November 2, 2016: Angewandte Chemie
https://www.readbyqxmd.com/read/27780125/thermohalochromism-of-phenolate-dyes-conjugated-with-nitro-substituted-aryl-groups
#6
Laura Hermosilla, Marcos Caroli Rezende, Vanderlei Gageiro Machado, Rafaela I Stock
The cationic halochromism and thermohalochromism of four phenolate dyes conjugated with aryl moieties substituted with one or two nitro groups were investigated in the presence of organic (tetra-n-butylammonium bromide and benzyltriethylammonium chloride) and inorganic (sodium perchlorate) salts, in hydrogen-bond donating (water, 1-propanol, 1-butanol and 2-propanol) and hydrogen-bond accepting (acetonitrile and dimethylsulfoxide) solvents. Although a positive halochromic response was observed in water for tetraalkylammonium salts, their thermohalochromic behavior was negligible...
February 15, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/27502897/inhibition-of-autophagy-enhances-curcumin-united-light-irradiation-induced-oxidative-stress-and-tumor-growth-suppression-in-human-melanoma-cells
#7
Tianhui Niu, Yan Tian, Zhusong Mei, Guangjin Guo
Malignant melanoma is the most aggressive form of skin carcinoma, which possesses fast propagating and highly invasive characteristics. Curcumin is a natural phenol compound that has various biological activities, such as anti-proliferative and apoptosis-accelerating impacts on tumor cells. Unfortunately, the therapeutical activities of Cur are severely hindered due to its extremely low bioavailability. In this study, a cooperative therapy of low concentration Cur combined with red united blue light irradiation was performed to inspect the synergistic effects on the apoptosis, proliferation and autophagy in human melanoma A375 cell...
2016: Scientific Reports
https://www.readbyqxmd.com/read/27472310/green-tea-leaves-extract-microencapsulation-physicochemical-and-storage-stability-study
#8
James A Zokti, Badlishah Sham Baharin, Abdulkarim Sabo Mohammed, Faridah Abas
Green tea polyphenols have been reported to possess many biological properties. Despite the many potential benefits of green tea extracts, their sensitivity to high temperature, pH and oxygen is a major disadvantage hindering their effective utilization in the food industry. Green tea leaves from the Cameron Highlands Malaysia were extracted using supercritical fluid extraction (SFE). To improve the stability, green tea extracts were encapsulated by spray-drying using different carrier materials including maltodextrin (MD), gum arabic (GA) and chitosan (CTS) and their combinations at different ratios...
July 26, 2016: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/27464665/effect-of-substituted-hydroxyl-groups-in-the-changes-of-solution-turbidity-in-the-oxidation-of-aromatic-contaminants
#9
N Villota, Lomas Jm, Camarero Lm
This paper deals with the changes of turbidity that are generated in aqueous solutions of phenol when they are oxidized by using different Fenton technologies. Results revealed that if the Fenton reaction was promoted with UV light, the turbidity that was generated in the water doubled. Alternatively, the use of ultrasonic waves produced an increase in turbidity which initially proceeded slowly, reaching intensities eight times higher than in the conventional Fenton treatment. As well, the turbidity showed a high dependence on pH...
July 28, 2016: Environmental Science and Pollution Research International
https://www.readbyqxmd.com/read/27440560/a-double-prodrug-with-improved-membrane-permeability-over-the-parent-chelator-hbed-provides-superior-cytoprotection-against-hydrogen-peroxide
#10
Nikki A Thiele, Kenneth B Sloan
The clinical use of N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) has been hindered by its lack of bioavailability. N,N'-bis(2-boronic pinacol ester benzyl)ethylenediamine-N,N'-diacetic acid methyl, ethyl, and isopropyl esters 7 a-c, respectively, and their dimesylate salts 8 a-c, are double prodrugs that mask the two phenolate and two carboxylate donors of HBED as boronic esters and carboxylate esters, respectively. Their activation by chemical hydrolysis and oxidation, their passive diffusivity, and their cytoprotective capabilities have been investigated here...
August 5, 2016: ChemMedChem
https://www.readbyqxmd.com/read/27334326/a-novel-technique-for-assessing-antioxidant-concentration-in-retrieved-uhmwpe
#11
Barbara H Currier, Douglas W Van Citters
BACKGROUND: Antioxidants added to UHMWPE to prevent in vivo oxidation are important to the long-term performance of hip and knee arthroplasty. Diffused vitamin E antioxidant polyethylene raised questions about potential in vivo elution that could cause inflammatory reactions in periprosthetic tissues and also potentially leave the implant once again prone to oxidation. Currently, there is no information on the elution, if any, of antioxidants from implant polyethylene materials in vivo...
June 22, 2016: Clinical Orthopaedics and related Research
https://www.readbyqxmd.com/read/27265033/catalytic-reductive-ortho-c-h-silylation-of-phenols-with-traceless-versatile-acetal-directing-groups-and-synthetic-applications-of-dioxasilines
#12
Yuanda Hua, Parham Asgari, Thirupataiah Avullala, Junha Jeon
A new, highly selective, bond functionalization strategy, achieved via relay of two transition metal catalysts and the use of traceless acetal directing groups, has been employed to provide facile formation of C-Si bonds and concomitant functionalization of a silicon group in a single vessel. Specifically, this approach involves the relay of Ir-catalyzed hydrosilylation of inexpensive and readily available phenyl acetates, exploiting disubstituted silyl synthons to afford silyl acetals and Rh-catalyzed ortho-C-H silylation to provide dioxasilines...
June 29, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27128183/novel-double-prodrugs-of-the-iron-chelator-n-n-bis-2-hydroxybenzyl-ethylenediamine-n-n-diacetic-acid-hbed-synthesis-characterization-and-investigation-of-activation-by-chemical-hydrolysis-and-oxidation
#13
Nikki A Thiele, Khalil A Abboud, Kenneth B Sloan
The development of iron chelators suitable for the chronic treatment of diseases where iron accumulation and subsequent oxidative stress are implicated in disease pathogenesis is an active area of research. The clinical use of the strong chelator N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) and its alkyl ester prodrugs has been hindered by poor oral bioavailability and lack of conversion to the parent chelator, respectively. Here, we present novel double prodrugs of HBED that have the carboxylate and phenolate donors of HBED masked with carboxylate esters and boronic acids/esters, respectively...
August 8, 2016: European Journal of Medicinal Chemistry
https://www.readbyqxmd.com/read/27077646/ligand-centred-oxidative-chemistry-in-sterically-hindered-salen-complexes-an-interesting-case-with-nickel
#14
F Thomas
Salen ligands are ubiquitous ligands because they can be readily prepared by condensation of a diamine with two equivalents of salicylaldehyde. They form stable complexes with a great variety of metal ions and find applications in various fields, especially catalysis. The introduction of chirality at the bridge and the adjunction of sterically demanding tert-butyl groups in ortho and para positions of the phenols allow for efficient enantioselective catalysis. On the other hand, early investigations on the oxidation chemistry of phenols highlighted that the incorporation of tert-butyl groups in ortho and para positions can stabilize enormously the one-electron oxidized product e...
July 5, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/27060896/phytochemical-composition-and-in-vitro-anti-tumour-activities-of-selected-tomato-varieties
#15
Rebeca P Ramos-Bueno, Roberto Romero-González, María J González-Fernández, José L Guil-Guerrero
BACKGROUND: Previous studies indicated that tomato is a rich source of phytochemicals that act on different tumours. In this research, the phytochemical composition of selected tomato varieties was assessed by GLC and UHPLC/HPLC-MS, as well as their anti-tumour activities on HT-29 colorectal cancer cells. RESULTS: Significant differences were found among tomato varieties; lycopene was high in Racimo, phenolics in Pera, sterols in Cherry, and linoleic acid predominated in all varieties...
January 2017: Journal of the Science of Food and Agriculture
https://www.readbyqxmd.com/read/27052717/phenolic-acid-degradation-potential-and-growth-behavior-of-lactic-acid-bacteria-in-sunflower-substrates
#16
Caroline Fritsch, Veronika Heinrich, Rudi F Vogel, Simone Toelstede
Sunflower flour provides a high content of protein with a well-balanced amino acid composition and is therefore regarded as an attractive source for protein. The use for human nutrition is hindered by phenolic compounds, mainly chlorogenic acid, which can lead under specific circumstances to undesirable discolorations. In this study, growth behavior and degradation ability of chlorogenic acid of four lactic acid bacteria were explored. Data suggested that significant higher fermentation performances on sunflower flour as compared to sunflower protein concentrate were reached by Lactobacillus plantarum, Pediococcus pentosaceus, Lactobacillus gasseri and Bifidobacterium animalis subsp...
August 2016: Food Microbiology
https://www.readbyqxmd.com/read/27012632/the-polyphenol-oleuropein-aglycone-hinders-the-growth-of-toxic-transthyretin-amyloid-assemblies
#17
Manuela Leri, Daniele Nosi, Antonino Natalello, Riccardo Porcari, Matteo Ramazzotti, Fabrizio Chiti, Vittorio Bellotti, Silvia Maria Doglia, Massimo Stefani, Monica Bucciantini
Transthyretin (TTR) is involved in a subset of familial or sporadic amyloid diseases including senile systemic amyloidosis (SSA), familial amyloid polyneuropathy and cardiomyopathy (FAP/FAC) for which no effective therapy has been found yet. These conditions are characterized by extracellular deposits primarily found in the heart parenchyma and in peripheral nerves whose main component are amyloid fibrils, presently considered the main culprits of cell sufferance. The latter are polymeric assemblies grown from misfolded TTR, either wt or carrying one out of many identified mutations...
April 2016: Journal of Nutritional Biochemistry
https://www.readbyqxmd.com/read/26987196/-determination-of-8-hindered-phenolic-antioxidantsin-olive-oil-by-ultra-performance-liquid-chromatography-and-its-migration-research
#18
Qifeng Ma, Zeng Fan'gang, Jie Lu
OBJECTIVE: To develop a method for determination of PG, TBHQ, NDGA, BHA, Ionox100, OG, DG and BHT in olive oil by ultra-performance liquid chromatography (UPLC), and to study the migration rule of hindered phenolic antioxidants in food simulation solvent. METHODS: The samples were extracted with acetonitrile, and C18 dispersion matrix solid-phase, the separation were performed by UPLC. The migration amount of PG, BHA, BHT from polyethylene film to different simulated solvent (olive oil, 20% ethanol, 10% ethanol, 3% acetic acid) were determined at 20, 60 and 100 degrees C...
January 2016: Wei Sheng Yan Jiu, Journal of Hygiene Research
https://www.readbyqxmd.com/read/26977176/scope-and-limitations-of-the-dual-gold-catalysed-hydrophenoxylation-of-alkynes
#19
Adrián Gómez-Suárez, Yoshihiro Oonishi, Anthony R Martin, Steven P Nolan
Due to the synthetic advantages presented by the dual-gold-catalysed hydrophenoxylation of alkynes, a thorough study of this reaction was carried out in order to fully define the scope and limitations of the methodology. The protocol tolerates a wide range of functional groups, such as nitriles, ketones, esters, aldehydes, ketals, naphthyls, allyls or polyphenols, in a milder and more efficient manner than the previously reported methodologies. We have also identified that while we are able to use highly steric hindered phenols, small changes on the steric bulk of the alkynes have a dramatic effect on the reactivity...
2016: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26908114/release-modulated-antioxidant-activity-of-a-composite-curcumin-chitosan-polymer
#20
Martin G O'Toole, Patricia A Soucy, Rajat Chauhan, Mandapati V Ramakrishnam Raju, Dhruvina N Patel, Betty M Nunn, Megan A Keynton, William D Ehringer, Michael H Nantz, Robert S Keynton, Andrea S Gobin
Curcumin is known to have immense therapeutic potential but is hindered by poor solubility and rapid degradation in solution. To overcome these shortcomings, curcumin has been conjugated to chitosan through a pendant glutaric anhydride linker using amide bond coupling chemistry. The hybrid polymer has been characterized by UV-visible, fluorescence, and infrared spectroscopies as well as zeta potential measurements and SEM imaging. The conjugation reactivity was confirmed through gel permeation chromatography and quantification of unconjugated curcumin...
April 11, 2016: Biomacromolecules
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