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https://www.readbyqxmd.com/read/28628319/on-the-mechanism-of-phenol-alkylation-in-zeolite-h-bea-using-in-situ-solid-state-nmr-spectroscopy
#1
Zhenchao Zhao, Hui Shi, Chuan Wan, Mary Y Hu, Yuanshuai Liu, Donghai Mei, Donald M Camaioni, Jian Zhi Hu, Johannes A Lercher
The reaction mechanism of solid-acid-catalyzed phenol alkylation with cyclohexanol and cyclohexene in the apolar solvent decalin has been studied using in situ (13)C MAS NMR spectroscopy. Phenol alkylation with cyclohexanol sets in only after a majority of cyclohexanol is dehydrated to cyclohexene. As phenol and cyclohexanol show similar adsorption strength, this strict reaction sequence is not caused by the limited access of phenol to cyclohexanol, but is due to the absence of a reactive electrophile as long as a significant fraction of cyclohexanol is present...
June 19, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28612283/cell-laden-microgel-prepared-using-a-biocompatible-aqueous-two-phase-strategy
#2
Yang Liu, Natalia Oshima Nambu, Masahito Taya
Microfluidic methods are frequently used to produce cell-laden microgels for various biomedical purposes. Such microfluidic methods generally employ oil-water systems. The poor distribution of crosslinking reagents in the oil phase limits the available gelation strategies. Extracting the microgel from the oil-phase also reduces its production efficiency. In this study, an aqueous two-phase system (ATPS) involving dextran (DEX) and polyethylene glycol (PEG) was used to prepare cell-laden microgel. This avoided the problems associated with an oil phase...
September 2017: Biomedical Microdevices
https://www.readbyqxmd.com/read/28602294/probing-the-specificity-of-polyurethane-foam-as-a-solid-phase-extractant-extractability-governing-molecular-attributes-of-lipophilic-phenolic-compounds
#3
Jie Han, Zhi Cao, Wei Qiu, Wei Gao, Jiangyong Hu, Baoshan Xing
The long-proposed use of open-cell polyurethane foam (PUF) as a convenient 'solid-phase extractant' for aqueous organic compounds has been hindered by a critical lack of understanding on the underlying specificity of its extraction mechanism. In this work, we tasked ourselves to understand the hierarchy of molecular structure, properties, and partitioning characteristics of compounds in PUF and aqueous phase by targeting lipophilic phenolic compounds (LPCs) as a group of primary targets for PUF extraction. Using six structurally related bisphenol analogs as comparative probes, we identified molecular lipophilicity and H-bond acidity as key molecular attributes that governed their extractability by PUF...
September 1, 2017: Talanta
https://www.readbyqxmd.com/read/28567247/polysulfide-1-oxides-react-with-peroxyl-radicals-as-quickly-as-hindered-phenolic-antioxidants-and-do-so-by-a-surprising-concerted-homolytic-substitution
#4
Jean-Philippe R Chauvin, Evan A Haidasz, Markus Griesser, Derek A Pratt
Polysulfides are important additives to a wide variety of industrial and consumer products and figure prominently in the chemistry and biology of garlic and related medicinal plants. Although their antioxidant activity in biological contexts has received only recent attention, they have long been ascribed 'secondary antioxidant' activity in the chemical industry, where they are believed to react with the hydroperoxide products of autoxidation to slow the auto-initiation of new autoxidative chain reactions. Herein we demonstrate that the initial products of trisulfide oxidation, trisulfide-1-oxides, are surprisingly reactive 'primary antioxidants', which slow autoxidation by trapping chain-carrying peroxyl radicals...
October 1, 2016: Chemical Science
https://www.readbyqxmd.com/read/28511540/effects-of-water-extractable-arabinoxylan-on-the-physicochemical-properties-and-structure-of-wheat-gluten-by-thermal-treatment
#5
Yunping Zhu, Yu Wang, Jinlong Li, Fang Li, Chao Teng, Xiuting Li
This study investigated the effects of water-extractable arabinoxylan (WEAX) on gluten by thermal treatment. Fourier transform infrared spectroscopy (FTIR) results showed that heating significantly decreased β-sheets and β-turn structures in gluten proteins between 25 and 55 °C. The addition of WEAX caused a transition from β-turn to β-sheets at >55 °C. The ratio of weakly hydrogen-bonded β-sheets to strongly hydrogen-bonded β-sheets demonstrated an increasing trend with temperature increasing, but WEAX can hinder this process...
June 14, 2017: Journal of Agricultural and Food Chemistry
https://www.readbyqxmd.com/read/28494396/a-comparative-study-of-the-spectral-fluorometric-properties-and-photostability-of-natural-curcumin-iron-and-boron-complexed-curcumin
#6
Fatima Mohammed, Fiza Rashid-Doubell, Seamas Cassidy, Fryad Henari
Curcumin is a yellow phenolic compound with a wide range of reported biological effects. However, two main obstacles hinder the use of curcumin therapeutically, namely its poor bioavailability and photostability. We have synthesized two curcumin complexes, the first a boron curcumin complex (B-Cur2) and the second an iron (Fe-Cur3) complex of curcumin. Both derivatives showed high fluorescence efficiency (quantum yield) and greater photostability in solution. The improved photostability could be attributed to the coordination structures and the removal of β-diketone group from curcumin...
April 21, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/28485929/trans-metal-trapping-meets-frustrated-lewis-pair-chemistry-ga-ch2sime3-3-induced-c-h-functionalizations
#7
Marina Uzelac, Alan R Kennedy, Eva Hevia
Merging two topical themes in main-group chemistry, namely, cooperative bimetallics and frustrated-Lewis-pair (FLP) activity, this Forum Article focuses on the cooperativity-induced outcomes observed when the tris(alkyl)gallium compound GaR3 (R = CH2SiMe3) is paired with the lithium amide LiTMP (TMP = 2,2,6,6-tetramethylpiperidide) or the sterically hindered N-heterocyclic carbene (NHC) 1,3-bis(tert-butyl)imidazol-2-ylidene (I(t)Bu). When some previously published work are drawn together with new results, unique tandem reactivities are presented that are driven by the steric mismatch between the individual reagents of these multicomponent reagents...
May 9, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28451271/hydroxide-bridged-five-coordinate-dy-iii-single-molecule-magnet-exhibiting-the-record-thermal-relaxation-barrier-of-magnetization-among-lanthanide-only-dimers
#8
Jin Xiong, Hai-Yan Ding, Yin-Shan Meng, Chen Gao, Xue-Jing Zhang, Zhao-Sha Meng, Yi-Quan Zhang, Wei Shi, Bing-Wu Wang, Song Gao
A hydroxide-bridged centrosymmetric Dy(III) dimer with each Dy(III) being five-coordinated has been synthesized using bulky hindered phenolate ligands. Magnetic studies revealed that this compound exhibits a slow magnetic relaxation of a single-ion origin together with a step-like magnetic hysteresis of the magnetic coupled cluster. The thermal relaxation barrier of magnetization is 721 K in the absence of a static magnetic field, while the intramolecular magnetic interaction is very large among reported 4f-only dimers...
February 1, 2017: Chemical Science
https://www.readbyqxmd.com/read/28208574/complexation-of-phytochemicals-with-cyclodextrin-derivatives-an-insight
#9
REVIEW
Vasanti Suvarna, Parul Gujar, Manikanta Murahari
Natural compounds have been attracting huge attention because of their broad therapeutic properties with specificity in their action in human health care as functional foods, pharmaceuticals and nutraceuticals. However poor bioavailability and reduced bioactivity attributed to poor solubility and instability is the major drawback hindering the incorporation of these therapeutically potential molecules in novel drug delivery systems. Based on the findings of reported research investigations; complexation of poorly water soluble phytochemicals with cyclodextrins has emerged to be a promising approach to improve their aqueous solubility, stability, rate of dissolution and bioavailability...
April 2017: Biomedicine & Pharmacotherapy, Biomédecine & Pharmacothérapie
https://www.readbyqxmd.com/read/28182626/ultrasensitive-detection-of-serum-hepatitis-b-virus-by-coupling-ultrafiltration-dna-extraction-with-real-time-pcr
#10
Bin Wu, Feng Xiao, Peiwen Li, Yan Du, Jinqiong Lin, Kaihua Ming, Bin Chen, Xiuxia Lei, Banglao Xu, Dayu Liu
BACKGROUND: A simple and reliable DNA extraction of hepatitis B virus (HBV) is critical in developing an ultrasensitive detection method for HBV infection. Current commercially available serum Hepatitis B Virus (HBV) DNA extraction methods are time-consuming, expensive and/or require specialized equipment, which hinders wide adoption of clinical laboratories. This study offers a report on an ultrasensitive HBV DNA detection method by coupling serum HBV DNA extraction by ultrafiltration (UF) with real-time PCR (qPCR) detection...
2017: PloS One
https://www.readbyqxmd.com/read/28177637/synthesis-of-the-pentacyclic-core-of-citreamicin-%C3%AE
#11
Shawn Blumberg, Stephen F Martin
The citreamicins comprise a novel class of polycyclic xanthone natural products that have not yet yielded to total synthesis. A concise 11-step synthesis of the pentacyclic core of citreamicin η is now reported that features the use of a general approach for the synthesis of 1,4-dioxygenated xanthones. The synthesis also showcases improved techniques for effecting regioselective bromination of certain substituted phenols and coupling of acetylides with hindered ketones.
February 8, 2017: Organic Letters
https://www.readbyqxmd.com/read/28004081/determination-of-the-activity-signature-of-key-carbohydrate-metabolism-enzymes-in-phenolic-rich-grapevine-tissues
#12
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
#13
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
#14
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
#15
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
#16
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
#17
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
#18
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
#19
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
#20
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...
January 2017: Environmental Science and Pollution Research International
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