Five new furofurans lignans, Brasesquilignan A-E (1-5), were isolated from the aqueous ethanol extract of Selaginella braunii Baker. Their structures were elucidated by extensive analysis of NMR and ...HRESIMS data. Their absolute configurations were determined by CD spectra, enzymatic hydrolysis, and GCMS analysis. Furthermore, all compounds were evaluated for anti-proliferative activities against various human cancer cellsin vitro. Compounds 2 and 3 exhibited weak inhibitorypotency against five human cancer cells.
We have recently derived a beta-N-acetylhexosaminidase, BbhI, from Bifidobacterium bifidum JCM 1254, which could regioselectively synthesize GlcNAcbeta1-3Galbeta1-4Glc with a yield of 44.9%. Here, ...directed evolution of BbhI by domain-targeted mutagenesis was carried out. Firstly, the GH20 domain was selected for random mutagenesis using MEGAWHOP method and a small library of 1300 clones was created. A total of 734 colonies with reduced hydrolytic activity were isolated, and three mutants with elevated transglycosylation yields, GlcNAcbeta1-3Galbeta1-4Glc yields of 68.5%, 74.7%, and 81.1%, respectively, were obtained. Subsequently, nineteen independent mutants were constructed according to all the mutation sites in these three mutants. After transglycosylation analysis, Asp714 and Trp773 were identified as key residues for improvement in transglycosylation ability and were chosen for the second round of directed evolution by site-saturation mutagenesis. Two most efficient mutants D714T and W773R that acted as trans-beta-N-acetylhexosaminidase were finally achieved. D714T with the substitution at the putative nucleophile assistant residue Asp714 by threonine showed high yield of 84.7% with unobserved hydrolysis towards transglycosylation product. W773R with arginine substitution at Trp773 residue locating at the entrance of catalytic cavity led to the yield up to 81.8%. The k.sub.cat/K.sub.m values of D714T and W773R for hydrolysis of pNP-beta-GlcNAc displayed drastic decreases. NMR investigation of protein-substrate interaction revealed an invariable mode of the catalytic cavity of D714T, W773R, and WT BbhI. The collective motions of protein model showed the mutations Thr714 and Arg773 exerted little effect on the dynamics of the inside but a large effect on the dynamics of the outside of catalytic cavity.
A new spiropyran containing a cationic 3Ð-indolium substituent and methoxy groups at positions 5 and 5" of the indoline cycles was synthesized. Hydrolysis of this compound was observed during ...crystallization from EtOH, leading to the formation of protonated merocyanine form of spiropyran containing a free formyl group. The hydrolysis product was characterized by X-ray structural analysis, the intermolecular interactions in crystal were studied with the CrystalExplorer 21.5 software suite. Quantum-chemical modeling based on the Fukui function distribution was used to establish the preferred site for nucleophilic attack, and a mechanism for hydrolysis was proposed.
This study utilizes Aspen Plus chemical process simulation software (V11), applies uniform nucleation theory and growth kinetics equations, and explores the particle formation mechanism of TiClsub.4 ...hydrolysis to prepare nano TiOsub.2. In the water/ethanol system, the effects of the reaction time, reaction temperature, water addition, pH value, and ethanol amount on the crystal nucleation rate and TiOsub.2 particle distribution (PSD) were studied in detail by adding triethanolamine dropwise and using the Aspen Plus chemical process software simulation calculation method. The calculation results indicate that at room temperature, the formation of TiOsub.2 crystal nuclei mainly occurs in the first 300 s and then enters the growth stage. The reaction was carried out under neutral conditions at room temperature for 4 h in 1 mL TiClsub.4, 6 mL Csub.6Hsub.15NOsub.3, 15 mL Hsub.2O, and 30 mL Csub.2Hsub.5OH. The maximum number of particles reached 195 mesh per cubic micrometer, and the particle size after crystal nucleus growth was smaller, with a Dsub.50 of 6.15 nm. The distribution curve shows a normal distribution, which is basically consistent with the experimental results. When studying various factors, it was found that controlling the reaction time within 60 min and maintaining the reaction temperature at room temperature can reduce the particle size Dsub.50 to 2.44 nm. Continuing to adjust the amount of water added, it was found that at 1 mL, Dsub.50 decreased again to 0.19 nm. Adjusting the pH value found that maintaining the neutrality did not change the particle size. Continuing to adjust ethanol, it was found that adding an appropriate amount of ethanol promoted nucleation and growth. At 4 mL, the maximum number of particles reached 199 mesh per cubic micrometer, but Dsub.50 slightly increased to 0.24 nm.
One-hundred percent stereo-complexation in poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) fibers with non-equivalent molecular weights could be achieved via thermal treatment. Stereo-complexed ...polylactide (sc-PLA) fibers exhibited excellent hydrolysis resistance and thermal resistance. Till now, preparation of sc-PLA fibers with satisfactory qualities required both PLLA and PDLA with equivalently high molecular weights. Moreover, the high-molecular-weight PDLAs are expensive, restricting industrial-scale production and applications of sc-PLA products. In this study, equal-weight mixtures of low-molecular-weight PDLA (L-PDLA) and high-molecular-weight PLLA (H-PLLA) were melt spun into sc-PLA fibers and then completely stereo-complexed via thermal treatment. The hydrolysis resistance of L3/D1 fibers PLLA (M.sub.v = 3.0 x 10.sup.5)/PDLA (M.sub.v = 1.0 x 10.sup.5) was similar to that of L3/D3 fibers PLLA (M.sub.v = 3.0 x 10.sup.5)/PDLA (M.sub.v = 3.2 x 10.sup.5), but much higher than that of L3 fibers PLLA (M.sub.v = 3.0 x 10.sup.5). Melting temperature and softening temperature of L3/D1 fibers (223 and 126 °C) were also similar to those of L3/D3 fibers (224 and 131 °C), but higher than that of L3 fibers (172 and 72 °C). Utilizing H-PLLA and L-PDLA to prepare sc-PLA fibers with excellent performance is conducive to the wide industrial application of sc-PLA.
This study utilized the exceptional optical and electrical properties of polypyrrole (Ppy) to fabricate high-performance optoelectronic devices. The synthesis of the porous-spherical ...Crsub.2Osub.3-Cr(OH)sub.3-Ppy/Ppy nanocomposite thin film was achieved by preparing a second thin film of Crsub.2Osub.3-Cr(OH)sub.3-Ppy on the initial Ppy film using Ksub.2Crsub.2Osub.7 as an oxidant. The nanocomposite’s properties were thoroughly characterized, including XRD and optical absorbance analyses. The XRD analysis showed that the crystalline size of the nanocomposite was 20 nm, while optical absorbance analysis demonstrated that the nanocomposite had a higher absorbance in a wide optical range compared to Ppy nanomaterials, as evidenced by the enhancement in bandgap (Eg) value from 3.33 eV for Ppy to 1.89 eV for Crsub.2Osub.3-Cr(OH)sub.3-Ppy. The fabricated nanocomposite thin film exhibited excellent light-sensing behavior, as evidenced by the evaluation of Jsub.ph values under different light conditions and various monochromatic lights with a detectivity (D) of 3.6 × 10sup.6 Jones (at 340 nm). The device demonstrated its potential as a solar cell, with a short circuit current (Jsub.SC) of 13 µA and an open circuit voltage (Vsub.OC) of 1.91 V. Given the nanocomposite’s low cost, high technical production, and superior optoelectronic properties, it has significant potential for use in commercially available high-tech devices.
Triarylantimony dibromides reacted with sodium nitrate, thiocyanate, and fluoride in aqueous acetone at room temperature to give bridged dinuclear antimony compounds ...(4-MeC.sub.6H.sub.4).sub.3SbONO.sub.2.sub.2O, (Ph.sub.3SbNCS).sub.2O, (3-MeC.sub.6H.sub.4).sub.3SbNCS.sub.2O, and (4-MeC.sub.6H.sub.4).sub.3SbNCS.sub.2O and mononuclear derivatives (2-MeC.sub.6H.sub.4).sub.3Sb(NCS).sub.2 and (3-FC.sub.6H.sub.4).sub.3SbF.sub.2. The antimony atoms in these compounds have a distorted trigonal-bipyramidal configuration with electronegative atoms in the axial positions.
Structure of the product of imidazolidine (1,3,5,7-tetra-tert-butyloctahydro-1H,4аH-imidazo4E,5E:5,6dioxino2,3-dimidazole) ether cocrytallization with 1,3-di-tert-butylimidazol-2-one and ...1,3-di-tert-butylimidazolin-2-ylidene was established by single crystal X-ray diffraction. The co-crystal is the product of the oxidation-hydrolysis of the 1,3-di-tert-butylimidazolin-2-ylidene complex with AlH.sub.3.
N-Acetylmuramyl-L-alanyl-D-isoglutamine alpha-phenylglycoside was synthesized from alpha-phenyl-D-glucosaminide peracetate, which was obtained by fusing beta-D-glucosamine pentaacetate with phenol ...and zinc chloride followed by deacetylation. alpha-Phenyl-N-acetylglucosaminide was converted in two steps into 4,6-O-isopropylidene-N-acetyl-D-muramic acid alpha-phenylglycoside, which was condensed with L-Ala-D-iGln benzyl ether using the activated ester method. Sequential removal of glycopeptide protecting groups via acid hydrolysis and catalytic hydrogenolysis gave the target product.
For the purpose of utilizing decomposition component analysis (DCA) for fault diagnosis of SF 6 gas insulated equipment further, SF 6 spark decomposition experiments under different spark energies ...were carried out on the frequency and energy-controllable SF 6 spark decomposition test platform. The amount of gaseous by-products of SF 6 sparks were measured by GC-MS. Atomic relative content of solid products were analyzed by XPS. The main gaseous by-products of SF 6 sparks include SOF 2 , SO 2 F 2 , SOF 4 , SO 2 , as well as CF 4 , and the amount of them increases with spark number. The amount of SOF 2 increases with single spark energy and tend to be saturated, while SO 2 F 2 decreases. It depends strongly on the differences of both the energies consumed in SF 6 dissociation process into SF 5 , SF 4 , SF 2 , and hydrolysis rates of SOF 4 and SF 4 . Besides, CF 4 increases with single spark energy and tend to be saturated, and SOF 4 shows a linear dependence, but SO 2 is hardly influenced by spark energy distinctly. In solid products, relative content of F, S, Fe, W increases with spark energy. The main existence forms of Fe include FeS, FeF 3 , Fe 2 O 3 , and pure Fe, thereunto the relative content of FeS and pure Fe increases with spark energy.
![Converting a [beta]-N-acety...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0175-7598/small "Converting a [beta]-N-acetylhexosaminidase into two trans-[beta]-N-acetylhexosaminidases by domain-targeted mutagenesis")
![Porous-Spherical Cr[sub.2]O...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2079-6412/small "Porous-Spherical Cr[sub.2]O[sub.3]-Cr[sub.3]-Polypyrrole/Polypyrrole Nanocomposite Thin-Film Photodetector and Solar Cell Applications")
