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111.
Eva Nezbedova Vladimir Pospisil Petr Bohaty Bohumil Vlach 《Macromolecular Symposia》2001,170(1):349-357
The commercial grade of isotactic polypropylene (iPP) homopolymer (Mosten 58.412) was doped with different amount of β‐nucleant (NJ Star NU‐100). The fracture behavior of the β‐iPP was examined on injection‐ and compression moulded specimens under dynamic load. The fracture toughness KId and JId, respectively, were used to describe the fracture behavior. The influence of processing conditions (the mould temperature and injection velocity) and the distance from the gate were also taken into the consideration. Structural changes during processing were characterized by DSC analysis. It was found that: (i) the amount of 0.03% of β‐nucleant gives the highest toughness (ii) the toughness of the β‐iPP depends on the distance from the moulding gate and on the processing conditions (iii) the degree of crystallinity correlates with the fracture parameters. 相似文献
112.
Alena Ryšavá Michaela Psotová Pavel Kosina Bohumil Zálešák Jitka Ulrichová Jitka Vostálová 《Photochemistry and photobiology》2017,93(5):1240-1247
Quercetin, one of the most abundant polyphenols in the plant kingdom has been shown to be photodegraded on exposure to UV light. Despite the fact, it is a component of several dermatological preparations. Its phototoxic potential has not been evaluated to date. The aim of this study was to assess whether photo‐induced degradation of quercetin is linked to phototoxic effects on living cells. Its dihydro derivative, taxifolin, was included in the study. For evaluation, the 3T3 Neutral Red Uptake Phototoxicity Test according to OECD TG 432 was used. To better approximate human skin, HaCaT keratinocytes, normal human epidermal keratinocytes and dermal fibroblasts were used, apart from the Balb/c 3T3 cell line. Quercetin showed a dose‐dependent photodegradation in aqueous and organic environments and a phototoxic effect on all used cells. Quercetin pretreatment and following UVA exposure resulted in increased reactive oxygen species production and intracellular glutathione level depletion in human dermal fibroblasts. Taxifolin was found completely nonphototoxic and photostable. As only in vitro methodology was used, further studies using 3D skin models and/or human volunteers are needed to confirm whether exposure to sunlight, tanning sunbeds and/or phototherapy in people using cosmetics containing quercetin is a health risk. 相似文献
113.
Stíbr B Holub J Bakardjiev M Janousek Z 《Dalton transactions (Cambridge, England : 2003)》2007,(5):581-584
Alkynes R(1)R(2)C(2) react with the neutral monocarbaborane arachno-4-CB(8)H(14) (1) at elevated temperatures (115-120 degrees C) under the formation of the derivatives of the ten-vertex dicarbaborane nido-5,6-C(2)B(8)H(12) (2) of general formula 9-Me-5,6-R1,R2-nido-5,6-C(2)B(8)H(9) (where R1,R2 = H,H 2a; Me,Me 2b; Et,Et 2c, H,Ph 2d, and Ph,Ph 2e) in moderate yields (26-52%). Side reaction with PhC(2)H also yields 1-Ph-6-Me-closo-1,2-C(2)B(8)H(8) (3d). In contrast, the reaction between [arachno-4-CB(8)H(13)](-) anion ((-)) and PhC(2)H produces a mixture of the closo anions [1-CB7H8]- (4-) and [1-CB6H7]- (5-) (yields 32 and 24%, respectively). Individual compounds were isolated and purified by liquid chromatography and characterized by NMR spectroscopy ((11)B, (1)H and (13)C) combined with two-dimensional [(11)B-(11)B]-COSY and (1)H-{(11)B(selective)}NMR techniques. 相似文献
114.
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116.
Bohumil Dolenský Jaroslav Kvíčala Oldřich Paleta Jan Lang Hana Dvořáková Jan Čejka 《Magnetic resonance in chemistry : MRC》2010,48(5):375-385
A new three‐component cyclisation reactions of methyl 3,3,3‐trifluoropyruvate, 2‐aminobenzylamine and oxo compounds afforded tetrahydropyrroloquinazolinones of the types 4 and 5 as mixtures of regio‐ and stereoisomers. Whereas standard 1D NMR spectroscopy was used for a facile assignment of the cyclization regioisomers, a combination of homo (proton–proton) and heteronuclear (proton–fluorine) NOE experiments allowed the determination of the relative configuration on stereogenic centres. The structure of some compounds was also confirmed by the X‐ray diffraction. Adaptation of the 1D double‐pulsed field‐gradient spin‐echo NOE for a heteronuclear case is presented. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
117.
Václav Šícha Bohumil Štíbr Bohumír Grüner Clara Viñas 《Journal of organometallic chemistry》2009,694(11):1599-281
The treatment of 1,2-, 1,7- and 1,12-carbaborane lithiated isomers with [3,3′-Co-8-(CH2CH2O)2-(1,2-C2B9H10)-(1′,2′-C2B9H11)] (1) at molar ratios 1:1 or 1:2 at room temperature in THF leads generally to the formation of a series of orange double-cluster mono and dianions. These were characterized by NMR and MS methods as [1′′-X-1′′,2′′-closo-C2B10H11]−, [2]−; [1′′-X-1′′,7′′-closo-C2B10H11]−, [3]− and [1′′-X-1′′,12′′-closo-C2B10H11], [4]− for the monoanions, whereas [1′′,2′′-X2-1′′,2′′-closo-C2B10H10]2−, [2]2−; [1′′,7′′-X2-1′′,7′′-closo-C2B10H10]2−, [3]2−; and [1′′,12′′-X2-1′′,12′′-closo-C2B10H10]2−, [4]2− for the dianions (where X = 3,3′-Co-8-(CH2CH2O)2-(1,2-C2B9H10)-1′,2′-(C2B9H11)). Moreover, these borane-cage subunits can be easily modified via attaching variable substituents onto cage carbon and boron vertices, which makes these compounds structurally flexible potential candidates for BNCT of cancer and HIV-PR inhibition. 相似文献
118.
Bohumil Proksa Richard Hercek Tibor Liptaj Nada Prónayová 《Monatshefte für Chemie / Chemical Monthly》2009,13(1):485-487
Abstract
A new compound was isolated from the reaction mixture after O-demethylation of 6-O-acetyl-10α-acetoxycodeine with boron tribromide. The structure of this compound, 10α-hydroxy-β-isomorphine, was elucidated by spectral data, and its spatial arrangement was deduced from an NOE experiment. Capillary zone electrophoresis was used for separation of morphine and its 10-hydroxy analogues. 相似文献119.
Bakardjiev M Štíbr B Holub J Růžička A Padělková Z 《Dalton transactions (Cambridge, England : 2003)》2012,41(23):7151-7155
Reactions between the mesitylene (mes) dication [(η(6)-mes)(2)Fe](2+) (1a) [(PF(6)(-))(2) salt] and lithium o-carboranes Li[1-R-1,2-C(2)B(10)H(11)] (2) (R = H, 2a; Me, 2b; Ph, 2c) at low temperature (-60 °C, 1 h, followed by stirring for 2 h at r.t.) in THF resulted in a clean addition of the corresponding carborane anions to one of the unsubstituted arene sites in 1a, forming a series of orange monocations of general structure [(η(5)-mes-exo-6-{2-R-1,2-C(2)B(10)H(11)})Fe(η(6)-mes)](+) (3) (R = H, 3a; Me, 3b; Ph, 3c) which were isolated as PF(6)(-) salts (3PF(6)) in yields ranging 50-75%. Individual complexes were obtained on purification by LC or preparative TLC on a silica gel substrate, using MeCN-CH(2)Cl(2) mixtures as the mobile phase. Interestingly, the room-temperature reaction between 2a (threefold excess) and 1a(PF(6))(2) with a reverse order of addition of the reaction components yielded an orange salt [(η(5)-mes-exo-6-{1,2-C(2)B(10)H(11)})Fe(η(6)-mes)](+)[closo-nido-H(11)B(10)C(2)-C(2)B(10)H(12)](-) (3acCA) (cCA = conjucto-carborane anion = [closo-nido-H(11)B(10)C(2)-C(2)B(10)H(12)](-)) as a sole product in 71% yield. The formation of this conjucto anion can be taken as a strong support for the participation of a radical-chain mechanism in the ostensible nucleophilic addition which we suppose to be initiated by the formation of the [(mes)(2)Fe(+)]˙ radical cation. The structures of both 3PF(6) and 3acCA have been established by X-ray diffraction and the constitution of all compounds isolated is in agreement with elemental analyses, multinuclear NMR data, and MS spectra. 相似文献
120.
Non-volatile matrices which cannot diffuse into the graphite walls of an electro-thermal atomizer (as obtained by direct sampling of solids, injection of solutions into tubes with pyrolytic coatings or with a hydrophobic film) make a “miniplatform” in the centre of the atomizing tube. A delay in the temperature increase of this platform at the beginning of the atomization step compared to that of the atomizer walls causes enhancement of the peak height sensitivity. This was proven by atomization of nanogram quantities of copper and iron from solutions of aluminium salts. 相似文献