Electromembrane extraction is affected by acid–base equilibria of the extracted substances as well as coupled equilibria associated with the partitioning of neutral substances to the supported liquid membrane. A theoretical model for this was developed and verified experimentally in the current work using pure 2‐nitrophenyl octyl ether as supported liquid membrane. From this model, extraction efficiency as a function of pH can be predicted. Substances with log P < 0–2 are generally extracted with low efficiency. Substances with log P > 2 are generally extracted with high efficiency when acceptor pH < pKaH ? log P. Twelve basic drug substances (2.07 < log P < 6.57 and 6.03 < pKaH < 10.47) were extracted under different pH conditions with 2‐nitrophenyl octyl ether as supported liquid membrane and fitted to the model. Seven of the drug substances behaved according to the model, while those with log P close to 2.0 deviated from prediction. The deviation was most probably caused by deprotonation and ion pairing within the supporting liquid membrane. Measured partition coefficients (log P) between 2‐nitrophenyl octyl ether and water, were similar to traditional log P values between n‐octanol and water. Thus, the latter have potential for pKaH ? log P predictions. 相似文献
The reaction of M(OAc)2 with 2,2′-bis(2-hydroxybenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl (H2L1) allows the synthesis of 2,2′-bis(2-oxidobenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl complexes of Cu(II) (CuL1), Co(II) (CoL1) and Ni(II) (NiL1) that were characterized by elemental analysis, FTIR spectroscopy and for CuL1 also by X-ray crystallography verifying a tetradentate binding mode of L1 via an (ONNO) motif of the two phenolic oxygen atoms and two azomethine nitrogen atoms. Recrystallization from a solvent mixture of dichloromethane and methanol promotes the formation of methanol adducts. Different binding modes of the methanol–complex were investigated using density functional theory calculations and binding energies, and thermodynamic data of the interaction are reported. The results show that the favored interaction occurs when the methanol molecule acts as a Lewis acid weakly binding via an O–H···O hydrogen bridge to a phenoxide moiety leading to an elongation of the respective M–O bond.
Trifolium balansae (Leguminosae) yielded a phytylester, phytyl-1-hexanoate, three steroids, stigmast-5-ene-3 beta,26-diol, stigmast-5-ene-3-ol and campesterol, and an alcohol, pentacosanol which were reported for the first time from T.balansae. The structures of the isolates were determined by 1D and 2D NMR techniques and MS spectroscopy. Compounds 1-5 were tested for their enzyme tyrosinase activity. While compounds 1 and 5 did not show any inhibition against the enzyme tyrosinase, compounds 2, 3, and 4 exhibited potent inhibition against tyrosinase. Highly potent (IC50 = 2.39 microM) inhibition was found by compound 2, when compared with the standard tyrosinase inhibitors Kojic acid and L-mimosine. 相似文献
The conformational changes of the bovine lens protein "α-crystallin" have been investigated in the presence of the photosensitizer Rose Bengal (RB), in the dark as well as after visible light irradiation. Absorption and fluorescence emission spectra of RB [5 × 10−6 m ] and Fourier transform-IR spectra of α-crystallin [5 mg mL−1] were significantly altered upon RB α-crystallin complex formation. RB was found to bind to α-crystallin in a molecular pocket characterized by a low polarity, with Trp most likely involved in this interaction. The binding constant ( K b) has been estimated to be of the order of 2.5 (mg/mL)−1. The intrinsic fluorescence of α-crystallin was quenched through both dynamic and static mechanisms. Light-induced photosensitized effects showed structural modifications in α-crystallin, including tertiary and secondary structure (an increase in unordered structure) alterations. Notwithstanding those photoinduced structural variations detected in α-crystallin when complexed with RB, the protein still retains its ability to play the role of chaperone for β-crystallin. 相似文献
In the present article, tyrosinase inhibition studies on fifteen diterpenoid alkaloids, with lycoctonine skeleton, and their semisynthetic derivatives 1-15 and six napelline-type compounds 16-21 are discussed. Their structure-activity relationship for tyrosinase inhibition is also discussed. These activities were compared with two referenced tyrosinase inhibitors, kojic acid and L-mimosine. The study showed that lappaconitine HBr (1) is the most potent member of the series (IC50 = 13.30 microM). 相似文献
It is shown for the first time that a representative member of the "cesium-selective" calix[4]arene-crown-6 family exhibits a high affinity for Fr+ ion. In the investigation, the transport of 221Fr+ and Cs+ ions by calix[4]arene-bis(benzocrown-6) from an aqueous sodium nitrate solution into the water-immiscible diluent 1,2-dichloroethane was measured and compared to address the question of selectivity of the calix-crown-6 cavity toward alkali metal ions of increasing size. Selective separation of 221Fr+ from its parent 225Ac and from the matrix Na+ ions was demonstrated. Higher distribution ratios were obtained than those for the Cs+ ion. The extraction equilibria were determined for the case of the Cs+ ion, and the same equilibria were shown to be applicable to the case of Fr+ with inclusion of additional competitive effects. 相似文献
AbstractUrease inhibition potential of compound (1), guaiane-type sesquiterpene (2), confertin (3) and scopoletin (4) was carried out with high throughout mechanism-based assay. These compounds were isolated from Hypochaeris radicata L., an Asteraceae family member. The pure compounds were screened for their urease and carbonic anhydrase inhibitory activities. The ethyl acetate fractions were subjected to column chromatography, which resulted in the isolation and purification of four compounds (1–4). On evaluation, compounds (1–4) exhibited selective activity against urease enzyme with an IC50 value of 180.11 ± 2.00, 27.18 ± 0.80, 24.12 ± 0.2 and 30.12 ± 1.10 µM respectively. The compounds (1–4) were found to be inactive against carbonic anhydrase enzyme. Thiourea was used as standard inhibitor (21 ± 0.14 µM) of urease enzyme. 相似文献
Journal of Thermal Analysis and Calorimetry - In this study, the stability, thermal conductivity and viscosity of carbide-derived carbon antifreeze thermal fluids were explored. The study also... 相似文献