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141.
Daria Larowska Dr. Aleksandra Wojcik Dr. Marta Mazurkiewicz-Pawlicka Dr. Artur Malolepszy Dr. Leszek Stobiński Prof. Bronislaw Marciniak Dr. Anna Lewandowska-Andralojc 《Chemphyschem》2019,20(8):1054-1066
Non-covalent nanohybrids composed of cationic 5,10,15,20-tetra(4-trimethylammoniophenyl)porphyrin tetra(p-toluenesulfonate) (TMAP) and the graphene oxide sheets were prepared under two pH values (6.2 vs. 1.8). The TMAP molecule was positively charged, regardless of the pH value during preparation. However, protonation of the imino nitrogens increased the overall charge of the porphyrin molecule from +4 to +6 (TMAP4+ and TMAP6+). It was found that at acidic pH, interaction of TMAP6+ with GO was largely suppressed. On the other hand, results of FTIR, Raman spectroscopy, thermogravimetric analysis, atomic force microscopy (AFM) and elemental analysis confirmed effective non-covalent functionalization of graphene oxide with cationic porphyrin at pH 6.2. The TMAP4+-GO hybrids exhibited well defined structure with a monolayer of TMAP4+ on the GO sheets as confirmed by AFM. Formation of the ground-state TMAP4+-GO complex in solution was monitored by the red-shift of the porphyrin Soret absorption band. This ground-state interaction between TMAP4+ and GO is responsible for the static quenching of the porphyrin emission. Fluorescence was not detected for the nanohybrid which indicated that a very fast deactivation process had to take place. Ultrafast time-resolved transient absorption spectroscopy clearly demonstrated the occurrence of electron transfer from the photoexcited TMAP4+ singlet state to GO sheets, as proven by the formation of a porphyrin radical cation. 相似文献
142.
Mateusz Maszczyk Zuzanna Rzepka Jakub Rok Artur Beberok Dorota Wrzeniok 《Molecules (Basel, Switzerland)》2021,26(15)
Despite many advances in therapy, glioblastoma (GB) is still characterized by its poor prognosis. The main reason for this is unsuccessful treatment, which slightly extends the duration of remission; thus, new regimens are needed. One of many types of chemotherapeutics that are being investigated in this field is topoisomerase inhibitors, mainly in combination therapy with other drugs. On the other hand, the search for new anti-cancer substances continues. Neobavaisoflavone (NBIF) is a natural compound isolated from Psoralea corylifolia L., which possesses anti-oxidant, anti-inflammatory, and anti-cancer properties. The aim of this study was to evaluate the effect of NBIF in human U-87 MG glioblastoma cells in comparison to normal human NHA astrocytes, and to examine if it influences the activity of irinotecan, etoposide, and doxorubicin in this in vitro model. We demonstrated that NBIF decreases U-87 MG cells viability in a dose-dependent manner. Furthermore, we found that it inhibits cell growth and causes glutathione (GSH) depletion more intensely in U-87 MG cells than in astrocytes. This study also provides, for the first time, evidence of the potentialization of the doxorubicin effect by NBIF, which was shown by the reduction in the viability in U-87 MG cells. 相似文献
143.
Nonlinear Dynamics - Classical method of Lyapunov exponents spectrum estimation for a n-th-order continuous-time, smooth dynamical system involves Gram–Schmidt orthonormalization and... 相似文献
144.
Martín Soto Dr. Raquel G. Soengas Prof. Artur M. S. Silva Prof. Vicente Gotor-Fernández Prof. Humberto Rodríguez-Solla 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(57):13104-13108
In this work, the first example of a radical stereodivergent reaction directed towards the stereoselective synthesis of both (R*,R*)- and (R*,S*)-2,2′-biflavanones promoted by samarium diiodide is reported. Control experiments showed that the selectivity of this reaction was exclusively controlled by the temperature. It was possible to generate a variety of 2,2′-biflavanones bearing different substitution patterns at the aromatic ring in good-to-quantitative yields, being both stereoisomers of the desired compounds obtained with total or high control of selectivity. A mechanism that explains both the generation of the corresponding 2,2′-biflavanones and the selectivity is also discussed. The structure and stereochemistry determination of each isomer was unequivocally elucidated by single-crystal X-ray diffraction experiments. 相似文献
145.
Pham The Anh Artur Babiarz Adam Czornik Michal Niezabitowski Stefan Siegmund 《Mathematical Methods in the Applied Sciences》2020,43(13):7815-7824
In this paper, we establish some criteria for boundedness, stability properties, and separation of solutions of autonomous nonlinear nabla Riemann-Liouville scalar fractional difference equations. To derive these results, we prove the variation of constants formula for nabla Riemann-Liouville fractional difference equations. 相似文献
146.
Jacob J. Lacharity Dr. Artur K. Mailyan Karen Y. Chen Prof. Dr. Armen Zakarian 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(28):11460-11464
An asymmetric total synthesis of [13C4]-anatoxin-a ([13C4]- 1 ) has been developed from commercially available ethyl [13C4]-acetoacetate ([13C4]- 15 ). The unique requirements associated with isotope incorporation inspired a new, robust, and highly scalable route, providing access to 0.110 g of this internal standard for use in the detection and precise quantification of anatoxin-a in freshwater. A highlight of the synthesis is a method that leverages a cyclic iminium ion racemization to achieve dynamic kinetic resolution in an enantioselective Morita–Baylis–Hillman (MBH) cyclization. 相似文献
147.
Artur J. M. Valente Cesar M. C. Filho Adley Rubira Edvani C. Muniz Hugh D. Burrows 《Colloid and polymer science》2014,292(7):1665-1673
Equilibrium and transport properties have been investigated of ephedrines, a class of sympathomimetic amines, through cryogel membranes of poly(vinyl alcohol) (PVA). The effect of the PVA (10 to 18 % (w/v)) on the release properties of (1S,2R)-(+)-ephedrine hydrochloride has been discussed on the basis of partition–diffusion and power-law models. The effect of PVA concentration on the swelling degree of PVA–ephedrine matrices have been measured, allowing the estimation of the volume fraction of polymer in the gel. Ephedrine release rate constants, computed by using a first-order kinetics approach, have been modeled by using free-volume and hydrodynamic-scaling models. Differences in the release properties of the ephedrine isomers, (1S,2R)-(+)- and (1R,2S)-(?)-ephedrine as their hydrochlorides, have also been studied at different temperatures. The release kinetic constants and the corresponding activation energies show a marked discrimination between the two ephedrine isomers. This suggests that PVA cryogel membranes possess high potential for enantiomeric differentiation. 相似文献
148.
Silva AM Filipe P Seixas RS Pinto DC Patterson LK Hug GL Cavaleiro JA Mazière JC Santus R Morlière P 《The journal of physical chemistry. B》2008,112(37):11456-11461
In micellar solutions, one-electron reduction of (*)O 2 (-) radical-anions by 3-alkylpolyhydroxyflavones (FnH) with alkyl chains of n = 1, 4, 6, 10 carbons produces phenoxyl radicals ( (*)Fn) identical to those obtained by one-electron oxidation by (*)Br 2 (-) radical-anions or by repair of tryptophan radicals. In cetyltrimethylammonium bromide (CTAB), F1H localizes in the Stern layer, and alkyl chains of other FnH solubilize in the hydrophobic interior, interacting with cetyl tails. This interaction produces more compact micelles with lower intramicellar fluidity, as suggested by the increase in the pseudo-first-order rate constant of (*)Fn formation ( k 1) from approximately 390 s (-1) for n = 1 to 610 s (-1) for n = 10, leading to an intramicellar bimolecular rate constant of 1 x 10 (5) M (-1) s (-1). Additionally, (*)F1 and (*)F4 decay by intermicellar bimolecular reaction (2 k = 20 and 2 x 10 (5) M (-1) s (-1), respectively) whereas other (*)Fn radicals are stable over seconds due to increased localization with regards to the Stern layer. In contrast, the thick uncharged hydrophilic palisade layer and the compact hydrophobic core of Triton X100 micelles are responsible for a much higher microviscosity resulting in a decrease in k 1 from approximately 15.6 s (-1) for n = 1 to 9.6 s (-1) for n = 10. 相似文献
149.
Valente AJ Burrows HD Cruz SM Pereira RF Ribeiro AC Lobo VM 《Journal of colloid and interface science》2008,323(1):141-145
Aggregation properties of sodium dodecyl sulfate (SDS) in the presence of cerium(III) chloride, at various temperatures (298.15-323.15 K) have been measured by the electrical conductance technique. The experimental data on aqueous solutions as a function of SDS concentration show the presence of two inflexion points indicating the presence of two distinct interaction mechanisms: the first, occurring at SDS concentrations below the critical micelle concentration of the pure surfactant, which can be explained by the formation of aggregates between dodecyl sulfate (DS-) and Ce(III), while the second one, at SDS concentrations around the critical micelle concentration (cmc) of the pure surfactant which is due to the SDS micellization. The aggregation between DS- and Ce(III) was confirmed by static light scattering. The binding ratio of DS-/Ce(III) changes from 6 to 4, shows a slight dependence on the Ce(III) concentration and is independent of the temperature. The thermodynamic micellization parameters, Gibbs energy, enthalpy and entropy of micellization were calculated on the basis of the experimental data for the aggregation concentration, and the degree of counterion dissociation of the micelles. The SDS micellization is energetically favoured by increasing either the concentration of CeCl3 or the temperature. Such behaviour is clearly dominated by a decrease of the micellization (exothermic) enthalpy. The entropy of micellization approaches zero as the cerium(III) chloride concentration and temperature increase. 相似文献