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121.
Tyrosinase immobilized magnetic nanobeads for the amperometric assay of enzyme inhibitors: application to the skin whitening agents 总被引:1,自引:0,他引:1
The immobilization of tyrosinase onto glutaraldehyde activated streptavidine magnetic particles and subsequent retention onto a magnetized carbon paste electrode for the amperometric assay of tyrosinase inhibitors is described. Tyrosine was used as substrate as it is the first substrate in the melanogenesis process. The sensing mode is based on monitoring the decrease of the amperometric signal corresponding to the electrochemical reduction of dopaquinone enzymatically generated. This current decrease is due to the presence of inhibitors acting directly on the enzyme or inhibitors acting on the product of the enzymatic reaction, i.e. dopaquinone. The methodology is designed for the evaluation of the inhibitory potency of the most frequently used active substances in cosmetic marketed products against hyperpigmentation such as kojic acid, azelaic acid and benzoic acid. These compounds bind to the tyrosinase active center. Ascorbic acid is also investigated as it interrupts the synthesis pathway of melanin by reducing the melanin intermediate dopaquinone back to l-dopa. By comparing the obtained IC50, under the same experimental conditions, the order of their inhibitory potency was: kojic acid (IC50 = 3.7 × 10−6 M, Ki = 8.6 × 10−7 M), ascorbic acid (IC50 = 1.2 × 10−5 M), benzoic acid (IC50 = 7.2 × 10−5 M, Ki = 2.0 × 10−5 M) and azelaic acid (IC50 = 1.3 × 10−4 M, Ki = 4.2 × 10−5 M) in close agreement with literature spectrophotometric inhibition data using the soluble tyrosinase. 相似文献
122.
For dynamic scheduling of multi-class systems where backorder cost is incurred per unit backordered regardless of the time
needed to satisfy backordered demand, the following models are considered: the cost model to minimize the sum of expected
average inventory holding and backorder costs and the service model to minimize expected average inventory holding cost under
an aggregate fill rate constraint. Use of aggregate fill rate constraint in the service model instead of an individual fill
rate constraint for each class is justified by deriving equivalence relations between the considered cost and service models.
Based on the numerical investigation that the optimal policy for the cost model is a base-stock policy with switching curves
and fixed base-stock levels, an alternative service model is considered over the class of base-stock controlled dynamic scheduling
policies to minimize the total inventory (base-stock) investment under an aggregate fill rate constraint. The policy that
solves this alternative model is proposed as an approximation of the optimal policy of the original cost and the equivalent
service models. Very accurate heuristics are devised to approximate the proposed policy for given base-stock levels. Comparison
with base-stock controlled First
Come
First
Served (FCFS) and Longest
Queue (LQ) policies and an extension of LQ policy (Δ policy) shows that the proposed policy performs much better to solve the service models under consideration, especially
when the traffic intensity is high. 相似文献
123.
Zeynep Serinyel Guillaume Dayma Valentin Glasziou Maxence Lailliau Philippe Dagaut 《Proceedings of the Combustion Institute》2021,38(1):329-336
Pyrolysis of diethyl (C4), di-n-propyl (C6), di-isopropyl (C6) and di-n-butyl (C8) ethers were studied in a jet-stirred reactor between 720 and 1140 K, at 10 atm with an initial ether mole fraction of 0.1%. Major common pyrolysis products were observed to be CO, CH4, H2, and C2H4. All ethers produced the n/2 alcohol and olefin as products of molecular reaction to a small extent. Under pyrolysis conditions at 10 atm, hydrogen abstraction reactions by H atoms and CH3 radicals were found to be important. Acetylene and benzene were formed for all ethers when T > 1000 K. A kinetic mechanism is used to represent these results. This study shows that there is need of systematic studies in determining site specific rate constants of important fuel related reactions of ethers. 相似文献
124.
Bahadir Altintas 《Journal of Physics and Chemistry of Solids》2011,72(11):1325-1329
Transition metal based monosilicide compounds (CrSi and RhSi) have been investigated theoretically from ab initio calculations. The structural and electronic band calculations of CrSi and different phases of RhSi crystals show that the metallic property and hypothetically constructed structures of RhSi(Pnma) under different pressures from 0 GPa to 75 GPa show a certain difference only along Γ–Z directions of the high symmetry points of first Brillouin zone. The character of the bands around fermi level was determined by partial density of state calculations. 相似文献
125.
The basic aim of this work is to design a new tridiagonal matrix enhanced multivariance products representation (TMEMPR) which uses not Cartesian vectors but matrices as the support entities. What we obtain after the construction of the representation has been a singular value decomposition like structure where the core matrix becomes a block tridiagonal matrix in contrast to the diagonal and tridiagonal matrix structures of the singular value decomposition of matrices and TMEMPR respectively. We have used support matrices in the construction and not directly orthogonality of the constructed support matrices but block orthogonality which means the mutual ortho normality of the columns of produced support matrices. Certain confirmative implementations finalize the paper. 相似文献
126.
127.
128.
Zeynep Demircioğlu Çiğdem Albayrak Kaştaş Orhan Büyükgüngör 《Molecular Crystals and Liquid Crystals》2017,656(1):169-184
The title compound was isolated and investigated by experimental X-ray diffraction method and density functional theory (DFT) calculational properties and spectroscopic methodologies. The experimental investigations of the compound indicated the molecule seems to be in enol form. DFT calculations are performed both for enol and keto tautomers of the title compound. Additionally chemical activity, electronic transmission and property effect on different solvents, molecular electrostatic potential (MEP), non-linear optical properties (NLO), Mulliken population method, natural population analysis (NPA), natural bond orbital (NBO) and Fukui function analyses have been studied. 相似文献
129.
R. Branzei O. Branzei S. Zeynep Alparslan Gök S. Tijs 《Central European Journal of Operations Research》2010,18(3):397-411
The (re)distribution of collective gains and costs is a central question for individuals and organizations contemplating cooperation under uncertainty. The theory of cooperative interval games provides a new game theoretical angle and suitable tools for answering this question. This survey aims to briefly present the state-of-the-art in this young field of research, discusses how the model of cooperative interval games extends the cooperative game theory literature, and reviews its existing and potential applications in economic and operations research situations with interval data. 相似文献
130.
The A/B ring synthon 13, previously converted into daunomycinone(6) by Keay and Rodrigo,6 has been prepared in seven steps and 38% overall yield using benzamide directed ortho metalation strategy. Significant steps are: the incorporation of a four-carbon Grignard unit (10) into 9, dibal reduction of 11, and intramolecular aldol condensation of the resulting product 12 to give the dihydronaphthalene 13. 相似文献