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排序方式: 共有6657条查询结果,搜索用时 31 毫秒
1.
《Arabian Journal of Chemistry》2021,14(11):103421
Processing of Carapa guianensis seeds to obtain oil on an industrial scale generates a significant amount of by-product, approximately 66% w/w, which is called cake and is a potential source of biomolecules, including simple phenolic structures. For this reason, studies were carried out on the chemical profiles of hydrolyzed extract from this agro-industrial by-product through High Performance Thin-Layer Chromatography (HPTLC) and Gas Chromatography coupled to Mass Spectrometry (GC–MS). These techniques were used to detect metabolic classes and/or groups, and to identify, for the first time, thirteen simple phenolic acids in this by-product. The sample antioxidant capacity was determined by methods of 2,2-diphenyl-1-picrylhydrazyl (DPPH)and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS+) radicals direct sequestration. The hydrolyzed fraction showed a total of 63.47% in the relative abundance of the total of compounds, standing out: p-hydroxybenzoic acid (39.19%) and protocatechuic acid (3,4-dihydroxybenzoic acid) (5.62%), both from hydroxybenzoic acids and 3-(3,4-dihydroxyphenyl)lactic acid, (7.76%) hydroxycinnamic acids derivatives. In these results, the fraction rich in simple phenolic acids was obtained, attributing the prominent behavior of this matrix antioxidant activity, expressed by (IC50: of 16.42 µg/mL and 6.52 µg/mL for DPPH and ABTS+ radicals, respectively). The research demonstrated an alternative to applicability that involves sustainability from agro-industrial. These techniques were used to detect metabolic classes and/or groups, and to identify, for the first time, thirteen simple phenolic acids in this by-product, generating a process capable of converting biomass into a bioproduct, consisting of bioactive compounds, in addition to adding value to the industrial chain. 相似文献
2.
Sze-Jack Tan Chee-Keong Lee Chee-Yuen Gan Olusegun Abayomi Olalere 《Molecules (Basel, Switzerland)》2021,26(7)
In this study, the combination of parameters required for optimal extraction of anti-oxidative components from the Chinese lotus (CLR) and Malaysian lotus (MLR) roots were carefully investigated. Box–Behnken design was employed to optimize the pH (X1: 2–3), extraction time (X2: 0.5–1.5 h) and solvent-to-sample ratio (X3: 20–40 mL/g) to obtain a high flavonoid yield with high % DPPHsc free radical scavenging and Ferric-reducing power assay (FRAP). The analysis of variance clearly showed the significant contribution of quadratic model for all responses. The optimal conditions for both Chinese lotus (CLR) and Malaysian lotus (MLR) roots were obtained as: CLR: X1 = 2.5; X2 = 0.5 h; X3 = 40 mL/g; MLR: X1 = 2.4; X2 = 0.5 h; X3 = 40 mL/g. These optimum conditions gave (a) Total flavonoid content (TFC) of 0.599 mg PCE/g sample and 0.549 mg PCE/g sample, respectively; (b) % DPPHsc of 48.36% and 29.11%, respectively; (c) FRAP value of 2.07 mM FeSO4 and 1.89 mM FeSO4, respectively. A close agreement between predicted and experimental values was found. The result obtained succinctly revealed that the Chinese lotus exhibited higher antioxidant and total flavonoid content when compared with the Malaysia lotus root at optimum extraction condition. 相似文献
3.
The total synthesis of an alkylcitrate secondary metabolite from the fungi Trichoderma viride is described. An ester dienolate [2,3]-Wittig rearrangement and a S. Julia-Kocienski olefination served as key C/C-connecting transformations. The highly convergent synthesis consists of a longest linear sequence of 17 steps. 相似文献
4.
Ernesto Quesada 《Tetrahedron letters》2004,45(25):4877-4881
The first syntheses of newly isolated members of the Preussomerin family, Preussomerins K and L, are reported. Key steps include the functionalisation of a 2-arylacetal anion, one-pot Friedel-Crafts cyclisation-deprotection and reductive opening of epoxides. 相似文献
5.
Parabolic Capacity and Soft Measures for Nonlinear Equations 总被引:2,自引:0,他引:2
We first introduce, using a functional approach, the notion of capacity related to the parabolic p-Laplace operator. Then we prove a decomposition theorem for measures (in space and time) that do not charge the sets of null capacity. We apply this result to prove existence and uniqueness of renormalized solutions for nonlinear parabolic initial boundary-value problems with such measures as right-hand side. 相似文献
6.
7.
G. Price 《Accreditation and quality assurance》1996,1(2):57-66
National measurement systems are infrastructures to ensure, for each nation, a consistent and internationally recognised
basis for measurement. Such complex systems have historical, technical, legal, organisational and institutional aspects to
connect scientific metrology with practical measurements. Underlying any valid measurement is a chain of comparisons linking
the measurement to an accepted standard. The ways the links are forged and the etalons (measurement standards) to which they
connect are defining characteristics of all measurement systems. This is often referred to as traceability which aims at basing
measurements in common measurement units – a key issue for the integration of quantitative chemical analysis with the evolving
physical and engineering measurement systems. Adequate traceability and metrological control make possible new technical capabilities
and new levels of quality assurance and confidence by users in the accuracy and integrity of quantitative analytical results.
Traceability for chemical measurements is difficult to achieve and harder to demonstrate. The supply of appropriate etalons
is critical to the development of metrology systems for chemical analysis. An approach is suggested that involves the development
of networks of specialised reference laboratories able to make matrix-independent reference measurements on submitted samples,
which may then be used as reference materials by an originating laboratory using its practical measurement procedures.
Received: 31 July 1995 Accepted: 19 August 1995 相似文献
8.
Valentin Brimkov 《Discrete Applied Mathematics》2007,155(14):1812-1825
We consider the problem of computing the Lovász theta function for circulant graphs Cn,J of degree four with n vertices and chord length J, 2?J?n. We present an algorithm that takes O(J) operations if J is an odd number, and O(n/J) operations if J is even. On the considered class of graphs our algorithm strongly outperforms the known algorithms for theta function computation. We also provide explicit formulas for the important special cases J=2 and J=3. 相似文献
9.
E. E. Ergozhin N. A. Bektenov A. K. Mekebaeva N. N. Chopabaeva 《Chemistry of Natural Compounds》2003,39(3):299-302
Phosphorus-containing cellulose cation exchangers were synthesized by reaction of wood cellulose with orthophosphoric acid and the ternary polymer from glycidylmethacrylate, styrene, and maleic anhydride. The effects of the ratio of reactants, temperature, and duration of the reaction on the phosphorylation and exchange capacity of the modified cellulose material were studied. 相似文献
10.
Capacity Constrained Transit Assignment with Common Lines 总被引:1,自引:0,他引:1
Fumitaka Kurauchi Michael G. H. Bell Jan-Dirk Schmöcker 《Journal of Mathematical Modelling and Algorithms》2003,2(4):309-327
This paper proposes the use of absorbing Markov chains to solve the capacity constrained transit network loading problem taking
common lines into account. The approach handles congested transit networks, where some passengers will not be able to board
because of the absence of sufficient space. The model also handles the common lines problem, where choice of route depends
on frequency of arrivals. The mathematical formulation of the problem is presented together with a numerical example.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献