Search results for "Concentration."
showing 10 items of 1849 documents
The smallest singular value of a shifted $d$-regular random square matrix
2017
We derive a lower bound on the smallest singular value of a random d-regular matrix, that is, the adjacency matrix of a random d-regular directed graph. Specifically, let $$C_1<d< c n/\log ^2 n$$ and let $$\mathcal {M}_{n,d}$$ be the set of all $$n\times n$$ square matrices with 0 / 1 entries, such that each row and each column of every matrix in $$\mathcal {M}_{n,d}$$ has exactly d ones. Let M be a random matrix uniformly distributed on $$\mathcal {M}_{n,d}$$ . Then the smallest singular value $$s_{n} (M)$$ of M is greater than $$n^{-6}$$ with probability at least $$1-C_2\log ^2 d/\sqrt{d}$$ , where c, $$C_1$$ , and $$C_2$$ are absolute positive constants independent of any other parameter…
Spatio-temporal statistical methods in environmental and biometrical problems
2017
This is the editorial letter for the Special Issue dedicated to the VIII International Workshop on Spatio-temporal Modelling (METMAVIII) which took place in Valencia (Spain) from 1 to 3 June 2016, and to the second Galician-Portuguese meeting of Biometry, with applications to Health Sciences, Ecology and Environmental Sciences (BIOAPP2016) held in Santiago de Compostela (Spain), 30–2 July 2016. This special issue summarises and discusses selected peer-reviewed contributions related to spatial and spatio-temporal statistical methodologies comprising both new methodological approaches and a wide range of applications related to environmental and biometrical problems. Point processes, lattice …
N-Heterocyclic choline analogues based on 1,2,3,4-tetrahydro(iso)quinoline scaffold with anticancer and anti-infective dual action
2016
Pharmacological effects of biologically active “small molecules” can be improved by their targeted modification, which affects drug delivery and interaction with tumor cells and microorganisms. We aimed to evaluate anticancer and antimicrobial activity of lipid-like choline derivatives modified via simultaneous introduction of tetrahydro(iso)quinoline based pharmacophore system at nitrogen atom and long chain alkyl substituent at oxygen atom. Target compounds were synthesized under phase-transfer catalysis conditions followed by quaternization, and evaluated for cytotoxicity and NO-generation ability on HT-1080 and MG-22A tumor cell lines and NIH 3T3 normal mouse fibroblasts, and screened f…
Antiproliferative agents that interfere with the cell cycle at the G(1)-->S transition: further development and characterization of a small library o…
2008
In this continuation of our research on derivatives containing the stilbene privileged structure or that are derived from it, we report the results of further studies carried out on the previously initiated collection of compounds. We used a parallel synthetic approach to rapidly obtain small sets of compounds and started the annotation of the library in progress by calculating some physicochemical properties to be eventually correlated with biological activities. A pharmacophore for the antiproliferative activity was also built to summarize the features of the library. We evaluated the antiproliferative and pro-apoptotic activities of all compounds as well as the cell-cycle effects of some…
Tucumanin, a β-hydroxy-γ-lactone bistetrahydrofuranic acetogenin from Annona cherimolia, is a potent inhibitor of mitochondrial complex I
2004
A new β-hydroxy-γ-methyl-γ-lactone bistetrahydrofuranic acetogenin, tucumanin, with the infrequent symmetrical threo/trans/threo/trans/ threo relative configuration at the tetrahydrofuran rings was isolated from Annona cherimolia (Annonaceae) seeds. The inhibitory potency on the mitochondrial complex I of acetogenins with this relative configuration (tucumanin and asimicin) was compared with that shown by the corresponding pairs with an asymmetrical threo/trans/threo/trans/erythro relative configuration (laherradurin/rolliniastatin-2, and itrabin/molvizarin). All these compounds act as selective inhibitors of mitochondrial complex 1 in the 0.18 - 1.55 nM range. Fil: Barrachina, Isabel. Univ…
Reaction Rate Modeling in Cryoconcentrated Solutions: Alkaline Phosphatase Catalyzed DNPP Hydrolysis
2000
The hydrolysis of disodium p-nitrophenyl phosphate catalyzed by alkaline phosphatase was chosen as a model to study the kinetics of changes in frozen food products. The initial reaction rate was determined in concentrated sucrose solutions down to -24 degrees C, and the enzymatic characteristics K(M) and V(max) were calculated. The experimental data were compared to the kinetics predicted by assuming that the reaction was viscosity dependent. Indeed, an analysis of the enzymatic reaction demonstrated that both the diffusion of the substrate and the flexibility of the enzyme segments were controlled by the high viscosity of the media. When the temperature was too low for the viscosity to be …
Synthesis and cytotoxic activity of novel C7-functionalized spongiane diterpenes.
2003
Based on two lead cytotoxic spongiane diterpenes, a new series of C7-oxygenated derivatives were synthesized and evaluated for their antitumor activity in vitro against the cancer cell lines HeLa and HEp-2. In general, introduction of either hydroxyl or acetoxy groups at C-7 did not improve the resultant cytotoxicity, while the presence of a butyrate ester led to more active compounds (CC(50)=4.0-9.5 microM).
Regioselective substitution of 6,7-dichloroquinoline-5,8-dione: synthesis and X-ray crystal structure of 4a,10,11-triazabenzo[3,2-a]fluorene-5,6-dion…
2003
6,7-Dichloroquinoline-5,8-dione (1) was reacted with a number of 2-aminopyridine derivatives. Of the several possible products of this reaction, 4a,10,11-triazabenzo[3,2-a]fluorene-5,6-dione (6), produced by condensation and rearrangement, was obtained as the major product, and its structure was subsequently unambigously determined by X-ray crystallographic study. Ortho-quinones were produced via nucleophilic substitution at position C7, which was unexpected, considering that para-quinones were produced via C6 substitution in the reaction between compound 1 and ethyl acetoacetate in our previous work. Such unexpected nucleophilic substitution at C7 provides an effective, yet simple route, t…
Synthesis and biological evaluation of 2-(3',4',5'-trimethoxybenzoyl)-3-N,N-dimethylamino benzo[b]furan derivatives as inhibitors of tubulin polymeri…
2008
Molecules that target microtubules have an important role in the treatment of cancer. A new class of inhibitors of tubulin polymerization based on the 2-(3,4,5-trimethoxybenzoyl)-2-dimethylamino-benzo[b]furan molecular skeleton was synthesized and evaluated for antiproliferative activity, inhibition of tubulin polymerization, and cell cycle effects. The most promising compound in this series was 2-(3,4,5-trimethoxybenzoyl)-3-dimethylamino-6-methoxy-benzo[b]furan, which inhibits cancer cell growth at nanomolar concentrations and interacts strongly with tubulin by binding to the colchicine site.
Synthesis and cytotoxicity of 6,11-Dihydro-pyrido- and 6,11-Dihydro-benzo[2,3-b]phenazine-6,11-dione derivatives
2003
6,11-Dihydro-pyrido[2,3-b]phenazine-6,11-diones and 6,11-dihydro-benzo[2,3-b]phenazine-6,11-diones were synthesized from 6,7-dichloro-5,8-quinolinedione and 2,3-dichloro-1,4-naphthoquinone. The study on the cytotoxicity on these products revealed that the pyridophenazinediones, tetracyclic heteroquinone analogues with three nitrogen atoms exhibited a high cytotoxicity on several human tumor cell lines. Compound 9c and 9e showed in vitro antitumor activity comparable or superior to doxorubicin against the human ovarian tumor cells (SK-OV-3) and the human CNS cells (XF 498). The IC(50) value for compound 9e was 0.06 microM against the human CNS cells (XF 498), which was 2.6 times higher than …