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Reaction Decreased (reaction + decreased)

Distribution by Scientific Domains

Chemistry	50%
Life Sciences	33%

Selected Abstracts

LOXL as a target to increase the elastin content in adult skin: a dill extract induces the LOXL gene expression

EXPERIMENTAL DERMATOLOGY, Issue 8 2006
Valérie Cenizo
Abstract:, The lysyl oxidases lysyl oxidase (LOX) and lysyl oxidase-like (LOXL) are responsible for elastin cross-linking. It was shown recently that LOXL is essential for the elastic fibres homeostasis and for their maintenance at adult age. We first determined whether or not elastin, LOX and LOXL are less expressed during adulthood. The LOX and LOXL mRNA level, quantified by real-time reverse transcriptase-polymerase chain reaction decreased in adult skin fibroblasts compared with fibroblasts from children. In contrast, the elastin mRNA level remains stable at all ages. The goal of this study was to induce elastogenesis at the adult age. Therefore, both enzymes, and in particular LOXL, of which expression is the most affected by age, could be targeted to induce elastogenesis in adult skin. We screened a library of about 1000 active ingredients to find activators capable to stimulate specifically the LOXL gene expression in adult dermal fibroblasts. The positive effect of selected active ingredients was confirmed on fibroblasts grown on monolayers and on dermal and skin equivalent cultures. One extract, obtained from dill (LYS'LASTINE V, Engelhard, Lyon, France), stimulates the LOXL gene expression in dermal equivalents (+64% increase in the LOXL mRNA level when compared with control). At the same time, the elastin detection is increased in dermal equivalents and under the dermal,epidermal junction of skin equivalents, without increase of the elastin mRNA. In conclusion, LOXL can be considered as a new target to reinduce elastogenesis. Its stimulation by a dill extract is correlated with increased elastin detection, suggesting an increase in elastogenesis efficiency. [source]

Reaction of 4-benzylidene-2-methyl-5-oxazolone with amines, Part 2: Influence of substituents in para-position in the phenyl ring and a substituent on amine nitrogen atom on the reaction kinetics

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2002
B. Bet, akowska
An influence of a structure of the amine (benzylamine, N -methyl-benzylamine, N -isopropyl-benzylamine, N -methyl-butylamine, N -ethyl-butylamine, sec -butylamine, and tert -butylamine) on a rate constant of the ring-opening reaction of 4-benzylidene-2-methyl-5-oxazolone (Ox) was studied. The good correlation between logarithm of the rate constants and Charton's steric substituent constant , as well as good correlation with a form of the simple branching equation indicate that there is a steric effect because of substitution at C1 carbon atom of nucleophile which decreases the reaction rate. Additionally, an influence of a structure of the benzylidene moiety of Ox on a rate of the oxazolone ring-opening reaction was studied. The substituents (OH, OCH3, N(CH3)2, Cl, NO2) in para-position of the phenyl ring of Ox substantially modified the rate of the reaction with benzylamine in acetonitrile. The rate of the Ox ring-opening reaction decreased with increase of the electron-donating properties of the substituent. A good correlation between the rate constants of the reaction of 4-(4,-substituted-benzylidene)-2-methyl-5-oxazolones with benzylamine and the electron density at the reaction center (carbon C5 of the oxazolone ring), calculated using ab initio method, and the Hammett substituent constants, and CR equation were established. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 148,155, 2002; DOI 10.1002/kin.10039 [source]

Effects of hydrogen peroxide on light emission by various strains of marine luminescent bacteria

JOURNAL OF BASIC MICROBIOLOGY, Issue 3 2004
Andrey M. Katsev
Light-emitting bacteria are the most abundant and widespread luminescent organisms. Most species of such bacteria live in marine environments. However, until recently, biological role of bacterial luminescence remained unknown. Recent studies indicated that light produced in bacterial cells may stimulate DNA repair. Therefore, it is not surprising that agents that cause DNA damage induce expression of lux genes. Moreover, it was proposed previously that bacterial luciferases may be involved in detoxification of reactive oxygen species. Recently, this hypothesis was confirmed experimentally. Here we investigated effects of hydrogen peroxide on light emission by various strains of luminescent bacteria. We found that luminescence of strains with luciferase of fast kinetics of reaction decreased at considerably lower concentrations of H2O2 than that of strains with luciferase of the slow kinetics. The action (either direct or indirect) of luciferases as anti-oxidants seemed to be independent of activity of catalase, which was found to be different in various strains. Therefore, it seems that luciferases of the slow kinetics are more efficient in detoxification of reactive oxygen species than those of the fast kinetics. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

X-Ray Photoelectron Spectroscopy and Reactivity Studies of a Series of Ruthenium Catalysts

CHEMCATCHEM, Issue 1 2009
Katarzyna Jarzembska
Abstract X-Ray photoelectron spectroscopy (XPS) was applied to six selected ruthenium precatalysts. The XPS data obtained were compared against reactivity and structural results. The XPS data confirmed some dependencies such as the electron-donor properties of the substituents at the ruthenium center. Additionally, the data combined with structural and reactivity results explain the differences between the character of Grubbs and Hoveyda catalysts. It was found that changing the PCy3 ligand to OiPr (PCy3=tricyclohexylphosphane, OiPr=isopropoxy) has a major influence on relative electron-donating properties of the N-heterocyclic carbene ligand (NHC) and PCy3 groups, which was supported by the relative charges on the Ru center for the examined compounds. Moreover, the turnover frequency (TOF) of a selected example reaction decreased when introducing a NHC group in the case of Grubbs catalysts, but increased in the case of Hoveyda-type catalysts. The XPS data also explained the relative activity values of some catalysts (higher reactivity of nitro-Hoveyda than Hoveyda second-generation catalysts). However, the binding energies do not predict TOFs. Sole examination of the XPS data does not provide a base for reaching unambiguous and binding conclusions as to the relative reactivity of all the investigated systems. [source]

Enantioselective [4+2]-Cycloaddition Reaction of a Photochemically Generated o -Quinodimethane: Mechanistic Details, Association Studies, and Pressure Effects

CHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2004
Benjamin Grosch Dipl.
Abstract 1,2,3,4-Tetrahydro-2-oxoquinoline-5-aldehyde (2) was prepared from m -aminobenzoic acid and 3-ethoxyacryloyl chloride (4) in 19,% overall yield. Compound 2 underwent a photochemically induced [4+2]-cycloaddition reaction with various dienophiles upon irradiation in toluene solution. The exo product 10,a was obtained with acrylonitrile (9,a) as the dienophile, whereas methyl acrylate (9,b) and dimethyl fumarate (9,c) furnished the endo products 11,b and 11,c (69,77,% yield). The reactions proceeded at ,60,°C in the presence of the chiral complexing agent 1 (1.2 equiv) with excellent enantioselectivity (91,94,% ee). The enantiomeric excess increases in the course of the photocycloaddition as a result of the lower product association to 1. The intermediate (E)-dienol 8 was spectroscopically detected at ,196,°C in an EPA (diethyl ether/isopentane/ethanol) glass matrix. The association of the substrate 2 to the complexing agent 1 was studied by circular dichroism (CD) titration. The measured association constant (KA) was 589,M,1 at room temperature (25,°C) and normal pressure (0.1 MPa). An increase in pressure led to an increased association. At 400 MPa the measured value of KA was 703,M,1. Despite the stronger association the enantioselectivity of the reaction decreased with increasing pressure. At 25,°C the enantiomeric excess for the enantioselective reaction 2 + 9,a,10,a decreased from 68,% ee at 0.1 MPa to 58,% ee at 350 MPa. This surprising behavior is explained by different activation volumes for the diastereomeric transition states leading to 10,a and ent - 10,a. 1,2,3,4-Tetrahydro-2-oxochinolin-5-aldehyd (2) wurde ausgehend von m -Aminobenzoesäure und 3-Ethoxyacryloylchlorid (4) in fünf Schritten und einer Gesamtausbeute von 19,% hergestellt. Die Verbindung ließ sich in Toluol als Lösungsmittel mit verschiedenen Dienophilen in einer photochemisch induzierten [4+2]-Cycloaddition umsetzen (69,77,% Ausbeute), wobei als Hauptprodukt mit Acrylnitril (9,a) das exo -Produkt 10,a entstand. Methylacrylat (9,b) und Dimethylfumarat (9,c) lieferten die endo -Produkte 11,b and 11,c. In Gegenwart des chiralen Komplexierungsreagenz, 1 (1.2 Äquiv.) verliefen die Reaktionen mit exzellenter Enantioselektivität (91,94,% ee). Der Enantiomerenüberschuß nahm im Verlauf der photochemischen Umsetzung zu, was man auf die relativ zum Substrat 2 niedrigere Assoziation des Produkts zurückführen kann. Das intermediär gebildete (E)-Dienol 8 wurde spektroskopisch in einer EPA (Ether/i -Pentan/Ethanol) Glasmatrix bei ,196,°C nachgewiesen. Die Assoziation des Substrats 2 an das Komplexierungsreagenz 1 wurde durch CD-Titration genauer untersucht. Die Assoziationskonstante (KA) wurde bei Zimmertemperatur (25,°C) und Normaldruck (0.1 MPa) zu 589,M,1bestimmt. Bei höherem Druck beobachtete man eine verstärkte Assoziation und bei 400 MPa wurde eine Assoziationskonstante von KA=703,M,1bestimmt. Trotz der stärkeren Assoziaion nahm die Enantioselektivität mit wachsendem Druck ab. Bei 25,°C sank der Enantiomerenüberschuß der enantioselektiven Reation 2 + 9,a,10,a von 68,% ee bei 0.1 MPa auf 58,% ee bei 350 MPa. Dieses überraschende Verhalten läßt sich möglicherweise durch die unterschiedlichen Aktivierungsvolumina für die Übergangszustände erklären, die zu 10,a und ent - 10,a führen. [source]

Sensitivity to bites by the bedbug, Cimex lectularius

MEDICAL AND VETERINARY ENTOMOLOGY, Issue 2 2009
K. REINHARDT
Abstract Bedbugs are a public health problem and can cause significant economic losses, but little is known about the effects of bites on humans. We reviewed case reports and published papers on bedbug bites to assess the empirical basis of the commonly cited figure that only , 80% of the population are sensitive to bedbug bites. We found the sensitivity estimate to be based on only one study carried out 80 years ago. However, this study did not account for the now well-established fact that only repeated exposure to external allergens leads to skin reactions. In our sample, 18 of 19 persons showed a skin reaction after bedbug exposure, but in most cases only after repeated controlled exposure. With repeated exposure, the latency between bite and skin reactions decreased from , 10 days to a few seconds. Our results are relevant for the hospitality industry, where apparently increasing infestation rates are likely to lead to an increase in the number of tourists and hotel employees exposed to bedbugs. Medical and public health professionals may expect to see an increase in the prevalence of people with bedbug bite sensitivity. The significance of the delayed reaction time of skin to bites may also have implications in litigation cases where people seek compensation. [source]