Search results for "transe"

The Catalytic Mechanism of Carboxylesterases: A Computational Study

2014

The catalytic mechanism of carboxylesterases (CEs, EC 3.1.1.1) is explored by computational means. CEs hydrolyze ester, amide, and carbamate bonds found in xenobiotics and endobiotics. They can also perform transesterification, a reaction important, for instance, in cholesterol homeostasis. The catalytic mechanisms with three different substrates (ester, thioester, and amide) have been established at the M06-2X/6-311++G**//B3LYP/6-31G* level of theory. It was found that the reactions proceed through a mechanism involving four steps instead of two as is generally proposed: (i) nucleophilic attack of serine to the substrate, forming the first tetrahedral intermediate, (ii) formation of the ac…

Selective Formal Transesterification of Fluorinated 2-(Trimethylsilyl)ethyl α-Imino Esters Mediated by TBAF

2008

The scope of the transesterification reaction between beta-fluorinated alpha-imino esters and various electrophiles in the presence of TBAF as fluorine source is described. The reaction is highly selective for alkyl iodides, bromides, and mesylates, while alkyl chlorides react at a significantly slower rate and tosylates do not react under the reaction conditions. This methodology represents a simple and useful alternative for the preparation of a wide variety of fluorinated alpha-imino esters.

1978

Synthesis and characterization of polymeric derivatives of the folic acid antagonist, Methotrexate, N-[4-(N-methyl-2,4-diamino-6-pteridinylmethylamino)benzoyl] glutamic acid (1a), a widely used antitumor agent, are described. Derivatives of poly(L-lysine), poly(iminoethylene), poly(vinyl alcohol), and carboxymethylcellulose with various contents (3–15 mole-%) of substituted repeating units were prepared by polymer-analogous amidation and transesterification of the dimethyl ester of 1a and with N-[2-(N-methylmorpholinio)ethyl]carbodiimide p-toluenesulfonate as coupling reagent. By nucleophilic addition reactions of the pteridinyl amino groups under mild conditions, 1a was bound without cross…

Water-Blown Polyisocyanurate Foams From Vegetable Oil Polyols

2008

Polyols with the hydroxyl value OHV from 290 to 318 mg KOH/g are synthesized from rapeseed, sunflower seed, flaxseed, or coconut oils by the way of their: (1) transesterification with triethanolamine or (2) amidization with diethanolamine. The influence of water as the blowing agent on the storage stability of the polyol premix system is assessed from values of the polyol premix system pH, acid value, and variations in such parameters as cream and gel time. Water-blown polyisocyanurate (PIR) foams (150 · II × 300; II—isocyanate index) characterized by good mechanical characteristics, dimensional stability at 70°C and at relative humidity RH = 95% as well as by a very low water absorbance, …

Mercury Speciation in Floodplain Soils and Sediments along a Contaminated River Transect

1998

A novel mercury-specific sequential extraction procedure (SEP) for the assessment of mercury (Hg) speciation in soils and sediments, with emphasis on studying the interaction between Hg and organic matter (OM), was developed and tested. It was applied to determine Hg speciation in floodplain topsoils and surface sediments along the Hg-contaminated part of the river Elbe, and to simultaneously derive some information on the (re)mobilization potentials for Hg from these matrices. The majority of the total Hg in the ecosystem today is bound in the floodplains, which also still geographically reflect the historic emission record. Most of the Hg in both matrices is bound strongly to OM, suggesti…

Über die polykondensation von diäthylphosphit mit aliphastischen diolen

1973

Die Umesterungsreaktion von Diathylphosphit mit linearen Diolen HO–(CH2)x–OH (x = 2–6 und 8) wurde untersucht. Ihre Bilanz zeigte, das neben der angestrebten Umesterungsreaktion in teilweise sehr erheblichem Umfang auch Atherstrukturen gebildet werden. Diese bis jetzt in diesem Zusammenhang noch nicht beschriebene Reaktion verlauft sehr wahrscheinlich im Sinn einer direkten Alkylierung der alkoholischen OH-Gruppen durch die Phosphitestergruppen, denn sie erfordert keinen Katalysator. Die Estergruppen gehen dabei in saure P-OH-Gruppen uber, die unter den angewendeten Bedingungen nicht mehr ohne weiteres zur Kondensation mit den Diolen befahigt sind. Das Verhaltnis von unerwunschter Atherbild…

Variability in inorganic and organic nitrogen uptake associated with riverine nutrient input in the Gulf of Riga, Baltic Sea

2001

Concentrations and rates of uptake of dissolved organic nitrogen (DON, free amino acids, and urea) and inorganic nitrogen (DIN, nitrate, and ammonium) were measured along two transects in the Gulf of Riga, a sub-basin of the Baltic Sea, during May and July 1996. Concentrations of total dissolved nitrogen (TDN) were 23±3 μg-at N 1−1 in the northern region (mouth) and 41±5 μg-at N 1−1 in the southern region (head) of the Gulf. Rates of nitrogen uptake, determined with15N-labeled substrates, reflected differences in TDN concentration between the regions. In May, uptake of DIN+DON measured 0.17 and 0.43 μg-at N 1−1 h−1 in the northern and southern parts of the Gulf, respectively. In July, DIN+D…

Virlet – Abbaye de Bellaigue

2021

Büttner S. 2020 : Étude archéologique du chevet et du transept de l’abbatiale de Bellaigue (Virlet – 63), rapport d’étude archéologique du bâti, Auxerre, Centre d’études médiévales Saint-Germain.

L’INEDITA CATEGORIA DELLE UNIONI AFFETTIVE CON VISSUTO GIURIDICO MATRIMONIALE. RIFLESSIONI CRITICHE A MARGINE DELLA SENTENZA DELLA CORTE COSTITUZIONA…

2014

Il saggio esamina le ricadute teoriche ed applicative della sentenza n. 170 del 2014 della Corte costituzionale in materia di scioglimento del matrimonio della persona che ha cambiato sesso. Dallo scrutinio della decisione, e dal confronto anche con la giurisprudenza della Corte EDU e delle supreme corti tedesca e austriaca, si sottolinea criticamente la perdurante attualità nell’ordinamento italiano del dogma della eterosessualità del matrimonio e del suo ancoraggio alla normativa costituzionale. Una lettura ribaltata del sistema delle fonti, infatti, induce la Corte costituzionale a desumere il concetto di matrimonio di cui all’art. 29 della Carta fondamentale dalla relativa disciplina co…

Population dynamics of fossorial water vole (Arvicola terrestris scherman): a land use and landscape perspective

1997

Abstract This study investigates the effect of land use, and landscape composition and structure on the population dynamics of fossorial water vole (Arvicola terrestris scherman Shaw). Water vole populations were monitored from 1989 to 1994 in the Doubs department, France, by using index methods. Land use patterns were studied based on agriculture and forestry data from the French Ministry of Agriculture collected in 1956, 1970, 1979 and 1988. Grassland quality and landscape structure were studied based on field transects, combined with the assessment of landscape structure from maps at 1:25,000 scale. Outbreaks of water vole populations occurred as a wave, spreading from epicentres over mo…