Carboxylated system

The electron-donating effect originates from the lone pair electrons on oxygen, with overlap into the Jt electron system. This electron donation will stabilize the non-ionized acid via electron delocalization, but would destabilize the conjugate base by creating a double charge in the carboxylate system. The net result is lower acidity. 

Figure 17-14 (A) The reductive carboxylation system used in reductive pentose phosphate pathway (Calvin-Benson cycle). The essential reactions of this system are enclosed within the dashed box. Typical subsequent reactions follow. The phosphatase action completes the phosphorylation-dephosphorylation cycle. (B) The reductive pentose phosphate cycle arranged to show the combining of three C02 molecules to form one molecule of triose phosphate. Abbreviations are RCS, reductive carboxylation system (from above) A, aldolase, Pase, specific phosphatase and TK, transketolase.

Occupying a central position in the spectrum of metal interaction in syn-syn bridged carboxylate systems lie dirhodium compounds. The Rh—Rh bond lengths in such compounds are generally in the range 239-247 pm, shorter than anticipated for what now seems well established as a single bond. This area has been reviewed.36... 

In this paper we report for the first time our studies of hydrogen bonding in the imidazole-carboxylate system, a common motif in enzyme active sites. The H solid state NMR data of polymorphic crystalline histidines were taken on a Chemagnetic... 

Although carboxylic as well as phosphoric esters are widely utilized in nature, phosphoric amides do not parallel their carboxylic counterpartners as the widespread biological struc -tures. This is most likely due to the low stability of the P(0)-N bond under acidic conditions a property resulting from the different bonding at the phosphoramidate function, relative to the carboxylic system. 

Figure 5.5.5-1 Chromophoric systems used in photography. It will be shown that the carboxylic system is also used in vision.

In Nd-carboxylate systems A1R3 and A1R2H cocatalysts are also replaced by alumoxanes, which were described by Sinn and Kaminsky et al. in 1980 [194-196]. Most of these studies focus on methyl alumoxane (MAO) [175,197-200]. Also tetraisobutyl dialumoxane (TIBAO) was investigated [175]. Differences between aluminum alkyl- and alumoxane-based cocatalysts are also addressed in Sect. 2.1.2. 

The RPP cycle displays four features which are necessary for its role as a fundamental carboxylating system [2]. 

V NMR spectroscopic studies have been carried out with simple dicarboxylates and simple mixed alkoxide-carboxylate systems.60 The complexes that form are generally stable in the acidic pH range. Recent investigations employ a combination of both solid state124 and solution studies, and provide benchmark data for one of the classes of a-hydroxycarboxylate complexes which form in aqueous solution (VL, VL2. V2L22. and V3L2-).8... 

Vecsler M, Loebstein R, Almog S, et al. Combined genetic profiles of components and regulators of the vitamin K-dependent gamma-carboxylation system affect individual sensitivity to warfarin. Thromb Haemost 2006 95(2) 205-ll. 

Many glycosidases exhibit such a pH-rate profile and the temptation to equate Ka with the dissociation constant of the acid-catalytic group and A b with the dissociation constant of the base or nucleophile frequently proves irresistible. Even in an Alberty-Bloomfield system, however, the equation should be not made unthinkingly. and A b are macroscopic dissociation constants, which are related to the four microscopic dissociation constants of the two-carboxylate system (Figure 5.13) by eqns (5.38) and (5.39) (since Figure 5.13... 

Carbocarbonylation reactions involve dicarborative alkene or alkyne addition reactions with the introduction ol at least one carbonyl group. In this way, linear and cyclic carbonyl and carboxyl systems can be generated1,2. 

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