Stoichiometry substrate

Nitrate respiration can support the synthesis of ATP, while proton pumping has been quantified for several physiological substrates. Stoichiometries of about 4H+/NO, and 2H+/N03" have been found for L-malate and formate, and succinate, D-lactate and glycerol respectively. There is evidence that about one mole of ATP is synthesized by oxidative phosphorylation per mole of nitrate reduced.1440... 

In an effort to follow modem trends toward green chemistry, a new odourless, water-soluble DMS equivalent (19) that is recyclable was introduced by the same group.5 Up to 89% of this new morpholino sulfide can be recovered using simple acid/base extraction techniques. Yields using this new DMS alternative are excellent and vary from 85% to 99% depending upon substrate, stoichiometry, and solvent choice. For example, the transformations illustrated above (12 to 14 and 15 to 17) were repeated using sulfide 19 and yields of 94% and 91%, respectively, were reported. In addition, the highly successful oxidation of benzylic alcohol 18 and allylic alcohol 21 were carried out at low temperatures. 

The procedure described above illustrates a general, two-step method for the preparation of secondary or tertiary amines. It can be considered as a reductive N-alkylation of a nitrile or an N-monoalkylation of a primary or secondary amine. The first step in the procedure involves direct addition of an aliphatic amine to a nitrile promoted by a stoichiometric amount of cuprous chloride, as fully described recently.4 This method may be used with a large variety of nitriles and primary or secondary aliphatic amines. The nitrile itself may be used as solvent (acetonitrile, benzonitrile). In the case of a primary amine, substrate stoichiometry must be adapted to obtain selectively either the N-monosubstituted amidine [1 eq amine, 1.2 eq Cu(l)CI in acetonitrile] or the N,N-disubstituted amidine [4 eq amine, 1 eq Cu(l)CI, 1 eq acetonitrile in alcohol or DMSO].4... 

R = Ph, R" = Me, R = Ph. [Ir(cod)(PCy3)(py)](PF ) serves as a catalyst in the hydroxyl-dircctcd hydrogenation of cyclic and acyclic alkenic alcohols, wherein the reaction shows diastcreoselectivity dependent on catalyst substrate stoichiometry. Park et have noted that the iridium(I)... 

Complexes of the type [Ir(bzn)(cod)(L)](C104) (bzn = benzonitrile L = tricyclohexylphosphine, neomenthyldiphenylphosphine) catalyze the homogeneous hydrogenation of tetrasubstituted prochiral amido alkenes R R C=CR N. Under very mild conditions, the catalysis occurs for N = NHCOR, R = COjMe R = R = Me, R" = Me, Ph R = Me, R- = Ph, R = Me, Ph R = Ph, R = Me, R = Ph. [Ir(cod)(PCy3)(py)](PFg) serves as a catalyst in the hydroxyl-directed hydrogenation of cyclic and acyclic alkenic alcohols, wherein the reaction shows diastereoselectivity dependent on catalyst substrate stoichiometry. Park el have noted that the iridium(I)... 

One particularly important use of DDQ has been in the dehydrogenation of reduced porphyrins, where the degree of aromatization of the product is highly dependent on the relative reagent substrate stoichiometry. Under optimal conditions, excellent yields of partially or fully conjugated products may be isolated. The formation of porphyrins from tetrahydro precursors on reaction with 3 equiv of DDQ under very mild conditions (eq 7) typifies one of the more commonly described transformations. More recently, DDQ has been used as part of a one-pot sequence for the formation of porphyrins from simple intermediates, although the overall yields in such reactions are generally comparatively low. ... 

Schmidt, A.L. and Briskin, D.P. (1993) Energy transduction in tonoplast vesicles from red beet (Beta vulgaris L.) storage tissue H+/substrate stoichiometries for the H(-H)-ATPase and H(-l-)-PPase. Arch. Biochem. Biophys., 301 (1), 165-173. 

The aquo-complexes of the lanthanides are often used as aqueous shift reagents. Their application, however, is restricted to the acidic side of neutral pH due to the precipitation of hydroxides at higher pH values. The use of the R(EDTA) chelates at higher pH has been suggested and a characterization study has been carried out in this laboratory, (Elgavish and Reuben, 1976). With carboxylates as substrates the useful pH range is between 6 and 10, confined on the acidic side by the formation of carboxylic acid and on the basic side by the formation of hydroxo complexes of the chelates. The reagent-substrate stoichiometry is practically 1 1. 

In a much more rigorous way, bond-breaking reconstmctions in compound semiconductors are always combined with significant chemical deviations from the substrate stoichiometry. In the simplest case, the stoichiometry is modified by adatoms or missing atoms. Often, however, the reconstraction is accompanied by the addition of entire layers of one of the elements. These cases are discussed in the next section. 

Thin oxide films may be prepared by substrate oxidation or by vapour deposition onto a suitable substrate. An example of the fomrer method is the preparation of silicon oxide thin-films by oxidation of a silicon wafer. In general, however, the thickness and stoichiometry of a film prepared by this method are difficult to control. 

Under similar conditions, perfluoroalkyl iodides react with alkyl phosphates to give fluorinated phosphine oxides, phosphinates, and phosphines [54 (equation 49) The product formed depends upon the stoichiometry and type of iodide used. When sodium alkyl trithiocarbonates are used as substrates, perfluoroalkyl tri-thiocarbonates ate formed [55]. 

For a reaction as complex as catalytic enantioselective cyclopropanation with zinc carbenoids, there are many experimental variables that influence the rate, yield and selectivity of the process. From an empirical point of view, it is important to identify the optimal combination of variables that affords the best results. From a mechanistic point of view, a great deal of valuable information can be gleaned from the response of a complex reaction system to changes in, inter alia, stoichiometry, addition order, solvent, temperature etc. Each of these features provides some insight into how the reagents and substrates interact with the catalyst or even what is the true nature of the catalytic species. 

Cytochrome P450 (CYP) mono-oxygenases, also called mixed function oxidases, are versatile hemoprotein enzymes that catalyze the cleavage of molecular oxygen to incoiporate one oxygen atom into a substrate molecule and one atom into water [1]. The general stoichiometry of the reaction is as follows (S-H, substrate) ... 

The hydrolytic step (Part D) uses conditions described by Narasaka, Sakashita, and Mukaiyama.11 It was necessary to modify the original stoichiometry, since the recommended molar ratio of substrate cupric chloride cupric oxide (1 2 4) gave only a 57% yield of 3-bcnzoylindole. 

There are, however, two disadvantages associated with use of the phenyldimethylsilyl group. Based on the reaction stoichiometry, for each equivalent of substrate, one silyl group is unused, and after work-up this appears as a relatively involatile by-product. Secondly, after synthetic use of such vinylsilanes involving desilylation, a similar problem of by-product formation arises. One solution to these problems lies in the use of the tri-methylsilyl group (Chapter 8), since the by-product, hexamethyldisiloxane, is volatile and normally disappears on work-up. 

The choice of solvent is not trivial and, generally, the reaction medium must be a good solvent for both monomers and polymer product. In addition, to obtain high molecular weight, water needs to be removed from the system to avoid hydrolyzing the activated substrate, since hydrolysis reduces the reaction rate and upsets the stoichiometry of the monomers.61 63... 

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