Donor compounds

Selenium is an essential element and is beneficial at low concentrations, serving as an antioxidant. Lack of selenium affects thyroid function, and selenium deficiencies have been linked to Keshan Disease (34). Selenium at high levels, however, is toxic. Hydrogen selenide (which is used in semiconductor manufacturing) is extremely toxic, affecting the mucous membranes and respiratory system. However, the toxicity of most organ oselenium compounds used as donor compounds for organic semiconductors is not weU studied. 

Tellurium is not an essential element, and teUurium compounds are in general more toxic than their selenium counterparts. MetaUic teUurium is known to have a teratogenic effect in rats, though no studies have been done on the toxicity of teUurium donor compounds (35). 

Of great concern for air pollution problems resulting from the incident are dioxin-like compounds. In general, dioxin-like compounds can be generated when chlorine donor compounds are present. Depending on the source of the coal tar, chlorine content may range between 1 and 5000 ppm. 

The macrocyclic hexamine [18]aneN6 was further found to recognize catechol, catecholamines and biologically relevant compounds (see Chart II)64). It interacts with all of these donor compounds in neutral pH solutions to form 1 1 complexes, which were determined polarographically. The stability constants pL are summarized in Table 6. 

The suppression of C60 crystallite formation in mixed LB films was attempted by mixing C60 and amphiphilic electron donor compounds [259]. Observation of the C60 LB film transferred horizontally by TEM clearly showed 10-40-nm-size crystallites. The diffraction pattern gave an fee lattice with unit cell length 1.410 nm. Examination of the mixed films with arachidic acid by TEM showed extensive crystallite formation. Mixed LB films of three different amphiphilic derivatives of electron donors with C60 were examined. One particular derivative showed very little formation of C60 crystallites when LB films were formed from monolayers of it mixed with C60 in a 1 2 ratio, while two others reduced C60 crystallite formation but did not eliminate it. 

It has been shown for many RPLC methods that correlations between log Pod and retention parameters were improved by separating compounds in two classes, i.e. H-bond acceptor and donor compounds. Minick et al. [23] propose to add 0.25% (v/v) of 1-octanol in the organic porhon of the mobile phase (methanol was preferred in this study) and to prepare the aqueous portion with 1-octanol-saturated water to minimize this discriminahon regarding H-bond properties. For a set of heterogenous neutral compounds, the addition of 0.25% (v/v) of 1-octanol in methanol and the use of water-saturated 1-octanol to prepare mobile phase improve the correlahon between log few obtained on the LC-ABZ column and log Poc, [13]. 

The synthesis of quadrupolar chromophores has also been achieved from 2,6-DTT-dicarboxaldehyde 117. Push-push (i.e., bis-donor) compound 118 was prepared via a double Wittig reaction carried out under solid-liquid phase transfer conditions. Pull-pull (i.e., bis-acceptor) compounds 119 were obtained from a symmetrical bis-aldehydes via a double Horner-Emmons-Wittig condensation (Scheme 9) <2002SM17, 1999CC2055>. 

B-NOD is a new NO donor compound. It has a chemical NO-releasing group similar to that of NTG, however, it releases NO in vitro and in vivo. After administration of B-NOD in vivo its activity persists for more than 7 h. In vitro, the release of NO from B-NOD was augmented by the presence ofliving cells (blood platelets). B-NOD increased cGMP levels and prevented thrombin-induced platelet aggregation in vitro in the same manner as SNP. In vivo, administration of B-NOD in rabbits did not cause a fall in blood pressure or an increase in heart rate [97]. 

In principle, the behaviour of any molecular species in forming donor-acceptor complexes depends on its ionization potential, electron affinity and polarizability. However, the donor (or acceptor) ability of a substance depends strongly on the requirements and properties of its partners. The same compound may act as a donor towards strong acceptor compounds or as an acceptor towards donor compounds. This is the case of the TT-amphoteric p-tricyanovinyl-AA/V-dimcthylaniline (41) which is a donor towards 2,4,7-trinitrofluorenone and an acceptor towards /V,/V-dirnclhy Ian Mine138. 

Shuck, A. T., Hogg, N., Thomas, J. P., and Kalyanaraman, B., 1995, Nitric oxide donor compounds inhibit the toxicity of oxidized low-density hpoprotein to endothehal cells, FEBS Lett. 361 291-294. 

Wink, D. A., Cook, J. A., Christodoulou, D., Krishna, M. C., Pacelh, R., Kim, S., DeGraff, W., Gamson, J., Vodovotz, Y., Russo, A., and Mitchell, J. B., 1997, Nitric oxide and some nitric oxide donor compounds enhance the cytotoxicity of cisplatin, Nitric Oxide 1 88-94. 

The hydrolysis, alcoholysis, and aminolysis of monoselenophosphate (294) have been reported for the first time (294) is the labile selenium donor compound required for the synthesis of Se-dependent enzymes and seleno-tRNAs, and is formed from ATP and selenide, HSe. The rate of hydrolysis of monoselenophosphate (294) is... 

If HB is a weak acid, this reaction is rather slow, but it nevertheless takes place. Substances that are unable to react with O2 can also be involved when the solvent-reactant mixtures contain water or other proton donor compounds, even in traces. Thus, benzaldehyde is absolutely resistant to the action of the superoxide ion. However, benzaldehyde transforms into benzylic alcohol and benzoic acid on the action of O2 in the presence of moisture. Sawyer and Gibian (1979) described the following superoxide variant of the Cannizzaro reaction 202 + H2O —>62 + HOO + OH and 2PhCHO + OH + H2O PhCOOH + PhCH20H. 

Cracking reactions produced only 3.5% of the product and most of the cracked product was substituted hydrophenanthrenes. One product positively identified was s-HgP resulting from the initial hydrocracking of one or both of the forms of decahydrophenanthrene which have low resonance stabilisation eneigies. This type of cracking reaction would not be unfavourable and could produce a better hydrogen donor compound. 

Chemical test using sulphur as an hydrogen acceptor Sulphur will readily accept donatable hydrogen to produce H2S whose partial pressure will be proportional to the concentration of H-donors. This reaction provides a simple method for monitoring H-donors contents and initial experiments showed that only small amounts of sulphur and the hydrogen donor compound were needed for the reaction. The method was calibrated using 0.5 g of sulphur with various amounts of 9,10 dihydrophenanthrene (H2) which were reacted at 275 C in a 10 cm3 microautoclave. Plots of pressure vs. time (Figure 3) indicates that an equilibrium pressure was reached in 30 mins or less. 

Synthesis. The synthases are present at the endomembrane system of the cell and have been isolated on membrane fractions prepared from the cells (5,6). The nucleoside diphosphate sugars which are used by the synthases are formed in the cytoplasm, and usually the epimerases and the other enzymes (e.g., dehydrogenases and decarboxylases) which interconvert them are also soluble and probably occur in the cytoplasm (14). Nevertheless some epimerases are membrane bound and this may be important for the regulation of the synthases which use the different epimers in a heteropolysaccharide. This is especially significant because the availability of the donor compounds at the site of the transglycosylases (the synthases) is of obvious importance for control of the synthesis. The synthases are located at the lumen side of the membrane and the nucleoside diphosphate sugars must therefore cross the membrane in order to take part in the reaction. Modulation of this transport mechanism is an obvious point for the control not only for the rate of synthesis but for the type of synthesis which occurs in the particular lumen of the membrane system. Obviously the synthase cannot function unless the donor molecule is transported to its active site and the transporters may only be present at certain regions within the endomembrane system. It has been observed that when intact cells are fed radioactive monosaccharides which will form and label polysaccharides, these cannot always be found at all the membrane sites within the cell where the synthase activities are known to occur (15). A possible reason for this difference may be the selection of precursors by the transport mechanism. 

It is likely that in addition to the synthases and epimerases there is also present at the membrane in close proximity to these, transporter systems for the transfer of the nucleoside diphosphate donor compounds to the transglycosylases situated on the lumen side of the membrane. 

Therefore, ThDP-dependent enzymes include the potential of both making and breaking of C-C bonds [1]. All enzymes have in common a ThDP-bound active aldehyde intermediate formed either by decarboxylation or by transfer from a suitable donor compound (e.g., from xylulose-5-phosphate by transketolase). Some of the decarboxylating enzymes also catalyze interesting side-reactions where two aldehydes are joined, resulting in so-called acyloin condensations [1,... 

Other ThDP enzymes catalyze the formation of C-C bonds by transferring C2 units from a donor compound to an acceptor compound (transferase activity). We have studied the E. coli transketolase with respect to structure-function relationships, as well as to possible applications in asymmetric syntheses (Section 2.2.2.2.1). During the late 1990s a transketolase-like enzyme, 1-deoxyxylulose 5-phosphate synthase, was discovered. Its structure and value in chemoenzymatic syntheses were also assessed in project B21 (Section 2.2.2.2.2). 

Xylulose 5-phosphate (D-threo-2-pentulose 5-phosphate) is the best donor compound for TKT [6]. As its cost is, however, prohibitively high for routine assays (formerly available batches from commercial suppliers were sold at ca. 1000 per 100 mg), a multi-enzymatic synthesis and subsequent chromatographic purification were developed which allowed the gram-scale synthesis of xylulose 5-phos-phate with a 82% yield [13]. 

FSA makes it possible to use dihydroxyacetone or hydroxyacetone as a donor compound for aldolization reactions this opens up the field for novel carbohydrate compounds such as 1-deoxysugars which otherwise can be obtained by DXS through a different reaction. 

The developmenf of self-curing resins, i.e., systems curing without photoinitiators or, in some cases, with just small amounts of photoinitiators, has been reported recently. Such resins are synthesized by Michael reaction of acrylic functional materials with Michael donor compounds such as acetoacetates. The resulting product has an increased molecular weight compared to the parent acrylate(s). This provides resins with reduced volatility and propensity for skin absorpfion. This new technology is versatile and flexible and opens a possibility of synfhesis of a large number of different acrylate resins. The novel resins reportedly exhibit unique depth of cure capability. In the absence of a photoinitiator (PI), film of approximately 10 mils (0.25 mm) thick can be cured at a line speed of 100 fpm (30.5 m/min). When only 1% of PI is added, the thickness of film that can be cured increases to over 100 mils (2.5 mm). 

Nitric oxide may be the active moiety of STZ that induces diabetes in this animal model. STZ contains a nitroso moiety and may release nitric oxide by a process analogous to the nitric oxide donor compounds SIN-1 and nitroprusside. Turk et al. (1993) have shown that incubation of rat islets with STZ at concentrations that impair insulin secretion results in the generation of nitrite and the accumulation of cGMP. STZ also inhibits mitochondrial aconitase activity of islets to a degree similar to that achieved by IL-1. These findings provide the first evidence that STZ impairs islet function by liberating nittic oxide. 

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