A-Dipyridyl

Two highly flexible crown ethers have recently been designed and reported for quite different reasons. The first of these is a dipyridyl system reported by Rebek and cowork-... 

The azido mesylate may also be reduced with lithium aluminum hydride in the same manner as previously described for iodo azide reductions. The sodium borohydride/cobalt(II)tris(a,a -dipyridyl)bromide reagent may be used, but it does not seem to offer any advantages over the more facile lithium aluminum hydride or hydrazine/Raney nickel procedures. 

There has been much interest recently in the reaction of a, o)-di-halogenoalkanes. 1,2-Dibromoethane reacts with phthalazine to give ethane 1,2-bis-phthalazinium dibromide (1), none of the mono salt being formed directly, but the same dibromo compound and a, a -dipyridyl give the cyclic compound 2. ... 

The remarkable strength of some XBs allows them to prevail over HBs in identifying the modules to be involved in self-assembly. For instance, in experiments of competitive co-crystal formation, a dipyridyl derivative prefers to co-crystallize with XB donors rather than HB donors and the same occurs for NjNjN jN -lclramclhylclhylcncdiaminc (TMEDA) [36]. In solution, solute-solute intermolecular HBs are considerably diminished if a strong XB donor co-solute is added. If haloperfluorocarbons (halo-PFCs) are used, the HB breaking potency increases moving from perfluorocarbons to chloro-, bromo-, and iodoperfluorocarbons [37-43], perfectly consistent with the order of the increasing XB donor ability of the halo-PFCs co-solutes, hi aque-... 

In the related compound a-a -dipyridyl-acetylacetonato trimethyl platinum, which is monomeric, five of the coordination positions are taken up by the dipyridyl nitrogen atoms and the methyl groups. The sixth position is occupied by the central carbon atom of the acetylacetone, not by one of the oxygen atoms 242a). The oxygen atoms then remain uncoordinated, and the rest of the acetylacetone group is considerably distorted from the highly symmetrical form it normally has in complexes. This is the only... 

L-histidine, L-glutamine, and L-histidine anhydride27 and by copper complexes of organic bases such as o-phenanthroline and a,a -dipyridyl has also been reported these complexes were more active than Cu++ ions alone.28... 

The enzyme activity is significantly inhibited by Tiron and 8-hydroxyquinoline, but not by a,a -dipyridyl and o-phenanthroline. The addition of thiol compounds such as cysteine, 2-mercaptoethanol and glutathione, and thiol inhibitors such as p-chloromercuribenzoate, N-ethylmaleimide and HgCl2 also markedly decreases the enzyme activity. The Michaelis constants of the enzyme are as follows 2-nitropropane (2.13 x 10-2M), nitroethane (2.43 x 10-2M), 3-nitro-2-pentanol (6.8 x 10 3M), 1-nitropropane (2.56 x 10-2 M) and oxygen (3.63 x 10 4M with 2-nitropropane)199. ... 

Lamport41 42,229 proposed that the extensibility of the cell wall is governed by the number of hydroxy-L-proline-arabinose links in the hy-droxy-L-proline-rich glycoprotein of the wall. a,a-Dipyridyl, which limits the synthesis of new hydroxy-L-proline,321,512 and, therefore, the synthesis of hydroxy-L-proline - arabinose links, causes some extension in soybean hypocotyls.513... 

In the first five cycles of in-vitro selection, very little (0.1-0.2%) of the total RNA reacted with biotin, predominantly because of the uncatalyzed background reaction. Several potential cofactors, for example Lewis acids, metal ions, a dipeptide compound, and a dipyridyl compound, were present in the reaction mixture. From cycle 6 onwards significant acceleration of the reaction was observed. As a consequence, in the following cycles the selection pressure was increased by shortening the reaction time and reducing the concentration of maleimide. Compared with the starting library a 6500-fold acceleration of the reaction was observed for the enriched pool after cycle 10. 

However, more frequently the name of a PCMU is made up of that of a polymer and metal compound (MXn). Thus compounds 5 and 6 are termed a complex of iron(III) chloride with a dipyridyl methane-based polymer [12] and that of copper(II) with the condensation product of p-hydroxybenzoic acid, urea and formaldehyde [26], respectively ... 

Bayer and his associates 16) are of the opinion, however, that the inorganic sulfide is of amino acid origin, being released from cysteine when ferredoxin is denatured. They reported the detection of inorganic sulfide from certain synthetic cysteine-iron derivatives, as well as a reconstitution of ferredoxin after the iron had been completely removed by treatment with a,a -dipyridyl. Since these data are in conflict with those discussed above, the resolution of this discrepancy will be awaited with interest. 

The determination of amino acid composition has been performed in hydrolysates of adrenodoxin in 6 N-HC1 at 110° C for various periods after the removal of iron from adrenodoxin by trichloroacetic acid precipitation or by a, a -dipyridyl treatment. The tentative amino acid composition is proposed to be as shown in Table 3. Adrenodoxin contains about 100 amino acid residues with an abundance of aspartic and glutamic acids, which may account for the strong affinity of adrenodoxin for... 

Bayer et al. (7) succeeded in reconstituting clostridial ferredoxin from a, a -dipyridyl-treated apoferredoxin in the presence of ferrous ion without the presence of a labile sulfur source. Based on this observation, they proposed that labile sulfur originates from cysteinyl residues in the presence of iron. Contrary to their finding, Rabinowitz and his coworkers (21, 33) demonstrated that the reconstitution of clostridial ferredoxin from mersaryl-, a, a -dipyridyl-, and trichloroacetic acid-treated apo-ferredoxins absolutely requires the addition of hydrogen sulfide. Consequently, they concluded that cysteine is not the source of labile sulfur . 

Fig. 12. Reconstitution of adrenodoxin from a, a -dipyridyl-treated apoadrenodoxin (62). Curve 1 represents apoadrenodoxin (0.40 mg per ml) curve 2, apoadreno-doxin treated with 2-mercaptoethanol (0.41 mg per ml) curve 3, apoadrenodoxin treated with 2-mercaptoethanol and H2S (0.40 mg per ml) curve 4, apoadrenodoxin treated with 2-mercaptoethanol and ferrous ammonium sulfate (0.40 mg per ml) curve 5, apoadrenodoxin treated with 2-mercaptoethanol, ferrous ammonium sulfate, and H2S (0.41 mg per ml)...

Table 13. Reconstitution from a, a -dipyridyl-treated adrenodoxin (62)...

In contrast to their previous report, Bayer et al. (5) recently reported the requirement of Na2S in reconstituted spinach ferredoxin from a, a -dipyridyl-treated apoferredoxin in the presence of ferrous ion and 2-mercaptoethanol. In this report, they mentioned that, if 2-mercapto-ethanol is not purified before use, the addition of Na2S is not required. Therefore, one can assume that unpurified 2-mercaptoethanol contains H2S. We checked for the presence of H2S in once distilled 2-mercapto-ethanol by gas chromatography. The presence of H2S in samples of 2-mercaptoethanol could not be detected by this method. Since an excess amount of 2-mercaptoethanol is required for the reconstitution experiment, minute contamination of H2S in the sample may serve for the labile sulfur source, or H2S may be produced from 2-mercaptoethanol under the conditions of the reaction. 

Although the mechanism of action of 2-mercaptoethanol may not be simple, its probable action is the reduction of disulfide bonds to sulfhy-dryl groups in a, a -dipyridyl- or heat-treated apoadrenodoxin, or regeneration of sulfhydryl groups from mercaptides in PCMB-treated apoadrenodoxin. At the present time, all three laboratories, that is Bayer s Rabinowitz s, and ours, agree on the necessity of the addition of Na2S as a labile sulfur source for better or perfect reconstitution of clostridial, spinach, and adrenal non-heme iron proteins from various types of apoproteins. 

Dioxane Limit Test, 757 Diphenylamine TS, 851 Diphenylcarbazone TS, 851 Diphenyl Ether, (S3)70, 98 Diphenyl Ketone, 458 Diphenyl Oxide, (S3)70 Diphenylthiocarbazone, 860 Dipotassium Monophosphate, 324, (S1 )38 Dipotassium Phosphate, 324, (S1 )38 a,a -Dipyridyl TS, 851 Disodium Dihydrogen Pyrophosphate, 350, (Sl)39, (S2)30, (S3)52 Disodium Edetate, 125 Disodium EDTA, 125 Disodium EDTA, 0.05 M, 856 Disodium Ethylenediaminetetraacetate, 125... 

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