Dimer types

Asymmetric Ring Opening of Some Terminal Epoxides Catalyzed by Dimeric Type Novel Chiral Co(Salen) Complexes... 

The asymmetric ring opening (ARO) of racemic terminal epoxides with H2O via hydrolytic kinetic resolution provides an efficient synthetic route to prepare optically pure terminal epoxides. The dimeric type chiral Co(salen)AlX3 complex has great potential to catalyze HKR of terminal epoxides in a highly reactive and enantioselective manner in comparison to their monomeric analogy. 

Antibody A52 with its epitope at residues 657-672 [129,139,274,275] inhibited the vanadate-induced crystallization of Ca " -ATPase and decreased the stability of preformed Ca " -ATPase crystals [285]. The vanadate-induced crystals arise by the association of the ATPase monomers into dimers (type A interaction), the dimers into dimer chains (type B interaction), and the dimer chains into 2-dimensional arrays (type C interaction). It is suggested that antibody A52 interferes with type B interactions, preventing the formation of dimer chains, without exerting major effect on the concentration of Ca -ATPase dimers in the membrane. The simplest interpretation of the destabilization of Ca -ATPase crystals by mAb A52 is that binding of the antibody to its antigenic site physically blocks the interaction between ATPase molecules [285]. Considering the large bulk of the antibody, such interference is not unexpected, yet only a few of the antibodies that bind to the Ca -ATPase in native sarcoplasmic reticulum interfered with crystallization. 

In addition, dimer-type black developing fluoran compounds such as 2,2-bis(4-[6 -(/V-cyclohexyl-/V-methylamino)-3 -methylfluoran-2 -yl-amino]phenyl propane (59)60 are also proposed. Fluoran 59 has much lower solubility in organic solvents to improve image stability to plasticizer for use in thermosensitive recording label paper. 

Phenyl cyclopropenone is not capable of thermal dimerization. On treatment with Cu2+ ions, however, a well-defined tetramer is formed54, to which structure 265 of a polyene dilactone was assigned. Its generation can be rationalized via 264 with both the above dimerization types contributing in metal-catalyzed reactions. 

Shift in the nature of DNA damage that occurred between 5.6 eV (220 nm) and 8.3 eV (150 nm). This shift is considered to be a shift from the base dimer-type damage to the strand-break type, which could be expected with work using DNA molecules. 

If, as a criterion of value to the study of lignin depolymerization by alkaline hydrolysis, the maximum yield of oxygen-bearing, phenylpropanoid derivatives is chosen, then the conditions of such a study have been optimized here at a treatment severity corresponding to a reaction temperature of 300°C for 1 hour. Under these conditions, 20% of the lignin is recovered as ether-solubles of which 55% is identifiable as monomeric derivatives. The rest of this material probably consists of dimeric-type compounds not identified by capillary gas chromatography. 

Fig. 3. Contour diagram for the correlated in-step motion of the two protons in a dimer-type system such as...

The 37-kDa 334-residue subunits of the dimeric type I tryptophanyl-tRNA synthetase238 are the smallest known the largest bacterial synthetase is an alanine-specific type II tetramer with 95-kDa 875-residue subunits.239 Gene deletions show that a much smaller core, comparable in size to that of the tryptophanyl-tRNA synthetase, is needed for amino acid activation. The synthetases share little sequence homology except for a short 11-residue part of the adenylate binding site near the N terminus.240 241 Some of the synthetases contain bound zinc ions.225,242... 

Three general dimer types were considered for both nitroanilines A, the optimal dimer with two distinct H-bonds, each between one amino-hydrogen and one nitro-oxygen B, a relaxed geometry, with at least one bifurcated H-bond that is the local minimum closest to the crystal structure, and, C, the structure obtained by fixing the H-bonds at their experimental (crystal structure) distances and optimizing the rest of the dimer within the same constraints as A and B. Structure C is closest to the experimental structure. 

Amino acids (L) have also been shown to form a dimeric-type complex of (V0(00)2L)2(00)L coordination, for which it has been proposed that one peroxo group and the carboxylate group of one amino acid form a bridge between the two vanadium nuclei, after the fashion displayed in Scheme 6.6 [24], The complex was found not to retain its integrity when dissolved in aqueous solution. 

In an investigation of another alkaloid of the dimeric type, vinblastine, high-resolution mass spectrometry was extensively used to determine the molecular formulas of the molecule ion and its cleavage products.117 This was veiy helpful in the structure determination.118 The structure elucidation of villastonine, also an indole alkaloid of the... 

Ebner and Thompson [58] proposed the termination of the surface with pendant H2P207 groups, which surround two vanadyl dimers (type B). Such surface termination may be envisioned by replacing every phosphate tetrahedron facing up in the bulk (200) planes of (V0)2P207 with pyrophosphate groups. In this type of surface termination, the pyrophosphate fence isolates pairs of vanadyl dimers from other pairs, which was proposed to be beneficial for the selectivity to maleic anhydride during n-butane oxidation. 

A half-rufhenocene complex, Ru(indenyl)Cl(PPh3)2 was similarly used for polymerization of MMA in conjunction wifh an MMA-dimer-type initiator, H(MMA)2C1 (Scheme 6.181) [233]. Addition of Al(Oi-Pr)3 accelerated the polymerization rate to afford similar living polymers (M /M = 1.1). The behavior of the Ru-Ind complex was similar in the polymerization of styrene. Polystyrene with narrow MWD (M /Mn= 1.1) was obtained by use of a suitable radical initiator -Me2C(CO2Et)Br. 

Benzo[c]cinnoline-5,6-dioxide is a colorless, high-melting (243°C), non-basic compound, sparingly soluble in organic solvents. There has been discussion of spectroscopic evidence as to whether it has a di-JV-oxide or a nitroso-dimer type structure, hut there has been little investigation of its chemistry and there appears to be no chemical evidence for its behaving as 2,2 -dinitrosobiphenyl i.e., it shows no nitroso group reactions. 

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