Covalent dimers

For a more complete treatment of the derivations and determination of experimental rate constants (to be discussed briefly below) refer to Ref. 46 for Gramicidin A and Ref. 47 for the malonyl dimer of Gramicidin A. (Malonyl Gramicidin A is formed by deformylation of Gramicidin A and then joining to amino ends together using the malonyl moiety, —CO—CH2—CO—, to form the covalent dimer.)... 

Weiland M, Brandenburg C, Brandenburg D et al (1990) Antagonistic effects of a covalently dimerized insulin derivative on insulin receptors in 3T3-L1 adipocytes. Proc Natl Acad Sci USA 87 1154-1158... 

Figure 1.19 Tyrosine and phenylalanine residues can undergo oxidation to modify their phenyl side-chain groups. Tyrosine can form covalent dimers that link two side chains together via a radical reaction. Both tyrosine and phenylalanine can be modified by oxidation to add oxygen-containing groups directly to their aromatic ring.

Figure 8.29 Illustration showing how all-anticlinic bilayer smectic should be ferroelectric is given. In case of covalent dimers (bent-core mesogens), equilibrium tilt of director combined with anti clinic layer interfaces in bow plane provides SmCsPF ferroelectric banana structure.

Strickley, R.G., and B.D. Anderson, Solid-state stability of human insulin. II. Effect of water on reactive intermediate partitioning in lyophiles from pH 2-5 solutions stabilization against covalent dimer formation. J Pharm Sci, 1997.86(6) 645-53. 

The solubility of the indium(I) halides in toluene/TMEDA was noted previously. Electron spectroscopy15 shows that InCl forms covalent dimers in the gas phase. The d-shell electrons can be regarded as being part of the core and play no part in bonding. 

In 1996 we reported on the first covalent dimerization of the [2]rotaxane with sulfonamide function in its wheel component to give a [3]rotaxane 32 (bis[2]rotaxane) [49], Subsequently, we expanded the concept of covalent bridging and produced more elaborate rotaxane assemblies such as an unsymmetrical bis[2]rotaxane 33, and 34,... 

Gallium(III) bromide is a hygroscopic, white solid which sublimes readily and melts at 122.5° to a covalent, dimeric liquid. The solid is ionic and its electrical conductivity at the melting point is twenty-three times that of the liquid.5 The vapor pressure of the liquid at T°K is given by the equation log p(mm.) = 8.554 — 3129/T and the heat of dissociation of the dimer in the gas phase is 18.5 kcal./mol.3 At 125° the liquid has the following properties 5,6 density, 3.1076 dynamic viscosity, 2.780 c.p. surface tension, 34.8 dynes/cm. and specific conductivity, 7.2 X 10-7 ohm-1 cm.-1 Gallium(III) bromide readily hydrolyzes in water and forms addition compounds with ligands such as ammonia, pyridine, and phosphorus oxychloride. 

Fig. 20 Supramolecular assembly of 26 formed via heteroassociation of an imidazolyl-substituted porphyrin-phthalocyanine covalent dimer...

Bouhallab, S., Morgan, F., Henry, G., Molle, D., and Leonil, J. 1999. Formation of stable covalent dimer explains the high solubility at pH 4.6 of lactose-(3-lactoglobulin conjugates heated near neutral pH. J. Agric. Food Chem. 47, 1489-1494. 

Most of the IL-lOs, as well as IL-19, IL-20, IL-22, and IL-24, have an even number of cysteine residues that all participate in disulfide bonds. However, human, simian, and baboon cmvIL-10 as well as IL-26 contain one additional unpaired cysteine residue (Eig. 6). The crystal structure of human cmvIL-10 revealed the unpaired cysteine forms an inter-chain disulfide bond resulting in a covalently linked dimer structure that differs from the non covalent dimers of ebv and cellular IL-10 and IEN-7 (Jones et aL, 2002b). The unpaired cysteine is located in the BG loop of cmvIL-10. However, the position of the unpaired cysteine in simian and baboon... 

Although both IFN-7 and lL-10 swap the same secondary structural elements (helices E and F) to form the dimers, their quaternary structures are very different. IFN-7 and lL-10 adopt inter-domain angles of approximately 60° and 90°, respectively. More recently, the structure of cmvIL-10 revealed a domain angle of approximately 150° (Jones et al, 2002b). In addition, the two cmvIL-10 peptide chains form an interchain disulfide bond while IFN-7 and cellular IL-10 are non-covalent dimers. The domain orientations of each dimer are essentially fixed at one unique inter domain angle which alters the orientation of the cell surface receptors and may ultimately modulate cellular signal transduction events. 

Irradiation of the matrix (420-500 nm, a range not corresponding to the pimer charge-transfer transition) produced an additional triplet (ti j 10 hours) with D = 0.0175 cm and E = O, r = 5.4 A. Careful examination of the spectra of concentrated solutions of 4 revealed absorption in the range of 420-500 nm Thin film spectroscopy of 4 revealed that covalent dimers (rather than singlet pairs) gave rise to the new triplet via a no ncr transition Formation of a triplet [D = 0.0146 cm" and E = O, r = 5.5 A] from the dimer of 2 , 2-2, has been accomplished by irradiation in an MTHF glass. The equilibria describe the relationship of the triplets and radicals in Eq. 13. The two triplet pairs (A and B) are not readily interconvertible. 

At room temperatures, formation of dimer from pyridinyl radical is a second-order process. However, in many cases (l-methyl-2-carbomethoxypyridinyl, 2, l-hydro-4-phenylpyridinyl and l-alkyl-4-phenylpyridinyl ), a slow first-order process appears after the fast second-order process at low temperatures. Similarily l-hydro-4-acetylpyridinyl dimerizes to a pinacol [RR(HO)C—C(OH)RR, i.e., a compound in which the dimer bond has been formed through the C=0 group of the acetyl] . Pinacol formation has also been noted for l-trimethylsilyl-4-acetyl-pyridinyl and l-trimethylgermylpyridinyl-4-carboxaldehyde The result has been interpreted in terms of rapid formation of a radical pair followed by slow formation of covalent dimer (Eq. 16)... 

The covalent dimer is not dissociated by SDS (linked by intennolecular disulfides). 

Several uninegative groups show a similarity to halide ions in both their ionic and covalent compounds. The corresponding pseudohalogen covalent dimer of four of these entities has been isolated (Table 93). (The name is due to Birckenbach and Kellermann, 1925.)... 

Among all the single Co porphyrins examined, a [3-pyrrole substituted species bearing two ester groups, mentioned briefly in Section 3.1.2, (see insert, Figure 3.51) was found to display a rather unique behavior upon adsorption on carbon surfaces. This macrocycle, to be denoted as CoPI, is a precursor to the synthesis of the first face-to-face porphyrin examined in an electrochemical environment [95] hence, a discussion of its properties serves to underscore the effects associated with changes in the electrocatalytic microenvironment following covalent dimerization (see below). 

Synthesis of the diabody was carried out by means of a modification of the method reported in Refs [4.17, 4.18] for synthesis of the ior-CEAI murine antibody scFv fragment. A non-covalent dimer association was obtained from two identical ior-CEAI scFv antibody fragments, in which VL and Vl domains were linked via a 5 amino acid residue. A hexahistidine tag at the C-terminus of the Vl domain aided protein purification. 

Fauch re, J. C., Rossier, M., Capponi, A., Vallotton, M. B. Potentiation of the antagonistic effect of ACTHu 24 steroidogenesis by synthesis of covalent dimeric conjugates. FEES Lett. 1985,183, 283-286. 

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