Oligomers covalent

Carbonyl anions react with AgNO, or CuCI in aqueous bis(2-methoxycthyI)ether to form covalent oligomers (n = 3 or 4) ... 

Oh, K. Jeong, K.-S. Moore, J. S. m-Phenylene ethynylene sequences joined by imine linkages Dynamic covalent oligomers. J. Org. Chem. 2003, 68, 8397-8403. 

Covalent aggregates form as a result of chemical degradation reactions which crosslink protein molecules, for example, disulfide-mediated reactions. Some proteins such as human serum albumin possess free thiol groups which are prone to intermolecular disulfide formation. More commonly, therapeutic protein candidates may contain one or more intramolecular disulfide group which can be prone to thiol-disulfide interchange. Although covalent oligomers. 

The propensity of many proteins to form noncovalent assemblies is not necessarily a problem in itself for the development of a pharmaceutically viable product. However, such behavior can impact pharmaceutical properties and stability by bringing reactive groups into close proximity leading to the formation of covalent oligomers. The increased size of the noncovalent assembly may impact absorption kinetics and bioavailability, the extent of which is influenced by the dissociation constant. Noncovalent association can confer beneficial effects. The conformational stability of the protein... 

Although covalent oligomers such as dimers may be relatively small and may remain fully soluble, they can possess enhanced toxicity and immunogenicity relative to the monomer. It is not trivial to isolate and characterize individual protein oligomers to the extent of resolving toxicology in preclinical models, so published examples are not plentiful. However, the rich history of insulin as a therapeutic protein provides a well-characterized example. Covalent insulin dimers have been detected in the blood of insulin... 

Copper(I) tends towards a tetrahedral coordination geometry in complexes. With 2,2 -bipyr-idine as a chelate ligand a distorted tetrahedral coordination with almost orthogonal ligands results. 2,2 -Bipyridine oligomers with flexible 6,6 -links therefore form double helices with two 2,2 -bipyridine units per copper(I) ion (J. M. Lehn, 1987,1988). J. M. Lehn (1990 U. Koert, 1990) has also prepared such helicates with nucleosides, e.g., thymidine, covalently attached to suitable spacers to obtain water-soluble double helix complexes, so-called inverted DNA , with internal positive charges and external nucleic bases. Cooperative effects lead preferentially to two identical strands in these helicates when copper(I) ions are added to a mixture of two different homooligomers. 

Size Isomers. In solution, hGH is a mixture of monomer, dimer, and higher molecular weight oligomers. Furthermore, there are aggregated forms of hGH found in both the pituitary and in the circulation (16,17). The dimeric forms of hGH have been the most carefully studied and there appear to be at least three distinct types of dimer a disulfide dimer connected through interchain disulfide bonds (8) a covalent or irreversible dimer that is detected on sodium dodecylsulfate- (SDS-)polyacrylamide gels (see Electroseparations, Electrophoresis) and is not a disulfide dimer (19,20) and a noncovalent dimer which is easily dissociated into monomeric hGH by treatment with agents that dismpt hydrophobic interactions in proteins (21). In addition, hGH forms a dimeric complex with ( 2). Scatchard analysis has revealed that two ions associate per hGH dimer in a cooperative... 

Chromatographic Packings Prepared by Covalently Bound Polymers and Oligomers... 

Handel, S.E., Hendry, K.A.K., Sheterline, P. (1990). Microinjection of covalently cross-linked actin oligomers causes disruption of existing actin filament architecmre in PtK2 cells. J. Cell Sci, 97, 325-333. 

An alternative to using van der Waals forces to organise molecules at surfaces is to covalently bond monomers. Haq and Richardson,34 for example, have attempted to develop PMDA-ODA oligomers using controlled imide coupling... 

One of the advances in the field of PET is the design of molecular devices, in which D and A pairs are ingeniously linked by covalent bridges (B) to form D-B-A dyads. Electron transfers between D and A across B in a controlled manner may thus display useful functionalities, such as molecular rectifiers [25], switches [26], biosensors [27], photovoltaic cells [28], and nonlinear optical materials [29]. Spacers that have been utilized are versatile, including small molecules, such as cyclohexane [30], adamantane [31], bicyclo[2.2.2]octane [32], steroids [33], and oligomers of... 

Brandi et al. [71] using culture fluid of Acidovorax delafieldii and cyclic 3HB oligomers were in agreement with the presence of endo-hydrolase activity of poly(3HB) depolymerases. Similar results were obtained by de Koning et al. [72] who demonstrated that covalently cross-linked poly(HAMCL) was hydrolyzed completely by P. fluorescens. It is assumed that most - if not all - extracellular poly(HA) depolymerases have endo- and exo-hydrolase activity. Depending on the depolymerase the hydrolysis products are only monomers, monomers and dimers, or a mixture of oligomers (mono- to trimers). 

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