Conjugation, direct

Neighboring group participation (a term introduced by Winstein) with the vacant p-orbital of a carbenium ion center contributes to its stabilization via delocalization, which can involve atoms with unshared electron pairs (w-donors), 7r-electron systems (direct conjugate or allylic stabilization), bent rr-bonds (as in cyclopropylcarbinyl cations), and C-H and C-C [Pg.150]

A meta nitro group is not directly conjugated to the phenoxide oxygen and thus stabi hzes a phenoxide ion to a smaller extent m Nitrophenol is more acidic than phenol but less acidic than either o or p nitrophenol... 

Substituents cannot directly conjugate with /3-pyridine-like nitrogen atoms. Azole substituents which are not a or y to a pyridine-like nitrogen react as they would on a benzene ring. Conjugation with an a-pyridine-like nitrogen is much more effective across a formal double bond thus the 5-methyl group in 3,5-dimethyl-l,2,4-oxadiazole (323) is by far the more reactive. 

The additional parameter r is adjusted from reaction to reaction it reflects the extent of the additional resonance contribution. A large r corresponds to a reaction with a large resonance component, whereas when r goes to zero, the equation is identical to the original Hammett equation. When there is direct conjugation with an electron-rich reaction center, an equation analogous to Eq. (4.17) can be employed, but a is used instead of [Pg.210]

An alternative approach is that adopted by Horrocks and co-workers, where the aromatic residues in metal-binding proteins are used as sensitizers. Since the distance between the metal and the donor is effectively fixed, this provides a rigid scaffold for the experiment, and the absence of a directly conjugated pathway between the metals means that Forster (through space) energy transfer can be assumed. The r-6 distance-dependence of this means that the extent of sensitized emission from the lanthanide ion provides information on the spatial relationship between the metal-ion binding site (lanthanide ions often bind at Ca2+ sites) and nearby aromatic residues. 58-60... 

Both enzymatic and nonenzymatic biotransformation of acrylonitrile occurs. Acrylonitrile is capable of covalently binding to proteins and other macromolecules such as lipids or nucleic acids, or acrylonitrile can also be directly conjugated to glutathione and excreted in urine as cyanoethylmercapturic acid. 

Van Bladeren PJ, Delbressine LP, Hoogeterp J J, et al. 1981. Formation of mercapturic acids from acrylonitrile, crotononitrile, and cinnamonitrile by direct conjugation and via an intermediate oxidation process. Drug Metab Dispos 9 246-249. 

The ability to direct conjugation or modification specifically through arginine residues using this chemistry has been exploited in the availability of the only photoreactive glyoxal derivative, APG. 

Alternatively, a thiol-containing protein may be directly conjugated to the SPDP-modified dendrimer to create a disulfide linkage. Add a sulfhydryl-containing protein... 

A-chain immunotoxins, however, may not be quite as cytotoxic as conjugates formed from intact toxin molecules (Manske et al., 1989). In an alternative approach to A chain use, the intact toxin of two-subunit proteins is directly conjugated to a monoclonal without isolation of the A chain. Conjugation of an antibody with intact A-B chain toxins can be done without a cleavable linker, as long as the A chain can still separate from the B chain once it is internalized. Therefore, it is important to avoid intramolecular crosslinking during the conjugation process which can prevent release of the A-B complex. In addition, since the B chain... 

Geoghegan, K.E, and Stroh, J.G. (1992) Site-directed conjugation of nonpeptide groups to peptides and proteins via periodate oxidation of a 2-amino alcohol. Applications to modification at N-terminal serine. Bioconjugate Chem. 3, 138-146. 

If the substituent is attached to an sp2-hybridized carbon atom that is not directly conjugated with the reaction site, then it is correlated with the Hammett equation using the am constants. 

Figure 13.5 Outline of the production strategy of CEA-SCAN. The antibody-producing hybridoma cell line was originally obtained by standard methods of hybridoma generation. Spleen-derived murine B-lymphocytes were fused with murine myeloma calls. The resulting stable hybridomas were screened for the production of anti-CEA monoclonals. The clone chosen produces an IgG anti-CEA antibody. Note that the finished product outlined above is not radiolabelled. The freeze-dried antibody preparation (which has a shelf life of 2 years at 2-8 °C) is reconstituted immediately prior to its medical use. The reconstituting solution contains 99mTc, and is formulated to facilitate direct conjugation of the radiolabel to the antibody fragment...

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