Differential binding of two

Although it is well understood that molecules must be able to enter the cavity of the cyclodextrin molecule for complexation to occur, and therefore, under chromatographic conditions, for retention to result, the differential binding of two stereoisomers within the cyclodextrin that allows for their differential retention is not always apparent. An understanding of this can be obtained through the use of three dimensional computer graphic imaging of the crystal structure of the inclusion complex. 

Treherne, J.M., Stern, J.S., Flack, W.J. and Young, J.M. (1991). Inhibition by cations of antagonist binding to histamine Hi-receptors differential effect of sodium ions on the binding of two radioligands. Br. J. Pharmacol. 103, 1745-1751. 

Xu H, Partilla JS, de Costa BR, Rice KC, Rothman RB. Differential binding of opioid peptides and other drugs to two subtypes of opioid deltancx binding sites in mouse brain further evidence for delta receptor heterogeneity. Peptides 1993 14 893-907. 

HIF-la and HIF-2a have the same domain architecture and common mechanisms for DNA binding, dimerization, oxygen-dependent degradation (NODD and CODD domains), and transactivation domains. The sequences of these domains are related closely but contain differences that may have functional consequences (e.g., with respect to HIF hydroxylase selectivity). The interdomain sequences are related less closely, and the differences may enable differential binding of regulatory proteins to HIF-la and HIF-2a. HIF-3a is more markedly different from the other two HIF-a isoforms as it apparently has no functional NODD domain, and only the CODD domain within the N-terminal TAD has been identified. Additionally, HIF-3a lacks the C-TAD that exists in both HIF-la and HIF-2a. (28). Relatively little is known about the importance of HIF-3a as compared with the intensively investigated HIF-l/2a isoforms. 

Acceptable accuracy and parallelism of the C-terminus assay are likely due to the C-terminal specificity of the capture antibody and the N-terminal location of the norleucine substitutions. Conversely, with the N-terminal specific assay, dramatic differences in recoveries were seen for the two forms of the drug, a direct consequence of these N-terminal modifications and differential binding of the immunoreagent directed at this region. Although each assay demonstrated good linearity upon... 

The reactions found are worthy of note in that binding to both pyrimidine and purine bases bases was found, the differential staining being made possible by binding of two platinum atoms per adenine residue at both pH 6.0 and pH 7.5, while at the lower pH one platinum and at high pH two platinum atoms were bound to guanine, albeit in a much slower reaction. 

The regioselectivity of LEH has been studied experimentally with different substrates. Studies with the enantiomers of 1-methylcyclohexene oxide (1 and 2, Scheme 2) revealed preferred attack at the methyl-substituted oxirane carbon, Cl, with a regioselectivity of 85(C1) 15(C2). This indicated an acid-catalyzed mechanism, which would result in preferred attack at the more substituted carbon. However, conversion of limonene-1,2-epoxide did not support this conclusion and showed somewhat intriguing results. Exclusive attack at the more substituted carbon (Cl) is seen for the stereoisomers 4 and 5, while exclusive attack at the less substituted carbon (C2) is observed for stereoisomers 3 and 6 (Scheme 2). Interestingly, the two limonene-1,2-epoxide stereoisomers with the same stereochemistry at the oxirane ring, (IR,2S) for 3 and 5 and IS,2R) for 4 and 6, exhibit attack at opposite carbons (Scheme 2). A suggested explanation for the differences was differential binding of the substrates in the active site, which would lead to attack at different carbons. ... 

A major criticism of the stochastic probability approach is that relatively slow secondary reactions, for which the near-equilibrium assumption does not apply, cannot be accommodated. In this situation, it is necessary to derive and solve simultaneous partial differential equations for mass conservation and obtain expressions for the first and second moments of the elution profile and the concomitant plate height arising from slow kinetics of secondary equilibrium. If, once again, the process can be represented as involving the reversible binding of two forms, the resolution of the interconverting species can be given by [59]... 

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