Receptor unit

KCff, or the dissociation constant of a diug, refers to the rate at which the drug-receptor complex dissociates into separate diug and receptor units. 

M -Dialkyldiazacrown ethers and their precursors fcis(alkylamino) derivatives of tri- and tetraethylene glycols were prepared <96CCCC622>. New hydroxy-bearing dibenzo-azocrown ethers have been conveniently prepared utilizing l,3-Ws(2-formylphenoxy)-2-propanol and a diamine, followed by reduction of the intermediate diimine <96P1197>. Fluorescent photoinduced electron transfer sensor 5 with monoaza-18-crown-6 and guanidinium receptor units demonstrated a fluorescence with T -aminobutyric acid in a mixed... 

A certain control of selectivity for simple ligands without altering their fluorescence features is possible when integrating them into more developed, often macrocyclic receptor units [45,46]. 

The separation of binding site and fluorophore by a nonconjugating spacer opens the path to other mechanisms of communication, most prominently ET and exci-mer/exciplex formation. In the first case, the electronic nature of both fluorophore and receptor unit and the steric nature of the spacer are the important parameters for signal generation. In the second case, for most systems the electronic nature of the fluorophores and the steric nature of the receptor as well as its change upon analyte binding determine the signal. 

Fig. 12 Left. ICT-PET probe 34 with a small and rigid spacer (thick black), decoupling the PET active donor = receptor unit from the 7c-conjugated ICT fluorophore. Middle and right probes 35 and 36 combining a conventional ICT and a virtually decoupled ICT process with two identical receptor units (35, for Hg2+) and two different receptor units (36, tetraoxa monoaza crown for Na+ and dithia monooxa monoaza crown for Ag+). For color code, see Fig. 10...

Rurack K, Kollmannsberger M, Resch-Genger U et al (2000) A selective and sensitive fluoroionophore for Hgll, Agl, and Cull with virtually decoupled fluorophore and receptor units. J Am Chem Soc 122 968-969... 

In the field of molecular biology, the substitution of a polyphenylene den-drimer with fluorescent dyes and receptor units can be used for fluorescence labeling of biologically active compounds. The multiplicative effect of the number of dyes or receptor units can result in an increase in fluorescence sensitivity and an augmentation of the binding constant in the substrate receptor complex. Since we have shown that perylenemonoimide dyes at the periphery of our den-... 

Fig. 6 Emission quenching of polymer 25 by different transition metal ions. The polymer concentrations are held fixed at 3.08x10" M corresponding to receptor unit. Transition metal ions are 1.54x10 M. (Reprinted with permission from Ref. [26]. Copyright 2002 American Chemical Society)...

The switching efficiency of lumophore-spacer-receptor systems can be improved by using multiple receptor modules. The PET rate is increased in the device when free of guest ions since more than one site can provide the transiting electron. The simplest cases, such as 4, are those where the receptor units are well separated to prevent interdependent ion binding with an interposed lumophore to minimize the lumophore-receptor spacing for maximum PET rates. Besides this statistical effect, receptors may also cooperatively participate in PET. This may be the case in 5 and 6. ... 

Lumophore-spacer-receptor systems are not by any means limited to the ami-noalkyl aromatic family even if we focus on the receptor unit. Still, the latter family is likely to remain a major provider of ionically switchable luminescent devices. Aminoalkyl aromatics also serve as the platform for the development of luminescent PET sensors for a whole class of nonionic saccharides. While aliphatic amines, either singly or in arrays, can serve as receptors for a variety of cationic... 

Macrocyclic 25 has been constructed with pseudocryptand 26 which can be discerned within Tsien s ratiometric fluorescent sensors as the Na receptor unit. Conformational changes by 26 upon ion binding allows strong off-on PET sensing action due to the ion-induced increase of its oxidation potential. X-ray structural evidence for the Na -induced conformational changes in 26 shows decreased conjugation with a 40° twist about the C-N bond of the 2-anisidine unit. X-ray evidence is also available for similar conformational changes in the non-macro-cyclic Ca " receptor 23. A related analysis has been made for a Ag" -phenyl-azacrown ether interaction which involves a soft-soft component. ... 

Host-guest Complexes as Analogues of the Interacting Substrate-Receptor Unit in Biochemistry... 

Sakatsume M, Igarashi K-I, Winestock KD, Garotta G, Larner AC, Finbloom DS. The Jak Kinases differentially associate with the a and b (accessory factor) chains of the interferon-g receptor to form a functional receptor unit capable of activating ST AT transcription factors. J Biol Chem 1995 270 17528-17534. 

By combining a receptor unit with a rigid shaping unit, hollow macropolycyclic speleands (Figure 3 20) have been synthesized. NMR experiments indicate that (20) forms both external and internal complexes with methylammonium cation.38... 

Chemical transformations may be induced by reaction between a bound substrate and functional groups borne by the macrocyclic receptor unit, as illustrated in structure 74. 

Biological Implications of Structural and Electrical Properties of Lipids. It is rather obvious that the structure of lipids is very important in connection with the function of living cells since most physiological processes occur in lipid environment. There is, for example, evidence that lipid-protein complexes are necessary for the proper functioning of mitochondria (56). Although lipids are most important in providing a suitable material for functional complexes (ionic channels, electron transport systems, receptor units, etc.), their own physical properties are certainly... 

Inclusion of guest species in dendritic host molecules 6.2.3.1 Dendrimers with multiple receptor units... 

The periphery of dendrimers is predestined for attachment of numerous receptor units. In principle, this is also possible in the core or in the branching units... 

One of the best known receptor units is that introduced by Hamilton et al. 

A substantial number of interesting luminescent molecular systems contain cy-clophane receptor units [110] and involve PET-type processes, particularly as a result of the collaboration between the teams of Stoddart (now at the University of California at Los Angeles) and Balzani (University of Bologna, Italy) [111]. 

This type of chromogenic sensor utilizes the coordination chemistry of transition metal complexes, which have vacant binding sites to bind specific anions or have pendant arms containing anion receptor units. Transition metal complexes already have their own specific colors due to their different electronic structures. Coordinating directly to anions or binding of anions by the pendant arms results in perturbations of their electronic structures and causes color changes. 

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