Selectivity relative

Table 11.17 Relative Selectivity of Various Counter Cations Table 11.18 Relative Selectivity of Various Counter Anions...

TABLE 11.17 Relative Selectivity of Various Counter Cations... 

Counterion Relative selectivity for AG 50W-X8 resin Counterion Relative selectivity for AG 50W-X8 resin... 

The relative selectivity of a chromatographic column for a pair of solutes is given by the selectivity factor, a, which is defined as... 

In general, activation of alpha-1 adrenergic receptors causes a contraction of smooth muscle and of blood vessels, pilomotor muscles, dilator pupillae, vas deferens, nictitating membrane, splenic capsule, and sphincters of the intestine and urinary bladder and of the bile duct. An exception is the relaxation of the smooth muscle of the intestine. Prazosin [19216-56-9] indoramin [26844-12-2] and WB-4101 are relatively selective antagonists of these receptors. 

Betazole (683) has been used as a chemical control substance for pharmacological characterization of histamine receptors (B-80MI40406), and shows a relative selective activity towards the H2-receptor. Betazole hydrochloride is used to diagnose impairment of the acid-producing cells of the stomach. 

On the basis of the reaction of alkyl radicals with a number of polycyclic aromatics, Szwarc and Binks calculated the relative selectivities of several radicals methyl, 1 (by definition) ethyl, 1.0 n-propyl, 1.0 trichloromethyl, 1.8. The relative reactivities of the three alkyl radicals toward aromatics therefore appears to be the same. On the other hand, quinoline (the only heterocyclic compound so far examined in reactions with alkyl radicals other than methyl) shows a steady increase in its reactivity toward methyl, ethyl, and n-propyl radicals. This would suggest that the nucleophilic character of the alkyl radicals increases in the order Me < Et < n-Pr, and that the selectivity of the radical as defined by Szwarc is not necessarily a measure of its polar character. 

Fig. 1. The relative selectivity of two mobile carriers. In both parts of the figure, the circles and squares represent the sodium and potassium ions transported, respectively. (Cited from Ref. 8))...

The relative selectivities of strongly acid and strongly basic polystyrene resins, with about 8 per cent DVB, for singly charged ions are summarised in Table 7.2. It should be noted that the relative selectivities for certain ions may vary with a change in the extent of cross-linking of the resin for example, with a 10 per cent DVB resin the relative selectivity values for Li+ and Cs+ ions are 1.00 and 4.15, respectively. 

Cation Relative selectivity Anion Relative selectivity... 

Relatively selective stimulation of Pi-adrenergic receptors can be achieved with dobutamine. This is a racemic drug of which both isomers activate the Pi-receptor, and in addition the (-) isomer activates ( -receptors whereas the (+) isomer activates p2-receptors the simultaneous activation of ai- and p2-receptors results in no major net effect on peripheral resistance, and thus the overall cardiovascular effects are mediated by Pi-stimulation leading to increases in cardiac contractility and output. Dobutamine is used for the short-term treatment of acute cardiac failure and for diagnostic purposes in stress echocardiography. 

German investigators (Brock et al) worked on the creation of alkylating pro-drugs that have cytostatic activity after specific biotransformation in the tumor tissue. Cyclophosphamide (CTX) has well pronounced antitumor activity with the broadest spectrum. It is metabolized to the cytotoxic phosphoamide mustard. In normal tissues with high enzyme level cyclophosphamide is converted to its inactive metabolites (Fig. 2). These differences in biotransformation can explain the relative selectivity of cyclophosphamide towards... 

Cladribine (2-Chlordeoxyadenosine) is a synthetic purine nucleoside that is converted to an active cytotoxic metabolite by the deoxycytidine kinase. The drug is relatively selective for both normal and malignant lymphoid cells. 

Tyiphostins are a group of substances, which block a variety of tyrosine kinases. Some of them have a relative selectivity for defined tyrosine kinase subtypes. 

VMATs are not inhibited by drugs such as cocaine, tricyclic antidqnessants and selective serotonin reuptake inhibitors that affect plasma membrane monoamine transport. Amphetamines have relatively selective effects on monoaminergic cells due to selective uptake by plasma membrane monoamine transporters, but their effect appears to be mediated by their ability as weak bases to reduce ApH, the driving force for vesicular monoamine transport that leads to efflux of the vesicular contents into the cytoplasm. 

As reviewed earlier in the section on the pharmacology of ethanol, several neurotransmitter systems appear to influence the reinforcing or discriminative stimulus effects of ethanol. Although these systems appear to function interactively in their influences on drinking behavior, the medications that have been employed to treat alcohol dependence affect neurotransmitter systems relatively selectively. Consequently, these systems will be discussed individually here. 

A -3-Ketosteroids, e.g. progesterone in plasma 150°C, 20 min Conversion of A -3-ketosteroids into fluorescent derivatives (Xn = 440 nm). Relatively selective for progesterone at 150°C, detection limit 2-5 ng. 

As with other monoamines, the actions of 5-HT are terminated by its reuptake from the synapse by another member of the family of Na+/CU-dependent transporters. The 5-HT transporter has many features in common with its catecholamine equivalent (described fully in Chapter 8 see Fig. 8.7), including its presumed 12 transmembrane-spanning domains. However, the cloned 5-HT transporter has a for 5-HT of about 450 nM whereas its K for both noradrenaline and dopamine is some ten thousand-fold greater (Povlock and Amara 1997) which means that it is relatively selective for uptake... 

A second way of increasing synaptic concentrations of noradrenaline and 5-HT is to block their neuronal reuptake. Several groups of compounds act in this way and can be classified according to their relative selectivity for the noradrenaline and 5-HT transporters. 

Moreover, while the change from cyclohexane to hexane as the reactant has produced a large change in the relative selectivity of the methane/pentane co-products with respect to other products, the ratio of propane to the ethane/butane couple is very close (46/30 or 1.5 for hexane and 24/20 or 1.2 for cyclohexane. Table 8). This small variation compared with the very large change in (methane + pentane) selectivity (18% for n-hexane, 56% for cyclohexane) suggests that the formation of ethane/butane is independent of the formation of methane/pentane, that is that intermediate E is not a major contributor to the formation of the ethane/butane couple. 

Much effort has been expanded in drawing mechanistic inferences from the observation that cofacial bismetalloporphyrins containing a non-redox-active metal ion are fairly selective catalysts (e.g., (DPA)CoM, where M = Lu, Sc, Al, Ag, Pd, 2H, i.e., monometallic porphyrins Fig. 18.15). At least two hypotheses have been proposed (i) polarization of the 0-0 bond in catalytic intermediates by the second ion (on an N-H moiety) acting as a Lewis acid [CoUman et al., 1987, 1994] and (ii) spatial positioning of H+ donors especially favorable for proton transfer to the terminal O atoms of coordinated O2 [Ni et al., 1987 Rosenthal and Nocera, 2007]. To the best of my knowledge, neither hypothesis has yet been convincingly proven nor resulted in improved ORR catalysts. When seeking stereoelectronic rational of the observed av values, it is useful to be mindful that a fair number of simple Co porphyrins are also relatively selective ORR catalysts (Section 18.4.2). 

In Figure 34.7b, the relative selectivity to byproducts such as EG and organic acids is shown (primarily acetic, lactic and glyceric acids). Not all carbon supports are equivalent, as there are a wide variety of source materials that are used in their production. Note that the highest acid selectivity is shown with the catalyst based on a graphitic carbon and on a carbon support first treated with titania. 

The relative selectivity of drugs such as haloperidol for the higher affinity (+)SKF-10,047 labeled sites allowed the determination of the pharmacological profile of the low affinity sites, which was very similar to that of 3H-TCP labeled sites. PCP and... 

Delta receptors are relatively selective for two related penta-peptides, methionine enkephalin and leucine enkephalin (met- and leu-enkephalin), which were isolated from porcine brain (Hughes 1975). Both met- and leu-enkephalin inhibit electrically induced contractions of guinea pig ileum, an effect that mimics those effects seen with opioid drugs, and is naloxone reversible. The enkephalins are processed posttranslational ly from proenkephalin, and secreted from central and peripheral neurons and endocrine cells in the adrenal medulla. 

The starting point for much of the work described in this article is the idea that quinone methides (QMs) are the electrophilic species that are generated from ortho-hydro-xybenzyl halides during the relatively selective modification of tryptophan residues in proteins. Therefore, a series of suicide substrates (a subtype of mechanism-based inhibitors) that produce quinone or quinonimine methides (QIMs) have been designed to inhibit enzymes. The concept of mechanism-based inhibitors was very appealing and has been widely applied. The present review will be focused on the inhibition of mammalian serine proteases and bacterial serine (3-lactamases by suicide inhibitors. These very different classes of enzymes have however an analogous step in their catalytic mechanism, the formation of an acyl-enzyme intermediate. Several studies have examined the possible use of quinone or quinonimine methides as the latent... 

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