What is Selectivity

I Beneficial results from the use of selectively toxic agents. 7 1.2 The physical basis of selectivity the three principles. 15 

These molecules interact with their complementary biopolymers to generate every response needed for the cell s continuity both as an individual and as a species. Collectively they are the natural agonists. 

Man s therapeutic agents are of three kinds. A few, such as vitamins. 

It is an achievement of prime importance for man that selectively toxic agents have been foimd not only for many of his ills, but also for use in his animal husbandry, fields, and forests. The continuance and even expansion of these benefits requires continuous discovery of improved selectively toxic agents. 

Whereas the task of chemotherapy is to rid the host of bacteria, viruses, fungi, protozoa, worms and insects, pharmacodynamics has a more difficult programme because the uneconomic cells are part of the organism of the economic species. For example, the uneconomic form may be an endocrine gland that has hypertrophied and upset the balance of metabolism of an otherwise healthy body it may simply be some part of the nervous system 

1 Beneficial results from the use of selectively toxic agents. 7 

A remedy is said to have selectivity if it can influence one kind of living cell without affecting others, even when these cells are close neighbours. Man has found many selective agents for treating his diseases and those of his farm animals and field crops. Most of the chemical substances that man uses in therapy differ from those evolved by nature, and yet are often related to them because both kinds may act on the same receptors. The substances employed by 

In chemotherapy, where the aim is to kill all the uneconomic cells, because they are invaders, it is evident that uneconomic and economic cells are related to one another as parasite and host. On the other hand, pharmacodynamics has as its goal the eventual normalization of the uneconomic cells because the economic and uneconomic cells with which it has to deal form parts of the same organism. 

Many antagonists produce such striking manifestations in Man that we can easily understand how our forefathers classed them, mistakenly, as agonists. For example, ethanol (alcohol) was spoken of as a stimulant whereas it is actually an inhibitor. What it does is to damp down some inhibitory nerves, in the central nervous system, so that any excitement reigns unchecked (see Sections 7.5.1 and 7.6.1). Strychnine, strongest of the convulsants, acts similarly, but lower down in the central nervous system. 

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What is selected-ion monitoring and what are the advantages of using this techniqne ... 

Kaejmaekers What is selected is a whole pattern of interactions, which includes some residual expression. 

What is selected reaction monitoring Why is it also called MS/MS Why does it improve the signal-to-noise ratio for a particular analyte ... 

Mixtures of metal ions in aqueous solution can sometimes be separated by selective precipitation. What is selective precipitation If a solution contained 0.10 A/ Mg, O.IOMCa, and 0.10 A/Ba, how could addition of NaF be used to separate the cations out of solution—that is, what would precipitate first, then second, then third How could addition of K3PO4 be used to separate out the cations in a solution that is 1.0 A/Ag, 1.0 A/Pb, and 1.0 A/Sr ... 

Accept/reject what is Select one over the Degree of like and ... 

What is selective precipitation Under which conditions does selective precipitation occur ... 

Although a number of enantioselective chiral selectors have been identified today, there is much that remains to be done to both improve them and understand the interaction processes. Furthermore, the user must know what chiral selector is involved (its chemical structure), what is selective for, and how it is used. When choosing a chiral method, the selectivity, efficiency, loadability, and reproducibility should also be considered. 

What is the minimum selectivity of decane which must be achieved for profitable operation The values of the materials involved together with their molecular weights are given in Table 4.1. 

One of the most cost effective forms of maintenance is to train the operators to visually Inspect the equipment on a daily basis. Careful selection of staff, appropriate training and incentives will help to improve what is often called first-line maintenance. 

A covalent bond (or particular nomial mode) in the van der Waals molecule (e.g. the I2 bond in l2-He) can be selectively excited, and what is usually observed experimentally is that the unimolecular dissociation rate constant is orders of magnitude smaller than the RRKM prediction. This is thought to result from weak coupling between the excited high-frequency intramolecular mode and the low-frequency van der Waals intemiolecular modes [83]. This coupling may be highly mode specific. Exciting the two different HE stretch modes in the (HF)2 dimer with one quantum results in lifetimes which differ by a factor of 24 [84]. Other van der Waals molecules studied include (NO)2 [85], NO-HF [ ], and (C2i J )2 [87]. 

What is the effect of water on the rate and selectivity of the Lewis-acid catalysed Diels-Alder reaction, when compared to oiganic solvents Do hydrogen bonding and hydrophobic interactions also influence the Lewis-acid catalysed process Answers to these questions will be provided in Chapter 2. 

What is the influence of ligands on the Lewis acid on the rate and selectivity of the Diels-Alder reaction If enantioselectivity can be induced in water, how does it compare to other solvents Chapter 3 deals with these topics. 

A method for the analysis of Ca + in water suffers from an interference in the presence of Zn +. When the concentration of Ca + is 100 times greater than that of Zn +, an analysis for Ca + gives a relative error of -1-0.5%. What is the selectivity coefficient for this method ... 

The population standard deviation for the amount of aspirin in a batch of analgesic tablets is known to be 7 mg of aspirin. A single tablet is randomly selected, analyzed, and found to contain 245 mg of aspirin. What is the 95% confidence interval for the population mean ... 

A sample contains a weak acid analyte, HA, and a weak acid interferent, HB. The acid dissociation constants and partition coefficients for the weak acids are as follows Ra.HA = 1.0 X 10 Ra HB = 1.0 X f0 , RpjHA D,HB 500. (a) Calculate the extraction efficiency for HA and HB when 50.0 mF of sampk buffered to a pH of 7.0, is extracted with 50.0 mF of the organic solvent, (b) Which phase is enriched in the analyte (c) What are the recoveries for the analyte and interferent in this phase (d) What is the separation factor (e) A quantitative analysis is conducted on the contents of the phase enriched in analyte. What is the expected relative erroi if the selectivity coefficient, Rha.hb> is 0.500 and the initial ratio ofHB/HA was lO.O ... 

The concentration of Ca + in a sample of sea water is determined using a Ca ion-selective electrode and a one-point standard addition. A 10.00-mL sample is transferred to a 100-mL volumetric flask and diluted to volume. A 50.00-mL aliquot of sample is placed in a beaker with the Ca ion-selective electrode and a reference electrode, and the potential is measured as -0.05290 V. A 1.00-mL aliquot of a 5.00 X 10 M standard solution of Ca + is added, and a potential of -0.04417 V is measured. What is the concentration of Ca + in the sample of sea water ... 

What is the maximum acceptable concentration of benzoate if this ion-selective electrode is to be used for analyzing samples containing as little as 10 M salicylate with an accuracy of better than 1% ... 

In the same chromatographic analysis for low-molecular-weight acids considered in Example 12.2, the retention time for isobutyric acid is 5.98 min. What is the selectivity factor for isobutyric acid and butyric acid ... 

In one study, when analyzing a solution of 10-ppb glutathione and 1.5-ppb ascorbic acid, the signal was 5.43 times greater than that obtained for the analysis of 10-ppb glutathione. What is the selectivity coeffiaent for this analysis The same study found that when analyzing a... 

According to these basic concepts, molecular recognition implies complementary lock-and-key type fit between molecules. The lock is the molecular receptor and the key is the substrate that is recognised and selected to give a defined receptor—substrate complex, a coordination compound or a supermolecule. Hence molecular recognition is one of the three main pillars, fixation, coordination, and recognition, that lay foundation of what is now called supramolecular chemistry (8—11). 

Every Hcense agreement is a negotiated contract between parties, and therefore there are no hard-and-fast rules as to what is required in a Hcense agreement. Since every provision is negotiable, the Hcense agreement should be viewed in its entirety, rather than as component parts. Nevertheless, for purposes of iUustration, select component parts wiU be discussed. 

What is the most meaningful way to express the controllable or independent variables For example, should current density and time be taken as the experimental variables, or are time and the product of current density and time the real variables affecting response Judicious selection of the independent variables often reduces or eliminates interactions between variables, thereby leading to a simpler experiment and analysis. Also inter-relationships among variables need be recognized. For example, in an atomic absorption analysis, there are four possible variables air-flow rate, fuel-flow rate, gas-flow rate, and air/fuel ratio, but there are really only two independent variables. 

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