First effect

Several synthetic pyrimidines and purines are useful drugs Acyclovir was the first effective antiviral compound and is used to treat herpes infections 6 Mercaptopunne is one of the drugs used to treat childhood leukemia which has become a very treatable form of cancer with a cure rate approaching 80%... 

Hydrolysis. The first effect of either acid hydrolysis or alkaline hydrolysis (saponification) is the removal of the fatty acids. The saponification value of commercial lecithin is 196. Further decomposition into glycerol, phosphoric acid, and head groups (ie, choline, ethanolamine, etc) may foUow prolonged heating. Lecithin may also be hydrolyzed by enzymes. 

Trigclic Antidepressants. Imipramine (38) was introduced in the late 1950s as one of the first pharmacotherapies for depression. At that time, chlorproma2ine [50-53-3] was the first effective antipsychotic treatment to be discovered. Researchers looked for similar chemical stmctures and imipramine was found to be effective in the symptomatic treatment of depression. Over the years, other congeners, such as desipramine (39), amitriptyline (40), and dothiepin (41), were synthesized and shown to be clinically efficacious antidepressant dmgs (121). These substances, known under the general mbric of tricycHc antidepressants, share a basic chemical stmcture comprising... 

In a detersive system containing a dilute surfactant solution and a substrate bearing a soHd polar sod, the first effect is adsorption of surfactant at the sod—bath interface. This adsorption is equivalent to the formation of a thin layer of relatively concentrated surfactant solution at the interface, which is continuously renewable and can penetrate the sod phase. Osmotic flow of water and the extmsion of myelin forms foHows the penetration, with ultimate formation of an equdibrium phase. This equdibrium phase may be microemulsion rather than Hquid crystalline, but in any event it is fluid and flushable... 

Sulfur dioxide, sulfites, and metabisulfites have had extensive use as antimicrobial preservatives in the food industry. In pharmaceuticals they have had a dual role, acting as preservatives and antioxidants. The sulfa dmgs, or sulfonamides, the first effective chemotherapeutic agents to be employed... 

Multiple-Effect Evaporators A number of approximate methods have been published for estimating performance and heating-surface requirements of a multiple-effect evaporator [Coates and Pressburg, Chem. Eng., 67(6), 157 (1960) Coates, Chem. Eng. Prog., 45, 25 (1949) and Ray and Carnahan, Trans. Am. Inst. Chem. Eng., 41, 253 (1945)]. However, because of the wide variety of methods of feeding and the added complication of feed heaters and condensate flash systems, the only certain way of determining performance is by detailed heat and material balances. Algebraic soluflons may be used, but if more than a few effects are involved, trial-and-error methods are usually quicker. These frequently involve trial-and-error within trial-and-error solutions. Usually, if condensate flash systems or feed heaters are involved, it is best to start at the first effect. The basic steps in the calculation are then as follows ... 

From assumed feed temperature (forward feed) or feed flow (backward feed) to the first effect and assumed steam flow, calculate evaporation in the first effect. Repeat for each succeeding effect, checking intermediate assumptions as the calculation proceeds. Heat input from condensate flash can be incorporated easily since the condensate flow from the preceding effects will have already been determined. 

The result of the calculation will be a feed to or a product discharge from the last effect that may not agree with actual requirements. The calciilation must then be repeated with a new assumption of steam flow to the first effect. 

Another way of representing shock-wave profiles is in the form of F-t histories of the pressure or another variable at a series of points along its direction of propagation, as in Fig. 2.9. In the above example, the leading part of the shock front arrives first, effectively increasing the pressure instantaneously. The rarefaction arrives later and decreases the pressure over a time... 

Vasquez [121] reviewed and commented on various approaches to side chain modeling. The importance of two effects on side chain conformation was emphasized. The first effect was the coupling between the main chain and side chains, and the second effect was the continuous nature of the distributions of side chain dihedral angles for example. 

There are two fundamental chromatography theories that deal with solute retention and solute dispersion and these are the Plate Theory and the Rate Theory, respectively. It is essential to be familiar with both these theories in order to understand the chromatographic process, the function of the column, and column design. The first effective theory to be developed was the plate theory, which revealed those factors that controlled chromatographic retention and allowed the... 

The kinetic problem is to distinguish among these mechanisms and particularly between the A1 and A2 routes. The first effective solution to this problem was provided by Zucker and Hammett. The key difference between these mechanisms is the presence (A2) or absence (Al) of a molecule of water in the transition state of the rate-determining step. 

Hie first effect has been exploited in numerous ligand-accelerated [30], enantioselective 1,2-additions of RyZn reagents to aldeliydes [26]. Dimetliylzinc, for example, has a linear structure and is not reactive towards aldehydes or ketones. Upon coordination of triazine, however, a tetraliedral configuration is produced at tlie zinc... 

Miltefosine, an alkylphosphocholine derivative, is a new antileishmanial drug and the first effective oral treatment of visceral leishmaniasis. However, there are concerns regarding teratogenicity, rapid emergence of resistance, and variable cure rates, possibly due to species differences in drug sensitivity. The mechanism of action of miltefosine is not known. 

The adsorption of gases on solid surfaces proceeds to such an extent that approximately 10 7 gr. is present per cm.2 in the equilibrium state. This is of the same order of magnitude as the strength of the limiting capillary layer of a liquid ( 184), hence it is not improbable, as suggested by Faraday (9) (1884), that the adsorbed gas is sometimes present in the liquid state. The adsorbed amount increases with the pressure and diminishes with rise of temperature. The first effect does not follow a law of simple proportionality, as in the case of the absorption of gases by liquids, rather the adsorbed amount does not increase so rapidly, and the equation ... 

In contrast, iproniazid, introduced in 1951 for treatment of tuberculosis, induced euphoria and was described as a psychic energiser . In fact, these patients, when given iproniazid, could become quite disruptive and this action was regarded as an undesirable side-effect However, its beneficial effects in depression were soon recognised and it was regarded as the first effective antidepressant drug. Studies of peripheral sympathetic neurons, later extended to noradrenergic neurons in the brain, showed that iproniazid irreversibly inhibits the catalytic enzyme, monoamine oxidase (MAO). Because only cytoplasmic monoamines are accessible to MAO, inhibition of this enzyme first increases the concentration of the pool of soluble transmitter but this leads to a secondary increase in the stores of vesicle-bound transmitter i.e. the pool available for impulse-evoked release (Fillenz and Stanford 1981). 

The increase in density on melting is assumed to arise from two competing effects that occur as water is heated. First, increasing translational freedom for the water molecules weakens the hydrogen-bonded network that exists in ice I. This network thus collapses, and reduces the volume. Second, increased vibrational energy for the molecules causes an effective increase in the volume occupied by any one molecule, thus enlarging the overall volume of the liquid. The first effect is considered to predominate below 4 °C, the second above 4 °C. 

It follows that convection of the hqnid has a twofold influence It levels the concentrations in the bnlk liquid, and it influences the diffusional transport by governing the diffusion-layer thickness. Shght convection is sufficient for the first effect, but the second effect is related in a qnantitative way to the convective flow velocity The higher this velocity is, the thinner will be the diffusion layer and the larger the concentration gradients and diffusional fluxes. 

The first effect is that of a concentration change of the charged reactant particles in the reaction zone this change is determined by Boltzmann s distribution law ... 

Selected clay stabilizers are shown in Table 1-10. Thermal-treated carbohydrates are suitable as shale stabilizers [1609-1611]. They may be formed by heating an alkaline solution of the carbohydrate, and the browning reaction product may be reacted with a cationic base. The inversion of nonreducing sugars may be first effected on selected carbohydrates, with the inversion catalyzing the browning reaction. 

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