Chemical factors

Chemical factors lipophilicity, size, structure, pKa, ionization, chirality. 

Biological factors species, strain, sex, genetic factors, disease and pathological conditions, hormonal influences, age, stress, diet, tissue and organ specificity, dose, and enzyme induction and inhibition. 

The importance of the physicochemical characteristics of compounds has already been alluded to in the previous two chapters. Thus, lipophilicity is a factor of major importance for the absorption, distribution, metabolism, and excretion of foreign compounds. Lipophilic compounds are more readily absorbed, metabolized, and distributed, but more poorly excreted, than hydrophilic compounds. 

This means that the drug molecule has a hydrophobic section and a cationic hydrophilic section (Fig. 5.1). The hydrophobic section will associate with lipid and the hydrophilic, cationic section will associate with the aqueous phase. 

Drugs that cause phospholipidosis are cationic amphiphiles they contain a hydrophobic ring structure and a hydrophilic side chain with a positively charged amine group. Such chemicals can interact with either the ionic (e.g., chlorophentermine) or hydrophobic (e.g., amiodarone) moieties of phospholipids. 

As an illustration, we will use the case of coupled chromatography, such as HPLC-DAD, as in case study 1. For a simple chromatogram, the underlying dataset can be described as a sum of responses for each significant compound in the data, which are characterised by (a) an elution profile and (b) a spectrum, plus noise or instrumental error. In matrix terms, this can be written as 

Consider the matrix of case study 1, a portion of a chromatogram recorded over 30 and 28 wavelengths, consisting of two partially overlapping compounds  

If we observe X, can we then predict C and SI In previous chapters we have used a hat notation to indicate a prediction, so it is also possible to write the equation above as 

Ideally, the predicted spectra and chromatographic elution profiles are close to the true ones, but it is important to realise that we can never directly or perfectly observe the underlying data. There will always be measurement error, even in practical spectroscopy. Chromatographic peaks may be partially overlapping or even embedded, meaning that chemometric methods will help resolve the chromatogram into individual components. 

One aim of chemometrics is to obtain these predictions after first treating the chromatogram as a multivariate data matrix, and then performing PCA. Each compound in the mixture is a chemical factor with its associated spectra and elution profile, which can be related to principal components, or abstract factors, by a mathematical transformation. 

A very important factor in a system that can lead to MIC is the water quahty if raw, untreated or poorly treated water is being used for an industrial activity such as hydrotesting, one may expect that the risk of MIC will be very high. 

What is meant by untreated water is water in which no specific physical/chem-ical treatment has been done to remove (mainly) corrosion-related bacteria. This water can be sea, river, or well water used for industrial activities. 

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Chemical Factors. Because knock is caused by chemical reactions in the engine, it is reasonable to assume that chemical stmcture plays an important role in determining the resistance of a particular compound to knock. Reactions that produce knock are generally free-radical chain-type reactions which are different from those that occur in the body of the flame the former occur at lower temperatures and are called cool flame reactions. 

Peroxy and hydroperoxy radicals play important roles ia the knock process. A number of good reviews have discussed the details of the chemical mechanisms (16). Ignition delay (tau) has also been used for description of the chemical tendency to knock (17). The chemical factors affecting knock are... 

Another problem occurs when some fire retardant formulations ate exposed to elevated temperatures (eg, when used as roof tmsses or as roof sheathing) thermal-induced strength reductions can occur in-service. The thermo-chemical factors were discussed by LeVan and Winandy (26), and a kinetic degrade model was developed (27). The treater should be consulted to obtain appropriate in-service modifications for specific fire retardant treatments. 

Controlled by diffusive mass transfer Controlled by chemical factors A major distinction is between reactions that are ... 

To understand the causes of signal change and therefore to explain the influence of physico-chemical factors on its shape and magnitude, the mathematical models are employed. A multitude of different and often contradictory models were proposed to describe the atom formation in ET AAS, but they do not take into account a number of effects influencing appreciably the atomic absorption profile. The surface effects (such as staictural changes in graphite tubes, surface porosity, analyte penetration into graphite etc.) ai e very important. 

Chemical Factors. These involve mainly the kinetics of the reaction. The design must provide sufficient residence time for the desired reaction to proceed to the required degree of conversion. 

An electrochemical reaction is said to be polarized or retarded when it is limited by various physical and chemical factors. In other words, the reduction in potential difference in volts due to net current flow between the two electrodes of the corrosion cell is termed polarization. Thus, the corrosion cell is in a state of nonequilibrium due to this polarization. Figure 4-415 is a schematic illustration of a Daniel cell. The potential difference (emf) between zinc and copper electrodes is about one volt. Upon allowing current to flow through the external resistance, the potential difference falls below one volt. As the current is increased, the voltage continues to drop and upon completely short circuiting (R = 0, therefore maximum flow of current) the potential difference falls toward about zero. This phenomenon can be plotted as a polarization diagram shown in Figure 4-416. 

Physico chemical factors Chemical attack, physical changes such as plasticiser bleed... 

B. Chemical Factors Contributing to Aging Many propint systems have built-in defects which contribute to degradation of the polymer system and reduce service life. The poly are ... 

Several factors can influence metal uptake by stream autotrophic biofllms in fluvial systems. These include chemical factors (pH, saUnity, phosphate concentration) which affect metal bioavailabiHty by either altering the speciation of the metal or by complexing it at the biotilm s matrix and cell surfaces [18, 40], and also other biological and physical factors. 

Wolfe NL, Kitchens BE, Macalady DL, et al. 1986. Physical and chemical factors that influence the anaerobic degradation of methyl parathion in sediment systems. Environ Toxicol Chem 5 1019-26. 

In Chapter 3, the distribution of enviromnental chemicals through compartments of the gross environment was related to the chemical factors and processes involved, and models for describing or predicting environmental fate were considered. In the early sections of the present chapter, the discnssion moves on to the more complex question of movement and distribntion in the living environment— within individuals, communities, and ecosystems—where biological as well as physical and chemical factors come into play. The movement of chemicals along food chains and the fate of chemicals in the complex communities of sediments and soils are basic issues here. 

Some Chemical Considerations Relevant to the Mouse Bioassay. Net toxicity, determined by mouse bioassay, has served as a traditional measure of toxin quantity and, despite the development of HPLC and other detection methods for the saxi-toxins, continues to be used. In this assay, as in most others, the molar specific potencies of the various saxitoxins differ, thus, net toxicity of a toxin sample with an undefined mixture of the saxitoxins can provide only a rough approximation of the net molar concentration. Still, to the extent that limits can be placed on variation in toxin composition, the mouse assay can in principle provide useful data on trends in net toxin concentration. However, the somewhat protean chemistry of the saxitoxins makes it difficult to define conditions under which the composition of a mixture of toxins will remain constant thus, attaining a reproducible level of mouse bioassay toxicity is difficult. It is therefore useful to review briefly some of the chemical factors that should be considered when employing the mouse bioassay for the saxitoxins or when interpreting results. Similar concepts will apply to other assays. 

However, if a reaction is dangerous in itself, it is much more difficult to determine the working mode than for a reaction in which there is no chemical factor, which would make us think that there is a danger. This is the reason why it is important to address this question. 

Although glycol-water formulations are not prone to foaming, mechanical and chemical factors may cause foaming in the system. The use of corrosion inhibitors and the presence of contaminants may enhance the tendency to form foams. For these reasons, antifoaming agents, such as silicones, polyglycols, or oils, are sometimes added. 

In order to explain the above-mentioned anomalies an original model of the m-component copolymerization has been put forward [48], taking into account chemical factors along with the also thermodynamic ones. It is pertinent to dwell briefly on the key points of this model. 

Most gasoline constituents are volatile organics. Volatilization depends on the potential volatility of the compounds and on the soil and environmental conditions, which modify the vapor pressure of the chemicals. Factors affecting volatility are water content, clay content, surface area, temperature, surface wind speed, evaporation rate, and precipitation. 

In September 1971 the seventh International Conference of Chemotherapy in Prague contained a full session on the use of platinum drugs. A set of papers will be published. Many of the points dealt with in passing in the above article are treated in detail confirming the general outline of the chemical factors which are of importance. The compound cis- Pt(NHs)2Cl2 proved sufficiently successful in tests on tumours in mice that it is now being used in clinical trials in the United States of America. 

Light (visible and ultraviolet) Mechanical (wind and flowing water) Chemical factors... 

The course taken by any particular fossilization process is, therefore, determined by the physical and chemical factors prevalent in the environment of the dead remains. The physical factors include temperature, degree of aeration, and rate of flow of groundwater. The nature of minerals and rocks, and of the groundwater at the site of burial, are the most important chemical factors. Reconstructing and explaining the processes undergone by dead remains, from the time of death to when they are fully fossilized, is the concern of taphonomy, the study of the processes taking place when dead remains pass from the biosphere to the lithosphere (see Textbox 69). 

Acids are selected based on the nature of the well treatment and the mineralogy of the formation. The critical chemical factors in properly selecting an acid are stoichiometry (how much formation material is dissolved by a given amount of acid), the equilibrium constant (complete reaction of the acid is desired), and reaction rate between the acid and the formation material (106). 

As early as in 1909, it was recognized that some chemical factor in the brain was responsible for recovery sleep. Cerebrospinal fluid (Legendre Pieron, 1911) or brain extract (Ishimori, 1909) from sleep-deprived dogs resulted in excess sleep when infused into the cerebral ventricles of recipient animals. The fact that the material was ineffective if heated or ultrafiltered pointed to a protein or peptide as sleep factor (Legendre Pieron, 1911). Later studies have... 

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