Physicochemical characteristics importance

Although isoxazole derivatives have been known for more than 80 years, the investigation of their chemistry commenced rather slowly. Earlier studies were mainly devoted to the development of synthetic methods. It is only recently that attention was focused on the investigation of chemical properties and in particular on the peculiarities of the behavior of isoxazole derivatives and the elucidation of their physicochemical characteristics. This enabled new data to be obtained that are of considerable importance. 

Comprehensive physicochemical characterization of any raw material is a crucial and multi-phased requirement for the selection and validation of that matter as a constituent of a product or part of the product development process (Morris et al., 1998). Such demand is especially important in the pharmaceutical industry because of the presence of several compounds assembled in a formulation, such as active substances and excipients, which highlights the importance of compatibility among them. Besides, variations in raw materials due to different sources, periods of extraction and various environmental factors may lead to failures in production and/or in the dosage form performance (Morris et al., 1998). Additionally, economic issues are also related to the need for investigating the physicochemical characteristics of raw materials since those features may determine the most adequate and low-cost material for specific procedures and dosage forms. 

Specific carotenoid-protein complexes have been reported in plants and invertebrates (cyanobacteria, crustaceans, silkworms, etc.), while data on the existence of carotenoproteins in vertebrates are more limited. As alternatives for their water solubilization, carotenoids could use small cytosolic carrier vesicles." Carotenoids can also be present in very fine physical dispersions (or crystalline aggregates) in aqueous media of oranges, tomatoes, and carrots. Thus these physicochemical characteristics of carotenoids as well as those of other pigments are important issues for the understanding of their bioavailability. 

Of all these formulations, it is the diverse semisolids that stand out as being uniquely topical. Semisolid systems fulfill a special topical need as they cling to the surface of the skin to which they are applied, generally until being washed off or worn off. In contrast, fluid systems have poor substantivity and readily streak and run off the desired area. Similarly, powders have poor staying properties. Importantly, the fundamental physicochemical characteristics of solutions, liquid emulsions and suspensions, and powders are independent of their route of application, and are discussed adequately elsewhere in this text and need not be reconsidered. This is not to say the compositions of such systems cannot be uniquely topical, for there are chemicals that can be safely applied to the... 

Microbial transformations and generally not chemical transformations characterize the sewer environment in terms of quality transformations of the wastewater. On the other hand, the physicochemical characteristics, e.g., diffusion in the biofilm and exchange of substances across the water-air interface, play an important role and must be integrated with the microbial transformations. The hydraulics and the sewer solids transport processes have a pronounced impact on the sewer performance. These physical processes, however, are typically dealt with in hydraulics and are, therefore, only included in the text when directly and closely related to the chemical and biological processes. 

Chemical and physicochemical characteristics, conditions and processes are crucial for any biological system. A chemical basis also defines the conditions for the microbiologically initiated quality changes of wastewater under transport in sewers. Equilibrium and process-related aspects are important. 

The physicochemical characterization of a colloidal carrier is necessary because important characteristics, such as particle size, hydrophobicity, and surface charge, determine the biodistribution after administration [129-132]. Preparation conditions, such as the pH of the polymerization medium, monomer concentration, and surfactant concentration, can influence the physicochemical characteristics of the particles [60, 62, 64]. It is, therefore, essential to perform a comprehensive physicochemical characterization of nanoparticles, which has been reviewed by Magenheim and Benita [133]. 

Pharmacological strategy of CNTs generally relies on four main critical issues (1) preparation of nanovectors, (2) uptake, (3) function, and (4) elimination (Fig. 12.4). The physicochemical characteristics of CNTs including size, shape, aggregation, chemical composition, surface functionalization, and solubility play an important role in the biodistribution and pharmacokinetics of nanomaterials (Champion et al., 2007 Kostarelos, 2003 Lacerda et al., 2006 Nishiyama, 2007 Oberdorster et al., 2005 Radomski et al., 2005)... 

The ex vivo methods lend themselves easily for the performance of mechanistic investigations. In order to optimize selection of drug candidates prior to further clinical development, it is important to decipher the contributive roles of permeation, metabolism, efflux, and toxicity. This will then make it possible to properly channel the optimization process, for instance, by permeation enhancement, mucoadhesion, modification of the physicochemical characteristics of the drug, or even change in the route of administration in case the drug and/or formulation turns out to be too toxic. Regarding permeability studies, it is possible not only to quantify passive diffusion but also to identify and characterize (compound)-specific carrier-mediated transport routes. These tools have been used to identify and characterize the relative contribution of... 

Another important consideration in investigation of the reaction of sorbed pesticides is the nature of the sorption process itself. Sorption/desorption kinetics and the physicochemical characteristics of the pesticide molecules in the sediment-sorbed state can be expected to influence the kinetic observations made in experimental systems. 

The physicochemical characteristics of the components (both drugs as well as excipients) used in dry powders are of significant importance for the performance of the inhalation sys-... 

The physicochemical characteristics of X-ray contrast agents strongly determine their pharmacological and toxicological behaviour and are therefore import features, particularly in guiding the search for improved substances. 

The importance of surface analysis for evaluating the environmental effects of toxic substances is becoming more apparent as the result of recent work in this field. Chapter 9 describes ESCA, Auger, Ion Microprobe, and SIMS surface analysis techniques for atmospheric particulates. These techniques overcome the obvious limitations of bulk analysis, that is, the wide variability in the physicochemical characteristics of different particles. 

The lipid components of food are known to be critical in the development of much of a food s flavor. Modifications to lipid modifying enzymes such as lipases have led to new products useful in the rapid preparation of other food components Chapter 13,14), Better utilization of lipid constituents in food products can be gained from a better understanding of the thermodynamic and physicochemical characteristics of emulsions. Significant advancement in emulsion chemistry and food engineering have recently appeared in the literature and are an important portion of this volume Chapter 19),... 

The physicochemical characteristics of raw materials play an important role in content uniformity and bioavailability. Therefore, bioavailability of the drug over time must be thoroughly investigated before any significant changes are made. Once the physicochemical properties of drug substances (e.g., particle size of raw materials) can influence the availability and clinical effect of a product, the main characteristics of raw materials should be considered in a validation program. The... 

The physicochemical characteristics of the chemical in question (i.e., lipid solubility, water solubility, vapor pressure, etc.) also will be important information. 

Perhaps the most important feature of the plasma membrane is that it is selectively permeable. Overall permeability of the membrane to a chemical depends on the nature of the membrane, its surface charge and rigidity, and the chemical in question. Therefore, only certain substances are able to pass through the membrane, depending on particular physicochemical characteristics. It will be apparent throughout this book that the physicochemical characteristics of molecules are major determinants of their disposition and often of their toxicity. 

Thus, with regard to the passage of foreign, potentially toxic molecules through membranes, the following physicochemical characteristics are important ... 

It is clear that the physicochemical characteristics of the compound and hence the extent and avidity of binding will determine the importance of plasma protein binding in the disposition of the compound. 

Absorption is necessary for the chemical to exert a systemic biological/toxic effect and involves crossing membranes. Membranes are semipermeable phospholipid/protein bilayers. The phospholipids and proteins are of variable structure, and the membrane is selectively permeable. The physicochemical characteristics of foreign molecules that are important include size/shape, lipid solubility, structure, and charge/polarity. 

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. 

In conclusion, it cannot be stressed too strongly that the physicochemical characteristics of a foreign compound are factors of paramount importance in determining its toxicity. 

The most important feature affecting the functional and organoleptic properties of a protein is its surface structure. Surface structures affect the interaction of a protein with water or other proteins. By modifying the structure of the protein, particular functional and organoleptic properties are obtained. Functional properties of a protein are physicochemical characteristics that affect the processing and behavior of protein in food systems (Kinsella, 1976). These properties are related to the appearance, taste, texture, and nutritional value of a food system. Hydrolysis is one of the most important protein structure modification processes in the food industry. Proteins are hydrolyzed to a limited extent and in a controlled manner to improve the functional properties of a foodstuff. 

From an analytical perspective, the single most important physicochemical characteristic of riboflavin is its photosensitivity (80-82). Exposure of this vitamin to ultraviolet and visible light results in irreversible photoreduction to lumiflavin and lumichrome and loss of vitamin activity. In addition, the coenzymes are subject to hydrolysis by endogenous phosphatases that are present in a number of foods. Since these enzymes are generally inactivated by thermal processing, they are a concern only in the analysis of fresh products. 

An analysis of the extensive literature data and the data of the authors of this book [1640, 1642, 1655] permits a conclusion that the variations in the physicochemical characteristics of Al(OR)3 are caused by the existence of different types of aggregates and the possibility oftheir mutual transformations. The molecular composition depends on the conditions in the course of sample preparation — temperature, nature ofthe solvent applied, and the age ofthe sample. An important role is also played by the presence in the samples of microamounts of oxocomplexes, which are always formed on sublimation, distillation, and any other thermal treatments. 

An important consideration in the development of soft gelatin capsules is the composition of the LII content, be it solution, suspension, or solid. The contents of soft gelatin capsules vary from solids, solid in liquid, solution or suspension, a combination of miscible liquid, ora simple liquid formulation. It is critical that each formulation is carefully developed depending on the physicochemical characteristics of the drug molecule. An optimum formulation consists of a minimum volume or weight that can be L lied in the smallest possible capsule for ease of administration and for maximum therapeutic effectiveness. Composition of the capsule content and shell composition of commonly available commercial products are presented in Tables 21.1 and 21.2, respectively. 

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