Physico-chemical characteristics

The pH of the alimentary canal has been reviewed by a number of authors (370, 796) most of the data referring to man and the more commonly used 

In the rat, the presence of Hymenolepis diminuta has a marked lowering effect on the pH 1 h after feeding, the lowest pH reached in the intestine of uninfected rats was found to be 6.4, but that in infected rats fell to 6 (524, 796), probably due to secretion of organic acids by the worm (Chapter 5). 

This characteristic, which may have considerable significance for cestode metabolism (especially in relation to electron transport) has been relatively little studied. In the rat, perhaps the most studied laboratory host, the stomach contents are reported to have an Eh value of + 150 mV and that of the upper and lower small intestine about -100 mV (796). That this negative potential is largely due to the presence of microflora is seen from the fact that, in germ-free rats, the Eh of the large intestine was found to be + 30 to +200 mV, but this became negative after contamination with various coliforms (970). The Eh may prove to be an important factor in in vitro culture systems (p. 258). 

C02 is frequently the predominant duodenal gas and plays an important role in the physiology of cestodes in two ways (a) as a source of carbon atoms for metabolic functions via C02 fixation (Chapter 5) (b) as a trigger in the hatching of cyclophyllidean eggs (p. 192) or the excystment of larval cysts. Production of C02 results from the interaction of HC03 and H+, the latter being derived from secretions from the gut, biliary and pancreatic 

In addition to 02 and C02, N2, H2 and CH4 are found in various concentrations in different vertebrates and these gases make up 99% of the intestinal gas in man. The source of H2 and CH4 appears to be bacterial metabolism and, in cattle rumen, CH4 is known to be produced by Methanobacterium rumentium. The composition and origin of intestinal gas in man has been reviewed in detail by Levitt et at. (444). 

---

Knowledge of the mechanism of action and investigations on the physico-chemical characteristics of the therapeutically used dalbaheptides has stimulated the transformation of natural antibiotics into new derivatives using both chemical and biosynthetic modification. 

Aerosols reach the alveolar space depending on their particle size and physico-chemical characteristics. Small particles that reach the alveiilar region (see Sections 2.3.7 and 3.1.1) may reach the circulation through the lymphatic drainage of the alveolar region. 

Physico-chemical characteristics greatly determine the entry of chemicals into the body, and also their behavior in the body (distribution, biotransformation, and excretion). Therefore, the physico-chemical characteristics of a compound affect its dose and its subsequent effects by determining how quickly and extensively a chemical reaches the target organs. In the following section, some of these important physical-chemical characteristics of chemicals will be discussed. 

The introduction of heteroatoms into cyclic systems produces significant variations in the molecular geometry that reflect the changes in covalent radii, relative electronegativity and effective hybridization. Consequently, there are changes in the bonding and the physico-chemical characteristics of these heterocyclic systems—particularly in small ring systems. 

On a global scale, the atmosphere serves as the major pathway for the transport and deposition of contaminants from emission sources to terrestrial and aquatic ecosystem receptors (22, 27). Once a contaminant is airborne, the processes of atmospheric di sion, transport, transformation, and deposition act to determine its fate. These processes are complex and the degree to which they influence the fate of a particular contaminant is dependent on its physico-chemical characteristics, the properties and concentrations of coexisting substances, and the prevailing meteorological conditions, including wind, precipitation, humidity, temperature, clouds, fog, and solar irradiation. 

Transformation of parent contaminants into secondary products may occur during the processes of atmospheric diffusion and transport as a result of physical, chemicjd, and photochemical processes (22). Chemical conversion within the atmosphere may also change the physico-chemical characteristics of contaminants, dramatically altering their atmospheric residence times and fates from those of the parent contaminants. The complex reactions within the atmosphere that are driven by chemical processes such as hydroxyl scavenging... 

Peret-Ahneida L. et ah, Separatiou aud deterruiuatiou of the physico-chemical characteristics of curcumin, demethoxycmcumiu and bisdemethoxycurcumin. Food Res. Int., 38, 1039, 2005. 

Main physico-chemical characteristics of the solids weight percents of metals and additives, specific surface area, metallic dispersion. 

Joshi, S. R., Pechhacker, H., Wiliam, W., and von der Ohe, W. (2000). Physico-chemical characteristics of Apis dorsata, A. cerana and A. mellifera honey from Chitwan district, central Nepal. Apidologie 21, 367-375. 

The physico-chemical characteristics of the sediment sample significantly influence the fate of agrochemicals in a paddy field and a waterway system. Therefore, the factors that influence adsorption, retention, and degradation of agrochemicals are very important. As a minimum the characteristics of the sediment sample listed below should be described ... 

An important consideration prior to sample collection is transportation and storage. Samples should be treated so as to retain the integrity of the sample from the moment of collection to the time of analysis. The physico-chemical characteristics of a sediment sample change during drying, with effects on the sorption-desorption behavior of chemicals. 

Separation processes, as could be seen from Figure 2.1, position themselves at the back end of the sequence in operations in the mineral processing flowsheet. The front-end operations has been found virtually to terminate with the liberation or the size-reduction processes involving crushing and grinding. It is important to limit the amount of size reduction to that at which adequate liberation is accomplished. The term adequacy is related to the cost involved in comminution and to performance of the concentration methods that follows. The concentration is obtained by separation processes which rely on differences in the properties of the particles, the physical and physico-chemical characteristics of minerals. In this context, it will only be relevant to refer to Table 2.5 which presents a summary of the processes along with the properties of the minerals that are exploited. 

UV/VIS spectrophotometry can be used to determine many physico-chemical characteristics of compounds and thus can provide information as to the identity of a particular compound. Although UV/VIS spectra do not enable absolute identification of an unknown, they are frequently used to confirm the identity of a substance through comparison of the measured spectrum with a reference spectrum. However, UV spectrophotometry is not highly specific, and can obviously only be applied to polymer additives which are absorbers of UV radiation, i.e. contain chromophoric groups. Both UV and IR monitor functional entities rather than the entire molecular structure. A functional group s proximity to other electropositive or electronegative structures in a molecule affects the absorbance spectrum, allowing one to infer some details of molecular structure. 

Principal component analysis (PCA) of the soil physico-chemical or the antibiotic resistance data set was performed with the SPSS software. Before PCA, the row MPN values were log-ratio transformed (ter Braak and Smilauer 1998) each MPN was logio -transformed, then, divided by sum of the 16 log-transformed values. Simple linear regression analysis between scores on PCs based on the antibiotic resistance profiles and the soil physico-chemical characteristics was also performed using the SPSS software. To find the PCs that significantly explain variation of SFI or SEF value, multiple regression analysis between SFI or SEF values and PC scores was also performed using the SPSS software. The stepwise method at the default criteria (p=0.05 for inclusion and 0.10 for removal) was chosen. 

Soil Physico-Chemical Characteristics and Soil Bacterial Most Probable Number On Glucose... 

Physico-chemical characteristics of the soils were summarized in Table 1. The values were comparable to that described in the previous reports about the SERS (Doi and Sakurai 2003 Doi et al. 2004 Sakurai et al. 1998). The one-way ANOVA indicated that most of the soil variables significantly reflected the land degradation with high values of bulk density, sand content and exchangeable acidity, and low values of moisture content, pH, OM, base (K, Ca, Mg) contents, EC, CEC, base saturation rate, TN and TC contents, available phosphorus and MPN on the glucose medium with no antibiotics. These results also told that the human activities induced several soil environmental gradients. 

Table 2. Principal components, the eigenvalues, the ratios of explaining variation and the eigenvectors based on the soil physico-chemical characteristics...

Table 5. Linear regression between principal component scores antibiotic resistance MPNs and soil physico-chemical characteristics based on the...

The physical and physico-chemical characteristics (e.g., hexagonal 2D surface structure, tetrahedral 3D molecular network) influence the mutual (in)solubili1y significantly chaotropic compounds lower the order by H-bond breaking... 

To assess the influence of some soil physico-chemical characteristics, viz., pH, organic matter, clay content, etc., and exchangeable cations, on the spatial variation and vertical distribution of the solid-phase Al species in the profile of Delhi soils at selected sites. 

Descriptive statistics of the soil physico-chemical characteristics and exchangeable cations are shown in Table 1. The mean concentrations of the operationally defined species of Al and Fe in the ridge and floodplain soils are shown in Table 2. 

Table 1. Physico-chemical characteristics and exchangeable cations in the soil profile...

The preparation methods of aluminum-deficient zeolites are reviewed. These methods are divided in three categories (a) thermal or hydrothermal dealumination (b) chemical dea-lumination and (c) combination of thermal and chemical dealumination. The preparation of aluminum-deficient Y and mordenite zeolites is discussed. The structure and physico-chemical characteristics of aluminum-deficient zeolites are reviewed. Results obtained with some of the more modern methods of investigation are presented. The structure, stability, sorption properties, infrared spectra, acid strength distribution and catalytic properties of these zeolites are discussed. 

Correlations between preparation method and properties. A review of the physico-chemical characteristics of aluminum-deficient Y zeolites has shown that certain characteristics are common to all DAY zeolites, regardless of preparation method, while other characteristics are strongly affected by the preparation method used. 

Surfactants are often used in agrochemical formulations as adjuvants, e.g. as wetting agents to improve the physico-chemical characteristics of the solution and to increase the uptake of active ingredients (e.g. pesticides) [6-8]. The surfactants can be included in pesticide products and/or added to the tank mix prior to use however, they rarely exceed 1% of the total applied spray. Examples of typical surfactants used in agrochemical formulations are shown in Table 2.8.3 [9]. 

As mentioned before, the presence of surfactants in anaerobic compartments cannot be separated from their physico-chemical characteristics and in fact surfactants which degrade extensively in the laboratory under anaerobic conditions, e.g. soap, are also found in considerable concentrations in anaerobic compartments. Due to their hydrophobic character surfactants are strongly sorbed to sludges and therefore a large amount of the load of these compounds into a sewage treatment plant (reportedly 20-50%) is associated with suspended solids [43,44]. The relevance of the presence of surfactants in the environment should be assessed, therefore, on the basis of their potential impact on the structure and function of the various compartments. In most cases, ionic surfactants are present as insoluble salts and therefore their potential impact is negligible as reflected in the lack of known negative impacts. 

---