Ionization of functional groups

Internal and External Phases. When dyeing hydrated fibers, for example, hydrophUic fibers in aqueous dyebaths, two distinct solvent phases exist, the external and the internal. The external solvent phase consists of the mobile molecules that are in the external dyebath so far away from the fiber that they are not influenced by it. The internal phase comprises the water that is within the fiber infrastmcture in a bound or static state and is an integral part of the internal stmcture in terms of defining the physical chemistry and thermodynamics of the system. Thus dye molecules have different chemical potentials when in the internal solvent phase than when in the external phase. Further, the effects of hydrogen ions (H" ) or hydroxyl ions (OH ) have a different impact. In the external phase acids or bases are completely dissociated and give an external or dyebath pH. In the internal phase these ions can interact with the fiber polymer chain and cause ionization of functional groups. This results in the pH of the internal phase being different from the external phase and the theoretical concept of internal pH (6). 

The presence of charge resulting from the ionization of functional groups is a fundamental property of humic substances. To some extent, it is this property that is exploited when humic acid is precipitated by acidification. The same property can be more exquisitely exploited by means of ion-exchange and electrophoretic techniques, and these techniques have been extensively used in the fractionation of humic substances. 

The solubility of a drug molecule in water greatly affects the routes of administration that are available as well as its absorption, distribution, and elimination. Two key concepts to keep in mind when considering the water (or fat) solubility of a molecule are the hydrogen bond-forming potential of the functional groups in the molecule and the ionization of functional groups. 

In the conditioning process, under suitable alkaline conditions, both ionization of functional groups at the bitumen surface [33, 105] and adsorption of the natural anionic surfactant molecules at the bitumen/ aqueous interface [100,101,104] occur. Descriptions of the experimental techniques, including microelectrophoresis, employed to study the effects are given elsewhere [100,102,104,106]. Figure 14 shows how addition of NaOH in the process increases the concentrations of surfactant in the aqueous phase, which in turn increases the extents of surfactant adsorption at all of the aqueous phase interfaces present in the system gas/ aqueous, bitumen/aqueous, and solid/aqueous. The adsorption increases until monolayer coverage is achieved and thereafter either levels off or continues into multilayer adsorption. 

Section 4.4 Connections to Biological Chemistry The Ionization of Functional Groups at Physiological pH Section 4.6 MCAT Practice Acid-Base Equilibria... 

Also macrocyclic antibiotics, erythromycin and vancomycin, were successfully employed as the chiral selectors [23,24] for separation of dansyl derivatives of DL-amino acids. It was shown that such chromatographic system is very sensitive especially to changes of pH and temperature, owing to possibility of ionization of functional groups or changing conformational structure of the antibiotic molecule. 

Fig. 5. Differential enthalpy of ionization of crosslinked MA-DMEG copolymers as a function of the degree of ionization of carboxylic groups. Crosslinking agent (DMEG) content (mol%) 1)3 2) 7.5 5) 12...

The relationship of thermodynamic functions of selective bonding of Hb to a series of carboxylic CP in the variation of the degree of ionization of carboxylic groups is expressed by the effect of enthalpy-entropy compensation (Fig. 18). The compensation effect of enthalpy and entropy components is the most wide-spread characteristic of many reactions in aqueous solutions for systems with a cooperative change in structure [78],... 

The partition coefficient (log P) describes the intrinsic lipophilicitY of the collection of functional groups and carbon skeleton, which combine to make up the structure of the compound, in the absence of dissociation or ionization. Methods to measure partition and distribution coefficients have been described [3,4]. 

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