Ionizing nature

Tyrosine contains a phenolic side chain with a pKa of about 9.7-10.1. Due to its aromatic character, tyrosine is second only to tryptophan in contributing to a protein s overall absorptivity at 275-280nm. Although the amino acid is only sparingly soluble in water, the ionizable nature of the phenolic group makes it often appear in hydrophilic regions of a protein—usually... 

The impetus for the development of synthesis and characterization of complexes of lanthanides with organic nitrogen donor ligands is due to the search for more efficient luminescent rare earth compounds. One of the difficulties is the risk of precipitating lanthanide hydroxides in the process of synthesis of lanthanide complexes with organic amines. In the early stages, lanthanide complexes of heterocyclic bases of low basicities were prepared in aqueous alcoholic media [224], In the synthesis section it was appropriately pointed out the need for the anhydrous conditions and involved procedures for the preparation of lanthanide complexes of ligands of non-ionizable nature. Some representative complexes of both aliphatic and aromatic amines are listed in Table 4.19. 

A well-defined method development plan with clear aim of analysis is critical to the success for fast and effective method development. The general approach for the method development for the separation of pharmaceutical compounds was discussed, emphasizing that modifications in the mobile phase (organic and pH) play a dramatic role on the separation selectivity. The knowledge of the Ka of the primary compound is of utmost importance prior to the commencement of HPLC method development. Moreover, pH screening experiments can help to discern the ionizable nature of the other impurities (i.e., synthetic by-products, metabolites, degradation products, etc.) in the mixture. 

Metformin is mainly absorbed in the upper part of the GI tract with high tendency to adsorb to the intestinal epithelium owing to its ionized nature at physiological pH, and thus its absorption patterns are affected (mainly paracellular), and it causes remarkable GI side effect. This fact, together with the finding that metformin active sites are mainly found in the GI tract and the liver, makes metformin a good candidate for GRDF.f" The blood concentrations of metformin... 

The presence and nature of surface charges (charge density, degree of ionization, nature of charge-determining ions, etc.)... 

Plasma Gas (atomic and/or molecular species) that is ionized. Naturally occurring plasmas usually contain magnetic fields. 

Pfeiffer, A.N., Cirelli, C., Smolarski, M Dorner, R., Keller, U. (2011) Timing the Release in Sequential Double Ionization. Nature Phys. 7 428-433. 

The explanation of the behavior in Figure 34 is the following. The auto-ionizing nature of the 8i nn ) state means that it is not the lowest energy excited state at the Sg geometry an electron-detached state is lower. As the finite basis set extends farther into space, more and more ODC states appear... 

Because of the charged nature of many Langmuir films, fairly marked effects of changing the pH of the substrate phase are often observed. An obvious case is that of the fatty-acid monolayers these will be ionized on alkaline substrates, and as a result of the repulsion between the charged polar groups, the film reverts to a gaseous or liquid expanded state at a much lower temperature than does the acid form [121]. Also, the surface potential drops since, as illustrated in Fig. XV-13, the presence of nearby counterions introduces a dipole opposite in orientation to that previously present. A similar situation is found with long-chain amines on acid substrates [122]. 

The mass spectra of phenylthiazoles are characterized by the presence of intense molecular ion peaks, due to the aromatic nature of the molecules, which represent 35, 41, and 44% of the total ionization for 2-, 4-, and 5-phenylthiazoles, respectively. 

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

A further important property of the two instruments concerns the nature of any ion sources used with them. Magnetic-sector instruments work best with a continuous ion beam produced with an electron ionization or chemical ionization source. Sources that produce pulses of ions, such as with laser desorption or radioactive (Californium) sources, are not compatible with the need for a continuous beam. However, these pulsed sources are ideal for the TOF analyzer because, in such a system, ions of all m/z values must begin their flight to the ion detector at the same instant in... 

The hybrid can be used with El, Cl, FI, FD, LSIMS, APCI, ES, and MALDI ionization/inlet systems. The nature of the hybrid leads to high sensitivity in both MS and MS/MS modes, and there is rapid switching between the two. The combination is particularly useful for biochemical and environmental analyses because of its high sensitivity and the ease of obtaining MS/MS structural information from very small amounts of material. The structural information can be controlled by operating the gas cell at high or low collision energies. 

Metastable ions yield valuable information on fragmentation in mass spectrometry, providing insight into molecular structure. In electron ionization, metastable ions appear naturally along with the much more abundant normal ions. Abundances of metastable ions can be enhanced by collisionally induced decomposition. 

The chemical shift is related to the part of the electron density contributed by the valence electrons, ft is a natural extension, therefore, to try to relate changes of chemical shift due to neighbouring atoms to the electronegativities of those atoms. A good illustration of this is provided by the X-ray photoelectron carbon Is spectmm of ethyltrifluoroacetate, CF3COOCH2CH3, in Figure 8.14, obtained with AlXa ionizing radiation which was narrowed with a monochromator. 

While the previous receptors are typically used in organic solvents, except for the cyclodextrins, there are special cases of cyclophane receptors supphed with peripheral charges (ammonium units) (107—12) or ionizable groups (carboxylate functions) (113,114) (Fig. 17) to allow substrate recognition, as in nature, in an aqueous medium, profiting from the solvophobic effects of water (115). 

The phenoxyalkanoic herbicides are acidic in nature and thus subject to some degree of ionization. The extent to which the herbicide ionizes is controlled by the acid dissociation constant (fQ of the herbicide in question and the soil solution pH (238). The leaching potential is significantly influenced by these reactions. 

The aromatic nature of lignin contrasts with the aliphatic stmcture of the carbohydrates and permits the selective use of electrophilic substitution reactions, eg, chlorination, sulfonation, or nitration. A portion of the phenoUc hydroxyl units, which are estimated to comprise 30 wt % of softwood lignin, are unsubstituted. In alkaline systems the ionized hydroxyl group is highly susceptible to oxidative reactions. 

Electronic and Electrical Applications. Sulfolane has been tested quite extensively as the solvent in batteries (qv), particularly for lithium batteries. This is because of its high dielectric constant, low volatUity, exceUent solubilizing characteristics, and aprotic nature. These batteries usuaUy consist of anode, cathode polymeric material, aprotic solvent (sulfolane), and ionizable salt (145—156). Sulfolane has also been patented for use in a wide variety of other electronic and electrical appHcations, eg, as a coil-insulating component, solvent in electronic display devices, as capacitor impregnants, and as a solvent in electroplating baths (157—161). 

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