Basic species

When we use any substance as a solvent for a protonic acid, the acidic and basic species produced by dissociation of the solvent molecules determine the limits of acidity or basicity in that solvent. Thus, in water, we cannot have any substance or species more basic than OH or more acidic than H30 in liquid ammonia, the limiting basic entity is NHf, the acidic is NH4. Many common inorganic acids, for example HCl, HNO3, H2SO4 are all equally strong in water because their strengths are levelled to that of the solvent species Only by putting them into a more acidic... 

Cations at the surface possess Lewis acidity, i.e. they behave as electron acceptors. The oxygen ions behave as proton acceptors and are thus Bronsted bases. This has consequences for adsorption, as we will see. According to Bronsted s concept of basicity, species capable of accepting a proton are called a base, while a Bronsted acid is a proton donor. In Lewis concept, every species that can accept an electron is an acid, while electron donors, such as molecules possessing electron lone pairs, are bases. Hence a Lewis base is in practice equivalent to a Bronsted base. However, the concepts of acidity are markedly different. 

Heparin is biosynthesized and stored (probably as a complex with histamine and other basic species) in basophilic granules of mast cells of many animal tissues. (Mast cells, whose function remains largely obscure, are located in connective tissues, near the capillaries, and in the walls of blood vessels.10 28 27)... 

Heparin has been reported to complex with a variety of basic species, including biogenic amines and drugs for reviews, see Refs. 10 and 391. For its possible relevance to the pharmacological properties of heparin and complexed species, mention is made here of complexes with histamine392,393 and anthracycline antibiotics.394 C.d. studies on the interaction of basic homopolypeptides with heparin and other glycosaminogly-cans have shown that heparin is able to induce an ordered, helical conformation in the polypeptide.395 397 Similar, and even more dramatic, effects were observed with mixed basic polypeptides, presumed to represent better models for the biologically relevant interactions with plasma proteins.368... 

When the relative flux is 1, reaction of the basic species with the acid does not contribute to the dissolution of HA since the concentration of B is too low relative to the saturated solubility of HA to impact the dissolution rate (CB < Cha )-As the concentration of the basic species in bulk increases (CB CHa ), the relative flux will approximately double and the reaction of B with HA will begin to dominate the dissolution process. The utility and elegance of Eq. (8) is that one can estimate the increase in dissolution of an acid due to reaction with a base by simply knowing the base concentration in the dissolution media and the... 

Removal of the proton (usually non rate-limiting) from (32) is assisted by one or other of the basic species present in solution. Coupling normally takes place largely in the p-, rather than the o-, position (cf. p. 154)—provided this is available—because of the considerable bulk of the attacking electrophile, ArN2 (cf. p. 159). 

A further unusual feature of the matrix-dependent polycondensation lies in the character of the nucleobases themselves. Purine mononucleotides undergo polycondensation, in good yields, at complementary matrices consisting of pyrimidine polymers. However, the synthesis of pyrimidine oligonucleotides from their mononucleotides at purine matrices is not effective. This important fact means that a pyrimidine-rich matrix leads to a purine-rich nucleic acid, which is itself not suitable to act as a matrix. This phenomenon also occurs when matrices are used which contain both basic species, i.e., purines and pyrimidines. An increase in the amount of purine in a matrix leads to a clear decrease in its effectiveness (Inoue and Orgel, 1983). However, the authors note self-critically that the condensation agent used cannot be considered to be prebiotic in nature. 

According to the Arrhenius theory of acids and bases, the acidic species in water is the solvated proton (which we write as H30+). This shows that the acidic species is the cation characteristic of the solvent. In water, the basic species is the anion characteristic of the solvent, OH-. By extending the Arrhenius definitions of acid and base to liquid ammonia, it becomes apparent from Eq. (10.3) that the acidic species is NH4+ and the basic species is Nl I,. It is apparent that any substance that leads to an increase in the concentration of NH4+ is an acid in liquid ammonia. A substance that leads to an increase in concentration of NH2- is a base in liquid ammonia. For other solvents, autoionization (if it occurs) leads to different ions, but in each case presumed ionization leads to a cation and an anion. Generalization of the nature of the acidic and basic species leads to the idea that in a solvent, the cation characteristic of the solvent is the acidic species and the anion characteristic of the solvent is the basic species. This is known as the solvent concept. Neutralization can be considered as the reaction of the cation and anion from the solvent. For example, the cation and anion react to produce unionized solvent ... 

That this reaction does not take place to a measurable extent does not prevent us from knowing that the ions produced would be the acidic and basic species. Therefore, we can predict that Na2S03 would be a base in liquid S02 because it contains S032 and SOCl2 would be an acid because it could formally produce S02+ if it were to dissociate. Thus, we predict that Na2S03 and SOCl2 would react according to the equation... 

The coordination model provides a way to explain many reactions that occur in nonaqueous solvents without having to assume that autoionization takes place. As shown in Eq. (10.17), the fact that FeCl4 is produced can be explained by substitution rather than autoionization. However, as has been shown earlier in this chapter, it is sometimes useful to assume that the solvent concept is valid, and many reactions take place just as if the solvent has ionized to a slight degree into an acidic and a basic species. 

Although it is not necessary for autoionization to occur, the solvent concept shows that the cation characteristic of the solvent is the acidic species and the anion is the basic species. Therefore, when... 

The basic species in liquid HF is the fluoride ion or the solvated fluoride ion, HF2 . As in the case of water in which OH forms hydroxo complexes, fluoride ion forms complexes in liquid HF. This behavior gives rise to amphoterism with metals ions such as Zn2+ and Al3 +. In the case of Al3+, A1F3 is relatively insoluble in liquid HF so the amphoteric behavior can be shown as follows. 

Although in this scheme the basic species is written as F for simplicity, the solvated species is actually HF2 in liquid HF. 

Even though liquid S02 does not autoionize, the acidic species would be SO2 + and the basic species would be S032-. Therefore, the neutralization reaction... 

In liquid S02 the basic species is S032 so [(CH3)4N]2S03 gives a basic solution in which aluminum sulfite dissolves by forming a sulfite complex, as shown in the equation... 

The interfacial acidity constant or apparent acidity constant in the membrane phase Kam refers to the relative ratio of acidic and corresponding basic species in the membrane at a given (aqueous) pH-value ... 

Weak bases which have KZ> values less than 10-6 can be titrated satisfactorily by non-aqueous titrations. The reason being that in aqueous medium and at higher K/> values (> 10 6) the solvent water competes progressively with the basic species in solution for the proton of the solvent. 

In order to perform feasible titrations of weak bases, the solvent system should be selected specifically in such a fashion so as to eliminate as far as possible the competing reaction of water for the proton besides enhancing the strength of the basic species. 

The effect of solution anionic concentration is probably related to effects on activity coefficients and ion pair formation of more highly charged buffer species. In more concentrated solutions, the activity of the highly charged species is reduced by both ionic strength and ion pair formation. The effect on less charged, acidic species is less. Therefore, as solutions become more concentrated, the activity of basic species is reduced relative to that of acidic species, and at a given fraction... 

The hydrogenation of a double bond during cathodic reductions generally results from addition of protons to an electrogenerated basic species. It is worth noting that partial and selective hydrogenation can take place according to the nature of the heterocycles and the experimental conditions. 

In the absence of more easily oxidized substrates, residual water in aprotic solvents will undergo oxidation at platinum anodes. However, the mechanism of proton formation is not necessarily by simple water oxidation with the evolution of O2 but may involve radical reactions of the solvent or oxidation of supporting electrolyte anions [6, 7]. The protons produced, together with the most basic species in solution, form... 

The potential of cIEF to assess the overall rMAb charge distribution is demonstrated in Figure 13. The electropherogram shows the various isoforms of the antibody between the p7 markers 7.9 and 5.3. The main peak or 0-Lys form of the antibody appears at 27min. The more basic species with one and two C-terminal Lys residues at the heavy chain are baseline resolved from each other and the main peak. Their results are similar to those obtained by... 

It is the position ortho to the maximum number of substituents that is most electron rich in an anion-radical of a starting aromatic compound. Being a less basic species, anion-radicals exhibit a more selective primary isotope effect than their more basic (and therefore... 

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