B-type ions

M - H] ions, the most likely site of deprotonation is at the most acidic sites, namely the phosphate sites. Deprotonation at these sites exposes an anionic oxygen base that facilitates charged anionic base loss via an intramolecular E2 mechanisms. Initial CID of the [M - H] ions showed neutral base loss pre-dominandy from the 5 terminus, followed by the 3 and internal positions in the order A > T > G > C. Notwithstanding the differences in mechanisms between the [M - H] and [M + H]+ ions, the net effect is the same with regard to the subsequent formation of sequence ions. Thus loss of the 5 base triggers formation of the w2-type ion, loss of the internal base yields wt- and the (a2-B )-type ions, while 3 base loss results in the formation of the (a -B -type ion. 

Structural information can be obtained by MS-MS techniques. The first MS (MS-1), such as ESI, separate/isolate the degradation product and the second MS (MS-2), such as collision-induced dissociation (CID), provides the necessary product identification. The suitable precursor ions for MS-MS generally comprise B -type ions, which are often form good yields due to the facile cleavage of the glycosidic bond under a variety of ionization conditions. 

As with protonated peptides, b-type ions have proved to be, perhaps, the most compelling in terms of potential stmctures. Peptide motifs with and without nucleophilic side chains have been investigated with quite interesting results which are not completely unlike their protonated counterparts. The first two systems studied, AlaAlaAla and AlaTyrAla, both gave rise to b2 ions taking the deprotonated oxazolone structure [38]. It is notable that tyrosine was seemingly uncompetitive as a deprotonation site, in clear contrast to c-type ions. 

The mechanism of the reaction, which is of the aldol type, involves the car-bonyl group of tlie aldehyde and an active methylene group of the anhydride the function of the basic catalyst B (acetate ion 0H3000 or triethylamine N(0,Hb)j) is to form the anion of the active hydrogen component, i.e., by the extraction of a proton from the anhydride ... 

Fig. 5. Bipolar transistor (a) schematic and (b) doping profiles of A, arsenic ion implanted into the silicon of the emitter ( -type) B, boron ion implanted into the silicon of the base (p-type) C, antimony ion implanted into the buried layer ( -type) and D, the epi layer...

The nature of the donor atoms in the chelating agent. Ligands which contain donor atoms of the soft-base type form their most stable complexes with the relatively small group of Class B metal ions (i.e. soft acids) and are thus more selective reagents. This is illustrated by the reagent diphenylthiocarbazone (dithizone) used for the solvent extraction of metal ions such as Pd2+, Ag+, Hg2+, Cu2+, Bi3+, Pb2+, and Zn2 +. ... 

F can he suppressed hy the high site symmetry of the central atom In many perovskite-like structures of the ABO3 type the lone pair of the B-cat-ion leads not to a structural distortion. In CsPbF3 under ambient conditions no lone-pair activity observed [27], but upon cooling a phase transition is observed that leads to less symmetrical surrounding of Pb by fluoride [28]. 

Ahrland et al. (1958) classified a number of Lewis acids as of (a) or (b) type based on the relative affinities for various ions of the ligand atoms. The sequence of stability of complexes is different for classes (a) and (b). With acceptor metal ions of class (a), the affinities of the halide ions lie in the sequence F > Cl > Br > I , whereas with class (b), the sequence is F < Cl" < Br < I . Pearson (1963, 1968) classified acids and bases as hard (class (a)), soft (class (b)) and borderline (Table 1.23). Class (a) acids prefer to link with hard bases, whereas class (b) acids prefer soft bases. Yamada and Tanaka (1975) proposed a softness parameter of metal ions, on the basis of the parameters En (electron donor constant) and H (basicity constant) given by Edwards (1954) (Table 1.24). The softness parameter a is given by a/ a - - P), where a and p are constants characteristic of metal ions. 

Present understanding of Lewis acidity and basicity is based mainly on the A and B type classification of metal ions of Ahrland, Chatt,... 

Fragmentation of the nitrite then yields a phenolic-type ion that can decompose further by elimination of CO. Thus, the characteristic series of [M-ld]" (generally weak signal), [M-30] and [M-46] ions is obtained (Fig. 6.49a,b). 

Formation of coordination complexes is typical of transition metals, but other metals also form complexes. The tendency to form complexes is a function of the metal s electron configuration and the nature of its outer electron orbitals. Metal cations can be classified into types A and B based on their coordination characteristics, as shown in Table 3.5. A-type cations, which tend to be from the left side of the Periodic Table, have the inert-gas type electron configuration with largely empty d-orbitals. They can be imagined as having electron sheaths not easily deformed under the influence of the electric fields around neighbouring ions. B-type cations have a more readily deformable electron sheath. 

In consequence, A-type cations form complexes preferentially with the fluoride ion and ligands having oxygen as their electron donor atom. They are attracted to H2O more strongly than to NH3 or CN, and they do not form sulfides because OH ions readily displace HS or ions. They tend to form sparingly soluble precipitates with OH, and P04. By contrast, B-type cations coordinate... 

Class B Type MA, . Neutral coordinatively saturated complexes formed between the metal ion and a lipophihc organic acid. This class contains the large group of metal-organic chelate compounds. For monbasic acids forming bifunctional chelates, z = N/2. They belong to the extraction Type in-B, treated in section 4.8. 

Fig. 4.3 Extraction curves for various types of metal chelate complexes, when log Du is plotted against free ligand ion concentration, pA = -log[A ], or against [HA][H ]. From such plots, the general type of metal chelate complex may be identified (a) type MA , (see also Fig. 4.10) (b) type MA (OH)p(HA) (see also Figs. 4.14 and 4.30) (c) type MA (OH)p, (see also Fig. 4.19). (From Refs. 3a and 3b.)...

An e.s.r. study has been made of [Co(salen)] in the solvents dimethylaceta-mide. CH Cl -toluene (1 1) (both A-type), dimethylacetamide containing NCS ions, DMSO, and pyridine-toluene (1 1) (all B-type). In the A-type solvents, the electronic configuration is and in B-type... 

The synthesis of B-type carbonate-fluoroapatites was reported by Montel et al. with fluoride ions present in two kinds of sites in the apatitic structure [126]. Moreover, the correlation between the respective amounts of fluoride and... 

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