Cation sequences

Fig. 33 MgaFe LDH in the 3Ri polytype with ordered cation sequence Fe - Mg - Mg -Fe- within the layers but no correlation of cation position between layers. Light large circles represent Mg ", dark large circles represent Fe small circles represent OH groups below open circles) and above (filled circles) the metal ion plane. Reprinted with permission from [100]. Copyright Nova Science Publishers...

The assembly of NLS in peptide-based gene delivery systems has been achieved by the non-covalent binding of plasmid to either free NLS embedded with polyplexes or to NLS linked to a cationic sequence, such as (PKKKRKV)4-K2o (Table 16.7), AKRARLSTSFNPVYPYEDES-K20 (Table 16.7) or H9-2 sequence (nls-H9-2) (Table 16.4). With nls-H9-2, the transfection efficiency with a formulation containing... 

The actual atomic arrangements are known for KH02F7 (Le Fur et al., 1982), KEr2F7 (A16onard et al., 1980), and KYb2F7 (Le Fur et al., 1980). The first structure type is a fluorite-related superstructure with the cation sequence -ABC-. Ordering of cations takes place in A and B with the ratio lK 3Ho, but lK lHo in C. The coordination number of Ho " is eight in all cases one quarter... 

The KErsFio structure can be regarded as fluorite-related with respect to the basic cation sequence of -ABC-, which is observed as a subunit (Aleonard et al., 1978b). As in the preceding structure types, six RFg square antiprisms form R6F32 clusters. The three-dimensional arrangement, however, leads to a very complicated cation sequence perpendicular to (001) ... 

SPECIFIC CATION SEQUENCES IN THE REVERSAL OF CHARGE OF COLLOIDS OF ACIDIC NATURE WITH INORGANIC CATIONS... 

As in the physical chemistry of electrolytes the solubility of salts possessing different cations but the same anion depends on the same factors as used in the above discussion viz., valency, radius and polarising power of the cation and polarisability of the anion, it may be expected, that cation sequences may occur similar to the cation sequences found in the reversal of charge concentrations of colloids. This indeed is the case, so the solubilities of phosphates (moles in 1 000 moles HgO) increases in the order Li < Na < K, however of sulphates in the order K Na < Li. 

The survey shows that by introduction of OH groups into oleate, the cation sequences change in the direction of those characteristic of arabinate, hexaoxystearate showing at pH 6 already almost wholly the sequences of arabinate. 

Further also all reversal of charge points could be reached with SiOg particles (without colloids). As we have already seen that the ionogenic surface of SiOg very much resembles the sulphate colloids in polarisability (see p. 296 2 m), the results obtained on Si02 have also been given in Fig. 29 to serve as a substitute for the cation sequences in sulphate colloids. 

Fig. 47. Cation sequences for the reversal of charge of Na arabinate in water (a) or in 25, 40, and 50% acetone (b) and for the flocculation maxima of gum arabic in 30, 40 and 50% alcohol (c). The concentrations in c were taken from Fig. 46 (intersections of the curves with horiziontal lines at 30, 40 or 50% alcohol).

The cation sequences obtained, see Fig. 47a, now again appear to be essentially the same as in b and c. Furthermore it is important that the reversal of charge concentrations are throughout considerably lower for the same cation in media containit acetone (b) than in water (a). It appears once more from this that acetone or alcohol strenghthens the attachment of the cations. 

Phosphatides can under certain conditions give coacervation or flocculation with cations which to judge by all kinds of properties belong to the dicomplex type. We shall not go into details on this point but merely mention a few peculiarities. The cation sequences are typically those of the phosphate colloids (see for more detail p. 280, Ch. IX, 2c p. 289 and 295) e.g. 

This latter consideration quite clearly plays a part in the interpretation of the cation sequence found, K ) Na ) Li (Fig. 59). 

Since the sequence is also Li ) Na ) K in the ion spectrum of negative proteins and these ions bring about fairly strong complex relations in this case also, the interpretation with regard to the cation sequence in the suppression of the tricomplex flocculation is exactly the same as that described in detail above. For the anion sequence, arguing similarly as above, the ion sequence in the ion spectrum of gelatin (p. 299, Fig. 22) is to be expected. This is indeed the same as that found experimentally in the suppression of the tricomplex. 

Specific cation sequences in the reversal of charge of colloids of acidic... 

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