Lyotropic number, series

The second empirical correlation that has been observed is between the ion pair enthalpy of hydration and the lyotropic number (Buchner, 23, 24). The lyotropic number was developed by Buchner as a quantitative eicpression of the position of the anion in the Hofmeister series. It... 

Comparison of Water and Methanol Solutions. Comparison of (-AA(7/RT)j for ions in both water and methanol solutions can be made by using (-AA(7/R2 )ua+ and (-AA(7/R2 )(j2 - as references for the alkali metal cations and halide anions respectively. These have been plotted in Figure 5 with the lyotropic numbers for each ion. Figure 5 shows that with respect to halide ions the correlation of lyotropic number with [ (-AAG/RT)j.-(-AA( /R2 )j,j -] is both linear and identical for both solvents, whereas the corresponding correlations with respect to alkali metal cations are different. In particular, with respect to these latter ions, the change of [ (-AAG/RT) j -(-AA( / )jjg+] with lyotropic number is greater in methanol solutions than in aqueous solutions. This means that for a given membrane, the variations in solute separation for alkali metal halide salts with common anions is much less in aqueous solutions than in methanol solutions, which is consistent with experimental results. Further, in the case of methanol solutions, the solute separation increases with increase in lyotropic number for the alkali metal cation series and decreases with an increase in lyotropic number for the halide series. 

Lyotropic numbers N o, Table 5.1, were assigned to ions in the 30s of the last century by Buchner and Voet (Buchner et al. 1932 Voet 1937a, 1937b) according to their effects on colloidal systems. The lyotropic series has nowadays been to some extent superseded by the Hofmeister series, with which it is taken to be practically synonymous, but it is not so exactly. For the alkali metal cations and the halide anions the lyotropic numbers obtained from colloidal phenomena are linearly related to their enthalpies of hydration. Voet (1937a) concluded that the lyotropic series are simply related to the electric field strengths of the ions. Note that the Myo values for the alkali metal cations are not commensurate with those of the alkaline earth cations and with those of the anions. 

Inversions of the positions of some anions in the series are noted when several related phenomena are nsed to establish it as reported by Cacace et al. and by Pinna et al. [98, 99], For instance, F was placed at the head of the series according to Hochachka and Somero [101] and to HaU and Drake [102], althongh other authors relegated it to nearer its middle. A related series, whose lyotropic numbers are given in Table 8.11, also has several reversals with respect to the Hofmeister series as pointed out by Schott [103] and by Lo Nostro et al. [104]. 

We have examined a number of different salts and have shown that the transition temperature can almost be altered at will (12), in many cases in line with the Hofmeister or lyotropic series (13-15J, a relationship found for many other aqueous systems such as hydrocarbon solubility and protein stability. 

The lytoropic number for an ion is a fundamental physicochemical parameter which expresses its relative tendency for electron transfer (30) which is also the basis for preferential sorption at interfaces for aqueous solutions involving polar solutes (31). Since the lyotropic series is valid in many fields of physical chemistry including solvation. 

With Other sols electrolytes may give similar effects. After a strong decrease at very low concentrations, to be discussed below, at higher concentrations ( ]s—V o)Mo may increase, which must be interpreted as increase of solvation. Fig. 15 gives an example, referring to amylum solubile and a number of potassium salts. The interpretation, that these changes in spec, viscosity are really related to changes in solvation seems fortified by the order of the curves, which is that of the so-called lyotropic series of the anions CNS > J > NO3 > Br > Cl > SO4... 

More recently El-Waki et al. reported the synthesis and characterization of a series of 4-alkyoxybenzoyloxypropyl cellulose (ABPC-n) samples, obtained via the esterification of hydroxypropyl cellulose (HPC) with 4-alkoxybenzoic acid bearing different numbers of carbOTi atoms (n= 1, 2, 3, 4, 5, 7, 8, 12). In this series the authors noted that only for the higher alkoxy chain lengths (7, 8 or 12) a thermotropic liquid crystal behavior was observed however all the esters of HPC within the series presented lyotropic behavior (El-Wakil et al. 2010). 

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