Methanol critical coordinates

If, however, the l,3-diaminopropan-2-ol is added to a methanolic solution of lanthanide(III) nitrate or thiocyanate and dap (in the molar ratio 1 1 1), and the reaction mixture refluxed for 2-3 h, kinetically stable Ln2(L798)(N03)4(H20)s (Ln = La, Pr) or Ln2(L798)(NCS)4(H20)4 (Ln = La, Pr, Nd, Sm, Eu) respectively are claimed to have been isolated [185], Unfortunately, the products were characterised only by elemental analysis, IR and NMR spectra, which do not permit a reliable assignment of the macrocycle formed as the 2 + 2 condensation product. For labile metal ions such as the lanthanides the sequence in which reagents are added should not have a critical influence on the stoichiometry of condensation. Nevertheless the occurence of a 2 + 2 condensation mechanism initiated by coordination of dap to a lanthanide(III) ion (in accordance with synthetic procedure employed) could not be totally excluded. 

Provided that the system (regression) parameters for a chromatographic method are known and the molecular descriptors for a new analyte are available, retention and thus selectivity should be predictable with the help of the LFER approach. Correlations of the calculated and the measured selectivities for nine pairs of solutes under six eluent compositions on a Merck Lichrospher 100 RP-18e column are shown in Fig. 6a for water/acetonitrile eluents and in Fig. 6b for water/ methanol eluents (taken from [14]). This plot, however, does not illustrate a real prediction of solute retention, since the depicted measured retention data served at the same time as a basis for the calculation of the theoretical selectivities. Even under these less critical conditions, relative deviations (expressed as the distances from the best linear fit in the x-coordinate) reach values of up to 20%, due to the significant residues from the multivariate regression (see confidence ranges in Fig. 4). To discuss the impact of these uncertainties on the quality of a possible prediction, a real example is discussed here. Starting from a selectivity of... 

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