N'-(2-Hydr-oxy-3,5-diiodo-benzyl-idene)-2-methoxy-benzohydrazide.

The title compound, C(15)H(12)I(2)N(2)O(3), was synthesized by the condensation of equimolar amounts of 3,5-diiodo-salicylaldehyde and 2-methoxy-benzohydrazide in a methanol solution. There are two independent mol-ecules, A and B, in the asymmetric unit. The dihedral angle between the two benzene rings is 30.2 (2)° for mol-ecule A and 21.7 (2)° for mol-ecule B. There are intra-molecular O-H⋯N and N-H⋯O hydrogen bonds in each mol-ecule. The crystal studied was an inversion twin with a 0.59 (3):0.41 (3) domain ratio.

3-Hydr-oxy-N'-(2-hydroxy-benzyl-idene)benzohydrazide.

The title compound, C(14)H(12)N(2)O(3), was synthesized by the condensation of salicylaldehyde with 3-hydroxy-benzo-hydrazide. The dihedral angle between the two benzene rings is 12.4 (2)°. The 2-hydr-oxy group forms an intra-molecular O-H⋯N hydrogen bond with the imide N atom. Mol-ecules are linked through inter-molecular O-H⋯O and N-H⋯O hydrogen bonds into a two-dimensional polymeric structure parallel to the ab plane.

N'-(5-Bromo-2-hydr-oxy-3-methoxy-benzyl-idene)isonicotinohydrazide.

The title compound, C(14)H(12)BrN(3)O(3), was prepared by reaction of 5-bromo-3-methoxy-salicylaldehyde and isonicotinohydrazide in methanol. The mol-ecule is not planar and adopts a trans configuration with respect to the C=N bond. There is an intra-molecular O-H⋯N hydrogen bond in the mol-ecule. The dihedral angle between the benzene and pyridine rings is 12.2 (2)°. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯N hydrogen bonds, forming chains running along the c-axis direction.

(E)-N'-(2-Hydr-oxy-4-methoxy-benzyl-idene)isonicotinohydrazide monohydrate.

The title compound, C(14)H(13)N(3)O(3)·H(2)O, was prepared by the reaction of 4-methoxy-salicylaldehyde and isonicotinohydrazide in ethanol. The Schiff base mol-ecule is not planar and has an E configuration with respect to the methyl-idene unit. The dihedral angle between the benzene and pyridine rings is 36.8 (2)°. In the mol-ecule there is an intra-molecular O-H⋯N hydrogen bond involving the hydroxyl substituent and the N atom of the 2-hydr-oxy-4-methoxy-benzyl-idene unit. In the crystal, the mol-ecules are linked through inter-molecular O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds, forming layers parallel to the bc plane.

Approach on quantitative structure-activity relationship for design of a pH neutral carrier containing tertiary amino group.

The quantitative structure-activity relationship (QSAR) for neutral carriers used to prepare hydrogen ion sensors has been studied. A series of synthesized carrier compounds were taken as the training set. Five molecular structure parameters of the compounds were calculated by using CNDO/2 algorithm and used as feature variables in constructing QSAR model. The lower and upper limits of the linear pH response range were taken as the activity measure. The corresponding model equations were derived from the stepwise regression procedure. With the established QSAR model, a new pH carrier, (4-hydroxybenzyl) didodecylamine (XIII) was proposed and synthesized. The PVC membrane pH electrode based on carrier XIII with a wide pH linear response range of 2.0-12.5 was prepared. Having a theoretical Nernstian response slope of 57.2+/-0.3 mV/pH (n=5 at 25 degrees C) without a super-Nernstian phenomenon, the sensor had low resistance, short response time, high selectivity and good reproducibility. Moreover, the sensor was successfully applied to detecting the pH value of serum samples.