Pseudopolymorphs of chelidamic acid and its dimethyl ester

Abstract

Different tautomeric and zwitterionic forms of chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid) are present in the crystal structures of chelidamic acid methanol monosolvate, C(7)H(5)NO(5)·CH(4)O, (Ia), dimethylammonium chelidamate (dimethylammonium 6-carboxy-4-hydroxypyridine-2-carboxylate), C(2)H(8)N(+)·C(7)H(4)NO(5)(-), (Ib), and chelidamic acid dimethyl sulfoxide monosolvate, C(7)H(5)NO(5)·C(2)H(6)OS, (Ic). While the zwitterionic pyridinium carboxylate in (Ia) can be explained from the pK(a) values, a (partially) deprotonated hydroxy group in the presence of a neutral carboxy group, as observed in (Ib) and (Ic), is unexpected. In (Ib), there are two formula units in the asymmetric unit with the chelidamic acid entities connected by a symmetric O-H···O hydrogen bond. Also, crystals of chelidamic acid dimethyl ester (dimethyl 4-hydroxypyridine-2,6-dicarboxylate) were obtained as a monohydrate, C(9)H(9)NO(5)·H(2)O, (IIa), and as a solvent-free modification, in which both ester molecules adopt the hydroxypyridine form. In (IIa), the solvent water molecule stabilizes the synperiplanar conformation of both carbonyl O atoms with respect to the pyridine N atom by two O-H···O hydrogen bonds, whereas an antiperiplanar arrangement is observed in the water-free structure. A database study and ab initio energy calculations help to compare the stabilities of the various ester conformations.

pH-dependent concatenation of an inorganic complex results in solid state helix formation

“…For comparison, while the enol tautomer was observed to be more stable than the keto form of the dianionic form of chelidamic acid (2 2-), the keto tautomer was preferred with the 2Me2 congener (Figure 5). 10,11 The shift in preference for enol vs. keto is due to the methyl ester being more electron-withdrawing than the deprotonated carboxyl. Therefore, it is reasonable to consider that the copper(II) cation of Cu1 has an electron-withdrawing effect on the pyridol ring, which would similarly stabilize the keto form of the complex.…”

Estimating temperature-dependent anisotropic hydrogen displacements with the invariom database and a new segmented rigid-body analysis program

“…hb6948 (Fadzillah et al, 2012) 0.0272 0.0278 +0.007 0.73 100 zj2091 (Matos et al, 2012) 0.0300 0.0307 +0.007 0.83 100 eg3095 (Tutughamiarso et al, 2012) 0.0298 0.0301 +0.003 0.82 173 dt3014 (de Sousa et al, 2012) 0.0533 0.0536 +0.003 0.80 173 yp3017 (Sonar et al, 2012) 0.0529 0.0532 +0.003 0.83 90 fg3251 (Sowa et al, 2012) 0.0580 0.0582 +0.002 0.81 100 bt5991 (Khalaji et al, 2012) 0.0228 0.0230 +0.002 0.88 120 sh5011 (Madsen et al, 2003) 0.0182 0.0182 +0.000 0.41 122 bi3042 (Liu et al, 2012) 0.0474 0.0472 -0.002 0.73 153 fg3250 (Smith & Wermuth, 2012) 0.0316 0.0314 -0.002 0.81 293 fa3263 (Pé rez et al, 2012) 0.0441 0.0430 -0.011 0.77 293 fg3262 (Helliwell et al, 2012) 0.0308 0.0280 -0.028 0.81 accurate estimates of the lattice vibrations, and H-ADPs appear unreasonable large. On the other hand, when the measurement temperature is low and the refined ADPs are reasonable, the model including the estimated ADPs fits the measured data better, therefore also providing a useful indicator of data quality in the low-order region.…”