P. Godlewska et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 304–313
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acid occurs in nature as an oxidative degradation product of alka-
loids, coenzymes and vitamins and it is a component of fulvic acids.
It is also a plant-sterilizing and water-germicidal agent and antiox-
idant for ascorbic acids in food [4] and is present in the bacterial
spores [5]. Pyridine-2,3-dicarboxylic acid is an intermediate prod-
uct in the tryptophan degradation pathway and a precursor of the
NAD synthesis [2].
hybrid (B3LYP) methods [11,12] with the 6-31 G(d,p) basis set
starting from the XRD data. The theoretical wavenumbers were
scaled to compare them with the experimental values. The linear
correlation method was applied in this procedure [13]. From the
mean square deviation, the 0.96 scaling factor was derived for all
normal modes.
The potential energy distribution of the normal modes (PED)
among the respective internal coordinates has been determined
using the BALGA program [14]. All calculations were performed
for an isolated molecule with one intra-molecular hydrogen bond
as a monomer and for the dimer unit in which the double HBs joint
two adjacent molecules forming an eight-atomic ring system. The
PED values have very similar contributions for the dimer and
monomer for majority of the normal modes. The vector displace-
ments of the atoms from their equilibrium positions during the
vibration and the graphical presentations of these displacements
were obtained using ANIMOL program [15].
It should be noted that the standardized internal coordinate
systems have been applied for the construction of potential func-
tion. Such an approach is now commonly used for the variety of or-
ganic molecules, functional groups and four-, five- and six-atomic
rings [16]. Redundancies between the stretching and bending coor-
dinates are eliminated by this choice. The ring deformational coor-
dinates involve the whole ring and are therefore non-local. In the
present work an internal coordinate system for eight-atomic ring
was constructed [17].
The natural bonding orbitals (NBO) calculations were per-
formed using NBO 3.1 program (E.D. E.D. Glengening, A.E. Reed,
J.E. Carpenter, F. Weinhold, NBO Version 3.1, TCI, University of Vis-
consin, Madison, 1998) as implemented in the Gaussian 03W pack-
age at DFT B3LYP/6-31G(d,p) levels [18].
Transition and heavy metal complexes of the naturally
occurring pyridine-2,3-dicarboxylic acid and 4-hydroxypyridine
2
,6-dicarboxylic acid have been synthesized and characterized
[
6]. It was reported that some of these compounds have positive
effect in normalizing blood glucose content in diabetic rats [7,8].
In this work we present the results of structural and spectro-
scopic studies of 2-hydroxy-5-methylpyridine-3-carboxylic acid
(
HMPC). Fourier transform IR and Raman spectra, XRD studies
and DFT quantum chemical calculations were used to characterize
these properties. Special attention has been focused on the vibra-
tional characteristics of the eight-membered ring joining two adja-
cent molecules in the unit cell. Such inter-molecular hydrogen
bonds (HB) should introduce additional structural and dynamical
effects revealed in XRD measurements, vibrational spectra and the-
oretical data. Intra-molecular hydrogen bonds are also formed in
the studied compound and have been analyzed in the present
work.
Experimental
Synthesis [9]
Two methods of the synthesis have been used: (a) carboxylation
of 2-hydroxypicolines by the Marasse method, and (b) carboxyla-
tion of 2-hydroxypicoline sodium salt.
In the method (a), a sample of 4.36 g (0.04 mole) of dried 2-
hydroxypicoline was mixed thoroughly with 9 g of freshly roasted
and finely ground potassium carbonate and treated with anhy-
drous carbon dioxide at 220 °C and 55–57 atm for 8–9 h After com-
pleting the reaction, the content of the beaker was dissolved in
Results and discussion
X-ray crystallography
A colorless single crystal of 3-carboxy-2-hydroxy-5-methyl pyr-
idine acid with approximate dimensions of 0.36 ꢃ 0.26 ꢃ 0.18 cm
was used for data collection on a four-circle KUMA KM-4 diffrac-
tometer equipped with a two-dimensional area CCD detector.
5
0 ml of water and acidified with concentrated hydrochloric acid
up to pH = 3. The obtained carboxylic acid crystals were recrystal-
lized from water with addition of some active carbon.
In the method (b), a sample of 4.36 g (0.04 mole) of 2-hydroxy-
picoline was dissolved in aqueous solution of 1.8 g (0.04 mole)
NaOH and evaporated to dryness. The dry residue was powdered
in a mortar and dried for 4 h at 120 °C. Prepared in this way sodium
salt of 2-hydroxypicoline was placed in a glass beaker in a steel
autoclave and carbon dioxide dried with a mixture of silica gel
with some anhydrous calcium chloride was introduced. The reac-
tion mixture was kept at 190–220 °C and 55–60 atm for 7–9 h.
The formed pyridinecarboxylic acid was isolated as described in
the method (a).
The graphite monochromatized Mo K
a radiation (k = 0.71073 Å)
and -scan technique with = 0.75° for one image were used
x
Dx
for data collection. The lattice parameters were refined by least-
squares methods on the basis of all collected reflections with
2
2
F > 2r(F ). One image was monitored as a standard for every 50
images. Integration of intensities, correction for Lorenz and polar-
ization effects were performed using KUMA KM-4 CCD software
[
19]. The face-indexed analytical absorption was calculated using
the SHELXTL program [20].
The structures were solved by direct methods and refined with
anisotropic thermal parameters for all non-hydrogen atoms using
the SHELXL-97 program [21]. The hydrogen atoms were located
in their calculated positions, and their temperature factors were
constrained with the Uiso = 1.2Uiso for all H atoms joined to the aro-
matic C atoms, or Uiso = 1.5Uiso for the H atoms of the hydroxyl or
methyl groups. The final difference Fourier maps showed no peaks
of chemical significance. The final agreement factors and details of
data collection are summarised in Table 1.
Spectral measurements
ꢂ1
IR spectra in the range 50–4000 cm range were recorded at
room temperature in Nujol suspension and KBr pellet with a FTIR
ꢂ1
Biorad 575C spectrometer. Raman spectra in the 80–4000 cm
range were measured in back scattering geometry with a FT Bruker
1
10/S spectrometer. The YAG:Nd laser was used as an excitation
ꢂ1
source. The resolution was 2.0 cm both in IR and Raman studies.
The studied compound crystallizes in centrosymmetric mono-
clinic space group P2
1
/c ðC2h5Þ with Z = 4. The X-ray experimental
Quantum chemical calculations
data are collected in Table 1. The molecular geometry of 3-car-
boxy-2-hydroxy-5-methyl pyridine acid with the labeling of the
atoms are shown in Fig. 1. The chosen theoretical and experimental
bond lengths and angles are specified in Table 2 together with the
ab initio fully optimized parameters that correspond to the
The geometry optimization of the studied compound was per-
formed using the Gaussian 03 program package [10]. All calcula-
tions were performed by the density functional three-parameters
Godlewska
