Complexes of uranyl(II), vanadyl(II) and zirconyl(II) with orotic acid vitamin B13 : Synthesis, spectroscopic, thermal studies and antibacterial activity

Article abstract of DOI:10.1016/j.molstruc.2006.12.006

A convenient method for the preparation of complexes of the uranyl [UO₂]²⁺, vanadyl [VO]²⁺ and [ZrO]²⁺ ions with vitamin B13 (Orotic acid; H₃OA) is reported and this has enabled three complexes of orotate anion (1-) to be formulated: [M(C₅H₃N₂O₄)₂(H₂O)₂]·(H₂O)_n [where M = [UO₂]²⁺, [VO]²⁺, [ZrO]²⁺; n = 1, 6, 3, respectively]. The new bisorotate (H₂OA)^1- complexes were synthesis and characterized by elemental analysis, molar conductivity, spectral methods (UV-vis, mass, ¹H NMR and mid infrared spectra), and simultaneous thermal analysis (TG and DTG) techniques. Physical measurements indicate that the neutral orotic acid ligand in its mono/anion form, is bonded to oxometal ions through the carboxylic groups (two monodentate orotate anions and complete the coordination sphere by coordinated water molecules). The molar conductance data confirm that the orotate complexes are non-electrolytes. The X-ray powder diffraction (XRD) as well as scanning electron microscopy (SEM) shows that the studied complexes have amorphous structures. The kinetic thermodynamic parameters, such as, E^*, ΔH^*, ΔS^* and ΔG^* are calculated from the DTG curves. The antibacterial activity of the orotic acid and their complexes was evaluated against gram positive/negative bacteria.

Full text of DOI:10.1016/j.molstruc.2006.12.006

Journal of Molecular Structure 842 (2007) 24–37
www.elsevier.com/locate/molstruc
Complexes of uranyl(II), vanadyl(II) and zirconyl(II) with orotic acid
‘‘vitamin B13’’: Synthesis, spectroscopic, thermal studies
and antibacterial activity
*
Moamen S. Refat
Department of Chemistry, Faculty of Education, Suez-Canal University, Port Said, Egypt
Received 31 August 2006; received in revised form 4 December 2006; accepted 4 December 2006
Available online 19 January 2007
Abstract
A convenient method for the preparation of complexes of the uranyl [UO2]2+, vanadyl [VO]2+ and [ZrO]2+ ions with vitamin B13
(Orotic acid; H3OA) is reported and this has enabled three complexes of orotate anion (1ꢀ) to be formulated: [M(C5H3N2O4)2(H2O)2]Æ
(H2O)n [where M = [UO2]2+, [VO]2+, [ZrO]2+; n = 1, 6, 3, respectively]. The new bisorotate (H2OA)1ꢀ complexes were synthesis and
characterized by elemental analysis, molar conductivity, spectral methods (UV–vis, mass, 1H NMR and mid infrared spectra), and
simultaneous thermal analysis (TG and DTG) techniques. Physical measurements indicate that the neutral orotic acid ligand in its
mono/anion form, is bonded to oxometal ions through the carboxylic groups (two monodentate orotate anions and complete the
coordination sphere by coordinated water molecules). The molar conductance data confirm that the orotate complexes are non-electrolytes.
The X-ray powder diffraction (XRD) as well as scanning electron microscopy (SEM) shows that the studied complexes have amorphous
structures. The kinetic thermodynamic parameters, such as, E*, DH*, DS* and DG* are calculated from the DTG curves. The antibacterial
activity of the orotic acid and their complexes was evaluated against gram positive/negative bacteria.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Vitamin B13; Infrared spectra; Antibacterial activity; Thermal analysis; Kinetic parameter
1. Introduction
complexes in cyclodextrins could be a possibility due to
the water solubility increase of these supramolecular com-
pounds. The perfect compatibility of these inclusion com-
plexes with the living organisms must be taken into
account by their frequent use now as antiinflammatory
[3,4], cardiovascular [5], antidepressive or ophthalmologic
drugs [6].
Orotic acid (6-carboxy uracil, 1,2,3,6-tetrahydro-2,6-
dioxo-4-pyrimi-dine carboxylic acid, H3OA) (Fig. 1) is
closely related to the biologically important pyrimidine
bases [7,8]. Besides its biological important, orotic acid
and its substituted derivatives which may be viewed as
substituted uracils are also interesting ligands. Since they
are potentially multidentate, the coordination may occur
through the heterocyclic nitrogens of the pyrimidine ring,
the exocyclic carbonyl oxygens, and the carboxylic group.
However, studies on its coordination properties in solution
Orotic acid (OA), also known as vitamin B13, is a pre-
cursor of nucleic acid bases acting as an intermediate in
pyrimidine synthesis, particularly the uracil base [1]. It
was found in cells and body fluids of many living organ-
isms. This compound is applied in medicine as bio-stimula-
tor of the ionic exchange processes. There is a great interest
in the orotic acid relation to food protection and nourish-
ment research. A reliable assignment of its vibrational spec-
tra [2] is a useful basis in the study of the interaction with
other chemical species present in the biological milieu.
From this point of view there are problems with the solu-
bility in water of this molecular compound. Inclusion
*
Tel: +20127649416.
E-mail address: msrefat@yahoo.com
0022-2860/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.12.006

M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
25
2. Experimental
2.1. Materials and instrumentation
All chemicals were reagent grade and were used without
further purification. Orotic acid was purchased from
Aldrich Chemical Co., UO2(NO3)2Æ6H2O (Fluka Co.),
VOSO4ÆxH2O and ZrOCl2ÆxH2O from (Aldrich Co).
Carbon and hydrogen contents were determined using a
Perkin-Elmer CHN 2400 in the Micro-analytical Unit at
the Faculty of Science, Cairo University, Egypt. The metal
content was found gravimetrically by converting the com-
pounds into their corresponding oxides.
IR spectra were recorded on Bruker FT-IR Spectropho-
tometer (4000–400 cmꢀ1) in KBr pellets. The UV–vis,
Spectra were obtained for the DMF solution (10ꢀ3 M) of
the orotic acid and their three complexes with a Jenway
6405 Spectrophotometer using 1 cm quartz cell, in the
range 500–200 nm. Molar conductivities of freshly pre-
pared 1.0 · 10ꢀ3 mol/dm3 DMF solutions were measured
using Jenway 4010 conductivity meter. Mass spectra of
the orotate (1ꢀ) complexes were checked using AEI MS
30 mass spectrometer at 70 eV. 1H NMR spectrum of
[UO2]2+ complex was recorded on Varian Gemini
200 MHz spectrometer using DMSO-d6 as solvent and
TMS as an internal reference. Thermogravimetric analysis
(TGA and DTG) were carried out in dynamic nitrogen
atmosphere (30 ml/min) with a heating rate of 10 ꢁC/min
using a Schimadzu TGA-50H thermal analyzer. The X-
ray diffraction patterns (XRD) were obtained on a Rikagu
diffractometer using Cu/Ka radiation. Scanning electron
microscopy (SEM) images were taken in JEOL-840 equip-
ment, with an accelerating voltage of 15 KV.
Fig. 1. Numbering Scheme of orotic acid (H3OA).
and in the solid state show that orotic acid coordinates
mainly via N(1) and the carboxylato group. The only
exceptions known thus far are the copper(II) complex of
5-nitroorotic acid, which coordinates via the N(1) and
N(3) nitrogens [9]. While one of the roles of the magnesium
ion is to change orotic acid to an N(1) deprotonated dian-
ion, orotic acid does not enter the inner coordination
sphere of the metal in magnesium bisorotate (1ꢀ, H2OA)
octahedydrate [10] and in zinc bisorotate octahydrate
[11]. However, the complexity of the pyrimidine system
results also from pH changes. Between pH 3 and 9, orotic
acid is present in aqueous solutions mainly as the orotate
anion (the carboxylic group has pK = 2.07). N(3)–H in
which the N(1) atom is unsubstituted, is obtained by
abstraction of a second proton (pK = 9.45) and, according
to previous observations on related uracil anion systems,
should be present together with the N(1)–H tautomer
[12,13]. UV light absorption studies, potentiometry and lin-
ear free energy relationships for proton dissociation [14]
have been used to investigate the complexation of zinc(II),
cobalt(II), manganese(II), cadmium(II), copper(II) and
nickel(II) with orotic acid in solution. It was concluded
that, in neutral or slightly acidic pH, the ions of Zn(II),
Co(II), Mn(II) and Cd(II) coordinate through the carbox-
ylate group while Cu(II) and Ni(II) through the carboxyl-
ate and adjacent N(1). Spectroscopic investigation of the
interaction of nickel(II) with orotic acid [15] revealed bind-
ing of the metal to the carboxylate and, in some cases, to
the adjacent N(1) and the O(4) sites. The crystal structures
of the Ni(II) [16,17], Mg(II) [18], Co(II) [19], Zn(II) [20]
orotate complexes have been described where orotate dia-
nions act as bidentate ligand.
Relatively little information is available regarding the
compounds with orotate monoanion (H2OA, 1ꢀ). Due to
the high reactivity and different coordination modes of
orotic acid towards metal ions, this paper, describes the
first structurally characterized solid complexes of neutral
orotic acid with uranyl(II), vanadyl(II) and zirconyl(II)
ions. The great importance of vanadyl that is work like
insulin in the body to increase the amount of glucose and
amino acids driven into the muscles, and zirconyl is a bro-
minated zirconium oxide. The investigation of these pre-
pared complexes was carried out using elemental analysis
CHN, molar conductivity, (infrared, electronic UV–vis,
1H NMR and mass spectra), X-ray diffraction analysis,
scanning electron microscope, TG and DTG techniques
as well as kinetic parameters.
2.2. Preparations
Initial experiments were performed in order to find, if
possible, a general method for the preparation of orotic
acid complexes. But because of the low solubility of orotic
acid in water and also the difficulty in controlling the extent
of ionization in alkaline medium, the reaction of orotic acid
with lithium hydroxide in water at room temperature; sub-
sequent addition of aqueous metal salt solutions did not
appear to lead to complex formation. However, it was
found that by heating the H3OA–LiOHÆH2O solution to
70 ꢁC for 30 min, followed by addition of the metal salts,
complexes formed readily (this method not carried out
previously).
A general method is: orotic acid (1.56 gm, 0.01 mol) and
LiOHÆH2O (0.42 gm, 0.01 mol) were dissolved in water
(40 ml) and the solution heated to 70 ꢁC for 30 min. The
metal salts were dissolved in a minimum quantity of water
and the solutions mixed with vigorous stirring (for (1:2);
(metal:ligand) ratio). Precipitations were almost instanta-
neous, but stirring was continued for 15 min. The complex-
es were filtered, washed with water (20 ml hot water),
alcohol (15 ml), and dried in vacuo over CaCl2. It was

26
M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
found that lithium hydroxide powder was preferable to
sodium or potassium hydroxides pellets as more accurate
weighting is possible with powder. The yields were found
around 70% based on the metal salts. The compounds
resulted have low solubility in water and in common organ-
ic solvents, except the [UO2]2+ compound has slightly par-
tially dissolves upon gentle heating in DMSO.
It is worth mentioning that most studies of orotic acid
complexes in the solid phase have found that orotic acid
is in the dianion form [16,20–23]. It is, therefore, of great
interest to examine the coordination behavior of orotic
acid at neutral pH values with using (LiOH). Attempts to
crystallize the products in DMF have failed so that, in this
study used many techniques of analysis to prove the struc-
ture of the synthesized complexes.
2.3. Antibacterial investigation
3.1. Infrared spectra
For these investigations the filter paper disc method was
applied. The investigated isolates of bacteria were seeded in
tubes with nutrient broth (NB). The seeded NB (1 cm3) was
homogenized in the tubes with 9 cm3 of melted (45 ꢁC)
nutrient agar (NA). The homogeneous suspensions were
poured into Petri dishes. The discs of filter paper (diameter
5 mm) were ranged on the cool medium. After cooling on
the formed solid medium, 2 · 10ꢀ5 dm3 of the investigated
compounds were applied using a micropipette. After incu-
bation for 24 h in a thermostat at 25–27 ꢁC, the inhibition
(sterile) zone diameters (including disc) were measured and
expressed mm. An inhibition zone diameter over 8 mm
indicates that the tested compound is active against the
bacteria under investigation.
The infrared spectra of orotic acid and their complexes
have received little attention [24,25]. In publications where
the spectrum appears minor assignments are attributed in
comparison with similar compounds [26–28]. By contrast,
the spectra of uracil and its derivatives have been studied
by quantum mechanical methods. Tentative assignments
of IR bands of [UO2]2+, [VO]2+ and [ZrO]2+ complexes
are present in Table 2, and Fig. 2. The assignments of
the studied complexes have been comparing with the spec-
tra of H3OA and NaH2OA (1ꢀ) [24].
The IR spectra of the [UO2]2+, [VO]2+ and [ZrO]2+ com-
plexes exhibited characteristic features (donation sites) in
the –OH (acid), ketone (C(2)@O and C(4)@O, carboxylate
and NH (N(1)–H and N(3)–H) regions. The spectrum of
the [VO]2+ complex has slightly different from [UO2]2+
and [ZrO]2+ complexes (in the region of crystallized water)
due to the presence of number of lattice water leading to
different hydrogen bonding interactions with the coordina-
tion water and orotate anions.
The antibacterial activities of the investigated com-
pounds were tested against Escherichia Coli and Salmonella
(Gram negative bacteria) and Bacillus subtillis and Staphy-
lococcus aureus (Gram positive bacteria). In the same time
with the antibacterial investigations of the [UO2]2+
,
[VO]2+, and [ZrO]2+ complexes, the ligand was also tested,
as well as the pure solvent. The concentration of each solu-
tion was 5 · 10ꢀ3 mol dmꢀ3. Commercial DMF was
employed to dissolve the tested samples.
(i) In the m(O–H)water region the spectra of the three
mentioned complexes show one strong broad band
in the range of 3420–3480 cmꢀ1 attributed to the
presence of coordination water [29]. Coordination
and crystal water stretching modes appear between
3600–3420 cmꢀ1 with the crystal water appearing at
frequencies higher than these of coordination
product.
(ii) Deprotonation of N(1) results in disappearance of the
bands at Ca. 3200 and 1430 cmꢀ1 attributed to the
stretching and bending N(1)–H vibrations. This is
noted in cases where the orotate bind through the
N(1) atom. The crystal structure of the [Ni(HOA)
(H2O)4]ÆH2O [16] and [Cu(HOA)(NH3)2] [21] com-
plexes showed bidentate binding of orotic acid
through N(1) and the carboxylate group. No such
3. Results and discussion
The results of the elemental analysis and some physical
characteristics of the obtained compounds are given in
Table 1. The complexes were synthesized using a 1:2
(metal:ligand) mole ratio of all reactants. The elemental
analysis (Table 1) of the complexes indicates a 1:2 metal
to ligand stoichiometry, too. The complexes are air-stable,
hygroscopic, with high melting points, insoluble in H2O,
but partly soluble in dimethylformamide, DMF. The molar
conductivities of 10ꢀ3 mol dmꢀ3 solutions of the complexes
in DMF (Table 1) indicate that the complexes as non-elec-
trolytes in DMF.
Table 1
Analytical and physical data of the investigated compounds
Complexes
M.Wt
Yield (%)
Color
M.P (ꢁC)
Anal. (%) found (Calcd.)
K (Xꢀ1 cm2 mol)
C
H
N
[UO2(C5H3N2O4)2(H2O)2]Æ(H2O)
[VO(C5H3N2O4)2(H2O)2]Æ6(H2O)
[ZrO(C5H3N2O4)2(H2O)2]Æ3(H2O)
634
521
507
73
69
71
Yellow
Green
White
>300
>300
>300
18.90 (18.90)
22.70 (23.00)
23.50 (23.70)
2.05 (1.89)
3.98 (4.22)
2.96 (3.16)
8.67 (8.83)
10.54 (10.70)
10.85 (11.00)
2.76
6.70
4.51

M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
27
Table 2
IR frequencies (cmꢀ1) of orotic acid (H3OA), sodium orotate (NaH2OA), uranyl, vanadyl and zirconyl complexes
H3OA
–
NaH2OA
[UO2]2+
[VO]2+
[ZrO]2+
Assignments
3500 w, sh
3570 sh
3589 w
3567 w
3476 s,br
3218 s
3117 w
2989 s,br
2812 s
3505 sh
m(OH); Cyst water
–
–
3447 s,br
3212 s
3114 w
2971 s,br
2800 s
3421 s,br
3213 s
3114 w
2972 br
2800 s
m(OH); Coord. water
m(N1–H)
m(C5–H)
3155 sh
3099 m
3020 vw
3002 w
2950 sh
2810 s
3200 s
3100 s
2950 s,br
2900 sh
m(N3–H)
2560 w
2490 s,br
1703 vs
1650 vs
–
–
–
–
m(OH) acid
Hydrogen bond
m(C@O) acid + m(C2@O)
m(C4@O) + m(C@C)
1740 s
1710 sh
1690 s
1625 sh
1493 m
1735 vs
1692 vs
1738 vs
1685 vs
1734 vs
1688 vs
1518 s
1653 sh
1625sh
1494 s
1426 s
1653 sh
1561 w
1497 s
1429 s
1654 sh
1495 s
m
asym(COOꢀ) + ring vib. + d(H2O)
1435 vs
1405 s
1327 s
1263 vs
1425 s
1426 s
d(N1–H) + ring vib.
sym(COOꢀ)
1385 s
1383 vs
1300 w,sh
1232 s
1389 vs
1300 w,sh
1233 m
1182 w
1113 s
1041 w
1017 m
960 vw
931 s
1384 vs
1300 w,sh
1232 s
m
1290 m
1270 sh
1233 m
1105 w
1015 m
960 w
m(C6–C7) + m(C–C) + m(C–N)
1126 m
1010 s
982 s
1106 vw
1039 vw
1017 s
1106 w
1039 vw
1017 s
CH wagging + ring dif. + ring vib. m(M@O) [M = V and Zr]
928 s
888 vw
860 s
832 vw
729 vs
925 s
880 sh
845 s
790 s
775 s
755 s
725 w
630 m
595 w
553 s
508 m
428 s
927 vs
854 s
792 w
778 s
928 s
855 s
793 sh
778 vs
759 sh
d(N–H) + ring vib. + m(U@O)
m(C–H) + m(C–C) + out-of-plane dr(H2O)
855 s
798 vw
780 s
759 vw
649 w
601 s
551 vs
460 s
637 s
598 s
553 vs
508 s
433 vs
640 s
598 s
552 vs
510 m
439 s
671 vw
637 s
599 s
553 vs
509 s
C2@O + C4@O bending + d(ring) ring def.
437 vw
432 vs
br, broad; m, medium; s, strong; sh, shoulder; w, weak; m, stretching; d, bending.
assignment (the stretching and binding bands of
N(1)–H) was possible in this study, that these assign-
ments, m(N(1)–H) + d(N(1)–H), are present in the
[UO2]2+, [VO]2+ and [ZrO]2+ complexes (Table 2)
confirming the interaction not through N(1)–H but
coordination mode is a monodentate.
interaction between the metal salt and the carboxylate
group that ranges from the covalent to ionic depend-
ing on the shifts of the two bands. It was found that
orotic acid interacts with all of these metal ions in the
anionic form and coordinates in a monodentate fea-
ture through its carboxylate group to [UO2]2+
,
(iii) The carbonyl groups (C(2)@O and C(4)@O) of the
ring appear as two main peaks at 1700 and
1650 cmꢀ1 in the free acid, the comparison between
the infrared spectra of the free acid and its sodium
salt, whose characterized [24], a shift is observed for
the 1700 and 1330 cmꢀ1 bands, corresponding to
the asymmetric and symmetric stretching of the car-
boxylate group which appear at 1625 and
1385 cmꢀ1 in sodium salt. These shifts are expected,
when going from the acid to the salt. Similar shifts
[VO]2+ and [ZrO]2+ ions. This result is in accord with
the n.m.r. data of [UO2]2+ complex, that also indicate
coordination of metal to the carboxylate group
(monodentate).
(iv) Another important band in distinguish between
mono and bidentate coordination of orotate ligand
(H3OA) is the stretching m(C(6)–C(7)) band that in
case of NaH2OA appears with medium intensity at
of 1290 cmꢀ1. This band shifted to higher frequencies
(48 and 35 cmꢀ1) in the complexes of orotate (2ꢀ)
ligand, it is found in the cases where the metal ion
coordinates through the carboxylate group and the
are observed in the complexes prepared ([UO2]2+
[VO]2+ and [ZrO]2+ complexes), indicating an
,

28
M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
meaning the presence of water molecules perhaps
outside or inside coordination sphere of the complex-
es, also the presence of strong band at 855 cmꢀ1 in all
complexes attributed to the rocking vibration
motion, dr(H2O), of coordination water molecules,
this confirm that H2O molecules in the complexes
are inside the coordination sphere. This notification
was also supported by thermal analysis.
(viii) The m(U@O) vibration in the uranyl complex is
observed as expected as a very strong band at
927 cmꢀ1 is a good agreement with those known for
many dioxouranium(VI) complexes [31,32]. On the
other hand concerning, the infrared spectra of
[ZrO]2+ and [VO]2+ complexes show a strong and
medium absorption band at 1017 cmꢀ1 due to
m(V@O) and m(Zr@O) as expected [33].
3.2. Molar conductance measurements
The molar conductivity values for the orotate complexes
in DMF solvent (10ꢀ3 mol dmꢀ3) were in the range of (2–7)
Xꢀ1 cm2 molꢀ1, suggesting them to be non-electrolytes
(Table 1). Conductivity measurements have frequently
been used in structural of metal chelates (mode of coordi-
nation) within the limits of their solubility. They provide
a method of testing the degree of ionization of the complex-
es, the molar ions that a complex liberates in solution (in
case of presence anions outside the coordination sphere),
the higher will be its molar conductivity and vice versa. It
is clear from the conductivity data that the complexes pres-
ent seem to be non-electrolytes. Also the molar conduc-
tance values indicate that the anions may be present
inside the coordination sphere or absent. This results were
confirmed from the chemical analysis (elemental analysis
Fig. 2. Infrared spectra of: (A), orotic acid; (B), uranyl(II); (C),
vanadyl(II); and (D), zirconyl(II) compounds.
data) where Clꢀ or SO4 ions are not precipitated colored
2ꢀ
N(1) [16,21]. While monodentate [24] of the metal
through the carboxylate group results in smaller up
by addition of AgNO3 or BaCl2 solutions, respectively, this
tested good matched with CHN data.
field shift (+2 to +15 cmꢀ1). For the [UO2]2+
,
All the complexes did not have electrolytic properties.
[VO]2+ and [ZrO]2+ orotate complexes, this shift to
10 cmꢀ1 (because it present in 1300 cmꢀ1 with weak
shoulder intensity) denoting coordination with the
carboxylate group as monodentate.
This fact elucidated that the Clꢀ, SO4 or NO3 are
absent, and that the water molecules completely the coor-
dination sphere of the orotato complexes.
2ꢀ
ꢀ
(v) The strong broad band around 2500 cmꢀ1, which
assigned to m(OH) acid is absent in the all complexes
resulted, this attributed to the involvement of carbox-
ylic group of the free acid in the complexation.
(vi) For the monodentate carboxylate coordination to the
metal ion, observed in the structure of all prepared
complexes, the relationship DComplex > Dsod. orotate to
apply [30], where D = masym(COO) ꢀ msym(COO).
3.3. Electronic absorption spectra
The spectra of the orotate complexes in DMF are shown
in Fig. 3. There are two detected absorption bands at
around (210, 235 nm) and 280 nm assigned to p–p* and
n–p* transitions, respectively, in the electronic spectrum
of the ligand. These transitions also found in the spectra
of the complexes, but they are shifted towards lower wave-
length, confirming the coordination of the ligand to the
metallic ions. The first band around 210 and 235 nm is
probably due to a p–p* of the exocyclic band in heterocy-
clic ring and also assigned to the two carbonyl groups.
However, the second band around 280 nm is due to pres-
ence of COOH group [34]. In case of [UO2]2+, [VO]2+
[Dsod. orotate = 240 cmꢀ1; UO2(II) = 242 cmꢀ1; [VO]2+
=
264 cmꢀ1 and [ZrO]2+ = 270 cmꢀ1].
(vii) The infrared spectra of all three complexes exhibit
bands refer to masym and msym(O–H) and d(H2O) vibra-
tion in the regions above 3400 cmꢀ1 and weak shoul-
der band around 1620 cmꢀ1
, respectively, this

M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
29
3,0
2,5
2,0
1,5
1,0
0,5
0,0
and coordinates in a monodentate chelating through its
carboxylate group. Vanadyl(II) and zirconyl(II) ions
react with orotic acid in alkaline medium to form the
four coordinated oxometal(IV) complexes of the type
[M(C5H3N2O4)2(H2O)2]Æ(H2O)n. The complexes are in the
mononuclear form where the two orotate molecules and
two water molecules occupy the four equatorial positions
in a plan perpendicular to metal oxygen forming a square
pyramid, and octahedral structure for [UO2]2+ orotate
complex see Scheme 1.
UO2(II)
VO(II)
Orotic acid
ZrO(II)
3.5. Mass spectra
The mass spectrum of orotic acid, (H3OA), ligand exhib-
its a prominent molecular ion at m/z (156, 64%). The frag-
mentation of orotic acid proceeds by loss of CO2 from the
molecular ion to give uracil molecule at m/z 113 with inten-
sity 10%, then the elimination of HNCO, lead to the forma-
tion of an ion at m/z (%), 68 (100%), which is the base peak
of the spectrum. On the other hand, the probable loss of
CO from the same ion (base peak, 68 (100%)) gives an
ion at m/z 40 (21%). The suggested pathway fragmentation
pattern is given in Table 4 and Scheme 2.
The corresponding mass spectra of the uranyl(II), vana-
dyl(II) and zirconyl(II) orotate complexes are given in
Table 4 and Fig. 5 and their fragmentation are presented
in Schemes 3–5, respectively. Mass spectrometry has been
applied in order to study the main fragmentation routes
of some 6-carboxyuracil (vit B13) complexes. Difference
in fragmentation was caused by the nature of the attached
metal ions.
200
300
400
500
Wavelenght
Fig. 3. Electronic spectra of orotic acid and their complexes.
and [ZrO]2+ orotate complexes, the carboxylic group is
blue shifted with increase the intensity (absorbance).
This result confirms the complexation of metal ions
via carboxylic group (monodentate chelating). The
[VO(C5H3O4N2)2(H2O)2]Æ6H2O complex has a shoulder
broad band at 325 nm may be assigned to the following
d–d transition.
1
3.4. H NMR spectra
1
The H NMR spectral data of the [UO2(C5H3O4N2)2
(H2O)2]Æ H2O complex and the free ligand (H3OA) orotic
acid are collected in Table 3 and its spectrum is shown in
1
Fig. 4. The literature values [35], of the H NMR chemical
3.6. X-ray powder diffraction and scanning electron
microscopy
shifts (d, ppm) of orotic acid are included in Table 3 for
comparison purposes. The presence of the N(1)–H and
N(3)–H protons resonance in the spectrum (Table 3 and
Fig. 4) clearly show that this nitrogen atoms not engaged
in the complex formation. The uranyl(II) moiety appear
to bind the orotic acid through carboxylate group, the
absence of proton of (COOH) confirm the mode of coordi-
nation (behaves as a monodentate chelating ligand, binding
through adjacent carboxylato group). The broad singlet
peak at 4.45 ppm is due to the presence of water molecules
protons and a multiplet signal around 6.57 ppm is due to
the (C5)–H aromatic protons. Note that H2O is seen in
aprotic solvents, while HOD is seen in protic solvents
due to exchange with the solvent deuteriums, this appeared
in the spectrum of the [UO2]2+ complex at 3.45 ppm.
It was found that orotic acid interacts with all of
[UO2]2+, [VO]2+ and [ZrO]2+ ions in the anionic form
X-ray powder diffraction patterns in the 10ꢁ < 2h < 70ꢁ
of the complexes were carried out in order to obtain an idea
about the lattice dynamics of the complexes. By compari-
son of the obtained X-ray powder diffraction patterns
shown in Fig. 6, the X-ray powder diffraction patterns
throws light only on the fact that each solid represents a
definite compound of a definite structure which is not con-
taminated with starting materials. This identification of the
complexes was done by the known method [36]. Such facts
suggest that the prepared compounds are amorphous.
Purity and morphology of the complexes obtained were
studied by SEM. The obtained SEM micrographs, shown
in Fig. 7, allow to verify that the [UO2]2+, [VO]2+ and
[ZrO]2+ complexes are the ones with the well formed amor-
phous shape. Such facts are in agreement with the obtained
Table 3
1H NMR data of orotic acid and uranyl(II) complex in DMSO-d6 solvent (d, ppm from TMS)
Compounds
Residual solvent
1H(HDO)
H2O coordination
N(1)–H
C(5)–H
N(3)–H
OH acid
H3OA
[UO2]2+
–
2.51
–
3.45
–
4.45
6.00
6.42
6.74
6.57
10.00
8.96
11.00
–

30
M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
Fig. 4. 1H NMR spectra of uranyl(II) orotate complex.
3.7. Thermogravimetric analysis
b
a
H
N
H
N
O
O
O
O
Thermal analysis curves (TG and DTG) of the studies
complexes are shown in Fig. 8. The thermoanalytical
results are summarized in Table 5.
HN
O
HN
O
O
O
O
O
OH2
OH2
V
U
O
. 6H2O
.H2O
O
O
O
O
H2O
H2O
3.7.1. [UO2(C5H3N2O4)2(H2O)2]Æ(H2O)
The thermal analysis curves of the complex show that
decomposition takes places in three stages in 25–800 ꢁC
temperature range (Fig. 8). The first and second exothermic
decomposition stages correspond to the dehydration pro-
cess. The DTG and TG curves of the complex show a
weight loss (Found 7.34, Calcd. 8.52%) in the 25–375 ꢁC
range corresponding to the loss of all three water mole-
cules. The following stage is also exothermic at 432 ꢁC
(DTG) showing the decomposition of orotic acid. The final
product, formed at Ca. 770 ꢁC, consists of (UO2 + 3C).
Reported data on thermal analysis studies in the nitrogen
atmosphere indicate that the [UO2]2+ complex decompose
to give oxide and few carbon atoms as final products, (no
sufficiently of oxygen atoms help to evolved carbon as car-
bon monoxide or dioxide).
NH
NH
O
N
H
O
O
N
H
O
H
c
O
N
O
HN
O
O
OH2
O
Zr
. 3H2O
O
O
H2O
NH
O
N
H
O
Scheme 1. Suggested structure of (a) uranyl(II), (b) vanadyl(II) and (c)
zirconyl(II)-orotate complexes.
3.7.2. [VO(C5H3N2O4)2 (H2O)2]Æ6(H2O)
Thermal decomposition of [VO(C5H3N2O4)2(H2O)2]Æ
6(H2O) proceeds in two ranged main stages. The first stage
is related to the dehydration of crystalline water molecules
(Found 20.20%; Calcd. 20.70%), in the temperature range,
25–408 ꢁC, by giving an exothermic effect (DTGmax: 126,
X-ray results. Single crystals of the complexes could not be
described. However, the spectroscopic data and elemental
analysis of CHN supported to predict possible structures.
Table 4
Mass spectra data of [UO2]2+, [VO]2+ and [ZrO]2+ complexes
Compounds
m/z (%)
Orotic acid (C5H4O4N2)
156(64); 113(10); 68(100); 40(21); 28(5)
[UO2(C5H3N2O4)2(H2O)2]Æ(H2O)
[VO(C5H3N2O4)2(H2O)2]Æ6(H2O)
[ZrO(C5H3N2O4)2(H2O)2]Æ3(H2O)
308(65); 290(21); 264(50); 247(37); 236(100); 220(56); 207(19); 130(58); 102(31); 76(37); 64(14); 51(28)
290(100); 263(32); 247(51); 207(31); 130(21); 103(7); 76(20); 65(7); 51(12)
224(3); 212(3); 171(5); 160(6); 152(5); 144(9); 131(11); 119(43); 106(34); 92(17); 78(19); 65(60); 54(100)

M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
31
O
OH
O
NH
NH
CO2
C
-HCNO
O
N
H
O
O
N
H
O
N
m/z 156 (64%)
m/z 113 (10%)
m/z 68 (100%)
CO
[CH2C
m/z 40(21%)
N ]
CO
m/z 28(5%)
Scheme 2. Fragmentation pattern of orotic acid.
Fig. 5. Mass spectra of: (a), [UO2]2+; (b), [VO]2+; and (c), [ZrO]2+ orotate complexes.
2þ
2þ
2þ
½UO2ꢁ ð432 ꢂCÞ > ½VOꢁ ð425 ꢂCÞ > ½ZrOꢁ ð417 ꢂCÞ
212 and 320 ꢁC). In the following stage the anhydrous
[VO]2+ complex decomposes in consecutive steps in the
The proposed structures of the synthesized complexes
which are presented in Scheme 1 are consistent with each
other in term of chemical, spectroscopic data and thermal
analysis.
408–750 ꢁC temperature range to give VO2.5
.
3.7.3. [ZrO(C5H3N2O4)2(H2O)2]Æ3(H2O)
This complex decomposes in five stages (collected in two
definite ranges). The first and second stages at (60 and
295 ꢁC DTGmax, respectively) are exothermic decomposi-
tion and corresponding to the loss of three moles of unco-
ordinated water molecules (Found 10.20, Calcd. 10.70%).
The anhydrous complex is stable up to 300 ꢁC. The follow-
ing stages involve the exothermic decomposition of the
orotic acid ligands and coordinated water molecules, and
then the final decomposition product is ZrO2. The overall
weight loss (Found 59.40, calcd. 59.60) agrees well with
the proposed structure. The cause of higher temperature
for liberated crystallized water molecules is due to the
hydrogen bonding interaction with the coordination water
molecules and orotate anions.
3.8. Kinetic parameters
Two methods are mentioned in the literature related to
decomposition kinetics studies, Coats–Redfern [37] and
Horowitz–Metzger [38], applied these two methods in this
study.
3.9. Coats–Redfern equation
The Coats–Redfern equation (1), which is a typical inte-
gral method, can be represented as:
Based on the essential DTGmax temperatures of the
decomposition of orotate complexes, the thermal stabilities
of the complexes follow the sequence:
Z
Z
1
T2
ꢃ
n
da=ð1 ꢀ aÞ ¼ ðA=uÞ
eꢀE =RT dT
ð1Þ
0
T1

32
M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
H
O
N
O
O
OH
NH
O
H
N
HN
O
O
HO
O
O
N
H
HN
O
m/z 308(65)
O
OH2
O
Cleavage
U
O
.H2O
O
O
H2O
NH
O
N
H
O
O
U
O
OH2
OH2
m/z 634
H2O
H
N
O
O
O
O
OH
NH
m/z 324
HN
HO
O
-H2O2
N
H
O
m/z 308(65)
O
H2O
U
OH2
-CO2
m/z 290(21)
H
O
N
O
O
-2H2O
- O
HN
NH
HO
O
O
N
H
U
m/z found 236 (100%) (Calc. 238)
m/z 264(50)
-CO2
H
O
N
O
O
HN
NH
O
N
H
m/z 220(56)
-C
H
- CO
-N2
- HNCO
-NH3
O
N
O
O
O
O
N
[ C5O]
m/z 76(37)
HN
NH
- O
N
O
N
H
C
C
m/z found 207 (19%) (Calc. 208)
Scheme 3. Fragmentation pattern of uranyl(II) orotate complex.
m/z found 130 (58%) (Calc. 132)
For convenience of integration, the lower limit T1 is usu-
ally taken as zero. This equation on integration gives
(Eq. (2));
A plot of left-hand side (LHS) against 1/T was drawn. E* is
the energy of activatiꢀo1n in KJ molꢀ1 and calculated from
the slop and A in (s ) from the intercept. The entropy
of activation DS* in (JKꢀ1 molꢀ1) was calculated by using
the equation:
Ln½ꢀ lnð1 ꢀ aÞ=T2ꢁ ¼ ꢀEꢃ=RT þ ln½AR=uEꢁ
ð2Þ

M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
33
H
O
N
O
H
HN
O
O
N
O
O
V
HN
O
Cleavage
OH2
O
.6H2O
O
O
O
H2O
OH2
O
-6H2O
- C5H3O2N2
V
O2
H2O
NH
m/z 290(100)
-CO2
O
N
O
H
m/z 521
H
N
O
O
N
OH2
O2
V
H2O
O
m/z found 247 (51%) (Calc. 246)
-2H2O
-H2
N
O
O
N
V
O2
O
m/z 207(31)
-NO2
-NO
[C4O2V]
m/z 131(21)
-2CO
[C2V]
m/z found 76 (20%) (Calc. 75)
Scheme 4. Fragmentation pattern of vanadyl(II) orotate complex.
DSꢃ ¼ R lnðAh=kTsÞ
ð3Þ
Log½logðwa=wcÞꢁ ¼ Eꢃh=2:303RT s2 ꢀ log 2:303
ð4Þ
Where k is the Boltzmann constant, h is the Plank’s con-
stant and Ts is the DTG peak temperature.
Where h = T ꢀ Ts, wc = wa ꢀ w, wa = mass loss at the
completion of the reaction; w = mass loss up to time t.
The plot of Log[log(wa/wc)] versus h was drawn and found
to be linear from the slope E* was calculated. The pre-ex-
ponential factor, A, was calculated from the Eq. (5):
3.10. Horowitz–Metzger equation
The Horowitz–Metzger (Eq. (4)) was written in the form
as follows:
Eꢃh=RT 2s ¼ A=½u expðꢀEꢃ=RT sÞꢁ
ð5Þ

34
M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
H
O
N
O
O
HN
O
Zr
O
O
Cleavage
-5H2O
OH2
O
O
Zr
.3H2O
O
O
OH
H2O
-C5H3O4N2
-C2N
NH
NH
O
N
O
H
HO
m/z 507
m/z 224(3)
- 4O
[ZrOC3H3N]
m/z 160(6)
- NH2
[ZrOC3H]
m/z 144(9)
- C
- 0.5H2
[ZrOC2]
m/z 131(11)
- C
[ZrOC]
m/z 119(43)
- C
- 0.5O2
Zr
[ZrO]
m/z 91(17)
m/z 106(34)
Scheme 5. Fragmentation pattern of zirconyl(II) orotate complex.
The entropy of activation, DS*, enthalpy activation, DH*,
and Gibbs free energy, DG*, were calculated from;
Table 6, together with the radii metal ions. The results
show that the values obtained by various methods are
comparable.
The kinetic data obtained with the two methods are in
harmony with each other. The activation energy of
[UO2]2+, [VO]2+ and [ZrO]2+ complexes is expected
increase in relation with decrease in their radius [39].
The E* values calculated with the method of Coats–Red-
fern for the definite decomposition stages of the complexes
are given below:
DHꢃ ¼ Eꢃ ꢀ RT
DGꢃ ¼ DHꢃ ꢀ TDSꢃ
The linearization curves of Coats–Redfern and Horowitz–
Metzger methods are shown in Fig. 9. Kinetic parameters
for the main stages around 400 ꢁC (decomposition of
orotic acid), calculated by employing Coats–Redfern
and Horowitz–Metzger equations, are summarized in

M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
35
100
75
DrTGA
mg/min
TGA
mg
a
4
0,1
0,0
3
2
50
-0,1
-0,2
-0,3
25
10
20
30
40
50
60
70
2theta
1
0
200
400
600
800
Temp [o C]
Fig. 6. X-ray diffraction patterns of uranyl(II) orotate complex.
TGA
mg
DrTGA
mg/min 0,1
b
0,0
2
-0,1
-0,2
1
-0,3
800
0
200
400
600
Temp [o C]
Fig. 7. SEM of uranyl(II) orotate complex.
c
TGA
mg
DrTGA
mg/min 0,1
EꢃUO2ðIIÞ ¼ 227 kjmolꢀ1 > EVꢃ OðIIÞ ¼ 165 kjmolꢀ1 > EZꢃ rOðIIÞ
¼ 127 kjmolꢀ1
2
1
0
rUO2ðIIÞ ¼ 52 pm < rVOðIIÞ ¼ 59 pm < rZrOðIIÞ ¼ 72 pm:
0,0
3.11. Antibacterial activity
-0,1
-0,2
The preparation of stable metal orotate complexes is
considerable important not only for their chemical but
also biological and medical aspects. It is proven that
orotic acid, formerly designated as vitamin B13, has a
strong influence on regeneration geriatric cells, especially
on the cells of the liver and the gastrointestinal tract.
This may explain its important role in the geriatry.
Moreover, orotic acid is a carrier for a lot of minerals
in the cells, which are partly of special important for
the anticancer effects [40,41] with platinum and palladi-
um(II) orotates.
-0,3
800
0
200
400
Temp [o C]
600
Fig. 8. Thermograms (TGA and DTG) of: (a), [UO2]2+; (b), [VO]2+; and
(c), [ZrO]2+ orotate complexes.

36
M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
Table 5
Thermoanalytical results (TG and DTGA) for isolated orotate complexes
Complexes
[UO2]2+
Stages
Temp./range (ꢁC)
DTGmax (ꢁC)
Residual species
UO2 + 3C
Decomposition species
Total losses (%)
Found
Calc.
1St
2St
3St
1St
2St
25–215
215–375
375–800
25–408
68
275
432
126, 212, 320
425, 540, 655
–H2O cyst.
2.20
5.14
2.84
5.68
–2H2O coord.
7CO + NO + 2NH3 + 0.5N2
–6H2O cyst.
4.5H2O + 4NO+
0.5H2
–3H2O cyst.
2H2O + 3CO+
4NO + 3H2+
43.60
20.20
39.40
43.20
20.70
38.80
[VO]2+
VO2.5 + 10C
ZrO2 + 7C
408–800
[ZrO]2+
1St
2St
25–390
390–800
60, 295
417, 471, 568
10.20
49.20
10.70
48.90
1
a
d
-12
-13
-14
-15
-16
-17
-18
0
-1
-2
-3
-4
-5
1,30
1,35
1,40
1,45
1,50
-80
-60
-40
-20
0
20
40
60
1000/T (K-1)
θ (Κ)
b
e
0,5
0,0
-12
-13
-14
-15
-16
-17
-0,5
-1,0
-1,5
-2,0
-2,5
1,40
1,42
1,44
1,46
1,48
1,50
1,52
1,54
1,56
1,58
-20
0
20
40
60
80
100
1000/T (K-1)
θ (Κ)
-10
-12
-14
-16
-18
-20
-22
c
f
0,0
-0,5
-1,0
-1,5
-2,0
-2,5
1,30
1,35
1,40
1,45
1000/T (K-1)
1,50
1,55
1,60
-50
-40
-30
-20
-10
0
10
20
θ (Κ)
Fig. 9. The Diagrams of kinetic parameters of: (a), CR of [UO2]2+–orotate complex; (b), HM of [UO2]2+–orotate complex; (c), CR of [VO]2+–orotate
complex; (d), HM of [VO]2+–orotate complex; (e), CR of [ZrO]2+–orotate complex; (f), HM of [ZrO]2+–orotate complex; Coats–Redfern, (CR); and
Horowitz–Metzger, (HM) equations.

M.S. Refat / Journal of Molecular Structure 842 (2007) 24–37
37
Table 6
Thermal behavior and kinetic parameters determined using the Coats–Redfern (CR) and Horowitz–Metzger (HM)
Complexes
[UO2]2+
Radius metal ion/pm
52
Ts (K)
432
Method
E* · 102
A
DS* · 102
DH* · 103
DG* · 104
r
CR
HM
CR
HM
CR
HM
2.27
2.58
1.65
1.82
1.27
1.40
1.99 · 1012
5.46 · 1016
1.60 · 107
4.64 · 1011
1.99 · 1012
5.46 · 1016
ꢀ1.64
ꢀ1.73
ꢀ1.14
ꢀ1.23
ꢀ1.64
ꢀ1.51
ꢀ 5.51
ꢀ4.88
ꢀ5.64
ꢀ4.97
ꢀ5.51
ꢀ4.55
5.83
5.42
7.40
6.96
5.83
4.92
0.9870
0.9812
0.9918
0.9876
0.9975
0.9961
[VO]2+
59
72
425
417
[ZrO]2+
Table 7
[10] O. Kumberger, J. Riede, H.Z. Schmidbaur, Naturforsch. 148 (1993)
961.
Antibacterial activity of orotic acid and their complexes
[11] I. Bach, O. Kumberger, H. Schmidbaur, Chem. Ber. 123 (1990)
2267.
[12] A. Psoda, Z. Kazimierczak, D. Shugar, J. Am. Chem. Soc. 96 (1974)
6832.
Compounds Gram positive
Gram negative
Escherichia Salmonella
Coli
Bacillus
subtillis
Staphylococcus
aureus
[13] O. Bensaude, J. Aubard, M. Dreyfus, C. Dodin, J.E. Dubois, J. Am.
Chem. Soc. 100 (1978) 2823.
[14] B.E. Doody, E.R. Tucci, R. Scruggs, N.C. Li, J. Inorg. Nucl. Chem.
28 (1966) 833.
Orotic acid ++
+
+++
–
++
++
+++
+
[UO2]2+
[VO]2+
[ZrO]2+
++++
++
+++
++++
+++
++
+++
+++
[15] A.K. Singh, R.P. Singh, Indian J. Chem. 17A (1979) 469.
[16] M. Sabat, D. Zglinska, B. Jeznowska-Trzebiatowska, Acta Crystal-
logr. B36 (1980) 1187.
(–), NO antibacterial activity; (+), mild activity; (++), moderate activity;
(+++), marked activity; (++++), strong marked activity.
[17] A.Q. Wu, L.Z. Cai, G.H. Guo, F.K. Zheng, G.C. Guo, E.G. Mao,
J.S. Huang, Chin. J. Inorg. Chem. 19 (2003) 879.
[18] I. Mutakainen, R. Hamalainen, M. Klinga, O. Orama, U. Turpeinen,
Acta Crystallogr. C52 (1996) 2480.
[19] H. Icbudak, H. Olmez, O.Z. Yesilel, F. Arslan, P. Naumov, G.
Javanowski, A.R. Ibrahim, A. Umsan, H.-K. Fun, S. Chant-
rapronma, S.W. Ng, J. Mol. Struct. 657 (2003) 225.
[20] A. Karipides, B. Thomas, Acta Crystallogr. C42 (1986) 1705.
[21] I. Mutikainen, P. Lumme, Acta Crystallogr. B36 (1980) 2233.
[22] T. Solin, K. Matsumoto, K. Fuwa, Bull. Chem. Soc. Jap. 54 (1981)
3731.
Applying the nutrient filter paper disc method all of the
newly synthesized orotate complexes were screened in vitro
for antibacterial activity against E. Coli and Salmonella
(Gram negative bacteria) and Bacillus subtillis and Staphy-
lococcus aureus (Gram positive bacteria). The activity was
determined by measuring the diameter of the inhabitation
zone. The screening results given in Table 7, indicated that
all the complexes exhibited antibacterial activities against
type of bacteria used.
An influence of the central ion of the complexes in the
antibacterial activity against the tested Gram positive and
Gram negative organisms. The results also show that the
complexes have an enhanced activity compared to the orot-
ic acid it self. This is specially showed against bacteria. The
metal activity increase in the order
[23] T.S. Khodashova, M.A. Porai-Koshits, N.K. Davidenko, N.N.
Vlasova, Koord. Khim. 10 (1984) 262.
[24] G. Maistralis, A. Koutsodimou, N. Katsaros, Trans. Met. Chem. 25
(2000) 166.
[25] D.A. Ko¨se, B. Zumreoglu-Karan, O. Sßahin, O. Buyukgungo¨r, J. Mol.
¨
¨
¨
¨
Struct. 789 (1–3) (2006) 147.
[26] J.R. Lacher, J.L. Bitner, D.J. Emery, E.M. Seffl, J.D. Park, J. Phys.
Chem. 59 (1955) 615.
[27] T.S. Hermann, J.M. Black, Appl. Spectr. 20 (1966) 413.
[28] E. Titov et al., Khim. Heter. Soedin. 6 (1972) 833.
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2þ
2þ
2þ
½UO2ꢁ > ½VOꢁ > ½ZrOꢁ
:
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