In vitro antibacterial and antifungal activities of some sulfur-nitrogen-oxygen and oxygen-nitrogen-oxygen donor bifunctional tridentate schiff bases and their boron(III) complexes

Article abstract of DOI:10.1080/10426500902797749

Antimicrobial properties of sulfur, nitrogen, and oxygen bonded organoboron (III) complexes with biologically potent ligands viz., 2-hydroxy-N-phenyl benzamide hydrazine carboxamide(HO∩N∩OH), 2-hydroxy-N-phenyl benzamide hydrazine carbothioamide (HO∩N∩∩SH), and 2-hydroxy-N-phenyl benzamide hydrazine carbodithioic acid (HO∩N∩SH), have been studied. The unimolar and bimolar reactions of triisopropoxy borane with dibasic tridentate ligands resulted in the formation of colored solids, which have been characterized by elemental analysis, molecular weight determinations, and conductance measurements. The UV, IR, and NMR (¹H, ¹³C, and ¹¹B) spectral studies indicate a tetra-coordinated geometry for the resulting complexes. The ligands and their complexes have been screened for their fungicidal and bactericidal activities, and the results indicate that they exhibit significant antimicrobial properties. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Full text of DOI:10.1080/10426500902797749

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In Vitro Antibacterial and
Antifungal Activities of Some
Sulfur–Nitrogen–Oxygen and
Oxygen–Nitrogen–Oxygen Donor
Bifunctional Tridentate Schiff Bases and
Their Boron(III) Complexes
Sunita Yadav a , Monika Swami a & R. V. Singh a
a Department of Chemistry University of Rajasthan , Jaipur, India
Published online: 03 Feb 2010.
To cite this article: Sunita Yadav , Monika Swami & R. V. Singh (2010) In Vitro Antibacterial and
Antifungal Activities of Some Sulfur–Nitrogen–Oxygen and Oxygen–Nitrogen–Oxygen Donor Bifunctional
Tridentate Schiff Bases and Their Boron(III) Complexes, Phosphorus, Sulfur, and Silicon and the
Related Elements, 185:2, 394-401
To link to this article: http://dx.doi.org/10.1080/10426500902797749
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Phosphorus, Sulfur, and Silicon, 185:394–401, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902797749
IN VITRO ANTIBACTERIAL AND ANTIFUNGAL
ACTIVITIES OF SOME SULFUR–NITROGEN–OXYGEN
AND OXYGEN–NITROGEN–OXYGEN DONOR
BIFUNCTIONAL TRIDENTATE SCHIFF BASES AND THEIR
BORON(III) COMPLEXES
Sunita Yadav, Monika Swami, and R. V. Singh
Department of Chemistry University of Rajasthan, Jaipur, India
Antimicrobial properties of sulfur, nitrogen, and oxygen bonded organoboron (III)
complexes with biologically potent ligands viz., 2-hydroxy-N-phenyl benzamide
hydrazine carboxamide(HO∩N∩OH), 2-hydroxy-N-phenyl benzamide hydrazine carboth-
ioamide (HO∩N∩SH), and 2-hydroxy-N-phenyl benzamide hydrazine carbodithioic acid
(HO∩N∩SH), have been studied. The unimolar and bimolar reactions of triisopropoxy
borane with dibasic tridentate ligands resulted in the formation of colored solids, which
have been characterized by elemental analysis, molecular weight determinations, and
conductance measurements. The UV, IR, and NMR (1H, 13C, and 11B) spectral studies
indicate a tetra-coordinated geometry for the resulting complexes. The ligands and their
complexes have been screened for their fungicidal and bactericidal activities, and the results
indicate that they exhibit significant antimicrobial properties.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Bactericidal activities; fungicidal activities; 2-hydroxy-N-phenyl benzamide
hydrazine carbodithioic acid; 2-hydroxy-N-phenyl benzamide hydrazine carbothioamide;
2-hydroxy-N-phenyl benzamide hydrazine carboxamide
INTRODUCTION
Interest in metal complexes of sulfur–nitrogen chelating agents, especially those
formed from thiosemicarbazide, 4N-substituted thiosemicarbazides,1–5 and S-alkyl esters
of dithiocarbazic acid,6–10 has been stimulated by their interesting physicochemical prop-
erties and potentially useful pharmacological properties.1,5,7,11 A variety of 5-nitrofuryl
semicarbazone derivatives have been developed for the therapy of Chagas disease.12 Some
derivatives of thiosemicarbazides are useful intermediates for drugs and agrochemicals.13
The coordinating properties of some semicarbazone metallic complexes have also been
studied.14 Semicarbazones and thiosemicarbazones present a wide range of bioactivities,
and their chemistry and pharmacological applications have been extensively investigated.
Thiosemicarbazide derivatives have antiviral and antitumor activities.15 The biological
Received 11 August 2008; accepted 13 January 2009.
Address correspondence to R. V. Singh, Department of Chemistry University of Rajasthan, Jaipur 302004,
India. E-mail: rvsjpr@hotmail.com
394

BIFUNCTIONAL TRIDENTATE SCHIFF BASES
395
Table I Analytical data and physical properties of the ligands and their organoboron (III) complexes
Analysis Found (Calcd.) (%)
Mol.
Compound
Color
Mp (◦C)
N
S
B
Wt Found/(Calcd.)
L1H2
Off white
Light pink
Gray
110–112 20.76 (20.84)
122–124 19.51 (19.57) 11.13 (11.20)
132–133 10.56 (10.68) 16.34 (16.30)
—
—
—
—
251.11(270.29)
267.46 (286.35)
407.70 (394.52)
353.30 (338.19)
562.41 (548.39)
338.13 (354.25)
564.27 (580.51)
474.55 (461.43)
808.11 (794.87)
L2H2
L3H2
(OPri)B(L1)
Light yellow 260–262 16.12 (16.57)
—
—
3.08 (3.20)
1.12 (1.97)
2.89 (3.05)
(L1 H)B(L1) Light yellow 280–281 20.23 (20.44)
(OPri)B(L2)
Cream
112–114 15.88 (15.82)
8.89 (9.05)
(L2 H)B(L2) Pink
134–136 19.01 (19.30) 10.81 (11.05) 1.51 (1.86)
104–106 8.91 (9.11) 13.51 (13.90) 2.04 (2.34)
120–122 10.15 (10.57) 16.01 (16.14) 1.12 (1.36)
(OPri)B(L3)
Light brown
(L3 H)B(L3) Brown
properties of semicarbazones and thiosemicarbazones are often related to metal ion co-
ordination. First, lipophilicity, which controls the rate of entry into the cell, is modified
by coordination.16 Also, the metal complexes can be more active than the free ligands,
and some side effects may decrease upon complexation. In addition, the complexes can
exhibit bioactivities that are not shown by the free ligands. The mechanism of action can
involve binding to a metal in vivo, or the metal complex may be a vehicle for activation
of the ligand as the cytotoxic agent. Moreover, coordination may lead to significant re-
duction of drug resistance.17 Boron is essential for healthy plants. The biochemical role
of boron is not fully understood even 60years after its recognition as an essential element,
although it is known to be involved in nucleic acid synthesis, possibly linked to adequate
provision of pyrimidine nucleotides. Boron also plays parts in carbohydrate metabolism,
hormone action, and membrane formation.18 Organoboron compounds are used as a source
of radicals.19 In view of these findings, we have synthesized and characterized some new
Schiff base complexes of boron with 2-hydroxy-N-phenyl benzamide hydrazine carboxam-
ide, 2-hydroxy-N-phenyl benzamide hydrazine carbothioamide, and 2-hydroxy-N-phenyl
benzamide hydrazine carbodithioic acid.
The physicochemical studies of these compounds suggest the tridentate nature of
the Schiff base ligands. Spectral analysis and molecular weight measurements have been
employed to throw light on the structure of these complexes (Tables I and II).
Table II IR spectral data (cm−1) of the ligands and their organoboron (III) complexes
Compound
ν( OH)
ν(C N)
ν( NH2)
ν(C O) ν(C S) ν(B N) ν(B O) ν(B S)
L1H2
3140–3256 1612
3150–3250 1620
3128–3245 1608
3478–3367
3480–3372
3470–3362
3478–3367
1685
—
—
1680
1683
—
—
—
—
—
—
—
—
1550
1548
1520
1514
1532
1530
—
—
—
1340
1334
1325
1321
1330
1328
—
—
—
860
854
830
824
840
832
L2H2
1030
1040
—
L3H2
(OPri)B(L1)
(L1 H)B(L1)
(OPri)B(L2)
(L2 H)B(L2)
(OPri)B(L3)
(L3 H)B(L3)
—
—
—
—
—
—
1608
1610–1625 3478–3367
1616 3480–3372
1612–1628 3480–3372
1606 3470–3362
1604–1616 3470–3362
—
1020
1025
1032
1036

396
S. YADAV ET AL.
RESULTS AND DISCUSSION
The reactions of triisopropoxy borane with dibasic tridentate 2-hydroxy-N-phenyl
benzamide hydrazine carboxamide, 2-hydroxy-N-phenyl benzamide hydrazine carboth-
ioamide, and 2-hydroxy-N-phenyl benzamide hydrazine carbodithioic acid in different
molar ratios yielded products according to the general Equations (1) and (2)
1:1
[B(OPri)3] + HO∩N∩XH → [(OPri)B(O∩N∩X)] + 2PriOH
(1)
(2)
1:2
[B(OPri)3] + 2HO∩N∩XH → [(O∩N∩XH)B(O∩N∩X)] + 3PriOH
where, HO∩N∩XH represents the donor set of the ligand molecules and X = O or S.
These reactions are quite facile and could be completed within 12–24 h of refluxing
in benzene. The resulting products are colored solids and insoluble in common organic sol-
vents but soluble in DMSO, THF, and DMF. The complexes are quite stable. The molecular
weight determinations indicate their monomeric nature. The low molar conductance values
(8–12 ꢀ−1 cm2 mol−1) of these derivatives in DMF at10−3 M concentrations show them to
be nonelectrolytes.
Electronic Spectra
The electronic spectra of the ligands L1H2, L2H2, and L3H2 exhibit three bands at
237, 272, and 332 nm. The bands in the regions 235 nm and 275 nm are assignable to
π–π∗ transitions of the azomethine group. The considerable hypsochromic shifting of the
third band in the spectra of boron complexes may be attributed to the coordination of the
azomethine nitrogen to the boron atom.
Infrared Spectra
The IR spectra of the free ligands and their complexes were scanned in the form of
KBr pellets. IR spectra of the free ligands show a medium intensity band at 3260–3128
cm−1 due to ν NH/ν OH vibrations, which is absent in the spectra of the complexes. The
bands due to ν (C O) and ν (C S) modes in the spectra of the ligands are observed at
1705 cm−1 and 1035 cm−1, respectively.20 In the ligand L3H2, a doublet at 2900 cm−1 and
2950 cm−1 is assigned to symmetric and asymmetric vibrations of S-CH2-C6H5 grouping
and is reduced to a weak doublet in the spectra of the complexes. These bands disappeared
in the spectra of the boron compounds, suggesting the enolization and thioenolization of
the ligands and their chelation through the amido oxygen and thiolic sulfur, respectively.
This fact is supported by the observation of the bands due to ν(C O) and ν (C S) modes
at lower frequencies in the spectra of the boron compounds. In the ligands L1H2, L2H2, and
L3H2, the most significant band in the region, 1620 cm−1 assignable to the ν(C N)21,22
group, shifts to the lower frequency in the complexes, suggesting the coordination23,24 of the
azomethine nitrogen to the boron atom. The absorption at ca. 1612 cm−1, characteristic of
the azomethine (>C N)25 group in the spectra of the ligands, gets split into two sharp bands
at ca 1612 cm−1 and 1625 cm−1 in 1:2 complexes. This splitting of the bands suggests that
the azomethine group is in different chemical environments. The shifting of the bands at ca.
1625cm−1 (higher wavenumber side) suggest the coordination of the azomethine nitrogen

BIFUNCTIONAL TRIDENTATE SCHIFF BASES
397
to the boron atom, whereas the band at ca. 1612 cm−1 is assigned to the uncoordinated
azomethine group. There are no changes in the ν sym and ν asym modes of the NH2 group26
appearing at ca 3360 cm−1 and 3480 cm−1, respectively, indicating the noninvolvement of
this amino group in chelation. The coordination through the azomethine nitrogen atom and
the enolic oxygen/thiolo sulfur is further substantiated by the appearance of new bands in
the regions 1320–1340 cm−1, 830–860 cm−1, and 1510–1550 cm−1 in the boron complexes
due to ν(B-O), ν(B-S),27 and ν(B← N)28 frequencies, respectively.
1H NMR Spectra
1
The H NMR spectra of the ligands and their complexes have been recorded in
DMSO–d6- using TMS as an internal standard. In the ligands, the signal in the region
δ 12.10–12.14 ppm, due to OH, disappears in the complexes, and this confirms the
deprotonation and complexation. The signal due to the –NH proton attached to the phenyl
ring remains unaltered in the complexes. The NH2 group gives singlet at δ 2.80–2.95 ppm
in the ligands (L1H2 and L2H2) and their complexes. This shows that the NH2 group is not
taking part in the complexation. The signal of the –NH proton in the ligands in the range δ
10.72–10.86 ppm that disappears29 in the spectra of the corresponding (1:1) complexes and
appears in 1:2 complexes is assigned to the uncoordinated –NH group. The free ligands
show multiplets in the region δ 6.67–8.36 ppm attributable to aromatic protons.30 The
resonance due to the SCH2 and aromatic protons in the complexes appears in almost the
same positions as in the respective free ligands. Chemical shift values of all the complexes
are listed in Table III.
13C NMR Spectra
The 13C NMR spectral data also support the authenticity of the proposed structures.
The considerable shifts in the positions of carbon atoms adjacent to the azomethine nitrogen
(δ 167.15–174.36 ppm) and thiolic sulfur/enolic oxygen (δ 176.24–184.20 ppm) support
the proposed coordination in the complexes. Thus the shifts in the position of carbon atoms
adjacent to the coordinating atoms clearly suggest the bonding of the azomethine nitrogen
and amido oxygen to the boron atom (Table IV).
Table III 1H NMR spectral data (δ, ppm) of the ligands and their organoboron (III) complexes
OH
(s)
NH
(bs)
NH2
(s)
S
CH2
(s)
ϕ
NH
(s)
Aromatic
protons (m)
Compound
L1H2
12.14
12.12
12.10
—
—
—
—
—
—
10.86
10.84
10.72
—
10.89
—
10.87
—
10.76
2.92
2.80
—
2.94
2.95
2.82
2.83
—
—
—
1.82
—
—
—
—
1.90
1.92
10.60
10.64
10.75
10.61
10.62
10.65
10.66
10.73
10.74
6.68–8.36
6.75–8.32
6.70–8.19
6.67–8.31
6.68–8.33
6.74–8.30
6.75–8.31
6.69–8.12
6.70–8.14
L2H2
L3H2
OPri)B(L1)
(L1 H)B(L1)
OPri)B(L2)
(L2 H)B(L2)
OPri)B(L3)
(L3 H)B(L3)
—

398
S. YADAV ET AL.
Table IV 13C NMR and 11B spectral data (δ, ppm) of the ligands and their organoboron (III) complexes
>C O/ >C N/
>C
Aromatic
carbons
11B chemical
shift
Compound
S
C N
L1H2
L2H2
L3H2
180.03 167.15 160.72, 138.92, 130.15, 129.83 129.88 125.42, 122.57,
120.51, 118.77, 119.79
179.52 168.01 160.86, 138.99, 130.18, 129.79, 129.95, 125.58, 122.64,
120.68, 118.94, 119.99
176.24 168.28 160.72, 138.84, 132.81, 129.84, 129.92, 125.46, 122.66,
120.72, 118.92, 118.98
—
—
—
(OPri)B((L1) 182.28 168.53 158.43, 137.56, 129.26, 129.31, 129.63, 125.37, 121.79,
120.19, 118.08, 118.27
3.98
4.84
3.54
4.42
4.25
4.29
(L1 H)B(L1) 184.20 169.98 159.32, 137.03, 130.25, 130.46, 129.62, 128.56, 121.31,
120.86, 118.83, 118.74
(OPri)B(L2) 181.42 170.28 158.01, 137.12, 129.46, 129.12, 129.11, 124.02, 121.01,
120.11, 117.91, 118.02
(L2 H)B(L2) 183.35 173.12 158.28, 137.67, 129.97, 129.86, 129.42, 125.32, 121.49,
120.22, 118.01, 118.22
(OPri)B(L3) 178.24 171.11 158.44, 137.33, 131.65, 128.99, 128.98, 125.36, 121.34,
120.43, 118.89, 118.93
(L3 H)B(L3) 179.35 174.36 159.33, 137.54, 130.23, 129.72, 128.96, 125.64, 121.52,
120.61, 118.93, 118.89
11B NMR Spectra
The 11B NMR spectra of the boron complexes have signals in DMSO-d6 at δ3.0–5.0
ppm, which unequivocally suggests a tetracoordinated environment around the boron atom
and the presence of a B←N coordinate bond.31,32
OPri
B
NH
O
H
R
N
C
X
C
C
N
C
N
X
O
N
R
NH
B
O
X
C
C
N
N
R
NH
1:1 Complex
Where X= O,S and R=NH2,S-CH2-C6H5
1:2 Complex
Where X= O,S and R=NH2,S-CH2-C6H5

BIFUNCTIONAL TRIDENTATE SCHIFF BASES
399
MICROBIAL ASSAY
Antifungal Screening
The complexes were screened against Alternaria alternata and Fusarium oxysporum
fungi. The antifungal activity of synthesized compounds was evaluated by the radial growth
method.33 (See the Supplemental Materials online, Tables 5S and 6S).
Antibacterial Screening
Various methods are available for the evaluation of the antibacterial activity of dif-
ferent types of compounds. In the present work, activities of synthesized compounds were
evaluated by the disc-diffusion method using inhibition zone technique.34 The complexes
were screened against Staphylococcus aureus and Xanthomonas compestris bacteria (see
the Supplemental Materials).
EXPERIMENTAL
The boron compound, boric acid, 2-hydroxy-N-phenylbenzamide, hydrazine hy-
drochloride, and hydrazinecarbothioamides were purchased from Sisco, Lancaster, and
Lobachemie and used as such. The triisopropoxy borane was prepared by the reaction of
boric acid with isopropanol in benzene medium.36 All the chemicals and solvents were
dried and purified by standard methods. The reactions were carried out under strictly
anhydrous conditions. Boron was estimated as boric acid in the presence of mannitol using
phenolphthalein as an indicator. Conductivity measurements were made with a Systronics
model 305 conductivity bridge in dry dimethylformamide. Molecular weights were deter-
mined by the Rast Camphor method. Nitrogen was estimated by the Kjeldahl’s method,
and sulfur was estimated by the Messenger’s method. The electronic spectra were recorded
on a Varian–Cary/2390 spectrophotometer at RSIC, I.I.T., Chennai. Infrared spectra of the
ligands and their complexes were recorded on a Nicolet Megna FTIR-550 spectrophotome-
ter using KBr pellets. 1H, 13C, and 11B NMR spectra were recorded on a JEOL-AL-300 FT
NMR spectrometer in DMSO-d6.
Preparation of the Ligands
The ligands (L1H2) and (L2H2) were prepared as reported.37 The ligand (L3H2) was
prepared by the reaction of 2-hydroxy-N-phenylbenzamide with S-benzyldithiocarbazate
in a 1:1 molar ratio, in absolute ethanol in a unimolar ratio. This reaction mixture was then
refluxed over a water bath for 3–4 h and allowed to stand overnight. The ligands (L1H2,
L2H2, and L3H2) that separated out were purified by recrystallization from the same solvent
and analyzed before use. The parent ligands exist in the tautomeric forms (Figure 1).
Preparation of the Complexes
The triisopropoxy borane was dissolved in dry benzene in a 100-mL RB flask, and
to this the requisite amounts (1:1 and 1:2 molar ratios) of the ligands were added. The
resulting mixture was refluxed for 12–24 h. The progress of the reaction was monitored
by the liberation of isopropanol azeotropically. The solid product was dried in vacuo.
The physical properties and analytical data of these complexes are listed in Table I. The

400
S. YADAV ET AL.
OH
OH
XH
C
X
C
C
N
N
NH2
C
N
NH
NH
NH2
NH
L1H2 and L2H2 (HO∩N∩XH) X= O, S
OH
OH
SH
S
C
N
C
C
N
C
N
SCH2C6H5
NH
SCH2C6H5
N
NH
H
L3H2 (HO∩N∩SH)
Figure 1 Schiff base ligands.
purity of the compounds was checked by TLC on silica gel-G using anhydrous methanol
and tetrahydrofuran (1:1) as a solvent. Each of the compounds moves as a single spot,
indicating the presence of only one component, hence validating their purity.
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