Synthesis, spectroscopic characterization, and in vitro antimicrobial potency of sulfur-bonded complexes of boron(III)

Article abstract of DOI:10.1080/10426500802445324

The present article describes the synthesis and characterization of tetracoordinated boron (III) complexes with monobasic bidentate ligands (L ¹H, L²H, L³H, L⁴H, L⁵H, and L⁶H) having the ge

Full text of DOI:10.1080/10426500802445324

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Synthesis, Spectroscopic
Characterization, and In Vitro
Antimicrobial Potency of
Sulfur-Bonded Complexes of
Boron(III)
Monika Swami a , Karuna Mahajan a , Neeti Gupta a
R. V. Singh a , Sunita Arya b & Sonalika Kushwah b
,
a Department of Chemistry , University of
Rajasthan , Jaipur, India
b Department of Zoology and Microbiology ,
University of Rajasthan , Jaipur, India
Published online: 22 Jul 2009.
To cite this article: Monika Swami , Karuna Mahajan , Neeti Gupta , R. V. Singh ,
Sunita Arya & Sonalika Kushwah (2009) Synthesis, Spectroscopic Characterization,
and In Vitro Antimicrobial Potency of Sulfur-Bonded Complexes of Boron(III),
Phosphorus, Sulfur, and Silicon and the Related Elements, 184:8, 2125-2139, DOI:
10.1080/10426500802445324
To link to this article: http://dx.doi.org/10.1080/10426500802445324
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Phosphorus, Sulfur, and Silicon, 184:2125–2139, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802445324
Synthesis, Spectroscopic Characterization, and In Vitro
Antimicrobial Potency of Sulfur-Bonded Complexes of
Boron(III)
Monika Swami,1 Karuna Mahajan,1 Neeti Gupta,1
R. V. Singh,1 Sunita Arya,2 and Sonalika Kushwah2
1Department of Chemistry, University of Rajasthan, Jaipur, India
2Department of Zoology and Microbiology, University of Rajasthan,
Jaipur, India
The present article describes the synthesis and characterization of tetracoordinated
1
2
3
4
boron (III) complexes with monobasic bidentate ligands (L H, L H, L H, L H,
5
6
L H, and L H) having the general formulae PhB(L)(OH) and PhB(L) . The 1:1 and
2
1:2 reactions of phenyl boronic acid with monobasic bidentate ligands resulted in
the formation of colored solids. The complexes have been characterized by elemental
1
13
11
analysis, molecular weight determinations, and IR and NMR ( H, C and B)
spectroscopy, as well as UV-vis spectral studies. Based on these studies, a tetrahedral
geometry has been proposed for the resulting complexes. The ligands, along with
their complexes, have been screened in vitro against a number of pathogenic fungal
and bacterial strains. The studies indicate that the boron chelates are more potent
than the parent ligands.
Keywords Antimicrobial potency; biological aspects; hydrazinecarbodithioic acid
phenyl methyl esters; phenylborane complexes; thiosemicarbazone
INTRODUCTION
Thiosemicarbazones and S-benzyldithiocarbazates play an important
role in inorganic chemistry, as they easily form stable complexes with
metal ions. The development in the field of bioinorganic chemistry has
increased the interest in these complexes, since it has been recognized
that many of these complexes may serve as models for biologically
important species.1−3 There is currently a resurgence of interest in
Received 13 April 2008; accepted 2 September 2008.
Address correspondence to R. V. Singh, Department of Chemistry, University of
Rajasthan, Jaipur-302 004, India. E-mail: rvsjpr@hotmail.com
2125

2126
M. Swami et al.
the coordination chemistry of boron, mainly due to the involvement
of the element in a number of biological systems4 that have created
and necessarily maintain our environment. An understanding of it
represents one of the greatest challenges to bio-inorganic chemists.
The element boron is a micronutrient for plants, and traces of it have
also been reported in some bacterial cells.5 Boron may play an ac-
tive role in human brain function and cognitive performance, and
there may be additional evidence that boron is an essential nutri-
ent for humans.6 Considerable interest in the studies of compounds
containing intramolecular B-N coordination7 is due to the remark-
able degree of hydrolytic and oxidative stability. The synthetic flex-
ible characteristic of boron, which has a wide range of applications
in various disciplines, has attracted a number of investigators in the
field.8 Several organoboranes find promising applications in the syn-
thesis of insect pheromones.9 Organoboron compounds are attracting
attention because of their importance as synthetic10,11 intermediates,
as well as a source of radicals.12 The mechanism of action for these
compounds is believed to arise from the ability of the boron atom to co-
ordinate through its empty p-orbitals to the active hydroxyl groups of
the enzyme.
Interest in metal complexes of sulfur–nitrogen chelating agents, es-
pecially those formed from thiosemicarbazide13−17 and S-alkyl/benzyl
esters of dithiocarbazic acid,18−22 has been stimulated by their interest-
ing physicochemical properties and potentially useful pharmacological
properties.13,17,19,23
Boron complexes of dihiocarbazates have aroused considerable in-
terest in view of their industrial, biological,24 and pharmacodynamic
importance.25 The applications of boron compounds in cancer ther-
apy have invoked considerable interest due to the unique nuclear
property.26,27
Boron complexes of thiosemicarbazones with N∩S donor system are
gaining enormous importance on account of their inherent biologi-
cal potential.28 Boron complexes of such ligands are known to func-
tion as antimicrobial and antifertility agents.29−31 The focus of our
present communication is on the exploration of the studies on the syn-
thetic, structural, and biological aspects of boron complexes of some
stereochemical as well as biological interest with monobasic bidentate
thiosemicarbazone and hydrazinecarbodithioic acid phenyl methyl es-
ter ligands. Antifungal and antibacterial activities of these boron com-
plexes have also been carried out to study the role of the coordinated
boron atom.

Sulfur-Bonded Complexes of Boron(III)
2127
EXPERIMENTAL
All the chemicals were dried and purified before use, and the purity
was checked by thin layer chromatography (TLC).
Preparation of Thiosemicarbazones(L1H, L2H, and L3H)
The reaction of an EtOH solution of 5-nitro, 6-nitro, and 7-nitro isatin
(synthesized by the Sandmeyer isonitrosoacetanilide method32) and
PhCOMe was carried out in an equimolar ratio. The reaction mixture
was refluxed for 2–3 h at 60◦C. The resulting substituted product was
dried and recrystallized from EtOH. This substituted product was then
condensed with thiosemicarbazide in EtOH. This mixture was then
refluxed on a water bath for 3–4 h and allowed to stand overnight.
Upon cooling, the ligands were separated out, then collected, dried,
and recrystallized in ethanol (Scheme 1).
C6H5
C6H5
C
N
S
O
C
N
SH
Z
O
N
H
CH
N
HN
CH
Z
HN
Y
Y
Where, Z= -NH2 / -SCH2C6H5,
Y= -NO2 / -CH3 / -Cl / 2, 4-CH3
SCHEME 1
Preparation of Hydrazinecarbodithioic Acid Phenyl Methyl
Esters (L4H, L5H, and L6H)
The reactions of an EtOH solution of 5-methyl, 5-chloro, and 5,7-
dimethyl isatin and PhCOMe were carried out in an equimolar ratio.
The reaction mixture was refluxed for 2–3 h at 60◦C. The resulting
substituted product was dried and recrystallized from EtOH. This sub-
stituted product was then condensed with S-benzyldithiocarbazates in
EtOH. These mixtures were then refluxed on a water bath for 3–4 h

2128
M. Swami et al.
TABLE I Analytical Data and Physical Properties of
Hydrazinecarbothioamides and Hydrazinecarbodithioic Acid Phenyl
Methyl Ester
Analyses (%) Found/(Calcd.) Mol. Wt.
S.
Empirical
Color and Mp
State
(◦C)
Found
(Calcd.)
No. Ligand Formula
C
H
N
S
1.
L1H C17H13N5O3S
L2H C17H13N5O3S
Gray, Solid 255 55.72 3.63 18.98 8.79
380.92
(55.57) (3.56) (19.06) (8.72) (367.37)
236 55.84 3.62 19.92 13.14 381.72
(55.57) (3.56) (19.00) (13.06) (367.37)
2.
Dark
brown,
Solid
3.
4.
L3H C17H13N5O3S
L4H C25H21N3O3S
Gray, Solid 244 55.62 3.73 19.14 13.27 352.86
(55.57) (3.56) (19.06) (13.06) (367.37)
Light
brown,
Solid
162 67.60 4.82 9.36 14.39 430.73
(67.65) (4.77) (9.47) (14.45) (443.57)
5.
7.
L5H C24H18N9O2OCl Gray, Solid 165 62.31 3.84 9.24 13.75 478.55
(62.12) (3.91) (9.05) (13.82) (463.99)
L6H C26H23N3O2O
Brown,
Solid
171 68.62 5.19 9.04 14.32 441.76
(68.24) (5.06) (9.18) (14.02) (457.60)
and allowed to stand overnight. Upon cooling, the ligands were sepa-
rated out (Table I), then collected, dried, and recrystallized in ethanol
(Scheme 1).
The resulting ligands are herein described:
L1H: 5-Nitro-1,3-dihydro-3-[2-(phenyl)-ethylidene]-2H-indol-2one-
hydrazinecarbothioamide.
L2H: 6-Nitro-1,3-dihydro-3-[2-(phenyl)-ethylidene]-2H-indol-2one-
hydrazinecarbothioamide.
L3H: 7-Nitro-1,3-dihydro-3-[2-(phenyl)-ethylidene]-2H-indol-2one-
hydrazinecarbothioamide.
L4H: 5-Methyl-1,3-dihydro-3-[2-(phenyl)-ethylidene]-2H-indol-2one-
hydrazinecarbodithioic acid phenyl methyl ester.
L5H: 5-Chloro-1,3-dihydro-3-[2-(phenyl)-ethylidene]-2H-indol-2one-
hydrazinecarbodithioic acid phenyl methyl ester.
L6H: 5,7-Dimethyl-1,3-dihydro-3-[2-(phenyl)-ethylidene]-2H-indol-
2one-hydrazinecarbodithioic acid phenyl methyl ester.
Preparation of Boron(III) Complexes
To a calculated amount of the ligands dissolved in dry benzene, the
dihydroxyphenylborane in unimolar and bimolar ratios was added. The

Sulfur-Bonded Complexes of Boron(III)
2129
reaction mixture was refluxed for 10–12 h on a fractionating column,
and the progress of the reaction was monitored by the liberation of the
azeotrope of water and benzene. After the completion of the reaction,
excess of the solvent was distilled off and the products were dried. The
resulting products were washed with dry cyclohexane and then finally
dried in vacuo for 3–4 h. The physical properties and analytical data of
these derivatives are recorded in Tables II and III.
Analytical Methods and Physical Measurements
Nitrogen and sulfur were estimated by the Kjeldahl’s and Messen-
ger’s methods,33 respectively. Boron was estimated volumetrically as
boric acid. The UV spectra were recorded on a Hitachi-U-2000 spec-
trophotometer. The IR spectra with KBr optics were obtained using
the Perkin–Elmer 577 grating spectrophotometer. The 1H (89.55 MHz)
and 13C NMR spectra (at 22.49 MHz) were recorded in DMSO-d6 using
TMS as the standard on a JEOL AL 300 FT NMR. 11B NMR spectra
(at 28.69 MHz) were recorded using BF3.Et2O as an external standard.
The molecular weights of the compounds were determined by the Rast
Camphor34 method.
MICROBIAL ASSAY
Fungicidal and bactericidal activities of the ligands and their corre-
sponding boron complexes against different fungi and bacteria have
been carried out by the methods reported earlier.35 On the basis of
these studies, it may be concluded that fungitoxicity and bacteriostatic
properties of a compound may be slightly enhanced upon chelation
with the boron atom. The antifungal activity was tested against Fusar-
ium oxysporum and Macrophomina phaseolina and bacterial activity
against Klebsilla aeurogenous, and Pseudomonas cepacicola (-). Proper
temperature (25–30◦C), necessary nutrients, and growth media free
from other microorganisms were employed for the preparation of cul-
ture media of fungi and bacteria using aseptic techniques.
In Vitro Study
Bactericidal Screening (Inhibition Zone Technique)36
For the evaluation of degree of inhibitory effects on the growth of
a wide spectrum of microorganisms, antibacterial activity was per-
formed, and the results are summarized in Table IV. The compounds
were dissolved in methanol at 500 and 1000 ppm concentrations.

2130

2131

2132
M. Swami et al.
TABLE IV Antibacterial Screening Data of the Ligands and Their
Boron(III) Complexes
% Inhibition after 1 day 25 2◦C
Klebsilla aeurogenous
Pseudomonas cepaciola
(Conc. in ppm)
(−) (Conc. in ppm)
S. No.
Complex
500
1000
500
1000
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
L1H
7
10
12
7
9
11
8
10
11
9
11
14
8
11
14
10
12
16
9
14
17
8
11
14
10
13
15
10
13
15
9
7
9
11
8
9
13
7
8
12
7
10
14
8
10
14
9
10
14
19
9
11
16
10
13
15
8
12
16
10
13
17
11
14
17
[PhB(OH)(L1)]
[PhB(L1)2]
L2H
[PhB(OH)(L2)]
[PhB(L2)2]
L3H
[PhB(OH)(L3)]
[PhB(L3)2]
L4H
[PhB(OH)(L4)]
[PhB(L4)2]
L5H
[PhB(OH)(L5)]
[PhB(L5)2]
L6H
13
16
12
16
20
[PhB(OH)(L6)]
[PhB(L6)2]
10
15
Whatman No. 1 paper discs with a diameter 5 mm were soaked in
these solutions. These discs were placed on the appropriate nutrient
medium (0.5% peptone, 0.15% yeast, 0.15% beef extract, 0.35% sodium
chloride, and 0.13% KH2PO4 in 1000 cm3 distilled water), autoclaved
for 20 min at 15 psi before inoculation with previously seeded organ-
isms in Petri dishes and stored in an incubator at 25 2◦C. The inhi-
bition zone thus formed around each disc was measured (in mm) after
24 h.
Fungicidal Screening (Poisoned Food Technique)36
Potato dextrose agar (PDA) medium was prepared in a flask and
autoclaved for 20 min at 15 psi before inoculation. The compounds were
directly mixed with the medium in 50, 100, and 200 ppm (in methanol)
concentrations. Aliquots of 15 mL medium were poured in sterilized
Petri plates. A culture of test fungus was grown on PDA in 24 h at the
25 2◦C temperature for growth. A small disc of the fungus culture was
cut with a sterile cork borer and transferred aseptically to the center

Sulfur-Bonded Complexes of Boron(III)
2133
TABLE V Antifungal Screening Data of The Ligands and Their
Boron(III) Complexes
% Inhibition after 4 days at 25 2◦C
Fusarium oxysporum
Macrophomina phaseolina
(Conc. in ppm)
(Conc. in ppm)
S. No.
Complex
50
100
200
50
100
200
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
L1H
28
35
36
25
36
39
24
35
38
46
57
58
42
53
55
48
59
61
39
43
43
35
47
50
36
42
46
59
61
63
56
61
64
60
70
72
48
58
56
49
61
65
45
58
60
68
79
81
65
71
74
79
81
83
27
36
34
23
35
37
23
32
37
45
55
57
39
48
50
46
57
59
38
45
44
31
42
47
32
43
47
62
59
61
54
61
36
64
74
76
49
59
57
43
54
62
43
56
59
75
78
79
62
64
69
79
83
84
[PhB(OH)(L1)]
[PhB(L1)2]
L2H
[PhB(OH)(L2)]
[PhB(L2)2]
L3H
[PhB(OH)(L3)
[PhB(L3)2]
L4H
[PhB(OH)(L4)]
[PhB(L4)2]
L5H
[PhB(OH)L5)]
[:PhB(L5)2
L6H
[PhB(OH)(L6)]
[PhB(L6)2
of a Petri disc containing the medium and incubated for 4 days at 25
2◦C. The colony diameter was measured after the incubation period
of growth. The results are summarized in Table V. The percentage
inhibition of growth was calculated by,
(C − T) C−1 × 100
Where, C = growth in control, T = growth in treatment.
RESULTS AND DISUSSION
Reactions of phenylboronic acid with monobasic bidentate ligands have
been carried out in refluxing benzene. These reactions may be repre-
sented as follows:
PhB(OH)2 + N∩SH → PhB(OH)(N∩S) + H2O
PhB(OH)2 + 2N∩SH → PhB(N∩S)2 + 2 H2O
N∩S is the donor system of the reacting ligand moiety.

2134
M. Swami et al.
The resulting colored solids are soluble in DMF and DMSO. The
UV, IR, and NMR spectra support the proposed structures. Their low
molar conductance values (10–15 ohm−1 cm2 mol−1) show that they are
nonelectrolytes in nature.
SPECTROSCOPIC STUDIES
UV Spectra
The UV spectra of the ligands (L1H, L2H, L3H) and (L4H, L5H, L6H)
show two maxima at ca. 274, 316 nm and 264, 328 nm, respectively,
assignable to π–π* transitions. These remain almost unchanged in
the complexes.37 Another band due to >C N is observed at 336 and
344–360 nm in the spectra of the ligands (L1H, L2H, L3H) and (L4H,
L5H, L6H), respectively. This is due to n–π* transitions and shows
bathochromic shifts of 20–30 nm in the complexes, due to donation of a
lone pair of electrons by the nitrogen of the ligands to the central boron
atom, indicating the delocalization of the electronic charge within the
chelate ring, thus stabilizing the resulting complexes.
IR Spectra
The IR spectra of the ligands (L1H, L2H, L3H) display two sharp bands
around 3360 cm−1 and 3500 cm−1, assignable to νsym and νasymNH2
vibrations, respectively. The spectra of the ligands (L1H, L2H, L3H)
and (L4H, L5H, L6H) show medium intensity bands at 3280 and 3395–
3100 cm−1 due to ν NH vibrations, which disappear in the spectra of
the complexes. The absorption at ca. 1615 cm−1, characterstics of the
azomethine (>C N)38 group in the spectra of the ligands, get split into
two sharp bands at ca. 1595 cm−1 and 1625 cm−1 in 1:2 complexes.
This splitting of the bands suggests that azomethine group is in differ-
ent chemical environments. The splitting of the bands at ca. 1625 cm−1
(higher wave number side) suggests the coordination of the azomethine
nitrogen to the boron atom, whereas the band at ca. 1595 cm−1 is as-
signed to the uncoordinated azomethine group. The νOH band in case
of 1:1 boron complexes appears at ca. 3450 cm−1. Another ν(NH) band,
which exists in the ring, appears at 3250 cm−1 in the free ligands as
well as in their complexes. It indicates noninvolvement of this group in
complexation. New bands in the complexes, which appeared in the re-
gions, 835–840 cm−1, 1525–1545 cm−1, and 1235–1250 cm−1, are due to
ν(B—S),39ν(B←N),40 and ν(Ph—B) frequencies, respectively, and indi-
cate that the azomethine nitrogen and thiolo sulfur are in coordinative
interaction at the boron center. The free ligands displayed bands at

Sulfur-Bonded Complexes of Boron(III)
2135
2900 and 2960 cm−1 are attributed to symmetric and asymmetric vi-
bration of –CH2 of SCH2 C6H5 grouping and are reduced to a weak
doublet in the spectra of the complexes.41
1H NMR Spectra
The 1H NMR spectra of the free ligands and the complexes were
recorded in DMSO-d6. The spectra of the ligands exhibits signals due
to the –NH of the isatin ring and the –NH of the thiosemicarbazone
(L1H) and hydrazinecarbodithioic acid phenyl methyl ester (L4H and
L5H). The disappearance of the –NH signal of the thiosemicarbazones
and hydrazinecarbodithioic acid phenyl methyl esters in the complexes
indicates coordination of the azomethine nitrogen as well as covalent
bond formation between boron and sulfur atom. Further the spectra of
the free ligands and their boron complexes show signals due to –NH of
the indol ring at δ10.23–11.96 ppm. It shows the noninvolvement of this
group in the complexation. The resonance due to the –SCH2 and aro-
matic protons in the complexes appears in almost the same positions
as in the respective free ligands (L4H and L5H). The aromatic protons
are observed in the range δ6.70–8.28 ppm in the boron complexes as
well as in the spectra of the ligands. The –OH proton signal in 1:1 com-
plexes is observed at δ4.22–4.77 ppm. The chemical shift values of all
the complexes/ligands are listed in Table VI.
TABLE VI 1H NMR Spectral Data (δ, ppm) of the Ligands L1H and
L5H and Their Boron(III) Complexes
NH2
(bs)
NH(1)
(bs)
NH(2)
(s)
Aromatic
OH (s) protons (m)
Compound
CH3
SCH2
L1H
3.46
3.53
3.43
—
—
—
—
—
—
11.53
—
—
12.56
—
—
11.26
—
—
11.82
11.82
11.92
10.26
10.23
10.24
11.92
11.96
11.94
—
—
—
2.68
2.69
2.66
—
—
4.77
—
—
4.45
—
—
4.22
—
6.78–8.23
6.82–8.25
6.80–8.28
8.09–7.74
8.42–7.72
8.26–7.77
6.78–8.28
6.70–8.18
6.76–8.22
—
—
—
4.85
4.81
4.87
4.60
4.66
4.67
(Ph)B(OH)(L1)
(Ph)B(L1)2
L4H
(Ph)B(OH)(L4)
(Ph)B(L4)2
L5H
(Ph)B(OH)(L5)
(Ph)B(L5)2
—
—
bs = broad singlet and m = complex pattern.

2136
M. Swami et al.
13C NMR Spectra
The chemical shift values of the carbon atoms attached to the azome-
thine nitrogen and thiolic sulfur further support the proposed coor-
dination in these complexes. The considerable shifts in the positions
of carbon atoms attached to the azomethine nitrogen (L1H, δ 154.32
and L5H, δ 154.13 ppm) and thiolic carbon (L1H, δ 163.83 and L5H, δ
161.12 ppm), respectively, for boron complexes of thiosemicarbazones
and hydrazinecarbodithioic acid phenyl methyl esters complexes were
also observed. The heterocyclic moiety carbon signals, especially those
of the carbon atoms directly bonded to the heteroatom, undergo slight
upfieldshifts relative to the other carbon atoms, which remain almost
unchanged. The upfield shift of the thiolo carbon and azomethine car-
bon in the complexes indicates participation of these groups in coordi-
nation to the boron atom (Table VII).
11B NMR Spectra
The signals in the 11B NMR spectra of the complexes were observed
in the range of δ 3.64–4.42 ppm, which suggest a tetracoordinated42−44
environment around the boron atom and formation of a coordinate
bond.
On the basis of the results discussed so far, including analytical and
spectroscopic data, a tetracoordinated geometry is suggested for the 1:1
and 1:2 complexes (Scheme 2).
Antimicrobial Studies
Fungicidal and bactericidal screening data show that under iden-
tical experimental conditions the compounds possess antimicrobial
TABLE VII 13C NMR Spectral Data (δ, ppm) of Ligands L1H and L5H
and Their Boron(III) Complexes
Thiolic Azomethine
11B Chemical
shift
Compound
L1H
carbon
carbon
Aromatic carbons carbons
163.83
154.32
158.41
157.74
154.13
155.36
158.33
139.64, 138.38, 138.43, 138.59
138.35, 137.63, 138.56, 138.72
138.15, 137.54, 137.47, 137.54
140.62, 138.65, 137.52, 138.31
137.32, 136.51, 136.43, 136.92
137.13, 137.54, 136.45, 137.59
—
(Ph)B(OH)(L1) 171.74
3.64
4.42
—
4.37
4.36
(Ph)B(L1)2
L5H
176.36
161.12
(Ph)B(OH)(L5) 161.17
(Ph)B(L5)2
164.54

Sulfur-Bonded Complexes of Boron(III)
2137
SCHEME 2
properties. However, a few compounds also possess good activity
against microorganisms. It is also noteworthy that the complexes are
more active than their parent ligands against the same microorgan-
isms. Giving a closer look at these results reveals a common feature,
which is that the bioactivity enhances due to the following points:
1. The chelation reduces the polarity and increase the lipophilic nature
of the central boron atom, which subsequently favors its permeation
through the lipid layer of the cell membrane. This can be well as-
cribed to Tweedy’s chelation theory.45
2. It is also noteworthy that concentration plays an important role in
inhibiting the growth of microorganisms. At lower concentration,
inhibition is less severe. Due to this fact the activities of the or-
ganisms will be slowed down, while at higher concentration, more
enzymes will become inhibited leading to a quicker death of the
organisms. Lower concentration of compounds can check the sporu-
lation in fungi, and a higher concentration inhibits the growth of
organisms almost completely.
3. The toxicity of antibacterial compounds against different species
of bacteria depends either on the difference in ribosomes or the
impermeability of the cell to the antimicrobial agent.46

2138
M. Swami et al.
4. The addition of the boron element to the ligands increases the an-
timicrobial activity of the complexes.29
CONCLUSIONS
1. Thiosemicarbazone and hydrazinecarbodithioic acid phenyl methyl
ester ligands behave as monofunctional bidentate with boron atom.
2. Boron complexes obtained by 1:1 and 1:2 molar reactions with dif-
ferent ligands were found to be tetracoordinated.
3. Antimicrobial activity of the complexes and the ligands showed that
the former are more active than the parent ligands.
4. The data given in Tables IV and V reveal that [PhB(L6)2] and
[PhB(L1)2] complexes are more toxic than the other complexes.
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