Spectral and Antimicrobial Studies of Organosilicon(IV) Complexes of a Bidentate Schiff Base Having Nitrogen-

Nitrogen Donor System

M u k t a Ja in and R . V . S i n g h *

Department of Chemistry, University of Rajasthan, Jaipur-302004, India E-mail: kudiwal@datainfosys.net; Fax : 91-141-2708621

A B S T R A C T

The complexes of composition R2SiCl(SB) and R2Si(SB)2 (R=CH 3 and C 6H 5 and SB = anion of the Schiff

base of sulphonamide and Ph3Si(SB) have been prepared by the reactions of Schiff base SBH with metal

chlorides. The newly synthesized complexes have been characterized by elemental analysis, conductance

measurements and molecular weight determinations. The mode of bonding and geometry of the complexes

have been suggested on the basis of IR, UV and multinuclear 'H, l 3C and 29Si N M R spectral studies. Schiff

base and its silicon complexes have also been screened for their antibacterial activities, antifungal activities

and nematicidal activities. The pathogenicity and virulence of certain microbial infections associated with

ions of complexes have been found to be potent and broad-spectrum antibiotics. These results made it

desirable to delineate a comparison between ligand and its silicon complexes.

I N T R O D U C T I O N

Organosil icon(IV) derivatives are known to be biologically active /1-4/ and exhibit interesting structural

features /5-9/. Among these derivatives the triorganosilicon(IV) compounds with monofunctional bidentate

ligands are of special interest, as in these derivatives silicon may be tetra- /5,6,9/ or penta- /1,5,8/

coordinated. The choice of the coordination number depends on the mono- or bidentate behaviour of ligands.

The condensation products of sulpha drugs with aldehydes and ketones are biologically active and have

good complexing ability too /10,11/. Sulpha drugs when administered in the form of metal complexes show

increased biological activity /12-14/. Silicon is one element which possesses properties of both a metal and a

nonmetal. This leads to a versatility in its chemical behaviour, so that silicon spreads itself throughout ionic,

covalent, organometallic and colloidal chemistry and its derivatives find applications in such diverse fields as

polymer chemistry, textile and paper industry, space exploration and even cosmetics.

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Vol. 26, No. 4. 2003 Spectral and Antimicrobial Studies of Organosilicon(lV)Complexes of a Bidentate Schiff Base Having

Sulpha drugs are a group of compounds used for eliminating a wide range of infections in human and

other animal systems. The present paper deals with the striking structural features, synthesis and appreciable

biological applications of the complexes of an important sulpha drug Schiff base.

EXPERIMENTAL

All the glass apparatus used during the experimental work was fitted with quick fit interchangeable

standard ground joints. The glassware was first cleaned with chromic acid and water and then rinsed with

acetone. These were then dried in an electric oven at 120°-125°C for few hours. The reactions were carried

out under anhydrous conditions. During the course of the reactions, guard tubes packed with fused calcium

chloride were used to protect the contents from moisture and melting points were determined in sealed

capillary tubes.

Synthesis of the Ligand (Fig.l)

To obtain the ligand 2-acetylnaphthalene sulphaguanidine, 2-acetyl-naphthalene was mixed with

sulphaguanidine in 1:1 molar ratio and retluxed on a water bath for five-six hours. Alcohol was used as the

solvent. On cooling overnight in a refrigerator, crystals separated out which were further purified by washing

with ethanol and finally recrystallized with acetone. The analyses and physical properties of the ligand are

given in Table I.

Synthesis of Organo Silicon(IV) Complexes

The unimolar and bimolar complexes were prepared by the reactions of triphenylchlorosilane,

diphenyldichlorosilane, and dimethyldichlorosilane with the sodium salt of 2-acetylnaphthalene

sulphaguanidine in dry methanol. The reaction mixture was refluxed for about 14-16 hours on a rotating

head, during which the white precipitate of sodium chloride separated out. The contents were cooled and the

precipitate of sodium chloride so formed was removed by filtration. Coloured solids were obtained on

removal of the excess of the solvent and drying under reduced pressure for 3-4 hours. These were purified by

repeated washing with a (1:1) mixture of dry methanol and cyclohexane, and their purity was checked by

thin-layer chromatography (TLC) on silica gel.. The physical characteristics and analytical properties of the

resulting isolated powdered solids are listed in Table I. The UV spectra of the silicon complexes were

recorded in DMSO solution at room temperature.

238

Mukla Jain and R. V. Singh Main Group Metal Chemistry

R 2 SiCl j + S B H > R 2 SiCl(SB)+ NaCl

R,SiCl 2 + 2 S B H Μ / ° " > R2Si(SB)2 + 2NaCl

Ph,SiCI + S B H M°°H > P h 3 S I ( S B ) + N a C l

SBH = 2-acetylnaplithalene sulphaguanidine

Conductivity measurements were made with a Systronic model 305 conductivity bridge in dry

dimethylformamide. Molecular weights were determined by the Rast camphor method. 1R spectra of the solid

samples were recorded as KBr discs on a Nicolet Magna FT-1R 550 spectrophotometer. The 'H N M R spectra

were recorded on a JEOL FX-90Q Spectrometer in DMSO-d 6 , using T M S as the internal standard. Nitrogen,

chlorine and sulphur were estimated by Kjeldahl 's , Volhard 's and Messenger ' s methods, respectively.

Silicon was estimated as silicon oxide gravimetrically.

Table I

Characteristic Properties of the Ligand and its Silicon Complexes.

Complex with Colour MP. Yield Elemental Analysis (%)

empirical fbnnula CO (%) Si Ν S C Η CI Mol. Wt

F a n d Found Found Found Found Found Found

(Glied) (Calcd.) (Calcd.) (Calcd.) (Calcd.) (Calcd.) (Calcd.)

SBH White 140- 78 - 15.19 8.67 62.02 4.86 - 346

C19H I8N4S02 142 (1529 (8.75) (6228) (4.95) (366.39)

Me2SiCl(SB) Brown 170- 75 6.08 12.09 6.88 54.75 4.95 7.45 430

C2lHz!N4S02CISi 172 (6.11) (1220) (6.98) (54.95) (5.05) (7.72) (458.99)

Me2Si(SB)2 Brownish 189- 79 329 14.12 8.05 60.65 5.02 - 762

Q o f W A S i yellow 191 (3.55) (1420) (8.12) (60.89) (5.11) (788.92)

Ph2SiCI(SB) Brown 88-90 71 4.65 9.49 529 63.71 4.49 5.85 555

CuFbNtSQCISi (4.81) (9.60) (5.49) (63.85) (4.66) (6.07) ' (583.13)

Ph2Si(SB)2 Pitch 203- 72 2.92 12.18 6.98 65.58 4.68 885

C50H44N8S2O4Si 205 (3.07) (1227) (7.02) (65.77) (4.85) (913.06)

Ph3Si(SB) 1 £111011 85-87 76 4.16 8.87 5.07 71.02 5.05 - 590

C37H12N4S02Si yellow (4.49) (8.96) (5.13) (71.12) (5.16) (624.78)

RESULTS A N D DISCUSSION

The resulting complexes are coloured solids. These are slightly soluble in methanol and benzene but

freely soluble in DMF, D M S O and THF. The complexes have sharp melting points. The metal derivatives are

stable at room temperature and are hygroscopic. Conductance values 11-27 ohm"' cm2 ιηοΓ' in anhydrous

DMF at 10"'Μ concentration show them to be non-electrolytes. The physical properties and analytical data

of the compounds are reported in Table I.

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Vol. 26, No. 4, 2003 Spectral and Antimicrobial Studies of Organosilicon(IV)Complexes of α Bidentale Schiff Base Having

U.V. Spectra

The UV-VIS absorption spectral data of the ligand and its silicon complexes are listed in Tab le II. In the

ultra violet spectra of the sulphonamide imine, a band due to >C=N chromophere is observed at 365 nm,

which shifts to a higher wave number or lower wave length region. The above η-π* band shift ing is probably

due to the donation of the lone pair of electrons by the nitrogen of the ligand to the central metal atom. The

ligand shows bands attributed to π -π* transitions at ~ 270 and ~ 292 nm. K-band of benzene ring is observed

with red shift and B-band of >C=N group is observed with hypsochromic shift. In this K-band shift ing can be

attributed to the over lapping of the silicon d orbital with the ρ orbital of the nitrogen atom, which causes an

increase in conjugat ion in the sulphonamide imine and thus increases the wave length and lowers the π-π*

energy.

Table II

Ultra Violet Visible Spectral Data of the Ligand and its Silicon Complexes

Group SBH Me 2 SiCl (SB) Me 2 Si(SB) 2 Ph2SiCI(SB) Ph 2Si(SB) 2 PhjS i (SB)

η - π *

ληΐ3χ/ηιη

>C=N 365 356 358 348 352 349

π- π*

λπΊβχ/ηΓη

C 6 H 5 r ing 270 285 287 290 294 296

π- π*

\ m a x / n m

> C = N 292 288 286 283 280 278

IR Spectra

The infrared spectra of the starting materials and their si l icon(IV) complexes were recorded and important

features are discussed.

The IR spectra of silicon compounds do not show any band in the region 3400 - 3150 cm"', which could

be assigned to v (NH) vibrations of the ligand. A medium intensity band at 1620 cm"', due to the free

azomethine group in the ligand, shifts to the lower f requency (ca. 10 cm"') in the silicon complexes , and this

indicates the coordinat ion of the azomethine nitrogen to the silicon atom.

A band at 1410 cm"' is due to the asymmetr ic deformat ion vibrations of (CH^-Si) group, whereas the band

at 1260 cm"' has been assigned to the symmetr ic deformation mode of ( C H r S i ) group. St rong and sharp

bands in the spectra of silicon complexes for C-H stretching and bending vibrations appear at 2824-3042 and

1404-1432 cm"', respectively. Aromatic ring stretch (C-C) appeared at 1645, 1530 and 1457 cm"'.

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Mukta Jain and R. V. Singh Main Group Metal Chemistry

T w o sha rp b a n d s at 3 4 4 0 and 3550 cm"', p robab ly due to the a symmet r i c and s y m m e t r i c v ib ra t ions o f the

N H 2 g r o u p in the l igand, remain a lmos t unchanged in the spect ra o f the metal c o m p l e x e s , s h o w i n g the non-

invo lvement of this g r o u p in complexa t ion .

T h e che la t ion th rough azome th ine n i t rogen gets suppor t by the a p p e a r a n c e o f new b a n d s at a round 575 +

5 cm"1 d u e to v(Si<—N) vibra t ions . A band due to v (S i -Cl ) at 4 4 0 - 4 2 5 cm"1 is o b s e r v e d in 1:1

d io rganos i l i con ( IV) der iva t ives . T h e p resence o f only one v (S i -N) band in the presen t case sugges t s that

c o m p l e x e s exis t in the trans f o rm . It has been repor ted that the cis form o f 1:2 c o m p l e x e s g ives rise to two

v (S i -N) bands , w h e r e a s in the trans fo rm only one IR act ive v ( S i - N ) band is obse rved .

T a b l e III

IR Spectra l Data (in cm"1) of the Ligand and its Si l icon C o m p l e x e s .

Compound v (NH) ν ( C = N ) ν (Si<—N) ν (Si-Cl)

SBH 3 4 0 0 - 3 1 5 0 m 1620 vs . Me 2 SiCl(SB) » 1613 vs 578 w 425 m

Me2Si(SB)2 1616 vs 582 w -

Ph2SiCl(SB)2 1610 vs 575 w 440 m

Ph2Si(SB)2 1607 vs 577 w _

PhjSi(SB) - 1609 vs 572 w

m = m e d i u m , vs = very s t rong, w = w e a k

'H NMR Spectra

In o r d e r to subs tan t ia te the nature of b o n d i n g in the c o m p l e x e s d iscussed above , the pro ton magne t i c

r e sonance spect ra o f the c o m p l e x e s were r eco rded in D M S O - d 6 . T h e d i s a p p e a r a n c e of N H pro ton signal at

510 .65 p p m and the d o w n f i e l d sh i f t ing in the posi t ion of ( C H 3 - C = N ) p ro tons a lso indica te the coord ina t ion o f

a zome th ine n i t rogen to si l icon a tom. For the a romat i c pro ton , the l igand shows a c o m p l e x mul t ip le t in the

region δ 8 .96 - 7 .56 p p m and its obse rved in the region δ 9 .40 - 7 .32 p p m in the spec t ra of the

o rganos i l i con ( IV) complexes . Further , a d o w n f i e l d shi f t in the posi t ion of the a r o m a t i c p ro tons in the spec t ra

of the c o m p l e x e s a l so indicates the coord ina t ion of the azome th ine n i t rogen to the si l icon a tom. T h e chemica l

shif t va lues re la t ive to the te t ramethyls i lane ( T M S ) peak are listed in T a b l e ( IV) .

29Si NMR Spectra

T h e s ignals at δ - 9 4 to - 9 0 and - 1 0 5 to - 1 2 5 ppm are indicat ive of penta- and h e x a c o o r d i n a t e d s tates of

the si l icon a tom in the 2 9Si N M R spectra o f the c o m p l e x e s Ph 3 Si (SB) or R 2 S i C l ( S B ) and R 2 S i ( S B ) 2 (R = Ph

or Me) , respec t ive ly .

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Vol. 26. No. 4, 2003 Spectral and Antimicrobial Studies of Organosilicon(IV)Complexes of a Didentate Schiff Base Having

Table IV

Proton N M R and 29Silicon N M R Spectral Data of the Ligand and its Silicon Complexes (δ/ppm).

Compound CH3 Si-CH3 /C6H5 NH Aromatic Protons 29Si N M R

SBH 2.26

(s,3H)

- 10.65

(br, 1H)

8 . 9 6 - 7 . 5 6 (m) -

Me2SiCI(SB) 2.37

(s ,3H)

1.08

(br,6H)

- 9.03 - 7.69 (m) - 94 ppm

Me2Si(SB)2 2.33

(s, 6H)

1.20

(br,6H)

* 9 . 4 0 - 7 . 3 2 (m) - 125 ppm

Ph2SiCl(SB) 2.35

(s,3H)

7.99

(br, 10H)

- 9.25 - 8.10 (m) - 91 ppm

Ph2Si(SB)2 2.30

(s,6H)

8.19

(br,10H)

- 9.30 - 8.25 (m) - 105 ppm

Ph3Si(SB) 2.36

(s,3H)

8.09

(br,15H)

- 9 . 2 7 - 8 . 1 5 (m) - 90 ppm

s = singlet, br = broad, m = multiplet

On the basis of the results discussed so far, including the analytical and spectral data, a pentacoordinated

trigonal bipyramidal geometry is suggested for 1:1 tri- and di- organometal derivatives and hexacoordinated

octahedral geometry for 1:2 diorganometal derivatives

Fig. 2

M I C R O B I A L ASSAY

Fungicidal and bactericidal activities of mono and bimetallic complexes against different fungi

{Aspergillus niger, Macrophomina phaseolina, Fusarium oxysporum and Alternaria alternata) and bacteria

(E. coli, Klebsiella aerogenous, Pseudomonas cepacicola and Staphylococcus aureus) have been recorded in

Tables V and VI by the following methods.

(i) Agar Plate Technique /14/ - The fungi were grown in agar medium prepared by dissolving glucose (20g),

starch (20g), agar-agar (20g) and 1000 ml of distilled water at 25 + 2°C. The compounds were dissolved in

242

Μιι kl a Jain and R. V. Singh Main Group Metal Chemistry

25, 50 and 100 ppm concentrations in D M F . Controls were also run and three replicates were used in each

case. The linear growth of the fungus was obtained by measuring the diameter of the fungal colony after four

days and the amount of growth inhibition in all the replicates were calculated.

Table V

Fungicidal Activity of the Ligand and its Silicon Complexes (Average % Inhibition after 96 hrs.).

Compound Aspergillus niger Macrophomina

phaseolina

Fusarium

oxysporum

Alternaria alternata

Cone. 25 50 100 25 50 100 25 50 100 25 50 100

S B H 34 45 62 35 46 61 39 51 60 41 52 61

Me 2 S iC I (SB) 36 49 64 40 51 65 41 54 64 44 55 63

Me 2S i (SB) 2 45 55 72 48 57 76 46 58 73 48 60 72

Ph 2SiCl(SB) 43 51 68 42 53 69 43 55 67 45 57 66

Ph2Si(SB)2 47 56 75 48 60 78 48 60 74 48 60 77

Ph 3Si(SB) 44 53 71 43 56 72 45 57 70 47 59 69

(ii) Inhibition Zone Technique /15/ - The agar medium having the composition peptone (5g), beef extract

(5g), NaC I (5g), agar-agar (20g) and distilled water 1000 ml and 5mm diameter paper discs of Whatman no.l

were used. The agar medium was poured in petri plates. After solidification, the petri plates were stored in a

freezer in inverted position so that water condensed in the upper lid. The solutions of the test compounds in

dimethylformamide in 500 and 1000 ppm concentrations were prepared, and either the discs were dipped in

solution of the test sample and placed on seeded plates, or, after placing the paper discs on seeded plates, the

required quantity of the test sample was pipetted on the disc. The petri plates having these discs on the seeded

agar should first be placed at low temperature for 2h to allow for the diffusion of a chemical before being

incubated at suitable optimum temperature (28 + 2°C) for 24 - 30 h. After the expiry of the incubation

period, the clear zone of inhibition associated with the treated disc was measured in mm.

Table V I

Bactericidal Activity of the Ligand and its Silicon Complexes (diameter of inhibition in mm).

Compound E. coli (-) Klebsiella

aerogenous (-)

Pseudomonas

cepacicola (-)

Staphylococcus

aureus (+)

Cone. 500ppm lOOOppm 500ppm lOOOppm 500ppm lOOOppm 500ppm lOOOppm

S B H 6 10 7 8 10 12 1 1 13

Me 2 S iC l (SB) 8 12 9 11 12 13 13 14

Me 2Si (SB) 2 10 13 10 12 14 15 14 16

Ph 2SiCI(SB) 9 12 10 12 13 14 14 15

Ph2Si(SB)2 11 14 12 14 16 17 15 16

PhjSi(SB) 10 12 11 13 14 15 14 16

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Vol. 26, No. 4. 2003 Spectral and Antimicrobial Studies of Organosilicon(IV)Complexes of a Bidentate Schiff Base Having

Potato dextrose media ( P D A ) rich in carbohydrates as the major nutrient source is utilized by the

microbes with the help of various enzymes (viz. amylase, cellulase, pectinase etc.). Metal based fungic ides

inhibit a wide range of enzymes involved in various metabol ic pathways, ultimately causing cell death . Early

work on the mode of action of fungicides showed that these compounds inhibit cell division. It was later /16/

shown that the specif ic site of action is ß-tubuline, a polymeric protein found in microtubules , which is an

essential component of the cytoskeleton. Phenyl and amine groups in complexes affect nucleic acid synthesis

and mitochondrial electron transport also. We might then expect at least the fol lowing regulatory processes to

be operat ive /17/.

(a) Carbon catabolic regulation During per iods of rapid utilization of the carbon source, particularly of g lucose or sucrose, either the

formation of enzymes in the secondary metabolic pathways leading to toxins would be repressed, or the

activity of these pathways would be inhibited.

(b) Nitrogen catabolic repression Excessive levels of rapidly assimilated forms of nitrogen (e.g. ammonium ion) could repress the

formation of enzymes concerned with nitrogen transformation of toxins intermediates.

(c) Feedback regulation As toxins accumulate they would, in some instances, limit their own biosynthesis by inhibiting the

activity of one or more enzymes earlier in their synthetic pathways.

(d) Feedback regulation by primary precursors Primary metaboli tes that are precursors of toxins could act similarly by inhibiting enzymes in primary

pathways, prior to where they branch off into secondary ones.

(e) Energy charge regulation High phosphate levels could reduce the availability of high-energy phosphate (i.e. A T P and ADP) . This

would effect ively inhibit a number of key reactions in primary metabolism which, in turn, would cause a

reduction in the activity of secondary pathways linked to toxin production.

(J) Induction The addition of certain primary metaboli tes ( termed effectors) could induce the formation of enzymes in

secondary pathways leading to toxin production. This effect would be aside f rom any function the effectors

might have as precursors of the toxins.

These results reveal that all the compounds are more active against all the organisms used than the ligand

itself. It may also be pointed out that the methyl substituted compound was found to be less potent than the

corresponding phenyl derivat ive of Si(IV). Further, it can also be noticed that a lower concentrat ion of the

compounds can check the sporulation in the fungi and a higher concentration inhibits the growth of

organisms completely. Nevertheless , it is difficult to make out an exact structure and activity relat ionship

244

Mukta Jain and R. V. Singh Main Group Metal Chemistry

between microbial activity and the structure of these complexes. It can possibly be concluded that the

chelation as well as the addition of a substrate enhance the activity of the complexes / 17/.

Nematicidal Activity

The yield of okra, tomato and brinjal suffered 90.9, 46.2 and 2-3 percent losses, respectively, due to

Meloidogyne incognita infestation @ 3-4 larvae/g soil under field conditions /18/. The nematode population

levels present in soil are directly correlated with damage to cereal crops / 19/.

The root-knot nematode (Meloidogyne spp.) produces galls on the roots of many vegetable crops, pulses,

some of the fruit crops, tobacco, ornamental crops and causes severe losses /20/. The avoidable yield losses

due to M. incognita were estimated to be 28.08, 33.68, 43.48 and 28.60 per cent in okra, brinjal, french bean

and cowpea, respectively /21/.

Treatment

The method followed for obtaining quantities of clean Meloidogyne incognita eggs was that of McClure

et al. 1221 and the step by step procedure was as follows :

Infected roots with M. incognita were washed thoroughly and cut into small 1-2 cm pieces. The chopped

pieces were placed in a beaker in 100 ml of tap water, 500 ml of 1% NaOCI added and the suspension was

vigorously shaken for 5 minutes; then the suspension was poured quickly through nested 150 and 400 mesh

sieves. The eggs which were retained on the 400 mesh sieve were washed with a sufficient quantity of

distilled water. Eggs which passed through the 400 mesh sieve were recovered by repeated sieving and

rinsing. Eggs were eluted from the sieves and transferred to 40ml of water.

A centrifuge tube was two-thirds filled with 20% sucrose solution and the egg water suspension was

centrifuged at 500g for 5 minutes. A silver layer containing the suspended eggs at the junction of sugar

solution and egg suspension was removed with the help of a pipette and quickly poured onto a 400 mesh

sieve. The eggs retained on the sieve were washed three times with distilled water thoroughly and collected

in a beaker. In each nematode hatching dish 230 eggs were taken and treated with the treatment. The number

of juveniles was counted after 24 hours.

Table VII

Nematicidal activity of the ligand and its silicon complexes (percentage of hatching in Meloidogyne incognita)

Compound 25ppm 50ppm 1 OOppm

SBH 24.1 19.8 15

Me2SiCI(SB) 21.9 17.2

Me2Si(SB)2 19.9 15.1 -

Ph2SiCI(SB) 21.1 16.8 _

Ph2Si(SB)2 18.0 13.2

Ph3Si(SB) 19.6 15.9 -

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Vol. 26, No. 4, 2003 Spectral and Antimicrobial Studies of Organosiliconf/VJComp/exes of a Bidentate Schiff Base Having

ACKNOWLEDGEMENT

The authors thank the UGC, New Delhi, for financial assistance.

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