Synthesis and Reactivity in Inorganic, Metal-Organic

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Jan 6, 2015 - Chemistry Department, Faculty of Science of Girls, Abha, King Khalid University, Abha,. Saudi Arabia b ... data reveal the coordination of acid as mononegative bidentate. NH, and ...... Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. Advanced Inorganic Chemistry, 6th ed.; Wiley, New York, 1999. 24.
This article was downloaded by: [Eskisehir Osmangazi Universitesi] On: 09 January 2015, At: 02:43 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lsrt20

A Series of Taurocholic Acid Complexes, Spectral, Kinetic, Molecular Modeling, and Antiviral Activity Studies a

Khlood Abou-Melha , Moamen S. Refat

bc

de

& Atif Sadik

a

Chemistry Department, Faculty of Science of Girls, Abha, King Khalid University, Abha, Saudi Arabia

Click for updates

b

Chemistry Department, Faculty of Science, Port Said University, Port Said, Egypt

c

Chemistry Department, Faculty of Science, Taif University, Taif, Saudi Arabia

d

Biology Department, Faculty of Science, Taif University, Taif, Saudi Arabia

e

Microbiology Department, Faculty of Agriculture, Ain Shams University, Cairo, Egypt Accepted author version posted online: 25 Sep 2014.Published online: 06 Jan 2015.

To cite this article: Khlood Abou-Melha, Moamen S. Refat & Atif Sadik (2015) A Series of Taurocholic Acid Complexes, Spectral, Kinetic, Molecular Modeling, and Antiviral Activity Studies, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 45:6, 884-895, DOI: 10.1080/15533174.2013.843566 To link to this article: http://dx.doi.org/10.1080/15533174.2013.843566

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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2015) 45, 884–894 Copyright © Taylor & Francis Group, LLC ISSN: 1553-3174 print / 1553-3182 online DOI: 10.1080/15533174.2013.843566

A Series of Taurocholic Acid Complexes, Spectral, Kinetic, Molecular Modeling, and Antiviral Activity Studies KHLOOD ABOU-MELHA1, MOAMEN S. REFAT2,3, and ATIF SADIK4,5 1

Chemistry Department, Faculty of Science of Girls, Abha, King Khalid University, Abha, Saudi Arabia Chemistry Department, Faculty of Science, Port Said University, Port Said, Egypt 3 Chemistry Department, Faculty of Science, Taif University, Taif, Saudi Arabia 4 Biology Department, Faculty of Science, Taif University, Taif, Saudi Arabia 5 Microbiology Department, Faculty of Agriculture, Ain Shams University, Cairo, Egypt

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2

Received 27 August 2013; accepted 8 September 2013

A series of taurocholic acid complexes was prepared with Cr(III), Fe(III), Co(II), Ni(II), and Cu(II) ions. The IR and Raman spectral data reveal the coordination of acid as mononegative bidentate. NH, and sulfonate (–O¡). The bidentate mode of coordination is proposed toward all the metal ions. The electronic spectral data as well as the magnetic moment measurements proposed the octahedral geometry for all investigated complexes. The presence of water molecules was supported by thermal analysis study. ESR spectrum of Cu(II) complex was carried out and acting as a further supporting for the octahedral geometry. The molecular modeling was performed for all complexes to assert on the lower energy content for all isolated complexes in comparing with their free ligand. Such concludes the comparative stability of all isolated complexes. Scanning electron micrography for the Cu(II) complex reveals the particle size is presented in the nano range. An elaborated biological investigation was carried out for all complexes in comparison with their free ligand. The highest antiviral activity was observed with the free ligand and its Ni(II) and Co(II) complexes and moderate activity was observed with Cr(III) and Fe(III) complexes, but the lowest activity was observed with Cu(II) complex. Keywords: taurocholic acid complexes, Raman, EPR, thermal, antiviral activity

Introduction The synthesis and characterization of metal complexes with bioactive organic ligands to produce novel potential chemotherapeutic agents is rapidly developing, and of particular note is the pressing need for new antibacterial to replace those losing their effectiveness because of the fast development of microorganisms resistance.[1] The controlled aggregation of small coordination complex– based building blocks to form larger architectures is of great interest in metal–ligand polyoxometalate chemistry.[2] Particularly, the ability to use both ligand design and adjustment of reaction conditions to understand and control the aggregation process is crucial. The combination of these approaches should yield the best chance of synthesizing sophisticated, potentially functional complexes and clusters.[3] The chemistry of transition metal complexes has been receiving considerable attention because of their biological relevance.[4–10] The coordination possibilities are increased if the substituents of the Address correspondence to Khlood Abou-Melha, Chemistry Department, Faculty of Science of Girls, Abha, King Khalid University, Saudi Arabia. E-mail: [email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsrt.

aldehyde or ketone include additional donor atoms. The p delocalization and the configurational flexibility of their molecular chain can give rise to a great variety of coordination modes.[11] Transition metal complexes containing N,S or N,O donors are of special interest due to their applications.[12,13] Compounds with N and S donor atoms such as N2S2 are considered to be good coordinating ligands because they involve both hard nitrogen and soft sulfur atoms. Taurocholic acid is an essential bioactive agent includes donor atoms (N, O, and S) characterized with their distinguish biological activity. This acid is conjugated mainly to glycine, and not only facilitates digestion, absorption, and excretion of dietary lipids, but also interacts with numerous cellular signaling pathways.[14] From all literature displayed in this work we focus on using taurocholic acid as a poly active central bioactive compound. Such, may permit the coordination of poly nucleus of metal ions, which expect to display priority in biological activity. The elemental analysis data of investigated complexes supposed the prepared complexes by 1:1 molar ratio between central atom and the ionized acid. In between a series prepared we expected the priority for one or more complexes than the drug itself. So the elaborated bioactive study was concerned with the deliberate chemical investigation for all isolated complexes.

Series of Taurocholic Acid Complexes

885 inoculation of Daturametel plant (Tobacco mosaic tobamovirus [TMV]) leaves as an indicator local lesion host. The inoculated leaves were sprayed with distilled H2O 1 h postinoculation. All healthy and virus-inoculated plants were kept at room temperature in the lab for a week. The total number of necrotic local lesions was counted for each substrate. Percent of infection and inhibition were determined.

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Physical Measurements

Fig. 1. The geometric and modeling structures of taurocholic acid (H5L).

Experimental Materials Chromium (III), iron(III), nickel(II), and copper(II) were used as chloride salts but cobalt(II) used as nitrate, all were Merck or BDH. Taurocholic acid (Figure 1) was obtained from the Egyptian International Pharmaceutical Industrial Company (EIPICO). Organic solvents—ethanol, methanol, diethylether, and dimethylsulfoxide (DMSO)—were of reagent grade. Synthesis of Metal Ion Complexes 2 mmol of taurocholic acid (1.031 g) dissolved in 20 mL ethanol was mixed with1 mmol of each metal salt dissolved in absolute ethanol (5 cm3). The pH of the reaction mixture was adjusted to 7–8 using few drops of diluted ammonium hydroxide. Each reaction mixture was heated under reflux for 2 h. The colored complexes were separated by filtration washed by using absolute methanol and diethylether then leaves for drying in desiccators over anhydrous CaCl2. Biological Studies Procedure A 0.001 g of the substrates was added to 1 cm3 of a viral infectious sap, and incubated for 24 h at room temperature. Each mixture was vortexed for 2 min either before or after incubation. A volume of 750 mL was separately used for

The element content as well as the scanning electron micrography (SEM) were determined using SEM images and energy-dispersive X-ray detection (EDX) was taken in Joel JSM-6390 equipment, with an accelerating voltage of 20 KV. For assurance, the metal content was determined using complexometric titrations and the Cl was quantitatively determined using AgNO3.[15] An observable difference was recorded for the two elements (Metal and Chloride) in between the two evaluation methods. IR spectra were recorded on a Mattson 5000 FTIR Spectrophotometer (4000–400 cm¡1) using KBr pellets. Raman laser spectra of samples were measured on the Bruker FT–Raman with laser 50 mW. The UV–vis spectra were determined in the DMSO solvent well as in Nujol mull for the free ligand and its complexes using Jenway 6405 spectrophotometer with 1 cm quartz cell, in the range of 200–800 nm. Magnetic measurements were carried out on a Sherwood Scientific magnetic balance using the Gouy method. The balance calibration was carried out by two very good solid calibrants, Hg[Co(CNS)4] and [Ni(en)3](S2O3). They are easily prepared in pure state, do not decompose or absorb moisture and pack well. Their susceptibilities at 20 C are 16.44 £ 10¡6 and 11.03 £ 10¡6 c. g.s. Units, decreasing by 0.05 £ 10¡6 and 0.04 £ 10¡6 per degree temperature, were raised to near room temperature. With the cobalt compound having the higher susceptibility, it also packs rather densely and is suitable for calibrating low fields, while the nickel compound with lower susceptibility and density is suitable for higher field. Here we are used Hg[Co(CNS)4] only as calibrant. Thermogravimetric and differential analysis (TGA/DTG) were carried out in dynamic nitrogen atmosphere (30 cm3/min) with a heating rate of 10 C/min using a Shimadzu TGA-50H thermal analyzer. ESR spectrum of solid Cu(II) complex was obtained on a Bruker EMX Spectrometer working in the X-band (9.44 GHz) with 100 kHz modulation frequency. The

Table 1. Analytical and physical data for the taurocholic acid complexes (H5L) and its metal complexes Elemental Anal. Calcd. (%) (Found) Compound empirical formula (M. Wt.) 1) [C26H45NO7S] (515.7) 2) [CrCl2(H4L).2H2O]H2O (691.64) 3) [FeCl2(H4L).2H2O]2H2O(713.5) 4) 4) [Co(NO3)(H4L).3H2O]2H2O(725.7) 5) [NiCl(H4L)3 H2O](662.88) 6) [CuCl(H4L) H2O]2H2O(667.73)

Color

C

H

S

M

Cl

Faint Yellow Green Brown Pale pink Green Green

60.55(60.54) 45.15(45.15) 43.77(43.76) 43.03(43.10) 47.11(47.10) 46.77(46.77)

8.79(8.79) 7.29(7.28) 7.34(7.34) 7.50(7.51) 7.60(7.62) 7.55(7.54)

6.21(6.11) 4.64(4.60) 4.49(4.49) 4.42(4.41) 4.84(4.84) 4.80(4.81)

— 7.52(7.50) 7.83(7.83) 8.12(8.12) 8.85(8.84) 9.52(9.51)

— 10.25(10.25) 9.94(9.93) — 5.35(5.35) 5.31(5.31)

886

1 [C26H45NO7S] (H5L) 2 [CrCl2(H4L).2H2O]H2O 3 [FeCl2(H4L).2H2O]2H2O 4 [Co(NO3)(H4L).3H2O]2H2O 5 [NiCl(H4L)3 H2O] 6 [CuCl(H4L) H2O]2H2O

Compound 3405 (3450) 3375 (3480) 3391 3394 (3450) 3385 (3450) 3402 (3480)

nOH 2932 (3200) 2934 (3150) 2933 2933 (3100) 2933 (3150) 3235 (3150)

nNH 1307 (1313) 1311 (1352) 1311 1320 (1320) 1350 (1320) 1400 (1428)

dOH (in plane) 1605 (1600) 1719 (1660) 1718 1628 (1660) 1626 (1650) 1606 (1640)

nCDO 1406,1219 (1405,1211) 1376,1201) — 1378 1310,1218 (1310,1211) 1416,1201 (1350,1210) 1309,1200 (1325,1210)

nas, ns SO2

Table 2. Assignments of the IR (Raman) Essential Spectral bands (cm¡1) of H5L and its metal complexes

1590 (1500) 1636 (1550) 1616 1550 1550 1550 (1550) 1550 (1572)

dNH

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nM-N — 520 (475) 419 460 422 450 (425) 450 (480)

nM-Cl — — (280) — —— — (261) — (280)

— 580 (500) 550 550 577 550 (523) 550 (550)

nM-O

Series of Taurocholic Acid Complexes

887

0.045

Raman Intenisty

0.035 0.030 0.025

-11

A B C D E F

-12

2 ln (-ln (1-α)/T )

0.040

0.020 0.015

-13

-14

0.010 0.005

-15

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0.000 -0.005 4000

-16 3500

3000

2500

2000

Wavenumbers

(cm

1500

-1

1000

500

Ni Co Fe Cu Cr 0.0024

0.0025

0.0026

0.0027

0.0028

0.0029

0.0030

1000/T(K)

)

Fig. 2. Raman spectra of (A) ligand, (B) Cu(II), (C) Mn(II), (D) Co(II), (E) Fe(III), (F) Ni(II).

Fig. 4. Coats-Redfern curves of all investigated complexes in the first decomposition step.

microwave power was set at 1 mW, and modulation amplitude was set at 4 Gauss. The low field signal was obtained after four scans with a 10-fold increase in the receiver gain. A powder spectrum was obtained in a 2 mm quartz

capillary at room temperature. The biological activity screening was tested against TMV virus.

Results and Discussion All the isolated complexes are stable in air, insoluble in common organic solvents except DMSO and DMF in which are sparingly soluble. The incomplete solubility prohibits the facility of determining the molar conductivity of the investigated complexes. Such lower solubility of the complexes supports the nonionizable coordination sphere. This supports the presence of conjugated anion inside the coordination sphere by direct attachment with the central atom. The analytical data as well as some physical properties of the complexes are summarized in Table 1.

IR Spectral Studies

Fig. 3. The structures proposed for all investigated complexes: M1 D Cr(II) and Fe(III) where X D 1 and 2, respectively; M2 D Ni(II) and Cu(II) where X D 0 and 2, respectively.

Table 2 summarizes the selected bands characteristic for the functional groups fingerprint in the IR spectra for the free ligand and its complexes. The ligand has multicoordination sites which are concerned in description of the spectrum as y OHs appeared as broad band centered at 3405 cm¡1, y NH at 2932 cm¡1, and a strong band at 1605 cm¡1 is attributed to y CHO, while the band at 1590 cm¡1 was assigned to dNH. The band at 1307 cm¡1 is attributed to dOH groups in a cis position upon the hydrocarbon moiety. The bands characteristic for R–SO2-OH group appeared at 1406, 1219, and 612 cm¡1 for yasSO2, ysSO2, and ysS-O, respectively. The ligand coordinates toward all metal ions by the same behavior as mononegative bidentate. The two ligating sites are NO. The relatively basic medium of reaction devoted the organic acid to react in its anionic form with all metal ion salts. IR spectral data abstracted from all complexes reveal more or less unshifted y OH bands, which proposed their ruling out from complexation especially with the formation of mononuclear complexes, although the presence of multi OH groups.

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Table 3. Magnetic moments (BM) and electronic spectra bands (cm¡1) of the complexes Complex

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1 [C26H45NO7S] 2 [CrCl2(H4L).2H2O]H2O 3 [FeCl2(H4L).2H2O]2H2O 4 [Co(NO3)(H4L).3H2O]2H2O 5 [NiCl(H4L)3 H2O] 6 [CuCl(H4L) H2O]2H2O

meff (BM)

d-d transition (cm¡1)

Intraligand and charge transfer (cm¡1)

Proposed geometry

— 4.12 5.03 4.24 3.12 1.92

— 34,303; 24,155; 17,123 24,641; 20,833 22,222; 19,455 25,000; 15,337 18,182; 14,286

36,496;34,722;29,940; 26,178 37,313 36,486; 28,614 36,496; 27,624 38,461; 26,738 36,765

—High Spin Octahedral High Spin Octahedral Octahedral Octahedral Octahedral

This is may be due to the farness distribution of OH groups over the organic compound. Strong bands appeared at 1719, 1616, 1650, 1606, and 1626 cm¡1 in Cr(III), Fe(III), Ni(II), Cu(II), and Co(II) spectra, respectively, assigned for highly shifted y CHO band instead of in free ligand. The CHO group is completely sided from coordination especially with the presence of NH group as a coordinating arm. The bands appear at 1376, 1378, 1306, 1309, and 1310 cm¡1 assigned for yasSO2[16] and the other band assigned for ysSO2 appeared at 1201 cm¡1 in Cr(III), Fe(III), Ni(II), Cu(II), and Co(II) complexes, respectively. These bands suffer lower shift due to the participation of sulfonate in coordination toward the central atom. The broad bands at  3375–3450, 832–854, and 620–680 cm¡1 region in the IR spectra of the complexes are referring to y(H2O), dr, and dw H2O of the coordinated water molecules. While, the broadness appeared at higher frequency region may support the presence of aqua complexes except the [NiCl(H4L)3H2O] complex, which displays a clear sharpness at this region. The TG analysis goes in a parallel way with this proposal. The conjugated Cl ion was proposed based on elemental analysis due to there being no facility for recording yM-Cl until the end of scanning range (400 cm¡1).

The [Co(NO3)(H4L)3H2O]2H2O spectrum shows two bands at 1450 and 1383 cm¡1 assignable to y5(NO3) and y1(NO3) by difference (Dy D 67 cm¡1) in agreement with the monodentate nature of NO3.[17] New bands observed in all complexes at 550–580 and 410–460 cm¡1 region are assigned to y(M-O) and y(M-N) bands.[18,19] Raman Spectra Resonance Raman spectroscopy is a very useful technique to find out the oxidation state of the ligand because it is sensible to slight changes in the electron distribution of the molecule. The Raman spectra were carried out for the complexes in solid state (Figure 2). All the complexes show a very similar pattern, which may support the unique behavior of the ligand toward the coordination. The assignment of some function groups was displayed in Table 2 beside the IR data for assurance. The low-frequency region gives important information about the nature of the metal–ligand bonds. The bands around 600 cm¡1 are assigned to M-O vibrations, the bands around 500 cm¡1 are assigned to M-N vibrations[20] and the bands around 300 cm¡1 are assigned to M-Cl vibrations in

Table 4. Thermogravimetric data of the investigated complexes Complex 2

3

4

5

6

Steps

Temp. range ( C)

Decomposed assignments

Weight loss% Found(Anal. Calcd.)

1st 2nd 3rd residue 1st 2nd 3rd 4th residue 1st 2nd 3rd 4th 5th residue 1st 2nd residue 1st 2nd residue

65–125 125–501 501–644

-3H2O C23H39O3 -Cl2 C3H5O4SN C Cr -2H2O -Cl2 C 2H2O C18H30O3 C4H7 C4H7SO4N C Fe -2H2O -3H2O -C7H12O -C9H14O2 -C8H13 NO C0.5 Cl2 C2H5SO3C Co -3H2O -0.5Cl2 C C19H31O3 C7H13O4SN C Ni -3H2O 0.5Cl2 C C23H39O3 Cu C C3H5NO4S

7.82(7.82) 52.14(52.56) 10.94(10.25) 29.10(10.25) 5.16(5.05) 14.64(14.99) 41.38(41.27) 7.36(7.72) 31.45(30.97) 5.55(5.15) 7.28(7.70) 16.3(16.04) 21.95(22.06) 24.39(24.98) 24.53(24.04) 8.29(8.15) 51.71(51.70) 40.0(40.12) 7.93(8.09) 59.74(59.76) 32.33(32.15)

55–123 123–324 324–492 492–719 62–135 135–243 243–390 390–476 476–668 102–150 150–434 54–148 148–412

Series of Taurocholic Acid Complexes

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Table 5. Kinetic parameters using the Coats-Redfern method operated for the ephedrine complexes Kinetic parameters Complex

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2 3 4 5 6

Step

E (Jmol¡1)

A (S¡1)

1st 1st 1st 1st 1st

4.73EC04 9.43EC04 4.70EC04 6.93EC04 5.19EC04

5.02EC04 7.37EC11 2.37EC04 1.35EC07 2.04EC05

D S (Jmol¡1K¡1)

D H (Jmol¡1)

D G (Jmol¡1)

¡1.57EC02 ¡1.93EC01 ¡1.63EC02 ¡1.11EC02 ¡1.45EC02

4.42EC04 9.12EC04 4.39EC04 6.59EC04 4.88EC04

1.02E C05 9.82E C04 1.04E C05 1.10E C05 1.03 EC 05

the investigated complexes. The intense resonance enhancement of the six-member ring containing the atoms indicates that the electron transition (ligand to metal charge transfer) involves the d-metal orbital in the excited state of the metal ion complexes for divelant and trivelant metals.

Magnetic Susceptibility and Electronic Spectral Studies The electronic spectral measurements (Table 3) were carried out in DMSO solvent for all investigated complexes and their free ligand in the range 200–900 nm. The relative solubility of the complexes is completely sufficient to display the d-d and C. T. transition bands. The spectra were scanned for the complexes in their solid state using Nujol mull to assert on the absence of solvent coordination role during the spectral recording in solution. The stereo structures for all investigated complexes (Figure 3) were proposed based on the deliberate view of the electronic spectra as well as the magnetic moment measurements. The ligand spectrum showed a band at 36,496 cm¡1 assigned to p! p* and two bands at 34,722 and 26,178 cm¡1 due to n! p* in CHO and SHO groups. The CT bands suffer changes strongly appears in the spectra of all complexes. The spectrum of [CrCl2(H4L)2H2O] H2O complex displays three characteristic absorption bands at 37,313, 24,155, and 17,123 cm¡1 attributed to 4A2g!4T1g (p)(y3), to 4A2g!4T1g (F)(y2), and to 4A2g!4T2g (F)(y1), respectively, in an octahedral geometry. The B value is calculated by B D (2y12 – 3 y1 y3 C y22) / (15y2 – 27 y1)[21] and the value of b is computed as b D B/B0 (B0 D 918cm¡1). The ligand field parameters (Dq D 1712.3, B D 709.6, and b D 0.77) values as well as the magnetic moment value (4.12 BM) toward us to the octahedral stereo structure. The spectrum of [FeCl2(H4L)2H2O]2H2O complex displays bands at 20,833 and 24,641 cm¡1 attributed to 6A1g!4T2g (G) and6A1g!4Eg (G) transitions, respectively, in an octahedral geometry.[22] The magnetic moment value (5.03 BM) strongly supports the high spin octahedral arrangement around Fe(III).The spectrum of [Co(NO3)(H4L)3H2O]2H2O pale pink complex displays two significant absorption bands at 22,222 (y3) and 19,455 cm¡1 attributed to 4T1g ! 4T1g (p) and 4T2g ! 4A2g transitions, respectively, in an octahedral geometry. The ligand field parameters (Dq D 1036, B D 952.9 and b D 0.98) were calculated as well as the magnetic moment value (4.24 BM) all are coinciding with each other to confirm the geometry proposed.[22] The spectrum of [NiCl (H4L)3H2O] complex displays two transition bands at 25,000

r 0.98426 0.96402 0.97817 0.96835 0.98457

and 15,337 cm¡1 attributed to 3A2g!3T1g (P)(y3) and 3 A2g!3T1g (G)(y2) transition, respectively, in an octahedral arrangement. The ligand field parameters (Dq D 946.7, B D 788.9 and b D 0.76) were calculated as well as the magnetic moment value (3.12 BM) all are coinciding with the geometry proposed of the green complex.[23] The spectrum of [CuCl (H4L)H2O]2H2O complex displays two d-d transition bands at 14,286 and 18,182 cm¡1 attributed to2Eg!2T2g and 2B1g ! 2A1g transition, respectively, in an octahedral geometry. The 2Eg and 2T2g states of octahedral Cu(II) ion split under the influence of the tetragonal distortion and the distortion cause the three transitions 2B1g ! 2B2g,2B1g ! 2Eg, and 2 B1g ! 2A1g to remain unresolved in the spectra. This assignment is in agreement with the general observation for Cu(II) d–d transitions are normally close in energy. The magnetic moment value (1.92 BM) falls within the normal range for d9 system.[24]

Thermal Analysis Studies Thermogravimetric studies (TG) for the complexes were carried out within the temperature range from room temperature up to 800 C. The TG analysis data (Table 4) are considered the further support for the analytical data. The TG tool is the only essential tool used for supporting the presence of solvent molecules in aggregation with the complex nucleus inside or outside the coordination sphere. The TG curve of [CrCl2(H4L)2H2O]H2O complex displays three degradation steps. The first step at the temperature range of 65–125 C is representing the decomposition of all water molecules associated with the central atom by 7.82 (calcd. 7.82%) weight loss. The second decomposition stage ended at 501 C and may be displaying the decomposition of C23H39O3 (organic moiety) by 52.14 (calcd. 52.56%) weight loss. The third degradation stage ended at 644 C may be displaying the decomposition of Cl2 by 10.94 (calcd. 10.25%) weight loss. The final residue was recorded at 644 C and displayed a relative higher weight percentage by 29.10 and may be referring to the presence of an organic part chalets directly with Cr atom. The TG curve of [FeCl2(H4L)2H2O]2H2O complex displays four degradation stages. The first stage at the temperature range of 55–123 C represents the removal of 2H2O by 5.16 (calcd. 5.05%) weight loss. The second decomposition stage ended at 324 C may be displaying the removal of remaining water molecules beside Cl2 by 14.64 (calcd. 14.99%) weight loss. The third stage ended at 492 C may be

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Abou-Melha et al. stages. The first stage at the temperature range of 54–147.8 C and corresponds with the removal of 3H2O by 7.93 (calcd. 8.09%) weight loss. The second degradation stage represents the removal of a major organic part (C23H39O3 C 0.5Cl2) by 59.74 (calcd. 59.76%) weight loss. The residual part recorded at lower temperature (411.7 C) and also leads to the presence of heavy organic part (C3H5NSO4) directly chelates with Cu atom by 32.33 (calcd. 32.15%).

1.0 0.5 0.0

0

1000

2000

3000

4000

5000

6000

-0.5 -1.0

Kinetic Measurements To access the influence of the structural properties of the ligand and the thermal behavior of the complexes, the order, n, and the heat of activation E of the various decomposition stages were determined from the TG and DTG thermograms using the Coats-Redfern[25] equations in the following forms:

-1.5

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-2.0

Fig. 5. The ESR spectrum of Cu(II) complex in solid state.

displaying the expel of C18H30O3 (an organic moiety) by 41.38 (calcd. 41.27%) weight loss. The final degradation stage ended at 719 C may be representing the expel of C4H7 by 7.36 (calcd. 7.72%) weight loss. The residue recorded at 719 C is displaying 31.45 wt%, which may be due to the presence of remaining organic part (C4H7SO4N) directly chelates with central atom. The TG curve of [Co(NO3)(H4L)3H2O]2H2O complex displays five degradation stages. The first one is found in the temperature range of 62–135 C and corresponds to 5.55 (calcd. 5.15%) weight loss. The second degradation stage ended at 243 C corresponds to the removal of coordinating water molecules by 7.28 (calcd. 7.7%) weight loss. The third stage ended at 389.5 C may represent the removal of an organic part (C7H12O) by 16.3 (calcd. 16.04%) weight loss. The fourth stage ended at 476 C may correspond with the removal of C9H4O2 by21.95 (calcd. 22.06%) weight loss. The final degradation stage ended at 668 C may correspond with the removal of C8H13NO C 0.5Cl2 by 24.39 (calcd. 24.98%) weight loss. The residual part was recorded at 668 C may be corresponding to the presence of an organic part directly chelates with central atom [C2H5SO3 CCo] by 24.53 (calcd. 24.04%) weight loss. The TG curve of [NiCl(H4L)3H2O] complex represents two degradation stages. The first stage at the temperature range of 102–150 C represents the removal of coordinating water molecules by 8.29 (calcd. 8.15%) weight loss. The second degradation stage ending at 434 C represents the removal of a major mass percentage and may be corresponding to the expel of C19H31O3 C0.5Cl2 by 51.71 (calcd. 51.70%). The residual part is recorded at lower temperature (434 C), so the residue includes heavy organic part chelates with the central atom[(C7H13O4SN) C Ni] by 40.0 (calcd. 40.2%) weight percentage. The TG curve of [CuCl (H4L)H2O]2H2O complex is displaying two degradation

ln; ; ; 1 ¡ ; 1 ¡ / j: ¡ 1 ¡ n: ¡ ; 1 ¡ n:; T ¡ 2 . . . D ; M ¡ T : C B for n 6¼ 1

(1)

ln; ; ¡ lnð1 ¡ / Þ ¡ ; T ¡ 2 . . . D ; M ¡ T : C B for n D 1 (2) where M D ¡E/R and B D lnAR/FE; E, R, A, and F are the heat of activation, the universal gas constant, pre-exponential factor, and heating rate, respectively. The correlation coefficient, r, was computed using the least square method for different values of n, by plotting the left-hand side of Eqs. 1 or 2 versus 1000/T (Figure 4). The n value, which gave the best fit (r1), was chosen as the order parameter for the decomposition stage of interest. From the intercept and linear slope of such stage, the A and E values were determined. The other kinetic parameters, DH, DS, and DG were computed using the relationships; DH D E¡RT, DS D R[ln(Ah/kT)¡1], and DG D DH¡TDS, respectively, where k is the Boltzmann constant and h is the Planck constant. The kinetic parameters are listed in Table 5. The following remarks can be pointed out. First, all complexes’ decomposition stages show a best fit for (n D 1), indicating a first-order decomposition in all cases. Other n values (e.g. 0,0.33 and 0.66) did not lead to better correlations. Second, the value of DG increases significantly for the subsequently decomposition stages of a given complex. This is due to increasing the values of TDS significantly from one stage to another which overrides the values of DH. Increasing the values of DG of a given complex as going from one decomposition step subsequently to another reflects that the rate of removal of the subsequent ligand will be lower than that of the precedent ligand.[26,27] This may be attributed to the structural rigidity of the remaining complex after the

Table 6. ESR data of Cu(II) complex at room temperature Complex [CuCl(H4L) H2O]2H2O

gjj

g?

f

A £ 10¡4 (cm¡1)

G

a2

b2

2.133

2.096

137.6

155

1.39

0.641

0.56

891

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Series of Taurocholic Acid Complexes

Fig. 6. The SEM images of Cr(III) (A), Fe(III) (B), Co(II) (C), Ni(II) (D), and Cu(II) (E) complexes.

expulsion of one and more surrounding compounds, as compared with the precedent complex, which require more energy, TDS, for its rearrangement before undergoing any compositional change. Third, the negative values of

activation entropies DS indicate a more ordered activated complex than the reactants and/or there actions are slow.[28] Last, the positive values of DH mean that the decomposition processes are endothermic.

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892

Abou-Melha et al. with g11>g&boxhuh;>2.0023, while giving 2A1g with g?>g11>2.0023 if the unpaired electron lies in the dz2 orbital. From the observed values, g11(2.133) > g?(2.096) > 2.0023, indicating that the copper site has a dx2-y2 ground state characteristic for a square pyramidal or octahedral geometry.[29] In axial symmetry, the g values are related by: G D (g11-2)/(g?-2) D 4, if G > 4, the exchange interaction between copper(II) centers in the solid state is negligible, whereas when G < 4, a considerable exchange interaction is indicated. The G value (1.39) of the complex suggests the presence of considerable exchange coupling between copper(II) centers in the solid state.[30] The tendency of A11 to decrease with increasing g11 is an index for the increase of the tetrahedral distortion in the coordination sphere of Cu.[31] To quantify the degree of distortion of the Cu(II) complexes, the f factor, g11/A11 (an empirical index of tetrahedral distortion),[32] was selected from the EPR spectrum. Although its value ranges between 105 and 135 for square planar complexes, the values can be much larger in the presence of a tetrahedral distorted structure. For the investigated complex, the g11/ A11 quotient is 137.6 cm¡1 supporting the presence of significant dihedral angle distortion in the xy-plane and indicating a tetrahedral distortion from square-planar geometry. Molecular orbital coefficients, a2 (covalency of the in-plane s-bonding) and b2 (covalency of the in plane p-bonding) were calculated using the following equations[33,34];

a2 D .A j j =0:036/ C .g j j ¡ 2:0023/ C 3=7.g? ¡ 2:0023/ C 0:04 b2 D .g j j ¡ 2:0023/E= ¡ 8la2 Fig. 7. The molecular modeling structures of some isolated complexes.

Electron Spin Resonance The spin Hamiltonian parameters for Cu(II) complex (S D 1/2, I D 3/2) were calculated. The g tensor values can be used to derive the ground state. In square-planar or square pyramidal complexes, the unpaired electron lies in the dx2-y2 orbital giving 2B1g as the ground state

where λ D –828 cm¡1 for the free copper ion and E is the electronic transition energy. From Table 6, the a2 value (0.64) is found to be higher than b2 (0.56), indicating more covalent character of p -bonding. The data agree with other reported values.[35] Superhyperfine structure is not seen at higher field, ruling out any interaction of the nuclear spins of the CHO with the electron density on Cu(II). Furthermore, it has been reported that g11 is 2.4 for copper-oxygen bonds and 2.3 for copper-nitrogen bonds; in the studied complex, the g11 is 2.3 in conformity with nitrogen metal bonds. Finally, the powder

Table 7. Antiviral activities of six chemical substrates against TMV Tested chemical substrates -ve Control Cve Control Substrate 1 Substrate 2 Substrate 3 Substrate 4 Substrate 5 Substrate 6

Percent of inhibition

Antiviral activities: percent of infection

No. NLL

000 430 20 110 48 244 125 72

00.00 100.00 04.65 25.58 11.16 56.74 29.07 16.74

00.00 00.00 95.35 74.42 88.84 43.26 70.93 83.26

Substrate no. 1, ligand; no. 2, Cr(III) complex; no. 3, Ni(II) complex; no. 4, Cu(II) complex; no. 5, Fe(III) complex; no. 6, Co(II) complex.

Series of Taurocholic Acid Complexes

893

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Fig. 8. Percentagess of infection and inhibition of six chemical substrates evaluated for their antiviral activities against TMV.

ESR (Figure 5) spectrum of the copper(II) complex as well as the g values agree with distorted octahedral copper(II) complex.[36]

SEM The morphology and particle size of all investigated complexes were obtained from SEM. Cr(III, Fe(III), Co(II), and Ni(II) have the same shapes (Figure 6). It is clear that these complexes have uniform matrix and homogeneity. The microstructure, surface morphology and chemical composition of HL complexes were studied using SEM with EDS. Typical scanning electron micrographs are shown in Figure 6. The surface morphology of SEM micrograph reveals the well-sintered nature of the complexes with variant grain sizes and shapes. Clear large grains are obtained with agglomerates for all complexes. The distribution of the grain size is inhomogeneous except for the copper(II) complex (Figure 6E), complex where medium to small particles of nearly same size and polyhedral shape with 3 mm are obtained. The EDX analysis confirms that all surface concentrations correspond, within §2.0 mol%, to the expected stoichiometric values of the complexes composition.

Biological Investigation Data in Table 7 and Figure 8 show that the six tested substrates were varied in their antiviral activities against TMV. The substrate 1 showed the highest (95.35%) inhibition against TMV followed by substrate 3 (88.84%) and substrate 6 (83.26%). Substrates two (74.42) and five (70.93) showed moderate antiviral activities. The lowest antiviral activity was obtained using the substrate four (43.26%). According to Overtone’s concept and chelation theory[38] of cell permeability, the lipid membrane that surrounds the cell favors the passage of only lipid soluble materials due to which liposolubility is an important factor that controls antimicrobial activity. On chelation, the polarity of the metal ion is reduced to a greater extent due to the overlap of the ligand orbital and partial sharing of the positive charge of the metal ion with donor groups. Further, it increases the delocalization of p-electrons over the whole chelate ring and enhances the lipophilicity of the complex. The increased lipophilicity enhances the penetration of the complexes into lipid membranes and blocking the metal binding sites on the enzymes of the microorganism. Also, however the metal salts alone exhibit a higher activity than the investigated complexes but cannot use as antibacterial agents because of their toxicity and the probability of binding to the free ligands presented in the biological systems such as the nitrogen bases of nucleic acid and proteins.

Molecular Modeling Structures An attempt to gain a better insight on the molecular structure of the ligand and its complexes geometry optimization and conformational analysis has been performed by the use of MMC[37] force field as implemented in HyperChem 7.5 (Figure 7).[37] The drawn modeling structure of the free ligand displays the stable stereo structure includes the lowest energy level (total energy D 72.23 kcal/mol) in between others may be proposed. This arrangement of sites welling to coordination may support the mode of coordination proposed in the investigated complexes. The optimized geometry for the investigated complexes was supported by the calculation of their lowest energies as follows: Cr(III) is 69.29, Fe(III) is 66.68, Co(II) is 68.44, Ni(II) is 65.42, and Cu(II) is 61.67 kcal/mol. The data reflect the relative stability for the proposed geometry in comparing with their free ligand.

Conclusion A series of taurocholic acid complexes was prepared. All the possible tools were used for investigating the isolated complexes. The IR and Raman spectral data reveal the coordination of acid as mononegative bidentate. The electronic spectral data as well as the magnetic moment measurements proposed the octahedral geometry for all investigated complexes. The attachment of water molecules was supported by thermal analysis study. ESR spectrum of Cu(II) complex was carried out and acting as a further supporting for the octahedral geometry. The molecular modeling was performed for all complexes to assert on the lower energy content for all isolated complexes in comparing with their free ligand. Such concludes the comparative stability of all

894 isolated complexes. SEM for Cu(II) complex revealed their particle size is presented in the nano range. An elaborated biological investigation was carried out and reveals the highest antiviral activity of the free ligand and its Ni(II) and Co (II) complexes.

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