Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 151 (2015) 322–334

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Synthesis, characterization, DNA binding and catalytic applications of Ru(III) complexes A.F. Shoair ⇑, A.R. El-Shobaky, E.A. Azab 1 Chemistry Department, Faculty of Science, Damietta University, Damietta 34517, Egypt

g r a p h i c a l a b s t r a c t

 Synthesis of some azo pyridine

0.9

(4) 0.8

Absorbance

derivatives.  Studying the molecular and electronic structures.  Studying the CT-DNA binding of the compounds.  Studying the catalytic oxidation of benzyl alcohol.

2 DNA/ (ε -ε ) x 10-8 M cm a f

h i g h l i g h t s

1.0x10-6 8.0x10-7 6.0x10-7 -7

4.0x10

2.0x10-7 0.0

0.7

-7

-2.0x10 0.0 3.0x10-56.0x10-59.0x10-51.2x10-4

[DNA] x 10-6 M

0.6

0.5

0.4

400

450

500

550

600

Wavelength (nm)

a r t i c l e

i n f o

Article history: Received 7 November 2014 Received in revised form 4 June 2015 Accepted 6 June 2015 Available online 25 June 2015 Keywords: Ru(III) complexes DNA binding Quantum chemical parameters Catalytic oxidation

a b s t r a c t A new series of azodye ligands 5-chloro-3-hydroxy-4-(aryldiazenyl)pyridin-2(1H)-one (HLn) were synthesized by coupling of 5-chloro-3-hydroxypyridin-2(1H)-one with aniline and its p-derivatives. These ligands and their Ru(III) complexes of the type trans-[Ru(Ln)2(AsPh3)2]Cl were characterized by elemental analyses, IR, 1H NMR and UV–Visible spectra as well as magnetic and thermal measurements. The molar conductance measurements proved that all the complexes are electrolytes. IR spectra show that the ligands (HLn) acts as a monobasic bidentate ligand by coordinating via the nitrogen atom of the azo group (AN@NA) and oxygen atom of the deprotonated phenolic OH group, thereby forming a six-membered chelating ring and concomitant formation of an intramolecular hydrogen bond. The molecular and electronic structures of the investigated compounds (HLn) were also studied using quantum chemical calculations. The calf thymus DNA binding activity of the ligands (HLn) and their Ru(III) complexes were studied by absorption spectra and viscosity measurements. The mechanism and the catalytic oxidation of benzyl alcohol by trans-[Ru(Ln)2(AsPh3)2]Cl with hydrogen peroxide as co-oxidant were described. Ó 2015 Elsevier B.V. All rights reserved.

1. Introduction Azo compounds are very important molecules and have attracted much attention in both academic and applied research [1]. Azo compounds consists of at least a conjugated chromophore azo (AN@NA) group in association with one or more aromatic or heterocyclic system. Commercially, these colorants are the largest ⇑ Corresponding author. 1

E-mail address: [email protected] (A.F. Shoair). Abstracted from her M.Sc. Thesis.

http://dx.doi.org/10.1016/j.saa.2015.06.011 1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

and most versatile class of organic dyestuffs [2]. The widest usage of the azodyes is due to the number of the variations in the chemical structure and the methods of application which are generally not complex. Arylazo pyridine dyes generally have a high molar extinction coefficient, medium to high light and wash fastness properties [3]. In recent years, azodyes have attracted wide interest and found many uses in various fields such as dyeing of textile fibers, coloring of different materials, biological–medical studies, organic synthesis and advanced applications including optical storage capacity, optical switching, holography and non-linear optical properties [4,5].

A.F. Shoair et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 151 (2015) 322–334

R

i) HCl

NH2

+

R

ii) NaNO2

N

Ru(III) complexes are discussed by different spectroscopic techniques. The calf thymus DNA binding activity of the ligands (HLn) and their Ru(III) complexes are studied by absorption spectra and viscosity measurements. The optimized bond lengths, bond angles and calculated the quantum chemical parameters for the ligands (HLn) are investigated. The Ru(III) complexes are tested as a catalysts for the oxidation of benzyl alcohol with hydrogen peroxide as co-oxidant at room temperature.

-

NCl

0-5 oC

Cl

HN

OH O

Cl

Cl N

N N

R HN

N

323

N

2. Materials and methods

R

OH

OH

2.1. Materials and apparatus

O

OH

Keto form

Enol form

(B)

(A)

Cl N HN

N

R

H

O O

(C)

R= -OCH3 (HL1), -CH3 (HL2), -H (HL3), -Cl (HL4) and –NO2 (HL5) Fig. 1. Structure of the investigated ligands (HLn).

Furthermore, azodyes with hydroxyl group at para to azo band display tautomerism depending on the proton transfer. Determination and characterization of tautomeric equilibrium are interesting and extensively studied during the recent decades using both theoretical calculations and experimental approaches [6–8]. Azo compounds and their metal complexes are known to be involved in a number of biological reactions, such as inhibition of DNA, RNA, and protein synthesis, nitrogen fixation and carcinogenesis [9,10]. The chemistry of ruthenium complexes is of significant importance [11,12], because of the fascinating reactivates exhibited by the resultant complexes and the nature of the ligands that dictates the property of those complexes. Ruthenium compounds have been the subject of great interest and impressive development in last decades for many reasons, especially due to their catalytic [13–15], anticancer activities and DNA [16–19]. The Ruthenium complexes have applications in the fields of biochemistry, photochemistry and photophysics [20,21]. The last few decades have seen an increased interest in ruthenium(II) polypyridyl complexes as building blocks in supramolecular devices due to their favorable excited state and redox properties as well as structural probes for DNA. Ruthenium complexes are also showing promising results in anti-tumor activity and they target a broad spectrum of cancers [22,23]. In this paper, the synthesis and characterization of 5-chlor o-3-hydroxy-4-(aryldiazenyl)pyridin-2(1H)-one (HLn) and their

AsPh3 O

N

Cl

Ru O

N AsPh3

Fig. 2. Structure of Ru(III) complexes (1–5).

All reagents were purchased from Aldrich, Fluka and Merck and were used without any further purification. CT-DNA was purchased from SRL (India). Double distilled water was used to prepare all buffer solutions. Microanalytical data (C, H and N) were collected on Automatic Analyzer CHNS Vario ELIII, Germany. Spectroscopic data were obtained using the following instruments: FTIR spectra (KBr discs, 4000–400 cm1) by Jasco FTIR-4100 spectrophotometer; the 1H NMR spectra by Bruker WP 300 MHz using DMSO-d6 as a solvent containing TMS as the internal standard. UV–Visible spectra by Perkin–Elmer AA800 spectrophotometer Model AAS. Thermal analysis of the ligands and their Ru(III) complexes were carried out using a Shimadzu thermogravimetric analyzer under a nitrogen atmosphere with heating rate of 10 °C/min over a temperature range from room temperature up to 800 °C. Magnetic susceptibility measurements were determined at room temperature on a Johnson Matthey magnetic susceptibility balance using Hg[Co(SCN)4] as calibrant. Conductivity measurements of the complexes at 25 °C were determined in DMF (103 M) using conductivity/TDS meter model Lutron YK-22CT. Viscosity measurements were carried out using an Ostwald’s capillary viscometer, immersed in a thermostated water bath at 25 °C. The molecular structures of the investigated compounds were optimized by HF method with 3-21G basis set. The molecules were built with the Perkin Elmer ChemBio Draw and optimized using Perkin Elmer ChemBio3D software [24,25].

2.2. Synthesis of azodye ligands (HLn) The azodye ligands (Fig. 1), 5-chloro-3-hydroxy-4-(aryldiazeny l)pyridin-2(1H)-one (HLn) were prepared by coupling of 5-chloro-3-hydroxypyridin-2(1H)-one with aniline and its p-derivatives [26]. A stoichiometric amount of aniline or its p-derivatives (0.01 mol) in 25 ml of hydrochloric acid (0.01 mol) was added dropwise to a solution of sodium nitrite (0.01 mol) in 20 ml of water at 5 °C. The formed diazonium chloride was consecutively coupled with an alkaline solution of 5-chloro-3-hydroxypyridin2(1H)-one (0.01 mol) in alkaline solution. The colored precipitate, which was formed immediately, was filtered through sintered glass crucible, washed several times with water and methanol then dried in a vacuum desiccator over anhydrous CaCl2. The product was purified by recrystallization from methanol. The resulting formed ligands are: HL1 = 5-Chloro-3-hydroxy-4-(4-methoxyphenyldiazenyl)pyridin-2(1H)-one. HL2 = 5-Chloro-3-hydroxy-4-(4-methylphenyldiazenyl)pyridin2(1H)-one. HL3 = 5-Chloro-3-hydroxy-4-(phenyldiazenyl)pyridin-2(1H)-one. HL4 = 5-Chloro-3-hydroxy-4-(4-chlorophenyldiazenyl)pyridin2(1H)-one. HL5 = 5-Chloro-3-hydroxy-4-(4-nitrophenyldiazenyl)pyridin2(1H)-one.

324

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½RuCl3 ðAsPh3 Þ2 CH3 OH þ 2HLn ! ½RuðLn Þ2 ðAsPh3 Þ2 Cl

(a) HL 5

78

Yield (%)

2.4. DNA binding experiments 72

HL 3

66

60

HL 4

HL 1 HL 2

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

R σ HL 5

(b) 240

½DNA=ðea  ef Þ ¼ ½DNA=ðeb  ef Þ þ 1=Kb ðea  ef Þ HL 2

M.P. (°C)

230

HL 3 220

HL 4

HL 1

2.5. Viscosity measurements

190 -0.4

-0.2

ð1Þ

where [DNA] is the concentration of CT-DNA in base pairs, ea is the extinction coefficient observed for the Aobs/[compound] at the given DNA concentration, ef is the extinction coefficient of the free compound in solution and eb is the extinction coefficient of the compound when fully bond to DNA. In plots of [DNA]/(ea  ef) versus [DNA], Kb is given by the ratio of the slope to the intercept.

210

200

The binding properties of the ligands and their complexes to CT-DNA have been studied using electronic absorption spectroscopy. The stock solution of CT-DNA was prepared in 5 mM Tris–HCl/50 mM NaCl buffer (pH 7.2), which a ratio of UV absorbances at 260 and 280 nm (A260/A280) of ca. 1.8–1.9, indicating that the DNA was sufficiently free of protein [28], and the concentration was determined by UV absorbance at 260 nm (e = 6600 M1 cm1) [29]. Electronic absorption spectra (200–700 nm) were carried out using 1 cm quartz cuvettes at 25 °C by fixing the concentration of ligand or complex (1.00  103 mol L1), while gradually increasing the concentration of CT-DNA (0.00–1.30  104 mol L1). An equal amount of CT-DNA was added to both the compound solutions and the references buffer solution to eliminate the absorbance of CT-DNA itself. The intrinsic binding constant Kb of the compound with CT-DNA was determined using the following Eq. (1) [30]:

0.0

0.2

0.4

0.6

0.8

R σ Fig. 3. The relation between Hammett’s substitution coefficient (rR) vs. (a) Yield (%) and (b) Melting point (°C) of ligands (HLn).

2.3. Synthesis of Ru(III) complexes (1–5) Ruthenium(III) complexes (Fig. 2) were synthesized according to the general procedure [27]: a stoichiometric amount of the desired ligand (0.02 mol) in methanol (20 cm3) was added dropwise to a hot methanol solution (20 cm3) of [RuCl3(AsPh3)2CH3OH] (0.01 mol) with stirring and the reaction mixture was refluxed for 3 h. The solution was concentrated to half of its original volume by evaporation and allowed to cool at room temperature. During this, a microcrystalline solid was separated, which was isolated by filtration, washed with hot methanol, ether and dried in a vacuum desiccator over anhydrous CaCl2:

Viscosity measurements were performed at compound concentration within the range of (0.2–2  104 mol L1) and each compound was added into a DNA solution (3  104 mol L1) present in the viscometer. The average flow times of three replicates were measured with a digital stopwatch. The data were presented as (g/go)1/3 versus [compound]/[DNA] ratio of the concentration of the compound to DNA [31], where g and go are the viscosity of the DNA in the presence and absence of complex, respectively [32]. The relative viscosities g were calculated using equation [33]:

g ¼ ðt  to Þ=to

ð2Þ

where t is the observed flow time of DNA containing solution and to is the flow time of buffer alone. 2.6. Catalytic oxidation of alcohols by trans-[Ru(Ln)2(AsPh3)2]Cl/H2O2 To a solution of the catalyst trans-[Ru(Ln)2(AsPh3)2]Cl (0.01 mmol) in 5 cm3 dimethyl formamide, benzyl alcohol (2 mmol) was added with stirring. Hydrogen peroxide (20 cm3,

Table 1 Physical properties and elemental analysis data of the ligands (HLn) and their Ru(III) complexes (1–5). Compound

Yield (%)

M.P. (°C)

HL1 [Ru(L1)2(AsPh3)2]Cl HL2 [Ru(L2)2(AsPh3)2]Cl HL3 [Ru(L3)2(AsPh3)2]Cl HL4 [Ru(L4)2(AsPh3)2]Cl HL5 [Ru(L5)2(AsPh3)2]Cl

60 59 60 71 65 74 67 72 78 65

195 150 228 90 223 110 220 135 245 100

(1) (2) (3) (4) (5)

% Calcd. (found) C

H

N

51.53(51.43) 55.85(55.70) 54.66(54.54) 56.55(55.90) 52.92(52.81) 55.89(55.01) 46.50(46.27) 52.96(51.19) 44.84(44.70) 52.13(51.90)

3.60(3.52) 3.75(3.60) 3.82(3.74) 3.80(3.66) 3.23(3.15) 3.56(3.49) 2.48(2.34) 3.22(3.54) 2.40(2.32) 3.17(2.98)

15.02(14.90) 6.51(6.40) 15.92(15.80) 6.60(6.80) 16.83(16.65) 6.74 (6.50) 14.79(14.64) 6.39(6.93) 19.02(18.88) 8.39(8.18)

A.F. Shoair et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 151 (2015) 322–334

comparing the IR spectra of ligands with those of their Ru(III) complexes, the following features can be pointed out:

(5)

Absorbance

0.9

(4)

(1) 0.6

0.3

(2) (3)

400

325

500

600

Wavelength (nm) Fig. 4. Electronic spectra of the Ru(III) complexes (1–5).

Table 2 Electronic spectral data for the Ru(III) complexes (1–5). Complex

d–d transition (nm)

Charge transfer (nm)

(1) (2) (3) (4) (5)

592 590 586 595 605

493 486 488 494 515

30%) was then added dropwise within half an hour and the reaction mixture was further stirred for 3 h at room temperature. The mixture was reduced in vacuo and the residues were collected in diethylether, filtered through a bed of silica gel and dried over anhydrous MgSO4. The carbonyl compounds formed were isolated and quantified as their 2,4-dinitrophenylhydrazone derivatives [6]. 3. Results and discussion The results of physical properties of the prepared ligands (HLn) and their Ru(III) complexes (1–5) along with their elemental analyses are collected in Table 1. The analytical data of Ru(III) complexes indicated that the complexes have 1:2 (metal:ligand) stoichiometry. The Ru(III) complexes are stable in air and soluble in most common organic solvents. The molar conductance values for the ruthenium(III) complexes (103 M) are measured in DMF and these values are (34–68 O1 cm2 mol1) range indicating the electrolytic nature of the complexes (presence of Cl ion) [9,34]. The room temperature magnetic moment values (leff) per ruthenium ion for the complexes were in 1.69–2.10 BM range. These values lies within the range of the spin only value of one unpaired electron [35], which corresponds to Ru3+ state (low spin). As shown in Table 1, the values of yield (%) and/or melting point are related to the nature of the p-substituent as they increase according to the following order p-(NO2 > Cl > H > CH3 > OCH3). This can be attributed to the fact that the effective charge increased due to the electron withdrawing p-substituent (HL4 and HL5) while it decreased by the electrons donating character of (HL1 and HL2). This is in accordance with that expected from Hammett’s constant (rR) as shown in Fig. 3, correlate the yield (%) and/or melting point values with rR it is clear that all these values increase with increasing rR. 3.1. IR spectra The FTIR spectra provide valuable information regarding the nature of the functional group attached to the metal atom. By

(1) The broad and strong intensity band due to m(OH) group which appear in the 3425–3450 cm1 region arises from the strong intra and intermolecular hydrogen bonding (Fig. 1C) of the free ligands [36]. (2) The two bands corresponding to m(NH) of pyridine and m(C@O) which appeared in the spectra of the ligands at 3280–3300 and 1620–1635 cm1 regions, respectively, appeared almost at the same position in the spectra of their Ru(III) complexes [37], which can be taken as evidence that NH (pyridine) and C@O groups are not taking part in the coordination to the Ru center. (3) The bands due to m(N@N) group which appeared in the spectra of the ligands at 1608–1644 cm1 region were shifted to lower wavenumbers by 4–12 cm1 indicating their coordination to the Ru center [11,25]. (4) The medium band corresponding to phenolic oxygen to m(CAO) which appeared in the spectra of the ligands at 1299–1330 cm1 disappear for all the complexes indicating that, the ligands coordinate through their deprotonated form and formation metal–oxygen bonds [11,38]. This can be taken as an indication for the complete removal of hydrogen of OH-group by the Ru(III) ion reacting with the ligands. (5) In addition, new bands were observed in the regions 512– 560 and 466–474 cm1 which were assigned to the formation of RuAO and RuAN bonds, respectively [39]. This further supports the coordination of the nitrogen atom of the azo group (AN@NA) and oxygen atom of the deprotonated phenolic OH (Fig. 1A). (6) The bands at 3050–3180 and 3830–2930 cm1 regions are assigned to m(CAH) vibrations of the aromatic system in the spectra of the ligands and their complexes, respectively [40–43]. Intramolecular hydrogen bonds in the ligands involving OH group with the AN@NA group increased their stabilities through ring structure (Fig. 1C) [44–47]. The strength of the hydrogen bond of compounds depends on the nature of substituents present in the coupling component from the arylazo group. 3.2. Electronic spectra The electronic spectra of all complexes (1–5) were recorded in dimethylformamide solvent in the range of 300–700 nm. The spectral data are listed in Table 2 and show in Fig. 4. The ground state of ruthenium(III) ion (t52g-configuration) is 2T1g and the first excited doublet levels, in order of increasing energy, are 2A2g and 2T1g arising from t42g e1g configuration. Bands that were observed in 586– 605 nm region have been assigned to d–d transitions, while bands in the 488–515 nm region have been assigned to charge transfer transitions. These features indicate a low-spin octahedral geometry around Ru(III) ion [48]. 3.3. 1H NMR spectrum The 1H NMR spectrum of ligand (HL3) as an example in DMSO-d6 showed a singlet signal at d 6.61 ppm due to C6-H pyridine, multiplet signal at d 7.11–7.16 ppm attributable to C4-H phenyl, dd signal at d 7.36–7.37 ppm (j = 7.8, 1.5 Hz) due to C2-H and C6-H phenyl, ddd signal at d 7.41–7.51 ppm (j = 7.8, 7.5, 1.5 Hz) as a result of C3-H and C5-H phenyl and two singlet signals (D2O-exchangable) at d 9.80 and 10.60 ppm due to OH and NH, respectively [35].

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3.4. Molecular structure

g¼

The molecular structures of the ligands (HLn) were optimized by HF method with 3–21G basis set. The molecules were built with the Perkin Elmer ChemBioDraw and optimized using Perkin Elmer ChemBio3D software. The geometrical parameters bond lengths and bond angles of HLn are calculated and the calculated molecular structures for HLn are shown in Fig. 5. Molecular structures (HOMO & LUMO) for HLn are presented in Fig. 6. The HOMO–LUMO energy gap, DE, which is an important stability index, is applied to develop theoretical models for explaining the structure and conformation barriers in many molecular systems. The smaller is the value of DE, the more is the reactivity of the compound has [25,49]. The calculated quantum chemical parameters are given in Table 3. Additional parameters such as separation energies, DE, absolute electronegativities, v, chemical potentials, Pi, absolute hardness, g, absolute softness, r, global electrophilicity, x [48], global softness, S, and additional electronic charge, DNmax, have been calculated according to the following Eqs. (3–10):

DE ¼ ELUMO  EHOMO

v¼

ðEHOMO þ ELUMO Þ 2

ELUMO  EHOMO 2

ð5Þ

r ¼ 1=g

ð6Þ

Pi ¼ v

ð7Þ

1 2g

ð8Þ

x ¼ Pi2 =2g

ð9Þ

S¼

DNmax ¼ Pi=g

ð10Þ

The value of DE for ligands HL1, HL2, HL3, HL4 and HL5 was found 0.0876, 0.0968, 0.1026, 0.0846 and 0.1629 a.u., respectively. The calculations indicated that the HL4 is more stable form than the other ligands [49]. The relation between Hammett’s substitution coefficients (rR) vs. energy gap (DE) as shown in Fig. 7. It is clear that that the values increase with increasing rR.

ð3Þ

3.5. Thermal analyses

ð4Þ

The thermal properties of ligands (HL2, HL3 and HL5) and their Ru(III) complexes (2, 3 and 5) were characterized on the basis of

Fig. 5. The calculated molecular structures of the investigated ligands (HLn).

A.F. Shoair et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 151 (2015) 322–334

327

Table 4. It is clear that the change of substituent affects the thermal properties of the ligands. HL2 ligand shows two decomposition steps, the first stage occur in the temperature range 50–246 °C is attributed to Loss of C6H7 (Found 33.33% and calc. 29.85%). The second stage in the temperature range 246–800 °C corresponding to loss of a part of the ligand (C6H2N3O2Cl) (Found 69.67%, calc. 69.33%). HL3 ligand shows loss of (Found 24.68%, calc. 24.63%) in the temperature range 50–250 °C corresponding to loss of C2H2 + ½Cl2 while the weight loss in the temperature range 250– 800 °C (Found 67.26%, calc. 65.69%), which is attributed to loss of a part of the ligand (C7H6N3O2). Finally, the residue is carbon atoms. TG curve of the HL5 ligand shows two steps of decomposition. The first stage of decomposition occur in the temperature range of 50–470 °C and are associated with the loss of a part of the ligand (C6H5N2O2) with an estimated weight loss of 46.93% (calcd. 45.99%). The second stage of decomposition occur in the temperature range of 470–800 °C and are associated with the loss of CH2N2O2Cl molecule and with an estimated weight loss of 38.50% (calcd. 37.04%). There after the weight of the residue corresponds to carbon atoms. All Ru(III) complexes (2, 3 and 5) showed TG curves in the temperature range 100–390 °C loss of 2(AsPh3) molecules. The second stage is related to loss of the part of ligand. The final weight losses are due to the decomposition of the rest of the ligand and metal oxides residue (Table 5). 3.6. Calculation of activation thermodynamic parameters The thermodynamic activation parameters of decomposition processes of the ligands (HL2, HL3 and HL5) and their Ru(III) complexes (2, 3 and 5) namely activation energy (Ea), enthalpy (DH*), entropy (DS*), and Gibbs free energy change of the decomposition (DG*) are evaluated graphically by employing the Coast–Redfern [50] and Horowitz–Metzger [51] methods. 3.6.1. Coast–Redfern equation The Coast–Redfern equation, which is a typical integral method, can represent as:

Z

a

0

dx A ¼ ð1  aÞn u

Z

T2

T1

  Ea dt exp  RT

ð11Þ

For convenience of integration, the lower limit T1 usually taken as zero. This equation on integration gives:

    lnð1  aÞ Ea AR ¼  ln  þ ln RT uEa T2

ð12Þ

A plot of left-hand side (LHS) against 1/T was drawn (Fig. 8). Ea is the energy of activation in J mol1 and calculated from the slope and A in (s1) from the intercept value. The entropy of activation (DS⁄) in (J mol1 K1) calculated by using the equation:

   Ah R DS ¼ 2:303 log kB T s

ð13Þ

where kB is the Boltzmann constant, h is the Plank’s constant and Ts is the TG peak temperature.

Fig. 6. The Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) of the investigated ligands (HLn).

thermogravimetric analysis (TGA). The temperature intervals and the percentage of loss of masses of the ligands are listed in

3.6.2. Horowitz–Metzger equation The Horowitz–Metzger equation is an illustrative of the approximation methods. These authors derived the relation:

log

" # 1  ð1  aÞ1n Ea h ¼ ; for n–1 1n 2:303RT 2s

ð14Þ

328

A.F. Shoair et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 151 (2015) 322–334

Table 3 The calculated quantum chemical parameters for the investigated ligands (HLn). Compound HL1 HL2 HL3 HL4 HL5

EHOMO (a.u.)

ELUMO (a.u.)

DE (a.u.)

v

g

r

(a.u.)

(a.u.)-1

Pi (a.u.)

S (a.u.)-1

x

(a.u.)

0.1488 0.1579 0.1636 0.1455 0.2279

0.0612 0.0611 0.0610 0.0609 0.0650

0.0876 0.0968 0.1026 0.0846 0.1629

0.1050 0.1095 0.1123 0.1032 0.1464

0.0438 0.0484 0.0513 0.0423 0.0815

22.8284 20.6612 19.4989 23.6407 12.2745

0.1050 0.1095 0.1123 0.1032 0.1464

11.4142 10.3306 9.7494 11.8203 6.1372

0.1259 0.1239 0.1229 0.1259 0.1316

HL 5

ΔE (a.u.)

0.14

0.12

Complexa

Temp. range (°C)

Found mass loss (calc.)%

Assignment

(2)

100–390 390–800 >800 100–340 340–470 >800 100–290 290–800 >800

48.27 38.71 11.05 49.87 33.29 16.84 28.87 42.17 27.83

Loss of Loss of RuO2 Loss of Loss of Loss of Loss of Loss of Loss of

(3)

HL 2

HL 3

HL 1

(5)

HL 4

0.08 a

0.06 -0.4

-0.2

0.0

0.2

0.4

0.6

2.3976 2.2626 2.1894 2.4395 1.7975

Table 5 The thermal analyses data for Ru(III) complexes.

0.16

0.10

DNmax

(a.u.)

0.8

(48.07) (38.87) (10.44) (49.14) (31.53) (16.46) (28.52) (46.25) (27.29)

2(AsPh3) C24H18N6O2Cl2 2(AsPh3) C16H14N6O2Cl2 carbon atoms + RuO2 (AsPh3) + As Ph3 + C8H12N8O6Cl2 carbon atoms + RuO2

Numbers as given in Table 1.

DG ¼ DH  T DS

R σ

ð18Þ ⁄

Fig. 7. The relation between Hammett’s substitution coefficients (rR) vs. energy gap (DE).

⁄

⁄

The calculated values of Ea, A, DS , DH and DG for the decomposition steps for ligands (HL2, HL3 and HL5) are summarized in Table 6. 3.7. DNA binding studies

Table 4 The thermal analyses data for the ligands. Compound

Temp. range (°C)

Found mass loss (calc.)%

Assignment

HL2

50–246 246–800

33.33 (29.96) 69.67 (69.59)

Loss of C6H7 Loss of C6H2N3O2Cl

HL3

50–250 250–800 >800

24.68 (24.63) 67.26 (65.69) 7.15 (9.61)

Loss of C2H2 + ½Cl2 Loss of C7H6N3O2 Loss of carbon atoms

HL5

50–470 470–800 >800

46.93 (46.50) 38.50 (37.16) 14.10 (16.23)

Loss of C6H5N2O2 Loss of CH2N2O2Cl Loss of carbon atoms

when n = 1, the LHS of Eq. (14) would be log[log(1  a)] (Fig. 9). For a first order kinetic process, the Horowitz–Metzger equation may write in the form:

   Wa Ea h ¼ log log  log 2:303 Wc 2:303RT 2s

ð15Þ

where h = T  Ts, wc = wa  w, wa = mass loss at the completion reaction; w = mass loss up to time t. The plot of log [log (wa/wc)] vs. h was drawn and found to be linear from the slope of which Ea was calculated. The pre-exponential factor, A, calculated from equation:

Ea RT 2s

¼h

A  i u exp  RTEas

ð16Þ

The entropy of activation, DS⁄, is calculated from Eq. (13). The enthalpy activation, DH⁄, and Gibbs free energy, DG⁄, calculated from:

DH ¼ Ea  RT

ð17Þ

3.7.1. Electronic absorption studies The intrinsic binding constant to CT-DNA by monitoring the absorption intensity of the charge transfer spectral bands near 494, 488, 486, 494, 514 nm for the ligands (HL1–HL5), respectively and 484, 488, 484, 492, 514 nm for Ru(III) complexes (1–5), respectively were determined. The absorption spectra of these ligands and Ru(III) complexes with increasing concentration of CT-DNA in the range 300–700 nm are shown in Figs. 10 and 11, respectively. Upon the addition of increasing amount of CT-DNA, a significant ‘‘hyperchromic’’ effect was observed accompanied by a moderate red shift of 2–3 nm, indicative of stabilization of the DNA helix. These spectral characteristic suggest that the ligands and complexes bind either to the external contact (electrostatic binding) or to the major and minor grooves of DNA. Moreover, this ‘‘hyperchromic effect’’ can be explained on the basis of two phenomena. Firstly, the large surface area of the ligand as well as presence of planar aromatic chromophore facilitates a strong binding interaction of the ligands with CT-DNA there by, providing ample opportunity for the complex to bind with the CT-DNA via, partial insertion of the aromatic moiety in between the stacking base pair. This groove binding results in structural reorganization of CT-DNA which entails partial unwinding or damage of the double helix at the exterior phosphate backbone leading to the formation of a cavity to accommodate the complex [52]. The intrinsic binding constants (Kb) of all the ligands (HL1–HL5) and Ru(III) complexes (1–5) with CT-DNA were determined (Eq. (1)) [53]. The Kb values obtained from the absorption spectral technique for ligands (HL1–HL5) were calculated as 2.526  105, 2.843  105, 3.842  105, 4.799  105 and 6.454  105 M1, respectively. The Kb values obtained from the absorption spectral technique for Ru(III) complexes (1–5) were calculated as 1.922  104, 2.099  104, 2.180  104, 2.385  104 and 2.879  104 M1, respectively. The binding constant of the complexes (1–5) are

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A.F. Shoair et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 151 (2015) 322–334 -11.5

-12.0

(2)

HL2

-12.5

-12.0

ln (-ln (1- α) / T2)

ln (-ln (1- α) / T2)

-13.0 -13.5 -14.0 -14.5 -15.0

-12.5

-13.0

-13.5

-15.5

170-370 oC

165-225 oC

-16.0

0.00200

0.00205

-14.0

0.00210

0.00215

0.00220

0.0016

0.00225

0.0018

0.0020

0.0022

-1

1/T (K )

-1 1/T (K ) -11

-11.5

(3)

HL 3

-12.0

-12

ln (-ln (1- α) / T2)

ln (-ln (1- α) / T2)

-12.5 -13.0 -13.5 -14.0 -14.5 -15.0 -15.5 -16.0

-13

-14

-15

190-330 oC

165-230 oC 0.00198

0.00204

-16

0.00210

0.00216

0.0017

0.00222

0.0018

0.0019

0.0020

0.0021

-1

1/T (K )

-1 1/T (K ) -12.0 -12

ln (-ln (1- α) / T2)

ln (-ln (1- α) / T2)

(5)

HL 5

-12.5

-13.0

-13.5

-14.0

-14.5

-14

140-290 oC

250-430 oC -15

-15.0 0.0014

-13

0.0015

0.0016

0.0017

0.0018

0.0019

-1

1/T (K )

0.0018

0.0019

0.0020

0.0021

0.0022

0.0023

-1 1/T (K )

Fig. 8. Coats–Redfern (CR) of the ligands (HL2, HL3 and HL5) and their Ru(III) complexes (2, 3 and 5).

comparatively lower than that of the ligands (HLn), may be due to the ligands considering that the phenolic AOH group may enhance their affinity towards DNA binding through formation of hydrogen bonding. The higher values of the binding constant of the ligands HL5 and HL4 are due to the presence of electron withdrawing group NO2 and Cl, respectively, as shown in Fig. 12. 3.7.2. Viscosity determination Viscosity measurements are proved to be least ambiguous to support a complex-DNA binding model, as these measurements are very much sensitive to length change [54]. When a small molecule intercalate between the DNA base pairs, it unwinds the DNA helix and hence increases lengthen it, resulting in significant increase in the viscosity of DNA solution. However, a partial and/or non-classical intercalation of ligand may bend the DNA helix, resulting in the decrease of its effective length and concomitantly

its viscosity [55]. The binding of the compounds with CT-DNA was further elucidated by measuring the relative specific viscosity of DNA after the addition of varying concentration of complexes. To further investigate the interaction mode of the binding mode of Ru(III) complexes (1–5) with DNA, a viscosity study was carried out at 25 °C as shown in Fig. 13. Viscosity experimental results clearly showed that the relative viscosity of CT-DNA increases steadily on addition of increasing concentration of Ru(III) complexes (1–5). The increased degree of viscosity, which may depend on its affinity to DNA follows the order of 2 > 5 > 3 > 4 > 1. This observation can be explained on the fact that, classical intercalation model demands that the DNA helix must lengthen as base pairs are separated to accommodate the binding complexes, leading to the increase of DNA viscosity, as for the behaviors of the known DNA intercalators.

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A.F. Shoair et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 151 (2015) 322–334 0.2

-0.2

HL2

-0.4

0.0

(2)

log [log (Wα/Wγ)]

log [log (Wα/Wγ)]

-0.6 -0.8 -1.0 -1.2 -1.4 -1.6

-0.2 -0.4 -0.6 -0.8

-1.8

165-225 oC

-2.0 -30

-20

-10

0

10

20

170-370 oC

-1.0 30

-80

-60

-40

-20

θ (K) 0.0 -0.2

20

40

60

80

100

0.4

HL3

(3) 0.0

log [log (Wα/Wγ)]

-0.4

log [log (Wα/Wγ)]

0

θ (K)

-0.6 -0.8 -1.0 -1.2 -1.4

-0.4

-0.8

-1.2

-1.6 -1.6

-1.8

190-330 oC

165-230 oC

-2.0

-2.0

-20

-10

0

10

20

30

-60

-40

-20

θ (K) 0.0

0

20

40

60

θ (K)

HL5

0.0

(5)

-0.2

log [log (Wα/Wγ)]

log [log (Wα/Wγ)]

-0.4 -0.6 -0.8 -1.0

-0.4

-0.8

-1.2

-1.2 -1.4

250-430 oC

-1.6 -72

-54

-36

-18

0

18

36

54

72

140-290 oC

-1.6 -60

90

-40

-20

0

20

40

60

θ (K)

θ (K)

Fig. 9. Horowitz–Metzger (HM) of the ligands (HL2, HL3 and HL5) and their Ru(III) complexes (2, 3 and 5). Table 6 Kinetic parameters of the ligands and their Ru(III) complexes. Compounda

a

Decomposition temperature (°C)

HL2

165–225

HL3

165–230

HL5

250–430

(2)

170–370

(3)

190–330

(5)

140–290

Numbers as given in Table 1.

Method

CR HM CR HM CR HM CR HM CR HM CR HM

Parameters

Correlation coefficient

Ea (kJ mol1)

A (s1)

DS ⁄ (J mol1 K1)

D H⁄ (kJ mol1)

DG ⁄ (kJ mol1)

131 139 143 150 51.2 61.1 28.1 36.5 70.1 78.2 51.7 60.1

1.32  1012 5.87  1013 3.38  1013 8.05  1014 3.11  101 5.24  102 7.44  101 8.13  10 2.29  104 2.50  105 8.31  102 1.36  104

1.67  101 1.49  101 1.03  101 3.66  101 2.22  102 1.99  102 2.52  102 2.32  102 1.66  102 1.46  102 1.93  102 1.70  102

127 135 139 146 46.1 56.0 23.6 32.0 65.7 73.7 47.6 56.0

135 128 134 128 182 178 161 158 154 152 142 139

0.98539 0.98734 0.99631 0.99387 0.98998 0.99116 0.97643 0.98488 0.99626 0.99562 0.98872 0.97719

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The result further suggests an intercalating binding mode of the compounds with DNA and also parallels the above spectroscopic results, such as hypochromism and red shift of the complexes in the presence of DNA. The information obtained from this study could be helpful to understand the mechanism of the interaction of small molecules with nucleic acids and should be useful in the development of potential probes of DNA structure and conformation. 3.8. Catalytic oxidation of benzyl alcohol to benzaldehyde Many ruthenium(III) complexes [56–58] have been used as catalysts for oxidation of benzyl alcohol to benzaldehyde with

different co-oxidants. However, catalytic methods based on transition metals need stringent reaction conditions and high cost of the ligand, or have the disadvantages like long reaction time and high temperature. Therefore, the development of practical, inexpensive, simple and green chemical process for oxidation is still needed. We are interested in the use of hydrogen peroxide, since it is cheap and sufficiently environment-friendly to be used on a commercial scale [27]. Herein, thus we present a simple protocol that adopts aqueous 30% hydrogen peroxide as a co-oxidant and the prepared ruthenium(III) complexes as a catalysts for oxidation of benzyl alcohol to benzaldehyde 70–85% yield. The catalytic oxidation 0.8

10

0.8

14

HL2

12

9

10

0.7

8 7 6

1

2

3

4

5

[DNA] x 10-6 M

Absorbance

Absorbance

HL1

2 DNA/ (ε -ε ) x 10-8 M cm a f

2 DNA/ (ε -ε ) x 10-8 M cm a f

1.0

0.6

8 6 4 2 0

0

1

2

3

[DNA] x 10-6 M

0.6 0.5

0.4 400

450

500

550

0.4 400

600

450

HL3

HL4

40

4

2

10

0.8

0

0

3

6

9

12

15

[DNA] x 10-6 M

0.7 0.6

Absorbance

Absorbance

20

0.9

600

6

0.7

30

1.0

550

2 DNA/ (ε -ε ) x 10-8 M cm a f

2 DNA/ (ε -ε ) x 10-8 M cm a f

1.1

500

Wavelength (nm)

Wavelength (nm)

0.6

0

0

3

6

9

12

15

18

[DNA] x 10-6 M

0.5

0.5 0.4 400

450

500

550

600

0.4 400

Wavelength (nm)

450

500

0.8

600

2 DNA/ (ε -ε ) x 10-8 M cm a f

HL5

3

2

0.7

Absorbance

550

Wavelength (nm)

1

0.6

0

0

1

2

3

4

[DNA] x 10-6 M

0.5

0.4 400

450

500

550

600

Wavelength (nm) Fig. 10. Absorption spectra of ligands (HL1–HL5) in buffer pH 7.2 at 25 °C in the presence of increasing amount of CT-DNA. Arrows indicate the changes in absorbance upon increasing the CT-DNA concentration. Inset: plot of [DNA]/(ea  ef)  108 M2 cm versus [DNA]  106 M for titration of DNA with ligands (HL1–HL5).

0.9

(1)

1.0

1.2

(2)

0.8

0.8

2 DNA/ (ε -ε ) x 10-8 M cm a f

A.F. Shoair et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 151 (2015) 322–334

2 DNA/ (ε -ε ) x 10-8 M cm a f

332

1.0

1.0

0.6

0.8 0.6

Absorbance

Absorbance

0.4 0.2

0.7

0.0 0 2 4 6 8 10 12 14 16

0.6

[DNA] x 10-6 M

0.4

0.8

0.2 2

4

6

8

10 12

[DNA] x 10-6 M

0.6

0.5

0.4

400

450

500

550

0.4

600

400

450

Wavelength (nm)

0.8

(4)

-6

2.5x10

0.8

-6

2.0x10

-6

1.5x10

-6

1.0x10

-7

5.0x10

0.0

0.7

0.0

-5

5.0x10

-4

1.0x10

-4

1.5x10

-4

2.0x10

[DNA] x 10-6 M

Absorbance

2 DNA/ (ε -ε ) x 10-8 M cm a f

0.9

2 DNA/ (ε -ε ) x 10-8 M cm a f

-6

3.0x10

(3)

550

600

Wavelength (nm) 0.9

1.0

Absorbance

500

-6

1.0x10

-7

8.0x10

-7

6.0x10

-7

4.0x10

-7

2.0x10

0.0

0.7

-7

-2.0x10 0.0

-5

-5

-5

-4

3.0x10 6.0x10 9.0x10 1.2x10

[DNA] x 10-6 M

0.6

0.6 0.5

0.5

0.4

0.4

400

450

500

550

400

600

450

550

600

Wavelength (nm)

Wavelength (nm) 2 DNA/ (ε -ε ) x 10-8 M cm a f

0.9

(5) 0.8

Absorbance

500

6

4

2

0.7 0

0

2

4

6

8

10 12

[DNA] x 10-6 M

0.6

0.5

0.4 400

450

500

550

600

Wavelength (nm) Fig. 11. Absorption spectra of complexes (1–5) in buffer pH 7.2 at 25 °C in the presence of increasing amount of CT-DNA. Arrows indicate the changes in absorbance upon increasing the CT-DNA concentration. Inset: plot of [DNA]/(ea  ef)  108 M2 cm versus [DNA]  106 M for titration of CT-DNA with complexes (1–5).

reactions were carried out at room temperature, in the presence of catalytic amount of the complexes, [Ru(Ln)2(AsPh3)2]Cl and an excess of H2O2 as a co-oxidant, according to the following: Benzyl alcohol (2 mmol) was added to the solution of the complex (5% mole in 5 cm3 CH3CN) and then H2O2 (10 cm3, 30%) was added dropwise within 30 min. The reaction mixture was stirred at room temperature for 3 h, then benzaldehyde was then quantified as its 2,4-dinitrophenylhydrazone derivative. The results for the catalytic oxidation of benzyl alcohol by the prepared complexes are summarized in Table 7. The yields and turnover frequency (TOF) are calculated. The use of oxygen as co-oxidant instead of H2O2 under the same reaction conditions showed no reaction.

This means that the oxygen released due to the decomposition of H2O2 plays no role in the catalytic oxidation of benzyl alcohol. A blank experiment was also carried out which revealed that in the absence of the complex, only less than 10% yield of benzaldehyde was detected, suggesting that in the absence of the ruthenium complex H2O2 itself is able to oxidize benzyl alcohol as a stoichiometric oxidant, while in the presence of the ruthenium complex, H2O2 is able to trigger a recycling of the active species which expected to be ruthenium-oxo species (RuIV@O) and thereby increase the final yield (75–85%). However, upon comparing our catalyst system with other systems in the literature [56–58] it was found that the catalyst systems, Au/CeO-direct anionic

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(a)

HL5

5 Kb x 10 (M-1)

6

HL4

5

HL3

4

3

HL1

2 -0.4

Complexa

Yield

TOF, h1

(1) (2) (3) (4) (5)

85 74 82 79 70

5.7 4.9 5.5 5.3 4.7

Reaction conditions: Reactions were carried out at room temperature: Benzyl alcohol (2 mmol), the complex (0.1 mmol in 5 cm3 CH3CN) and H2O2 (10 cm3, 30%), reaction time = 3 h. (TOF = turnover frequency = moles of product/moles of catalyst/time). a Numbers as given in Table 1.

HL2 -0.2

0.0

0.2

0.4

0.6

0.8

R

OH

σ

3.0

Table 7 Catalytic oxidation of benzyl alcohol by the prepared ruthenium(III) complexes.

CHO

0.1 mmole Ru-catalyst 5 ml CH3CN 10 ml 30% H2O2

(b) 5

4 Kb x 10 (M-1)

Scheme 1. Catalytic oxidation of benzyl alcohol.

4 2.5

3 2 2.0

-0.4

1

-0.2

0.0

0.2

0.4

0.6

0.8

R

σ

Fig. 12. The relation between Hammett’s substitution coefficients (rR) vs. intrinsic binding constants (Kb) of the a) ligands (HL1–HL5) and b) Ru(III) complexes (1–5).

(2) (5)

3

(η/ηο)

1/3

(3) (4) (1)

2

1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

[Complex]/[DNA] Fig. 13. Effect of increasing amounts of Ru(III) complexes (1–5) on the relative viscosity of DNA at 25 °C.

exchange/O2 [56] and HNO3-promoted/nanotubes (CNTs/O2 [57] oxidized benzyl alcohol to benzaldehyde in 89% and the reaction is 5 h (Scheme 1). Recently, A metal organic framework encapsulated gold nanoparticles noted as Au/UiO-66 were developed and used as

catalyst with O2 as co-oxidant for oxidation of benzyl alcohol to benzaldehyde in 60% at 90 °C [58]. It was noticed that our reaction times are shorter and yields of obtained benzaldehyde by our catalysts systems are nearly comparable with those reported in the previously mentioned catalyst systems in addition reactions were carried out at room temperature. The catalytic oxidation of benzyl alcohol under the same conditions has been repeated in the presence of some other co-oxidants like NaIO4, K2S2O8, NaBrO3 and NaOCl instead of H2O2 and gave very low yield of benzaldehyde (less than 5%). This is probably due to the formation of the solid precipitates NaIO3, K2SO4, NaBr and NaCl, respectively, which remain at the end of the reaction and make the workup, is difficult. We conclude that the use of H2O2 is preferred co-oxidant for oxidation of these substrates in the presence of these complexes. In summary, these complexes catalytically oxidize benzyl alcohol to benzaldehyde in good yields at room temperature and in the presence of excess H2O2 as co-oxidant as well as this procedure is safe and simple for the catalytic oxidation of these substrates. 4. Conclusions The structure of Ru(III) complexes of the ligands (HLn) were confirmed by elemental analyses, IR, 1H NMR, molar conductance and thermal analysis data. Therefore, from IR spectrum, it is concluded that HLn binds to the Ru(III) as a monobasic bidentate ligand by coordinating via the nitrogen atom of the azo group (AN@NA) and oxygen atom of the deprotonated phenolic OH group. The optimized bond lengths, bond angles and calculated the quantum chemical parameters for the ligands (HLn) were investigated. The thermogravimetric analysis of the compounds shows that the values of activation energies of decomposition (Ea) are found to be 131, 143 and 51.2 kJ/mol for the ligands HL2, HL3 and HL5, respectively, and the values of Ea are found to be 28.1, 70.1 and 51.7 kJ/mol for the complexes 2, 3 and 5, respectively. The calf thymus DNA binding activity of the ligands (HLn) and their Ru(III) complexes were studied by absorption spectra and viscosity measurements. The ligands considering that the phenolic AOH group may enhance their affinity towards DNA binding through formation of hydrogen bonding. The mechanism and the catalytic oxidation of benzyl alcohol, and by trans[Ru(Ln)2(AsPh3)2]Cl with hydrogen peroxide as co-oxidant were described.

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