Ramakrishnan Sethu | University of Illinois at Urbana-Champaign (original) (raw)
Papers by Ramakrishnan Sethu
Journal of Chemical Sciences
Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO4)2, where dipica is di(2-... more Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO4)2, where dipica is di(2-picolyl)amine and diimine is 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6- dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) or dipyridoquinoxaline (dpq), have been isolated and characterized by analytical and spectral methods. The copper(II) complexes exhibit a broad band in the visible region around 675 nm and axial EPR spectra in acetonitrile glass (77 K) with g|| and A|| values of ~2×22 and 185 ´ 10–4 cm–1 respectively, suggesting the presence of a square-based coordination geometry for the CuN5 chromophore involving strong axial interaction. The interaction of the complexes with CT DNA has been studied using absorption, emission and circular dichroic spectral methods and viscosity measurements. Absorption spectral titrations reveal that the intrinsic DNA binding affinities are dependent upon the nature of the diimine ligand: dpq > 5,6-dmp > phen > 2,9-dm...
Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO 4 ) 2 , where dipica is d... more Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO 4 ) 2 , where dipica is di(2-picolyl)amine and diimine is 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) or dipyridoquinoxaline (dpq), have been isolated and characterized by analytical and spectral methods. The copper(II) complexes exhibit a broad band in the visible region around 675 nm and axial EPR spectra in acetonitrile glass (77 K) with g || and A || values of ~2⋅22 and 185 × 10 -4 cm -1 respectively, suggesting the presence of a square-based coordination geometry for the CuN 5 chromophore involving strong axial interaction. The interaction of the complexes with CT DNA has been studied using absorption, emission and circular dichroic spectral methods and viscosity measurements. Absorption spectral titrations reveal that the intrinsic DNA binding affinities are dependent upon the nature of the diimine ligand: dpq > 5,6-dmp > phen > 2,9-dmp. This suggests the involvement of the diimine rather than the dipica 'face' of the complexes in DNA binding. An intercalative mode of DNA interaction, which involves the insertion of dpq and to a lesser extent the phen ring of the complexes in between the DNA base pairs, is proposed. However, interestingly, the 5,6-dmp complex is involved in hydrophobic interaction of the 5,6-dmp ring in the grooves of DNA. The large enhancement in the relative viscosity of DNA on binding to the dpq and 5,6-dmp complexes supports the proposed DNA binding modes. Further, remarkably, the 5,6-dmp complex is selective in exhibiting a positive-induced CD band on binding to DNA suggesting the transition of the B form of CT DNA to A-like conformation. The variation in relative emission intensities of DNA-bound ethidium bromide observed upon treatment with the complexes parallels the trend in DNA binding affinities.
ACS Chemical Biology, 2014
Fur family proteins, ubiquitous in prokaryotes, play a pivotal role in microbial survival and vir... more Fur family proteins, ubiquitous in prokaryotes, play a pivotal role in microbial survival and virulence in most pathogens. Metalloregulators, such as Fur and PerR, regulate the transcription of genes connected to iron homeostasis and response to oxidative stress, respectively. In Bacillus subtilis, Fur and PerR bind with high affinity to DNA sequences differing at only two nucleotides. In addition to these differences in the PerR and Fur boxes, we identify in this study a residue located on the DNA binding motif of the Fur protein that is critical to discrimination between the two close DNA sequences. Interestingly, when this residue is introduced into PerR, it lowers the affinity of PerR for its own DNA target but confers to the protein the ability to interact strongly with the Fur DNA binding sequence. The present data show how two closely related proteins have distinct biological properties just by changing a single residue.
Inorganic Chemistry, 2012
A series of mononuclear mixed ligand copper(II) complexes [Cu(bba)(diimine)](ClO 4 ) 2 1−4, where... more A series of mononuclear mixed ligand copper(II) complexes [Cu(bba)(diimine)](ClO 4 ) 2 1−4, where bba is N,N-bis(benzimidazol-2-ylmethyl)amine and diimine is 2,2′-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (3), or dipyrido[3,2-d:2′,3′-f ]quinoxaline (dpq) (4), have been isolated and characterized by analytical and spectral methods. The coordination geometry around copper(II) in 2 is described as square pyramidal with the two benzimidazole nitrogen atoms of the primary ligand bba and the two nitrogen atoms of phen (2) co-ligand constituting the equatorial plane and the amine nitrogen atom of bba occupying the apical position. In contrast, the two benzimidazole nitrogen atoms and the amine nitrogen atom of bba ligand and one of the two nitrogen atoms of 5,6-dmp constitute the equatorial plane of the trigonal bipyramidal distorted square based pyramidal (TBDSBP) coordination geometry of 3 with the other nitrogen atom of 5,6-dmp occupying the apical position. The structures of 1−4 have been optimized by using the density functional theory (DFT) method at the B3LYP/6-31G(d,p) level. Absorption spectral titrations with Calf Thymus (CT) DNA reveal that the intrinsic DNA binding affinity of the complexes depends upon the diimine co-ligand, dpq (4) > 5,6-dmp (3) > phen (2) > bpy (1). The DNA binding affinity of 4 is higher than 2 revealing that the π-stacking interaction of the dpq ring in between the DNA base pairs with the two bzim moieties of the bba ligand stacked along the DNA surface is more intimate than that of phen. The complex 3 is bound to DNA more strongly than 1 and 2 through strong hydrophobic interaction of the methyl groups on 5,6-positions of the phen ring in the DNA grooves. The extent of the decrease in relative emission intensities of DNA-bound ethidium bromide (EB) upon adding the complexes parallels the trend in DNA binding affinities. The large enhancement in relative viscosity of DNA upon binding to 3 and 4 supports the DNA binding modes proposed. Interestingly, the 5,6-dmp complex 3 is selective in exhibiting a positive induced CD band (ICD) upon binding to DNA suggesting that it induces a B to A conformational change. In contrast, 2 and 4 show induced CD responses indicating their involvement in strong DNA binding. Interestingly, only the dpq complex 4, which displays the strongest DNA binding affinity and is efficient in cleaving DNA in the absence of an activator with a rate constant of 5.8 ± 0.1 h −1 , which is higher than the uncatalyzed rate of DNA cleavage. All the complexes exhibit oxidative DNA cleavage ability, which varies as 4 > 2 > 3 > 1 (ascorbic acid) and 3 > 2 > 4 > 1 (H 2 O 2 ). Also, the complexes cleave the protein bovine serum albumin in the presence of H 2 O 2 as an activator with the cleavage ability varying in the order 3 > 4 > 2 > 1. The highest efficiency of 3 to cleave both DNA and protein in the presence of H 2 O 2 is consistent with its strong hydrophobic interaction with the biopolymers. The IC 50 values of 1−4 against cervical cancer cell lines (SiHa) are almost equal to that of cisplatin, indicating that they have the potential to act as effective anticancer drugs in a time-dependent manner. The morphological assessment data obtained by using acridine orange/ethidium bromide (AO/EB) and Hoechst 33258 staining reveal that 3 induces apoptosis much more effectively than the other complexes. Also, the alkaline single-cell gel electrophoresis study (comet assay) suggests that the same complex induces DNA fragmentation more efficiently than others.
Inorganic Chemistry, 2009
Dalton Transactions, 2014
The water soluble mixed ligand copper(II) complexes of the type [Cu(sal)(diimine)(ClO 4 )] 2 1-5,... more The water soluble mixed ligand copper(II) complexes of the type [Cu(sal)(diimine)(ClO 4 )] 2 1-5, where sal is salicylaldehyde and diimine is 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline ( phen, 2), 5,6-dimethyl-1,10phenanthroline (5,6-dmp, 3), 3,4,7,8-tetramethyl-1,10-phenanthroline (3,4,7,8-tmp, 4) or dipyrido-[3,2-d:2',3'-f ]quinoxaline (dpq, 5), and [Cu(sal)(phen)(NO 3 )] 2 (2a) have been successfully isolated and characterized by elemental analysis and other spectral techniques. The DNA binding and cleavage properties of 1-5 have been explored by using various physical and biochemical methods. The coordination geometry around copper(II) in the X-ray structures of 1, 2, 2a and 4 is described as an elongated octahedron. The UV-Vis and EPR spectral and ESI-MS studies reveal that in solution the dinuclear complexes dissociate into essentially mononuclear [Cu(sal)(diimine)] + species with square-based geometry. The absorption spectral titrations and competitive DNA binding studies reveal that the intrinsic DNA binding affinity of the complexes depends upon the diimine co-ligand and is of the order of dpq (5) > 3,4,7,8-tmp (4) > 5,6dmp (3) > phen (2) > bpy (1). The complexes 2 and 5 are involved in a partial intercalative interaction with DNA base pairs, while 3 and 4 are involved in a hydrophobic interaction with DNA and 1 is involved in an electrostatic interaction with DNA, which is supported by viscosity studies. Interestingly, only 3 and 4 are selective in exhibiting a positive induced CD band (ICD) upon binding to DNA suggesting that they induce a B to A conformational change in DNA. All the complexes exhibit an oxidative DNA cleavage ability, which varies as 5 > 4 > 3 > 2 > 1. While 4 and 5 are unique in displaying prominent double-strand DNA cleavage even in the absence of an activator, 2 and 3 display only single-strand DNA cleavage. Interestingly, all the complexes exhibit oxidative double-strand DNA cleavage in the presence of ascorbic acid, with 4 and 5 showing a DNA cleavage activity more prominent than 1 and 2. The ability of the complexes to bind and cleave the protein BSA varies in the order, 4 > 3 > 5 > 2 > 1. Interestingly, 3 and 4 cleave the protein in the presence of H 2 O 2 as an activator in a non-specific manner suggesting that they can act as chemical proteases. It is remarkable that all the complexes exhibit cytotoxicity against human breast cancer cell lines (MCF-7) with a potency more than the widely used drug cisplatin indicating that they have the potential to act as effective anticancer drugs in a time dependent manner. The morphological assessment data obtained by using Hoechst 33258 staining reveal that 3 and 4 induce apoptosis much more effectively than the other complexes. Also, the alkaline single-cell gel electrophoresis study (comet assay) suggests that the same complexes induce DNA fragmentation more efficiently than others.
Dalton Transactions, 2011
The complexes rac-[Fe(diimine)(3)](ClO(4))(2)1-4, where diimine = 2,2'-bipyridine... more The complexes rac-[Fe(diimine)(3)](ClO(4))(2)1-4, where diimine = 2,2'-bipyridine (bpy) 1, 1,10-phenanthroline (phen) 2, 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) 3 and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) 4, have been isolated, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structure of rac-[Fe(5,6-dmp)(3)](ClO(4))(2)3 has been determined and the packing diagram shows the presence of two enantiomeric forms of the complex cations in the same unit cell. The structures of 1-4 in solution have also been studied using UV-Visible, Cyclic Voltammetry and ESI-MS data and all data available suggests that they retain their solid state structures even in solution. The absorption spectral titrations of the iron(ii) complexes with CT DNA reveal that the DNA binding affinities of the complexes vary in the order, 4 (K(b): 9.0 × 10(3)) > 2 (6.8 × 10(3)) > 3 (4. 8 × 10(3)) > 1 (2.9 × 10(3) M(-1)). The DNA interaction of dpq complex (4) involves partial insertion of the extended phen ring in between the DNA base pairs, which is deeper than that of phen (2). The 5,6-dmp (3) complex is involved in groove binding in the major groove of DNA. The lower DNA binding affinity of 1 is due to electrostatic interaction of the cationic complexes with exterior phosphates of DNA. The EthBr displacement assay and DNA viscosity study support these DNA binding modes and the above trend in DNA binding affinities. The complexes of 1 and 2 show induced CD (ICD) upon interaction with CT DNA while 3 and 4 bound to DNA exhibit inversion in the positive band with the helicity band showing very small changes, which implies that 3 and 4 bind enantiopreferentially to DNA. The DNA cleavage abilities of 1-4 have been observed at 10 μM concentration of complexes in the presence of 100 μM H(2)O(2) and the DNA cleavage efficiency (> 90%) follows the order 3 > 1 > 2 > 4. The anticancer activity of 1-4 against human breast cancer cell line (MCF-7) has also been studied. The IC(50) values of the complexes at different incubation time intervals of 24 and 48 h follow the order, 3 (0.8, 0.6) < 4 (20.0, 17.0) < 2 (28.0, 22.0) < 1 (32.0, 29.0 μM). Interestingly, 3 exhibits anticancer activity more potent than 1, 2 and 4 and cisplatin for both 24 and 48 h. It induces cell death both through apoptosis and necrosis mechanisms, as revealed by morphological assessment data obtained by using AO/EB and Hoechst 33258 fluorescence staining methods.
Dalton Transactions, 2011
The complexes [Co(diimine)(3)](ClO(4))(2)1-3 and [Ni(diimine)(3)](ClO(4))(2)4-6, where diimine = ... more The complexes [Co(diimine)(3)](ClO(4))(2)1-3 and [Ni(diimine)(3)](ClO(4))(2)4-6, where diimine = 1,10-phenanthroline (phen) (1,4), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (2,5) and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (3,6), have been isolated, characterized and their interaction with CT DNA studied by using a host of physical methods. The X-ray crystal structures of rac-[Co(5,6-dmp)(3)](ClO(4))(2)2 and rac-[Ni(5,6-dmp)(3)](ClO(4))(2)5 have been determined and the isostructural and also isomorphous complex cations possess distorted octahedral coordination geometries. The absorption spectral titrations of the complexes with DNA reveal that the CT DNA binding affinity (K(b)) of the complexes varies as 3>2>1; 6>5>4. The Ni(II) complexes display DNA binding stronger than the corresponding Co(II) analogues, which is expected of their bigger sizes. The higher DNA binding affinity of 3 and 6 is due to the involvement in partial insertion of the extended phen ring in between the DNA base pairs. In contrast, 2 and 5 interact with DNA in the major groove through hydrophobic forces involving the methyl groups on the 5,6 positions of phen ring. An enhancement in relative viscosities of DNA upon binding to 1-6 is consistent with the DNA binding affinities. The CD spectral studies show only an induced CD band on the characteristic positive band of CT DNA for both the phen (1,4) complexes. In contrast, the 5,6-dmp (2,5) and dpq (3,6) complexes bound to CT DNA exhibit biphasic CD signals in place of the positive CD band and the negative helicity band disappears. This reveals that the complexes bind to DNA enantiopreferentially and effect changes in secondary structure of DNA. The CV and DPV responses indicate that the DNA-bound dpq complexes are stabilized in the lower oxidation state of Co(II) more than in the Co(III) oxidation state. The prominent DNA cleavage abilities of 1-3 observed in the presence of H(2)O(2) (200 μM) follows the order 2>1>3 with efficiencies of more than 90% even at 10 μM complex concentration. Interestingly, Ni(II) complexes 4-6 exhibit higher cytotoxicity (IC(50): 1, 28.0; 2, 15.0; 3, 20.0; 4, 8.0; 5, 2.0; 6, 2.0 μM at 48 h; IC(50): 1, 30.0; 2, 20.0; 3, 25.0; 4, 10.0; 5, 3.0; 6, 3.0 μM at 24 h) against human breast cancer (MCF 7) cell lines than the Co(II) complexes 1-3 as well as cisplatin in spite of their inability to cleave DNA. Also, the 5,6-dmp complex 5 shows cytotoxicity higher than the dpq complex 6 at 24 h incubation time and both 5 and 6 display apoptotic and necrotic modes of cell death.
Dalton Transactions, 2008
The complexes [Cu(phen)(3)](ClO(4))(2) 1, [Cu(5,6-dmp)(3)](ClO(4))(2) 2, [Cu(dpq)(3)](ClO(4))(2) ... more The complexes [Cu(phen)(3)](ClO(4))(2) 1, [Cu(5,6-dmp)(3)](ClO(4))(2) 2, [Cu(dpq)(3)](ClO(4))(2) 3, [Zn(phen)(3)](ClO(4))(2) 4, [Zn(5,6-dmp)(3)](ClO(4))(2) 5 and [Zn(dpq)(3)](ClO(4))(2) 6, where phen = 1,10-phenanthroline, 5,6-dmp = 5,6-dimethyl-1,10-phenanthroline and dpq = dipyrido[3,2-d:2',3'-f]quinoxaline, have been isolated, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structures of rac-[Cu(5,6-dmp)(3)](ClO(4))(2) and rac-[Zn(5,6-dmp)(3)](ClO(4))(2) have been determined. While 2 possesses a regular elongated octahedral coordination geometry (REO), 5 possesses a distorted octahedral geometry. Absorption spectral titrations of the Cu(II) complexes with CT DNA reveal that the red-shift (12 nm) and DNA binding affinity of 3 (K(b), 7.5 x 10(4) M(-1)) are higher than those of 1 (red-shift, 6 nm; K(b), 9.6 x 10(3) M(-1)) indicating that the partial insertion of the extended phen ring of dpq ligand in between the DNA base pairs is deeper than that of phen ring. Also, 2 with a fluxional Cu(II) geometry interacts with DNA (K(b), 3.8 x 10(4) M(-1)) more strongly than 1 suggesting that the hydrophobic forces of interaction of 5,6 methyl groups on the phen ring is more pronounced than the partial intercalation of phen ring in the latter with a static geometry. The DNA binding affinity of 1 is lower than that of its Zn(ii) analogue 4, and, interestingly, the DNA binding affinity 2 of with a fluxional geometry is higher than that of its Zn(II) analogue 5 with a spherical geometry. It is remarkable that upon binding to DNA 3 shows an increase in viscosity higher than that the intercalator EthBr does, which is consistent with the above DNA binding affinities. The CD spectra show only one induced CD band on the characteristic positive band of CT DNA upon interaction with the phen (1,4) and dpq (3,6) complexes. In contrast, the 5,6-dmp complexes 2 and 5 bound to CT DNA show exciton-coupled biphasic CD signals with 2 showing CD signals more intense than 5. The Delta-enantiomer of rac-[Cu(5,6-dmp)(3)](2+) 2 binds specifically to the right-handed B-form of CT DNA at lower ionic strength (0.05 M NaCl) while the Lambda-enantiomer binds specifically to the left-handed Z-form of CT DNA generated by treating the B-form with 5 M NaCl. The complex 2 is stabilized in the higher oxidation state of Cu(II) more than its phen analogue 1 upon binding to DNA suggesting the involvement of electrostatic forces in DNA interaction of the former. In contrast, 3 bound to DNA is stabilized as Cu(I) rather than the Cu(II) oxidation state due to partial intercalative interaction of the dpq ligand. The efficiencies of the complexes to oxidatively cleave pUC19 DNA vary in the order, 3> 1 > 2 with 3 effecting 100% cleavage even at 10 microM complex concentration. However, interestingly, this order is reversed when the DNA cleavage is performed using H(2)O(2) as an activator and the highest cleavage efficiency of 2 is ascribed to its electrostatic interaction with the exterior phosphates of DNA.
Angewandte Chemie International Edition, 2013
Journal of Inorganic Biochemistry, 2014
A series of mononuclear mixed ligand copper(II) complexes of the type [Cu(L)(2,9-dmp)](ClO 4 ) 2 ... more A series of mononuclear mixed ligand copper(II) complexes of the type [Cu(L)(2,9-dmp)](ClO 4 ) 2 1-4, where L is a tridentate 3N ligand such as diethylenetriamine (L1) (1)orN-methyl-N′-(pyrid-2-yl-methyl)ethylenediamine (L2) (2) or di(2-picolyl)amine (L3) (3) or bis(pyrid-2-ylmethyl)-N-methylamine (L4) (4) and 2,9-dmp is 2,9dimethyl-1,10-phenanthroline, has been isolated and characterized. The complexes 1 and 3 possess squarebased pyramidal coordination geometry. Absorption spectral studies reveal that the intrinsic DNA binding affinity varies as 1 N 2 N 3 N 4. The higher DNA binding affinity of 1 arises from L1, which offers lower steric hindrance toward intercalation of 2,9-dmp co-ligand into DNA base pairs and is involved in hydrogen bonding interaction with DNA. Interestingly, all the complexes cleave pUC19 supercoiled DNA in the absence of an activating agent. They also exhibit oxidative (H 2 O 2 ) DNA cleavage ability, which varies as 1 N 2 N 3 N 4, the highest cleavage efficiency of 1 being due to the largest amount of ROS it generates. The tryptophan emission-quenching experiment reveals that the stronger binding of 3 and 4 with bovine serum albumin (BSA) in the hydrophobic region, which is in line with DNA viscosity measurements. The IC 50 values of 1-4 for MCF-7 breast cancer cell line are lower than that of cisplatin. Flow cytometry analysis reveals that 1 mediates the arrest of S and G2/M phases in the cell cycle progression at 24 h harvesting time, which progresses into apoptosis. Hoechst 33258 staining studies indicate the higher potency of 1 to induce apoptosis.
Journal of Chemical Sciences
Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO4)2, where dipica is di(2-... more Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO4)2, where dipica is di(2-picolyl)amine and diimine is 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6- dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) or dipyridoquinoxaline (dpq), have been isolated and characterized by analytical and spectral methods. The copper(II) complexes exhibit a broad band in the visible region around 675 nm and axial EPR spectra in acetonitrile glass (77 K) with g|| and A|| values of ~2×22 and 185 ´ 10–4 cm–1 respectively, suggesting the presence of a square-based coordination geometry for the CuN5 chromophore involving strong axial interaction. The interaction of the complexes with CT DNA has been studied using absorption, emission and circular dichroic spectral methods and viscosity measurements. Absorption spectral titrations reveal that the intrinsic DNA binding affinities are dependent upon the nature of the diimine ligand: dpq > 5,6-dmp > phen > 2,9-dm...
Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO 4 ) 2 , where dipica is d... more Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO 4 ) 2 , where dipica is di(2-picolyl)amine and diimine is 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) or dipyridoquinoxaline (dpq), have been isolated and characterized by analytical and spectral methods. The copper(II) complexes exhibit a broad band in the visible region around 675 nm and axial EPR spectra in acetonitrile glass (77 K) with g || and A || values of ~2⋅22 and 185 × 10 -4 cm -1 respectively, suggesting the presence of a square-based coordination geometry for the CuN 5 chromophore involving strong axial interaction. The interaction of the complexes with CT DNA has been studied using absorption, emission and circular dichroic spectral methods and viscosity measurements. Absorption spectral titrations reveal that the intrinsic DNA binding affinities are dependent upon the nature of the diimine ligand: dpq > 5,6-dmp > phen > 2,9-dmp. This suggests the involvement of the diimine rather than the dipica 'face' of the complexes in DNA binding. An intercalative mode of DNA interaction, which involves the insertion of dpq and to a lesser extent the phen ring of the complexes in between the DNA base pairs, is proposed. However, interestingly, the 5,6-dmp complex is involved in hydrophobic interaction of the 5,6-dmp ring in the grooves of DNA. The large enhancement in the relative viscosity of DNA on binding to the dpq and 5,6-dmp complexes supports the proposed DNA binding modes. Further, remarkably, the 5,6-dmp complex is selective in exhibiting a positive-induced CD band on binding to DNA suggesting the transition of the B form of CT DNA to A-like conformation. The variation in relative emission intensities of DNA-bound ethidium bromide observed upon treatment with the complexes parallels the trend in DNA binding affinities.
ACS Chemical Biology, 2014
Fur family proteins, ubiquitous in prokaryotes, play a pivotal role in microbial survival and vir... more Fur family proteins, ubiquitous in prokaryotes, play a pivotal role in microbial survival and virulence in most pathogens. Metalloregulators, such as Fur and PerR, regulate the transcription of genes connected to iron homeostasis and response to oxidative stress, respectively. In Bacillus subtilis, Fur and PerR bind with high affinity to DNA sequences differing at only two nucleotides. In addition to these differences in the PerR and Fur boxes, we identify in this study a residue located on the DNA binding motif of the Fur protein that is critical to discrimination between the two close DNA sequences. Interestingly, when this residue is introduced into PerR, it lowers the affinity of PerR for its own DNA target but confers to the protein the ability to interact strongly with the Fur DNA binding sequence. The present data show how two closely related proteins have distinct biological properties just by changing a single residue.
Inorganic Chemistry, 2012
A series of mononuclear mixed ligand copper(II) complexes [Cu(bba)(diimine)](ClO 4 ) 2 1−4, where... more A series of mononuclear mixed ligand copper(II) complexes [Cu(bba)(diimine)](ClO 4 ) 2 1−4, where bba is N,N-bis(benzimidazol-2-ylmethyl)amine and diimine is 2,2′-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (3), or dipyrido[3,2-d:2′,3′-f ]quinoxaline (dpq) (4), have been isolated and characterized by analytical and spectral methods. The coordination geometry around copper(II) in 2 is described as square pyramidal with the two benzimidazole nitrogen atoms of the primary ligand bba and the two nitrogen atoms of phen (2) co-ligand constituting the equatorial plane and the amine nitrogen atom of bba occupying the apical position. In contrast, the two benzimidazole nitrogen atoms and the amine nitrogen atom of bba ligand and one of the two nitrogen atoms of 5,6-dmp constitute the equatorial plane of the trigonal bipyramidal distorted square based pyramidal (TBDSBP) coordination geometry of 3 with the other nitrogen atom of 5,6-dmp occupying the apical position. The structures of 1−4 have been optimized by using the density functional theory (DFT) method at the B3LYP/6-31G(d,p) level. Absorption spectral titrations with Calf Thymus (CT) DNA reveal that the intrinsic DNA binding affinity of the complexes depends upon the diimine co-ligand, dpq (4) > 5,6-dmp (3) > phen (2) > bpy (1). The DNA binding affinity of 4 is higher than 2 revealing that the π-stacking interaction of the dpq ring in between the DNA base pairs with the two bzim moieties of the bba ligand stacked along the DNA surface is more intimate than that of phen. The complex 3 is bound to DNA more strongly than 1 and 2 through strong hydrophobic interaction of the methyl groups on 5,6-positions of the phen ring in the DNA grooves. The extent of the decrease in relative emission intensities of DNA-bound ethidium bromide (EB) upon adding the complexes parallels the trend in DNA binding affinities. The large enhancement in relative viscosity of DNA upon binding to 3 and 4 supports the DNA binding modes proposed. Interestingly, the 5,6-dmp complex 3 is selective in exhibiting a positive induced CD band (ICD) upon binding to DNA suggesting that it induces a B to A conformational change. In contrast, 2 and 4 show induced CD responses indicating their involvement in strong DNA binding. Interestingly, only the dpq complex 4, which displays the strongest DNA binding affinity and is efficient in cleaving DNA in the absence of an activator with a rate constant of 5.8 ± 0.1 h −1 , which is higher than the uncatalyzed rate of DNA cleavage. All the complexes exhibit oxidative DNA cleavage ability, which varies as 4 > 2 > 3 > 1 (ascorbic acid) and 3 > 2 > 4 > 1 (H 2 O 2 ). Also, the complexes cleave the protein bovine serum albumin in the presence of H 2 O 2 as an activator with the cleavage ability varying in the order 3 > 4 > 2 > 1. The highest efficiency of 3 to cleave both DNA and protein in the presence of H 2 O 2 is consistent with its strong hydrophobic interaction with the biopolymers. The IC 50 values of 1−4 against cervical cancer cell lines (SiHa) are almost equal to that of cisplatin, indicating that they have the potential to act as effective anticancer drugs in a time-dependent manner. The morphological assessment data obtained by using acridine orange/ethidium bromide (AO/EB) and Hoechst 33258 staining reveal that 3 induces apoptosis much more effectively than the other complexes. Also, the alkaline single-cell gel electrophoresis study (comet assay) suggests that the same complex induces DNA fragmentation more efficiently than others.
Inorganic Chemistry, 2009
Dalton Transactions, 2014
The water soluble mixed ligand copper(II) complexes of the type [Cu(sal)(diimine)(ClO 4 )] 2 1-5,... more The water soluble mixed ligand copper(II) complexes of the type [Cu(sal)(diimine)(ClO 4 )] 2 1-5, where sal is salicylaldehyde and diimine is 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline ( phen, 2), 5,6-dimethyl-1,10phenanthroline (5,6-dmp, 3), 3,4,7,8-tetramethyl-1,10-phenanthroline (3,4,7,8-tmp, 4) or dipyrido-[3,2-d:2',3'-f ]quinoxaline (dpq, 5), and [Cu(sal)(phen)(NO 3 )] 2 (2a) have been successfully isolated and characterized by elemental analysis and other spectral techniques. The DNA binding and cleavage properties of 1-5 have been explored by using various physical and biochemical methods. The coordination geometry around copper(II) in the X-ray structures of 1, 2, 2a and 4 is described as an elongated octahedron. The UV-Vis and EPR spectral and ESI-MS studies reveal that in solution the dinuclear complexes dissociate into essentially mononuclear [Cu(sal)(diimine)] + species with square-based geometry. The absorption spectral titrations and competitive DNA binding studies reveal that the intrinsic DNA binding affinity of the complexes depends upon the diimine co-ligand and is of the order of dpq (5) > 3,4,7,8-tmp (4) > 5,6dmp (3) > phen (2) > bpy (1). The complexes 2 and 5 are involved in a partial intercalative interaction with DNA base pairs, while 3 and 4 are involved in a hydrophobic interaction with DNA and 1 is involved in an electrostatic interaction with DNA, which is supported by viscosity studies. Interestingly, only 3 and 4 are selective in exhibiting a positive induced CD band (ICD) upon binding to DNA suggesting that they induce a B to A conformational change in DNA. All the complexes exhibit an oxidative DNA cleavage ability, which varies as 5 > 4 > 3 > 2 > 1. While 4 and 5 are unique in displaying prominent double-strand DNA cleavage even in the absence of an activator, 2 and 3 display only single-strand DNA cleavage. Interestingly, all the complexes exhibit oxidative double-strand DNA cleavage in the presence of ascorbic acid, with 4 and 5 showing a DNA cleavage activity more prominent than 1 and 2. The ability of the complexes to bind and cleave the protein BSA varies in the order, 4 > 3 > 5 > 2 > 1. Interestingly, 3 and 4 cleave the protein in the presence of H 2 O 2 as an activator in a non-specific manner suggesting that they can act as chemical proteases. It is remarkable that all the complexes exhibit cytotoxicity against human breast cancer cell lines (MCF-7) with a potency more than the widely used drug cisplatin indicating that they have the potential to act as effective anticancer drugs in a time dependent manner. The morphological assessment data obtained by using Hoechst 33258 staining reveal that 3 and 4 induce apoptosis much more effectively than the other complexes. Also, the alkaline single-cell gel electrophoresis study (comet assay) suggests that the same complexes induce DNA fragmentation more efficiently than others.
Dalton Transactions, 2011
The complexes rac-[Fe(diimine)(3)](ClO(4))(2)1-4, where diimine = 2,2'-bipyridine... more The complexes rac-[Fe(diimine)(3)](ClO(4))(2)1-4, where diimine = 2,2'-bipyridine (bpy) 1, 1,10-phenanthroline (phen) 2, 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) 3 and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) 4, have been isolated, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structure of rac-[Fe(5,6-dmp)(3)](ClO(4))(2)3 has been determined and the packing diagram shows the presence of two enantiomeric forms of the complex cations in the same unit cell. The structures of 1-4 in solution have also been studied using UV-Visible, Cyclic Voltammetry and ESI-MS data and all data available suggests that they retain their solid state structures even in solution. The absorption spectral titrations of the iron(ii) complexes with CT DNA reveal that the DNA binding affinities of the complexes vary in the order, 4 (K(b): 9.0 × 10(3)) > 2 (6.8 × 10(3)) > 3 (4. 8 × 10(3)) > 1 (2.9 × 10(3) M(-1)). The DNA interaction of dpq complex (4) involves partial insertion of the extended phen ring in between the DNA base pairs, which is deeper than that of phen (2). The 5,6-dmp (3) complex is involved in groove binding in the major groove of DNA. The lower DNA binding affinity of 1 is due to electrostatic interaction of the cationic complexes with exterior phosphates of DNA. The EthBr displacement assay and DNA viscosity study support these DNA binding modes and the above trend in DNA binding affinities. The complexes of 1 and 2 show induced CD (ICD) upon interaction with CT DNA while 3 and 4 bound to DNA exhibit inversion in the positive band with the helicity band showing very small changes, which implies that 3 and 4 bind enantiopreferentially to DNA. The DNA cleavage abilities of 1-4 have been observed at 10 μM concentration of complexes in the presence of 100 μM H(2)O(2) and the DNA cleavage efficiency (> 90%) follows the order 3 > 1 > 2 > 4. The anticancer activity of 1-4 against human breast cancer cell line (MCF-7) has also been studied. The IC(50) values of the complexes at different incubation time intervals of 24 and 48 h follow the order, 3 (0.8, 0.6) < 4 (20.0, 17.0) < 2 (28.0, 22.0) < 1 (32.0, 29.0 μM). Interestingly, 3 exhibits anticancer activity more potent than 1, 2 and 4 and cisplatin for both 24 and 48 h. It induces cell death both through apoptosis and necrosis mechanisms, as revealed by morphological assessment data obtained by using AO/EB and Hoechst 33258 fluorescence staining methods.
Dalton Transactions, 2011
The complexes [Co(diimine)(3)](ClO(4))(2)1-3 and [Ni(diimine)(3)](ClO(4))(2)4-6, where diimine = ... more The complexes [Co(diimine)(3)](ClO(4))(2)1-3 and [Ni(diimine)(3)](ClO(4))(2)4-6, where diimine = 1,10-phenanthroline (phen) (1,4), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (2,5) and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (3,6), have been isolated, characterized and their interaction with CT DNA studied by using a host of physical methods. The X-ray crystal structures of rac-[Co(5,6-dmp)(3)](ClO(4))(2)2 and rac-[Ni(5,6-dmp)(3)](ClO(4))(2)5 have been determined and the isostructural and also isomorphous complex cations possess distorted octahedral coordination geometries. The absorption spectral titrations of the complexes with DNA reveal that the CT DNA binding affinity (K(b)) of the complexes varies as 3>2>1; 6>5>4. The Ni(II) complexes display DNA binding stronger than the corresponding Co(II) analogues, which is expected of their bigger sizes. The higher DNA binding affinity of 3 and 6 is due to the involvement in partial insertion of the extended phen ring in between the DNA base pairs. In contrast, 2 and 5 interact with DNA in the major groove through hydrophobic forces involving the methyl groups on the 5,6 positions of phen ring. An enhancement in relative viscosities of DNA upon binding to 1-6 is consistent with the DNA binding affinities. The CD spectral studies show only an induced CD band on the characteristic positive band of CT DNA for both the phen (1,4) complexes. In contrast, the 5,6-dmp (2,5) and dpq (3,6) complexes bound to CT DNA exhibit biphasic CD signals in place of the positive CD band and the negative helicity band disappears. This reveals that the complexes bind to DNA enantiopreferentially and effect changes in secondary structure of DNA. The CV and DPV responses indicate that the DNA-bound dpq complexes are stabilized in the lower oxidation state of Co(II) more than in the Co(III) oxidation state. The prominent DNA cleavage abilities of 1-3 observed in the presence of H(2)O(2) (200 μM) follows the order 2>1>3 with efficiencies of more than 90% even at 10 μM complex concentration. Interestingly, Ni(II) complexes 4-6 exhibit higher cytotoxicity (IC(50): 1, 28.0; 2, 15.0; 3, 20.0; 4, 8.0; 5, 2.0; 6, 2.0 μM at 48 h; IC(50): 1, 30.0; 2, 20.0; 3, 25.0; 4, 10.0; 5, 3.0; 6, 3.0 μM at 24 h) against human breast cancer (MCF 7) cell lines than the Co(II) complexes 1-3 as well as cisplatin in spite of their inability to cleave DNA. Also, the 5,6-dmp complex 5 shows cytotoxicity higher than the dpq complex 6 at 24 h incubation time and both 5 and 6 display apoptotic and necrotic modes of cell death.
Dalton Transactions, 2008
The complexes [Cu(phen)(3)](ClO(4))(2) 1, [Cu(5,6-dmp)(3)](ClO(4))(2) 2, [Cu(dpq)(3)](ClO(4))(2) ... more The complexes [Cu(phen)(3)](ClO(4))(2) 1, [Cu(5,6-dmp)(3)](ClO(4))(2) 2, [Cu(dpq)(3)](ClO(4))(2) 3, [Zn(phen)(3)](ClO(4))(2) 4, [Zn(5,6-dmp)(3)](ClO(4))(2) 5 and [Zn(dpq)(3)](ClO(4))(2) 6, where phen = 1,10-phenanthroline, 5,6-dmp = 5,6-dimethyl-1,10-phenanthroline and dpq = dipyrido[3,2-d:2',3'-f]quinoxaline, have been isolated, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structures of rac-[Cu(5,6-dmp)(3)](ClO(4))(2) and rac-[Zn(5,6-dmp)(3)](ClO(4))(2) have been determined. While 2 possesses a regular elongated octahedral coordination geometry (REO), 5 possesses a distorted octahedral geometry. Absorption spectral titrations of the Cu(II) complexes with CT DNA reveal that the red-shift (12 nm) and DNA binding affinity of 3 (K(b), 7.5 x 10(4) M(-1)) are higher than those of 1 (red-shift, 6 nm; K(b), 9.6 x 10(3) M(-1)) indicating that the partial insertion of the extended phen ring of dpq ligand in between the DNA base pairs is deeper than that of phen ring. Also, 2 with a fluxional Cu(II) geometry interacts with DNA (K(b), 3.8 x 10(4) M(-1)) more strongly than 1 suggesting that the hydrophobic forces of interaction of 5,6 methyl groups on the phen ring is more pronounced than the partial intercalation of phen ring in the latter with a static geometry. The DNA binding affinity of 1 is lower than that of its Zn(ii) analogue 4, and, interestingly, the DNA binding affinity 2 of with a fluxional geometry is higher than that of its Zn(II) analogue 5 with a spherical geometry. It is remarkable that upon binding to DNA 3 shows an increase in viscosity higher than that the intercalator EthBr does, which is consistent with the above DNA binding affinities. The CD spectra show only one induced CD band on the characteristic positive band of CT DNA upon interaction with the phen (1,4) and dpq (3,6) complexes. In contrast, the 5,6-dmp complexes 2 and 5 bound to CT DNA show exciton-coupled biphasic CD signals with 2 showing CD signals more intense than 5. The Delta-enantiomer of rac-[Cu(5,6-dmp)(3)](2+) 2 binds specifically to the right-handed B-form of CT DNA at lower ionic strength (0.05 M NaCl) while the Lambda-enantiomer binds specifically to the left-handed Z-form of CT DNA generated by treating the B-form with 5 M NaCl. The complex 2 is stabilized in the higher oxidation state of Cu(II) more than its phen analogue 1 upon binding to DNA suggesting the involvement of electrostatic forces in DNA interaction of the former. In contrast, 3 bound to DNA is stabilized as Cu(I) rather than the Cu(II) oxidation state due to partial intercalative interaction of the dpq ligand. The efficiencies of the complexes to oxidatively cleave pUC19 DNA vary in the order, 3> 1 > 2 with 3 effecting 100% cleavage even at 10 microM complex concentration. However, interestingly, this order is reversed when the DNA cleavage is performed using H(2)O(2) as an activator and the highest cleavage efficiency of 2 is ascribed to its electrostatic interaction with the exterior phosphates of DNA.
Angewandte Chemie International Edition, 2013
Journal of Inorganic Biochemistry, 2014
A series of mononuclear mixed ligand copper(II) complexes of the type [Cu(L)(2,9-dmp)](ClO 4 ) 2 ... more A series of mononuclear mixed ligand copper(II) complexes of the type [Cu(L)(2,9-dmp)](ClO 4 ) 2 1-4, where L is a tridentate 3N ligand such as diethylenetriamine (L1) (1)orN-methyl-N′-(pyrid-2-yl-methyl)ethylenediamine (L2) (2) or di(2-picolyl)amine (L3) (3) or bis(pyrid-2-ylmethyl)-N-methylamine (L4) (4) and 2,9-dmp is 2,9dimethyl-1,10-phenanthroline, has been isolated and characterized. The complexes 1 and 3 possess squarebased pyramidal coordination geometry. Absorption spectral studies reveal that the intrinsic DNA binding affinity varies as 1 N 2 N 3 N 4. The higher DNA binding affinity of 1 arises from L1, which offers lower steric hindrance toward intercalation of 2,9-dmp co-ligand into DNA base pairs and is involved in hydrogen bonding interaction with DNA. Interestingly, all the complexes cleave pUC19 supercoiled DNA in the absence of an activating agent. They also exhibit oxidative (H 2 O 2 ) DNA cleavage ability, which varies as 1 N 2 N 3 N 4, the highest cleavage efficiency of 1 being due to the largest amount of ROS it generates. The tryptophan emission-quenching experiment reveals that the stronger binding of 3 and 4 with bovine serum albumin (BSA) in the hydrophobic region, which is in line with DNA viscosity measurements. The IC 50 values of 1-4 for MCF-7 breast cancer cell line are lower than that of cisplatin. Flow cytometry analysis reveals that 1 mediates the arrest of S and G2/M phases in the cell cycle progression at 24 h harvesting time, which progresses into apoptosis. Hoechst 33258 staining studies indicate the higher potency of 1 to induce apoptosis.