DNA binding and photocleavage specificities of a group of tricationic metalloporphyrins

Synthesis, Characterization, DNA Binding, Biological Significance, and Molecular Docking Approaches of a Palladium(II) Complex with Ciprofloxacin for More Efficient Therapy

To evaluate the biotransformation and the mechanism of binding as well as the biological impact of metal-based- drugs involving Pd(II), known to have high potency and low toxicity for use as anticancer therapeutics, in the present study, a newly synthesized palladium (II) complex, [Pd(CPF)(OH2)2]2+ (where CPF is ciprofloxacin), has been synthesized and characterized and thoroughly evaluated for its antimicrobial properties. The interaction of the diaqua complex with CT-DNA and BSA was studied through various techniques, including UV-vis spectroscopy, thermal denaturation, viscometry, gel electrophoresis, ethanol precipitation, and molecular docking studies. The results indicate that the complex exhibits a robust binding interaction with CT-DNA, possibly via minor groove binding and (or) electrostatic interactions. Furthermore, the complex displays good binding affinity towards BSA, indicating its potential as a target for DNA and BSA in biological media. The invitro cytotoxicity assay reveals that this complex can be classified as a promising cell growth inhibitor against MCF-7, HT-29, and A549. Thus, this newly synthesized palladium (II) complex is a promising candidate for further exploration as a potential anticancer therapeutic.

Benzopyrone-mediated quinolones as potential multitargeting antibacterial agents

A new type of benzopyrone-mediated quinolones (BMQs) was rationally designed and efficiently synthesized as novel potential antibacterial molecules to overcome the global increasingly serious drug resistance. Some synthesized BMQs effectively suppressed the growth of the tested strains, outperforming clinical drugs. Notably, ethylidene-derived BMQ 17a exhibited superior antibacterial potential with low MICs of 0.5-2 μg/mL to clinical drugs norfloxacin, it not only displayed rapid bactericidal performance and inhibited bacterial biofilm formation, but also showed low toxicity toward human red blood cells and normal MDA-kb2 cells. Mechanistic investigation demonstrated that BMQ 17a could effectually induce bacterial metabolic disorders and promote the enhancement of reactive oxygen species to disrupt the bacterial antioxidant defense system. It was found that the active molecule BMQ 17a could not only form supramolecular complex with lactate dehydrogenase, which disturbed the biological functions, but also effectively embed into calf thymus DNA, thus affecting the normal function of DNA and achieving cell death. This work would provide an insight into developing new molecules to reduce drug resistance and expand antibacterial spectrum.

Investigation on CT-DNA and Protein Interaction of New Pd(II) Complexes Involving Ceftazidime and 3-Amino-1,2,3-triazole: Synthesis, Characterization, Biological Impact, Anticancer Evaluation, and Molecular Docking Approaches

Two new palladium (II) complexes, [Pd(CAZ)(OH2 )2 ]2+ (1) and [Pd(3-AT)(OH2 )2 ]2+ (2), (CAZ=ceftazidime, and 3-AT=amitrole) were synthesized and studied for their potential as anticancer drugs with low toxicity and high potency. To fully characterize these complexes, we conducted elemental analysis and FT-IR studies. Furthermore, we irradiated the complexes with Indian 60 Co gamma rays and thoroughly evaluated their antimicrobial properties. Our results demonstrate that the inhibitory activity of complexes was significantly enhanced against (G+) bacteria and fungi. Additionally, we probed the complexes' interaction with CT-DNA and BSA using various techniques, including UV-vis spectroscopy, thermal denaturation, viscometry, gel electrophoresis, and molecular docking studies. Our findings conclusively demonstrate that these complexes possess a strong binding interaction with CT-DNA via minor groove binding and/or electrostatic interactions, as well as excellent binding affinity to BSA. Finally, we conducted a cytotoxicity assay that clearly indicates these complexes hold immense promise as cell growth inhibitors against MCF-7 and HCT-116.

DNA groove binder and significant cytotoxic activity on human colon cancer cells: Potential of a dimeric zinc (II) phthalocyanine derivative

The interaction of a multi-component system consisting of benzene-1,4-diyldimethanimine-bridged dimeric zinc-phthalocyanine groups (4OMPCZ) with calf thymus DNA (ct-DNA) was investigated using UV-Vis absorption, fluorescence emission spectroscopy methods, and viscosity measurements. The binding constant, K_b, which is an important parameter to gain information about the binding mode, was found as 9.7 × 10⁷ M^-1 from the UV-Vis absorption studies. Another important spectrophotometric tool is competitive displacement assays with Ethidium bromide and Hoechst 33342. Through this experiment, a higher K_SV value was obtained with Hoechst for the phthalocyanine derivative, 4OMPCZ, and the ct-DNA complex than with ethidium bromide. Additionally, molecular docking studies were conducted to calculate the theoretical binding constant and visualize the interactions of 4OMPCZ with a model DNA. According to docking results, although the interactions are mainly located in the major groove of the DNA helix, due to the wrapping, these interactions can also be extended to the minor groove of the DNA. Spectrophotometric, molecular docking, and viscosity studies revealed that the interaction of 4OMPCZ with DNA is likely to be via the major and minor grooves. The in vitro cytotoxic activity of 4OMPCZ was evaluated by MTT assay on human colon cancer cells (HT29) after 72 h of treatment. 4OMPCZ indicated significant cytotoxic activity when stimulated with UV light compared to the standard chemotherapy drugs, fluorouracil (5-FU), and cisplatin on HT29 colon cancer cells. The IC₅₀ value of 4OMPCZ displayed considerably lower concentrations compared to the standard drugs, 5-FU, and cisplatin.

Interactions of porphyrins with DNA: A review focusing recent advances in chemical modifications on porphyrins as artificial nucleases

The advance of porphyrins as artificial nucleases along the years have developed a class of compounds having potential therapeutic applications. Being an extrovert of chemistry, a variety of chemical modifications have been done on porphyrin macrocycle in order to improve the spectroscopic properties and to adapt as artificial receptors that can recognize molecules. The last twenty years has witnessed broad research in the arena of porphyrin- DNA interactions and their evolution from simple to more complex entities. In this review, we summarize the recent advances in the porphyrin-based structural modifications, with a specific emphasis on various effects of porphyrin on DNA cleavage potency. We particularly detailed the nuclease activity of cationic and anionic porphyrins, porphyrin dimers and conjugates as well as heme proteins till the third generation porphyrins as artificial nucleases.

Synthesis, electrochemistry, DNA binding and in vitro cytotoxic activity of tripodal ferrocenyl bis-naphthalimide derivatives

A series of tripodal ferrocenyl bis-naphthalimide derivatives were synthesized and characterized. All of the bis-naphthalimide derivatives exhibited good DNA binding ability which was confirmed by ethidium bromide (EB) displacement experiment and ultraviolet (UV)-visible absorption titration. And the binding mode of these compounds was proved to be a hybrid binding mode by experiments. The cytotoxicity of synthesized compounds against 4 different human cancer cell lines (EC109, BGC823, SGC7901 and HEPG2) was evaluated by thiazolyl blue tetrazolium bromide (MTT) assay. All of the bis-naphthalimide derivatives exhibited good anticancer activity than the positive control drug (amonafide), which was due to the promotion of reactive oxygen species (ROS) level in test cancer cells by the reversible one-electron redox process of ferrocenyl bis-naphthalimide derivatives. Although there was no obvious relationship between the binding constants and the chain length, the structure cytotoxicity relationship revealed that the linker of n = 3, m = 1 was the best choice for the tested tripodol bis-naphthalimide derivatives. SYNOPSIS: A series of tripodal ferrocenyl bis-naphthalimide derivatives were synthesized to study the DNA binding ability and the cytotoxicity induced by reactive oxygen species. All of the compounds exhibited good DNA binding ability. And the structure cytotoxicity relationship revealed that the structure of 5h was the best choice.

Studies on the Interaction of [SnMe2Cl2(bu2bpy)] Complex with ct-DNA Using Multispectroscopic, Atomic Force Microscopy (AFM) and Molecular Docking

The interaction of SnMe₂Cl₂(bu₂bpy)complex with calf thymus DNA (ct-DNA) has been explored following, using spectroscopic methods, viscosity measurements, Atomic force microscopy, Thermal denaturation and Molecular docking. It was found that Sn(IV) complex could bind with DNA via intercalation mode as evidenced by hyperchromism and bathochromic in UV-Vis spectrum; these spectral characteristics suggest that the Sn(IV) complex interacts with DNA most likely through a mode that involves a stacking interaction between the aromatic chromophore and the base pairs of DNA. In addition, the fluorescence emission spectra of intercalated methylene blue (MB) with increasing concentrations of SnMe₂Cl₂(bu₂bpy) represented a significant increase of MB intensity as to release MB from MB-DNA system. Positive values of ΔH and ΔS imply that the complex is bound to ct-DNA mainly via the hydrophobic attraction. Large complexes contain the DNA chains with an average size of 859 nm were observed by using AFM for Sn(IV) Complex-DNA. The Fourier transform infrared study showed a major interaction of Sn(IV) complex with G-C and A-T base pairs and a minor perturbation of the backbone PO₂ group. Addition of the Sn(IV)complex results in a noticeable rise in the Tm of DNA. In addition, the results of viscosity measurements suggest that SnMe₂Cl₂(bu₂bpy) complex may bind with the classical intercalative mode. From spectroscopic and hydrodynamic studies, it has been found that Sn(IV)complex interacts with DNA by intercalation mode. Optimized docked model of DNA-complex mixture confirmed the experimental results.

Spectrophotometric study on binding of 2-thioxanthone acetic acid with ct-DNA

Thioxanthone and its derivatives are the most remarkable molecules due to their vast variety of application such as radiation curing that is, until using them as a therapeutic drug. Therefore, in this study it was intended to use 2-Thioxanthone acetic acid with and without NaCl in Tris HCl buffer solution (pH:7.0) to represent the interaction with ct-DNA. The UV-vis absorption spectra of TXCH₂COOH in the presence of ct-DNA showed hypochromism and the intrinstic binding constant (K_b) was determined as 6 × 10³ L mol^-1. The fluoresence intensity of TXCH₂COOH with ct-DNA clearly increased up to 101% which indicated that the fluorescence intensity was very sensitive to ct-DNA concentration. The binding constant (K) and the values of number of binding sites (n) and were calculated as 1.8 × 10³ L mol^-1 and 0.69, respectively. When the quenching constants (K_sv) of free TXCH₂COOH and TXCH₂COOH, which were bonded with ct-DNA were compared, slightly changed values of Ksv were seen. Moreover, displacement assay with Hoechst 33,258 and viscosity measurements in the presence and absence of NaCl salt also confirmed the binding mode which noted the electrostatic interaction following groove binding between TXCH₂COOH and ct-DNA. Last but not least, the salt effect was examined on ct-DNA binding with TXCH₂COOH. The results of the experiments indicated that the groove binding was strengthened by NaCl whereas in the high NaCl concentration, the binding ability of TXCH₂COOH to ct-DNA was inversely affected.

DNA binding and in vitro anticarcinogenic activity of a series of newfashioned Cu(II)-complexes based on tricationic metalloporphyrin salicyloylhydrazone ligands

Four novel water-soluble Cu(II) derivatives based on the meso-10, 15, 20-Tris (N-methyl-X-pyridyl)-5-(4'-salicyloylhydrazone) metalloporphyrin ligands (X=4, M=Zn(1) Co(2); X=2, M=Zn(3), Co(4)), have been prepared and isolated. Various physicochemical techniques indicate that complex 2 interacts with calf thymus DNA stronger than the others through partial intercalation, suggesting that Co(II) has no axial ligands at porphyrin core plays a crucial role, interestingly, 2 exhibits higher DNA binding affinity compared to 4, which could be ascribed to the influences of peripheral electronic effect of porphyrin ring. Cytotoxicity studies manifest all conjugates possess superior cytotoxicity towards non-small cell lung cancer (A549) and liver hepatocellular carcinoma (HepG2) but weak toxicity for human normal breast cells (Hs 578Bst) boiled down to the tumor selectivity of porphyrin. In addition, the IC₅₀ value of 1 is lower than its analogues against HepG2 cells when cultivated 72h, thus the effects of representative complex 1 on cell morphological and cell cycle have been tailed.

Photoactive meso-tetra(4-pyridyl)porphyrin-tetrakis-[chloro(2,2′bipyridine)platinum(ii) derivatives recognize and cleave DNA upon irradiation

Photoactive platinum porphyrins may be interesting as photosensitizers in photodynamic therapy and photochemotherapy, and we demonstrate their activity towards DNA cleavage under exposure to light.

Synthesis, structure, electrochemical, DNA interaction and antimicrobial studies of fluorinated trans-dicationic pyridinium porphyrins

trans-Dicationic pyridinium porphyrins are superior artificial nucleases compared to their non-fluorinated analogues and bind with calf thymus DNA by outside groove binding with or without self-stacking, also show significant antimicrobial activities.

Cationic porphyrin@SPION nanospheres as multifunctional anticancer therapeutics: magnetic targeting, photodynamic potential and bio-safety research

Porphyrin@SPION nanospheres are described as pH-controllable, multifunctional photosensitizations with delivery bio-safety.

Studies on the interaction of apigenin with calf thymus DNA by spectroscopic methods

The interaction between apigenin and calf thymus deoxyribonucleic acid (ctDNA) in a pH 7.4 Tris-HCl buffer solution was investigated by UV-Vis spectroscopy, fluorescence spectroscopy, DNA melting techniques, and viscosity measurements. It was found that apigenin molecules could intercalate into the base pairs of DNA, forming a apigenin-DNA complex with a binding constant of K310K=6.4×10(4)Lmol(-1). The thermodynamic parameters enthalpy change (ΔH), entropy change (ΔS) and Gibbs free energy (ΔG) were calculated to be 7.36×10(4)Jmol(-1), 329JK(-1)mol(-1) and -2.84×10(4)Jmol(-1) at 310K, respectively. Hydrophobic interaction was the predominant intermolecular force in stabilizing the apigenin-DNA complex. Thermal denaturation study suggested that the stabilization of the ctDNA helix was increased when the apigenin binding to ctDNA as indicated by the increase in thermal denaturation temperature of ctDNA at around 5.0°C in the presence of apigenin. Spectroscopic techniques together with melting techniques and viscosity determination provided evidences of intercalation mode of binding for the interaction between apigenin and ctDNA.

Dihydroisoquinoline copper(ii) complexes: crystal structures, cytotoxicity, and action mechanism

Three new copper(ii) complexes with dihydroisoquinoline were synthesized. They exhibited considerable cytotoxicity, achieved through the induction of cell apoptosisviathe intrinsic pathways of caspase–mitochondria.

Spectroscopic and molecular modeling methods to investigate the interaction between 5-Hydroxymethyl-2-furfural and calf thymus DNA using ethidium bromide as a probe

In this work, the interaction of 5-Hydroxymethyl-2-furfural (5-HMF) with calf thymus DNA (ctDNA) under simulated physiological conditions (Tris-HCl buffer of pH 7.40), was explored by UV absorption spectroscopy, fluorescence spectroscopy and molecular modeling method, using ethidium bromide (EB) as a fluorescence probe of DNA. The fluorescence quenching mechanism of EB-ctDNA by 5-HMF was confirmed to be a static quenching, which derived from the formation of a new complex. The binding constants of 5-HMF with DNA in the presence of EB were calculated to be 2.17×10(3), 4.24×10(3) and 6.95×10(3) L mol(-1) at 300, 305 and 310 K, respectively. The calculated thermodynamic parameters, enthalpy change ΔH and entropy change ΔS, suggested that both hydrophobic interactions and hydrogen bonds played a predominant role in the binding of 5-HMF to DNA. According to the UV absorption spectroscopy and melting temperature (Tm) curve results, the binding mode of 5-HMF with DNA was indicative of a non-intercalative binding, which was supposed to be a groove binding. The molecular modeling results showed that 5-HMF could bind into the hydrophobic region of ctDNA and supported the conclusions obtained from the above experiments.

Molecular spectroscopic studies on the interaction of ferulic acid with calf thymus DNA

The interaction between ferulic acid and calf thymus deoxyribonucleic acid (ctDNA) under physiological conditions (Tris-HCl buffer solutions, pH 7.4) was investigated by UV-Vis spectroscopy, fluorescence spectroscopy, DNA melting techniques, and viscosity measurements. Results indicated that a complex of ferulic acid with ctDNA was formed with a binding constant of K(290K)=7.60×10(4) L mol(-1) and K(310K)=4.90×10(4) L mol(-1). The thermodynamic parameters enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy (ΔG°) were calculated to be -1.69×10(4) J mol(-1), 35.36 J K(-1) mol(-1) and -2.79×10(4) J mol(-1) at 310 K, respectively. The acting forces between ferulic acid and DNA mainly included hydrophobic interaction and hydrogen bonds. Acridine orange displacement studies revealed that ferulic acid can substitute for AO probe in the AO-DNA complex which was indicative of intercalation binding. Thermal denaturation study suggested that the interaction of ferulic acid with DNA could result in the increase of the denaturation temperature, which indicated that the stabilization of the DNA helix was increased in the presence of ferulic acid. Spectroscopic techniques together with melting techniques and viscosity determination provided evidences of intercalation mode of binding for the interaction between ferulic acid and ctDNA.

Shedding light on the interactions of guanine quadruplexes with tricationic metalloporphyrins

G-quadruplex DNA presents a potential target for the design and development of novel anticancer drugs. The porphyrin TMPyP4 was early reported to be a suitable motif for G-quadruplex DNA interaction. We inserted various metal ions such as Zn(II), Cu(II), Co(III) in the center of the aromatic core of tricationic TMPyP4-like porphyrin and examined their interactions with an antiparallel G-quadruplex DNA by a combination of spectroscopy and Job plot methods. Porphyrin metallation allowed the conclusion that the presence of one axial ligand perpendicular to the aromatic plane did not hamper π-π stacking interactions between quadruplex and the aromatic parts of porphyrin on the other face while porphyrin with two axial ligands was unable to undergo such interaction due to geometrical factors. Free base porphyrin and porphyrin without axial ligands are able to stabilize the quadruplex structure to a greater extent than the other metal complexes and thus may be potential anti-cancer drugs.

Spectroscopic studies of DNA interactions with food colorant indigo carmine with the use of ethidium bromide as a fluorescence probe

The interaction of indigo carmine (IC) with calf thymus DNA in physiological buffer (pH 7.4), using ethidium bromide (EB) dye as a fluorescence probe, was investigated by ultraviolet-visible absorption, fluorescence, and circular dichroism (CD) spectroscopy, coupled with viscosity measurements and DNA-melting studies. Hypochromicity of the absorption spectra of IC and enhancement in fluorescence polarization of IC were observed with the addition of DNA. Moreover, the binding of IC to DNA was able to decrease iodide and single-stranded DNA (ssDNA) quenching effects, increase the melting temperature and relative viscosity of DNA, and induce the changes in CD spectra of DNA. All of the evidence indicated that IC interacted with DNA in the mode of intercalative binding. Furthermore, the three-way synchronous fluorescence spectra data obtained from the interaction between IC and DNA-EB were resolved by parallel factor analysis (PARAFAC), and the results provided simultaneously the concentration information and the pure spectra for the three reaction components (IC, EB, and DNA-EB) of the system at equilibrium. This PARAFAC demonstrated that the intercalation of IC molecules into DNA proceeded by substituting for EB in the DNA-EB complex. The calculated thermodynamic parameters, ΔH° and ΔS°, suggested that both hydrophobic interactions and hydrogen bonds played a predominant role in the binding of IC to DNA.

A three-layer ONIOM model for the outside binding of cationic porphyrins and nucleotide pair DNA

In this work we investigated the outside binding mode between a cationic porphyrin and a nucleotide pair of DNA, adenine-thymine and guanine-cytosine, in a supramolecular assembly. We used two structural models (semi-extended, extended) that differ in the size of porphyrin, two kinds of theoretical methods: a three layer ONIOM (B3LYP/6-31G(d)/PM3/UFF), and DFT B3LYP/6-31G(d,p), and three cationic porphyrins. ONIOM method was first tested on the semi-extended model that was calculated in four environments: gas phase, solution phase using an explicit solvent model (H(2)O), in the presence of a sodium cation (Na(+)) and in both (H(2)O + Na(+)). From interaction energy results, we found that the affinity of the cationic substituent by the adenine nucleotide is favored upon the thymine nucleotide. The extended model that considers the whole porphyrin was applied in the gas phase to the four nucleotides. All the cationic porphyrins showed affinity by the nucleotides in the order adenine > guanine > thymine > cytosine. The interaction energy values for outside binding showed a strong porphyrin-nucleotide interaction (≈-90 kcal mol(-1)), that slightly varies between the nucleotides suggesting that this kind of cationic porphyrin has a little selectivity for some of them. We also found that the effect of the nature of the cationic substituent (chain length) in the porphyrin on the outside binding is small (≈2-13 kcal mol(-1)). Coherence between the results showed that ONIOM is a useful tool to get a reasonable molecular geometry to be used as a starting point in calculations of density functional theory.

DNA-binding, spectroscopic and antimicrobial studies of palladium(II) complexes containing 2,2'-bipyridine and 1-phenylpiperazine

With the purpose of evaluating the ability of Pd(II) complex to interact with DNA molecule as the main biological target, two new complexes [Pd(bpy)(OH(2))(2)] (1) and [Pd(Phenpip)(OH(2))(2)] (2), where (bpy=2,2'-bipyridine; Phenpip=1-phenylpiperazine), have been synthesized and the binding properties of these complexes with CT-DNA were investigated. The intrinsic binding constants (K(b)) calculated from UV-Vis absorption studies were 3.78×10(3) M(-1) and 4.14×10(3)M(-1) for complexes 1 and 2 respectively. Thermal denaturation has been systematically studied by spectrophotometric method and the calculated ΔT(m) was nearly 5 °C for each complex. All the results suggest an electrostatic and/or groove binding mode for the interaction between the complexes and CT-DNA. The redox behavior of the two complexes in the absence and in the presence of calf thymus DNA has been investigated by cyclic voltammetry. The cyclic voltammogram exhibits one quasi-reversible redox wave. The change in E(1/2), ΔE(p) and I(pc)/I(pa) supports that the two complexes exhibit strong binding to calf thymus DNA. Further insight into the binding of complexes with CT-DNA has been made by gel electrophoresis, where the binding of complexes is confirmed through decreasing the intensity of DNA bands. The two complexes have been screened for their antimicrobial activities using the disc diffusion method against some selected Gram-positive and Gram-negative bacteria. The activity data showed that both complexes were more active against Gram-negative than Gram-positive bacteria. It may be concluded that the antimicrobial activity of the compounds is related to cell wall structure of bacteria.

Synthesis, spectroscopic, crystal structure and DNA binding of Ru(II) complexes with 2-hydroxy-benzoic acid [1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-ethylidene]-hydrazide

Reactions of 2-hydroxy-benzoic acid [1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-ethylidene]-hydrazide (H(2)L) with [RuHCl(CO)(EPh(3))(3)] (E = P or As) were carried out and the new complexes obtained were characterized by elemental analysis, electronic, IR, (1)H NMR and (13)C NMR spectroscopic techniques and single crystal X-ray diffraction studies. Complex (1) crystallizes in the monoclinic space group P2(1)/c with unit cell dimensions a=18.6236(17) Å, b=12.8627(12) Å, c=21.683(2) Å, α=90.00, β=114.626(2), γ=90.00 V=4721.8(8) Å, Z=4. The crystal structure of the complex shows Ru(II) atom is six-coordinated, forming a slightly distorted octahedral geometry with two P atoms in axial positions, and three chelating donor atoms of the tridentate Schiff base ligand and one carbonyl group located in the equatorial plane. The molecular structure is stabilized by intramolecular O-H···N interactions. No intermolecular hydrogen bond was observed. The intramolecular hydrogen bond exists between the oxygen atom from salicylic acid moiety and nitrogen from the same moiety. A variety of solution studies were carried out for the determination of DNA binding mode of the complexes. The results suggest that both complexes bind to Herring sperm DNA via non intercalative mode.

Molecular spectroscopic studies of farrerol interaction with calf thymus DNA

The interaction between farrerol and calf thymus DNA in a pH 7.4 Tris-HCl buffer was investigated with the use of neutral red (NR) dye as a spectral probe by UV-vis absorption, fluorescence, and circular dichroism (CD) spectroscopy, as well as viscosity measurements and DNA melting techniques. It was found that farrerol molecules could intercalate into the base pairs of DNA as evidenced by decreases in iodide quenching effect and single-stranded DNA (ssDNA) quenching effect, induced CD spectral changes, and significant increases in relative viscosity and denaturation temperature of DNA. Furthermore, the spectral data matrix of the competitive reaction between farrerol and NR with DNA was resolved with an alternative least-squares (ALS) algorithm, and the concentration profiles in the reaction and the corresponding pure spectra for three species (farrerol, NR, and DNA-NR complex) were obtained. This ALS analysis demonstrated the intercalation of farrerol to the DNA by substituting for NR in the DNA-NR complex. Moreover, the thermodynamic parameters enthalpy change (ΔH°) and entropy change (ΔS°) were calculated to be -16.49 ± 0.51 kJ mol(-1) and 32.47 ± 1.02 J mol(-1) K(-1) via the van't Hoff equation, which suggested that the binding of farrerol to DNA was driven mainly by hydrophobic interactions and hydrogen bonds.

Spectroscopic studies of the interaction between pirimicarb and calf thymus DNA

The interaction between pirimicarb and calf thymus DNA in physiological buffer (pH 7.4) was investigated with the use of Neutral Red (NR) dye as a spectral probe by UV-vis absorption, fluorescence and circular dichroism (CD) spectroscopy, as well as viscosity measurements and DNA melting techniques. The results revealed that an intercalation binding should be the interaction mode of pirimicarb to DNA. CD spectra indicated that pirimicarb induced conformational changes of DNA. The binding constants of pirimicarb with DNA were obtained by the fluorescence quenching method. The thermodynamic parameters, enthalpy change (ΔHθ) and entropy change (ΔSθ) were calculated to be -52.13±2.04 kJ mol(-1) and -108.8±6.72 J mol(-1) K(-1) according to the van't Hoff equation, which suggested that hydrogen bonds and van der Waals forces might play a major role in the binding of pirimicarb to DNA. Further, the alternative least squares (ALS) method was applied to resolve a complex two-way array of the absorption spectra data, which provided simultaneously the concentration information for the three reaction components, pirimicarb, NR and DNA-NR. This ALS analysis indicated that the intercalation of pirimicarb into the DNA by substituting for NR in the DNA-NR complex.