DNA Melting Studies Research Articles

Interaction between antidepressant drug trazodone with double-stranded DNA: Multi-spectroscopic and computational analysis

Trazodone (TZD) is an antidepressant drug used to treat major depressive and sleeping disorders. Elevated doses of trazodone are associated with central nervous system depression, which manifests as nausea, drowsiness, confusion, vertigo, exhaustion, etc. To develop a clinically viable active pharmaceutical compound with minimal adverse effects, it is imperative to possess a comprehensive knowledge of the drug's action mechanism on DNA. Hence, we investigate the mode of interaction between trazodone and DNA utilizing various spectroscopic and computational techniques. Studies using UV–vis titration showed that the DNA and trazodone have an effective interaction. The magnitude of the Stern-Volmer constant (KSV) has been calculated to be 5.84 × 106 M−1 by the Lehrer equation from a steady-state fluorescence study. UV–vis absorption, DNA melting, dye displacement, and circular dichroism studies suggested that trazodone binds with DNA in minor grooves. Molecular docking and molecular dynamic simulation demonstrated that the TZD-DNA system was stable, and the mode of binding was minor groove. Furthermore, ionic strength investigation demonstrates that DNA and trazodone do not have a substantial electrostatic binding interaction.

Synthesis, characterization and multi-spectroscopic DNA/HSA interaction studies of synthetic human Follicle-Stimulating Hormone Beta 33–53 peptide conjugated PEGylated graphene oxide nanoparticles

The objective of the current study was to synthesize, characterize and explore the interaction of PEGylated graphene oxide (pGO) and synthetic human Follicular stimulating hormone β 33–53 peptide conjugated PEGylated graphene oxide nanoparticles (pGO-FSH) with human serum albumin (HSA) and calf thymus DNA (CT-DNA). The pGO/ pGO-FSH nanoparticles were synthesized using a modified Hummer’s method, and the FSH peptide was conjugated through a maleimide crosslinking reaction. Synthesized nanoparticles were then characterized using techniques like FT-IR, UV–Visible absorbance, CD and Raman spectroscopy, and XRD and TGA. Morphological and particle size analysis was studied using SEM, TEM, DLS, and zeta potential measurements. The presence of FSH β 33–53 peptide was confirmed qualitatively and quantitatively using CD spectroscopy and Bradford’s assay. Binding studies of pGO/pGO-FSH nanoparticles with HSA and DNA were carried out using biophysical techniques. The complex formation between pGO/pGO-FSH nanoparticles and HSA was revealed by UV absorbance spectroscopy, and the observed fluorescence quenching was confirmed by steady-state fluorescence spectroscopy. Time-resolved fluorescence quenching studies have shown that dynamic quenching plays an important role in binding HSA with pGO/pGO-FSH nanoparticles. However, structurally no significant changes were observed in the native structure of HSA upon binding with pGO/pGO-FSH nanoparticles suggesting that the latter did not induce any structural distortions together, confirmed by DSC, FT-IR, and CD spectroscopy experimental findings. Binding constants and thermodynamic parameters calculated using double logarithmic and Van’t Hoff plots suggested weak and moderate binding affinity along with the involvement of hydrophobic and hydrogen bonding interactions between HSA and pGO/pGO-FSH nanoparticles, respectively. UV absorbance and fluorescence spectroscopy have revealed that pGO/pGO-FSH nanoparticles interact with DNA by binding at the minor groove region. These findings were further confirmed by DNA melting and viscosity studies. CD and FT-IR spectroscopy studies have shown no changes in the helical structure of B-form of DNA, thereby emphasizing the groove-binding nature of pGO/pGO-FSH nanoparticles. The obtained results are useful in further considering the potentiality of pGO-FSH nanoparticles as drug-delivery systems for in vivo applications, especially to target ovarian cancer.

Multi-spectroscopic, thermodynamic and molecular simulation studies on binding of pyrroloquinoline quinone with DNA: coexistence of intercalation and groove binding modes

The interaction between enzyme-like pyrroloquinoline quinone (PQQ) and calf-thymus DNA (CT-DNA) has been investigated by means of multi-spectroscopic (UV-Vis, fluorescence and circular dichroism), isothermal titration calorimetric (ITC), viscometry and molecular docking and metadynamics simulation techniques. Absorption spectral data suggested the formation of a PQQ/CT-DNA complex, which quenched the fluorescence of PQQ via the dynamic quenching process. The results of CD spectral studies coupled with viscosity measurements, competitive binding assays with Hoechst 33258 and ethidium bromide (EB), KI quenching experiments, gel electrophoresis and DNA melting studies indicated groove binding mode of interaction of PQQ with CT-DNA. ITC experiment revealed that the complex formation is a spontaneous process (ΔGo < 0) with a binding constant of 1.05 × 104 M−1. The observed ΔHo < 0 and ΔSo < 0 pointed out that the complex is stabilized by van der Waals forces along with H-bonding interactions. The outcomes of molecular docking and simulation studies confirmed the binding of PQQ with DNA. The free energy surface (FES) analysis pointed out the existence of an equilibrium between partial intercalation and groove binding modes, which is in good agreement with the competitive binding assays. Communicated by Ramaswamy H. Sarma

DNA binding studies of antifungal drug posaconazole using spectroscopic and molecular docking methods

The binding studies of DNA with small molecules have been an emerging field of research all the time since DNA as the genetic material is a major biological target for various drugs. Interpretation of small molecule-DNA binding helps in understanding their interactions with designing new drugs of greater medicinal activity. Posaconazole is an antifungal drug in the class of triazoles which are known to possess numerous pharmacological properties. In this work, the nature of the binding of posaconazole with calf-thymus DNA has been studied using spectroscopic techniques and molecular docking studies. A binding constant of the order of 103 M−1 was observed from UV–visible and fluorescence studies for the interaction between posaconazole and calf-thymus DNA. The fluorescence property of posaconazole was found to be quenched by calf-thymus DNA with a quenching constant of the order of 103 M−1. Competitive displacement of ethidium bromide and Hoechst 33258 by posaconazole using fluorescence technique suggested minor groove binding of posaconazole in calf-thymus DNA. Confirmation of the binding mode was further complemented by the viscosity measurement and DNA melting studies followed by KI quenching experiments. The studies on the effect of ionic strength on the binding suggested a possible role of electrostatic force in the interaction. Molecular docking studies reflected a crescent shape of the posaconazole within the minor groove of calf-thymus DNA validating the experimental findings showing the residues involved in the interaction.

Deciphering the nature of binding of dexlansoprazole with DNA: Biophysical and docking approaches

Drugs, in general, exhibit their pharmacological activity in binding with intracellular targets. Numerous anticancer and antibacterial drugs target DNA as one of their primary intracellular targets. Dexlansoprazole (DLP) is a heterocyclic compound containing benzimidazole moiety and a proton pump inhibitor used to treat gastroesophageal reflux disease. The interaction of dexlansoprazole with calf thymus DNA (ct-DNA) has been studied using biophysical methods. The UV–Visible studies revealed a binding constant of 2.15 ± 0.3 × 104 M−1 which is close to the value of 2.44 ± 0.3 × 104 M−1 obtained from the fluorescence studies. Competitive displacement studies using the fluorescence spectroscopic method with ethidium bromide and Hoechst as DNA markers suggested the groove binding mode of DLP in ct-DNA. The groove binding mode of DLP in ct-DNA was complemented by the results of viscosity and DNA melting studies. Further studies on the effect of ionic strength and potassium iodide on DLP binding with ct-DNA supported the observed binding mode. Circular dichroism studies reflected no significant conformational variation in ct-DNA after the interaction. The binding mode obtained from the experimental studies was corroborated by the molecular docking studies that showed the position of DLP in the minor groove of ct-DNA along with the receptor interface restudies involved in the interaction.

DNA-Triggered Enhancement of Singlet Oxygen Production by Pyridinium Alkynylanthracenes.

There is an ongoing interest in 1 O2 sensitizers, whose activity is selectively controlled by their interaction with DNA. To this end, we synthesized three isomeric pyridinium alkynylanthracenes 2 o-p and a water-soluble trapping reagent for 1 O2 . In water and in the absence of DNA, these dyes show a poor efficiency to sensitize the photooxygenation of the trapping reagent as they decompose due to electron transfer processes. In contrast, in the presence of DNA 1 O2 is generated from the excited DNA-bound ligand. The interactions of 2 o-p with DNA were investigated by thermal DNA melting studies, UV/vis and fluorescence spectroscopy, and linear and circular dichroism spectroscopy. Our studies revealed an intercalative binding with an orientation of the long pyridyl-alkynyl axis parallel to the main axis of the DNA base pairs. In the presence of poly(dA : dT), all three isomers show an enhanced formation of singlet oxygen, as indicated by the reaction of the latter with the trapping reagent. With green light irradiation of isomer 2 o in poly(dA : dT), the conversion rate of the trapping reagent is enhanced by a factor >10. The formation of 1 O2 was confirmed by control experiments under anaerobic conditions, in deuterated solvents, or by addition of 1 O2 quenchers. When bound to poly(dG : dC), the opposite effect was observed only for isomers 2 o and 2 m, namely the trapping reagent reacted significantly slower. Overall, we showed that pyridinium alkynylanthracenes are very useful intercalators, that exhibit an enhanced photochemical 1 O2 generation in the DNA-bound state.

Interaction of two peptide drugs with biomacromolecules analyzed by molecular docking and multi-spectroscopic methods

Peptide drugs, which are mainly used for the treatment of AIDS, myeloma, and breast cancer, have evolved rapidly owing to their high efficacy and low side effects. The interaction mechanisms of two peptide drugs with two biological macromolecules (protein and DNA), which are of great significance in disease prevention and drug design, were investigated using molecular docking, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, UV–visible spectroscopy and viscosity measurements. The interaction between a series of common drugs and ovalbumin (OVA) was simulated by molecular docking, and two peptide drugs with the highest energy values, namely atazanavir and carfilzomib, were selected; the binding energy values of these drugs with OVA were −59.20 and −55.93 kcal/mol, respectively. The Kb values of the interaction of the two drugs with OVA/DNA were in the range of 104-107 M−1, and the binding affinity of the drugs was stronger with OVA than with DNA. Hydrogen bonds and van der Waals forces were very important for the binding between drugs and OVA through molecular docking studies, and it was consistent with experimental results (ΔH < 0, ΔH < 0). The synchronous fluorescence spectrum showed that the interaction caused a change to the original structure of OVA, and atazanavir had a greater effect on OVA than carfilzomib. CD spectrum analysis also demonstrated that the conformation of OVA changed slightly. The interaction between atazanavir and DNA was mainly driven by hydrophobic forces (ΔH > 0 and ΔH > 0), whereas the major interaction forces involved in the binding of carfilzomib with DNA were hydrogen bonds and van der Waals forces. DNA melting studies, UV–visible spectroscopy, CD spectroscopy and viscosity measurements established that the interaction between the drugs and DNA was groove binding.

A concise synthesis of isoguanine 2ʹ-deoxyriboside and its adenine-like triplex formation when incorporated into DNA

A concise synthesis of 2’-deoxyisoguanosine is achieved whereby 2,6-dichloropurine is glycosylated using the Hoffer sugar to give a pair of beta-configured nucleoside N9/N7 regioisomers that are aminated using methanolic ammonia with concomitant deprotection of the sugar. Following chromatographic separation, pure 2-chloro-2’-deoxyadenosine was isolated as a single isomer. Displacement of the C2 chlorine atom using sodium benzyloxide, followed by hydrogenolysis of the benzyl group, gives 2’-deoxyisoguanosine. Isoguanine was incorporated into DNA by solid supported synthesis using the suitably protected 2-allyloxy-2’-deoxyadenosine phosphoramidite with the allyl group being removed post-oligomerisation under Noyori conditions. DNA melting studies showed isoguanine to exhibit adenine-like triplex formation.

Interaction of memantine with calf thymus DNA: an in-vitro and in-silico approach and cytotoxic effect on the cancerous cell lines

Memantine belongs to the class of cognition enhancers that functions as NMDA receptor antagonist, used to treat Alzheimer's disease. The interaction of memantine with DNA was not investigated. In the present study, the interaction of memantine with ct-DNA, as well as its cytotoxicity on cancer cells, was evaluated. UV-visible spectroscopy, steady-state fluorescence spectroscopic studies revealed the interaction between memantine and ct-DNA. The quenching studies, chemical denaturation, (CD), and DNA melting studies showed the groove binding mode of memantine with ct-DNA. The thermodynamic parameters revealed that the interaction between memantine and ct-DNA is enthalpically driven, and the stabilizing forces involved were hydrogen bonding and van der Waals interaction. The groove-binding was also observed by molecular docking studies, which corroborated the findings of spectroscopic investigations. Density function theory calculations confirmed the existence of electron donor and recipient groups. The stability of memantine and DNA interaction, as well as the critical residues involved in the interaction, was identified by molecular dynamics simulations. Memantine showed cytotoxicity towards the cancer cells as compared to normal cells, as observed by MTT assay. Inverted compound microscopy analysis of memantine treated cancer cell lines further confirmed the results obtained by MTT assay. Communicated by Ramaswamy H. Sarma

Structural motives controlling the binding affinity of 9,10-bis(methylpyridinium)anthracenes towards DNA

In the search of new DNA groove binding agents a series of substituted 9,10-methylpyridiniumanthracenes have been synthesized and their interactions with DNA have been studied by UV/vis absorption, CD and fluorescence spectroscopy. A minor groove binding mode is confirmed by DNA melting studies, strong CD effects, the dependence of the binding affinity on ionic strength, and the differentiation between AT and GC base pairs. No binding occurs to GC sequences. Binding constants to calf thymus DNA (ct-DNA) and poly(dA:dT) in the range between 1 × 104 and 3 × 105 M−1 have been determined. The binding strength decreases with the size of substituents attached at the anthracene site. Variation of the substitution pattern of the charged groups shows that methyl groups in meta position cause slightly stronger binding than methyl groups in para position. In contrast, with these groups in ortho position, no binding interaction has been observed. The strongest binding is achieved with an expansion of the peripheral heterocycle from pyridine to quinoline. Molecular modeling reveals the pivotal role of the substitution pattern: Anthracenes with para and meta pyridines align along the minor grooves. On the other hand, the ortho derivative adopts no groove-alignment.

Antimicrobial activity and DNA/HSA interaction of fluorinated 3,6,9-trisubstituted acridines

A series of four new 3,6,9-trisubstituted acridine derivatives (two with fluorine substituents on phenyl ring) were synthesized and their interaction with calf thymus DNA and HSA was investigated using a combination of biochemical, biophysical and biological techniques. Analysis using fluorescent spectra provided valuable information about the formation of the acridine–DNA complex, while several other experiments suggest that acridine may bind to DNA through intercalation. These observations are further supported by LD spectral analysis, viscosity measurements and DNA melting studies. The interaction between HSA and four compounds were studied by fluorescence quenching spectra. In addition, the method was used for the calculation of characteristic binding parameters. These result and result obtained by synchronous fluorescence spectra of acridines with HSA determined that compounds create complexes with HSA and induce conformational changes. KB values were found to be of 1.51–7.34 × 106 M−1. The studied 8c compound were the most sensitive against S. epidermidis ATCC 12228.

Investigating the mechanism of binding of nalidixic acid with deoxyribonucleic acid and serum albumin: a biophysical and molecular docking approaches

Nalidixic acid is a bacterial DNA gyrase inhibitor and the first member of the synthetic quinolone antibiotics. It is used in the treatment of various infectious diseases like urinary tract infections, respiratory infections, sexually transmitted diseases, acute bronchitis, and sinusitis. Interactions studies are of great significance as it will be beneficial for designing new therapeutic molecules with preferable plasma solubility and its efficacy. In this paper, we have aim to ascertain the binding mode of nalidixic acid with calf thymus DNA (ct-DNA) and bovine serum albumin (BSA) through various biophysical and in silico method. UV-visible absorption and fluorescence spectroscopic experiments confirmed the formation of a complex between nalidixic acid with ct-DNA. The binding constant is in the range of 103 M−1, indicating the groove binding mode between ct-DNA and nalidixic acid. Groove binding mode was also validated by competitive displacement assay, potassium iodide quenching experiment, circular dichroism, DNA melting studies. In the case of BSA, UV-visible absorption and fluorescence spectroscopic experiments confirmed the formation of a complex between nalidixic acid with BSA. The value of a binding constant in the case of BSA was found to be 1.517 × 105 M−1. The site marker displacement experiment revealed the binding location of nalidixic acid to a site I in BSA. Secondary structural and microenvironmental changes also studied through circular dichroism and three-dimensional fluorescence. Furthermore, the synchronous fluorescence spectra of BSA with nalidixic acid showed that there were changes in the microenvironment around tryptophan residues. In silico molecular docking further confirmed the binding of nalidixic acid to site I in BSA and the minor groove of DNA.Communicated by Ramaswamy H. Sarma

Room temperature synthesis of NIR emitting Ag2S nanoparticles through aqueous route and its influence on structural modulation of DNA.

Near infra-red (NIR) light emitting nanomaterials had shown great promise in clinical imaging in view of negligible absorption by skin or tissue of mammalian. Thus, it demands for synthesizing stable NIR emitting nanomaterials in water environment. The present work presents synthesis of biologically acceptable luminescent near-IR emitting silver sulfide nanoparticles through an aqueous route using 2-mercaptoethanol. The prepared as-synthesized Ag2S nanoparticles exhibited bright photoluminescence with quantum yield of ca. 4%. X-ray diffraction (XRD) analysis indicated that the products were monoclinic α-Ag2S. Fourier transform infrared spectral analysis revealed that the stretching vibration at 2560 cm-1 responsible for S-H bond of thiol group disappeared suggesting the conjugation of 2-mercaptoethanol with Ag2S nanoparticles. In view of investigating any possible effect on genetic materials, interactions of the synthesized particles with calf thymus DNA was investigated employing Ethidium bromide (EB) as structural probe. To understand the binding mechanism, the UV-vis absorption, fluorescence and circular dichroism (CD) spectroscopic, as well as DNA melting studies measurements were carried out. The observed results confirm that nanoparticles interact with DNA through groove binding.

Spectroscopic studies of interactions of 2-(2-Oxo-2-Phenylethyl)-1, 2-benzisothiazol-3(2H)-one-1, 1-dioxide with human DNA

The interaction of small molecules with DNA has become the most prominent area of research for the discovery of new drugs that may be helpful in curing of the diseases. The present research work was designed to explore the interactions of 2-(2-Oxo-2-Phenylethyl)-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (BTZDO) with DNA by spectroscopic methods in physiological buffers of pH 4.7 and 7.4. Spectral results showed the hypochromic and bathochromic shifts after addition of DNA. The binding constant (Kf) of 5.18 × 102 and 8.62 × 102 Lmol−1 were determined at pH 4.7 (stomach pH) and 7.4 (blood pH) respectively. Strong values of binding constants reflected strong complex between BTZDO and DNA. The observed values of binding constant suggested that the intake of BTZDO inside human body via blood is more effective as compared to the oral intake. The interpretation of physical mode to intake the newly synthesized BTZDO drug into human body is the novelty of this research work. An intercalation binding of the BTZDO with DNA was supported by the results obtained from DNA melting studies. The Gibbs free energy calculated at pH 4.7 was −15.22 kJmol-1 and at pH 7.4 was −16.46 kJmol-1. The negative values of free energies are the prerequisite that the binding process to be spontaneous. Thermodynamic parameters (enthalpy and entropy) were also calculated. The enthalpy calculated for this system was −29.23 kJmol−1K−1 at pH 4.7 and −52.56 kJmol−1K−1 at pH 7.4. The entropy calculated for present system at pH 4.7 was −48.22 Jmol−1K−1 and at 7.4 the value was −122.89 Jmol−1K−1. Negative values of entropy predicted that a compact complex was formed between BTZDO and DNA. The focal point of this investigation was the observation of the effect of temperature on binding between the BTZDO and DNA, nature of complex formed and especially, the preferred mode adopted for the intake of medicine.

Interaction studies of sodium cyclamate with DNA revealed by spectroscopy methods.

The interaction between sodium cyclamate (SC) and calf thymus DNA in simulated physiological buffer (pH 7.4) using ethidium bromide (EB) as fluorescence probe was investigated by UV-vis spectrometry (UV), fluorescence, resonance light scattering (RLS) and Fourier transform infrared (FT-IR) spectroscopy, along with DNA melting studies and cyclic voltammetric (CV) measurements. The results indicate that SC can not only bind into the minor groove of DNA, but also intercalate into the DNA Base pairs. Based on UV data, the binding constant K and binding sites n of the formed DNA/SC complex were estimated to be 2.83 × 103 mol/L and 2.0, respectively. Fluorescence results demonstrate that the quenching of DNA/EB induced by SC can mainly be attributed to static procedure. The melting studies and CV analysis further confirm that the interaction mechanism between the SC and DNA is similar to that of DNA intercalator.The results of FT-IR spectra show that a specific interaction mainly exist between SC and adenine and guanine bases of DNA, which resulting in potential damage due to some change in the information structure. The DNA saturation binding value estimated to be 1.67 based on the RLS data also indicated that SC may cause damage of DNA.

Capecitabine as a minor groove binder of DNA: molecular docking, molecular dynamics, and multi-spectroscopic studies

The interaction mechanism and binding mode of capecitabine with ctDNA was extensively investigated using docking and molecular dynamics simulations, fluorescence and circular dichroism (CD) spectroscopy, DNA thermal denaturation studies, and viscosity measurements. The possible binding mode and acting forces on the combination between capecitabine and DNA had been predicted through molecular simulation. Results indicated that capecitabine could relatively locate stably in the G-C base-pairs-rich DNA minor groove by hydrogen bond and several weaker nonbonding forces. Fluorescence spectroscopy and fluorescence lifetime measurements confirmed that the quenching was static caused by ground state complex formation. This phenomenon indicated the formation of a complex between capecitabine and ctDNA. Fluorescence data showed that the binding constants of the complex were approximately 2 × 104 M−1. Calculated thermodynamic parameters suggested that hydrogen bond was the main force during binding, which were consistent with theoretical results. Moreover, CD spectroscopy, DNA melting studies, and viscosity measurements corroborated a groove binding mode of capecitabine with ctDNA. This binding had no effect on B-DNA conformation.

Spectroscopic and computational approaches to unravel the mode of binding between a isoflavone, biochanin-A and calf thymus DNA

In the present study, attempt was made to explore the interaction between biochanin-A (BioA) and calf thymus DNA (ctDNA) by employing fluorescence spectroscopy, absorption spectroscopy, circular dichroism (CD), DNA melting studies, viscosity measurements, and molecular modeling methods. A well-known fluorescence probe, acridine orange (AO) was used in the present study in order to enhance the emission intensity of weakly fluorescent ctDNA. Quenching in emission intensity of ctDNA-AO system was observed in the presence of different concentrations of BioA, suggesting that BioA has interacted with ctDNA. The hyperchromic effect observed upon the addition of BioA in the absorption spectra of ctDNA-AO without any shift in its absorption maximum revealed that BioA was bound to ctDNA through groove mode of binding. Further the groove mode of binding of BioA to ctDNA was confirmed by DNA melting studies, viscosity measurements, and molecular docking studies. The results of fluorescence measurements that were carried out at different temperature indicated that the BioA has quenched the emission intensity of ctDNA-AO through static mode of quenching mechanism. Thermodynamic parameters revealed that the BioA-ctDNA-AO system was stabilized by van der Waals forces and hydrogen bonding. The effect of binding of BioA on the conformation of ctDNA was examined by circular dichroism studies.

In vitro DNA binding studies of therapeutic and prophylactic drug citral

The study of drug-DNA interactions is of great importance, as it paves the way towards the design of better therapeutic agents. Here, the interaction of DNA with a therapeutic and prophylactic drug citral has been studied. We have attempted to ascertain the mode of binding of citral with calf thymus DNA (Ct-DNA) through various biophysical techniques. Analysis of the UV–visible absorbance spectra and fluorescence spectra indicated the formation of a complex between citral and Ct-DNA. Competitive binding assays with ethidium bromide (EB), acridine orange (AO) and Hoechst 33258 reflected that citral possibly intercalates within the Ct-DNA. These observations were further confirmed by circular dichroism (CD) spectral analysis, viscosity measurements, DNA melting and molecular docking studies. This study is expected to contribute to a better understanding of molecular mechanisms of citral, and design of new drugs in the future.

Cytotoxicity of Aconitum alkaloid and its interaction with calf thymus DNA by multi-spectroscopic techniques

The cytotoxicities of three aconitum alkaloids- aconitine, hypaconitine and mesaconitine, and their abilities to bind DNA have been explored. Rat myocardial cells H9c2 were treated with aconitum alkaloids and assessed the cytotoxicities by using MTT assay and flow cytometry. Apoptosis was evidenced by the results of the annexin V/propidium iodide (PI) assay. Aconitine was found to be the most toxic in rat myocardial cells H9c2 in three aconitum alkaloids. At the same time, DNA adducts were isolated and then analyzed by UV-Vis spectroscopy after exposure to alkaloids, which indicated that three alkaloids could bind to DNA in rat myocardial cells H9c2. Furthermore, their binding modes were investigated by UV-Visible, fluorescence, DNA melting studies and ionic strength effect. Results indicated that the interaction between three alkaloids and DNA were intercalation coupled with electrostatic effect. The estimated binding constants were between 4.83 × 105 M−1 to 9.85 × 105 M−1 for three alkaloids at 298 K.

Relating DNA base-pairing in aqueous media to DNA polymerase fidelity.

Controversy surrounds the perceived absence of a relationship between DNA polymerase fidelity (kinetic discrimination) and free energy changes determined from DNA melting studies (thermodynamic discrimination). Thermodynamic discrimination together with aqueous solvent effects can account for kinetic fidelities on the order of those observed experimentally.