Spectroscopic studies on the interactions between novel bisnaphthalimide derivatives and calf thymus DNA

A phenanthroline-based erbium (III) complex: molecular docking, DNA/BSA -binding and biological evaluation

With the help of both theoretical as well as experimental research, in vitro binding research with CT-DNA (calf thymus) and BSA (bovine serum albumin) were carefully examined to figure out the chemotherapeutic and pharmacokinetic facets of the Erbium complex, which contains 1,10-phenanthroline (Phen). The binding characteristics and the mechanism of complex's interaction with DNA as well as the protein were determined utilizing fluorescence quenching method. Findings indicated that the complex's interaction with DNA via groove binding into DNA's minor grooves, with their binding constants falling within the 104 M-1 range. Furthermore, thermodynamic characteristics and the fluorescence emission of the tryptophan residues of the protein were obtained through fluorescence quenching studies at different temperatures. According to the results of the binding constants, the protein's interactions with the Er- complex were moderate, demonstrating that the compound may be transported effectively by the protein. Molecular docking results supported that of the experimental research. The HeLa and MCF-7 cancer cell lines, along with the normal human fibroblast cell line, were used in an MTT assay evaluation of the Er-complex cytotoxicity. The Er-complex displayed a selective inhibitory effect on the proliferation of different cancer cells.

Insight into the intercalation of N-substituted acridine-9-amines into DNA based on spectroscopic and calorimetric analysis

The study delves into the binding properties of acridine-9-amine and its selected, mainly N-substituted derivatives (A9As), with calf thymus deoxyribonucleic acid (CT-DNA). This investigation, conducted using UV-Vis spectrophotometry, steady-state fluorescence spectroscopy and isothermal titration calorimetry, provides insights into the relationship between their structure and activity. The absorption spectra of the A9As exhibited a slight red shift and significant hypochromic effects, while the fluorescence emission intensities decreased in the presence of CT-DNA. These results suggest that all fluorescent substrates intercalate into the double helix of native DNA to varying degrees. The binding constants for the A9As/CT-DNA complexes (log(KA) were determined using various techniques in the range from 2.59 to 5.50). The thermodynamic parameters of A9As binding to DNA were obtained from ITC measurements (ΔG from - 7.51 to - 6.75 kcal·mol-1, ΔH from - 11.58 to - 3.83 kcal·mol-1, and TΔS from - 4.83 to 3.68 kcal·mol-1) and indicated that the formation of all the investigated A9As-DNA complexes is an enthalpy-driven process. The study also discusses the influence of the emitters' structure and electronic properties of substituents on intercalation efficiency. This knowledge serves as a guide for further research and offers directions for functionalising new acridines as potential reagents. It also provides the latest information on the ability of intercalation to DNA, which can be instrumental in studies on the mechanism of binding small aromatic molecules to DNA and can potentially contribute to new anticancer drug designs.

Rational design and synthesis of triazene-amonafide derivatives as novel potential antitumor agents causing oxidative damage towards DNA through intercalation mode

In this work, we rationally designed and synthesized two novel triazene-amonafide derivatives 2-(2-(diisopropylamino)ethyl)-5-(3,3-dimethyltriaz-1-en-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (D-11) and 5-(3,3-diethyltriaz-1-en-1-yl)-2-(2-(diisopropylamino)ethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (D-12) as potential antitumor agents. The DNA damage induced by the intercalation mode of D-11 (D-12) towards DNA was electrochemically detected through the construction of efficient biosensors. The consecutive processes of reversible redox of naphthylimide ring and irreversible oxidation of triazene moiety were elucidated on the surface of glassy carbon electrode (GCE) by CV, SWV, and DPV methods. Electrochemical biosensors were obtained through the immobilization of ctDNA, G-quadruplexes, poly(dG), and poly(dA), respectively, on the clean surface of GCE. After the incubation of biosensors with D-11 or D-12, the peaks of dGuo and dAdo decreased prominently, and the peak of 8-oxoGua appeared at +0.50 V, suggesting that the interaction between D-11 (D-12) and DNA could result in the oxidative damage of guanine. Unexpected, the as-prepared DNA biosensor possessed satisfactory anti-interference property and good practicability in real samples. UV-vis and fluorescence spectra, and gel electrophoresis assays were employed to further confirm the intercalation mode of D-11 (D-12) towards DNA base pairs. Moreover, D-11 was proved to exhibit stronger anti-proliferation activity than mitionafide and amonafide against both A549 and HeLa cell lines.

Studying the interaction between the new neodymium (Nd) complex with the ligand of 1,10-phenanthroline with FS-DNA and BSA

To learn more about the chemotherapeutic and pharmacokinetic properties of a neodymium complex containing 1,10-phenanthroline (dafone), In vitro binding was investigated with bovine serum albumin and fish-salmon DNA, using a variety of molecular modeling research and biophysical approaches. A variety of spectroscopic techniques including fluorescence and absorption were used to investigate the interplay between DNA/BSA and the neodymium complex. The findings revealed that the Nd complex had a high affinity for BSA and DNA interplays through van der Waals powers. In addition, the binding of the Nd complex to FS-DNA mainly in the groove binding mode clearly reflects with iodide quenching studies, ethidium bromide (EtBr) exclusion assay, ionic strength effect, and viscosity studies. It was observed that the Nd complex binds to FS-DNA through a minor groove with 3.81 × 105 (M-1). Also, Kb for BSA at 298 K was 5.19×105 (M-1), indicating a relatively high affinity of the Nd complex for DNA and BSA. In addition, a competitive study of a docking investigation revealed that the neodymium complex interacts at BSA site III. The results obtained from the binding calculations are well consistent with the experimental findings. Also, cytotoxicity studies of Nd complex were performed in MCF-7 and A-549 cell lines and the results show that this new complex has a selective inhibitory effect on the growth of various cancer cells.

Spectroscopic studies on noncovalent binding of nicotinamide-modified BRCA1 (856-871) analogs to calf thymus DNA

Various peptide drugs have entered the market with the development of molecular biology. Peptide drugs are used for treat diseases such as diabetes, breast cancer, and HIV infection. In this study, three nicotinamide-modified peptides were synthesized by modifying the N-terminus of BRCA1 (856-871, Y856R, K862Y, R866W) peptide with three nicotinic acid derivatives using solid-phase peptide synthesis. The results of calf thymus DNA (ctDNA) binding activity indicated that binding constants of BRCA1 (856-871, Y856R, K862Y, R866W) (P0) and three nicotinamide-modified peptides (P1, P2, and P3) to ctDNA were 1.89 × 10³, 2.97 × 10⁴, 7.61 × 10⁴, and 8.09 × 10⁴ L·mol^-1, respectively. The binding affinity of the modified peptides was superior to that of BRCA1 (856-871, Y856R, K862Y, R866W). ΔH^θ < 0 and ΔS^θ < 0 indicated that van der Waals force and hydrogen bond contributed most to peptide-ctDNA binding. Results obtained by Circular dichroism (CD) indicated that peptide binding interaction led to conformational changes in ctDNA. Ultraviolet-visible (UV) spectroscopy, ethidium bromide (EB) competition experiments, DNA melting experiments, and viscosity measurements verified that peptides interacted with ctDNA via groove binding. Ionic strength experiments manifested that electrostatic binding was also involved in peptide-ctDNA binding.

Structural, spectroscopic, in silico, in vitro and DNA binding evaluations of tyrosyl-lysyl-threonine

The main objective of the present study is to investigate the molecular structure and DNA binding interaction of the tyrosyl-lysyl-threonine (YKT) tripeptide, which has anticancer, antioxidant and analgesic properties, using various in silico (MD, QM, molecular docking), spectroscopic (UV, FT-IR, FTIR-ATR, Raman, gel electrophoresis) and in vitro (MCF-7 and HeLa cancer cell lines and BEAS-2B cell line) methods. The optimized geometry, vibrational wavenumbers, molecular electrostatic potential (MEP), natural bond orbital (NBO) and HOMO-LUMO (highest occupied molecular orbital- lowest unoccupied molecular orbital) calculations were carried out with Density Functional Theory (DFT) using B3LYP/6-311++G(d,p) basis set to indicate conformational, vibrational and intramolecular charge transfer characteristics. The assignment of all fundamental theoretical vibration wavenumbers was performed using potential energy distribution analysis (PED). DNA is a significant pharmacological target of drugs in several diseases such as cancer. For this reason, molecular docking calculation was used to elucidate the binding and interaction between YKT tripeptide and DNA at the atomic level. Also, the dynamic behaviors of YKT and DNA was examined using MD simulations. Besides, the interaction of YKT with DNA was experimentally examined by UV titration method and agarose gel electrophoresis method. Experimental results showed that YKT was intercalatively and electrostatically bound to CT-DNA (Calf thymus DNA) and cleavage pBR322 DNA in the presence of H₂O₂. The pharmacokinetic profile of YKT was also obtained. Cytotoxic effect of YKT was evaluated on MCF-7, HeLa and BEAS-2B cell lines. Hence, these studies about YKT tripeptide may pave the way for the development of various cancer drugs. Communicated by Ramaswamy H. Sarma.

Synergistically activated dual-locked fluorescent probes to monitor H2S-induced DNA damage

Naphthalimide-based fluorescent probes (NAN0-N3 and NAN6-N3) were developed with dual locked fluorescence. Here, ≥1.9 × 10^-2 mM of H₂S and ≥2.2 × 10^-2 μg mL^-1 of DNA could unlock a highly sensitive off-on fluorescence response through synergistic changes of the molecular structure and conformation. As such, the probes could monitor DNA damage induced by the overexpression of H₂S, and were able to evaluate the degree of apoptosis of living cells mediated by H₂S-induced mtDNA or nDNA damage.

Exploring the binding characteristics of febuxostat, an inhibitor of xanthine oxidase with calf thymus DNA: Multi-spectroscopic methodologies and molecular docking

In this paper, the interacting characteristics of febuxostat (FBST), an inhibitor of xanthine oxidase for treating gout patients with hyperuricemia with calf thymus DNA (ctDNA) was investigated through multi-spectroscopic methodologies combined with theoretical calculation for understanding the interacting mode on ctDNA, affinity with ctDNA, interacting forces, as well as the alteration in the conformation of ctDNA after interacting FBST The experimental results demonstrated that interacting FBST with ctDNA formed 1:1 complex, the association constant was 913 M^-1 at 298 K, suggesting the affinity of FBST on ctDNA was very weak, the interacting mode of FBST on ctDNA was groove binding, and it inserted into the minor groove with rich A-T region of ctDNA. Based on the results of the thermodynamic analysis and theoretical calculation, it can be inferred that the dominated interacting forces between FBST and ctDNA were van der Waals forces and hydrogen bond. And, interacting FBST with ctDNA was a spontaneous, enthalpy-driven, and exothermic process because of ΔG⁰ < 0, ΔH⁰ < 0, and |ΔH⁰| > T|ΔS⁰|. The results of the circular dichroism (CD) measurements indicated the conformation of ctDNA was weakly disturbed after interacting with FBST but still maintained B-conform. The studied results offer significant insight into further clarifying whether it has genotoxicity.

Laurus nobilis L. Essential Oil-Loaded PLGA as a Nanoformulation Candidate for Cancer Treatment

The aim of this study was to obtain essential oil (LNEO) from the Laurus nobilis L. plant, and to prepare LNEO-loaded poly lactic-co-glycolic acid (PLGA) nanoparticles (NPs) as an approach in cancer treatment. The components of the obtained LNEO were analyzed using GC-MS. The LNEO-NPs were synthesized by the single-emulsion method. The LNEO-NPs were characterized using UV-Vis spectrometry, Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM), and a DNA binding assay, which was performed via the UV-Vis titration method. According to the results, the LNEO-NPs had a 211.4 ± 4.031 nm average particle size, 0.068 ± 0.016 PdI, and -7.87 ± 1.15 mV zeta potential. The encapsulation efficiency and loading capacity were calculated as 59.25% and 25.65%, respectively, and the in vitro drug release study showed an LNEO release of 93.97 ± 3.78% over the 72 h period. Moreover, the LNEO was intercalatively bound to CT-DNA. In addition, the mechanism of action of LNEO on a dual PI3K/mTOR inhibitor was predicted, and its antiproliferative activity and mechanism were determined using molecular docking analysis. It was concluded that LNEO-loaded PLGA NPs may be used for cancer treatment as a novel phytotherapeutic agent-based controlled-release system.

In vitro anticancer and antibacterial activates of the yttrium(III) complex and its nano-carriers toward DNA cleavage and biological interactions with DNA and BSA; An experimental and computational studie

OBJECTIVES

In this research, the biological properties of the yttrium (III) (Y) complex, with 2,9-dimethyl- 1,10-phenanthroline (Me₂Phen) ligand, were examined for in vitro fish DNA (FS-DNA)/ bovine serum albumin (BSA) interactions, DNA-cleavage, anticancer and antibacterial activities.

METHODS

Multi-spectrophotometric techniques and computational calculations were used for the interaction studies of the BSA and FS-DNA with the Y-complex. Absorption and fluorescence spectroscopy methods were used to define thermodynamic parameters, the binding constants (K_b), and the probable binding mechanism. Also, the DFT (density functional theory) study and molecular docking calculation of the Y-complex were done. Besides, the nanocarriers of Y-complex (lipid nanoencapsulation (LNEP) and the starch nanoencapsulation (SNEP)), as active anticancer candidates, were prepared. Finally, DNA-cleavage, anticancer, and antibacterial activities of this complex were investigated.

RESULTS

The absorption and fluorescence measurements were exhibited that the Y-complex has a high binding affinity to FS-DNA and BSA through a static mechanism. The negative thermodynamic parameter values for both DNA/BSA binding were confirmed that the hydrogen bonds and van der Waals forces played an essential role in the spontaneous bonding procedure. The site marker competitive studies for BSA confirmed that the Y-complex bonds to the sub-domain IB of protein (site III) on BSA, which was entirely agreement by docking calculation. The complex has displayed efficient DNA cleavage, antifungal and antibacterial activities. The anticancer activity of the Y-complex and its starch/lipid nano-encapsulated was carried out in cancer cell lines, which exposed considerably high activity.

CONCLUSIONS

Thus, Y-complex can be transported professionally through BSA in the blood and bonds in the groove of DNA. Base on biological applications of the Y-complex, it can be concluded that this complex and its nanocarriers can suggest as novel anticancer and antibacterial candidates.

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 K_b 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.

Increasing DNA binding affinity of doxorubicin by loading on Fe3O4 nanoparticles: A multi-spectroscopic study

Magnetic Fe₃O₄ nanoparticles were synthesized successfully by co-precipitation method and characterized using XRD, SEM and EDS analyses. Then doxorubicin (DOX, a known anticancer drug) was loaded onto nanoparticles. In vitro DNA interaction of free DOX and loaded DOX onto Fe₃O₄ nanoparticles (DOX-Fe₃O₄) was investigated by DNA-viscosity measurements, UV-visible and fluorescence spectroscopies. The obtained values for binding constant of DOX and DOX-Fe₃O₄ compounds from UV-visible spectroscopies were 0.04 × 10⁵ and 0.68 × 10⁵ L mol^-1, respectively, which confirms DOX-Fe₃O₄ compound have a stronger interaction with CT-DNA compared to DOX. Considerable changes on viscosity of the compounds recommended that their binding mode with CT-DNA is intercalative binding. Fluorescence intensity of DOX and DOX-Fe₃O₄ was quenched via static process by regular addition of CT-DNA. Thermodynamic parameters suggest that Van der Waals forces and hydrogen bonding for DOX and electrostatic forces for DOX-Fe₃O₄ are predominantly responsible for interaction with CT-DNA. Competition fluorescence studies were done by Hoechst 33258 as a well-known groove binder and ethidium bromide (EtBr) as a known intercalator probe. Percentage of displacement for EtBr-DNA complex with DOX and DOX-Fe₃O₄ was 39% and 61%, and for Hoechst-DNA complex was 9% and 5%, respectively. These results confirmed that both compounds are intercalator binders, although DOX-Fe₃O₄ with a further 22% displacement is a stronger intercalator binder than DOX. The stronger interaction of DOX-Fe₃O₄ compared to DOX suggests that the current system can be used as a new and effective way to targeted therapy of anticancer drugs.

Parent and nano-encapsulated ytterbium(iii) complex toward binding with biological macromolecules, in vitro cytotoxicity, cleavage and antimicrobial activity studies

To determine the chemotherapeutic and pharmacokinetic aspects of an ytterbium complex containing 2,9-dimethyl-1,10-phenanthroline (Me₂Phen), in vitro binding studies were carried out with FS-DNA/BSA by employing multiple biophysical methods and a molecular modeling study. There are different techniques including absorption spectroscopy, fluorescence spectroscopy, circular dichroism studies, viscosity experiments (only in the case of DNA), and competitive experiments used to determine the interaction mode between DNA/BSA and the ytterbium-complex. The results showed that the Yb-complex exhibited a high propensity for the interaction of BSA and DNA via hydrophobic interactions and van der Waals forces. Further, a competitive examination and docking study showed that the interaction site of the ytterbium complex on BSA is site III. The results of docking calculations for DNA/BSA were in good agreement with experimental findings. The complex displays efficient DNA cleavage in the presence of hydrogen peroxide. Moreover, antimicrobial studies of different bacteria and fungi indicated its promising antibacterial activity. In vitro cytotoxicity studies of the Yb-complex, starch nano-encapsulated, and lipid nano-encapsulated were carried out in MCF-7 and A-549 cell lines, which revealed significantly good activity. The results of anticancer activity studies showed that the cytotoxic activity of the Yb-complex was increased when encapsulated with nanocarriers. Based on biological applications of the Yb-complex, it can be concluded that this complex and its nanocarriers can act as novel anticancer and antimicrobial candidates.

The biological applications of Yb-complexes including anticancer, antimicrobial and DNA cleavage ability, and their interaction with FS-DNA and BSA were examined.

In vitro anticancer activity of parent and nano-encapsulated samarium(iii) complex towards antimicrobial activity studies and FS-DNA/BSA binding affinity

Based on the potential anticancer properties of lanthanide complexes, the anticancer activity of the Sm(iii) complex containing a 2,2′-bipyridine ligand (bpy) and its interaction with FS-DNA (Fish-Salmon DNA) and BSA (Bovine Serum Albumin) were examined experimentally and by molecular docking in this paper. Absorption and fluorescence spectroscopic methods were used to define the thermodynamic parameters, binding constant (K_b), and the probable binding mechanism. It was concluded that the Sm complex interacts with FS-DNA through a minor groove with a K_b of 10⁵ M⁻¹. Also, the K_b for the BSA binding at 298 K was found to be 5.89 × 10⁵ M⁻¹, showing relatively a high tendency of the Sm complex to DNA and BSA. Besides, the Sm complex was docked to BSA and DNA by the autodock program. The results of the docking calculations were in good agreement with the experimental examinations. Additionally, the antifungal and antibacterial properties of this complex were investigated. The anticancer tests on the effect of the Sm complex, starch nano-encapsulation, and lipid nano-encapsulation in MCF-7 and A-549 cell lines were performed by the MTT method. It can be observed that the Sm complex and its nanocarriers presented a selective inhibitory effect on various cancer cell growths.

The biological properties of the Sm-complex, such as its interaction with FS-DNA and BSA, anticancer, and antimicrobial activities were studied.

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.

Synthesis, characterization and antitumor properties of selenium nanoparticles coupling with ferulic acid

Selenium nanoparticles (Se NPs) attract a lot of attention as potential cancer therapeutic agents. However, the antitumor activities of pure Se NPs are poor, and some modifiers are needed to enhance the activities. In the present study, we prepared Ferulic Acid (FA)-modified selenium nanoparticles in a facile synthetic approach. The obtained FA-Se NPs were characterized using transmission electron microscope (TEM), dynamic light scattering (DLS), ultraviolet-visible spectrophotometer (UV-VIS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Energy dispersive X-ray (EDX) spectroscopy. In vitro antitumor effects of FA, Se NPs and FA-Se NPs in HepG-2 cells were examined by methyl thiazolyl tetrazolium (MTT) assay. It showed that FA-Se NPs effectively inhibited the growth of HepG-2 cells with IC₅₀ value of 11.57 ± 3.6 μg/ml, while the value of Se NPs was >100 μg/ml. In addition, FA behaves no obvious antitumor effects at high concentrations up to 100 μg/ml. In order to investigate the antitumor mechanism of FA-Se NPs, fluorescence morphological examination and Annexin V-FITC/PI staining analysis were performed to observe the apoptosis of HepG-2 cells induced by FA-Se NPs. Meanwhile, mitochondrial membrane potential (MMP), intracellular reactive oxygen species (ROS) levels and caspase-3 and -9 activities were detected. The results revealed that FA-Se NPs induced intracellular ROS generation and MMP disruption by finally activating caspase-3/9 to trigger HepG-2 cells apoptosis through mitochondrial pathway. Further investigation on the interactions of FA-Se NPs with calf thymus DNA (ctDNA) indicated that the antitumor activities may be associated with the DNA-binding properties of FA-Se NPs.

Multi-spectroscopic and molecular docking studies on the interaction of darunavir, a HIV protease inhibitor with calf thymus DNA

Molecular interaction of darunavir (DRV), a HIV protease inhibitor with calf thymus deoxyribonucleic acid (ct-DNA) was studied in physiological buffer (pH7.4) by multi-spectroscopic approaches hand in hand with viscosity measurements and molecular docking technique. The UV absorption and fluorescence results together revealed the formation of a DRV-ct-DNA complex having binding affinities of the order of 10³M^-1, which was more in keeping with the groove binding. The results that DRV bound to ct-DNA via groove binding mode was further evidenced by KI quenching studies, viscosity measurements, competitive binding investigations with EB and Rhodamine B and CD spectral analysis. The effect of ionic strength indicated the negligible involvement of electrostatic interaction between DRV and ct-DNA. The thermodynamic parameters regarding the binding interaction of DRV with ct-DNA in terms of enthalpy change (ΔH⁰) and entropy change (ΔS⁰) were -63.19kJ mol^-1 and -141.92J mol^-1K^-1, indicating that hydrogen bonds and van der Waals forces played a predominant role in the binding process. Furthermore, molecular simulation studies suggested that DRV molecule was prone to bind in the A-T rich region of the minor groove of DNA.

Studies on free radical scavenging, cancer cell antiproliferation, and calf thymus DNA interaction of Schiff bases

Thirty-nine Schiff bases were synthesized by performing microwave-assisted condensation of the corresponding aldehydes and aromatic amines. Their reactive nitrogen species (RNS) scavenging activity and inhibitory effects against cancer cell growth were then subsequently investigated. Additionally, the interaction between the calf thymus DNA (ctDNA) and selected Schiff bases was evaluated using fluorescence spectroscopy, and their binding parameters were determined. The yields of the various compounds ranged from moderate to excellent (43-99%) after only a 2-min reaction. The hydroxylated Schiff bases 2, 8, 15, 16, 18, 20, 29, 32, 34, and 37 were found to be potent scavengers of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals with half-maximal scavenging concentration (SC₅₀) values lower than that of the positive control, resveratrol. The presence of hydroxyl substituents on the aromatic rings also proved essential to the cytotoxicity of the compounds. The binding constants (K_b) obtained using fluorescence spectroscopy ranged from 0.37 to 3.07×10⁵Lmol^-1, and were strongly influenced by the structure and hydroxylation degree. Schiff bases 3 and 8 showed promising cytotoxic activity, with half-maximal growth inhibitory (GI₅₀) values in the same order of magnitude as those exhibited by the reference drug, doxorubicin against various cell lines. Interestingly, these compounds also showed the highest K_b, suggesting that the cytotoxic activity could be related to their interaction with the DNA of the tumor cells. The results of this study highlighted some Schiff bases as potential lead compounds for the design of new free radical scavengers and anticancer agents.