Spectroscopic exploring the affinities, characteristics, and mode of binding interaction of curcumin with DNA

Solvent Effects on the Photophysical Properties of a Donor-acceptor Based Schiff Base

In this work, a donor-acceptor substituted aromatic system ((E)-N-((E)-3-(4 (dimethylamino)phenyl) allylidene)-4-(trifluoromethyl) benzenamine (DPATB) has been synthesized and its detailed photophysics of intramolecular charge transfer process have been explored on the basis of steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state. Effect on addition of acid and pH on steady state spectral properties further reveals excited state charge transfer character. Quantum chemical calculations were performed in order to study the conformation and polarity of DPATB at their ground as well as excited electronic states. The HOMO and LUMO molecular orbital pictures are obtained at DFT level using B3LYP functional and 6-311 + g(d,p) basis set which clearly support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction. In this work, detailed photophysics of excited state intramolecular charge transfer process in donor-acceptor system (DPATB) was evaluated using steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring in DPATB. Molecular orbital pictures as obtained from DFT based computational analysis reveals a significant change in the distribution of electron density upon transition from HOMO to LUMO which confirms an ICT process occurring from the donor group to the acceptor moiety in the excited state.

Multiple phenyl ring appended Re-based complexes for strong visible light absorption and DNA binding

A series of facial-Re(CO)3-based acyclic complexes (1-3) possessing N∩O bis-chelating ligands and a triphenylphosphine oxide donor was synthesized and characterized. The most interesting structural feature of these complexes is that both the coordinated ligands are functionalized with external phenyl rings. Single crystal X-ray diffraction analysis confirms that each molecule demonstrates a variety of intermolecular supramolecular interactions via the external phenyl rings. All the complexes displayed strong absorption (ε = 14 000-40 000 M-1 cm-1) over wide visible region (400-600 nm). Due to the interesting structural and photophysical properties of the complexes, a satisfactory DNA binding ability was observed. The binding of the complexes with DNA grooves was confirmed by a significant increase in the absorption intensities of the complexes in the visible region, absorption enhancement of DNA and circular dichroism.

UV-Vis Spectrophotometric Analysis of DNA Retrieval for DNA Storage Applications

Informational Deoxyribonucleic Acid (iDNA) has gained the attention of many researchers and pioneer companies for the development of novel storage systems for the long-term and high-density storing of information. This research focuses on the physical storage of iDNA strands to address some of the current challenges by evaluating the accuracy of the process of iDNA retrieval from the surface after the dehydration process. For this aim, a UV-Vis spectrophotometric technique was used to measure the concentration of the DNA samples. Although spectroscopy has been widely employed for the evaluation of DNA concentration and contamination in a solution, it has not been used to investigate dry-state DNA, which is one of the preferred storage formats for the long-term retention of information. These results demonstrate that the UV-Vis spectrophotometric technique can be used to accurately measure dry-state DNA before the retrieval and its residues after the DNA retrieval process. This paper further examines the storage/retrieval process by investigating the relationship between the storage time and the amount of retrieved DNA or the DNA residue left on various surfaces. Based on the experimental results demonstrated and discussed in this paper, UV-Vis spectrophotometry can be used for monitoring dry-state DNA with a high accuracy larger than 98%. Moreover, these results reveal that the hydrophilicity and hydrophobicity of the surface do not significantly affect DNA retrieval over a one-month time period.

Novel electro self-assembled DNA nanospheres as a drug delivery system for atenolol

We describe new method for preparing DNA nanospheres for a self-assembled atenolol@DNA (core/shell) drug delivery system. In this paper, we propose the electrochemical transformation of an alkaline polyelectrolyte solution of DNA into DNA nanospheres. We successfully electrosynthesized DNA nanospheres that were stable for at least 2 months at 4 °C. UV-visible spectra of the prepared nanospheres revealed a peak ranging from 372 to 392 nm depending on the DNA concentration and from 361 to 398.3 nm depending on the electrospherization time. This result, confirmed with size distribution curves worked out from transmission electron microscopy (TEM) images, showed that increasing electrospherization time (6, 12 and 24 h) induces an increase in the average size of DNA nanospheres (48, 65.5 and 117 nm, respectively). In addition, the average size of DNA nanospheres becomes larger (37.8, 48 and 76.5 nm) with increasing DNA concentration (0.05, 0.1 and 0.2 wt%, respectively). Also, the affinity of DNA chains for the surrounding solvent molecules changed from favorable to bad with concomitant extreme reduction in the zeta potential from -31 mV to -17 mV. Principally, the attractive and hydrophobic interactions tend to compact the DNA chain into a globule, as confirmed by Fourier transform infrared spectroscopy (FTIR) and TEM. To advance possible applications, we successfully electro self-assembled an atenolol@DNA drug delivery system. Our findings showed that electrospherization as a cost-benefit technique could be effectively employed for sustained drug release. This delivery system achieved a high entrapment efficiency of 68.03 ± 2.7% and a moderate drug-loading efficiency of 3.73%. The FTIR spectra verified the absence of any chemical interaction between the drug and the DNA during the electrospherization process. X-ray diffraction analysis indicated noteworthy lessening in atenolol crystallinity. The present findings could aid the effectiveness of electrospherized DNA for use in various other pharmaceutical and biomedical applications.

DNA-BINDING and DNA-protecting activities of small natural organic molecules and food extracts

The review summarizes literature data on the DNA-binding, DNA-protecting and DNA-damaging activities of a range of natural human endogenous and exogenous compounds. Small natural organic molecules bind DNA in a site-specific mode, by arranging tight touch with the structure of the major and minor grooves, as well as individual bases in the local duplex DNA. Polyphenols are the best-studied exogenous compounds from this point of view. Many of them demonstrate hormetic effects, producing both beneficial and damaging effects. An attempt to establish the dependence of DNA damage or DNA protection on the concentration of the compound turned out to be successful for some polyphenols, daidzein, genistein and resveratrol, which were DNA protecting in low concentrations and DNA damaging in high concentrations. There was no evident dependence on concentration for quercetin and kaempferol. Probably, the DNA-protecting effect is associated with the affinity to DNA. Caffeine and theophylline are DNA binders; at the same time, they favor DNA repair. Although most alkaloids damage DNA, berberine can protect DNA against damage. Among the endogenous compounds, hormones belonging to the amine class, thyroid and steroid hormones appear to bind DNA and produce some DNA damage. Thus, natural compounds continue to reveal beneficial or adverse effects on genome integrity and provide a promising source of therapeutic activities.

Label-Free Fluorescent Aptasensor for Small Targets via Displacement of Groove Bound Curcumin Molecules

Signal transduction based on fluorescence is one of the most common optical aptasensors for small molecules. Sensors with a number of unique features including high sensitivity, low cost, and simple operation can be constructed easily. However, the label-free fluorescent approach is limited to synthetic dyes that bind strongly to the aptamer sequence and result in a diminished sensor operation with high detection limits. In this study, we report the use of curcumin as a fluorescent probe to signal aptamer/small target binding events. A substantial enhancement in curcumin's fluorescent emission was observed when bound into the grooves of vitamin D₃ (VTD3) binding aptamer, as an example. However, the introduction of the target molecule causes the aptamer to undergo a conformational change that favors complexing the target molecule over binding the curcumin dye. The sensor was able to detect VTD3 down to 1 fM concentration in buffer solutions and extracted blood samples, operate at a wide dynamic range, and discriminate against potential biological interfering molecules including VTD2. The operation of the curcumin based fluorescent sensor is at least six orders of magnitude more sensitive than a VTD3 sensor constructed with the synthetic dye SYBR Green I. The generality of the reported label-free approach was applied with a previously isolated 75-mer bisphenol-A (BPA) aptamer, confirming that the reported sensing strategy is not confined on a particular aptamer sequence. Our work not only reports a novel sensor format for the detection of small molecules, but also serves fluorescent sensor's most pressing need being novel fluorophores for multiplex targets detection.

Cooperativity effect of the ππ interaction between drug and DNA on intercalative binding induced by H-bonds: a QM/QTAIM investigation of the curcuminadenineH2O model system

In order to reveal the nature of intercalative binding of drug to DNA, the cooperativity effect of the ππ interaction was investigated in the curcuminadenineH2O model system by applying a combined QM and QTAIM computational approach. The H-bonds between the electron-donating group of curcumin and adenine induce the formation of the ππ stacking. The introduction of H2O weakens the H-bonding and ππ interactions, leading to an anti-cooperativity effect, as is confirmed by the AIM (atoms in molecules) and RDG (reduced density gradient) analysis. Thus, it can be inferred that the anti-cooperative effect is the main driving force for the intercalative binding of drug to DNA bases, which is in agreement with many experimental phenomena. Therefore, the designed DNA-targeted intercalating drugs should possess not only hydrophobic moieties, but also strong electron-donating groups bound to the DNA bases with H-bonds, which can slow the variation rates of the strengths of the H-bonding and ππ interactions between drug and DNA bases in the anti-cooperative process, leading to the intercalation formation. The enthalpy change is the major factor driving the positive thermodynamic cooperativity.

Curcumin stably interacts with DNA hairpin through minor groove binding and demonstrates enhanced cytotoxicity in combination with FdU nucleotides

We report, based on biophysical studies and molecular mechanical calculations that curcumin binds DNA hairpin in the minor groove adjacent to the loop region forming a stable complex. UV-Vis and fluorescence spectroscopy indicated interaction of curcumin with DNA hairpin. In this novel binding motif, two ɣ H of curcumin heptadiene chain are closely positioned to the A₁₆-H8 and A₁₇-H8, while G₁₂-H8 is located in the close proximity of curcumin α H. Molecular dynamics (MD) simulations suggest, the complex is stabilized by noncovalent forces including; π-π stacking, H-bonding and hydrophobic interactions. Nuclear magnetic resonance (NMR) spectroscopy in combination with molecular dynamics simulations indicated curcumin is bound in the minor groove, while circular dichroism (CD) spectra suggested minute enhancement in base stacking and a little change in DNA helicity, without significant conformational change of DNA hairpin structure. The DNA:curcumin complex formed with FdU nucleotides rather than Thymidine, demonstrated enhanced cytotoxicity towards oral cancer cells relative to the only FdU substituted hairpin. Fluorescence co-localization demonstrated stability of the complex in biologically relevant conditions, including its cellular uptake. Acridine orange/EtBr staining further confirmed the enhanced cytotoxic effects of the complex, suggesting apoptosis as mode of cell death. Thus, curcumin can be noncovalently complexed to small DNA hairpin for cellular delivery and the complex showed increased cytotoxicity in combination with FdU nucleotides, demonstrating its potential for advanced cancer therapy.

Curcumin "Drug" Stabilized in Oxidovanadium(IV)-BODIPY Conjugates for Mitochondria-Targeted Photocytotoxicity

Ternary oxidovanadium(IV) complexes of curcumin (Hcur), dipicolylamine (dpa) base, and its derivatives having pendant noniodinated and di-iodinated boron-dipyrromethene (BODIPY) moiety (L₁ and L₂, respectively), namely, [VO(dpa)(cur)]ClO₄ (1), [VO(L₁)(cur)]ClO₄ (2), and [VO(L₂)(cur)]ClO₄ (3) and their chloride salts (1a-3a) were prepared, characterized, and studied for anticancer activity. The chloride salts were used for biological studies due to their aqueous solubility. Complex 1 was structurally characterized by single-crystal X-ray crystallography. The complex has a VO²⁺ moiety bound to dpa ligand showing N,N,N-coordination in a facial mode, and curcumin is bound in its mono-anionic enolic form. The V-O(cur) distances are 1.950(18) and 1.977(16) Å, while the V-N bond lengths are 2.090(2), 2.130(2), and 2.290(2) Å. The bond trans to V═O is long due to trans effect. The complexes are stable in a solution phase over a long period of time of 48 h without showing any apparent degradation of the curcumin ligand. The diiodo-BODIPY ligand (L₂) or Hcur alone showed limited solution stability in dark. The emissive BODIPY (L₁) containing complex 2a showed preferential mitochondrial localization in MCF-7 cells in cellular imaging experiments. The cytotoxicity of the complexes was studied by MTT assay. The BODIPY complex 3a showed excellent photodynamic therapy effect in visible light (400-700 nm) giving IC₅₀ values of 2-6 μM in HeLa and MCF-7 cancer cells, while being less toxic in dark (∼100 μM). The cell death was apoptotic in nature involving reactive oxygen species (ROS). Mechanistic data from pUC19 DNA photocleavage studies revealed photogenerated ROS as primarily ¹O₂ from the BODIPY moiety and ·OH radicals from the curcumin ligand.

A comprehensive approach to ascertain the binding mode of curcumin with DNA

Curcumin is a natural phytochemical from the rhizoma of Curcuma longa, the popular Indian spice that exhibits a wide range of pharmacological properties like antioxidant, anticancer, anti-inflammatory, antitumor, and antiviral activities. In the published literatures we can see different studies and arguments on the interaction of curcumin with DNA. The intercalative binding, groove binding and no binding of curcumin with DNA were reported. In this context, we conducted a detailed study to understand the mechanism of recognition of dimethylsulfoxide-solubilized curcumin by DNA. The interaction of curcumin with calf thymus DNA (ctDNA) was confirmed by agarose gel electrophoresis. The nature of binding and energetics of interaction were studied by Isothermal Titration Calorimetry (ITC), Differential Scanning Calorimetry (DSC), UV-visible, fluorescence and melting temperature (T_m) analysis. The experimental data were compared with molecular modeling studies. Our investigation confirmed that dimethylsulfoxide-solubilized curcumin binds in the minor groove of the ctDNA without causing significant structural alteration to the DNA.

Binding properties of palmatine to DNA: spectroscopic and molecular modeling investigations

Palmatine, an isoquinoline alkaloid, is an important medicinal herbal extract with diverse pharmacological and biological properties. In this work, spectroscopic and molecular modeling approaches were employed to reveal the interaction between palmatine and DNA isolated from herring sperm. The absorption spectra and iodide quenching results indicated that groove binding was the main binding mode of palmatine to DNA. Fluorescence studies indicated that the binding constant (K) of palmatine and DNA was ~ 10(4)L·mol(-1). The associated thermodynamic parameters, ΔG, ΔH, and ΔS, indicated that hydrogen bonds and van der Waals forces played major roles in the interaction. The effects of chemical denaturant, thermal denaturation and pH on the interaction were investigated and provided further support for the groove binding mode. In addition to experimental approaches, molecular modeling was conducted to verify binding pattern of palmatine-DNA.

Biophysical studies on curcumin-deoxyribonucleic acid interaction: spectroscopic and calorimetric approach

The interaction of the dietary pigment curcumin with herring testes deoxyribonucleic acid was studied by biophysical and microcalorimetric techniques. Curcumin bound to DNA exhibiting hypochromic effect in absorbance and enhanced intensity of its fluorescence. The binding a affinity value evaluated from spectroscopy data was of the order 10(4) M(-1). The quantum efficiency value testified the occurrence of energy transfer from the DNA base pairs to the curcumin molecules. Displacement studies of DNA bound DAPI, Hoechst and ethidium bromide suggested binding of curcumin to be in the minor groove of the DNA. Moderate conformational perturbations of the B-form structure of DNA occurred on binding. The binding affinity weakened as the DNA GC content enhanced. The binding was characterized by negative enthalpy and positive entropy changes; the binding affinity from calorimetry was in good agreement with that evaluated from the spectral data. The binding was dominated by hydrophobic and other non-polyelectrolytic forces; the polyelectrolytic forces contributing only a quarter to the total Gibbs energy at 50 mM [Na(+)].