Rumana Qureshi

Negotiation of Intracellular Membrane Barriers by TAT-Modified Gold Nanoparticles

This paper contributes to the debate on how nanosized objects negotiate membrane barriers inside biological cells. The uptake of peptide-modified gold nanoparticles by HeLa cells has been quantified using atomic emission spectroscopy. The TAT peptide from the HIV virus was singled out as a particularly effective promoter of cellular uptake. The evolution of the intracellular distribution of TAT-modified gold nanoparticles with time has been studied in detail by TEM and systematic image analysis. An unusual trend of particles disappearing from the cytosol and the nucleus and accumulating massively in vesicular bodies was observed. Subsequent release of the particles, both by membrane rupture and by direct transfer across the membrane boundary, was frequently found. Ultimately, near total clearing of particles from the cells occurred. This work provides support for the hypothesis that cell-penetrating peptides can enable small objects to negotiate membrane barriers also in the absence of dedicated transport mechanisms.

Voltammetric and spectroscopic investigations of 4-nitrophenylferrocene interacting with DNA.

Cyclic voltammetry (CV) coupled with UV-vis and fluorescence spectroscopy were used to probe the interaction of potential anticancer drug, 4-nitrophenylferrocene (NFC) with DNA. The electrostatic interaction of the positively charged NFC with the anionic phosphate of DNA was evidenced by the findings like negative formal potential shift in CV, ionic strength effect, smaller bathochromic shift in UV-vis spectroscopy, incomplete quenching in the emission spectra and decrease in viscosity. The diffusion coefficients of the free and DNA bound forms of the drug were evaluated from Randles-Sevcik equation. The binding parameters like binding constant, ratio of binding constants (K(red)/K(ox)), binding site size and binding free energy were determined from voltammetric data. The binding constant was also determined from UV-vis and fluorescence spectroscopy with a value quite close to that obtained from CV.

Redox Behavior of Anticancer Chalcone on a Glassy Carbon Electrode and Evaluation of its Interaction Parameters with DNA

The interaction of anticancer chalcone [AMC, 1-(4′-aminophenyl)-3-(4-N,N-dimethylphenyl)-2-propen-1-one] with DNA has been explored using electrochemical, spectroscopic and viscometric techniques. A shift in peak potential and decrease in peak current were observed in cyclic voltammetry and hypochromism accompanied with bathochromic shift were noticed in UV-Vis absorption spectroscopy. These findings were taken as evidence for AMC –DNA intercalation. A binding constant (K) with a value of 6.15 × 105 M−1 was obtained from CV data, which was also confirmed by UV-Vis absorption titration. Moreover, the diffusion coefficient of the drug with and without DNA (Db and Du), heterogeneous electron transfer rate constant (ko) and electron affinity (A) were also calculated from electrochemical data.

Synthesis, spectroscopic characterization, X-ray structure and evaluation of binding parameters of new triorganotin(IV) dithiocarboxylates with DNA

Three new triorganotin(IV) dithiocarboxylates (1-3) with general formula R(3)SnL, where R=C(4)H(9) (1), C(6)H(11) (2), C(6)H(5) (3) and L=4-(4-nitrophenyl)piperazine-1-carbodithioate, have been synthesized and characterized by elemental analysis, Raman, FT-IR, multinuclear NMR ((1)H, (13)C and (119)Sn) and mass spectrometry. The crystal structure of complex 3 confirmed distorted trigonal-bipyramidal geometry around Sn atom. The interaction of compounds 1-3 with DNA was investigated by cyclic voltammetry (CV) and UV-vis spectroscopy. The positive peak potential shift in CV and hypochromic effect in spectroscopy evidenced intercalative mode of interaction. The results indicate that the binding affinity varies in this sequence: 1>3>2.

Spectrophotometric analysis of flavonoid-DNA binding interactions at physiological conditions.

Mode of interactions of three flavonoids [morin (M), quercetin (Q), and rutin (R)] with chicken blood ds.DNA (ck.DNA) has been investigated spectrophotometrically at different temperatures including body temperature (310 K) and at two physiological pH values, i.e. 7.4 (human blood pH) and 4.7 (stomach pH). The binding constants, K(f), evaluated using Benesi-Hildebrand equation showed that the flavonoids bind effectively through intercalation at both pH values and body temperature. Quercetin, somehow, showed greater binding capabilities with DNA. The free energies of flavonoid-DNA complexes indicated the spontaneity of their binding. The order of binding constants of three flavonoids at both pH values were found to be K(f(Q)) > K(f(R)) > K(f(M)) and at 310 K.

Characterization and DNA binding studies of unexplored imidazolidines by electronic absorption spectroscopy and cyclic voltammetry

UV-Vis spectroscopic behavior of four imidazolidine derivatives i.e., [5-benzylideneimidazolidine-2,4-dione (NBI), 5-(2-hydroxybenzylidene)imidazolidine-2,4-dione (HBI), 5-(4-methoxybenzylidene)imidazolidine-2,4-dione (MBI) and 5-(3,4-di-methoxybenzylidene)imidazolidine-2,4-dione (DBI)] was studied in a wide pH range. Spectroscopic response of the studied compounds was found sensitive to pH and the attached substituents. Incited by anti-tumor activity, structural miscellany and biological applications of imidazolidines, the DNA binding affinity of some novel derivatives of this class of compounds was examined by cyclic voltammetry (CV) and UV-Vis spectroscopy at pH values of blood (7.4) and lysosomes (4.5). The CV results showed the following order of binding strength: KNBI (6.40×10(6)M(-1))>KHBI (1.77×10(5)M(-1))>KMBI (2.06×10(4)M(-1))>KDBI (1.01×10(4)M(-1)) at pH 7.4. The same order was also obtained from UV-Vis spectroscopy. The greater affinity of NBI justified its preferred candidature as an effective anti-cancer drug. The DNA binding propensity of these compounds was found comparable or greater than most of the clinically used anticancer drugs.

Electrochemical behavior of 1-ferrocenyl-3-phenyl-2-propen-1-one on glassy carbon electrode and evaluation of its interaction parameters with DNA

The electrochemical behavior of 1-ferrocenyl-3-phenyl-2-propen-1-one (ferrocenylone) and its interaction with DNA was studied by a glassy carbon electrode using cyclic voltammetry (CV) technique. The results from CV were supported by UV-Visible spectroscopy performed under the similar conditions. The positive peak potential shift in CV and the bathochromic shift in the UV-Vis absorption spectra suggested an intercalative mode of binding. The binding constant (K = 1.39 ± 0.02 × 104 mol-1 L) and the binding site size (0.53 bp) were obtained from voltammetric data which leads to a standard Gibbs free energy change (ΔGo= -RT lnK) of -23.64 kJ mol-1 and hence indicated the spontaneity of the binding interaction. The values of binding constants obtained from UV-Vis absorption and CV measurements, 1.26 ± 0.01 × 104 and 1.39 ± 0.02 × 104 mol-1 L respectively, were in close agreement.

Electrochemical behaviour of dimethyl-2-oxoglutarate on glassy carbon electrode

The electrochemical behaviour of dimethyl-2-oxoglutarate (MOG), a key intermediate in the Krebs cycle and an important nitrogen transporter in the metabolic pathways in biological processes, was investigated by cyclic voltammetry, square wave voltammetry and differential pulse voltammetry using a glassy carbon electrode. The reduction of MOG is an irreversible diffusion-controlled process that occurs in a cascade mechanism. For electrolytes with pH <3.0 and pH >7.0 one peak occurred and for 3.0<pH<8.0 two peaks corresponding to consecutive charge transfer reactions were observed. The effects of scan rate, concentration and pH of the electrolyte solution were monitored, and both peaks were found to shift cathodically with the increase in pH. DPV measurements allowed the determination of the number of electrons and protons i.e., one electron and one proton, involved in the reduction mechanism of MOG. Based upon the results obtained a reduction mechanism was proposed and the observed waves were attributed to the hydroxylation of the keto group of MOG to form dimethyl-2-hydroxyglutarate. Furthermore, two methodologies for the electroanalytical determination of MOG were also compared.

Electrochemical reduction mechanism of camptothecin at glassy carbon electrode

Camptothecin (CPT) is a cytotoxic quinoline alkaloid endowed with the inhibition of topoisomerase I, an essential enzyme for the normal functioning of DNA. The redox behaviour of CPT was investigated at a glassy carbon electrode using cyclic, differential pulse and square wave voltammetry. It was shown that CPT can undergo reduction in a pH-dependent mechanism. In acid media only one irreversible charge transfer reaction was observed whereas by increasing the pH of the supporting electrolyte, two reduction peaks occurred. The diffusion coefficient of CPT was calculated in pH 4.5 0.1M acetate buffer using cyclic voltammetry to be D(CPT)=5.77x10(-6)cm(2)s(-1). Differential pulse voltammetry measurements were carried out over a wide pH range and allowed the determination of the number of electrons and protons transferred during each step in the CPT reduction mechanism, one electron and one proton. The use of square wave voltammetry proved the quasi-reversibility of CPT reduction as a function of the pH of the supporting electrolyte. Based upon the results obtained a reduction mechanism was proposed and the observed waves were attributed to the hydroxylation of the lactone ring of CPT to a lactol ring.

Monitoring of 2-butanone using a Ag–Cu bimetallic alloy nanoscale electrochemical sensor

Spherical shaped silver–copper alloy nanoparticles of 10–15 nm size were synthesized by an aqueous polymer solution method. The synthesized nanoscale Ag–Cu alloy was characterized by UV-Visible spectroscopy, X-ray diffraction spectroscopy, transmission electron microscopy (TEM), high resolution TEM, and energy dispersive spectroscopy. The XRD pattern showed high crystallinity and phase formation of the nanoparticles. The bimetallic alloy nanoparticles were coated over a well-polished glassy carbon electrode and the designed sensor was applied for the detection of a highly carcinogenic carbonyl compound, 2-butanone. Electrochemical studies revealed that PEI used as a capping agent also enhances the sensing of the modified electrode for the recognition of 2-butanone. The sensor developed from Ag–Cu (1 : 1) alloy nanoparticles showed the best sensing properties for the detection of 2-butanone as evidenced by electrochemical impedance spectroscopy and a 0.1 μM detection limit.