Plot of variation of enthalpy of binding (Δ<i>H^O</i>) with temperature.

<p>Plots for the binding of (A) spermine with CP DNA (▪), EC DNA (•), ML DNA (▴), (B) spermidine with CP DNA (□), EC DNA (○), ML DNA (▵), (C) putrescine with CP DNA (▪), EC DNA (•), ML DNA (▴) and (D) cadaverine with CP DNA (□), EC DNA (○), ML DNA (▵).</p

Thermal melting data and the binding constants from melting data at saturating concentrations of polyamines with CP DNA, EC DNA and ML DNA^a.

a<p>Melting stabilization of DNA (Δ<i>T</i>_m) in the presence of saturating amounts of polyamines are average of optical melting and DSC data.</p>b<p><i>K_T</i>_m is the binding constant at the melting temperature.</p>c<p><i>K</i>_obs is the polyamine binding constant at 293.15 K determined using equations described in the text.</p

Chemical structure of polyamines.

<p>Chemical structure of polyamines.</p

Displacement plots of ethidium bromide-DNA complexes by polyamines.

<p>Relative fluorescence intensity decrease of ethidium bromide (1.2 μM)-DNA(12.0 μM) complex induced by the binding of (A) spermine with CP DNA(-▪-), EC DNA (-•-), ML DNA (-▴-) and (B) spermidine with CP DNA(-▪-), EC DNA (-•-), ML DNA (-▴-) conducted in 10 mM SHE buffer pH 7.0 at 293.15 K (Inset: The values of IC₅₀ of CP, EC and ML DNA shown as a bar graph).</p

Melting profiles of DNA and DNA polyamine complexes.

<p>Optical melting profiles (upper panels) of (A) CP DNA (□), spermine-CP DNA(▵), spermidine-CP DNA (O), (B) EC DNA (□), spermine-EC DNA(▵), spermidine-EC DNA(O), (C) ML DNA (□), spermine-ML DNA(▵), spermidine-ML DNA(O). DSC melting profiles (lower panels) of (D) CP DNA (solid lines) (E) EC DNA (solid lines), (F) ML DNA (solid lines) and respective DNA–spermine complex (- - - -) and DNA-spermidine complex (….).</p

Plots of variationof thermodynamic parameters with entropy contribution.

<p>Plot of Δ<i>G^O</i> and Δ<i>H^O</i> versus <i>T</i>Δ<i>S^O</i> for the binding of (A) spermine with CP DNA (▪,•), EC DNA (▴,▾), ML DNA (♦,◂) (B) Plot of Δ<i>G^O</i> and Δ<i>H^O</i> versus <i>T</i>Δ<i>S^O</i> of spermidine with CP DNA (□,○), CT DNA (▵,▿), ML DNA (⋄,⊲), (C) Plot of Δ<i>G^O</i> and Δ<i>H^O</i> versus <i>T</i>Δ<i>S^O</i> of putrescine with CP DNA (▪,•), EC DNA (▴,▾), ML DNA (♦,◂) and (D) Plot of Δ<i>G^O</i> and Δ<i>H^O</i> versus <i>T</i>Δ<i>S^O</i> of cadaverine with CP DNA (□,○), EC DNA (▵,▿), ML DNA (⋄,⊲).</p

ITC profiles for the titration of polyamines with DNAs.

<p>Titration of spermine with (A) CP DNA (B) EC DNA (C) ML DNA and spermidine with (D) CP DNA (E) EC DNA (F) ML DNA at 293.15 K. The top panels represent the raw data for the sequential injection of polyamines into a solution of DNA and the bottom panels show the integrated heat data after correction of heat of dilution against molar ratio of DNA/[polyamine]. The data points were fitted to one site model and the solid line represent the best fit data.</p

Structural and Thermodynamic Studies on the Interaction of Iminium and Alkanolamine Forms of Sanguinarine with Hemoglobin

Binding of the iminium and alkanolamine forms of the benzophenanthridine anticancer alkaloid sanguinarine to hemoglobin (Hb) was investigated by absorbance, fluorescence, and circular dichroism spectral techniques, and by calorimetry. The binding affinity of the charged iminium was found to be of the order of 10⁶ M^–1, higher by one order than that of the neutral alkanolamine, from the analysis of the absorbance data. The fluorescence spectral data revealed that the quenching of Hb fluorescence by both forms of sanguinarine is due to the formation of a complex in the ground state and is of an unusual, static nature. Thermodynamic data revealed that the binding of the iminium form was exothermic in nature while that of the alkanolamine was endothermic; the former case predominantly involved electrostatic and hydrogen bonding interactions but the latter was dominated by mostly hydrophobic interactions. Calculation of the molecular distances (<i>r</i>) between the donor (β-Trp37) and acceptor (iminium and alkanolamine) according to Förster’s theory suggests both forms of the alkaloid to be bound close to β-Trp37 at the α1β2 interface of the protein. The iminium form induced greater secondary structural changes in Hb than the alkanolamine as revealed by synchronous fluorescence, circular dichroism and three-dimensional fluorescence spectroscopic studies. These results are consistent with a stronger binding of the iminium over the alkanolamine form. Nevertheless, the hydrophobic probe ANS was displaced from hemoglobin more easily by the alkanolamine form than by the iminium. The study showed that Hb binds more strongly to the biologically active iminium form than the alkanolamine, in contrast to the stronger binding of the latter to plasma protein serum albumin. Overall, this study presents insights on the interaction dynamics and energetics of the binding of the two forms of sanguinarine to hemoglobin

Circular dichroism spectral titration of DNA-poyamine complexes.

<p>Intrinsic CD spectra of (A) CP DNA (30 µM) treated with 0–63 µM (curves 1 to 7) spermine (B) CP DNA (30 µM) treated with 0–135 µM (curves 1 to 7 ) spermidine (C) EC DNA (30 µM) treated with 0–95 µM (curves 1 to 7) spermine (D) EC DNA (30 µM) treated with 0–175 µM (curves 1 to 7) spermidine (E) ML DNA (30 µM) treated with 0–120 µM (curves 1 to 7) spermine and (F) ML DNA (30 µM) treated with 0–250 µM (curves 1 to 7 ) spermidine at 293.15 K.</p

Targeting Double-Stranded RNA with Spermine, 1‑Naphthylacetyl Spermine and Spermidine: A Comparative Biophysical Investigation

RNA targeting is an evolving new approach to anticancer therapeutics that requires identification of small molecules to selectively target specific RNA structures. In this report, the interaction of biogenic polyamines spermine, spermidine and the synthetic analogue 1-naphthylacetyl spermine with three double-stranded RNA polynucleotidespoly­(I)·poly­(C), poly­(C)·poly­(G), and poly­(A)·poly­(U)has been described to understand the structural and thermodynamic basis of the binding and the comparative efficacy of the analogue over the natural polyamines. Circular dichroism spectroscopy, thermal melting experiments, and ethidium bromide displacement assay were used to characterize the interaction. Microcalorimetry studies were performed to deduce the energetics of the interaction and atomic force microscopy experiments done to gain insight into the interaction at the molecular level. The experiments demonstrated structural perturbations in the polynucleotides on binding of the polyamines. Thermal melting studies showed enhanced stabilization of RNA–polyamine complexes with increase in the total standard molar enthalpy of transition. The binding affinity was strongest for poly­(I)·poly­(C) as revealed by microcalorimetry results and varied as poly­(I)·poly­(C) > poly­(C)·poly­(G) > poly­(A)·poly­(U). The order of affinity for the polyamines was spermine >1-naphthylacetyl spermine > spermidine. Total enthalpy–entropy compensation and high standard molar heat capacity values characterized the interactions. The results of the study on the binding of polyamines to dsRNAs presented here have been compared to those reported earlier with dsDNAs. The present findings advance our knowledge on the mechanism of interaction of polyamines with RNA and may help in the search for analogues that can interfere with biogenic polyamine metabolism and function