How Do Structure and Charge Affect Metal-Complex Binding to DNA? An Upper-Division Integrated Laboratory Project Using Cyclic Voltammetry

Abstract

An advanced undergraduate laboratory project is described that integrates inorganic, analytical, physical, and biochemical techniques to reveal differences in binding between cationic metal complexes and anionic DNA (herring testes). Students were guided to formulate testable hypotheses based on the title question and a list of different metal complexes. Student teams synthesized the target complexes, such as tris(1,10-phenanthroline)cobalt(III) or tris(2,2′-bipyrydyl)cobalt(III), and characterized them by voltammetry and spectroscopy. Separately, DNA stock solutions were prepared and analyzed via published spectroscopic methods. Aliquots of the DNA solutions, added into a metal-complex solution, gave decreases in the cyclic voltammetry peak currents due to the slower diffusion rate of the DNA−metal complex. A nonlinear curve fit analysis of the 1:1 binding isotherms confirmed the literature result (unknown to students) of larger binding constants for the phenanthroline complex due to intercalative binding. Student team results were shared in a group meeting and assessment was by group reports and individual portfolios. The project was an effective way to link the various laboratory techniques common to the chemical disciplines and encouraged team building in a research atmosphere.

Electrochemiluminescence of the [Ru(bpy)3]2+ Complex: The Coreactant Effect of PAMAM Dendrimers in an Aqueous Medium

“…Thus, on the average, the anionic species, PO 4 H 2– , PO 4 H 2 – , and Cl – , in the medium basically bind to the positively charged interior, whereas the cationic species, [Ru(bpy) 3 ] 2+ and Na + , interact with the end carboxylate groups. Hence, an electrostatic binding of [Ru(bpy) 3 ] 2+ species with the electric field arising from a negatively charged surface of the G1.5 dendrimer could be operative. ,, Accordingly, it has been pointed out that E °′ values of the couples show a negative shift , when the concentrations of macromolecular receptor increase if the electrostatic interactions between the oxidized and reduced forms of the redox couple with the receptor are effective: italicE normalb ° ′ − italicE normalf ° ′ = 0.0592 nobreak0em0.25em⁡ log ( K 2 + K 3 + ) where the subscripts b and f refer to fully bound and free probes and K 2+ and K 3+ are the binding constants of the reduced and oxidized species of the couple, respectively. With the purpose of checking this question, the redox potentials of the [Ru(bpy) 3 ] 3+/2+ couple in several dendrimer solutions were determined.…”

“…Hence, an electrostatic binding of [Ru(bpy) 3 ] 2+ species with the electric field arising from a negatively charged surface of the G1.5 dendrimer could be operative. 2,11,27 Accordingly, it has been pointed out that E°′ values of the couples show a negative shift 28,29 when the concentrations of macromolecular receptor increase if the (5) where the subscripts b and f refer to fully bound and free probes and K 2+ and K 3+ are the binding constants of the reduced and oxidized species of the couple, respectively. With the purpose of checking this question, the redox potentials of the [Ru(bpy) 3 ] 3+/2+ couple in several dendrimer solutions were determined.…”

“…From Table , it can be seen that both negative and positive shifts for the redox potentials of the [Ru(bpy) 3 ] 3+/2 couple are found: a minimum value of E °′ is attained at 3.98 × 10 –5 mol dm –3 G1.5 dendrimer, whereas a positive shift is reached for the G4.5 dendrimer. The negative shift is in agreement with predictions taking into account electrostatic long-range interactions for binding, , in such a way that one expects a greater stabilization of the oxidized form of the couple, that is, K 3+ > K 2+ . Nevertheless, a positive shift of the E °′ values at higher concentrations of G1.5 dendrimer is also observed as previously indicated.…”

Trispyrazolylborate Complexes: An Advanced Synthesis Experiment Using Paramagnetic NMR, Variable-Temperature NMR, and EPR Spectroscopies

“…Inquiry experiments are intended to help students make connections between their prior knowledge and new information . However, only a few experiments developed for upper-division inorganic laboratory courses use inquiry elements. − …”

Introduction to Electrochemistry and the Use of Electrochemistry to Synthesize and Evaluate Catalysts for Water Oxidation and Reduction

“…To date, electrochemical techniques have been utilized in a wide range of applications in experimental laboratory procedures reported in this journal, including measurement of redox potentials, − determination of diffusion coefficients, , modification of electrode surfaces, − biochemical analysis, measurement of changes to redox potentials as ligand or micellar environments are modified, − and monitoring of isomerization reactions, among many others. , The first tutorial section of this laboratory experiment is well-positioned as a foundational experience in electrochemistry that could precede any number of other experiments that employ electrochemical analysis and characterization. This protocol contains an additional application section that draws real-world connections between electrochemistry and chemical research through the lens of clean, renewable energy, which is currently of massive global importance.…”