Alfred Delville

Determination of the correlation time for a slowly reorienting spin-32 nucleus: Binding of Na+ with the 5′-GMP supramolecular assembly

Abstract The 23 Na NMR lineshape for Na + exchanging between the free state in aqueous solution and the bound state on a slowly reorienting macromolecule is the superposition of two lorentzians, corresponding to a fast relaxation (60% of the total intensity) and a slow relaxation (40% of the total intensity). Separation of these two components is achieved by full deconvolution of the experimental lineshape. An alternate and more easily implemented procedure uses only measurement of the linewidth at one-half and one-eight of the total height. We apply both methods to the determination of the correlation time τ c = 4–9 nsec for Na + bound to the aggregates resulting from self-assembly, in D 2 O solution, of the 5′-guanosine monophosphate nucleotide (0.1 M), in the presence of K + ions (0.4–1 M). These correlation times are discussed in terms of the structure of these aggregates, involving plausibly a C 2 h dimer obtained from the interaction of planar tetramers whose core includes a K + ion.

The theoretical interpretation of sodium-23 NMR chemical shifts and quadrupolar coupling constants, as supported by new experimental evidence

Abstract The changes in 23N chemical shifts and linewidths for Na+ with the composition of binary solvent mixtures of THF with amines: aniline, pyridine, pyrrolidine, piperidine, propylamine, and i-propylamine, are analyzed in terms of successive displacement steps involving the species (Na+)4THF, (Na+)3THF,LA, (Na+)2THF,2LA, (Na+)THF,3LA, and (Na+)4L4. Each of these discrete solvates is fully characterized by its individual chemical shift and linewidth. Under the reasonable assumption of the equality of their molecular volumes, these two quantities are related to one another by the very simple relation: (Δv 1 2 ∗ ) 1 2 ∞ δ . This correlation obtains because changes in chemical shifts arise solely from variations of the paramagnetic part of the shielding constant, as determined by electronic transfer from the ligand into the 3p orbitals on Na+ Quadrupolar relaxation originates in modulation of the direction of the electrostatic field gradient, which is set up permanently in all cases (inclusive of pure solvents), by the reorientational diffusion of the solvates. Therefore, observed linewidths should be normalized to unit viscosity, if they are to be related to chemical shift changes, which are found to be approximately additive.

Ion binding or condensation to polyelectrolytes? A detailed comparison, on the example of sodium heparinate.

A modified Poisson-Boltzmann treatment is applied to aqueous solutions of sodium heparinate, in the presence of added salts (NaCl, LiCl, KCl, CaCl2). The results show that 23Na-NMR line widths for the counterions are determined nearly exclusively by Na+ in the immediate vicinity of the linear polyelectrolyte. Hence, two-state treatments, despite their crude character, can reproduce such experimental data rather well.

Displacement of sodium ions by surfactant ions from DNA. A 23Na-NMR investigation.

23Na-NMR probes the ionic composition in the immediate vicinity of the DNA molecule, in the presence of a series of quaternary ammonium bromides, of varying hydrocarbon chain length. The 23Na-NMR line shows two Lorentzian components, in accordance with quadrupolar relaxation theory for S = 3/2 nuclei under slow modulation. Deconvolution of the observed lineshape provides, in a reliable manner, the relative fraction of sodium counterions neutralizing the phosphate sites on DNA. This quantity (p B chi 2) serves as an index of the relative affinities of various surfactant ions toward DNA, Na+ being the reference cation. The results are consistent with site binding of detergent ions to the nucleic acid, an interaction dominated by hydrophobic forces.

Calculation of activity coefficients from a novel numerical solution of the Poisson–Boltzmann equation and application to 23Na NMR of sodium polystyrene sulfonate

Interaction of sodium cations with polystyrene sulfonate (PSS) is studied. The Poisson–Boltzmann equation, modified in order to incorporate ion–ion correlation, is solved numerically using a cell model. Outstanding agreement is found between the calculated and measured activity coefficients γ± for systems consisting of NaPSS+NaCl, KPSS+KCl, CaPSS+CaCl2, and the more complex system, the quarternary mixture NaPSS+CaPSS+NaCl+CaCl2. A complementary study by sodium‐23 NMR provides a reliable estimate of the fractions of bound, atmospherically condensed, and free sodium ions for NaPSS in the presence of added NaCl, HCl, MgCl2, and MnCl2. We find a nice correlation (ρ = 0.93, N = 16) between the observed 23Na line broadenings and the calculated electrostatic field gradients for these various cases.

Binding of surfactant cations to DNA. A dual analysis considering ionic condensation and site binding

Abstract Attachment of surfactant counterions to DNA is represented with a model simultaneously incorporating atmospheric condensation and site binding. Condensation is described with equations deriving from the Poisson-Boltzmann approach while a cooperative site-binding model, including steric effects, is used for the chemical equilibrium binding. The agreement between calculated and observed mole fractions of bound univalent cations is gratifying.

Interactions between ions and polyelectrolytes. A note on determination of ionic activities, with reference to a modified poisson-boltzmann treatment.

We compare the numerous available data on ionic activities, in the presence of polyelectrolytes, with evaluation of these quantities from a modified Poisson-Boltzmann equation in the framework of a cell model. This treatment gives an excellent description of the mean activity for various ions. The activity of counterions is well-predicted, that of co-ions is generally overestimated.

Chelation of Na+ cations in nonaqueous solvents. Structural requirements and methodological considerations

Intrinsic formation constants for complexes of Na+ ions with a series of polyamines have been determined from23Na NMR measurements in binary mixtures of tetrahydrofuran (THF) and amines. The results show in a totally unambiguous manner a regular decrease in the magnitude of the chelate effect with the number of atoms intervening between the nitrogen ligators. The key assumption, tetracoordination of the cation, is critically examined, and experimental evidence is adduced in its support.

A simple solution to the poisson-boltzmann equation for ion binding to a polyelectrolyte

Abstract Solution of the Poisson-Boltzmann equation for a polyelectrolyte is made considerably easier, in a self-consistent calculation based upon a cell model. Site binding and atmospheric condensation of ions are both included, and determine together the magnitude of the activity coefficient, this quantity is obtained accurately, which indicates the reliability of this approach.

A modified Poisson-Boltzmann treatment of ionic activity in the presence of biopolyelectrolytes

Abstract Ionic activities (M 2+ = Zn 2+ , Ca 2+ ) are calculated for complex mixtures of salts (NaCl and MCl 2 ) and polyelectrolytes (sodium dextran sulfate) from a numerical solution of a modified Poisson-Boltzmann equation according to a cell model. These results compare very well with experimental spectrophotometric determinations using tetramethylmurexide as a dye indicator.