Conformational possibilities of double-helical nucleic acids: Theory and experiment

This survey covers the following topics: (1) Theoretical calculation of the total multitude of the energetically permitted regular DNA helices. (2) Theoretical study of flexibility of the double helix with emphasis on nucleosome structure. (3) Experimental data on the properties of the B to A transition of DNA in solution: the degree of cooperativity and influence of sequence. (4) The B -A transition and its possible role in genes activation.     

New aspects of the reaction of silver(I) cations with the ethylenediaminetetraacetate ion

The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95–99% as Y⁴⁻ anion) precipitates with Ag⁺ cations to form the Ag₄Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y⁴⁻ to form a complex, AgY³⁻. Equilibrium studies at 25°C and ionic strength 0.50 M (NaNO₃) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) β₁ = (1.93 ± 0.07) × 10⁵ M⁻¹ and the solubility products are K_S0 = [Ag +]⁴[Y⁴⁻] = (9.0 ± 0.4) × 10⁻¹⁸ M⁵ and K_S1 = [Ag +]³[AgY³⁻] = (1.74 ± 0.08) × 10⁻¹² M⁴. The presence of Na⁺, rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: β₁ = (1.19 ± 0.03) × 10⁶ M⁻¹, K_S0 = (1.6 ± 0.4) × 10⁻¹⁹ M⁵ and K_S1 = (1.9 ± 0.5) × 10⁻¹³ M⁴; at ionic strength tending to zero; β₁ = (1.82 ± 0.05) × 10⁷ M⁻¹, K_S0 = (2.6 ± 0.8) × 10⁻²² M⁵ and K_S1 = (5 ± 1) × 10⁻¹⁵ M⁴. The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO₃. Well-defined potentiometric titration curves can be taken in the range 1–2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142°C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135–157°C), tending to pure silver at 600°C, consistent with the original Ag₄Y salt.     

Modified ethylenediaminetetraacetate method for the direct estimation of magnesium

Magnesium and calcium are determined together, using EDTA solution with Solochrome Black T indicator. Calciuin is then precipitated out as molybdate and the magnesium is determined in the filtrate.     

Features of pectin biodegradation in the presence of sodium ethylenediaminetetraacetate

We have studied the effect of sodium ethylenediaminetetraacetate on enzyme-induced degradation of apple pectin. Capillary viscometry and IR spectroscopy data have shown that the ligand binds Ca²⁺ ions (present in pectin) thus accelerating its biodegradation 1.2–1.6 times at relatively low concentration of the complexone. At the same time, sodium ethylenediaminetetraacetate reduces enzymatic activity of lytic enzymes thus slowing down pectin hydrolysis as higher concentration of the complexone.     

Studies in heavy ion activation analysis trace determination possibilities with9Be bombardment

⁹Be induced radioactivation was used to study the trace determination of 19 elements at 3 different ion beam energies (E_lab=14, 32 and 63 MeV⁹Be²⁺). Nine nuclear reactions, yielding radionuclides with half-lives longer than 2.5 m, present potential analytical features. Beside the very sensitive detection of B and N, the multielemental determination of Na, Si, Ca, Sc, and Zn is possible with a⁹Be ion beam of appropriate incident energy. Nuclear interferences have also been investigated and quantified.     

Conformational studies of Zn-Ligand-Hexose diastereomers using ion mobility measurements and density functional theory calculations

Ion mobility studies and density functional theory calculations were used to study the structures of [Zn/diethylenetriamine/Hexose/Cl]+ complexes in an effort to probe differences in the three-dimensional conformations. This information allows us to gain insight into the structure of these complexes before collisional activation, which is the first step in understanding the stereoselective dissociations observed under collisionally activated conditions. The collision cross sections obtained from the ion mobility measurements showed that the mannose structure is more compact than the galactose and glucose complexes, respectively. Using density functional theory, candidate structures for each of the experimentally observed complexes were generated. Two criteria were used to determine the most likely structures of these complexes before activation: (1) The allowed relative energies of the molecules (between 0-90 kJ/mol) and (2) collision cross section agreement (within 2%) between the theoretically determined structures and the experimentally determined cross section. It was found that the identity of the monosaccharide made a difference in the overall conformation of the metal-ligand-monosaccharide complex. For glucose and galactose, metal coordination to O(6) was found to be favorable, with the monosaccharide occupying the 4C1 chair conformation, while for mannose, O(2) metal coordination was found with the monosaccharide in a B3,0 conformation. Coordination numbers varied between four and six for the Zn(II) metal centers. Given these results, it appears that the stereochemistry of the monosaccharide influences the conformation and metal coordination sites of the Zn(II)/monosaccharide/dien complex. These differences may influence the dissociation products observed under collisionally activated conditions.     

The zirconium compounds of ethylenediaminetetraacetate. a heterometric study

The compounds formed at pH's 1–7 between zirconium and ethylenediaminetetraacctate (= E) were studied. The following soluble or insoluble compounds were obtained either as intermediates or as final compounds: Zr₁E₁ ↑, Zr₃E₂ ↓, Zr₂E₁ ↓, Zr₃E₁ ↓↑, Zr₄E₁ ↑↓ and Zr₆E₁ ↓The composition and sturcture of the compounds and the reactions occurring were discussed.