Coagulation of Colloidal Solutions by Electrolytes

Influence of acid-base equilibrium on interactions of some monofunctional coumarin Pd(II) complexes with biologically relevant nucleophiles-comprehensive kinetic study

This aimed to develop a comprehensive theoretical protocol for examining substitution reaction processes. The researchers used a theoretical quantum-mechanical protocol based on the QM-ORSA approach, which estimates the kinetic parameters of thermodynamically favourable reaction pathways. This theoretical protocol was validated by experimentally investigating substitution mechanisms in two previously synthesised Pd(II) complexes: chlorido-[(3-(1-(2-hydroxypropylamino)ethylidene)chroman-2,4-dione)]palladium(II) (C1) and chlorido-[(3-(1-(2-mercaptoethylamino)-ethylidene)-chroman-2,4dione)]palladium(II) (C2), along with biologically relevant nucleophiles, namely L-cysteine (l-Cys), L-methionine (l-Met), and guanosine-5'-monophosphate (5'-GMP). Reactions were investigated under pseudo-first-order conditions, monitoring nucleophile concentration and temperature changes using stopped-flow UV-vis spectrophotometry. All reactions were conducted under physiological conditions (pH = 7.2) at 37 °C. The reactivity of the studied nucleophiles follows the order: l-Cys > l-Met > 5'-GMP, and the reaction mechanism is associative based on the activation parameters. The experimental and theoretical data showed that C2 is more reactive than C1, confirming that the complexes' structural and electronic properties greatly affect their reactivity with selected nucleophiles. The study's findings have confirmed that the primary interaction occurs with the acid-base species L-Cys, mostly through the involvement of the partially negative sulfur atom (87.2%). On the other hand, C2 has a higher propensity for reacting with L-Cys-, primarily through the partially negative oxygen atom (92.6%). The implementation of this theoretical framework will significantly restrict the utilization of chemical substances, hence facilitating cost reduction and environmental protection.

Early (pre-DLVO) studies of particle aggregation

The history of colloid science, from its modern foundations in the mid-nineteenth century, has been strongly concerned with studies of the aggregation of colloidal particles. It was Thomas Graham (1861) who defined the word "colloid" (from the Greek word for glue) for those materials which could not pass through membranes, unlike smaller, truly-dissolved materials. Subsequently, Graham (1864), following earlier studies, principally by Selmi and Faraday, described "the power possessed by salts for destroying colloidal solutions". Although numerous, quantitative studies of particle aggregation were made in the years that followed, in particular, the determination of minimum electrolyte concentrations for the onset of particle aggregation and aggregation rates, no general theoretical framework emerged to account for these quantitative findings until the middle of the twentieth century. It was during and immediately following the Second World War that two sets of authors, Derjaguin and Landau, in Russia, and Verwey and Overbeek, in the Netherlands, independently came up with the theory that is now universally referred to as the DLVO theory of particle interactions and aggregation. All modern developments of the theory of particle aggregation use the DLVO theory as the keystone. However, the DLVO theory itself was based on a large body of experimental data in regard to particle aggregation obtained over the previous hundred years or so. This article is an attempt to review that body of experimental data and to show how this guided the DLVO authors in their thinking.