A kinetic study of the interaction of gold nanoparticles capped with N-(2-mercaptopropionyl)glycine with double stranded DNA was carried out in water and in salt (NaCl) solutions. The kinetic curves are biexponential and reveal the presence of three kinetic steps. The dependence of the reciprocal fast and slow relaxation time, on the DNA concentration, is a curve and tends to a plateau at high DNA concentrations. The simplest mechanism consistent with the kinetic results involves a simple three-step series mechanism reaction scheme. The first step corresponds to a very fast step that is related to a diffusion controlled formation of an external precursor complex (DNA, AuNPs); the second step involves the formation of a (DNA/AuNPs)_I complex, as a result of the binding affinity between hydrophilic groups of the tiopronin and the DNA grooves. Finally, the third step has been interpreted as a consequence of a conformational change of the (DNA/AuNPs)_I complex formed in the second step, to a more compacted form (DNA/AuNPs)_II. The values of the rate constants of each step decrease as NaCl concentration increases. The results have been discussed in terms of solvation of the species and changes in the viscosity of the solution.

Compacted Au@16-mph-16/DNA-AMOX (NSi) nanosystems were prepared from amoxicillin (AMOX) and precursor Au@16-mph-16 gold nanoparticles (Ni) using a Deoxyribonucleic acid (DNA) biopolymer as a glue. The synthesized nanocarrier was tested on different bacterial strains of Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae to evaluate its effectiveness as an antibiotic as well as its internalization. Synthesis of the nanosystems required previous structural and thermodynamic studies using circular dichroism (CD) and UV-visible techniques to guarantee optimal complex formation and maximal DNA compaction, characteristics which facilitate the correct uptake of the nanocarrier. Two nanocomplexes with different compositions and structures, denoted NS₁ and NS₂, were prepared, the first involving external Au@16-mph-16 binding and the second partial intercalation. The Ni and NSi nanosystems obtained were characterized via transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) techniques to measure their charge, aggregation state and hydrodynamic size, and to verify their presence inside the bacteria. From these studies, it was concluded that the zeta potential values for gold nanoparticles, NS₁, and NS₂ nanosystems were 67.8, −36.7, and −45.1 mV. Moreover, the particle size distribution of the Au@16-mph-16 gold nanoparticles and NS₂ nanoformulation was found to be 2.6 nm and 69.0 nm, respectively. However, for NS₁ nanoformulation, a bimodal size distribution of 44 nm (95.5%) and 205 nm (4.5%) was found. Minimal inhibitory concentration (MIC) values were determined for the bacteria studied using a microdilution plates assay. The effect on Escherichia coli bacteria was notable, with MIC values of 17 µM for both the NS₁ and NS₂ nanosystems. The Staphylococcus aureus chart shows a greater inhibition effect of NS₂ and NP₂ in non-diluted wells, and clearly reveals a great effect on Streptococcus pneumoniae, reaching MIC values of 0.53 µM in more diluted wells. These results are in good agreement with TEM internalization studies of bacteria that reveal significant internalization and damage in Streptococcus pneumoniae. In all the treatments carried out, the antibiotic capacity of gold nanosystems as enhancers of amoxicillin was demonstrated, causing both the precursors and the nanosystems to act very quickly, and thus favoring microbial death with a small amount of antibiotic. Therefore, these gold nanosystems may constitute an effective therapy to combat resistance to antibiotics, in addition to avoiding the secondary effects derived from the administration of high doses of antibiotics.