Hydroxyapatite (HAp) particles with very different surface charges and compositions (i.e. different Ca/P and CO₃ ²⁻/PO₄ ³⁻ ratios) have been obtained by varying the experimental conditions used during the chemical precipitation process. The DNA adsorption capacity and protection imparted against the attack of nucleases of HAp particles have been proved to depend on the surface charge while the buffering capacity is affected by the chemical composition. On the basis of both the surface charge and the crystallinity, the predominant planes at the surfaces of HAp particles have been identified. Atomistic molecular dynamics simulations of surfaces constructed with these planes (i.e. (001) and the two terminations of (010)) with the adsorbed B-DNA double helix have been performed to get microscopic understanding of the influence of the mineral in the biomolecule structure and the interaction energies. The results indicate that the DNA secondary structure is perfectly preserved on the (001) surface, this stability being accompanied by an attractive binding energy. In contrast, the (010) surface with PO₄ ³⁻, OH⁻ and Ca²⁺ ions in the termination induces significant local and global deformations in the double helix, repulsive OH⁻(HAp)⋯PO₄ ³⁻ (DNA) interactions provoking the desorption of the biomolecule. Finally, although the termination of the (010) surface with PO₄ ³⁻ and Ca²⁺ ions also deforms the double helix, it forms very strong attractive interactions with the biomolecule. These binding characteristics are in excellent agreement with the DNA adsorption and protection abilities experimentally determined for the HAp samples. Finally, the surface charge has been found less decisive than the chemical composition in the efficacy of the transfection process.

Encapsulation of DNA into hydroxyapatite (HAp) has been investigated using a rational approach that involves computer simulation and experimental techniques. The temporal evolution of the radial distribution functions derived from atomistic molecular dynamics simulations of Ca²⁺, PO₄ ³⁻ and OH⁻-containing aqueous solutions in the presence and absence of B-DNA has been used to conclude that the backbone of the double helix acts as a template for HAp growth. More specifically, results reveal the formation of calcium phosphate clusters at the first stages of the simulations, which subsequently re-organize to nucleate HAp. This effect is produced in the absence and, especially, presence, of DNA indicating that the biomolecules do not inhibit but even promote mineral growth. Furthermore, computer simulations suggest that the diffusion of the OH⁻ anions through the inorganic solution is the limiting step for the nucleation of the biomineral. Nanocapsules and crystalline nanorods of HAp containing DNA molecules inside have been prepared by mixing solutions containing Ca²⁺ and PO₄ ³⁻ ions with fish sperm DNA at high pH. The dimensions and morphology of such nanostructures have been examined by transmission electron microscopy, while the characterization of the biomineral has been focused on the identification of DNA inside HAp using infrared, X-ray photoelectron and UV-vis spectroscopies, as well as gel electrophoresis. The biominerals reported in this work are important for biomedical applications requiring the protection of DNA from aggressive environmental conditions.

Part of the “signature sequence” that defines the voltage-gated proton channel (H_V1) is a tryptophan residue adjacent to the second Arg in the S4 transmembrane helix: RxWRxxR, which is perfectly conserved in all high confidence H_V1 genes. Replacing Trp²⁰⁷ in human H_V1 (hH_V1) with Ala, Ser, or Phe facilitated gating, accelerating channel opening by 100-fold, and closing by 30-fold. Mutant channels opened at more negative voltages than wild-type (WT) channels, indicating that in WT channels, Trp favors a closed state. The Arrhenius activation energy, E_a, for channel opening decreased to 22 kcal/mol from 30–38 kcal/mol for WT, confirming that Trp²⁰⁷ establishes the major energy barrier between closed and open hH_V1. Cation–π interaction between Trp²⁰⁷ and Arg²¹¹ evidently latches the channel closed. Trp²⁰⁷ mutants lost proton selectivity at pH_o >8.0. Finally, gating that depends on the transmembrane pH gradient (ΔpH-dependent gating), a universal feature of H_V1 that is essential to its biological functions, was compromised. In the WT hH_V1, ΔpH-dependent gating is shown to saturate above pH_i or pH_o 8, consistent with a single pH sensor with alternating access to internal and external solutions. However, saturation occurred independently of ΔpH, indicating the existence of distinct internal and external pH sensors. In Trp²⁰⁷ mutants, ΔpH-dependent gating saturated at lower pH_o but not at lower pH_i. That Trp²⁰⁷ mutation selectively alters pH_o sensing further supports the existence of distinct internal and external pH sensors. Analogous mutations in H_V1 from the unicellular species Karlodinium veneficum and Emiliania huxleyi produced generally similar consequences. Saturation of ΔpH-dependent gating occurred at the same pH_o and pH_i in H_V1 of all three species, suggesting that the same or similar group(s) is involved in pH sensing. Therefore, Trp enables four characteristic properties: slow channel opening, highly temperature-dependent gating kinetics, proton selectivity, and ΔpH-dependent gating.