Mechanistic Insights into Interactions at Urea–Hydroxyapatite Nanoparticle Interface

Abstract

Development of controlled release biomolecules by surface modification of hydroxyapatite nanoparticles has recently gained popularity in the areas of bionanotechnology and nanomedicine. However, optimization of these biomolecules for applications such as drug delivery, nutrient delivery requires a systematic understanding of binding mechanisms and interfacial kinetics at the molecular level between the nanomatrix and the active compound. In this research, urea is used as a model molecule to investigate its interactions with two morphologically different thin films of hydroxyapatite nanoparticles. These thin films were fabricated on quartz crystal piezoelectric sensors to selectively expose Ca 2+ and PO 4 3− sites of hydroxyapatite. Respective urea adsorption and desorption on both of these sites were monitored in situ and in real time in the phosphate buffer solution that mimics body fluids. The measured kinetic parameters, which corroborate structural predisposition for controlled release, show desorption rates that are one-tenth of the adsorption rates on both surfaces. Furthermore, the rate of desorption from the PO 4 3− site is one-half the rate of desorption from the Ca 2+ site. The Hill kinetic model was found to satisfactorily fit data, which explains cooperative binding between the hydroxyapatite nanoparticle thin film and urea. Fourier transform infrared spectra and X-ray photoemission spectra of the urea adsorbed on the above surfaces confirm the cooperative binding. It also elucidates the different binding mechanisms between urea and hydroxyapatite that contribute to the changes in the interfacial kinetics. These findings provide valuable information for structurally optimizing hydroxyapatite nanoparticle surfaces to control interfacial kinetics for applications in bionanotechnology and nanomedicine.

Solid-State Encapsulation of Urea via Mechanochemistry-Driven Engineering of Metal–Phenolic Networks

“… For example, it is reported that the binding of urea with polyphenols under mechanochemical conditions is predominantly through hydrogen binding, where −NH 2 of the amide binds to deprotonated catechol groups. Also, the formation of such an intermediate Ti IV –NH 2 –TA complex is likely, ,− in which urea can act as a catalyst to facilitate the formation of MPNs under solvent-free conditions. Furthermore, the temperature of the internal jar wall was ∼42 °C (recorded by an infrared thermometer gun).…”

Urea-Loaded Hydroxyapatite–Carboxylated Cellulose Composites as Slow-Release N Fertilizer Pellets for Efficient Delivery of Nitrogen

“…11,12 The development of novel slow-release systems by encapsulating macro or micronutrients into hydroxyapatite nanoparticles (HAPs) have recently received tremendous interest by the scientific commonalty. 15 Hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] nanoparticles are rated as one of the prominent platform carriers for the immobilization of macronutrients owing to their rich surface chemistry and abundant surface reactive functional groups. It is also a rich source of phosphorus and can be used in the field of agriculture as a phosphorus source for the plants.…”

Theoretical Investigations on the Interactions of Urea with Hydroxyl and Non-Hydroxyl Hydroxyapatite Surface

“…Besides, the N-H stretching showed marked shift in urea-HA and the shifted energy in Ca 2p core level for HA suggested that the chemical environment near calcium ions is affected by the presence of urea on HA surface. Energy core level of phosphorus 2p in HA also changed to higher binding energy after binding to urea that implies a new interaction happened between oxygen atom in phosphate group on HA and hydrogen atom of amide in urea [18]. In addition, many previous studies were using HA as binding site for other molecules to attach.…”

“…Urea-HA is to be used as a slow-release fertilizer [2,3], in which the application of the said compound has also been performed, in the field trial in rice paddy [3]. With the success in the previous experimental study of urea-HA [1][2][3][4]17,18,[22][23][24][25][26], we set out to investigate, theoretically, the behavior of the urea attached to HA. This article focused on the interaction between urea-HA in identifying the strength of this combination, the functional groups involved in IR spectra, the reactive side on HA surfaces and the interactions involved in the bonding.…”