Noncovalent Modification of Nanodiamonds with Tritium-Labeled Pantothenic Acid Derivatives

Abstract

The efficiency of tritium labeling of salts of pantothenic (HO–R–COOH), hopantenic (HO–R–CH₂–COOH), and 4-D-phosphopantothenic [(HO)₂P(=O)–O–R–COOH] acids [R = CH₂C(CH₃)₂CHOH–CONH(CH₂)₂] with thermal activation of tritium at target temperatures of 77 and 295 K was studied. The phosphate group inhibits the isotope exchange. The tritium-labeled compounds were used for studying the adsorption of pantothenic acid derivatives from aqueous solutions and in the presence of 0.9% NaCl at 297 ± 3 K onto nanodiamonds prepared by detonation synthesis (NDs). Preparation of stable ND suspensions in advance enhances the ability of NDs to adsorb the compounds studied. The parameters of the equation describing the sorption isotherms at different ionic strengths of the solution were calculated. The strength of the adsorbate retention in contact with water, 0.9% NaCl solution, 0.01 M HCl solution, and 40 g L⁻¹ bovine serum albumin (BSA) solution was determined. The data obtained allow two mechanisms of the adsorbate retention on the ND surface to be considered: reversible adsorption due to ionic interactions and irreversible binding due to hydrophobic interactions. The strongly bound molecules undergo slow desorption in the presence of BSA. The revealed trends confirm high potential of NDs as a drug delivery platform.