The atomic structure of prilocaine in solution

Abstract

Prilocaine is an aminoamide local anesthetic (LA). LAs are known to act on functional proteins as well as mediating membrane structure in order to induce anesthetic action, however there is no consensus as to which molecular mechanisms exert these effects. As such, this project aims to understand the structure of prilocaine in physiologically relevant environments, by means of two techniques: neutron diffraction with isotopic substitution (NDIS) and computational modelling with Empirical Potential Structure Refinement (EPSR). EPSR is a reverse Monte Carlo technique used to model liquids, which is constrained by diffraction data obtained by NDIS. Two distinct solutions have been investigated: prilocaine hydrochloride in water (1:150 molar ratio) and prilocaine freebase in methanol and water (1:75:75). The former system provides insight as to how prilocaine is hydrated. This occurs by water coordinating around its -C=O carbonyl oxygen, amide and amine nitrogens, as well as through relatively highly localized, but non-oriented, water molecules around the benzene ring. The latter system has shed light on amphiphilic interactions in- volving prilocaine, as methanol molecules are also amphiphilic; they possess a hydrophilic hydroxyl -OH group and a hydrophobic methyl -CH 3 group. Prilocaine in an amphiphilic environment is slightly dehydrated overall, as compared to a purely aqueous environment; this is especially interesting in the amide group, where hydration shifts from the nitrogen to the carbonyl oxygen. In addition, methanol, but not water, seems to bind to the ben- zene ring, which could have implications as to how the benzene ring could confer solubility in a hydrophobic milieu, as well as to how prilocaine could alter the structure of the hydrocarbon interior of membranes. These two systems have also been exploited to observe differences in the charged and uncharged form of prilocaine, as uncharged prilocaine is not soluble in water. Uncharged prilo- caine appears to coordinate water more weakly, but presents a single highly localized water molecule binding to both amide oxygen and amine nitrogen, which could shield these hydrophilic groups in penetrating the hydrophobic region of cell membranes.

Prilocaine is an aminoamide local anesthetic (LA). LAs are known to act on functional proteins as well as mediating membrane structure in order to induce anesthetic action, however there is no consensus as to which molecular mechanisms exert these effects. As such, this project aims to understand the structure of prilocaine in physiologically relevant environments, by means of two techniques: neutron diffraction with isotopic substitution (NDIS) and computational modelling with Empirical Potential Structure Refinement (EPSR). EPSR is a reverse Monte Carlo technique used to model liquids, which is constrained by diffraction data obtained by NDIS. Two distinct solutions have been investigated: prilocaine hydrochloride in water (1:150 molar ratio) and prilocaine freebase in methanol and water (1:75:75). The former system provides insight as to how prilocaine is hydrated. This occurs by water coordinating around its -C=O carbonyl oxygen, amide and amine nitrogens, as well as through relatively highly localized, but non-oriented, water molecules around the benzene ring. The latter system has shed light on amphiphilic interactions in- volving prilocaine, as methanol molecules are also amphiphilic; they possess a hydrophilic hydroxyl -OH group and a hydrophobic methyl -CH 3 group. Prilocaine in an amphiphilic environment is slightly dehydrated overall, as compared to a purely aqueous environment; this is especially interesting in the amide group, where hydration shifts from the nitrogen to the carbonyl oxygen. In addition, methanol, but not water, seems to bind to the ben- zene ring, which could have implications as to how the benzene ring could confer solubility in a hydrophobic milieu, as well as to how prilocaine could alter the structure of the hydrocarbon interior of membranes. These two systems have also been exploited to observe differences in the charged and uncharged form of prilocaine, as uncharged prilocaine is not soluble in water. Uncharged prilo- caine appears to coordinate water more weakly, but presents a single highly localized water molecule binding to both amide oxygen and amine nitrogen, which could shield these hydrophilic groups in penetrating the hydrophobic region of cell membranes.

Prilocaine is an aminoamide local anesthetic (LA). LAs are known to act on functional proteins as well as mediating membrane structure in order to induce anesthetic action, however there is no consensus as to which molecular mechanisms exert these effects. As such, this project aims to understand the structure of prilocaine in physiologically relevant environments, by means of two techniques: neutron diffraction with isotopic substitution (NDIS) and computational modelling with Empirical Potential Structure Refinement (EPSR). EPSR is a reverse Monte Carlo technique used to model liquids, which is constrained by diffraction data obtained by NDIS. Two distinct solutions have been investigated: prilocaine hydrochloride in water (1:150 molar ratio) and prilocaine freebase in methanol and water (1:75:75). The former system provides insight as to how prilocaine is hydrated. This occurs by water coordinating around its -C=O carbonyl oxygen, amide and amine nitrogens, as well as through relatively highly localized, but non-oriented, water molecules around the benzene ring. The latter system has shed light on amphiphilic interactions in- volving prilocaine, as methanol molecules are also amphiphilic; they possess a hydrophilic hydroxyl -OH group and a hydrophobic methyl -CH 3 group. Prilocaine in an amphiphilic environment is slightly dehydrated overall, as compared to a purely aqueous environment; this is especially interesting in the amide group, where hydration shifts from the nitrogen to the carbonyl oxygen. In addition, methanol, but not water, seems to bind to the ben- zene ring, which could have implications as to how the benzene ring could confer solubility in a hydrophobic milieu, as well as to how prilocaine could alter the structure of the hydrocarbon interior of membranes. These two systems have also been exploited to observe differences in the charged and uncharged form of prilocaine, as uncharged prilocaine is not soluble in water. Uncharged prilo- caine appears to coordinate water more weakly, but presents a single highly localized water molecule binding to both amide oxygen and amine nitrogen, which could shield these hydrophilic groups in penetrating the hydrophobic region of cell membranes.