16 research outputs found
Cation-pi interactions in aromatics of biological and medicinal interest: Electrostatic potential surfaces as a useful qualitative guide
The cation-pi interaction is an important, general force for molecular recognition in biological receptors. Through the sidechains of aromatic amino acids, novel binding sites for cationic ligands such as acetylcholine can be constructed. We report here a number of calculations on prototypical cation-pi systems, emphasizing structures of relevance to biological receptors and prototypical heterocycles of the type often of importance in medicinal chemistry. Trends in the data can be rationalized using a relatively simple model that emphasizes the electrostatic component of the cation-pi interaction. In particular, plots of the electrostatic potential surfaces of the relevant aromatics provide useful guidelines for predicting cation-pi interactions in new systems
A Selective Receptor for Arginine Derivatives in Aqueous Media. Energetic Consequences of Salt Bridges That Are Highly Exposed to Water
Quantitative measures of salt-bridge-type interactions in a highly exposed aqueous environment have been obtained by modifying the well-studied cyclophane platform 1 to include carboxylates in close proximity to bound, cationic guests, producing hosts 2 and 3. Many guests show significantly enhanced binding to 2 and 3, but cations of the RNMe_3+ type show little or no enhancement. We propose that the latter observations result from the fact that RNMe_3+ compounds have very diffuse positive charges. Guests that show enhanced binding have focused regions of large, positive electrostatic potential. The highly charged 3 is able to bind very polar, very well-solvated guests, including a series of arginine-based dipeptides. Neutral, water-soluble host 4 was prepared and found to show a decreased affinity for cationic guests. We propose a novel induced dipole mechanism to rationalize these results
Multicompartment Theranostic Nanoemulsions Stabilized by a Triphilic Semifluorinated Block Copolymer
The presence of a perfluorocarbon
block in a multiblock polymer
has been shown to be an additional driving force toward nanoparticle
assembly. In the preparation of nanoemulsions, this perfluorocarbon
block also provides enhanced particle stability. Herein, the synthesis
of a new triphilic, semifluorinated copolymer, M2F8H18, is introduced.
This ABC type block copolymer can be used to formulate extremely stable
nanoemulsions, assembled around a lipophilic droplet, with lifetimes
of one year or more. The central oil droplet can stably solubilize
high concentrations of hydrophobic drugs, making this system an ideal
drug delivery vehicle. The incorporation of the perfluorocarbon block
modulates drug release from the lipophilic core via the surrounding
fluorous shell. Fluorous imaging agents incorporated into the fluorous
shell prolong drug release even further as well as provide potent <sup>19</sup>F-MRI contrast ability. <i>In vitro</i> studies
show that these nanoemulsions efficiently inhibit cancer cell growth,
thus providing a theranostic drug delivery system
A Selective Receptor for Arginine Derivatives in Aqueous Media. Energetic Consequences of Salt Bridges That Are Highly Exposed to Water
Quantitative measures of salt-bridge-type interactions in a highly exposed aqueous environment have been obtained by modifying the well-studied cyclophane platform 1 to include carboxylates in close proximity to bound, cationic guests, producing hosts 2 and 3. Many guests show significantly enhanced binding to 2 and 3, but cations of the RNMe_3+ type show little or no enhancement. We propose that the latter observations result from the fact that RNMe_3+ compounds have very diffuse positive charges. Guests that show enhanced binding have focused regions of large, positive electrostatic potential. The highly charged 3 is able to bind very polar, very well-solvated guests, including a series of arginine-based dipeptides. Neutral, water-soluble host 4 was prepared and found to show a decreased affinity for cationic guests. We propose a novel induced dipole mechanism to rationalize these results