title: Structure and dynamics of H2O vis-á-vis phenylalanine recognition at a DPPC lipid membrane via interfacial H-bond types: insights from polarized FT-IRRAS and ADMP simulations.
abstract: Preferential and enantioselective interactions of L-/D-Phenylalanine (L-Phe and D-Phe) and butoxycarbonyl-protected L-/D-Phenylalanine (LPA and DPA) as guest with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (L-DPPC) as host were tapped by using real time Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). Polarization-modulated FT-IRRAS of DPPC monolayers above the phenylalanine modified subphases depicted fine structure/conformation differences under considerations of controlled 2D surface pressure. Selective molecular recognition of D-enantiomer over L-enantiomer driven by the DPPC head group via H-bonding and electrostatic interactions was evident spectroscopically. Accordingly, binding constants (K) of 145, 346, 28, and 56 M(-1) for LPA, DPA, L-Phe, and D-Phe, respectively, were estimated. The real time FT-IRRAS water bands were strictly conformation sensitive. The effect of micro-solvation on the structure and stability of the 1:1 diastereomeric L-lipid⋯, LPA/DPA and L-lipid⋯, (L/D)-Phe adducts was investigated with the aid of Atom-centered Density Matrix Propagation (ADMP), a first principle quantum mechanical molecular dynamics approach. The phosphodiester fragment was the primary site of hydration where specific solvent interactions were simulated through single- and triple- "water-phosphate" interactions, as water cluster's "tetrahedral dice" to a "trimeric motif" transformation as a partial de-clusterization was evident. Under all the hydration patterns considered in both static and dynamic descriptions of density functional theory, L-lipid/D-amino acid enantiomer adducts continued to be stable structures while in dynamic systems, water rearranged without getting "squeezed-out" in the process of recognition. In spite of the challenging computational realm of this multiscale problem, the ADMP simulated molecular interactions complying with polarized vibrational spectroscopy unraveled a novel route to chiral recognition and interfacial water structure.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India.
authors.forename: Nirod Kumar
authors.initials: NK
authors.lastname: Sarangi
authors.affiliation: Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India.
authors.forename: Nivarthi
authors.initials: N
authors.lastname: Ramesh
authors.affiliation: Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India.
authors.forename: Archita
authors.initials: A
authors.lastname: Patnaik
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D002462:Cell Membrane / Q000737:chemistry*; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D010649:Phenylalanine / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D010710:Phosphates; D012997:Solvents; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D010649:Phenylalanine