| Characterization of the nano scale heterogeneity at the solvent – interface of bio-structures Esther Nachliel1; Menachem Gutman2; 1TEL AVIV UNIVERSITY, Tel Aviv, Israel; 2TEL AVIV UNIVERSITY, Ramat Gan, Israel; PAPER: 232/Medicine/Regular (Oral) SCHEDULED: 14:50/Wed. 30 Nov. 2022/Ballroom A ABSTRACT: On the nm scale, cellular constituents are highly heterogeneous: the dielectric constant boundaries, the uneven dispersion of fixed and mobile charges, partial ordering of water molecules create an environment where the local chemical and physical properties differ from one site to another. The study of this ‘ensemble” requires a methodology that can discriminate among nm size sites, where a “gauging” particle will remain for not more than few ns. This requirement is readily met by proton pule experiments (1). The photo-excited state of certain aromatic compound are very acidic (pK*< 2) and by illumination ejects a proton to the solvent. The released proton diffuses within the immediate vicinity and may recombine with the excited anion (ϕO-*) in response to its electric field reforming the ϕOH* state. Altogether, the observation time is few ns and the distance the proton can disperse, before the molecule relaxes to its ground state, is ~2-4 nm, thus assuring a localized observation (2). Judicious insertion of the photo-acids, like pyranine, into a well-defined environment (3) enables quantitative evaluation of the physical-chemical properties of the immediate vicinity of the site. The various studies were spread over a large biological domains; like active site of proteins (Apomyiglobin, lac permease), or the water filled space of a Large-Pore Channel protein (PhoE) or the interface between solvent and carbohydrate molecule (cyclodextrine), the aquose phase between lipid bilayer (multilamentar) and the reverse micelles of different radiuses. The micro loci are characterized by a lower chemical activity of the water, modulated diffusion coefficient, enhanced electrostatic field and highly affected by the geometry of the local space. References: 1. Time-resolved dynamics of proton transfer in proteinous systems; M. Gutman and E. Nachliel. Annu. Rev. Phys. Chem. 1997. 48:329–56 2. Elementary Steps in Excited-State Proton Transfer† Noam Agmon. J. Phys. Chem. A 2005, 109, 13-35. 3. Gauging of the PhoE Channel by a Single Freely Diffusing Proton Sharron Bransburg-Zabary, Esther Nachliel, and Menachem Gutman. Biophysical Journal Volume 83 December 2002 2987–3000. |
