Hyaluronan orders water molecules in its nanoscale extended hydration shells

Hyaluronan (HA) is an anionic, highly hydrated bio-polyelectrolyte found in the extracellular environment, like the synovial fluid between joints. We explore the extended hydration shell structure of HA in water using femtosecond elastic second-harmonic scattering (fs-ESHS). HA enhances orientational water-water correlations. Angle-resolved fs-ESHS measurements and nonlinear optical modeling show that HA behaves like a flexible chain surrounded by extended shells of orientationally correlated water. We describe several ways to determine the concentration-dependent size and shape of a polyelectrolyte in water, using the amount of water oriented by the polyelectrolyte charges as a contrast agent. The spatial extent of the hydration shell is determined via temperature-dependent measurements and can reach up to 475 nm, corresponding to a length of 1600 water molecules. A strong isotope effect, stemming from nuclear quantum effects, is observed when light water (H2O) is replaced by heavy water (D2O), amounting to a factor of 4.3 in the scattered SH intensity.

Second Harmonic Scattering of Molecular Aggregates

A general model is developed to describe the polarization-resolved second harmonic scattering (SHS) response from a liquid solution of molecular aggregates. In particular, the molecular spatial order is introduced to consider the coherent contribution, also known as the retarded contribution, besides the incoherent contribution. The model is based on the description of a liquid suspension of molecular dyes represented by point-like nonlinear dipoles, locally excited by the fundamental field and radiating at the harmonic frequency. It is shown that for a non-centrosymmetrical spatial arrangement of the nonlinear dipoles, the SHS response is very similar to the purely incoherent response, and is of electric dipole origin. However, for centrosymmetrical or close to centrosymmetrical spatial arrangements of the nonlinear dipoles, the near cancellation of the incoherent contribution due to the inversion symmetry rule allows the observation of the coherent contribution of the SHS response, also known as the electric quadrupole contribution. This model is illustrated with experimental data obtained for aqueous solutions of the dye Crystal Violet (CV) in the presence of sodium dodecyl sulfate (SDS) and mixed water-methanol solutions of the dye 4-(4–dihexadecylaminostyryl)-N-methylpyridinium iodide (DiA), a cationic amphiphilic probe molecule with a strong first hyper-polarizability; both CV and DiA form molecular aggregates in these conditions. The quantitative determination of a retardation parameter opens a window into the spatial arrangements of the dyes in the aggregates, despite the small nanoscale dimensions of the latter.

PySHS : A Python Open Source Software For Second Harmonic Scattering

PySHS package is a python open source software which simulates the Second Harmonic Scattering (SHS) of different kind of colloidal nano-object in various experimental configuration. This package is able to compute polarization resolved at a fixed scattered angle or angular distribution for different polarization configurations.

PySHS : A Python Open Source Software For Second Harmonic Scattering

PySHS package is a python open source software which simulates the Second Harmonic Scattering (SHS) of different kind of colloidal nano-object in various experimental configuration. This package is able to compute polarization resolved at a fixed scattered angle or angular distribution for different polarization configurations.