Jean-Philippe Biron

Determination of Individual Diffusion Coefficients in Evolving Binary Mixtures by Taylor Dispersion Analysis: Application to the Monitoring of Polymer Reaction

This study demonstrates that it is possible to get valuable information on the individual populations of a binary mixture from the signal obtained by Taylor dispersion analysis (TDA). In the case of mixtures composed of two populations of different sizes (such as a monomer/polymer mixture), the information available from TDA is not restricted to an average diffusion coefficient or an average hydrodynamic radius calculated on the entire binary mixture. In this work, TDA was used to monitor a polymerization reaction. In this scope, it has been possible to determine the degree of conversion and the weight average hydrodynamic radius of the polymer at different reaction times. Three different methods are proposed for the data processing of taylorgrams derived from polymerization mixtures or, more generally, for taylorgrams of binary mixtures. These three methods, either based on deconvolution or on integration of the signal, were found to give similar results. TDA results obtained for a model binary mixture of acrylamide and standard polyacrylamide were consistent with DLS experiments provided that the differences in the type of average hydrodynamic radius values between the two methods are taken into account. An example of application to the monitoring of acrylamide radical polymerization is shown.

DYNAMIC CO-EVOLUTION OF PEPTIDES AND CHEMICAL ENERGETICS, A GATEWAY TO THE EMERGENCE OF HOMOCHIRALITY AND THE CATALYTIC ACTIVITY OF PEPTIDES

We propose a scenario for the dynamic co-evolution of peptides and energy on the primitive Earth. From a multi component system consisting of hydrogen cyanide, several carbonyl compounds, ammonia, alkyl amine, carbonic anhydride, borate and isocyanic acid, we show that the reversibility of this system leads to several intermediate nitriles, that irreversibly evolve to α-amino acids and N-carbamoyl amino acids via selective catalytic processes. On the primitive Earth these N-carbamoyl amino acids combined with energetic molecules (NOx) may have been the core of a molecular engine producing peptides permanently and assuring their recycling and evolution. We present this molecular engine, a production example, and its various selectivities. The perspectives for such a dynamic approach to the emergence of peptides are evoked in the conclusion.

Polydispersity analysis of Taylor dispersion data: the cumulant method.

Taylor dispersion analysis is an increasingly popular characterization method that measures the diffusion coefficient, and hence the hydrodynamic radius, of (bio)polymers, nanoparticles, or even small molecules. In this work, we describe an extension to current data analysis schemes that allows size polydispersity to be quantified for an arbitrary sample, thereby significantly enhancing the potentiality of Taylor dispersion analysis. The method is based on a cumulant development similar to that used for the analysis of dynamic light scattering data. Specific challenges posed by the cumulant analysis of Taylor dispersion data are discussed, and practical ways to address them are proposed. We successfully test this new method by analyzing both simulated and experimental data for solutions of moderately polydisperse polymers and polymer mixtures.

Measuring Arbitrary Diffusion Coefficient Distributions of Nano-Objects by Taylor Dispersion Analysis

Taylor dispersion analysis is an absolute and straightforward characterization method that allows determining the diffusion coefficient, or equivalently the hydrodynamic radius, from angstroms to submicron size range. In this work, we investigated the use of the Constrained Regularized Linear Inversion approach as a new data processing method to extract the probability density functions of the diffusion coefficient (or hydrodynamic radius) from experimental taylorgrams. This new approach can be applied to arbitrary polydisperse samples and gives access to the whole diffusion coefficient distributions, thereby significantly enhancing the potentiality of Taylor dispersion analysis. The method was successfully applied to both simulated and real experimental data for solutions of moderately polydisperse polymers and their binary and ternary mixtures. Distributions of diffusion coefficients obtained by this method were favorably compared with those derived from size exclusion chromatography. The influence of the noise of the simulated taylorgrams on the data processing is discussed. Finally, we discuss the ability of the method to correctly resolve bimodal distributions as a function of the relative separation between the two constituent species.

Taylor Dispersion Analysis of Polysaccharides Using Backscattering Interferometry

Taylor dispersion analysis (TDA) allows the determination of the molecular diffusion coefficient (D) or the hydrodynamic radius (Rh) of a solute from the peak broadening of a plug of solute in a laminar Poiseuille flow. The main limitation plaguing the broader applicability of TDA is the lack of a sensitive detection modality. UV absorption is typically used with TDA but is only suitable for UV-absorbing or derivatized compounds. In this work, we present a development of the TDA method for non-UV absorbing compounds by using a universal detector based on refractive index (RI) sensing with backscattering interferometry (BSI). BSI was interfaced to a capillary electrophoresis-UV instrument using a polyimide coated fused silica capillary and an in-house designed flow-cell assembly. Polysaccharides were selected to demonstrate the application of TDA-BSI for size characterization. Under the conditions of validity of TDA, D and Rh average values and the entire Rh distributions were obtained from the (poly)saccharide taylorgrams, including non-UV absorbing polymers.