Diffusing wave spectroscopy (DWS) is one of the few techniques enabling the investigation of structures and dynamics in turbid systems that is in the multiple light scattering domain. This makes it an important technique to study colloidal dispersions such as foam, gel or emulsion. In this article, DWS in both back-and forward-multiple scattering was used to monitor the in vitro digestion of turbid undiluted emulsions. Eight formulations were tested using two triglycerides, two emulsifiers and two emulsifier concentrations. The main goal of the study was to interpret the DWS data and compare the results to those from other techniques. We first extended the cumulants/moments fit method used for single scattering to obtain a particle size distribution (PSD) by DWS for multiple scattering. In the case of unimodal distributions, this compares well to PSD obtained from single scattering by dynamic light scattering (DLS). A second interpretation based on the multiple forward-scattering allowed the timeresolved diffusion coefficient to be measured. This was compared to the diffusion monitored by nuclear magnetic resonance (NMR) of turbid undiluted emulsions. Both techniques report similar diffusion coefficients, although NMR measures a true molecular diffusion in different environments whereas DWS measures the diffusion of supramolecular objects in the aqueous phase. These techniques are thus complementary, NMR resolving the kinetics of lipolysis, and DWS resolving the structural transitions, found to be first from a droplet to a vesicle and then from a vesicle to a micelle. In this study, the main formulation parameter influencing the digestion was found to be the type of triglyceride.

No abstract

The chemical interaction between DNA macromolecules and hard tissues in vertebrate is of foremost importance in paleogenetics, as bones and teeth represent a major substrate for the genetic material after cell death. Recently, the empirical hypothesis of DNA "protection" over time thanks to its adsorption on hard tissues was revisited from a physico-chemical viewpoint. In particular, the existence of a strong interaction between phosphate groups of DNA backbone and the surface of apatite nanocrystals (mimicking bone/dentin mineral) was evidenced on an experimental basis. In the field of nanomedicine, DNA or RNA can be used for gene transport into cells, and apatite nanocarriers then appear promising. In order to shed some more light on interactions between DNA molecules and apatite, the present study focuses on the adsorption of a "model" nucleotide, cytidine 5' monophosphate (CMP), on a carbonated biomimetic apatite sample. The follow-up of CMP kinetics of adsorption pointed out the rapidity of interaction with stabilization reached within few minutes. The adsorption isotherm could be realistically fitted to the Sips model (Langmuir-Freundlich) suggesting the influence of surface heterogeneities and adsorption cooperativity in the adsorption process. The desorption study pointed out the reversible character of CMP adsorption on biomimetic apatite. This contribution is intended to prove helpful in view of better apprehending the molecular interaction of DNA fragments and apatite compounds, independently of the application domain, such as bone diagenesis or nanomedicine. This study may also appear informative for researchers interested in the origins of life on Earth and the occurrence and behavior of primitive biomolecules.