Structural Behavior of Amphiphilic Triblock Copolymer P104/Water System.

A detailed study of the different structural transitions of the triblock copolymer PEO27-PPO61-PEO27 (P104) in water, in the dilute and semi-dilute regions, is addressed here as a function of temperature and P104 concentration (CP104) by mean of complimentary methods: viscosimetry, densimetry, dynamic light scattering, turbidimetry, polarized microscopy, and rheometry. The hydration profile was calculated through density and sound velocity measurements. It was possible to identify the regions where monomers exist, spherical micelle formation, elongated cylindrical micelles formation, clouding points, and liquid crystalline behavior. We report a partial phase diagram including information for P104 concentrations from 1 × 10-4 to 90 wt.% and temperatures from 20 to 75 °C that will be helpful for further interaction studies with hydrophobic molecules or active principles for drug delivery.

Multivalent Elastin-Like Glycopolypeptides: Subtle Chemical Structure Modifications with High Impact on Lectin Binding Affinity.

A library of synthetic elastin-like glycopolypeptides were synthesized and screened by microscale thermophoresis to identify key structural parameters affecting lectin binding efficacy. While polypeptide backbone size and glycovalency were found to have little influence, the presence of a linker at the anomeric position of galactose and the absence of positive charge on the polypeptide residue holding the sugar unit were found to be critical for the binding to RCA120.

Chitosan-DNA polyelectrolyte complex: Influence of chitosan characteristics and mechanism of complex formation.

Polyelectrolyte complexes formed between DNA and chitosan present different and interesting physicochemical properties combined with high biocompatibility; they are very useful for biomedical applications. DNA in its double helical structure is a semi-rigid polyelectrolyte chain. Chitosan, an abundant polysaccharide in nature, is considered as one of the most attractive vectors due to its biocompatibility and biodegradability. Here we study chitosan/DNA polyelectrolyte complex formation mechanism and the key factors of their stability. Compaction process of DNA with chitosan was monitored in terms of the ζ-potential and hydrodynamic radius variation as a function of charge ratios between chitosan and DNA. The influence of chitosan degree of acetylation (DA) and its molecular weight on the stoichiometry of chitosan/DNA complexes characteristics was also studied. It is shown that the isoelectric point of chitosan/DNA complexes, as well as their stability, is directly related to the degree of protonation of chitosan (depending on pH), to the DA and to the external salt concentration. It is demonstrated that DNA compaction process corresponds to an all or nothing like-process. Finally, since an important factor in cell travelling is the buffering effect of the vector used, we demonstrated the essential role of free chitosan on the proton-sponge effect.

Exchange dynamics between amphiphilic block copolymers and lipidic membranes through hydrophobic pyrene probe transfer.

Vectorization has experienced significant development over the last few years and has been used to control the distribution of active ingredients to a target by their association with a vector. However, controlled drug delivery suffers from "burst release" as the drugs are released before the targeted site. Very few studies have examined the collective mechanisms of fission-fusion on micelles in the transport and expulsion of active ingredients. Endocytosis and exocytosis of cells are examples of fusion and fission in biological matter. Understanding these dynamics becomes crucial for the design and the control of new materials and new processes effective in controlled drug delivery. In this work, a study of the exchange dynamics between amphiphilic block copolymers and lipid membranes for vectorization of hydrophobic molecules using a fluorescence technique is presented. A highly hydrophobic alkylated pyrene, PyC18, is used as a fluorescent probe that can be exchanged between amphiphilic block copolymer micelles and liposomes via different mechanisms. It is demonstrated that the exchange dynamics evaluated for different liposome concentrations is a collective mechanism characterized by having two rate constants.

DNA/chitosan electrostatic complex.

Up to now, chitosan and DNA have been investigated for gene delivery due to chitosan advantages. It is recognized that chitosan is a biocompatible and biodegradable non-viral vector that does not produce immunological reactions, contrary to viral vectors. Chitosan has also been used and studied for its ability to protect DNA against nuclease degradation and to transfect DNA into several kinds of cells. In this work, high molecular weight DNA is compacted with chitosan. DNA-chitosan complex stoichiometry, net charge, dimensions, conformation and thermal stability are determined and discussed. The influence of external salt and chitosan molecular weight on the stoichiometry is also discussed. The isoelectric point of the complexes was found to be directly related to the protonation degree of chitosan. It is clearly demonstrated that the net charge of DNA-chitosan complex can be expressed in terms of the ratio [NH3(+)]/[P(-)], showing that the electrostatic interactions between DNA and chitosan are the main phenomena taking place in the solution. Compaction of DNA long chain complexed with low molar mass chitosan gives nanoparticles with an average radius around 150nm. Stable nanoparticles are obtained for a partial neutralization of phosphate ionic sites (i.e.: [NH3(+)]/[P(-)] fraction between 0.35 and 0.80).

Rheological Properties of DNA Molecules in Solution: Molecular Weight and Entanglement Influences.

Molecular weight, stiffness, temperature, and polymer and ionic concentrations are known to widely influence the viscosity of polymer solutions. Additionally, polymer molecular weight-which is related to its dimensions in solution-is one of its most important characteristics. In this communication, low molecular weight DNA from salmon sperm was purified and then studied in solutions in a wide concentration range (between 0.5 and 1600 mg/mL). The intrinsic viscosity of this low molecular weight DNA sample was firstly determined and the evidence of the overlap concentration was detected around the concentration of 125 mg/mL. The chain characteristics of these short molecules were studied in terms of the influence of their molecular weight on the solution viscosities and on the overlap parameter CDNA[η]. Furthermore, to complete previously reported experimental data, solutions of a large molecular weight DNA from calf-thymus were studied in a high concentration range (up to 40 mg/mL). The rheological behavior is discussed in terms of the generalized master curve obtained from the variation of the specific viscosity at zero shear rate (ηsp,0) as a function of CDNA[η].

Conformation and Rheological Properties of Calf-Thymus DNA in Solution.

Studies of DNA molecule behavior in aqueous solutions performed through different approaches allow assessment of the solute-solvent interactions and examination of the strong influence of conformation on its physicochemical properties, in the presence of different ionic species and ionic concentrations. Firstly, the conformational behavior of calf-thymus DNA molecules in TE buffer solution is presented as a function of temperature. Secondly, their rheological behavior is discussed, as well as the evidence of the critical concentrations, i.e., the overlap and the entanglement concentrations (C* and Ce, respectively) from steady state flow and oscillatory dynamic shear experiments. The determination of the viscosity in the Newtonian plateau obtained from flow curves η ( ) allows estimation of the intrinsic viscosity and the specific viscosities at zero shear when C[η] < 40. At end, a generalized master curve is obtained from the variation of the specific viscosity as a function of the overlap parameter C[η]. The variation of the exponent s obtained from the power law η~ -s for both flow and dynamic results is discussed in terms of Graessley's analysis. In the semi-dilute regime with entanglements, a dynamic master curve is obtained as a function of DNA concentration (CDNA > 2.0 mg/mL) and temperature (10 °C < T < 40 °C).