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The study of the dynamics of nucleic acids in solution, their flow properties, and viscoelasticity is of great importance for understanding their biological functions. Many important properties of nucleic acids, such as DNA, depend on polymer concentration, CDNA, molecular weight (MW), rigidity, and external salt content, the latter parameter affecting electrostatic interactions. Furthermore, DNA molecular chains can organize, in vitro, into liquid crystalline phases at high CDNA. In this work, three DNA samples with different MW were studied in solution in a broad concentration range (CDNA from 0.025 to 200 mg mL−1, depending on DNA MW). Firstly, the intrinsic viscosities and MW for all DNA samples were determined through capillary and rheological measurements. Then, the overlap concentrations, C*, were estimated from the relation C* ≈ [η]−1. DNA chain characteristics were then analyzed in terms of the influence of DNA MW on the solution viscosities and on the overlap parameter, CDNA[η]. Flow birefringence appearance was identified by screening a wide CDNA range through visual observations with crossed polarizers. Finally, crossed‐light polarized microscopy was used to identify the appearance of liquid crystals at rest, confirming that higher CDNA are needed to obtain liquid crystals for low MW DNA samples. [ABSTRACT FROM AUTHOR]

Nanogels are nanostructures with dimensions within the nanoscale, composed of crosslinked polymers through their functional groups. Nanogels can display sensitiveness to stimuli, such as pH or temperature. This characteristic has been used in the design of new platforms for the transport and release of active ingredients. Biopolymer‐based nanogels are of great interest due to their biodegradability, biocompatibility, nontoxicity, and among others. In this project, pH‐responsive nanogels are synthesized through a novel methodology, using two polysaccharides classified as safe, biocompatible, and easily accessible materials, i.e., chitosan (CS) and maltodextrin (MD). A reductive amination reaction between CS and partially oxidized MDs allows to synthesized MD/CS nanogels with sizes ranging from 90 ± 5 to 194 ± 40 nm and with a colloidal stability up to 7 weeks. It is found that the variation of nanogels size and charge depends on CS concentration, molecular weight, and pH, as well as on the % oxidation of the MD. As evidence of nanogels pH‐responsiveness, an increase of size and ζ‐potential is observed by decreasing the pH. This size increase is attributed to the swelling of the nanogels upon a change in pH. Finally, doxorubicin is encapsulated in MD/CS nanogels, with a loading capacity up to 57%. [ABSTRACT FROM AUTHOR]

Natural or synthetic polycations are used in nucleic acid‐based therapies as complexing agents which interact electrostatically with nucleic acids, condense them into nanoparticles, protect them and control their entry into cells. However, although the literature on the formation of nanoparticles known as complexes is well documented, fewer studies have focused on the physical chemistry behind their disassembly, especially under physicochemical conditions found in an intracellular environment. There are several theories of the disassembly of these complexes, one of them consisting in the exchange between the polycations of these particles with biological polyanions. This project is focused on the study of the complexation mechanism of chitosan and calf‐thymus DNA, as well as the stability of the obtained complexes in presence of biological polyanions, i.e., glycosaminoglycans (GAGs). In the presence of polyelectrolyte complexes, GAGs that are present in cells are expected to compete with nucleic acids and dissociate the complex if polycation–GAG association is thermodynamically favored. It is found that chitosan/DNA complexes colloidal stability depends on its [N+]/[P−] charge ratio (R). Furthermore, it is determined that the aggregation onset of the complexes, generated by the addition of different GAGs, depends on the structure and the charge density of the GAGs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]

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]. [ABSTRACT FROM AUTHOR]

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 [NH 3 + ]/[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 150 nm. Stable nanoparticles are obtained for a partial neutralization of phosphate ionic sites (i.e.: [NH 3 + ]/[P − ] fraction between 0.35 and 0.80). [ABSTRACT FROM AUTHOR]

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 (γ) 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 ~γ -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). [ABSTRACT FROM AUTHOR]

A graph is presented that depicts reduced slastic and viscous moduli as a function of the reduced frequency for the concentration variation of calf-thymus DNA.