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Abstract: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 C e , respectively) from steady state flow and oscillatory dynamic shear experiments. The determination of the viscosity in the Newtonian plateau obtained from flow curves η ( 9 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~9 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 (C DNA > 2.0 mg/mL) and temperature (10˝C < T < 40˝C).

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DNA dynamics and flow properties are of great importance for understanding its functions. DNA is a semiflexible polymer chain characterized by having a large persistence length of around 50 nm and high charge density; DNA chains are interacting efficiently at high concentrations, in dependence of the ionic concentration. In relation with DNA molecular characteristics, it is also known that DNA solutions are able to form liquid crystalline phases over a critical polymer concentration. In this work, the supramolecular organization in calf-thymus DNA solution, with low degree of entanglement, appearing under flow was studied in a wide DNA concentration range from 2 to 10 mg/mL, at a pH of 7.3 and 20 °C. The rheological behavior of the system was studied using steady state flow and oscillatory measurements. Transient regimes were also tested by imposing controlled shear rates on a short time up to steady state. Furthermore, a combination of visual observations and flow birefringence measurements was proposed to reach a better understanding of the obtained rheological behavior. The presence of a shear-induced texture is revealed under flow for the calf-thymus DNA solutions at C DNA> 5 mg/mL and attributed to organized domains of DNA molecules, named in the text as crystalline parts, which are progressively oriented under shear. Finally, at high shear rates (over 100 s–1), it is shown that for the DNA solutions the orientation of these organized DNA domains and connecting chains under flow goes to an anisotropic monodomain.

Positively charged elastin-like polypeptides (ELPs) were synthesized for the compaction of genetic material. A recombinant ELP (VPGXG) 40 with X=V,M (3:1) was post-modified in two steps to introduce chemoselectively either primary or secondary amine pendant groups at each methionine residue. Positively charged ELPs were characterized by SDS-PAGE, size exclusion chromatography, 1 H NMR, potentiometric titrations and dynamic light scattering to assess their purity and determine their degree of functionalization, molecular weight, isoelectric point and thermo-responsive behaviour. Electrostatic complexation between the different ELP derivatives and nucleic acids was studied to determine the stoichiometry of ELP S /nucleic acids complex formation, and to find optimal conditions leading to stable nanoparticles with controlled size and surface potential. The stability of these complexes was investigated in the presence of salts at physiological concentrations and in the presence of surfactant. This study revealed that two regimes of stable nanoparticles in terms of size and charge can be obtained from the electrostatic complexation between the primary amine containing ELP derivative, ELP(-NH 2 ), and plasmid DNA. Resulting complexes were found to be stable to dissociation for charge ratios up to 2.5 under physiological salt concentrations (154 mM NaCl), showing that plasmid DNA was completely condensed by the polycationic ELP and protected against electrolyte-mediated dissociation.

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 C DNA [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 (η sp,0 ) as a function of C DNA [η].

A library of synthetic elastin-like glycopolypeptides was 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 absence of positive charge on the polypeptide residue holding the sugar unit were found critical for the binding to RCA120. MAIN TEXT:Found in most organisms and involved in many different cellular processes, glycoproteins constitute a wide family of natural biomacromolecules composed of glycans covalently attached to proteins. Glycoproteins play crucial roles in major biological phenomena such as infection, cellular recognition and signal transduction. 1, 2 Carbohydrates in glycoproteins interact with a specific class of proteins, termed lectins, through weak monomeric interactions, the high binding affinity between a specific glycoprotein and a lectin being insured by the architecture of the protein and by the presentation of the carbohydrate ligands in a multivalent manner, a phenomenon termed as the "glycoside cluster effect". 3,4 Considerable efforts have been made to synthesize glycoprotein mimics as powerful tools for glycobiology or as lead compounds for therapeutic applications. A wide variety of scaffolds have been explored to access multivalent glycoarchitectures, 5 dendrimers and polymers being the widest families of synthetic compounds explored so far. Polymer chemistry affords myriads of possibilities in terms of glycopolymer design: different architectures can be engineered, chain lengths, sugar numbers and sugar density can also be tuned to increase the potency of glycopolymers towards specific lectins. 6 Because any polymer backbone may not closely mimic the chemical structure of glycoproteins, particular attention was paid to glycopolymers composed of polypeptide backbones decorated with pendant carbohydrates, so designated as glycopolypeptides, as simplified analogues of glycoproteins. [7][8][9][10] Glycopolypeptides obtained by polymerization techniques are accessible at large scales 7,11,12 and impressive advances have been made towards well-defined glycopolypeptides. Inherent macromolecular dispersity arising from polymerization techniques has also encouraged the development of unimolecular multivalent glycoconjugates. To access multivalent glycopeptides with precise compositions, scientists have explored a wide range of chemical strategies ranging from solid-phase synthesis of glycopeptides, 13, 14 ligation techniques 15, 16 or enzymatic syntheses. 5,17 Despite significant progresses, limitations still remain regarding the high complexity of these macromolecular structures and low amount of materials accessible. We believe recombinant DNA and genetic engineering are unique opportunities to access high precision polypeptides with an exact control over monomer sequence and chain length at reasonable scales, while chemoselective modification reactions can be ...

Previous investigations were conducted on two concentrations of DNA solution: 4 mg/mL, for which it has been shown that no supramolecular organization is induced under flow at low shear rates; and 10 mg/mL, in which a liquid crystalline-type texture is formed under flow at low shear rates, attesting to an orientation of pre-organized chains. Rheological experiments are discussed and their results supported by small-angle X-ray scattering (SAXS) and flow birefringence visualization experiments. Scattering from polyelectrolytes has a characteristic signal, which is here observed in SAXS, showing a strong correlation peak between charged chains in water, for both concentrations. This peak is weaker in the presence of 0.01 M NaCl and suppressed in salt excess at 0.1 M NaCl. No plateau in the σ( γ ˙ ) plot was observed in analysis of rheological experiments on low DNA concentration (4 mg/mL). As typically observed in polyelectrolyte systems both the dynamic moduli and shear viscosity were higher in water as electrostatic forces dominate, than in the presence of salt, especially at low shear rates. The rheological results for concentrations of 0.01 M NaCl are lower than in water as expected due to partial screening of electrostatic repulsions. Rheological data for concentrations of 0.1 M NaCl are unexpected. Electrostatic forces are partially screened in the low salt concentration, leading to a drop in the rheological values. For high salt concentration there are no longer interchain repulsions and so steric interactions dominate within the entangled network leading to the subsequent increase in rheological parameters. Regardless of the solvent, at high shear rates the solutions are birefringent. In the 10 mg/mL case, under flow, textures are formed at relatively low shear rate before all the chains align going to a pseudonematic liquid crystalline phase at high shear rate. The electrostatic repulsion between semi-rigid chains induces a correlation between the chains leading to an electrostatic pseudo-gel in water and loosely in 0.01 M NaCl at low stress applied. To the best of our knowledge, this is the first time that such behavior is observed. In 0.1 M NaCl, DNA behavior resembles the corresponding neutral polymer as expected for polyelectrolyte in salt excess, exhibiting a yield stress. When texture appears in water and in 0.01 M NaCl, a critical transition is observed in rheological curves, where the viscosity decreases sharply at a given critical shear stress corresponding to a plateau in the σ( γ ˙ ) plot also observed in creep transient experiment.