Speaker: T. Vuleti?
Affiliation: Zagreb Institute of Physics, Croatia
Abstract Details: Biomacromolecules are mostly polyelectrolytes (PE), dissociating into polyions and small counterions. Their long-range electrostatic interaction leads to arrangements different than for neutral polymers and leads both to difficulties in understanding these systems [1] and to distinctive technical applications (gene therapy, gene chips, DNA sequencing) [2]. All studies necessarily reflect effects of both polyions and the ionic cloud, all the while being designed to distinguish between the effects of the two by, e.g., studying the polyion conformation in varying (counter)ion atmospheres, or by studying the changes to the atmosphere that may occur with variation in polyion length, stiffnes or concentration. Two most prominent issues are counterion (atmosphere) condensation and the electrostatic contribution to the polyion persistence length. For the last decade we have adressed these by studying the structure and dynamics of two semirigid (bio)PEs, DNA and HA (hyaluronic acid) [3] and comparing these to results on flexible PE, polystyrene sulfonate (PSS). We employed dielectric/impedance spectroscopy (DS), diffusion measurements by fluorescence correlation spectroscopy (FCS) and structural studies by small- angle X-ray scattering (SAXS). We have demonstrated the complementarity of DS and FCS dynamics study of PE conformations to well-established SAXS structural studies of DNA, HA and PSS samples – obtaining the same parameter, polyion mesh size ? by both approaches. We have also quantitated and confirmed counterion condensation concepts with DS and FCS of monodisperse dsDNA fragments. Currently, by SAXS and polarizing microscopy we are studying the generality of the equation of state for PEs – whether it should be simply derived from the free, uncondensed counterion concentration. That is, we found that HA generates 4-5 times weaker pressure per free counterion than DNA or PSS. The latter are strong PEs and counterions atmospheres are “rarified” due to the condensation. On the contrary, HA should be a weak polyelectrolyte where no condensation occurs and all the counterions are free to contribute to the osmotic pressure – which appears not to be the case. [1] P.-G. de Gennes et al., J. Phys. (Paris) 37, 1461 (1976); G. S. Manning, Q. Revs. Biophys. 11, 179 (1978); T. Odijk, Macromolecules 12, 804 (1979); A. V. Dobrynin and M. Rubinstein, Prog. Polym. Sci. 30, 1049 (2005); G.C. Wong and L. Pollack, Annu. Rev. Phys. Chem. 61, 171 (2010). A.K. Mazur and M.Maaloum PRL 112, 068104 (2014). [2] D. Branton et al., Nature Biotechnology 26, 1146 (2008); A.Buxboim et al., Nano Lett. 9, 909 (2009); C.R.Safinya et al., Top Curr Chem. 296, 191(2010); C.A.Merchant and M.Drndi? Methods Mol Biol.;870:211-26 (2012). [3] T. Vuleti? et al., Phys. Rev. Lett., 97, 098303(2006); Phys. Rev. E 75, 021905.(2007); Europhys. Lett., 81, 68003 (2008); Phys. Rev. E, 82, 011922 (2010); Phys. Rev. E 83, 041803 (2011); Macromolecules 46, 1107 (2013)

About The Speaker: T. Vuleti? (Ph.D. Uni Zagreb, postdoc Uni Paris XI) is building his research group at the Institute of physics in Zagreb. He is now looking beyond basic studies of polyelectrolytes towards the application of this knowledge in hybrid bio/nano systems, e.g. DNA and graphene in gene chips or nanopore systems. He is also the secretary of Croatian Biophysical Society (http://biofizika.hr) and Chair of International School of Biophysics (http://soft.ifs.hr/school)

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