Institute of Physics Belgrade

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Browsing Institute of Physics Belgrade by Author "Adžić, Nataša"

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    Engineering Ultrasoft Interactions in Stiff All‐DNA Dendrimers by Site‐Specific Control of Scaffold Flexibility
    Adžić, Nataša; Jochum, Clemens; Likos, Christos; Stiakakis, Emmanuel
    A combined experimental and theoretical study of the structural correlations in moderately concentrated suspensions of all‐DNA dendrimers of the second generation (G2) with controlled scaffold rigidity is reported here. Small‐angle X‐ray scattering experiments in concentrated aqueous saline solutions of stiff all‐DNA G2 dendritic constructs reveal a novel anomalous liquid‐like phase behavior which is reflected in the calculated structure factors as a two‐step increase at low scattering wave vectors. By developing a new design strategy for adjusting the particle's internal flexibility based on site‐selective incorporation of single‐stranded DNA linkers into the dendritic scaffold, it is shown that this unconventional type of self‐organization is strongly contingent on the dendrimer's stiffness. A comprehensive computer simulation study employing dendritic models with different levels of coarse‐graining, and two theoretical approaches based on effective, pair‐potential interactions, remarkably confirmed the origin of this unusual liquid‐like behavior. The results demonstrate that the precise control of the internal structure of the dendritic scaffold conferred by the DNA can be potentially used to engineer a rich palette of novel ultrasoft interaction potentials that could offer a route for directed self‐assembly of intriguing soft matter phases and experimental realizations of a host of unusual phenomena theoretically predicted for ultrasoft interacting systems.
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    Self assembling cluster crystals from DNA based dendritic nanostructures
    Stiakakis, Emmanuel; Jung, Niklas; Adžić, Nataša; Balandin, Taras; Kentzinger, Emmanuel; Rücker, Ulrich; Ralf Biehl; Dhont, Jan K. G.; Jonas, Ulrich; Likos, Christos N.
    Cluster crystals are periodic structures with lattice sites occupied by several, overlapping building blocks, featuring fluctuating site occupancy, whose expectation value depends on thermodynamic conditions. Their assembly from atomic or mesoscopic units is long-sought-after, but its experimental realization still remains elusive. Here, we show the existence of well-controlled soft matter cluster crystals. We fabricate dendritic-linear-dendritic triblock composed of a thermosensitive water-soluble polymer and nanometer-scale all-DNA dendrons of the first and second generation. Conclusive small-angle X-ray scattering (SAXS) evidence reveals that solutions of these triblock at sufficiently high concentrations undergo a reversible phase transition from a cluster fluid to a body-centered cubic (BCC) cluster crystal with density-independent lattice spacing, through alteration of temperature. Moreover, a rich concentration-temperature phase diagram demonstrates the emergence of various ordered nanostructures, including BCC cluster crystals, birefringent cluster crystals, as well as hexagonal phases and cluster glass-like kinetically arrested states at high densities. Experimental realization of cluster crystals- periodic structures with lattice sites occupied by several, overlapping building blocks, has been elusive. Here, the authors show the existence of well-controlled soft matter cluster crystals composed of a thermosensitive water-soluble polymer and nanometer-scale all-DNA dendrons.
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    Self assembling cluster crystals from DNA based dendritic nanostructures
    Stiakakis, Emmanuel; Jung, Niklas; Adžić, Nataša; Balandin, Taras; Kentzinger, Emmanuel; Rücker, Ulrich; Biehl, Ralf; Dhont, Jan K. G.; Jonas, Ulrich; Likos, Christos N.
    Cluster crystals are periodic structures with lattice sites occupied by several, overlapping building blocks, featuring fluctuating site occupancy, whose expectation value depends on thermodynamic conditions. Their assembly from atomic or mesoscopic units is long-sought-after, but its experimental realization still remains elusive. Here, we show the existence of well-controlled soft matter cluster crystals. We fabricate dendritic-linear-dendritic triblock composed of a thermosensitive water-soluble polymer and nanometer-scale all-DNA dendrons of the first and second generation. Conclusive small-angle X-ray scattering (SAXS) evidence reveals that solutions of these triblock at sufficiently high concentrations undergo a reversible phase transition from a cluster fluid to a body-centered cubic (BCC) cluster crystal with density-independent lattice spacing, through alteration of temperature. Moreover, a rich concentration-temperature phase diagram demonstrates the emergence of various ordered nanostructures, including BCC cluster crystals, birefringent cluster crystals, as well as hexagonal phases and cluster glass-like kinetically arrested states at high densities.
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    Semi-flexible compact polymers in two dimensional nonhomogeneous confinement
    Marčetić, Dušanka; Elezović-Hadžić, Sunčica; Adžić, Nataša; Zivić, Ivan
    We have studied the compact phase conformations of semi-flexible polymer chains confined in two dimensional nonhomogeneous media, modelled by fractals that belong to the family of modified rectangular (MR) lattices. Members of the MR family are enumerated by an integer p  and fractal dimension of each member of the family is equal to 2. The polymer flexibility is described by the stiffness parameter s, while the polymer conformations are modelled by weighted Hamiltonian walks (HWs). Applying an exact recurrence equations method, we have found that partition function Z N for closed HWs consisting of N steps scales as , where constants and depend on both p  and s. We have calculated numerically the stiffness dependence of the polymer persistence length, as well as various thermodynamic quantities (such as free and internal energy, specific heat and entropy) for a large set of members of the MR family. Analysis of these quantities has shown that semi-flexible compact polymers on MR lattices can exist only in the liquid-like (disordered) phase, whereas the crystal (ordered) phase has not appeared. Finally, behavior of the examined system at zero temperature has been discussed.
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    Structure and stimuli-responsiveness of all-DNA dendrimers: Theory and experiment
    Jochum, Clemens; Adžić, Nataša; Stiakakis, Emmanuel; Derrien, Thomas L.; Luo, Dan; Kahl, Gerhard; Likos, Christos N.
    We present a comprehensive theoretical and experimental study of the solution phase properties of a DNA-based family of nanoparticles - dendrimer-like DNA molecules (DL-DNA). These charged DNA dendrimers are novel macromolecular aggregates, which hold high promise in targeted self-assembly of soft matter systems in the bulk and at interfaces. To describe the behaviour of this family of dendrimers (with generations ranging from G1 to G7), we use a theoretical model in which base-pairs of a single DL-DNA molecule are modeled by charged monomers, whose interactions are chosen to mimic the equilibrium properties of DNA correctly. Experimental results on the sizes and conformations of DL-DNA are based on static and dynamic light scattering; and molecular dynamics simulations are employed to model the equilibrium properties of DL-DNA, which compare favorably to the findings from experiments while at the same time providing a host of additional information and insight into the molecular structure of the nanostructures. We also examine the salt-responsiveness of these macromolecules, finding that despite the strong screening of electrostatic interactions brought about by the added salt, the macromolecules shrink only slightly, their size robustness stemming from the high bending rigidity of the DNA-segments. The study of these charged dendrimer systems is an important field of research in the area of soft matter due to their potential role for various interdisciplinary applications, ranging from molecular cages and carriers for drug delivery in a living organism to the development of dendrimer- and dendron-based ultra-thin films in the area of nanotechnology. These findings are essential to determine if DL-DNA is a viable candidate for the experimental realization of cluster crystals in the bulk, a novel form of solid with multiple site occupancy.