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  • 1.
    Jena, Naresh K.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Lyne, ÅL.
    Natarajan Arul, Murugan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Birgisson, B.
    Atomic level simulations of the interaction of asphaltene with quartz surfaces: role of chemical modifications and aqueous environment2017In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 50, no 1, article id 99Article in journal (Refereed)
    Abstract [en]

    Understanding the properties of bitumen and its interaction with mineral aggregates is crucial for future strategies to improve roads and highways. Knowledge of basic molecular and electronic structures of bitumen, one out of the two main components of asphalt, poses a major step towards achieving such a goal. In the present work we employ atomistic simulation techniques to study the interaction of asphaltenes, a major constituent of bitumen, with quartz surfaces. As an effective means to tune adhesion or cohesion properties of asphaltenes and mineral surfaces, we propose chemical modification of the pristine asphaltene structure. By the choice of substituent and site of substitution we find that adhesion between the asphaltene molecule and the quartz surface can easily be improved at the same time as the cohesive interaction between the asphaltene units is reduced, while other substituents may lead to the opposite effect. We also provide insight at the molecular level into how water molecules affect interactions between asphaltenes and quartz. Our approach emphasizes a future role for advanced atomistic modeling to understand the properties of bitumen and suggest further improvements.

  • 2.
    Osella, Silvio
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Murugan, N. Arul
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Jena, Naresh K.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Knippenberg, Stefan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Investigation into Biological Environments through (Non)linear Optics: A Multiscale Study of Laurdan Derivatives2016In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 12, no 12, p. 6169-6181Article in journal (Refereed)
    Abstract [en]

    The fluorescent marker Laurdan and its new derivative, C-Laurdan, have been investigated by means of theoretical calculations in a DOPC lipid bilayer membrane at room temperature, and a comparison is made with results from fluorescence experiments. Experimentally, the latter probe is known to have a higher sensitivity to the membrane polarity at the lipid headgroup region and has higher water solubility. Results from Molecular Dynamics (MD) simulations show that C-Laurdan is oriented with the carboxyl group toward the head of the membrane, with an angle of 50 degrees between the molecular backbone and the normal to the bilayer, in contrast to the orientation of the Laurdan headgroup whose carbonyl group is oriented toward the polar regions of the membrane and which describes an angle of ca. 70-80 degrees with the membrane normal. This contrast in orientation reflects the differences in transition dipole moment between the two probes and, in turn, the optical properties. QM/MM results of the probes show little differences for one- (OPA) and two-photon absorption (TPA) spectra, while the second harmonic generation (SHG) beta component is twice as large in Laurdan with respect to C-Laurdan probe. The fluorescence anisotropy decay analysis of the first excited state confirms that Laurdan has more rotational freedom in the DOPC membrane, while C-Laurdan experiences a higher hindrance, making it a better probe for lipid membrane phase recognition.

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