Publications

2019

• Fast P-THG microscopy for the characterization of biomaterials
  
  • Morizet Joséphine
  • Ducourthial Guillaume
  • Supatto Willy
  • Boutillon Arthur
  • Legouis Renaud
  • Schanne-Klein Marie-Claire
  • Stringari Chiara
  • Beaurepaire Emmanuel
  Proceedings of SPIE, the International Society for Optical Engineering, SPIE, The International Society for Optical Engineering, 2019, 11076, pp.1107613. (10.1117/12.2527209)
  DOI : 10.1117/12.2527209
• Implementation of artifact-free circular dichroism SHG imaging of collagen
  
  • Schmeltz Margaux
  • Teulon Claire
  • Latour Gaël
  • Ghoubay Djida
  • Borderie Vincent
  • Aimé Carole
  • Schanne-Klein Marie-Claire
  Optics Express, Optical Society of America - OSA Publishing, 2019, 27 (16), pp.22685. Second harmonic generation (SHG) enables in situ imaging of fibrillar collagen architecture in connective tissues. Recently, Circular Dichroism SHG (CD-SHG) microscopy has been implemented to take advantage of collagen chirality to improve 3D visualization. It measures the normalized difference in the SHG signal obtained upon excitation by left versus right circular polarizations. However, CD-SHG signal is not well characterized yet, and quite different CD-SHG values are reported in the literature. Here, we identify two major artifacts that may occur in CD-SHG experiments and we demonstrate that thorough optimization and calibration of the experimental setup are required for CD-SHG imaging. Notably it requires a careful calibration of the incident circular polarizations and a perfect mechanical stabilization of the microscope stage. Finally, we successfully record CD-SHG images in human cornea sections and confirm that this technique efficiently reveals collagen fibrils oriented out of the focal plane. (10.1364/OE.27.022685)
  DOI : 10.1364/OE.27.022685
• A Molecular Mechanics Model for Flavins
  
  • Aleksandrov Alexey
  Journal of Computational Chemistry, Wiley, 2019, 40 (32), pp.2834-2842. Flavin containing molecules form a group of important cofactors that assist a wide range of enzymatic reactions. Flavins use the redox‐active isoalloxazine system, which is capable of one‐ and two‐electron transfer reactions and can exist in several protonation states. In this work, molecular mechanics force field parameters compatible with the CHARMM36 all‐atom additive force field were derived for biologically important flavins, including riboflavin, flavin mononucleotide, and flavin adenine dinucleotide. The model was developed for important protonation and redox states of the isoalloxazine group. The partial charges were derived using the CHARMM force field parametrization strategy, where quantum mechanics water–solute interactions are used to target optimization. In addition to monohydrate energies and geometries, electrostatic potential around the compound was used to provide additional restraints during the charge optimization. Taking into account the importance of flavin‐containing molecules special attention was given to the quality of bonded terms. All bonded terms, including stiff terms and torsion angle parameters, were parametrized using exhaustive potential energy surface scans. In particular, the model reproduces well the butterfly motion of isoalloxazine in the oxidized and reduced forms as predicted by quantum mechanics in gas phase. The model quality is illustrated by simulations of four flavoproteins. Overall, the presented molecular mechanics model will be of utility to model flavin cofactors in different redox states. (10.1002/jcc.26061)
  DOI : 10.1002/jcc.26061