Diatom biosilica is an inorganic/organic hybrid material with outstanding properties. The molecular architecture of the organic material at atomic and nanometer scale has remained unknown. A solid- state NMR approach assisted by dynamic nuclear polarization (DNP) and molecular dynamics (MD) simulations was applied to study the structural organization of fully 13C, 15N, and 29Si- enriched biosilica [1]. For the first time, in situ insight into the secondary structure elements of tightly biosilica-associated native proteins in diatom biosilica was obtained. Our data suggest that these proteins are rich in a limited set of amino acids and adopt a mixture of random coil and β- strand conformations. Furthermore, biosilica-associated long-chain polyamines (LCPAs) were characterized leading to a model for the supramolecular organization of intact biosilica. LCPAs are embedded into the silica whereas proteins are located at the surface [1]. Close LCPA-silica contact was also revealed by 1H-13C-{29Si}-rotational echo double resonance (REDOR) and 1H-13C-29Si double cross polarization (DCP) [2]. Functional groups in contact with silica were identified but accurate distance determination by REDOR is impossible for fully isotope-labeled biosilica with its complicated biomolecular composition [2].
Distances and spin system geometries can now be determined by using well defined synthetic model systems employing selective isotope labeling. As an example, in vitro prepared nanocomposites containing silica and selectively 13C and 15N labeled polyamines of similar structure as found in diatoms are available meanwhile. Precise REDOR data with maximum REDOR fractions exceeding 90 % are measured [3]. These experiments in combination with extended MD simulations provide reliable distance and spin system information beyond the simple 2-spin-approximation. LCPAs from diatoms sometimes bear quaternary nitrogen moieties as found in choline. Choline is therefore an interesting model compound which in addition exhibits an OH group capable of forming hydrogen bonds. Choline-silica nanocomposites exhibit 1H-13C-{29Si}- REDOR fractions up to 30 % and 13C chemical shift changes for 13C1-choline [4]. This indicates the formation of hydrogen bonds between the choline C1-OH and ionized silanols at the silica surface as could be verified by MD simulations and 1H-29Si-1H DCP experiments.
[1] A. Jantschke, E. Koers, D. Mance, M. Weingarth, E. Brunner, M. Baldus, Angew. Chem. Int. Ed. 2015, 54, 15069-15073.
[2] D. Wisser, S. I. Bru&x308;ckner, F. M. Wisser, G. Althoff-Ospelt, J. Getzschmann, S. Kaskel, E. Brunner, Solid State Nucl. Magn. Reson. 2015, 66-67, 33-39.
[3] S. I. Bru&x308;ckner,
S. Donets, A. Dianat, M. Bobeth, R. Gutierrez, G. Cuniberti, E. Brunner, Langmuir 2016, 32, 11698–11705.
[4] M. Abacilar, F. Daus, C. Haas, S. I. Bru&x308;ckner, E. Brunner, A. Geyer, RSC Adv. 2016, 6, 93343- 93348.
Diatom biosilica is an inorganic/organic hybrid material with outstanding properties. The molecular architecture of the organic material at atomic and nanometer scale has remained unknown. A solid- state NMR approach assisted by dynamic nuclear polarization (DNP) and molecular dynamics (MD) simulations was applied to study the structural organization of fully 13C, 15N, and 29Si- enriched biosilica [1]. For the first time, in situ insight into the secondary structure elements of tightly biosilica-associated native proteins in diatom biosilica was obtained. Our data suggest that these proteins are rich in a limited set of amino acids and adopt a mixture of random coil and β- strand conformations. Furthermore, biosilica-associated long-chain polyamines (LCPAs) were characterized leading to a model for the supramolecular organization of intact biosilica. LCPAs are embedded into the silica whereas proteins are located at the surface [1]. Close LCPA-silica contact was also revealed by 1H-13C-{29Si}-rotational echo double resonance (REDOR) and 1H-13C-29Si double cross polarization (DCP) [2]. Functional groups in contact with silica were identified but accurate distance determination by REDOR is impossible for fully isotope-labeled biosilica with its complicated biomolecular composition [2].
Distances and spin system geometries can now be determined by using well defined synthetic model systems employing selective isotope labeling. As an example, in vitro prepared nanocomposites containing silica and selectively 13C and 15N labeled polyamines of similar structure as found in diatoms are available meanwhile. Precise REDOR data with maximum REDOR fractions exceeding 90 % are measured [3]. These experiments in combination with extended MD simulations provide reliable distance and spin system information beyond the simple 2-spin-approximation. LCPAs from diatoms sometimes bear quaternary nitrogen moieties as found in choline. Choline is therefore an interesting model compound which in addition exhibits an OH group capable of forming hydrogen bonds. Choline-silica nanocomposites exhibit 1H-13C-{29Si}- REDOR fractions up to 30 % and 13C chemical shift changes for 13C1-choline [4]. This indicates the formation of hydrogen bonds between the choline C1-OH and ionized silanols at the silica surface as could be verified by MD simulations and 1H-29Si-1H DCP experiments.
[1] A. Jantschke, E. Koers, D. Mance, M. Weingarth, E. Brunner, M. Baldus, Angew. Chem. Int. Ed. 2015, 54, 15069-15073.
[2] D. Wisser, S. I. Bru&x308;ckner, F. M. Wisser, G. Althoff-Ospelt, J. Getzschmann, S. Kaskel, E. Brunner, Solid State Nucl. Magn. Reson. 2015, 66-67, 33-39.
[3] S. I. Bru&x308;ckner,
S. Donets, A. Dianat, M. Bobeth, R. Gutierrez, G. Cuniberti, E. Brunner, Langmuir 2016, 32, 11698–11705.
[4] M. Abacilar, F. Daus, C. Haas, S. I. Bru&x308;ckner, E. Brunner, A. Geyer, RSC Adv. 2016, 6, 93343- 93348.
