Alanine Adsorption and Thermal Condensation at the Interface of Fumed Silica Nanoparticles: A Solid-State NMR Investigation

Abstract

Investigating the interface between biomolecules and nanoparticles has attracted considerable attention in recent years since it has great significance in numerous fields including nanotechnology, biomineralization, cancer therapy, and origin of life. In this paper, we present a thorough solid-state NMR study on alanine adsorption and thermal condensation on fumed silica nanoparticles. The structure and dynamics at the interface between alanine and fumed silica nanoparticles were probed with a combination of 1 H, 13 C, and 15 N one-and two-dimensional (2D) magic angle spinning (MAS) solid-state NMR methods at different alanine surface coverages and hydration levels. It is illustrated at high surface coverages both crystalline and adsorbed states of alanine exist in the samples while only adsorbed alanine is observed at low surface coverage (approximately a monolayer). At high hydration levels, the adsorbed alanine exhibits enhanced mobility, and both the carboxyl and amine group interact with mobile water molecules on the silica nanoparticle surface. At low hydration levels, the adsorbed alanine interacts with surface silanols via the protonated amine group and the carboxylate group. The thermal condensation of alanine on fumed silica nanoparticles was also investigated, and the results indicate that alanine can undergo thermal condensation at ∼170 °C at the interface of fumed silica nanoparticles as confirmed by a battery of 13 C and 15 N 2D MAS solid-state NMR experiments. By combining the adsorption and thermal condensation results, a possible mechanism for the silica surface-catalyzed thermal condensation reaction of alanine is proposed.

One Step up the Ladder of Prebiotic Complexity: Formation of Nonrandom Linear Polypeptides from Binary Systems of Amino Acids on Silica

“…This has been observed in the present investigationf or Leu/SiO 2 and Val/SiO 2 , and in previouss tudies for Gly/SiO 2 [29] or Ala/SiO 2 . [53] DKPs are often considered as a"dead-end" for the evolution of complexity.E ven though more complex scenarios in fluctuating environments(wetting/drying, or WD, cycles) may allow ar edistribution of the peptide bonds of DKP and the formation of longero ligomers, there is no straightforward ascent to complexity.G lu/SiO 2 behaves somewhat differently because the first thermal transformation the AA undergoes is the internal cyclization to PyroGlu.O ncea gain this is aw ell-known reaction:g lutamic acid is sensitivet ot emperature and easily transforms into PyroGlu even without surfaces upport. [54] Its ulterior dimerization to aD KP is probable but, in contrast to other amino acids, this DKP is unstable and readily hydrolyzed.…”

Characterizing gold nanoparticles by NMR spectroscopy

“…Until recently, only the structures of Au 23 (SC 6 H 11 ) 16 , Au 25 (PET) 18 , Au 25 (SEt) 18 , Au 28 (TBBT) 20 , Au 36 (SPh‐tBu) 24 , Au 38 (SR) 24 , and Au 102 (p‐MBA) 44 have been successfully determined by X‐ray crystallography. Comparing with all these techniques, nuclear magnetic resonance (NMR) spectroscopy has been demonstrated to be a universal and versatile technique for characterization of nanomaterials . One‐dimensional/multidimensional NMR spectroscopy combined with homonuclear/heteronuclear NMR spectroscopy provides considerable methods for characterizing nanostructures including purity, ligand density, and surface chemistry .…”

Experimental characterization and simulation of amino acid and peptide interactions with inorganic materials

“…Other destructive techniques, like induced coupled plasma, also yield the equilibrium constant by quantifying individual elements . While a determination of the binding capacity of organic molecules on inorganic surfaces is possible, the equilibrium constant K D calculated from TGA results is often higher than with other methods indicating a lower thermodynamic probability of the surface to bind the molecules but the lower sensitivity might falsify the binding constant . In several cases the analysis of the binding affinity by analysis of adsorbent in the supernatant (liquid sample) and adsorbate on the adsorber (solid sample) yielded similar results .…”