Solvent‐Free Protein Liquids and Liquid Crystals

Abstract

Nanostructures such as functionalized nanoparticles and superlattices have wide-ranging applications in diverse areas. [1][2][3][4] Although these materials are invariably used in the form of aqueous/organic dispersions, ultrathin films, or bulk powders, Giannellis and co-workers have recently pioneered an approach to preparing functionalized inorganic nanostructures with liquidlike behavior. [5,6] These are produced by electrostatically grafting an organic canopy layer onto the surface of charged nanoparticles of silica, [7] iron oxides, [7] and titania [8] for example, to provide a fluidization medium for the preparation of solvent-free nanoparticle ionic fluids. Like nanoscale objects in general, proteins exhibit persistent structures with dimensions that exceed the range of their intermolecular forces, such that liquid-vapor co-existence is unattainable. [9] As a consequence, solid-state proteins sublime at low pressures or thermally degrade under ambient conditions: thus, there are no known liquid proteins in the absence of solvent.Herein, we report, to our knowledge, the first example of a solvent-free liquid protein. Specifically, we report the preparation and properties of a protein melt based on a stoichiometric ferritin-polymer nanoscale construct with surface modifications that extend the range of intermolecular interactions to a length scale that is commensurate with fluidity in the absence of water. Moreover, we show that these spherically shaped nano-constructs undergo anisotropic ordering during melting at 30 8C to produce a viscoelastic protein liquid that exhibits thermotropic liquid-crystalline behavior, and which subsequently transforms to a Newtonian fluid at temperatures above 40 8C and is stable up to a temperature of 405 8C. The method, which utilizes the sitespecificity of surface amino acid residues and high degree of uniformity in ferritin molecular architecture to produce discrete single-component ferritin-polymer constructs (Supporting Information, Figure S1), should be readily accessible to exploitation as a facile route to solvent-free liquid proteins and enzymes in general.Electrostatically induced complexation of cationized ferritin (C-Fn), comprising approximately 240 covalently coupled N,N-dimethyl-1,3-propanediamine (DMPA) groups per molecule (10 DMPA per subunit; Supporting Information, Figure S2), with the anionic polymer surfactant C 9 H 19 -C 6 H 4 -(OCH 2 CH 2 ) 20 O(CH 2 ) 3 SO 3 À (S) resulted in the formation of the ionic nanoconstruct [C-Fn][S]. Sedimentationcoefficient distributions obtained by analytical ultracentrifugation of extensively dialyzed aqueous solutions of [C-Fn][S] showed a single peak centered at 37 S compared with values of 51 or 0.5 S for C-Fn or S alone (Supporting Information, Figure S3). The decrease in density of the conjugate compared with non-complexed C-Fn, as well as the absence of unbound surfactant, were consistent with a discrete proteinpolymer ionic construct. Significantly, calculations based on comparative density variations coupled with ...

High‐Temperature Electrochemistry of a Solvent‐Free Myoglobin Melt

“…[1][2][3][4][5][6] These studies are significant because they extend previousm ethodology for accessing the liquid state of inorganic particles [7][8][9] to soft biomolecular nanoscale objectss uch as globular proteins,e nzymes, and viruses. Conjugation of the cationized proteins andp olymer surfactant was performed under aqueousc onditions, and subsequent freeze-drying and thermala nnealing at 60 8Cy ieldedasolvent-free meltc lose to room temperature.…”

Creation of energetic biothermite inks using ferritin liquid protein

“…Ferritin protein ionic liquids were prepared using the procedure developed by Mann et al 28,. whereby ferritin was cationized using dimethylaminopropylamine and electrostatically paired with an anionic polymer surfactant (poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether potassium salt (C 9 H 19 -C 6 H 4 -(OCH 2 CH 2 ) 20 O(CH 2 ) 3 SO 3 − )) (ref.…”

“…whereby ferritin was cationized using dimethylaminopropylamine and electrostatically paired with an anionic polymer surfactant (poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether potassium salt (C 9 H 19 -C 6 H 4 -(OCH 2 CH 2 ) 20 O(CH 2 ) 3 SO 3 − )) (ref. 29, 29). Synthesis of ferritin-based ionic liquids was monitored by titration of cationized ferritin with increasing amounts of polymer anion.…”

“…Nanoscale liquids composed of protein ionic liquids (cationized protein/anion pair) represent multifunctional solvent systems that exhibit excellent dispersion and uniformity, yield high protein content and offer the potential to disperse high mass fractions of energetic nanoparticles and overcome particle agglomeration24252627282930. Protein ionic liquids are also particularly appealing because of their unique activity and biological functionality.…”

“…Protein-based ionic liquids feature all the desired properties of both organic ionic liquids and aqueous solvents, and more importantly retain their biological function/activity2427. To date, ionic liquid proteins have been created using ferritin, lipase, lysozyme, myoglobin, DNA and a plant virus2628293031. For energetic applications, previous work has shown that ferritin assembled with nAl led to the formation of multi-layer biothermite powders with enhanced and tunable energetic properties19.…”