Sugar-derived Glasses Support Thermal and Photo-initiated Electron Transfer Processes over Macroscopic Distances

Abstract

Trehalose-derived glasses are shown to support long range electron transfer reactions between spatially well separated donors and protein acceptors. The results indicate that these matrices can be used not only to greatly stabilize protein structures but also to facilitate both thermal and photo-initiated hemeprotein reduction over large macroscopic distances. To date the promise of exciting new protein-based technologies that can harness the exceptional tunability of protein functionality has been significantly thwarted by both intrinsic instability and stringent solvent/environment requirements for the expression of functional properties. The presented results raise the prospect of overcoming these limitations with respect to incorporating redox active proteins into solid state devices such as tunable batteries, switches, and solar cells. The findings also have implications for formulations intended to enhance long term storage of biomaterials, new protein-based synthetic strategies, and biophysical studies of functional intermediates trapped under nonequilibrium conditions. In addition, the study shows that certain sugars such as glucose or tagatose, when added to redox-inactive glassy matrices, can be used as a source of thermal electrons that can be harvested by suitable redox active proteins, raising the prospect of using common sugars as an electron source in solid state thermal fuel cells.Many plants and animals express large amounts of sugars when osmotically stressed (1). The ability of sugars as such trehalose to form glassy matrices under conditions of drying is generally thought to be responsible for anhydrobiosis (2, 3), whereby the cellular machinery is essentially frozen in the glass allowing for long term survival of the organism under conditions of extreme dryness. This phenomenon is the basis for substantial efforts directed toward the creation of suitable carbohydrate-based glassy matrices for the purpose of long term preservation of pharmaceuticals and food items (4 -7). Biophysical studies show that glassy matrices can significantly damp protein motions (8 -12), which results in dramatic conformational stabilization with respect to thermal denaturation and degradation. Both the damping of macromolecular dynamics and the dramatic decrease in the mobility of water within sugar-derived glasses are viewed as the foundation for designing stable sugar-based matrices for long-term maintenance of proteins and other biomolecules under relatively severe conditions. Under such conditions it is assumed that the matrix would be chemically inert. In the present study it is demonstrated that dry glassy matrices can support very long range electron transfer initiated by generating either thermal or photo electrons.Most proteins when incorporated into glassy matrices can no longer function due to the extreme damping of many functionally important motions. Redox reactions, although influenced by protein dynamics, can still occur even when the proteins are immobilized. In a preliminary study (13) it was shown...

Proteins in Saccharides Matrices and the Trehalose Peculiarity: Biochemical and Biophysical Properties

“…In particular, by doping trehalose based solid matrices with the reducing sugar glucose, it was possible to reduce metmyoglobin to deoxymyoglobin (or met-Hb to deoxy-Hb) by thermal inducing the electron transfer from the doping glucose molecules to the iron Fe 3+ ions contained in the active site of the embedded proteins [238]. The same process could be obtained using two distinct trehalose sandwich layers, one containing met-Hb without any glucose, the other doped with glucose (or other reducing monosaccharides such as fructose or tagatose) but free of any protein; if the two glassy sandwiches are put in contact and heated at 75 °C for 45 min, full reduction of met-Hb to deoxy-Hb is obtained [239]. This long range electron transfer process can also be activated with light: if a protein free glassy sandwich is doped with deazaflavin rather than with glucose, put in contact with a met-Hb glassy sandwich, and the two are illuminated with low intensity light at 390 nm, again full reduction of met-Hb to deoxy-Hb is obtained [239].…”

“…The same process could be obtained using two distinct trehalose sandwich layers, one containing met-Hb without any glucose, the other doped with glucose (or other reducing monosaccharides such as fructose or tagatose) but free of any protein; if the two glassy sandwiches are put in contact and heated at 75 °C for 45 min, full reduction of met-Hb to deoxy-Hb is obtained [239]. This long range electron transfer process can also be activated with light: if a protein free glassy sandwich is doped with deazaflavin rather than with glucose, put in contact with a met-Hb glassy sandwich, and the two are illuminated with low intensity light at 390 nm, again full reduction of met-Hb to deoxy-Hb is obtained [239]. Interestingly, a similar two-layer sandwich device can be used to induce the formation of ferrous nitric oxide hemoglobin (HbNO) if one of the layers contains initially met-Hb and the other layer contains nitrite and a thermal electron source (such as the monosaccharides glucose or tagatose): as the sample is heated at 50 °C, the hemoglobin optical spectrum gradually turns to the ferrous NO form indicating that: (i) NO can be easily generated in the second glassy layer by thermal reduction of nitrite; (ii) NO is able to diffuse across the interface separating the two layers [240].…”

Nanoengineering bactericidal nitric oxide therapies

“…11 The general platform for preparing the NO releasing materials is based on sugar-derived glassy matrices that support redox reactions, initiated using thermally generated electrons from glucose. 12 This matrix supports the reduction of nitrite to NO. Additionally, it is a composite material having both sol-gel and glassy properties; thus, the NO generated remains trapped within the dry matrix until the matrix is exposed to moisture.…”

Nitric oxide-releasing porous silicon nanoparticles

“…Sugar-mediated thermal reduction of nitrite-loaded THCPSi NPs produces and entraps NO inside of THCPSi NPs [18,33]. NO formation is the consequence of chemical acidification and redox conversion.…”

“…Finally, after removing the supernatant, the THCPSi NP pellet was dried by heating at 65°C overnight. The drying temperature was held at 70°C to avoid glucose caramelization [23,33,34]. An alternative drying procedure, overnight lyophilization (FD1 freeze dryer, Dynavac Co., MA, USA), was also assessed, as described in the text [23].…”