Inorganic anions strongly influence the electron transfer rate from the ascorbate to the ferrocene-terminated self-assembled monolayer (SAM) composed of 9-mercaptononyl-5'-ferrocenylpentanoate (Fc(CH2)4COO(CH2)9SH, MNFcP). At the 1 M concentration level of the supporting anion (sodium salt electrolyte), a more than 10-fold increase in the electrocatalytic oxidation rate constant of the ascorbate is observed in the following sequence: PF6-, ClO4-, BF4-, NO3-, Cl-, SO4(2-), NH2SO3- (sulfamate), and F-. The sequence corresponds to the direction of increasing hydration energy of the corresponding anion, suggesting that highly hydrated ions promote electrocatalytic electron transfer to the ferrocene-terminated SAMs, while poorly hydrated ions inhibit it. Fourier transform surface-enhanced Raman spectroscopy (FT-SERS), in combination with cyclic voltammetry, indicates the formation of surface ion pairs between the ferricinium cation (Fc+) and low hydration energy anions, while, on the contrary, no ion pairs were observed in the electrolytes dominated by the high hydration energy anions. Though it is evident that the ion-pairing ability of hydrophobic anions is directly responsible for the electrocatalytic electron transfer inhibition, an estimate of the free, ion-unpaired Fc+ surface concentration shows that it cannot be directly related to the electron transfer rate. This suggests that the principal reason of the anion-induced electron transfer rate modulation might be related to the molecular level changes of the physical and chemical properties as well as the structure of the self-assembled monolayer.

A simple and versatile method for the preparation of functional enzyme-gold nanoparticle conjugates using "click" chemistry has been developed. In a copper-catalyzed 1,2,3-triazole cycloaddition, an acetylene-functionalized Thermomyces lanuginosus lipase has been attached to azide-functionalized water-soluble gold nanoparticles under retention of enzymatic activity. The products have been characterized by gel electrophoresis and a fluorometric lipase activity assay. It is estimated that the equivalent of approximately seven fully active lipase molecules are attached to each nanoparticle.

Cytochrome c (cyt c) has been studied as an example of a peripheral membrane protein that forms a cubic phase with monooleoylglycerol (monoolein, MO) and aqueous solutions. The unit cell dimensions of the cubic phases (space group Pn3m) in relation to the composition of the aqueous solution and protein concentration were analyzed according to the concept of a lipid packing parameter in the bilayer. The interaction between cyt c and MO in the cubic phase was studied by FT-IR spectroscopy and differential scanning calorimetry (DSC). The FT-IR data indicated a somewhat higher conformational order of the MO acyl chain and structural rearrangements of the polar head-group region in the cubic MO−cyt c−H2O phase. These findings, together with the increase in unit cell dimension, suggested a decrease of the MO packing parameter upon protein incorporation. Furthermore, a competitive interaction between the protein and buffer ions at the lipid bilayer was observed. DSC measurements showed that incorporation of cyt c into the cubic MO−H2O phase resulted in a significant decrease in temperature during the phase transitions cubic → reversed hexagonal → reversed micellar, and the unfolding of the protein took place simultaneously with the first phase transition. Additionally, voltammetric and chronoamperometric studies of the direct redox conversions of cyt c at the 4,4‘-dithiodipyridine-modified gold electrode revealed that the mobility of the protein molecules within the cubic phase was highly restricted. Altogether, these findings indicate that nonelectrostatic interactions between peripheral proteins and lipid molecules in membranes might also play a role in regulating biological function.