ABSTRACT
The present work deals with the optical properties of hybrid organic metal halide material namely (C9H8NO)2SnCl6·2H2O. Its structure is built up from isolated [SnCl6]2- octahedral dianions surrounded by Hydroxyl quinolinium organic cations (C9H8NO)+, abbreviated as [HQ]+. Unlike the usual hybrid materials, where metal halide ions are luminescent semiconductors while the organic ones are optically inactive, [HQ]2SnCl6·2H2O contains two optically active entities: [HQ]+ organic cations and [SnCl6]2- dianions. The optical properties of the synthesized crystals were studied by optical absorption spectroscopy, photoluminescence measurements and DFT calculations of electronic density of states. These studies have shown that both organic and inorganic entities have very close HOMO-LUMO gaps and very similar band alignments favoring the resonant energy transfer process. In addition, measurements of luminescence under variable excitations reveal an intense green luminescence around 497 nm under UV excitation (down conversion) and infrared excitation (up conversion luminescence). The down conversion luminescence is assigned to the π-π* transition within the [HQ] + organic cations involving charge transfer between the organic and inorganic entities, whereas the up-conversion luminescence is based on the triplet-triplet annihilation mechanism (TTA).
ABSTRACT
Description of the relationship between protein structure and function remains a primary focus in molecular biology, biochemistry, protein engineering and bioelectronics. Moreover, the investigation of the protein conformational changes after adhesion and dehydration is of importance to tackle problems related to the interaction of proteins with solid surfaces. In this paper the conformational changes of wild-type Discosoma recombinant red fluorescent proteins (DsRed) adhered on silver nanoparticles (AgNPs)-based nanocomposites are explored via surface-enhanced Raman scattering (SERS). Originality in the present approach is to work on dehydrated DsRed thin protein layers in link with natural conditions during drying. To enable the SERS effect, plasmonic substrates consisting of a single layer of AgNPs encapsulated by an ultra-thin silica cover layer were elaborated by plasma process. The achieved enhancement of the electromagnetic field in the vicinity of the AgNPs is as high as 105. This very strong enhancement factor allowed detecting Raman signals from discontinuous layers of DsRed issued from solution with protein concentration of only 80 nM. Three different conformations of the DsRed proteins after adhesion and dehydration on the plasmonic substrates were identified. It was found that the DsRed chromophore structure of the adsorbed proteins undergoes optically assisted chemical transformations when interacting with the optical beam, which leads to reversible transitions between the three different conformations. The proposed time-evolution scenario endorses the dynamical character of the relationship between protein structure and function. It also confirms that the conformational changes of proteins with strong internal coherence, like DsRed proteins, are reversible.
Subject(s)
Anthozoa/metabolism , Luminescent Proteins/chemistry , Nanocomposites/chemistry , Silver/chemistry , Animals , Desiccation , Metal Nanoparticles/chemistry , Models, Molecular , Protein Conformation , Spectrum Analysis, Raman , Surface Properties , Red Fluorescent ProteinABSTRACT
Low size dispersity silver nanoparticles (ca. 6 nm) have been synthesized by the hydrogenolysis of silver amidinate in the presence of hexadecylamine. Combining NMR techniques with SERS and DFT modeling, it is possible to observe an original stabilization mechanism. Amidine moiety is strongly coordinated to the Ag(0) nanoparticles surface whereas HDA ligand is necessary to prevent agglomeration, although it is only weakly interacting with the surface.
