19 research outputs found
Au(I) N-heterocyclic carbenes from bisimidazolium amphiphiles: synthesis, cytotoxicity and incorporation onto gold nanoparticles
A gold(I) N-heterocyclic carbene 4 from a bis-imidazolium-amphiphile was synthesized and characterized. The cytotoxicity against HT-29 colon carcinoma and MDA-MB-231 breast adenocarcinoma cells was assessed for the NHC complex 4, the imidazolium salt precursor 2, and its methyl analogue 3, indicating that compounds 2ā4 are promising cytotoxic agents. Furthermore, the ability of these compounds to be associated with gold nanoparticles was also explored, in order to develop an anticancer drug delivery system. The free ligands displayed more activity when compared with the ligands immobilized on the gold nanoparticles. The synthesized gold particles incorporating the bis-imidazolium salts either 2 or 3 showed monodisperse spherical shape with sizes of approximately 5 nm
Developing Biotemplated Data Storage: Room Temperature Biomineralization of L1<inf>0</inf> CoPt Magnetic Nanoparticles
L10 cobalt platinum can be used to record data at approximately sixfold higher densities than it is possible to on existing hard disks. Currently, fabricating L10 CoPt requires high temperatures (ā500 Ā°C) and expensive equipment. One ecological alternative is to exploit biomolecules that template nanomaterials at ambient temperatures. Here, it is demonstrated that a dual affinity peptide (DAP) can be used to biotemplate L10 CoPt onto a surface at room temperature from an aqueous solution. One part of the peptide nucleates and controls the growth of CoPt nanoparticles from solution, and the other part binds to SiO2. A native silicon oxide surface is functionalized with a high loading of the DAP using microcontact printing. The DAP biotemplates a monolayer of uniformly sized and shaped nanoparticles when immobilized on the silicon surface. X-ray diffraction shows that the biotemplated nanoparticles have the L10 CoPt crystal structure, and magnetic measurements reveal stable, multiparticle zones of interaction, similar to those seen in perpendicular recording media. This is the first time that the L10 phase of CoPt has been formed without high temperature/vacuum treatment (e.g., annealing or sputtering) and offers a significant advancement toward developing environmentally friendly, biotemplated materials for use in data storage
Modulating Semiconductor Surface Electronic Properties by Inorganic PeptideāBinders Sequence Design
The use of proteins and peptides as part of biosensors
and electronic
devices has been the focus of intense research in recent years. However,
despite the fact that the interface between the bioorganic molecules
and the inorganic matter plays a significant role in determining the
properties of such devices, information on the electronic properties
of such interfaces is sparse. In this work, we demonstrate that the
identity and position of single amino acid in short inorganic binding
protein-segments can significantly modulate the electronic properties
of semiconductor surfaces on which they are bound. Specifically, we
show that the introduction of tyrosine or tryptophan, both possessing
an aromatic side chain which higher occupied molecular orbitals are
positioned in proximity to the edge of GaAs valence band, to the sequence
of a peptide that binds to GaAs (100) results in changes of both the
electron affinity and surface potential of the semiconductor. These
effects were found to be more pronounced than the effects induced
by the same amino acids once bound on the surface in a headātail
configuration. Furthermore, the relative magnitude of each effect
was found to depend on the position of the modification in the sequence.
This sequence dependent behavior is induced both indirectly by changes
in the peptide surface coverage, and directly, probably, due to changes
in the orientation and proximity of the tyrosine/tryptophan side group
with respect to the surface due to the preferred conformation the
peptide adopts on the surface. These studies reveal that despite the
use of short protein oligomers and aiming at a non-natural-electronic
task, the well-known relations between the proteinsā structure
and function is preserved. Combining the ability to tune the electronic
properties at the interface with the ability to direct the growth
of inorganic materials makes peptides promising building blocks for
the construction of novel hybrid electronic devices and biosensors
Surface characterization of U(AlxSi1-x)3 alloy and its interaction with O2 and H2O, at room temperature
Surface characterization and the interactions of U(AlxSi1-x)3 alloy (x = 0.57) with oxygen and water vapor were studied, utilizing X-Ray Photoelectron Spectroscopy and Direct Recoil Spectrometry, at room temperature. The U 4f spectrum of U(AlxSi1-x)3 alloy exhibits weak correlation satellites, suggesting an itinerant description of the U 5f states for this compound. The Al and Si 2p lines are chemically shifted to lower binding energies. Exposing the alloy to oxygen and water vapor results in oxidation of mainly the uranium and aluminum components, while silicon is only slightly oxidized. Oxygen was found to be a stronger oxidizer than water vapor and the trend is consistent with the more negative enthalpies of formation of metal oxides produced by the O2 reaction, as compared to H2O. During oxygen exposure, fast oxidation occurs by oxide islands nucleation and lateral growth, followed by oxidation of the sub-surface, up to ā¼4 nm, at 1000 L exposure. Water initially reacts with the surface by full dissociation and oxide islands formation, which is then covered by hydroxides. Only a minor increase in the oxide thickness of up to ā¼2.5 nm, was observed after coalescence.JRC.G.I.5-Advanced Nuclear Knowledg
Transient Fibril Structures Facilitating Nonenzymatic Self-Replication
An emerging new direction of research focuses on developing āself-synthesizing materialsā, those supramolecular structures that can promote their own formation by accelerating the synthesis of building blocks and/or an entire assembly. It was postulated recently that practical design of such systems can benefit from the ability to control the assembly of amphiphilic molecules into nanostructures. We describe here the self-assembly pathway of short amphiphilic peptides into various forms of soluble Ī²-sheet structuresīøĪ²-plates, fibrils, and hollow nanotubesīøand their consequent activity as autocatalysts for the synthesis of monomeric peptides from simpler building blocks. A detailed kinetic analysis of both the self-assembly and self-replication processes allows us to suggest a full model and simulate the replication process, revealing that only specific structures, primarily fibrils that are stable within the solution for a time shorter than a few hours, can be active as catalysts. Interestingly, we have found that such a process also induces fibril reproduction, in a mechanism very similar to the propagation of prion proteins by transmission of misfolded states
Filling the Green Gap of a Megadalton Photosystem I Complex by Conjugation of Organic Dyes
Photosynthesis
is Natureās major process for converting
solar into chemical energy. One of the key players in this process
is the multiprotein complex photosystem I (PSI) that through absorption
of incident photons enables electron transfer, which makes this protein
attractive for applications in bioinspired photoactive hybrid materials.
However, the efficiency of PSI is still limited by its poor absorption
in the green part of the solar spectrum. Inspired by the existence
of natural phycobilisome light-harvesting antennae, we have widened
the absorption spectrum of PSI by covalent attachment of synthetic
dyes to the protein backbone. Steady-state and time-resolved photoluminescence
reveal that energy transfer occurs from these dyes to PSI. It is shown
by oxygen-consumption measurements that subsequent charge generation
is substantially enhanced under broad and narrow band excitation.
Ultimately, surface photovoltage (SPV) experiments prove the enhanced
activity of dye-modified PSI even in the solid state