29 research outputs found
Extending the Electron Spin Coherence Time of Atomic Hydrogen by Dynamical Decoupling
We study the electron spin decoherence of encapsulated atomic hydrogen in
octasilsesquioxane cages induced by the 1H and 29Si nuclear spin bath. By
applying the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence we significantly
suppress the low-frequency noise due to nuclear spin flip-flops up to the point
where a maximum T2 = 56 us is observed. Moreover, dynamical decoupling with the
CPMG sequence reveals the existence of two sources of high-frequency noise:
first, a fluctuating magnetic field with the proton Larmor frequency,
equivalent to classical magnetic field noise imposed by the 1H nuclear spins of
the cage organic substituents, and second, decoherence due to entanglement
between the electron and the inner 29Si nuclear spin of the cage
Long Electron Spin Coherence Times of Atomic Hydrogen Trapped in Silsesquioxane Cages
Encapsulated atomic hydrogen in cube-shaped octa-silsesquioxane (POSS) cages
of the SiOR type (where R is an organic group) is the simplest
alternative stable system to paramagnetic endohedral fullerenes (N@C or
P@C) that have been regarded as key elements of spin-based quantum
technologies. Apart from common sources of decoherence like nuclear spin and
spectral diffusion, all H@POSS species studied so far suffer from additional
shortening of at low temperatures due to methyl group rotations. Here we
eliminate this factor for the first time by studying the relaxation properties
of the smallest methyl-free derivative of this family with R=H, namely
H@TH. We suppress nuclear spin diffusion by applying dynamical
decoupling methods and we measure electron spin coherence times up to 280
76 s at K. We observe a linear dependence of the decoherence
rate on trapped hydrogen concentrations ranging between 9 cm and 5 cm which we attribute to the
spin dephasing mechanism of instantaneous diffusion and a nonuniform spatial
distribution of encapsulated H atoms
Structure and spin density of ferric low-spin heme complexes determined with high-resolution ESEEM experiments at 35GHz
The wide use of the heme group by nature is a consequence of its unusual "electronic flexibility.” Major changes in the electronic structure of this molecule can result from small perturbations in its environment. To understand the way the electronic distribution is dictated by the structure of the heme site, it is extremely important to have methods to reliably determine both of them. In this work we propose a way to obtain this information in ferric low-spin heme centers via the determination of g, A, and Q tensors of the coordinated nitrogens using electron spin echo envelope modulation experiments at Q-band microwave frequencies. The results for two bisimidazole heme model complexes, namely, PPIX(Im)2 and CPIII(Im)2, where PPIX is protoporphyrin IX, CPIII is coproporphyrin III, and Im is imidazole, selectively labeled with 15N on the heme or imidazole nitrogens are presented. The planes of the axial ligands were found to be parallel and oriented approximately along one of the N-Fe-N directions of the slightly ruffled porphyrin ring (approximately 10°). The spin density was determined to reside in an iron dorbital perpendicular to the heme plane and oriented along the other porphyrin N-Fe-N direction, perpendicular to the axial imidazoles. The benefit of the method presented here lies in the use of Q-band microwave frequencies, which improves the orientation selection, results in no/fewer combination lines in the spectra, and allows separation of the contributions of hyperfine and quadrupole interactions due to the fulfillment of the exact cancellation condition at g Z and the possibility of performing hyperfine decoupling experiments at the g X observer position. These experimental advantages make the interpretation of the spectra straightforward, which results in precise and reliable determination of the structure and spin distributio
Structural analysis of Cu(II) ligation to the 5′-GMP nucleotide by pulse EPR spectroscopy
Simple copper salts are known to denature poly d(GC). On the other hand, copper complexes of substituted 1,4,7,10,13-pentaazacyclohexadecane-14,16-dione are able to convert the right-handed B form of the same DNA sequence to the corresponding left-handed Z form. A research program was started in order to understand why Cu(II) as an aquated ion melts DNA and induces the conformational change to Z-DNA in the form of an azamacrocyclic complex. In this paper, we present a continuous wave and pulse electron paramagnetic resonance study of the mononucleotide model system Cu(II)-guanosine 5′-monophosphate . Pulse EPR methods like electron-nuclear double resonance and hyperfine sublevel correlation spectroscopy provide unique information about the electronic and geometric structure of this model system through an elaborate mapping of the hyperfine and nuclear quadrupole interactions between the unpaired electron of the Cu(II) ion and the magnetic nuclei of the nucleotide ligand. It was found that the Cu(II) ion is directly bound to N7 of guanosine 5′-monophosphate and indirectly bound via a water of hydration to a phosphate group. This set of experiments opens the way to more detailed structural characterization of specifically bound metal ions in a variety of nucleic acids of biological interest, in particular to understand the role of the metal-(poly)nucleotide interactio
In-depth synthetic, physicochemical and in vitro biological investigation of a new ternary V(IV) antioxidant material based on curcumin.
Curcumin is a natural product with a broad spectrum of beneficial properties relating to pharmaceutical applications, extending from traditional remedies to modern cosmetics. The biological activity of such pigments, however, is limited by their solubility and bioavailability, thereby necessitating new ways of achieving optimal tissue cellular response and efficacy as drugs. Metal ion complexation provides a significant route toward improvement of curcumin stability and biological activity, with vanadium being a representative such metal ion, amply encountered in biological systems and exhibiting exogenous bioactivity through potential pharmaceuticals. Driven by the need to optimally increase curcumin bioavailability and bioactivity through complexation, synthetic efforts were launched to seek out stable species, ultimately leading to the synthesis and isolation of a new ternary V(IV)-curcumin-(2,2’-bipyridine) complex. Physicochemical characterization (elemental analysis, FT-IR, Thermogravimetry (TGA), UV-Visible, NMR, ESI-MS, Fluorescence, X-rays) portrayed the solid-state and solution properties of the ternary complex. Pulsed-EPR spectroscopy, in frozen solutions, suggested the presence of two species, cis- and trans-conformers. Density Functional Theory (DFT) calculations revealed the salient features and energetics of the two conformers, thereby complementing EPR spectroscopy. The well-described profile of the vanadium species led to its in vitro biological investigation involving toxicity, cell metabolism inhibition in S. cerevisiae cultures, Reactive Oxygen Species (ROS)-suppressing capacity, lipid peroxidation, and plasmid DNA degradation. A multitude of bio-assays and methodologies, in comparison to free curcumin, showed that it exhibits its antioxidant potential in a concentration-dependent fashion, thereby formulating a bioreactivity profile supporting development of new efficient vanado-pharmaceuticals, targeting (extra)intra-cellular processes under (patho)physiological conditions
Quantum control of hybrid nuclear-electronic qubits
Pulsed magnetic resonance is a wide-reaching technology allowing the quantum
state of electronic and nuclear spins to be controlled on the timescale of
nanoseconds and microseconds respectively. The time required to flip either
dilute electronic or nuclear spins is orders of magnitude shorter than their
decoherence times, leading to several schemes for quantum information
processing with spin qubits. We investigate instead the novel regime where the
eigenstates approximate 50:50 superpositions of the electronic and nuclear spin
states forming "hybrid nuclear-electronic" qubits. Here we demonstrate quantum
control of these states for the first time, using bismuth-doped silicon, in
just 32 ns: this is orders of magnitude faster than previous experiments where
pure nuclear states were used. The coherence times of our states are five
orders of magnitude longer, reaching 4 ms, and are limited by the
naturally-occurring 29Si nuclear spin impurities. There is quantitative
agreement between our experiments and no-free-parameter analytical theory for
the resonance positions, as well as their relative intensities and relative
Rabi oscillation frequencies. In experiments where the slow manipulation of
some of the qubits is the rate limiting step, quantum computations would
benefit from faster operation in the hybrid regime.Comment: 20 pages, 8 figures, new data and simulation
Structure and spin density of ferric low-spin heme complexes determined with high-resolution ESEEM experiments at 35 GHz
ISSN:0949-8257ISSN:1432-132
Advanced Pulse EPR Methods for the Characterization of Metalloproteins
Electron Spin Echo Envelope Modulation (ESEEM) and pulse Electron Nuclear Double Resonance (ENDOR) experiments are considered to be two cornerstones of pulse EPR spectroscopy. These techniques are typically used to obtain the static spin Hamiltonian parameters of powders, frozen solutions, and single crystals. The development of new methods based on these two effects is mainly driven by the need for higher resolution, and therefore, a more accurate estimation of the magnetic parameters. In this chapter, we describe the inner workings of ESEEM and pulse ENDOR experiments as well as the latest developments aimed at resolution and sensitivity enhancement. The advantages and limitations of these techniques are demonstrated through examples found in the literature, with an emphasis on systems of biological relevance