Publications by authors named "Dane McCamey"

16 Publications

  • Page 1 of 1

Phosphorylation of Troponin I finely controls the positioning of Troponin for the optimal regulation of cardiac muscle contraction.

J Mol Cell Cardiol 2021 01 18;150:44-53. Epub 2020 Oct 18.

Department of Molecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia. Electronic address:

Troponin is the Ca molecular switch that regulates striated muscle contraction. In the heart, troponin Ca sensitivity is also modulated by the PKA-dependent phosphorylation of a unique 31-residue N-terminal extension region of the Troponin I subunit (NH-TnI). However, the detailed mechanism for the propagation of the phosphorylation signal through Tn, which results in the enhancement of the myocardial relaxation rate, is difficult to examine within whole Tn. Several models exist for how phosphorylation modulates the troponin response in cardiac cells but these are mostly built from peptide-NMR studies and molecular dynamics simulations. Here we used a paramagnetic spin labeling approach to position and track the movement of the NH-TnI region within whole Tn. Through paramagnetic relaxation enhancement (PRE)-NMR experiments, we show that the NH-TnI region interacts with a broad surface area on the N-domain of the Troponin C subunit. This region includes the Ca regulatory Site II and the TnI switch-binding site. Phosphorylation of the NH-TnI both weakens and shifts this region to an adjacent site on TnC. Interspin EPR distances between NH-TnI and TnC further reveal a phosphorylation induced re-orientation of the TnC N-domain under saturating Ca conditions. We propose an allosteric model where phosphorylation triggered cooperative changes in both the interaction of the NH-TnI region with TnC, and the re-orientation of the TnC interdomain orientation, together promote the release of the TnI switch-peptide. Enhancement of the myocardial relaxation rate then occurs. Knowledge of this unique role of phosphorylation in whole Tn is important for understanding pathological processes affecting the heart.
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http://dx.doi.org/10.1016/j.yjmcc.2020.10.007DOI Listing
January 2021

Fluctuating exchange interactions enable quintet multiexciton formation in singlet fission.

J Chem Phys 2019 Oct;151(16):164104

School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia.

Several recent electron spin resonance studies have observed a quintet multiexciton state during the singlet fission process. Here, we provide a general theoretical explanation for the generation of this state by invoking a time-varying exchange coupling between pairs of triplet excitons and subsequently solving the relevant time-varying spin Hamiltonian for different rates at which the exchange coupling varies. We simulate experimental ESR spectra and draw qualitative conclusions about the adiabatic and diabatic transitions between triplet pair spin states.
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http://dx.doi.org/10.1063/1.5115816DOI Listing
October 2019

Ultra-fast intramolecular singlet fission to persistent multiexcitons by molecular design.

Nat Chem 2019 09 12;11(9):821-828. Epub 2019 Aug 12.

Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, MA, USA.

Singlet fission-that is, the generation of two triplets from a lone singlet state-has recently resurfaced as a promising process for the generation of multiexcitons in organic systems. Although advances in this area have led to the discovery of modular classes of chromophores, controlling the fate of the multiexciton states has been a major challenge; for example, promoting fast multiexciton generation while maintaining long triplet lifetimes. Unravelling the dynamical evolution of the spin- and energy conversion processes from the transition of singlet excitons to correlated triplet pairs and individual triplet excitons is necessary to design materials that are optimized for translational technologies. Here, we engineer molecules featuring a discrete energy gradient that promotes the migration of strongly coupled triplet pairs to a spatially separated, weakly coupled state that readily dissociates into free triplets. This 'energy cleft' concept allows us to combine the amplification and migration processes within a single molecule, with rapid dissociation of tightly bound triplet pairs into individual triplets that exhibit lifetimes of ~20 µs.
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http://dx.doi.org/10.1038/s41557-019-0297-7DOI Listing
September 2019

Phase-Encoded Hyperpolarized Nanodiamond for Magnetic Resonance Imaging.

Sci Rep 2019 04 11;9(1):5950. Epub 2019 Apr 11.

ARC Centre of Excellence for Engineered Quantum Systems, School of Physics, University of Sydney, Sydney, NSW, 2006, Australia.

Surface-functionalized nanomaterials are of interest as theranostic agents that detect disease and track biological processes using hyperpolarized magnetic resonance imaging (MRI). Candidate materials are sparse however, requiring spinful nuclei with long spin-lattice relaxation (T) and spin-dephasing times (T), together with a reservoir of electrons to impart hyperpolarization. Here, we demonstrate the versatility of the nanodiamond material system for hyperpolarized C MRI, making use of its intrinsic paramagnetic defect centers, hours-long nuclear T times, and T times suitable for spatially resolving millimeter-scale structures. Combining these properties, we enable a new imaging modality, unique to nanoparticles, that exploits the phase-contrast between spins encoded with a hyperpolarization that is aligned, or anti-aligned with the external magnetic field. The use of phase-encoded hyperpolarization allows nanodiamonds to be tagged and distinguished in an MRI based on their spin-orientation alone, and could permit the action of specific bio-functionalized complexes to be directly compared and imaged.
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http://dx.doi.org/10.1038/s41598-019-42373-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6459867PMC
April 2019

The concerted movement of the switch region of Troponin I in cardiac muscle thin filaments as tracked by conventional and pulsed (DEER) EPR.

J Struct Biol 2017 12 31;200(3):376-387. Epub 2017 Aug 31.

Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia. Electronic address:

The absence of a crystal structure of the calcium free state of the cardiac isoform of the troponin complex has hindered our understanding of how the simple binding of Ca triggers conformational changes in troponin which are then propagated to enable muscle contraction. Here we have used continuous wave (CW) and Double Electron-Electron Resonance (DEER) pulsed EPR spectroscopy to measure distances between TnI and TnC to track the movement of the functionally important regulatory 'switch' region of cardiac Tn. Spin labels were placed on the switch region of Troponin I and distances measured to Troponin C. Under conditions of high Ca, the interspin distances for one set (TnI151/TnC84) were 'short' (9-10Å) with narrow distance distribution widths (3-8Å) indicating the close interaction of the switch region with the N-lobe of TnC. Additional spin populations representative of longer interspin distances were detected by DEER. These longer distance populations, which were ∼16-19Å longer than the short distance populations, possessed notably broader distance distribution widths (14-29Å). Upon Ca removal, the interspin population shifted toward the longer distances, indicating the release of the switch region from TnC and an overall increase in disorder for this region. Together, our results suggest that under conditions of low Ca, the close proximity of the TnI switch region to TnC in the cardiac isoform is necessary for promoting the interaction between the regulatory switch helix with the N-lobe of cardiac Troponin C, which, unlike the skeletal isoform, is largely in a closed conformation.
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http://dx.doi.org/10.1016/j.jsb.2017.08.007DOI Listing
December 2017

Tuning Singlet Fission in π-Bridge-π Chromophores.

J Am Chem Soc 2017 09 1;139(36):12488-12494. Epub 2017 Sep 1.

Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States.

We have designed a series of pentacene dimers separated by homoconjugated or nonconjugated bridges that exhibit fast and efficient intramolecular singlet exciton fission (iSF). These materials are distinctive among reported iSF compounds because they exist in the unexplored regime of close spatial proximity but weak electronic coupling between the singlet exciton and triplet pair states. Using transient absorption spectroscopy to investigate photophysics in these molecules, we find that homoconjugated dimers display desirable excited-state dynamics, with significantly reduced recombination rates as compared to conjugated dimers with similar singlet fission rates. In addition, unlike conjugated dimers, the time constants for singlet fission are relatively insensitive to the interplanar angle between chromophores, since rotation about σ bonds negligibly affects the orbital overlap within the π-bonding network. In the nonconjugated dimer, where the iSF occurs with a time constant >10 ns, comparable to the fluorescence lifetime, we used electron spin resonance spectroscopy to unequivocally establish the formation of triplet-triplet multiexcitons and uncoupled triplet excitons through singlet fission. Together, these studies enable us to articulate the role of the conjugation motif in iSF.
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http://dx.doi.org/10.1021/jacs.7b05204DOI Listing
September 2017

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity.

J Vis Exp 2017 03 6(121). Epub 2017 Mar 6.

ARC Centre of Excellence in Exciton Science; School of Physics, University of New South Wales;

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.
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http://dx.doi.org/10.3791/55232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5408890PMC
March 2017

Spectral dependence of direct and trap-mediated recombination processes in lead halide perovskites using time resolved microwave conductivity.

Phys Chem Chem Phys 2016 04;18(17):12043-9

School of Physics, UNSW, Sydney, NSW 2052, Australia.

Elucidating the decay mechanisms of photoexcited charge carriers is key to improving the efficiency of solar cells based on organo-lead halide perovskites. Here we investigate the spectral dependence (via above-, inter- and sub-bandgap optical excitations) of direct and trap-mediated decay processes in CH3NH3PbI3 using time resolved microwave conductivity (TRMC). We find that the total end-of-pulse mobility is excitation wavelength dependent - the mobility is maximized (172 cm(2) V(-1) s(-1)) when charge carriers are excited by near bandgap light (780 nm) in the low charge carrier density regime (10(9) photons per cm(2)), and is lower for above- and sub-bandgap excitations. Direct recombination is found to occur on the 100-400 ns timescale across excitation wavelengths near and above the bandgap, whereas indirect recombination processes displayed distinct behaviour following above- and sub-bandgap excitations, suggesting the influence of different trap distributions on recombination dynamics.
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http://dx.doi.org/10.1039/c5cp07360jDOI Listing
April 2016

Deuteration of Perylene Enhances Photochemical Upconversion Efficiency.

J Phys Chem Lett 2015 Aug 22;6(15):3061-6. Epub 2015 Jul 22.

†School of Chemistry, The University of New South Wales, Sydney, New South Wales 2052, Australia.

Photochemical upconversion via triplet-triplet annihilation is a promising technology for improving the efficiency of photovoltaic devices. Previous studies have shown that the efficiency of upconversion depends largely on two rate constants intrinsic to the emitting species. Here, we report that one of these rate constants can be altered by deuteration, leading to enhanced upconversion efficiency. For perylene, deuteration decreases the first order decay rate constant by 16 ± 9% at 298 K, which increases the linear upconversion response by 45 ± 21% in the low excitation regime.
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http://dx.doi.org/10.1021/acs.jpclett.5b01271DOI Listing
August 2015

Beyond Shockley-Queisser: Molecular Approaches to High-Efficiency Photovoltaics.

J Phys Chem Lett 2015 Jun 9;6(12):2367-78. Epub 2015 Jun 9.

†School of Photovoltaic and Renewable Energy Engineering, ‡School of Physics, and ¶School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia.

Molecular materials afford abundant flexibility in the tunability of physical and electronic properties. As such, they are ideally suited to engineering low-cost, flexible, light-harvesting materials that break away from the single-threshold paradigm. Single-threshold solar cells are capable of harvesting a maximum of 33.7% of incident sunlight, whereas two-threshold cells are capable of energy harvesting efficiencies exceeding 45%. In this Perspective, we provide the theoretical background with which upper efficiency limits for various multiple-threshold solar cell architectures may be calculated and review and discuss various reports that employ processes such as triplet-triplet annihilation and singlet fission in multiple-threshold devices comprised of molecular materials.
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http://dx.doi.org/10.1021/acs.jpclett.5b00716DOI Listing
June 2015

An agnostic approach.

Nat Nanotechnol 2013 Dec;8(12):886-7

School of Physics, The University of New South Wales, Sydney, New South Wales 2052, Australia.

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http://dx.doi.org/10.1038/nnano.2013.261DOI Listing
December 2013

Physics. Nuclear-spin quantum memory poised to take the lead.

Science 2012 Jun;336(6086):1239-40

Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA.

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http://dx.doi.org/10.1126/science.1223439DOI Listing
June 2012

Ceramide mediates vascular dysfunction in diet-induced obesity by PP2A-mediated dephosphorylation of the eNOS-Akt complex.

Diabetes 2012 Jul 14;61(7):1848-59. Epub 2012 May 14.

College of Health, University of Utah, Salt Lake City, Utah, USA.

Vascular dysfunction that accompanies obesity and insulin resistance may be mediated by lipid metabolites. We sought to determine if vascular ceramide leads to arterial dysfunction and to elucidate the underlying mechanisms. Pharmacological inhibition of de novo ceramide synthesis, using the Ser palmitoyl transferase inhibitor myriocin, and heterozygous deletion of dihydroceramide desaturase prevented vascular dysfunction and hypertension in mice after high-fat feeding. These findings were recapitulated in isolated arteries in vitro, confirming that ceramide impairs endothelium-dependent vasorelaxation in a tissue-autonomous manner. Studies in endothelial cells reveal that de novo ceramide biosynthesis induced protein phosphatase 2A (PP2A) association directly with the endothelial nitric oxide synthase (eNOS)/Akt/Hsp90 complex that was concurrent with decreased basal and agonist-stimulated eNOS phosphorylation. PP2A attenuates eNOS phosphorylation by preventing phosphorylation of the pool of Akt that colocalizes with eNOS and by dephosphorylating eNOS. Ceramide decreased the association between PP2A and the predominantly cytosolic inhibitor 2 of PP2A. We conclude that ceramide mediates obesity-related vascular dysfunction by a mechanism that involves PP2A-mediated disruption of the eNOS/Akt/Hsp90 signaling complex. These results provide important insight into a pathway that represents a novel target for reversing obesity-related vascular dysfunction.
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http://dx.doi.org/10.2337/db11-1399DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3379648PMC
July 2012

Embracing the quantum limit in silicon computing.

Nature 2011 Nov 16;479(7373):345-53. Epub 2011 Nov 16.

Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.

Quantum computers hold the promise of massive performance enhancements across a range of applications, from cryptography and databases to revolutionary scientific simulation tools. Such computers would make use of the same quantum mechanical phenomena that pose limitations on the continued shrinking of conventional information processing devices. Many of the key requirements for quantum computing differ markedly from those of conventional computers. However, silicon, which plays a central part in conventional information processing, has many properties that make it a superb platform around which to build a quantum computer.
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http://dx.doi.org/10.1038/nature10681DOI Listing
November 2011

Tuning hyperfine fields in conjugated polymers for coherent organic spintronics.

J Am Chem Soc 2011 Feb 28;133(7):2019-21. Epub 2011 Jan 28.

Department of Physics, University of Utah, Salt Lake City, Utah 84112, United States.

An appealing avenue for organic spintronics lies in direct coherent control of the spin population by means of pulsed electron spin resonance techniques. Whereas previous work has focused on the electrical detection of coherent spin dynamics, we demonstrate here the equivalence of an all-optical approach, allowing us to explore the influence of materials chemistry on the spin dynamics. We show that deuteration of the conjugated polymer side groups weakens the local hyperfine fields experienced by electron-hole pairs, thereby lowering the threshold for the resonant radiation intensity at which coherent coupling and spin beating occur. The technique is exquisitively sensitive to previously obscured material properties and offers a route to quantifying and tuning hyperfine fields in organic semiconductors.
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http://dx.doi.org/10.1021/ja108352dDOI Listing
February 2011

Coherent spin manipulation in molecular semiconductors: getting a handle on organic spintronics.

Chemphyschem 2010 Oct;11(14):3040-58

Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, UT 84112-0830, USA.

Organic semiconductors offer expansive grounds to explore fundamental questions of spin physics in condensed matter systems. With the emergence of organic spintronics and renewed interest in magnetoresistive effects, which exploit the electron spin degree of freedom to encode and transmit information, there is much need to illuminate the underlying properties of spins in molecular electronic materials. For example, one may wish to identify over what length of time a spin maintains its orientation with respect to an external reference field. In addition, it is crucial to understand how adjacent spins arising, for example, in electrostatically coupled charge-carrier pairs, interact with each other. A periodic perturbation of the field may cause the spins to precess or oscillate, akin to a spinning top experiencing a torque. The quantum mechanical characteristic of the spin is then defined as the coherence time, the time over which an oscillating spin, or spin pair, maintains a fixed phase with respect to the driving field. Electron spins in organic semiconductors provide a remarkable route to performing "hands-on" quantum mechanics since permutation symmetries are controlled directly. Herein, we review some of the recent advances in organic spintronics and organic magnetoresistance, and offer an introductory description of the concept of pulsed, electrically detected magnetic resonance as a technique to manipulate and thus characterize the fundamental properties of electron spins. Spin-dependent dissociation and recombination allow the observation of coherent spin motion in a working device, such as an organic light-emitting diode. Remarkably, it is possible to distinguish between electron and hole spin resonances. The ubiquitous presence of hydrogen nuclei gives rise to strong hyperfine interactions, which appear to provide the basis for many of the magnetoresistive effects observed in these materials. Since hyperfine coupling causes quantum spin beating in electron-hole pairs, an extraordinarily sensitive probe for hyperfine fields in such pairs is given.
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http://dx.doi.org/10.1002/cphc.201000186DOI Listing
October 2010
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