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Intermolecular quantum coherence

Kaiyu Wang, Yuqing Huang, Pieter E S Smith, Zhiyong Zhang, Shuhui Cai, Zhong Chen
OBJECTIVE: A method is proposed to obtain high-resolution 2-D -resolved nuclear magnetic resonance (NMR) spectra in inhomogeneous magnetic fields. METHODS: The proposed experiment enables the acquisition of an entire 2-D spectrum in a single scan by utilizing intermolecular double-quantum coherences and the spatial encoding of NMR observables. RESULTS: Chemical shifts, coupling constants, and multiplet patterns are recovered even when field inhomogeneities are severe enough to completely obscure conventional NMR spectra...
February 2018: IEEE Transactions on Bio-medical Engineering
Jacob C Dean, Gregory D Scholes
The role of coherences, or coherently excited superposition states, in complex condensed-phase systems has been the topic of intense interest and debate for a number of years. In many cases, coherences have been utilized as spectators of ultrafast dynamics or for identifying couplings between electronic states. In rare cases, they have been found to drive excited state dynamics directly. Interestingly though, the utilization of coherences as a tool for high-detail vibronic spectroscopy has largely been overlooked until recently, despite their encoding of key information regarding molecular structure, electronically sensitive vibrational modes, and intermolecular interactions...
October 18, 2017: Accounts of Chemical Research
Kiyoshi Miyata, Yuki Kurashige, Kazuya Watanabe, Toshiki Sugimoto, Shota Takahashi, Shunsuke Tanaka, Jun Takeya, Takeshi Yanai, Yoshiyasu Matsumoto
Singlet fission, in which a singlet exciton is converted to two triplet excitons, is a process that could be beneficial in photovoltaic applications. A full understanding of the dynamics of singlet fission in molecular systems requires detailed knowledge of the relevant potential energy surfaces and their (conical) intersections. However, obtaining such information is a nontrivial task, particularly for molecular aggregates. Here we investigate singlet fission in rubrene crystals using transient absorption spectroscopy and state-of-the-art quantum chemical calculations...
October 2017: Nature Chemistry
Wooseok Heo, Nizam Uddin, Jae Woo Park, Young Min Rhee, Cheol Ho Choi, Taiha Joo
Detailed molecular dynamics simulations of an acid-base reaction have been the subject of extensive investigations. Here we report the excited state proton transfer dynamics of pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, HPTS) in acetate buffer by time-resolved fluorescence (TF) and quantum mechanical/effective fragment potential molecular dynamics (QM/EFP-MD) simulations. High time resolution in TF and TF spectra measurements allows the acquisition of accurate reaction kinetics. Upon the photoexcitation of HPTS, the proton (deuterium) is transferred coherently to acetate in 60 fs (80 fs) for a contact pair of HPTS (DPTS) and acetate by a hydrogen bond, which comprises approximately 28% of the population...
July 19, 2017: Physical Chemistry Chemical Physics: PCCP
Le Zhang, Andrew McCallister, Karl M Koshlap, Rosa Tamara Branca
PURPOSE: Because the resonance frequency of water-fat intermolecular zero-quantum coherences (iZQCs) reflects the water-fat frequency separation at the microscopic scale, these frequencies have been proposed and used as a mean to obtain more accurate temperature information. The purpose of this work was to investigate the dependence of the water-fat iZQC resonance frequency on sample microstructure and on the specific choice of the correlation distance. METHODS: The effect of water-fat susceptibility gradients on the water-methylene iZQC resonance frequency was first computed and then measured for different water-fat emulsions and for a mixture of porcine muscle and fat...
March 2018: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Hao Chen, Shuhui Cai, Zhong Chen
The spin-lattice relaxation time (T1) plays a crucial role in the study of spin dynamics, signal optimization and data quantification. However, the measurement of chemical shift-specific T1 constants is hampered by the magnetic field inhomogeneity due to poorly shimmed external magnetic fields or intrinsic magnetic susceptibility heterogeneity in samples. In this study, we present a new protocol to determine chemical shift-specific T1 constants in inhomogeneous fields. Based on intermolecular double-quantum coherences, the new method can resolve overlapped peaks in inhomogeneous fields...
May 24, 2017: Journal of Magnetic Resonance
Ioana Fugariu, Wolfgang Bermel, Daniel Lane, Ronald Soong, Andre J Simpson
Although current NMR techniques allow organisms to be studied in vivo, magnetic susceptibility distortions, which arise from inhomogeneous distributions of chemical moieties, prevent the acquisition of high-resolution NMR spectra. Intermolecular single quantum coherence (iSQC) is a technique that breaks the sample's spatial isotropy to form long range dipolar couplings, which can be exploited to extract chemical shift information free of perturbations. While this approach holds vast potential, present practical limitations include radiation damping, relaxation losses, and non-phase sensitive data...
May 22, 2017: Angewandte Chemie
Yang Zhang, Yang Luo, Yao Zhang, Yun-Jie Yu, Yan-Min Kuang, Li Zhang, Qiu-Shi Meng, Yi Luo, Jin-Long Yang, Zhen-Chao Dong, J G Hou
Many important energy-transfer and optical processes, in both biological and artificial systems, depend crucially on excitonic coupling that spans several chromophores. Such coupling can in principle be described in a straightforward manner by considering the coherent intermolecular dipole-dipole interactions involved. However, in practice, it is challenging to directly observe in real space the coherent dipole coupling and the related exciton delocalizations, owing to the diffraction limit in conventional optics...
March 31, 2016: Nature
Yuqing Huang, Yung-Ya Lin, Shuhui Cai, Yu Yang, Huijun Sun, Yanqin Lin, Zhong Chen
High spectral resolution in nuclear magnetic resonance (NMR) is a prerequisite for achieving accurate information relevant to molecular structures and composition assignments. The continuous development of superconducting magnets guarantees strong and homogeneous static magnetic fields for satisfactory spectral resolution. However, there exist circumstances, such as measurements on biological tissues and heterogeneous chemical samples, where the field homogeneity is degraded and spectral line broadening seems inevitable...
March 14, 2016: Journal of Chemical Physics
Alberto Ghirri, Alessandro Chiesa, Stefano Carretta, Filippo Troiani, Johan van Tol, Stephen Hill, Inigo Vitorica-Yrezabal, Grigore A Timco, Richard E P Winpenny, Marco Affronte
Controlling and understanding transitions between molecular spin states allows selection of the most suitable ones for qubit encoding. Here we present a detailed investigation of single crystals of a polynuclear Cr8Zn molecular wheel using 241 GHz electron paramagnetic resonance (EPR) spectroscopy in high magnetic field. Continuous wave spectra are well reproduced by spin Hamiltonian calculations, which evidence that transitions in correspondence to a well-defined anticrossing involve mixed states with different total spin...
December 17, 2015: Journal of Physical Chemistry Letters
Guoxing Lin
Inter-molecular multiple quantum coherence (iMQC) has important applications in NMR and MRI. However, the current theoretical methods still have some difficulties in analyzing the behavior of iMQC signal attenuation of pulsed field gradient diffusion experiments. In this paper, the iMQC diffusion experiments were analyzed by an effective phase shift diffusion equation (EPSDE) method, which is based on the idea that the accumulating phase shift (APS) can be viewed as the result of a diffusion process in virtual phase space (VPS) with effective diffusion coefficient K(2)(t) D (rad(2)/s) where K(t)=∫0 (t)γg(t')dt' is a wavenumber and D is the physical diffusion coefficient of the spin carrier in the real space...
October 28, 2015: Journal of Chemical Physics
Thomas Stangl, Philipp Wilhelm, Klaas Remmerssen, Sigurd Höger, Jan Vogelsang, John M Lupton
An appealing definition of the term "molecule" arises from consideration of the nature of fluorescence, with discrete molecular entities emitting a stream of single photons. We address the question of how large a molecular object may become by growing deterministic aggregates from single conjugated polymer chains. Even particles containing dozens of individual chains still behave as single quantum emitters due to efficient excitation energy transfer, whereas the brightness is raised due to the increased absorption cross-section of the suprastructure...
October 13, 2015: Proceedings of the National Academy of Sciences of the United States of America
Hiroyuki Tamura, Miquel Huix-Rotllant, Irene Burghardt, Yoann Olivier, David Beljonne
Singlet excitons in π-stacked molecular crystals can split into two triplet excitons in a process called singlet fission that opens a route to carrier multiplication in photovoltaics. To resolve controversies about the mechanism of singlet fission, we have developed a first principles nonadiabatic quantum dynamical model that reveals the critical role of molecular stacking symmetry and provides a unified picture of coherent versus thermally activated singlet fission mechanisms in different acenes. The slip-stacked equilibrium packing structure of pentacene derivatives is found to enhance ultrafast singlet fission mediated by a coherent superexchange mechanism via higher-lying charge transfer states...
September 4, 2015: Physical Review Letters
Jianfeng Bao, Xiaohong Cui, Yuqing Huang, Jianhui Zhong, Zhong Chen
High-resolution (1)H magnetic resonance spectroscopy (MRS) is generally inaccessible in red bone marrow (RBM) tissues using conventional MRS techniques. This is because signal from these tissues suffers from severe inhomogeneity in the main static B0 field originated from the intrinsic honeycomb structures in trabecular bone. One way to reduce effects of B0 field inhomogeneity is by using the intermolecular double quantum coherence (iDQC) technique, which has been shown in other systems to obtain signals insensitive to B0 field inhomogeneity...
August 21, 2015: Physics in Medicine and Biology
Chunhua Tan, Shuhui Cai, Yuqing Huang
BACKGROUND AND PURPOSE: Magnetic resonance spectroscopy (MRS) constitutes a mainstream technique for characterizing biological samples. Benefiting from the separation of chemical shifts and J couplings, spatially localized two-dimensional (2D) J-resolved spectroscopy (JPRESS) shows better identification of complex metabolite resonances than one-dimensional MRS does and facilitates the extraction of J coupling information. However, due to variations of macroscopic magnetic susceptibility in biological samples, conventional JPRESS spectra generally suffer from the influence of field inhomogeneity...
2015: PloS One
Ryan M Davis, Zijian Zhou, Hyunkoo Chung, Warren S Warren
PURPOSE: Intermolecular multiple quantum coherences (iMQCs) are a source of MR contrast with applications including temperature imaging, anisotropy mapping, and brown fat imaging. Because all applications are limited by signal-to-noise ratio (SNR), we developed a pulse sequence that detects intermolecular zero quantum coherences with improved SNR. METHODS: A previously developed pulse sequence that detects iMQCs, HOMOGENIZED with off resonance transfer (HOT), was modified with a multi-spin echo spatial encoding scheme (MSE-HOT)...
May 2016: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Geoffrey S Payne, Nandita M deSouza, Christina Messiou, Martin O Leach
Measurement of tissue lactate using (1) H MRS is often confounded by overlap with intense lipid signals at 1.3 ppm. Single-voxel localization using PRESS is also compromised by the large chemical shift displacement between voxels for the 4.1 ppm (-CH) resonance and the 1.3 ppm -CH3 resonance, leading to subvoxels with signals of opposite phase and hence partial signal cancellation. To reduce the chemical shift displacement to negligible proportions, a modified semi-LASER sequence was written ("FOCI-LASER", abbreviated as fLASER) using FOCI pulses to permit high RF bandwidth even with the limited RF amplitude characteristic of clinical MRI scanners...
April 2015: NMR in Biomedicine
Yusuke Morisawa, Manaka Yasunaga, Harumi Sato, Ryoichi Fukuda, Masahiro Ehara, Yukihiro Ozaki
Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 145-260 nm region were measured for surfaces (thickness 50-200 nm) of various kinds of nylons in cast films to explore their electronic transitions in the FUV region. ATR-FUV spectra show two major bands near 150 and 200 nm in the surface condensed phase of nylons. Transmittance (Tr) spectra were also observed in particular for the analysis of valence excitations. Time-dependent density functional theory (TD-DFT/CAM-B3LYP) calculations were carried out using the model systems to provide the definitive assignments of their absorption spectra and to elucidate their peak shifts in several nylons, in particular, focusing on their crystal alignment structures and intermolecular hydrogen bondings...
October 9, 2014: Journal of Physical Chemistry. B
Ryan M Davis, Warren S Warren
PURPOSE: Red bone marrow metastases are common in breast and prostate cancer patients, but those metastases are currently incurable. Recent developments show that hyperthermia could be a successful treatment for bone metastasis, but thermometry remains difficult or inaccurate in red marrow. METHOD: The technique evaluated in this study measures the evolution frequency of intermolecular zero quantum coherences (iZQCs) between fat and water. The iZQC evolution frequency was mapped linearly to temperature...
July 18, 2014: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Yuqing Huang, Shuhui Cai, Zhiyong Zhang, Zhong Chen
NMR spectroscopy is a principal tool in metabolomic studies and can, in theory, yield atom-level information critical for understanding biological systems. Nevertheless, NMR investigations on biological tissues generally have to contend with field inhomogeneities originating from variations in macroscopic magnetic susceptibility; these field inhomogeneities broaden spectral lines and thereby obscure metabolite signals. The congestion in one-dimensional NMR spectra of biological tissues often leads to ambiguities in metabolite identification and quantification...
May 6, 2014: Biophysical Journal
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