Hyperpolarized Multi-Metal 13C-Sensors for Magnetic Resonance

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Letter 13

Hyperpolarized Multi-metal C-Sensors for MRI Anurag Mishra, Giorgio Pariani, Thomas Oerther, Markus Schwaiger, and Gil Gregor Westmeyer Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b03546 • Publication Date (Web): 21 Oct 2016 Downloaded from http://pubs.acs.org on October 27, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Analytical Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

Hyperpolarized Multi-metal 13C-Sensors for MRI Anurag Mishra*,‡, Giorgio Pariani*,‡, Thomas Oerther ξ, Markus Schwaiger †, Gil G. Westmeyer†,‡ †

Department of Nuclear Medicine, Technical University of Munich (TUM), Ismaninger Str. 22, 81675 Munich, Germany. Institute for Biological and Medical Imaging & Institute of Developmental Genetics, Helmholtz Zentrum München, Germany. ξ Microimaging Applications, Bruker, Rheinstetten, Germany *Authors contributed equally. Author names are listed in alphabetical order. ‡

ABSTRACT: We introduce hyperpolarizable 13C-labelled probes that identify multiple biologically important divalent metals via metal-specific chemical shifts. These features enable NMR measurements of calcium concentrations in human serum in the presence of magnesium. In addition, signal enhancement through Dynamic Nuclear Polarization (DNP) increases the sensitivity of metal detection to afford measuring micromolar concentrations of calcium as well as simultaneous multi-metal detection by chemical shift imaging. The hyperpolarizable 13C-MRI sensors presented here enable sensitive NMR measurements and MR imaging of multiple divalent metals in opaque biological samples. Divalent metal ions are of fundamental importance for biological processes as they are essential elements of proteins and biominerals and function as key signalling molecules. A prominent example of the latter category is calcium (Ca2+), essential for many signal-transduction cascades in e.g. neurons, immune and muscle cells 1. The spatiotemporal distribution of divalent metals in organ(ism)s is tightly controlled and deviations from the physiological concentration ranges in e.g. blood samples can indicate metabolic or endocrine dysregulations 2. Some divalent metals such as cadmium (Cd2+), lead (Pb2+), or arsenic (As2+) can appear as toxic contaminants in air, food, soils, or ground water 3,4. To enable NMR-based detection of divalent metals, relaxation agents were developed that respond with a change of either their longitudinal (r1) and/or transverse (r2) relaxivity have been synthesized based on macrocyclic lanthanide complexes 5-10 or constructed from functionalized superparamagnetic iron-oxide nanoparticles (SPIOs) undergoing a Ca2+-dependent change in their agglomeration state 11. Sensors that exhibit a chemical shift in response to metals rather than a relaxivity change have also been generated based on 19F-labelled variants of the chelators BAPTA and Quin 2 12,13. 19F-BAPTA derivatives have also been used to detect Ca2+, zinc (Zn2+) and iron (Fe2+) with signal amplification via the chemical exchange saturation transfer (CEST) mechanism 14,15. Furthermore, a Ca2+-responsive paramagnetic 19Fchemical shift agent 16 as well as a PARACEST agent have been developed 17. The sensitivity of NMR-based sensing can be further improved by dissolution Dynamic Nuclear Polarization (DNP), a technique that increases the polarization of nuclear spins via transferring spin polarization from electrons to nuclei by microwave irradiation of the compound

together with a radical at low temperatures 18. Hyperpolarized 13C-enriched analogues of endogenous substrates were successfully used to determine the in vivo distribution of enzymatic activity via detecting their enzymatic conversion by chemical shift imaging 19. Besides mapping enzyme activities, only few 13C-labelled molecules have been designed to function as sensing moieties 20 for e.g. pH 21, redox status 22,23, or molecular interaction 24. Here, we introduce a new class of hyperpolarizable reversible 13C-sensors for imaging of multiple metal ions via DNP-MRI. By positioning the 13C-label directly at the metal coordination site of the probes, well separated chemical shifts were obtained that specifically identify the bound divalent metal. We tested a short list of molecules from which we selected EDTA and EGTA because of their sufficiently long relaxation times (up to 15 s) and large chemical shifts (up to 10 ppm) of their carboxyl resonances in response to coordination of Ca2+ (Tables S1, S2 and Fig. S1 in the Supplementary Information) 25,26. 13C-EDTA and 13CEGTA were synthesized in two steps by stepwise alkylation of 1,8-Diamino-3,6-dioxaoctane/1-2-diaminoethane with 113C-ethyl bromoacetate in acetonitrile, which afforded tetra-esters of 1/3 respectively in good yield. The 13 C-tetra acids (13C-EGTA (1)/ 13C-EDTA (3)) were obtained by base hydrolysis of 1/3 at room temperature (Scheme S1 in the Supplementary Information). As can be seen in Figure 1, a distinct pattern of chemical shifts was obtained from the two sensors 13C-EDTA and 13C-EGTA in response to a range of divalent cations with important biological functions in cell signalling (Ca2+, Mg2+, Zn2+) or known for their toxic effects (Cd2+, As2+, Pb2+). The narrow bandwidth of the NMR signals measured for most tested metals indicates slow exchange on the NMR time scale at the field strengths used

ACS Paragon Plus Environment

Analytical Chemistry 27,28,29,30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

. In the case of 13C-EGTA however, complete or strong line broadening was observed for coordination of Mg2+, Zn2+, and Cd2+ respectively. The Ca2+-dependent chemical shifts of ~10 ppm for 13C-EGTA (stability constants at pH 7.4: log kCa = 7.18; kCa/kMg = 72,202 31) and

Figure 1. Identification of divalent metals by metal-specific chemical shifts of 13C-EDTA and 13C-EGTA. (a,b) The structural sketches illustrate the coordination of divalent metals to the two 13C-sensors. Atoms marked in orange indicate the positions at which 13C was incorporated. NMR spectra obtained from both sensors (2 mM in 0.3 M MOPS/D2O 1:1 at pH 7.4) show metal-specific chemical shifts in response to divalent metals (2.2 mM of Ca2+, Mg2+, Zn2+, Cd2+, As2+, or Pb2+). (c) To obtain binding curves for different metals, the Area under the curve (AUC, normalized to the sum of all AUCs) was computed for the chemical shift peak originating from metal-bound or unbound 13C-EDTA.

Page 2 of 6

~5 ppm for 13C-EDTA (log kCa = 10.61; log kMg = 8.83 32) were robust against changes in pH, whereas the unbound carboxyl groups of 13C-EDTA exhibited a pH-dependent chemical shift (~4 ppm from pH 5 to 8, Fig. S2). We also measured a linear relationship between concentration of Ca2+, Mg2+, and Zn2+ and the Area under the curve (AUC) of the NMR peaks corresponding to metal-bound and unbound 13C-EDTA (Fig. 1c). We consequently assessed whether the metal-specific chemical shifts would allow us to determine the concentration of Ca2+ in the presence of Mg2+ in human serum. These two cations exert distinct biological functions but are usually difficult to differentiate by molecular sensors because they possess similar physicochemical properties and are present in comparable intra- and extracellular concentrations. To obtain a reference titration curve for Ca2+ (0-6 mM) in the presence of Mg2+ (0.45 mM) and protein (4 g/dL Bovine Serum Albumin(BSA)), we plotted the AUC for the NMR peaks corresponding to Ca2+-bound or unbound 13C-EGTA. We then determined the AUC obtained from 13C-EGTA in human serum (50% v/v) and measured 1.2 mM for the Ca2+ concentration via the fitted reference curve (Fig. 2a). The concentration of total Ca2+ we obtained was confirmed by a standard colorimetric clinical chemistry assay conducted at the university hospital as part of the routine diagnostic pipeline (the concentration of Mg2+ in the sample was 0.4 mM). In analogy to the routine colorimetric titration method, we also performed a titration of 13CEGTA into the same serum sample to determine at which point the concentration of the chelator exceeds the concentration of Ca2+ as indicated by the appearance of an NMR peak corresponding to the unbound chelator. This titration confirmed that the total concentration of Ca2+ in the sample was 1.2 mM (X-intercept of the fitted curve). Although 13C-EGTA was chosen over 13C-EDTA for these experiments with human serum because of its higher selectivity for Ca2+ over Mg2+, we found that also for 13C-EDTA linear titration curves were obtained for Ca2+ that were only marginally altered by competitive binding of Mg2+ at 1.4 mM (Fig. S3 in the Supplementary Information). To increase the sensitivity of our NMR-based metal detection, we next subjected both 13C-EDTA and 13CEGTA (0.5 M with 15 mM OX063 radical in D2O:DMSO (8:2) mixture) to DNP using a HyperSense machine (Oxford Instruments). The resulting signal enhancement as well as the large chemical shifts of both sensors allowed us to clearly differentiate the unbound sensors from the Ca2+-bound species at half-saturating and saturating concentrations of Ca2+ on a benchtop 1T spectrometer (Fig. 3 a,b). To increase the spin-lattice relaxation time (T1) and thus reduce the signal loss in the time interval between the dissolution and NMR/MRI readout, we also synthesized the deuterated (d = 2H) variant 13C-EGTA-d8. We exchanged the 1H of neighbouring methylene of carboxylate with 2H and obtained an about two-fold longer T1 of 25.0 ± 0.5 seconds (1 T, 298K, pH 7.4 in MOPS buffer) as


Page 3 of 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


compared to the non-deuterated molecule (Fig. 3c, Relaxation rates for each peak are given in Table S2.) Importantly, hyperpolarization of 13C-EGTA increases the sensitivity of Ca2+-detection to the micromolar concentration range with a linear response to as low as 40 µM of Ca2+ (inset in Fig. 3d). Furthermore, hyperpolarized 13 C-EGTA also detected Ca2+ in human serum without any substantial decrease in the relaxation times compared to those measured in MOPS buffer (Fig. S4 in the Supplementary Information). In a final step, we sought to test how the two hyperpolarized sensors spatially resolve metal distributions via DNP-MRI. We thus hyperpolarized the 13 C-sensors and transferred the dissolution into a phantom consisting of tubes prefilled with saturating concentrations of Ca2+, Zn2+, Mg2+, or just MOPS buffer as control. We then moved the samples into the bore of a 7T small animal scanner (GE/Agilent MRI 901 7T) and ran a fast spiral sequence with spectral-spatial encoding 25,26 . As can be seen in Figure 4, the tubes containing Ca2+ were clearly differentiated based on the spectral information from the samples containing no metal. In the case of 13C-EDTA, the specific chemical shifts for Mg2+ and Zn2+ enabled also differentiation of these metals (Fig. 4b). Whereas with DNP-MRI, metal detection was achieved within 5 seconds, the same information took ~10 hours to extract from chemical shift imaging (CSI) of the non-hyperpolarized probes used at 20 times higher concentrations (Fig. S5 in the Supplementary Information) illustrating the substantial gains in sensitivity achieved by DNP-MRI. The hyperpolarizable multi-metal sensors we introduce here identify divalent metal ions via metal-specific chemical shifts of the 13C-labels positioned directly at the

metal-coordinating carboxyl groups. This is in distinction to work with 15N-labelled APTRA in which metal identification is solely dependent on the selectivity of the chelator 33,34. Similar to the ion CEST method based on 19 F-BAPTA derivatives 14,15, the 13C-MRI sensors thus allow for simultaneous metal detection via chemical shift imaging. Analogously, it would be possible to enhance the signal of metal-specific 13C-sensors by CEST when used as non-hyperpolarized probes (as in Figures 1 and 2), i.e. when there are no time constraints due to polarization decay. This detection mode would also be applicable to detection of the bioavailable fraction of toxic metals present as contaminations in opaque soils. For fast detection with increased sensitivity after hyperpolarization, extracellular metal ions are a preferred target, e.g. Zn2+ for which both cell-impermeable 13 C-sensors show selectivity over Ca2+ and Mg2+ such that it could be detected when e.g. co-released with insulin from cultured pancreatic or stem-cell derived beta-cells for functional assessment 35,36. This mode of operation would be similar to the therapeutic use of CaNa2EDTA in

Figure. 2. Measuring Ca2+ concentration in human serum. (a) A reference titration curve for Ca2+ was obtained from 13 C-EGTA in the presence of 0.45 mM Mg2+ in 0.1 M MOPS (50% D2O) buffer also containing 4 g/dL Bovine Serum Albumin (BSA) by plotting the AUC of the NMR peak at the chemical shift specific for the calcium-bound or unbound 13CEGTA (normalized to the total AUC). The AUC of the Ca2+-bound peak was then measured from the same concentration of 13C-EGTA in human serum (50% v/v) and yielded a Ca2+-concentration of 1.2 mM (dashed lines) (b) Determination of the Ca2+ concentration was also performed via titration of 13C-EGTA into the same human serum sample. The normalized AUC was plotted for NMR peaks corresponding to the Ca2+-bound or unbound chelator. The Ca2+ concentration is determined by observing the appearance of the chemical shift corresponding to the unbound chelator (X-intercept of the fitted titration curve at 1.2 mM, dashed line.)

Figure. 3. Calcium detection by hyperpolarized 13C-EDTA and 13 C-EGTA. The 13C sensors (~13 mM) were hyperpolarized by DNP and analyzed by NMR (1T and 298 K) in the absence (top panel in a and b), and presence of half-saturating (middle panel) or saturating concentrations of Ca2+ (bottom panel). NMR spectra were obtained every 5 seconds (FA = 10 and TR = 3 s) and are plotted with an offset for better visibility. Panel (c) shows the spectra of the deuterated variant 13C-EGTA-d8 with halfsaturating concentrations of Ca2+; the inset illustrates the increased T1 time of 13C-EGTA-d8 (25 s) compared with 13 C-EGTA (15 s). (d) Detection of micromolar concentrations of Ca2+ via hyperpolarized 13C-EGTA in 0.1 M MOPS buffer (50% D2O). The inset is a plot of the area under the curve (AUC) of the chemical shift peaks (ratio bound/unbound) as a function of Ca2+ concentration.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 6

* Email: [email protected] (GGW) Notes: The authors declare no competing financial interest.

Figure. 4. Simultaneous detection of divalent metals via DNP-MRI. (a) 13C-EGTA (10 mM) was hyperpolarized, dissolved and filled into NMR tubes containing buffers without and with Ca2+ (15 mM) prior to chemical shift imaging at 7T using a spiral sequence with spectral-spatial encoding. MR images reconstructed for the chemical shifts (referenced against 13C-Urea) of the Ca2+-bound (180 ppm) or free chelator (170 ppm) are overlaid as thresholded color images on the corresponding Fast Spin Echo (FSE) images shown on grayscale. (b) Analogous experiments with 13C-EDTA (10 mM) which differentiate Ca2+ (180 ppm) from the unbound chelator (175 ppm) as well as (c) Zn2+ (176.5 ppm) from Mg2+ (178 ppm). 2+

ACKNOWLEDGMENT

We thank Prof. Eisenreich for assistance with NMR measurements, Dr. Geoff Topping, Stephan Düwel, Eugen Kubala, and Christian Hundshammer for help with DNP, as well as Dr. Alan Jasanoff, Dr. Franz Schilling, Dr. Leif Schröder, Dr. Norbert Hertkorn and Dr. Gerd Gemmecker for helpful comments on the manuscript. Dr. Barth van Rossum created the graphical abstract. We are thankful for generous support by the Helmholtz Alliance ICEMED (GGW, AM, GP), the Technical University of Munich and the European Research Council under grant agreements ERC2012-StG-311552 (GGW) and ERC-2011-ADG-294582 (MS).

lead poisoning in which lead displaces Ca from the chelator 37,38. This intervention could thus potentially be monitored with 13C-EDTA, as could EDTA chelation therapy for atherosclerotic coronary disease 39,40. The set of metal-specific chemical shift sensors we presented here can also be expanded by probes with lower affinities (e.g. amide derivatives) and supplemented with NMR-silent metal-specific chelators to modify the selectivity of metal detection. More generally, 13C-labelled designer probes that reversibly sense binding of (multiple) ligands are an interesting class of sensors to complement the successful work on in vivo mapping of enzyme activities via hyperpolarized 13C-labelled substrates. In summary, we demonstrated the use of 13C-EDTA and 13C-EGTA as hyperpolarizable multi-metal sensors for detection and imaging of biologically important metals via NMR and MRI spectroscopy in opaque biological samples. To achieve metal-specific MRI with high sensitivity, we positioned 13C-labels directly at the metalcoordination site of selected chelators to enhance their NMR signal by Dynamic Nuclear Polarization (DNP) and receive distinct carboxyl resonances upon metal coordination. We demonstrated that the metal-specific chemical shifts of 13C-EDTA and 13C-EGTA can be used to differentiate between biologically essential and toxic divalent metals and determine the calcium concentration in human serum. NMR signal increase after Dynamic Nuclear Polarization (DNP) afforded metal detection at micromolar concentrations and enabled simultaneous detection of multiple metals via DNP-MRI.

ASSOCIATED CONTENT

Supporting Information The Supporting Information is available free of charge on the ACS Publications website. General and synthetic description of compounds, Supplementary Tables, Figures, and Experimental Methods

AUTHOR INFORMATION

Corresponding Authors


Page 5 of 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40)


REFERENCES Plattner, H.; Verkhratsky, A. Cell Calcium 2015, 57 (3), 121–122. Nordenström, E.; Katzman, P.; Bergenfelz, A. Clin. Biochem. 2011, 44 (10-11), 849–852. Zang, Y.; Bolger, P. M. In Encyclopedia of Food Safety; Elsevier, 2014; pp 346–348. Bosch, A. C.; O'Neill, B.; Sigge, G. O.; Kerwath, S. E.; Hoffman, L. C. J. Sci. Food Agric. 2015, 96 (1), 32–48. MacRenaris, K. W.; Ma, Z.; Krueger, R. L.; Carney, C. E.; Meade, T. J. Bioconjugate Chem. 2015, acs.bioconjchem.5b00561. Li, W.; Fraser, S. E.; Meade, T. J. J Am Chem Soc 1999, 121 (6), 1413–1414. Li, W.-H.; Parigi, G.; Fragai, M.; Luchinat, C.; Meade, T. J. Inorg Chem 2002, 41 (15), 4018–4024. Que, E. L.; Chang, C. J. Chem Soc Rev 2010, 39 (1), 51–60. Kadjane, P.; Platas-Iglesias, C.; Boehm-Sturm, P.; Truffault, V.; Hagberg, G. E.; Hoehn, M.; Logothetis, N. K.; Angelovski, G. Chem. Eur. J. 2014, 20 (24), 7351–7362. Mishra, A.; Logothetis, N. K.; Parker, D. Chem. Eur. J. 2011, 17 (5), 1529–1537. Atanasijevic, T.; Shusteff, M.; Fam, P.; Jasanoff, A. Proc. Natl. Acad. Sci. U.S.A. 2006, 103 (40), 14707–14712. Smith, G. A.; Hesketh, R. T.; Metcalfe, J. C.; Feeney, J.; Morris, P. G. Proc. Natl. Acad. Sci. U.S.A. 1983, 80 (23), 7178–7182. Steenbergen, C.; Murphy, E.; Levy, L.; London, R. E. Circulation Research 1987, 60 (5), 700–707. Bar-Shir, A.; Gilad, A. A.; Chan, K. W. Y.; Liu, G.; van Zijl, P. C. M.; Bulte, J. W. M.; McMahon, M. T. J Am Chem Soc 2013, 135 (33), 12164–12167. Bar-Shir, A.; Yadav, N. N.; Gilad, A. A.; van Zijl, P. C. M.; McMahon, M. T.; Bulte, J. W. M. J Am Chem Soc 2015, 137 (1), 78–81. Harvey, P.; Chalmers, K. H.; De Luca, E.; Mishra, A.; Parker, D. Chemistry 2012, 18 (28), 8748–8757. Angelovski, G.; Chauvin, T.; Pohmann, R.; Logothetis, N. K.; Tóth, É. Bioorganic & Medicinal Chemistry 2011, 19 (3), 1097–1105. Ardenkjaer-Larsen, J. H.; Fridlund, B.; Gram, A.; Hansson, G.; Hansson, L.; Lerche, M. H.; Servin, R.; Thaning, M.; Golman, K. Proc. Natl. Acad. Sci. U.S.A. 2003, 100 (18), 10158–10163. Brindle, K. M. J Am Chem Soc 2015, 137 (20), 6418–6427. Keshari, K. R.; Wilson, D. M. Chem Soc Rev 2014, 43 (5), 1627. Gallagher, F. A.; Kettunen, M. I.; Brindle, K. M. NMR Biomed. 2011, 24 (8), 1006–1015. Lippert, A. R.; Keshari, K. R.; Kurhanewicz, J.; Chang, C. J. J Am Chem Soc 2011, 133 (11), 3776–3779. Bohndiek, S. E.; Kettunen, M. I.; Hu, D.-E.; Kennedy, B. W. C.; Boren, J.; Gallagher, F. A.; Brindle, K. M. J Am Chem Soc 2011, 133 (30), 11795–11801. Keshari, K. R.; Kurhanewicz, J.; Macdonald, J. M.; Wilson, D. M. Analyst 2012, 137 (15), 3427–3429. Wiesinger, F.; Weidl, E.; Menzel, M. I.; Janich, M. A.; Khegai, O.; Glaser, S. J.; Haase, A.; Schwaiger, M.; Schulte, R. F. Magnetic Resonance Medicine 2012, 68 (1), 8–16. Durst, M.; Koellisch, U.; Frank, A.; Rancan, G.; Gringeri, C. V.; Karas, V.; Wiesinger, F.; Menzel, M. I.; Schwaiger, M.; Haase, A.; Schulte, R. F. NMR Biomed. 2015, 28 (6), 715–725. Bryson, A.; Fletcher, I. S. Aust. J. Chem. 1970, 23 (6), 1095–1110. Kula, R. J.; Reed, G. H. Anal. Chem. 1966. Hagen, R.; Warren, J. P.; Hunter, D. H.; Roberts, J. D. J Am Chem Soc 1973, 95 (17), 5712–5716. Alam, T. M.; Assink, R. A. Magnetic resonance in chemistry 1997, 35.7, 427–431. Bers, D. M.; Patton, C. W.; Nuccitelli, R. In Calcium in Living Cells; Methods in Cell Biology; Elsevier, 2010; Vol. 99, pp 1–26. Martell, A. E.; Smith, R. M. Critical Stability Constants; Springer Science & Business Media: Boston, MA, 2013. Nonaka, H.; Hata, R.; Doura, T.; Nishihara, T.; Kumagai, K.; Akakabe, M.; Tsuda, M.; Ichikawa, K.; Sando, S. Nat Commun 2013, 4, 2411. Hata, R.; Nonaka, H.; Takakusagi, Y.; Ichikawa, K.; Sando, S. Chem. Commun. 2015, 51 (61), 12290–12292. Pagliuca, F. W.; Millman, J. R.; Gürtler, M.; Segel, M.; Van Dervort, A.; Ryu, J. H.; Peterson, Q. P.; Greiner, D.; Melton, D. A. Cell 2014, 159 (2), 428–439. Yu, J.; Martins, A. F.; Preihs, C.; Clavijo Jordan, V.; Chirayil, S.; Zhao, P.; Wu, Y.; Nasr, K.; Kiefer, G. E.; Sherry, A. D. J Am Chem Soc 2015, 137 (44), 14173–14179. Aaseth, J.; Crisponi, G.; Anderson, O. Chelation Therapy in the Treatment of Metal Intoxication; Academic Press, 2016. Nordberg, G. F.; Fowler, B. A.; Nordberg, M. Handbook on the Toxicology of Metals; Academic Press, 2014. Lamas, G. A.; Goertz, C.; Boineau, R.; Mark, D. B.; Rozema, T.; Nahin, R. L.; Lindblad, L.; Lewis, E. F.; Drisko, J.; Lee, K. L.; TACT Investigators. JAMA 2013, 309 (12), 1241–1250. Avila, M. D.; Escolar, E.; Lamas, G. A. Curr. Opin. Cardiol. 2014, 29 (5), 481–488.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 6

TOC

“The loud sound of metal”: Hyperpolarized 13C-MRI sensors differentiate multiple metals via the frequency of their carbon-13 spins.


6

Hyperpolarized Multi-Metal 13C-Sensors for Magnetic Resonance

Recommend Documents