@article {3228, title = {Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy}, journal = {The Journal of Physical Chemistry C}, year = {2019}, month = {06/2019}, abstract = {

For the first time, chemical exchange saturation transfer (CEST) nuclear magnetic resonance (NMR) is utilized to study short-lived hydride intermediates in the catalytic cycle of an organometallic complex [Ir(IMes)(Py)3(H)2]Cl. These complexes are typically not observable by other NMR techniques because they are low concentrated and undergo reversible ligand exchange with the main complex. The intermediatecomplexes [Ir(Cl)(IMes)(Py)2(H)2] and [Ir(CD3OD)(IMes)(Py)2(H)2]are detected, assigned, and characterized in solution, in situ and at room temperature. Understanding the spin dynamics in these complexes is necessary for enhancing the performance of the nuclear spin hyperpolarization technique signal amplification by reversible exchange. By eliminating [Ir(Cl (IMes)(Py)2(H)2] and manipulating the spin system by radiofrequency irradiation, the nuclear spin singlet lifetime of the hydride protons was increased by more than an order of magnitude, from 2.2 \± 0.1 to 27.2 \± 1.2 s. Because of its simplicity and ability to unravel unobservable chemical species, the utilized CEST NMR approach has a large application potential for studying short-lived hydride intermediates incatalytic reactions.

}, doi = {https://doi.org/10.1021/acs.jpcc.9b04179}, url = {https://pubs.acs.org/doi/10.1021/acs.jpcc.9b04179$\#$}, author = {Stephan Knecht and Sara Hadjiali and Danila A Barskiy and Alexander Pines and Grit Sauer and Alexey Kiryutin and Konstantin Ivanov and Alexandra Yurkovskaya and Gerd Buntkowsky} } @article {2963, title = {Rapid Catalyst Capture Enables Metal-Free para-Hydrogen-Based Hyperpolarized Contrast Agents}, journal = {The Journal of Physical Chemistry Letters}, volume = {9}, year = {2018}, month = {05/2018}, pages = {2721{\textendash}2724}, abstract = {

Hyperpolarization techniques based on the use of\ para-hydrogen provide orders of magnitude signal enhancement for magnetic resonance spectroscopy and imaging. The main drawback limiting widespread applicability of\ para-hydrogen-based techniques in biomedicine is the presence of organometallic compounds (the polarization transfer catalysts) in solution with hyperpolarized contrast agents. These catalysts are typically complexes of platinum-group metals, and their administration in vivo should be avoided. Herein, we show how extraction of a hyperpolarized compound from an organic phase to an aqueous phase combined with a rapid (less than 10 s) Ir-based catalyst capture by metal scavenging agents can produce pure\ para-hydrogen-based hyperpolarized contrast agents, as demonstrated by high-resolution nuclear magnetic resonance (NMR) spectroscopy and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The presented methodology enables fast and efficient means of producing pure hyperpolarized aqueous solutions for biomedical and other uses.

}, doi = {10.1021/acs.jpclett.8b01007}, url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.8b01007}, author = {Danila A Barskiy and Lucia A Ke and Xingyang Li and Vincent Stevenson and Nevin Widarman and Hao Zhang and Ashley Truxal and Alexander Pines} }