Mixed-Valence Compounds as Polarizing Agents for Overhauser Dynamic Nuclear Polarization in Solids*.

Herein, we investigate a novel set of polarizing agents-mixed-valence compounds-by theoretical and experimental methods and demonstrate their performance in high-field dynamic nuclear polarization (DNP) NMR experiments in the solid state. Mixed-valence compounds constitute a group of molecules in which molecular mobility persists even in solids. Consequently, such polarizing agents can be used to perform Overhauser-DNP experiments in the solid state, with favorable conditions for dynamic nuclear polarization formation at ultra-high magnetic fields.

Constant-adiabaticity ultralow magnetic field manipulations of parahydrogen-induced polarization: application to an AA'X spin system.

The field of magnetic resonance imaging with hyperpolarized contrast agents is rapidly expanding, and parahydrogen-induced polarization (PHIP) is emerging as an inexpensive and easy-to-implement method for generating the required hyperpolarized biomolecules. Hydrogenative PHIP delivers hyperpolarized proton spin order to a substrate via chemical addition of H in the spin-singlet state, but it is typically necessary to transfer the proton polarization to a heteronucleus (usually C) which has a longer spin lifetime. Adiabatic ultralow magnetic field manipulations can be used to induce the polarization transfer, but this is necessarily a slow process, which is undesirable since the spins continually relax back to thermal equilibrium.

Sequential assignment of NMR spectra of peptides at natural isotopic abundance with zero- and ultra-low-field total correlation spectroscopy (ZULF-TOCSY).

A novel method dubbed ZULF-TOCSY results from the combination of Zero and Ultra-Low Field (ZULF) with high-field, high-resolution NMR, leading to a generalization of the concept of total correlation spectroscopy (TOCSY). ZULF-TOCSY is a new building block for NMR methods, which has the unique property that the polarization is evenly distributed among all NMR-active nuclei such as 1H, 13C, 15N, 31P, etc., provided that they belong to the same coupling network, and provided that their relaxation is not too fast at low fields, as may occur in macromolecules.

A previously unknown way of heme detoxification in the digestive tract of cats.

Free heme is a highly toxic molecule for a living organism and its detoxification is a very important process, especially for carnivorous animals. Here we report the discovery of a previously unknown process for neutralizing free heme in the digestive tract of domestic cats. The cornerstone of this process is the encapsulation of heme into carbonated hydroxyapatite nanoparticles, followed by their excretion with faeces.

Correlation of high-field and zero- to ultralow-field NMR properties using 2D spectroscopy.

The field of zero- to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is currently experiencing rapid growth, owing to progress in optical magnetometry and attractive features of ZULF-NMR such as low hardware cost and excellent spectral resolution achieved under ZULF conditions. In this work, an approach is proposed and demonstrated for simultaneous acquisition of ZULF-NMR spectra of individual C-containing isotopomers of chemical compounds in a complex mixture. The method makes use of fast field cycling such that the spin evolution takes place under ZULF conditions, whereas signal detection is performed in a high-field NMR spectrometer.

Synthetic Approaches for N-Labeled Hyperpolarized Heterocyclic Molecular Imaging Agents for N NMR Signal Amplification by Reversible Exchange in Microtesla Magnetic Fields.

NMR hyperpolarization techniques enhance nuclear spin polarization by several orders of magnitude resulting in corresponding sensitivity gains. This enormous sensitivity gain enables new applications ranging from studies of small molecules by using high-resolution NMR spectroscopy to real-time metabolic imaging in vivo. Several hyperpolarization techniques exist for hyperpolarization of a large repertoire of nuclear spins, although the C and N sites of biocompatible agents are the key targets due to their widespread use in biochemical pathways.

Exchange interaction in short-lived flavine adenine dinucleotide biradical in aqueous solution revisited by CIDNP (chemically induced dynamic nuclear polarization) and nuclear magnetic relaxation dispersion.

Flavin adenine dinucleotide (FAD) is an important cofactor in many light-sensitive enzymes. The role of the adenine moiety of FAD in light-induced electron transfer was obscured, because it involves an adenine radical, which is short-lived with a weak chromophore. However, an intramolecular electron transfer from adenine to flavin was revealed several years ago by Robert Kaptein by using chemically induced dynamic nuclear polarization (CIDNP).

Photo-CIDNP in Solid State.

Photo-CIDNP (photo-chemically induced dynamic nuclear polarization) refers to nuclear polarization created by the spin-chemical evolution of spin-correlated radical pairs (SCRPs). This phenomenon occurs in gases, liquids and solids. Based on the solid-state photo-CIDNP effect observed under magic-angle spinning (MAS), photo-CIDNP MAS NMR has been developed as analytical method.

Pd-based bimetallic catalysts for parahydrogen-induced polarization in heterogeneous hydrogenations.

Production of hyperpolarized catalyst-free gases and liquids by heterogeneous hydrogenation with parahydrogen can be useful for various technical as well as biomedical applications, including in vivo studies, investigations of mechanisms of industrially important catalytic processes, enrichment of nuclear spin isomers of polyatomic gases, and more. In this regard, the wide systematic search for heterogeneous catalysts effective in pairwise addition required for the observation of parahydrogen-induced polarization (PHIP) effects is crucial. Here in this work we demonstrate the competitive advantage of Pd-based bimetallic catalysts for PHIP in heterogeneous hydrogenations (HET-PHIP).

Initializing 2 Pure 14-Qubit Entangled Nuclear Spin States in a Hyperpolarized Molecular Solid.

Quantum entanglement has been realized on a variety of physical platforms such as quantum dots, trapped atomic ions, and superconductors. Here we introduce specific molecular solids as promising alternative platforms. Our model system is triplet pentacene in a host single crystal at level anticrossing (LAC) conditions.

Bridging the Gap: From Homogeneous to Heterogeneous Parahydrogen-induced Hyperpolarization and Beyond.

Demonstration of parahydrogen-induced polarization effects in hydrogenations catalyzed by heterogeneous catalysts instead of metal complexes in a homogeneous solution has opened an entirely new dimension for parahydrogen-based research, demonstrating its applicability not only for the production of catalyst-free hyperpolarized liquids and gases and long-lived non-equilibrium spin states for potential biomedical applications, but also for addressing challenges of modern fundamental and industrial catalysis including advanced mechanistic studies of catalytic reactions and operando NMR and MRI of reactors. This essay summarizes the progress achieved in this field by highlighting the research contributed to it by our colleague and friend Kirill V. Kovtunov whose scientific career ended unexpectedly and tragically at the age of 37.

Stabilization of Re/Re Metalloclusters by Cyanide Ligands in New Trinuclear Rhenium Cluster Complexes [{ReX}(CN)]/[{ReX}(CN)] (X = Br or I).

The interaction of rhenium(III) halides ReBr and ReI with aqueous solution of sodium cyanide resulted in the formation of the first trinuclear halide-cyanide rhenium cluster complexes [{ReX}(CN)]/[{ReX}(CN)] (X = Br or I) crystallized as salts of the compositions CsNa[{ReBr}(CN)]·5.25HO (), CsNa[{ReI}(CN)]·6HO (), Cs[{ReBr}(CN)]·2HO·0.5CsCl (), and Cs[{ReI}(CN)]·().

Intersystem Crossing and Electron Spin Selectivity in Anthracene-Naphthalimide Compact Electron Donor-Acceptor Dyads Showing Different Geometry and Electronic Coupling Magnitudes.

Anthracene-naphthalimide (An-NI) compact electron donor-acceptor dyads were prepared, in which the orientation and distance between the two subunits were varied by direct connection or with intervening phenyl linker. Efficient intersystem crossing (ISC) and long triplet state lifetime (Φ =92 %, τ =438 μs) were observed for the directly connected dyads showing a perpendicular geometry (81°). This efficient spin-orbit charge transfer ISC (SOCT-ISC) takes 376 fs, inhibits the direct charge recombination (CR) to ground state ( CT→S , takes 3.

Synthesis and N NMR Signal Amplification by Reversible Exchange of [ N]Dalfampridine at Microtesla Magnetic Fields.

Signal Amplification by Reversible Exchange (SABRE) technique enables nuclear spin hyperpolarization of wide range of compounds using parahydrogen. Here we present the synthetic approach to prepare N-labeled [ N]dalfampridine (4-amino[ N]pyridine) utilized as a drug to reduce the symptoms of multiple sclerosis. The synthesized compound was hyperpolarized using SABRE at microtesla magnetic fields (SABRE-SHEATH technique) with up to 2.

PHIP hyperpolarized [1-C]pyruvate and [1-C]acetate esters via PH-INEPT polarization transfer monitored by C NMR and MRI.

Parahydrogen-induced polarization of C nuclei by side-arm hydrogenation (PHIP-SAH) for [1-C]acetate and [1-C]pyruvate esters with application of PH-INEPT-type pulse sequences for H to C polarization transfer is reported, and its efficiency is compared with that of polarization transfer based on magnetic field cycling (MFC). The pulse-sequence transfer approach may have its merits in some applications because the entire hyperpolarization procedure is implemented directly in an NMR or MRI instrument, whereas MFC requires a controlled field variation at low magnetic fields. Optimization of the PH-INEPT-type transfer sequences resulted in C polarization values of 0.

Versatile Reactivity of Mn Complexes in Reactions with N-Donor Heterocycles: Metamorphosis of Labile Homometallic Pivalates vs. Assembling of Endurable Heterometallic Acetates.

Reaction of 2,2'-bipyridine (2,2'-bipy) or 1,10-phenantroline (phen) with [Mn(Piv)(EtOH)] led to the formation of binuclear complexes [Mn(Piv)L] (L = 2,2'-bipy (), phen (); Piv is the anion of pivalic acid). Oxidation of or by air oxygen resulted in the formation of tetranuclear Mn complexes [MnO(Piv)L] (L = 2,2'-bipy (), phen ()). The hexanuclear complex [Mn(OH)(Piv)(pym)] () was formed in the reaction of [Mn(Piv)(EtOH)] with pyrimidine (pym), while oxidation of produced the coordination polymer [MnO(Piv)(pym)] ().

Reduction of transient histidine radicals by tryptophan: influence of the amino group charge.

Second-order rate constants of the reduction of histidine radicals by tryptophan were obtained for all combinations of the two amino acids and their N-acetyl derivatives. For the dipeptide N-acetyl histidine-tryptophan, contributions from inter- and intramolecular reduction were revealed. The pH dependences of the rate constants were found to be determined by the protonation state of the amino group of tryptophan.

Parahydrogen-Induced Polarization of Amino Acids.

Nuclear magnetic resonance (NMR) has become a universal method for biochemical and biomedical studies, including metabolomics, proteomics, and magnetic resonance imaging (MRI). By increasing the signal of selected molecules, the hyperpolarization of nuclear spin has expanded the reach of NMR and MRI even further (e.g.

The glymphatic system and meningeal lymphatics of the brain: new understanding of brain clearance.

The glymphatic system and meningeal lymphatics have recently been characterized. Glymphatic system is a glia-dependent system of perivascular channels, and it plays an important role in the removal of interstitial metabolic waste products. The meningeal lymphatics may be a key drainage route for cerebrospinal fluid into the peripheral blood, may contribute to inflammatory reaction and central nervous system (CNS) immune surveillance.

Metal-Organic Frameworks Derived from Calcium and Strontium Complexes of a Redox-Active Ligand.

The reactions of monomeric [(dpp-Bian)M(thf)] (M = Ca (), Sr (); dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with 4,4'-bipyridyl (4,4'-bipy) proceed with electron transfer from dpp-Bian to 4,4'-bipy to afford calcium and strontium complexes containing simultaneously radical-anionic dpp-Bian and 4,4'-bipy ligands. In tetrahydrofuran (thf) the reactions result in 1D coordination polymers [{(dpp-Bian)M(4,4'-bipy)(thf)}·4thf] (M = Ca (), Sr ()), while in a thf/benzene mixture the reaction between and 4,4'-bipy affords the 2D metal-organic framework [{(dpp-Bian)Ca(4,4'-bipy)}·2thf·2CH] (). The structures of compounds , and have been determined by single-crystal X-ray analyses.

Brain Networks Connectivity in Mild to Moderate Depression: Resting State fMRI Study with Implications to Nonpharmacological Treatment.

Network mechanisms of depression development and especially of improvement from nonpharmacological treatment remain understudied. The current study is aimed at examining brain networks functional connectivity in depressed patients and its dynamics in nonpharmacological treatment. Resting state fMRI data of 21 healthy adults and 51 patients with mild or moderate depression were analyzed with spatial independent component analysis; then, correlations between time series of the components were calculated and compared between-group (study 1).

Blatter-Radical-Grafted Mesoporous Silica as Prospective Nanoplatform for Spin Manipulation at Ambient Conditions.

Quantum computing and quantum information processing (QC/QIP) crucially depend on the availability of suitable quantum bits (qubits) and methods of their manipulation. Most qubit candidates known to date are not applicable at ambient conditions. Herein, we propose radical-grafted mesoporous silica as a versatile and prospective nanoplatform for spin-based QC/QIP.