NMR Nomenclature: Nuclear Spin Properties and Conventions for Chemical Shifts. IUPAC Recommendations 2001

Probing the Molecular and Macroscopic Structure of Solid Solutions by Dynamic Nuclear Polarization (DNP) Enhanced 13C and 15N Solid-State NMR Spectroscopy

Crystallization is a widely used purification technique in the manufacture of active pharmaceutical ingredients (APIs) and precursor molecules. However, when impurities and desired compounds have similar molecular structures, separation by crystallization may become challenging. In such cases, some impurities may form crystalline solid solutions with the desired product during recrystallization. Understanding the molecular structure of these recrystallized solid solutions is crucial to devise methods for effective purification. Unfortunately, there are limited analytical techniques that provide insights into the molecular structure or spatial distribution of impurities that are incorporated within recrystallized products. In this study, we investigated model solid solutions formed by recrystallizing salicylic acid (SA) in the presence of anthranilic acid (AA). These two molecules are known to form crystalline solid solutions due to their similar molecular structures. To overcome challenges associated with the long 1H longitudinal relaxation times (T1(1H)) of SA and AA, we employed dynamic nuclear polarization (DNP) and 15N isotope enrichment to enable solid-state NMR experiments. Results of solid-state NMR experiments and DFT calculations revealed that SA and AA are homogeneously alloyed as a solid solution. Heteronuclear correlation (HETCOR) experiments and plane-wave DFT structural models provide further evidence of the molecular-level interactions between SA and AA. This research provides valuable insights into the molecular structure of recrystallized solid solutions, contributing to the development of effective purification strategies and an understanding of the physicochemical properties of solid solutions.

MRI Application and Challenges of Hyperpolarized Carbon-13 Pyruvate in Translational and Clinical Cardiovascular Studies: A Literature Review

Cardiovascular disease shows, or may even be caused by, changes in metabolism. Hyperpolarized magnetic resonance spectroscopy and imaging is a technique that could assess the role of different aspects of metabolism in heart disease, allowing real-time metabolic flux assessment in vivo. In this review, we introduce the main hyperpolarization techniques. Then, we summarize the use of dedicated radiofrequency 13C coils, and report a state of the art of 13C data acquisition. Finally, this review provides an overview of the pre-clinical and clinical studies on cardiac metabolism in the healthy and diseased heart. We furthermore show what advances have been made to translate this technique into the clinic in the near future and what technical challenges still remain, such as exploring other metabolic substrates.

Lead-Free Semiconductors: Phase-Evolution and Superior Stability of Multinary Tin Chalcohalides

Tin-based semiconductors are highly desirable materials for energy applications due to their low toxicity and biocompatibility relative to analogous lead-based semiconductors. In particular, tin-based chalcohalides possess optoelectronic properties that are ideal for photovoltaic and photocatalytic applications. In addition, they are believed to benefit from increased stability compared with halide perovskites. However, to fully realize their potential, it is first necessary to better understand and predict the synthesis and phase evolution of these complex materials. Here, we describe a versatile solution-phase method for the preparation of the multinary tin chalcohalide semiconductors Sn2SbS2I3, Sn2BiS2I3, Sn2BiSI5, and Sn2SI2. We demonstrate how certain thiocyanate precursors are selective toward the synthesis of chalcohalides, thus preventing the formation of binary and other lower order impurities rather than the preferred multinary compositions. Critically, we utilized 119Sn ssNMR spectroscopy to further assess the phase purity of these materials. Further, we validate that the tin chalcohalides exhibit excellent water stability under ambient conditions, as well as remarkable resistance to heat over time compared to halide perovskites. Together, this work enables the isolation of lead-free, stable, direct band gap chalcohalide compositions that will help engineer more stable and biocompatible semiconductors and devices.

Silylenes with a Small Chalcogenide Substituent: Tuning Frontier Orbital Energies from O to Te

The general synthesis of heteroleptic acyclic silylenes with a bulky carbazolyl substituent (dtbpCbz) is detailed and a series of compounds with a chalcogenide substituent of the type [(dtbpCbz)SiE16R] (E16R=OtBu, SEt, SePh, TePh) is reported. With the bulky carbazolyl substituent present, the chalcogenide moiety can be very small, as is shown by incorporating groups as small as ethyl, phenyl or tert-butyl. For the first time, the electronic properties of the silylene can be tuned along a complete series of chalcogenide substituents. The effects are clearly visible in the NMR and UV/Vis spectra, and were rationalised by DFT computations. The reactivity of the heaviest chalcogenide-substituted silylenes was probed by reactions with trimethylphosphine selenide and the terphenyl azide TerN3 (Ter=2,6-dimesitylphenyl).

Redox-Active Triazole-Derived Mesoionic Imines with Ferrocenyl Substituents and their Metal Complexes: Directed Hydrogen-Bonding, Unusual C-H Activation and Ion-Pair Formation

We present herein the synthesis, characterization and complexation of ferrocenyl-substituted MIIs (mesoionic imines) and their metal complexes. In the free MIIs, strong hydrogen bonding interactions are observed between the imine-N and the C-H bonds of the ferrocenyl substituents both in the solid state and in solution. The influence of this hydrogen bonding is so strong that complexation of the MIIs with [IrCp*Cl2]2 yields unique six-membered iridacycles via C-H-activation of the corresponding C-H-site at the Fc-substituent and not the Ph-substituent. This result is in contrast to previous reports in which always a preferential C-H activation at the phenyl substituent is observed in competitive reactions in the presence of ferrocenyl substituents. The corresponding Ir complexes formed after in-situ halide exchange reaction exist in either [Ir-I] contact or as [Ir]+I- solvent separated ion-pairs depending on the solvent polarity. The iodide coordinated and solvent separated ion-pairs display drastically different physical properties. The TEP (Tolman-electronic-parameter) of these ligands was determined and lines up with previously reported MII-ligands. The redox properties were investigated by a combination of electrochemical and spectroelectrochemical methods. We show here how non-covalent interactions can have a drastic influence on the physical and chemical properties of these new class of compounds.

Amplified photomodulation of a bis(dithienylethene)-substituted phosphine

Phosphine ligands play a crucial role in homogeneous catalysis, allowing fine-tuning of the catalytic activity of various metals by modifying their structure. An ultimate challenge in this field is to reach controlled modulation of catalysis in situ, for which the development of phosphines capable of photoswitching between states with differential electronic properties has been proposed. To magnify this light-induced behavior, in this work we describe a novel phosphine ligand incorporating two dithienylethene photoswitchable moieties tethered to the same phosphorus atom. Double photoisomerization was observed for this ligand, which remains unhindered upon gold(I) complexation. As a result, the preparation of a fully ring-closed phosphine isomer was accomplished, for which amplified variation of phosphorus electron density was verified both experimentally and by computational calculations. Accordingly, the presented molecular design based on multiphotochromic phosphines could open new ways for preparing enhanced photoswitchable catalytic systems.

Ruddlesden-Popper Oxyfluorides La2Ni1-xCuxO3F2 (0 ≤ x ≤ 1): Impact of the Ni/Cu Ratio on the Structure

Ruddlesden-Popper oxyfluorides La2Ni1-xCuxO3F2 (0 ≤ x ≤ 1) were obtained by topochemical reaction of oxide precursors La2Ni1-xCuxO4, prepared by citrate-based soft chemistry synthesis, with polyvinylidene fluoride (PVDF) as the fluorine source. Systematic changes of the crystal structure in the oxide as well as the oxyfluoride substitution series were investigated. For 0.2 ≤ x ≤ 0.9, the oxyfluorides adopt the monoclinic (C2/c) structural distortion previously solved for the x = 0.8 compound based on neutron powder diffraction data, whereas the sample with a lower Cu content of x = 0.1 crystallizes in the orthorhombic (Cccm) structure variant of La2NiO3F2. The orthorhombic-to-monoclinic structural transition was found to be the result of an additional tilt component of the Jahn-Teller elongated CuO4F2 octahedra. The structural transitions were additionally studied by DFT calculations, confirming the monoclinic space group symmetry. The "channel-like" anionic ordering of the endmembers La2NiO3F2 and La2CuO3F2 was checked by 19F MAS NMR experiments and was found to persist throughout the entire substitution series.

Carboranes as Potent Phenyl Mimetics: A Comparative Study on the Reversal of ABCG2-Mediated Drug Resistance by Carboranylquinazolines and Their Organic Isosteres

Multidrug resistance is a major challenge in clinical cancer therapy. In particular, overexpression of certain ATP-binding cassette (ABC) transporter proteins, like the efflux transporter ABCG2, also known as breast cancer resistance protein (BCRP), has been associated with the development of resistance to applied chemotherapeutic agents in cancer therapies, and therefore targeted inhibition of BCRP-mediated transport might lead to reversal of this (multidrug) resistance (MDR). In a previous study, we have described the introduction of a boron-carbon cluster, namely closo-dicarbadodecaborane or carborane, as an inorganic pharmacophore into a polymethoxylated 2-phenylquinazolin-4-amine backbone. In this work, the scope was extended to the corresponding amide derivatives. As most of the amide derivatives suffered from poor solubility, only the amide derivative QCe and the two amine derivatives DMQCc and DMQCd were further investigated. Carboranes are often considered as sterically demanding phenyl mimetics or isosteres. Therefore, the organic phenyl and sterically demanding adamantyl analogues of the most promising carborane derivatives were also investigated. The studies showed that the previously described DMQCd, a penta-methoxylated N-carboranyl-2-phenylquinazolin-4-amine, was by far superior to its organic analogues in terms of cytotoxicity, inhibition of the human ABCG2 transporter, as well as the ability to reverse BCRP-mediated mitoxantrone resistance in MDCKII-hABCG2 and HT29 colon cancer cells. Our results indicate that DMQCd is a promising candidate for further in vitro as well as in vivo studies in combination therapy for ABCG2-overexpressing cancers.

An atypical GABARAP binding module drives the pro-autophagic potential of the AML-associated NPM1c variant

The nucleolar scaffold protein NPM1 is a multifunctional regulator of cellular homeostasis, genome integrity, and stress response. NPM1 mutations, known as NPM1c variants promoting its aberrant cytoplasmic localization, are the most frequent genetic alterations in acute myeloid leukemia (AML). A hallmark of AML cells is their dependency on elevated autophagic flux. Here, we show that NPM1 and NPM1c induce the autophagy-lysosome pathway by activating the master transcription factor TFEB, thereby coordinating the expression of lysosomal proteins and autophagy regulators. Importantly, both NPM1 and NPM1c bind to autophagy modifiers of the GABARAP subfamily through an atypical binding module preserved within its N terminus. The propensity of NPM1c to induce autophagy depends on this module, likely indicating that NPM1c exerts its pro-autophagic activity by direct engagement with GABARAPL1. Our data report a non-canonical binding mode of GABARAP family members that drives the pro-autophagic potential of NPM1c, potentially enabling therapeutic options.

Structural characterization of tin in toothpaste by dynamic nuclear polarization enhanced 119Sn solid-state NMR spectroscopy

Stannous fluoride (SnF2) is an effective fluoride source and antimicrobial agent that is widely used in commercial toothpaste formulations. The antimicrobial activity of SnF2 is partly attributed to the presence of Sn(II) ions. However, it is challenging to directly determine the Sn speciation and oxidation state within commercially available toothpaste products due to the low weight loading of SnF2 (0.454 wt% SnF2, 0.34 wt% Sn) and the amorphous, semi-solid nature of the toothpaste. Here, we show that dynamic nuclear polarization (DNP) enables 119Sn solid-state NMR experiments that can probe the Sn speciation within commercially available toothpaste. Solid-state NMR experiments on SnF2 and SnF4 show that 19F isotropic chemical shift and 119Sn chemical shift anisotropy (CSA) are highly sensitive to the Sn oxidation state. DNP-enhanced 119Sn magic-angle turning (MAT) 2D NMR spectra of toothpastes resolve Sn(II) and Sn(IV) by their 119Sn chemical shift tensor parameters. Fits of DNP-enhanced 1D 1H → 119Sn solid-state NMR spectra allow the populations of Sn(II) and Sn(IV) within the toothpastes to be estimated. This analysis reveals that three of the four commercially available toothpastes contained at least 80% Sn(II), whereas one of the toothpaste contained a significantly higher amount of Sn(IV).

Recent technical developments and clinical research applications of sodium (23Na) MRI

Sodium is an essential ion that plays a central role in many physiological processes including the transmembrane electrochemical gradient and the maintenance of the body's homeostasis. Due to the crucial role of sodium in the human body, the sodium nucleus is a promising candidate for non-invasively assessing (patho-)physiological changes. Almost 10 years ago, Madelin et al. provided a comprehensive review of methods and applications of sodium (23Na) MRI (Madelin et al., 2014) [1]. More recent review articles have focused mainly on specific applications of 23Na MRI. For example, several articles covered 23Na MRI applications for diseases such as osteoarthritis (Zbyn et al., 2016, Zaric et al., 2020) [2,3], multiple sclerosis (Petracca et al., 2016, Huhn et al., 2019) [4,5] and brain tumors (Schepkin, 2016) [6], or for imaging certain organs such as the kidneys (Zollner et al., 2016) [7], the brain (Shah et al., 2016, Thulborn et al., 2018) [8,9], and the heart (Bottomley, 2016) [10]. Other articles have reviewed technical developments such as radiofrequency (RF) coils for 23Na MRI (Wiggins et al., 2016, Bangerter et al., 2016) [11,12], pulse sequences (Konstandin et al., 2014) [13], image reconstruction methods (Chen et al., 2021) [14], and interleaved/simultaneous imaging techniques (Lopez Kolkovsky et al., 2022) [15]. In addition, 23Na MRI topics have been covered in review articles with broader topics such as multinuclear MRI or ultra-high-field MRI (Niesporek et al., 2019, Hu et al., 2019, Ladd et al., 2018) [16-18]. During the past decade, various research groups have continued working on technical improvements to sodium MRI and have investigated its potential to serve as a diagnostic and prognostic tool. Clinical research applications of 23Na MRI have covered a broad spectrum of diseases, mainly focusing on the brain, cartilage, and skeletal muscle (see Fig. 1). In this article, we aim to provide a comprehensive summary of methodological and hardware developments, as well as a review of various clinical research applications of sodium (23Na) MRI in the last decade (i.e., published from the beginning of 2013 to the end of 2022).

Strain-Driven, Non-Catalysed Ring Expansion of Silicon Heterocycles

Silacycles are ubiquitous building blocks. Small silacycles can typically be expanded catalytically. A silirane, silirene and phosphasilirene as well as a siletane and a silolene were prepared starting from the base-free bromosilylene [(dtbp Cbz)SiBr] (dtbp Cbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl). As these heterocycles were derived from a dicoordinated silylene, they are susceptible to reactions with an external base. The three-membered silacycles readily undergo non-catalysed ring expansion reactions with isonitriles yielding the related four-membered silacycles. Surprisingly, the ring-expanded derivatives of the silirane undergo up to two further isomerisation reactions, first by enamine formation and then by another ring expansion. DFT computations were utilised to gauge the scope of this reactivity pattern. Three-membered silacycles should essentially universally undergo a ring expansion with isonitriles, while for four-membered silacycles, only very few instances are predicted to accommodate more challenging kinetic requirements of this ring expansion. Larger silacycles lack the ring strain energy required for this ring expansion reaction and are not expected to be expanded.

Quantitative 67Zn, 27Al and 1H MAS NMR spectroscopy for the characterization of Zn species in ZSM-5 catalysts

67Zn MAS NMR spectroscopy was used to characterize the state of Zn in Zn-modified zeolites ZSM-5. Two 67Zn enriched zeolite samples were prepared: by solid-state exchange with metal 67Zn (Zn2+/ZSM-5 sample) and by ion exchange with zinc formate solution (ZnO/H-ZSM-5 sample), both containing ca. 3.8 wt% Zn. The elemental analysis, TEM, and quantitative BAS and aluminum analyses with 1H and 27Al MAS NMR have shown that Zn2+/ZSM-5 contains zinc in the form of Zn2+ cations, while both ZnO species and Zn2+ cations are present in ZnO/H-ZSM-5 besides BAS. 67Zn MAS NMR has detected the signal of Zn in a tetrahedral environment from ZnO species for both the activated and hydrated ZnO/H-ZSM-5 zeolite. The signal of Zn in an octahedral environment was detected for the hydrated Zn2+/ZSM-5 and ZnO/H-ZSM-5 zeolites. This signal may belong to zinc cation [HOZn]+ or Zn(OH)2 species surrounded by water molecules. Quantitative 67Zn MAS NMR analysis has shown that only 27 and 38% of zinc loaded in the zeolite is visible for the activated and hydrated ZnO/H-ZSM-5 zeolite, and 24% of Zn is visible for the hydrated Zn2+/ZSM-5. Zinc in the form of ZnO species is entirely visible in both the activated and hydrated ZnO/H-ZSM-5 zeolite, while Zn2+ cations are not detected at all for the activated sample and only 29% of Zn2+ cations is visible for the hydrated zeolite. Detection of only a part of Zn2+ cations in the form of [HOZn]+ or Zn(OH)2 species in octahedral environment presumes only partial hydrolysis of the bond of Zn2+ cation with framework oxygen and further solvation of the Zn species formed at hydrolysis by the adsorbed water.

Ring-Opening Reaction of 1-Phospha-2-Azanorbornenes via P-N Bond Cleavage and Reversibility Studies

The reactive P-N bond in 1-phospha-2-azanorbornenes is readily cleaved by simple alcohols to afford P-chiral 2,3-dihydrophosphole derivatives as a racemic mixture. The isolation of the products was not possible due to the reversibility of the reaction, which could, however, be stopped by sulfurization of the phosphorus atom, thus efficiently blocking the lone pair of electrons, as exemplified for 6b yielding structurally characterized 8b. Additionally, the influence of the substituent in the α position to the phosphorus atom (H, Ph, 2-py, CN) on the reversibility of the reaction was studied. Extensive theoretical calculations for understanding the ring-closing mechanism suggested that a multi-step reaction with one or more intermediates was most probable.

Modular Synthesis of Phosphino Hydrazones and Their Use as Ligands in a Palladium-Catalysed Cu-Free Sonogashira Cross-Coupling Reaction

Phosphino hydrazones represent a versatile class of nitrogen-containing phosphine ligands. Herein, we report a modular synthesis of phosphino hydrazone ligands by hydrazone condensation reaction of three different aryl hydrazines with 3-(diphenylphosphino)propanal (PCHO). Complexation reactions of these phosphino hydrazone ligands with palladium(II) and platinum(II) were investigated and the catalytic activity of the palladium(II) complexes was explored in a Cu-free Sonogashira cross-coupling reaction achieving yields up to 96 %. Additionally it was shown that the catalytically active species is homogeneous.

Access to Enantiomerically Pure P-Chiral 1-Phosphanorbornane Silyl Ethers

Sulfur-protected enantiopure P-chiral 1-phosphanorbornane silyl ethers 5a,b are obtained in high yields via the reaction of the hydroxy group of P-chiral 1-phosphanorbornane alcohol 4 with tert-butyldimethylsilyl chloride (TBDMSCl) and triphenylsilyl chloride (TPSCl). The corresponding optically pure silyl ethers 5a,b are purified via crystallization and fully structurally characterized. Desulfurization with excess Raney nickel gives access to bulky monodentate enantiopure phosphorus(III) 1-phosphanorbornane silyl ethers 6a,b which are subsequently applied as ligands in iridium-catalyzed asymmetric hydrogenation of a prochiral ketone and enamide. Better activity and selectivity were observed in the latter case.

3D printed hybrid scaffolds for bone regeneration using calcium methoxyethoxide as a calcium source

Introduction: Hybrids consist of inorganic and organic co-networks that are indistinguishable above the nanoscale, which can lead to unprecedented combinations of properties, such as high toughness and controlled degradation. Methods: We present 3D printed bioactive hybrid scaffolds for bone regeneration, produced by incorporating calcium into our "Bouncy Bioglass", using calcium methoxyethoxide (CME) as the calcium precursor. SiO2-CaOCME/PTHF/PCL-diCOOH hybrid "inks" for additive manufacturing (Direct Ink Writing) were optimised for synergy of mechanical properties and open interconnected pore channels. Results and Discussion: Adding calcium improved printability. Changing calcium content (5, 10, 20, 30, and 40 mol.%) of the SiO2-CaOCME/PTHF/PCL-diCOOH hybrids affected printability and mechanical properties of the lattice-like scaffolds. Hybrids containing 30 mol.% calcium in the inorganic network (70S30CCME-CL) printed with 500 µm channels and 100 µm strut size achieved the highest strength (0.90 ± 0.23 MPa) and modulus of toughness (0.22 ± 0.04 MPa). These values were higher than Ca-free SiO2/PTHF/PCL-diCOOH hybrids (0.36 ± 0.14 MPa strength and 0.06 ± 0.01 MPa toughness modulus). Over a period of 90 days of immersion in simulated body fluid (SBF), the 70S30CCME-CL hybrids also kept a stable strain to failure (~30 %) and formed hydroxycarbonate apatite within three days. The extracts released by the 70S30CCME-CL hybrids in growth medium did not cause cytotoxic effects on human bone marrow stromal cells over 24 h of culture.

Nuclear spin diffusion in the central spin system of a GaAs/AlGaAs quantum dot

The spin diffusion concept provides a classical description of a purely quantum-mechanical evolution in inhomogeneously polarized many-body systems such as nuclear spin lattices. The central spin of a localized electron alters nuclear spin diffusion in a way that is still poorly understood. Here, spin diffusion in a single GaAs/AlGaAs quantum dot is witnessed in the most direct manner from oscillatory spin relaxation dynamics. Electron spin is found to accelerate nuclear spin relaxation, from which we conclude that the long-discussed concept of a Knight-field-gradient diffusion barrier does not apply to GaAs epitaxial quantum dots. Our experiments distinguish between non-diffusion relaxation and spin diffusion, allowing us to conclude that diffusion is accelerated by the central electron spin. Such acceleration is observed up to unexpectedly high magnetic fields - we propose electron spin-flip fluctuations as an explanation. Diffusion-limited nuclear spin lifetimes range between 1 and 10 s, which is sufficiently long for quantum information storage and processing.

Mapping of exogenous choline uptake and metabolism in rat glioblastoma using deuterium metabolic imaging (DMI)

Introduction

There is a lack of robust metabolic imaging techniques that can be routinely applied to characterize lesions in patients with brain tumors. Here we explore in an animal model of glioblastoma the feasibility to detect uptake and metabolism of deuterated choline and describe the tumor-to-brain image contrast.

Methods

RG2 cells were incubated with choline and the level of intracellular choline and its metabolites measured in cell extracts using high resolution 1H NMR. In rats with orthotopically implanted RG2 tumors deuterium metabolic imaging (DMI) was applied in vivo during, as well as 1 day after, intravenous infusion of 2H9-choline. In parallel experiments, RG2-bearing rats were infused with [1,1',2,2'-2H4]-choline and tissue metabolite extracts analyzed with high resolution 2H NMR to identify molecule-specific 2H-labeling in choline and its metabolites.

Results

In vitro experiments indicated high uptake and fast phosphorylation of exogenous choline in RG2 cells. In vivo DMI studies revealed a high signal from the 2H-labeled pool of choline + metabolites (total choline, 2H-tCho) in the tumor lesion but not in normal brain. Quantitative DMI-based metabolic maps of 2H-tCho showed high tumor-to-brain image contrast in maps acquired both during, and 24 h after deuterated choline infusion. High resolution 2H NMR revealed that DMI data acquired during 2H-choline infusion consists of free choline and phosphocholine, while the data acquired 24 h later represent phosphocholine and glycerophosphocholine.

Discussion

Uptake and metabolism of exogenous choline was high in RG2 tumors compared to normal brain, resulting in high tumor-to-brain image contrast on DMI-based metabolic maps. By varying the timing of DMI data acquisition relative to the start of the deuterated choline infusion, the metabolic maps can be weighted toward detection of choline uptake or choline metabolism. These proof-of-principle experiments highlight the potential of using deuterated choline combined with DMI to metabolically characterize brain tumors.

Metal phosphine aldehyde complexes and their application in Cu-free Sonogashira and Suzuki-Miyaura cross-coupling reactions

Transition metal coordination chemistry and catalysis are rife with phosphine ligands. One of the rather less studied members of the phosphine ligand family are phosphine aldehydes. We have synthesised 3-(diphenylphosphino)propanal (PCHO) with a slight modification of the known procedure and studied its complexation behaviour with palladium(II) and platinum(II). The catalytic activity of the palladium(II) phosphine aldehyde complexes was investigated in Cu-free Sonogashira and Suzuki-Miyaura cross-coupling reactions. Furthermore, the homogeneous nature of the catalytically active species was confirmed.

The More the Better-Investigation of Polymethoxylated N-Carboranyl Quinazolines as Novel Hybrid Breast Cancer Resistance Protein Inhibitors

The ineffectiveness and failing of chemotherapeutic treatments are often associated with multidrug resistance (MDR). MDR is primarily linked to the overexpression of ATP-binding cassette (ABC) transporter proteins in cancer cells. ABCG2 (ATP-binding cassette subfamily G member 2, also known as the breast cancer resistance protein (BCRP)) mediates MDR by an increased drug efflux from the cancer cells. Therefore, the inhibition of ABCG2 activity during chemotherapy ought to improve the efficacy of the administered anti-cancer agents by reversing MDR or by enhancing the agents' pharmacokinetic properties. Significant efforts have been made to develop novel, powerful, selective, and non-toxic inhibitors of BCRP. However, thus far the clinical relevance of BCRP-selective MDR-reversal has been unsuccessful, due to either adverse drug reactions or significant toxicities in vivo. We here report a facile access towards carboranyl quinazoline-based inhibitors of ABCG2. We determined the influence of different methoxy-substitution patterns on the 2-phenylquinazoline scaffold in combination with the beneficial properties of an incorporated inorganic carborane moiety. A series of eight compounds was synthesized and their inhibitory effect on the ABCG2-mediated Hoechst transport was evaluated. Molecular docking studies were performed to better understand the structure-protein interactions of the novel inhibitors, exhibiting putative binding modes within the inner binding site. Further, the most potent, non-toxic compounds were investigated for their potential to reverse ABCG2-mediated mitoxantrone (MXN) resistance. Of these five evaluated compounds, N-(closo-1,7-dicarbadodecaboran(12)-9-yl)-6,7-dimethoxy-2-(3,4,5-trimethoxyphenyl)-quinazolin-4-amine (DMQCd) exhibited the strongest inhibitory effect towards ABCG2 in the lower nanomolar ranges. Additionally, DMQCd was able to reverse BCRP-mediated MDR, making it a promising candidate for further research on hybrid inorganic-organic compounds.

Practical Aspects of NMR-Based Metabolomics

While NMR-based metabolomics is only about 20 years old, NMR has been a key part of metabolic and metabolism studies for >40 years. Historically, metabolic researchers used NMR because of its high level of reproducibility, superb instrument stability, facile sample preparation protocols, inherently quantitative character, non-destructive nature, and amenability to automation. In this chapter, we provide a short history of NMR-based metabolomics. We then provide a detailed description of some of the practical aspects of performing NMR-based metabolomics studies including sample preparation, pulse sequence selection, and spectral acquisition and processing. The two different approaches to metabolomics data analysis, targeted vs. untargeted, are briefly outlined. We also describe several software packages to help users process NMR spectra obtained via these two different approaches. We then give several examples of useful or interesting applications of NMR-based metabolomics, ranging from applications to drug toxicology, to identifying inborn errors of metabolism to analyzing the contents of biofluids from dairy cattle. Throughout this chapter, we will highlight the strengths and limitations of NMR-based metabolomics. Additionally, we will conclude with descriptions of recent advances in NMR hardware, methodology, and software and speculate about where NMR-based metabolomics is going in the next 5-10 years.

Design, synthesis and evaluation of 15N- and 13C-labeled molecular probes as hyperpolarized nitric oxide sensors

Nitric oxide (NO) is an important signaling molecule involved in a wide range of biological processes. Development of non-invasive, real-time detection of NO is greatly desired yet remains challenging. Here we report the design and development of novel 15N- and 13C-labeled NO-sensing probes for hyperpolarized nuclear magnetic resonance (HP-NMR) studies. These probes undergo selective and rapid reaction with NO to generate in situ AZO-products that can be monitored with distinguishable NMR signals as a read-out. This study also allows for a direct comparison of the 15N and 13C nuclei performances in hyperpolarized reaction-based probes. The simple and general SABRE-SHEATH hyperpolarization method works on the 15N- and 13C-NO-sensing probes. Measured long spin-lattice relaxation (T1) values, especially for 15N-NO probes, will allow for real-time reaction-based imaging of NO.

HSIL-Based Synthesis of Ultracrystalline K,Na-JBW, a Zeolite Exhibiting Exceptional Framework Ordering and Flexibility

A reproducible synthesis strategy for ultracrystalline K,Na-aluminosilicate JBW zeolite is reported. The synthesis uses a Na-based hydrated silicate ionic liquid (HSIL) as a silicon source and gibbsite as the aluminum source. ²⁷Al and ²³Na NMR spectra exhibit crystalline second-order quadrupole patterns in the hydrated as well as dehydrated states and distinct resonances for different T-sites demonstrating an exceptional degree of order of the elements of the JBW framework, observed for the first time in a zeolite. Detailed structural analysis via NMR crystallography, combining powder X-ray diffraction and solid-state NMR of all elements (²⁷Al, ²⁹Si, ²³Na, ³⁹K, and ¹H), reveals remarkable de- and rehydration behavior of the JBW framework, transforming from its as-made hydrated structure via a modified anhydrous state into a different rehydrated symmetry while showing astonishing flexibility for a semicondensed aluminosilicate. Its crystallinity, exceptional degree of ordering of the T atoms and sodium cations, and the fully documented structure qualify this defect-free K,Na-aluminosilicate JBW zeolite as a suitable model system for developing NMR modeling methods.

Annellated 1,3,4,2-Triazaphospholenes-Simple Modular Synthesis and a First Exploration of Ligand Properties

The successful use of 1,3,4,2-triazaphospholenes (TAPs) as organo-catalysts stresses the need for efficient synthetic routes to these molecules. In this study, we establish the [1 + 4]-cycloaddition of PBr₃ to azo-pyridines as a new approach to preparing pyrido-annellated TAPs in a single step from easily available precursors. The modular assembly of the azo-component via condensation of primary amines and nitroso compounds along with the feasibility of post-functionalization at the P–Br bond under conservation of the heterocyclic structure allows, in principle, to address a wide range of target molecules, which is illustrated by prototypical examples. The successful synthesis of a transition metal complex confirms for the first time the ability of a TAP to act as a P-donor ligand. Crystallographic studies suggest that hyperconjugation effects and intermolecular interactions induce a qualitatively similar ionic polarization of the P–Br bonds in TAPs as in better known isoelectronic diazaphospholenes.

State-of-the-art accounts of hyperpolarized 15N-labeled molecular imaging probes for magnetic resonance spectroscopy and imaging

Hyperpolarized isotope-labeled agents have significantly advanced nuclear magnetic resonance spectroscopy and imaging (MRS/MRI) of physicochemical activities at molecular levels. An emerging advance in this area is exciting developments of 15N-labeled hyperpolarized MR agents to enable acquisition of highly valuable information that was previously inaccessible and expand the applications of MRS/MRI beyond commonly studied 13C nuclei. This review will present recent developments of these hyperpolarized 15N-labeled molecular imaging probes, ranging from endogenous and drug molecules, and chemical sensors, to various 15N-tagged biomolecules. Through these examples, this review will provide insights into the target selection and probe design rationale and inherent challenges of HP imaging in hopes of facilitating future developments of 15N-based biomedical imaging agents and their applications.

4a-methyl-dodecahydro-1H-pyrrolo[3,4-b]quinoline-6-one produced by Endophytic Fungi Aspergillus niger E12 obtained from Dodonaea viscosa Plant Leaves as a Novel Antibacterial Compound

Endophytic fungi were isolated from forty plant leaf samples from Gudiyam forest. The potent antibacterial strain Aspergillus niger E12 isolated from the plant Dodonaea viscosa showed maximal antibacterial activity against all the test organisms, viz., Staphylococcus aureus, Bacillus coagulans, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. The production of the antibacterial compound was optimized using the yeast extract sucrose medium (2% YES) using response surface methodology (RSM). For the production, the optimal parameters were carbon/nitrogen (C:N) ratio, 9:1; temperature, 25 °C; pH, 5.7; incubation time, 240 h; and rpm, 30. A zone of inhibition of 19.33 mm was observed as maximal bioactivity against Pseudomonas aeruginosa. The antibacterial compound was purified by extraction with ethyl acetate, activity-guided fractionation, and preparative high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) studies showed that the Aspergillus niger E12 bioactive substance is 4a-methyl-dodecahydro-1H-pyrrolo [3,4-b] quinoline-6-one.

Multiphase Drug Distribution and Exchange in Oil-in-Water Nanoemulsion Revealed by High-Resolution 19F qNMR

An oil-in-water (o/w) nanoemulsion (NE), composed of oil globules, stabilized by a surfactant, and dispersed in an aqueous phase, is increasingly developed in complex drug formulation. Kinetically stable NEs are used to formulate hydrophobic drugs and typically provide higher dosage strengths and better content uniformity. However, little is known accurately about drug distribution in its multiphase solution, especially for the possible drug presence in the surfactant (s) phase, the interface layer between the dispersed oil (o) and the continuous water (w) phases. Here, high-resolution ¹⁹F quantitative NMR spectroscopy was applied directly and noninvasively on an o/w NE drug product containing difluprednate (DFPN). The well-resolved ¹⁹F peaks of DFPN depended on the shielding molecules in each phase, which revealed mass-balanced DFPN distribution in multiple phases of (w), (s), and (o) of NE globules at a quantity of 1.8 ± 0.1, 35 ± 2, and 59 ± 3% per labeled content, respectively. Furthermore, the dilution-dependent ¹⁹F peak line broadening and shift suggested a millisecond dynamic exchange between the NE and the less-noticed smaller but thermodynamically stable microemulsion (ME) globules in NE solution. The high-resolution NMR result revealed that the drug availability could be quickly achieved using an o/w NE formulation because of the drug multiphase distribution and the ME-assisted fast drug exchange among globules.

Enantioselective, Copper-Catalyzed Addition of Nucleophilic Silicon to Alkenyl-Substituted Phosphine Oxides

An enantioselective β-silylation of α,β-unsaturated phosphine oxide derivatives using a silylboronic ester as the silicon pronucleophile is reported. The reaction is catalyzed by copper salts in the presence of chiral pyridine–oxazoline (PyOx) ligands. Good to high enantioselectivities (≤95% ee) are obtained for β-aryl-substituted acceptors whereas alkyl residues in the β-position led to a lower ee value for 1° and no reaction for 2° and 3°. The new method represents another way of accessing α-chiral silanes and complements the known β-borylation.

Characterization of an aged alkali-activated slag roof tile after 30 years of exposure to Northern Scandinavian weather

The phase assemblage and nanostructural characterization results reported here further elucidate the long-term changes occurring in alkali activated blast furnace slag binders.

Phosphorus guiding palladium: [4+4] metallomacrocyclic PdII complex and self-assembly of heterometallic PdII/ZnII grid-type complex

The reaction of heteroditopic ligand 1 featuring a hard pyridine-hydrazone-pyrimidine (N,N,N) site and a softer pyrimidine-hydrazone-phosphane (N,N,P) pocket with [Pd(CH3CN4)](OTf)2 in different metal-to-ligand ratios (M:L) gave the homobimetallic PdII complex...

Heterobimetallic Pd/Mn and Pd/Co complexes as efficient and stereoselective catalysts for sequential Cu-free Sonogashira coupling-alkyne semi-hydrogenation reactions

A series of heterobimetallic Pd^II/M^II complexes (M^II = Mn, Co) were synthesised and tested as precatalysts for sequential Sonogashira coupling-alkyne semi-hydrogenation reactions to form Z-aryl alkenes. The carbometalated heterobimetallic Pd^II/Co^II complex CoPdL3' demonstrated an apparent cooperative effect compared to the corresponding monometallic counterparts. This compound was identified as a potent single-molecule catalyst for the one-pot Cu-free Sonogashira coupling of aryl bromides with terminal alkynes followed by chemo- and stereoselective semi-hydrogenation of the alkyne intermediate using NH₃·BH₃ as a hydrogen source. Furthermore, different aromatic substrates have been tested to show the generality of the reaction for the synthesis of Z-alkenes, including biologically active combretastatin A-4. In addition, the homogeneous nature of the catalytically active species was demonstrated.

Revealing Brønsted Acidic Bridging SiOHAl Groups on Amorphous Silica-Alumina by Ultrahigh Field Solid-State NMR

Amorphous silica-aluminas (ASAs) are important acidic catalysts and supports for many industrially essential and sustainable processes. The identification of surface acid sites with their local structures on ASAs is of critical importance for tuning their catalytic properties but still remains a great challenge and is under debate. Here, ultrahigh magnetic field (35.2 T) ²⁷Al-{¹H} D-HMQC (dipolar-mediated heteronuclear multiple-quantum correlation) two-dimensional NMR experiments demonstrate two types of Brønsted acid sites in ASA catalysts. In addition to the known pseudobridging silanol acid sites, the use of ultrahigh field NMR provides the first direct experimental evidence for the existence of bridging silanol (BS: SiOHAl) acid sites in ASAs, which has been hotly debated in the past few decades. This discovery provides new opportunities for scientists and engineers to develop and apply ASAs in various reaction processes due to the significance of BS in chemical and fuel productions based on its strong Brønsted acidity.

Single-Crystal X-ray and Solid-State NMR Characterisation of AND-1184 and Its Hydrochloride Form

In this study, we report on a structural investigation of AND-1184, with the chemical name N-[3-[4-(6-fluoro-1,2-benzoxazol-3-yl)piperidin-1-yl]propyl]-3-methylbenzenesulfonamide (MBS), and its hydrochloride form (MBS^HCl); AND-1184 is a potential API for the treatment of dementia. The single-crystal X-ray investigation of both forms results in monoclinic crystal systems with P2₁/c and C2/c symmetry for MBS and MBS^HCl, respectively. This solid-state NMR study, combined with quantum-chemical calculations, allowed us to assign all ¹³C and most ¹H signals. The MBS structure was defined as a completely rigid system without significant dynamic behaviours, whereas MBS^HCl exhibited limited dynamic motion of the aromatic part of the molecule.

Deuterium Metabolic Imaging of the Healthy and Diseased Brain

Altered brain metabolism contributes to pathophysiology in cerebrovascular and neurodegenerative diseases such as stroke and Alzheimer's disease. Current clinical tools to study brain metabolism rely on positron emission tomography (PET) requiring specific hardware and radiotracers, or magnetic resonance spectroscopy (MRS) involving technical complexity. In this review we highlight deuterium metabolic imaging (DMI) as a novel translational technique for assessment of brain metabolism, with examples from brain tumor and stroke studies. DMI is an MRS-based method that enables detection of deuterated substrates, such as glucose, and their metabolic products, such as lactate, glutamate and glutamine. It provides additional detail of downstream metabolites compared to analogous approaches like fluorodeoxyglucose (FDG)-PET, and can be implemented and executed on clinical and preclinical MR systems. We foresee that DMI, with future improvements in spatial and temporal resolutions, holds promise to become a valuable MR imaging (MRI) method for non-invasive mapping of glucose uptake and its downstream metabolites in healthy and diseased brain.

Structure and surface properties of size-tuneable CsPbBr3 nanocrystals

This investigation has characterised the structure and surface chemistry of CsPbBr₃ nanocrystals with controlled diameters between 6.4 to 12.8 nm. The nanocrystals were investigated via a thorough ¹³³Cs solid state NMR and nuclear relaxation study, identifying and mapping radially-increasing nanoscale disorder. This work has formalised ¹³³Cs NMR as a highly sensitive probe of nanocrystal size, which can conveniently analyse nanocrystals in solid forms, as they would be utilised in optoelectronic devices. A combined multinuclear solid state NMR and XPS approach, including ¹³³Cs-¹H heteronuclear correlation 2D (HETCOR) NMR, was utilised to study the nanocrystal surface and ligands, demonstrating that the surface is Cs-Br rich with vacancies passivated by didodecyldimethylammonium bromide (DDAB) ligands. Furthermore, it is shown that a negligible amount of phosphonate ligands remain on the powder nanocrystal surface, despite the key role of octylphosphonic acid (OPA) in controlling the colloidal nanocrystal growth. The CsPbBr₃ NCs were shown to be structurally stable under ambient conditions for up to 6 months, albeit with some particle agglomeration.

A saccharide-based binder for efficient polysulfide regulations in Li-S batteries

The viability of lithium-sulfur batteries as an energy storage technology depends on unlocking long-term cycle stability. Most instability stems from the release and transport of polysulfides from the cathode, which causes mossy growth on the lithium anode, leading to continuous consumption of electrolyte. Therefore, development of a durable cathode with minimal polysulfide escape is critical. Here, we present a saccharide-based binder system that has a capacity for the regulation of polysulfides due to its reducing properties. Furthermore, the binder promotes the formation of viscoelastic filaments during casting which endows the sulfur cathode with a desirable web-like microstructure. Taken together this leads to 97% sulfur utilisation with a cycle life of 1000 cycles (9 months) and capacity retention (around 700 mAh g-1 after 1000 cycles). A pouch cell prototype with a specific energy of up to 206 Wh kg-1 is produced, demonstrating the promising potential for practical applications.

Ternary ACd4P3 (A = Na, K) Nanostructures via a Hydride Solution-Phase Route

Complex pnictides such as I-II₄-V₃ compounds (I = alkali metal; II = divalent transition metal; V = pnictide element) display rich structural chemistry and interesting optoelectronic properties, but can be challenging to synthesize using traditional high-temperature solid-state synthesis. Soft chemistry methods can offer control over particle size, morphology, and properties. However, the synthesis of multinary pnictides from solution remains underdeveloped. Here, we report the colloidal hot-injection synthesis of ACd₄P₃ (A = Na, K) nanostructures from their alkali metal hydrides (AH). Control studies indicate that NaCd₄P₃ forms from monometallic Cd⁰ seeds and not from binary Cd₃P₂ nanocrystals. IR and ssNMR spectroscopy reveal tri-n-octylphosphine oxide (TOPO) and related ligands are coordinated to the ternary surface. Computational studies show that competing phases with space group symmetries R3̅m and Cm differ by only 30 meV/formula unit, indicating that synthetic access to either of these polymorphs is possible. Our synthesis unlocks a new family of nanoscale multinary pnictide materials that could find use in optoelectronic and energy conversion devices.

Evidence for even parity unconventional superconductivity in Sr2RuO4

Unambiguous identification of the superconducting order parameter symmetry in [Formula: see text] has remained elusive for more than a quarter century. While a chiral p-wave ground state analogue to superfluid 3He-A was ruled out only very recently, other proposed triplet-pairing scenarios are still viable. Establishing the condensate magnetic susceptibility reveals a sharp distinction between even-parity (singlet) and odd-parity (triplet) pairing since the superconducting condensate is magnetically polarizable only in the latter case. Here field-dependent 17O Knight shift measurements, being sensitive to the spin polarization, are compared to previously reported specific heat measurements for the purpose of distinguishing the condensate contribution from that due to quasiparticles. We conclude that the shift results can be accounted for entirely by the expected field-induced quasiparticle response. An upper bound for the condensate magnetic response of <10% of the normal state susceptibility is sufficient to exclude all purely odd-parity candidates.

Palladium Goes First: A Neutral Asymmetric Heteroditopic N,P Ligand Forming Pd-3d Heterobimetallic Complexes

A facile two-step synthesis of bis(1-methylhydrazinyl)pyrimidine from pyridine-2-carbaldehyde and 2-diphenylphosphanylbenzaldehyde gave access to the new asymmetric ligand 1. The phosphane selectively guides Pd^II into the softer tridentate N,N,P pocket, yielding monometallic complex 2. A second reaction with a 3d transition metal complex precursor (groups 7 to 12) fills the vacant N,N,N pocket and thus provides a variety of heterobimetallic complexes of the type Pd^II/M^II (M = Mn (3), Fe (4), Co (5), Ni (6), Cu (7), Zn (8)). Single-crystal X-ray diffraction studies were performed for all complexes. The assembly of μ₂-chlorido-bridged dimers was observed for complexes 5-7 in the solid state, while DOSY NMR experiments have shown that 5-7 are unbridged monomers in solution. As an exception, Fe^II prefers to form the homoleptic meridional complex [Fe{PdCl(1)}₂](OTf)₄ (4). The electrochemical behavior and the effective magnetic moment in solution were investigated for all complexes by cyclic voltammetry and Evans method, respectively. Experimental UV/vis results were interpreted by performing TD-DFT calculations on 1, 2, and 3.

Feasibility of deuterium magnetic resonance spectroscopy of 3-O-Methylglucose at 7 Tesla

Deuterium Magnetic Resonance Spectroscopy (DMRS) is a non-invasive technique that allows the detection of deuterated compounds in vivo. DMRS has a large potential to analyze uptake, perfusion, washout or metabolism, since deuterium is a stable isotope and therefore does not decay during biologic processing of a deuterium labelled substance. Moreover, DMRS allows the distinction between different deuterated substances. In this work, we performed DMRS of deuterated 3-O-Methylglucose (OMG). OMG is a non-metabolizable glucose analog which is transported similar to D-glucose. DMRS of OMG was performed in phantom and in vivo measurements using a preclinical 7 Tesla MRI system. The chemical shift (3.51 ± 0.1 ppm) and relaxation times were determined. OMG was injected intravenously and spectra were acquired over a period of one hour to monitor the time evolution of the deuterium signal in tumor-bearing rats. The increase and washout of OMG could be observed. Three different exponential functions were compared in terms of how well they describe the OMG washout. A mono-exponential model with offset seems to describe the observed time course best with a time constant of 1910 ± 770 s and an offset of 2.5 ± 1.2 mmol/l (mean ± std, N = 3). Chemical shift imaging could be performed with a voxel size of 7.1 mm x 7.1 mm x 7.9 mm. The feasibility of DMRS with deuterium labelled OMG could be demonstrated. These data might serve as basis for future studies that aim to characterize glucose transport using DMRS.

Modulation of γ-Secretase Activity by a Carborane-Based Flurbiprofen Analogue

All over the world, societies are facing rapidly aging populations combined with a growing number of patients suffering from Alzheimer's disease (AD). One focus in pharmaceutical research to address this issue is on the reduction of the longer amyloid-β (Aβ) fragments in the brain by modulation of γ-secretase, a membrane-bound protease. R-Flurbiprofen (tarenflurbil) was studied in this regard but failed to show significant improvement in AD patients in a phase 3 clinical trial. This was mainly attributed to its low ability to cross the blood-brain barrier (BBB). Here, we present the synthesis and in vitro evaluation of a racemic meta-carborane analogue of flurbiprofen. By introducing the carborane moiety, the hydrophobicity could be shifted into a more favourable range for the penetration of the blood-brain barrier, evident by a logD7.4 value of 2.0. Furthermore, our analogue retained γ-secretase modulator activity in comparison to racemic flurbiprofen in a cell-based assay. These findings demonstrate the potential of carboranes as phenyl mimetics also in AD research.

Photoresponsive host-guest chemistry and relaxation time of fluorinated cyclodextrin and arylazopyrazole-functionalized DOTA metal complexes

Light-responsive modulation of the longitudinal (T1) and transversal relaxation times of a fluorinated cyclodextrin has been achieved by host-guest complexation with arylazopyrazole-modified metal complexes in aqueous solution. This supramolecular concept can potentially be applied to the development of contrast agents for 19F magnetic resonance imaging (MRI).