Synthesis,structure, and magnetic properties of iron — yttrium complexes containing acetylacetonate ligands

Two new compounds have been obtained by the synthesis of heteronuclear iron-yttrium acetylacetonate, using the modified electrochemical dissolution of the [YFe₂] alloy. One of these compounds, with the Fe(acac)₂ · 2H₂O composition, has been studied by X-ray diffraction analysis. X-ray diffraction data: a=11.002(5), b=5.412(2), c=11.179(5) Å;=106.39(4)°;V=638.6 ų, space group P2₁/c, Z=2. According to the data on magnetic susceptibility, Mössbauer spectroscopy, and X-ray electron microanalysis, single crystals of this complex are covered with an amorphous film containing finely dispersed [Y_1–aFe_a]n clusters and, probably, superparamagnetic -Fe₂O₃ species. The second oligomeric acetylacetonate complex contains ions of high-spin two-valence iron, yttrium, and finely dispersed ferromagnetic [Y_1–aFe_a)n intermetallide clusters.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1454–1458, August, 1995.The studies were financially supported by the International Science Foundation (Grants Nos. MI 8000, MI 8300).     

Improved methods for 1H-3H heteronuclear shift correlation

A better understanding of the structure of complex 3H-labeled molecules can be obtained by complete assignment of their 1H and 3H solution-state NMR spectra. The assignment process is aided by the detection of heteronuclear chemical shift correlations between 1H and 3H nuclei. Heteronuclear correlation (HETCOR) experiments previously applied to this task exhibit several drawbacks caused by the nature of both the pulse sequences and 1H-3H spin systems. The range of J-couplings involved in 1H-3H coupling networks make it challenging to perform correlation experiments using methods that rely on coherences created during free precession periods and interrupted by transfer pulses. Two alternative HETCOR experiments are demonstrated for 1H-3H systems in the present work and are shown to have advantages over earlier methods. The first experiment is known as hetero-TOCSY and correlates heteronuclear chemical shifts using J-cross polarization. This experiment achieves both homonuclear and heteronuclear mixing and connects the chemical shifts of all 1H and 3H nuclei in a coupling network. A second HETCOR experiment uses the heteronuclear Overhauser effect to obtain through-space correlations between nearby nuclei. The 1H-3H HETCOR experiments are phase sensitive and typically contain more correlations than other methods, which is beneficial for assignment purposes, while being sensitive enough to be applicable to routine analytical samples. The experiments were used to analyze 3H incorporation in sub-milligram quantities of 3H-labeled pharmaceutical derivatives with complex labeling schemes.     

Modified coumarins. 23. Synthesis and structure of cyclohexyldihydroxanthyletin derivatives

Cyclohexyldihydroxanthyletin derivatives with S and N in place of the exocyclic O atom were synthesized. The structures of the products were proved by NMR correlation spectroscopy. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 531–533, November–December, 2006.     

Through-Bond Correlation of Sugar and Base Protons in Unlabeled Nucleic Acids

This work presents two methods for through-bond correlation between sugar and base protons in view of model-independent assignment in unlabeled or slightly enriched nucleic acids. Each method uses a combination of multiple-bond and one-bond heteronuclear J-couplings to the aromatic carbon C6 for pyrimidines ((3)J(H1',C6) and (1)J(H6,C6)) or C8 for purines ((3)J(H1',C8) and (1)J(H8,C8)). The techniques are demonstrated in the duplex [d(CGCGAATTCGCG)](2) and the dimeric G-quadruplex [d(GGGTTCAGG)](2) at natural abundance.     

Fluorine–proton correlation from isolated trifluoromethyl groups using unresolved J‐couplings

Fluorine‐containing compounds are rare in biological systems, so fluorine NMR spectroscopy can selectively detect and quantify fluorinated xenobiotics in crude biological extracts. The high sensitivity of fluorine NMR allows the detection of compounds containing isolated trifluoromethyl groups at nanogramme levels. However, it only provides limited structural information about trifluoromethyl‐containing compounds owing to the difficulty of interpreting fluorine chemical shifts and the low sensitivity of HOESY experiments used to correlate fluorine nuclei with protons in the same compound. This paper demonstrates that long‐range fluorine–proton J‐couplings can be used to correlate isolated trifluoromethyl groups with nearby protons with significantly higher sensitivity than HOESY. Fluorine‐observe fluorine–proton HMQC can even give correlations when the fluorine–proton J‐couplings are less than the observed fluorine resonance linewidth, so it provides a useful alternative source of structural information about fluorinated xenobiotics. Copyright © 2012 John Wiley & Sons, Ltd.     

19F NMR transverse and longitudinal relaxation filter experiments for screening: a theoretical and experimental analysis

Ligand‐based ¹⁹F NMR screening represents an efficient approach for performing binding assays. The high sensitivity of the methodology to receptor binding allows the detection of weak affinity ligands. The observable NMR parameters that are typically used are the ¹⁹F transverse relaxation rate and isotropic chemical shift. However, there are few cases where the ¹⁹F longitudinal relaxation rate should also be used. A theoretical and experimental analysis of the ¹⁹F NMR transverse and longitudinal relaxation rates at different magnetic fields is presented along with proposed methods for improving the sensitivity and dynamic range of these experiments applied to fragment‐based screening. Copyright © 2016 John Wiley & Sons, Ltd.     

Technical and practical aspects of 19F NMR‐based screening: toward sensitive high‐throughput screening with rapid deconvolution

The technical and practical aspects of ¹⁹F NMR‐based screening against a macromolecular target are analyzed in detail. A novel method utilizing the relaxation of ¹⁹F homonuclear double quantum coherence is proposed for performing NMR‐based binding assays in a direct‐ or competition‐mode format. A combined strategy based on ¹⁹F NMR chemical shift prediction, 2D ¹⁹F NMR DOSY, and 2D ¹⁹F–¹H NMR long‐range COSY experiments is presented for the deconvolution of complex mixtures of fluorinated molecules generated by either addition of single compounds or by chemical synthesis. The approaches presented here allow the screening of complex mixtures, even in the case where the exact composition is not known, and the rapid identification of the binders contained in the mixtures. Copyright © 2012 John Wiley & Sons, Ltd.     

Using pure shift HSQC to characterize microgram samples of drug metabolites

Difficulties in isolating samples from complex biological matrices and sensitivity limitations have long stymied the utilization of heteronuclear 2D NMR for the characterization of drug metabolites. Small diameter cryogenic NMR probes have largely ameliorated sensitivity limitations and the recently reported pure shift HSQC 2D NMR pulse sequence offers a further and marked improvement in both resolution and sensitivity. Using a 7.4 μg sample of the commercially available metabolite 3-hydroxy carbamazepine dissolved in 30 μL of deuterated solvent and a 600 MHz NMR equipped with a 1.7 mm cryogenic NMR probe, it was possible to acquire high signal-to-noise pure shift HSQC data in just over 30 min. A conventional HSQC spectrum acquired with identical parameters had approximately half the signal-to-noise of the pure shift HSQC spectrum. Collapsing the vicinal homonuclear couplings in the pure shift HSQC spectrum also significantly improves resolution. A practical, real world application of the technique is illustrated with the chromatographically isolated metabolite 3-hydroxy amiodarone from incubation with CYP2J2 recombinant enzyme. High quality pure shift HSQC data were recorded in slightly over 14 h for a 3 μg sample of the metabolite.     

NMR-based characterization of a novel yellow chlorophyll catabolite, Ed-YCC,isolated from Egeria densa

A novel yellow chlorophyll catabolite, Ed-YCC, was isolated from leaves detached from Egeria densa shoots, in which chlorophyll degradation and anthocyanin synthesis were induced in 0.1 M fructose solution under light illumination as a plant senescence process, a model of autumnal leaf coloration. Structure elucidation was accomplished by various NMR techniques including 2D-INADEQUATE.     

Pure In‐Phase Heteronuclear Correlation NMR Experiments

A general NMR approach to provide pure in‐phase (PIP) multiplets in heteronuclear correlation experiments is described. The implementation of a zero‐quantum filter efficiently suppresses any unwanted anti‐phase contributions that usually distort the multiplet pattern of cross‐peaks and can hamper their analysis. The clean pattern obtained in PIP‐HSQMBC experiments is suitable for a direct extraction of coupling constants in resolved signals, for a peak‐fitting process from a reference signal, and for the application of the IPAP technique in non‐resolved multiplets.