Evaluation of double-tuned single-sided planar microcoils for the analysis of small 13C enriched biological samples using 1H-13C 2D heteronuclear correlation NMR spectroscopy

Microcoils provide a cost-effective approach to improve detection limits for mass-limited samples. Single-sided planar microcoils are advantageous in comparison to volume coils, in that the sample can simply be placed on top. However, the considerable drawback is that the RF field that is produced by the coil decreases with distance from the coil surface, which potentially limits more complex multi-pulse NMR pulse sequences. Unfortunately, ¹H NMR alone is not very informative for intact biological samples due to line broadening caused by magnetic susceptibility distortions, and ¹H-¹³C 2D NMR correlations are required to provide the additional spectral dispersion for metabolic assignments in vivo or in situ. To our knowledge, double-tuned single-sided microcoils have not been applied for the 2D ¹H-¹³C analysis of intact ¹³C enriched biological samples. Questions include the following: Can ¹H-¹³C 2D NMR be performed on single-sided planar microcoils? If so, do they still hold sensitivity advantages over conventional 5 mm NMR technology for mass limited samples? Here, 2D ¹H-¹³C HSQC, HMQC, and HETCOR variants were compared and then applied to ¹³C enriched broccoli seeds and Daphnia magna (water fleas). Compared to 5 mm NMR probes, the microcoils showed a sixfold improvement in mass sensitivity (albeit only for a small localized region) and allowed for the identification of metabolites in a single intact D. magna for the first time. Single-sided planar microcoils show practical benefit for ¹H-¹³C NMR of intact biological samples, if localized information within ~0.7 mm of the 1 mm I.D. planar microcoil surface is of specific interest.     

Reaction of the Heteronuclear Cluster RuOs3(μ − H)2(CO)13 with Diphenylacetylene: An Alkyne Bound to a Tetrahedral Metal Core

Reaction of the heteronuclear cluster RuOs₃(μ−H)₂(CO)₁₃, 1, with diphenylacetylene afforded the tetrahedral cluster RuOs₃(μ−H)₂(μ₃,η¹:η²:η¹−C₂Ph₂)(CO)₁₁, 2, in good yield. Spectroscopic evidence suggests that 2 exist as two isomers in solution.     

New heteropolynuclear metallomesogens: copper(II), palladium(II), nickel(II) and oxovanadium(IV) chelates with [3]ferrocenophane‐containing Schiff's base and β‐aminovinylketone

New mesogenic heteropolynuclear complexes of Cu(II), Pd(II), Ni(II) and VO(IV) with the [3]ferrocenophane‐containing Schiff's base, and Cu(II) and Pd(II) complexes with the [3]ferrocenophane‐containing β‐aminovinylketone have been synthesised. The obtained heterometallic mesogenes are identified by elemental analysis, proton nuclear magnetic resonance, infrared and ultraviolet–visible spectroscopies. Liquid crystalline properties are studied by thermal polarising optical microscopy and differential scanning calorimetry techniques. Both ligands and heteropolynuclear complexes exhibit thermotropic nematic and smectic C mesophases in various temperature ranges except for the Ni(II) complex. Mesomorphism of the prepared complexes is correlated with the geometry of their central chelate core. Considerably broader mesophases and lower transition temperatures are achieved in the synthesised metallomesogens by using the alkylidene‐bridged ferrocene as a building unit.     

Determination of glucan phosphorylation using heteronuclear 1H,13C double and 1H,13C,31P triple‐resonance NMR spectra

Phosphorylation and dephosphorylation of starch and glycogen are important for their physicochemical properties and also their physiological functions. It is therefore desirable to reliably determine the phosphorylation sites. Heteronuclear multidimensional NMR‐spectroscopy is in principle a straightforward analytical approach even for complex carbohydrate molecules. With heterogeneous samples from natural sources, however, the task becomes more difficult because a full assignment of the resonances of the carbohydrates is impossible to obtain. Here, we show that the combination of heteronuclear ¹H,¹³C and ¹H,¹³C,³¹P techniques and information derived from spectra of a set of reference compounds can lead to an unambiguous determination of the phosphorylation sites even in heterogeneous samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Adiabatic Low‐Pass J Filters for Artifact Suppression in Heteronuclear NMR

NMR artifact purging: Modern NMR experiments depend on efficient coherence transfer pathways for their sensitivity and on suppression of undesired pathways leading to artifacts for their spectral clarity. A novel robust adiabatic element suppresses hard‐to‐get‐at artifacts (see picture).

     

Synthesis and NMR spectroscopic assignment of chlorinated benzimidazole-2-thione derivatives

The benzimidazole-2-thione scaffold is present in many drugs encompassing various therapeutic areas. Due to the broad spectrum of bioactivities it also represents an important starting point in drug discovery campaigns, especially those based on fragment-based design. Despite simple structures the tautomerism and regioisomerism of substituted benzimidazole-2-thiones makes unambiguous structural analysis difficult. Tautomeric duplicates are present in commercial libraries resulting in two tautomers being sold as different products. To showcase an example of appropriate structural determination, we synthesized and characterized a set of benzimidazole-2-thiones with different positions of a chlorine atom on the ring. Using NOESY and ¹³C NMR spectroscopy, we determined that the thione tautomer predominates in the thione-thiol equilibrium. Furthermore, NOESY and HMBC experiments confirmed the position of the substituents on the benzimidazole-2-thione ring.     

Long-range JCH heteronuclear coupling constants in cyclopentane derivatives. Part II

Here we report the detailed measurement of long-range heteronuclear spin-spin coupling constants, especially 2, 3JCH spin-spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G-BIRDR, X-CPMG-HSQMBC and the 2D-coupled gHSQC {1H-13C} experiment     

Crystal Structure and Magnetic Property of Heteronuclear Copper—Lanthanum Carboxylate Complex

ＥｘｐｅｒｉｍｅｎｔａｌＳｙｎｔｈｅｓｉｓａｎｄｅｌｅｍｅｎｔａｌａｎａｌｙｓｉｓＬａＬ3·2Ｈ2 Ｏ (86 0ｍｇ ,2 0ｍｍｏｌ ;ＨＬ =ＣＨ2 Ｃ(ＣＨ3) ＣＯＯＨ)ａｎｄＣｕ(ＮＯ3) 2 ·3Ｈ2 Ｏ (2 4 2ｍｇ ,1 0ｍｍｏｌ)ｗｅｒｅｄｉｓｓｏｌｖｅｄｉｎｔｏ 2 0ｍＬｏｆＨ2 ＯａｎｄａｄｊｕｓｔｅｄｔｏｐＨ 4 1ｗｉｔｈＨＬ (0 1ｍｍｏｌ/ｃｍ3) .Ａｎｅｔｈａｎｏｌｓｏｌｕｔｉｏｎｏｆ 1,10 ｐｈｅｎａｎｔｈｒｏｌｉｎｅ (2 0 0ｍｇ ,1 0ｍｍｏｌ)ｗａｓａｄｄｅｄｉｎｔｏｔｈｅｍｉｘｅｄｓｏｌｕｔｉｏｎｗｉｔｈｓｔｉ…     

Synthesis, Spectroscopic, Thermal, and Structural Characterization of Complex Ferrocyanides KLnFe(II)(CN)6 ⋅ 3.5H2O (Ln = Gd-Ho)

Four new mixed metal cyanides of lanthanides (Ln = Gd-Ho) and iron with the general formula KLnFe(CN)₆ 3.5H₂O have been synthesized and characterized by chemical, infrared and thermal techniques. X-ray diffraction (XRD) analysis have shown that all the complexes have orthorhombic unit cells with space group Cmcm. Cyanide bridges link to nine coordinated LnN₆(H₂O)₃ groups to the octahedral FeC₆ groups. Cavities within the structure are occupied by uncoordinated zeolitic water molecules and potassium ions. The potassium cations form a pseudo-hexagonal 2D sublattice. Thermal decomposition involves two consecutive steps: dehydration and inorganic residue evolution to ternary oxides.