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Two‐dimensional J‐resolved (Jres) NMR experiments offer a simple, user‐friendly spectral representation where the information of coupling constants and chemical shifts are separated into two orthogonal frequency axis. Since its initial proposal 40 years ago, Jres has been the focus of considerable interest both in improving the basic pulse sequence and in its successful application to a wide range of studies. Here, the latest developments in the design of novel Jres pulse schemes are reviewed, mainly focusing on obtaining pure absorption lineshapes, minimizing strong coupling artifacts, and also optimizing sensitivity and experimental measurements. A discussion of several Jres versions for the accurate measurement of a different number of homonuclear (JHH) and heteronuclear (JCH) coupling constants is presented, accompanied by some illustrative examples. [ABSTRACT FROM AUTHOR]

Homonuclear 13C-13C couplings at natural abundance can be measured using the J-modulated Adequate DoublE QUAntumTransfer Experiment (ADEQUATE) experiment. To somewhat ameliorate F1 digitization requirements, a scaling factor was incorporated into the original pulse sequence. Non-uniform sampling provides an obvious avenue to further facilitate the acquisition of 1 JCC and n JCC homonuclear coupling constant data. We introduce homonuclear decoupling (HD) analogous to that described for the 1,1-HD-ADEQUATE and 1,n-HD-ADEQUATE experiments and evaluate the combination of non-uniform sampling and HD on the acquisition of both 1 JCC and n JCC homonuclear 13C-13C coupling constants using ibuprofen as a model compound. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In recent years, a great interest in the development of new broadband 1H homonuclear decoupled techniques providing simplified JHH multiplet patterns has emerged again in the field of small molecule NMR. The resulting highly resolved 1H NMR spectra display resonances as collapsed singlets, therefore minimizing signal overlap and expediting spectral analysis. This review aims at presenting the most recent advances in pure shift NMR spectroscopy, with a particular emphasis to the Zangger-Sterk experiment. A detailed discussion about the most relevant practical aspects in terms of pulse sequence design, selectivity, sensitivity, spectral resolution and performance is provided. Finally, the implementation of the different reported strategies into traditional 1D and 2D NMR experiments is described while several practical applications are also reviewed. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The presence of a highly abundant passive nucleus (Z = 19 F or 31P) allows the simultaneous determination of the magnitude and the sign of up to three different heteronuclear coupling constants from each individual cross-peak observed in a 2D 1H-X selHSQMBC spectrum. Whereas J(HZ) and J(XZ) coupling constants are measured from E.COSY multiplet patterns, J(XH) is independently extracted from the complementary IPAP pattern generated along the detected F2 dimension. The incorporation of an extended TOCSY transfer allows the extraction of a complete set of all these heteronuclear coupling constants and their signs for an entire 1H subspin system. 1H-X/1H-Y time-shared versions are also proposed for the simultaneous measurement of five different couplings ( J(XH), J(YH), J(XZ), J(YZ), and J(ZH)) for multiple signals in a single NMR experiment. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A rapid NMR data acquisition strategy in terms of enhanced resolution per time unit for the simple and efficient determination of multiple coupling constants is described. The use of 13C spectral aliasing combined by broadband 1H homodecoupling allows accurate measurements from ultra high resolved 2D HSQC cross-peaks. [ABSTRACT FROM AUTHOR]

NMR enantiodifferentiation studies are greatly improved by the simultaneous determination of ¹H and 13C chemical shift differences through the analysis of highly resolved cross-peaks in spectral aliased pure shift (SAPS) HSQC spectra. [ABSTRACT FROM AUTHOR]

Abstract: Simple modifications of the sensitivity-improved HSQC–TOCSY pulse sequence are proposed for the easy determination of the sign and the magnitude of homonuclear and heteronuclear coupling constants. Whereas in well-resolved regions, a clean two-component E.COSY-like pattern allows a direct measurement from a single 2D spectrum, separate acquisition of equivalent single-component TROSY/anti-TROSY spectra becomes highly interesting when spectral crowding complicates the spectral analysis. It is also demonstrated that an additional restricted planar mixing element after the isotropic TOCSY process completely retains all spin-editing features and permits the accurate measurement of the sign and the size of the corresponding homonuclear proton–proton coupling constants. Among others, the proposed techniques are particularly suited for molecules presenting a great number of CH and NH spin systems. Examples and practical details of the implementation of these techniques on standard carbohydrates and peptides at 13C and 15N natural abundance are provided. [Copyright &y& Elsevier]

A suite of multiple-purpose sensitivity-enhanced 2D correlation NMR experiments based on heteronuclear J-cross polarization (HCP) techniques are introduced for isotropic liquid samples. Several pulse sequences using an adaptable heteronuclear TOCSY mixing building block are proposed for different types of effective coherence-order-selective (COS) heteronuclear coherence-transfer mechanisms. They are based on the anisotropic behaviour of the involved HCP process that is easily described and analysed in terms of cartesian product-operator formalism. A number of different versions are given for in-phase to in-phase (II-COS: S- \to I-), in-phase to anti-phase (IA-COS: S- \to 2I-Sz), in-phase to spin-state-selective (IS3-COS: S- \to 2I-Sα /β), anti-phase to in-phase (AI-COS: 2IzS- \to I-), anti-phase to anti-phase (AA-COS: 2IzS- \to 2I-Sz), anti-phase to spin-state-selective (AS3-COS: 2IzS- \to 2I-Sα /β) and spin-state-selective to spin-state-selective (S3S3-COS: 2Iα /βS- \to 2I-Sα /β ) coherence transfers. The combination of the echo/anti-echo approach, heteronuclear gradient echoes and the preservation of equivalent pathways (PEP) methodology affords a general approach to obtain sensitivity-enhanced pure-absorption 2D spectra that can be used as interesting alternatives to conventional pulse-interrupted free-precession INEPT-based pulse schemes, such as HSQC-type and TROSY-type experiments. [ABSTRACT FROM AUTHOR]

The utility of 13C NMR spectroscopy for the differentiation of enantiomers using chiral solvating agents (CSA) is stated. Three examples involving the enantiodifferentiation of a drug, a metabolite and a reactant in aqueous and organic solutions have been chosen to show it. The intrinsic high dispersion of 13C nucleus, as well as the singlet nature of the signals in standard experiments makes 13C NMR experiments a powerful alternative or complement to 1H NMR experiments; specially, when studying pure compounds with complex proton spectra or mixtures of compounds, as in chiral metabonomics, where severe overlapping exists in proton spectrum. To evaluate and compare the quality of the enantioresolution of a NMR signal we introduce the enantiodifferentiation quotient, E, that considers the complexity of 1H multiplets (and in general the width) of the original signal. It has been observed that the error in the measurement of the enantiomeric molar ratio can be related to the E value. The sensitivity and experimental time of a wide range of chiral analyte concentrations were also assessed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fast measurement of heteronuclear coupling constants by 1D NMR. [•] Simultaneous determination of the sign and the magnitude of coupling constants. [•] Direct analysis of 1D multiplets showing Up&Down or Left&Right coupling pattern. [Copyright &y& Elsevier]

Abstract: A new NMR approach is proposed for the measurement of long-range heteronuclear coupling constants ( n JXH , n >1) in natural abundance molecules. Two complementary in-phase (IP) and anti-phase (AP) data are separately recorded from a modified HSQMBC experiment and then added/subtracted to provide spin-state-selective α/β–HSQMBC spectra. The magnitude of n JXH can be directly determined by simple analysis of the relative displacement between α- and β-cross-peaks. The robustness of this IPAP–HSQMBC experiment is evaluated experimentally and by simulation using a variety of different conditions. Important aspects such as signal intensity dependence and presence of unwanted cross-talk effects are discussed and examples on the measurement of small proton–carbon ( n JCH ) and proton–nitrogen ( n JNH ) coupling constants are provided. [ABSTRACT FROM AUTHOR]

This study presents a simple method for measuring long-range heteronuclear coupling constants between protons and proton-bearing carbons. The approach involves recording two conventional 1D-TOCSY experiments in which the offset of the selective proton pulse is set on the low- and high-frequency 13C satellites of an isolated proton signal, Hi. Long-range heteronuclear coupling values between the 13Ci bonded to Hi and the protons Hj,k…n that belong to the same spin system were easily determined from the relative displacement of the relayed Hj,k…n signals in the satellite-selective TOCSY spectra. The sense of the displacement indicated the sign of the coupling constants. [ABSTRACT FROM AUTHOR]

Covariance processing is a versatile processing tool to generate synthetic NMR spectral representations without the need to acquire time-consuming experimental datasets. Here we show that even experimentally prohibited NMR spectra can be reconstructed by introducing key features of a reference 1D CH n -edited spectrum into standard 2D spectra. This general procedure is illustrated with the calculation of experimentally infeasible multiplicity-edited pure-shift NMR spectra of some very popular homonuclear (ME-psCOSY and ME-psTOCSY) and heteronuclear (ME-psHSQC-TOCSY and ME-psHMBC) experiments. [ABSTRACT FROM AUTHOR]

Abstract: The novel tetradentate ligand 1,4-bis(4-(4′-methyl)-2,2′-bipyridyl)-2,3-diaza-1,3-butadiene (BBDB) was synthesized and characterized by spectroscopic techniques. New complexes of Re and Ru of formulae: [Re(BBDB)(CO)3(Cl)], [(CH3CN)(CO)3Re(μ-BBDB)Re–(CO)3(CH3CN)]2+, [(bpy)2Ru-(μ-BBDB)Ru(bpy)2]4+, [(NH3)4Ru(μ-BBDB)–Ru(NH3)4]4+ (bpy=2,2′-bipyridine) and complexes of Ru with 4-Me-4′-CO2H-bpy (=4-methyl-4′-carboxylic acid-2,2′-bipyridine) – the hydrolyzed derivative of BBDB – of formulae: [(Ru(4-Me-4′-CO2H-bpy)(bpy)2]2+ and [Ru(4-Me-4′-CO2H-bpy)(CN)4]2− were prepared and characterized by spectroscopic, electrochemical and computational techniques. The disclosed enhanced electronic coupling in the mixed-valent complex with ruthenium ammines can be explained by the electronic delocalization imposed by the C N N C backbone. DFT and TD-DFT calculations can predict the optical properties and electronic structures of the reported complexes and comparisons with calculations performed on previously reported complexes with 4-pyridinaldazine can account for their photophysical behaviour. [Copyright &y& Elsevier]

The synthesis of a family of new Ru complexes containing the meddional trpy ligand with general formula [RuII(l)- (D)(X)/1+(1 = 2,2':6',2"-terpyridine (trpy); D = 3,5-dimethyt-2-(2-pyridyl)pyrrolate (pyrpy), and 2-(1-Methyl-3-pyrazo- lyl)pyridine (pypz-Me); X = Cl, H2O) have been described. All complexes have been spectroscopically charactedzed in sotution through 1H NMR and UV-vis techniques, and the chloro complexes have also been characterized in the solid state through monocrystal X-ray diffraction analysis. The pyrpy ligand undergoes an oxidation at the 3-position of the pyrrolate ring during the formation of the corresponding aqua complex thus generating the analogous compound containing the oxidized ligand pyrpy-O. The redox properties of all complexes have also been studied by means of CV and OPV techniques, where both geometrical (trans vs cis) and electronic (neutral vs anionic) effects can be unveiled and rationalized. Finally, the reactivity of the whole set of Ru-OH2 complexes has been tested with regard to the epoxidation of different alkenes with Phl(OAc)2. In all cases good selectivities and conversions were obtained. Furthermore, total retention of the initial cis configuration was achieved when using these catalysts to epoxidize cis-β-methylstyrene. [ABSTRACT FROM AUTHOR]

Abstract: New coordination compounds of formulae: [Ru(trpy)(bpy)(4,4′-azpy)]2+, 1, [Ru(tpm)(bpy)(4,4′-azpy)]2+, 2, [(trpy)(bpy)Ru(4,4′-azpy)Ru(NH3)5]4+, 3, and [(trpy)(bpy)Ru(4,4′-azpy)Ru(bpy)(trpy)]4+, 5, with trpy=2,2′:6′,2″-terpyridine, tpm=tris(1-pyrazolyl)methane), bpy=2,2′-bipyridine and 4,4′-azpy=4,4′-azobis(pyridine), have been synthesized as salts and characterized by spectroscopic and electrochemical techniques. The structure of the cation [Ru(trpy)(bpy)(4,4′-azpy)]2+ has been determined by X-ray diffraction analysis, which reveals a trans-configuration of coordinated 4,4′-azpy and a packing structure that is based on extensive π-interactions within neighboring molecules. Upon controlled potential electrolysis of the dinuclear [RuII,RuII] complex 3, a stable [RuII, RuIII] mixed-valent species, 4, was detected. From spectral data and Gaussian deconvolution analysis of the intervalence transition in 4, a strong electronic interaction between both ruthenium centers is disclosed (H AB =550cm−1), pointing to possible applications of 4,4′-azpy as a conducting bridge in “molecular wires”. [Copyright &y& Elsevier]