Janocchio--a Java applet for viewing 3D structures and calculating NMR couplings and NOEs

We present a Java applet, based on the open source Jmol program, which allows the calculation of coupling constants and NOEs from a three-dimensional structure. The program has all the viewing features of Jmol, but adds the capability to calculate both H-H and H-C 3-bond couplings constants. In the case of H--H couplings, the Altona equation is used to perform this. The program also calculates NOEs using the full relaxation matrix approach. All these calculations are driven from a simple point and click interface. The program can calculate values for multi-structure files, and can produce input files for the conformational fitting program NAMFIS.     

利用二维核磁共振方法研究取代茚基金属钛、锆配合物 的空间结构

通过^1H-^1HTOCSY和^1H-^1HNOESY谱对一系列新型结构的取代茚基钛、锆配合物进行了结构上的解析，并由此发现夹心结构的锆配合物中，两个茚环(或茚环和茂环)以及茚环上的取代基之间存在核的Overhauser效应，这对于茚环相对空间结构的判断提供了有效的证据。     

Resolving overlap in two-dimensional NMR spectra: nuclear Overhauser effects in a polysaccharide

Overlapping resonances in the two-dimensional nuclear Overhauser (NOESY) spectrum of the O-antigenic polysaccharide from Escherichia coli O147 have been resolved by recording a tilted projection of a three-dimensional NOESY-HSQC spectrum, where the carbon-13 and proton evolutions are linked together. Through the introduction of small contributions from the appropriate carbon-13 shifts, a cluster of five unresolved proton peaks is separated into its components without the need to perform the full three-dimensional measurement, a time saving of at least an order of magnitude.     

Carbon-fluorine two-dimensional NMR correlation spectra

Direct detection heteronuclear correlation (HETCOR) ¹³C{¹⁹F} and indirect detection gHMQC and gHSQC ¹⁹F{¹³C} two-dimensional correlation spectra have been compared for 1,3-perfluoro dimethylcyclohexane. Correlations to the geminally non-equivalent fluorine atoms in the CF₂ groups are more difficult to unambiguously observe using gHMQC or HETCOR in this typical cyclic fluorochemical in which ²J_FF ∼ > ¹J_CF, but they are readily observed and assigned in the gHSQC experiment. Excellent 2D gHSQC ¹⁹F{¹³C} correlation spectra have also been obtained on H(CF₂)₄CH₂OH without proton decoupling, although half of the correlations within the several FH multiplets have zero intensity.     

A Java applet for multiple linked visualization of protein structure and sequence

The amount of biological data available from experimental techniques is huge, and rapidly expanding. The ability to make sense of this vast amount of data requires that we make correlations between distinct biological disciplines using visualization techniques to highlight the critical information. This article describes the visualization techniques of dynamic data brushing, view context maintenance, fisheye sequence view, and a magic lens that have been developed to display protein structure and sequence information.     

Everything you wanted to know about phase and reference frequency in one- and two-dimensional NMR spectroscopy

The fundamental concept of phase discussed in this tutorial aimed at providing students with an explanation of the delays and processing parameters they may find in nuclear magnetic resonance (NMR) pulse programs. We consider the phase of radio-frequency pulses, receiver, and magnetization and how all these parameters are related to phases and offsets of signals in spectra. The impact of the off-resonance effect on the phase of the magnetization is discussed before presenting an overview of how adjustment of the time reference of the free induction decay avoids first-order correction of the phase of spectra. The main objective of this tutorial is to show how the relative phase of a pulse and the receiver can be used to change the reference frequency along direct and indirect dimensions of NMR experiments. Unusual of phase incrementation with non-90° angles will be illustrated on one- and two-dimensional NMR spectra.     

Microstructure elucidation of poly(epichlorohydrin) modified with thiol compounds using one- and two-dimensional NMR spectroscopy

Poly(epichlorohydrin) has been modified chemically using aromatic and aliphatic thiol compounds. The NMR results show that using both aromatic and aliphatic thiols, one achieves degrees of modification of up to 90% without any elimination side reaction. As a consequence no degradative chain-scission takes place. A microstructural analysis of the modified polymers has been carried out by ¹³C NMR, ¹H NMR and ¹³C DEPT spectroscopy. Additionally, 2D heteronuclear correlated spectroscopy (HMQC and HMBC) were used in order to determine the chemical shifts of quaternary carbons.     

Characterization of tri-o-methylcellulose by one- and two-dimensional NMR methods

Tri-O-methylcellulose was prepared from partially O-methylated cellulose and its chemical shifts (¹H and ¹³C), and proton coupling constants were assigned using the following NMR methods: (1) One-dimensional ¹H and ¹³C spectra of the title compound were used to assign functional groups and to compare with literature data; (2) double quantum filtered proton–proton correlation spectroscopy (¹H, ¹H DQF-COSY) was used to assign the chemical shifts of the network of 7 protons in the anhydroglucose portion of the repeat unit; (3) the heteronuclear single-quantum coherence (HSQC) spectrum was used to establish connectivities between the bonded protons and carbons; (4) the heteronuclear multiple-bond correlation (HMBC) spectrum was used to connect the hydrogens of the methyl ethers to their respective sugar carbons; (5) the combination of HSQC and HMBC spectra was used to assign the ¹³C shifts of the methyl ethers; (6) all spectra were used in combination to verify the assigned chemical shifts; (7) first-order proton coupling constants data (J_H,H in Hz) were obtained from the resolution-enhanced proton spectra. The NMR spectra of tri-O-methylcellulose and other cellulose ethers do not resemble the spectra of similarly substituted cellobioses. Although the ¹H and ¹³C shifts and coupling constants of 2,3,6-tri-O-methylcellulose closely resemble those of methyl tetra-O-methyl-β-D -glucoside, there are differences with regard to the chemical shifts and the order of appearances of the resonating nuclei of the methyl ether appendages and the proton at position 4 in the pyranose ring. H4 in tri-O-methylcellulose is deshielded by the acetal system comprising the β-1→4 linkage, and it resonates downfield. H4 in the permethylated glucoside is not as deshielded by the equitorial O-methyl group at C4, and it resonates upfield. The order of appearance of the ¹H and ¹³C resonances in the spectra of the tri-O-methylcellulose repeat unit (from upfield to downfield) are H2 < H3 < H5 < H6a < H3a < H2a < pro R H6B < H4 < pro S H6A ≪ H1 and C6a < C3a < C2a < C6 < C5 < C4 < C2 < C3 ≪ C1, respectively. Close examination of the pyranose ring coupling constants of the repeat unit in tri-O-methylcellulose supports the ⁴C₁ arrangement of the glucopyranose ring. Examination of the proton coupling constants about the C5-C6 bond (J_5,6A and J_5,6B) in the nuclear Overhauser effect difference spectra revealed that the C6 O-methyl group is predominantly in the gauche gauche conformation about the C5-C6 bond for the polymer in solution. © 1999 John Wiley & Sons, Inc.* J Polym Sci A: Polym Chem 37: 4019–4032, 1999     

Complete NMR spectral assignments of two lactucin-type sesquiterpene lactone glycosides from Picris conyzoides

Complete (1)H and (13)C NMR signal assignments of two lactucin-type sesquiterpene lactone glycosides, derivatives of 11β,13-dihydrolactucin, isolated from roots of Picris conyzoides, were achieved by one- and two-dimensional NMR experiments, allowing the correction of previously published data for cichorioside B and the structure elucidation of its new ester with 3-hydroxy-2-methylpropanoic acid. In addition, seven known sesquiterpene lactones and three phenolic compounds were isolated from the plant material.     

One‐dimensional TOCSY 1H NMR experiments on adducts of amino acid esters with cobalt(III) tetramethylchiroporphyrin. Prospects for the analysis of amino acid mixtures

Cobalt(III) tetramethylchiroporphyrin, CoCl(TMCP), is a useful chiral shift reagent for structure attribution, absolute configuration assignment and enantiomeric excess determination of amino acid methyl esters by ¹H NMR spectroscopy. However, it has two axial sites available for amine coordination, a structural feature which generates n(n + 1)/2 diastereomeric species and n² distinct spin systems from a mixture of n amino ester enantiomers, making the analysis of complex amino acid samples exceedingly difficult by classical 1‐D or 2‐D NMR methods when n > 3. The 1‐D TOCSY experiment is shown to be a powerful tool for the selective excitation and detection of every single component of a mixture of four amino acid methyl esters bound to CoCl(TMCP): those of(S)‐Leu, (S)‐Asp, (R)‐Asp and (S)‐Glu, for example. The potential utility of this methodology for the determination of amino acid enantiomers in carbonaceous meteorites or other extraterrestrial samples is suggested. Copyright © 2002 John Wiley & Sons, Ltd.     

Characterization of signals in the solution 1H NMR spectrum of poly(isobutylene‐co‐p‐methylstyrene) and their utility

Poly(isobutylene‐co‐p‐methylstyrene) is an important precursor to Exxpro™ elastomers. A previous report detailed the characterization of both the proton and the carbon NMR spectra of the copolymer. 1 However, several resonances in the proton NMR spectrum of the copolymer were not assigned. Specifically, the proton methine resonance of the BSB triad sequence is now identified and used to calculate BSB triad contribution to the copolymer microstructure. This report describes the assignment of this resonance and other resonances associated with microstructural sequence distribution around p‐methylstyrene. The proton NMR signals of interest resonate at 2.8 ppm and 2.5 ppm in a typical spectrum for poly(isobutylene‐co‐p‐methylstyrene). The nature of these resonances were determined by preparation and characterization of specifically deuterated poly(isobutylene‐co‐p‐methylstyrene)s employing both one and two dimensional NMR techniques. The 2.8 ppm signal is assigned as the methine proton of a p‐methylstyrene incorporated between two isobutylene units (the BSB triad). The signal at 2.5 ppm is assigned to the meso‐BSS triad. Determination of these resonances allows for rapid evaluation of isolated p‐methylstyrene units (BSB triads) present in the copolymer using only ¹H NMR. The utility of this technique is demonstrated by comparing BSB triad values determined by ¹H and ¹³C NMR analysis. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1680–1686, 2000     

1H and 13C NMR spectra of N-substituted morpholines

(1)H and (13)C NMR data for N-substituted morpholines 1-20 were measured using 1D (DEPT, 1D NOE difference) and 2D NMR spectroscopic methods including (1)H-(1)H COSY, long-range (1)H-(1)H COSY, NOESY, gHMBC and gHMQC experiments. At room temperature the (1)H NMR spectra of protonated compounds 2 and 9 show the chair conformation for the morpholine ring. Spin-spin coupling constants were deduced from the resolution-enhanced proton spectra.     

jsNMR: an embedded platform‐independent NMR spectrum viewer

jsNMR is a lightweight NMR spectrum viewer written in JavaScript/HyperText Markup Language (HTML), which provides a cross‐platform spectrum visualizer that runs on all computer architectures including mobile devices. Experimental (and simulated) datasets are easily opened in jsNMR by (i) drag and drop on a jsNMR browser window, (ii) by preparing a jsNMR file from the jsNMR web site, or (iii) by mailing the raw data to the jsNMR web portal. jsNMR embeds the original data in the HTML file, so a jsNMR file is a self‐transforming dataset that may be exported to various formats, e.g. comma‐separated values. The main applications of jsNMR are to provide easy access to NMR data without the need for dedicated software installed and to provide the possibility to visualize NMR spectra on web sites. Copyright © 2015 John Wiley & Sons, Ltd.     

17O NMR spectra of alpha-diesters

17O NMR spectra of title compounds were measured at natural abundance in acetonitrile solutions. Intercarbonyl dihedral angles have been estimated by molecular mechanics, which show invariance except in one case. Because of this invariance, contrary to other alpha-dicarbonyl compounds, a correlation between chemical shifts and dihedral intercarbonyl angles could not be developed. Spectroscopic and computational results allowed us to evaluate other conformational features.     

Poly(vinylpyrrolidone): Configurational assignments by one- and two-dimensional NMR spectroscopy

The configurational assignment of poly(vinylpyrrolidone) (PVP) prepared by peroxide-initiated solution polymerization was studied by the combination of one- and two-dimensional NMR spectroscopy. The broad and overlapping ¹H-NMR and ¹³C{¹H}-NMR spectra of PVP were assigned to the configurational triad, pentad (CH, ²CH₂, ³CH₂, and ⁴CH₂ regions), and tetrad (β-CH₂ region) sequences. The configurational assignments of the various carbon resonances were confirmed with the help of two-dimensional experiments such as heteronuclear single quantum correlation (HSQC), heteronuclear single quantum correlation–total correlation spectroscopy (2-D HSQC–TOCSY). The various geminal and vicinal couplings within the configurational sequences were assigned with the help of total correlation spectroscopy (TOCSY low mixing time). The propagation pathway was studied using the ¹³C{¹H}-NMR (carbonyl carbon) and ¹⁵N{¹H}-NMR spectra. The ¹⁵N{¹H} resonance signals were assigned to pentad-level configurational sequences. The results obtained by the analysis of the area under the resonance signals confirmed that poly(vinylpyrrolidone) obeys Bernoullian statistics. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3922–3928, 1999     

Multiplicity-edited broadband HMBC NMR spectra

A new, edited HMBC experiment is introduced that leads to two subspectra according to the number of protons attached to 13C nuclei being even or odd, i.e. one subspectrum with C + CH2 and another with CH + CH3. This experiment can be useful for resolving spectral overlap among the typically large number of peaks in HMBC spectra. It is implemented in a broadband version similar to broadband HMBC and demonstrated on prednisolone [(11beta)-11,17,21-trihydroxypregna-1,4-diene-3,20-dione].     

NMR spectra and isotope analysis of hexaethyldistannane

The ¹³C-{¹H} and ¹¹⁹Sn-{¹H} NMR spectra of hexaethyldistannane were measured and analyzed using an iteration program for the calculation of the complete line shape with correction of a residual inhomogeneity of the magnetic field and phase distortions. Signals of 22 isotopomers containing magnetic isotopes of tin and carbon in different pairwise and triple combinations were identified, and their spectral parameters were determined. The content of isotopes ¹¹⁹Sn, ¹¹⁷Sn, and ¹¹⁵Sn in the molecule was determined with a high accuracy sufficient for the study of isotope effects in chemical reactions.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2102–2104, October, 2004.     

High-resolution solid-state 73Ge NMR spectra of hexacoordinated germanium compounds

High-resolution solid-state magic angle spinning 73Ge NMR spectra of hexavalent germanium compounds, i.e. diiodogermylene (1a) and bis(1-pyrrolyl)(meso-tetraphenylporphyrinato)germanium (3a), were determined. To the best of our knowledge, this is the first example of high-resolution solid-state 73Ge NMR spectra of hexacoordinated germanium nuclei. The symmetry requirement for observation of high-resolution solid-state 73Ge NMR spectra is discussed.