Indirect detection of 31P,X connectivities with proton sensitivity: application of two‐dimensional 31P‐relayed 1H,X correlation spectroscopy

Experiments for ¹H‐detected heteronuclear ¹H,X correlation spectroscopy with ³¹P‐relayed coherence transfer are described which allow the indirect detection of δX and ⁿJ(X,P) even in the absence of a direct J(X,H) coupling. The use of these techniques for the assignments of ¹³C, ¹⁵N, and ¹⁸³W NMR data of organophosphorus compounds is demonstrated. Copyright © 2003 John Wiley & Sons, Ltd.     

Usage de l'algégbre de lie su(n) dans l'étude des systémes quantiques á n états. IV. Geometrie du domaine des vecteurs de cohérence

The density operator of an n level quantum system is known to be a positive semidefinite, hermitian operator of trace one. In a previous article we have established, through su(n) algebras, a formalism where density operators are built from coherence vectors in a n² ? 1 dimension, real, Euclidean space. The last two conditions are then automatically satisfied. Being positive semidefinite means a restriction to the domain of coherence vectors. In this article we clarify this domain and obtain several equivalent tests to know if a given vector is part of it.     

Theoretical and experimental study of the structure and stability of multiply Na-substituted glucose and 2,4,6-trihydroxyacetophenone derivatives

The equilibrium geometric parameters and the energetic and spectroscopic characteristics of low lying conformers for series of polyhydroxyl molecules and ions in which sodium atoms are successively substituted for the hydroxyl hydrogen atoms have been calculated by the density functional theory B3LYP method with the 6−31G* and 6−311+G** basis sets. The glucose derivatives [Glu − nH + nNa] and [Glu − nH + (n + 1)Na]⁺ (n = 1−5) and the 2,4,6-trihydroxyacetophenone derivatives [THAP − nH + nNa] and [THAP − nH + (n + 1)Na]⁺ (n = 1−4) have been considered. The affinities of the neutral [Glu − nH + nNa] and [THAP − nH + nNa] molecules for adding Na⁺ cations, as well as the energies of successive substitution of Na atoms for H atoms in the Glu and THAP molecules and the Glu⁺ and THAP⁺ ions in their reaction with sodium acetate molecules, have been estimated. Computations show that the first substitution of Na for H in ions is slightly exothermic and, presumably, can spontaneously occur under common conditions. Further substitutions are endothermic, but the required energy inputs are small. Therefore, successive substitutions for two, three, or more hydroxyl H atoms in the molecules and ions under consideration are possible at relatively low energy inputs. The computation results and conclusions are compared with the MALDI TOF mass spectral data for Na-substituted glucose and 2,4,6-trihydroxyacetophenone derivatives in the [glucose + CH₃COONa + THAP] system where, in addition to common Glu · Na⁺ and THAP · Na⁺ ion-molecular complexes, multiply substituted positive ions of the [Glu − nH + (n + 1)Na]⁺ (n = 1−4) and [THAP − nH + (n + 1)Na]⁺ (n = 1−3) type have been identified.     

HMBC‐1,1‐ADEQUATE via generalized indirect covariance: a high sensitivity alternative to n,1‐ADEQUATE

1,1‐ADEQUATE and the related long‐range 1,n‐ and n,1‐ADEQUATE variants were developed to provide an unequivocal means of establishing ²J_CH and the equivalent of ⁿJ_CH correlations where n = 3,4. Whereas the 1,1‐ and 1,n‐ADEQUATE experiments have two simultaneous evolution periods that refocus the chemical shift and afford net single quantum evolution for the carbon spins, the n,1‐variant has a single evolution period that leaves the carbon spin to be observed at the double quantum frequency. The n,1‐ADEQUATE experiment begins with an HMBC‐type ⁿJ_CH magnetization transfer, which leads to inherently lower sensitivity than the 1,1‐ and 1,n‐ADEQUATE experiments that begin with a ¹J_CH transfer. These attributes, in tandem, serve to render the n,1‐ADEQUATE experiment less generally applicable and more difficult to interpret than the 1,n‐ADEQUATE experiment, which can in principle afford the same structural information. Unsymmetrical and generalized indirect covariance processing methods can complement and enhance the structural information encoded in combinations of experiments e.g. HSQC‐1,1‐ or ?1,n‐ADEQUATE. Another benefit is that covariance processing methods offer the possibility of mathematically combining a higher sensitivity 2D NMR spectrum with for example 1,1‐ or 1,n‐ADEQUATE to improve access to the information content of lower sensitivity congeners. The covariance spectrum also provides a significant enhancement in the F₁ digital resolution. The combination of HMBC and 1,1‐ADEQUATE spectra is shown here using strychnine as a model compound to derive structural information inherent to an n,1‐ADEQUATE spectrum with higher sensitivity and in a more convenient to interpret single quantum presentation. Copyright © 2012 John Wiley & Sons, Ltd.     

ADEQUATE CR: 13C connectivity mapping in indirect detection mode with composite refocusing

We report a novel rare spin correlation experiment termed ADEQUATE with composite refocusing (CR), which is the ¹H‐detected version of 2D INADEQUATE CR. ADEQUATE CR begins with a polarization transfer from protons to the attached carbon, followed by ¹³C–¹³C double‐quantum (DQ) preparation. Unlike the ADEQUATE class of experiments, ¹³C DQ coherence is converted after evolution to single‐quantum single transitions (SQ‐STs) by CR. ¹³C SQ‐ST is then transferred back to the coupled protons by a coherence order selective reconversion. The present sequence produces partial transition selectivity in the ¹H dimension as does ¹H Indirect detected ¹³C Low‐Abundance Single‐transition correlation Spectroscopy (HICLASS), thereby mitigating the reduction in sensitivity enhancement because of the presence of homonuclear proton couplings. However, unlike HICLASS (which is an experiment that involves SQ‐TS evolution), no homonuclear zero quantum mixing is required on the ¹³C channel in the present experiment. Experimental results are demonstrated on a variety of samples, establishing the efficiency of the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.     

Efficient measurement of the sign and the magnitude of long‐range proton‐carbon coupling constants from a spin‐state‐selective HSQMBC‐COSY experiment

A spin state‐selective Heteronuclear Single‐Quantum Multiple‐Bond Connectivities (HSQMBC‐COSY) experiment is proposed to measure the sign and the magnitude of long‐range proton‐carbon coupling constants (ⁿJ(CH); n > 1) either for protonated or for non‐protonated carbons in small molecules. The simple substitution of the selective 180° ¹H pulse in the original selHSQMBC pulse scheme by a hard one allows the simultaneous evolution of both proton‐proton and proton‐carbon coupling constants during the refocusing period and enables a final COSY transfer between coupled protons. The successful implementation of the IPAP principle leads to separate mixed‐phase α/β cross‐peaks from which ⁿJ(CH) values can be easily measured by analyzing their relative frequency displacements in the detected dimension. Copyright © 2012 John Wiley & Sons, Ltd.     

Complete assignments of the 1H and 13C NMR spectra of five rearranged abietane diterpenoids

An NMR study of five highly functionalized and rearranged abietane diterpenoids is described. In addition to 1D NMR methods, including 1D NOESY spectra, 2D shift‐correlated experiments [¹H, ¹³C‐gHSQC‐¹J (C,H) and ¹H, ¹³C‐gHMBC‐ⁿJ (C,H) (n = 2 and 3)] were used for the complete and unambiguous ¹H and ¹³C chemical shift assignments of these substances. Copyright © 2002 John Wiley & Sons, Ltd.     

Complete assignments of the 1H and 13C NMR spectra of 15 limonoids

Unambiguous and complete assignments of ¹H and ¹³C NMR chemical shifts for 15 limonoids, eight of them found in natural sources and seven other synthetic derivatives, are presented. The assignments are based on 2D shift‐correlated [¹H,¹H‐COSY, ¹H,¹³C‐gHSQC‐¹J(C,H), ¹H,¹³C‐gHMBC‐ⁿJ(C,H) (n = 2 and 3)] and NOE experiments. Copyright © 2003 John Wiley & Sons, Ltd.     

Atom transfer radical copolymerizationof acrylonitrile/n‐butyl acrylate: Microstructure determination by two‐dimensional nuclearmagnetic resonance spectroscopy

Atom transfer radical polymerization conditions were optimized and standardized with different initiator and catalyst systems. Acrylonitrile/n‐butyl acrylate copolymers were synthesized with 2‐bromopropionitrile as the initiator and CuCl/Cu(0)/2,2′‐bipyridine as the catalyst system. Variations of the feed composition led to copolymers with different compositions. The number‐average molecular weight and the polydispersity index were determined by gel permeation chromatography. Quantitative ¹³C{¹H} NMR was employed to determine the copolymer composition. The reactivity ratios calculated with a methodology based on the Mao–Huglin terminal model were r_A = 1.30 and r_B = 0.68 for acrylonitrile and n‐butyl acrylate, respectively. The reactivity ratios determined by the modified Kelen–Tudos method were r_A = 1.29 ± 0.01 and r_B = 0.67 ± 0.01. ¹³C{¹H} NMR and distortionless enhancement by polarization transfer (DEPT‐45, 90, and 135) were used to distinguish methyl, methylene, methine, and quaternary carbon resonance signals. The overlapping and broad signals of the copolymers were assigned completely to various compositional and configurational sequences by the correlation of one‐dimensional (¹H, ¹³C{¹H}, and DEPT) and two‐dimensional (heteronuclear single quantum coherence, total correlation spectroscopy, and heteronuclear multibond correlation) NMR spectral data. The complete spectral assignments of carbonyl and nitrile carbons were performed with the help of heteronuclear multibond correlation spectra. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2810–2825, 2005     

1H and 13C NMR spectral assignments of some natural abietane diterpenoids

An NMR study of 11 naturally occurring abietane diterpenoids is described. In addition to one‐dimensional NMR methods, including DPFGSE 1D‐NOE spectra, two‐dimensional shift‐correlated experiments [¹H,¹H COSY, ¹H,¹³C‐gHSQC ¹J(C,H) and ¹H,¹³C‐gHMBC ⁿJ(C,H) (n = 2 and 3)] were used for the complete and unambiguous ¹H and ¹³C chemical shift assignments of these substances. Copyright © 2003 John Wiley & Sons, Ltd.     

Linear and nonlinear feature of electronic excitation energy in carbon chains HC2n+1H and HC2nH

Density functional theory has been used to investigate the geometries, bonding, and vibrational frequencies of HC_2nH (n = 1–13) and HC_2n+1H (n = 2–12). Vertical excitation energies for the X¹Σ → 1¹Σ transition of HC_2nH (n = 1–5) and for the X³Σ → 1³Σ transition of HC_2n+1H (n = 2–5) have been calculated by the time‐dependent density functional theory and ab initio second‐order multiconfiguration perturbation method, respectively. On the basis of the present calculations, explicit expressions for the size dependence of excitation energy in linear polyynes HC_2n+1H and HC_2n+1H are suggested. Such analytical λ ? n relationships show good agreement with experimental observations. Theoretical investigations of relevant excited states demonstrate that distinct linear and nonlinear spectroscopic features in such polyynes can be ascribed to similarity and difference in bonding between the ground and excited states in HC_2n+1H and HC_2nH. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

The complete 1H and 13C chemical shift assignments of a cyclopropylpyrroloindole analog: Adozelesin

The ¹H and ¹³C nmr spectral assignments of [7bR]-N-[2-[(4,5,8,8a-tetrahydro-7-methyl-4-oxocyclo-propa[c]pyrrolo[3,2-e]indol-2(1H)-ylcarbonyl]-1H-indol-5-yl]-2-benzofurancarboxamide (Adozelesin) (1) are described. Complete and unambiguous assignments of the hydrogen and carbon spectra were made using a combination of conventional homonuclear and gradient-selected inverse-detected heteronuclear nmr experiments: double quantum filtered ¹H-¹H correlation spectroscopy (COSY), gradient-selected heteronuclear single quantum coherence spectroscopy (gs-HSQC), and gradient-selected heteronuclear multiple bond coherence spectroscopy (gs-HMBC). The enhanced sensitivity of these experiments allowed a smaller sample concentration and shorter spectral collection times for a full nmr analysis of this compound. The nmr data corroborates the published structure of this compound.     

A new technique for differentiating between 2J(C,H) and 3/4J(C,H) connectivities

We present a new pulse sequence that yields two simultaneously detected types of long‐range correlation spectra. The one spectrum is to show all ⁿJ(C,H) connectivities and the other is to show exclusively ²J(C,H) connectivities. The method is demonstrated by using strychnine as a test sample. A comparison with HMBC shows that the ²J(C,H)/ⁿJ(C,H) experiment supplies a ⁿJ(C,H) spectrum that is of equal standard with regard to sensitivity and spectral information. The additional ²J(C,H) spectrum allows the disentanglement of ²J(C,H) and ⁿJ(C,H) signals (n > 2) in HMBC type spectra, which greatly simplifies signal assignment and structure elucidation in general. Copyright © 2003 John Wiley & Sons, Ltd.     

3D Heteronuclear long‐range 1H–13C scalar correlation at natural abundance: application to oligosaccharide analysis

A 3D ¹H–¹³C–¹H refocused INEPT transfer experiment is proposed in which the initial coherence transfer of ¹H longitudinal to ¹³C transverse magnetization is tuned to the long‐range ¹H, ¹³C couplings while the reverse INEPT component transfers the magnetization to the directly bonded ¹H. Integration of a constant time ¹H evolution period into the long‐range coherence transfer interval provides absorption mode signals for each dimension. A ¹³C purge component at the beginning of the sequence selects for ¹²C‐bound ¹H magnetization that is then transferred to a ¹³C‐bound hydrogen, thus strongly suppressing the diagonal signals. This experiment is expected to be of particular value for situations in which resonance overlap in the ¹³C dimension renders 2D long‐range heteronuclear correlation data ambiguous. In combination with a diagonal‐suppressed 3D ¹H–¹³C–¹H TOCSY‐HSQC experiment, complete assignment of the ring resonances of the Lewis‐b hexasaccharide was obtained on a 4.2 mM sample using a conventional 500 MHz probe (0.1% ethylbenzene signal‐to‐noise ratio of 600), suggesting its applicability to sub‐millimolar samples using cryoprobe technology. Copyright © 2002 John Wiley & Sons, Ltd.     

Precise Measurement of Long‐Range Heteronuclear Coupling Constants by a Novel Broadband Proton–Proton‐Decoupled CPMG‐HSQMBC Method

A broadband proton–proton‐decoupled CPMG‐HSQMBC method for the precise and direct measurement of long‐range heteronuclear coupling constants is presented. The Zangger–Sterk‐based homodecoupling scheme reported herein efficiently removes unwanted proton–proton splittings from the heteronuclear multiplets, so that the desired heteronuclear couplings can be determined simply by measuring frequency differences between singlet maxima in the resulting spectra. The proposed pseudo‐1D/2D pulse sequences were tested on nucleotides, a metal complex incorporating P heterocycles, and diglycosyl (di)selenides, as well as on other carbohydrate derivatives, for the extraction of ⁿJ(¹H,³¹P), ⁿJ(¹H,⁷⁷Se), and ⁿJ(¹H,¹³C) values, respectively.     

Potential and Limitations of 2D <Superscript>1</Superscript>H–<Superscript>1</Superscript>H Spin-Exchange CRAMPS Experiments to Characterize Structures of Organic Solids

Summary.  A brief overview of our recent results concerning the application of 2D CRAMPS experiments to investigate a wide range of materials is presented. The abilities of the 2D ¹H–¹H spin-exchange technique to characterize the structure of organic solids as well as the limitations resulting from segmental mobility and from undesired coherence transfer are discussed. Basic principles of ¹H NMR line-narrowing and procedures for analysis of the spin-exchange process are introduced. We focused to the qualitative and quantitative analysis of complex spin-exchange process leading to the determination of domain sizes and morphology in heterogeneous multicomponent systems as well as the characterization of clustering of surface hydroxyl groups in polysiloxane networks. Particular attention is devoted to the determination of the ¹H–¹H interatomic distances in the presence of local molecular motion. Finally we discuss limitations of the ¹³C–¹³C correlation mediated by ¹H–¹H spin exchange to obtain structural constraints. The application of Lee-Goldburg cross-polarization to suppress undesired coherence transfer is proposed. Corresponding author. E-mail: brus@imc.cas.cz Received May 28, 2002; accepted (revised) July 1, 2002     

The study of longifolene by two-dimensional NMR spectroscopy

The complete assignment of the ¹³C NMR spectrum of longifolene was achieved from double quantum coherence measurements, while combined evaluation of a ¹H? ¹³C heteronuclear chemical shift correlation diagram and a homonuclear ¹H J-resolved diagram provided all proton chemical shifts. Conformational information on the seven-membered ring of the tricyclic sesquiterpene was obtained from proton chemical shift considerations.     

Synthesis and mesomorphism behaviour of chalcones and pyrazoles type compounds as photo-luminescent materials

The following organic and organic–inorganic hybrid compounds were prepared as photo-luminescent materials following efficient and practical synthetic methods: 1,3-bis[4-(n-alkoxy)phenyl]-2-propen-1-one (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10); 3,5-bis[4-(n-alkoxy)phenyl]-1H-pyrazole (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10) (in case of n = 7, a mixture of 3,5-bis(4-heptyloxyphenyl)-1H-pyrazole and 3,5-bis(4-heptyloxyphenyl)-4H-pyrazole was detected) and bis(3,5-bis [4-(n-alkoxy) phenyl]-1H-pyrazole) silver(I) nitrate (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10). The prepared compounds have been characterised and their structures were elucidated depending upon (FTIR, UV-Vis, ¹HNMR, ¹³CNMR, 2D ¹H-¹H-COSY, 2D ¹H-¹³C-HSQC and mass spectra) in addition to molar conductivity measurements for silver(I) complexes. The mesomorphism behaviour of the prepared compounds was studied using polarised light optical microscopy and confirmed with differential scanning calorimetry and X-ray powder diffraction techniques. The studies showed that among all of these compounds only the pyrazole derivatives are liquid crystal materials. The luminescent properties of all the prepared compounds were also investigated which confirmed that all of these compounds are photo-luminescent in the crystalline solid state and in the mesophase.     

Fourier Transform and Multi Dimensional EPR Spectroscopy for the Characterization of Sol-Gel Derived Hydroxyapatite

Calcium hydroxyapatite powder was prepared by sol-gel method using calcium acetate and PO(OC₂H₅)₃ as initial compounds, and alcohol (methyl, ethyl, and propyl-alcohol) as solvent. Homogeneous solution and gels were prepared using a molar ratio of Ca/P=1.67. The evolution of the structure was detected by X-ray diffraction, IR, and FT-n(=1,2,3)D-EPR spectroscopy. The dried gels exhibit a signal characterized by a central line and two satellites. The 2D spectrum (ESEEM vs. field sweep) showed the same modulation for the central line. The FT-EPR spectrum vs. field sweep 2D-spectrum indicated that the satellites are due to an hfs splitting with water. The central region of this 2D spectrum is influenced by P and H in a concentration ratio of [H]/[P]=2.5. The ESEEM spectrum was simulated assuming the equation V_mod=V_mod(P)^mV_mod(H)ⁿ for two spin systems S=1/2 and I=1/2. This simulation gave form andn the values of 2 and 5, respectively. This finding suggests the structure: for the unpaired state. It appears that one ethyl group does not hydrolyse in the gelation process. The ESEEM spectra of hydroxyapatite exhibit a modulation generated by P, H and Ca atoms.     

Self‐Assembled Multimetallic/Peptide Complexes: Structures and Unimolecular Reactions of [Mn(GlyGly−H)2n−1]+ and Mn+1(GlyGly−H2n]2+ Clusters in the Gas Phase

The unimolecular chemistry and structures of self‐assembled complexes containing multiple alkaline‐earth‐metal dications and deprotonated GlyGly ligands are investigated. Singly and doubly charged ions [M_n(GlyGly?H)_n‐1]⁺ (n=2–4), [M_n+1(GlyGly?H)_2n]²⁺ (n=2,4,6), and [M(GlyGly?H)GlyGly]⁺ were observed. The losses of 132 Da (GlyGly) and 57 Da (determined to be aminoketene) were the major dissociation pathways for singly charged ions. Doubly charged Mg²⁺ clusters mainly lost GlyGly, whereas those containing Ca²⁺ or Sr²⁺ also underwent charge separation. Except for charge separation, no loss of metal cations was observed. Infrared multiple photon dissociation spectra were the most consistent with the computed IR spectra for the lowest energy structures, in which deprotonation occurs at the carboxyl acid groups and all amide and carboxylate oxygen atoms are complexed to the metal cations. The N?H stretch band, observed at 3350 cm^?1, is indicative of hydrogen bonding between the amine nitrogen atoms and the amide hydrogen atom. This study represents the first into large self‐assembled multimetallic complexes bound by peptide ligands.