2D HETCOR Research Articles

Design and construction of a versatile dual volume heteronuclear double resonance microcoil NMR probe

Improved NMR detection of mass limited samples can be obtained by taking advantage of the mass sensitivity of microcoil NMR, while throughput issues can be addressed using multiple, parallel sample detection coils. We present the design and construction of a double resonance 300-MHz dual volume microcoil NMR probe with thermally etched 440-nL detection volumes and fused silica transfer lines for high-throughput stopped-flow or flow-through sample analysis. Two orthogonal solenoidal detection coils and the novel use of shielded inductors allowed the construction of a probe with negligible radio-frequency cross talk. The probe was resonated at 1H– 2D (upper coil) and 1H– 13C (lower coil) frequencies such that it could perform 1D and 2D experiments with active locking frequency. The coils exhibited line widths of 0.8–1.1 Hz with good mass sensitivity for both 1H and 13C NMR detection. 13C-directly detected 2D HETCOR spectra of 5% v/v 13C labeled acetic acid were obtained in less than 5 min. Demonstration of the probe characteristics as well as applications of the versatile two-coil double resonance probe are discussed.

Characterization of sinking particles from the northwest Mediterranean Sea using advanced solid-state NMR

Sinking particles are the major transporter of organic carbon from surface to the deep ocean, and their chemical composition changes dramatically with depth. However, the exact mechanism controlling the chemical transformation as particles sink is not well understood, and little detail is known about the structural changes. This is mainly due to the paucity of techniques available to analyze the major macromolecular components of sinking particles. Here we applied advanced solid-state NMR techniques, including cross polarization/magic angle spinning (CPMAS), direct polarization/magic angle spinning (DPMAS), two-dimensional 1H– 13C heteronuclear correlation (2D HETCOR) and 1H T 1 inversion recovery, on sinking particles collected in the northwest Mediterranean Sea. The CPMAS 13C NMR spectrum of the 200-m particles is significantly different from that of the DPMAS 13C NMR spectrum: CPMAS overestimates the NCH and CHO groups, but underestimates the aliphatic components, which is attributed to the high mobility of polymethylene units. Thus DPMAS is more suitable for quantifying organic composition of sinking particles. Using 2D HETCOR with 1H spin diffusion, we estimated that the size of domains (similar structural entities either physically or chemically grouped together) in the 200-m sinking particles can be as large as tens of nanometers. The results of CPMAS 13C NMR and 1H inversion recovery on sinking particles from 200, 520 and 920 m indicate that the macromolecular heterogeneity observed in surface particles virtually disappears as particles sink into the deep ocean. This suggests that the macromolecular components at depth are different in structural composition than those in surface waters, and may be compositionally homogenized as particles sink.

Through-space MP-CPMAS experiments between spin-1/2 and half-integer quadrupolar nuclei in solid-state NMR

We present a new CPMAS method that allows the acquisition of through-space 2D HETCOR spectra between spin-1/2 nuclei and half-integer quadrupolar nuclei in the solid state. It uses rotor-synchronized selective pulses on the quadrupolar nucleus and continuous-wave RF irradiation on the spin-1/2 nucleus to create hetero-nuclear dipolar coherences. The method is more robust, more efficient, and easier to set up than the standard CPMAS transfer.

Through-bond and through-space connectivities of amorphous aluminophosphate by two-dimensional 27Al– 31P heteronuclear NMR

The connectivities between Al and P through chemical bond and internuclear distance have been studied for an amorphous aluminophosphate (a-AlPO 4) using two-dimensional (2D) solid-state 27Al– 31P correlation NMR (MAS J-HMQC and CP HETCOR). Whereas the conventional 31P MAS spectrum provides less informative results because of poor resolution caused by large distributions of the nucleus surroundings, the 2D HETCOR shows much better resolution and at least four non-equivalent P sites in the a-AlPO 4. These P sites are found to be correlated with one [4]Al, two [5]Al and one [6]Al species, and have different chemical shifts. This result might indicate that the mean P–O– [ n] Al ( n = 4, 5, 6) bond angles are different each other, and they are estimated using the relationship with the 31P chemical shifts in crystalline AlPO 4 previously reported.

Through-space R 3-HETCOR experiments between spin-1/2 and half-integer quadrupolar nuclei in solid-state NMR

We present several new methods that allow to obtain through-space 2D HETCOR spectra between spin-1/2 and half-integer quadrupolar nuclei in the solid state. These methods use the rotary-resonance concept to create hetero-nuclear coherences through the dipolar interaction instead of scalar coupling into the HMQC and refocused INEPT experiments for spin n/2 ( n > 1). In opposite to those based on the cross-polarization transfer to quadrupolar nuclei, the methods are very robust and easy to set-up.

Direct Solid-State NMR Observation of Tetrahedral Aluminum Fluorides in Zeolite HY Fluorinated by Ammonium Fluoride

19F to 27Al CPMAS and 27Al{19F} 2D HETCOR NMR experiments provide direct evidence of the formation of tetrahedral Al−F species in zeolite HY fluorinated by an aqueous solution of ammonium fluoride ...

Non-covalent interactions of a drug molecule encapsulated in a hybrid silica gel

The drug molecule Propranolol has been encapsulated by a sol-gel process in an organic-inorganic hybrid matrix by in-situ self-assembly; the 2D HETCOR solid state NMR spectroscopy provides direct proof of the intimate spatial relationship between the host matrix and guest drug molecules.

Better Characterization of Surface Organometallic Catalysts through Resolution Enhancement in Proton Solid State NMR Spectra

Delayed-acquisition methods, namely, echo and constant-time-acquisition approaches, allow a significant improvement in resolution in the proton solid state NMR spectra of surface organometallic catalysts such as [syn-(SiO)Mo(=NAr)(=CH(t)Bu)(CH2(t)Bu)] and [(SiO)Re(C(t)Bu)(=CH(t)Bu)(CH2(t)Bu)] (syn/anti ratio = 1:1). This enables the observation of all of the proton resonances, which is not possible with the simple proton single-pulse technique under magic-angle spinning. For example, the methylene protons of the neopentyl ligands, buried in the large peak associated with all of the methyls in the 1H MAS spectrum, can easily be identified by recording a delayed-acquisition spectrum (resolution enhancement of a factor of 3 is obtained). Moreover, combining constant-time acquisition with heteronuclear carbon-proton correlation spectroscopy also improves the resolution of the 2D HETCOR spectra.

Synthesis, spectral studies of salicylidine-pyridines: Crystal and molecular structure of 2-[(1 E)-2-aza-2-(5-methyl(2-pyridyl)ethenyl)]-4-bromobenzen-1-ol

Schiff bases derived from different meta-substituted salicylaldehyde and 5-methylaminopyridine have been synthesized and characterized by elemental analysis, FT-IR, NMR and UV–vis techniques. NMR assignments were made using 1H, 13C NMR and aided by 2D HETCOR and HMBC heteronuclear correlation techniques. The UV–vis spectra of the compounds were found useful in understanding the existence of tautomeric equilibria [phenol-imine (O–H⋯N) and keto-amine (O⋯H–N) forms] in polar and non-polar solvents. In order to rationalize the stabilization of tautomer in solid state, X-ray structure of 2-[(1 E)-2-aza-2-(5-methyl(2-pyridyl)ethenyl)]-4-bromobenzen-1-ol ( 6) was determined. According to our crystallographic result, it has enol-imine tautomeric form.

Crystal Structure of 2-thiophene-2-yl-3(thiophene-2-carboxylideneamino)-1, 2-dihydroquinazolin-4(3H)-one and the Synthesis, Spectral and Thermal Studies of its Transition Metal(II) Complexes

The synthesis of manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes of a new ligand 2-thiophene-2-yl-3(thiophene-2-carboxylidene-amino)-1,2-dihydroquinazolin-4(3H)-one (TTCADQ) is described. The ligand and metal complexes were characterized by elemental analysis, conductivity measurements, spectral (u.v.–vis., i.r., 1D n.m.r., 2D hetcor and e.p.r.) and thermal studies. The formation of 1,2-dihydroquinazolin-4(3H)-one rather than hydrazone, in the reaction of aromatic aldehyde and o-aminobenzoylhydrazide is proved by single crystal X-ray diffraction and 2D hetcor n.m.r. studies. On the basis of elemental analysis, u.v.–vis.spectroscopy and magnetic moment studies, six coordinate geometry for all the complexes was proposed. The i.r. spectral studies reveal the bidentate behaviour of the ligand.

X-ray crystallographic and 2D HETCOR NMR studies of 2-acetylthiophene- o-aminobenzoylhydrazone: synthesis and spectral studies of its transition metal complexes

The coordination chemistry of the ligand 2-acetylthiophene- o-aminobenzoylhydrazone (ATABZ) with oxovanadium(IV), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) has been studied wherein the complexes were characterized by elemental analyses, magnetic moments, conductivity measurements, spectral (IR, 1D and 2D HETCOR NMR, EPR and UV-VIS) and thermal studies. The ligand ATABZ crystallizes in the orthorhombic system, space group Pca21 with lattice parameters a=8.5279(17) Å, b=5.8101(11) Å, c=25.720(5) Å, V=1274.3(4) Å 3 and Z=4. All the complexes are neutral in nature and possess four-coordinate geometry around the metal ion except oxovanadium(IV) complex, which is five-coordinate. The X-band EPR spectra of the copper(II) and oxovanadium(IV) complexes at both room temperature and liquid nitrogen temperature have been recorded and their salient features are reported. The antibacterial and antifungal activities of the ligand and complexes have been carried out.

Flavonóides O-glicosilados de Croton campestris St. Hill. (Euphorbiaceae)

Do extrato butanólico de Croton campestris St. Hill. (Euphorbiaceae) foram isolados quatro flavonóides, todos O-glicosídeos da quercetina. Estas substâncias foram identificadas como 3-O-b-D-apiofuranosil-(1®2)-galactopiranosil quercetina (1), 3-O-b-D-galactopiranosil quercetina (hiperina) (2), 3-O-a-L-arabinopiranosil quercetina (guaijaverina) (3) e 3-O-a-L-ramnopiranosil quercetina (quercitrina) (4).O presente trabalho relata a presença destas substâncias pela primeira vez para esta espécie de Croton, cuja elucidação estrutural deu-se por espectroscopia em UV, EM e RMN, incluindo as técnicas bidimensionais: ¹H-¹H (2D NOESY, 2D COSY), ¹H-13C (2D HETCOR) e 13C (APT), além de comparações com os dados da literatura.

Five-coordinate Cobalt(II), Nickel(II) and Zinc(II) Complexes Derived from 2-pyridine-2-yl-3-(pyridine-2-carboxylideneamino)-1,2-dihydroquinazolin-4(3H)-one. The Crystal Structure of the Cobalt(II) Complex

The synthesis of cobalt(II), nickel(II) and zinc(II) complexes of 2-pyridine-2-yl-3(pyridine-2-carboxylideneamino)1,2-dihydroquinazolin-4(3H)-one is described. The ligand and metal complexes were characterized by elemental analysis, conductivity measurements, spectral (u.v.-vis.,i.r., 1D n.m.r., 2D hetcor and mass) and thermal studies. The cobalt(II) complex crystallizes as pink crystals in the monoclinic crystal system, space group P21/n with a = 10.066(6) Angstrom over circle, b= 15.929(9) Angstrom over circle, c = 12.624(7) Angstrom over circle, \alpha =90.00(9)degrees, \beta = 110.850 (8)degrees, \gamma = 90.00, V = 1891.5(18) Angstrom over circle (3) and Z = 4. The geometry around the cobalt atomis distorted trigonal bipyramidal with T = 0.83 [structuralparameter, T = (\beta - \alpha)/60; where \alpha and \beta are the two basal angles in a five coordinate complex].

Two-Dimensional Spin-Diffusion NMR Reveals Differential Mixing in Biodegradable Polymer Blends

Length scales of mixing in amorphous blends of solid PCL (polycaprolactone) and PLLA (poly-l-lactic acid) were investigated as a function of preparation method. A recently described two-dimensional heteronuclear correlation (Hetcor) spin-diffusion technique (Jia et al. Macromolecules 2003, 36, 712) revealed that PCL/PLLA blends with shorter length scales of mixing, relative to solution blending, could be prepared using inclusion-compound coalescence methods (Rusa et al. Macromolecules 2000, 33, 5321). These biocompatible and biodegradable polymer blends provide a clear example of the utility of the 2D Hetcor spin-diffusion method for quantitative miscibility and phase analysis in amorphous macromolecules and their blends. The rates for intrapolymer polarization transfer vs interchain/interdomain polarization equilibration were easily differentiated using the 2D technique for either blend. As a result, spin-diffusion coefficients and miscibility length scales could be calculated by direct measurement on th...

Boron Sites in Borosilicate Zeolites at Various Stages of Hydration Studied by Solid State NMR Spectroscopy

The local structures of framework boron atoms in borosilicate zeolites B-β, B-SSZ-33 and B-SSZ-42 have been studied in the course of hydration/dehydration by employing solid-state NMR methods. In particular, characterization of trigonal boron sites has been studied in great detail. 11B MAS NMR spectra showed that boron trigonally coordinated to the framework (B(OSi)3, denoted as B[3]) can be readily transformed to a defective trigonal boron site (B(OSi)2(OH), denoted as B[3]-I) as a result of hydration. The presence of B[3]-I sites was proven by utilizing a number of different NMR methods including 11B MAS NMR at two different fields (11.7 and 19.6 T), 11B MQMAS, 11B CPMAS, and 11B 2D HETCOR experiments. The B[3]-I species can be converted into B[3] upon dehydroxylation, but its presence can also be sustained even after very high-temperature treatment (at least up to 500 °C). The formation of deboronated species, B(OH)3, in distorted form was detected even under a mild hydration treatment. HETCOR NMR revealed that hydroxyl protons with chemical shifts at 2.4 and 3.3 ppm in 1H NMR are correlated with B[3] and B[3]-I sites, respectively. The presence of a new hydroxyl proton at 3.8 ppm in 1H NMR that showed selective correlation with B[3]-I in HETCOR NMR was also identified.

Reaction of 5‐Halo‐1,2,3‐thiadiazoles with Aliphatic Diamines. Synthesis and Intramolecular Cyclization of Bis(1,2,3‐triazolyl‐1,2,3‐thiadiazolyl)sulfides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structural investigations of acrylonitrile–vinyl acid copolymers by NMR spectroscopy

Abstract1H, 13C [1H]‐, and 2D HETCOR NMR spectroscopy have been employed to characterize polyacrylonitrile (PAN) homopolymer and copolymers of methacrylic acid (MAA) and itaconic acid (IA) prepared by solvent–water suspension polymerization technique in a mixture containing DMF (solvent) and water. The chemical composition of P(AN–MAA) copolymers was determined using 1H‐NMR and that of P(AN–IA) using quantitative 13C[1H]‐NMR spectra. P(AN–IA) copolymers show two separate signals due to two carboxylic groups in different magnetic environments of IA, whereas P(AN–MAA) shows only one in the region of δ 6.32–7.60 ppm in 1H‐NMR and δ 171.0–176.0 ppm in 13C[1H]‐NMR spectra. Evidence of acrylamide formation by the partial hydrolysis of AN groups is obtained by the small broad signal at δ 7.9 ppm in 1H‐NMR spectra. No carboxylic proton signal was observed in copolymers containing 12 mol % of comonomer, which indicates the formation of anhydride. The microstructure was obtained in terms of the A‐ and M‐centered triad sequences from 13C[1H]‐and 1H‐NMR spectra of the copolymers, which showed configurational and compositional sequences. For example, at higher comonomer content, the concentration of AAM and AAI sequencing increases. This is confirmed by 2D HETCOR NMR spectra also. The distribution of AN sequences is found to be random (n0 ∼ nm ≃ 2.0). The tacticity values are not affected by the comonomer content. The isotacticity remained almost same at 27% (mm, 26.5–29.3) in all acrylonitrile polymers irrespective of the nature of the comonomer and polymerization medium, that is, DMF/H2O ratio. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1211–1217, 2003

Reaction of 5-halo-1,2,3-thiadiazoles with aliphatic diamines. Synthesis and intramolecular cyclization of bis(1,2,3-triazolyl-1,2,3-thiadiazolyl)sulfides.

Bis[1,2,3]triazolo[1,5-f:5',1'-b][1,3,6]thiadiazepine and [1,5-g:5',1'-b][1,3,7]thiadiazocine ring systems have been synthesized from 5-halo-1,2,3-thiadiazoles and aliphatic diamines. We have found that the last step of the process is the cyclization of initially formed bis(1,2,3-triazolyl-1,2,3-thiadiazolyl)sulfides. The structures of the intermediates and products were supported by different NMR spectroscopic methods (1H coupled 13C NMR, 2D HETCOR, HMBC and 1D INADEQUATE experiments) and mass spectrometry. Differences in the reaction pathway for aliphatic and less nucleophilic aromatic diamines were determined.

2-Polyfluoroalkylchromones. 12. Nitration of 5,7-dimethyl-2-polyhaloalkylchromones and complete assignment of signals in the 1H and 13C NMR spectra of 5,7-dimethyl-2-trifluoromethylchromone and its mono- and dinitro derivatives

The nitration of 5,7-dimethyl-2-polyhaloalkylchromones affords either 5,7-dimethyl-6-nitro- or 5,7-dimethyl-6,8-dinitro-2-polyhaloalkylchromones, depending on the reaction conditions. Signals in the 1H and 13C NMR spectra of the sterically hindered chromones were completely assigned using the 2D NOESY, HETCOR, and COLOC spectra. The influence of nonplanar nitro groups on chemical shifts of carbon atoms was studied. Some spectral peculiarities of the peri-methyl group were revealed. The 1H-1H and 13C-1H spin-spin coupling constants, including the extreme six-bond long-range coupling between the protons of the Me(5) group and H(8), were determined.

Molecular Insight Into Surface Organometallic Chemistry Through the Combined Use of 2D HETCOR Solid-State NMR Spectroscopy and Silsesquioxane Analogues We are also indebted to the CNRS, ENS Lyon, and ESCPE Lyon for financial support. M.C. is grateful to the French ministry of education, research, and technology (MENRT) for a pre-doctoral fellowship. E.A.Q. gratefully acknowledges Università di Pisa and S.N.A.M. for

Reference EPFL-ARTICLE-204460doi:10.1002/1521-3773(20011203)40:23 3.0.CO;2-XView record in Web of Science Record created on 2015-01-08, modified on 2017-12-03