Nuclear quadrupole hyperfine structure in the microwave spectrum of HCl-N2O: electric field gradient perturbation of N2O by HCl

The microwave spectra of six isotopomers of HCl-N(2)O have been obtained in the 7-19 GHz region with a pulsed molecular beam, Fourier transform microwave spectrometer. The nuclear quadrupole hyperfine structure due to all quadrupolar nuclei is resolved and the spectra are analyzed using the Watson S-reduced Hamiltonian with the inclusion of nuclear quadrupole coupling interactions. The spectroscopic constants determined include rotational constants, quartic and sextic centrifugal distortion constants, and nuclear quadrupole coupling constants for each quadrupolar nucleus. Due to correlations of the structural parameters, the effective structure of the complex cannot be obtained by fitting to the spectroscopic constants of the six isotopomers. Instead, the parameters for each isotopomer are calculated from the A and C rotational constants and the chlorine nuclear quadrupole coupling constant along the a-axis, chi(aa). There are two possible structures; the one in which hydrogen of HCl interacts with the more electronegative oxygen of N(2)O is taken to represent the complex. The two subunits are approximately slipped parallel. For H (35)Cl-(14)N(2)O, the distance between the central nitrogen and chlorine is 3.5153 A and the N(2)O and HCl subunits form angles of 72.30 degrees and 119.44 degrees with this N-Cl axis, respectively. The chlorine and oxygen atoms occupy the opposite, obtuse vertices of the quadrilateral formed by O, central N, Cl, and H. Nuclear quadrupole coupling constants show that while the electric field gradient of the HCl subunit remains essentially unchanged upon complexation, there is electronic rearrangement about the two nitrogen nuclei in N(2)O.     

(1)H relaxation dispersion in solutions of nitroxide radicals: Effects of hyperfine interactions with (14)N and (15)N nuclei

(1)H relaxation dispersion of decalin and glycerol solutions of nitroxide radicals, 4-oxo-TEMPO-d(16)-(15)N and 4-oxo-TEMPO-d(16)-(14)N was measured in the frequency range of 10 kHz-20 MHz (for (1)H) using STELAR Field Cycling spectrometer. The purpose of the studies is to reveal how the spin dynamics of the free electron of the nitroxide radical affects the proton spin relaxation of the solvent molecules, depending on dynamical properties of the solvent. Combining the results for both solvents, the range of translational diffusion coefficients, 10(-9)-10(-11) m(2)∕s, was covered (these values refer to the relative diffusion of the solvent and solute molecules). The data were analyzed in terms of relaxation formulas including the isotropic part of the electron spin - nitrogen spin hyperfine coupling (for the case of (14)N and (15)N) and therefore valid for an arbitrary magnetic field. The influence of the hyperfine coupling on (1)H relaxation of solvent molecules depending on frequency and time-scale of the translational dynamics was discussed in detail. Special attention was given to the effect of isotope substitution ((14)N∕(15)N). In parallel, the influence of rotational dynamics on the inter-molecular (radical - solvent) electron spin - proton spin dipole-dipole coupling (which is the relaxation mechanism of solvent protons) was investigated. The rotational dynamics is of importance as the interacting spins are not placed in the molecular centers. It was demonstrated that the role of the isotropic hyperfine coupling increases for slower dynamics, but it is of importance already in the fast motion range (10(-9)m(2)∕s). The isotope effects is small, however clearly visible; the (1)H relaxation rate for the case of (15)N is larger (in the range of lower frequencies) than for (14)N. It was shown that when the diffusion coefficient decreases below 5 × 10(-11) m(2)∕s electron spin relaxation becomes of importance and its role becomes progressively more significant when the dynamics slows done. As far as the influence of the rotational dynamics is concerned, it was show that this process is of importance not only in the range of higher frequencies (like for diamagnetic solutions) but also at low and intermediate frequencies.     

The impact of excitation frequency on the nuclear modulation of electron spin echoes: 14N hyperfine and quadrupole interactions of DPPH in disordered solids

Electron spin-echo envelope modulations of DPPH in glassy and polycrystalline solids at 100 K have been measured at 4.6 and 9.1 GHz electron spin excitation frequencies. ¹⁴N hyperfine and quadrupole coupling parameters have been evaluated through comparison of the experimental data waveforms and the corresponding spectra with simulated modulation patterns and associated frequency histograms. Because of the strong excitation frequency dependence of ESEEM, agreement between the observed and the simulated results at octave-separated excitation frequencies leads to a significant improvement in the accuracy of the derived couplings.     

Spin-orbit-induced anomalous pH-dependence in (1)H NMR spectra of Co(III) amine complexes: a diagnostic tool for structure elucidation

The pH-dependent (1)H NMR characteristics of a series of Co(III)-(polyamin)-aqua and Co(III)-(polyamin)-(polyalcohol) complexes, [Co(tach)(ino-kappa(3)-O(1,3,5))](3+) (1(3+)), [Co(tach)(ino-kappa(3)-Omicron(1,2,6))](3+) (2(3+)), [Co(tach)(taci-kappa-Nu(1)-kappa(2)-O(2,6))](3+) (3(3+)), [Co(ditame)(H(2)O)](3+) (4(3+)), and [Co(tren)(H(2)O)(2)](3+) (5(3+)), were studied in D(2)O by means of titration experiments (tach = all-cis-cyclohexane-1,3,5-triamine, ino = cis-inositol, taci = 1,3,5-triamino-1,3,5-trideoxy-cis-inositol, tren = tris(2-aminoethyl)amine, ditame = 2,2,6,6-tetrakis-(aminomethyl)-4-aza-heptane). A characteristic shift was observed for H(-C) hydrogen atoms in the alpha-position of a coordinated amino group upon deprotonation of a coordinated oxygen donor. For a cis-H-C-N-Co-O-H arrangement, deprotonation of the oxygen donor resulted in an additional shielding (shift to lower frequency) of the H(-C) proton, whereas for a trans-H-C-N-Co-O-H arrangement, deprotonation resulted in a deshielding (shift to higher frequency). The effect appears to be of rather general nature: it is observed for primary (1(3+)-5(3+)), secondary (4(3+)), and tertiary (5(3+)) amino groups, and for the deprotonation of an alcohol (1(3+)-3(3+)) or a water (4(3+), 5(3+)) ligand. Spin-orbit-corrected density functional calculations show that the high-frequency deprotonation shift for the trans-position is largely caused by a differential cobalt-centered spin-orbit effect on the hydrogen nuclear shielding. This effect is conformation dependent due to a Karplus-type behavior of the spin-orbit-induced Fermi-contact shift and thus only significant for an approximately antiperiplanar H-C-N-Co arrangement. The differential spin-orbit contribution to the deprotonation shift in the trans-position arises from the much larger spin-orbit shift for the protonated than for the deprotonated state. This is in turn due to a trans-effect of the deprotonated (hydroxo or alkoxo) ligand, which weakens the trans Co-N bond and thereby interrupts the Fermi-contact mechanism for transfer of the spin-orbit-induced spin polarization to the hydrogen nucleus in question. The unexpectedly large long-range spin-orbit effects found here for 3d metal complexes are traced back to small energy denominators in the perturbation theoretical expressions of the spin-orbit shifts.     

Stable carbon ((12/13)C) and nitrogen ((14/15)N) isotopes as a tool for identifying the sources of cyanide in wastes and contaminated soils--a method development

The occurrence of iron-cyanide complexes in the environment is of concern, since they are potentially hazardous. In order to determine the source of iron-cyanide complexes in contaminated soils and wastes, we developed a method based on the stable isotope ratios ¹³C/¹²C and ¹⁵N/¹⁴N of the complexed cyanide-ion (CN⁻). The method was tested on three pure chemicals and two industrials wastes: blast-furnace sludge (BFS) and gas-purifier waste (GPW). The iron-cyanide complexes were converted into the solid cupric ferrocyanide, Cu₂[Fe(CN)₆]·7H₂O, followed by combustion and determination of the isotope-ratios by continuous flow isotope ratio mass spectrometry. Cupric ferrocyanide was obtained from the materials by (i) an alkaline extraction with 1 M NaOH and (ii) a distillate digestion. The [Fe(CN)₆]⁴⁻ of the alkaline extraction was precipitated after adding Cu²⁺. The CN⁻ of the distillate digestion was at first complexed with Fe²⁺ under inert conditions and then precipitated after adding Cu²⁺. The δ¹³C-values obtained by the two methods differed slightly up to 1-3‰ for standards and BFS. The difference was larger for alkaline-extracted GPW (4-7‰), since non-cyanide C was co-extracted and co-precipitated. Therefore the distillate digestion technique is recommended when determining the C isotope ratios in samples rich in organic carbon. Since the δ¹³C-values of BFS are in the range of −30 to −24‰ and of −17 to −5‰ for GPW, carbon seems to be a suitable tracer for identifying the source of cyanide in both wastes. However, the δ¹⁵N-values overlapped for BFS and GPW, making nitrogen unsuitable as a tracer.     

15N and 13C{14N} NMR investigation of the major nitrogen-containing segment in an aquatic fulvic acid: evidence for a hydantoin derivative

A nitrogen-rich segment in a fulvic acid (FA) from Pony Lake, a coastal pond in Antarctica, was investigated by (15)N and (13)C{(14)N} solid-state NMR techniques. As reported previously, the (13)C{(14)N} spectrum of C bonded to N exhibits a peak at 157 ppm that is assigned to an sp(2)-hybridized carbon bonded to at least two nitrogen atoms. This segment contains 48% of all N in the sample. (15)N NMR shows distinct signals, 20 ppm upfield and downfield from the typical peptide resonance; dipolar dephasing confirmed that they are due to protonated N. The well-resolved downfield peak, which accounts for 1/4 of the spectral area, cannot be assigned to aromatic heterocycles, such as purines, because the fraction of aromatic C bonded to N in this sample is very small. Analysis of (15)N chemical-shift trends and (15)N NMR of model compounds, such as arginine and its derivatives, excludes assignment to a guanidinium ion or to substituted guanidino groups. Similarly, ureido groups, -NH-CO-NH-, that are not bonded to a second C = O do not match the observed (15)N peaks in the FA, since both N resonate upfield from the peptide resonance. On the other hand, all chemical shifts are matched within the observed range by the -C(alkyl)-NH-CO-NH-CO-C structure found in two nonaromatic heterocycles, hydantoin and dihydrouracil. The five-membered hydantoin ring, which is found in the purine metabolite allantoin, provides a better match than the six-membered dihydrouracil ring. Regular uracil or thymine fails to produce adequate agreement with observed chemical shifts.     

Determination of the kinetic profile of a dinuclear platinum anticancer complex in the presence of sulfate: introducing a new tool for the expedited analysis of 2D [(1)H,( 15)N] HSQC NMR spectra

Two-dimensional (2D) [(1)H, (15)N] heteronuclear single-quantum coherence (HSQC) NMR experiments of the kinetics of aquation and sulfation of the dinuclear platinum anticancer complex [{trans-PtCl(NH(3))(2)}(2)(μ-NH(2)(CH(2))(6)NH(2))](2+) (1,1/t,t, 1) in 15 mM sulfate solution are reported using conditions (298 K, pH 5.4) identical to those previously used for other anionic systems (phosphate and acetate), allowing for a direct comparison. Sulfate is the fourth most abundant anion in human plasma. The rate constant for the aquation step (k(H)) is higher than that previously found in the presence of phosphate, but the anation rate constants are similar. The rate constant for sulfate displacement of the aqua ligand (k(L)) is approximately three times higher than that of phosphate, and a further major difference between these two anions is the very high k(-L) for loss of sulfate, suggesting that when formed in plasma the sulfato species will be substitution labile. We also introduce a novel (free) plug-in, '2D NMR analysis', developed for the expedited integration and analysis of 2D [(1)H, (15)N] HSQC NMR spectra. We have found that this plug-in significantly reduces the amount of time taken in the analysis of experiments with no loss to the quality of the data.     

CN-HMBC: a powerful NMR technique for the simultaneous detection of long-range 1H,13C and 1H,15N connectivities

[structure: see text] A new one-shot NMR experiment (CN-HMBC) is proposed for the simultaneous acquisition of 2D 1H,13C and 1H,15N HMBC spectra. Important sensitivity enhancements (up to 41% simultaneously for both 13C and 15N) or time savings (about 50%) can be achieved when compared to the separate acquisition of individual HMBC spectra. The experiment is highly recommended for the complete structural analysis and simultaneous chemical shift assignments of protonated and nonprotonated 13C and 15N resonances in nitrogen-containing organic compounds.     

Synthesis,crystal structure,vibrational, optical properties,and a theoretical study of a new Pb(II) complex with bis(1-methylpiperazine-1,4-diium): [C5H14N2]2PbCl6·3H2O

An investigation of the solid-state X-ray structure of the new organic–inorganic compound [C₅H₁₄N₂]₂PbCl₆·3H₂O shows a layered organization of the (PbCl₆)^4– anions, with (R₂NH₂)⁺ groups and water molecules developed in the [001 A. Hu, H.L. Ngo, W. Lin. J. Am. Chem. Soc., 125, 11490 (2003).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] plane at x = (2n?+?1)/4. The crystal structure is stabilized by N???H···Cl, N???H···O, O???H···Cl, O???H···O, and C???H···Cl hydrogen bonds. The powder X-ray diffraction and X-ray photoelectron spectroscopic (XPS) analyses confirm the phase purity of the crystal sample. The intermolecular contacts are quantified using the Hirshfeld surfaces computational method. The major inter-contacts contributing to the Hirshfeld surfaces are H…Cl, H…H, and O…H. The vibrational modes were identified and assigned by IR and Raman spectroscopies. The optical properties were investigated by UV–visible and photoluminescence spectroscopic studies. The compound was characterized by thermal analysis to determine its thermal behavior with respect to the temperature. Finally, X-ray photoelectron spectroscopy analysis is reported for analyzing the surface chemistry of [C₅H₁₄N₂]₂PbCl₆·3H₂O.     

Characterisation of uniformly 13C, 15N labelled bacteriochlorophyll a and bacteriopheophytin a in solution and in solid state: complete assignment of the 13C, 1H and 15N chemical shifts

In this investigation we report a complete assignment of (13)C, (1)H and (15)N solution and solid state chemical shifts of two bacterial photosynthetic pigments, bacteriochlorophyll (BChl) a and bacteriopheophytin (BPheo) a. Uniform stable-isotope labelling strategies were developed and applied to biosynthetic preparation of photosynthetic pigments, namely uniformly (13)C, (15)N labelled BChl a and BPheo a. Uniform stable-isotope labelling with (13)C, (15)N allowed performing the assignment of the (13)C, (15)N and (1)H resonances. The photosynthetic pigments were isolated from the biomass of photosynthetic bacteria Rhodopseudomonas palustris 17001 grown in uniformly (13)C (99%) and (15)N (98%) enriched medium. Both pigments were characterised by NMR in solution (acetone-d(6)) and by MAS NMR in solid state and their NMR resonances were recorded and assigned through standard liquid 2D (13)C-(13)C COSY, (1)H-(13)C HMQC, (1)H-(15)N HMBC and solid 2D (13)C-(13)C RFDR, (1)H-(13)C FSLG HETCOR and (1)H-(15)N HETCOR correlation techniques at 600 MHz and 750 MHz. The characterisation of pigments is of interest from biochemical to pharmaceutical industries, photosynthesis and food research.     

Nuclear magnetic resonance chemical shifts and quadrupole couplings for different hydrogen-bonding cases occurring in liquid water: a computational study

Nuclear magnetic resonance (NMR) parameters are determined theoretically for the oxygen and hydrogen/deuterium nuclei of differently hydrogen-bonded water molecules in liquid water at 300 K. The parameters are the chemical shift, the shielding anisotropy, the asymmetry parameter of shielding, the nuclear quadrupole coupling constant, and the asymmetry parameter of the nuclear quadrupole coupling. We sample instantaneous configurations from a Car-Parrinello molecular dynamics simulation and feed nuclear coordinates into a quantum chemical program for the calculation of NMR parameters using density-functional theory with the three-parameter hybrid exchange-correlation (B3LYP) functional. In the subsequent analysis, molecules are divided into groups according to the number of hydrogen bonds they possess, and the full average NMR tensors are calculated separately for each group. The classification of the hydrogen-bonding cases is performed using a simple distance-based criterion. The analysis reveals in detail how the NMR tensors evolve as the environment changes gradually from gas to liquid upon increasing the number of hydrogen bonds to the molecule of interest. Liquid-state distributions of the instantaneous values of the NMR properties show a wide range of values for each hydrogen-bonding species with significant overlap between the different cases. Our study shows how local changes in the environment, along with classical thermal averaging, affect the NMR parameters in liquid water. For example, a broken or alternatively extra hydrogen bond induces major changes in the NMR tensors, and the effect is more pronounced for hydrogen or deuterium than for oxygen. The data sheds light on the usefulness of NMR experiments in investigating the local coordination of liquid water.     

Study of E/Z isomerization of (arylamino)methylidenefuran‐2(3H)‐ones by 1H, 13C, 15N spectroscopy and DFT calculations in different solvents

The structure and configuration of the series of previously unknown arylaminomethylidenefuran‐2(3H)‐ones have been determined in solution by ¹H, ¹³C, ¹⁵N nuclear magnetic resonance spectroscopy including two‐dimensional experiments such as ¹H─¹H COSY, dqCOSY, ¹H─¹³C HSQC, ¹H─¹³C HMBC. It was found that synthesized substances exist as an equilibrium mixture of E‐ and Z‐enamines in solution. It was established on the basis of density functional theory calculations that the exchange between the two push–pull enamines is a simple rotation around an exocyclic partial double bond that depends on the effect of the solvents. Copyright © 2017 John Wiley & Sons, Ltd.     

A systematic investigation of hydrogen-bonding effects on the 17O, 14N, and 2H nuclear quadrupole resonance parameters of anhydrous and monohydrated cytosine crystalline structures: a density functional theory study

A systematic computational study was carried out to characterize the 17O, 14N, and 2H nuclear quadrupole resonance (NQR) parameters in the anhydrous and monohydrated cytosine crystalline structures. To include the hydrogen-bonding effects in the calculations, the most probable interacting molecules with the central molecule in the crystalline phase were considered in the pentameric clusters of both structures. To calculate the parameters, couples of the methods B3LYP and B3PW91 and the basis sets 6-311++G** and CC-pVTZ were employed. The mentioned methods calculated reliable values of 17O, 14N, and 2H NQR tensors in the pentameric clusters, which are in good agreements with the experiment. The different influences of various hydrogen-bonding interactions types, N-H...N, N-H...O, and O-H...O, were observed on the 17O, 14N, and 2H NQR tensors. Lower values of quadrupole coupling constants and higher values of asymmetry parameters in the crystalline monohydrated cytosine indicate the presence of stronger hydrogen-bonding interactions in the monohydrated form rather than that of crystalline anhydrous cytosine.     

Protein Backbone 1H(N)-13Calpha and 15N-13Calpha residual dipolar and J couplings: new constraints for NMR structure determination

A simple, sensitivity-enhanced experiment was devised for accurate measurement of backbone 15N-13Calpha and 1HN-13Calpha couplings in proteins. The measured residual dipolar couplings 2DHCA, 1DNCA, 3DHCA, and 2DNCA for protein GB1 display very good agreement with the refined NMR structure (PDB code: 3GB1). A Karplus-type relationship between the one-bond 1JNCA couplings and the backbone dihedral psi angles holds, and on the basis of the two-bond 2JNCA couplings a secondary structure index can be established.     

Experimental and Theoretical Investigations of the Formation of the Diazene PhSN=C(H)N=NC(H)=NSPh from HCN(2)(SPh)(3) by a Thiyl-Radical-Catalyzed Mechanism: Identification of the HC(NSPh)(2)(*) Radical and X-ray Structures of HCN(2)(SPh)(3) and PhSN=C(H)N=NC(H)=NSPh

The reaction of HCN(2)(SiMe(3))(3) with benzenesulfenyl chloride in a 1:3 molar ratio produces HCN(2)(SPh)(3) (4) as thermally unstable, colorless crystals. The decomposition of (4) in toluene at 95 degrees C was monitored by UV-visible, (1)H NMR and ESR spectroscopy. The major final products of the decomposition were identified as PhSN=C(H)N=NC(H)=NSPh (5) and PhSSPh. The structures of 4 and 5 were determined by X-ray crystallography. The crystals of 4 are monoclinic, space group P2(1)/a, with a = 9.874(2) ?, b = 19.133(2) ?, c = 10.280(2) ?, beta = 113.37(1) degrees, V = 1782.8(5) ?(3), and Z = 4. The final R and R(w) values were 0.042 and 0.049, respectively. The crystals of 5 are monoclinic, space group P2(1)/n, with a = 5.897(6) ?, b = 18.458(10) ?, c = 7.050(8) ?, beta = 110.97(5) degrees, V = 716(1) ?(3), and Z = 2. The final R and R(w) values were 0.075 and 0.085, respectively. The diazene 5 adopts a Z,E,Z structure with weak intramolecular S.N contacts of 2.83 ?, giving rise to four-membered NCNS rings. During the thermolysis of 4 at 95 degrees C in toluene a transient species (lambda(max) 820 nm) was detected. It decomposes with second-order kinetics to give 5 (lambda(max) 450 nm). The ESR spectrum of the reaction mixture consisted of the superposition of a three-line 1:1:1 spectrum (g = 2.0074, A(N) = 11.45 G), attributed to (PhS)(2)N(*), upon a doublet of quintets (1:2:3:2:1) with g = 2.0070, A(N) = 6.14 G, A(H) = 2.1 G assigned to the radical HCN(2)(SPh)(2)(*). Density functional theory (DFT) calculations for the models of the radical showed the E,Z isomer to have the lowest energy. Thermochemical calculations indicate that the decomposition of HCN(2)(SH)(3) into the diazene (Z,E,Z)-HSN=C(H)N=NC(H)=NSH (and 2 HSSH) is substantially more exothermic (DeltaH = -176.1 kJ mol(-)(1)) than the corresponding formation of the isomeric eight-membered ring (HC)(2)N(4)(SH)(2) (DeltaH = -40.6 kJ mol(-)(1)). These calculations also indicate that the diazene is formed by a mechanism in which the RS(*) radical acts as a catalyst.     

DMSO/N2H4.H2O/I2/H2O/CH3CN: a new system for selective oxidation of alcohols in hydrated media

A new alternative system for the oxidation of secondary alcohols to ketones with DMSO/N2H4.H2O/I2/H2O/CH3CN in hydrated media has been developed. The system also selectively oxidizes the secondary alcoholic groups to the corresponding ketones in the presence of primary alcoholic groups present within the same molecule in moderate to very good yields at reflux temperature.     

The first X-ray crystal structure of a mercury(II) complex with an SP(N)3-based ligand: Synthesis and crystal structure of SP(NC5H10)3 and [Hg{SP(NC5H10)3}Cl2]2

The synthesis, spectral characteristics (IR and NMR), elemental analysis and X-ray crystal structure of phosphorothioic triamide SP(NC₅H₁₀)₃ (1) and its dinuclear mercury(II) complex [Hg₂(μ-Cl)₂(Cl)₂{SP(NC₅H₁₀)₃}₂] (2) were investigated. A survey using the Cambridge Structural Database (CSD, version 5.38, May 2017) shows structures of coordination compounds of Au, Ag, Cd, Cu, Li, Mo, Ni, Pd, Te, Ti, Zn, and Zr with sulfur-donor SP(N)₃-based ligands; the complex 2 is the first example of a mercury complex with the SP(N)₃-based ligand studied by X-ray crystallography. Valence bond calculation was performed for the Hg–S bond in 2 and compared with the Hg–O bond in the only structure with a Cl₂Hg–OP(N)₃ structural motive in the CSD. The calculation confirms a more covalent nature of the Hg–S bond with respect to the Hg–O bond made by the EP(N)₃-based ligands (E?=?S, O). The supramolecular structures based on C–H···S?=?P contacts in 1 and C–H···S═P and C–H···Cl–Hg assemblies in 2 are discussed.