Hydrogen bond interactions in sulfamerazine: DFT study of the O-17, N-14, and H-2 electric field gradient tensors

Hydrogen bond (HB) interactions are studied in the real crystalline structure of sulfamerazine by density functional theory (DFT) calculations of the electric field gradient (EFG) tensors at the sites of O-17, N-14, and H-2 nuclei. One-molecule (single) and four-molecule (cluster) models of sulfamerazine are created by available crystal coordinates and the EFG tensors are calculated in both models to indicate the influence of HB interactions on the tensors. Directly relate to the experiments, the calculated EFG tensors are converted to the experimentally measurable nuclear quadrupole resonance (NQR) parameters, quadrupole coupling constant (qcc) and asymmetry parameter (η_Q). The evaluated NQR parameters reveal that due to contribution of the target molecule to N–HN and N–HO types of HB interactions, the EFG tensors at the sites of various nuclei are influenced from single model to the target molecule in cluster. Additionally, O2, N4, and H2 nuclei of the target molecule are significantly influenced by HB interactions, consequently, they have the major contributions to HB interactions in cluster model of sulfamerazine. The calculations are performed employing B3LYP method and 6-311++G** basis set using GAUSSIAN 98 suite of program.     

Study of hydrogen bonds in N-methylacetamide by DFT calculations of oxygen, nitrogen, and hydrogen solid-state NMR parameters

Solid-state nuclear magnetic resonance (NMR) parameters of ¹⁷O, ¹⁴N/¹⁵N, and ²H/¹H nuclei were evaluated in two available neutron crystalline structures of N-methylacetamide (NMA) at 250 and 276 K, NMA-I and NMA-II, respectively. Density functional theory calculations were performed by B3LYP method and 6-311++G** and IGLO-II type basis sets to calculate the electric field gradient (EFG) and chemical shielding (CS) tensors at the sites of mentioned nuclei. In order to investigate hydrogen bonds (HBs) effects on NMR tensors, calculations were performed on four-model systems of NMA: an optimized isolated gas-phase, crystalline monomers, crystalline dimers, and crystalline trimers. Comparing the calculated results reveal the influence of N–H···O=C and C–H···O=C HB types on the NMR tensors which are observable by the evaluated parameters including quadrupole coupling constant, C _Q, and isotropic CS, σ _iso. Furthermore, the results demonstrate more influence of HB on the EFG and CS tensors of NMA at 276 K rather than that of 250 K.     

B<Subscript>24</Subscript>N<Subscript>24</Subscript> nanocages: a GIAO density functional theory study of <Superscript>14</Superscript>N and <Superscript>11</Superscript>B nuclear magnetic shielding and electric field gradient tensors

Abstract  Density functional theory (DFT) calculations were performed to determine boron-11 and nitrogen-14 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) spectroscopy parameters in the three most stable B₂₄N₂₄ fullerenes for the first time. The considered samples were first allowed to relax entirely, and then the NMR and NQR calculations were performed on the geometrically optimized models. The calculations of the ¹¹B and ¹⁴N nuclear magnetic shielding tensors and electric field gradient tensors employed the Gaussian 98 software implementation of the gauge-including atomic orbital (GIAO) method using the Becke3, Lee-Yang-Parr (B3LYP) DFT level and 6-311G** and 6-311++G** standard basis sets in each of the three optimized forms, and converted the results to experimentally measurable NMR parameters.The calculated NMR chemical shieldings of the three cages show significant differences, providing a way to identify these clusters. The evaluated NQR parameters of the ¹¹B and ¹⁴N nuclei in the clusters are also reported and discussed. Graphical abstract        

Configurational and conformational preferences in stereoselective acylations of <Emphasis Type="Italic">N</Emphasis>-methyl-1,3-diaminopropane with acyl chlorides

Evidence for a stereoinduction profile of the reaction of N-methyl-1,3-diaminopropane with acyl chlorides has been provided. A possibility to engage in intramolecular CH₂⋯HN and Cl⋯H-N interactions and the proton migration process to the methylamino group leads to the E secondary amides carrying the N⋯H⁺⋯N or N-H⋯N bridges, that show unusual spectroscopic images. Empirical relations between the Δδ _C chemical shift differences, the polarizability of the CO(S) groups and hydrogen bonding strength have been found. Both ¹H-¹⁵N-GHSQC and GHMBC experiments provide insight into the nature of hydrogen bonding and confirm the cyclic array of atoms.     

Density functional theory investigation of hydrogen bonding effects on the oxygen, nitrogen and hydrogen electric field gradient and chemical shielding tensors of anhydrous chitosan crystalline structure

A systematic computational investigation was carried out to characterize the 17O, 14N and 2H electric field gradient, EFG, as well as 17O, 15N, 13C and 1H chemical shielding tensors in the anhydrous chitosan crystalline structure. To include the hydrogen-bonding effects in the calculations, the most probable interacting molecules with the target molecule in the crystalline phase were considered through a hexameric cluster. The computations were performed with the B3LYP method and 6-311++G(d,p) and 6-31++G(d,p) standard basis sets using the Gaussian 98 suite of programs. Calculated EFG and chemical shielding tensors were used to evaluate the 17O, 14N and 2H nuclear quadrupole resonance, NQR, and 17O, 15N, 13C and 1H nuclear magnetic resonance, NMR, parameters in the hexameric cluster, which are in good agreement with the available experimental data. The difference between the calculated NQR and NMR parameters of the monomer and hexamer cluster shows how much hydrogen bonding interactions affect the EFG and chemical shielding tensors of each nucleus. These results indicate that both O(3)-H(33)...O(5-3) and N-H(22)...O(6-4) hydrogen bonding have a major influence on NQR and NMR parameters. Also, the quantum chemical calculations indicate that the intra- and intermolecular hydrogen bonding interactions play an essential role in determining the relative orientation of EFG and chemical shielding principal components in the molecular frame axes.     

High-field solid-state <Superscript>35</Superscript>Cl NMR in selenium(IV) and tellurium(IV) hexachlorides

We report solid-state ³⁵Cl NMR spectra in three hexachlorides, (NH₄)₂SeCl₆, (NH₄)₂TeCl₆ and Rb₂TeCl₆. The C_Q(³⁵Cl) quadrupole coupling constants in the three compounds were found to be 41.4±0.1 MHz, 30.3±0.1 MHz and 30.3±0.1 MHz, respectively, some of the largest C_Q(³⁵Cl) quadrupole coupling constants ever measured in polycrystalline powdered solids directly via ³⁵Cl NMR spectroscopy. The ³⁵Cl EFG tensors are axial in all three cases reflecting the C_4v point group symmetry of the chlorine sites. ³⁵Cl NMR experiments in these compounds were only made possible by employing the WURST-QCPMG pulse sequence in the ultrahigh magnetic field of 21.1 T. ³⁵Cl NMR results agree with the earlier reported ³⁵Cl NQR values and with the complementary plane-wave DFT calculations. The origin of the very large C_Q(³⁵Cl) quadrupole coupling constants in these and other main-group chlorides lies in the covalent-type chlorine bonding. The ionic bonding in the ionic chlorides results in significantly reduced C_Q(³⁵Cl) values as illustrated with triphenyltellurium chloride Ph₃TeCl. The high sensitivity of ³⁵Cl NMR to the chlorine coordination environment is demonstrated using tetrachlorohydroxotellurate hydrate K[TeCl₄(OH)]?0.5H₂O as an example. ¹²⁵Te MAS NMR experiments were performed for tellurium compounds to support ³⁵Cl NMR findings.     

Synthesis and structure of the cadmium(II) complex [Cd2(Ph(NH2)2)5(DMFA)4](B10H10)2

A new binuclear cadmium(II) complex with neutral ligands, 1,2-diaminobenzene (DMB) and dimethylformamide (DMF), [Cd₂(Ph(NH₂)₂)₅(DMFA)₄](B₁₀H₁₀)₂, was synthesized and studied by IR spectroscopy and X-ray diffraction. The crystals are monoclinic, a = 26.198(3) ?, b = 12.742(3) ?, c = 21.658(3) ?, β = 119.985(10)°, Z = 8, space group C2/c. The distorted octahedral environment of Cd is formed by four nitrogen atoms of three DAB molecules and two oxygen atoms of DMF molecules. Three independent DAB molecules perform different functions: one chelates the Cd atom, another is linked to cadmium as a monodentate ligand, and the third one bridges two Cd atoms, thus forming the dimer. The amino groups of the DAB molecules are involved in the N-H⋯O and N-H⋯N hydrogen bonds and in N-H⋯B and N-H⋯H-B specific interactions with the cluster boron anion. Original Russian Text ? E.A. Malinina, V.V. Drozdova, L.V. Goeva, I.N. Polyakova, N.T. Kuznetsov, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 6, pp. 922–926.     

Theoretical 14N and 17O nuclear quadrupole resonance parameters for tirapazamine and related metabolites

Density functional theory (DFT) calculations were performed to realize the effects of the N–O group on the reactivity and electronic properties of 3-amino-1,2,4-benzotriazines. The electric field gradient, EFG, tensors of ¹⁴N and ¹⁷O nuclei and natural bond orbital (NBO) analysis in the tirapazamine (TPZ) and its four derivatives were calculated at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) method in the gas phase. The NBO analysis reveal that the bond strength, proton affinity and position of N–O group in the heterocyclic ring have major influence on the reactivity of considered molecules. Accordingly, we suggest that the TPZ and 4-oxide (d) structures due to having a weaker N–O bond with larger negative charge on the oxygen atom at the 4-position are more active than the other ones. Calculated ¹⁴N and ¹⁷O EFG tensors were used to evaluate nuclear quadrupole coupling tensors, χ, and asymmetry parameters, η _Q . Results showed that oxidation of a nitrogen atom at any position have significant influence on its ¹⁴N nuclear quadrupole resonance (NQR) parameters. Also, the occupancy of nitrogen lone pair plays an important role in determination of the q _zz and χ values of mentioned nuclei. It is found that the η _Q and χ are appropriate parameters to study the contribution of lone pair electrons of nitrogen atom in the formation of chemical bond or conjugation with the aromatic system. Finally, a linear correlation is observed between the χ(¹⁴N) and χ(¹⁷O) values in the N–O bond which may be associated with the reactivity of these compounds.     

Charge distribution and mobility of lithium ions in Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> from <Superscript>6,7</Superscript>Li NMR data

A comparative analysis of ^6,7Li NMR spectra is performed for the samples of monoclinic lithium titanate obtained at different synthesis temperatures. In the ⁷Li NMR spectra three lines are found, which differ in quadrupole splitting frequencies v _Q and according to ab initio EFG calculations are assigned to three crystallographic sites of lithium: Li1 (v _Q ～ 27 kHz); Li2 (v _Q ～ 59 kHz); Li3 (v _Q ～ 6 kHz). The dynamics of lithium ions is studied in a wide temperature range from 300 K to 900 K. It is found that the narrowing of ⁷Li NMR spectra as a result of thermally activated diffusion of lithium ions in the low-temperature Li₂TiO₃ sample is observed at a higher temperature in comparison with a sample of high-temperature lithium titanate. Based on the analysis of ⁶Li NMR spectra it is assumed that there is mixed occupancy of lithium and titanium sites in the corresponding layers of the crystal structure of low-temperature lithium titanate, which hinders lithium ion transfer over regular crystallographic sites.     

A study of the electronic structure of polyvinylsiloxane (CH<Superscript>2</Superscript>CHSiO<Subscript>1.5</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> by X-ray photoelectron spectroscopy and quantum chemical modeling in the DFT approximation

The electronic structure of polyvinylsiloxane polymeric chains (Si₂O₃(CHCH₂)₂)_n is studied by X-ray photoelectron spectroscopy and quantum chemistry in the DFT approximation. The binding energy of C and O ls electrons occupying inequivalent positions in the polymer coincides within the experimental accuracy. The binding energies for C and O (284.9 eV and 532.4 eV) and for Si2p-electrons (102.7 eV) well agree with the values for related compounds. The experimental data for the binding energy are reproduced in HF and DFT calculations only with the extended 6–311**(d) basis set. The highest occupied levels of the polymer are fy orbitals of vinyl groups     

Density Functional Theory calculations on the magnetic properties of the model tyrosine radical-histidine complex mimicking tyrosyl radical Y<Subscript>D</Subscript><Superscript>·</Superscript> in photosystem II

Results of Density Functional Theory (DFT) theoretical investigations, which use a model tyrosyl (Tyr) radical and tyrosyl-histidine (Tyr-His) complex to mimick the Y _D ^· radical in Photosystem II (PSII) are presented and compared to experimental results from ¹⁵N Electron-Nuclear Double Resonance spectroscopy (ENDOR) studies of the τ nitrogen coupling from His-189 in the PSII Tyr-His complex. The DFT calculations are performed using an optimized geometry of the tyrosine radical and Tyr-His complex. The conformational space of the Tyr-His tandem is explored by varying the relative geometry of the two components; relevant parameters, such as the spin distribution on the phenoxy-ring carbons of the Tyr radical and the EPR hyperfine tensors, are calculated at each geometry and compared with the available experimental data. The isotropic ¹⁵N-ENDOR signal arising from spin delocalization on the His hydrogen-bonded to the PSII tyrosine radical is analyzed in terms of the DFT obtained parameters. The calculations of the g tensor using the Gauge Independent Atomic Orbital (GIAO) approach are presented and the influence of the geometry of the Tyr-His complex on the deviation of the g-tensor elements from the free electron values is discussed.     

Crystal structures of [Hg(<Emphasis Type="Italic">N</Emphasis>-ethylthiourea)<Subscript>2</Subscript>(CN)<Subscript>2</Subscript>] and [Hg(<Emphasis Type="Italic">N</Emphasis>-propylthiourea)<Subscript>2</Subscript>(CN)<Subscript>2</Subscript>]

Two mercury(II) cyanide complexes of N-ethylthiourea (Ettu) and N-propylthiourea (Prtu) ligands, [Hg(Ettu)₂(CN)₂] (1) and [Hg(Prtu)₂(CN)₂] (2), were prepared and their crystal structures were determined by X-ray crystallography. In both structures, the mercury atom is coordinated to two sulfur atoms of thioureas and two cyanide carbon atoms in a pseudo-tetrahedral mode with the bond angles in the range of 90.52(11)–162.2(3)°. The structures are stabilized by N-H—S, N-H—N, and C-H—N intramolecular and intermolecular hydrogen bonds.     

A theoretical investigation of hydrogen bonding effects on oxygen and hydrogen chemical shielding tensors of aspirin

A computational investigation was carried out to characterize the ¹⁷O and ¹H chemical shielding (CS) tensors in crystalline aspirin. It was found that O–H⋯O and C–H⋯O hydrogen bonds around the aspirin molecule in the crystal lattice have a different influence on the calculated ¹⁷O and ¹H CS eigenvalues and their orientations in the molecular frame of axes. The calculations were performed with the BLYP, B3LYP, and M06 functionals employing 6-311++G(d,p) standard basis set. Calculated CS tensors were used to evaluate the ¹⁷O and ¹H chemical shift isotropy (δ_iso) and anisotropy (Δσ) in crystalline aspirin, which are in reasonable agreement with available experimental data. The difference between the calculated NMR parameters of the monomer and molecular clusters shows how much hydrogen-bonding interactions affect the CS tensors of each nucleus.     

Structures and bonding of the complexes [M(η<Superscript>5</Superscript>-E<Subscript>5</Subscript>)] and [M(η<Superscript>5</Superscript>-E<Subscript>5</Subscript>)<Subscript>2</Subscript>] (M = Sc,Y, E = N,P): a DFT study

The mono- and bisligands complexes formed by rare earth cation (Sc, Y) with pentazolato anion or cyclo-P₅⁻ anion, the all-nitrogen counterparts of metallocenes or the all-phosphorus counterparts of metallocenes, have been studied at hybrid basis sets level with the DFT method. The geometric parameters, binding energy and the charge distributions of these complexes were characterized. And their stable orders were obtained. Monoligand complexes incline to become bisligands complexes due to their destabilization. The charge transferring between ligand and metallic cation has affinity with the stability of complex. The possibility of forming stable [M(η ⁵-E₅)₂] (M = Sc, Y, E = N, P) complexes is predicted and they are viable synthetic targets theoretically, especially Sc(η ⁵-N₅)₂.     

Extraction of metal ions (Fe<Superscript>3+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) using immobilized-polysiloxane iminobis(n-2-aminophenylacetamide) ligand system

A new insoluble solid functionalized ligand system bearing chelating ligand group of the general formula P-(CH₂)₃-N[CH₂CONH(C₆H₄)NH₂]₂, where P represents [Si–O] _n polysiloxane network, was prepared by the reaction of the immobilized diethyliminodiacetate polysiloxane ligand system, P-(CH₂)₃N(CH₂CO₂Et)₂ with 1,2-diaminobenzene in toluene. ¹³C CP-MAS NMR, XPS and FTIR results showed that most ethylacetate groups (–COOEt) were converted into the amide groups (–N–C=O). The new functionalized ligand system exhibits high capacity for extraction and removal of the metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with efficiency of 95–97% after recovery from its primary metal complexes. This functionalized ligand system formed 1:1 metal to ligand complexes.     

Molecular modeling of hydration properties of hydrophobic ions Li<Superscript>+</Superscript>@C<Subscript>60</Subscript> and K<Superscript>+</Superscript>@C<Subscript>60</Subscript>

The Gibbs free energies of solvation (ΔG _s) and the electronic structures of endohedral metallofullerenes M⁺@C₆₀ (M⁺= Li⁺, K⁺) were calculated within the framework of the density functional theory and the polarizable continuum model. In water environment, the equilibrium position of K⁺ is at the center of the fullerene cavity whereas that of Li⁺ is shifted by 0.14 nm toward the fullerene cage. The Li⁺ cation is stabilized by interactions with both the fullerene and solvent. The equilibrium structures of both endohedral metallofullerenes are characterized by very close ΔG _s values. In particular, the calculated ΔG _s values for K⁺@C₆₀ are in the range from −124 to −149 kJ mol⁻¹ depending on the basis set and on the type of the density functional. Molecular dynamics simulations (TIP3P H₂O, OPLS force field, water sphere of radius 1.9 nm) showed that the radial distribution functions of water density around C₆₀ and M⁺@C₆₀ are very similar, whereas orientations of water dipoles around the endohedral metallofullerenes resemble the hydration pattern of isolated metal ions.     

Preparation and characterization of diethylnicotinamidium perchlorate

The title compound is the first example of N,N′-diethylnicotinamidium, [denaH]⁺, salt which has been characterized by X-ray analysis and IR spectra. [denaH]ClO₄ was obtained from the reaction mixture prepared from N,N′-diethylnicotinamide (dena) and Fe(ClO₄)₃ in ethanol without any addition of HClO₄. The proton required for protonation of dena is produced by hydrolysis of aquairon(III) cations. In the crystal structure, cations and anions are held together by ionic interactions. The cations are linked to each other by pyridinium-carbonyl N-H⋯O=C hydrogen bonds and an infinite linear chain along axis a is formed. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

An Investigation of Lanthanum Coordination Compounds by Using Solid‐State 139La NMR Spectroscopy and Relativistic Density Functional Theory

Lanthanum‐139 NMR spectra of stationary samples of several solid La^III coordination compounds have been obtained at applied magnetic fields of 11.75 and 17.60 T. The breadth and shape of the ¹³⁹La NMR spectra of the central transition are dominated by the interaction between the ¹³⁹La nuclear quadrupole moment and the electric field gradient (EFG) at that nucleus; however, the influence of chemical‐shift anisotropy on the NMR spectra is non‐negligible for the majority of the compounds investigated. Analysis of the experimental NMR spectra reveals that the ¹³⁹La quadrupolar coupling constants (C_Q) range from 10.0 to 35.6 MHz, the spans of the chemical‐shift tensor (Ω) range from 50 to 260 ppm, and the isotropic chemical shifts (δ_iso) range from ?80 to 178 ppm. In general, there is a correlation between the magnitudes of C_Q and Ω, and δ_iso is shown to depend on the La coordination number. Magnetic‐shielding tensors, calculated by using relativistic zeroth‐order regular approximation density functional theory (ZORA‐DFT) and incorporating scalar only or scalar plus spin–orbit relativistic effects, qualitatively reproduce the experimental chemical‐shift tensors. In general, the inclusion of spin–orbit coupling yields results that are in better agreement with those from the experiment. The magnetic‐shielding calculations and experimentally determined Euler angles can be used to predict the orientation of the chemical‐shift and EFG tensors in the molecular frame. This study demonstrates that solid‐state ¹³⁹La NMR spectroscopy is a useful characterization method and can provide insight into the molecular structure of lanthanum coordination compounds.     

Crystal structure of the molecular adduct of antimony(III) fluoride with L-phenylalanine

The crystal structure of a newly synthesized molecular adduct of antimony(III) fluoride with L-phenylalanine of the composition SbF₃(C₉H₁₁NO₂) is determined for the first time (monoclinic crystal system: a = 5.8742(1) ?, b = 6.2079(1) ?, c = 15.5401(3) ?, β = 90.741(1)°, Z = 2, P2₁ space group). The structure consists of SbF₃ molecules and L-phenylalanine bound into polymer chains by bidentate bridging carboxyl groups of amino acid molecules. Weak Sb⋯F(3)^b bonds organize the adjacent chains into polymer ribbons that are bound into layers by N-H⋯F and N-H⋯O hydrogen bonds.     

An Isotope (<Superscript>18</Superscript>O, <Superscript>15</Superscript>N,and <Superscript>2</Superscript>H) Technique to Investigate the Metal Ion Interactions Between the Phosphoryl Group and Amino Acid Side Chains by Electrospray Ionization Mass Spectrometry

Cationic metal ion-coordinated N-diisopropyloxyphosphoryl dipeptides (DIPP-dipeptides) were analyzed by electrospray ionization multistage tandem mass spectrometry (ESI-MS ⁿ ). Two novel rearrangement reactions with hydroxyl oxygen or carbonyl oxygen migrations were observed in ESI-MS/MS of the metallic adducts of DIPP-dipeptides, but not for the corresponding protonated DIPP-dipeptides. The possible oxygen migration mechanisms were elucidated through a combination of MS/MS experiments, isotope (¹⁸O, ¹⁵N, and ²H) labeling, accurate mass measurements, and density functional theory (DFT) calculations at the B3LYP/6-31 G(d) level. It was found that lithium and sodium cations catalyze the carbonyl oxygen migration more efficiently than does potassium and participation through a cyclic phosphoryl intermediate. In addition, dipeptides having a C-terminal hydroxyl or aromatic amino acid residue show a more favorable rearrangement through carbonyl oxygen migration, which may be due to metal cation stabilization by the donation of lone pair of the hydroxyl oxygen or aromatic π-electrons of the C-terminal amino acid residue, respectively. It was further shown that the metal ions, namely lithium, sodium, and potassium cations, could play a novel directing role for the migration of hydroxyl or carbonyl oxygen in the gas phase. This discovery suggests that interactions between phosphorylated biomolecules and proteins might involve the assistance of metal ions to coordinate the phosphoryl oxygen and protein side chains to achieve molecular recognition.