Structural characterization of hypoglycin B,a diastereomeric dipeptide from the ackee fruit (Blighia sapida Koenig) by NMR experiments

The dipeptide hypoglycin B, one of two toxins of the ackee fruit (Blighia sapida Koenig), was characterized for the first time by NMR spectral data, which led to the discovery that it exists naturally as a pair of diastereomers. No distinction was observed in the ¹H NMR signals of the diastereomers; however, complete and distinct ¹³C NMR assignments for the individual diastereomers were made. The ¹³C NMR spectrum of hypoglycin B compared very well with that of the corresponding signals in the spectrum for hypoglycin A, which is one of its constituent amino acids. The ¹H and ¹³C NMR assignments were further supported by DEPT, gCOSY, gHSQC and gHMBC experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

Partial least squares modeling of combined infrared, H NMR and C NMR spectra to predict long residue properties of crude oils

Research has been carried out to determine the potential of partial least squares (PLS) modeling of mid-infrared (IR) spectra of crude oils combined with the corresponding ¹H and ¹³C nuclear magnetic resonance (NMR) data, to predict the long residue (LR) properties of these substances. The study elaborates further on a recently developed and patented method to predict this type of information from only IR spectra. In the present study, PLS modeling was carried out for 7 different LR properties, i.e., yield long-on-crude (YLC), density (D_LR), viscosity (V_LR), sulfur content (S), pour point (PP), asphaltenes (Asph) and carbon residue (CR). Research was based on the spectra of 48 crude oil samples of which 28 were used to build the PLS models and the remaining 20 for validation. For each property, PLS modeling was carried out on single type IR, ¹³C NMR and ¹H NMR spectra and on 3 sets of merged spectra, i.e., IR + ¹H NMR, IR + ¹³C NMR and IR + ¹H NMR + ¹³C NMR. The merged spectra were created by considering the NMR data as a scaled extension of the IR spectral region. In addition, PLS modeling of coupled spectra was performed after a Principal Component Analysis (PCA) of the IR, ¹³C NMR and ¹H NMR calibration sets. For these models, the 10 most relevant PCA scores of each set were concatenated and scaled prior to PLS modeling. The validation results of the individual IR models, expressed as root-mean-square-error-of-prediction (RMSEP) values, turned out to be slightly better than those obtained for the models using single input ¹³C NMR or ¹H NMR data. For the models based on IR spectra combined with NMR data, a significant improvement of the RMSEP values was not observed neither for the models based on merged spectra nor for those based on the PCA scores. It implies, that the commonly accepted complementary character of NMR and IR is, at least for the crude oil and bitumen samples under study, not reflected in the results of PLS modeling. Regarding these results, the absence of sample preparation and the straightforward way of data acquisition, IR spectroscopy is preferred over NMR for the prediction of LR properties of crude oils at site.     

Partial least squares modeling of combined infrared, 1H NMR and 13C NMR spectra to predict long residue properties of crude oils

Research has been carried out to determine the potential of partial least squares (PLS) modeling of mid-infrared (IR) spectra of crude oils combined with the corresponding ¹H and ¹³C nuclear magnetic resonance (NMR) data, to predict the long residue (LR) properties of these substances. The study elaborates further on a recently developed and patented method to predict this type of information from only IR spectra. In the present study, PLS modeling was carried out for 7 different LR properties, i.e., yield long-on-crude (YLC), density (D_LR), viscosity (V_LR), sulfur content (S), pour point (PP), asphaltenes (Asph) and carbon residue (CR). Research was based on the spectra of 48 crude oil samples of which 28 were used to build the PLS models and the remaining 20 for validation. For each property, PLS modeling was carried out on single type IR, ¹³C NMR and ¹H NMR spectra and on 3 sets of merged spectra, i.e., IR + ¹H NMR, IR + ¹³C NMR and IR + ¹H NMR + ¹³C NMR. The merged spectra were created by considering the NMR data as a scaled extension of the IR spectral region. In addition, PLS modeling of coupled spectra was performed after a Principal Component Analysis (PCA) of the IR, ¹³C NMR and ¹H NMR calibration sets. For these models, the 10 most relevant PCA scores of each set were concatenated and scaled prior to PLS modeling. The validation results of the individual IR models, expressed as root-mean-square-error-of-prediction (RMSEP) values, turned out to be slightly better than those obtained for the models using single input ¹³C NMR or ¹H NMR data. For the models based on IR spectra combined with NMR data, a significant improvement of the RMSEP values was not observed neither for the models based on merged spectra nor for those based on the PCA scores. It implies, that the commonly accepted complementary character of NMR and IR is, at least for the crude oil and bitumen samples under study, not reflected in the results of PLS modeling. Regarding these results, the absence of sample preparation and the straightforward way of data acquisition, IR spectroscopy is preferred over NMR for the prediction of LR properties of crude oils at site.     

Synthesis and DFT study of the spectral behavior of new 4‐hydroxycoumarins

4‐Hydroxycoumarins are compounds with a lot of applications as drugs and herbicides. They have very interesting spectral and chemical properties, which are investigated theoretically and experimentally. Some new 4‐hydroxycoumarins with arylydene‐β‐ketoester or arylydene‐2,4‐pentanedione side chain were synthesized by two step synthetic scheme. Their structure was characterized by UV–vis, IR, and ¹H NMR methods. The spectral behavior of the optimized structures of these compounds was reproduced by the hybrid DFT methods B3LYP and B3P86 with 6‐31G** and aug‐cc‐pVDZ basis sets. Electronic excited states and vibrational frequencies were calculated. HF method was also used for comparison, because of the lack of electronic correlation. The theoretical spectra were compared with the experimental ones. A lot of compounds show good agreement between experimental and some of the theoretical data, especially obtained by aug‐cc‐pVDZ basis set. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Effects of different GIAO and CSGT models and basis sets on 2-aryl-1,3,4-oxadiazole derivatives

The direct molecular structure implementations of the gage-including atomic orbital (GIAO), individual gages for atoms in molecules (IGAIM) and continuous set of gage transformations (CSGT) methods for calculating nuclear magnetic shielding tensors at both the Hartree-Fock (HF) and density functional (B3LYP) levels of theory with 6-31G(d), 6-311G(d), 6-31++G(d,p), 6-311++G(d,p), and 6-311++G(df,pd) basis sets are presented. Dependence on the ¹H and ¹³C NMR chemical shifts on the choice of method and basis set have been investigated. Also, these chemical shifts of 2-aryl-1,3,4-oxadiazoles 5a–g have been performed related to dihedral angles (C4–C3–C2–O) of two conformers. The optimized molecular geometries and ¹H and ¹³C chemical shift values of 2-aryl-1,3,4-oxadiazoles 5a–g in the ground state have been obtained. The linear correlation coefficients of ¹³C NMR chemical shifts for these molecules were given. The new nuclear magnetic shielding tensors of tetramethylsilane (TMS) were calculated. The data of 2-aryl-1,3,4-oxadiazole derivatives display significant molecular structure and NMR analysis. Also, these provide the basis for future design of efficient materials having the 1,3,4-oxadiazole core.     

Disentangling Complex Mixtures of Compounds with Near‐Identical 1H and 13C NMR Spectra using Pure Shift NMR Spectroscopy

The thorough analysis of highly complex NMR spectra using pure shift NMR experiments is described. The enhanced spectral resolution obtained from modern 2D HOBS experiments incorporating spectral aliasing in the ¹³C indirect dimension enables the distinction of similar compounds exhibiting near‐identical ¹H and ¹³C NMR spectra. It is shown that a complete set of extremely small Δδ(¹H) and Δδ(¹³C) values, even below the natural line width (1 and 5 ppb, respectively), can be simultaneously determined and assigned.     

1H, 13C, 19F and 11B NMR spectral reference data of some potassium organotrifluoroborates

Complete ¹H, ¹³C, ¹⁹F and ¹¹B NMR spectral data for 28 potassium organotrifluoroborates are described. The resonance for the carbon bearing the boron atom is described for most of the studied compounds. A modified ¹¹B NMR pulse sequence was used and better resolution was observed allowing the observation of ¹¹B–¹⁹F coupling constants for some of the studied compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of fluorine substituents on the NMR properties of phenylboronic acids

The paper presents results of a systematic NMR studies on fluorinated phenylboronic acids. All possible derivatives were studied. The experimental ¹H, ¹³C, ¹⁹F, ¹¹B, and ¹⁷O spectral data were compared with the results of theoretical calculations. The relation between the calculated natural bond orbital parameters and spectral data (chemical shifts and coupling constants) is discussed. The first examples of ¹⁰B/¹¹B isotopic effect on the ¹⁹F spectra and ⁴J_FO scalar coupling in organic compounds are reported. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of GIAO and CSGT for calculating 13C and 15N nuclear magnetic resonance chemical shifts of substituent neutral 5‐aminotetrazole and 5‐nitrotetrazole compounds

The comparison of the gauge‐including atomic orbital (GIAO) and the continuous set of gauge transformation methods for calculating nuclear magnetic chemical shifts (CSs) mainly at density functional levels of theory are presented. Isotropic ¹³ C and ¹⁵ N magnetic CS for 14 compounds of tetrazoles are reported. Compared with establishing a convenient and consistent protocol to be employed for confirming the experimental ¹³ C and ¹⁵ N NMR spectra of tetrazole compounds, different combinations of functionals and basis sets were considered. The most reliable results were obtained at GIAO/B3LYP/aug‐cc‐pVDZ with integral equation formulation for the polarizable continuum model (PCM), which has the smallest root mean square errors and can be used to calculate ¹³ C and ¹⁵ N NMR CS with a very high accuracy for tetrazoles. These results show that the accurately calculated ¹⁵N NMR CS of tetrazoles could be used for the evaluation of the intrinsic relationship between structure and explosive properties. Copyright © 2012 John Wiley & Sons, Ltd.     

NMR Chemical Shift and Quadrupolar Interaction Parameters of Carbon‐Coordinated 27Al in Aluminium Carbide,Al4C3

Aluminium carbide, Al₄C₃, was characterised by ¹³C and ²⁷Al solid‐state NMR spectroscopy. The ¹³C NMR spectra display two resonances with an intensity ratio of 1:2, which is in agreement with the reported crystal structure. The ²⁷Al NMR spectra of Al₄C₃ under both static and MAS conditions were deconvoluted into two spectral components, belonging to the two aluminium species Al1 and Al2 in the crystal structure of Al₄C₃. The spectral fit allowed for determination of the relatively large quadrupolar coupling constants (χ ≈? 16 MHz) of both ²⁷Al species. One aluminium species displayed a tendency of having a χ of slightly smaller magnitude compared to the other. By carrying out DFT calculations of the EFG tensor at the ²⁷Al sites using the Wien2k software, we could tentatively assign the smaller χ site to be the crystallographic Al1 species. Also, the isotropic chemical shift for the carbon‐coordinated aluminium in Al₄C₃ could be determined, being in the range of 111 to 120 ppm. This is somewhat larger than those shift values observed for ²⁷Al in nitrogen coordination.     

Synthesis of new thiophene,furan and pyridine substituted 1,2,4,5-oxadiazaboroles

Twenty-two new 3,4,5-trisubstituted 1,2,4,5-oxadiazaboroles were prepared by the cyclocondensation reaction of N-substituted thiophene, furan and pyridine carboxamidoximes with phenylboronic acid in refluxing toluene in good yields. The structures of the new oxadiazaboroles were elucidated by means of spectral measurements (IR, ¹H, ¹³C, ¹¹B NMR, MS, X-ray) and physical data (melting points, elemental compositions by HRMS).     

Quantum‐chemical,IR, NMR,and X‐ray diffraction studies on 2‐(4‐chlorophenyl)‐1‐methyl‐ 1H‐benzo[d]imidazole

The title molecule, 2‐(4‐chlorophenyl)‐1‐methyl‐1H‐benzo[d]imidazole (C₁₄H₁₁ClN₂), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, and single‐crystal X‐ray diffraction. The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated by using the Hartree‐Fock (HF) and density functional theory (DFT/B3LYP) method with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and GIAO ¹H and ¹³C NMR chemical shifts show good agreement with experimental values. The energetic behavior of the title compound in solvent media has been examined using B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, and nonlinear optical (NLO) properties of the title compound were investigated by theoretical calculations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Prediction of the reduction potential in transition‐metal containing complexes: How expensive? For what accuracy?

Accurate computationally derived reduction potentials are important for catalyst design. In this contribution, relatively inexpensive density functional theory methods are evaluated for computing reduction potentials of a wide variety of organic, inorganic, and organometallic complexes. Astonishingly, SCRF single points on B3LYP optimized geometries with a reasonably small basis set/ECP combination works quite well‐‐B3LYP with the BS1 [modified‐LANL2DZ basis set/ECP (effective core potential) for metals, LANL2DZ(d,p) basis set/LANL2DZ ECP for heavy nonmetals (Si, P, S, Cl, and Br), and 6‐31G(d') for other elements (H, C, N, O, and F)] and implicit PCM solvation models, SMD (solvation model based on density) or IEFPCM (integral equation formalism polarizable continuum model with Bondi atomic radii and α = 1.1 reaction field correction factor). The IEFPCM‐Bondi‐B3LYP/BS1 methodology was found to be one of the least expensive and most accurate protocols, among six different density functionals tested (BP86, PBEPBE, B3LYP, B3P86, PBE0, and M06) with thirteen different basis sets (Pople split‐valence basis sets, correlation consistent basis sets, or Los Alamos National Laboratory ECP/basis sets) and four solvation models (SMD, IEFPCM, IPCM, and CPCM). The MAD (mean absolute deviation) values of SCRF‐B3LYP/BS1 of 49 studied species were 0.263 V for SMD and 0.233 V for IEFPCM‐Bondi; and the linear correlations had respectable R ² values (R ² = 0.94 for SMD and R ² = 0.93 for IEFPCM‐Bondi). These methodologies demonstrate relatively reliable, convenient, and time‐saving functional/basis set/solvation model combinations in computing the reduction potentials of transition metal complexes with moderate accuracy. © 2017 Wiley Periodicals, Inc.     

Synthesis,Characterization, and Biological Activity of Substituted Thiazole-5-carboxaldehydes and Their Ylidenenitriles Derivatives

The Vilsmeier–Haack reaction of 2-amino -4-(4-substituted phenyl)-thiazoles 1, in the presence of micellar media, gives formylated derivatives 2, which upon hydrolysis afforded thiazole-5-carboxaldehydes 3. Microwave-assisted Knoevenagel condensation of 3 with active methylene compounds, in the presence of piperidine as catalyst, gives excellent yields of ylidenenitrile compounds 4. The structures of the newly synthesized compounds were established on the basis of elemental analysis, IR, ¹H NMR, and ¹³C NMR spectral analysis. All newly synthesized compounds were screened for antibacterial activity using two Gram-positive and one Gram-negative bacterial species and their antifungal activity was screened using two fungal species.     

Synthesis and characterization of novel phthalocyanines bearing quaternizable coumarin

The synthesis of novel metal-free and zinc phthalocyanines with four 3-[(2-diethylamino)ethyl]-7-oxo-4-methylcoumarin dye groups on the periphery were prepared by cyclotetramerization of a novel 3-[(2-diethylamino)ethyl]-7-[(3,4-dicyanophenoxy)]-4-methylcoumarin. The novel chromogenic compounds were characterized by elemental analysis, ¹H NMR, ¹³C NMR, MALDI-TOF, IR and UV–Vis spectral data. The electronic spectra exhibit bands of coumarin identity along with characteristic Q and B bands of the phthalocyanine (Pc) core. The IR spectra of all the Pcs showed three characteristic intense bands, at 1704 cm⁻¹ for the lactone carbonyl and two bands at 1489–1604 cm⁻¹ for the conjugated olefinic system.     

Synthesis and antimicrobial evaluation of tricyclic macrocycles containing a chalcone moiety

A series of new tricyclic macrocycles containing a chalcone moiety were synthesized from chalcones through alkylation using different dibromoalkanes. All the synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, and mass spectral data and evaluated for their in vitro antimicrobial activity.     

Synthesis and NMR Spectroscopic Characteristics of a Series of Hydrazide‐Hydrazones Containing Furoxan Ring Derived from Isoeugenoxyacetic Acid

A novel hydrazide, 2‐methoxy‐4‐(3‐methyfuroxan‐4‐yl)‐5‐nitrophenoxyacetylhydrazine, was prepared from isoeugenoxyacetic acid. The hydrazide was condensed with aromatic aldehydes to give a series of 20 hydrazide‐hydrazones incorporating the furoxan ring. The structure of obtained compounds was determined by analytical and spectral data. It was demonstrated that the two sets of resonance signals in the ¹H‐NMR and ¹³C‐NMR spectra of the examined hydrazide‐hydrazones are caused by E_N–C(O) and Z_N–C(O) conformers. The energy barriers for the conformation exchange were determined by ¹H‐NMR‐measurement at various temperatures. Among seven tested hydrazide‐hydrazones, four compounds exhibit inhibition activities in vitro on human epidermis carcinoma (KB‐cell) with IC₅₀ = 47, 68, 79, and 103 μg/mL.     

Crystal structures of anti- and syn-9,10-di(1′-naphthyl)anthracene and isomerization in solid state

9,10-Di-(1′-naphthyl)anthracene is often used as electroluminescence materials in organic light-emitting diodes. Because of the hindered rotation about the σ-bond between naphthyl and anthracene chromophore, two possible stereoisomers can be isolated. HPLC, ¹H NMR, and ¹³C NMR spectra gave two different sets of peaks and the X-ray single crystal analysis confirmed the structures of the two isomers, anti and syn. syn was more soluble than anti in THF as well as toluene and the thermal properties of the two were quite different. Differential scanning calorimetry study and HPLC analysis showed that the isomerization between anti and syn in the solid state took place at >370 °C.