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81.
Seven new diterpenes, featuring the rare 2,6-cyclo-xenicane skeleton, along with eleven previously reported metabolites were isolated from the organic extracts of the brown algae Dilophus fasciola and Dilophus spiralis. The structure elucidation of the isolated natural products was based on detailed analyses of their spectroscopic data (NMR, MS, IR, UV), whereas the assignment of their relative configurations was assisted by molecular modelling studies. 相似文献
82.
T. O. Denisova E. V. Amel’chenkova I. S. Kislina N. B. Librovich S. E. Nefedov 《Russian Journal of Inorganic Chemistry》2006,51(11):1755-1762
3,5-Dimethylpyrazole complexes with HCl (an 1 : 1 complex) and trifluoromethanesulfonic acid (1 : 1 and 2 : 1 complexes) were structurally studied using X-ray crystallography. 相似文献
83.
Kadari A Moncomble A Ciofini I Brahimi M Adamo C 《The journal of physical chemistry. A》2011,115(42):11861-11865
Iridium(III) complexes are among the most used phosphorescent materials for the development of organic light emitting diodes (OLEDs). In this work, the photophysical properties of a family of complexes based on phenyldiazine ligands were studied. Their ground state geometric and electronic structures as well as their absorption and emission spectra were investigated by the means of density functional theory (DFT) and time-dependent DFT (TD-DFT). An extremely good agreement between the computed and experimental values is obtained, thus suggesting that the computational protocol here applied could be used for the in silico screening and design of new Ir-based emitting complexes. 相似文献
84.
Hassina Attoui Yahia Ouassila Attoui Yahia Djameleddine Khatmi Roubila Belghiche Amel Bouzitouna 《Journal of inclusion phenomena and macrocyclic chemistry》2017,89(3-4):353-365
Structure and stability of an inclusion complex formed by Benzocaine (BZC) and β-cyclodextrin (β-CD) were investigated computationally using different levels of theory. The conformational research based on PM6 method allowed reach two minimum-energy structures: model A and model B. The lowest conformers have been exposed to fully geometry optimization employing four DFT functionals: B3LYP, CAM-B3LYP, M05-2X and M06-2X. The performed DFT calculations have identified the model B, in which the amino group is located at the primary face of β-CD, as the most stable complex by an amount up to ?40 kcal/mol. Further, the greater stabilization of model B in respect to model A, has been ascertained through AIM and NBO analyses which clarified the main hydrogen bonds HBs interactions governing the reactivity of BZC inside the hydrophobic cavity of β-CD. Finally, the estimated isotropic 1H nuclear magnetic shielding constants generated from the gauge-including-atomic-orbital calculation have been analyzed and then compared with the available experimental data. 相似文献
85.
Calix[4]arene-based, Hg2+ -induced intramolecular fluorescence resonance energy transfer chemosensor 总被引:1,自引:0,他引:1
Othman AB Lee JW Wu JS Kim JS Abidi R Thuéry P Strub JM Dorsselaer AV Vicens J 《The Journal of organic chemistry》2007,72(20):7634-7640
A novel calix[4]arene-based chemosensor 1 based on Hg2+-induced fluorescence resonance energy transfer (FRET) was synthesized, and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of Hg2+ to a CH3CN solution of 1 gave a significantly enhanced fluorescence at approximately 575 nm via energy transfer (FRET-ON) from the pyrenyl excimer to a ring-opened rhodamine moiety. In contrast, addition of Al3+ induced a distinct increase of pyrenyl excimer emission ( approximately 475 nm), while no obvious FRET-ON phenomenon was observed. Different binding behaviors of 1 toward Hg2+ and Al3+ were also proposed for the interesting observation. 相似文献
86.
In acetonitrile, the tren-N-tricalix[4]arene 4 with three appended pyrenyl groups showed an enhanced fluorescence in the presence of Al3+ and, to a lesser extent, of In3+. Compound 4 was shown to form a 1:1 complex with Al3+, the metal cation being located in the tren part. The association constant (Ka) of 4 for the Al3+ cation was calculated to be 8.7×103 M−1 in acetonitrile. 相似文献
87.
Benjamin C. Moeller Luis Flores Amel Clifford Gwendolyne Alarcio Mary Mosburg Rick M. Arthur 《Molecules (Basel, Switzerland)》2021,26(19)
Methylphenidate is a powerful central nervous system stimulant with a high potential for abuse in horse racing. The detection of methylphenidate use is of interest to horse racing authorities for both prior to and during competition. The use of hair as an alternative sampling matrix for equine anti-doping has increased as the number of detectable compounds has expanded. Our laboratory developed a liquid chromatography–high-resolution mass spectrometry method to detect the presence of methylphenidate in submitted samples. Briefly, hair was decontaminated, cut, and pulverized prior to liquid–liquid extraction in basic conditions before introduction to the LC-MS system. Instrumental analysis was conducted using a Thermo Q Exactive mass spectrometer using parallel reaction monitoring using a stepped collision energy to obtain sufficient product ions for qualitative identification. The method was validated and limits of quantitation, linearity, matrix effects, recovery, accuracy, and precision were determined. The method has been applied to confirm the presence of methylphenidate in official samples submitted by racing authorities. 相似文献
88.
The acoustic characteristics of cries are an exhibition of an infant’s health condition and these characteristics have been acknowledged as indicators for various pathologies. This study focused on the detection of infants suffering from sepsis by developing a simplified design using acoustic features and conventional classifiers. The features for the proposed framework were Mel-frequency Cepstral Coefficients (MFCC), Spectral Entropy Cepstral Coefficients (SENCC) and Spectral Centroid Cepstral Coefficients (SCCC), which were classified through K-nearest Neighborhood (KNN) and Support Vector Machine (SVM) classification methods. The performance of the different combinations of the feature sets was also evaluated based on several measures such as accuracy, F1-score and Matthews Correlation Coefficient (MCC). Bayesian Hyperparameter Optimization (BHPO) was employed to tailor the classifiers uniquely to fit each experiment. The proposed methodology was tested on two datasets of expiratory cries (EXP) and voiced inspiratory cries (INSV). The highest accuracy and F-score were 89.99% and 89.70%, respectively. This framework also implemented a novel feature selection method based on Fuzzy Entropy (FE) as a final experiment. By employing FE, the number of features was reduced by more than 40%, whereas the evaluation measures were not hindered for the EXP dataset and were even enhanced for the INSV dataset. Therefore, it was deduced through these experiments that an entropy-based framework is successful for identifying sepsis in neonates and has the advantage of achieving high performance with conventional machine learning (ML) approaches, which makes it a reliable means for the early diagnosis of sepsis in deprived areas of the world. 相似文献
89.
90.
L. A. Kartsova O. V. Markova A. I. Amel’chenko N. D. Ostryanina 《Journal of Analytical Chemistry》2000,55(3):270-279
The use of crown compounds (18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6, benzo-15-crown-5, dibenzo-24-crown-8, 4,13-diaza-18-crown-6,4,13-dibenzyl-diaza-18-crown-6,
and cryptand [2.2.2]) as components of stationary phases in the determination of organic compounds by gas chromatography is
studied. The polarity, selectivity, efficiency, and working temperature ranges of stationary phases based on crown ethers
and cryptand as well as conventional stationary phases for gas chromatography are compared. The influence of the type and
number of heteroatoms, the conformational lability of the cavity, and the presence of substituents on the polarity and selectivity
of the stationary phases under study is revealed. Preferable types of interactions of stationary phases containing crown compounds
with organic compounds of different classes are discussed. It is concluded that phases of the mixed type based on crown ethers
are promising for improving the selectivity and efficiency of gas-chromatographic separation 相似文献