Vibrational circular dichroism study and gas chromatographic analysis of chiral epichlorohydrin

In recent years, there have been numerous incidents of serious accidents related to impurities of optical isomers, particularly in pharmaceutical treatment, environmental problems, and pesticide application. Among these impurities, chiral epichlorohydrin (ECH) is an important C3 synthon and a potentially genotoxic impurity. The enantiopure forms of S-ECH and R-ECH are key raw materials for synthesizing many drugs, which make it important to accurately quantify the specific conformation of chiral epichlorohydrin in pharmaceuticals. In this paper, we achieved the separation of chiral ECH by gas chromatography (GC) and based on the combination of vibrational circular dichroism (VCD) experiments and theoretical calculations, the qualitative method of chiral ECH was achieved without relying on a single enantiomeric standard.

Synergy between Fe and Ni in the optimal performance of (Ni,Fe)OOH catalysts for the oxygen evolution reaction

The oxygen evolution reaction (OER) is critical to solar production of fuels, but the reaction mechanism underlying the performance for a best OER catalyst, Fe-doped NiOOH [(Ni,Fe)OOH], remains highly controversial. We used grand canonical quantum mechanics to predict the OER mechanisms including kinetics and thus overpotentials as a function of Fe content in (Ni,Fe)OOH catalysts. We find that density functional theory (DFT) without exact exchange predicts that addition of Fe does not reduce the overpotential much. However, DFT with exact exchange predicts dramatic improvement in performance for (Ni,Fe)OOH, leading to an overpotential of 0.42 V and a Tafel slope of 23 mV/decade (dec), in good agreement with experiments, 0.3-0.4 V and 30 mV/dec. We reveal that the high spin [Formula: see text] Fe(IV) leads to efficient formation of an active O radical intermediate, while the closed shell [Formula: see text] Ni(IV) catalyzes the subsequent O-O coupling, and thus it is the synergy between Fe and Ni that delivers the optimal performance for OER.

Partition coefficients for the SAMPL5 challenge using transfer free energies

SAMPL challenges (Mobley et al. in J Comput Aided Mol Des 28:135-150, 2014; Skillman in J Comput Aided Mol Des 26:473-474, 2012; Geballe in J Comput Aided Mol Des 24:259-279, 2010; Guthrie in J Phys Chem B 113:4501-4507, 2009) provide excellent opportunities to assess theoretical approaches on new data sets with a goal of gaining greater insight towards protein and ligand modeling. In the SAMPL5 experiment, cyclohexane-water partition coefficients were determined using a vertical solvation scheme in conjunction with the SMD continuum solvent model. Several DFT functionals partnered with correlation consistent basis sets were evaluated for the prediction of the partition coefficients. The approach chosen for the competition, a B3PW91 vertical solvation scheme, yields a mean absolute deviation of 1.9 logP units and performs well at estimating the correct hydrophilicity and hydrophobicity for the full SAMPL5 molecule set.

UV-MALDI mass spectrometric quantitation of uracil based pesticides in fruit soft drinks along with matrix effects evaluation

This study focused on the development of the accurate and precise quantitative method for the determination of pesticides bromacil (1), terbacil (2), lenacil (3), butafenacil (4) and flupropacil (5) in fruit based soft drinks. Three different types of drinks are bought from market; huddled orange fruit drink (100%) (I), red-oranges (II) and multivitamin drink containing strawberry, orange, banana and maracuja (III). Samples were analyzed "with" and "without" pulp utilizing LC-ESI (or APCI) MS/MS, HPLC-ESI-(or APCI)-MS/MS and UV-MALDI-Orbitrap-MS methods. The effect of high complexity of the food matrix on the analysis was discussed. Study focuses on the advantages of the UV-MALDI-Orbitrap-MS method compared to the traditionally involved GC alone or hybrid methods such as GC-MS and LC-MS/MS for quantification of pesticides in water and soft drinks. The developed method included the techniques performed for validation, calibration and standardization. The target pesticides are widely used for the treatment of citrus fruits and pineapples, but for soft drink products, there are still no clear regulations on pesticide residues limits. The matrix effects in the analysis of fruit drinks required implementation of the exact standard reference material corresponds to the variety of food matrices. This paper contributed to the broad analytical implementation of the UV-MALDI-Orbitrap-MS method in the quality control and assessment programs for monitoring of pesticide contamination in fruit based sodas.

Identification of (-)(E)-N-[2(S)-Hydroxy-2-(4-hydroxyphenyl) ethyl]ferulamide, a natural product isolated from Croton pullei: theoretical and experimental analysis

Ferulic acid (FA) and its derivatives (FADs) are known for a variety of biological activities, such as photo-protective agent, antioxidant, antiatherogenic and antiplasmodial activities. During structural definition of a FAD isolated from Croton pullei, the possibility of a heterologous series made this definition difficult. In this regard, computational simulations were performed using theoretical calculations at DFT level to predict Infrared (IR) and Nuclear Magnetic Resonance (NMR) data. The IR and NMR ¹³C and ¹H data were compared with the theoretical calculations performed for three structural possibilities of a heterologous series. The theoretical results were compared with the experimental data through linear regression in order to define the most probable structure and showed satisfactory values.