Solvation Structure of Surface-Supported Amine Fragments: A Molecular Dynamics Study

Amine-grafted silica gel is an efficient heterogeneous catalyst for the Knoevenagel condensation and draws much attention in green chemistry for applications like heavy metal adsorption and CO₂ fixation. Despite its successful usage in diverse areas, fundamental questions remain on how the silica substrate affects the local chemical environment of the tethered amines. In this work, we use all-atom molecular dynamics simulation to investigate the solvation structures of two primary amines tethered onto a silica surface at different pHs of aqueous solutions. The atomic density profiles in the solvation shell are analyzed with a spherical harmonics expansion method for both isolated and silica-supported amines in different aqueous environments. The simulation results provide direct evidence for the strong influence of the silica surface on the hydration structure that is often ignored in the theoretical analysis of surface reactions. The surface effect becomes less prominent on the tethered amine as the alkyl chain length increases

Mechanistic Insights into the Pore Confinement Effect on Bimolecular and Monomolecular Cracking Mechanisms of <i>N</i>‑Octane over HY and HZSM‑5 Zeolites: A DFT Study

Bimolecular and monomolecular cracking mechanisms of alkanes simultaneously occur and have a competitive relationship, which strongly influences the product distribution. In this work, the density functional theory (DFT) calculation is first carried out to elucidate two cracking mechanisms in HZSM-5 and HY zeolites. It is found that the overall apparent reaction barrier for the monomolecular cracking reaction at 750 K in the HZSM-5 zeolite is 5.30 kcal/mol, much lower than that (23.12 kcal/mol) for bimolecular cracking reaction, indicating that the monomolecular mechanism is predominant in the HZSM-5 zeolite. In contrast, the bimolecular mechanism is predominant in the HY zeolite because of a lower apparent reaction barrier energy barrier (6.95 kcal/mol) for bimolecular cracking reaction than that (24.34 kcal/mol) for the monomolecular cracking reaction. Moreover, the intrinsic reason for the different mechanisms is further elucidated. The confinement effect can effectively decrease the energy barrier when the size of transition states is comparable to the pore size of zeolite. The insights in this work will be of great significance to the understanding of confinement on catalytic cracking mechanism and to the design of highly efficient cracking catalysts

Chemical and Radiation Stability of Ionic Liquids: A Computational Screening Study

Using a variety of density functional theory (DFT) methods, we present a systematic computational screening effort to analyze the chemical and radiation stability for a large number of anions and cations that constitute room-temperature ionic liquids (RTILs). We compute various electronic properties such as the HOMO–LUMO gap, the ionization potential, and the electron affinities for a large library of ions (42 cations and 42 anions). The theoretical analysis provides the most comprehensive characterization of the chemical and radiation stability of individual ions in RTILs to date. Our calculations reveal that cation stability is closely related to constituent alkyl chain length and branching, whereas the anion stability is mostly dictated by ion size and electronegativity. Furthermore, these calculations show that the ωB97XD functional is the most internally consistent for predicting the chemical and radiation stability. These calculations establish a chemical stability database and a theoretical procedure for further experimental and computational studies of RTILs

Growth Mechanism of Highly Branched Titanium Dioxide Nanowires via Oriented Attachment

Understanding fundamental crystal nucleation and growth mechanisms is critical for producing materials with controlled size and morphological features and uncovering structure–function relationships in these semiconducting oxides. Under hydro-solvothermal conditions, uniform branched and spherulitic TiO₂ rutile nanostructures were formed via (101) twins. On the basis of detailed, high-resolution scanning electron microscopy and transmission electron microscopy analyses, we propose a mechanism of branched growth and the (101) twin formation via oriented attachment and subsequent transformation from anatase to rutile

Correlation between PLK4 expression and clinicopathologic parameters in HCC.

a<p>Chi-square test;</p>b<p>patients were divided according to the median age; AFP, alpha-fetoprotein; HBsAg, hepatitis B surface antigen; PLK4, polo-like kinase 4.</p

Univariate analysis of different prognostic factors in 246 HCC patients.

<p>CI, confidence interval; HR, hazard ratio; AFP, alpha-fetoprotein; HBsAg, hepatitis B surface antigen; PLK4,polo-like kinase4.</p

The expression of PLK4 in HCC by IHC.

<p>The micrographs showed negative (<b>A</b>), weak (<b>B</b>), moderate (<b>C</b>), strong (<b>D</b>) staining of PLK4 in tumor tissues, as well as strong (<b>E</b>) staining of normal liver tissues. (Left panel: magnification ×40; Right panel: magnification ×400.) <b>F.</b> Reproducibility of the measurement in all 246 patients was calculated by the Wilcoxon matched paired test.</p

Analysis of PLK4 protein expression in relation to overall survival and disease-free survival of subclassified HCC patients.

<p>In term of overall survival and disease-free survival, subgroup analysis indicated that PLK4 had prognostic role when classified by the following variables: tumor size (A–B), AFP (C–D), stage (III–IV) (E–F) (log-rank test).</p

The mRNA and protein expression of PLK4 in HCC by qRT-PCR and western blot. A.

<p>Down-regulated expression of PLK4 mRNA was detected by qRT-PCR in 13 out of 20 HCC cases. The relative PLK4 mRNA expression was indicated by histogram (T, tumor tissue; N, the corresponding adjacent non-tumor liver tissues). <b>B.</b> The PLK4 mRNA levels was significantly decreased in HCC as determined by the Wilcoxon matched paired test. <b>C.</b> Decreased expression of PLK4 protein was shown by western blot in 15 out of 20 HCC tumor tissues. The relative PLK4 protein expression was shown. GAPDH was used as loading control. <b>D.</b> Intensity of PLK4 normalized to GAPDH was indicated Wilcoxon matched paired test.</p

Multivariate analysis of overall and disease-free survival rates of HCC patients.

<p>β, Regression coefficient; SE, standard error; CI, confidence interval; AFP, alpha-fetoprotein; PLK4, polo-like kinase4.</p