Numerical Study of Vapor Condensation on Patterned Hydrophobic Surfaces Using the String Method

Vapor condensation on solid surfaces plays a crucial role across a wide range of industrial applications. Recent advances of nanotechnology have made possible the manipulation of the condensation process through the control of surface structures. In this work, we study vapor condensation on hydrophobic surfaces patterned with microscale pillars. The critical nuclei, the activation barriers, and the minimum energy paths are computed using the climbing string method. The effects of pillar height, interpillar spacing, the level of supersaturation, and the intrinsic wettability of the solid surface on the nucleation process are investigated. Two nucleation scenarios are obtained from the computation. In the case of high pillar, narrow interpillar spacing, low supersaturation, and/or low surface wettability, the critical nucleus prefers the suspended Cassie state; otherwise, it prefers the impaled Wenzel state. A comparison of the nucleation barrier with that on a flat surface of the same material reveals that vapor condensation is inhibited by the microstructures in the former case, while enhanced in the latter case. The critical values of the pillar height, the interpillar spacing, and the supersaturation at which the critical nucleus changes from the Cassie state to the Wenzel state are identified from the phase diagram of the critical nucleus. It is found that the dependence of the critical interpillar spacing on the supersaturation follows closely the curve of the critical radii in a homogeneous nucleation. The relaxation dynamics of the condensate after the critical nucleus is formed is computed by solving the steepest descent equation. It is observed that when the pillar is low and/or the interpillar spacing is wide, a condensate initially in the Cassie state may evolve into the Wenzel state during the relaxation

New bisesquiterpenoid lactone from the wild rhizome of <i>Atractylodes macrocephala</i> Koidz grown in Qimen

<p>The rhizomes of <i>Atractylodes macrocephala</i> are used as both a food source and traditional Chinese medicine in China. A phytochemical investigation was carried out on wild <i>A. macrocephala</i> grown in Qimen County in eastern China, and yielded a novel bisesquiterpenoid lactone, namely, biatractylenolide II (<b>1</b>), along with two known compounds, atractylenolide II (<b>2</b>) and taraxeryl acetate (<b>3</b>). The structure and relative configuration of the new compound were elucidated mainly by 1D and 2D NMR spectroscopic methods in combination with HRESIMS experiments. This paper describes the isolation and structural elucidation of the new bisesquiterpenoid lactone (<b>1</b>).</p

Generalized Energy-Based Fragmentation Approach for Localized Excited States of Large Systems

We have extended the generalized energy-based fragmentation (GEBF) approach to localized excited states of large systems. In this approach, the excited-state energy of a large system could be expressed as the combination of the excited-state energies of “active subsystems”, which contains the chromophore center, and the ground-state energies of “inactive subsystems”. The GEBF approach has been implemented at the levels of time-dependent density functional theory (TDDFT) and approximate coupled cluster singles and doubles (CC2) method. Our results show that GEBF-TDDFT can reproduce the TDDFT excitation energies and solvatochromic shifts for large systems and that GEBF-CC2 could be used to validate GEBF-TDDFT result (with different functionals). The GEBF-TDDFT method is found to be able to provide satisfactory or reasonable descriptions on the experimental solvatochromic shifts for the <i>n</i> → π* transitions of acetone in various solutions, and the lowest π → π* transitions of pyridine and uracil in aqueous solutions

Benchmark Relative Energies for Large Water Clusters with the Generalized Energy-Based Fragmentation Method

The generalized energy-based fragmentation (GEBF) method has been applied to investigate relative energies of large water clusters (H₂O)_<i>n</i> (<i>n</i> = 32, 64) with the coupled-cluster singles and doubles with noniterative triple excitations (CCSD­(T)) and second-order Møller–Plesset perturbation theory (MP2) at the complete basis set (CBS) limit. Here large water clusters are chosen to be representative structures sampled from molecular dynamics (MD) simulations of liquid water. Our calculations show that the GEBF method is capable of providing highly accurate relative energies for these water clusters in a cost-effective way. We demonstrate that the relative energies from GEBF-MP2/CBS are in excellent agreement with those from GEBF-CCSD­(T)/CBS for these water clusters. With the GEBF-CCSD­(T)/CBS relative energies as the benchmark results, we have assessed the performance of several theoretical methods widely used for <i>ab initio</i> MD simulations of liquids and aqueous solutions. These methods include density functional theory (DFT) with a number of different functionals, MP2, and density functional tight-binding (the third generation, DFTB3 in short). We find that MP2/aug-cc-pVDZ and several DFT methods (such as LC-ωPBE-D3 and ωB97XD) with the aug-cc-pVTZ basis set can provide satisfactory descriptions for these water clusters. Some widely used functionals (such as B3LYP, PBE0) and DFTB3 are not accurate enough for describing the relative energies of large water clusters. Although the basis set dependence of DFT is less than that of <i>ab initio</i> electron correlation methods, we recommend the combination of a few best functionals and large basis sets (at least aug-cc-pVTZ) in theoretical studies on water clusters or aqueous solutions

New neolignan glycoside from the root of <i>Aralia echinocaulis</i> Hand. -Mazz

<p>A phytochemical investigation was carried out to the root of <i>Aralia echinocauis</i>, and a new neolignan glycoside, 3-{3,5-dimethoxy-4β-d-Glucopyranoside-2-[3-(3-β-d-Glucopyranoside-4-methoxy-phenyl)-allyl]-phenyl}-prop-2-en-1-ol (<b>1</b>), together with a known saponin, araliasaponin II (<b>2</b>) for the first time was obtained<i>.</i> The chemical structure of compound <b>1</b> was identified mainly by the analysis of NMR including 1D and 2D NMR in combination with High Resolution Electrospray Ionisation Mass (HR-ESI-MS). This paper herein describes the isolation and structural elucidation of compound <b>1</b>.</p

Regulating Circularly Polarized Luminescence Signals of Chiral Binaphthyl-Based Conjugated Polymers by Tuning Dihedral Angles of Binaphthyl Moieties

A series of chiral binaphthyl-based conjugated polymers enantiomers incorporating boron dipyrromethene (BODIPY) chromophore in the main chain backbone were designed and synthesized by Pd-catalyzed Sonogashira cross-coupling reaction. All of them can exhibit strong Cotton effects and circularly polarized luminescence (CPL) emission signals in THF solution. The CD absorption dissymmetry factors (<i>g</i>_abs) and the luminescence dissymmetry factors (<i>g</i>_lum) can be regulated by tuning the dihedral angles of binaphthyl arising from different substitutions of BINOL hydroxyls. Interestingly, the chiral polymers can exhibit the gradual increase of both <i>g</i>_abs and <i>g</i>_lum as the decrease of dihedral angles of the chiral binaphthyl moiety. This work can provide a new strategy for the development of CPL emission materials

Molecular Dynamics Simulations of Hydrogen Bond Dynamics and Far-Infrared Spectra of Hydration Water Molecules around the Mixed Monolayer-Protected Au Nanoparticle

Molecular dynamics simulations have been performed to systematically investigate the structure and dynamics properties, hydrogen bond (HB) dynamics, and far-infrared (far-IR) spectra of hydration water molecules around the mixed monolayer-protected Au nanoparticles (MPANs) with different ligand compositions and length. Our simulation results demonstrate that the translational and rotational motions of hydration water molecules in the proximity of charged terminal NH₃⁺ and COO^– groups are suppressed significantly with respect to the bulk water. Compared to the bulk water, meanwhile, longer structural relaxation times of hydration H₂O–H₂O HBs indicate enhanced strength of H₂O–H₂O HBs at the interface of mixed MPANs. Accordingly, these hydration water molecules around the charged terminal groups can exhibit a considerable blue-shift in far-IR spectra for all ligand compositions and length studied here. A series of detailed HB analyses manifest that above restricted behavior of hydration water molecules can be attributed to the stronger H₂O–NH₃⁺ and H₂O–COO^– HBs and the corresponding structural relaxation times are much greater than those of hydration H₂O–H₂O HBs. Furthermore, we find that increasing ligand length can affect much the morphology of self-assemble monolayers in water owing to enhanced hydrophobic interactions between alkane chains and water molecules and favor the translational mobility of hydration water molecules owing to weaken electrostatic interactions. Unlike the translational motions, our comparison results among different ligand lengths clearly confirm that the rotational relaxation of hydration water molecules should be dominated by the local and directional HBs at the interfaces, rather than the previous explanation of the ratio between hydrophobic/hydrophilic exposed regions. More importantly, our simulations reveal at a molecular level that the ligand composition has a little influence on the structure, dynamics, HBs, and far-IR spectra of hydration water molecules around the mixed MPANs mainly due to the comparable strength between H₂O–NH₃⁺ and H₂O–COO^– HBs

Structural Properties and Vibrational Spectra of Ethylammonium Nitrate Ionic Liquid Confined in Single-Walled Carbon Nanotubes

The structures and relevant vibrational spectra of an ethylammonium nitrate (EAN) ionic liquid (IL) confined in single-walled carbon nanotubes (SWCNTs) with various diameters have been investigated in detail by using classical molecular dynamics simulation. Our simulation results demonstrate that the EAN IL confined in larger SWCNTs can form well-defined multishell structures with an additional cation chain located at the center. However, a different single-shell hollow structure has been found for both the cations and the anions in the 1 nm SWCNT. For the cations confined in SWCNTs, the CH₃ groups stay closer to the nanotube walls because of their solvophobic nature, while the NH₃⁺ groups prefer to point toward the central axis. Accordingly, the NO₃^– anions tend to lean on the SWCNT surface with three O atoms facing the central axis to form hydrogen bonds (HBs) with the NH₃⁺ groups. In addition, in the 1 nm SWCNT, the CH₃ groups of cations exhibit an obvious blue shift of around 16 cm^–1 for the C–H stretching mode with respect to the bulk value, and the N–H stretching mode of NH₃⁺ groups is split into two characteristic peaks with one peak appearing at a higher frequency. Such a blue shift is attributed to the existence of more free space for the C–H bonds of confined CH₃ groups, while the splitting phenomenon is due to the fact that more than 60% of the confined NH₃⁺ groups have one dangling N–H bond. For the anions confined in the 1 nm SWCNT, the N–O stretching mode of NO₃^– has a maximum red shift of around 24 cm^–1 with respect to the bulk value, which is attributed to enhanced HBs between anions and cations. Our simulation results reveal a molecular-level correlation between confined structural configurations and the corresponding vibrational spectra changes for the ILs confined in nanometer scale environments

Molecular-Level Insights into Size-Dependent Stabilization Mechanism of Gold Nanoparticles in 1‑Butyl-3-methylimidazolium Tetrafluoroborate Ionic Liquid

Here we report a series of classical molecular dynamics simulations for the icosahedral Au nanoparticles with four different diameters of 1.0, 1.4, 1.8, and 2.3 nm in 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]­[BF₄]) room-temperature ionic liquid (RTIL). Our simulation results reveal for the first time a size-dependent stabilization mechanism of the Au nanoparticles in the [bmim]­[BF₄] RTIL, which may help to clarify the relevant debate on the stabilization mechanism from various experimental observations. By comparison, the alkyl chains in the [bmim]⁺ cations are found to dominate the stabilization of the smallest Au₁₃ nanoparticle in the RTIL while the imidazolium rings should be mainly responsible for the stabilization of other larger nanoparticles in the RTIL. Compared to the [bmim]⁺ cations, the [BF₄]⁻ anions are found to have an indirect influence on stabilizing the Au nanoparticles in the RTIL because of the weak interaction between the Au nanoparticles and the anions. However, such differences in the stabilization mechanism between the small and the large Au nanoparticles can be attributed to the unique hydrogen bond (HB) network between the cations and the anions in the first solvation shell. Meanwhile, increasing the particle size can lead to the enhanced HBs on the surface of Au nanoparticles, so slower rotational motions and more pronounced orientation distribution of cations can be observed around the larger nanoparticles. Our simulation results in this work provide a molecular-level understanding of the unique size-dependent stabilization mechanism of the Au nanoparticles in the imidazolium-based RTILs