Machine-Learning Approach in Prediction of the Wettability of a Surface Textured with Microscale Pillars.

Tuning the wettability of a flat surface by introducing an array of microscale pillars finds wide applications, especially in engineering a superhydrophobic surface. The wettability of such a pillared surface is quantified by the contact angle (CA) of a water droplet. It is desired to know the CA prior to construction of pillars, in order to obviate the trial-and-errors in experimenting with many different topographies. Given an accurate theoretical prediction of CA has been elusive, we propose a convolutional neural network (CNN) model of CA for a surface patterned with rectangular or cylindrical pillars. By employing a three-dimensional descriptor of the surface topography, the present CNN model can predict experimental CAs within errors comparable to the uncertainties in measuring CAs.

Depolymerized Chitosan-g-[Poly(MMA-co-HEMA-cl-EGDMA)] Based Nanogels for Controlled Local Release of Bupivacaine.

This study is designed to formulate and characterize chitosan-based nanogels that provide the controlled delivery of anesthetic drugs, such as bupivacaine (BPV), for effective postoperative pain management over prolonged periods of time. Drug carriers of chitosan/poly (MMA-co-HEMA-cl-EGDMA) (CsPMH) nanogels were prepared by varying the composition of comonomers such as MMA, HEMA, and redox initiator CAN. The nanogels were then characterized using FTIR, TGA, SEM, and TEM. The CsPMH nanogels showed greater encapsulation efficiencies from 43.20-91.77%. Computational studies were also conducted to evaluate the interaction between the drug and CsPMH nanoparticles. Finally, BPV-loaded nanoparticles were used to examine their in vitro release behavior. At pH 7.4, all the drug carriers displayed the "n" value around 0.7, thus the BPV release follows anomalous diffusion. Drug carrier 7 demonstrated a steady and sustained release of BPV for approximately 24 h and released about 91% of BPV, following the K-P mechanism of drug release. On the other hand, drug carrier 6 exhibited controlled release for approximately 12 h and released only 62% of BPV.

Molecular Simulation Study on the Wettability of a Surface Texturized with Hierarchical Pillars.

By using molecular dynamics simulation, we investigate the wettability of a surface texturized with a periodic array of hierarchical pillars. By varying the height and spacing of the minor pillars on top of major pillars, we investigate the wetting transition from the Cassie-Baxter (CB) to Wenzel (WZ) states. We uncover the molecular structures and free energies of the transition and meta-stable states existing between the CB and WZ states. The relatively tall and dense minor pillars greatly enhance the hydrophobicity of a pillared surface, in that, the CB-to-WZ transition requires an increased activation energy and the contact angle of a water droplet on such a surface is significantly larger.

Modulating Optoelectronic and Elastic Properties of Anatase TiO2 for Photoelectrochemical Water Splitting.

Titanium dioxide (TiO2) has been investigated for solar-energy-driven photoelectrical water splitting due to its suitable band gap, abundance, cost savings, environmental friendliness, and chemical stability. However, its poor conductivity, weak light absorption, and large indirect bandgap (3.2 eV) has limited its application in water splitting. In this study, we precisely targeted these limitations using first-principle techniques. TiO2 only absorbs near-ultraviolet radiation; therefore, the substitution (2.1%) of Ag, Fe, and Co in TiO2 significantly altered its physical properties and shifted the bandgap from the ultraviolet to the visible region. Cobalt (Co) substitution in TiO2 resulted in high absorption and photoconductivity and a low bandgap energy suitable for the reduction in water without the need for external energy. The calculated elastic properties of Co-doped TiO2 indicate the ductile nature of the material with a strong average bond strength. Co-doped TiO2 exhibited fewer microcracks with a mechanically stable composition.

Molecular Insights on the Wetting Behavior of a Surface Corrugated with Nanoscale Domed Pillars.

Using all-atom molecular dynamics simulation, we investigated the wettability of a surface texturized with nanoscale pillars of domed, rectangular, or cylindrical shapes. The dewetted and wetted states of the gaps between the pillars were related to the Cassie-Baxter (CB) and Wenzel (WZ) states of a macroscopic water droplet resting on top of the pillars. We uncovered the structures and free energies of the intermediate states existing between the CB and WZ states. The contact line of the liquid-vapor-solid interface could not be depinned for the domed pillars due to their smooth curvatures unlike for the rectangular or cylindrical pillars. The liquid symmetrically penetrated down into the gap between the domed pillars by a liquid-vapor interface shape like a paraboloid, while the penetration for the rectangular or cylindrical pillars was often asymmetrical, giving a half-tubular liquid-vapor interface.

Wetting Behavior of a Surface with Dual-Scale Structures.

Theoretical and numerical studies were conducted to investigate the transitional interpillar spacing for dual-scale structures, where wetting transition between the Wenzel and Cassie-Baxter states occurs in the primary and secondary pillars. A theoretical formula was derived for the transitional interpillar spacing based on the continuum picture of water. Molecular dynamics (MD) simulations were carried out by varying the interpillar spacing for the primary pillars for single- and dual-scale structures with various pillar heights. The results obtained from the theoretical formula agreed reasonably well with the results obtained from MD simulations, especially when the primary pillar height was relatively high. The transitional interpillar spacing increases as the pillar height and the number of secondary pillars increase. The effect of the secondary pillars on the transitional interpillar spacing was also evaluated using the difference in the grand potentials between the Wenzel and Cassie-Baxter states. These results show that the dual-scale structures increase the transitional interpillar spacing with an increase in the surface hydrophobicity.

A density functional theory study on the underwater adhesion of catechol onto a graphite surface.

Mussel foot proteins (MFPs) strongly adhere to both hydrophilic and hydrophobic surfaces under wet conditions. This water-resistant adhesion of MFP is ascribed to catechol (1,2-dihydroxybenzene) which is highly contained in the MFP. Currently, little is known about the molecular details of the underwater adhesion of catechol onto a nonpolar hydrophobic surface. By using the density functional theory, we investigate the adhesion of catechol onto a wet graphite surface. We unveil the molecular geometry and energy in the course of the wet adhesion of catechol. Catechol adheres through π-π stacking with the underlying graphite. The surrounding water molecules further strengthen the adhesion by forming hydrogen bonds with catechol. In addition, a significant charge transfer has been observed from wet graphite to the catechol. Consequently, catechol adheres onto the present hydrophobic surface as strongly as onto a hydrophilic silica surface.

Thermal Effect on Positive Patterned Self-Assembled Monolayer Grown from a Droplet of Alkanethiol.

Atomic force microscope technique is widely used for the spatial narrow deposition of molecules inside the bare space of preexisting self-assembled monolayer (SAM) matrix. Using molecular dynamics simulation, we studied the formation of positively patterned SAM from a globule of 1-octadecanethiol (ODT) on predesigned SAM matrix of 1-dodecanethiol (DDT) and effect of temperature on it. The alkyl chains of ODT SAM were densely packed and ordered by means of chemisorption through sulfur atoms. The circular SAM of ODT contained defects due to the molecules those were standing upside down or trapped inside ODT SAM. We found that with the increase of temperature, these defects moved out by flipping of inverted ODT molecules or building spaces to be adsorbed on Au surface. The ODT molecules on the top of the pile of stable circular SAM or those are upside down and trapped disperse in a unique fashion namely serial pushing through which molecules firstly make a free space to enter inside the adsorbed thiol molecules and then push neighboring molecules to get enough space to be adsorbed on the gold surface. The stability of ODT SAM was confirmed by analyzing different structural properties such as tilt angle, tilt orientation. and backbone orientation. We also calculated the diffusion coefficient of the ODT molecules which were on the top of SAM island. © 2019 Wiley Periodicals, Inc.

Adenine-Based Zn(II)/Cd(II) Metal-Organic Frameworks as Efficient Heterogeneous Catalysts for Facile CO2 Fixation into Cyclic Carbonates: A DFT-Supported Study of the Reaction Mechanism.

We synthesized two new adenine-based Zn(II)/Cd(II) metal-organic frameworks (MOFs), namely, [Zn2(H2O)(stdb)2(5H-Ade)(9H-Ade)2]n (PNU-21) and [Cd2(Hstdb)(stdb)(8H-Ade)(Ade)]n (PNU-22), containing auxiliary dicarboxylate ligand (stdb = 4,4'-stilbenedicarboxylate). Both MOFs were characterized by multiple analytical techniques such as single-crystal X-ray diffraction (SXRD), powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, as well as temperature program desorption and Brunauer-Emmett-Teller measurements. Both MOFs were structurally robust and possessed unsaturated Lewis acidic metal centers [Zn(II) and Cd(II)] and free basic N atoms of adenine molecules. They were used as heterogeneous catalysts for the fixation of CO2 into five-membered cyclic carbonates. Significant conversion of epichlorohydrin (ECH) was attained at a low CO2 pressure (0.4 MPa) and moderate catalyst (0.6 mol %)/cocatalyst (0.3 mol %) amounts, with over 99% selectivity toward the ECH carbonate. They showed comparable or even higher catalytic activity than other previously reported MOFs. Because of high thermal stability and robust architecture of PNU-21/PNU-22, both catalysts could be reused with simple separation up to five successive cycles without any considerable loss of their catalytic activity. Densely populated acidic and basic sites in both Zn(II)/Cd(II) MOFs facilitated the conversion of ECH to ECH carbonate in high yields. The reaction mechanism of the cycloaddition reaction between ECH and CO2 is described by possible intermediates, transition states, and pathways, from the density functional theory calculation in correlation with the SXRD structure of PNU-21.

A New Series of EDOT Based Co-Sensitizers for Enhanced Efficiency of Cocktail DSSC: A Comparative Study of Two Different Anchoring Groups.

Herein, we report the design and synthesis strategy of a new class of five EDOT based co-sensitizers (CSGR1-5) by introducing different donors (2,3,4-trimethoxypheny, 2,4-dibutoxyphenyl, and 2,4-difluorophenyl) and anchoring groups (rhodamine-3-acetic acid and cyanoacetic acid) systematically. The synthesized metal-free organic co-sensitizers were employed for cocktail dye-sensitized solar cells along with N749 (black dye). The DSSC devices with a mixture of co-sensitizers (CSGR1-5) and N749 have shown a 7.95%, 8.40%, 7.81%, 6.56% and 6.99% power conversion efficiency (PCE) respectively, which was more than that of single N749 dye PCE (6.18%). Enhanced efficiency could be ascribed to the increased short circuit current (Jsc) and open circuit voltage (Voc). The increased Jsc was achieved due to enhanced light harvesting nature of N749 device upon co-sensitization with CSGR dyes and feasible energy levels of both the dyes. The Voc was improved due to better surface coverage which helps in decreasing the rate of recombination. The detailed optical and electrochemical properties were investigated and complimented with theoretical studies (DFT).

Molecular features of hydration layers probed by atomic force microscopy.

Structurally-ordered layers of water are universally formed on a solid surface in aqueous solution or under ambient conditions. Although such hydration layers are commonly probed via atomic force microscopy (AFM), the current understanding on how the hydration layers manifest themselves in an AFM experiment is far from complete. By using molecular dynamics simulation, we investigate the hydration layers on a hydrophilic or hydrophobic surface probed by a nanoscale tip. We study the density and molecular orientation of water, the free energy, and the force on the tip by varying the tip-surface distance. The force-distance curve oscillates due to the transition between the mono-, bi-, and tri-layers of water confined between the tip and the surface. If both the tip and the surface are hydrophobic, water confined between the tip and the surface evaporates due to the dewetting transition, giving a hydrophobic force without oscillation. The periodicity of oscillation in the force differs from the structural periodicity of water. With a close proximity of the tip, the molecular dipoles align parallel to the surface, regardless of whether the tip and the surface are hydrophilic or hydrophobic.

The impact of heteroatom substitution on cross-conjugation and its effect on the photovoltaic performance of DSSCs - a computational investigation of linear vs. cross-conjugated anchoring units.

The unusual bonding pattern and proximal heteroatom substitution in π-cross conjugation produced distinct changes in the energy levels and photophysical behaviour of the dyes. To seek an understanding of the origin of these fluctuations, we have carried out a detailed computational investigation on a series of D-π1-π2 (A1)-A2 structured dyes comprised of common donor-spacer (auxiliary acceptor) units but varied the anchoring parts. In this study, we introduced a novel dimethylamino substituted fluorene-based triarylamine donor unit and evaluated its donating strength. Based on the comparison of DFT computed energy levels with experimental results, we have proposed an orbital splitting pattern to explain the energy level and photophysical properties of the linear vs. cross-conjugated dyes with respect to the linking position of the anchoring unit and benzo[1,2,5]thiadiazole (BTD) substitution. The smallest HOMO-LUMO gap of B3 mainly originated from the weak overlap of the directionality mismatch of the orbital interaction imposed by cross-conjugation. The inefficient overlap in B3 can possibly influence the energy levels but failed to enhance the charge transfer transitions upon photoexcitation. On the other hand, ß-heteroatom substitution in bridged dyes partially enhanced π-delocalization over the cross conjugation and produced a significant ICT absorption with an optoelectronic response in the NIR region. BTD acceptor substitution increased the HOMO-LUMO gap of the bridged dyes. NBO analysis was performed to corroborate our predictions. DOS-PDOS analysis of the dyes@TiO2 was employed to investigate the electron injection rate of linear vs. bridged dyes. The anchoring pattern and large torsional deviation of the carboxylate anchoring group upon TiO2 adsorption drastically decreased the photovoltaic performance of the bridged dyes. The results obtained from this study provided a detailed understanding of how to surmount the cross-conjugation with the aid of ß-heteroatom substitution. These design guidelines would be helpful in developing novel NIR dyes with better hole mobility for various optoelectronic applications. Furthermore, π-delocalization over the cross-conjugation concept opens a new pathway in the field of functional molecular devices to increase the charge conductance over several orders of magnitude with a significant reduction of destructive quantum interference at the molecular junction.

Spectral, Electrochemical and Computational Investigations of Binding of n-(4-Hydroxyphenyl)-imidazole with p-Sulfonatocalix[4]arene.

The interaction of n-(4-hydroxyphenyl)-imidazole with p-sulfonatocalix[4]arene is studied using fluorescence technique. The quenching of fluorescence intensity explains the efficiency of binding via binding constant and quenching constant. The excited state lifetime of n-(4-hydroxyphenyl)-imidazole is decreased upon interaction with p-sulfonatocalix[4]arene. The cyclic voltametric studies emphasized the interaction of n-(4-hydroxyphenyl)-imidazole with p-sulfonatocalix[4]arene. Quantum chemical calculations are carried out to study the interactions as well as charge transfer between the host and the guest upon complexation. The simulations revealed that the n-(4-hydroxyphenyl)-imidazole interacts with p-sulfonatocalix[4]arene with horizontal orientation with in the p-sulfonatocalix[4]arene cavity.

Synthesis, Spectral Properties and DFT Calculations of new Ruthenium (II) Polypyridyl Complexes; DNA Binding Affinity and in Vitro Cytotoxicity Activity.

In this paper a novel ligand debip (2-(4-N,N-diethylbenzenamine)1H-imidazo[4,5-f] [1, 10]phenanthroline) and its Ru(II) polypyridyl complexes [Ru(L)2(debip)]2+, (L = phen (1), bpy (2) and dmb (3)) have been synthesized and characterized by spectroscopic techniques. The DNA binding studies for all these complexes were examined by absorption, emission, quenching studies, viscosity measurements and cyclic voltammetry. The light switching properties of complexes 1-3 have been evaluated. Molecular docking, Density Functional Theory (DFT) and time dependent DFT calculations were performed. The Ru(II) complexes exhibited efficient photocleavage activity against pBR322 DNA upon irradiation and exhibited good antimicrobial activity. Also investigated 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay, lactate dehydrogenase (LDH) release assay and reactive oxygen species (ROS) against selected cancer cell lines (HeLa, PC3, Lancap, MCF-7 and MD-MBA 231).

Molecular Dynamics Study of the Hydrophilic-to-Hydrophobic Switching in the Wettability of a Gold Surface Corrugated with Spherical Cavities.

This paper reports a large scale molecular dynamics (MD) simulation study of the wettability of a gold surface engraved with (hemi)spherical cavities. By increasing the depth of cavities, the contact angle (CA) of a water droplet on the surface was varied from a hydrophilic (69°) to a hydrophobic value (>109°). The nonmonotonic behavior of the CA vs the depth of the cavities was consistent with the Cassie-Baxter theory, as found in the experiment by Abdelsalam et al. (Abdelsalam, M. E.; Bartlett, P. N.; Kelf, T.; Baumberg, J. Wetting of Regularly Structured Gold Surfaces. Langmuir 2005, 21, 1753-1757). Depending on the depth of cavities, however, the droplet existed not only in the Cassie-Baxter state, but also in the Wenzel or an intermediate state, where the cavities were penetrated partially by the droplet.

Gold nanoparticle silica nanopeapods.

A subnanometer gap-separated linear chain gold nanoparticle (AuNP) silica nanotube peapod (SNTP) was fabricated by self-assembly. The geometrical configurations of the AuNPs inside the SNTPs were managed in order to pose either a single-line or a double-line nanostructure by controlling the diameters of the AuNPs and the orifice in the silica nanotubes (SNTs). The AuNPs were internalized and self-assembled linearly inside the SNTs by capillary force using a repeated wet-dry process on a rocking plate. Transmission electron microscopy (TEM) images clearly indicated that numerous nanogap junctions with sub-1-nm distances were formed among AuNPs inside SNTs. Finite-dimension time domain (FDTD) calculations were performed to estimate the electric field enhancements. Polarization-dependent surface-enhanced Raman scattering (SERS) spectra of bifunctional aromatic linker p-mercaptobenzoic acid (p-MBA)-coated AuNP-embedded SNTs supported the linearly aligned nanogaps. We could demonstrate a silica wall-protected nanopeapod sensor with single nanotube sensitivity. SNTPs have potential application to intracellular pH sensors after endocytosis in mammalian cells for practical purposes. The TEM images indicated that the nanogaps were preserved inside the cellular constituents. SNTPs exhibited superior quality SERS spectra in vivo due to well-sustained nanogap junctions inside the SNTs, when compared to simply using AuNPs without any silica encapsulation. By using these SNTPs, a robust intracellular optical pH sensor could be developed with the advantage of the sustained nanogaps, due to silica wall-protection.

Molecular dynamics study on the wettability of a hydrophobic surface textured with nanoscale pillars.

Using molecular dynamics simulation, we studied the wetting properties of a surface textured with hydrophobic pillars, several nanometers in size. The drying transition of water confined between square or circular pillars was related to the Wenzel (WZ) to Cassie-Baxter (CB) transition of a water droplet deposited on periodic pillars. The inter-pillar spacing at which the drying occurs was compared to that predicted from the continuum theory. Such a comparison revealed that the line tension plays an important role in the drying behavior of the present nm-sized pillars. The water molecules near the pillar walls were layered and ordered in orientation. Our simulation showed a long-lived CB state which eventually turns into the WZ state. In this transition, water slowly penetrated down into the inter-pillar gap until it reached the half height of the pillar, and then quickly reached the base of the pillar.

Development of novel chromones as antioxidant COX2 inhibitors: in vitro, QSAR, DFT, molecular docking, and molecular dynamics studies.

The chromone derivatives are playing a prominent role in many plant cycles, for instance, the regulation of growth, stimulation of oxygen uptake in plants, and essential food constituents with valuable pro-health properties. Determination of the antioxidant activity of these compounds is an interesting approach to drug design and development. The antioxidant activity of the novel fifteen chromone compounds was estimated by using a spectrophotometric Dichloro-5,6-dicyano 1,4-benzoquinone (DDQ) assay method and the mechanism of antioxidant activity was discussed based on the Density functional theory (DFT) calculations. The compounds showed significant antioxidant activity which was correlated to their molecular structure by considering various molecular descriptors. Further, by using regression analysis QSAR-modeled equation was proposed and it has shown a high correlation coefficient value (0.946. We perform molecular docking and molecular dynamics simulations against the cyclooxygenase (COX2) enzyme to investigate the molecule's anti-inflammatory activity and stability of protein-ligand complexes. Molecular docking and dynamics simulations revealed the compounds B3 and B8 were interacting with essential residues TYR385, HIS386, ASN382, TRP387, and HIS388 in the binding site that were crucial for optimizing heme and the resultant peroxidase and cyclooxygenase activities. The root mean square displacement and root mean square fluctuation plots revealed the stability of the B3-COX2 and B8-COX2 complexes. Based on our results, B3 and B8 compounds are considered as best antioxidants as well as COX2 inhibitors.Communicated by Ramaswamy H. Sarma.

Machine Learning-Assisted Computational Screening of Adhesive Molecules Derived from Dihydroxyphenyl Alanine.

Marine mussels adhere to virtually any surface via 3,4-dihydroxyphenyl-L-alanines (L-DOPA), an amino acid largely contained in their foot proteins. The biofriendly, water-repellent, and strong adhesion of L-DOPA are unparalleled by any synthetic adhesive. Inspired by this, we computationally designed diverse derivatives of DOPA and studied their potential as adhesives or coating materials. We used first-principles calculations to investigate the adsorption of the DOPA derivatives on graphite. The presence of an electron-withdrawing group, such as nitrogen dioxide, strengthens the adsorption by increasing the π-π interaction between DOPA and graphite. To quantify the distribution of electron charge and to gain insights into the charge distribution at interfaces, we performed Bader charge analysis and examined charge density difference plots. We developed a quantitative structure-property relationship (QSPR) model using an artificial neural network (ANN) to predict the adsorption energy. Using the three-dimensional and quantum mechanical electrostatic potential of a molecule as a descriptor, the present quantum NN model shows promising performance as a predictive QSPR model.

Monte Carlo study on the self-assembly of nanoparticles into a nanorod structure.

It is well known that semiconductor nanoparticles (NPs) can assemble into a range of low dimensional structures, such as nanowires, nanorods and nanosheets. In this study, we investigate the self-assembly of CdTe NPs by using Monte Carlo simulation. Using a simple model for the anisotropic interaction of NPs, the present Monte Carlo simulation demonstrated that NPs with large dipole moments assemble spontaneously into a nanorod even if the short range interactions among NPs is isotropic. Interestingly, we found that the present nanorod grew by forming a transient structure which looks similar to a double ring. For NPs similar to CdTe, the dipole-dipole interaction had a dominant effect over van der Waals attractions and steric repulsion on the final structure of the NP aggregates. The simulated rods are similar to those observed in the experimental self-assembly of CdTe NPs. The NPs with relatively small electric dipole moments aggregated into more or less isotropic structures.