Conjugation through Si-O-Si bonds, silsesquioxane (SQ) half cage copolymers, extended examples via SiO0.5/SiO1.5 units: multiple emissive states in violation of Kasha's rule.

We previously reported that phenyl- and vinyl-silsesquioxanes (SQs), [RSiO1.5]8,10,12 (R = Ph or vinyl) functionalized with three or more conjugated moieties show red-shifted absorption- and emission features suggesting 3-D conjugation via a cage centered LUMOs. Corner missing [PhSiO1.5]7(OSiMe3)3 and edge opened, end capped [PhSiO1.5]8(OSiMe2)2 (double decker, DD) analogs also offer red shifted spectra again indicating 3-D conjugation and a cage centered LUMO. Copolymerization of DD [PhSiO1.5]8(OSiMevinyl)2 with multiple R-Ar-Br gives copolymers with emission red-shifts that change with degree of polymerization (DP), exhibit charge transfer to F4TNCQ and terpolymer averaged red-shifts suggesting through chain conjugation even with two (O-Si-O) end caps possibly via a cage centered LUMO. Surprisingly, ladder (LL) SQ, (vinylMeSiO2)[PhSiO1.5]4(O2SiMevinyl) copolymers offer emission red-shifts even greater for analogous copolymers requiring a different explanation. Here we assess the photophysical behavior of copolymers of a more extreme SQ form: the half cage [PhSiO1.5]4(OSiMe2Vinyl)4, Vy4HC SQs. We again see small red-shifted absorptions coupled with significant red-shifted emissions, even with just a half cage, thus further supporting the existence of pπ-dπ and/or σ*-π* conjugation through Si-O-Si bonds and contrary to most traditional views of Si-O-Si linked polymers. These same copolymers donate an electron to F4TCNQ generating the radical anion, F4TCNQ-. as further proof of conjugation. Column chromatographic separation of short from longer chain oligomers reveals a direct correlation between DP and emission λmax red-shifts as another indication of conjugation. Further, one- and two-photon absorption and emission spectroscopy reveals multiple excited fluorescence-emitting states in a violation of Kasha's rule wherein emission occurs only from the lowest excited state. Traditional modeling studies again find HOMO LUMO energy levels residing only on the aromatic co-monomers rather than through Si-O-Si bonds as recently found in related polymers.

Siamfuranones A-C, three novel furanone derivatives from the flowers of Uvaria siamensis and their biological activities.

Three previously undescribed furanone derivatives named siamfuranones A-C (1-3), together with 11 known compounds (4-14), were isolated from the flowers of Uvaria siamensis. Their planar structures were determined through analysis of spectrometric and spectroscopic evidence, while electronic circular dichroism (ECD) calculations were used to determine their absolute configurations. In addition, gauge-including atomic orbitals (GIAO) NMR chemical shift calculation, supported by the advanced statistical method DP4 plus, was used to confirm the relative configuration of siamfuranone B (2). All the isolated compounds were evaluated against two cancer cell lines (A549 and Hela), and screened for antibacterial activities. Furthermore, they were assessed for cytotoxicity against a normal cell line (Vero cell).

Unraveling the Electrocatalytic Activity in HMF Oxidation to FDCA by Fine-Tuning the Degree of NiOOH Phase Over Ni Nanoparticles Supported on Graphene Oxide.

The development of an efficient electrocatalyst for HMF oxidation to FDCA has been in the early stages. Herein, the NiNPs/GO-Ni-foam is fabricated as an electrocatalyst for FDCA production. However, the electrocatalytic performance of the untreated NiNPs/GO-Ni-foam is observed with moderate Faradaic efficiency (FE) (73.0%) and FDCA yield (80.2%). By electrochemically treating the NiNPs/GO-Ni-foam in an alkaline solution with positive potential at different treatment durations, the degree of NiOOH on metal surfaces is changed. The distinctive electrocatalytic activity obtained when using the different NiOOH degrees allows to understand the crucial impact of NiOOH species in HMF electrooxidation. Enhancing the portion of the NiOOH phase on the electrocatalyst surface improves electrocatalytic activity in terms of FE and FDCA yield up to 94.8±4.8% and 86.9±4.1%, respectively. Interestingly, as long as the NiOOH portion on the electrocatalyst surface is preserved or regenerated, the electrocatalyst performance can be intact even after several catalytic cycles. The theoretical study via density functional theory (DFT) also agrees with the experimental observations and confirms that the NiOOH phase facilitates the electrochemical transformation of HMF to FDCA through the HMFCA pathway, and the potential limiting step of the overall reaction is the oxidation of FFCA to FDCA.

Photochemical engineering unsaturated Pt islands on supported Pd nanocrystals for a robust pH-universal hydrogen evolution reaction.

The rational design of heterostructured nanocrystals (HNCs) is of great significance for developing highly efficient hydrogen evolution reaction (HER) electrocatalysts. However, a significant challenge still lies in realizing the controllable synthesis of desired HNCs directly onto a support and exploring their structure-activity-dependent HER performance. Herein, we reported various controllable Pd7@Ptx core-shell HNCs with optimal hybrid structures via a photochemical deposition strategy. The growth patterns of a Pt shell can be finely controlled by adjusting the growth kinetics, resulting in a varying deposition rate. In particular, the as-prepared Pd7@Pt3 HNCs with a Pt shell in the Stranski-Krastanov mode showed the best performances over a wide pH range media, delivering low overpotentials of 33, 18 and 49 mV, resulting in a catalytic current density of 10 mA cm-2 at a low effective catalyst loading of 0.021 mg cm-2. The resulting Tafel slopes were 23.1, 52.6 and 42.7 mV dec-1 in 0.5 M H2SO4, 1.0 M phosphate-buffered saline (PBS) and 1.0 M KOH electrolyte, respectively. It was found that the increased fraction of unsaturated coordination of Pt islands in the resultant material is the key to the enhanced and robust HER activity, which has been confirmed through density functional theory (DFT) calculations. This strategy could be extended to the rational design and synthesis of other heterostructured catalysts for energy conversion and storage.

Unraveling the Adsorption Behavior of Thymol on Carbon and Silica Nanospheres for Prolonged Antibacterial Activity: Experimental and DFT Studies.

Functionalization of thymol (Thy) on nanocarriers is a key step in achieving prolonged antimicrobial activity. This requires nanomaterials with uniform particle diameters and suitable thymol sorption. Herein, hollow carbon (HC) and SiO2-carbon core-shell (SiO2@C) were investigated due to their diverse morphologies and ease of surface modification. HC (14 ± 1 nm size) and SiO2@C (10 ± 1.5 nm size) were synthesized by the Stöber method before thymol was loaded by incipient wetness impregnation. Nanoparticle physicochemical properties were characterized by advanced techniques, including X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). Adsorption energies of thymol on the carbon and SiO2 surfaces were elucidated by density functional theory (DFT) simulations. Moreover, the in vitro thymol release profiles and antibacterial activity were evaluated. The experimental results indicated that the oxy-carbon surface species of HC led to longer thymol release profiles than the -OH group of SiO2@C. The DFT calculations revealed that the weaker physical interaction of thymol on HC was better for drug release than that on SiO2@C. Thus, a longer thymol release profile of HC with hollow structures showed better antibacterial performance against Gram-positive bacteria Staphylococcus aureus than that of SiO2@C with core-shell structures. This work confirms the important role of carbon morphology and specific functional groups in thymol release profiles for the further development of inhibition products.

Impact of exposed crystal facets on oxygen reduction reaction activity in zeolitic imidazole frameworks.

ZIF-67 is a representative type of metal-organic framework (MOF) developed for the oxygen reduction reaction (ORR) owing to its robust structure in alkaline electrolytes and the presence of the redox-active Co2+ species in the structure. In this work, the improvement of the ORR electrolytic performance of ZIF-67 in its pure phase by optimization of its crystal morphology and crystal facets has been presented. ZIF-67 nanocubes exhibit higher ORR activity than their bulk crystals. The enriched (100) facet in the nanocube crystals provides a higher number of exposed Co2+ sites resulting in improved ORR performances. Moreover, DFT study suggests a distinguished mechanism in the (100) facet highlighting the importance of crystal facets in electrochemical performances.

Metal-organic framework MIL-100(Fe) as a promising sensor for COVID-19 biomarkers detection.

The development of fast and non-invasive techniques to detect SARS-CoV-2 virus at the early stage of the infection would be highly desirable to control the COVID-19 outbreak. Metal-organic frameworks (MOFs) are porous materials with uniform porous structures and tunable pore surfaces, which would be essential for the selective sensing of the specific COVID-19 biomarkers. However, the use of MOFs materials to detect COVID-19 biomarkers has not been demonstrated so far. In this work, for the first time, we employed the density functional theory calculations to investigate the specific interactions of MOFs and the targeted biomarkers, in which the interactions were confirmed by experiment. The five dominant COVID-19 biomarkers and common exhaled gases are comparatively studied by exposing them to MOFs, namely MIL-100(Al) and MIL-100(Fe). The adsorption mechanism, binding site, adsorption energy, recovery time, charge transfer, sensing response, and electronic structures are systematically investigated. We found that MIL-100(Fe) has a higher sensing performance than MIL-100(Al) in terms of sensitivity and selectivity. MIL-100(Fe) shows sensitive to COVID-19 biomarkers, namely 2-methylpent-2-enal and 2,4-octadiene with high sensing responses as 7.44 x 105 and 9 x 107 which are exceptionally higher than those of the common gases which are less than 6. The calculated recovery times of 0.19 and 1.84 x 10-4 s are short enough to be a resuable sensor. An experimental study also showed that the MIL-100(Fe) provides a sensitivity toward 2-methylpent-2-enal. In conclusion, we suggest that MIL-100(Fe) could be used as a potential sensor for the exhaled breath analysis. We hope that our research can aid in the development of a biosensor for quick and easy COVID-19 biomarker detection in order to control the current pandemic.

Understanding the interaction between transition metal doping and ligand atoms of ZnS and ZnO monolayers to promote the CO2 reduction reaction.

Single-atom catalysts (SACs) obtained by doping transition metal (TM) atoms into stable monolayers are a promising way to improve the CO2 reduction reaction (CRR) performance. In this work, we theoretically investigated the effect of ligand atoms around the doped TM (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) in ZnO and ZnS for promoting the CRR performance. We found that the ligand atoms around the TM can influence its oxidation state and the electronic properties of the SACs, thus affecting their CRR activity. Due to the smaller charge transfer between the TM and substrate for TM-ZnS compared to TM-ZnO, the TM binding is weaker for the former. In addition, the more negatively charged oxygen ligand atoms in TM-ZnO interact with reaction intermediates, resulting in CRR products with less electron transfer. Pristine ZnS and ZnO monolayers can produce HCOOH but require a high limiting potential (UL) of about -1.2 V. Doping with TMs can reduce UL compared to the pristine surface. At the same time, the ligand can alter the preferred CRR pathway and product selectivity. We found that Mn-ZnS is selective to the CH4 product with a UL of only -0.29 V, which is a nearly 1 V improvement in the UL compared to ZnS.

Ti4-Decorated B/N-doped graphene as a high-capacity hydrogen storage material: a DFT study.

The adsorption properties of the hydrogen atom on our newly designed materials were investigated using density functional theory (DFT) calculations, focusing on the role of dopants in modulating the binding properties of the metal. We proposed decorating Ti4 on pristine, B- and N-doped graphene surfaces for preparing a large-capacity hydrogen-storage device. Computational results indicate that the doping of B on graphene enhances the interaction between the metal cluster and the supporting substrate with a very strong binding energy of -6.45 eV, which is the strongest interaction among our proposed catalysts. This binding energy prevents the aggregation and formation of Ti-metal clusters. Dissociative chemisorption of the first H2 molecule occurs on all materials. Metal hydrides preferentially exhibit strong hybridization between the H-1s and Ti-3d orbitals. Furthermore, Ti4 decorated B-graphene is the most effective, with a high capacity of hydrogen adsorption which could be released under practical conditions. We confirmed that eight H2 molecules could stably adsorb on Ti4/BGr with six reversible hydrogen adsorptions. Our proposed B-doped graphene-based material, Ti4/BGr, offers high cluster-stability on the substrate with high-capacity hydrogen storage compared to various other surfaces in the previous work. Therefore, Ti4 decorated B-graphene is a promising candidate material for use as a reversible hydrogen storage material.

Mimicking Peroxidase-Like Activity of Nitrogen-Doped Carbon Dots (N-CDs) Coupled with a Laminated Three-Dimensional Microfluidic Paper-Based Analytical Device (Laminated 3D-µPAD) for Smart Sensing of Total Cholesterol from Whole Blood.

This work presents a simple hydrothermal synthesis of nitrogen-doped carbon dots (N-CDs), fabrication of microfluidic paper-based analytical device (µPAD), and their joint application for colorimetric determination of total cholesterol (TC) in human blood. The N-CDs were characterized by various techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD), and the optical and electronic properties of computational models were studied using the time-dependent density functional theory (TD-DFT). The characterization results confirmed the successful doping of nitrogen on the surface of carbon dots. The N-CDs exhibited high affinity toward 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)-diammonium salt (ABTS) with the Michaelis-Menten constant (KM) of 0.018 mM in a test for their peroxidase-like activity. Particularly, since hydrogen peroxide (H2O2) is the oxidative product of cholesterol in the presence of cholesterol oxidase, a sensitive and selective method of cholesterol detection was developed. Overall, the obtained results from TD-DFT confirm the strong adsorption of H2O2 on the graphitic N positions of the N-CDs. The laminated three-dimensional (3D)-µPAD featuring a 6 mm circular detection zone was fabricated using a simple wax screen printing technique. Classification of TC according to the clinically relevant criteria (healthy, <5.2 mM; borderline, 5.2-6.2 mM; and high risk, >6.2 mM) could be determined by the naked eye within 10 min by simple comparison using a color chart. Overall, the proposed colorimetric device serves as a low-cost, rapid, simple, sensitive, and selective alternative for TC detection in whole blood samples that is friendly to unskilled end users.

Conjugated Copolymers That Shouldn't Be.

Multiple studies have explored using cage silsesquioxanes (SQs) as backbone elements in hybrid polymers motivated by their well-defined structures and physical and mechanical properties. As part of this general exploration, we report unexpected photophysical properties of copolymers derived from divinyl double decker (DD) SQs, [vinyl(Me)Si(O0.5 )2 ][PhSiO1.5 ]8 [(O0.5 )2 Si(Me)vinyl] (vinylDDvinyl). These copolymers exhibit strong emission red-shifts relative to model compounds, implying unconventional conjugation, despite vinyl(Me)Si(O-)2 siloxane bridges. In an effort to identify minimum SQ structures that do/do not offer extended conjugation, we explored Heck catalyzed co-polymerization of vinyl-ladder(LL)-vinyl compounds, vinyl(Me/Ph)Si(O0.5 )2 [PhSiO1.5 ]4 (O0.5 )2 Si(Me/Ph)vinyl, with Br-Ar-Br. Most surprising, the resulting oligomers show 30-60 nm emission red-shifts beyond those seen with vinylDDvinyl analogs despite lacking a true cage. Further evidence for unconventional conjugation includes apparent integer charge transfer (ICT) between LL-co-thiophene, bithiophene, and thienothiophene with 10 mol % F4 TCNQ, suggesting potential as p-type doped organic/inorganic semiconductors.

Lithium-Templated Formation of Polyhedral Oligomeric Silsesquioxanes (POSS).

A coordination complex, lithium hepta(i-butyl)silsesquioxane trisilanolate (1; Li-T7), a stable intermediate in silsesquioxane (SQ) syntheses, was successfully isolated in 65% yield and found to be highly soluble in nonpolar solvents such as hexane. The structure of Li-T7 was confirmed by NMR, IR spectroscopy, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, electrospray ionization mass spectrometry, and computational simulation, providing detailed elucidation of the intermolecular self-association of the SQ cage with a box-shaped Li6O6 polyhedron through strong coordination bonds. After acid treatment, Li-T7 undergoes lithium-proton cationic exchange, yielding hepta(i-butyl)silsesquioxane trisilanol (2; H-T7) quantitatively. The high yield of H-T7 seems to be influenced by Li-O bonding in the Li-T7 complex that affects the selective formation of hepta(i-butyl)silsesquioxane trisilanolate and the bulky i-butyl groups which may prevent decomposition or SQ cage-rearrangement even at reflux under alkaline conditions. Single-crystal X-ray crystallography confirms the presence of the dumbbell-shaped SQ partial cages through strong intermolecular hydrogen bonds. Interestingly, lowering the polarity of the reaction solution by adding dichloromethane results in formation of the cubic octa(i-butyl)silsesquioxane (3; T8) cage in a good yield (47%), which is isolated by crystallization from the reaction solution.

Influence of hydrogen spillover on Pt-decorated carbon nanocones for enhancing hydrogen storage capacity: A DFT mechanistic study.

We used density functional theory (DFT) to investigate hydrogen adsorption and diffusion on platinum-decorated carbon nanocones (Pt-CNCs). The curvature presented in the conical section of CNC materials affects the Pt binding stability. The role of Pt atoms as an active catalyst for H2 adsorption and dissociation has been investigated in perfect Pt-4CNC and defect Pt-v4CNC systems. Then, the spillover mechanism of dissociated hydrogen atoms in Pt-v4CNC is explored via two reaction steps: (i) H-migration from Pt to carbon atoms and (ii) H-diffusion via the C-C route throughout the CNC surface. Our results show that the presence of the hydrogen atom on the Pt catalyst can efficiently induce the H-diffusion process through the C-C surface, and the Pt-H bond significantly facilitates the H-migration from C-H bonds near to the active Pt catalyst to the adjacent carbon atom with an energy barrier <0.5 eV under ambient conditions. Altogether, the theoretical results support the concept of the spillover mechanism as a key process for enhancing the hydrogen storage capacity of metal-decorated CNCs. These results improve our understanding about the hydrogen spillover mechanism and the catalytic reactions which are very important for the development of highly efficient hydrogen storage materials.