Simultaneous Pd Nanoparticle Deposition and Enhancement in the Surface Oxygen Vacancy of Bi₂MoO₆ Nanoflakes for Room Temperature Vanillin Hydrodeoxygenation

A promising method for transforming lignin derivatives into high-value chemicals and biofuels is hydrodeoxygenation (HDO), which is anticipated to be a viable and feasible protocol for the biorefinery. Nonetheless, the requirements of high temperature and high H2 pressure are two main hurdles in the HDO process. Herein, we developed highly active Pd-decorated Bi2MoO6 nanoflakes for complete and selective vanillin (a typical lignin-derived platform molecule) conversion at room temperature and mild H2 pressure. The acquired results reveal that the selection of solvents in vanillin HDO has a detrimental effect, specifically on the product selectivity. When the reaction was performed in dichloromethane solvent, 2-methoxy-4-methylphenol (MMP) was obtained after a 4 h reaction with >99% vanillin conversion and >99% MMP selectivity. Conversely, if water is the reaction medium, it suppresses the formation of MMP, resulting in the selective formation of vanillin’s hydrogenation product vanillyl alcohol (VOL) with 88% vanillin conversion and 91% VOL selectivity. X-ray photoelectron spectroscopy (XPS), Raman, Fourier transform infrared (FT-IR), and ultraviolet (UV)–visible adsorption experimental studies revealed that the superior catalytic performance of the presented catalyst was due to the efficient adsorption of the reactant preferentially through the aldehyde moiety over the catalyst surface and enhancement in surface oxygen vacancies (SOVs) of bismuth molybdate nanoflakes as a result of the treatment with NaBH4 used for Pd nanoparticle deposition. No significant loss in the catalytic activity after multiple cycles proves the stability and good recyclability of the proposed catalyst. This study improves the catalysis strategy of HDO of lignin derivatives and paves the path toward the development of advanced and highly efficient metal-based catalysts for valuable fuels and chemical production from biomass under mild conditions

Synthesis of Triptycene-Based Organosoluble, Thermally Stable, and Fluorescent Polymers: Efficient Host–Guest Complexation with Fullerene

We report a facile synthesis of 2,6-diethynyltriptycene (DET) in high yield. Application of DET as monomer in polymer chemistry has been shown (for the first time) in syntheses of two novel polymers via Sonogashira cross-coupling reaction in high yield. The newly synthesized polymers were characterized by FT-IR, UV–vis absorption, and NMR spectroscopic techniques. The polymers prepared using DET have interesting properties such as high solubility in common organic solvents, high thermal stability [decomposition temperatures (<i>T</i>_d) > 495 °C], and high char yield (greater than 81% at 900 °C). Additionally, polymers are fluorescent. Host–guest interaction between triptycene-based polymers and fullerene (C₆₀) has been studied for the first time. Fluorescence quenching of our polymers by C₆₀ has been used to study the extent of (polymer·C₆₀) host–guest complex formation. Fluorescence quenching studies indicate binding constant for polymer·C₆₀ complexation on the order of 10⁵ M^–1

Synthesis of Triptycene-Based Organosoluble, Thermally Stable, and Fluorescent Polymers: Efficient Host–Guest Complexation with Fullerene

We report a facile synthesis of 2,6-diethynyltriptycene (DET) in high yield. Application of DET as monomer in polymer chemistry has been shown (for the first time) in syntheses of two novel polymers via Sonogashira cross-coupling reaction in high yield. The newly synthesized polymers were characterized by FT-IR, UV–vis absorption, and NMR spectroscopic techniques. The polymers prepared using DET have interesting properties such as high solubility in common organic solvents, high thermal stability [decomposition temperatures (<i>T</i>_d) > 495 °C], and high char yield (greater than 81% at 900 °C). Additionally, polymers are fluorescent. Host–guest interaction between triptycene-based polymers and fullerene (C₆₀) has been studied for the first time. Fluorescence quenching of our polymers by C₆₀ has been used to study the extent of (polymer·C₆₀) host–guest complex formation. Fluorescence quenching studies indicate binding constant for polymer·C₆₀ complexation on the order of 10⁵ M^–1

Pd Nanoparticle-Decorated Bi₂MoO₆ Nanoflakes with Surface Oxygen Vacancies for Selective Room-Temperature Furfural Hydrogenation and Benzyl Phenyl Ether Hydrogenolysis

Biomass-derived feedstock plays a crucial role in a sustainable economy due to its renewable nature, energy security, greenhouse gas reduction, waste management, and commercial prospects. A wide range of catalytic materials have been developed to make the process efficient and selective for the production of valuable chemicals. The present study focuses on the significance of surface defects, the surface oxygen vacancies (SOVs), in conjunction with Pd nanoparticles for selective biomass conversion under ambient conditions. Herein, biomass-derived furfural (FAL) is converted into furfuryl alcohol (FOL), tetrahydrofurfuryl alcohol (THFOL), and 2-methyltetrahydrofuran (2-MTHF) under ambient reaction conditions over Pd nanoparticle-supported Bi2MoO6 (BMO) catalysts. The versatility of the fabricated catalyst is further explored for the selective cleavage of a lignin model ether, benzyl phenyl ether (BPE), into toluene and phenol again at room temperature. The mechanistic insights are carried out using UV–visible and Fourier transform infrared (FT-IR) adsorption experiments, demonstrating the improvement in the reactant’s adsorption after an enhancement in the number of SOVs. Furthermore, the impact of the reaction medium on the adsorption strength and mode of adsorption was also rationalized based on adsorption and controlled experimental studies. The X-ray photoelectron (XPS), Raman, and electron paramagnetic resonance (EPR) spectroscopic studies reveal an enhancement in SOVs of BMO after its treatment with NaBH4, which was used for Pd nanoparticle deposition over the BMO surface. Further study using XPS and transmission electron microscopy (TEM) shows that the support is critical in regulating the concentration of Pd0 species and the size of Pd nanoparticles. In brief, the present research aims to demonstrate how the induction of surface defects in metal oxides can enhance the efficiency of biomass processing

Cooperativity in a New Role: Stabilization of the Ammonium Salts in the Solid State over Their H‑Bonded Complexes in the Gas Phase

Crystal structure of ammonium halides, carbonates, and sulfates like NH₄X (X = F^–, Cl^–, Br^–, NO₃^–) and (NH₄)₂X (X = CO₃^2– and SO₄^2–) exhibit a mode of aggregation in which the cation (NH₄⁺) and counterion are well separated, typical of ionic salts. However, in the stoichiometric limit of the gas phase, they exist only as H-bonded molecular complexes of the type, H₃N···HX. Following a bottom up approach, calculations were performed on these molecular complexes by increasing the number of molecules to investigate the limit in which these molecular complexes transformed to their respective salts. Molecular complex → salt transition is shown to occur for the 2:2 complexes in NH₄Cl, NH₄Br, NH₄HCO₃, and NH₄NO₃, 3:3 complexes for NH₄F, and 4:2 complex for (NH₄)₂SO₄. The relative stability of the salt form in comparison to the H-bonded molecular complex is shown to exhibit interesting cooperative enhancement as the number of molecules increases. Dispersion corrected solid state density functional theory calculations for the crystalline salts reveal that the structures of the higher order aggregates of these complexes resemble the bulk salt-like structures. The computed terahertz (THz) spectra for both the H-bonded complexes and the solid state ionic structures are well resolved to distinguish between the two forms. Calculations for three solid phases of NH₄Cl are in agreement with experimental temperature-dependent relative order of their stability, and the low frequency THz spectra decipher the orientational disorder of the phases due to tumbling/rotational motion of the NH₄⁺ ion within the crystals

Anion-Assisted Formation of Discrete Homodimeric and Heterotetrameric Assemblies by Benzene Based Protonated Heteroaryl Receptors

Anion-assisted formation of discrete homodimeric and heterotetrameric assemblies by benzene based protonated heteroaryl receptors <b>L</b>^<b>1</b>–<b>L</b>^<b>6</b> have been studied thoroughly by single crystal X-ray diffraction studies. Crystallographic results elucidate the fact that protonated tripodal receptor <b>L</b>^<b>1</b> formed staggered homodimeric capsular assemblies <b>2</b> and <b>3</b> with CF₃COO^– and ClO₄^– ions, respectively. Protonation of <b>L</b>^<b>3</b> with trimesic acid also showed the formation homodimeric assembly, <b>6</b>. In all these cases the anions are hydrogen bonded to the receptor molecules and show remarkable influence on the outcome of the self-assembly process to form discrete capsules. The necessity of the alkyl substitution on the benzene platform has been established from complexes <b>8</b>, <b>9</b>, and <b>10</b>, which were obtained upon protonation of <b>L</b>^<b>6</b> with HNO₃, HI, and HClO₄, respectively. Interestingly, when a 1:1 mixture of <b>L</b>^<b>1</b> (tripodal) and <b>L</b>^<b>5</b> (dipodal) were treated with HClO₄ and HBF₄, discrete heterotetrameric assemblies have been isolated as complexes <b>11</b> and <b>12</b>. The detailed solid state structural analysis of these complexes revealed the formation of heterotetrameric assemblies assisted by anion–water clusters. Correlation of these solid state structural assemblies with our previously reported complexes <b>1</b>, <b>4</b>, <b>5</b>, and <b>7</b> has also been described. The role of anionic templates in assisting the formation of discrete capsular assemblies from receptors possessing heteroaryl units and 1,3,5-methyl substituted benzene platform has been established

Pyrazine Motif Containing Hexagonal Macrocycles: Synthesis, Characterization, and Host–Guest Chemistry with Nitro Aromatics

The synthesis and characterization of cationic two-dimensional metallamacrocycles having a hexagonal shape and cavity are described. Both macrocycles utilize a pyrazine motif containing an organometallic acceptor tecton with platinum­(II) centers along with different donor ligands. While one macrocycle is a relatively larger [6 + 6], the other is a relatively smaller [2 + 2] polygon. A unique feature of the smaller ensemble is that it is an irregular polygon in which all six edges are not of equal length. Molecular modeling of these macrocycles confirmed the presence of hexagonal cavities. The ability of these π-electron rich macrocycles to act as potential hosts for relatively electron deficient nitroaromatics (DNT = 2,4-dinitrotoluene and PA = picric acid) has been studied using isothermal titration calorimetry (ITC) as a tool. Molecular dynamics simulation studies were subsequently performed to gain critical insight into the binding interactions between the nitroaromatic guest molecules (PA/DNT) and the ionic macrocycles reported herein

Synthesis of a Preorganized Hybrid Macrobicycle with Distinct Amide and Amine Clefts: Tetrahedral versus Spherical Anions Binding Studies

A new <i>C</i>_3<i>v</i> symmetric amido-amine hybrid macrobicycle, <b>L</b> is synthesized toward anion recognition in its protonated states. <b>L</b> contains tri-amide and tetra-amine clefts separated by <i>p</i>-phenylene spacers. The solid-state structure of methanol-encapsulated <b>L</b> exhibits an overall cavity length of ∼12.0 Å where the amide and amine -NH protons are converged toward the center of the respective cavities. Conformational analysis of <b>L</b> in solution is established by NOESY NMR. Anion binding of [H₃<b>L</b>]³⁺ with spherical (Cl^–, Br^–, I^–) and tetrahedral (ClO₄^–, SO₄^2–) anions are carried out by isothermal titration calorimeter in dimethylsulfoxide. The association of halides with [H₃<b>L</b>]³⁺ is endothermic and entropy driven. However, association of tetrahedral anions is exothermic in nature and both entropy- and enthalpy-driven. The overall association constants show the following order: HSO₄^– > Br^–> Cl^– ≈ ClO₄^–. Single crystal X-ray structures of ClO₄^– and Br^– complexes of protonated <b>L</b> show encapsulation of ClO₄^– in the amide cleft of [H₂<b>L</b>]²⁺ (complex <b>1</b>) and encapsulation of Br^– in the ammonium cleft of [H₃<b>L</b>]³⁺ (complex <b>2</b>). Further, preorganization of <b>L</b> toward encapsulation of spherical and tetrahedral anions is established by comparing its amide, amine, and overall cavity dimensions with <b>1</b> and <b>2</b>

Optimization of ultrasound-assisted extraction of phenolic compounds from <i>Sesamum indicum</i>

Effective extraction of phyto-biomolecules insures retaining maximum functionality along with higher recovery. In this study, ultrasound-solvent assisted extraction (USAE) was employed for optimal extraction of phyto-biomolecules from Sesamum indicum (sesame) leaves using the approach of Response Surface Methodology (RSM). The optimized condition of 200 W power, 59% methanol concentration with 1:14 g/mL solid–liquid ratio and 15 min of extraction time yielded 367.39 ± 1.85 mg GAE/100 g of total phenolic content, 96.72 ± 3.27% of free radical scavenging activity and 81.20 ± 2.87% of iron chelating activity respectively. The extract consist of essential phytocomponents like gallic acid, chlorogenic acid, and quercetin with lipid peroxidation activities of >50% over incubation time of 48 h. Also, showed antimicrobial activity against various Gram’s negative and positive food borne pathogens. The results of this study implied the importance of USAE for effective and optimum recovery of phyto-biomolecules from Sesame leaves with retained functional properties. </p

Binding Studies on an Arene-Capped Bicyclic Cyclophane with π‑Rich Neutral Guests and Anions

Structural aspects of binding of π-rich neutral guests with <b>L</b> and anions with [H₆<b>L</b>]⁶⁺ are examined thoroughly. <b>L</b> forms inclusion complexes with π-rich solvents, 2DMSO⊂<b>L</b> (<b>1</b>), 3DMF⊂<b>L</b>₂ (<b>2</b>), (DMF·benzene·DMF)⊂<b>L</b>₂ (<b>3</b>), MeCN⊂<b>L</b> (<b>4</b>), and MeCOMe⊂<b>L</b> (<b>5</b>) in dimethylsulfoxide (DMSO), dimethyl formamide (DMF), benzene/DMF, acetonitrile (MeCN), and acetone (MeCOMe) respectively. The single crystal X-ray structural analysis of complexes illustrates cavity and cleft binding of these guests via N–H···O interactions in <b>1</b>, <b>2</b>, <b>3</b>, <b>5</b> and N–H···N interactions in <b>4</b> with the secondary nitrogen center of <b>L</b> and the hydrogen bonding acceptor atoms of the solvent guests. Inclusion of benzene in the side pocket is also observed in <b>3</b>. Our efforts to isolate single crystals with solvents such as MeOH, EtOH, CHCl₃, and CH₂Cl₂ are unsuccessful. Single crystal X-ray diffraction study has also shown the encapsulation of nitrate in the cleft of [H₆<b>L</b>]⁶⁺ via N–H···O hydrogen bonding interactions in [H₆<b>L</b>]­[NO₃]₆·HNO₃·6H₂O (<b>6</b>), whereas in [H₆<b>L</b>]₂[ClO₄]₁₂·CH₃OH·17H₂O (<b>7</b>) perchlorates are recognized in the cavity and side pockets of [H₆<b>L</b>]⁶⁺. This receptor has previously shown encapsulation of iodide (<b>8</b>), and Cl^–···H₂O (<b>9</b>). A potentiometric study of <b>L</b> exhibits the maximum concentration of [H₆<b>L</b>]⁶⁺ species at pH 2–3 in MeOH/H₂O 1:1 (v/v) binary solvent. Anion binding studies with <b>L</b> at pH 2.0 in MeOH/H₂O 1:1 (v/v) solvent system are examined by isothermal titration calorimetric (ITC) experiments