Search Results (99)

The paper analyses the effect of the solvent amount and nature on the structure and mechanical properties of hydrogels based on copolymers of 2-hydroxyethylmethacrylate (HEMA) with polyvinylpyrrolidone (PVP). The synthesis of pHEMA-gr-PVP copolymers was carried out by the copolymerization method in the presence of metal ions of variable oxidation states in solvents with various nature: water, dimethyl sulfoxide (DMSO), diethylene glycol (DEG), and cyclohexanol (HOCy). The structure of the copolymers was evaluated by the PVP grafting efficiency, its actual content in the copolymer, and the molecular weight between crosslinks (M_C). Taking the example of water, an increase in the solvent content up to 50 mass parts causes an increase in the efficiency of PVP grafting, which occurs due to enhanced macromolecule mobility through the dilution of the starting composition, hence the decrease in its viscosity. It was established that the nature of the solvent significantly affects the crosslinking density of the polymer network in the series H₂O, DEG, DMSO, HOCy, an increase in the M_C is observed causing a decrease in the hardness and elasticity of hydrogels and an increase in their water-retention capacity and swelling coefficient. The obtained results prove the possibility of targeted regulation within wide limits of the structure and properties of hydrogels based on pHEMA-gr-PVP copolymers through control of polymerization conditions (selection of the type and concentration of solvent). Full article

An excellent regioselectivity of vapor-phase catalytic transfer hydrogenation (CTH) of substituted oxiranes (methyl-, n-butyl-, and phenyloxirane) with alkanols (EtOH, 2-PrOH or 2-PeOH) as hydrogen donors in the presence of magnesium oxide as a catalyst was attained. In the vapor phase, all of these oxiranes as well as 1,2-epoxycyclohexane were hydrogenated. Moreover, it was found that primary alcohols were always the main products of CTH of methyl-, n-butyl-, and phenyloxirane with very good regioselectivity towards the alcohols: 93, 73, and 100%, respectively. It was shown that vapor-phase CTH of methyloxirane with 2-pentanol led to three products, two regioisomeric propanols, (1-PrOH and 2-PrOH), and also 1-(2-pentyloxy)-2-propanol. Their yields were 48%, 4%, and 35%, respectively. Two regioisomeric hexanols (1-HeOH, 54% yield and 2-HeOH, 20% yield) and 2-hexanone (14% yield) were found as products of the CTH of n-butyloxirane with 2-propanol as the hydrogen donor. For vapor-phase CTH of phenyloxirane, only 2-phenylethanol (95% yield) was observed together with minor amounts of phenylacetaldehyde. In vapor-phase CTH of 1,2-epoxycyclohexane, the presence of the transfer hydrogenation products (2-cyclohexenone, cyclohexanol, and cyclopentylmethanol) as well as isomerization products (cyclohexanone, 2-cyclohexenol, and 3-cyclohexenol) were found. It was noted that at 623 K, the yields of the former products were 18, 22, and 14%, respectively. Liquid-phase CTH of n-butyl- or phenyloxirane with 2-pentanol (b.p. 392 K) was unsuccessful. Full article

Catalysis plays a pivotal role in green chemistry practices, particularly in reducing waste generated during chemical synthesis. Decatungstate (DT) emerges as a potent photocatalyst for Type I oxidations, exhibiting remarkable resilience to oxygen quenching, a characteristic that sets it apart from other excited triplet state photocatalysts. While homogeneous DT catalysis demonstrates effectiveness, its solubility poses challenges for its separation and recycling. To address these limitations, we focus on the development and comparison of heterogeneous DT photocatalysts, aiming to optimize their yield, recovery, and reusability. We synthesized tetrabutylammonium decatungstate (TBADT)-supported catalysts using silica, alumina, titanium dioxide, and glass wool and characterized them using diffuse reflectance measurements. Subsequently, we evaluated their photocatalytic performance by monitoring the oxidation of 1-phenylethanol and cyclohexanol under UVA irradiation. Our findings reveal that TBADT@silica emerges as the most effective catalyst, achieving approximately 20% conversion of cyclohexanol and 50% conversion of 1-phenylethanol with good reusability. Interestingly, we observed that 3-aminopropyl-triethoxysilane (APTES) treatment, intended to enhance DT anchoring, unexpectedly quenches the ³DT* triplet state, reducing catalytic activity. This unexpected finding underscores the importance of careful consideration in designing robust and recyclable heterogeneous decatungstate catalysts. Our research contributes significantly to the advancement of heterogeneous photocatalysis, paving the way for future applications in flow photochemistry. Further, we share a Python code (Google 3.12.11) to correct spectra obtained in Cary spectrometers. Full article

Catalytic upgrading of pyrolysis oils is an important step for producing replacement hydrocarbon-rich liquid biofuels from biomass and can help to advance pyrolysis technology. Catalysts play a pivotal role in influencing the selectivity of chemical reactions leading to the formation of main compounds in the final upgraded liquid products. The present work involved a systematic study of solvent-free catalytic reactions of cyclohexanone in the presence of hydrogen gas at 160 °C for 3 h in a batch reactor. Cyclohexanone can be produced from biomass through the selective hydrogenation of lignin-derived phenolics. Three types of catalysts comprising undoped NbOPO₄, 10 wt% NiO/NbOPO₄, and 30 wt% NiO/NbOPO₄ were studied. Undoped NbOPO₄ promoted both aldol condensation and the dehydration of cyclohexanol, producing fused ring aromatic hydrocarbons and hard char. With 30 wt% NiO/NbOPO₄, extensive competitive hydrogenation of cyclohexanone to cyclohexanol was observed, along with the formation of C₆ cyclic hydrocarbons. When compared to NbOPO₄ and 30 wt% NiO/NbOPO₄, the use of 10 wt% NiO/NbOPO₄ produced superior selectivity towards bi-cycloalkanones (i.e., C₁₂) at cyclohexanone conversion of 66.8 ± 1.82%. Overall, the 10 wt% NiO/NbOPO₄ catalyst exhibited the best performance towards the production of precursor compounds that can be further hydrodeoxygenated into energy-dense aviation fuel hydrocarbons. Hence, the presence and loading of NiO was able to tune the activity and selectivity of NbOPO₄, thereby influencing the final products obtained from the same cyclohexanone feedstock. This study underscores the potential of lignin-derived pyrolysis oils as important renewable feedstocks for producing replacement hydrocarbon solvents or feedstocks and high-density sustainable liquid hydrocarbon fuels via sequential and selective catalytic upgrading. Full article

Background: The natural compounds caracasine acid (1) and its methyl ester, caracasine (2), isolated from the flowers of Croton micans, are effective against several tumor cell lines. Five semi-synthetic derivatives (3–7) were synthesized based on these structures. The study aimed to evaluate the cytotoxic activity of these compounds in 2D and spheroid cultures. Methods: The assays were performed in a panel of 12 human cell lines, 8 cancer and 4 normal cell lines. The compounds were evaluated on spheroids derived from the HCT116, HCT116 p53 knockout (p53KO), A549, and U2OS cell lines, as well as mixed spheroids comprising tumor cells and normal fibroblasts. Results: The parent compound (1), the natural ester (2), and two novel derivatives, the anhydride (7) and the cyclohexanol ester (3), demonstrated cytotoxicity against different leukemic cells and HCT116, HCT116 p53 knockout (p53KO), A549, and U2OS cell lines in conventional two-dimensional cultures. Peroxide formation, however, was significantly higher in leukemic cell lines (p < 0.01) in 2D culture as compared with the other tumor cell lines. The compounds did not induce cell death in spheroid cultures; caspases 8, 9, and 3 were not activated upon treatment. Conclusions: These findings indicate potential applications in leukemia treatment, albeit with limited efficacy against solid tumors. Full article

Adipic acid (AA), a pivotal precursor for nylon-6,6 and polyurethane, was synthesized via an innovative catalytic electrocatalytic oxidation strategy in this study. Four distinct MnO_x/CNT nanocatalysts were prepared by hydrothermal and co-precipitation methods and fabricated into electrodes for the oxidation of cyclohexanol (Cy-OH) in a K₂SO₄ neutral solution. Comprehensive characterization revealed that the catalytic performance depended on both crystalline phase configuration and manganese valence states. MnO(OH) and MnO_x were identified as the main active species, with the synergy between MnO species and carbon nanotubes significantly enhancing catalytic activity. Mechanistic investigations demonstrated that under Mn⁴⁺-dominant conditions, low-valence manganese species facilitated Cy-OH-to-cyclohexanone (Cy=O) conversion, while an optimal O_ads/O_lat ratio (≈1) effectively promoted subsequent Cy=O oxidation to AA. Under optimized conditions (1.25 V vs. Ag/AgCl, 80 °C, 15 h), complete Cy-OH conversion was achieved with 56.4% AA yield and exceptional Faradaic efficiency exceeding 94%. This work elucidates manganese-based electrocatalytic oxidation mechanisms, proposes a sequential reaction pathway, and establishes an environmentally benign synthesis protocol for AA, advancing sustainable industrial chemistry. Full article

Background: Chemosensation in ticks opens a novel and unique field for scientific research. This study highlights ticks’ chemosensory system to comprehend its host-searching behavior and other integrated chemistry and biology involving Haller’s structure. Methodology: This study combines microanatomical, electrophysiological, and behavioral experiments to investigate the role of Haller’s organ in adult ticks in response to different classes of organic compounds. Results: We showed the microscopic anatomy of Haller’s organ in Haemaphysalis darjeeling, present at the terminal segment of the first pair of appendages. Haller’s structure serves a vital function in perceiving odor. The electrophysiological activity of adult ticks to different classes of organic compounds via electroscutumography was explored at five different concentrations: w/v 0.001, 0.01, 0.1, 1.0, and 2.0%. Among 55 organic compounds, moderate to high stimulation was recorded with pyruvate (13.28 mv at 2%), ammonia (12.26 mv at 2%), benzoic acid (1.99 mv at 0.001%), isobutyric acid (1.39 mv at 0.001%), 2,6-dichlorophenol (1.34 mv at 0.001%), p-Tolualdehyde (1.26 mv at 2%), tetradecane (1.23 mv at 2%), docosane (1.17 mv at 2%), citronellal (1.13 mv at 0.1%), isopropyl acetate (1.05 mv at 0.01%), cyclohexanol (1.03 mv at 2%), 1-octane-3-ol (1.02 mv at 2%), and 1-octanol (1.01 mv at 0.001%). Olfactometric bioassays at w/v 2.0% concentration further confirmed that ammonia, pyruvate, 1-octane-3-ol, hematin porcine, p-Tolualdehyde, methyl salicylate, uric acid, tetradecane, carbon dioxide, propanoic acid, 3-hexanol, hexanoic acid, adenine, 2,6-dichlorophenol, hexadecane, heptanoic acid, pentanoic acid, octadecane, guanine, and nonanoic acid acted as strong attractants, while citronellal, eugenol, butyric acid, geraniol, benzaldehyde, and tiglic aldehyde showed an active repellent effect against the tick species. Conclusions: This investigation provides knowledge of the olfactory sensilla of Haller’s structure as biosensors behind tick olfaction and the possibility for chemical detection of diverse attractants and repellents for future development of anti-tick compounds. Full article

Background: This study explored the biotransformation of (–)-isopulegol using immobilized cells of Rhodococcus rhodochrous IEGM 1362 to optimize the production of new bioactive compounds. Methods: An efficient biocatalyst based on R. rhodochrous IEGM 1362 cells immobilized in a macroporous polyvinyl alcohol (PVA) cryogel matrix was developed for the production of bioactive derivatives of (–)-isopulegol. The biological characteristics of the immobilized cells were investigated using scanning and transmission electron microscopy and energy-dispersive X-ray spectroscopy methods. Results: The use of the biocatalyst increased the overall yield of target products from 54% with free cells to 87% with immobilized cells in a single cycle. Major derivatives identified included (1R,2S,5R)-5-(hydroxymethyl)-2-(prop-1-en-2-yl)cyclohexanol and (1R,3R,4S)-3-hydroxy-4-(prop-1-en-2-yl)cyclohexanecarboxylic acid, both exhibiting potential pharmacological activity. The biocatalyst retained functional activity toward monoterpenoid over 13 exploitation cycles, meeting industrial biotechnology requirements. Immobilized cells were characterized by the absence of endogenous reserve inclusions (in particular lipids) and a high intracellular iron content. Conclusions: The developed immobilized biocatalyst is promising for scaling up the production of biologically active compounds. Full article

Structural degradation in liquid environments can hinder the applications of polymer composites as structural materials. In this work, we study the impacts of methanol on surface cracking and the propagation of pre-formed cracks in UV-irradiated poly(methyl methacrylate)/functionalized graphene (PMMA/FG) composites, followed by the uptake of three different crack-generated solvents, namely 1-butanol, cyclohexanol, and 2EA, respectively. The density of surface cracks increases with the increase in the uptake of the crack-generated solvent. The dependence of the nominal diffusivity for the surface cracking on temperature follows an Arrhenius-like law. The methanol in the composites enhances the uptake of the crack-generated solvent, accompanied by the desorption of methanol, and accelerates the initiation and propagation of surface cracks. The activation energy for the initiation of surface cracks shows an increasing dependence on the Hansen solubility distance from methanol. The progression of the pre-formed crack length with time follows a parabolic law. The nominal diffusivity of the crack-generated solvent for the propagation of the single-crack is greater in the healing zone than in the crack-free zone; the corresponding activation energies exhibit an opposite trend. Increasing the fraction of functionalized graphene and decreasing the UV-irradiation dose cause increases in the energy barriers that need to be overcome for the surface cracking and propagation of preexisting cracks. Full article

Partial hydrogenation of benzene is the main approach to cyclohexene synthesis in industry. Here, the reaction mechanisms of benzene hydrogenation on Pd-Zn bimetallic catalysts were studied using density functional theory, with the aim of understanding the effect of different Pd/Zn ratios on catalytic activity and cyclohexene selectivity. Three different surfaces, Pd(111), Pd₄Zn₁(111), and Pd₂Zn₁(111), were considered as catalyst models. It was found that increasing the Zn concentration decreases the hydrogenation energy barriers while also hindering the reverse reactions. These findings are corroborated by microkinetic simulations and also indicate that cyclohexene selectivity increases with higher Zn concentration but at the expense of reaction activity, which decreases due to the weaker C₆H₆* and H* adsorption strength in systems with high Zn concentration. The hydrogen coverage has a significant effect on the reaction activity, degree of rate control coefficient, and apparent activation energy as well. For the high hydrogen coverage situations, C₆H₉ hydrogenation is the rate-controlling step on H₁.₀/Pd(111) at all considered temperatures, but the degree of rate control for the C₆H₁₁ hydrogenation step significantly increases at high temperatures. For H₀.₈/Pd₄Zn₁(111), the rate-controlling step changes from C₆H₇ hydrogenation to C₆H₉ hydrogenation with increasing temperature, and for H₀.₆₇/Pd₂Zn₁(111), it changes from C₆H₇ and C₆H₈ hydrogenation to C₆H₁₀ hydrogenation. Full article

Using methods of DFT, we investigated the effect of electron withdrawing and electron donating groups on the relative stability of tentative glycosyl donor reaction intermediates. The calculation shows that by changing the stereoelectronic properties of the protecting group, we can influence the stability of the dioxolenium type of intermediates by up to 10 kcal mol⁻¹, and that by increasing nucleophillicity of the 4-O-Bz group, the dioxolenium intermediate becomes more stable than a triflate–donor pair. We exploited this mechanism to design galactosyl donors with custom protecting groups on O2 and O4, and investigated the outcome of the reaction with cyclohexanol. The reaction showed no change in the product distribution, which suggests that the neighboring group participation takes precedence over remote group participation due to kinetic barriers. Full article

The catalytic activity and selectivity of Co-based catalysts supported on home-made nanoporous carbon was studied as a function of the type of alkali promoter (Ca and Mg). The catalysts were characterized by N₂ adsorption/desorption isotherms, temperature-programmed reduction, CO chemisorption, and X-ray diffraction patterns. The catalysts were compared against carbon-supported alkali-promoted Ni-based catalysts and Re-containing catalysts. The catalytic activity of the Co-based catalyst was clearly enhanced in the presence of Ca and Mg, and it was higher than the Ni-based catalysts and comparable to that obtained using an ReC catalyst. The initial activity of the Mg-promoted catalyst increased by a factor of up to 2.5 times higher compared to the non-promoted catalyst. Moreover, this catalyst showed a turnover frequency of up to 5 times higher than equivalent carbon-supported Re-based catalysts. Significant changes were not observed in the selectivity of products after the incorporation of alkali, with cyclohexane being the main product. However, it was demonstrated that the presence of alkali led to a faster and higher production of cyclohexane from the demethoxylation of phenol and the dehydrogenation of cyclohexanol. The present results suggest that Co-based catalysts are an economical alternative for the catalytic conversion of representative target molecules from bio-oil feed. Full article

Aroma in food plays an important role in food perception and acceptance, which depends on various mixtures of volatile organic compounds (VOCs). Moreover, VOCs are of great significance for aroma identification. In this study, headspace solid-phase microextraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC-MS) technology was used to determine the VOCs in 10 pear syrups. A total of 127 VOCs were quantitatively determined, including 9 common VOCs and 46 characteristic VOCs of 10 pear syrups. The pear syrups were divided into three categories by cluster analysis, and thirty-eight differential VOCs were obtained using orthogonal partial least squares discrimination analysis (OPLS-DA) and fourteen key VOCs were selected by odor activity value (OAV). It was revealed that the key and common aroma components of pear syrups were butanoic acid, methyl ester, 2-methyl-, methyl ester and Hexanoic acid, and ethyl ester. The characteristic and differential VOCs were 10-Undecen-1-ol, Hexadecanal, n-Propylacetate, Cyclohexanol, 5-methyl-2-(1-methylethyl)-, (1S,2R,5S)-, Methional, Disulfide, dimethyl, 8-Nonenoic acid, ethyl ester, Naphthalene, 1,2-dihydro-1,1,6-trimethyl-, 3H-Purin-6-amine, N,N,3-trimethyl-, 2-Octanol,2,6-dimethyl-, Furyl hydroxymethyl ketone, Heptane, 2,2,4,6,6-pentamethyl-, and Butanoic acid,2-methyl-,methyl ester. The above results showed that different pear syrups had rich diversity in aroma compounds, with some components being shared among them while others are exclusive to specific syrups. Full article

Scenting is an important process for the formation of aroma quality in floral Longjing tea. There are differences in the aroma quality of osmanthus Longjing teas processed by different scenting processes. The efficient isolated scenting method was employed to process a new product of osmanthus Longjing tea in this study, and this was compared with the traditional scenting method. The volatile compounds of osmanthus Longjing tea were analyzed by a GC-MS instrument. In addition, the effects of scenting time and osmanthus consumption on the aroma quality of Longjing tea were studied. The results indicated that there were 67 kinds of volatile compounds in the osmanthus Longjing tea produced by the isolated scenting process (O-ISP), osmanthus Longjing tea produced by the traditional scenting process (O-TSP), and raw Longjing tea embryo (R), including alcohols, ketones, esters, aldehydes, olefins, acids, furans, and other aroma compounds. The proportions of alcohol compounds, ester compounds, aldehyde compounds, and ketone compounds in O-ISP were higher than in O-TSP and R. When the osmanthus consumption was increased, the relative contents of volatile aroma compounds gradually increased, which included the contents of trans-3,7-linalool oxide II, dehydrolinalool, linalool oxide III (furan type), linalool oxide IV (furan type), 2,6-Dimethyl cyclohexanol, isophytol, geraniol, 1-octene-3-alcohol, cis-2-pentenol, trans-3-hexenol, β-violet alcohol, 1-pentanol, benzyl alcohol, trans-p-2-menthene-1-alcohol, nerol, hexanol, terpineol, 6-epoxy-β-ionone, 4,2-butanone, 2,3-octanedione, methyl stearate, cis-3-hexenyl wasobutyrate, and dihydroanemone lactone. When the scenting time was increased, the relative contents of aroma compounds gradually increased, which included the contents of 2-phenylethanol, trans-3,7-linalool oxide I, trans-3,7-linalool oxide II, dehydrolinalool, isophytol, geraniol, trans-3-hexenol, β-ionol, benzyl alcohol, trans-p-2-menthene-1-ol, nerol, hexanol, terpineol, dihydroβ-ionone, α-ionone, and β-ionone,6,10. The isolated scenting process could achieve better aroma quality in terms of the floral fragrance, refreshing fragrance, and tender fragrance than the traditional scenting process. The isolated scenting process was suitable for processing osmanthus Longjing tea with high aroma quality. This study was hoped to provide a theoretical base for the formation mechanism and control of quality of osmanthus Longjing tea. Full article

Commercial NH₄-Beta and Na-ZSM-5 zeolites were fluorinated with different amounts of NH₄F and using different procedures (room temperature, conventional refluxing, microwave refluxing). Samples were characterized by XRD, N₂ physisorption, FTIR, ¹H NMR, SEM-EDS, and TGA of adsorbed cyclohexylamine. An increase in the concentration of NH₄F led to fluorinated zeolites with higher surface areas and slightly lower amounts of Brønsted acid sites due to some dealumination. Fluorination by conventional or microwave refluxing at shorter times did not dealuminate ZSM-5, resulting in the formation of higher particle sizes. Ni/fluorinated beta catalysts were more active than Ni/fluorinated ZSM-5 catalysts for the hydrodeoxygenation of guaiacol at 180 °C and 15 bar of H₂ for 1 h due to their higher amount of acid sites. The appropriate proportion of metallic and Brønsted acid centers allowed for the selective obtention of cyclohexane (58%) for the Ni supported on beta fluorinated with NH₄F 0.1 M catalyst. The combination of this fluorinated beta to a Ni/ordered mesoporous carbon catalyst significantly boosted its selectivity to cyclohexane from 0 to 65%. Fluorinated ZSM-5 samples, although having stronger Brønsted acid sites, as observed by ¹H NMR, they had lower amounts, leading to higher selectivity to cyclohexanol when used as catalytic supports. Full article