d-Glucose Isomerization with PAMAM Dendrimers as Environmentally Friendly Catalysts

Interfacial Thermoconvection and Atomic Relay Catalysis Enable Equilibrium Shifting and Rapid Glucose-to-Fructose Isomerization

The aqueous glucose-to-fructose isomerization is controlled by thermodynamics to an equilibrium limit of ~50 % fructose yield. However, here we report an in situ fructose removal strategy enabled by an interfacial local photothermal effect in combination with relay catalysis of geminal and isolated potassium single atoms (K SAs) on graphene-type carbon (Ksg/GT) to effectively bypass the equilibrium limit and markedly speed up glucose-to-fructose isomerization. At 25 °C, an unprecedented fructose yield of 68.2 % was obtained over Ksg/GT in an aqueous solution without any additives under 30-min solar-like irradiation. Mechanistic studies expounded that the interfacial thermoconvection caused by the local photothermal effect of the graphene-type carbon and preferable glucose adsorption on single-atom K could facilitate the release of in situ formed fructose. The geminal K SAs were prone to form a stable metal-glucose complex via bidentate coordination, and could significantly reduce the C-H bond electron density by light-driven electron transfer toward K. This facilitated the hydride shift rate-determining step and expedited glucose isomerization. In addition, isolated K SAs favored the subsequent protonation and ring-closure process to furnish fructose. The integration of the interfacial thermoconvection-enhanced in situ removal protocol and tailored atomic catalysis opens a prospective avenue for boosting equilibrium-limited reactions under mild conditions.

Magnetic dummy template molecularly imprinted particles functionalized with dendritic nanoclusters for selective enrichment and determination of 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) in tobacco products

The compound 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), one of the tobacco specific nitrosamines (TSNAs), is widely recognized as a major carcinogen found in tobacco products, environmental tobacco smoke and wastewater. Thus, a selective enrichment and sensitive detection method for monitoring the risk of NNK exposure is highly desirable. In this study, a magnetic molecularly imprinted polymer (MMIP) functionalized with dendritic nanoclusters was synthesized to selectively recognize NNK via the dummy template imprinting strategy, aiming to avoid residual template leakage and increase the imprinting efficiency. The nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, as well as vibrating sample magnetometry (VSM) and nitrogen adsorption/desorption analysis. The resulting MMIPs exhibited high adsorption capacity, fast binding kinetics and good selectivity for trace amounts of NNK. A rapid, low cost and efficient method for detecting NNK in tobacco products was established using magnetic dispersive solid-phase extraction coupled with HPLC-DAD with a good linear range of 0.1-250 μg mL^-1. The limit of detection (LOD) and limit of quantification (LOQ) of NNK were 13.5 and 25.0 ng mL^-1, respectively. The average recoveries were 87.8-97.3% with RSDs lower than 3%. The results confirmed that the MMIPs could be used as an excellent selective adsorbent for NNK, with potential applications in the pretreatment of tobacco products.

Solvent Effects Enable Efficient Tandem Conversion of Cellulose and Its Monosaccharides Towards 5-Hydroxymethylfurfural

The biomass-derived platform compound 5-hydroxymethylfurfural (HMF) has been hailed as the "Sleeping Giant" due to its promising applications, and it occupies a critical spot in the biomass upgrading roadmap. HMF is typically produced from cellulose and its monosaccharides via a complex tandem conversion with multiple steps (i. e., cellulose depolymerization, glucose isomerization, fructose dehydration, etc.). Previous investigations have confirmed the irreplaceable contribution of solvents in regulating the tandem conversion of cellulose and its monosaccharides to HMF. However, the potential effects of solvents in contributing to this multi-step tandem process have not yet been clearly elucidated. In this context, this Review aims to provide in-depth insights into the intrinsic interactions between solvent system and substrate conversion (cellulose and its monosaccharides conversion), reaction regulation (reaction activity and selectivity regulation), as well as product acquisition (humins formation inhibition and product purification). It attempts to elucidate specific solvent effects to promote a more efficient tandem conversion of cellulose and its monosaccharides towards HMF. The insights provided in this Review may contribute to a more sustainable HMF production from biomass feedstocks and a further development of greener solvent systems.

Study of base-catalyzed isomerization of d-glucose with a focus on reaction kinetics

We explored the isomerization of d-glucose into d-fructose using the simplest possible base catalyst, aqueous NaOH, to maintain a constant pH value during the reaction. Under the applied mild conditions (T 50–90 °C, pH 9.5–11.5), yields of d-fructose of up to 31% were observed. Selectivity-conversion plots were not significantly influenced by variation of the temperature, pH value or substrate concentration. A reaction network for kinetic modelling includes d-glucose-d-fructose interconversion, co-production of d-mannose and d-allulose (also known as d-psicose) as well as decomposition paths after deprotonation of the hexoses. All four hexoses were employed as substrates in the isomerization. Thermodynamic ionization constants of the saccharides were measured by means of potentiometric titration. In the kinetic studies, pH-independent rate constants as well as activation energies were determined. The obtained kinetic and thermodynamic results as well as selectivity-conversion correlations present a useful benchmark for soluble and solid base catalysts.

Revealing the contributions of homogeneous and heterogeneous catalysis to isomerization of d-glucose into d-fructose in the presence of basic salts with low solubility

Hydroxide anions are identified as catalytically active species for the isomerization of d-glucose to d-fructose over low soluble basic salts. The highest selectivity for d-fructose was obtained for catalysis by MgCO3.

Interactions between PAMAM-NH2 and 6-Mercaptopurine: Qualitative and Quantitative NMR studies

Despite being used as an anti-leukemic drug, the poor solubility of 6-mercaptopurine (6-MP) limits its use in topical and parenteral applications. Dendrimers are commonly used as drug carriers to improve their solubility in aqueous solution. In this work, the interactions between 6-MP and the amine-terminated poly(amidoamine) dendrimers (PAMAM-NH₂ ) were investigated by various NMR technology. The chemical shift titrations disclosed that the 6-MP interacted with the surface of PAMAM-NH₂ mainly through electrostatics. The determination of diffusion coefficient and relaxation measurements further confirmed the presence of interactions in 6-MP/PAMAM-NH₂ complexes. In addition, the encapsulation of 6-MP within the cavity of PAMAM-NH₂ was revealed through nuclear Overhauser effect spectroscopy and Saturation Transfer Double Difference analysis. Finally, the binding strength (H-8 is 100% and H-2 is 70%) of 6-MP to PAMAM-NH₂ was quantitatively expressed using epitope maps. This study provides a systematic methodology for qualitative and quantitative studies of the interactions between dendrimers and drug molecules in general.