A Review of Applications of Solid-State Nuclear Magnetic Resonance (ssNMR) for the Analysis of Cyclodextrin-Including Systems

Cyclodextrins, cyclic oligosaccharides composed of five or more α-D-glucopyranoside units linked by α-1,4 glycosidic bonds, are widely used both in their native forms as well as the components of more sophisticated materials. Over the last 30 years, solid-state nuclear magnetic resonance (ssNMR) has been used to characterize cyclodextrins (CDs) and CD-including systems, such as host-guest complexes or even more sophisticated macromolecules. In this review, the examples of such studies have been gathered and discussed. Due to the variety of possible ssNMR experiments, the most common approaches have been presented to provide the overview of the strategies employed to characterize those useful materials.

Removal of p-nitrophenol from simulated sewage using MgCo-3D hydrotalcite nanospheres: capability and mechanism

4-Nitrophenol (4-NP) is an organic pollutant found in the wastewater discharged from coking and petrochemical industries, and it is highly toxic, persistent, and bioaccumulative. 4-NP is difficult to degrade and causes serious damage to human health and the ecological environment. In this study, MgCo-3D hydrotalcite nanospheres were synthesized via the hot solvent method using ZIF-67 as a template for 4-NP removal from wastewater. The composition and structure of MgCo-3D hydrotalcite nanospheres were characterized via X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission Electron Microscope (TEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Energy Dispersive Spectroscopy (EDS), and BET analyses. The maximum adsorption capacity was 131.59 mg g-1 under the optimized conditions (pH = 7, t = 298 K, C 0 = 50 mg L-1, dose = 0.4 g L-1). The adsorption obeyed the Langmuir, Redlich-Peterson and Sips models and pseudo-second-order kinetics, and the adsorption activation energy was 29.4 kJ mol-1, indicating a monolayer physical adsorption phenomenon. The adsorption of 4-NP on the MgCo-3D hydrotalcite nanospheres mainly involved hydrogen bonding and electrostatic interactions. The nanospheres were regenerated using the hot-air purging method. After five adsorption-desorption cycles, the adsorption capacity reached 107.6 mg g-1, indicating the good regeneration performance of the MgCo-3D hydrotalcite nanospheres.

Removal of p-Nitrophenol from simulated sewage using steel slag: Capability and mechanism

The steel slag was investigated for the removal of p-nitrophenol (4-NP) from simulated sewage by batch adsorption and fixed-bed column absorption experiments. The results showed that the maximum adsorption capacity was 109.66 mg/g at 298 K, pH of 7, initial concentration 100 mg/L, and dose 0.8 g/L. The adsorption process fitted the Langmuir isothermal adsorption model and followed pseudo-second-order kinetic models, the activation energy of adsorption (Ea) was 10.78 kJ/mol, which indicated that the adsorption was single-molecule layer physical adsorption. The regeneration efficiency was still maintained at 84.20% after five adsorption-desorption cycles. The column adsorption experiments showed that the adsorption capacity of the Thomas model reached 13.69 mg/g and the semi-penetrating time of the Yoon-Nelson model was 205 min at 298 K. Fe₃O₄ was identified as the main adsorption site by adsorption energy calculation, XRD and XPS analysis. The FT-IR, Zeta potential, and ionic strength analysis indicated that the adsorption mechanism was hydrogen bonding interaction and electrostatic interaction. This work proved that steel slag could be utilized as a potential adsorbent for phenol-containing wastewater treatment.

An atomistic view on the uptake of aromatic compounds by cyclodextrin immobilized on mesoporous silica

The effect of immobilized $$\upbeta$$ β -cyclodextrin (bCD) molecules inside a mesoporous silica support on the uptake of benzene and p-nitrophenol from aqueous solution was investigated using all-atom molecular dynamics (MD) simulations. The calculated adsorption isotherms are discussed with respect to the free energies of binding for a 1:1 complex of bCD and the aromatic guest molecule. The adsorption capacity of the bCD-containing material significantly exceeds the amount corresponding to a 1:1 binding scenario, in agreement with experimental observations. Beside the formation of 1:2 and, to a lesser extent, 1:3 host:guest complexes, also host–host interactions on the surface as well as more unspecific host–guest interactions govern the adsorption process. The demonstrated feasibility of classical all-atom MD simulations to calculate liquid phase adsorption isotherms paves the way to a molecular interpretation of experimental data that are too complex to be described by empirical models.

Boron, and nitrogen co-doped carbon dots as a multiplexing probe for sensing of p-nitrophenol, Fe (III), and temperature

Boron and nitrogen co-doped carbon dots (B, N-CDs) were fabricated through a simple, one-step hydrothermal reaction of citric acid, boric acid, and tris base. The obtained B, N-CDs exhibit excitation-dependent fluorescence, high quantum yield (QY), biocompatibility, photostability, and aqueous solubility. The QY was substantially increased to 57% by doping boron atoms. Furthermore, the fluorescence intensity of B, N-CDs was temperature-dependent and decreased linearly from 283 to 333 K. The prepared B, N-CDs were used as a fluorescence probe for the detection ofpara-nitrophenol (p-NP) and Fe (III) ions with low detection limits of 0.17μM and 0.30μM, respectively. Moreover, the presence of p-NP could be further confirmed by a colorimetric assay. The fluorescent probe has been applied to determine p-NP and Fe (III) in a spiked serum sample and spiked water samples (lake and tap water). Moreover, the as-prepared B, N-CDs were of low toxicity and capable of bioimaging.

Immobilization of cellulase proteins on zeolitic imidazolate framework (ZIF-8)/polyvinylidene fluoride hybrid membranes

ZIF-8/PVDF hybrid membranes have been applied in cellulase immobilization for the first time, which improves cellulase stability with preserved activity.

Structural Variety and Adsorptive Properties of Mesoporous Silicas with Immobilized Oligosaccharide Groups

In this research, we report on the synthesis of mesoporous silicas with various quantities of immobilized oligosaccharide groups and different pore ordering degree. The hydrothermal co-condensation of tetraethyl orthosilicate and β-cyclodextrin-containing organosilane in the presence of cetyltrimethylammonium bromide template was employed. The purpose of this investigation was to show the opportunity of increasing β-cyclodextrin content in silica matrix by changing the molar ratio of initial reagents during organosilane synthesis and to determine whether the enhancing of immobilized groups on the surface influences on model aromatic compound adsorption from water. It was prepared several β-cyclodextrin-organosilanes by modification of (3-aminopropyl)triethoxysilane with oligosaccharide (the molar composition of reaction mixtures were 1:1, 3:1, and 5:1) with using N,N'-carbonyldiimidazole as linking agent. Three types of MCM-41 materials were obtained with 0.018, 0.072, and 0.095 mmol g^-1 β-cyclodextrin-group loading according to chemical analysis of silicas. The IR spectroscopy and potentiometric titration were also performed to confirm the presence of functional groups in the silica matrix. Nitrogen sorptometry experiments exhibited the decrease of high surface area (from 812 to 457 m² g^-1) and the average pore diameter (from 1.06 to 0.60 cm³ g^-1) of synthesized silicas with increasing of immobilized oligosaccharide groups. The influence of β-cyclodextrin-organosilane presence on the forming of hexagonally arranged porous structure of silicas was evaluated by X-ray diffraction and TEM analyses. As the loading of oligosaccharide groups increases in obtained silicas, the (100) reflex in diffraction patterns is even less intense and broader, denoting the decrease of long-range pore ordering. Adsorption experiments were carried out to study the effect of β-cyclodextrin groups' attendance in silica matrix on benzene uptakes from aqueous solutions. Experimental kinetic curves of benzene adsorption on synthesized silicas were compared with theoretical models of Lagergren and Ho-McKay for pseudo-first and pseudo-second-order processes. Langmuir and Freundlich isotherm models were used to evaluate adsorption processes and parameters. Obtained β-cyclodextrin-containing MCM-41 silicas demonstrate adsorption level performance of known samples and could be very promising for benzene uptakes from aqueous solutions in water treatment processes.

Immobilization of lysozyme proteins on a hierarchical zeolitic imidazolate framework (ZIF-8)

A hierarchical zeolitic imidazolate framework-8 containing micropores and mesopores showed superior adsorption activity than micro-ZIF-8 towards enzyme proteins.

Metal-free chemoselective oxidation of sulfides to sulfoxides catalyzed by immobilized l-aspartic acid and l-glutamic acid in an aqueous phase at room temperature

Immobilized l-aspartic and l-glutamic acid were employed in the oxidation of sulfides, and 99% conversion and 97% selectivity were achieved.