Electronic Structure Calculations on Endohedral Complexes of Fullerenes: Reminiscences and Prospects

The history of electronic structure calculations on the endohedral complexes of fullerenes is reviewed. First, the long road to the isolation of new allotropes of carbon that commenced with the seminal organic syntheses involving simple inorganic substrates is discussed. Next, the focus is switched to author's involvement with fullerene research that has led to the in silico discovery of endohedral complexes. The predictions of these pioneering theoretical studies are juxtaposed against the data afforded by subsequent experimental developments. The successes and failures of the old and modern quantum-chemical calculations on endohedral complexes are summarized and their remaining deficiencies requiring further attention are identified.

Improving the Energy Storage Performance of All-Polymer Composites By Blending PVDF and P(VDF-CTFE)

Organic film capacitors have incredibly high power density and have an irreplaceable position in pulsed power systems, high-voltage power transmission networks and other fields. At present, the energy storage density and energy storage efficiency of organic film capacitors are relatively low, resulting in excessive equipment volume. The performance of organic film capacitors is determined by polymer materials, so it is crucial to develop a polymer composite with high energy storage density and high charge-discharge efficiency. Poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) is incorporated into the polyvinylidene fluoride (PVDF) matrix by solution blending. The successful preparation of the all-polymer composite material solves the problems of low breakdown electric field strength, low discharge energy density, and low charge-discharge efficiency of high-dielectric ferroelectric materials. The discharge energy density of the PVDF/P(VDF-CTFE) (70/30) film is more than twice that of pure PVDF due to the increase of phases α and γ and the decrease of crystallinity. Under the breakdown electric field (380 kV mm^-1 ), PVDF/P(VDF-CTFE) (70/30) film also has an ultrahigh energy storage efficiency of 64%. The relationship between the structure and properties of composite materials is investigated in this study, which has important implications for the development of capacitors with high energy storage density.

Oxidations of N-coordinated Arsinidene and Stibinidene by Substituted Quinones: A Remarkable Follow-Up Reactivity

The reactivity of pnictinidenes [2-(DippN=CH)-6-(DippNHCH₂ )C₆ H₃ ]E (where E=As (1) or Sb (2)) toward substituted ortho- and para-quinones is reported. The central pnictogen atom is easily oxidized by ortho-quinones closing five-membered EO₂ C₂ ring. The oxidized antimony derivatives are stable species, while in the case of arsenic compounds the hydrogen of the pendant amino NHCH₂ group cleaves one newly formed As-O bonds leading to the closure of a new azaarsole ring. Furthermore, a heating of these arsenic heterocycles resulted in a C-H bond activation at the NCH₂ group involved in this heterocycle followed by a reductive elimination of corresponding catechols and arsinidene [2,6-(DippN=CH)C₆ H₃ ]As. Using of para-quinones, resulted in the oxidation of the central atom with a concomitant hydrogen migration from NHCH₂ group even in the case of the antimony derivatives. The reductive elimination of hydroquinones is in this case feasible for all compounds. Studied compounds were characterized by multi-nuclear NMR, IR and Raman spectroscopy and single-crystal X-ray diffraction analysis. The theoretical study focusing the key compounds and reactions is also included.

Solvent effects on the photooxidation of indolepyrazines

Photodestruction of 2-(pyrazin-2'-yl)-1H-indole and 2,5-di(1H-indol-2'-yl)pyrazine involves singlet oxygen generation and its rapid insertion into the indole ring with the formation of benzoxazinone derivatives: 2-(pyrazin-2-yl)-4H-3,1-benzoxazin-4-one and 2-[5-(1H-indol-2-yl)pyrazin-2-yl]-4H-3,1-benzoxazin-4-one. The quantum yield of this reaction strongly depends on the environment. It is definitely smaller in protic methanol than in aprotic acetonitrile or n-hexane. The observed effect of photostabilization is explained by formation of hydrogen bonded complexes between the chromophore and alcohol, which results in lower triplet formation efficiency and, in consequence, decrease of singlet oxygen formation quantum yield.

Use of metabolic glycoengineering and pharmacological inhibitors to assess lipid and protein sialylation on cells

Metabolic glycoengineering (MGE) has been developed to visualize carbohydrates on live cells. The method allows the fluorescent labeling of sialic acid (Sia) sugar residues on neuronal plasma membranes. For instance, the efficiency of glycosylation along neurite membranes has been characterized as cell health measure in neurotoxicology. Using human dopaminergic neurons as model system, we asked here, whether it was possible to separately label diverse classes of biomolecules and to visualize them selectively on cells. Several approaches suggest that a large proportion of Sia rather incorporated in non-protein components of cell membranes than into glycoproteins. We made use here of deoxymannojirimycin (dMM), a non-toxic inhibitor of protein glycosylation, and of N-butyl-deoxynojirimycin (NBdNM) a well-tolerated inhibitor of lipid glycosylation, to develop a method of differential labeling of sialylated membrane lipids (lipid-Sia) or sialylated N-glycosylated proteins (protein-Sia) on live neurons. The time resolution at which Sia modification of lipids/proteins was observable was in the range of few hours. The approach was then extended to several other cell types. Using this technique of target-specific MGE, we found that in dopaminergic or sensory neurons >60% of Sia is lipid bound, and thus polysialic acid-neural cell adhesion molecule (PSA-NCAM) cannot be considered the major sialylated membrane component. Different from neurons, most Sia was bound to protein in HepG2 hepatoma cells or in neural crest cells. Thus, our method allows visualization of cell-specific sialylation processes for separate classes of membrane constituents.

Copper sulphide/cuprous sulphide doped zero-valent iron@carbon (ZVI@C/CuS/Cu2S) activate PMS for rapid and effective decomposition of Ni-EDTA

Ni-EDTA is widely present in electroplating effluents. It cannot be effectively removed by traditional wastewater treatment methods due to its chemical stability. In this study, copper sulphide/cuprous sulphide doped zero-valent iron@carbon (ZVI@C/CuS/Cu₂S) was prepared to active peroxymonsulphate (PMS) to decomposition Ni-EDTA. The ZVI@C/CuS/Cu₂S + PMS process shows excellent performance under neutral or even alkaline conditions. This is due to the acceleration of ZVI electron transport by CuS/Cu₂S, the autocatalysis of CuS/Cu₂S itself, and the synergistic effect of CuS/Cu₂S and Ni-EDTA. The removal efficiency of 50 ppm Ni-EDTA electroplating effluents reached 99.53% at 10 min, and the discharge water can meet the Chinese emission standard. The influences of the main parameters such as initial pH value, catalyst, PMS and initial Ni-EDTA concentration on removal efficiency was systematically investigated.

Biochar-goethite composites inhibited/enhanced degradation of triphenyl phosphate by activating persulfate: Insights on the mechanism

In this study, the biochar-goethite composites (MBC@FH) were synthesized through co-ball milling and the degradation of triphenyl phosphate (TPhP) was compared in persulfate (PDS) alone system and MBC@FH&PDS systems. The results showed that TPhP can be effectively degraded in PDS alone system and degradation efficiency reached up to 90 % within reaction of 8 h, at a PDS concentration of 10 mM, a reaction temperature of 30 °C and a system pH of 6.12. The obvious degradation can be ascribed to the reactive oxygen species (ROS) generated by self-decompose of PDS, among which ¹O₂, ∙OH and O₂∙^- play a major role in the degradation process. Although 350 °C biochar-goethite composites (MBC35@FH) and 800 °C biochar-goethite composites (MBC80@FH) facilitated PDS activation to produce more ROS, the catalytic degradation of TPhP was different in their systems. The degradation of TPhP was inhibited by MBC35@FH due to its stronger adsorption for TPhP, while MBC80@FH promoted TPhP degradation and degradation efficiency was up to 100 % within 6 h. ¹O₂ and SO₄∙^- played a stronger degradation role than ∙OH and O₂∙^- in above systems. The transformation of Fe species, functional groups (oxygen-containing functional groups, pyrrolic nitrogen) and persistent free radicals (PFRs) on the MBC@FH were involved in the PDS activation to produce ROS. Furthermore, MBC80@FH was more capable of activating PDS than MBC35@FH due to its abundant defect sites, larger specific surface area, more PFRs, higher Fe content and stronger electron transfer capability. In addition, seven possible TPhP intermediates were identified and possible degradation pathways of TPhP were proposed accordingly. This study illustrated that not all metallic carbon catalysts are necessarily beneficial for organic contaminants degradation.

Nitrogen-doped magnetic porous carbon material from low-cost anion-exchange resin as an efficient adsorbent for tetracyclines in water

In this work, nitrogen-doped magnetic porous carbon material (N-MPC) was prepared through the high-temperature calcination of low-cost [Fe(CN)₆]^3--loaded anion-exchange resin, which was experimentally demonstrated to have significant adsorption performance for tetracycline (TC) in water. The N-MPC adsorbent with a large specific surface area (781.1 m² g^-1) was able to maintain excellent performance in a wide pH range from 4 to 10 or in high ionic strength solution. The adsorption of TC on N-MPC was found to be more consistent with the pseudo-second-order model and Langmuir adsorption model, and the maximum adsorption capacity (q_{m, cal}) was calculated to be 603.4 mg g^-1. As a recoverable magnetic adsorbent, the N-MPC remained a TC removal rate higher than 70% after four adsorption cycles. The adsorption mechanism was speculated on the basis of characterizations, where pore filling, hydrogen bonding interaction, and π-π electron donor-acceptor (EDA) interaction were crucial adsorption mechanisms. A variety of antibiotics were selected for adsorption, and excellent performance was found especially for TCs, indicating that the N-MPC can be used for the efficient removal of TCs from water.

Bioconcentration of imidazolium ionic liquids: In vivo evaluation in marine mussels Mytilus trossulus

Although imidazolium ionic liquids (ILs) are beginning to be used more widely in many industrial fields e.g., as reaction media, electrolytes, stationary phases in gas chromatography), there is still little information about their potential environmental fate. Among the uncertainties regarding the risks associated with these compounds, bioconcentration is one of the key issues, about which many doubts have been raised in recent years. While in vitro data suggest that permanently charged compounds can also bioconcentrate, conclusive evidence in the form of studies on organisms, at least for selected compounds, is needed. Therefore, the main objective of this work was to determine whether imidazolium cations of ILs, namely 1-methyl-3-octylimidazolium ([IM18]⁺) and 1-methyl-3-dodecylimidazolium ([IM1-12]⁺), can bioconcentrate in marine invertebrates tissues. During 21-day experiments, Mytilus trossulus mussels were exposed to these cations individually, at a concentration of 10 μg/L. In our study, it has been demonstrated for the first time during in vivo study, that long-chain imidazolium ionic liquids can bioconcentrate. The determined BCF value for [IM1-12]⁺ of 21,901 ± 3400 L/kg makes this compound to be considered highly bioaccumulative according to commonly accepted criteria. However, the obtained BCF for [IM18]⁺ (with the value below 100) suggests that this cation has little potential for bioconcentration. On the other hand, no salinity or anion influence on the bioconcentration of the tested cations was observed. Our tests also confirm that imidazolium ILs exhibit acute toxicity only at relatively high concentration levels, as LC₅₀ reached 0.68 mg/L for [IM1-12][Br], and 11.66 mg/L for [IM18][C(CN)₃]. This further confirms that the risks associated with the potential presence of these compounds in the environment should be attributed to their high persistence and potential bioconcentration, rather than acute toxicity.

Chitosan cross-linked β-cyclodextrin polymeric adsorbent for the removal of perfluorobutanesulfonate from aqueous solution: adsorption kinetics, isotherm, and mechanism

The existence of per- and polyfluoroalkyl substances (PFASs) in water is of serious interest due to their toxic, bioaccumulative, and persistent nature, and adsorption is an effective approach for the PFASs removal. In the present study, we developed a polymeric adsorbent by cross-linking chitosan and β-cyclodextrin using glutaraldehyde (Chi-Glu-β-CD) and evaluated its removal performance for perfluorobutanesulfonate (PFBS) from water. The results indicate that the performance was highly affected by solution pH; under a more acidic condition (e.g., pH 2.0), a higher removal efficiency was detected, and faster adsorption kinetics was observed with the rate constant (k₂) of 0.001 ± 3×10^-4 g mg^-1 min^-1. Adsorption isotherm data agreed to the Sips model with a maximum heterogeneous adsorption capacity of 135.70 ± 25.70 mg g^-1, probably due to protonated amine (NH⁺) and electron-deficient β-CD cavities. The adsorption mechanism was confirmed using energy dispersive X-ray and Fourier transform infrared (FTIR) spectroscopy, showing the role of electrostatic attractions between the protonated amine and the negatively charged PFBS molecule (especially, with sulfonate side (N-H--O-S)) and host-guest inclusion formations with β-CD cavity in adsorption. Additionally, the synthesized adsorbent was recovered using methanol without any significant decline in adsorption efficiency even after four continuous adsorption/desorption cycles. All these findings suggested that the Chi-Glu-β-CD composite could be a promising adsorbent in the removal of PFBS from water.

Estimate of the degradation potentials of cellulose, xylan, and chitin across global prokaryotic communities

Complex polysaccharides (e.g. cellulose, xylan, and chitin), the most abundant renewable biomass resources available on Earth, are mainly degraded by microorganisms in nature. However, little is known about the global distribution of the enzymes and microorganisms responsible for the degradation of cellulose, xylan, and chitin in natural environments. Through large-scale alignments between the sequences released by the Earth Microbiome Project and sequenced prokaryotic genomes, we determined that almost all prokaryotic communities have the functional potentials to degrade cellulose, xylan, and chitin. The median abundances of genes encoding putative cellulases, xylanases, and chitinases in global prokaryotic communities are 0.51 (0.17-1.01), 0.24 (0.05-0.57), and 0.33 (0.11-0.71) genes/cell, respectively, and the composition and abundance of these enzyme systems are environmentally varied. The taxonomic sources of the three enzymes are highly diverse within prokaryotic communities, and the main factor influencing the diversity is the community's alpha diversity index rather than gene abundance. Moreover, there are obvious differences in taxonomic sources among different communities, and most genera with degradation potentials are narrowly distributed. In conclusion, our analysis preliminarily depicts a panorama of cellulose-, xylan-, and chitin-degrading enzymatic systems across global prokaryotic communities.

Hydrogen-deuterium exchange coupled to mass spectrometry: A multifaceted tool to decipher the molecular mechanism of transporters

Transporters regulate trafficking through the biological membrane of living cells and organelles. Therefore, these proteins play an important role in key cellular processes. Obtaining a molecular-level description of the mechanism of transporters is highly desirable to understand and modulate such processes. Different challenges currently complicate this effort, mostly due to transporters' intrinsic properties. They are dynamic and often averse to in vitro characterization. The crossing of the membrane via a transporter depends on both global and local structural changes that will enable substrate binding from one side of the membrane and release on the other. Dedicated approaches are required to monitor these dynamic changes, ideally within the complex membrane environment. Hydrogen-deuterium exchange coupled to mass spectrometry (HDX-MS) has recently emerged as a powerful biophysical tool to understand transporters' mechanism. This mini-review aims to offer to the reader an overview of the field of HDX-MS applied to transporters. It first summarizes the current workflow for HDX-MS measurements on transporters. It then provides illustrative examples on the molecular insights that are accessible thanks to the technique; following conformational transitions between different states, observing structural changes upon ligand binding and finally understanding the role of lipid-protein interactions.

In silico identification and characterization of small-molecule inhibitors specific to RhoG/Rac1 signaling pathway

Rho family GTPases serve as molecular switches in numerous cellular processes, and their overexpression is involved in disease conditions. RhoG is one of the less explored Rho GTPases with significant sequential and structural homology with Rac1. Experimental mutations in RhoG (i.e., RhoGG12V and RhoGQ61L) are shown to dysregulate cell migration. Thus, targeting upstream activators of RhoG, such as guanine nucleotide exchange factors (GEFs), maybe an important strategy for inhibiting RhoG activation. In the current study, we have modelled the 3D structure of RhoG with greater accuracy as confirmed through PROCHECK, ProSA, and Verify3D. Our results indicate that 90.4% of residues are in the Ramachandran plots favoured region, with the Z-score of -6.46, and 87.96% of residues had an averaged 3D-1D score ≥0.2. Further, we have evaluated and binding dynamics of ten Rac1 inhibitors to investigate their potential to inhibit RhoG by targeting GEFs binding grooves. To this end, the binding energy of the docked complexes of the wild-type (WT) RhoG and its mutant proteins with inhibitor molecules was calculated using the MM/PBSA method. Our results from docking studies showed that macrolide1 binds efficiently with the GEF site of WT RhoG and the mutants mentioned above. However, an extensive analysis using MD simulations (200 ns) showed that the Rac1 based inhibitor, EHop-016, and NSC23766 might bind with greater affinity to GEF sites of mutants and WT RhoG. Thus, the results from the study indicate that Rac1 inhibitors have the potential for use as therapeutics in conditions involving dysregulation of RhoG.Communicated by Ramaswamy H. Sarma.

Development of microwave-assisted nitrogen-modified activated carbon for efficient biogas desulfurization: a practical approach

Removal of H₂S (hydrogen sulfide) from biogas is anticipated for higher energy conversion of methane (CH₄), while reducing the detrimental impacts of corroding the metal parts in the plant and its hazardous effect on humans and the environment. The introduction of microwave (MW) heating and nitrogen-modification could generate superior adsorbent features, contributing to high H₂S removal. Up to date, there is no work reported on the influence of physicochemical characteristics of nitrogen-modified carbon synthesized via MW and conventional heating (TH) methods and their performance in H₂S removal. Palm shell activated carbon (PSAC) was functionalized with nitrogen groups via urea impregnation, followed by the synthesis of MW and TH at 950 °C, 500 ml/min of N₂ flow rate and 30 min of heating time. MW and TH heating effects on the modified PSAC adsorbent were analysed and compared towards hydrogen sulfide (H₂S) removal. PSAC with nitrogen functionalization produced using MW heating (PSAC-MW) demonstrates superior performance, with an adsorption capacity of 356.94 mg/g. The adsorbent sample generated using MW heating exhibited notable properties, including a large surface area and a sponge-like structure, with new pores developed within the current pores. Instead of that, there was an observation of 'hot spot' appearance during the MW heating process, which is believed to be responsible for the development of physical and chemical characteristics of the adsorbent. Thus, it is believed that MW heating was assisted in the development of the adsorbent's properties and at the same time contributed to the high removal of H₂S at low adsorption temperature. The utilization of biomass-based adsorbent (PSAC) for H₂S removal can address the lignocellulosic waste disposal problem, while mitigating the H₂S release from the biogas production plants thus has several environmental merits. This indirectly contributed to zero-waste generation, while overcoming the adverse effects of H₂S.

Exploring the Potential of Multinuclear Solid-State 1 H, 13 C, and 35 Cl Magnetic Resonance To Characterize Static and Dynamic Disorder in Pharmaceutical Hydrochlorides

Crystallographic disorder, whether static or dynamic, can be detrimental to the physical and chemical stability, ease of crystallization and dissolution rate of an active pharmaceutical ingredient. Disorder can result in a loss of manufacturing control leading to batch-to-batch variability and can lengthen the process of structural characterization. The range of NMR active nuclei makes solid-state NMR a unique technique for gaining nucleus-specific information about crystallographic disorder. Here, we explore the use of high-field ³⁵ Cl solid-state NMR at 23.5 T to characterize both static and dynamic crystallographic disorder: specifically, dynamic disorder occurring in duloxetine hydrochloride (1), static disorder in promethazine hydrochloride (2), and trifluoperazine dihydrochloride (3). In all structures, the presence of crystallographic disorder was confirmed by ¹³ C cross-polarization magic-angle spinning (CPMAS) NMR and supported by GIPAW-DFT calculations, and in the case of 3, ¹ H solid-state NMR provided additional confirmation. Applying ³⁵ Cl solid-state NMR to these compounds, we show that higher magnetic fields are beneficial for resolving the crystallographic disorder in 1 and 3, while broad spectral features were observed in 2 even at higher fields. Combining the data obtained from ¹ H, ¹³ C, and ³⁵ Cl NMR, we show that 3 exhibits a unique case of disorder involving the ⁺ N-H hydrogen positions of the piperazinium ring, driving the chloride anions to occupy three distinct sites.

Enzyme Kinetics Features of the Representative Engineered Recombinants of Chondroitinase ABC I

Chondroitinase ABC I (cABC I) from Proteus vulgaris is an important enzyme in medicinal biotechnology due to its ability to help axon regeneration after spinal cord injury. Its practical application involves solving several problems at the molecular and cellular levels. Structurally, most residues at the C-terminal domain of cABC I are arranged as organized strands, and only a small fraction of residues have helical conformation. The structural and functional features of modified residues on two specific helix fragments have previously been reported. The single mutant M889K has been combined with L679S and L679D mutants to make enzyme variants containing simultaneously modified helix. Here, the pH stability and temperature-based analysis of the transition state structure for the catalysis reaction were investigated. We found that double mutant L679D/M889K is the better choice to use in physiological conditions due to its higher pH stability at physiological pH as well as its different optimum temperature as compared with the (wild-type) WT protein. According to Arrhenius's analysis, the values of the Gibbs free energy of the transition state (∆G^#) are not changed upon mutation. However, the relative contribution and absolute values of the enthalpy and entropy change to the total value of ∆G^#, varied between the WT and mutants.