Effects of Metal Cations and Counter Anions on the Structural Stability of Isoquinoline‐Based Metallo‐Supramolecular Cages

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Effects of Metal Cations and Counter Anions on the Structural Stability of Isoquinoline-Based Metallo-Supramolecular Cages

A series of octahedral metallo-cages that are capable of tolerating with five metal cations (Pd2+, Cu2+, Ni2+, Co2+ and Zn2+), and five counter anions (ClO4 –, OTf–, BF4 –, NTf2 – and NO3 –) are constructed by the coordination-driven self-assembly of a well-designed tritopic isoquinoline-based ligand with corresponding metal salts. Structural stability studies show that metal cations and counter anions play a critical role in the stability of the resulting cages depending on their coordination abilities and stacking manners.


Comprehensive Summary

Metallo-supramolecular architectures that are constructed by coordination-driven self-assembly have received tremendous attention on account of their diverse yet molecular-level precise structures and broad applications. Of particular, metal cations and counter anions are fundamentally important in terms of self-assembly, characterization and property; however, their effects on the structural stabilities of metallo-supramolecular architectures have seldom been investigated. To address this issue, herein, a series of octahedral metallo-cages that are capable of tolerating with five metal cations (Pd2+, Cu2+, Ni2+, Co2+ and Zn2+), and five counter anions (ClO4 –, OTf–, BF4 –, NTf2 – and NO3 –) are constructed by the coordination-driven self-assembly of a well-designed tritopic isoquinoline-based ligand with corresponding metal salts. Structural stability studies show that metal cations and counter anions play a critical role in the stability of the resulting cages depending on their coordination abilities and stacking manners. This work provides deep insights in the ever-diversifying field of metallo-supramolecular chemistry, and will enable us to design more sophisticated assembled structure with desired function.

Selective Photocatalytic Reduction of 3‐Nitrophenol to 3‐Aminophenol by Anatase and Rutile TiO2 – What Stands Behind the Photoactivity?

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The photocatalytic selective reduction of 3-nitrophenol to 3-aminophenol was studied in the presence of titanium dioxide in the form of various anatase and rutile compositions. The reaction progress is altered by various parameters, which can be classified as intrinsic (depending on the chemical, structural, and electronic features) and extrinsic (depending on the reaction and conditions). The goal of the studies was to understand the influence of intrinsic factors and to compare the performance of anatase and rutile materials. The (photo)electrochemical analysis revealed unequivocally the differences in interfacial electron transfer, charge recombination, reduction driving force, and methanol photooxidation efficiency for titania polymorphs. It appeared that all mentioned processes were phase-dependent, and they contributed unequally to overall photocatalytic activity. In particular, methanol oxidation was the most efficient at the rutile phase, which overcame the critical limitation of the oxidation pathway and facilitated the reduction of 3-nitrophenol. On the other hand, the dark electron transfer efficiency was highest at the anatase phase, despite the lower driving force in this case. The presented thorough and systematic analysis of the discussed photocatalytic system (the photocatalyst and the reaction) should allow the rational design of efficient and selective photocatalysts.

Revealing the influence of tether length on the intramolecular [3 + 2] cycloaddition reactions of nitrones from the molecular electron density theory perspective

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Revealing the influence of tether length on the intramolecular [3 + 2] cycloaddition reactions of nitrones from the molecular electron density theory perspective

The influence of the ethylene substitution and the tether in the intramolecular [3+2] cycloaddition reactions of cyclic nitrones have been studied within the Molecular Electron Density Theory. The increase in the polar character of the reaction decreases the activation Gibbs free energies, while the highly polar reactions are disfavored. The preferred regioselectivity in low polar reactions having three methylene units is reversed to that in nitrones separated with four methylene units, in conformity with the experimental outcome.


Abstract

The influence of ethylene substitution and the tether length between the two reacting counterparts on the selectivity and reactivity of the intramolecular [3 + 2] cycloaddition (IM32CA) reactions of cyclic nitrones leading to tricyclic isoxazolidines have been studied within the Molecular Electron Density theory at the MPWB1K/6-311G(d,p) computational level. These zw-type IM32CA reactions follow one-step mechanism, and the activation barrier decreases with the introduction of electron withdrawing (EW) substituent at the alkene moiety in both the intramolecular and intermolecular versions. The IM32CA reactions involving unsubstituted alkene have non-polar character with minimal electron density flux classified as null electron density flux type, while that involving the EW nitro substituted ethylene is more facile with a strong electron density flux from the nitrone to the ethylene moiety, classified as forward electron density flux type. The increase in the polar character of the IM32CA reaction decreases the activation Gibbs free energies associated with these intramolecular processes, while the highly polar IM32CA reactions are disfavored with respect to the intermolecular ones. Interestingly, the preferred regioselectivity observed in low polar IM32CA reactions having three methylene units between the nitrone and ethylene frameworks is reversed to that in nitrones separated with four methylene units, in conformity with the experimental outcome. Finally, electron localization function and quantum theory of atoms-in-molecules studies reveal that, in general, these IM32CA reactions involve early transition state structures in which the formation of new C-C and C-O single bonds have not yet started.

Phyto‐synthesis of silver nanoparticles from Tephrosia purpurea and its in‐vitro biogenic actions

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Phyto-synthesis of silver nanoparticles from Tephrosia purpurea and its in-vitro biogenic actions

T. purpurea leaf extract has been utilized to synthesize facile and non-toxic silver nanoparticles. Analytical techniques were used to characterize the TP-AgNPs, including FE-SEM, EDX, UV–visible spectroscopy, FTIR spectroscopy, XRD, and zeta potential. Further, the biological activities of TP-AgNPs were examined, which advanced their applications for futuristic research purposes.


Tephrosia purpurea silver nanoparticles (TP-AgNPs) were synthesized with water-based leaf extract of the plant T. purpurea. UV–Vis characterization had shown the maximum absorbance at 436 nm. The surface morphology was examined via electron microscopy (FE-SEM) analysis (average size: ~100 nm, shape: spherical). The zeta potential (ZP) of TP-AgNPs revealed values of −41.72 mV suggesting appropriate physical stability. Besides, an X-ray crystallography (XRD) study had shown the crystalline size of 20 nm approximately having 2θ values of 32°, 38°, 44°, 64°, and 77° for the silver crystals. The energy dispersive (EDAX) study manifests the absorption peak at 2.983 keV for TP-AgNPs. Infrared spectroscopy analysis (Fourier-transform infrared spectroscopy) indicated the presence of alcoholic as well as aromatic groups in the extract that took part in the stability and silver reduction mechanisms. Biologically, TP-AgNPs had shown prominent anti-oxidant activities against 2,2-diphenyl-1-picrylhydrazyl radicals (IC50 50 μg/mL) and H2O2 radicals (IC50 106 μg/mL). It had also inhibited the proliferation of breast cell lines (MCF 7) showing total growth inhibition (TGI) at 8.2 μg/mL with the LC50 of 44 μg/mL for TP-AgNPs. Further, hemolysis analysis revealed that TP-AgNPs are non-toxic to human erythrocyte cells (RBCs) as they do not cause the breakdown of RBCs. Thus, TP-AgNPs were found to be an effective agent to be studied further for chemotherapeutic mechanisms.

Exploring the structural, mechanical and thermodynamic properties of Ti‐V solid solutions

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Exploring the structural, mechanical and thermodynamic properties of Ti-V solid solutions

This work investigates the structural stability, mechanical and thermodynamic properties of two Ti-V solid solutions. It is found that the Ti-V compound prefers to form the V(Ti)ss solid solution, which remains the cubic structure. Based on the Born stability criteria, the V(Ti)ss solid solution is a mechanical stability. In particular, the V(Ti)ss solid solution shows higher volume deformation resistance and better ductility compared to the pure Ti.


Abstract

Although Ti-V based high-temperature alloys are used in aerospace engine, rocket engine and hot sections, the structure and mechanical properties of Ti-V alloys remains controversy. To explore the correlation between structural and mechanical properties, we apply employed the DFT method to study the phases stability, mechanical and thermodynamic properties of Ti-V solid solution. Two Ti-V solid solutions: Ti(V)ss solid solution and V(Ti)ss solid solution are discussed. Two Ti-V solid solutions are thermodynamic stability. In particular, the Ti-V solid solution prefers to form V(Ti)ss solid solution, in while the V(Ti)ss solid solution remains cubic structure. Furthermore, the Ti(V)ss solid solution is a mechanical instability. However, the V(Ti)ss solid solution is a mechanical stability. Here, the bulk modulus, shear modulus and Young's modulus of V(Ti)ss solid solution are 136.9, 23.5 and 66.7 GPa. In particular, the bulk modulus of V(Ti)ss solid solution is higher than the bulk modulus of the pure Ti. In addition, the V(Ti)ss solid solution shows better ductility compared to the pure Ti and V. Naturally, the stability and mechanical properties of V(Ti) solid solution is related to the Ti-V metallic bond because of the localized hybridization between the Ti(3d) and V(3d).

Revealing the impact of polystyrene‐functionalization of Au octahedral nanocrystals of different sizes on formation and structure of mesocrystals

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The self-assembly of anisotropic nanocrystals (stabilized by organic capping molecules) with pre-selected composition, size, and shape allows for the creation of nanostructured materials with unique structures and features. For such a material, the shape and packing of the individual nanoparticles play an important role. This work presents a synthesis procedure for ω-thiol-terminated polystyrene (PS-SH) functionalized gold nanooctahedra of variable size (edge length 37, 46, 58, and 72 nm). The impact of polymer chain length (Mw: 11k, 22k, 43k, and 66k g∙mol-1) on the growth of colloidal crystals (e.g. mesocrystals) and their resulting crystal structure is investigated. Small-angle X-ray scattering (SAXS) and scanning transmission electron microscopy (STEM) methods provide a detailed structural examination of the self-assembled faceted mesocrystals based on octahedral gold nanoparticles of different size and surface functionalization. Three-dimensional angular X-ray cross-correlation analysis (AXCCA) enables high-precision determination of the superlattice structure and relative orientation of nanoparticles in mesocrystals. This approach allows us to perform non-destructive characterization of mesocrystalline materials and reveals their structure with resolution down to the nanometer scale.

Antibacterial and Toxic Activity of Geopropolis extracts from Melipona subnitida (Ducke, 1910) (Hymenoptera: Apidae) and Scaptotrigona depilis (Moure, 1942) (Hymenoptera: Apidae).

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Bacteria are associated with many infections that affect humans and present antibiotic resistance mechanisms, causing problems in health organisations and increased mortality rates. Therefore, it is necessary to find new antibacterial agents that can act in the treatment of these microorganisms. Geopropolis is a natural product made by stingless bees, formed by a mixture of plant resins, salivary secretions, wax and soil particles, presenting a diverse chemical composition. Thus, this study aimed to evaluate antibacterial activity, antibiotic modulation and the toxicity of geopropolis extract from the stingless bees, Melipona subnitida (Ducke, 1910) and Scaptotrigona depilis (Moure, 1942) against standard and multi-resistant Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa bacteria. Geopropolis samples were collected in a meliponary located in Camaragibe, Pernambuco, Brazil. To determine the Minimum Inhibitory Concentration (MIC) and antibiotic modulation we performed broth microdilution tests. Mortality tests were used to verify extract toxicity in the model Drosophila melanogaster. The microbiological tests showed that the M. subnitida extracts had better inhibitory effects compared to S. depilis, presenting direct antibacterial activity against standard and multi-resistant strains. The extracts potentialized antibiotic effects, suggesting possible synergy and did not present toxicity in the model used.

Adduct‐Type Compounds for Nonlinear Optical Crystals

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The performance prerequisites for nonlinear optical (NLO) crystals encompass a substantial second-harmonic generation (SHG), a considerable laser induced damage threshold, and a moderate degree of birefringence. Nevertheless, the presence of particular anions may result in deficiencies within certain properties. The utilization of mixed anionic groups has emerged as an effective strategy to achieve a balance among numerous performance parameters of NLO crystals, particularly in terms of SHG responses and bandgaps. Compared with other heteroanionic compounds, adduct-type compounds feature more concise structures with specific properties. Herein, we aim to provide an overview of the recent advancements in adduct-type NLO crystals, focusing on their structures and properties. Furthermore, we analyze the coordination chemistry and disadvantages involved in adducts, and discuss the current synthesis methods as well as future directions for further exploration.

Quantifying the Ground‐State Hydrogen‐Bond Formation of a Super‐Photoacid by Inspecting Its Excited‐State Dynamics

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The identification and quantification of hydrogen (H)-bonded complexes form the cornerstone of reaction-mechanism analysis in ultrafast proton transfers. Traditionally, the Benesi-Hildebrand method has been employed to obtain the formation constants of H-bonded complexes, given that H-bonding additives induce an alteration in spectral features exclusively through H-bond formation. However, if the additive introduction impacts the bulk polarity of the solution, inducing a spectral shift, the spectroscopic method's accuracy in analyzing the H-bond formation becomes compromised. In this study, we scrutinize H-bond formation under the influence of an H-bond accepting solute in an aprotic solvent. This is achieved by quantifying the fractions of two concurrent pathways involved in the excited-state proton transfer (ESPT) of a super-photoacid: the ultrafast ESPT of an H-bonded complex vs. the diffusion-controlled ESPT of the free acid. Our method offers improved accuracy compared to conventional steady-state spectroscopic techniques, by directly quantifying the H-bonded complexes using the time-resolved spectroscopic method, thereby circumventing the aforementioned limitation.