Navigating through the coordination preferences of heavy alkaline earth metals: Laying the foundations for 223Ra- and 131/135mBa-based targeted alpha therapy and theranostics of cancer.

The clinical success of [223Ra]RaCl2 (Xofigo®) for the palliative treatment of bone metastases in patients with prostate cancer has highlighted the therapeutic potential of α-particle emission. Expanding the applicability of radium-223 in Targeted Alpha Therapy of non-osseous tumors is followed up with significant interest, as it holds the potential to unveil novel treatment options in the comprehensive management of cancer. Moreover, the use of barium radionuclides, like barium-131 and -135m, is still unfamiliar in nuclear medicine applications, although they can be considered as radium-223 surrogates for imaging purposes. Enabling these applications requires the establishment of chelators able to form stable complexes with radium and barium radionuclides. Until now, only a limited number of ligands have been suggested and these molecules have been primarily inspired by existing structures known for their ability to complex large metal cations. However, a systematic inspection of chelators specifically tailored to Ra2+ and Ba2+ has yet to be conducted. This work delves into a comprehensive investigation of a series of small organic ligands, aiming to unveil the coordination preferences of both radium-223 and barium-131/135m. Electronic binding energies of both metal cations to each ligand were theoretically computed via Density Functional Theory calculations (COSMO-ZORA-PBE-D3/TZ2P), while thermodynamic stability constants were experimentally determined for Ba2+-ligand complexes by potentiometry, NMR and UV-Vis spectroscopies. The outcomes revealed malonate, 2-hydroxypyridine 1-oxide and picolinate as the most favorable building blocks to design multidentate chelators. These findings serve as foundation guidelines, propelling the development of cutting-edge radium-223- and barium-131/135m-based radiopharmaceuticals for Targeted Alpha Therapy and theranostics of cancer.

Theoretical design of alkaline earthides M+(36 adz) Be- (M+ = V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) with excellent nonlinear optical response and ultraviolet transparency.

A novel series of alkaline earthides containing eight complexes based upon 36adz complexant are designed by placing carefully transition metals (V-Zn) on inner side and alkaline earth metal outer side of the complexant i.e., M+(36adz) Be- (M+ = V, Cr, Mn, Fe, Co, Ni, Cu and Zn). All the designed compounds are electronically and thermodynamically stable as evaluated by their interaction energy and vertical ionization potential respectively. Moreover, the true nature of alkaline earthides is verified through NBOs and FMO study, showing negative charge and excess electrons on alkaline earth metal respectively. Furthermore, true alkaline earthides characteristics are evaluated graphically by spectra of partial density state (PDOS). The energy gap (HOMO -LUMO gap) is very small (ranging 2.95 eV-1.89 eV), when it is compared with pure cage 36adz HOMO-LUMO gap i.e., 8.50 eV. All the complexes show a very small value of transition energy ranging from 1.68eV to 0.89eV. Also, these possess higher hyper polarizability values up to 2.8 x 105au (for Co+(36adz) Be-). Furthermore, an increase in hyper polarizability was observed by applying external electric field on complexes. The remarkable increase of 100fold in hyper polarizability of Zn+(36adz) Be- complex is determined after application of external electric field i.e., from 1.7 x 104 au to 1.7 x 106 au when complex is subjected to external electric field of 0.001 au strength. So, when external electric field is applied on complexes it enhances the charge transfer, polarizability and hyper polarizability of complexes and proves to be effective for designing of true alkaline earthides with remarkable NLO response.

Alkali and alkaline earth elements in follicular fluid and the likelihood of diminished ovarian reserve in reproductive-aged women: a case‒control study.

BACKGROUND: Imbalances in alkali elements (AEs) and alkaline earth elements (AEEs) cause reproductive disorders. However, it remains unclear whether AEs/AEEs in follicular fluid have a relationship with the serious reproductive disorder known as diminished ovarian reserve (DOR). METHODS: A nested case‒control study was carried out in China. Follicular fluid samples from 154 DOR patients and 154 controls were collected and assessed for nine AEs/AEE levels. Both the mixed and single effects of the elements on DOR were estimated with a Bayesian kernel machine (BKMR) and logistic regressions. RESULTS: The DOR group had higher median concentrations of Li, Na, and K in follicular fluid (all P values < 0.05). The logistic regression showed that compared with their lowest tertile, the high tertiles of K [OR:2.45 (1.67-4.43)], Li [OR: 1.89 (1.06-3.42)], and Cs [OR: 1.97 (1.10-3.54)] were significantly associated with the odds of DOR. The BKMR model reported that the DOR likelihood increased linearly across the 25th through 75th percentiles of the nine-AE/AEE mixture, while the AE group contributed more to the overall effect. CONCLUSION: This study revealed an association in which the likelihood of DOR increased with higher overall concentrations of AE/AEEs in follicular fluid. Among the nine detected elements, K, Li, and Cs exhibited significant individual associations with DOR. We provide new clues for the environmental factors on female fertility decline. TRIAL REGISTRATION: Retrospectively registered.

Effects of alkali and alkaline earth metals on co-combustion of sewage sludge and coal slime: Combustion characteristics, interactions, and kinetics.

The co-combustion of sewage sludge (SS) and coal slime (CS) is a preferred method for their resource utilization, however, alkali and alkaline earth metals (AAEMs) in SS may affect the co-combustion process. In this work, the co-combustion behavior of AAEMs-rich SS and CS was investigated in terms of combustion characteristics, interactions, and combustion kinetics using a thermogravimetric analyzer. Further, the role of AAEMs in co-combustion was evaluated by loading Ca, K, Na, and Mg individually after pickling. The results revealed that co-combustion compensated for the limitations of the individual combustion processes, with SS reducing ignition and burnout temperatures and CS improving the comprehensive combustion characterization. Principal component analysis (PCA) showed that the effect of CS on co-combustion was more significant compared to SS. Significant synergies were observed in the weight loss phase of fixed carbon in the blends with 40%, 50%, and 60% CS ratios, where the peak temperature of fixed carbon combustion was reduced by 9.8 °C, 12.6 °C, and 13.1 °C, respectively, compared to the theoretical values. The effects of AAEMs on combustion were as follows: all AAEMs promoted the precipitation of volatiles except Ca, which showed inhibition of light volatiles; AAEMs had a significant catalytic effect on fixed carbon combustion. The improvement effect of AAEMs on the comprehensive combustion characteristics during co-combustion was Na > K > Mg > Ca. The catalytic effect of Na on fixed carbon was strongest at a loading of 5%, leading to a decrease in the apparent activation energy of fixed carbon combustion by 22.2 kJ/mol and a change in reactor order from n = 1 to n = 1.2 during co-combustion. This work provides a better understanding of the role of AAEMs in SS-CS co-combustion.

Structural insight and in silico prediction of the pharmacokinetic parameters and toxicity of alkaline earth metal compounds strontium and barium with the non-steroidal anti-inflammatory drug nimesulide.

In the crystals of alkaline earth metal compounds strontium and barium with the non-steroidal anti-inflammatory drug nimesulide, the strontium cation is nine-coordinated with a distorted tricapped trigonal prismatic geometry TCTPR-9, whereas the ten-coordinated barium ion exhibits a distorted tetracapped trigonal prismatic geometry TCTPR-10.

The unexplored role of alkali and alkaline earth elements (ALAEs) on the structure, processing, and biological effects of bioactive glasses.

Bioactive glass has been employed in several medical applications since its inception in 1969. The compositions of these materials have been investigated extensively with emphasis on glass network formers, therapeutic transition metals, and glass network modifiers. Through these experiments, several commercial and experimental compositions have been developed with varying chemical durability, induced physiological responses, and hydroxyapatite forming abilities. In many of these studies, the concentrations of each alkali and alkaline earth element have been altered to monitor changes in structure and biological response. This review aims to discuss the impact of each alkali and alkaline earth element on the structure, processing, and biological effects of bioactive glass. We explore critical questions regarding these elements from both a glass science and biological perspective. Should elements with little biological impact be included? Are alkali free bioactive glasses more promising for greater biological responses? Does this mixed alkali effect show increased degradation rates and should it be employed for optimized dissolution? Each of these questions along with others are evaluated comprehensively and discussed in the final section where guidance for compositional design is provided.

Biochar obtained from alkaline earth metal-treated mushroom residue: Thermal behavior and methyl orange adsorption capability.

To achieve the resource utilization of edible fungi residue and obtain efficient adsorbents for treating dyeing wastewater, biochars were prepared from mushroom residue (MR) with the introduction of alkaline-earth metals (AEMs) and used for methyl orange (MO) wastewater treatment. The thermal behavior of the AEM-treated MR was analyzed using thermogravimetric analysis. The physicochemical properties of the biochars obtained from AEM-treated MR (MRCs) were characterized using Fourier transform infrared spectroscopy, laser particle size analyzer, N2 adsorption/desorption, and scanning electron microscopy. The adsorption performance of MRCs on MO was also investigated. The involvement of AEMs was found to obviously move the main pyrolysis zone of MR to a low temperature region and reduce the temperature corresponding to the maximum weight loss rate and activation energy, which is highly dependent on the concentration of AEMs, the anion and cationic species of the AEMs. Moreover, the addition of AEMs resulted in a decrease in oxygen-containing functional groups (-OH, CO, or C-O), a weakening of surface negative charges, an enhancement in aromatic functional groups, and an increase in specific surface area of the MRCs. The adsorption performance of MO on MRCs was significantly improved with the introduction of AEMs as well. Among them, MR pre-treated with 5 mmol/g MgCl2 (MR-MgCl2-5) shows the lowest temperature corresponding to the maximum weight loss rate and the lowest activation energy of 278.52 °C and 4.28 kJ/mol, respectively. The biochar prepared from MR-MgCl2-5 under 400 °C (MR-MgCl2-5-400C) has the weakest surface negative charge and the highest adsorption capacity for MO. The adsorption isotherms, adsorption kinetics, and thermodynamic analysis results showed that the adsorption of MO on MR-MgCl2-5-400C was a spontaneous, chemically dominant monolayer adsorption, with a theoretical maximum adsorption capacity of 81.30 mg/g. This study suggests that AEMs treatment, especially with 5 mmol/g MgCl2, can readily transform edible fungi residue into a low-cost, high-efficient dyeing wastewater adsorbent.

Prediction of alkaline earth metal ion adsorption on goethite for various background electrolytes with the CD-MUSIC model.

As water scarcity drives the use of more saline water sources, contaminant fate and transport models must capture the impact of high concentrations of alkaline earth metal ions (AEMs) and background electrolytes in these more complex waters. By utilizing macroscopic adsorption data from various electrolyte systems, a Charge Distribution - Multisite Complexation (CD-MUSIC) model, capable of incorporating electrolyte adsorption, was able to accurately simulate the adsorption behavior of alkaline earth metal ions onto goethite. The modeling effort was guided by previous spectroscopic and surface complexation modeling of alkaline earth metal adsorption and built on previous CD-MUSIC modeling that accounted for changes in crystal face contributions to the surface site density as a function of specific surface area. The model was constrained to consider only two dominant surface complex species for each metal ion adsorption reaction. These two species were selected from 44 possible species through objective curve fitting of single-solute macroscopic adsorption data. While most of the alkaline earth metal surface complexes formed outer-sphere complexes at the goethite surface, an inner-sphere species was utilized for Mg2+. With the surface complex species and equilibrium constants obtained from this study, the calibrated model successfully predicted alkaline earth metal ion adsorption over a wide range of solution and surface conditions; the model predictions encompassed a wide range of pH (5-11), solute/solid ratio (1.37 × 10-5- 8.33 × 10-4 mol-solute/g-solid), ionic strengths (0.01 M - 0.7 M), and background electrolytes (Na+, Cs+, Rb+, Cl-, and NO3-) using the same crystal face contribution methodology for site density, capacitance values, and surface acidity constants adopted for proton and cadmium adsorption in previous work (Han and Katz, 2019). Model simulations for a range of background water chemistries demonstrated the potential for Mg2+ to reduce Cd2+ adsorption to goethite in model seawater and oil- and gas-produced waters.

Quantum Chemical Approach of Hexaammine (NH3)6 complexant with alkali and alkaline earth metals for their potential use as NLO materials.

In this study, nine new electron rich compounds are presented, and their electronic, geometrical, and nonlinear optical (NLO) characteristics have been investigated by using the Density functional theory. The basic design principle of these compounds is placing alkaline earth metal (AEM) inside and alkali metal (AM) outside the hexaammine complexant. The properties of nine newly designed compounds are contrasted with the reference molecule (Hexaammine). The effect of this doping on Hexaamine complexant is explored by different analyses such as electron density distribution map (EDDM), frontier molecular orbitals (FMOs), density of states (DOS) absorption maximum (λmax), hyperpolarizabilities, dipole moment, transition density matrix (TDM). Non-covalent interaction (NCI) study assisted with isosurfaces has been accomplished to explore the vibrational frequencies and types of synergy. The doping of hexaammine complexant with AM and AEM significantly improved its characteristics by reducing values of HOMO-LUMO energy gaps from 10.7eV to 3.15eV compared to 10.7 eV of hexaammine. The polarizability and hyperpolarizability (αo and ßo) values inquisitively increase from 72 to 919 au and 4.31 × 10-31 to 2.00 × 10-27esu respectively. The higher values of hyperpolarizability in comparison to hexaammine (taken as a reference molecule) are credited to the presence of additional electrons. The absorption profile of the newly designed molecules clearly illustrates that they are highly accompanied by higher λmax showing maximum absorbance in red and far-red regions ranging from 654.07 nm to 783.94 nm. These newly designed compounds have superior outcomes having effectiveness for using them as proficient NLO materials and have a gateway for advanced investigation of more stable and highly progressive NLO materials.

Alkaline earth metals for osteogenic scaffolds: From mechanisms to applications.

Regeneration of bone defects is a significant challenge today. As alternative approaches to the autologous bone, scaffold materials have remarkable features in treating bone defects; however, the various properties of current scaffold materials still fall short of expectations. Due to the osteogenic capability of alkaline earth metals, their application in scaffold materials has become an effective approach to improving their properties. Furthermore, numerous studies have shown that combining alkaline earth metals leads to better osteogenic properties than applying them alone. In this review, the physicochemical and physiological characteristics of alkaline earth metals are introduced, mainly focusing on their mechanisms and applications in osteogenesis, especially magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Furthermore, this review highlights the possible cross-talk between pathways when alkaline earth metals are combined. Finally, some of the current drawbacks of scaffold materials are enumerated, such as the high corrosion rate of Mg scaffolds and defects in the mechanical properties of Ca scaffolds. Moreover, a brief perspective is also provided regarding future directions in this field. It is worth exploring that whether the levels of alkaline earth metals in newly regenerated bone differs from those in normal bone. The ideal ratio of each element in the bone tissue engineering scaffolds or the optimal concentration of each elemental ion in the created osteogenic environment still needs further exploration. The review not only summarizes the research developments in osteogenesis but also offers a direction for developing new scaffold materials.

Organic small-molecule fluorescent probe-based detection for alkali and alkaline earth metal ions in biological systems.

Metal ions widely exist in biological systems and participate in many vital biochemical processes. Monitoring and analyzing metal ions in biological systems can help reveal physiological processes and understand disease causes. There are various detection methods for metal ions, among which organic small-molecule fluorescent probes have significant advantages, such as high fluorescence quantum yield, easy modification, good biocompatibility, high sensitivity, and fast real-time detection. This review presents recent studies on fluorescent probes for alkali and alkaline earth metal ions (including Na+, K+, Ca2+, and Mg2+) in biological systems. All the candidates are organized according to their structures, and the sensing mechanisms of fluorescent probes are also highly taken into account. Finally, the challenges, trends and prospects of fluorescent probes in metal ion detection are discussed. We hope that this review can provide guidance for the development of fluorescent molecular probe-based alkali and alkaline earth metal ion detection methods in the future.

Efficient delivery of anticancer 5-fluorouracil drug by alkaline earth metal functionalized porphyrin-like porous fullerenes: A DFT study.

Finding and developing effective targeted drug delivery systems has emerged as an attractive approach for treating a wide range of diseases. In the present study, the potential of alkaline earth metal functionalized porphyrin-like porous C24N24 fullerenes for delivering 5-fluorouracil (5FU) anticancer drug is assessed using density functional theory calculations. The goal is to evaluate how the addition of alkaline earth metals to C24N24 enhances the adsorption capabilities of this system towards 5FU drug. The adsorption energies and charge transfers are determined in order to evaluate the strength of the interaction between the 5FU and fullerene surfaces. According to the results, adding alkaline earth metals increases the drug's adsorption energy on the C24N24 fullerene. In all cases, the drug molecule interacts with the metal atom through its CO group. Furthermore, the adsorption strength of the 5FU increases with metal atom size (Ca > Mg > Be), which is connected to the polarizability of these atoms. The adsorption energies of 5FU are shown to be highly sensitive on solvent effects and the acidity of the environment. The adsorption strength of 5FU decreases within the solvent (water), allowing it to be released more easily. The moderate adsorption energies and short desorption times of 5FU imply that it is reversibly adsorbed on the functionalized fullerenes.

A comprehensive study on the electronic structure, dielectric and optical properties of alkali-earth metals and transition metal hydroxides M(OH)2.

In the present work, the physical properties of alkali-earth metal and transition metal hydroxides are comprehensively investigated using the density functional theory. Here, the alkali-earth metals Ca, Mg, and transition metals Cd, Zn are considered from the II-A and II-B groups in the periodic table of elements. The first principle electronic structure calculations show that these bulk hydroxide materials are direct band gap material. Ca(OH)2 and Mg(OH)2 exhibit an insulating behavior with a very large band gap. However, Cd(OH)2 and Zn(OH)2 are found to be wide band gap semiconductors. The dielectric and optical studies reveal that these materials have a high degree of anisotropy. Hence, the light propagation in these materials behaves differently in the direction perpendicular and parallel to the optical axis, and exhibits birefringence. Therefore, these materials may be useful for optical communication. The calculated electron energy loss suggests that these materials can also be used for unwanted signal noise suppression. The wide band gap makes them useful for high-power applications. Moreover, Ca(OH)2 and Mg(OH)2 are found to be suitable for dielectric medium.

Reversible Assembly of an Artificial Protein Nanocage Using Alkaline Earth Metal Ions.

Protein nanocages are of increasing interest for use as drug capsules, but the encapsulation and release of drug molecules at appropriate times require the reversible association and dissociation of the nanocages. One promising approach to addressing this challenge is the design of metal-dependent associating proteins. Such designed proteins typically have Cys or His residues at the protein surface for connecting the associating proteins through metal-ion coordination. However, Cys and His residues favor interactions with soft and borderline metal ions, such as Au+ and Zn2+, classified by the hard and soft acids and bases concept, restricting the types of metal ions available to drive association. Here, we show the alkaline earth (AE) metal-dependent association of the recently designed artificial protein nanocage TIP60, which is composed of 60-mer fusion proteins. The introduction of a Glu (hard base) mutation to the fusion protein (K67E mutant) prevented the formation of the 60-mer but formed the expected cage structure in the presence of Ca, Sr, or Ba ions (hard acids). Cryogenic electron microscopy (cryo-EM) analysis indicated a Ba ion at the interface of the subunits. Furthermore, we demonstrated the encapsulation and release of single-stranded DNA molecules using this system. Our results provide insights into the design of AE metal-dependent association and dissociation mechanisms for proteins.

Dissociation and removal of alkali and alkaline earth metals from sewage sludge flocs during separate and assisted thermal hydrolysis.

High levels of alkali and alkaline earth metals (AAEM, including K, Na, Ca, and Mg) in sludge needs to be removed in pretreatment process for alleviating adverse effects on subsequent disposal. Theoretically, the liquid environment provided by the pretreatment technology of thermal hydrolysis (TH) is the ideal condition for the dissolution of AAEM. Therefore, this work quantified AAEM removal efficiency of TH and carbonaceous skeleton (CSkel) assisted TH that we previously proposed for sludge dewatering. Then the mechanism of AAEM dissociating from sludge was explored through the new perspective of biological structure evolution and chemical species transformation. The results showed that all of the AAEM in raw sludge was trapped in extracellular polymer substances (EPS) and cells. Only the water-soluble K/Na in EPS could be released by TH to the supernatant, the residual K/Na in EPS was organically linked with humic matters that were generated through the degradation of proteins. Water/NH4Ac-soluble K/Na in cells still stayed inside with a more stable form of HCl-soluble after TH. Fortunately, with the assistance of CSkel, this part of K/Na could be leached out due to organic acids derived from hemicellulose decomposition. In such a case, the removal efficiency of K/Na was elevated to 55.5% and 72.5%, respectively. Unlike K/Na, nearly all the Ca/Mg in EPS were transferred to cell residuals during TH. They were combined with the bio-phosphorus in cell residuals as the form of HCl-soluble Ca/Mg-P precipitates, rather than carbonates, sulfates or other compounds. This precipitation reaction was also moderately suppressed in CSkel-assisted TH with low pH, then 7.7% and 34.1% of Ca/Mg were taken away by filtrate. This means that appropriately raising the reaction temperature and adding CSkel with high hemicellulose/cellulose contents can promote the removal of AAEM in sludge during TH process.

High-Throughput Screening of Bicationic Redox Materials for Chemical Looping Ammonia Synthesis.

Ammonia recently has gained increasing attention as a carrier for the efficient and safe usage of hydrogen to further advance the hydrogen economy. However, there is a pressing need to develop new ammonia synthesis techniques to overcome the problem of intense energy consumption associated with the widely used Haber-Bosch process. Chemical looping ammonia synthesis (CLAS) is a promising approach to tackle this problem, but the ideal redox materials to drive these chemical looping processes are yet to be discovered. Here, by mining the well-established MP database, the reaction free energies for CLAS involving 1699 bicationic inorganic redox pairs are screened to comprehensively investigate their potentials as efficient redox materials in four different CLAS schemes. A state-of-the-art machine learning strategy is further deployed to significantly widen the chemical space for discovering the promising redox materials from more than half a million candidates. Most importantly, using the three-step H2 O-CL as an example, a new metric is introduced to determine bicationic redox pairs that are "cooperatively enhanced" compared to their corresponding monocationic counterparts. It is found that bicationic compounds containing a combination of alkali/alkaline-earth metals and transition metal (TM)/post-TM/metalloid elements are compounds that are particularly promising in this respect.

The influence of a two-step leaching pretreatment on the steam gasification properties of cornstalk waste.

Knowing the effect of specific alkali and alkali earth metals forms is vital for the high-efficient gasification of biomass. This work developed a two-step leaching method to pretreat cornstalk, dividing the inorganic metals into water-soluble (K+, 74 wt%), acid-soluble (Al3+, Ca2+, Fe2+, etc) and insoluble (Si4+) substances. The water-soluble K+ was mainly in KCl form, the acid-soluble metals were removed in phosphates and sulfates forms. The rapid gasification properties of raw material, water leaching residue and acid leaching residue indicated that KCl was the key factor to enhance the hydrogen yield and gasification efficiency. Apart from K+, the alkali earth metals (Ca2+, Mg2+) also had a little catalytic effect on producing hydrogen. When the feedstock was out of metal cations, the syngas was mainly composed of CO. The basic ions to acid ions ratio was linearly related to the syngas quality, which could conduct the flux additives.

Stepwise dissociation of ion pairs by water molecules: cation-dependent separation mechanisms between carboxylate and alkali-earth metal ions.

Microhydrated H2-tagged ion pairs (Ca2+, AcO-)(H2O)n=0-8 and (Ba2+, AcO-)(H2O)n=0-5 are investigated by IR photodissociation laser spectroscopy and DFT-D frequency calculations. The detailed picture of the first steps of ion dissociation reveals two mechanisms, where water molecules promote dissociation either directly or indirectly depending on the nature of the cation.

Products of Photo- and Thermochemical Rearrangement of 19-Membered di-tert-Butyl-Azoxybenzocrown.

The preparation and characterization of products of the photochemical and thermochemical rearrangements of 19-membered azoxybenzocrowns with two, bulky, tert-butyl substituents in benzene rings in the para positions to oligooxyethylene fragments (meta positions to azoxy group, i.e., t-Bu-19-Azo-O have been presented. In photochemical rearrangement, two colored typical products were expected, i.e., 19-membered o-hydroxy-m,m'-di-tert-butyl-azobenzocrown (t-Bu-19-o-OH) and 19-membered p-hydroxy-m,m'-di-tert-butyl-azobenzocrown (t-Bu-19-p-OH). In experiments, two colored atypical macrocyclic derivatives, one 6-membered and one 5-membered ring, bearing an aldehyde group (t-Bu-19-al) or intramolecular ester group (t-Bu-20-ester), were obtained. Photochemical rearrangement led to one more macrocyclic product being isolated and identified: a 17-membered colorless compound, without an azo moiety, t-Bu-17-p-OH. The yield of the individual compounds was significantly influenced by the reaction conditions. Thermochemical rearrangement led to t-Bu-20-ester as the main product. The structures of the four crystalline products of the rearrangement-t-Bu-19-o-OH, t-Bu-19-p-OH, t-Bu-20-ester and t-Bu-17-p-OH-were determined by the X-ray method. Structures in solution of atypical derivatives (t-Bu-19-al and t-Bu-20-ester) and t-Bu-19-p-OH were defined using NMR spectroscopy. For the newly obtained hydroxyazobenzocrowns, the azo-phenol⇄quinone-hydrazone tautomeric equilibrium was investigated using spectroscopic methods. Complexation studies of alkali and alkaline earth metal cations were studied using UV-Vis absorption spectroscopy. 1H NMR spectroscopy was additionally used to study the cation recognition of metal cations. Cation binding studies in acetonitrile have shown high selectivity towards calcium over magnesium for t-Bu-19-o-OH.

Permeation selectivity of pristine and vacancy defected hexagonal boron membranes for alkaline earth metal and ions.

Permeation and selectivity of alkaline metal atoms and ions through normal and defected hexagonal boron nitride is explored in the presence and absence of water. The defects include one (VB and VN), two (VBN) and three atoms (VB(2N) and VN(2B)) vacancies. The barriers are obtained by scanning potential energy surface for the movement of alkaline earth metal atoms and ions through the nanosheet. The size and morphology of defects in h-BN sheet significantly affect the energy barrier. h-BN sheet with VN defect possess good Be/Be2+ selectivity. Permeation of Be atoms through VBN-h-BN, VB(2N)-h-BN and VN(2B)-h-BN is a barrierless process. Mostly, the permeation barriers are reduced in the presence of water molecule for Be, Ca and Ca2+. The effect of water molecule is more pronounced on the permeation of Ca atom and ion through normal and defected h-BN sheet as compared to smaller alkaline earth metal atoms and ions. The study can be extended to investigate the separation capability of porous hexagonal boron nitride nanosheet for other metal atoms and ions. HighlightsPermeability of pristine and vacancy defected h-BN nanosheet is studied for alkaline earth metal atoms and ions.Increase in pore size and applied electric field decrease the permeation barriers for alkaline earth metal atoms and ions.VN h-BN sheet possess good Be/Be2+ selectivity.Permeation of Be atoms through VBN-h-BN, VB(2N)-h-BN and VN(2B)-h-BN is a barrierless process.Permeation barriers are reduced in the presence of water molecule for Be, Ca and Ca2+.Communicated by Ramaswamy H. Sarma.