Effect of Enhanced UV-B Radiation and Low-Energy N+ Ion Beam Radiation on the Response of Photosynthesis, Antioxidant Enzymes, and Lipid Peroxidation in Rice (Oryza sativa) Seedlings

To understand the effect of enhanced UV-B radiation and low-energy N⁺ ion beam radiation on the response of photosynthesis, antioxidant enzymes, and lipid peroxidation in rice seedlings, Oryza sativa was exposed to three different doses of low-energy N⁺ ion beam and enhanced UV-B alone and in combination. Enhanced UV-B caused a marked decline in some photosynthetic parameters (net photosynthetic rate, transpiration rate, and stomatal conductance) and photosynthetic pigments, whereas it induced an increase in hydrogen peroxide (H₂O₂) accumulation, the rate of superoxide radical production, and the content of malondialdehyde (MDA). Enhanced UV-B also induced an increase in the activity of antioxidant enzymes (superoxide dismutase [SOD], peroxidase (POD), and catalase [CAT]) and some nonenzymatic antioxidants such as proline. Under the combined treatment of enhanced UV-B and low-energy N⁺ ion beam at the dose of 3.0?×?10¹⁷ N⁺ cm^?2, the activity of antioxidant compounds (SOD, POD, CAT, proline, and glutathione), photosynthetic pigments, and some photosynthetic parameters (net photosynthetic rate, transpiration rate, and stomatal conductance) increased significantly; however, the MDA content, H₂O₂ accumulation, and rate of superoxide radical production showed a remarkable decrease compared with the enhanced UV-B treatment alone. These results implied that the appropriate dose of low-energy N⁺ ion beam treatment may alleviate the damage caused by the enhanced UV-B radiation on rice.     

Ligand fishing and identification of acetylcholinesterase inhibitors in Mahonia bealei (Fort.) Carr. using high performance liquid chromatography-mass spectrometry

Abstract

A fishing platform was developed using immobilized capillary enzyme reactors in combination with liquid chromatography-mass spectrometry (LC-MS) to fish acetylcholinesterase inhibitor (AChEI) from Mahonia bealei (Fort.) Carr. (M. bealei) extract. Four potential AChEIs (columbamine, jatrorrhizine, berberine, and palmatine) were successfully screened out and identified. Their AChE inhibitory activities were further verified by an in vitro assay with IC₅₀ values of 0.93?±?0.12?μg/mL (columbamine), 3.50?±?0.15?μg/mL (jatrorrhizine), 2.51?±?0.12?μg/mL (berberine), and 1.52?±?0.13?μg/mL (palmatine). A synergy study of these AChEIs was subsequently investigated. In comparison with the IC₅₀ value of M. bealei extract (IC₅₀=0.83?±?0.21?μg/mL), it can be stated that M. bealei extract is much more active than any single AChEI. Thereafter, the determination of these four alkaloids were investigated and AChE inhibitory effect were compared in terms of the extract and corresponding contents of these four alkaloids. The inhibitory effects of extract at each concentration were stronger than four alkaloids mixture. The results demonstrated that not the four AChEI mixture cause the synergistic effect but rather than the concentrations or ratios of these AChEIs play a vital role in their synergy study.     

Biodegradable Polycaprolactone (PCL) Nanosphere Encapsulating Superoxide Dismutase and Catalase Enzymes

Biodegradable polycaprolactone (PCL) nanosphere encapsulating superoxide dismutase (SOD) and catalase (CAT) were successfully synthesized using double emulsion (w/o/w) solvent evaporation technique. Characterization of the nanosphere using dynamic light scattering, field emission scanning electron microscope, and Fourier transform infrared spectroscopy revealed a spherical-shaped nanosphere in a size range of 812?±?64 nm with moderate protein encapsulation efficiency of 55.42?±?3.7 % and high in vitro protein release. Human skin HaCat cells were used for analyzing antioxidative properties of SOD- and CAT-encapsulated PCL nanospheres. Oxidative stress condition in HaCat cells was optimized with exposure to hydrogen peroxide (H₂O₂; 1 mM) as external stress factor and verified through reactive oxygen species (ROS) analysis using H₂DCFDA dye. PCL nanosphere encapsulating SOD and CAT together indicated better antioxidative defense against H₂O₂-induced oxidative stress in human skin HaCat cells in comparison to PCL encapsulating either SOD or CAT alone as well as against direct supplement of SOD and CAT protein solution. Increase in HaCat cells SOD and CAT activities after treatment hints toward uptake of PCL nanosphere into the human skin HaCat cells. The result signifies the role of PCL-encapsulating SOD and CAT nanosphere in alleviating oxidative stress.     

Oxidative Stress Response of Blakeslea trispora Induced by Iron Ions During Carotene Production in Shake Flask Culture

The adaptive response of the fungus Blakeslea trispora to the oxidative stress induced by iron ions during carotene production in shake flask culture was investigated. The culture response to oxidative stress was studied by measuring the specific activities of catalase (CAT) and superoxide dismutase (SOD). The addition of 1.0 mM of FeCl₃ to the medium was associated with a mild oxidative stress as evidenced by remarkable increase of the specific activities of SOD and CAT. On the other hand, the addition 5.0 mM of FeCl₃ caused a strong oxidative stress resulting in a drastic decrease in carotene concentration. The oxidative stress in B. trispora changed the composition of the carotenes and caused a significant increase of γ-carotene ratio. The highest concentration of carotenes (115.0?±?3.5 mg/g dry biomass) was obtained in the basal medium without the addition of FeCl₃ after 8 days of fermentation. In this case, the carotenes consisted of β-carotene (46.3 %), γ-carotene (40.1 %), and lycopene (13.6 %). The addition of 1.0 mM of FeCl₃ into the medium did not change the concentration of carotenes. But, the composition of carotenes was changed with a drastic increase of γ-carotene ratio (61.6 %) and a decrease in β-carotene and lycopene ratio (31.2 and 7.2 %, respectively).     

Complexation study of Schiff base ligand: pyridin-2-ylimino methyl naphthanol with Co+2, Mn+2 and Ni+2 ions in solid and solution phase

Schiff base pyridin-2-ylimino methyl naphthanol (HL) was synthesized and characterized by spectroscopic (FTIR, ESIMS, and NMR) techniques. The ligand was reacted with perchlorate salts of Mn⁺², Co⁺², and Ni⁺². ESIMS mass spectra indicate the formation of mononuclear complex ML₂ for all three complexes. CoL₂ crystallizes in P₂1/n space group, adopting a distorted tetrahedral geometry where Co is in a N₂O₂ donor environment. Structure of the Co complex was optimized by DFT calculation. Solution-phase complexation between the ligand and the three metals ions: Mn⁺², Co⁺², and Ni⁺² (pH 7.2 in tris buffer), in CH₃CN–H₂O was performed spectrophotometrically by UV–vis spectral study. Job’s plot from each titration suggests a 1 : 2 metal to ligand combination. The association constants for the formation of ML₂ are as follows: Mn (19.80 × 10³ M^?1), Co (14.54 × 10³ M^?1) and Ni (19.04 × 10³ M^?1).     

Antibacterial activity of Thymus vulgaris essential oil alone and in combination with cefotaxime against blaESBL producing multidrug resistant Enterobacteriaceae isolates

The aim was to evaluate the susceptibility of bla_ESBL producing Enterobacteriaceae to Slovakian Thymus vulgaris essential oil (TVEO) alone and in combination with cefotaxime (CTX). TVEO composition was determined by gas chromatograph-mass spectrometer (GC/MS). Susceptibility to 21 antibiotics was determined by disc diffusion assay. Genes characterization for resistance to β-lactams was accomplished by polymerase chain reaction (PCR). The antibacterial activity was investigated by standard methods. The synergistic interaction was determined by checkerboard test. Thymol (34.5%), p-cymene (22.27%) and linalool (5.35%) were the major components present in the TVEO. The identified strains were multi-drug resistant (MDR). TVEO showed high activity against all MDR strains, including bla_ESBL producing isolates, with inhibition zones and MIC values in the range of 24–40 mm/10μL and 2.87–11.5 μg/mL, respectively. TVEO in combination with CTX showed a synergistic action against bla_SHV-12 producing Escherichia coli (FICI 0.28) and an additive effect vs ESBL producing Enterobacter cloacae (FICI 0.987).     

Interaction between tetramethylcucurbit[6]uril with α-furaldehyde-isonicotinyl-hydrazone hydrochloride

Interaction between tetramethylcucurbit[6]uril (TMeQ[6], host) and the hydrochloride salt of α-furaldehyde-isonicotinyl-hydrazone hydrochloride (FIHH⁺, guest) was investigated using X-ray crystallography and spectroscopic methods. X-ray crystallography showed that the π–π stacking effect and hydrogen bonding resulted in the formation of a dumbbell-shaped supramolecule which contained two FIHH⁺@TMeQ[6] host–guest inclusion complexes. The host–guest interaction provided identifiable changes in the vibrational frequencies in the IR spectra. ¹H NMR spectral analysis established a similar interaction model and revealed that TMeQ[6] preferred to include the furan moiety over the pyridine moiety of the FIHH⁺ guest molecule. Absorption spectrophotometric analysis suggested that the host and guest interact in a ratio of 1:1 with a stability constant K _s = (3.52 ± 0.74) × 10⁶ l mol^? 1.pH titration confirmed that the host–guest interaction led to a clear change in the protonation constant of the title guest. Quantum chemical calculations were used to determine the possible mechanism of formation of the dumbbell-shaped complex.     

Self‐Assembly of Multi‐nanozymes to Mimic an Intracellular Antioxidant Defense System

In this work, for the first time, we constructed a novel multi‐nanozymes cooperative platform to mimic intracellular antioxidant enzyme‐based defense system. V₂O₅ nanowire served as a glutathione peroxidase (GPx) mimic while MnO₂ nanoparticle was used to mimic superoxide dismutase (SOD) and catalase (CAT). Dopamine was used as a linker to achieve the assembling of the nanomaterials. The obtained V₂O₅@pDA@MnO₂ nanocomposite could serve as one multi‐nanozyme model to mimic intracellular antioxidant enzyme‐based defense procedure in which, for example SOD, CAT, and GPx co‐participate. In addition, through assembling with dopamine, the hybrid nanocomposites provided synergistic antioxidative effect. Importantly, both in vitro and in vivo experiments demonstrated that our biocompatible system exhibited excellent intracellular reactive oxygen species (ROS) removal ability to protect cell components against oxidative stress, showing its potential application in inflammation therapy.     

Trixis angustifolia hexanic extract displays synergistic antibacterial activity against M. tuberculosis

A phytochemical and antibacterial study of Trixis angustifolia, a species endemic to Mexico, was performed allowing the isolation of six flavones. The minimal inhibitory concentration (MIC) of the hexanic extract, against Mycobacterium tuberculosis H37Rv was 25 μg/mL. The hexanic extract caused a significant inhibition of intracellular mycobacterial growth at 12.5 μg/mL. The biodirected assay of hexane extract enabled the detection of an active fraction (AF) against M. tuberculosis (MIC = 12.5 μg/mL), and a major flavone 1 (pebrellin) with no antimycobacterial activity (MIC > 200 μg/mL). A subsequent combination antimicrobial assay showed a synergistic antimycobacterial effect of AF in combination with pebrellin; the results of the synergistic activity suggest that the antimycobacterial activity found in T. angustifolia is due to the combined action of diverse metabolites present in the plant.     

Drug–tea polyphenol interaction

Propericiazine (PCZ) is an antipsychotic agent used for the treatment and the prevention of relapse of schizophrenia. We found that when an oral solution containing PCZ was mixed with a green tea drink, the residual content of PCZ was reduced by forming an insoluble complex between PCZ and tea polyphenol. In this study, the mechanism underlying the incompatibility of PCZ with green tea polyphenol (GTP) in the solution was clarified by isothermal titration microcalorimetry (ITC). Both solutions of 27.4 mM PCZ and 2.2 mM (?)-epigallocatechin gallate (EGCg), which is a main ingredient of GTP, were mixed and then PCZ in the filtrate was reduced to approximately 60 %. According to measurement at 298 K by ITC, PCZ formed an insoluble complex with EGCg at an associate constant (K) of 4.75 × 10² M^?1 exothermically, ΔH = ?40.0 kJ mol^?1. When (?)-epicatechin gallate (ECg) was used as the GTP, PCZ interacted with ECg with K and ΔH values of 3.74 × 10² M^?1 and ?22.1 kJ mol^?1, respectively. On the other hand, little heat of the reaction between PCZ and (?)-epigallocatechin or (?)-epicatechin was observed. The results indicated that the main reason for this incompatibility was the formation of an insoluble complex by PCZ and a gallate-type GTP such as EGCg and ECg in the aqueous solution.     

Determination of antioxidant activities in fruit juices based on rapid colorimetric measurement and characterisation of gold nanoparticles

A simple and green synthesis of gold nanoparticles (AuNPs) was achieved in tea solution and fruit juices with auric tetrachloride (HAuCl₄) without the addition of any other chemicals. Natural antioxidants present in tea leaves and fruit juices were able to reduce Au³⁺ ions to form AuNPs spheres with an average diameter of 22.9 ± 2.7 nm in the tea solution and 12.8 ± 2.4 nm in the orange juice. A colorimetric determination of antioxidant activities based on the formation of citrate-capped AuNPs has been developed. It was found that the colorimetric response of AuNPs was dependent on the concentration of antioxidants tested. As compared with the standard reference assay, i.e., the Folin–Ciocalteu method, the colorimetric method reported in this study showed a very good correlation (R² = 0.9996). The results indicate that the AuNPs-based colorimetric method provides a simple, effective and reliable measurement of the antioxidant capacity in the tested fruit juices.     

Composition and stability constants of copper(II) complexes with succinic acid determined by capillary electrophoresis

The advantage of capillary electrophoresis was demonstrated for studying a complicated system owing to the dependence of direction and velocity of the electrophoretic movement on the charge of complex species. The stability constants of copper(II) complexes with ions of succinic acid were determined by capillary electrophoresis, including the 1?:?2 metal to ligand complexes which are rarely mentioned. The measurements were carried out at 25 °C and ionic strength of 0.1, obtained by mixing the solutions of succinic acid and lithium hydroxide up to pH 4.2–6.2. It was shown that while pH was more than 4.5 the zone of copper(II) complexes with succinate moves as an anion. It is impossible to treat this fact using only the complexes with a metal-ligand ratio of 1?:?1 (CuL⁰, CuHL⁺). The following values of stability constants were obtained: log β(CuL) = 2.89 ± 0.02, log β(CuHL⁺) = 5.4 ± 0.5, log β(CuL₂^2?) = 3.88 ± 0.05, log β(CuHL₂^?) = 7.2 ± 0.3.     

Kinetics and mechanism of the substitution reactions of some monofunctional Pd(II) complexes with different nitrogen-donor heterocycles

Substitution reactions of five monofunctional Pd(II) complexes, [Pd(terpy)Cl]⁺ (terpy = 2,2′;6′,2″-terpyridine), [Pd(bpma)Cl]⁺ (bpma = bis(2-pyridylmethyl)amine), [Pd(dien)Cl]⁺ (dien = diethylenetriamine or 1,5-diamino-3-azapentane), [Pd(Me₄dien)Cl]⁺ (Me₄dien = 1,1,7,7-tetramethyldiethylenetriamine), and [Pd(Et₄dien)Cl]⁺ (Et₄dien = 1,1,7,7-tetraethyldiethylenetriamine), with unsaturated N-heterocycles such as 3-amino-4-iodo-pyrazole (pzI), 5-amino-4-bromo-3-methyl-pyrazole (pzBr), 1,2,4-triazole, pyrazole, pyrazine, and imidazole were investigated in aqueous 0.10 M NaClO₄ in the presence of 10 mM NaCl using variable-temperature stopped-flow spectrophotometry. The second-order rate constants k₂ indicate that the reactivity of the Pd(II) complexes decrease in the order [Pd(terpy)Cl]⁺ > [Pd(bpma)Cl]⁺ > [Pd(dien)Cl]⁺ > [Pd(Me₄dien)Cl]⁺ > [Pd(Et₄dien)Cl]⁺. The most reactive nucleophile of the heterocycles is pyrazine, while the slowest reactivity is with pyrazole. Activation parameters were determined for all reactions and negative entropies of activation, ΔS^≠, supporting an associative mode of substitution. The reactions between [Pd(bpma)Cl]⁺ and 1,2,4-triazole, pzI, and pzBr were also investigated by ¹H NMR to define the manner of coordination. These results could be useful for better explanation of structure-reactivity relationships of Pd(II) complexes as well as for the prediction of potential targets of Pd(II) complexes toward common N-heterocycles, constituents of biomolecules and different N-bonding pharmaceutical agents.     

Evaluation inhibitory activity of catechins on trypsin by capillary electrophoresis–based immobilized enzyme microreactor with chromogenic substrate

In this study, a capillary electrophoresis‐based online immobilized enzyme microreactor was developed for evaluating the inhibitory activity of green tea catechins and tea polyphenol extracts on trypsin. The immobilized trypsin activity and other kinetic parameters were evaluated by measuring the peak area of the hydrolyzate of chromogenic substrate S‐2765. The results indicated that the activity of the immobilized trypsin remained approximately 90.0% of the initial immobilized enzyme activity after 30 runs. The value of Michaelis–Menten constant (K_m) was (0.47 ± 0.08) mM, and the half‐maximal inhibitory concentration (IC₅₀) and inhibition constant (K_i) of benzamidine were measured as 3.34 and 3.00 mM, respectively. Then, the inhibitory activity of four main catechins (epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate) and three tea polyphenol extracts (green tea, white tea, and black tea) on trypsin were investigated. The results showed that four catechins and three tea polyphenol extracts had potential trypsin inhibitory activity. In addition, molecular docking results illustrated that epigallocatechin gallate, epicatechin gallate, epicatechin, and epigallocatechin were all located not only in the catalytic cavity, but also in the substrate‐binding pocket of trypsin. These results indicated that the developed method is an effective tool for evaluating inhibitory activity of catechins on trypsin.     

Li<Superscript>+</Superscript> ionic conduction properties on NaI doped with a small amount of LiBH<Subscript>4</Subscript>

In the present work, Li⁺ conductor is synthesized via small doping of LiBH₄ into “Li-free” compound (or solid solvent), NaI. The formation of solid solution between NaI and LiBH₄ is confirmed by XRD measurement, and the solubility limit of LiBH₄ exists between 6 to 13 mol%. The value of σ for 15NaI·LiBH₄ (6 mol% LiBH₄) showed 1.7 × 10^?6 S/cm at room temperature, which is comparable to that for LiI. From the plot of log σT vs. 1000/T, an activation energy for Li⁺ conduction in NaI is estimated to be 0.68 and 0.32 eV for heating and cooling cycle, respectively. The results of AC impedance measurement and DC polarization test indicate that Li⁺ plays a major role in ionic conduction in NaI regardless of the slight molar fraction of Li⁺. The present results suggest that the expansion in the material choice for solid solvent and other alkali halides can also work as a base material for Li⁺ ion conductors.     

Experimental and computational approaches to reveal the potential of Ficus deltoidea leaves extract as α-amylase inhibitor

Ficus deltoidea leaves extract are known to have good therapeutic properties such as antioxidant, anti-inflammatory and anti-diabetic. We showed that 50% ethanol-water extract of F. deltoidea leaves and its pungent compounds vitexin and isovitexin exhibited significant (p < 0.05) α-amylase inhibition with IC₅₀ (vitexin: 4.6 μM [0.02 μg/mL]; isovitexin: 0.06 μg/mL [13.8 μM] and DPPH scavenging with IC₅₀ (vitexin: 92.5 μM [0.4 μg/mL]; isovitexin: 0.5 μg/mL [115.4 μM]). Additionally, molecular docking analysis confirmed that vitexin has a higher binding affinity (-7.54 kcal/mol) towards α-amylase compared to isovitexin (?5.61 kcal/mol). On the other hand, the molecular dynamics findings showed that vitexin-α-amylase complex is more stable during the simulation of 20 ns when compared to the isovitexin-α-amylase complex. Our results suggest that vitexin is more potent and stable against α-amylase enzyme, thus it could develop as a therapeutic drug for the treatment of diabetes.     

Antioxidant Response of Stevia rebaudiana B. to Polyethylene Glycol and Paclobutrazol Treatments Under In Vitro Culture

This investigation was carried out with the aim of determining the effect of paclobutrazol (PBZ) (0 and 2 mg l^?1) and polyethylene glycol (PEG) (0, 2, 4 and 6 %?w/v of PEG 6000) treatments on antioxidant system of Stevia rebaudiana Bertoni under in vitro condition. Analysis of data showed that PEG treatment significantly increased hydrogen peroxide (H₂O₂) and phenolic contents, while PBZ treatment limited the effect of PEG on them. Our data revealed that PEG treatment significantly increased total antioxidant capacity, catalase (CAT), ascorbate peroxidase (APX), polyphenol oxidase (PPO) and peroxidase (POD) activity, while it inversely decreased glutathione reductase (GR) activity. The superoxide dismutase (SOD) activity was not affected by PEG treatment. PBZ treatment induced significantly higher levels of CAT and GR activity and lower levels of SOD activity in PEG-treated plants. PBZ in combination with PEG resulted in no significant difference on APX activity with PEG treatment alone. PBZ treatment prevented the effect of PEG on the PPO activity. PEG (with or without PBZ) treatment increased the ascorbate pool, whereas total glutathione level was not affected by PEG. Our finding indicated that PBZ reduced the negative effect of PEG treatment by quenching H₂O₂ accumulation and increasing the CAT activity. Collectively, the antioxidant capacity of S. rebaudiana in PEG treatment condition was associated with active enzymatic and non-enzymatic defence systems which partly could be improved by the PBZ treatment. In addition, a higher accumulation of phenolic compounds leads to a more potent reactive oxygen species scavenging activity in S. rebaudiana.     

Bioactive constituents from Croton sparsiflorus Morong

Whole plant extracts of Croton sparsiflorus in methanol have shown significant enzyme inhibition and antioxidant activities. Bioassay-guided isolation of chloroform fraction at pH 3 resulted in the identification of crotsparinine (1) and crotsparine (2), while sparsiflorine (3) was purified from the chloroform fraction at pH 9. The structures of the compounds were confirmed through spectral analyses (EI-MS, ¹H and ¹³C NMR). The isolated compounds 1–3 exhibited remarkable enzyme inhibition activity with IC₅₀ values 27.01 ± 1.1, 22.26 ± 1.0 and 18.02 ± 1.3 μM in xanthine oxidase and 48.42 ± 1.5, 48.05 ± 1.4 and 7.42 ± 1.0 μM in acetylcholine esterase assays, respectively. These compounds also showed potent radical scavenging and reducing properties in DPPH and FRAP assays, respectively. The present results suggest the validity of the traditional uses of C. sparsiflorus in rheumatism and gout. Furthermore, the isolated noraporphine alkaloids can be useful in the treatment of neurodegenerative diseases.     

Biologically Active Constituents from Salix viminalis Bio-Oil and Their Protective Activity Against Hydrogen Peroxide-Induced Oxidative Stress in Chinese Hamster Ovary Cells

The protective antioxidative effect of the phenolic extract (PE) isolated from Salix viminalis pyrolysis derived bio-oil was shown in vitro on the Chinese hamster ovary (CHO) cells exposed to hydrogen peroxide (H₂O₂). Cells pretreated with 0.05 μg/ml PE after exposure to different concentrations of H₂O₂ (300–900 μM) showed up to 25 % higher viability than the unpretreated ones. The antioxidative effect of PE was also observed in a time-dependent manner. The results were confirmed by visual examination of the specimens using microscopy. Finally, superoxide dismutase (SOD) activity modulation was shown by SOD assay, designed to determine the activity of enzymes removing free radicals.     

Host–guest interaction of hemicucurbiturils with phenazine hydrochloride salt

The host–guest interactions between phenazine hydrochloride salt (PheH⁺) and hemicucurbit[n]uril (n = 6 or 12) (HemiQ[6 or 12]) have been studied by ¹H NMR, UV–vis, IR, mass spectrometry (MS) and quantum chemistry. In ¹H NMR spectra, the broadening of proton resonances of the hosts suggests the interactions of PheH⁺ with HemiQs. The quantitative stabilities of the host–guest systems have been obtained by UV–vis titration experiments, that is, the stoichiometric interactions of PheH⁺ with HemiQ[6] have been observed with an association constant of K_a = (2.5 ± 1.2) × 10⁶ L mol^? 1, while the 2:1 ratio complexes of PheH⁺ with HemiQ[12] are formed with stepwise association constants of K₁ = (9.2 ± 2.8) × 10⁴ L mol^? 1 and K₂ = (6.4 ± 0.9) × 10⁵ L mol^? 1, respectively, which induce a total association constant of K_a = 5.9 × 10¹⁰ L² mol^? 2. Both the 1:1 and 2:1 complexes have been detected by MS. Quantum chemistry calculations have been used to understand the static structures and thermodynamic stabilities of the supramolecular assemblies.