Carbon quantum dots from hemicucur[6]bit and the application for the detection of Pb2.

A macrocyclic compound, hemicucurbit[6]uril (HemiQ[6]), is employed as the carbon source to produce a novel sort of carbon quantum dots (CQDs) with blue fluorescence in aqueous solution. The CQDs are fully identified by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Nuclear Magnetic Resonance (NMR), zeta potential, ultraviolet/visible (UV-vis) and photoluminescence spectroscopy (PL). The nanomaterial is developed for the analysis of Pb2+ in the light of the Resonance Rayleigh scattering (RRS) changes with the increasing Pb2+ concentration. The proposed probe emerges a high selectivity to Pb2+ and excellent sensitivity in the linear concentration range of 0-6 µM with a detection limit low to 0.42 µM, which is superior to the previous values of Pb2+ sensors, as well as the good anti-interference ability is confirmed by the specifical response to Pb2+ in the presence of other metal cations. Therefore, the proposed analysis of Pb2+ is explored for the application in real samples of tap water and lake water, in satisfied results of acceptable recoveries.

Selective removal of Cr2O72- in aqueous solution by nonporous pure crystals of cucurbit[6]uril.

Cucurbit[6]uril (Q[6]) could serve as a selective absorbent for the toxic anion Cr2O72-, which was demonstrated by the results of UV-vis, ICP, XPS, SEM, and EDS experiments. Single-crystal X-ray diffraction analysis revealed that capture capacity could be attributed to the outer-surface interactions of cucurbit[n]uril between Cr2O72- and the outer surface of Q[6].

Supramolecule-Controlled Enantioselectivity for Electrochemical Asymmetric Hydrogenation of Coumarins with a Chiral Macrocyclic Compound.

The supramolecular strategy was subjected to the asymmetric hydrogenation of 4-methylumbelliferone by electrochemical reduction in the presence of a chiral macrocyclic multifarane[3,3], which offered a l-7-hydroxy-4-methylchroman-2-one product with a chemical yield of 65% and enantioselectivity up to >99% ee. The high stability of the developed chiral supramolecular electrode guaranteed the recyclability and repeatability in the electrolysis, and therefore, the application was extended to more coumarin derivatives to provide satisfactory chemical yields and enantioselectivities.

Recent Breakthroughs in Supercapacitors Boosted by Macrocycles.

Supercapacitors are essential for electrochemical energy storage because of their high-power density, good cycle stability, fast charging and discharging rates, and low maintenance cost. Macrocycles, including cucurbiturils, calixarene, and cyclodextrins, are cage-like organic compounds (with a nanocavity that contains O and N heteroatoms) with unique potential in supercapacitors. Here, we review the applications of macrocycles in supercapacitor systems, and we illustrate the merits of organic macrocycles in electrodes and electrolytes for improving the electrochemical double-layer capacitors and pseudocapacitance via supramolecular strategies. Then, the observed relationships between electrochemical performance and macrocyclic structures are introduced. This comprehensive review describes recent progress on macrocycle-block supercapacitors for researchers.

Highly selective recognition of the Al(ClO4)3 molecule by a mono-pyrene substituted thiacalix[4]arene chemosensor.

A mono-pyrene substituted thiacalix[4]arene chemosensor (TCA-Py) was successfully synthesized in satisfactory yield. Fluorescence analysis revealed that TCA-Py exhibited a high recognition selectivity toward the Al(ClO4)3 molecule due to the synergy between the Al3+ cation and ClO4- anion. This unique ability to recognise an entire inorganic molecule broadens the field of molecular recognition.

Quantitatively Switchable pH-Sensitive Photoluminescence of Carbon Nanodots.

pH sensing plays a key role in the life sciences as well as the environmental, industrial, and agricultural fields. Carbon nanodots (C-dots) with small size, low toxicity, and excellent stability hold great potential in pH sensing as nanoprobes due to their intrinsic pH-sensitive photoluminescence (PL). Nonetheless, the undesirable sensitivity and response range of C-dot PL toward pH cannot meet the requirements of practical applications, and the unclear pH-sensitive PL mechanism makes it difficult to control their pH sensitivity. Herein, the quantitative correlation of pH-sensitive PL with specific surface structures of C-dots is uncovered for the first time, to our best knowledge. The association of carboxylate and H+ increases the ratio of nonradiation to radiation decay of C-dots through excited-state proton transfer, resulting in the decrease of PL intensity. Meanwhile, the dissociation of α-H in ß-dicarbonyl forming enolate increases the extent of delocalization of the C-dots conjugated system, which induces the PL broadening to the red region and a decreasing intensity. Based on the understanding of the pH-sensitive PL mechanism, the pH-sensitive PL of C-dots can be switched by quantitative modulation of carboxyl and ß-dicarbonyl groups to achieve a desirable pH response range with high sensitivity. This work contributes to a better understanding of the pH-sensitive PL of C-dots and therefore presents an effective strategy for controllably tuning their pH sensitivity, facilitating the rational design of C-dot-based pH sensors.

Molecular Tweezers-like Calix[4]arene Based Alkaline Earth Metal Cation (Ca2+, Sr2+, and Ba2+) Chemosensor and Its Imaging in Living Cells and Zebrafish.

Although alkaline earth metal cations play an important role in our daily life, little attention has been paid to the field of fast quantitative analysis of their content due to a lack of satisfactory precision and a fast and convenient means of detection. In this study, we have designed a set of molecular tweezers based on the calix[4]arene chemosensor L, which was found to exhibit high selectivity and sensitivity toward Ca2+, Sr2+, and Ba2+ (by UV-vis and fluorescence methods) with low detection limits of the order of 10-7 to 10-8 M and high association constants (of the order of 106). More significantly, sensor L not only can recognize Ca2+, Sr2+, and Ba2+ but also can further discriminate between these three cations via the differing red shifts in their UV-vis spectra (560 nm for L·Ca2+, 570 nm for L·Sr2+, and 580 nm for L·Ba2+ complex) which is attributed to their different atomic radii. A rare synergistic effect for the recognition mechanism has been demonstrated by 1H NMR spectroscopic titration. Sensor L constructed a high shielding field by the cooperation of Tris with alkaline earth metal ion after complex. Additionally, the presence of acetoxymethyl group in sensor L results in enhancement of cell permeability, and as a consequence, sensor L exhibited excellent sensing and imaging (in vivo) in living cells and in zebrafish.

An efficient ICT-based ratio/colorimetric tripodal azobenzene probe for the recognition/discrimination of F-, AcO- and H2PO4- anions.

The tripodal probe L was readily prepared via introducing rhodamine and azobenzene groups in a two-step procedure. Studies of the recognition properties indicated that probe L exhibited high sensitivity and selectivity towards F-, AcO- and H2PO4- through a ratiometric colorimetric response with low detection limits of the order of 10-7 M. The complexation behaviour was fully investigated by spectral titration, 1H NMR spectroscopic titration and mass spectrometry. Probe L not only recognizes F-, AcO- and H2PO4-, but can also distinguish between these three anions via the different ratiometric behaviour in their UV-vis spectra (387/505 nm for L-H2PO4-, 387/530 nm for L-AcO- and 387/575 nm for L-F- complex) or via different colour changes (light coral for L-H2PO4-, light pink for L-AcO- and violet for the L-F- complex). Additionally, given the presence of NH and OH groups in probe L, which can be protonated and deprotonated, probe L further exhibited an excellent pH response over a wide pH range (pH 3 to pH 12).

Recognition of silver cations by multifarene[2,2] chemosensors with unexpected fluorescence response.

Fluorescent chemosensors based on a new macrocyclic compound, multifarene[2,2], with modification by triazole-linked pyrene or anthracene were synthesized. These macrocyclic sensors exhibited high affinity and selectivity toward Ag+ over other metal ions, with ratiometric or enhanced response of their fluorescence emissions depending upon the substituent species for coordination to Ag+, and an unexpected response to a concentration threshold of the metal cations was discovered. The experimental evidences of fluorescence spectra, 1H NMR titration, IR spectra, and high-resolution mass spectra suggested the coordination behaviors of the sensors with Ag+, that is, the 1:1 complexes were formed with moderate association constants of about 105 L·mol-1, and the sulfur atoms on macrocyclic ligand should affinite to the metal cations. Energy-minimized structures and frontier orbitals were estimated by quantum chemical calculations with a view to rationalizing the fluorescence response of the multifarene[2,2] sensors upon binding to Ag+.

A three-dimensional (time, wavelength and intensity) functioning fluorescent probe for the selective recognition/discrimination of Cu2+, Hg2+, Fe3+ and F- ions.

We have strategically incorporated three different fluorophores at tren to construct a multi-energy donor/acceptor "smart" probe L. This probe operates by using three-dimensional scales (response time, wavelength and fluorescence intensity) which allows for the selective recognition and discrimination of the Cu2+, Hg2+, Fe3+ and F- ions.

Coordination supramolecular assemblies of a monohydroxycucurbit[7]uril and their potential applications in gas sorption.

Coordination supramolecular assemblies of monohydroxycucurbit[7]uril ((HO)Q[7]) with alkaline earth metal ions (AE2+) have been formed in aqueous HCl solution in the presence of tetrachloride cadmium anions ([CdCl4]2-) as a structure directing agent. The driving force for the assembly could be attributed to the interaction of the positive electro-potential outer-surface of (HO)Q[7] molecules with [CdCl4]2- anions and ionic dipole interaction of the hydroxyl of (HO)Q[7] molecules with [CdCl4]2- anions. Moreover, the porous structure of the (HO)Q[7]/AE2+-based coordination supramolecular assemblies could result in potential applications in the selective sorption of polar volatile organic molecules, which may be useful in molecular sieves, sensors, absorption and separation.

Highly selective recognition of Al3+ and I- ions using a bi-functional fluorescent probe.

A tripodal fluorescent probe L1 armed with Rhodamine B and 1-naphthaleneisothiocyanates was prepared in high yield. A study of the recognition properties revealed that probe L1 exhibited high sensitivity and selectivity towards Al3+ through a "FRET" fluorescence response and colorimetric response with low detection limits of the order of 10-8 M. Meanwhile, probe L1 also possessed high recognition ability for I- through fluorescence decay, which given there are comparatively few selective fluorescent probes for I-, is significant. Furthermore, the complexation mechanisms were fully investigated by spectral titrations, 1H NMR spectroscopic titrations and mass spectrometry. The utility of probe L1 as a biosensor in living cells (PC3 cells) towards Al3+ ions has also been demonstrated.

A novel fluorescence "on-off-on" chemosensor for Hg(2+)via a water-assistant blocking heavy atom effect.

Upper rim pyrene-functionalized hexahomotrioxacalix[3]arene L was synthesized via Click chemistry, and its fluorescence behaviors toward several common metal cations were investigated. L exhibited a significant fluorescence quenching response to Hg(2+) in CH3CN solution, which was unaffected by the coexistence of other competitive metal cations. Thus, L can be utilized as a highly selective and sensitive fluorescent chemosensor for Hg(2+) with a detection limit in the nM level. Interestingly, the quenched fluorescence emission can be successfully revived upon the addition of water. In this process, the heavy atom effect of Hg(2+) can be blocked by further coordination of a water molecule and resulted in the revival of the fluorescence emission of L/Hg(2+) complex. Particularly, other polar solvents such as CH3OH and CH3CH2OH also have the ability to revive the fluorescence emission of the L/Hg(2+) complex, but on a much smaller scale than observed for H2O. The heavy atom effect and blocking thereof were demonstrated within the same system by the use of a C3-symmetric homooxacalix[3]arene scaffold. The present studies provided further evidence for the blocking heavy atom effect.

Click-modified hexahomotrioxacalix[3]arenes as fluorometric and colorimetric dual-modal chemosensors for 2,4,6-trinitrophenol.

A new type of chemosensor-based approach to the detection of 2,4,6-trinitrophenol (TNP) is described in this paper. Two hexahomotrioxacalix[3]arene-based chemosensors 1 and 2 were synthesized through click chemistry, which exhibited high binding affinity and selectivity toward TNP as evidenced by UV-vis and fluorescence spectroscopy studies. (1)H NMR titration analysis verified that CH⋯O hydrogen bonding is demonstrated as the mode of interaction, which possibly facilitates effective charge-transfer.

An Unprecedented Photochemical Reaction for Anthracene-Containing Derivatives.

A series of anthracene-containing derivatives have been synthesised and characterised. The photochemical behaviour of these derivatives have been investigated by 1 H NMR spectroscopy. An unprecedented photolysis reaction for anthracene-containing derivatives was observed in the case of anthracenes directly armed with a -CH2 O-R group upon UV irradiation. The photolysis reaction process has been demonstrated to occur in three steps. Firstly, the anthracene-containing derivatives are converted into the corresponding endoperoxide intermediate upon UV irradiation in the presence of air; then, the endoperoxide intermediate is decomposed to the corresponding starting compound and 9-anthraldehyde; finally, 9-anthraldehyde is further oxidised to anthraquinone. Additionally, the photolysis reaction of anthracene-containing derivatives is significantly promoted in the presence of a thiacalix[4]arene platform.

A Rare and Exclusive Endoperoxide Photoproduct Derived from a Thiacalix[4]arene Crown-Shaped Derivative Bearing a 9,10-Substituted Anthracene Moiety.

A rare and exclusive endoperoxide photoproduct was quantitatively obtained from a thiacalix[4]arene crown-shaped derivative upon irradiation at λ=365 nm; the structure was unambiguously confirmed by (1) H/(13) C NMR spectroscopy and X-ray crystallography. The prerequisites for the formation of the endoperoxide photoproduct have also been discussed. Furthermore, the photochemical reaction rate could be greatly enhanced in the presence of the thiacalix[4]arene platform because it served as a host to capture oxygen.

Manganese coordination chemistry of bis(imino)phenoxide derived [2 + 2] Schiff-base macrocyclic ligands.

The [2 + 2] Schiff-base macrocycles [2,2'-(CH2CH2)(C6H4N[double bond, length as m-dash]CH)2-2,6-(4-RC6H2OH)]2 ((R)H2), upon reaction with MnCl2 (two equivalents) afforded the bimetallic complex [Cl3Mn(µ-Cl)Mn((Me)H2)] (1) or the salt complex [Cl3Mn(NCMe)][MnCl((tBu)H2)] (2). Under similar conditions, use of the related [2 + 2] oxy-bridged macrocycle [2,2'-O(C6H4N[double bond, length as m-dash]CH)2-4-RC6H2OH] (II(R)H2), afforded the bimetallic complexes [(MnCl)2II(R)] (R = Me 3, tBu 4), whilst the macrocycle derived from 1,2-diaminobenzene and 5,5'-di-tert-butyl-2,2'-dihydroxy-3,3'-methylenedibenzaldehyde (H4) afforded the complex [(MnCl)2(III)]·2MeCN (5·2MeCN). For comparative studies, the salt complexes [2,6-(ArNHCH)2-4-MeC6H2O][MnCl3(NCMe)] (Ar = 2,4-Me2C6H3, 6) and {[(2-ArN[double bond, length as m-dash]CH),6-(ArNHCH)-4-Me-C6H2O]MnCl}2[MnCl4]7·8CH2Cl2 (Ar = 4-MeC6H4, ·8CH2Cl2) were prepared. The crystal structures of 1 - 7 are reported (synchrotron radiation was necessary for complexes 1, 3 and 5). Complexes 1 - 7 (not 5) were screened for their potential to act as pre-catalysts for the ring opening polymerization (ROP) of ε-caprolactone; 3, 4 and 6, 7 were inactive, whilst 1 and 2 exhibited only poor activity with low conversion (<15%) at temperatures above 60 °C.

The first study about the relationship between the extractability of thiacalix[4]arene derivatives and the position of the coordination binding sites.

Three organic ionophores (2-4) based on the p-tert-butylthiacalix[4]arene backbone, blocked in the 1,3-alternate conformation, bearing two pyridyl coordinating moieties (ortho for 2, meta for 3 and para for 4), have been synthesized and characterized in the solid state. The solvent extraction experiments with the metal ions showed that the ability of these derivatives to complex with Ag(+) appeared to be largely dependent on the position of the nitrogen atoms of the pyridyl ring. Two different complexation modes have been confirmed by 1H NMR titration. Ionophore 2 armed with two pyridyl moieties, complexed with Ag(+) cation through N···Ag(+)···S interactions; however, ionophore 3 and ionophore 4 complexed with Ag(+) through metal-nitrogen (N···Ag(+)) interactions. The DFT computational studies were consistent with the experimental findings. These findings will provide us with an important rule to design an appropriate thiacalix[4]arene ionophore in the future. Another study on the possibility for application of ionophores 2-4 for the treatment of waste water containing Cr(VI) and Cr(III), showed that ionophore 3 was useful in the application of the solvent extraction method in selective treatment of waste water containing Cr(VI) and Cr(III) prior to discharge.

Efficient production of flavonoids in Fagopyrum tataricum hairy root cultures with yeast polysaccharide elicitation and medium renewal process.

BACKGROUND: Tartary buckwheat (Fagopyrum tataricum), an excellent edible and medicinal crop, has been widely used as a daily diet and traditional medicine for a long time. The major functional components of Fagopyrum tataricum have been demonstrated to be flavonoids (i.e. rutin and quercetin), which had notable andioxidant, antidiabetic, hypocholesterolemic and antitumor activities. Hairy root culture is a convenient and efficient plant tissue culture system for large scale production of bioactive metabolites. OBJECTIVE: To enhance the functional flavonoids production in hairy root culture of F. tataricum. MATERIALS AND METHODS: The elicitation treatment in combination with medium renewal strategy was applied for efficient promoting flavonoids production in F. tataricum hairy root cultures. RESULTS: The exogenous yeast polysaccharide (YPS) elicitor notably stimulated the functional metabolites production in F. tataricum hairy root cultures, and the stimulation effect was concentration-dependent. Combination with the YPS elicitation (200 mg/L) and medium renewal process, the maximal flavonoids yield was enhanced to 47.13 mg/L, about 3.2-fold in comparison with the control culture of 14.88 mg/L. Moreover, this research also revealed the accumulation of these bioactive metabolites resulted from the stimulation of the phenylpropanoid pathway by YPS treatment. These results indicated that the F. tataricum hairy root culture could be an effective system for rutin and quercetin production.

Response surface modeling and optimization of ultrasound-assisted extraction of three flavonoids from tartary buckwheat (Fagopyrum tataricum).

BACKGROUND: Buckwheat (Fagopyrum spp., Polygonaceae) is a widely planted food crop. Flavonoids, including quercetin, rutin, and kaempferol, are the main bioactive components in tartary buckwheat (Fagopyrum tataricum (L.) Gaertn). From the nutriological and pharmacological perspectives, flavonoids have great value in controlling blood glucose and blood pressure levels, and they also have antioxidant properties. OBJECTIVE: To optimize the conditions for extraction of quercetin, rutin, and kaempferol from F. tataricum. MATERIALS AND METHODS: A combination of ultrasound-assisted extraction (UAE) and response surface methodology (RSM) was used for flavonoid extraction and yield assessment. The RSM was based on a three-level, three-variable Box-Behnken design. RESULTS: Flavonoids were optimally extracted from F. tataricum by using 72% methanol, at 60°C, for 21 minutes. Under these conditions, the obtained extraction yield of the total flavonoids was 3.94%. CONCLUSION: The results indicated that the UAE method was effective for extraction of flavonoids from tartary buckwheat.