Cryptate Complex Research Articles

Reversible CO2 Fixation and Release by a Trinuclear Zn(II) Cryptate Complex and Operando Analysis of the Complex Structure.

Metal complexes inspired by carbonic anhydrase (CA), which is a metalloenzyme containing Zn(II), have been investigated as alternatives for CO2 fixation systems operating under ambient temperature and pressure conditions. In this study, we designed a trinuclear Zn(II) cryptate complex (Zn3L) and demonstrated rapid CO2 fixation with carbonation of CO2 using Zn3L. The CO2 fixation performance of Zn3L surpassed that of a standard CO2 absorbent (KOH(aq) solution) under conditions of the same solute concentration. In addition, the reaction achieved operation without support with addition of a base, which has been often required in systems of CA-inspired complexes. Fixed CO2 was released by protonating polyazacryptate ligand (L) and breaking the complex structure, and deprotonation of L induced the reconstruction of Zn3L, allowing it to refix CO2. This reaction mechanism was proposed based on the analysis of operando extended X-ray absorption fine structure spectroscopy. Zn3L also demonstrated the ability to capture dilute CO2 from air, and the volume of CO2 captured by Zn3L was approximately 2.6 times that captured by the KOH(aq) solution. Our Zn3L exhibited three valuable properties: rapid CO2 fixation without a base, reversibility, and ability to capture dilute CO2; thus Zn3L is a promising candidate as CO2 fixatives.

A theoretical mechanistic study of [K ⊂ [2.2.2]]+ enantiomerization

AbstractDensity functional calculations at three different levels of theory (B3LYP/LANL2DZp, B3LYP‐GD3/LANL2DZp, and ωB97XD/def2tzvp) were applied to different conformers of the Lehn‐type macrobicyclic polyether cryptate complex [K ⊂ [2.2.2]]+ to construct the enantiomerization pathway and to compute the energy barrier for the change in symmetry. Changes in the conformation of the investigated complex are discussed in terms of energy and geometric criteria, where changes in the structures follow a trend of activation energies prohibiting the achiral pathways. The investigated D3‐symmetric cryptate [K ⊂ [2.2.2]]+ shows enantiomerization through an all chiral five step pathway with two local minima (C2 and C2′) and three C1 transition states ending in the D3′‐symmetric cryptate [K ⊂ [2.2.2]]+, the mirror image of the starting structure. The potential achiral transition states are higher order saddle points with a minimum twice as high in energy as an all‐chiral path. This study unambiguously accounts for Lehn's NMR data showing fluxionality of the studied complex. The obtained results were further rationalized by means of energy decomposition analysis (EDA) and natural bond orbital (NBO) calculations performed for the metal cation and the host in its different conformations.

Understanding the Stabilization and Tunability of Divalent Europium 2.2.2B Cryptates.

Lanthanides such as europium with more accessible divalent states are useful for studying redox stability afforded by macrocyclic organic ligands. Substituted cryptands, such as 2.2.2B cryptand, that increase the oxidative stability of divalent europium also provide coordination environments that support synthetic alterations of Eu(II) cryptate complexes. Two single crystal structures were obtained containing nine-coordinate Eu(II) 2.2.2B cryptate complexes that differ by a single coordination site, the occupation of which is dictated by changes in reaction conditions. A crystal structure containing a [Eu(2.2.2B)Cl]+ complex is obtained from a methanol-THF solvent mixture, while a methanol-acetonitrile solvent mixture affords a [Eu(2.2.2B)(CH3OH)]2+ complex. While both crystals exhibit the typical blue emission observed in most Eu(II) containing compounds as a result of 4f65d1 to 4f7 transitions, computational results show that the substitution of a Cl- anion in the place of a methanol molecule causes mixing of the 5d excited states in the Eu(II) 2.2.2B cryptate complex. Additionally, magnetism studies reveal the identity of the capping ligand in the Eu(II) 2.2.2B cryptate complex may also lead to exchange between Eu(II) metal centers facilitated by π-stacking interactions within the structure, slightly altering the anticipated magnetic moment. The synthetic control present in these systems makes them interesting candidates for studying less stable divalent lanthanides and the effects of precise modifications of the electronic structures of low valent lanthanide elements.

The development of a wash-free homogeneous immunoassay method for the detection of tetracycline in environmental samples.

Antibiotic residues have become the major source of environmental pollutants. In order to monitor tetracycline (TC) in the environment, we have established a highly sensitive and wash-free homogeneous time-resolved immunoassay. This analytical method was based on a rare earth chelate with excellent fluorescence properties. The cryptate organic ligand had good stability and acted as an antenna for Eu3+ excitation. In a homogeneous system, the Eu3+ cryptate complex was used as a label to bind to antibodies. Under the action of immunoaffinity, fluorescent donors and acceptors were close to each other, which induced the FRET effect to produce proportional fluorescence. Under the optimal parameters, the half-inhibitory concentration (IC50) and limit of detection (LOD, IC10) of TC were 0.4188 ng mL-1 and 0.0106 ng mL-1, respectively. The linear range (IC20-IC80) was 0.0273-9.2645 ng mL-1. With the environmental samples, the recovery rate of TC was 84.3-107.2%, and the standard deviation (RSD) was 4.6-12.9%. The results showed the good sensitivity and reliability of the method. Compared with the traditional ELISA, our method has less background interference, only one step was required without the washing procedure, and the detection result can be obtained by 30 min incubation, which improves the detection efficiency. Because of the characteristics of immunoassays, different pollutants can be monitored by changing the antibodies. This method provides an alternative path for detecting environmental pollutants and has the potential to develop into an on-site detection kit.

Phenol Reduces Nitrite to NO at Copper(II): Role of a Proton-Responsive Outer Coordination Sphere in Phenol Oxidation.

In the view of physiological significance, the transition-metal-mediated routes for nitrite (NO2-) to nitric oxide (NO) conversion and phenol oxidation are of prime importance. Probing the reactivity of substituted phenols toward the nitritocopper(II) cryptate complex [mC]Cu(κ2-O2N)(ClO4) (1a), this report illustrates NO release from nitrite at copper(II) following a proton-coupled electron transfer (PCET) pathway. Moreover, a different protonated state of 1a with a proton hosted in the outer coordination sphere, [mCH]Cu(κ2-O2N)(ClO4)2 (3), also reacts with substituted phenols via primary electron transfer from the phenol. Intriguingly, the alternative mechanism operative because of the presence of a proton at the remote site in 3 facilitates an unusual anaerobic pathway for phenol nitration.

An Automatic Molecular Dispenser of Chloride

The combined activity of the 1.1.1-cryptand and of a dicopper(II) bistren cryptate complex including chloride makes the Cl(-) ion be continuously and slowly delivered to the solution, without any external intervention. The 1.1.1-cryptand slowly releases OH(-) ions, according to a defined kinetics, and each OH(-) ion displaces a Cl(-) ion from the cryptate. Chloride displacement induces a sharp colour change from bright yellow to aquamarine and can be conveniently monitored spectrophotometrically, even in diluted solutions. The 1.1.1-cryptand is the motor of a molecular dispenser (the dicopper(II) cryptate) delivering chloride ion automatically, from the inside of the solution.

The unprecedented role of a CuII cryptand in the luminescence properties of a EuIII cryptate complex

A EuIII cryptate complex constructed from a CuII cryptand with an L tBu ligand, [EuIIICu 2 II (L tBu)2(NO3)3(MeOH)], and the corresponding CaII and NaI cryptates, [CaIICu 2 II (L tBu)2(NO3)2(MeOH)2] and [NaICu 2 II (L tBu)2(Me2CO)](BPh4), have been synthesized and characterized in order to shed light on the essential role of CuII in the luminescence of a EuIII cryptate. The unprecedented role of a CuII cryptand makes it possible to produce lanthanide luminescence in a EuIII cryptate complex and is successfully elucidated by comparison with the corresponding CaII and NaI cryptates.

Halide ion inclusion into a dicopper(II) bistren cryptate containing ‘active’ 2,5-dimethylfuran spacers: The origin of the bright yellow colour

The inclusion of halide ions into a dicopper(II) bistren cryptate complex containing 2,5-dimethylfuran spacers has been investigated through spectrophotometric titration experiments in MeCN solution. X-ray diffraction studies on the 1:1 chloride inclusion complex have shown that the encapsulated halide ion and the furan oxygen atoms lie at an interacting distance. Such an interaction perturbs the energy of the halide-to-copper(II) charge transfer transition, which is shifted to the visible region. As a consequence, an intense yellow colour develops on halide inclusion. Such a colour change is not observed on chloride or bromide inclusion into the dicopper(II) bistren cryptate containing spacers which are not capable to interact with the encapsulated halide and do not perturb the charge transfer transition, e.g. 1,3-xylyl fragments.

Barium induced modulation of NIR emission in a neodymium cryptate complex

The complex [NdL](III) is based upon a crown ether-appended ditopic cryptate ligand and demonstrates a near-infrared fluorescence response to Ba(II).

Ion Exchange Separation of Lead from Strontium in Certified Reference Samples and Spectrophotometric Determination of Lead as Extractable Ion-Pair of Eosin2−and the Lead–Cryptand (2.2.2)2+Complex

Abstract A two-step procedure including anion exchange separation of lead from strontium in geological reference samples and a spectrophotometric determination of the separated lead as lead–cryptate (2.2.2) complex is presented. The exchangeable anion Cl− of the ion exchange resin (Dowex 1 × 4) is changed to Br− in 6 M HBr solution. Lead is quantitatively retained in the column from 0.5 M HBr medium, while Sr2+, Ba2+, Ca2+, Mg2+, Na+, K+, Fe3+, Cr3+, and Al3+ are passed through. Subsequently the retained Pb is eluted from the column with 6 M HBr. The separation efficiency of the resin is controlled using mixed standard solution of (Pb, Sr, Ca, Mg, Ba, Na, K, Fe, Cr and Al), and radioactive tracers of 85Sr and 131Ba. The resin selectivity coefficient (K) of separating Pb from Sr is found to be . The Spectrophotometric method of lead determination is based on the formation of lead–cryptate (2.2.2) complex at pH 8.3 using borate/HCl as a buffer solution. Then the ion-pair of eosin2+ and lead–cryptand (2.2.2)...

Coordination properties of a polyamine cryptand with two different binding moieties. A case of a pH-modulated antenna device based on a new Eu(III) cryptate complex.

Protonation and alkali- and alkaline-earth-metal coordination by the dipyridine-containing cryptand L have been studied by means of potentiometric and spectroscopic (UV-vis, (1)H NMR) measurements in aqueous solutions. This ligand is constituted by an aliphatic polyamine chain and a coordinating cleft, delimited by two dipyridine units, where the metal ion is lodged. The resulting complexes are characterized by an unusually high stability. The polyamine chain is not involved, or weakly involved, in metal coordination, and facile protonation can occur on the nitrogen atoms of this moiety. Similar coordination features are found in the Eu(III) complex. A fluorescence emission study reveals that the Eu(III) cryptate shows the characteristic visible emission of the metal, due to the intramolecular energy transfer to the metal ion mainly from the lower energy triplet state of the cryptand. On the other hand, the emission intensity is modulated by pH, giving a maximum at neutral pH and decreasing at both acidic and alkaline pH values.

NMR observation of hydrolysis of acetonitrile to acetamide catalyzed by binuclear silver cryptate

NMR analyses (TOCSY, HMQC and DOSY) indicate that, in the presence of water, acetonitrile is exclusively hydrolyzed to acetamide catalyzed by bisilver cryptate complex, which contains coordinating acetonitrile molecule.

PH Modulation of the luminescence emission of a new europium cryptate complex

The luminescence emission of a new dipyridyl-containing Eu(III) cryptate complex is modulated by pH, due to protonation of the polyamine chain strategically inserted within the ligand backbone.

Synthesis and crystal structure of the cryptate complex [Gd(L) (DMF)] · KSCN · CH 3CN · 3H20 (L is a deprotonated phenol-based N 80 3 cryptand)

The cryptate complex [Gd(L)(DMF)] ·d KSCN ·d CH 3CN ·d 3H 20 has been synthesized by the reaction of gadolinium isothiocyanate and potassium thiocyanate with cryptate [Na(H 2L)], which was prepared by a (2 + 3) Schiff-base condensation of tris(2-aminoethyl)amine and 2,6-diformyl-4-methoxyphenol in the presence of NaOH. The Gd atom is encapsulated in the cryptand with an unsymmetric eight-coordinate environment.

Light Harvesting Molecular Assemblies in the Design of Highly Luminescent Sol-Gel Derived Glasses

ABSTRACTSol-gel derived molecular composites exhibiting intense luminescence, induced from efficient energy transduction processes, have been prepared. The composites are comprised of an Eu3+⊂ 2.2.1 cryptate complex or native Eu3+ ion embedded in sol-gel derived titania glass films. The titania glasses contain interconnected porous networks that permit the diffusion of exogenous substrates, such as the salts of benzoic and 4-tert-butylbenzoic acids, through the film. Interaction of the substrate with the embedded lanthanide complex is indicated by enhanced luminescence from the lanthanide ion. The carboxylic acid salts whose electronic excited states are produced upon capture of incident photons, undergo facile transfer of their electronic energy to the lanthanide ion. By monitoring europium ion luminescence, the diffusion constants of the benzoate and 4-tert-butylbenzoate salts have been measured. Although the diffusion of the 4-tert-butylbenzoate is slower than that of benzoate, the overall higher sensitivity of the former is consistent with hydrophobic guest-host interactions. These new molecular composites relying on the immobilization of an absorption-energytransfer- emission molecular assembly in porous, optically transparent ceramic glasses may be useful in the design of practical sensing devices.

Template synthesis of a novel macrobicyclic ligand and the crystal structure of its unique dinuclear copper(I) complex

The condensation of a tris(3-aminopropyl)amine with benzene-1,3-dicarbaldehyde in the presence of AgNO3 produces the dinuclear silver(I) complex of an octa-aza hexa Schiff's base macrobicyclic ligand, which is converted to a unique dinuclear copper(I) hexa Schiff's base cryptate complex by transmetallation.

Solvent dependence of kinetics and equilibria of thallium(I) cryptates in relation to the free energies of solvation of thallium(I)

Stability constants and dissociation rate constants of thallium (I) cryptates have been measured in several solvents at 25 °C. The Tl+ cryptates are more stable and less sensitive to ligand cavity size than the corresponding complexes of the alkali-metal cations. The stability constants vary strongly with solvent, and the solvent dependence of the complex stabilities appears to reflect mainly changes in the solvation of Tl+. It is shown that free energies of transfer of the solvated Tl+ among non–aqueous solvents calculated on the assumption that the difference in the free energies of transfer of the Tl+ cryptates and the corresponding cryptands is zero are in good agreement with literature data. Changes in the stability constants with solvent and ligand are reflected in changes in both dissociation and formation rate constants, but more so in the former. Thus the solvation of the transition state, (Tl+⋯Cry)[graphic omitted], is rather closer to that of the reactants, and includes additional solvent interactions compared with the stable cryptate complex, TlCry+.

Study of Strontium Extraction as a Cryptate Complex for Separation of Element 102 from the Actinides

Study of Strontium Extraction as a Cryptate Complex for Separation of Element 102 from the Actinides

ChemInform Abstract: Coordination Chemistry and Structure Characterization of C18H36O6N2Eu2(NO3)6·H2O

Abstract The crystal structure of a cryptate complex of europium, C18H36O6N2Eu2(NO3)6·H2O, has been determined from three-dimensional single-crystal X-ray diffraction data collected on a computer-automated diffractometer. The compound crystallizes in the triclinic space group P l with unit cell dimensions a = 14.815(5), b = 8.828(2), c = 13.302(4) A, α = 91.57(2), β = 92.64(3), γ = 86.90(3)° and Z = 2. The structure was solved by a heavy atom method and refined by a blocked-matrix least-squares procedure to a conventional R index of 0.029 for 5422 reflections. The molecule is composed of cations (C18H36O6EuNO3)2+ and anions [Eu(NO3)5· H2O]2−. In the cation, the europium(III) ion enclosed in a [2.2.2] molecule is coordinated with eight oxygen and two nitrogen atoms, forming a 10-coordinate complex ion (cryptate), while the other europium(III) ion is bonded to eleven oxygen atoms in the anion.

Coordination chemistry and structure characterization of C 18H 36O 6N 2Eu 2(NO 3) 6·H 2O

The crystal structure of a cryptate complex of europium, C 18H 36O 6N 2Eu 2(NO 3) 6·H 2O, has been determined from three-dimensional single-crystal X-ray diffraction data collected on a computer-automated diffractometer. The compound crystallizes in the triclinic space group P l with unit cell dimensions a = 14.815(5), b = 8.828(2), c = 13.302(4) Å, α = 91.57(2), β = 92.64(3), γ = 86.90(3)° and Z = 2. The structure was solved by a heavy atom method and refined by a blocked-matrix least-squares procedure to a conventional R index of 0.029 for 5422 reflections. The molecule is composed of cations (C 18H 36O 6EuNO 3) 2+ and anions [Eu(NO 3) 5· H 2O] 2−. In the cation, the europium(III) ion enclosed in a [2.2.2] molecule is coordinated with eight oxygen and two nitrogen atoms, forming a 10-coordinate complex ion (cryptate), while the other europium(III) ion is bonded to eleven oxygen atoms in the anion.