Complexation Properties of a Carbon-Bridged Cryptand with Metal Ions in Aqueous Solution at 25°C

Abstract

Thermodynamic quantities (log K, ΔH, and ΔS) for the interactions of a carbon-bridged cryptand with Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺ were determined at 25° C by calorimetric titration in aqueous solution. The cryptand forms complexes with Na⁺, Sr²⁺, Ba²⁺, and Pb²⁺ with log K ≤ 2. Complexation was not detected for Li⁺, K⁺, and Ca²⁺. Weak interactions with Li⁺ and K⁺ and a log K value of 2.4 for Na⁺ suggest that the cavity size of the cryptand is close to that of Na⁺ but too small for K⁺ and too large for Li⁺. The carbon-bridged cryptand selectively binds Sr²⁺ (log K = 3.2) over Ca²⁺ and Ba²⁺ by more than one order of magnitude.     

Beiträge zur Chemie der Pyrrolpigmente, 3. Mitt.1: Die NH-Tautomerie von substituierten Pyrromethenen: Protonenresonanzspektrometrische Untersuchungen

NMR-spectra of several pyrromethenes were measured at different temperatures, concentrations and in different solvents. The chemical shifts of all protons were assigned and long range coupling constants determined. This variation of temperature, concentration and solvent provided evidence forintra- andinter-molecular proton transfer. In all pyrromethenes investigated the tautomeric NH exchanges are too fast—even at –100°C—to be measured by NMR.

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Mit 2 Abbildungen     

An examination of intermolecular and intramolecular hydrogen bonding in biomolecules by AM1 and MNDO/M semiempirical molecular orbital studies

The recent NMDO/M modification and parameterization of the MNDO molecular orbital method has been used to analyze intermolecular hydrogen bonding between amino acids and water, and intramolecular hydrogen bonding in monosaccharides. The results have been compared to AM1 calculations on the same systems. The MNDO/M calculations gave values which were similar to ab initio calculations with respect to the intermolecular interactions, but yielded significantly poorer results for the intramolecular interactions. The AM1 procedure performed better on the intramolecular interactions than the MNDO/M procedure, but frequently provided unfavorable three-centered hydrogen bonding geometries for the intermolecular interactions.     

STEREOSELECTIVITY OF ELECTRON TRANSFER REACTIONS (II); REACTION OF Λ-[Co(EDDS)]− AND Co(II) COMPLEXES WITH STEREOSPECIFIC DIAMINE LIGANDS

Abstract

Stereoselective electron-transfer between optically active Λ-[Co(EDDS)]^? and [Co(diamine)₃]²⁺ (diamine = racemic-1,2-diaminopropane (pn); R-1,2-diaminopropane (R-pn)) have been investigated in aqueous and in DMSO solutions. In aqueous solution, the reaction between Λ-[Co(EEDS)]^? and [Co(pn)₃]²⁺ produces four conformational isomers of the [Co(pn)₃]³⁺ complex which have the Λ-forms in excess. Their optical purities are increased ob₃>lelob₂> lel₂ob> lel₃ . In contrast, the reaction in DMSO results in more δ isomers than Λ and the sequence of optical purities are in reversed order.

The reaction between Λ-[Co(EDDS)]^? and [Co(R-pn)₃]²⁺ in aqueous solution produces two conformational isomers of [Co(R-pn)₃]³⁺; their absolute configurations are identified as δ-lel₂ob and Λ-ob₃ . In DMSO, in contrast, the reaction produces only one isomer which is identified as δ-lel₂ob.     

Host‐Guest Complexes of [TriPip222], the Piperazine Analogue of [2.2.2]: Prediction of Ion Selectivity by Quantum Chemical Calculations VIII[#]

The selectivity of the cryptand [TriPip222], a per‐aza analogue of cryptand [2.2.2], in which each of the linking arms contains a piperazine ring for the endohedral complexation of metal cations of the I, II, and III main groups and group 12 of the periodic table of elements, was predicted on the basis of DFT [B3LYP/LANL2DZp (LANL2DZp = LANL2DZ augmented with polarization functions on non‐hydrogen atoms)] calculated structures and complex‐formation energies. The cavity size of the studied cryptand is similar to that of [bpy.bpy.bpy], [2.bpy.bpy] and [2.phen.phen], such that the complexation of K⁺ > Na⁺ and of Sr²⁺ ≈ Ca²⁺ > Ba²⁺ are most favorable. The essential flexibility for achieving the selectivity of the cryptand is mainly associated with a twist of the CH₂–N_bridgehead ··· N_bridgehead–CH₂ angle and not with the piperazine moiety.     

(Ca,Me)La4Si3O13:Eu3+(Me=Sr,Ba)荧光粉的结构和发光特性

采用高温固相法制备了(Ca,Me)La4Si3O13∶Eu3+(Me=Sr,Ba)系列红色荧光体,考察了Eu3+掺杂浓度和Sr2+,Ba2+置换对荧光体结构和发光特性的影响。Eu3+最佳掺杂浓度为nEu3+∶nLa3+=1∶7,5D0-7F2与5D0-7F1跃迁发射强度比为2.55。Eu3+掺杂使晶胞参数a和c呈线性变小,对c的影响大于a,使a/c比增大。Sr2+和Ba2+分别置换基质中的Ca2+可以形成完全固溶体,晶胞参数随Sr2+或Ba2+的置换量增加呈线性增大,使a/c比减小。各发射峰强度在Sr2+置换量为0.4 mol时出现极大值,但随Ba2+置换量的增加而不断增强,全置换后荧光强度最大。荧光体的色坐标为(0.638 5,0.353 0)。     

Relation between stability constants of metal ion cryptates in two solvents and the transfer activity coefficients of the metal ions

The extrathermodynamic assumption of Lejaille and Bessière that _1,2 log K (LM ⁿ⁺ )=–G _tr (M ⁿ⁺ ) in which K is stability constant and L is cryptand 2.2.2, 2 _B 2 _B 2, 2.2.1, or 2.1.1 has been tested in dipolar aprotic solvents for M ⁿ⁺ being Li⁺, Na⁺, K⁺, Ag⁺, Tl⁺, and Ba²⁺. The relation has been found generally acceptable for the dipolar aprotic solvents propylene carbonate, acetonitrile, N,N-dimethylformamide and dimethylsulfoxide, provided the size of the ion is equal to or smaller than the cavity of the cryptand. The relation does not hold for the hydrogen bonded donating solvents, water, and methanol.     

Self-assembly of a (benzothiazolyl)ethenylbenzocrown ether into a sandwich complex and stereoselective [2+2] photocycloaddition

In the presence of Ba²⁺ ions, (benzothiazolyl)ethenylbenzocrown ether forms the stable sandwich complex 2L⋅Ba²⁺ with an unusual structure, in which the benzothiazole fragments are arranged one above the other. Irradiation of the sandwich complex with visible light induces stereoselective [2+2] cycloaddition giving rise to two “head-to-head” isomers of biscrown-cyclobutane. The addition of dibasic dicarboxylic acids that additionally stabilize the sandwich complex in a favorable conformation affects the isomer ratio of the cyclobutanes formed. The conformational equilibria for the sandwich complex and cyclobutanes were studied by ¹H NMR spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1524–1533, July, 2005.     

Host-guest complexes of the Beer-Can-cryptand: prediction of ion selectivity by quantum chemical calculations XI

Abstract

Based on DFT calculations (B3LYP/LANL2DZp) and the application of model equations, as well as a comparison of M-N-donor length with an unstrained reference ([M(solvent)₆]ⁿ⁺), the selectivity of the alkali and alkaline earth cations (Li⁺ – Cs⁺ and Be²⁺ – Ba²⁺) for the recently synthesized cryptand bis-triazacyclononane tris-pyridyl N₉-azacryptand (Beer-Can) was investigated. The host can bind the alkali cation K⁺ best, followed by the alkaline earth cations Ca²⁺ and Sr²⁺, and by Na⁺ and Ba²⁺. This selectivity pattern is identical to the selectivity of the Lehn-type cryptand [phen.phen.phen], which suggests a similar cavity size. The good flexibility of the Beer-Can is provided by the aza-crown-like top and bottom of the “can,” and the pyridines on the “can-wall.”     

室温电化学沉积Ba1-xCaxMoO4多晶固溶体薄膜

近年发展起来的制备功能薄膜的电化学沉积技术,是软溶液工艺路线(Soft Solution Processing简记为SSP)中的重要技术[1]。与传统的薄膜制备技术相比,电化学沉积技术在反应控制、形貌控制、沉积速度、能量消耗、环境影响、薄膜晶化以及沉积设备等方面都有较明显的优势,同时避免了     

Host‐Guest Complexes of Dodeka(ethylene)octamine: Prediction of Ion Selectivity by Quantum Chemical Calculations IX

In this contribution we investigated the ion complexation of Bühl's cryptand, dodeka(ethylene)octamine by quantum chemical methods (B3LYP/LANL2DZp). This cryptand is an isomer of a well‐known Lehn‐type cryptand [TriPip222]. The ion selectivity was determined based on the energetic criteria derived by model reactions starting from solvated metal ions and empty dodeka(ethylene)octamine, and by comparing the M–N bond length in [M ? dodeka(ethylene)octamine]^m+ and [M(NH₃)₆]^m+. We calculated that Bühl's cryptand will complex best Na⁺ followed by Li⁺ as alkaline cations and Ca²⁺ followed by Mg²⁺ as alkaline earth metal ions. Based on this data we conclude that Bühl's cryptand offers a smaller cavity to nest ions than the Lehn‐type [TriPip222].     

Extraction of barium picrate into nitrobenzene in the presence of benzo-15-crown-5

From extraction experiments with ¹³³Ba as a tracer, the extraction constant corresponding to the equilibrium Ba²⁺(aq) + 2A^-(aq) + 2L(nb) BaL₂ ²⁺(nb) + 2A^-(nb) in the two-phase water-nitrobenzene system (A^- = picrate, L = benzo-15-crown-5; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (BaL₂ ²⁺, 2A^-) = 5.7. Furthermore, the stability constant of the benzo-15-crown-5 - barium complex in nitrobenzene saturated with water was calculated: log b_nb (BaL₂ ²⁺) = 14.6.     

Effect of complexation on spectral and kinetic properties of crown-substituted photochromic spironaphthoxazines

The insertion of benzo-15-crown-5 or benzo-18-crown-6 as a substituent at the 9'-position of a spironaphthoxazine molecule increases the lifetime of the open form of spironaphthoxazine by a factor ofca. 2. The complex formation between the crown groups and Mg²⁺ or Ba²⁺ ions changes the lifetime slightly. The addition of benzo-18-crown-6 at the 5'-position leads to an increase in the lifetime of the open form by an order of magnitude and the appearance of absorption with a maximum at 16420 cm^–1 under dark conditions, which testifies to the stabilization of the open form. The addition of Ba²⁺ ions to this compound results in a further increase in the lifetime byca. 35% due to complex formation. The luminescence of the benzo-15-crown-5-substituted compound is probably caused by both the complexation with Mg²⁺ and the photochemical reaction induced by photoactive light and is accompanied by the irreversible loss of photochromism.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2220–2224, September. 1996.     

Synthesis,Persistent Luminescence,and Thermoluminescence Properties of Yellow Sr3SiO5:Eu2+,RE3+ (RE=Ce,Nd, Dy,Ho, Er,Tm, Yb) and Orange‐Red Sr3−xBaxSiO5:Eu2+, Dy3+ Phosphor

Sunlight‐excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange‐red Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ persistent luminescence phosphor was successfully developed by a two‐step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non‐equivalent trivalent rare earth co‐dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu²⁺ in Sr₃SiO₅ was significantly modified. The yellow persistent emission intensity of Eu²⁺ was greatly enhanced by a factor of 4.5 in Sr₃SiO₅:Eu²⁺,Nd³⁺ compared with the previously reported Sr₃SiO₅:Eu²⁺, Dy³⁺. Furthermore, Sr ions were replaced with equivalent Ba to give Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ phosphor, which shows yellow‐to‐orange‐red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu²⁺ is significantly improved by a factor of 2.7 in Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ (x=0.2) compared with Sr₃SiO₅:Eu²⁺,Dy³⁺. A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu²⁺ in Sr_3?xBa_xSiO₅:Eu²⁺,RE³⁺ (RE=rare earth) is also proposed and discussed.     

High-Resolution Infrared Synchrotron Investigation of (HCN)2 and a Semi-Experimental Determination of the Dissociation Energy D0

The high-resolution infrared absorption spectrum of the donor bending fundamental band ν of the homodimer (HCN)₂ has been collected by long-path static gas-phase Fourier transform spectroscopy at 207 K employing the highly brilliant 2.75 GeV electron storage ring source at Synchrotron SOLEIL. The rovibrational structure of the ν transition has the typical appearance of a perpendicular type band associated with a Σ–Π transition for a linear polyatomic molecule. The total number of 100 assigned transitions are fitted employing a standard semi-rigid linear molecule Hamiltonian, providing the band origin ν₀ of 779.05182(50) cm⁻¹ together with spectroscopic parameters for the degenerate excited state. This band origin, blue-shifted by 67.15 cm⁻¹ relative to the HCN monomer, provides the final significant contribution to the change of intra-molecular vibrational zero-point energy upon HCN dimerization. The combination with the vibrational zero-point energy contribution determined recently for the class of large-amplitude inter-molecular fundamental transitions then enables a complete determination of the total change of vibrational zero-point energy of 3.35±0.30 kJ mol⁻¹. The new spectroscopic findings together with previously reported benchmark CCSDT(Q)/CBS electronic energies [Hoobler et al. ChemPhysChem. 19 , 3257–3265 (2018)] provide the best semi-experimental estimate of 16.48±0.30 kJ mol⁻¹ for the dissociation energy D₀ of this prototypical homodimer.     

Spirobifluorene-Based o-Carboranyl Compounds: Insights into the Rotational Effect of Carborane Cages on Photoluminescence

9,9′-Spirobifluorene-based closo-o-carboranyl ( SFC1 and SFC2 ) compounds and their nido-derivatives (nido- SFC1 and nido- SFC2 ) were prepared and characterized. The two closo-compounds displayed major absorption bands assignable to π–π* transitions involving the spirobifluorene group, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their spirobifluorene moieties. The nido-compounds exhibited slightly blueshifted absorption bands resulting from the absence of the ICT transitions corresponding to the o-carborane moieties due to the anionic character of the nido-o-carboranes. While SFC1 exhibited only high-energy emissions in THF at 298 K (only from locally excited (LE) states assignable to π–π* transitions on the spirobifluorene group), remarkable emissions in the low-energy region were observed in the rigid state such as in THF at 77 K and in the film state. SFC2 displayed intense emissions in the low-energy region in all states. The fact that neither of the nido-derivatives of SFC1 and SFC2 exhibited low-energy emissions and the TD-DFT calculation results of each closo-compound clearly verified that the low-energy emission was based on ICT-based radiative decay. The conformational barriers from each relative energy calculation upon changing the dihedral angles around the o-carborane cages for both compounds confirmed that the rotation of the o-carborane cages and terminal phenyl rings for SFC1 is freer than that for SFC2 .     

Template‐Assembled Synthetic G‐Quadruplex (TASQ): A Useful System for Investigating the Interactions of Ligands with Constrained Quadruplex Topologies

A new biomolecular device for investigating the interactions of ligands with constrained DNA quadruplex topologies, using surface plasmon resonance (SPR), is reported. Biomolecular systems containing an intermolecular‐like G‐quadruplex motif 1 (parallel G‐quadruplex conformation), an intramolecular G‐quadruplex 2 , and a duplex DNA 3 have been designed and developed. The method is based on the concept of template‐assembled synthetic G‐quadruplex (TASQ), whereby quadruplex DNA structures are assembled on a template that allows precise control of the parallel G‐quadruplex conformation. Various known G‐quadruplex ligands have been used to investigate the affinities of ligands for intermolecular 1 and intramolecular 2 DNA quadruplexes. As anticipated, ligands displaying a π‐stacking binding mode showed a higher binding affinity for intermolecular‐like G‐quadruplexes 1 , whereas ligands with other binding modes (groove and/or loop binding) showed no significant difference in their binding affinities for the two quadruplexes 1 or 2 . In addition, the present method has also provided information about the selectivity of ligands for G‐quadruplex DNA over the duplex DNA. A numerical parameter, termed the G‐quadruplex binding mode index (G4‐BMI), has been introduced to express the difference in the affinities of ligands for intermolecular G‐quadruplex 1 against intramolecular G‐quadruplex 2 . The G‐quadruplex binding mode index (G4‐BMI) of a ligand is defined as follows: G4‐BMI=K_D^intra/K_D^inter, where K_D^intra is the dissociation constant for intramolecular G‐quadruplex 2 and K_D^inter is the dissociation constant for intermolecular G‐quadruplex 1 . In summary, the present work has demonstrated that the use of parallel‐constrained quadruplex topology provides more precise information about the binding modes of ligands.     

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

Abstract  

A Eu^III cryptate complex constructed from a Cu^II cryptand with an L ^tBu ligand, [Eu^IIICu₂^II(L ^tBu)₂(NO₃)₃(MeOH)], and the corresponding Ca^II and Na^I cryptates, [Ca^IICu₂^II(L ^tBu)₂(NO₃)₂(MeOH)₂] and [Na^ICu₂^II(L ^tBu)₂(Me₂CO)](BPh₄), have been synthesized and characterized in order to shed light on the essential role of Cu^II in the luminescence of a Eu^III cryptate. The unprecedented role of a Cu^II cryptand makes it possible to produce lanthanide luminescence in a Eu^III cryptate complex and is successfully elucidated by comparison with the corresponding Ca^II and Na^I cryptates.     

Synthesis and structural studies of N-(p-toluenesulfonyl)-amino acid 3,5-di-tert-butyl-2-phenolamides

This paper describes the synthesis and structural studies of N-(p-toluenesulfonyl)-amino acid 3,5-di-tert-butyl-2-phenolamides by ¹H, ¹³C, and ¹⁵N. The presence of intra- and intermolecular hydrogen bonds were studied by variable temperature NMR spectroscopy. The molecular structure of two amides in the solid state was determined by X-ray diffraction experiments. The results show that tert-butyl substituents in the phenolic ring have important effects in the nature of hydrogen bonds and conformation of these amides. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:114–120, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10223     

Solution thermodynamics of Lanthanide–Cryptand 222 complexation processes

The thermodynamics of trivalent cations (Y³⁺, La³⁺, Pr³⁺, Nd³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Ho³⁺, Er³⁺, Yb³⁺) and cryptand 222 in acetonitrile at 298.15?K is discussed. Recent reports regarding the behavior of lanthanide(III) trifluoromethane sulfonate salts in acetonitrile are considered. Thus, the experimental work was carried out under conditions in which ions (M³⁺) are predominantly in solution. Therefore, conductiometric titrations were carried out to establish the composition of the cation–cryptand 222 complexes and their ionic behavior in solution. Stability constants and derived standard Gibbs energies, enthalpies and entropies were determined by competitive titration microcalorimetry. Previously reported thermodynamic data for the complexation of cryptand 222 and a few lanthanide cations (La³⁺, Pr³⁺ and Nd³⁺) in acetonitrile are revisited. The medium effect on the stability of complex formation in acetonitrile relative to N,N-dimethylformamide is demonstrated. Thus, a drop in stability by a factor of 8 × 10¹⁰ is observed for the latter relative to the former solvent. The selectivity of cryptand 222 for these cations relative to La³⁺ in acetonitrile is discussed.