Synthesis,spectroscopic and spectrophotometric study of BODIPY appended crown ether sensor for ion detection

A novel fluoroionophore compound was synthesized from a boron dipyrromethene (BODIPY) fluorophore and 4′-formylbenzo-15-crown-5 ionophore groups. Photophysical properties of the BODIPY-crown compound were studied with UV–Vis and fluorescence spectroscopy. The effect of metalic cations (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Al³⁺, Fe³⁺, Cu²⁺, Co²⁺, Zn²⁺, Ag⁺, Hg²⁺, Pb²⁺) on the absorption and fluorescence spectra of compound 2 was investigated. Blue shifts were detected in UV–Vis spectra upon addition of some metal ions (Al³⁺ > Fe³⁺ > Na⁺). At the same time, the emission intensity of this complex increased due to binding of Na⁺ ion to the benzo crown cavity. Additionally, a decrease in the intensity of the 630 nm emission peak and an increase in the intensity of the 570 nm emission peak was observed in the fluorescence emission spectra following addition of Al³⁺ and Fe³⁺ ions.     

Thiazole sulfonamide based ratiometric fluorescent chemosensor with a large spectral shift for zinc sensing

A new thiazole sulfonamide (TTP, 1) based Zn²⁺ selective intrinsic chemosensor has been synthesized and investigated. The chemosensor shows a selective fluorescence enhancement (3.0 fold) with Zn²⁺ over biologically relevant cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) and biologically non-relevant cations (Cd²⁺) in an aqueous ethanol system. It produces an increase in the quantum yield and a longer emission wavelength shift (64 nm) on Zn²⁺ binding with the potential of a ratiometric assay.     

Use of Ionic liquids as additives in ion exchange chromatography for the analysis of cations

The behavior of acids (citric acid, nitric acid, oxalic acid, tartaric acid) as a mobile phase and imidazolium ionic liquids (the bromides, tetrafluoroborates and hexafluorophosphates of 1‐ethyl, 1‐butyl, and 1‐hexyl‐3‐methylimidazolium) as additives in ion exchange chromatography for cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) separation were studied. The results showed that nitric acid and 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate offered the most interesting features in the separation of cations, such as lower retention time and better resolution. The selected optimal conditions were achieved by adding 0.10 mM 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate in 4.0 mM HNO₃ mobile phase for the separation of four cations with the flow rate of 0.9 mL/min at room temperature (25°C). The linear regression equations of Na⁺, K⁺, Mg²⁺, Ca²⁺ were S  = 4.4763c  + 0.0209, S  = 3.8903c  – 0.0087, S  = 6.3974c  – 0.0173, and S  = 7.601c  – 0.0339 and the limits of detection of Na⁺, K⁺, Mg²⁺, Ca²⁺ were 0.296, 4.98, 0.0970, and 1.22 μg/L, respectively. In this work, four cations in samples were successfully detected.     

CORRELATION BETWEEN DELAYED LIGHT EMISSION AND FLUORESCENCE OF CHLOROPHYLL a IN SYSTEM II PARTICLES DERIVED FROM SPINACH CHLOROPLASTS

Abstract— The induction transient of delayed light of chlorophyll a, excited by repetitive flashes (0.5 ms in duration) and emitted 0.1 - 1.2 ms after the flashes, was measured in system II particles derived from spinach chloroplasts. An uncoupler, gramicidin S, was always added to the particles in order to eliminate the influence of the phosphorylation system on the delayed light and to isolate a direct relationship between the delayed light emission and the primary photochemical reaction, except for the experiments described in the next paragraph. The yield of delayed light emission from the system II particles was found to be about three–times higher than that of chloroplasts on a chlorophyll content basis. System I particles, on the other hand, emitted much weaker delayed light than chloroplasts. Upon intermittent illumination, induction of delayed light in system II particles showed a decrease from the initial rise level to the steady-state level. The initial rise level was the maximum. The fluorescence induction, on the other hand, exhibited an increase from the initial rise level to the maximum steady-state level. The induction of both delayed light emission and fluorescence arrived at their final steady-state levels after the same period of illumination. Induction of delayed light emission was measured under various conditions that changed the oxidation-reduction state of the primary electron acceptor, X, of photoreaction II: by adding an electron acceptor and an inhibitor of electron transport, and by changing the light intensity. The state of A'was monitored by measuring the fluorescence yield. The yield of delayed light emission excited by each flash was found to depend on the amount of oxidized form of X present before the flash. To examine the role of the primary electron donor Y of photoreaction II in delayed light emission, effects of electron donors of photoreaction II such as Mn²⁺, hydroquinone and p-phenylenediamine were investigated. These agents were found to markedly decrease the yield of delayed light emission without altering the pattern of its induction. They had little effect on the induction of fluorescence. These findings are interpreted by a mechanism in which transformation of the reaction center from the form (X^-Y⁺) into (X Y) produces a singlet excitation of chlorophyll a that is the source of millisecond delayed light emission. This reaction is probably non–physiological and must be very slow if compared to the transformation of (X^-Y⁺) into (X^-Y). Since the form (X^-Y⁺) is produced when the excitation is transferred to the reaction center in the form (XY), it is expected in this scheme that the yield of delayed light emission should depend on the amount of the form (X Y) present before the excitation flashes. Electron donors stimulate transformation of the reaction center from (X^-Y⁺) into (X^-Y). Since this reaction competes with the process of delayed light emission, electron donors are expected to suppress delayed light emission.     

A Highly Selective Potassium Sensor for the Detection of Potassium in Living Tissues

The development of highly selective sensors for potassium is of great interest in biology. Two new hydrosoluble potassium sensors (Calix‐COU‐Alkyne and Calix‐COU‐Am) based on a calix[4]arene bis(crown‐6) and an extended coumarin were synthesized and characterized. The photophysical properties and complexation studies of these compounds have been investigated and show high molar extinction coefficients and high fluorescence quantum yields. Upon complexation with potassium in the millimolar concentration range, an increase of one‐ and two‐photon fluorescence emission is detected. A twofold fluorescence enhancement is observed upon excitation at λ=405 nm. The ligands present excellent selectivity for potassium in the presence of various competitive cations in water and in a physiological medium. The photophysical properties are not affected by the presence of a large amount of competing cations (Na⁺, Ca²⁺, Mg²⁺, etc.). Ex vivo measurements on mouse hippocampal slices show that Calix‐COU‐Alkyne accumulates extracellularly and does not alter the neuronal activity. Furthermore, the sensor can be utilized to monitor slow extracellular K⁺ increase induced by inhibition of K⁺ entry into the cells.     

Switch-On Diketopyrrolopyrrole-Based Chemosensors for Cations Possessing Lewis Acid Character

For the first time diketopyrrolopyrroles (DPPs) have been synthesized directly from nitriles possessing (aza)crown ethers leading to macrocycle-dye hybrids. Depending on the nature of the linkage between DPP and macrocyclic ring, various coordination effects are found. The strong interaction of the cations possessing Lewis acid character such as Li⁺, Mg²⁺ and Zn²⁺ with 2-aminopyridin-4-yl-DPPs, leading to a bathochromic shift of both emission and absorption, as well as to strong enhancement of fluorescence was rationalized in terms of strong binding of these cations to the N=C−NR₂ functionality. The same effect has been observed for protonation. Depending on the size and the structure of the macrocyclic ring the complexation of cations by aza-crown ethers plays an important but secondary role. The interaction of Na⁺ and K⁺ with 2-aminopyridin-4-yl-DPPs leads to moderate enhancement of fluorescence due to the aza-crown ethers binding. The very weak fluorescence of DPP bearing 2-dialkylamino-pyridine-4-yl substituents is due to the closely lying T₂ state and the resulting intersystem crossing.     

Metal ion complexation in acetonitrile by di-ionized calix[4]arenes bearing two dansyl fluorophores

The influence of metal cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ag⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) on the spectroscopic properties of two dansyl (1-dimethylaminonaphthalene-5-sulfonyl) groups linked to the lower rims of a series of three, structurally related, di-ionized calix[4]arenes was investigated by means of absorption and emission spectrophotometry. Di(tetramethylammonium) salts of the di-ionized ligands, (TMA)₂L1, (TMA)₂L2 and (TMA)₂L3, which differ in having zero, two and four tert-butyl groups, respectively, on the upper rim of the calix[4]arene scaffold were utilized for the spectrofluorimetric titration experiments in acetonitrile. On complexation by alkaline earth metal cations, both the absorption and emission spectra undergo marked red shifts and quenching of the dansyl fluorescence. These effects are weaker with alkali metal cations. Transition metal cations interact strongly with the ligands. In particular, Fe³⁺, Hg²⁺ and Pb²⁺ cause greater than 97% quenching of the dansyl fluorescence in the di-ionized ligands.     

Metal ion complexation in acetonitrile by upper-rim allyl-substituted, di-ionized calix[4]arenes bearing two dansyl fluorophores

The influence of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ag⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺ on the spectroscopic properties of two dansyl (1-dimethylaminonaphthalene-5-sulfonyl) groups linked to the lower rims of a series of three, structurally related, di-ionized calix[4]arenes is investigated by means of absorption and emission spectrophotometry. Di(tetramethylammonium) salts of the di-ionized ligands, L, L1, and L2, which differ in having no, two and four allyl groups, respectively, on the upper rim of the calix[4]arene scaffold, are utilized for the spectrofluorimetric titration experiments in MeCN. On complexation by alkaline earth metal cations, the emission spectra undergo marked red shifts and quenching of the dansyl fluorescence. These effects are weaker with alkali metal cations. Transition metal cations and Pb²⁺ interact strongly with the ligands. In particular, Fe³⁺, Hg²⁺ and Pb²⁺ cause greater than 99% quenching of the dansyl fluorescence.     

Benzimidazole-based optical probe for selective detection of multiple-cations via dual-channel analysis

A benzimidazole-based optical probe having pendant carboxyl, amine, and imine groups as ionophore has been prepared for screening various metal ions. The 4-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-5-carboxylic acid (1) has been obtained in good yield and characterized by full battery of complementary physico-chemical techniques including ¹H NMR, UV-Vis, fluorescence spectroscopy, and single crystal X-ray crystallography. Metal ion-binding properties of 1 have been studied using ppm level concentration of representative alkali metal (Na⁺, K⁺), alkaline earth metal (Mg²⁺, Ca²⁺), and transition metal (Zn²⁺, Co²⁺, Fe³⁺, Cd²⁺, Hg²⁺, Pb²⁺, Cu²⁺, Ag⁺) ions and the output signal was monitored via two different channels viz chromogenically and fluorogenically. Selective recognition of Hg²⁺ has been explored with absorption spectra whereas emission spectra of 1 display differential response for multiple cations at parts-per-million (ppm) level concentration that allow selective detection of Ca²⁺, Mg²⁺, and Na⁺ ions. The results have been discussed in light of selectivity, sensitivity, response time, mode of binding/interactions, and sensing properties.     

Heats of adsorption of water on vermiculite having large singly-charged cations in the exchange complex

The isotherms and differential heats of adsorption of water vapor on K-, NH₄-, Rb-, and Cs-vermiculites have been studied by means of a Calvet microcalorimeter having a microweighing adsorption attachment. The results are interpreted taking into account that the large cations K₊, NH₄ ⁺, Rb⁺, and especially Cs⁺, may not replace the initial exchange complexes (Na⁺ or Mg²⁺) of the mineral completely, so that besides hydration of the principal exchange cations the reaction of water molecules being adsorbed with the residual Na⁺ or Mg⁺ cations also takes place. The presence of a certain number of the initial cations (Na⁺ or Mg²⁺) in the Cs form of vermiculite is confirmed by the results of studying the ion exchange equilibria on the Na and natural (Mg) forms of the mineral involving the participation of the Cs₊ ions. The nature of the variation in the dependence of the differential heats of adsorption with an increase in the amount of adsorbed substance indicates the segregation (isolation) of the principal (K⁺, NH₄ ⁺, Rb⁺, Cs⁺) and the residual (Na⁺, Mg²⁺) exchange cation in the structure of the mineral.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 91–96, January–February, 1986.     

Electromembrane extraction and capillary electrophoresis with capacitively coupled contactless conductivity detection: Multi‐extraction capabilities to analyses trace metals from saline samples

Simultaneous electromembrane extraction (EME) of six trace metal cations (Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Pb²⁺, Cd²⁺) from saline samples was investigated. CE with capacitively coupled contactless conductivity detection (C⁴D) was used to determine the metals in acceptor solutions due to its excellent compatibility with the minute volumes of acceptor solutions. Bis(2‐ethylhexyl)phosphate (DEHPA) was selected as a suitable nonselective modifier for EME transport of target metal cations. Both, the individual effect of each major inorganic cation (Na⁺, K⁺, Ca²⁺, Mg²⁺) and their synergistic effect on EME of the trace metal cations were evaluated. In both cases, a decrease in extraction efficiency was observed when major inorganic cations were present in the sample. This effect was more significant for Ca²⁺ and Mg²⁺. The system was optimized for simultaneous extractions of the six target metals from saline samples (50 mM Na⁺, 5 mM Mg²⁺, 1 mM K⁺, and 1 mM Ca²⁺) and following EME conditions were applied. Organic phase consisted of 1‐nonanol containing 1% (v/v) DEHPA, acceptor solution was 1 M acetic acid (HAc) and sample pH was adjusted to 5. Sample was stirred at 750 rpm and EMEs were carried out at extraction potential of 10 V for 20 min. The method presented a repeatability between 8 and 21.8% (n = 5), good linearity in 0.5–10 μM concentration range (R² = 0.987‐0.999) and LOD better than 2.6 nM. Applicability of the EME–CE–C⁴D method to the analyses of metal cations in drinking water, seawater, and urine samples was also demonstrated.     

Theoretical study of interaction of 2,6-dithiopurine with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cations

The geometries of the complexes of Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ metal cations with different possible 2,6-dithiopurine anions (DTP) were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d, p) basis set. The interactions of the metal cations at different nucleophilic sites of various possible 2,6-dithiopurine anions were considered. It was revealed that metal cations would interact with 2,6-dithiopurine anions in a bicoordinate manner. In the gas phase, the most preferred position for the interaction of Li⁺, Na⁺, and K⁺ cations is between the N₃ and S₂ sites, while all divalent cations Be²⁺, Mg²⁺, and Ca²⁺ prefer binding between the N₇ and S₆ sites of the corresponding 2,6-dithiopurine. The influence of aqueous solvent on the relative stability of different complexes has been examined using the Tomasi’s polarized continuum model. The basis set superposition error (BSSE) corrected interaction energy was also computed for complexes. The AIM theory has been applied to analyze the properties of the bond critical points (electron densities and their Laplacians) involved in the coordination between 2,6-dithiopurine anions and the metal cations. It was revealed that aqueous solution would have significant effect on the relative stability of complexes obtained by the interaction of 2,6-dithiopurine anions with Mg²⁺ and Ca²⁺ cations. The effect of metal cations on different NH and CS stretching vibrational modes of 2,6-dithiopurine has also been discussed.     

Strukturchemische und impedanzspektroskopische Untersuchungen an Mg2+-stabilisierten Na+/Pr3+-β″-Al2O3-Kristallen

Structural Chemistry and Impedance Spectroscopy of Mg²⁺ stabilized Na⁺/Pr³⁺-β″-Aluminas The structure with the ionic distribution in the conduction planes of a Pr³⁺-exchanged Mg²⁺ stabilized Na⁺-β″-alumina crystal, composition determined by electron microprobe analysis to Na_1.19Pr_0.13Mg_0.49Al_10.49O₁₇ (degree of exchange ξ = 25%, related to Na⁺ content), has been investigated by single crystal X-ray diffraction methods at room temperature (R3 m, Z = 3, a = 561.8(2) pm, c = 3 361.5(11) pm). Pr³⁺ is slightly shifted in the ab-plane from the centrosymmetric 9 d (mO) into a 18 h site. Na⁺ occupies 18 h as well as 6 c (BR) positions. Ionic conductivity data of Mg²⁺ stabilized Na⁺/Pr³⁺-β″-Al₂O₃ crystals with varying degree of exchange determined by impedance spectroscopy are given in an Arrhenius diagram. With growing Pr³⁺ content the conductivity σ decreases with increasing activation energy.     

一个基于NBD-NH2荧光团的增强型pH荧光探针及其细胞造影研究

本文以NBD-NH₂荧光团偶联N-(4-吡啶甲基)乙二胺质子受体构建了基于光致电子转移(PET)机制的pH探针NBD-Py。探针在pH5.0~8.5范围内显示pH降低导致的荧光增强响应,pK_a为6.48。响应不受胞内常见金属离子干扰且有良好的可逆性。研究表明质子受体中引入4-甲基吡啶修饰乙二胺是探针实现对弱酸/近中性pH响应的关键。HeLa细胞中的造影证实了探针的pHi造影能力和溶酶体靶向性能,为溶酶体pH相关的生理过程研究提供了新的可靠手段。     

Spectrophotometric studies of alkali and alkali earth metal ions complexes of mono amino derivative of calix[4]arene

The synthesis and complexive abilities of 5,11,17-tris(tert-butyl)-23 amino-25,26,27,28-tetra-propoxycalix[4]arene towards alkali cations Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and alkali earth cations Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ in methanol-chloroform mixture have been evaluated at 25°C, using UV-Vis spectrophotometric techniques. The results showed that the ligand is capable to complex with all the cations by 1: 1 metal to ligand ratios. The selectivity presented considering the calculated formation constants are in the order Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺ and Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ with the ligand.     

A theoretical study of cation--π interactions: Li+, Na+, K+, Be2+, Mg2+ and Ca2+ complexation with mono- and bicyclic ring-fused benzene derivatives

DFT (B3LYP functional) and MP2 methods using 6-311+G(2d,2p) basis set have been employed to examine the effect of ring fusion to benzene on the cation--π interactions involving alkali metal ions (Li⁺, Na⁺, and K⁺) and alkaline earth metal ions (Be²⁺, Mg²⁺ and Ca²⁺). Our present study indicates that modification of benzene (π-electron source) by fusion of monocyclic or bicyclic (or mixture of these two kinds of rings) strengthens the binding affinity of both alkali and alkaline earth metal cations. The strength of interaction decreases in the following order: Be²⁺ > Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺ for any considered aromatic ligand. The interaction energies for the complexes formed by divalent cations are 4–6 times larger than those for the complexes involving monovalent cations. The structural changes in the ring wherein metal ion binds are examined. The distance between ring centroid and the metal ion is calculated for all of the complexes. Strained bicyclo[2.1.1]hexene ring fusion has substantially larger effect on the strength of cation--π interactions than the monocyclic ring fusion for all of the cations due to the π-electron localization at the central benzene ring.     

The effect of different valency cations on DMFC performance

An in situ study of the effects of Na⁺, Mg²⁺ and Cr³⁺ on direct methanol fuel cell (DMFC) performance is reported. The result showed that dramatic decrease of the cell voltage was mainly ascribed to the increase of the cathode overpotential. Meanwhile, the different contamination effects by introducing Na⁺, Mg²⁺ and Cr³⁺ to the anode and the cathode were compared. When the same molar concentration of different cations was added to the anode feed, the contamination effect on the cell performance followed the order of Na⁺ > Mg²⁺ > Cr³⁺. Owing to the fast transfer speed and the low affinity to the sulfonic acid groups in the ionomer phase, the low-valent cations may cause much more proton losses than the high-valent cations in the cathode catalyst layer (CCL) within the same time. So the low-valent cations led to the higher cathode overpotential than the high-valent cations. When the same molar concentration of cations was directly added to the CCL, the contamination effects on the cell voltage showed an opposite trend which is Na⁺ < Mg²⁺ < Cr³⁺. This is presumably because a high-valent cation can exchange more protons than a low-valent cation in the CCL.     

Effect of ring annelation on cations [M = H+, Li+, Na+, K+, Be2+, Mg2+, and Ca2+]…benzene interaction: A density functional theory investigation

Density functional theory calculation was carried out on cation‐π complexes formed by cations [M = H⁺, Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺] and π systems of annelated benzene. The cation‐π bonding energy of Be²⁺ or Mg²⁺ with annelated benzene is very strong in comparison with the common cation‐π intermolecular interaction, and the bonding energies follow the order Be²⁺ > Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. Similarly, the interaction energies follow the trend 1‐M < 2‐M < 3‐M for all the metal cations considered. These outcomes may be due to the weak interactions of the metal cations with C? H and the interactions of metal cations with π in addition to the nature of a metal cation. We have also investigated on all the possible substituted sites, and find that the metal ion tends to interact with all ring atoms while proton prefers to bind covalently to one of the ring carbons. The binding of metal cations with annelated benzenes has striking effect on nuclear magnetic resonance chemical shifts using the gauge independent atomic orbital method. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Ions Can Move a Proton‐Coupled Electron‐Transfer Reaction into Tunneling Regime

The effects of charged species on proton‐coupled electron‐transfer (PCET) reaction should be of significance for understanding/application of important chemical and biological PCET systems. Such species can be found in proximity of activated complex in a PCET reaction, although they are not involved in the charge transfer process. Reported here is the first study of the above‐mentioned effects. Here, the effects of Na⁺, K⁺, Li⁺, Ca²⁺, Mg²⁺, and Me₄N⁺ observed in PCET reaction of ascorbate monoanions with hexacyanoferrate(III) ions in H₂O reveal that, in presence of ions, this over‐the‐barrier reaction entered into tunneling regime. The observations are: a) dependence of the rate constant on the cation concentration, where the rate constant is 71 (at I = 0.0023), and 821 (at 0.5M K⁺), 847 (at 1.0M Na⁺), and 438 M ^?1 s^?1 (at 0.011M Ca²⁺); b) changes of kinetic isotope effect (KIE) in the presence of ions, where k_H/k_D=4.6 (at I = 0.0023), and 3.4 (in the presence of 0.5M K⁺), 3.3 (at 1.0M Na⁺), 3.9 (at 0.001M Ca²⁺), and 3.9 (at 0.001M Mg²⁺), respectively; c) the isotope effects on Arrhenius pre‐factor where A_H/A_D=0.97 (0.15) in absence of ions, and 2.29 (0.60) (at 0.5M Na⁺), 1.77 (0.29) (at 1.0M Na⁺), 1.61 (0.25) (at 0.5M K⁺), 0.42 (0.16) (at 0.001M Ca²⁺) and 0.16 (0.19) (at 0.001M Mg²⁺); d) isotope differences in the enthalpies of activation in H₂O and in D₂O, where ΔΔH^?(D,H)=3.9 (0.4) kJ mol^?1 in the absence of cations, 1.3 (0.6) at 0.5M Na⁺, 1.8 (0.4) at 0.5M K⁺, 1.5 (0.4) at 1.0M Na⁺, 5.5 (0.9) (at 0.001M Ca²⁺), and 7.9 (2.8) (at 0.001M Mg²⁺) kJ mol^?1; e) nonlinear proton inventory in reaction. In the H₂O/dioxane 1 : 1, the observed KIE is 7.8 and 4.4 in the absence and in the presence of 0.1M K⁺, respectively, and A_H/A_D=0.14 (0.03). The changes when cations are present in the reaction are explained in terms of termolecular encounter complex consisting of redox partners, and the cation where the cation can be found in a near proximity of the reaction‐activated complex thus influencing the proton/electron double tunneling event in the PCET process. A molecule of H₂O is involved in the transition state. The resulting ‘configuration’ is more ‘rigid’ and more appropriate for efficient tunneling with Na⁺ or K⁺ (extensive tunneling observed), i.e., there is more precise organized H transfer coordinate than in the case of Ca²⁺ and Mg²⁺ (moderate tunneling observed) in the reaction.     

Quantum chemical study of the interaction between selenium analog of methimazole as an anti-thyroid drug and metal cations

Energetic and structural properties of complexes formed from interaction between selenium analog of methimazole (MSeI) as an anti-thyroid drug and M^z+ (Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺ and Ca²⁺) cations have been investigated using B3LYP, M062X, PBE1PBE, and MP2 methods with 6-311++G(d,p) and 6-311++G(2d,2p) basis sets. Two planar and perpendicular complexes were predicted from interaction of MSeI and M^z+ cations. From the Gibbs free energy difference between the planar and perpendicular forms of MSeI–M^z+ complexes, it is found that the perpendicular forms are the predominant ones. In addition, the comparison of interaction energies shows that the order of energies increases in the following order: K⁺ < Na⁺ < Li⁺ < Ca²⁺ < Mg²⁺ < Be²⁺. The results of natural bond orbital analysis showed that the charge transfer occurs from MSeI to metal cations. The atom in molecule analysis shows that the charge density and its Laplacian at the Se–M^z+ bond critical point of the MSeI–M²⁺ complexes are greater than the MSeI–M¹⁺ ones. Also, it was revealed that the Se–M^z+ interactions in perpendicular complexes of alkali and alkaline metal cations are electrostatic and partially covalent in nature, respectively.