Comparison of the stability of thymine tautomers and the interaction of its tautomers with Na+, K+, Mg2+ and Ca2+ in gas and solvent phases

The present study compared the interactions among Na ⁺, K ⁺, Mg²⁺ and Ca²⁺, thymine and its tautomers in the gas and solvent phase, an interaction dependent upon the electronic construction of the tautomers. Three types of cation interaction with thymine and its tautomers were observed. In the first one, the metal cations interacted with a lone pair of nitrogen or oxygen of the tautomers. In the second type, there was an interaction among the cations, nitrogen and oxygen at the same time; the last one was that of cations with the electron density of thymine π-system, where the cations were perpendicular to the ring of thymine. The interaction of metals cation with tautomers was studied in the gas and solvent phases; a comparison was then made between interactions in two phases. The interaction energy for all complexes indicated the stability of complexes, an energy which was higher in Ca²⁺ and Mg²⁺ compared with Na⁺ and K⁺. Concerning K⁺ and Na⁺, the stability of all complexes of tautomers was greater than that of thymine complexes; however, the stability of certain Ca²⁺ and Mg²⁺ complexes was lower than the complexes of thymine.     

Interaction of cations with 2′‐deoxythymidine nucleoside and analysis of the nature and strength of cation bonds

Binding of Mg²⁺, Ca²⁺, Zn²⁺, and Cu⁺ metal ions with 2′‐deoxythymidine (dT) nucleoside was studied using a density functional theory method and a 6‐311++G(d,p) basis set. This work demonstrated that the interaction of dT with these cations is tri‐coordinated η (O2, O4′, O5′). Among the four types of cations, Zn²⁺ cation exhibited the most tendency to interact with the dT. Cations via their interaction with dT can affect the N‐glycosidic bond length, the values of pseudorotation of the sugar ring, the orientation of the base unit with respect to the sugar ring, and the acidity of the O5′H, O3′H, and N3H groups in the dT nucleoside. Natural bond orbital analysis was performed to calculate the charge transfer and natural population analysis of the complexes. Quantum theory of atoms in molecules was also applied to determine the nature of interactions. It was shown that in dT–Mg²⁺ and dT–Ca²⁺ complexes, the bonds are electrostatic (closed‐shell) interactions, although they are partially covalent and partially electrostatic interactions in dT–Zn²⁺ and dT–Cu⁺ complexes. Copyright © 2011 John Wiley & Sons, Ltd.     

8-Hydroxyquinoline Functionalized Graphene Oxide: an Efficient Fluorescent Nanosensor for Zn<Superscript>2+</Superscript> in Aqueous Media

A nanosensor, based on 8-hydroxyquinoline functionalized graphene oxide, was developed for the fluorescence detection of Zn²⁺. It showed high selectivity and sensitivity for Zn²⁺ion in aqueous solution over other metal ions such as Li⁺, Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Cd²⁺, Co²⁺, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Fe²⁺, Fe³⁺and Cr³⁺. Due to the linearity of the emission intensity toward Zn²⁺ concentration, fluorescent technique could be used for the detection of Zn²⁺ ion even at very low concentrations.     

Boron-, nitrogen-, aluminum-, and phosphorus-doped graphite electrodes for non-lithium ion batteries

Intercalation of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, and Al³⁺ ions into B-, N-, Al-, and P-doped graphite has been studied using density functional theory calculations. While the intercalation of Li⁺, K⁺, and Ca²⁺ ions into graphite is thermodynamically favorable, that of Na⁺, Mg²⁺, Zn²⁺, and Al³⁺ ions into graphite is unfavorable. When doped in the form of graphitic structure, B, Al, and P dopants significantly stabilize the ion-intercalated graphite compounds. As a result, Na⁺ ions that are unable to intercalate into graphite can intercalate into B-, Al-, and P-doped graphite. The electron transfer from B, Al, and P dopants to host C atoms reinforces the ion–graphene electrostatic interaction, enhancing the thermodynamic driving force for ion intercalation. The catalytic activity of the dopant to promote the ion intercalation increases in the order of N < B < P < Al, which is associated with the electronegativity of the dopant.     

Rhod-5N as a Fluorescent Molecular Sensor of Cadmium(II) Ion

The photophysical and complexing properties of Rhod-5N (commercially available) in MOPS buffer are reported. This fluorescent molecular sensor consists of a BAPTA chelating moiety bound to a rhodamine fluorophore. Its fluorescence quantum yield is low and a drastic enhancement of fluorescence intensity upon cation binding was observed. Special attention was paid to the complexation with Cd²⁺, a well known toxic metal ion. Possible interference with other metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Pb²⁺) was examined. Rhod-5N was found to be highly selective of Cd²⁺ over those interfering cations except Pb²⁺. The limit of detection is 3.1 μg l⁻¹.     

Electrointercalation into 2H-TaS2 single crystals:in situ dilatometry and superconducting properties

Summary The electrointercalation of the following hydrated metal ions into 2H-TaS₂ crystals was investigated: Na⁺, K⁺, Ca²⁺, Zn²⁺, Mn²⁺, Co²⁺, La³⁺, Gd³⁺, Pr³⁺. We report onin situ dilatometric studies of the reaction and on superconducting properties of these compounds. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Effect of Pendant Group Length Upon Metal Ion Complexation in Acetonitrile by Di-Ionized Calix[4]Arenes Bearing Two Dansyl Fluorophores

A series of three di-ionizable calix[4]arenes with two pendant dansyl (1-dimethylaminonaphthalene-5-sulfonyl) groups linked to the lower rims was synthesized. Structures of the three ligands were identical except for the length of the spacers which connected the two dansyl groups to the calix[4]arene scaffold. Following conversion of the ligands into their di-ionized di(tetramethylammonium) salts, absorption and emission spectrophotometry were utilized to probe the influence of metal cation (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ag⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) complexation in acetonitrile. Upon complexation with these metal cations, emission spectra underwent marked red shifts and quenching of the dansyl group fluorescence for the di-ionized ligand with the shortest spacer. A similar effect was noted for the di-ionized ligand with an intermediate spacer for all of the metal ions, except Ba²⁺. For the di-ionized ligand with the longest spacer, the metal cations showed different effects on the emission spectrum. Li⁺, Mg²⁺, Ca²⁺ and Ba²⁺ caused enhancement of emission intensity with a red shift. Other metal cations produce quenching with red shifts in the emission spectra. Transition metal cations interacted strongly with all three di-ionized ligands. In particular, Fe³⁺ and Hg²⁺ caused greater than 99% quenching of the dansyl fluorescence in the di-ionized ligands.     

Theoretical studies on the single proton transfer process in adenine base

The effect of metal ions (Mⁿ⁺ = Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺ and hydrated Mg²⁺ ions) and water molecules on the tautomerism of adenine induced by single intramolecular proton transfer (SPT) have been investigated theoretically. Calculated results show that the single proton transfer process in adenine base is favored and even becomes thermodynamically spontaneous because of the presence of Mⁿ⁺ interacting at the N₃ position of adenine. On the contrary, if Mⁿ⁺ coordinated to N₇ site, the single proton transfer process will become unfavorable than that in the neutral system. The effects of metal ions on the SPT of adenine base are more pronounced if Lewis acidity of metal ion is increased. Water plays a more important role than metal ions during the SPT process. It is found that water can act not only as a solvent but also as a mediator which gives and accepts protons to promote SPT, playing a bridge role. As a result, inclusion of a water molecule drastically reduces the energy barrier for the SPT. Moreover, two water molecules can yield larger assisting effect on the SPTs compared with one water molecule. We can conclude that the tautomerism of DNA adenine base can be modulated by the metal ions and water molecules. Copyright © 2015 John Wiley & Sons, Ltd.     

Density functional investigation of metal encapsulated X@C12Si8 heterofullerene (X=Li, Na, K, Be, Mg, Ca, Al, Ga)

The stability and the possible application of our recently reported SiC heterofullerenes inspire the investigation of their further stabilization through ion encapsulation. The endohedral complexes X@C₁₂Si₈, where X=Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺, Al³⁺, and Ga³⁺, are probed at the MPWB1K/6-311G? and B3LYP/6-311G* levels of theory. The optimized geometries show the expanding or contracting capability of C₁₂Si₈ in order to accommodate metal ion guests. The inclusion energies indicate the stability of the complexes compared to the components. Meanwhile, the calculated binding energies show the stabilization of C₁₂Si₈ through the inclusion of Be²⁺, Mg²⁺, Al³⁺, and Ga³⁺. The host-guest interaction that is probed through NBO atomic charges supports the obtained results. This study refers to “metal ion encapsulation” as a strategy for stabilization of SiC heterofullerenes.     

A theoretical density functional study of association of Zn2+ with oxazolidine and its thio derivatives in the gas phase

We have performed density functional theory (DFT) calculations in order to study the gas‐phase interaction of oxo‐ and thio‐oxazolidine derivatives with Zn²⁺. The calculations were performed at B3LYP/6‐311+(2df,2p) level of theory. It has been found, in all cases, that the direct association of Zn²⁺ with the carbonyl and thiocarbonyl groups takes place at the heteroatom attached to position 2 irrespective of its nature. This preference has been attributed to the resonance effects caused by the nearest heteroatoms (oxygen and nitrogen). The most stable complexes correspond to structures with Zn²⁺ bridging between the heteroatom at position 2 or 4 of the 4‐ or 2‐enol (or the 4‐ or 2‐enethiol) tautomer and the dehydrogenated ring nitrogen atom, N3. Zn²⁺ association has a clear catalytic effect on the tautomerization processes which connect the oxo–thione forms with the enol–enethiol tautomers. Hence, although the enol–enethiol tautomers of oxazolidine and its thio derivatives should not be observed in the gas phase, the corresponding Zn²⁺ complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Zn²⁺ binding energies. Copyright © 2010 John Wiley & Sons, Ltd.     

A Novel Highly Sensitive and Selective Fluorescent Sensor for Imaging Copper (II) in Living Cells

In this work, we designed and synthesized a novel quinolin-based derivative which exhibited signaling behaviors for Cu²⁺. Upon the addition of Cu²⁺ to the solution of the molecule, it displayed an obvious fluorescence quenching in a linear fashion due to the formation of a 1:1 metal–ligand complex. This fluorescent sensor exhibited a rare sensitivity toward Cu(II) (the level of magnitude could be 6?×?10^?8), a rapid response (<10 s) and also high selectivity toward Cu²⁺ over other metal ions such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Ba²⁺, Fe³⁺, Mn²⁺, Hg²⁺, Pb²⁺, Cd²⁺, Cr³⁺, Co²⁺, Zn²⁺ and Al³⁺. Simultaneously, the cell imaging experiments and filter paper test demonstrated its extensive applicability.     

Spectroscopic Study of Some Alkali and Alkaline Earth Complexes with Benzo Crown Ethers in Ethanol Solution

The interaction between Na⁺, K⁺, Mg²⁺ and Ca²⁺ ions and benzo crown ethers B15C5, DB18C6, DB21C7, DB24C8 and DB30C10 in ethanol solution has been studied spectrophotometrically at 25°C. The formation constants for 1:1 complexes were determined by computer fitting of the resulting UV-absorbance-mole ratio data. In the case of all crown ethers used, K⁺ ion was found to form the most stable complexes. The observed selectivities of different benzo crowns for the cations used are discussed in terms of the cavity-cation size ratio, number of the donating oxygens participating in the cation binding, conformations of the free and complexed ligands and ionic solvation.     

A Novel Naphthalene-Immobilized Nanoporous SBA-15 as a Highly Selective Optical Sensor for Detection of Fe<Superscript>3+</Superscript> in Water

A novel organic-inorganic hybrid optical sensor (SBA-NCO) was designed and synthesized through immobilization of isocyanatopropyl-triethoxysilane and 1-amino-naphthalene onto the surface of SBA-15 by post-grafting method. The characterization of materials using XRD, TEM, N₂ adsorption-desorption, and FT-IR techniques confirmed the successful attachment of organic moieties and preserving original structure of SBA-15 after modification step. Fluorescence experiments demonstrated that SBA-NCO was a highly selective optical sensor for the detection of Fe³⁺ directly in water over a wide range of metal cations including Na⁺, Mg²⁺, Al³⁺, K⁺, Ca²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ in a wide pH values.     

Interaction between 1-[p-(dimethylamino) benzoyl]-4′-phenyl-semicarbazide and Cu

A new compound, 1-[p-(dimethylamino)benzoyl]-4′-phenyl-semicarbazide (1) was synthesized and showed highly selective response to Cu²⁺ over other metal ions such as Pb²⁺, Mg²⁺, Fe²⁺, Co²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Ni²⁺, Ca²⁺, Ag⁺, Na⁺, K⁺, and Li⁺. The control compound, 1-[p-(dimethylamino)benzoyl]-4-phenyl-thiosemicarbazide (2), showed different fluorescence spectral response to Cu²⁺. A 1:1 complex between Cu²⁺ and 1 was formed while 1:1 and 1:2 complexes between Cu²⁺ and 2 were formed. The binding model between the receptor (1 or 2) and Cu²⁺ was supported by IR spectra, mass spectra, and computation model. 1 possessed higher selectivity towards Cu²⁺ compared with 2 owing to the difference of complexation ability between urea and thiourea groups.     

A Selective Fluorescent Sensor for Hg2+

A novel rhodamine based fluorescent chemosensor RQP was prepared and characterized by ¹HNMR, ¹³CNMR and HR-MS. The properties of RQP were studied through UV–Vis spectroscopy and fluorescence spectroscopy. RQP showed highly selectivity toward Hg²⁺ over other metal ions, including Ag⁺, Cd²⁺, Cu²⁺, Na⁺, Mg²⁺, Ni²⁺, Pb²⁺, Fe³⁺, and Zn²⁺ in aqueous solutions. The recognition process is reversible and confirmed by EDTA experiment.     

A New Reactive 1,8-Naphthalimide Derivative for Highly Selective and Sensitive Detection of Hg<Superscript>2+</Superscript>

A 1,8-naphthalimide derivative with a reactive aliphatic hydroxyl was designed and synthesized as a fluorescent probe. Its structure was characterized by IR, ¹H NMR, ¹³C NMR, LC-MS and HPLC. The probe showed high selectivity and sensitivity to Hg²⁺ over other metal ions such as Pb²⁺, Na⁺, K⁺, Cd²⁺, Cr³⁺, Zn²⁺, Cu²⁺, Ni²⁺, Ca²⁺, Fe³⁺, Fe²⁺, Co²⁺, Mn²⁺ and Mg²⁺ in MeCN/H₂O (15/85, v/v). The increase in fluorescence intensity was linearly proportional to the concentration of Hg²⁺ in the range of 18–40 μM with a detection limit of 1.38 × 10^?7 mol/L. The probe could work in a pH span of 4.3–9.0 and respond to Hg²⁺ quickly with strong anti-interference ability. Job’s plot suggested a 1:2 complex of the probe and Hg²⁺.     

Interaction studies of cysteine with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cation complexes

The coordination geometries, electronic features, metal ion affinities, entropies, and the energetics of Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ metal cations with different possible conformations of cysteine complexes were studied. The complexes were optimized using density functional theory (B3LYP) and second order Moller–Plesset Perturbation (MP2) theory methods using 6‐311 + +G** basis set. The interactions of the metal cations at different nucleophilic sites of cysteine conformations were considered after a careful selection among several binding sites. All the metal cations coordinate with cysteine in a tridentate manner and also the most preferred position for the interaction. It is found that, the overall structural parameters of cysteine are not altered by metal ion substitution, but, the metal ion‐binding site has undergone a noticeable change. All the complexes were characterized by an electrostatic interaction between ligand and metal ions that appears slightly more pronounced for lithium and beryllium metal complexes. The metal ion affinity (MIA) and basis set superposition error (BSSE) corrected interaction energy were also computed for all the complexes. The effect of metal cations on the infrared (IR) stretching vibrational modes of amino N? H bond, side chain thiol group S? H bond, hydroxyl O? H bond, and Carbonyl C?O bond in cysteine molecules have also been studied. The nature of the metal ion‐ligand bond and the coordination properties were examined using natural bond order (NBO) at bond critical point (electron density and their Laplacian of electron density) through Atoms in Molecules (AIM) analyses. Copyright © 2010 John Wiley & Sons, Ltd.     

A Novel Ratiometric Fluorescent Chemosensor for Cd2+

Novel ratiometric fluorescent chemosensor C7 was synthesized and characterized by UV–vis and fluorescence spectroscopy. C7 showed high sensitivity for Cd²⁺ among Na⁺, Mg²⁺, Cu²⁺, Pb²⁺, Ni²⁺, Fe³⁺, Zn²⁺, Ag⁺ Hg²⁺ and Cd²⁺ in ethanol.     

Complexation and DFT studies of lower rim hexahomotrioxacalix[3]arene derivatives bearing pyridyl groups with transition and heavy metal cations. Cone versus partial cone conformation

The binding of representative alkali, alkaline earth, transition and heavy metal cations by 2‐pyridylmethoxy derivatives (1b, in cone and partial cone conformations) of p‐tert‐butylhexahomotrioxacalix[3]arene was studied. Binding was assessed by extraction studies of the metal picrates from water into dichloromethane and by stability constant measurements in acetonitrile and methanol, using spectrophotometric and potentiometric techniques. Microcalorimetric studies of some selected complexes in acetonitrile were performed, as well as proton NMR titrations. Computational methods (density functional theory calculations) were also employed to complement the NMR data. The results are compared with those obtained with the dihomooxacalix[4]arene 2b and the calix[4]arene 3b derivative analogues. Partial cone‐1b is the best extractant for transition and heavy metal cations. Both conformers of 1b exhibit very high stability constants for soft and intermediate cations Pb²⁺, Cd²⁺, Hg²⁺, Zn²⁺ and Ni²⁺, with cone‐1b the strongest binder (ML, log β ≥ 7) and partial cone‐1b the most selective. Both derivatives show a slight preference for Na⁺. Besides the formation of ML complexes, ML₂ and M₂L species were also observed. The former complexes were, in general, formed with the transition and heavy metal cations, whereas the latter were obtained with Ag⁺ and Hg²⁺ and partial cone‐1b. In most cases, these species were corroborated by the proton NMR and density functional theory studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Selective Recognition of Cobalt (II) Ion by a New Cryptand Compound with N2O2S2 Donor Atom Possessing 2-Hydroxy-1-Naphthylidene Schiff Base Moiety

A new cryptand compound carrying 2-hydroxy-1-naphthylidene Schiff base moiety (3) was designed and synthesized by reaction of the corresponding macrobicyclic amine compound (1) and 2-hydroxy-1-naphthaldehyde (2). The influence of metal cations such as Mg²⁺, Ca²⁺, Sr²⁺, Fe²⁺,Co²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Al³⁺ and Pb²⁺ on the spectroscopic properties of the new fluoroionophore was investigated in acetonitrile-dichloromethane solution (9.5/0.5) by means of absorption and emission spectrometry. The blue shifts on the fluorescence spectrum were observed for all metal cations at 504nm. At the same time the fluorescence spectrum of the ligand showed quenching in the intensity of the signal at 504 nm for all metal cations except for Zn²⁺. Interaction of Co²⁺ with the ligand caused quenching of naphtyl fluorescence higher than 84%. The method showed good selectivity and sensitivity for Co²⁺ with respect to other metal cations with linear range and detection limit of 1.5 × 10⁻⁷ to 3.3 × 10⁻⁶M and 4.8 × 10⁻⁸M respectively.