Interaction Of Metal Cations Research Articles

Influence of metal ions (Zn2+, Cu2+, Ca2+, Mg2+and Na+) on the water coordinated neutral and zwitterionicl-histidine dimer

The interaction of metal cations with mono hydrated, neutral and zwitterionic histidine dimer complexes are studied using the density functional theory (DFT-B3LYP) method in both gas and liquid phase. It is found that the metal interaction with histidine is governed by two types of bonds (I) N–Mn+ (Mn+ = Zn2+, Cu2+, Ca2+, Mg2+ and Na+), O–Mn+ bonds and (II) N⋯H–O and N–H⋯O hydrogen bonds. For both the liquid and gas phase, the coordination of metals with the nitrogen atom is strong in neutral systems, whereas the coordination with the oxygen atom is strong in the zwitterions systems. Among all the metal ions considered, the Cu2+ ion strongly coordinates with both the neutral and the zwitterionic forms of histidine dimer. AIM analysis indicates that the N–Mn+, O–Mn+ and hydrogen bonds are partially covalent and electrostatic in nature. The enthalpy of the reaction indicates that the reaction is energetically favoured and exothermic in nature. For all the metal complexes, pKa values decrease with the increase in hydrogen bond strength. Redox potential is high for the zwitterionic complex because of the transfer of electrons from the carboxylic group to amine moiety in all the metal complexes. From the MD calculations, we find that the backbone Mg2+ substituted complexes are stabilized around 0.9 nm, while for the other metal ions it is more than 1.0 nm. Kirkwood's potential indicates the presence of antiparallel dipole–dipole interactions.

Toward understanding of the role of Lewis acidity in aldol condensation of acetone and furfural using MOF and zeolite catalysts

The aldol condensation of furfural and acetone allow producing higher value products from simple organic compounds resulting from biomass processing. In this paper, a number of metal organic framework (MOF) materials possessing Lewis acidity were investigated as catalysts in this reaction. Experiments were carried out under batch reaction conditions in Parr stirred autoclave at 100°C during 0–4h. The catalytic results indicated that the aldol condensation over MOFs took place with the participation of acidic rather than basic centers. The catalytic performance of these materials exhibited could not be explained by their reported Lewis acidity. Experiments with heat-activated and re-hydrated samples showed that Brønsted acid sites could also be present in MOFs as a consequence of interaction of metal cation with surrounding water molecules. As a consequence, the catalysts having such generated Brønsted acidity exhibited enhanced activity in the reaction.

Cation···π interactions: QTAIM and NBO studies on the interaction of alkali metal cations with heteroaromatic rings

The cation···π interactions of alkali metal cations (Li+, Na+, and K+) with five-membered heteroaromatic rings [furan(C4H4O), thiophene(C4H4S), pyrrole(C4H5N)] were examined by high level ab initio calculations, to investigate the different roles of C4H4O, C4H4S, and C4H5N as the electron donor, the influential factors that affect these interactions, the nature of this kind of cation···π interaction, and to determine topological and energetical properties to characterize these interactions. The sulfur atom in C4H4S plays a certain role in the cation···π interactions except the C–C π bond, which is different from C4H4O and C4H5N. The size of cation and the character of heteroaromatic ring are two influential factors that affect the cation···π interactions. The studied cation···π interactions can be classified as “closed-shell” and noncovalent interactions. The electron density and its Laplacian at the bond critical points and ring critical points generated upon complexation are useful measurements for the strength of cation···π interactions.

Alkali Metal Cation Interactions with 15-Crown-5 in the Gas Phase: Revisited

Quantitative interactions of the alkali metal cations with the cyclic 15-crown-5 polyether ligand (15C5) are studied. In this work, Rb(+)(15C5) and Cs(+)(15C5) complexes are formed using electrospray ionization and studied using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. The energy-dependent cross sections thus obtained are interpreted to yield bond dissociation energies (BDEs) using an analysis that includes consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. 0 K BDEs of 175.0 ± 9.7 and 159.4 ± 9.6 kJ/mol, respectively, are determined and exceed those previously measured [J. Am. Chem. Soc. 1999, 121, 417-423] by 68 and 57 kJ/mol, respectively, consistent with the hypothesis proposed there that excited conformers had been studied. Because the analysis techniques have advanced since this early study, we also reanalyze the published data for the Na(+)(15C5) and K(+)(15C5) systems to ensure a self-consistent interpretation of all four systems. Revised BDEs for these systems are 296.1 ± 15.5 and 215.6 ± 10.6 kJ/mol, respectively, which are within experimental uncertainty of the previously reported values. In addition, quantum chemical calculations are conducted at the B3LYP/def2-TZVPPD level of theory with theoretical BDEs in reasonable agreement with experiment. Computations are also used to explore features of the potential energy surfaces for isomerization of the M(+)(15C5) complexes.

Metal Cation Dependence of Interactions with Amino Acids: Bond Dissociation Energies of Rb+ and Cs+ to the Acidic Amino Acids and Their Amide Derivatives

Metal cation-amino acid interactions are key components controlling the secondary structure and biological function of proteins, enzymes, and macromolecular complexes comprising these species. Determination of pairwise interactions of alkali metal cations with amino acids provides a thermodynamic vocabulary that begins to quantify these fundamental processes. In the present work, we expand a systematic study of such interactions by examining rubidium and cesium cations binding with the acidic amino acids (AA), aspartic acid (Asp) and glutamic acid (Glu), and their amide derivatives, asparagine (Asn) and glutamine (Gln). These eight complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) are determined experimentally using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy-dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory using def2-TZVPPD basis sets, with results showing reasonable agreement with experiment. At 0 and 298 K, most levels of theory predict that the ground-state conformers for M(+)(Asp) and M(+)(Asn) involve tridentate binding of the metal cation to the backbone carbonyl, amino, and side-chain carbonyl groups, although tridentate binding to the carboxylic acid group and side-chain carbonyl is competitive for M(+)(Asn). For the two longer side-chain amino acids, Glu and Gln, multiple structures are competitive. A comparison of these results to those for the smaller alkali cations, Na(+) and K(+), provides insight into the trends in binding energies associated with the molecular polarizability and dipole moment of the side chain. For all four metal cations, the BDEs are inversely correlated with the size of the metal cation and follow the order Asp < Glu < Asn < Gln.

γ-radiation effect on dicyclohexano-18-crown-6 aqueous solution in the presence of metal cations

Abstract γ-radiation effect on dicyclohexano-18-crown-6 (DCH18C6) aqueous solution in the presence of metal cations, such as K+ and Sr2+, was investigated, and some pale yellow precipitates were obtained at doses above 100 kGy. It was found that the complexation interaction of metal cations could accelerate the conversion of DCH18C6 into oligomers and the formation of precipitates, but it did not affect the formation mechanism of precipitates. Furthermore, the salting-out effect of metal cations played an important role in the precipitation. In order to inhibit the radiation-induced precipitation of DCH18C6 in water phase, nitric acid with a concentration of more than 1 M could be added to the system. The methods and results for analyzing radiation-induced products reported in this work are useful to understand the radiation chemistry behavior of DCH18C6 which is used as the extractant in the separation of long half-life radionuclides from spent nuclear fuel.

Selective complexation of alkali metal ions and nanotubular cyclopeptides: a DFT study

A density functional theory based on interaction of alkali metal cations (Li+, Na+, K+, Rb+ and Cs+) with cyclic peptides constructed from 3 or 4 alanine molecule (CyAla3 and CyAla4), has been investigated using mixed basis set (C, H, O, Li+, Na+ and K+ using 6-31+G(d), and the heavier cations: Rb+ and Cs+ using LANL2DZ). The minimum energy structures, binding energies, and various thermodynamic parameters of free ligands and their metal cations complexes have been determined with B3LYP and CAM-B3LYP functionals. The order of interaction energies were found to be Li+ > K+ > Na+ > Rb+ > Cs+ and Li+ > Na+ > K+ ≫ Rb+ > Cs+, calculated at CAM-B3LYP level for the M/CyAla3 and M/CyAla4 complexes, respectively. Their selectivity trend shows that the highest cation selectivity for Li+ over other alkali metal ions has been achieved on the basis of thermodynamic analysis. The main types of driving force host–guest interactions are investigated, the electron-donating O offers lone pair electrons to the contacting LP* of alkali metal cations.

Noncovalent Interactions of Metal Cations and Arenes Probed with Thallium(I) Complexes

The synthesis, characterization, and computational analysis of Tl(I) complexes bearing the bis(imino)pyridine scaffold, [{ArN═CPh}2(NC5H3)]Tl(+)(OTf)(-) (Ar = 2,6-Et2C6H33, 2,5-(t)Bu2C6H3, 4), are reported. The cations of these species showed long Tl-N and Tl-OTf distances indicating only weak or no ligand coordination. Computational analysis of the interactions between the Tl cation and the ligands (orbital populations, bond order, and energy decomposition analysis) point to only minimal covalent interactions of the cation with the ligands. The weak ligand-to-metal donation allows for additional interactions between the Tl cation and arene rings that are either intramolecular, in the case of 3, or intermolecular. From benzene or toluene, 4 crystallizes with inverted sandwich structures having two [{(2,5-(t)Bu2C6H3)N═CPh}2(NC5H3)]Tl(+) cations bridged by either benzene or toluene. A density functional computational description of these Tl-arene contacts required exchange-correlation functionals with long-range exchange corrections (e.g., CAM-B3LYP or LC-PBE) and show that Tl-arene contacts are stabilized by noncovalent interactions.

Cations Bind Only Weakly to Amides in Aqueous Solutions

We investigated salt interactions with butyramide as a simple mimic of cation interactions with protein backbones. The experiments were performed in aqueous metal chloride solutions using two spectroscopic techniques. In the first, which provided information about contact pair formation, the response of the amide I band to the nature and concentration of salt was monitored in bulk aqueous solutions via attenuated total reflection Fourier transform infrared spectroscopy. It was found that molar concentrations of well-hydrated metal cations (Ca(2+), Mg(2+), Li(+)) led to the rise of a peak assigned to metal cation-bound amides (1645 cm(-1)) and a decrease in the peak associated with purely water-bound amides (1620 cm(-1)). In a complementary set of experiments, the effect of cation identity and concentration was investigated at the air/butyramide/water interface via vibrational sum frequency spectroscopy. In these studies, metal ion-amide binding led to the ordering of the adjacent water layer. Such experiments were sensitive to the interfacial partitioning of cations in either a contact pair with the amide or as a solvent separated pair. In both experiments, the ordering of the interactions of the cations was: Ca(2+) > Mg(2+) > Li(+) > Na(+) ≈ K(+). This is a direct cationic Hofmeister series. Even for Ca(2+), however, the apparent equilibrium dissociation constant of the cation with the amide carbonyl oxygen was no tighter than ∼8.5 M. For Na(+) and K(+), no evidence was found for any binding. As such, the interactions of metal cations with amides are far weaker than the analogous binding of weakly hydrated anions.

Fabrication of transition‐metal‐doped polypyrrole/multiwalled carbon nanotubes nanocomposites for supercapacitor applications

AbstractCopper chloride (CuCl2)‐doped polypyrrole (PPy)/multiwalled carbon nanotube (MWCNTs) nanocomposites were synthesized by an in situ oxidative polymerization method with ammonium persulfate as the oxidant in HCl medium and investigated as electrode materials for supercapacitors. The interaction of metal cations (Cu2+ ions) with PPy was confirmed by Fourier transform infrared spectroscopic analysis. The morphology of the nanocomposites was characterized by field emission scanning electron microscopy and high‐resolution transmission electron microscopy. Electrochemical characterizations of the composites materials were carried out by a three‐electrode probe method, where platinum and a saturated standard calomel electrode were used as the counter and reference electrodes, respectively. A 1M KCl solution was used as the electrolyte for all of the electrochemical characterizations. The transition‐metal‐ion doping enhanced the electrochemical properties of the conducting polymer. Among all of the composites, the CuCl2‐doped PPy/MWCNTs showed the highest specific capacitance value of 312 F/g at a 10 mV/s scan rate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Copper chloride‐doped polyaniline/multiwalled carbon nanotubes nanocomposites: Superior electrode material for supercapacitor applications

AbstractIn this study, copper chloride (CuCl2)‐doped polyaniline (PANI)/multiwalled carbon nanotubes (MWCNTs) nanocomposite (PANI C2 CNT), CuCl2‐doped PANI (PANI C2) and pure PANI was synthesized by in situ oxidative polymerization method, using ammonium peroxodisulfate as oxidant in HCl medium. These composites were investigated as electrode materials for supercapacitors. The interaction of metal cation (Cu2+) with PANI was confirmed by Fourier transform infrared spectroscopy. The morphology of the composites was characterized by field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy analysis. Electrochemical characterizations of the materials were carried out by three electrode probe method, where platinum and saturated standard calomel electrode were used as counter and reference electrode, respectively. 1 M KCl solution was used as electrolyte for all the electrochemical characterizations. The transition metal ion doping enhanced the electrochemical properties of the conducting polymer. Among all the composites, CuCl2‐doped PANI/MWCNT showed highest specific capacitance value of 724 F/g at 10 mV s−1 scan rate. The Nyquist plot of the polymeric materials showed low equivalent series resistance of the electrode materials. Thermal stability of the composites was examined by thermogravimetric analysis.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers

H2 interaction with divalent cations in isostructural MOFs: a key study for variable temperature infrared spectroscopy

Systematic studies of H2 adsorption by variable temperature infrared (VTIR) spectroscopy have added value in the characterization of hydrogen storage materials. As a key study to describe the potential of the method, here we report VTIR spectroscopy results of H2 adsorption at isostructural MOFs CPO-27-M (M = Mg, Mn, Co, Ni, Zn). The strongest perturbation of H2 vibrational frequency is due to the interaction with an open metal site. Although ionic radius is an empirical value, the direct correlation between ionic radii of the metal cation and H2 interaction energy is found in MOFs of the same topology. The highest enthalpy of hydrogen adsorption 15 ± 1 kJ mol(-1) was found for Ni(2+). VTIR results of H2 adsorption at isostructural MOFs CPO-27-M (M = Mg, Mn, Co, Ni, Zn) were compared with data obtained from analogous studies performed on a large variety of microporous materials (MOFs and zeolites), underlining the relevance of the approach to get reliable energetic and entropic (ΔH(0) and ΔS(0)) values to be compared with computational data and isosteric heats.

Selectivity of ion exchangers in extracting cesium and rubidium from alkaline solutions

We compare the ion exchange selectivity of phenol-type sorbents based on phenol formaldehyde resins, products of condensation of diatomic phenols with formaldehyde, and crosslinked polymer based on C-phenyl[4]resorcinarene resin, for cesium and rubidium ions. It is shown that phenol formaldehyde sorbents are the ones most selective. The interaction of alkali metal cations with the anion of calix[4]arene is investigated via quantum-chemical modeling. It is shown that the selectivity toward cesium and rubidium ions in ion exchangers of the phenolic type is not due to specific interactions of ions with phenolic groups.

Thermochemistry of Alkali Metal Cation Interactions with Histidine: Influence of the Side Chain

The interactions of alkali metal cations (M(+) = Na(+), K(+), Rb(+), Cs(+)) with the amino acid histidine (His) are examined in detail. Experimentally, bond energies are determined using threshold collision-induced dissociation of the M(+)(His) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy dependent cross sections provide 0 K bond energies of 2.31 ± 0.11, 1.70 ± 0.08, 1.42 ± 0.06, and 1.22 ± 0.06 eV for complexes of His with Na(+), K(+), Rb(+), and Cs(+), respectively. All bond dissociation energy (BDE) determinations include consideration of unimolecular decay rates, internal energy of reactant ions, and multiple ion-neutral collisions. These experimental results are compared to values obtained from quantum chemical calculations conducted previously at the MP2(full)/6-311+G(2d,2p), B3LYP/6-311+G(2d,2p), and B3P86/6-311+G(2d,2p) levels with geometries and zero point energies calculated at the B3LYP/6-311+G(d,p) level where Rb and Cs use the Hay-Wadt effective core potential and basis set augmented with additional polarization functions (HW*). Additional calculations using the def2-TZVPPD basis set with B3LYP geometries were conducted here at all three levels of theory. Either basis set yields similar results for Na(+)(His) and K(+)(His), which are in reasonable agreement with the experimental BDEs. For Rb(+)(His) and Cs(+)(His), the HW* basis set and ECP underestimate the experimental BDEs, whereas the def2-TZVPPD basis set yields results in good agreement. The effect of the imidazole side chain on the BDEs is examined by comparing the present results with previous thermochemistry for other amino acids. Both polarizability and the local dipole moment of the side chain are influential in the energetics.

On The Lower Lewis Basicity of Siloxanes Compared to Ethers

Abstract1,3‐Dimethyldisiloxane, O(SiH2Me)2, diethyl ether, OEt2, and their metal complexes (Li+,Ag+) have been used as model systems to uncover the reasons underlying the lower Lewis basicity of siloxanes compared to analogous ethers. Bonding in the metal complexes has been analyzed with quantum theory of atoms in molecules as well as natural bond orbital theory. The binding to Li+ by O(SiH2Me)2 and OEt2 is largely of monopole – dipole type whereas binding of Ag+ also shows small charge transfer components. The more ionic Si–O bonds in O(SiH2Me)2 compared to C–O bonds in OEt2 lead to more negative charge on the oxygen atom of O(SiH2Me)2 but the electrostatic attraction between metal cations and OEt2 is calculated to be slightly stronger by interacting quantum atoms energy decomposition analysis. The lower electrostatic attraction by O(SiH2Me)2 is due to repulsion between positively charged silicon atoms and the metal cations that compensate for the stronger attraction from the oxygen atom relative to OEt2. The total interaction of metal cations with O(SiH2Me)2 was calculated to be almost as strong as that with OEt2 and the lower stability of O(SiH2Me)2 complexes and the lower Lewis basicity of O(SiH2Me)2 is attributed to changes in the bonding and polarization of the ligands in the presence of metal cations. The polarization of O–Si bonds in O(SiH2Me)2 raises the energy of the molecule more than does the polarization O–C bonds in OEt2. Despite the lower stability of O(SiH2Me)2 metal complexes, solid state reaction enthalpies arising from a volume‐based thermodynamics approach suggest that they could be stabilized with a sufficiently large anion such as [Al(ORF)4]–.

Post-synthesis surface-modified silicas as adsorbents for heavy metal ion contaminants Cd(II), Cu(II), Cr(III), and Sr(II) in aqueous solutions

To analyze the influence of silica surface modification and confined space effects on specific interactions of divalent and trivalent metal cations with surface functionalities, three different high surface area silicas with different pore size distributions were modified with the following organosilanes: 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-(trimethoxysilylpropyl)diethylenetriamine, N-(triethoxysilylpropyl)ethylenediaminetriacetic acid (EDTrA), and 3-(2,4-dinitrophenylamino)propyltriethoxysilane. The silicas were characterized by N2 adsorption and reflectance FTIR spectroscopy before and after surface modification. N2 adsorption and pore size distributions showed an increase in the pore width for all EDTrA-modified silicas, opposite to what occurred with the other organosilanes. Adsorption isotherms of Cd(II), Cr(III), Cu(II), and Sr(II) obtained from aqueous solutions were compared and analyzed by silica type, organosilane functional group, and metal adsorbed. Reflectance FTIR spectroscopy was used to probe the acetate functionality in EDTrA as a function of adsorbed metal content. A band shift to higher energy for Cr(III) on the wide pore silica studied indicated that the interaction with the acetate groups can be probed in this manner. In general, the wider pore distribution silica provided larger adsorption maxima, whereas the narrower pore distribution silica provided more favorable ΔG because of stronger binding of the cations. Cr(III) and Cu(II) exhibited larger adsorption maxima compared to Cd(II) and Sr(II), with the grafted organosilanes studied since the first cations have a greater charge/radius ratio than the second ones that provide a greater binding energy.

Removal of endotoxins from plasmid DNA: Analysis of aggregative interaction of mobile divalent metal cations with endotoxins and plasmid DNA

Endotoxin lipopolysaccharide removal from plasmid DNA-based vaccine remains a very challenging task for bioprocess engineers. This paper examined the potential use and advantages of divalent cation (Zn(2+), Ca(2+), Mg(2+)) induced aggregation as a plasmid DNA purification method for lipopolysaccharide removal. Analysis of zeta potential, hydrodynamic size, percentage of aggregation; UV-Vis spectroscopy and electron microscopy were performed to determine the optimal cation for preferential aggregation of lipopolysaccharide over plasmid DNA. The results from the hydrodynamic size analysis showed that the addition of Zn(2+) resulted in the maximum theoretical number of lipopolysaccharide molecules per aggregate particle. Dynamic light scattering analysis showed that plasmid DNA aggregates formed a larger maximum hydrodynamic size when it was treated with Ca(2+) than the other two cations. The K(m) value for lipopolysaccharide-Zn(2+) was substantially low (0.28 M) and considerably large (>2 M) for plasmid DNA-Zn(2+). Scatchard plots for plasmid DNA cations showed positive slopes indicating that there was a minimum concentration of plasmid DNA or cations before a significant aggregation occurred. This work concluded that Zn(2+) had the most preferential aggregative interaction with lipopolysaccharide compared to Mg(2+) and Ca(2+).

Alkali metal cation interactions with 12-crown-4 in the gas phase: Revisited

Quantitative interactions of alkali metal cations with the cyclic 12-crown-4 polyether ligand (12C4) are studied. Experimentally, Rb+(12C4) and Cs+(12C4) complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) determined using threshold collision-induced dissociation of these complexes with xenon in a guided ion beam tandem mass spectrometer. The energy-dependent cross sections thus obtained are interpreted using an analysis that includes consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. 0K BDEs of 151.5±9.7 and 137.0±8.7kJ/mol, respectively, are determined and exceed those previously measured by 60 and 54kJ/mol, respectively, consistent with the hypothesis proposed there that excited conformers had been studied. In order to provide comparable thermochemical results for the Na+(12C4) and K+(12C4) systems, the published data for these systems are reinterpreted using the same analysis techniques, which have advanced since the original data were acquired. Revised BDEs for these systems are obtained as 243.9±12.6 and 182.0±17.3kJ/mol, respectively, which are within experimental uncertainty of the previously reported values. In addition, quantum chemical calculations are conducted at the B3LYP and MP2(full) levels of theory with geometries and zero point energies calculated at the B3LYP level using both HW*/6-311+G(2d,2p) and def2-TZVPPD basis sets. The theoretical results are in reasonable agreement with experiment, with B3LYP/def2-TZVPPD values being in particularly good agreement. Computations also allow the potential energy surfaces for dissociation of the M+(12C4) complexes to be elucidated. These are used to help explain why the previous studies formed excited conformers of Rb+(12C4) and Cs+(12C4) but apparently not of Na+(12C4) and K+(12C4).

Adsorption of Carbon Dioxide on Sodium and Potassium Forms of STI Zeolite

AbstractSodium and potassium forms of STI zeolite synthesized with Si/Al ratios 15, 25, and 35 were characterized using X‐ray powder diffraction and nitrogen adsorption at 77 K. To obtain detailed information on the effect of alkali metal cations on CO2 adsorption, the temperature dependence of CO2 isotherms was investigated in the temperature range from 273 to 333 K. Based on these data, isosteric heats of adsorption of CO2 were determined. It was found that the isosteric heat of CO2 adsorption attains the highest values on the sodium form of STI zeolite with a Si/Al ratio of 15. The lowest values were found with both sodium and potassium forms of STI zeolite having a Si/Al ratio of 35. Heats of adsorption of CO2 obtained for STI zeolites were discussed in detail and compared with those of FER, MFI, MEL, TUN, and IMF structural types. This comparison revealed that isosteric heats of adsorption of CO2 on STI zeolites are lower by approximately 8 kJ mol−1 compared with heats of adsorption for FER, MFI, MEL, TUN, and IMF zeolites composed of the eight‐ or/and ten‐ring channel systems as well as STI zeolites. This effect was explained on the basis of stronger interaction of alkali metal cations with oxygen atoms of the zeolitic framework.

Density functional theory study of interaction, bonding and affinity of group IIb transition metal cations with nucleic acid bases

The structure, bonding, and energetics of the complexes obtained from the interaction between the most stable tautomeric forms of free DNA and RNA bases and Zn2+, Cd2+ and Hg2+ cations have been studied using density functional B3LYP method. The 6-311+G (2df, 2p) basis set along with LANL2DZ pseudopotentials for the cations are used in the calculations. The tautomerization paths of the nucleobases are investigated and transition states between the tautomeric forms of the free bases are located. The relative stability of the complexes and the tautomers of the free nucleobases are discussed referring to MIA and relative energy values. For uracil, thymine and adenine, interaction of the metal cations with the most stable tautomers form the least stable molecular complexes. For cytosine and guanine, the stability of the metalated complexes differs significantly. The enthalpy (ΔH), entropy (TΔS) and free energy (ΔG) of the complexes at 298K have also been calculated.