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Substituting the O-C2H4-O-moiety of [2.2.2] by the O2CCO2-core of oxalic acid leads to the new Lehn-type cryptand [M ⊂ 2Oxa.2Oxa.2Oxa]m+. We explored by quantum chemical methods (B3LYP/LANL2DZp) the complexation behaviour and compared it with the original cryptand [2.2.2]. The cryptands [2Oxa.2Oxa.2Oxa] and [2.2.2] exhibit the same ion selectivity against alkaline and alkaline earth metal cation (K+ followed by Rb+; Ba2+ preferred over Sr2+). The exchange of the OC2H4O-moiety by the O2CCO2-moiety (the subsequent exchange of sp3- by sp2-carbon atoms) makes [2Oxa.2Oxa.2Oxa] less flexible in the OCCO-diether angle as [2.2.2]. This rigidity results in higher complexation energies for [M ⊂ 2Oxa.2Oxa.2Oxa]m+ and that the twisting of the dihedral angle CN...NC improves the nesting of the guest cations in the cryptand [2Oxa.2Oxa.2Oxa]. [ABSTRACT FROM AUTHOR]

The cryptand developed by Virgil L. Goedken and Shie-Ming Peng, along with its interactions with alkaline and alkaline earth metal ions, was investigated using computational chemistry (B3LYP/LANL2DZp) to gain insight into the influence of the flexibility of the chelating N-C-C-N group on overall selectivity towards metal ions. According to DFT calculations, the most suitable cation for the cryptand is Li+, as Na+ is too large and would prefer a longer bond between Na+ and the N-donor. Additionally, the Be2+-N bond in the Goedken-Peng cryptand is excessively long compared to the Mg2+-N-cryptate bond, which is too short. The most effective method for hosting the guest cations is for the cryptand to twist itself, and the flexibility of the chelating N-C-C-N group serves as the most effective structural motive for the Goedken-Peng cryptand to interact with the guest cation. [ABSTRACT FROM AUTHOR]

The interaction of dibutyltin(IV) dichloride (DBT) with 1,4-diazacycloheptane (homopiperazine, HP) was investigated. In solutions, the complexes formed a 1:1 complex, its protonated and hydrolyzed forms. The formation constants of the complexes and thermodynamic parameters as ΔH° and ΔS° were estimated. The optimization of the structure of the (Bu)2Sn(HP)Cl2 complex reveals that the tin is six-coordinate in a distorted octahedral geometry, where the two nitrogen atoms of homopiperazine and the two chloride ions are in one plane. The solid (Bu)2Sn(HP)Cl2 complex with homopiperazine was synthesized, and the composition was assigned by elemental micro-analysis and mass spectrum. The complex was investigated by infrared, mass spectra, and thermal measurements. The ligand and its complex were tested against antimicrobial Staphylococcus aureus (+ve), Escherichia coli (−ve), and antifungal Candida albicans and Aspergillus flavus. Anticancer activities of homopiperazine and its dibutyltin(IV) complex were tested against breast cancer cell lines. The molecular docking investigations were performed to know the possible modes of binding to the most active sites of the breast cancer oxidoreductase receptor and those of Escherichia coli. [ABSTRACT FROM AUTHOR]

Selective alkaline and earth alkaline metal ion encapsulation by six different Lehn-type cryptands was predicted by DFT (B3LYP/LANL2DZp) computational chemistry. All cryptands contain three identical moieties connected by the aliphatic nitrogen atom, constructing a very structurally flexible system for accommodating different-sized metal cations. Inspiration for selected hosts was taken from already well-known Lehn-type Cryptand [phen.phen.phen] where one phenanthroline was substituted by 5H-cyclopenta[2,1-b:3,4b′]pyridine in which the CH2– group was replaced by a series of heteroatoms forming the selected series of investigated hosts. The ion selectivity and the ability of the hosts to adjust their structure to accommodate the metal cations successfully were based on energy and geometric criteria. Medium-size cations have been proven to be best fitted for the selected host series. [ABSTRACT FROM AUTHOR]

The mechanisms for water exchange on [Zn(L)H2O]2+⋅H2O (L = tren: tris(2-aminoethyl)amine, trep: tris(2-phosphinoethyl)phosphine, and tres: tris(2-arsinoethyl)arsine) were studied using density functional theory (B3LYP/6-311 + G**) and evaluated by MP2 and B3LYP(PCM) energy calculations. The activation barriers for the water exchange reaction on [Zn(L)H2O]2+⋅H2O (L = tren, trep and tres) are (B3LYP/6-311 + G**) 9.9, 10.13 and 11.23 kcal mol−1, respectively. Topological analyses of the investigated ground state complexes were performed. The energy and structural data support an associative interchange (Ia) water exchange pathway. [ABSTRACT FROM AUTHOR]

The reaction of [RuIII(EDTA)(H2O/OH)]−/2− (EDTA4− = ethylenediaminetetraacetate) with bisulfide (HS−) and persulfide (HSS−) leading to the formation of a dinuclear disulfur-bridged [(EDTA)RuIIISSRuIII(EDTA)]4− product has been studied spectrophotometrically. Kinetics of the reaction of [RuIII(EDTA)(H2O/OH)]−/2− with HS− was studied in aqueous solution as a function of [HS-] at a constant pH of 8.2 (phosphate buffer) and temperature (20 °C). Formation of the product complex, [(EDTA)RuIIISSRuIII(EDTA)]4−, in the reaction of [RuIII(EDTA)(H2O/OH)]−/2− with HSS− was identified by ESI-MS studies. A working mechanism in agreement with the spectroscopic and kinetic data is presented. [ABSTRACT FROM AUTHOR]

The release of NO by [Fe(NO)(Et2NpyS4)], where (Et2NpyS4)2− = 2,6-bis(2-mercaptophenylthiomethyl)-4-substituted pyridine(2-), has been studied in the absence and presence of a trapping agent. The results show that [Fe(NO)(Et2NpyS4)] releases NO spontaneously in solution with a slow rate,k-NO = 1.7 × 10−4s−1at 23 °C, in a reversible reaction. NO release becomes faster when the reaction intermediate [Fe(Et2 NpyS4)] was trapped by CO, thereby preventing the back reaction. The release of NO was studied as a function of CO concentration and temperature. The reported activation parameters, especially the positive activation entropy values for the release of NO, favor the operation of a dissociative interchange (Id) mechanism. Thus, [Fe(NO)(Et2NpyS4)] can serve as a NO deliverer. [ABSTRACT FROM PUBLISHER]

The complex formation equilibria in the reaction of [Pd(en)(H2O)2]2+with 4,4′-bipiperidine (Bip) and DNA constituents such as inosine, inosine-5′-monophosphate, uracil, uridine, thymine, and thymidine were investigated at 25 °C and 0.1 M ionic strength. The [(H2O)(en)Pd(Bip)Pd(en)(H2O)]4+complex and its hydrolyzed species were formed. Substitution of coordinated water by inosine (Ino) as DNA constituent formed the complexes [(Ino)(en)Pd(Bip)Pd(en)(H2O)]3+and [(Ino)(en)Pd(Bip)Pd(en)(Ino)]2+. The formation of the binuclear complexes was further supported by spectral measurements. The formation constants of all possible mono- and binuclear complexes were determined and their speciation diagrams were evaluated. Binuclear complexes involving 4,4′-bipiperidine linkage of two Pd(en)2+species were investigated. The binding of DNA constituents to the binuclear complex was studied. [ABSTRACT FROM AUTHOR]

Density functional (B3LYP, B3PW91, X3LYP, BP86, PBEPBE, PW91PW91, and M06) and ab initio (MP2, MP4sdq, CCSD, and CCSD(T)) calculations with extended basis sets (6-311+G**, TZVP, LANL2DZ+p, and SDD+p, the latter including extra polarization and diffuse functions) indicate that HCN exchange on [Cu(HCN)4]+ proceeds via an associative interchange (Ia) mechanism and a D3h transition structure {[Cu(HCN)5]+}‡. The activation barrier, relative to the model complex [Cu(HCN)4]+·HCN, varies modestly, depending on the computational level. Typical values are 8.0 kcal M−1 (B3LYP/6-311+G**), 6.0 kcal M−1 (M06/6-311+G**), and 4.8 kcal M−1 (CCSD(T)/6-311+G**//MP2(full)/6-311+G**). Inclusion of an implicit solvent model (B3LYP(CPCM)/6-311+G**) leads to an activation barrier of 5.8 kcal mol−1. Comparison of the HCN exchange mechanisms on [Li(HCN)4]+ (limiting associative, A) and [Cu(HCN)4]+ (associative interchange, Ia) reveals that π back donation in the equatorial Cu–N bonds in the transition state determines the mechanism. Computed structural and energetic data indicate an associative interchange (Ia) mechanism for HCN exchange on [Cu(HCN)4]+. [ABSTRACT FROM AUTHOR]

Density functional (B3LYP, B3PW91, X3LYP, BP86, PBEPBE, PW91PW91, and M06) andab initio(MP2, MP4sdq, CCSD, and CCSD(T)) calculations with extended basis sets (6-311+G**, TZVP, LANL2DZ+p, and SDD+p, the latter including extra polarization and diffuse functions) indicate that HCN exchange on [Cu(HCN)4]+proceeds via an associative interchange (Ia) mechanism and aD3htransition structure {[Cu(HCN)5]+}‡. The activation barrier, relative to the model complex [Cu(HCN)4]+·HCN, varies modestly, depending on the computational level. Typical values are 8.0 kcal M−1(B3LYP/6-311+G**), 6.0 kcal M−1(M06/6-311+G**), and 4.8 kcal M−1(CCSD(T)/6-311+G**//MP2(full)/6-311+G**). Inclusion of an implicit solvent model (B3LYP(CPCM)/6-311+G**) leads to an activation barrier of 5.8 kcal mol−1. Comparison of the HCN exchange mechanisms on [Li(HCN)4]+(limiting associative, A) and [Cu(HCN)4]+(associative interchange,Ia) reveals thatπback donation in the equatorial Cu–N bonds in the transition state determines the mechanism. Computed structural and energetic data indicate an associative interchange (Ia) mechanism for HCN exchange on [Cu(HCN)4]+. [ABSTRACT FROM PUBLISHER]

The reaction of pyridine-2,6-dicarbaldehyde or 2,6-diacetylpyridine with 1,2-bis(o-aminophenylthio)ethane (1) in acetonitrile in the presence of stoichiometric amounts of iron(II) perchlorate gave the complexes [(pyN3S2)FeII(ClO4)2] (4) and [(pyN3Me2S2)FeII(ClO4)2] (5) of the 15-membered N3S2 macrocyclic ligands, pyN3S2  = {6,7-dihydro-15,19-nitrilobenzo(e,p)(1,4,7,15)dithiadiazacyclo-heptadecine-N,N′,N″,S,S′} and pyN3Me2S2 = {6,7-dihydro-16,18-dimethyl-15,19-nitrilobenzo(e,p)(1,4,7,15)dithiadiazacyclo-heptadecine-N,N′,N″,S,S′}, respectively. Physical measurements led to the conclusion that these complexes contained seven-coordinate iron(II) and a single-crystal X-ray examination of 4 confirmed this. Coordination of the Fe(II) center in 4 is best described as distorted pentagonal-bipyramidal with the three nitrogen atoms and two sulfur donors of the macrocycle defining the pentagonal plane and the perchlorate ions occupying axial positions. Room temperature (293 K) magnetic moments of 4 and 5 (μ eff = 4.9 and 4.7 B.M., respectively) are close to the value predicted for high-spin d6 systems. [ABSTRACT FROM PUBLISHER]

Different semi-empirical methods (PM3(tm), AM1*, and PM6) that have parameters for Ni were evaluated for structural and energy calculations in comparison with DFT calculations (B3LYP/LANL2DZp) and X-ray structures. The reported crystal structure for K4[Ni(nta)2)] · 4H2O (nta = nitrilotriacetate, monoclinic space group P21/n (No. 14), a = 10.024(2) Å, b = 10.838(2) Å, c = 10.631(2) Å, β = 96.46(3)°, V = 1147.6(4) Å3, Z = 2) and the published X-ray structures for {(2S,3S)-1,4-dimethoxy-2,3-bis[(salicylidene)amino]-butane}nickel(II) and amine(salicylaldehyde thiosemicarbazonato)nickel(II), [Ni(AST)NH3], were used for structural evaluation. The performance of the methods was also tested for typical ligand-substitution reactions at Ni(II) centers involving displacement of NH3 by L (L = PH3, AsH3, SbH3, H2O, H2S, H2Se, H2Te) in [Ni(NH3)3NH3]2+ and [Ni(AST)NH3]. Whereas PM6 performed well for the evaluation of the structural data, AM1* was found to reproduce the energies in an excellent way. [ABSTRACT FROM AUTHOR]

Reaction of [RuII(tpy)(pic)(H2O)]+ (1) with KHSO5 resulting in the formation of [RuIV(tpy)(pic)(O)]+ (2) was studied kinetically as a function of [KHSO5], temperature (15-35°C), and pressure (10-30 MPa) at a fixed pH of 5.1 using spectrophotometric techniques. A suggested mechanism that is in agreement with the observed rate and activation parameters is presented. Complex 1 was found to induce DNA (pBluescript) cleavage in the presence of KHSO5, which proceeds via oxygen transfer from 2. [ABSTRACT FROM AUTHOR]