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Precipitation and dissolution of calcium oxalate monohydrate (CaOx) crystals are relevant due to their major role in kidney stone diseases. To such an extent, small molecules and ions can act as inhibitors to prevent the formation of calcium oxalate monohydrate crystals. Herein, we explored the role of citrate and the counter cation Na+ ions in the dissolution of CaOx crystals. Citrate binds on the Ca2+ sites of the CaOx crystals to form calcium citrate. Dissolution of CaOx increases with the increase in the concentration of citrate ions and time of incubation. We observed that corrugations were formed on the surface of the CaOx crystals after the sodium citrate treatment during the dissolution process. Theoretical studies revealed that Na+ occupies the vacant site of Ca2+ in CaOx making a strain on the surface which leads to the subsequent deformation of the crystal.

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Recently, it was shown that µ-oxo-µ-peroxodiiron(III) is converted to high-spin µ-oxodioxodiiron(IV) through O-O bond scission. Herein, the formation and high reactivity of the anti-dioxo form of high-spin µ-oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic-absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. Decay of µ-oxodioxodiiron(IV) was greatly accelerated on addition of substrate. The reactivity order of substrates is toluene

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Catalytic activity of [Os(III)(OH)(H2O)(L-N4Me2)](PF6)2 (1: L-N4Me2 = N,N'-dimethyl-2,11-diaza-[3,3](2,6)pyridinophane) in 1,2-cis-aminohydroxylation of alkenes with sodium N-chloro-4-methylbenzenesulfonamide (chloramine-T) is explored. Simple alkenes as well as those containing several types of substituents are converted to the corresponding 1,2-aminoalcohols in modest to high yields. The aminoalcohol products have exclusively cis conformation with respect to the introduced -OH and -NHTs groups. The spectroscopic measurements including cold mass spectroscopic study of the reaction product of complex 1 and chloromine-T as well as density functional theory (DFT) calculations indicate that an oxido-aminato-osmium(V) species [Os(V)(O)(NHTs)(L-N4Me2)](PF6)2 (2) is an active oxidant for the aminohydroxylation. The DFT calculations further indicate that the reaction involves a [3 + 2] cycloaddition between 2 and alkene, and the regioselectivity in the aminohydroxylation of unsymmetrical alkenes is determined by the orientation that bears less steric hindrance from the tosylamino group, which leads to the energetically more preferred product isomer.

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Density-functional-theory (DFT) calculations are performed for the proposal of a plausible mechanism on the reduction of NO to N2O by a dinuclear ruthenium complex, reported by Arikawa and co-workers [J. Am. Chem. Soc. 2007, 129, 14160]. On the basis of the experimental fact that the reduction proceeds under strongly acidic conditions, the role of protons in the mechanistic pathways is investigated with model complexes, where one or two NO ligands are protonated. The reaction mechanism of the NO reduction is partitioned into three steps: reorientation of N2O2 (cis-NO dimer), O-N bond cleavage, and N2O elimination. A key finding is that the protonation of the NO ligand(s) significantly reduces the activation barrier in the rate-determining reorientation step. The activation energy of 43.1 kcal/mol calculated for the proton-free model is reduced to 30.2 and 17.6 kcal/mol for the mono- and diprotonated models, respectively. The protonation induces the electron transfer from the Ru(II)Ru(II) core to the O═N-N═O moiety to give a Ru(III)Ru(III) core and a hyponitrite (O-N═N-O)(2-) species. The formation of the hyponitrite species provides an alternative pathway for the N2O2 reorientation, resulting in the lower activation energies in the presence of proton(s). The protonation also has a marginal effect on the O-N bond cleavage and the N2O elimination steps. Our calculations reveal a remarkable role of protons in the NO reduction via N2O formation and provide new insights into the mechanism of NO reduction catalyzed by metalloenzymes such as nitric oxide reductase (NOR) that contains a diiron active site.

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Trans and cis influences of various X ligands in two isomeric structures of acyclic hypervalent compound Ph[XI(OH)] and heterocyclic λ(3)-iodane Ph[(heterocycle)I(OH)] have been investigated on the basis of I-OH bond distance (d), electron density at I-OH bond critical point (ρ), I-OH stretching frequency (ν), and molecular electrostatic potential minimum (Vmin) at the OH lone pair. d, ρ, ν, and Vmin are found to be good parameters for quantifying trans and cis influences, and among them, Vmin is the most sensitive parameter. Heterocyclic λ(3)-iodanes showed a smaller trans influence than acyclic λ(3)-iodanes. All systems showed higher trans influence than cis influence while relative order of both is in accordance with the inductive nature of the ligands. Among the heterocyclic λ(3)-iodanes, strong trans/cis influence is observed with N or B in the ring while P gave moderate and S gave weak trans/cis influence. Among the substituents on the cis-positioned phenyl ring in heterocyclic λ(3)-iodanes, electron withdrawing ortho substitution significantly strengthened the hypervalent I-OH bond. The stability of a product resulting from the nucleophilic attack of Cl(-) on a λ(3)-iodane is directly correlated with the trans/cis influence of the ligands. This relationship is helpful to make good prediction on the interaction energy of a nucleophile in trivalent hypervalent iodine complex and hence useful in designing stable acyclic and heterocyclic hypervalent complexes.

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The trans influence of various X ligands in hypervalent iodine(III) complexes of the type CF(3)[I(X)Cl] has been quantified using the trans I-Cl bond length (d(X)), the electron density ρ(r) at the (3, -1) bond critical point of the trans I-Cl bond, and topological features of the molecular electrostatic potential (MESP). The MESP minimum at the Cl lone pair region (V(min)) is a sensitive measure of the trans influence. The trans influence of X ligands in hypervalent iodine(V) complexes is smaller than that in iodine(III) complexes, while the relative ordering of this influence is the same in both complexes. In CF(3)[I(X)Y] complexes, the mutual trans influence due to the trans disposition of the X and Y ligands is quantified using the energy E(XY) of the isodesmic reaction CF(3)[I(X)Cl] + CF(3)[I(Y)Cl] → CF(3)[I(Cl)Cl] + CF(3)[I(X)Y]. E(XY) is predicted with good accuracy using the trans-influence parameters of X and Y, measured in terms of d(X), ρ(r), or V(min). The bond dissociation energy (E(d)) of X or Y in CF(3)[I(X)Y] is significantly influenced by the trans influence as well as the mutual trans influence. This is confirmed by deriving an empirical equation to predict E(d) using one of the trans-influence parameters (d(X), ρ(r), or V(min)) and the mutual trans-influence parameter E(XY) for a large number of complexes. The quantified values of both the trans influence and the mutual trans-influence parameters may find use in assessing the stability of hypervalent iodine compounds as well as in the design of new stable hypervalent complexes. Knowledge about the I-X bond dissociation energies will be useful for explaining the reactivity of hypervalent iodine complexes and the mechanism of their reactions.

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The trans influence of various phosphine ligands (L) in direct as well as dissociative reductive elimination pathways yielding CH(3)CH(3) from Pd(CH(3))(2)L(2) and CH(3)Cl from Pd(CH(3))(Cl)L(2) has been quantified in terms of isodesmic reaction energy, E(trans), using the MPWB1K level of density functional theory. In the absence of a large steric effect, E(trans) correlated linearly with the activation barrier (E(act)) of both direct and dissociation pathways. The minimum of molecular electrostatic potential (V(min)) at the lone pair region of phosphine ligands has been used to assess their electron donating power. E(trans) increased linearly with an increase in the negative V(min) values. Further, the nature of bonds that are eliminated during reductive elimination have been analyzed in terms of AIM parameters, viz. electron density (ρ(r)), Laplacian of the electron density (∇(2)ρ(r)), total electron energy density (H(r)), and ratio of potential and kinetic electron energy densities (k(r)). Interestingly, E(act) correlated inversely with the strength of the eliminated metal-ligand bonds measured in terms of the bond length or the ρ(r). Analysis of H(r) showed that elimination of the C-C/C-Cl bond becomes more facile when the covalent character of the Pd-C/Pd-Cl bond increases. Thus, AIM details clearly showed that the strength of the eliminated bond is not the deciding factor for the reductive elimination but the nature of the bond, covalent or ionic. Further, a unified picture showing the relationship between the nature of the eliminated chemical bond and the tendency of reductive elimination is obtained from the k(r) values: the E(act) of both direct and dissociative mechanisms for the elimination of CH(3)CH(3) and CH(3)Cl decreased linearly when the sum of k(r) at the cleaved bonds showed a more negative character. It means that the potential electron energy density dominates over the kinetic electron energy density when the bonds (Pd-C/Pd-Cl) become more covalent and the eliminated fragments attain more radical character leading to the easy formation of C-C/C-Cl bond.

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Isodesmic reactions of the type Pd(II)Cl(2)X + Pd(II)Cl(3) --> Pd(II)Cl(2) + Pd(II)Cl(3)X have been designed to study the trans influence of a variety of 'X' ligands (X = H(2)O, NH(3), Py, CO, SMe(2), C(2)H(4), AsH(3), PH(3), AsMe(3), PMe(3), PEt(3), ONO(-), F(-), Cl(-), Br(-), N(3)(-), NO(2)(-), OH(-), CN(-), Ph(-), H(-), CH(3)(-), SiH(3)(-)) using density functional theory (MPWB1K) and COSMO continuum solvation model. We find that the isodesmic reaction energy E(1) is a good quantitative measure of the trans influence of X. E(1) showed good linear relationships to trans Pd-Cl bond length and the electron density rho(r) at the (3, -1) bond critical point of the trans Pd-Cl bond. On the basis of E(1) values, ligands are classified into three trans influencing groups, viz. strong, moderate, and weak. Isodesmic reactions of the type Pd(II)Cl(2)X + Pd(II)Cl(2)Y --> Pd(II)Cl(2) + Pd(II)Cl(2)X(Y) with ligands 'X' and 'Y' in the trans positions are also modelled to obtain the energy of the reaction E(2). E(2) is a measure of the mutual trans influence of X and Y and the highest (99.65 kcal mol(-1)) and the lowest (-3.95 kcal mol(-1)) E(2) are observed for X = Y = SiH(3)(-) and X = Y = H(2)O, respectively. Using the E(1) values of X (E(1X)) and Y (E(1Y)), the empirical equation 0.02026(E(1X) + (E(1Y)/radical2))(2) is derived for predicting the E(2) values (standard error = 2.33 kcal mol(-1)). Further, using the rho(r) of the trans Pd-Cl bond in [Pd(II)Cl(3)X](n-) (rho(1X)) and [Pd(II)Cl(3)Y](n-) (rho(1Y)), and a multiple linear regression (MLR) approach with rho(1X), rho(1Y), and rho(1X)rho(1Y) as variables, accurate prediction is made for predicting E(2) of any combination of X and Y (standard error = 2.20 kcal mol(-1)). We also find that the contribution of trans influence to the bond dissociation energy of ligands X or Y in complexes of the type [Pd(II)Cl(2)X(Y)](n-) can be quantified in terms of E(1X) and E(1Y) or the corresponding rho(1X) and rho(1Y). The calculated E(1) values may find use in the development of new trans influence-incorporated force field models for palladium.

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Density functional theory computations at the B3LYP/6-31G(d,p) level have been carried out for three types of model compounds, viz. (i) 4-substituted bicyclo[2.2.2]octane carboxylic acids, (ii) anions of 4-substituted bicyclo[2.2.2]octane carboxylic acids and (iii) 4-substituted quinuclidines where the substituents are NO(2), CN, Cl, Br, CF(3), F, CHO, CH(2)Cl, COOH, COCH(3), CONH(2), OH, OCH(3), C(6)H(5), NH(2), H, CH(3), CH(2)CH(3), CH(CH(3))(2), and C(CH(3))(3) to study the dependencies between molecular electrostatic potential minimum (V(min)) and the inductive substituent constant sigma(I). All the three model systems show excellent linear correlation between V(min) and sigma(I) suggesting that the calculation of V(min) parameter in these systems offers a simple and efficient computational approach for the evaluation of inductive substituent constants. The calculated linear equation for the models (i), (ii), and (iii) are V(min) = 12.982 sigma(I)- 48.867, V(min) = 13.444 sigma(I)- 182.760, and V(min) = 18.100 sigma(I)- 65.785, respectively. Considering the simplicity of the quinuclidine model, V(min) value at the nitrogen lone pair region of a 4-substituted quinuclidine system is recommended for the evaluation of sigma(I). Further, the additivity effect of sigma(I) is tested on multiply substituted quinuclidine and bicyclo[2.2.2]octane carboxylic acid derivatives using the V(min) approach and the results firmly supported the additivity rule of inductive effect. The systems showing considerable deviations from the additivity rule are easily recognized as those showing either steric effect or intramolecular hydrogen bond interactions at the V(min) response site. However, the distance relation of sigma(I) is not well represented in the caged molecular systems.

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