Hypersensitivity and its application to structural analysis of lanthanide complexes

Hypersensitivity of the ternary complexes Ln(β-dik)4HMQ(where Ln=Nd, Ho, Er,β-dik=acetylacetonate(AA), dibenzoylmethanate(DBM) and MQ=4-methylquinoline) in acetone solution is studied based on the dynamic coupling model. The structures of these complexes in solution are deduced. Their coordination polyhedrons are all distorted square antiprism. Neodymium complexes have D2 symmetry, while holmium and erbium complexes have exact D2d symmetry.     

Solution chemistry of lanthanide complexes—III: Spectroscopic studies of lanthanide complexes of glycine and polyglycines

The lanthanide complexes of glycine, diglycine and triglycine have been studied by a variety of physical means. Measurements of differential absorption of Ho(III) complexes, luminescence intensities of Tb(III) complexes, and intermolecular energy transfer from Tb(III) to Eu(III) complexes were all used to characterize the nature of the solution chemistry. The complexes tend to remain mononuclear at low pH, but associate through hydroxide linkages above neutral pH. The degree of association is much less for complexes of diglycine relative to those of glycine, suggesting that the steric nature of the amino acid ligand plays a dominant role in determining the degree of association.     

Can the DFT-D method describe the full range of noncovalent interactions found in large biomolecules?

The DFT-D method is shown to yield interaction energies between biologically important groups to an accuracy comparable to that obtained using state-of-the-art ab initio methods.     

The precipitation of the lanthanide elements complexes with hexammine cobalt(III) cation—I: The sulfate complexes of the trivalent lanthanide elements

Precipitation behaviors of the trivalent lanthanide elements from (NH₄)₂SO₄ and H₂SO₄ solutions were studied using hexammine cobalt(III) cation as the precipitant. Trivalent lanthanide elements from La to Ho precipitate as crystalline complexes of the same composition, [Co(NH₃)₆][Ln(SO₄)₃]·nH₂O. The solubility increases rapidly with increase of the atomic number after a minimum at Nd, Sm and Eu. Somewhat different behavior of Ce(III) was observed.     

The precipitation of lanthanide elements complexes with hexammine cobalt(III) cation—II: The carbonate complexes of the trivalent lanthanide elements

Precipitation behaviors of the trivalent lanthanide elements and yttrium in potassium and ammonium carbonate solutions with addition of hexammine cobalt(III) chloride as the precipitant were examined. La to Tb in K₂CO₃ solution and La to Lu and Y in (NH₄)₂CO₃ solution precipitated as scarcely soluble crystalline complexes. Lighter lanthanide elements are more easily precipitated and their solubilities are smaller than the heavier ones. Three different compositions of the precipitates are formed, as follows: [I] [Co(NH₃)₆][Ln(CO₃)₃]·nH₂O, [II] [Co(NH₃)₆][Ln(CO₃)₃]·1/2[Ln₂(CO₃)₃]·nH₂O and [Co(NH₃)₆][Ln(CO₃)₃]·α[Co(NH₃)₆]₂(CO₃)₃·nH₂O(α=0.1–0.3)     

The determination of the stability constants of the lanthanide α-hydroxyisobutyrate and lactate complexes by potentiometric titration

The stability constants of the lanthanide and yttrium, complexes with α-hydroxyisobutyrate and lactate, have been determined by potentiometric titration. The average numbor of ligands bound per metal ion has been calculated by the method of calvin-wilson and indicates the formation of uninegative tetra-ligand complexes of the form ML₄-. The ₄ formation constants have been derived by ₄ procedures; bjerrum's half-n¯;-method. fronaeus' and poulsen's extrapolation methods, and by least squares calculation, using an IBM 1620 digital computer.     

DFT study of the ring opening polymerization of ε-caprolactone by grafted lanthanide complexes: 1--Effect of the grafting mode on the reactivity of borohydride complexes

The influence of the grafting mode of a borohydride lanthanum complex on a silica surface on the energetic (kinetic and thermodynamic parameters) of the Ring Opening Polymerization (ROP) reaction of ε-caprolactone has been studied in the framework of density functional theory (DFT). For all considered grafted catalysts (monografted, bigrafted, or bigrafted after breaking of a Si-O-Si bridge), it is shown that lanthanum borohydride grafted complexes are efficient in lactone polymerization. Moreover, the reaction pathways (leading to a -CH(2) OBH(2) chain end) are predicted to be energetically similar for the three grafting modes, indicating that all grafted modes can account for the activity for silica treated at 700 °C. The catalytic activity of the grafted complexes is also very similar to that of the homogeneous complexes.     

How accurate are TD-DFT excited-state geometries compared to DFT ground-state geometries?

In this work, we take a different angle to the benchmarking of time-dependent density functional theory (TD-DFT) for the calculation of excited-state geometries by extensively assessing how accurate such geometries are compared to ground-state geometries calculated with ordinary DFT. To this end, we consider 20 medium-sized aromatic organic compounds whose lowest singlet excited states are ideally suited for TD-DFT modeling and are very well described by the approximate coupled-cluster singles and doubles (CC2) method, and then use this method and six different density functionals (BP86, B3LYP, PBE0, M06-2X, CAM-B3LYP, and ωB97XD) to optimize the corresponding ground- and excited-state geometries. The results show that although each hybrid functional reproduces the CC2 excited-state bond lengths very satisfactorily, achieving an overall root mean square error of 0.011 Å for all 336 bonds in the 20 molecules, these errors are distinctly larger than those of only 0.004–0.006 Å with which the hybrid functionals reproduce the CC2 ground-state bond lengths. Furthermore, for each functional employed, the variation in the error relative to CC2 between different molecules is found to be much larger (by at least a factor of 3) for the excited-state geometries than for the ground-state geometries, despite the fact that the molecules/states under investigation have rather uniform chemical and spectroscopic character. Overall, the study finds that even in favorable circumstances, TD-DFT excited-state geometries appear intrinsically and comparatively less accurate than DFT ground-state ones.     

Application of the oscillator strength of “hypersensitive” transitions to the investigation of complex equilibria of lanthanide ions—II: Spectroscopy,stability and thermodynamics of lanthanide complexes with monocarboxylic and α-hydroxyacids

Stability constants and thermodynamic parameters of Nd³⁺, Ho³⁺ and Er³⁺ complexes with acetates, propionates, glycolates, lactates and α-hydroxyisobutyrates were determined by a spectroscopic method based upon the measurements of the variation of oscillator strengths of “hypersensitive” 4f-4f-transitions [2].The sets of β_n values at 21°C are in a good agreement with those found potentiometrically [3–8]. The stability constants of the complexes evaluated at 5 different temperatures were used for the calculation of ΔG, ΔH, ΔS values. The evaluated thermodynamic parameters are in a satisfactory agreement with those found calorimetrically [5,8]. The thermodynamic parameters calculated from two independent “hypersensitive” transitions of the Er³⁺ ion are also consistent.     

Effect of the nature of lanthanide on intramolecular C-F→Ln dative interactions in hexafluoroisopropoxide complexes

Russian Chemical Bulletin - Electronic structures of a series oflanthanide complexes with hexafluoroisopropoxide ligands [Ln(OCH(CF3)2)2(μ2-OCH(CF3)2)(DME)]2 (Ln = Ce, Sm, Tm, Yb; DME is...     

The applicability of the “straight-line method” of asmus in the determination of the composition of polynuclear complexes

The straight-line method of Asmus was originally developed for the determination of n in mononuclear complexes of the general form AB_n (n≧ 1). In the present investigation it is demonstrated that the method also can be used for determining the value of n in polynuclear complexes of the form A[_mB_n (m > 1). The method as suggested by Asmus, is, however, not capable of distinguishing between mono- and polynuclear species. It is further shown, that the straight-line method can be applied for the determination of the value of m.     

DFT study of the ring opening polymerization of ε-caprolactone by grafted lanthanide complexes: 2--Effect of the initiator ligand

The influence of the initiator ligand on the Ring Opening Polymerization (ROP) of ε-caprolactone by lanthanide complexes grafted on silica have been investigated by means of density functional theory (DFT) calculations. Three different initiator ligands (alkyl, dialkylamido and borohydride) and three grating modes (mono-grafted, bi-grafted or bi-grafted after breaking of a Si-O-Si bridge) have been considered. This study highlights that lanthanum grafted complexes (alkyl, amide or borohydride) are active in lactone polymerization. In any case the reaction process is demonstrated to be similar to the one found for homogeneous catalysts. However, even if the different grafting modes are energetically equivalent for the ε-caprolactone ROP initiation reaction, some differences are observed according to the ligand involved in the initiation reaction. In agreement with experimental data, grafted lanthanide amides rapidly polymerise the ε-caprolactone. The grafted alkyl lanthanum complexes are also predicted to be very efficient catalysts. The borohydride is thus predicted to be the least efficient due to the difficulties in the ring opening. Indeed, the rate-determining step is the nucleophilic attack for the methyl and dialkylamido ligands (occuring with a low barrier) whereas it is the ring opening for the borohydride ligands (highest barrier) and the formation of -CH(2)C(=O)(X) (X = CH(3) or NMe(2)) terminal group is more favorable than that of a -CH(2)OBH(2) end group.     

Does equilibrium polymerization describe the dynamic heterogeneity of glass-forming liquids?

A significant body of evidence indicates that particles with excessively high or low mobility relative to Brownian particles form in dynamic equilibrium in glass-forming liquids. We examine whether these "dynamic heterogeneities" can be identified with a kind of equilibrium polymerization. This correspondence is first checked by demonstrating the presence of a striking resemblance between the temperature dependences of the configurational entropy s(c) in both the theory of equilibrium polymerization and the generalized entropy theory of glass formation in polymer melts. Moreover, the multiple characteristic temperatures of glass formation are also shown to have analogs in the thermodynamics of equilibrium polymerization, supporting the contention that both processes are varieties of rounded thermodynamic transitions. We also find that the average cluster mass (or degree of polymerization) varies in nearly inverse proportionality to s(c). This inverse relation accords with the basic hypothesis of Adam-Gibbs that the number of particles in the cooperatively rearranging regions (CRR) of glass-forming liquids scales inversely to s(c) of the fluid. Our identification of the CRR with equilibrium polymers is further supported by simulations for a variety of glass-forming liquids that verify the existence of stringlike or polymeric clusters exhibiting collective particle motion. Moreover, these dynamical clusters have an exponential length distribution, and the average "string" length grows upon cooling according to the predictions of equilibrium polymerization theory. The observed scale of dynamic heterogeneity in glass-forming liquids is found to be consistent with this type of self-assembly process. Both experiments and simulations have revealed remarkable similarities between the dynamical properties of self-assembling and glass-forming liquids, suggesting that the development of a theory for the dynamics of self-assembling fluids will also enhance our understanding of relaxation in glass-forming liquids.     

Should the AOAC use-dilution method be continued for regulatory purposes?

Despite its very poor reproducibility, AOAC INTERNATIONAL's use-dilution method (UDM) for bactericidal activity (AOAC Methods 964.02, 955.14, and 955.15) has been required by the U.S. Environmental Protection Agency (EPA) since 1953 for regulatory purposes, while methods with better reproducibility have been adopted in Canada and Australia. This study reviews UDM from a statistical perspective. Additionally, the test's expected results were compared to those obtained from actual evaluation of several formulations. Significant gaps have been identified in the reproducibility of the test data as predicted by statistical analysis and those presented to the EPA for product registration. UDM's poor reproducibility, along with its qualitative nature, requires the concentration of the active ingredient to be high enough to ensure all or most carriers to be free of any viable organisms. This is not in accord with the current trends towards sustainability, human safety, and environmental protection. It is recommended that the use of the method for regulatory purposes be phased out as soon as possible, and methods with better design and reproducibility be adopted instead.     

Is a radical bridge a route to strong exchange interactions in lanthanide complexes? A computational examination

The origin of very strong antiferromagnetic exchange in N(2)(3-) bridged complex, [{[(Me(3)Si)(2)N](2)Gd(THF)}(2)(μ-η(2):η(2)-N(2))](-) (1) has been probed using density functional theory (DFT) combined with molecular orbital (MO) and natural bond orbital (NBO) analysis. The analysis helps us to propose a generic mechanism of coupling for a {2p-4f} class of compounds.     

Application of the method of chromatographic plates toΒ-dicarbonyl compounds

Summary The chromatographic behavior of-dicarbonyl compounds was investigated using as an adsorbent silica gel — starch fastened to a glass plate.     

Can radical cations of the constituents of nucleic acids be formed in the gas phase using ternary transition metal complexes?

Electrospray ionization (ESI) tandem mass spectrometry (MS/MS) of ternary transition metal complexes of [M(L(3))(N)](2+) (where M = copper(II) or platinum(II); L(3) = diethylenetriamine (dien) or 2,2':6',2'-terpyridine (tpy); N = the nucleobases: adenine, guanine, thymine and cytosine; the nucleosides: 2'deoxyadenosine, 2'deoxyguanosine, 2'deoxythymine, 2'deoxycytidine; the nucleotides: 2'deoxyadenosine 5'-monophosphate, 2'deoxyguanosine 5'-monophosphate, 2'deoxythymine 5'-monophosphate, 2'deoxycytidine 5'-monophosphate) was examined as a means of forming radical cations of the constituents of nucleic acids in the gas phase. In general, sufficient quantities of the ternary complexes [M(L(3))(N)](2+) could be formed for MS/MS studies by subjecting methanolic solutions of mixtures of a metal salt [M(L(3))X(2)] (where M = Cu(II) or Pt(II); L(3) = dien or tpy; X = Cl or NO(3)) and N to ESI. The only exceptions were thymine and its derivatives, which failed to form sufficient abundances of [M(L(3))(N)](2+) ions when: (a) M = Pt(II) and L(3) = dien or tpy; (b) M = Cu(II) and L(3) = dien. In some instances higher oligomeric complexes were formed; e.g., [Pt(tpy)(dG)(n)](2+) (n = 1-13). Each of the ternary complexes [M(L(3))(N)](2+) was mass-selected and then subjected to collision-induced dissociation (CID) in a quadrupole ion trap. The types of fragmentation reactions observed for these complexes depend on the nature of all three components (metal, auxiliary ligand and nucleic acid constituent) and can be classified into: (i) a redox reaction which results in the formation of the radical cation of the nucleic acid constituent, N(+.); (ii) loss of the nucleic acid constituent in its protonated form; and (iii) fragmentation of the nucleic acid constituent. Only the copper complexes yielded radical cations of the nucleic acid constituent, with [Cu(tpy)(N)](2+) being the preferred complex due to suppression, in this case, of the loss of the nucleobase in its protonated form. The yields of the radical cations of the nucleobases from the copper complexes follow the order of their ionization potentials (IPs): G (lowest IP) > A > C > T (highest IP). Sufficient yields of the radical cations of each of the nucleobases allowed their CID reactions (in MS(3) experiments) to be compared to their even-electron counterparts.