Reaction pathways of Sc+ (3D, 1D) and Fe+ (6D, 4F) with acetone in the gas phase: metal ion oxidation and acetone deethanization

The reactions of Sc⁺ (³D, ¹D) and Fe⁺ (⁶D, ⁴ F) with acetone have been investigated in both high‐ and low‐spin states using density functional theory. Our calculations have indicated that oxidation of Sc⁺ by acetone can take place by (1) metal‐mediated H migration, (2) direct methyl‐H shift and/or (3) C = O insertion. The most energetically favorable pathway is metal‐mediated H migration followed by intramolecular ScO⁺ rotation and dissociation. For the deethanization of acetone mediated by Fe⁺, the reaction occurs on either the quartet or sextet surfaces through five elementary steps, i.e. encounter complexation, C–C bond activation, methyl migration, C–C coupling and non‐reactive dissociation. The rate‐determining step along the quartet‐state potential‐energy surface (PES) is similar to that in the case of Ni⁺ (² F, 3d⁹), namely the methyl‐migration step. For the sextet‐state PES, however, the energy barrier for methyl migration is lower than that for C–C bond activation, and the rate‐determining step is C–C coupling. In general, the low‐spin‐state pathways are lower in energy than the high‐spin‐state pathways; therefore, the reaction pathways for the oxidation of Sc⁺ and the Fe⁺‐mediated deethanization of acetone mostly involve the low‐spin states. Copyright © 2012 John Wiley & Sons, Ltd.     

Electronic transitions in collinear H+ + D2 (ν = 0) → HD+ (ν = 0,1) + D via classical trajectories in complex time and complex phase space

A semiclassical treatment of electronic transitions in the collinear rearrangement H⁺ + D₂ (ν = 0) → HD⁺ (ν = 0,1) + D is presented. The treatment represents an extension of Stueckelberg's method for a single nuclear degree of freedom to collisions involving several nuclear degrees of freedom. The classical limit of scattering amplitudes (S-matrix elements) is calculated for the transition between the two adiabatic potential energy surfaces corresponding to the two lowest singlet states of HD⁺₂. S-matrix elements are constructed from trajectories propagating in complex time and complex phase space, which make localized transitions between the two surfaces by crossing their complex line of intersection. The action along each trajectory acquires an imaginary part, which contributes exponential damping to the corresponding amplitude for electronic transition.     

Extraction of UO22+ by two highly sterically hindered (X1) (X2) PO(OH) extractants from an aqueous chloride phase

The comparative extraction behavior of tracer-level UO₂²⁺ into benzene solutiosn of two highly sterically hindered extractants, di(2,6-di-iso-propyl phenyl) phosphoric acid, HD(2,6-i-PΦ)P and di-tertiary-butyl phosphinic acid, H[Dt-BP], vs an aqueous 1.0 F (NaCl + HCl) phase was studied. The extraction of UO₂²⁺ in both systems is directly second-power dependent upon extractant concentration and inversely second-power dependent upon hydrogen ion concentration, the stoichiometry of extraction being UO_2A²⁺+2(HY)₂₀ ⇆ UO₂(HY₂)₂₀ + 2H_A⁺ The expression for the distribution ratio, K, is K=K₅F²/[H⁺]² the general expression for the extraction of any metallic species being K=K₅F^a/[H⁺]^b where K_s is a constant characteristic of the system, F the concentration in formality units of extractant in the organic phase, [H⁺] the concentration of hydrogen ion in the aqueous phase, and a and b the respective extractant and hydrogen-ion dependencies.Both extractants have a high degree of steric hindrance. The HD(2,6-i-PΦ)P is the more highly acidic, the pK_A value, in 75% ethanol, being 3.2. The pK_A, previously reported, for H[Dt-BP] is 6.26. The K_s for UO₂²⁺ in the system HY in benzene diluent vs an aqueous 1.0 F (NaCl + HCl) phase is 2 × 10⁴ for H[Dt-BP] and 3 × 10⁻¹ for HD(2,6-i-PΦ)P; the ratio of the K_s values, nearly 7 × 10³, favors the less acidic extractant. For comparative purposes, the K_s values for UO₂²⁺ and for Eu³⁺ in other (X₁)(X₂)PO(OH), in benzene diluent vs 1.0 F (NaCl + HCl) systems are presented. The variations are discussed in terms of the pK_A of the extractant and the steric hindrance within the extractant.     

Modeling the phase behavior of H2S+n-alkane binary mixtures using the SAFT-VR+D approach

A statistical associating fluid theory for potential of variable range has been recently developed to model dipolar fluids (SAFT-VR+D) [Zhao and McCabe, J. Chem. Phys. 2006, 125, 104504]. The SAFT-VR+D equation explicitly accounts for dipolar interactions and their effect on the thermodynamics and structure of a fluid by using the generalized mean spherical approximation (GMSA) to describe a reference fluid of dipolar square-well segments. In this work, we apply the SAFT-VR+D approach to real mixtures of dipolar fluids. In particular, we examine the high-pressure phase diagram of hydrogen sulfide+n-alkane binary mixtures. Hydrogen sulfide is modeled as an associating spherical molecule with four off-center sites to mimic hydrogen bonding and an embedded dipole moment (micro) to describe the polarity of H2S. The n-alkane molecules are modeled as spherical segments tangentially bonded together to form chains of length m, as in the original SAFT-VR approach. By using simple Lorentz-Berthelot combining rules, the theoretical predictions from the SAFT-VR+D equation are found to be in excellent overall agreement with experimental data. In particular, the theory is able to accurately describe the different types of phase behavior observed for these mixtures as the molecular weight of the alkane is varied: type III phase behavior, according to the scheme of classification by Scott and Konynenburg, for the H2S+methane system, type IIA (with the presence of azeotropy) for the H2S+ethane and+propane mixtures; and type I phase behavior for mixtures of H2S and longer n-alkanes up to n-decane. The theory is also able to predict in a qualitative manner the solubility of hydrogen sulfide in heavy n-alkanes.     

Significant nonadiabatic effects in the S(1D) + HD reaction

A nonadiabatic quantum dynamics calculation involving four coupled potential energy surfaces (two degenerate 3A' ', one 3A', and one 1A') and the spin-orbit coupling matrix for these states is reported for the title reaction. The results show that the important discrepancy between theoretically calculated and experimentally measured intramolecular isotope effects can at least in part be attributed to significant nonadiabatic effects.     

A multicomponent formal [1+2+1+2]-cycloaddition for the synthesis of dihydropyridines

Reaction of methoxyvinylmethylketone with different amines and aldehydes under Lewis-acid catalysed conditions results in a novel, formal, step-wise [1+2+1+2]-cycloaddition to give dihydropyridine products.     

Gas phase synthesis and reactivity of Agn+ and Ag(n-1)H+ cluster cations

Multi-stage mass spectrometry (MSn) on [(M + Ag - H)x + Ag]+ precursor ions (where M = an amino acid such as glycine or N,N-dimethylglycine) results in the formation of stable silver (Ag3+, Ag5+ and Ag7+) and silver hydride (Ag2H+, Ag4H+ and Ag6H+) cluster cations in the gas phase. Deuterium labelling studies reveal that the source of the hydride can be either from the alpha carbon or from one of the heteroatoms. When M = glycine, the silver cyanide clusters Ag4CN+ and Ag5(H,C,N)+ are also observed. Collision induced dissociation (CID) and DFT calculations were carried out on each of these clusters to shed some light on their possible structures. CID of the Agn+ and Ag(n-1)H+ clusters generally results in the formation of the same Ag(n-2)+ product ions via the loss of Ag2 and AgH respectively. DFT calculations also reveal that the Agn+ and Ag(n-1)H+ clusters have similar structural features and that the Ag(n-1)H+ clusters are only slightly less stable than their all silver counterparts. In addition, Agn+ and Ag(n-1)H+ clusters react with 2-propanol and 2-butylamine via similar pathways, with multiple ligand addition occurring and a coupled deamination-dehydration reaction occurring upon condensation of a third (for Ag2H+) or a fourth (for all other silver clusters) 2-butylamine molecule onto the clusters. Taken together, these results suggest that the Agn+ and Ag(n-1)H+ clusters are structurally related via the replacement of a silver atom with a hydrogen atom. This replacement does not dramatically alter the cluster stability or its unimolecular or bimolecular chemistry with the 2-propanol and 2-butylamine reagents.     

Nonlinear (Fluctuational) dynamics and mathematical modeling of homogenous oxidation of biological substrates

Nonlinear dynamics and mathematical modeling approaches were presented for studying chemical oscillations during homogeneous oxidation of biological substrates in the presence of oxygenated complexes of iron(II). It was shown that examination of fluctuational dynamics is only possible via consistent use of several algorithms for time series processing and that flicker-noise spectroscopic technique is best suited to deriving the most exhaustive information from the patterns of temporal variation of signals. The qualitative analysis was performed, and numerical solution was found for the system of differential equations modeling the reactions kinetics. The nature of the steady state was elucidated, and the possibility of Andronov-Hopf type bifurcation with realization of an oscillatory mode was demonstrated.     

Molecular beam scattering studies of the reaction D + H2 (v = 0) and D + H2 (v = 1) → HD + H

The reaction D + H₂ → HD + H has been investigated in two molecular beam scattering experiments. Angular and time-of-flight distributions have been measured for the initial vibrational ground state (v = 0) at a most probable collision energy of E_cm = 1.5 eV and for the first vibrational excited state (v = 1) at E_cm = 0.28 eV with the same apparatus. Results for the ground-state experiment are compared with quasiclassical trajectory calculations(QCT) on the LSTH-hypersurface transformed into the laboratory system and averaged over the apparatus distributions. The agreement isquite satisfactory. At this high collision energy the HD products are no longer scattered in a backward direction but in a wide angular region concentrated about θ = 90° in the center-of-mass system. The absolute reactive cross section has been determined and the agreement with the theoretical value from QCT calculations is within the experimental error. The high sensitivity of the experiment to different properties of the doubly differential cross section has also been demonstrated. A preliminary evaluation of the experiment with initial vibrational excitation (v = 1) shows that the HD-product molecules are preferably backward scattered and the change of internal energy is small supporting the concept of a reaction which is adiabatic with respect to the internal degrees of freedom.     

Electroosmotic flow in fused deposition modeling (FDM) 3D-printed microchannels

Electroosmotic flow (EOF) was determined in tridimensional (3D)-printed microchannels with dimensions smaller than 100 µm. Fused deposition modeling 3D printing using thermoplastic filaments of PETG (polyethylene terephthalate glycol), PLA (polylactic acid), and ABS (acrylonitrile butadiene styrene) were used to fabricate the microchannels. The current monitoring method and sodium phosphate solutions at different pH values (3–10) were used for the EOF mobility (µ_EOF) measurements, which ranged from 2.00 × 10⁻⁴ to 12.52 × 10⁻⁴ cm² V⁻¹ s⁻¹. The highest and the smallest µ_EOF were obtained for the PLA and PETG microchannels, respectively. Adding the cationic surfactant cetyltrimethylammonium bromide to the sodium phosphate solution caused EOF direction reversion in all the studied microchannels. The obtained results can be interesting for developing 3D-printed microfluidic devices, in which EOF is relevant.     

1-Naphthols as components for multifunctional material systems (MFMS): the molecular modeling approach

Structural Chemistry - Increasing research interests have been paid to developing efficient multifunctional material systems (MFMS) by using various composite materials, owing to their useful...     

Energy partitioning in the reaction O(1D) + H2O → OH + OH.: The influence of O(1D) translational energy on the reaction rate constant

For the exothermic reaction O (¹D) + H₂O → OH + OH the rate constant and its energy dependence were determined by monitoring the concentration of the OH product. This was done by integrating the distribution of product molecules over all accessible states. The rate constant, determined at different velocity distributions of the reacting metastable over a wide range, is energy independent.     

A mathematical modeling approach toward magnetic fluid hyperthermia of cancer and unfolding heating mechanism

Journal of Thermal Analysis and Calorimetry - Magnetic nanoparticles (MNPs)-induced hyperthermia is capable of heating the tumor without side effects. In this technique, the tumor temperature is...     

IR kinetic spectroscopy investigation of the CH4 + O(1D) reaction

The branching of the title reaction into several product channels has been investigated quantitatively by laser infrared kinetic spectroscopy for CH(4) and CD(4). It is found that OH (OD) is produced in 67 +/- 5% (60 +/- 5%) yield compared to the initial O((1)D) concentration. H (D) product is produced in 30 +/- 10%(35 +/- 10%). H(2)CO is produced in 5% yield in the CH(4) system (it was not possible to measure the CD(2)O yield in the CD(4) case). D(2)O is produced in 8% yield in the CD(4) system (it was not feasible to measure the H(2)O yield). The ratio of the overall rate constant of the CD(4) reaction to the overall rate constant of the O((1)D) + N(2)O reaction was determined to be 1.2(5) +/- 0.1. A measurement of the reaction of O((1)D) with NO(2) gave 1.3 x 10(-10) cm(3) molecule(-1) s(-1) relative to the literature values for the rate constants of O((1)D) with H(2) and CH(4). Hot atom effects in O((1)D) reactions were observed.     

Cycloaddition of Dialkylalumanyl Anion toward Unsaturated Hydrocarbons in (1+2) and (1+4) Modes

The reactivity of dialkylalumanyl anion ( 1 ) towards naphthalene, anthracene, diphenylacetylene, and (E)/(Z)-stilbenes was investigated. The compound 1 reacts with naphthalene and anthracene through (1+4) cyclization, giving Al-containing norbornadiene derivatives. In the reaction of 1 with diphenylacetylene and (E)/(Z)-stilbenes, (1+2) cyclization proceeded to form Al-C-C three-membered rings. Cyclization toward (E)- or (Z)-stilbenes solely gave a trans-cycloadduct. DFT calculations revealed that the cycloaddition of 1 with (Z)-stilbene proceeds via a single transition state with a carbanion character, which results in the selectivity towards the trans-cycloadduct.