RuBisCO‐Inspired CO2 Activation and Transformation by an Iridium(I) Complex

The synthesis of a new iridium(I) complex containing an enamido phosphine anion (dbuP^?) and its unique reactivity with CO₂ is reported. The complex binds two equivalents of CO₂ and initiates a highly selective reaction cascade. The reaction leads to the reversible cleavage of CO₂ and the enamido ligand as well. Computational analysis points to the existence of a relatively stable Ir‐CO₂ complex as a reaction intermediate prior to CO₂ cleavage, which was confirmed experimentally. The observed transformation resembles several aspects of enzymatic CO₂ fixation by RuBisCO.     

Hydrogenated carbon clusters produced by highly charged ion impact on solid

The emission of small (hydrogenated) carbon cluster ions C_nHm ⁺ (n =2-22) upon highly charged Xe^q+ (q =20-44) impact on C₈₄ surfaces is studied by means of time-of-flight secondary ion mass spectrometry. The respective stage of hydrogenation/protonation of a certain carbon cluster ion Cn ⁺ is a strong indication for its geometrical structure. From the cluster ion yield as a function of cluster size it can be concluded, that the hydrogenation takes place after the initial carbon cluster formation. The carbon clusters seem to be emitted as an entity in agreement with “equilibrium” and “shock wave” models. Received 4 February 2000     

Reactions with Carbo(heterylhydrazonoyl) Halides. I. Chemistry of Carbo(3-phenylpyrazol-5-yl-hydrazonoyl) Chlorides

The Carbo(3-phenylpyrazol-5-yl-hydrazonoyl) halides 1a , b react with active methylene compounds to yield the 1-(3-phenylpyrazol-5-yl)-pyrazole derivatives 2a – k (Scheme 1). The acyclic intermediates 3a , b could be isolated from reaction of 1a , b with acetylacetone, thus establishing the substitution mechanism for these reactions. Compounds 1a , b reacted with carbon disulfide, phenyl isothiocyanate, methyl cyanide, and with p-chlorobenzaldehyde to yield the corresponding heterocyclic derivatives 5 – 8 , respectively (Scheme 2). The behaviour of compounds 2 with hydrazine hydrate is reported.     

Magnetic resonance imaging of velocity fields, the void fraction and gas dynamics in a cavitating liquid

In acoustic cavitation, the relationship between the bubble dynamics on the microscale and the flow properties on the macroscale is critical in determining sonochemical reaction kinetics. A new technique was developed to measure the void fraction and estimate water mobility in the vicinity of cavitating bubbles using phase-encoded magnetic resonance imaging with short characteristic measurement timescales (0.1–1 ms). The exponential behavior of the NMR signal decay indicated the fast diffusion regime, with the relationship between local mechanical dispersion D _mix and the average bubble radius R, D_mix >> \frac2R²10^-4s, D_{\rm mix}\gg \frac{2R^2}{10^{-4}\hbox{s}}, resulting in dispersion of orders of magnitude greater than diffusion in quiescent water. For two different samples (water and a surfactant solution), the independent measurements of three-dimensional void fraction and velocity fields permitted the calculation of compressibility, divergence and vorticity of the cavitating medium. The measured dynamics of the dissolved gas, compared with that of the surrounding liquid, reflected the difference in the bubble coalescence and lifetimes and correlated with the macroscopic flow parameters.     

Spin-polarized structural, electronic and magnetic properties of intermetallic Dy2Ni2Pb from computational study

We report a first-principles study of structural, electronic and magnetic properties of ternary plumbides (rare earth-transition metal-Plumb) Dy₂Ni₂Pb crystallizes with the orthorhombic structure of the Mn₂AlB₂ type (space group Cmmm), were studied by means of the full-relativistic version of the full-potential augmented plane wave plus local orbital method within the frame work of spin-polarized density functional theory (SP-DFT). The electronic exchange-correlation energy is described by generalized gradient approximation (GGA). We have calculated the lattice parameters, bulk modulii and the first pressure derivatives of the bulk modulii, total densities of states and magnetic properties. The calculated total magnetic moment is found to be equal to 9.52 μB.     

Correlated Markov Quantum Walks

We consider the discrete time unitary dynamics given by a quantum walk on ${\mathbb {Z}^d}$ performed by a particle with internal degree of freedom, called coin state, according to the following iterated rule: a unitary update of the coin state takes place, followed by a shift on the lattice, conditioned on the coin state of the particle. We study the large time behavior of the quantum mechanical probability distribution of the position observable in ${\mathbb {Z}^d}$ for random updates of the coin states of the following form. The random sequences of unitary updates are given by a site-dependent function of a Markov chain in time, with the following properties: on each site, they share the same stationary Markovian distribution and, for each fixed time, they form a deterministic periodic pattern on the lattice. We prove a Feynman–Kac formula to express the characteristic function of the averaged distribution over the randomness at time n in terms of the nth power of an operator M. By analyzing the spectrum of M, we show that this distribution possesses a drift proportional to the time and its centered counterpart displays a diffusive behavior with a diffusion matrix we compute. Moderate and large deviation principles are also proven to hold for the averaged distribution and the limit of the suitably rescaled corresponding characteristic function is shown to satisfy a diffusion equation. An example of random updates for which the analysis of the distribution can be performed without averaging is worked out. The random distribution displays a deterministic drift proportional to time and its centered counterpart gives rise to a random diffusion matrix, the law of which we compute. We complete the picture by presenting an uncorrelated example.     

Activated nitriles in heterocyclic synthesis. Part III. Synthesis of N-amino-2-pyridone,pyranopyrazole and thiazolopyridine derivatives

The reaction of 2-cyanoethanoic acid hydrazide and arylidenemalononitrile was studied as a new route for the synthesis of N-amino-2-pyridones. Pyrano[2,3-c]pyrazole and thiazolo[2,3-a]pyridine could be prepared from the reaction of arylideneazolones with the same reagent.     

Equilibrium and kinetic studies on the reactions of alkylcobalamins with cyanide

Ligand substitution equilibria of different alkylcobalamins (RCbl, R = Me, CH(2)Br, CH(2)CF(3), CHF(2), CF(3)) with cyanide have been studied. It was found that CN(-) first substitutes the 5,6-dimethylbenzimidazole (Bzm) moiety in the alpha-position, followed by substitution of the alkyl group in the beta-position trans to Bzm. The formation constants K(CN) for the 1:1 cyanide adducts (R(CN)Cbl) were found to be 0.38 +/- 0.03, 0.43 +/- 0.03, and 123 +/- 9 M(-1) for R = Me, CH(2)Br, and CF(3), respectively. In the case of R = CH(2)CF(3), the 1:1 adduct decomposes in the dark with CN(-) to give (CN)(2)Cbl. The unfavorable formation constants for R = Me and CH(2)Br indicate the requirement of very high cyanide concentrations to produce the 1:1 complex, which cause the kinetics of the displacement of Bzm to be too fast to follow kinetically. The kinetics of the displacement of Bzm by CN(-) could be followed for R = CH(2)CF(3) and CF(3) to form CF(3)CH(2)(CN)Cbl and CF(3)(CN)Cbl, respectively, in the rate-determining step. Both reactions show saturation kinetics at high cyanide concentration, and the limiting rate constants are characterized by the activation parameters: R = CH(2)CF(3), DeltaH = 71 +/- 1 kJ mol(-1), DeltaS = -25 +/- 4 J K(-1) mol(-1), and DeltaV = +8.9 +/- 1.0 cm(3) mol(-1); R = CF(3), DeltaH = 77 +/- 3 kJ mol(-1), DeltaS = +44 +/- 11 J K(-1) mol(-1), and DeltaV = +14.8 +/- 0.8 cm(3) mol(-1), respectively. These parameters are interpreted in terms of an I(d) and D mechanism for R = CH(2)CF(3) and CF(3), respectively. The results of the study enable the formulation of a general mechanism that can account for the substitution behavior of all investigated alkylcobalamins including coenzyme B(12).     

Measurement of deuterium in water by the falling drop method

Summary The falling drop method for the isotopic analysis of water sample is fully described. The optimum parameters of the ultra thermostat, the micropipet, the drop size, and the dropping medium for maximum accuracy are discussed. The o-fluorotoluene used should be of the highest purity elsewhere non-reproducible results are obtained. The accuracy obtained is 0.001% up to 0.096 mole% D₂O and 0.01% up to 0.994 mole% D₂O, although the relative accuracy is the same ±1.4% through the whole calibration curve and is comparable with that of mass spectrometry.

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Bestimmung von Deuterium in Wasser mit Hilfe der Methode des fallenden Tropfens

Zusammenfassung Das Verfahren wird beschrieben und die optimalen Arbeitsbedingungen diskutiert. Das als Medium verwendete o-Fluortoluol muß von höchster Reinheit sein, da sonst keine reproduzierbaren Ergebnisse erhalten werden. Die Genauigkeit beträgt 0,001%–0,096 Mol-% D₂O und 0,01%–0,994 Mol-% D₂O. Die relative Genauigkeit, die im gesamten Bereich ±1,4% beträgt, ist mit der von massenspektrometrischen Bestimmungen vergleichbar.

     

Time-Dependent Density Functional Theory Study on Hydrogen and Dihydrogen Bonding in Electronically Excited State of 2-Pyridone–Borane–Trimethylamine Cluster

In this work, the intermolecular dihydrogen and hydrogen bonding interactions in electronically excited states of a 2-pyridone (2PY)–borane–trimethylamine (BTMA) cluster have been theoretically studied using time-dependent density functional theory method. Our computational results show that the S₁ state of 2PY–BTMA cluster is a locally excited state, in which only 2PY moiety is electronically excited. The theoretical infrared (IR) spectra of the 2PY–BTMA cluster demonstrate that the N–H stretching vibrational mode is slightly blue-shifted upon the electronic excitation. Moreover, the computed IR spectrum of the 2PY–BTMA cluster exhibits no carbonyl character due to the extension of the C=O bond length in the S₁ state. However, the N–H bond is shortened slightly upon photoexcitation. At the same time, the H···H and H···O distances are obviously lengthened in the S₁ sate by comparison with those in ground state. In addition, the electron density of the carbonyl oxygen is diminished due to the electronic excitation. Consequently, the proton acceptor ability of carbonyl oxygen is decreased in the electronic excited state. As a result, it is demonstrated that the intermolecular dihydrogen and hydrogen bonds are significantly weakened in the electronically excited state.