Ultrafast dynamics of Cu(I)-phenanthrolines in dichloromethane

Transient absorption spectrometry of Cu(I)-phenanthrolines in CH2Cl2 reveals ligand-independent dynamic processes lasting 15 ps, which are associated with the peculiar structural rearrangements occurring for this class of compounds upon photoexcitation.     

Dioxygenase-catalysed oxidation of monosubstituted thiophenes: sulfoxidation versus dihydrodiol formation

Toluene dioxygenase (TDO)-catalysed sulfoxidation, using Pseudomonas putida UV4, was observed for the thiophene substrates 1A-1N. The unstable thiophene oxide metabolites, 6A-6G, 6K-6N, spontaneously dimerised yielding the corresponding racemic disulfoxide cycloadducts 7A-7G, 7K-7N. Dimeric or crossed [4 + 2] cycloaddition products, derived from the thiophene oxide intermediates 6A and 6D or 6B and 6D, were found when mixtures of thiophene substrates 1A and 1D or 1B and 1D were biotransformed. The thiophene sulfoxide metabolite 6B was also trapped as cycloadducts 17 or 18 using stable dienophiles. Preferential dioxygenase-catalysed oxidation of the substituent on the thiophene ring, including exocyclic sulfoxidation (1H-1J) and cis-dihydroxylation of a phenyl substituent (1G and 1N), was also observed. An enzyme-catalysed deoxygenation of a sulfoxide in P. putida UV4 was noticed when racemic disulfoxide cyclo-adducts 7A, 7B and 7K were converted to the corresponding enantioenriched monosulfoxides 8A, 8B and 8K via a kinetic resolution process. The parent thiophene 1A and the 3-substituted thiophenes 1K-1N were also found to undergo ring dihydroxylation yielding the cis/trans-dihydrodiol metabolites 9A and 9K-9N. Evidence is provided for a dehydrogenase-catalysed desaturation of a heterocyclic dihydrodiol (9Kcis/9Ktrans) to yield the corresponding 2,3-dihydroxythiophene (24) as its preferred thiolactone tautomer (23). A simple model to allow prediction of the structure of metabolites, formed from TDO-catalysed bacterial oxidation of thiophene substrates 1, is presented.     

The trajectory scaling function for period doubling bifurcations in flows

We extend the trajectory scaling function as defined for maps to flows whose dynamics is governed by ordinary differential equations. The results are obtained for the Duffing oscillator and are expected to be the same for other dissipative flows as well.     

Photoelectron imaging spectroscopy and theoretical investigation of ZrSi

The photoelectron spectrum of ZrSi(-) has been measured at two different photon energies: 2.33 eV and 3.49 eV, providing electron binding energy and photoelectron angular distribution information. The obtained vertical detachment energy of ZrSi(-) is 1.584(14) eV. The neutral ground and excited state terms are assigned based on experimental and theoretical results. The ground state of ZrSi is tentatively assigned as a (3)Σ(+) state with a configuration of 1σ(2) 1π(4) 1δ(0) 2σ(1) 3σ(1). A low lying (3)Π(i) neutral excited state is identified to be 0.238 eV (1919 cm(-1)) above the ground state. The anion ground state is designated as a (2)Σ(+) state with a 1σ(2) 1π(4) 1δ(0) 2σ(2) 3σ(1) valence electron configuration. A Franck-Condon (FC) simulation of the photoelectron spectrum has been carried out. For the (3)Σ(+) ← (2)Σ(+) band, theoretically calculated bond lengths and frequencies are used in the FC calculation which give good agreement with experiment, while for the (3)Π(i) ← (2)Σ(+) band, the ZrSi bond length is estimated from the FC spectrum. Comparisons are made with previously published theoretical studies and inconsistencies are pointed out. To the best of our knowledge, this study provides the first spectroscopic information on the transition metal-silicon diatomic, ZrSi.     

State preparation and excited electronic and vibrational behavior in hemes

The temporally overlapping, ultrafast electronic and vibrational dynamics of a model five-coordinate, high-spin heme in a nominally isotropic solvent environment has been studied for the first time with three complementary ultrafast techniques: transient absorption, time-resolved resonance Raman Stokes, and time-resolved resonance Raman anti-Stokes spectroscopies. Vibrational dynamics associated with an evolving ground-state species dominate the observations. Excitation into the blue side of the Soret band led to very rapid S2 --> S1 decay (sub-100 fs), followed by somewhat slower (800 fs) S1 --> S0 nonradiative decay. The initial vibrationally excited, non-Boltzmann S0 state was modeled as shifted to lower energy by 300 cm(-1) and broadened by 20%. On a approximately 10 ps time scale, the S0 state evolved into its room-temperature, thermal distribution S0 profile largely through VER. Anti-Stokes signals disappear very rapidly, indicating that the vibrational energy redistributes internally in about 1-3 ps from the initial accepting modes associated with S1 --> S0 internal conversion to the rest of the macrocycle. Comparisons of anti-Stokes mode intensities and lifetimes from TRARRS studies in which the initial excited state was prepared by ligand photolysis [Mizutani, T.; Kitagawa, T. Science 1997, 278, 443, and Chem. Rec. 2001, 1, 258] suggest that, while transient absorption studies appear to be relatively insensitive to initial preparation of the electronic excited state, the subsequent vibrational dynamics are not. Direct, time-resolved evaluation of vibrational lifetimes provides insight into fast internal conversion in hemes and the pathways of subsequent vibrational energy flow in the ground state. The overall similarity of the model heme electronic dynamics to those of biological systems may be a sign that the protein's influence upon the dynamics of the heme active site is rather subtle.     

Martingales, detrending data, and the efficient market hypothesis

We discuss martingales, detrending data, and the efficient market hypothesis (EMH) for stochastic processes x(t) with arbitrary diffusion coefficients D(x,t). Beginning with x-independent drift coefficients R(t) we show that martingale stochastic processes generate uncorrelated, generally non-stationary increments. Generally, a test for a martingale is therefore a test for uncorrelated increments. A detrended process with an x-dependent drift coefficient is generally not a martingale, and so we extend our analysis to include the class of (x,t)-dependent drift coefficients of interest in finance. We explain why martingales look Markovian at the level of both simple averages and 2-point correlations. And while a Markovian market has no memory to exploit and presumably cannot be beaten systematically, it has never been shown that martingale memory cannot be exploited in 3-point or higher correlations to beat the market. We generalize our Markov scaling solutions presented earlier, and also generalize the martingale formulation of the EMH to include (x,t)-dependent drift in log returns. We also use the analysis of this paper to correct a misstatement of the ‘fair game’ condition in terms of serial correlations in Fama's paper on the EMH. We end with a discussion of Levy's characterization of Brownian motion and prove that an arbitrary martingale is topologically inequivalent to a Wiener process.     

Preparative Mass Spectrometry Using a Rotating-Wall Mass Analyzer

The design of functional interfaces is central to both fundamental and applied research in materials science and energy technology. We introduce a new, broadly applicable technique for the precisely controlled high-throughput preparation of well-defined interfaces containing polyatomic species ranging from small ions to nanocrystals and large protein complexes. The mass-dispersive deposition of ions onto surfaces is achieved using a rotating-wall mass analyzer, a compact device which enables the separation of ions using low voltages and has a theoretically unlimited mass range. We demonstrate an efficient deposition of singly charged Au₁₄₄(SC₄H₉)₆₀ ions (33.7 kDa), which opens up exciting opportunities for the structural characterization of nanocrystals and their assemblies using transmission electron microscopy. Our approach also enables the high-throughput deposition of mass-selected ions from multicomponent mixtures, which is of interest to the controlled preparation of surface gradients and rapid screening of molecules in mixtures for a specific property.