Zearalenone-malonyl-glucosides as phase II metabolites in plant cell suspension cultures

Background and objectives Conjugation of mycotoxins in the phase II metabolism of plants results in modified mycotoxins such as glucosides and malonyl‐glucosides. However, malonyl‐glucosides have not yet been completely elucidated for zearalenone (ZEN). Thus, the aim of this study was to produce and isolate malonyl‐glucosides of ZEN for an unambiguous identification by NMR spectroscopy. Findings Zearalenone was incubated in plant cell suspension cultures of wheat, soy, and tobacco, and phase II metabolites were analyzed by using LC‐DAD‐MS, ‐HRMS, and NMR spectroscopy. Four main metabolites of ZEN were detected in the cell extracts and identified as two glucosides (attached in positions 14 and 16) and their 6´‐malonyl derivatives. Conclusions Zearalenone‐malonyl‐glucosides should be incorporated in future analyses of modified mycotoxins because of their potential relevance for food and feed safety. Significance and novelty For the first time, the structures of the two malonyl‐glucosides of ZEN were unambiguously identified by NMR spectroscopy after preparative isolation as 14‐O‐(6’‐O‐malonyl‐β‐D‐glucopyranosyl)ZEN and 16‐O‐(6’‐O‐malonyl‐β‐D‐glucopyranosyl)ZEN

Nonuniqueness and derivative discontinuities in density-functional theories for current-carrying and superconducting systems

Current-carrying and superconducting systems can be treated within density-functional theory if suitable additional density variables (the current density and the superconducting order parameter, respectively) are included in the density-functional formalism. Here we show that the corresponding conjugate potentials (vector and pair potentials, respectively) are {\it not} uniquely determined by the densities. The Hohenberg-Kohn theorem of these generalized density-functional theories is thus weaker than the original one. We give explicit examples and explore some consequences.Comment: revised version (typos corrected, some discussion added) to appear in Phys. Rev.

Density-functionals not based on the electron gas: Local-density approximation for a Luttinger liquid

By shifting the reference system for the local-density approximation (LDA) from the electron gas to other model systems one obtains a new class of density functionals, which by design account for the correlations present in the chosen reference system. This strategy is illustrated by constructing an explicit LDA for the one-dimensional Hubbard model. While the traditional {\it ab initio} LDA is based on a Fermi liquid (the electron gas), this one is based on a Luttinger liquid. First applications to inhomogeneous Hubbard models, including one containing a localized impurity, are reported.Comment: 4 pages, 4 figures (final version, contains additional applications and discussion; accepted by Phys. Rev. Lett.

Theory of valley-orbit coupling in a Si/SiGe quantum dot

Electron states are studied for quantum dots in a strained Si quantum well, taking into account both valley and orbital physics. Realistic geometries are considered, including circular and elliptical dot shapes, parallel and perpendicular magnetic fields, and (most importantly for valley coupling) the small local tilt of the quantum well interface away from the crystallographic axes. In absence of a tilt, valley splitting occurs only between pairs of states with the same orbital quantum numbers. However, tilting is ubiquitous in conventional silicon heterostructures, leading to valley-orbit coupling. In this context, "valley splitting" is no longer a well defined concept, and the quantity of merit for qubit applications becomes the ground state gap. For typical dots used as qubits, a rich energy spectrum emerges, as a function of magnetic field, tilt angle, and orbital quantum number. Numerical and analytical solutions are obtained for the ground state gap and for the mixing fraction between the ground and excited states. This mixing can lead to valley scattering, decoherence, and leakage for Si spin qubits.Comment: 18 pages, including 4 figure

Efficient method for simulating quantum electron dynamics under the time dependent Kohn-Sham equation

A numerical scheme for solving the time-evolution of wave functions under the time dependent Kohn-Sham equation has been developed. Since the effective Hamiltonian depends on the wave functions, the wave functions and the effective Hamiltonian should evolve consistently with each other. For this purpose, a self-consistent loop is required at every time-step for solving the time-evolution numerically, which is computationally expensive. However, in this paper, we develop a different approach expressing a formal solution of the TD-KS equation, and prove that it is possible to solve the TD-KS equation efficiently and accurately by means of a simple numerical scheme without the use of any self-consistent loops.Comment: 5 pages, 3 figures. Physical Review E, 2002, in pres

Time Dependent Floquet Theory and Absence of an Adiabatic Limit

Quantum systems subject to time periodic fields of finite amplitude, lambda, have conventionally been handled either by low order perturbation theory, for lambda not too large, or by exact diagonalization within a finite basis of N states. An adiabatic limit, as lambda is switched on arbitrarily slowly, has been assumed. But the validity of these procedures seems questionable in view of the fact that, as N goes to infinity, the quasienergy spectrum becomes dense, and numerical calculations show an increasing number of weakly avoided crossings (related in perturbation theory to high order resonances). This paper deals with the highly non-trivial behavior of the solutions in this limit. The Floquet states, and the associated quasienergies, become highly irregular functions of the amplitude, lambda. The mathematical radii of convergence of perturbation theory in lambda approach zero. There is no adiabatic limit of the wave functions when lambda is turned on arbitrarily slowly. However, the quasienergy becomes independent of time in this limit. We introduce a modification of the adiabatic theorem. We explain why, in spite of the pervasive pathologies of the Floquet states in the limit N goes to infinity, the conventional approaches are appropriate in almost all physically interesting situations.Comment: 13 pages, Latex, plus 2 Postscript figure