Circular‐Dichroism Studies on Artemisinin and Epiartemisinin and Their β‐Cyclodextrin Complexes in Solution

The circular dichroism (CD) spectra of the powerful antimalarian active principle artemisinin (ART; 1 ) from Artemisia annua, and of epiartemisinin (EPI, 2), its C(7) epimer, were studied in solution in the presence and absence of β‐cyclodextrin (β‐cd). A significant inversion of sign in the region of the second electronic transition was detected. The rotational strengths were successfully calculated within the time‐dependent density functional theory (DFT), which enabled us to establish a correlation between the molecular recognition and the biological acitivities of the two isomers.     

Classical limit of the quantized hyperbolic toral automorphisms

The canonical quantization of any hyperbolic symplectomorphismA of the 2-torus yields a periodic unitary operator on aN-dimenional Hilbert space,N=1/h. We prove that this quantum system becomes ergodic and mixing at the classical limit (N,N prime) which can be interchanged with the time-average limit. The recovery of the stochastic behaviour out of a periodic one is based on the same mechanism under which the uniform distribution of the classical periodic orbits reproduces the Lebesgue measure: the Wigner functions of the eigenstates, supported on the classical periodic orbits, are indeed proved to become uniformly speread in phase space.     

Conformational equilibrium and potential energy surface of 1-fluorobutane by microwave spectroscopy and Ab initio calculations

The rotational spectra of four (GT, TT, TG, and GG) of the five possible conformers of 1-fluorobutane have been assigned by combining free jet and conventional microwave spectroscopy. The geometry optimization was performed at the MP2 (full) level of theory with the 6-31G (d) and 6-311G (d, p) basis sets and by using the B3LYP (3df, 3pd) density functional method. The relative stability of the five rotamers is calculated at the QCISD (T)/6-311G (d, p) level of theory. In spite of the fact that ab initio calculations indicated the unobserved GG' conformer to be more stable than at least one of the observed conformers it was not possible to detect its rotational spectrum. GT and TG are the most and the least stable species, respectively. The rotational spectra of several vibrational satellites of the four conformers have been studied by conventional microwave spectroscopy. The overall conformational equilibrium is governed by the two-dimensional potential energy surface of the skeletal torsions MeC-CC and FC-CC, which have been evaluated by a flexible model analysis, based on the experimental values of the relative conformational and vibrational energy spacings, and on the shifts of second moments of inertia upon conformational change and vibrational excitation. The relative energy of the fifth stable conformer (GG') was determined to be 333 cm(-1) from flexible model calculations, and to be 271 cm(-1) from the most accurate ab initio calculations.     

Synchronization of neurons in micro-electrode array cultures

A lot of methods were created in last decade for the spatio-temporal analysis of multi-electrode array (MEA) neuronal data sets. In this paper we show how a new simple analysis approach that considers the total network activity, is able to show interesting neuronal network system dynamical features. In particular, we perform two different analyses: a neuronal connectivity examination studying networks at different days in vitro (div) and an analysis of the long per- iod effects of the administration of two common neuroactive drugs, Tetrodotoxin (TTX) and D-2-amino-5-phosphonovalerate (AP5), to spontaneously spiking mature neuronal networks. Our analysis is performed considering burst topology, i.e., cataloguing network bursts as Global (if they involve more than the 25% of the MEA channels) or Local (if less that 25%). In the first analysis, this division allows to understand the network connectivity developments. The networking increases from div 1 to 6 building up an undifferentiated highly connected network. From div 6 to 10 the networking decreases (pruning) till reaching a plateau in a small-world like organization. The second analysis highlights substantial differences between long period effects of TTX and AP5. Results show that AP5, selectively blocking NMDA receptors and inhibiting long term potentiation, is unable to produce activity twisting in a network that already reached a developmental plateau, but it is able to desynchronize sub-network (Local) activity. TTX, on the other side, blocking any type of electrical communication among neurons, acts on the whole network synchronization. The important activity increment in the post-TTX epoch (+66%), together with the Global activity explosion, suggests the possibility of a long-term inhibitory-synapse depression mechanism.     

On $\mathsf{c = 1}$ critical phases in anisotropic spin-1 chains

Quantum spin-1 chains may develop massless phases in presence of Ising-like and single-ion anisotropies. We have studied c = 1 critical phases by means of both analytical techniques, including a mapping of the lattice Hamiltonian onto an O(2) NL M, and a multi-target DMRG algorithm which allows for accurate calculation of excited states. We find excellent quantitative agreement with the theoretical predictions and conclude that a pure Gaussian model, without any orbifold construction, describes correctly the low-energy physics of these critical phases. This combined analysis indicates that the multicritical point at large single-ion anisotropy does not belong to the same universality class as the Takhtajan-Babujian Hamiltonian as claimed in the past. A link between string-order correlation functions and twisting vertex operators, along the c = 1 line that ends at this point, is also suggested.Received: 16 July 2003, Published online: 24 October 2003PACS: 75.40.-s Critical-point effects, specific heats, short-range order - 75.10.Jm Quantized spin models - 02.70.-c Computational techniques     

Millimeter-Wave Spectroscopy of HCCCP in Excited Vibrational States

The rotational spectra of the unstable HCCCP molecule have been investigated in the millimeter-wave region for the main excited vibrational states which lie below 1000 cm(-1), namely nu(4) (C&bond;C stretch), nu(5) (HCC bend), nu(6) (CCC bend), nu(7) (CCP bend), 2nu(6), 2nu(7), 3nu(7), 4nu(7), nu(5) + nu(7), and nu(6) + nu(7). l-type resonance effects have been taken into account in the analysis of the spectra, so that the values of the anharmonicity constants x(L(66)), x(L(77)), x(L(57)), and x(L(67)) could be determined. The anharmonic interactions which couple the nu(4) state with nu(6) + nu(7), 2nu(6), and 4nu(7) have been also considered, yielding the unperturbed value of the alpha(4) vibration-rotation coupling constant. Copyright 2001 Academic Press.     

Generalized Farey Trees,Transfer Operators and Phase Transitions

We consider a family of Markov maps on the unit interval, interpolating between the tent map and the Farey map. The latter is not uniformly expanding. Each map being composed of two fractional linear transformations, the family generalizes many particular properties which for the case of the Farey map have been successfully exploited in number theory. We analyze the dynamics through the spectral properties of the generalized transfer operator. Application of the thermodynamic formalism to the family reveals first and second order phase transitions and unusual properties like positivity of the interaction function.     

Sequence distance via parsing complexity: Heartbeat signals

We compare and discuss the use of different symbolic codings of electrocardiogram (ECG) signals in order to distinguish healthy patients from hospitalized ones. To this aim, we recall a parsing-based similarity distance and compare the performances of several methods of classification of data.     

Incommmensurability and unconventional superconductor to insulator transition in the hubbard model with bond-charge interaction

We determine the quantum phase diagram of the one-dimensional Hubbard model with bond-charge interaction X in addition to the usual Coulomb repulsion U>0 at half-filling. For large enough X相似文献   

Microwave spectrum of 18O14NF in excited vibrational states: Equilibrium structure of nitrosyl fluoride

The rotational spectra of ¹⁸O¹⁴NF were observed in the vibrationally excited ν₁, ν₂, and ν₃ states. The equilibrium structure of nitrosyl fluoride was determined using the equilibrium rotational constants of the two isotopic species, ¹⁶O¹⁴NF and ¹⁸O¹⁴NF. The newly determined spectroscopic parameters of ¹⁸O¹⁴NF were used to refine the quadratic and cubic force fields of nitrosyl fluoride.