Microwave measurement of the α3 vibrationrotation constant of ClCN and BrCN vibrational energy transfer from active nitrogen

Vibrational energy transfer between active nitrogen N*₂, and the (0,0⁰, 1) state of ClCN and BrCN has allowed the determination of the α₃ vibrationrotation constant by microwave spectroscopy, with the values: α₃(³⁵ClCN) = 32.25 MHz, α₃(³⁷ClCN) = 31.68 MHz, α₃(⁷⁹BrCN) = 20.37 MHz and α₃(⁸¹BrCN) = 20.24 MHz. For ³⁵ClCN the α₁ vibrationrotation constant has also been determined with a standard technique, giving α₁ = 24.65 MHz. A new evaluation has been made of the equilibrium structure of ClCN as follows: r_e(CN) = 1.1606 A, r_e(CCL) = 1.6290 A.     

Determination of sugars by liquid chromatography with post-column catalytic derivatization and fluorescence detection

Summary A method for the determination of reducing sugars such as fructose and glucose and nonreducing sugar such as sucrose by high performance liquid chromatography followed by an acidic hydrolysis and a derivatization with benzamidine has been developed. After separation of sugars on a gel column packed with a polymer-based cation exchange material (Sugar-Pak I, Waters-Millipore), the sucrose is first hydrolysed in a solid phase reactor to convert it into reducing subunits. A post-column fluorigenic reaction with benzamidine under alkaline condition allows the selective determination of both natural and converted reducing carbohydrates.This procedure has proven to be selective (fluorigenic detection) and highly sensitive (allowing detection as little as picomoles amounts), reproducible and linear over a broad range of concentrations: 5×10^–4 to 1.0×10^–2 M.The applicability of this method to natural matrices such as plant extracts and beverages is also described. The sugar content of a barley extract has been determined and compared with a specific enzymatic test. The determined sugar content of natural and commercial lemon juices as well as of Cola beverages has been compared with those found by the conventional LC refractive index analytical procedure. In all cases, the results were comparable and were within the experimental errors of the methods.     

Quantization of a class of piecewise affine transformations on the torus

We present a unified framework for the quantization of a family of discrete dynamical systems of varying degrees of chaoticity. The systems to be quantized are piecewise affine maps on the two-torus, viewed as phase space, and include the automorphisms, translations and skew translations. We then treat some discontinuous transformations such as the Baker map and the sawtooth-like maps. Our approach extends some ideas from geometric quantization and it is both conceptually and calculationally simple.The authors would like to thank Prof. Sandro Graffi for suggesting the problem addressed in this paper and for many stimulating discussions. The first author thanks the department of mathematics of the University of Bologna, where part of this work was performed for its hospitality and the C.N.R. for partial financial support.     

Millimeter-Wave Spectroscopy of Sulfur Dichloride

The rotational spectra of (32)S(35)Cl(2), (32)S(35)Cl(37)Cl, (32)S(37)Cl(2), and (34)S(35)Cl(2) in their ground vibrational states, as well as those of (32)S(35)Cl(2) and (32)S(35)Cl(37)Cl in their nu(2) and 2nu(2) excited states, have been studied in selected frequency regions between 100 and 370 GHz. Transitions involving a large range of quantum numbers have been observed, so that precise rotational and quartic centrifugal distortion constants could be determined for each of the spectra investigated. The complete set of sextic distortion constants was also obtained for the most abundant isotopomer in its ground vibrational state. The newly determined rotational constants of (34)S(35)Cl(2) and (32)S(37)Cl(2) allowed us to calculate the complete r(s) structure of sulfur dichloride using both single- and double-isotopic substitution methods. The quadratic force field has been refined using a larger set of quartic distortion constants and inertial defects. Copyright 2000 Academic Press.     

In situ isobaric lipid mapping by MALDI–ion mobility separation–mass spectrometry imaging

The highly diverse chemical structures of lipids make their analysis directly from biological tissue sections extremely challenging. Here, we report the in situ mapping and identification of lipids in a freshwater crustacean Gammarus fossarum using matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) in combination with an additional separation dimension using ion mobility spectrometry (IMS). The high‐resolution trapped ion mobility spectrometry (TIMS) allowed efficient separation of isobaric/isomeric lipids showing distinct spatial distributions. The structures of the lipids were further characterized by MS/MS analysis. It is demonstrated that MALDI MSI with mobility separation is a powerful tool for distinguishing and localizing isobaric/isomeric lipids.     

Vibrationally excited states of HC5N: millimeter-wave spectroscopy and coupled cluster calculations

The rotational spectrum of HC₅N has been investigated in the millimeter-wave region, from 60 to 290 GHz, for 15 vibrationally excited states which lie approximately between 500 and 860 cm⁻¹, namely (v₆ v₇ v₈ v₉ v₁₀ v₁₁) = (000005), (000006), (000007), (000008), (000020), (000030), (001000), (010000), (100000), (000021), (000101), (001001), (010001), (000110), and (001010). Gas-phase copyrolysis of pyridine and phosphorus trichloride or, alternatively, a dc discharge in a gaseous mixture of vinyl cyanide and acetylene were used to produce the semi-stable HC₅N molecule. A large number of vibrational and rovibrational interactions has been taken into account to fit properly the measured transition frequencies of the states investigated. The most important perturbations are caused by the high-order Coriolis resonances observed between the (v₈, v₁₀) and (v₈ − 1, v₁₀ + 2) states, and between the (v₇, v₁₀, v₁₁) and (v₇ − 1, v₁₀ + 3, v₁₁ − 1) states, and by the cubic anharmonic interactions which mix the (v₆, v₈, v₁₁) states with the (v₆ − 1, v₈ + 1, v₁₁ + 1) states, and the (v₆, v₁₀) states with the (v₆ − 1, v₁₀ + 2) states. The analysis of the spectra was facilitated by CCSD(T) calculations with the cc-pVQZ basis, which provided accurate predictions of a large variety of spectroscopic constants like harmonic vibrational wavenumbers, vibration–rotation coupling constants, l-type doubling constants, and normal-coordinate cubic force constants. Excellent agreement between experiment and theory was generally observed, even when the experimental data were strongly perturbed by resonance effects.     

Quantum Variance and Ergodicity for the Baker's Map

We prove an Egorov theorem, or quantum-classical correspondence, for the quantised baker's map, valid up to the Ehrenfest time. This yields a logarithmic upper bound for the decay of the quantum variance, and, as a corollary, a quantum ergodic theorem for this map.     

A Cahn‐Hilliard–type equation with application to tumor growth dynamics

We consider a Cahn‐Hilliard–type equation with degenerate mobility and single‐well potential of Lennard‐Jones type. This equation models the evolution and growth of biological cells such as solid tumors. The degeneracy set of the mobility and the singularity set of the cellular potential do not coincide, and the absence of cells is an unstable equilibrium configuration of the potential. This feature introduces a nontrivial difference with respect to the Cahn‐Hilliard equation analyzed in the literature. We give existence results for different classes of weak solutions. Moreover, we formulate a continuous finite element approximation of the problem, where the positivity of the solution is enforced through a discrete variational inequality. We prove the existence and uniqueness of the discrete solution for any spatial dimension together with the convergence to the weak solution for spatial dimension d=1. We present simulation results in 1 and 2 space dimensions. We also study the dynamics of the spinodal decomposition and the growth and scaling laws of phase ordering dynamics. In this case, we find similar results to the ones obtained in standard phase ordering dynamics and we highlight the fact that the asymptotic behavior of the solution is dominated by the mechanism of growth by bulk diffusion.     

Spectrofluorimetric Evidence of the Transport of Marine Organic Matter in Antarctic Snow Via Air-Sea Interaction

Abstract

This paper considers the importance of marine aerosol in the atmosphere. As a consequence of its peculiar generation mechanism, it is also considered as a possible contributor to the transport of man-made microcomponents via air-sea interaction, especially in remote sites.

In view of future marine aerosol studies, the dominant presence of marine aerosol components in coastal Antarctic snow is discussed the presence of fluorescent marine organic matter in Antarctic snow is shown. Its “marum” nature is evidenced.

We give a tentative interpretation of the experimental data, and make a hypothesis concerning the variations in marine aerosol composition in correspondence to various altitudes.     

New Insights on Rotenone Resistance of Complex I Induced by the m.11778G>A/MT-ND4 Mutation Associated with Leber’s Hereditary Optic Neuropathy

The finding that the most common mitochondrial DNA mutation m.11778G>A/MT-ND4 (p.R340H) associated with Leber’s hereditary optic neuropathy (LHON) induces rotenone resistance has produced a long-standing debate, because it contrasts structural evidence showing that the ND4 subunit is far away from the quinone-reaction site in complex I, where rotenone acts. However, recent cryo-electron microscopy data revealed that rotenone also binds to the ND4 subunit. We investigated the possible structural modifications induced by the LHON mutation and found that its amino acid replacement would disrupt a possible hydrogen bond between native R340 and Q139 in ND4, thereby destabilizing rotenone binding. Our analysis thus explains rotenone resistance in LHON patients as a biochemical signature of its pathogenic effect on complex I.