Compact fibre-based coherent anti-Stokes Raman scattering spectroscopy and interferometric coherent anti-Stokes Raman scattering from a single femtosecond fibre-laser oscillator

We demonstrate a new approach to CARS spectroscopy by efficiently synthesizing synchronized narrow-bandwidth (less than 10 cm⁻¹) pump and Stokes pulses (frequency difference continuously tunable upto ≈3000 cm⁻¹) based on spectral compression together with second harmonic generation (in periodically-poled nonlinear crystals) of femtosecond pulses emitted by a single compact Er-fibre oscillator. For a far better signal to non-resonant background contrast, interferometric CARS (I-CARS) is demonstrated and CARS signal enhancement upto three orders of magnitude is achieved by constructive interference with an auxiliary local oscillator at anti-Stokes field, also synthesized by spectral compression of pulses emitted from the same fibre oscillator.     

Gold-mediated synthesis of α-ionone

A simple and convenient synthesis of α-ionone, an important component of flowers and fragrances, is reported. The key step in the formation of the α,β-unsaturated ketone moiety involves an NHC-Au^I catalyzed Meyer-Schuster-like rearrangement of readily prepared propargylic esters. The complex [{Au(IPr)}₂(μ-OH)][BF₄] proved to be the most efficient catalyst leading to α-ionone in 70% yield from a propargylic benzoate. This optimized procedure represents a valuable and attractive alternative to classical methods leading to α,β-unsaturated ketones, such as the Wittig or aldol reactions.     

Modeling the multi-layer nature of the European Air Transport Network: Resilience and passengers re-scheduling under random failures

We study the dynamics of the European Air Transport Network by using a multiplex network formalism. We will consider the set of flights of each airline as an interdependent network and we analyze the resilience of the system against random flight failures in the passenger’s rescheduling problem. A comparison between the single-plex approach and the corresponding multiplex one is presented illustrating that the multiplexity strongly affects the robustness of the European Air Network.     

Anti-Multiple Myeloma Potential of Secondary Metabolites from Hibiscus sabdariffa—Part 2

Multiple Myeloma (MM) is an aggressive tumor causing millions of deaths every year and currently available therapies are often unsuccessful or correlated with severe side effects. In our previous work we demonstrated that the Hibiscus sabdariffa hydroalcoholic extract inhibits the growth of the MM cell line and we isolated two metabolites responsible for the activity: Hib-ester and Hib-carbaldehyde. Herein we report their interaction with proteasome, one of the main targets in the fight against MM. The molecular modelling study outlined a good interaction of both compounds with the target and these results prompted us to investigate their potential to inhibit proteasome. Metabolites were then isolated from the calyces and an extract with a high content of Hib-ester and Hib-carbaldehyde was prepared. An anticancer profile was drawn, evaluating apoptosis, autophagy and proteasome inhibition, with the anticancer properties being mainly attributed to the Hib-ester and Hib-carbaldehyde, while the proteasome inhibition of the extract could also be ascribed to the presence of anthocyanins, a class of secondary metabolites already known for their proteasome inhibitory activity.     

Using Steady-State Kinetics to Quantitate Substrate Selectivity and Specificity: A Case Study with Two Human Transaminases

We examined the ability of two human cytosolic transaminases, aspartate aminotransferase (GOT1) and alanine aminotransferase (GPT), to transform their preferred substrates whilst discriminating against similar metabolites. This offers an opportunity to survey our current understanding of enzyme selectivity and specificity in a biological context. Substrate selectivity can be quantitated based on the ratio of the k_cat/K_M values for two alternative substrates (the ‘discrimination index’). After assessing the advantages, implications and limits of this index, we analyzed the reactions of GOT1 and GPT with alternative substrates that are metabolically available and show limited structural differences with respect to the preferred substrates. The transaminases’ observed selectivities were remarkably high. In particular, GOT1 reacted ~10⁶-fold less efficiently when the side-chain carboxylate of the ’physiological’ substrates (aspartate and glutamate) was replaced by an amido group (asparagine and glutamine). This represents a current empirical limit of discrimination associated with this chemical difference. The structural basis of GOT1 selectivity was addressed through substrate docking simulations, which highlighted the importance of electrostatic interactions and proper substrate positioning in the active site. We briefly discuss the biological implications of these results and the possibility of using k_cat/K_M values to derive a global measure of enzyme specificity.     

New Histamine-Related Five-Membered N-Heterocycle Derivatives as Carbonic Anhydrase I Activators

A series of histamine (HST)-related compounds were synthesized and tested for their activating properties on five physiologically relevant human Carbonic Anhydrase (hCA) isoforms (I, II, Va, VII and XIII). The imidazole ring of HST was replaced with different 5-membered heterocycles and the length of the aliphatic chain was varied. For the most interesting compounds some modifications on the terminal amino group were also performed. The most sensitive isoform to activation was hCA I (K_A values in the low micromolar range), but surprisingly none of the new compounds displayed activity on hCA II. Some derivatives (1, 3a and 22) displayed an interesting selectivity for activating hCA I over hCA II, Va, VII and XIII.     

Cationic oligomerization of isoprene and structure of its oligomers

The results obtained in a study of isoprene cationic oligomerization in the presence of some oxyacids (H₂SO₄, CH₃SO₃H, Nafion^® H) are reported. Oligomers up to pentamers are obtained which were examined through gas chromatography/mass spectrometry analysis either of the reaction products or of the hydrogenated products. The structure of the dimer fraction was investigated and revealed the prevalent presence of α-pinene and p-cymene together with different cyclic unsaturated hydrocarbons. Only small quantities of linear dimers were found. Possible reaction mechanisms are presented.     

Stationary layered solutions in {\mathbb{R}}^2 for a class of non autonomous Allen-Cahn equations

We consider a class of non autonomous Allen-Cahn equations where is a multiple-well potential and is a periodic, positive, non-constant function. We look for solutions to (0.1) having uniform limits as corresponding to minima of W. We show, via variational methods, that under a nondegeneracy condition on the set of heteroclinic solutions of the associated ordinary differential equation the equation (0.1) has solutions which depends on both the variables x andy. In contrast, when a is constant such nondegeneracy condition is not satisfied and all such solutions are known to depend only on x. Received April 16, 1999 / Accepted October 1, 1999 / Published online June 28, 2000     

Second-order moving average and scaling of stochastic time series

Long-range correlation properties of stochastic time series y(i) have been investigated by introducing the function σ² _MA = [y(i) - (i)]², where (i) is the moving average of y(i), defined as 1/n y(i - k), n the moving average window and N_max is the dimension of the stochastic series. It is shown that, using an appropriate computational procedure, the function σ _MA varies as n^H where H is the Hurst exponent of the series. A comparison of the power-law exponents obtained using respectively the function σ _MA and the Detrended Fluctuation Analysis has been also carried out. Interesting features denoting the existence of a relationship between the scaling properties of the noisy process and the moving average filtering technique have been evidenced. Received 31 December 2001