Synthesis and Antiproliferative Effect of Halogenated Coumarin Derivatives

A series of 6- and 6,8-halocoumarin derivatives have been investigated as potential antiproliferative compounds against a panel of tumor and normal cell lines. Cytotoxic effects were determined by the MTT method. To investigate the potential molecular mechanism involved in the cytotoxic effect, apoptosis assay, cell cycle analysis, reactive oxygen species (ROS), and reduced glutathione analysis were performed. Among the screened compounds, coumarins 6,8-dibromo-2-oxo-2H-chromene-3-carbonitrile 2h and 6,8-diiodo-2-oxo-2H-chromene-3-carbonitrile 2k exhibited the most antiproliferative effect in thyroid cancer-derived cells TPC-1. The apoptosis assay showed that both 2h and 2k induced apoptosis in TPC-1 thyroid cancer cells. According to these experiments, both coumarins induced a slight increase in TPC-1 cells in the G2/M phase and a decrease in the S phase. A significant increase in ROS levels was observed in TPC-1 treated with diiodocoumarin 2k, while the dibromocoumarin 2h induced a decrease in ROS in a dose and time-dependent manner.     

Desorption of Rb and Cs from PDMS induced by non resonant light scattering

Simultaneous light-induced desorption of rubidium and cesium atoms has been observed in polydimethylsiloxane (PDMS) coated Pyrex cells at room temperature and at low light intensity. The two alkali atoms show the same dynamics and the same dependence on the desorbing light frequency. No competition in the free sites occupancy exists. An interpretation of the experimental results in terms of non-resonant light scattering from the PDMS coating is discussed.     

White-light laser cooling of ions in a storage ring

We propose the use of a white laser for laser cooling of ions in a storage ring. The use of a broad-band laser provides a radiation pressure force with wide velocity capture range and high magnitude, which is promising to improve the performance of both longitudinal and indirect transverse cooling. This wide-range force could also be suitable for direct transverse cooling of low-density beams.     

A Monte Carlo simulation of a stroboscopic laser diagnostics of ordered ion beams in a storage ring

A Monte Carlo code combined with a particle tracking program has been used to study a stroboscopic laser diagnostic system that is able to detect a string-like ordered ion beam. Different ion species have been studied to evaluate the diagnostics capability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Francium sources and traps for fundamental interaction studies

Francium is one of the best candidates for atomic parity nonconservation (APNC) and for the search of permanent electric dipole moments (EDMs). APNC measurements test the weak force between electrons and nucleons at very low momentum transfers. They also represent a unique way to detect weak nucleon-nucleon interactions. EDMs are instead related to the time-reversal symmetry. Preliminary to these fundamental measurements are precision studies in atomic spectroscopy and the development of magneto-optical traps (MOT), which partially compensate for the lack of stable Fr isotopes. At LNL Legnaro, francium is produced by fusion of 100-MeV ¹⁸O with ¹⁹⁷Au in a thick target, followed by evaporation of neutrons from the compound nucleus. Francium diffuses inside the hot target (1200 K) and is surface ionized for injection at 3 keV in an electrostatic beamline. Typically, we produce 1×10⁶ (²¹⁰Fr ions)/s for a primary flux of 1.5×10¹² particles/s. We have studied Fr yields as a function of primary beam energy, intensity, and target temperature. Information on the efficiency of bulk diffusion, surface desorption and ionization is deduced. The beam then enters a Dryfilm-coated cell, where it is neutralized on a heated yttrium plate. The escape time of neutral Fr (diffusion + desorption) is approximately 20 s at 950 K, as measured with a dedicated setup. In the MOT, we use 6 orthogonal Ti:sapphire laser beams for the main pumping transition and 6 beams from a stabilized diode repumper. Fluorescence from trapped atoms is observed with a cooled CCD camera, in order to reach noise levels from stray light equivalent to approximately 50 atoms. Systematic tests are being done to improve the trapping efficiency. We plan to further develop Fr traps at LNL; in parallel, we will study APNC and EDM techniques and systematics with stable alkalis at Pisa, Siena, and Ferrara.     

Two-color coherent population trapping in a single Cs hyperfine transition,with application in magnetometry

We investigate the coherent population trapping effect occurring between the Zeeman sublevels of a given hyperfine state of Cs when excited by a single-mode diode laser, which is frequency modulated in the kHz–MHz range. In the presence of a dc magnetic field, simultaneous excitation of pairs of ground-state magnetic sublevels to common excited magnetic sublevels is performed. As a result, coherent population trapping resonance is detected at only a given modulation frequency, whose value gives a measure of the magnetic field. The parameters of the resonances are measured in order to determine the ultimate accuracy of the magnetic field measurement. Received: 6 December 2002 / Revised version: 24 February 2003 / Published online: 2 June 2003 RID="*" ID="*"Corresponding author. Fax: +39-0577/23-4689, E-mail: biancalana@unisi.it     

Heterodyne detection of Rydberg atom maser emission

Using a very sensitive heterodyne receiver developed for millimeter radioastronomy, we have for the first time directly observed the microwave emission of Rydberg atoms in the laboratory. The source is a small system (～10⁵ atoms) of Na Rydberg atoms optically pumped in a microwave cavity, which acts as a pulsed maser on the 33 S → 32 P transition at 107.8 GHz. Typical signals have a power of several 10^-12 watts and a duration of 0.3 μs.     

Kinetics and mechanism of biphasic substitution reactions of a platinum(II) complex with thioglycollic acid and 4-methyl-3-thiosemicarbazide in aqueous solution

The kinetics of interactions between cis-diaqua(2-aminomethylpyridine)platinum(II) perchlorate (1) [Pt(pic)(OH₂)₂](ClO₄)₂, thioglycollic acid (TGA), and 4-methyl-3-thiosemicarbazide (MTSC) have been studied spectrophotometrically in aqueous medium as a function of the [complex (1)] as well as [TGA] or [MTSC], pH and temperature at constant ionic strength. The observed pseudo-first-order rate constants were proportional to [TGA] or [MTSC]. At pH 4.0, the interactions of (1) with both TGA and MTSC show two distinct consecutive steps; the first step is dependent and second independent of [TGA] or [MTSC]. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated, along with the rate constants for the two steps. The first step is assigned to ligand-assisted anation and the second to chelation of TGA or MTSC. The activation parameters for both the steps were evaluated using Eyring’s equation. On the basis of the kinetic observations and evaluated activation parameters, an associative mechanism is proposed for both the reactions.     

Three-body collisions between laser-excited Na and K atoms in the presence of buffer gas

Summary Energy pooling in alkali vapour mixtures has been previously investigated by us in an amalgam of sodium and potassium. In this paper we describe the peculiar features appearing when some buffer gas is introduced in the cell. We demonstrate that the buffer gas enhances the energy transfer between Na(3P) and K(4S), which is detected through the effects induced on the highly excited states populated by the Na(3P)/Na(3P) and K(4P)/K(4P) collisions.

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Riassunto Abbiamo in precedenza studiato il processo di collisione di energy pooling in una miscela di sodio e potassio. In questo lavoro si analizzano i particolari effetti indotti dalla presenza di alcuni Torr di gas tampone introdotti nella cella. Viene dimostrato che il gas tampone favorisce il processo di trasferimento di energia fra Na(3P) e K(4S), che viene rivelato attraverso gli effetti indotti sugli stati altamente eccitati popolati dalle collisioni Na(3P)/Na(3P) e K(4P)/K(4P).

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Резюме Ранее авторы в амальгаме натрия и калия исследовали распределение энергии в смесях щелочных паров. В этой статье мы описываем особенности, возникающие при введении буферного газа в ячейку. Мы поквзываем, что буферный газ усиливает обмен энергией между Na(3P) и K(4S), который детектируется через эффекты, связанные с высоко возбужденными состояниями, заселенными при Na(3P)/Na(3P) и K(4P)/K(4P) соударенияш.

     

Peptide Cysteine Thiols Act as Photostabilizer of Avobenzone through Stabilizing the Transition State of Keto-Enol Tautomerization

Photostabilizers have been used to impart stability to an FDA-approved chemical UV-A filter avobenzone against the UV-A radiations and sunlight. The thiol group of glutathione plays a critical role in imparting the photostabilization activity of glutathione on avobenzone. The current report aims to evaluate the photostabilization activity of multiple thiols containing cysteine peptides on avobenzone. Cysteine-tripeptide and cysteine-pentapeptide were chemically synthesized and characterized using mass spectrometry. Synthetic peptides were assessed for their photostabilization activity on the enolic-form of the avobenzone under natural sunlight using UV spectroscopy in both protic and aprotic solvents. Unlike glutathione, which has pronounced activity in protic solvents, cysteine-pentapeptide exhibits similar photoprotection activity in both protic and aprotic solvents. Computational calculations using DFT suggest that peptide cysteine thiols may assist in the reversal of the photoketonization process of avobenzone thereby exhibiting the photoprotection activity to the enolic-form of avobenzone. Peptide cysteine thiols lower the activation energy barrier of keto-to-enol tautomerization of avobenzone by 30 kcal mol⁻¹ by assisting the proton shuttle through a six-membered transition state. The current report emphasizes the applications of peptide thiols in cosmetics and may help in the development of peptides as aesthetic medicines.