Enzymatic synthesis of neopentylpolyol esters in organic media

Utilization of lipases for synthesis of esters of hydrophilic polyols has been investigated. The choice of a suitable solvent is crucial in this type of reaction. An interesting case is fatty acid esters from neopentylpolyols, such as trimethylolpropane, which are of great interest as high temperature lubricants. Enzymatic synthesis of trimethylolpropane tricaprylate was studied as an alternative to chemical manufacturing. Triester production occurred only if the water produced by esterification was continuously removed from the medium. In these condition, kinetics of appearance and transformation of mono-, di- and triesters were determined in order to define optimal conditions.     

Direct spectroscopic observation of multiple-charged-ion acceleration by an intense femtosecond-pulse laser

We have observed evidence of the emission of energetic He-and H-like ions of fluorine more than 1 MeV produced via the optical field ionization (OFI) from a solid target irradiated by an intense I=(2-4)x10(18) W/cm(2) (60 fs, lambda=800 nm), obliquely incident p-polarized pulse laser. The measured blue wing of He(alpha), He(beta), and Ly(alpha) lines of fluorine shows a feature of the Doppler-shifted spectrum due to the self-similar ion expansion dominated by superthermal electrons with the temperature T(h) approximately 100 keV. Using a collisional particle-in-cell simulation, which incorporates the nonlocal-thermodynamic-equilibrium ionization including OFI, we have obtained the plasma temperature, line shape, and maximal energy of accelerated ions, which agree well with those determined from the experimental spectra. The red wing of ion spectra gives the temperature of bulk plasma electrons.     

Probing hot and dense laser-induced plasmas with ultrafast XUV pulses

In this Letter, we demonstrate the instantaneous creation of a hot solid-density plasma generated by focusing an intense femtosecond, high temporal contrast laser on an ultrathin foil (100 nm) in the 10(18) W/cm2 intensity range. The use of high-order harmonics generated in a gas jet, providing a probe beam of sufficiently short wavelengths to penetrate such a medium, enables the study of the dynamics of this plasma on the 100 fs time scale. The comparison of the transmission of two successive harmonics permits us to determine the electronic density and the temperature with accuracies better than 15%, never achieved up to this date in the regime of laser pulses at relativistic intensity.     

High order harmonic generation by non-linear reflection of a pedestal-free intense laser pulse on a plasma

We demonstrate the influence of the prepulses and ASE of ultrashort pulses interacting with a solid target by addressing the direct comparison of the harmonic spectra generated by reflection onto a solid target with and without the introduction of a plasma mirror system. Harmonics up to the 20th of the fundamental of the Ti-Sa laser are clearly visible in a situation free from any plasma expansion. PACS 42.65. Ky; 52.38.-r; 52.38.Ph; 52.50.Jm     

On the interaction of femtosecond laser pulses with cluster targets

The heating of clusters by femtosecond laser pulses is studied theoretically and experimentally. Both the formation of a cluster target and the results of experimental studies of the cluster plasma by the methods of X-ray emission spectroscopy are considered. A numerical model of cluster formation in a supersonic gas jet is proposed. It is shown that detailed studies of two-phase gas-dynamic processes in a nozzle forming the jet give the spatial distributions of all parameters required for the correct calculation of the cluster heating by short laser pulses. Calculations of nozzles of different configurations show that in a number of cases an almost homogeneous cluster target can be formed, whereas in other cases the distributions of parameters prove to be not only inhomogeneous but also even nonmonotonic. A simple physical model of the plasma production by a femtosecond laser pulse and a picosecond prepulse is proposed. It is shown that a comparison of X-ray spectra with detailed calculations of the ion kinetics makes it possible to determine the main parameters of the plasma being produced.     

激光化学沉积膜层的结构与形成

本文以四甲基锡与Pt(CFACAC)作为工作物质,通过激光光致热分解和光分解,在石英基片上和电子显微镜碳膜上沉积锡膜与铂膜,研究光分解和光致热分解产生的膜层的结构与形成,测定膜层的沉积速率。文中给出了膜层沉积速率的一种新测定方法,用该方法可测定工作物质的蒸汽压。由光分解引起的锡膜沉积速率与光强成线性关系,并一直保持到小银灯的微弱光强,说明了四甲基锡的分解是单光子过程。由于涉条纹的最小距离可知,光分解沉积的分辨本领可小于0.2微米。     

Towards zirconium phosphonate-based microarrays for probing DNA-protein interactions: critical influence of the location of the probe anchoring groups

Terminal phosphate groups on double-stranded DNA probes bind strongly to glass substrates coated with a zirconium phosphonate monolayer, and probes immobilized in this way as microarrays can be used to detect protein targets. The sensitivity of the microarray was shown to be enhanced by the use of a polyguanine segment ((G)n , n > or = 5) as a spacer between the phosphate linker and the protein interaction domain. More importantly, the presence of phosphate linkers on both ends of the dsDNA probes leads to significant enhancement of target capture. The relevant characteristics of the different probes when bound to the surface were determined, by the original use of a combination of surface characterization techniques (XPS, AFM, and Sarfus). In this context, the location of the phosphate linkers in the duplex probes was found to result in different probe surface coverage and presentation on the surface, which affect subsequent interactions with the target protein.     

High-order harmonic generation from plasma mirrors

We discuss the two mechanisms involved in high-order harmonic generation from plasma mirrors, and show that they can be clearly identified experimentally. The very different phase properties of the corresponding harmonics lead to light beams with different divergences. This can be exploited to select a particular type of harmonic by spatial filtering in the far-field.     

Cationic Gallium(III) Halide Complexes: A New Generation of π-Lewis Acids

Ga-neration X: Well-defined neutral and cationic gallium(III) halide complexes have been synthesized and evaluated in catalysis. Both the (NHC)GaX(3) /AgSbF(6) catalytic mixture and isolated (NHC)GaX(2) (+) species function as exquisite π-Lewis acids in typical GaX(3) -catalyzed reactions. The cationic complexes are more active than GaX(3) and yet more resistant to hydrolysis, which allows lower catalytic loadings and faster reactions.     

Unsupported lead clusters and electron diffraction

A beam of Pb clusters is produced with the inert gas aggregation method and probed by electron diffraction. Analysis of the diffraction patterns indicates that average cluster size can vary between 3 and 7 nm, according to nucleation conditions. The diffraction patterns from beams with larger average cluster size are very similar to patterns calculated from model decahedron clusters, while those for smaller cluster size do not appear to have simple geometrical face-centred cubic, decahedral, or icosahedral structure. Received 30 November 2000