Photothermal displacement spectroscopy: An optical probe for solids and surfaces

We present a sensitive technique for determining the optical and thermal properties of solids, surfaces and thin films. This technique, photothermal displacement Spectroscopy, is based on the detection of the thermal expansion of a sample upon absorption of electromagnetic radiation. The technique is well suited for in situ ultrahigh vacuum studies and for experiments where wide temperature ranges are required. We show that surface and bulk optical absorption can be distinguished and that surface absorptions of αL=10^?6/W of incident power can be measured. The theoretical basis of the signal generation is given, and excellent experimental and theoretical agreement is demonstrated. The implications of our findings to imaging and microscopy are discussed.     

On the Uniqueness for the Spatially Homogeneous Boltzmann Equation with a Strong Angular Singularity

We prove an inequality on the Wasserstein distance with quadratic cost between two solutions of the spatially homogeneous Boltzmann equation without angular cutoff, from which we deduce some uniqueness results. In particular, we obtain a local (in time) well-posedness result in the case of (possibly very) soft potentials. A global well-posedness result is shown for all regularized hard and soft potentials without angular cutoff. Our uniqueness result seems to be the first one applying to a strong angular singularity, except in the special case of Maxwell molecules. Our proof relies on the ideas of Tanaka (Z. Wahrscheinlichkeitstheor. Verwandte. Geb. 46(1):67–105, [1978]) we give a probabilistic interpretation of the Boltzmann equation in terms of a stochastic process. Then we show how to couple two such processes started with two different initial conditions, in such a way that they almost surely remain close to each other.     

Absorption of short laser pulses on solid targets in the ultrarelativistic regime

We report the first direct measurements of total absorption of short laser pulses on solid targets in the ultrarelativistic regime. The data show an enhanced absorption at intensities above 10(20) W/cm(2), reaching 60% for near-normal incidence and 80%-90% for 45 degrees incidence. Two-dimensional particle-in-cell simulations demonstrate that such high absorption is consistent with both interaction with preplasma and hole boring by the intense laser pulse. A large redshift in the second harmonic indicates a surface recession velocity of 0.035c.     

Thermosensitive and Switchable Terpyridine‐Functionalized Metallo‐Supramolecular Poly(N‐isopropylacrylamide)

Metallo‐supramolecular polymers offer attractive possibilities to combine the properties of polymers with the characteristics offered by the metal–ligand coordination. Here we present for the first time the combination of metal‐bis(terpyridine) complexes and lower critical solution temperature (LCST) polymers that can be switched by addressing either the thermosensitive polymer or the metal complex. We describe a new strategy for the synthesis of poly(N‐isopropylacrylamide) (PNIPAM) end functionalized with a terpyridine moiety, which is further used for the preparation of Fe^II and Zn^II‐bis(terpyridine PNIPAM). The comparison of the LCST behavior of the uncomplexed ligands and their metal complexes that bear different counter ions is included. Furthermore, the switchability of the synthesized Fe^II system is demonstrated by a decomplexation reaction followed by the characterization of the uncomplexed ligand.

     

N-3 alkylation of uracils with unprotected amino alcohols using the Mitsunobu reaction

During our search for novel CGRP antagonists, we had great difficulty in accessing one of our key motifs. Herein, we communicate how we solved the problem by an unprecedented Mitsunobu alkylation using unprotected amino alcohols.     

Zn7Cu6: a magic cluster of brass?

Density functional theory was applied to a series of 13-atom Zn–Cu alloy clusters. We did a thorough search for the low-energy isomers by global optimization, plus explicit optimization of all homotops of the icosahedron. Structures of copper rich clusters tend to be compact, often icosahedra, whereas zinc rich clusters ( ${{\rm Zn}_8{\rm Cu}_{5}^{+}}$ , Zn₉Cu₄, Zn₁₁Cu₂) have compact copper cores surrounded by an incomplete shell of solvating Zn atoms. The icosahedral structure, low total energy, and large hardness of Zn₇Cu₆ indicate that it has special stability among Zn _x Cu _y clusters. However, Zn₇Cu₆ has many low lying isomers and a small cohesive energy compared to brass, which suggest that it is not stable in a broader sense.     

Effectiveness of the suzuki-miyaura cross-coupling reaction for solid-phase peptide modification

The Suzuki-Miyaura (SM) cross-coupling reaction has recently become one of the most efficient methods for C-C bond construction opening a wide range of opportunities in organic synthesis. This study focused on the evaluation of the use of the SM reaction to modify peptides using a solid-phase synthesis approach, an avenue that was still not investigated intensively. We used as a peptide model [Ala (1,2,3), Leu (8)]Enk linked to a polystyrene support on which it was previously assembled. The aromatic residues Tyr (4) and Phe (7) of [Ala (1,2,3), Leu (8)]Enk were respectively substituted with p-iodo-Phe, and an SM-related strategy was developed. Results indicated that the reaction conditions involving K 3PO 4 or Na 2CO 3 (base), DMF (solvent), Pd(PPh 3) 4 (catalyst), and temperatures ranging from 50 to 80 degrees C during 20 h were found as optimal. Finally applying those optimal conditions, a series of [Ala (1,2,3), Leu (8)]Enk analogs modified at Tyr (4) or Phe (7) positions was synthesized using diverse boronic acid derivatives.     

Decongestion of methylene spectra in biological and non-biological systems using picosecond 2DIR spectroscopy measuring electron-vibration–vibration coupling

Methylene is found in the repeat units of many polymers including proteins. In some cases it appears to be a useful reporter of variation in local environment whilst in other contexts average behaviour seems to dominate. In this paper we apply a particular 2DIR technique to a range of systems containing methylene groups, showing that mode frequencies, linewidths and splittings can be easily extracted even when the infrared absorption bands are too congested to allow reliable analysis. 2DIR spectra of polyethylene and several liquid alkanes are compared and it is shown for the case of l-arginine that the methylene scissor modes are split and that this can be resolved by tracking the 2DIR spectrum as a function of time. Calculations from first principles reveal that for most of the methylene modes studied, electrical anharmonicity is the dominant contributor to the 2DIR cross-peak intensity, with the mechanical anharmonicity making only a small contribution.     

X‐Tream quality assurance in synchrotron X‐ray microbeam radiation therapy

Microbeam radiation therapy (MRT) is a novel irradiation technique for brain tumours treatment currently under development at the European Synchrotron Radiation Facility in Grenoble, France. The technique is based on the spatial fractionation of a highly brilliant synchrotron X‐ray beam into an array of microbeams using a multi‐slit collimator (MSC). After promising pre‐clinical results, veterinary trials have recently commenced requiring the need for dedicated quality assurance (QA) procedures. The quality of MRT treatment demands reproducible and precise spatial fractionation of the incoming synchrotron beam. The intensity profile of the microbeams must also be quickly and quantitatively characterized prior to each treatment for comparison with that used for input to the dose‐planning calculations. The Centre for Medical Radiation Physics (University of Wollongong, Australia) has developed an X‐ray treatment monitoring system (X‐Tream) which incorporates a high‐spatial‐resolution silicon strip detector (SSD) specifically designed for MRT. In‐air measurements of the horizontal profile of the intrinsic microbeam X‐ray field in order to determine the relative intensity of each microbeam are presented, and the alignment of the MSC is also assessed. The results show that the SSD is able to resolve individual microbeams which therefore provides invaluable QA of the horizontal field size and microbeam number and shape. They also demonstrate that the SSD used in the X‐Tream system is very sensitive to any small misalignment of the MSC. In order to allow as rapid QA as possible, a fast alignment procedure of the SSD based on X‐ray imaging with a low‐intensity low‐energy beam has been developed and is presented in this publication.