Towards quantum superpositions of a mirror: an exact open systems analysis

We analyze the recently proposed mirror superposition experiment of Marshall, Simon, Penrose, and Bouwmeester, assuming that the mirror's dynamics contains a nonunitary term of the Lindblad-type proportional to -[q,[q,rho]], with q the position operator for the center of mass of the mirror, and rho the statistical operator. We derive an exact formula for the fringe visibility for this system. We discuss the consequences of our result for tests of environmental decoherence and of collapse models. In particular, we find that with the conventional parameters for the continuous spontaneous localization model of state vector collapse, maintenance of coherence is expected to within an accuracy of at least 1 part in 10(8). Increasing the apparatus coupling to environmental decoherence may lead to observable modifications of the fringe visibility, with time dependence given by our exact result.     

Ultrashort-pulse modulation in adiabatically prepared Raman media

We demonstrate the efficient modulation of an approximately 100-femtosecond pulse in a Raman medium coherently prepared by nanosecond pulses. Raman sidebands of the ultrashort pulse spanning 360 THz are generated with an efficiency of >5%. We show that the mechanism permitting the sidebands to be generated is the preparation of a significant vibrational coherence in the medium that is robust to disturbance by an intense short pulse. If the observed sidebands were phase compensated, they would form a short train of approximately ten 3-fs pulses. Focusing would permit the realization of a peak intensity of >10(13) W cm(-2).     

Chaotic imaging in frequency downconversion

We analyze and recover, by means of spatial intensity correlations, the image obtained by a seeded frequency-downconversion process in which the seed field is chaotic and an intensity modulation is encoded in the pump field. Although the field generated is as chaotic as the seed field and does not carry any information about the modulation of the pump, one can extract an image of the pump by measuring the spatial intensity correlations between the generated field and one Fourier component of the seed.     

Ethyl 2-acetamido-4,6-di-O-benzyl-2,3-N,O-carbonyl-2-deoxy-1-thio-beta-D-glycopyranoside as a versatile GlcNAc donor

The title donor, ethyl 2-acetamido-4,6-di-O-benzyl-2,3-N,O-carbonyl-2-deoxy-1-thio-beta-D-glycopyranoside, is shown to be an excellent glycosyl donor giving immediate and efficient access to variant GlcNAc-containing oligosaccharides.     

Generalization of the theorem of L. G. Schnirelman

In this note we generalize a theorem of L. G. Schnirelman on the existence of a limit in the minimal diophantic deviations from zero in [a, b], for the case of a continuous function φ(κ) that possesses a finite number of zeros in [a, b]. The quadratic deviation is also considered.     

Combined X-ray absorption and X-ray diffraction under high pressure

ABSTRACT

X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are two complementary structural techniques. Their combination improves the understanding of the effect of pressure on materials as illustrated by examples taken from studies on different types of materials (semiconductors, molecular solid, ferroelectric perovskite and gas mixture). The introduction of nanopolycrystalline diamonds anvils has extended XAS to high-energy edges with the possibility to use energy-scanning XAS beamlines where XRD can be performed in addition to XAS experiments.     

Investigating the effect of hydrogen bonding environments in amide cleavage reactions at zinc(II) complexes with intramolecular amide oxygen co-ordination

Amide oxygen co-ordination to a zinc(II) ion around a hydrogen bonding microenvironment is a common structural/functional feature of metalloproteases. We report two strategies to position hydrogen bonding groups in the proximity of a zinc(II)-bound amide oxygen, and we investigate their effect on the stability of the amide group. Polydentate tripodal ligands (6-R1-2-pyridylmethyl)-R2 (R1= NHCOtBu, R2= N(CH2-py-6-X)2 X = H L1, X = NH2, H L2, X = NH2 L3) form [(L)Zn]2+ cations (L =L1, 1; L2, 2; L3, 3) with intramolecular amide oxygen co-ordination (1-3), and intramolecular N-H...O=C(amide) hydrogen bonding (2, 3) rigidly fixed by the ligand framework. 1-3 undergo cleavage of the tert-butyl amide upon addition of Me4NOH.5H2O (1 equiv.) in methanol at 50(1) degrees C. Under these conditions the half-life, t(1/2), of the amide bond is 0.4 h for 1, 9 h for 2 and 320 h for 3. Mononuclear zinc(II) complexes of (6-NHCOtBu-2-pyridylmethyl)-R2(R2= N(CH2CH2)2S) L4 and chelating N2 ligands without hydrogen bonding groups (1,10-phenanthroline L5, 2-(aminomethyl)pyridine L6) as control compounds, and with an amino hydrogen bonding group (6-amino-2-(aminomethyl)pyridine L7) have been synthesised. Amide cleavage is in this case faster at the zinc(II) complex with the amino hydrogen bonding group. Thus, hydrogen bonding environments can both accelerate and slow down amide bond cleavage reactions at zinc(II) sites. Importantly, the magnitude of the effect exerted by the hydrogen bonding environments was found to be significant; 800-fold rate difference. This result highlights the importance of hydrogen bonding environments around metal centres in amide cleavage reactions, which may be relevant to the chemistry of natural metalloproteases and applicable to the design of more efficient artificial protein cleaving agents.     

Synthesis and characterization of gels from polyallylamine and carbon dioxide as gellant

The synthesis and characterization of a novel series of polymer gels are reported. They are formed at ambient temperatures by bubbling CO(2) through solutions of polyallylamine (PAA; a latent gellant) in several organic liquids, including aliphatic alcohols and 1-methyl-2-pyrrolidone. The stabilities of the alcohol gels, as indicated by the (irreversible) degelation temperature, T(g)(dt), were strongly dependent on the number of carbon atoms (C(n)) in the alkyl chains of the alcohol liquids. The mechanism of formation and the microenvironmental properties of PAA-based gels containing a small amount of a pH-sensitive probe, 2,6-naphthalenedicarboxylic acid (2,6-NDCA), have been probed using static and dynamic fluorescence measurements. A measurable pH change and significant alterations to the fluorescence spectra were coincident with gelation of PAA solutions in 1-butanol as CO(2) was bubbled through, and the fluorescence spectra were monitored over several hours until no further changes were detected. Analyses of dynamic fluorescence decay histograms indicate the presence of three decay times due to different microenvironments where the 2,6-NDCA molecules are located.     

Two-photon photosensitized production of singlet oxygen: sensitizers with phenylene-ethynylene-based chromophores

[reaction: see text] Singlet molecular oxygen (a(1)Delta(g)) has been produced and optically monitored in time-resolved experiments upon nonlinear two-photon excitation of photosensitizers that contain triple bonds as an integral part of the chromophore. Both experiments and ab initio computations indicate that the photophysical properties of alkyne-containing sensitizers are similar to those in the alkene-containing analogues. Most importantly, however, in comparison to the analogue that contains double bonds, the sensitizer containing alkyne moieties is more stable against singlet-oxygen-mediated photooxygenation reactions. This increased stability can be advantageous, particularly with respect to two-photon singlet oxygen imaging experiments in which data are collected over comparatively long time periods.