Radical addition fragmentation chain transfer (RAFT) polymerization of ferrocenyl (Meth)acrylates

We report on the controlled free radical homopolymerization of 1‐ferrocenylethyl acrylate as well as of three new ferrocene bearing monomers, namely 4‐ferrocenylbutyl acrylate, 2‐ferrocenylamido‐2‐methylpropyl acrylate, and 4‐ferrocenylbutyl methacrylate, by the RAFT technique. For comparison, the latter monomer was polymerized using ATRP, too. The ferrocene containing monomers were found to be less reactive than their analogues free of ferrocene. The reasons for the low polymerizability are not entirely clear. As the addition of free ferrocene to the reaction mixture did not notably affect the polymerizations, sterical hindrance by the bulky ferrocene moiety fixed on the monomers seems to be the most probable explanation. Molar masses found for 1‐ferrocenylethyl acrylate did not exceed 10,000 g mol^?1, while for 4‐ferrocenylbutyl (meth)acrylate molar masses of 15,000 g mol^?1 could be obtained. With PDIs as low as 1.3 in RAFT polymerization of the monomers, good control over the polymerization was achieved. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Subcentimeter depth resolution using a single-photon counting time-of-flight laser ranging system at 1550 nm wavelength

We demonstrate subcentimeter depth profiling at a stand off distance of 330 m using a time-of-flight approach based on time-correlated single-photon counting. For the first time to our knowledge, the photon-counting time-of-flight technique was demonstrated at a wavelength of 1550 nm using a superconducting nanowire single-photon detector. The performance achieved suggests that a system using superconducting detectors has the potential for low-light-level and eye-safe operation. The system's instrumental response was 70 ps full width at half-maximum, which meant that 1 cm surface-to-surface resolution could be achieved by locating the centroids of each return signal. A depth resolution of 4 mm was achieved by employing an optimized signal-processing algorithm based on a reversible jump Markov chain Monte Carlo method.     

Noise from neighbours and the sound insulation of party walls in houses

Nine-hundred-and-seventeen residents in a sample of attached houses constructed since 1970 were interviewed in the course of a national survey dealing with nuisance occasioned by noise from neighbours. The airborne sound insulation of the party walls, measured prior to occupation, ranged from zero to 120 dB AAD. Two-thirds of the respondents heard noise from their neighbours and even at performance levels meeting or exceeding the minimum requirements of the Building Regulations nearly 50% did so. Of the total sample, some 18% were seriously bothered by neighbours' noise. Highly significant relationships were found between physical performance rated in dB AAD (Aggregate Adverse Deviation) and a variety of subjective responses. These include reports of hearing neighbours' noise, of being bothered by it, hearing neighbours' conversation, and, in particular, the direct rating of sound insulation quality by respondents, which last appears to provide the most reliable and consistent indication of the likelihood of experiencing nuisance from neighbours' noise. These results provide, for the first time, empirical validation of the U.K. performance rating procedure. In addition, the survey findings emphasize the importance of impact noises, not included in the standardized performance measurements, but which contribute substantially to nuisance, particularly between houses where airborne sound insulation is comparatively good. Other findings indicate that occupants were very satisfied with their general environment and only slightly less so with their homes. Poor sound insulation was a prominent criticism of the dwellings, being ranked third among spontaneous adverse comments and first in a ranking of nine commonly encountered building defects. These results indicate the importance of sound insulation to occupants of recently built houses, placing this aspect of design and construction within a wider context. The overall results of the survey provide a practical guide to estimating the consequences, in terms of occupants' attitudes to noise from neighbours, of raising or lowering standards of sound insulation performance between houses.     

Energy Exchange at Degenerate Mixing of Four Fast TE 2 Modes of a Thin Left-Handed Film on a Nonlinear Substrate

Frequency-degenerate mixing of forward and backward propagating fast modes is considered in a planar optical waveguide based on a thin left-handed film and a right-handed substrate exhibiting the Kerr effect. Nonlinear coupled-mode equations are solved for the intensities of these modes in the neglect of the contributions of elementary processes that fail to satisfy the phase-matching condition. It is shown that the intramode self-action of four TE modes is accompanied by energy exchange between these modes. The efficiency of energy exchange varies periodically along the propagation direction of modes, thus leading to the inversion of the intensities of forward and backward propagating light fields on the interaction half-period.     

Engineered Biocatalytic Synthesis of β-N-Substituted-α-Amino Acids

Non-canonical amino acids (ncAAs) are useful synthons for the development of new medicines, materials, and probes for bioactivity. Recently, enzyme engineering has been leveraged to produce a suite of highly active enzymes for the synthesis of β-substituted amino acids. However, there are few examples of biocatalytic N-substitution reactions to make α,β-diamino acids. In this study, we used directed evolution to engineer the β-subunit of tryptophan synthase, TrpB, for improved activity with diverse amine nucleophiles. Mechanistic analysis shows that high yields are hindered by product re-entry into the catalytic cycle and subsequent decomposition. Additional equivalents of l -serine can inhibit product reentry through kinetic competition, facilitating preparative scale synthesis. We show β-substitution with a dozen aryl amine nucleophiles, including demonstration on a gram scale. These transformations yield an underexplored class of amino acids that can serve as unique building blocks for chemical biology and medicinal chemistry.     

Exploring the Biocatalytic Potential of Fe/α-Ketoglutarate-Dependent Halogenases

Freestanding Fe/α-ketoglutarate-dependent halogenases are oxidoreductases that catalyze the installation of halogen atoms into unactivated sp³-hybridized carbon centers with high stereo- and regioselectivity. Since their discovery in 2014, a small number of indole alkaloid and amino acid halogenases have been identified and characterized. First enzyme engineering examples suggest that the accessible substrate range of these enzymes may be expanded through the use of rational enzyme design and directed evolution. Structural investigations of non-heme iron halogenases acting on freestanding as well as tethered substrates are beginning to inform about the principles of the underlying halogenation mechanism.     

Optically bistable nonlinear interference filters for use with near-infrared laser diodes

ZnSe nonlinear interference filters, configured as optothermal bistable etalons with absorbed transmission (BEAT) devices, have been operated as all-optical switches using 830 nm diode laser illumination and fibre-optic coupling. Stable switching at powers down to 3 mW have been demonstrated for spot diameters of 10 μm. An observed increase in switch power when using large numerical-aperture illumination is analysed in terms of a reduction in effective cavity finesse.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.