The Spin-Echo System Reconsidered

Simple models have played an important role in the discussion of foundational issues in statistical mechanics. Among them the spin-echo system is of particular interest since it can be realized experimentally. This has led to inferences being drawn about approaches to the foundations of statistical mechanics, particularly with respect to the use of coarse-graining. We examine these claims with the help of computer simulations.     

Multiple periodic solutions for a nonlinear suspension bridge equation

We investigate nonlinear oscillations in a fourth-order partialdifferential equation which models a suspension bridge. Previouswork establishes multiple periodic solutions when a parameterexceeds a certain eigenvalue. In this paper, we use Leray-Schauderdegree theory to prove that if the parameter is increased further,beyond a second eigenvalue, then additional solutions are created.     

Trimethyl lock: a stable chromogenic substrate for esterases

p-Nitrophenyl acetate is the most commonly used substrate for detecting the catalytic activity of esterases, including those that activate prodrugs in human cells. This substrate is unstable in aqueous solution, limiting its utility. Here, a stable chromogenic substrate for esterases is produced by the structural isolation of an acetyl ester and p-nitroaniline group using a trimethyl lock moiety. Upon ester hydrolysis, unfavorable steric interactions between the three methyl groups of this o-hydroxycinnamic acid derivative encourage rapid lactonization to form a hydrocoumarin and release p-nitroaniline. This "prochromophore" could find use in a variety of assays.     

Synthesis of a Far‐Red Photoactivatable Silicon‐Containing Rhodamine for Super‐Resolution Microscopy

The rhodamine system is a flexible framework for building small‐molecule fluorescent probes. Changing N‐substitution patterns and replacing the xanthene oxygen with a dimethylsilicon moiety can shift the absorption and fluorescence emission maxima of rhodamine dyes to longer wavelengths. Acylation of the rhodamine nitrogen atoms forces the molecule to adopt a nonfluorescent lactone form, providing a convenient method to make fluorogenic compounds. Herein, we take advantage of all of these structural manipulations and describe a novel photoactivatable fluorophore based on a Si‐containing analogue of Q‐rhodamine. This probe is the first example of a “caged” Si‐rhodamine, exhibits higher photon counts compared to established localization microscopy dyes, and is sufficiently red‐shifted to allow multicolor imaging. The dye is a useful label for super‐resolution imaging and constitutes a new scaffold for far‐red fluorogenic molecules.     

Experiments with longitudinally polarized electrons in a storage ring using a siberian snake

We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space.     

N‐Ethylazatribenzo‐21‐crown‐7

The structure of the title compound, 25‐ethyl‐2,5,12,15,22,28‐hexa­oxa‐25‐aza­tetra­cyclo­[27.4.0.0^6,11.0^16,21]­tri­tria­conta‐1(29),6(11),7,9,16(21),17,19,30,32‐nona­ene, C₂₈H₃₃NO₆, does not exhibit a binding cavity for cations, but is collapsed in on itself. The conformation is unique among known tri­benzo‐21‐crown‐7 structures, and may be a result of intermolecular (C—H?π) and intramolecular (C—H?O) hydrogen bonding.     

Synthesis of rhodamines from fluoresceins using Pd-catalyzed C-N cross-coupling

A unified, convenient, and efficient strategy for the preparation of rhodamines and N,N'-diacylated rhodamines has been developed. Fluorescein ditriflates were found to undergo palladium-catalyzed C-N cross-coupling with amines, amides, carbamates, and other nitrogen nucleophiles to provide direct access to known and novel rhodamine derivatives, including fluorescent dyes, quenchers, and latent fluorophores.