Quantitative evaluation of mechanosensing of cells on dynamically tunable hydrogels

Thin hydrogel films based on an ABA triblock copolymer gelator [where A is pH-sensitive poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) and B is biocompatible poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC)] were used as a stimulus-responsive substrate that allows fine adjustment of the mechanical environment experienced by mouse myoblast cells. The hydrogel film elasticity could be reversibly modulated by a factor of 40 via careful pH adjustment without adversely affecting cell viability. Myoblast cells exhibited pronounced stress fiber formation and flattening on increasing the hydrogel elasticity. As a new tool to evaluate the strength of cell adhesion, we combined a picosecond laser with an inverted microscope and utilized the strong shock wave created by the laser pulse to determine the critical pressure required for cell detachment. Furthermore, we demonstrate that an abrupt jump in the hydrogel elasticity can be utilized to monitor how cells adapt their morphology to changes in their mechanical environment.     

Practical synthesis of (2'R)-2'-deoxy-2'-C-methyluridine by highly diastereoselective homogeneous hydrogenation

Diastereoselective hydrogenation of 2'-deoxy-2'-exo-methyleneuridine was carried out under homogeneous conditions using a low loading of a chiral Rh catalyst. This, coupled with improvements in the synthesis of the substrate, allowed the smooth pilot plant preparation of the title compound on >10 kg scale.     

Dielectric characterization of samples showing the SmCPA/B7 transition

Dielectric measurements on samples consisting of banana-shaped molecules with a polymorphism I/SmCP_A/B₇ have been performed for the first time. The dielectric increment for the reorientation of the molecules about the long axis, and the corresponding relaxation time, surprisingly decrease at the SmCP_A/B₇ transition. This effect is discussed in terms of the undulated structure which partially destroys the ferroelectric short range order. Decreasing temperature gives an even stronger hindrance for this reorientation and could explain controversial results obtained in the B₇ phases of different samples. At lower temperatures a further mesophase was detected. This was additionally observed by calorimetric and atomic force microscopy methods.     

Absorption and emission spectroscopy in scattering media: modelling of fluorescence decay curves and photometric laws for systems with inhomogeneous absorber distribution

Summary The optical absorption and fluorescence of scattering samples is investigated theoretically and experimentally under the condition of steady-state and pulsed irradiation, taking into account inhomogeneous distribution of the absorbing species. Based on the Kubelka-Munk model, numerical iterative expressions for the steady-state and time-resolved light flues of excitation and emission are derived. The intensities of reflected, transmitted and forward or backward emitted radiation in layered samples with vertical concentration gradients are discussed. Modification of fluorescence spectra and decay curves due to self absorption, background absorption, secondary emission and time of flight dispersion are calculated and compared to experimental data of hydrocarbons adsorbed on polycrystalline silica gel.     

Ten microseconds in the life of a superhelix

Dynamic light scattering measurement data of DNA topoisomers are compared with two different computer models: a Monte Carlo model and a Brownian dynamics model. First results on the kinetics of formation of a superhelix and on the influence of curved sequences on the dynamics of superhelical DNA are reported.To whom correspondence should be addressed     

Photon statistics in saturated m-photon amplification and attenuation of coherent light

The change of photon statistics of a nearly coherent single-mode light beam travelling through a saturable m-photon-amplifying or absorbing medium (m = 1, 2, …) is theoretically investigated. With the help of an approximation scheme valid for $\text{n}$ ? 1, Δn² ? $\text{n}$² ($\text{n}$ mean value and Δn² variance of the photon number) an analytical expression is derived for the quantity Δn²/$\text{n}$. The results holds for arbitrary values of the initial population inversion and of the degree of saturation. It turns out that for both amplification and attenuation processes after sufficiently strong interaction Δn²/$\text{n}$ tends to an asymptotic value.