New Red‐Emitting Tetrazine‐Phenoxazine Fluorogenic Labels for Live‐Cell Intracellular Bioorthogonal Labeling Schemes

The synthesis of a set of tetrazine‐bearing fluorogenic dyes suitable for intracellular labeling of proteins in live cells is presented. The red excitability and emission properties ensure minimal autofluorescence, while through‐bond energy‐transfer‐based fluorogenicity reduces nonspecific background fluorescence of unreacted dyes. The tetrazine motif efficiently quenches fluorescence of the phenoxazine core, which can be selectively turned on chemically upon bioorthogonal inverse‐electron‐demand Diels–Alder reaction with proteins modified genetically with strained trans‐cyclooctenes.     

Pair potentials from diffraction data on liquids: a neural network solution

The inverse theorem of liquids states a one to one correspondence between classical mechanical pair potentials and structural functions. Molecular-dynamics and Monte Carlo simulations provide exact structural functions for known pair interactions. There is no exact or widespread method in the opposite direction, where the pair interactions are to be determined from a priori known pair-correlation functions or structure factors. The methods based on the integral equation theories of liquids are approximate and the iterative refinements of pair potentials with simulations take a long time. We applied artificial neural networks to get pair interactions from known structure factors in this study. We performed molecular-dynamics simulations on one-component systems with different pair potentials and the structure factors were calculated. To optimize (train) the weights of neural networks 2000 pair interaction-structure factor pairs were used. The performance of the method was tested on further 200 data pairs. The method provided reasonable potentials for the majority of the systems opening a "quick and dirty" method to determine pair interactions.     

Rate constant for the reaction CH3CO?+ HBr and the enthalpy of formation of the CH3CO?radical

Summary Pulsed laser photolysis coupled with time-resolved UV-absorption monitoring of CH₃CO^•radicals was applied to obtain the rate constant, k₁, for the reaction CH₃CO^•+ HBr → CH₃C(O)H + Br (1); k₁(298 K) = (3.59 ± 0.23 (2σ))x10^-12cm³molecule^-1s^-1. Utilization of k₁in a third law procedure has provided the standard enthalpy of formation value ofD_fH°₂₉₈(CH₃CO^•) = -10.04 ± 1.10 (2σ) kJ mol^-1in excellent agreement with a very recent IUPAC recommendation.     

Absolute rate constants for the reactions ofOHradicals withCH3CH2OH, CF2HCH2OHandCF3CH2OH

Summary Pulsed laser photolysis with resonance fluorescence monitoring of OH radicals was applied at T = 300±2 K to obtain the rate constants of k₁= (3.38±0.60)x10^-12, k₂= (2.52±0.44)x10^-13and k₃ = (1.06±0.30)x10^-13cm³molecule^-1s^-1with 2σprecision given for the overall reactions OH + CH₃CH₂OH (1), OH + CF₂HCH₂OH (2) and OH + CF₃CH₂OH (3), respectively. k₂is the first direct kinetic data for the reaction of OH radicals with CF₂HCH₂OH reported in the literature.</o:p>     

Effects of deep-freezing and storage time on human femoral cartilage

Surgical techniques including new, possible resources to repair injured joints and damaged cartilage are still evolving. The exact effects of cryopreservation on the collected cartilage samples require accurate determination prior to utilization. The aim of our study was to analyze the impact of cryopreservation at ?80 °C on the structural properties of the human cartilage. The effects of storage time were also evaluated in conjunction with optimal utilization. The human cartilage samples were derived during operation and considered to be waste material. Samples were fresh frozen and stored at ?80 °C. Cryopreservation times were: 0, 1, 3, 6, and 12 weeks. To assess the biological and structural properties of the frozen human cartilage, we performed calorimetric examinations using differential scanning calorimetry (DSC). During the first 3 weeks, the calorimetric enthalpy (ΔH _cal) showed an increasing tendency compared to controls, parallel with the denaturation temperature (T _m): ΔH _cal (J g^?1) = 1.60 versus 2.49, T _m1 (°C) = 61.73 versus 63.64. After the sixth week, both the enthalpy and the transition temperature decreased, compared to the control samples. The decrease in both the calorimetric enthalpy and T _m could be explained by the decrease in bound water and the time-related degeneration in the structure of the cartilage. Here we found that the duration of cryopreservation interferes with the morphology of human cartilage samples only after 6 weeks of storage time. The thermal analyzes of human cartilage by DSC could be a useful method to follow the morphological changes in the clinical practice.     

TEM study of the fibre cross-section attack in δ-Al2O3/Mg8Li metal matrix composites

During manufacturing of -Al₂O₃/Mg8Li composites by melt infiltration reactive diffusion of Mg and Li into the fibre bulk takes place. No remarkable reaction zone was found at the fibre periphery, although, a Mg enrichment zone (approx. 100 nm thick) was detected there by EDX and EELS. In addition, MgO, Li₂O and Mg₂Si minority phases were identified by SAED within the fibre cross-section.The crystalline structure of the -Al₂O₃ fibres in the Mg8Li matrix remained of the alumina spinel type at all the time, however, a set of crystallographically coherent products assigned as (Li) was detected by XRD and SAED within the fibre cross-section. As believed, the (Li) results from topotactic Li⁺ incorporation into the -Al₂O₃ lattice so that no significant changes in terms of size and morphology of the alumina crystallites are observed.