Thermo-stimulated surface segregation in the ordering alloy Pt80Co20(1 1 1): Experiment and modeling

In this paper, a method of Ionization Spectroscopy (IS) is proposed for the non-destructive layer-by-layer analysis of the elemental composition of a solid surface. Using ionization energy loss spectra, a layer-by-layer concentration profile of the Pt₈₀Co₂₀(1 1 1) alloy surface is obtained for different annealing temperatures. For the disordered Pt₈₀Co₂₀(1 1 1) at room temperature, the first atomic layer consists of pure Pt with damped oscillations in the deeper layers. Heating the sample reduces the oscillations. However, at a temperature of 823 K, a sandwich-like structure of the type Pt/Co/Pt was found in the first three atomic layers. For the ordered state the first atomic layer also consists of pure Pt with bulk concentration in other layers. LEED analysis shows a p(2 × 2) superstructure for the surface of the ordered Pt₈₀Co₂₀(1 1 1) alloy. The segregation behavior in this alloy is further studied by Monte Carlo (MC) simulations combined with the Constant Bond Energy (CBE) model. The results of the MC simulations agree well with the experiments at the higher temperatures, both for the surface composition and the concentration depth profile. At lower temperatures, some discrepancies exist between the MC results and the measured concentration profile.     

Positive parity giant multipole resonances in16O

Distributions of the (J =0⁺, 1⁺, 2⁺, 3⁺, 4⁺) isoscalar and isovector strength in¹⁶O have been calculated in then particle —n hole (n=0, 1, 2) shell model. The isoscalar quadrupole giant resonance comes out fragmentated over eight peaks which exhaust 33% of the EWSR betweenE ^*=17 and 25 MeV. This result agrees nicely with the recent³He and alpha inelastic scattering experiments. Giant monopole isoscalar (isovector) resonance appears to exhaust more than 50% of the EWSR nearE ^*=30 MeV (E ^*=40 MeV). Several collective states of other multipolarities are predicted either near to 30 MeV or between 50 and 60 MeV. The ground state correlations of the 2p2h type give rise to a considerable strength redistributions as compared with the case of the closed shell ground state.On leave fromInstitute of Nuclear Physics, Czechosl. Acad. Sci., 250 68 e, Czechoslovakia.     

Characterization of ultrasound-mediated destruction of drug-loaded microbubbles using an improved in vitro model

Introduction

Ultrasound mediated destruction of microbubbles (MBs) has become a promising tool for site specific drug and gene delivery. One of the most important properties of drug-loaded MBs is their destructibility by ultrasound. Therefore, the aim of this study was to establish a new in vitro model that allows evaluation of the kinetics of ultrasound-mediated MB destruction at near physiological conditions.In this work, a newly developed drug-loaded MB formulation was compared with unloaded MBs in order to assess the influence of drug-loading on their acoustic destructibility. Furthermore, drug-loaded MBs were compared to acoustically active lipospheres (AALs), comprising an additional layer of triacetin, as well as to a marketed MB contrast agent (SonoVue^®, Bracco Diagnostics, USA), used as standard.

Methods

MBs with phospholipid monolayer shells were produced by mechanical agitation of liposomal dispersions and octafluoropropane gas. AALs were accordingly produced by agitation of phospholipid-stabilized aqueous triacetin microemulsions with gas.The in vitro experimental setup for acoustic destructibility testing comprised a membrane cell, pressurized and brought to 37 °C in order to imitate human blood pressure and body temperature. The optimized egg-like cell shape provided optimal flow conditions and a minimized dead volume.Ultrasound with frequencies of 1 and 3 MHz and intensities, varying from 1 to 4 W/cm², was applied through a silicone membrane window to the cell. MB size distribution and concentration were measured by light blockage in equal time intervals during the sonication.

Results

The optimized in vitro setup demonstrated differences in the ultrasound destructibility of the MB formulations used. The fastest decay upon ultrasound exposure was found for SonoVue^®. Unloaded and drug-loaded MBs appeared to be comparably destructible to SonoVue^®. AALs were about 4.5-fold more stable than SonoVue^®. MB destructibility was also found to depend on particle diameter, corresponding to theoretical models described in the literature.

Conclusion

The optimized in vitro setup has rendered a fast and reliable laboratory tool for characterization of MB formulations.     

Computational assessment of environmental hazards of nitroaromatic compounds: influence of the type and position of aromatic ring substituents on toxicity

Structural Chemistry - This study summarizes the results of our recent QSAR and QSPR investigations on prediction of numerous aspects of environmental behavior of nitro compounds. In this study, we...     

Radiohalogenation of terguride via organotin intermediate

New (radio)halogen derivatives of 1-allylterguride have been prepared by method of destannylation-halogenation. 1-Alylterguride shows relatively high binding affinity, which can be used in the case of its radiolabeled derivatives with imaging methods like PET or SPET in studies of properties of receptor's binding places and ligand affinity. The (radio)halogenation was performed via organotin precursors: 1-tributylstannyl-3-chlorprop-1-ene and 2-tributylstannyl-3-chloroprop-1-ene, which were prepared from appropriate alcohols. Linkers of the tin group were used for alkylation of N1 of terguride both under microwave irradiation and under conventional heating. In the last step (destannylation-halogenation), fluoro-, bromo- and iododerivatives as well as ¹²⁵I iodo- and ⁸²Br bromoderivatives of 1-allylterguride were obtained.This revised version was published online in November 2005 with corrections to the Cover Date.     

Prediction of an Organic Compound’s Biotransformation Time: A Study Using Avermectins

Moscow University Chemistry Bulletin - The current spread of the SARS-CoV-2 coronavirus is a challenge for the entire world. Ivermectin is a promising agent, which could be used to combat the...