Sliding of a spherical indenter on a viscoelastic foundation with the forces of molecular attraction taken into account

The problem of sliding of a spherical indenter on a viscoelastic foundation is solved in a quasistatic formulation taking account the forces of adhesive attraction which are considered different at the entrance to and exit from the contact region due to changes in the surface properties during the interaction. It is found that the contact characteristics and the frictional force due to the imperfect elasticity of the foundation depend on the surface and bulk properties of the materials of the interacting bodies and the interaction conditions (load, velocity, etc.).     

Quantitative Aspects of the Competition of Substitution and Addition Pathways in Polyisobutylene Chlorination

The competition of the substitution and addition chlorination pathways was studied. A quantitative model was developed to describe the rate ratio of the substitution and addition pathways in chlorination of polyisobutylene.     

SERS detection of ceftriaxone and sulfadimethoxine using copper nanoparticles temporally protected by porous calcium carbonate

The authors describe a new composite based on SERS-active copper nanoparticles (CuNPs; 10?±?2 nm) incorporated into calcium carbonate microspheres (CaCO₃-CuNPs; 3.4?±?0.3 μm). The CaCO₃ coating acts as a temporal protector of CuNPs against oxidation. Incorporated CuNPs have significantly improved stability during storage and a month-long shelf lifetime. The composite was used for SERS detection of rhodamine 6G and two antibacterial drugs (ceftriaxone and sulfadimethoxine). Two analytical formats, one with and one without solid phase extraction, are introduced to demonstrate the flexibility of the method. Both formats imply the dissolution of CaCO₃ matrix before SERS analysis to release CuNP used as SERS substrate. The study of the influence of pH value and acid nature on the SERS signal demonstrated that HCl is the most efficient candidate to release the CuNPs. Sensitivity (expressed as LOD) is shown to be improved by more than one order when solid phase extraction is used. The average SERS enhancement factor is 10^7 which makes the material efficiency comparable to the one of silver nanoparticles. The LOD (<5 μM), precision (RSDs between 20 and 24% at LOD levels), and trueness (apparent recoveries 84–113%) for the two antibiotics (ceftriaxone and sulfadimethoxine) make the method quite useful for quantitative analysis and therapeutic drug monitoring at physiologically relevant concentrations.

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Graphical abstract A composite with temporally stable copper nanoparticles was synthesized, studied, and used for SERS detection of two antibacterial drugs. The analytical efficiency of the composite was found appropriate for quantitative analysis due to Raman enhancement comparable with silver nanostructures.

     

Acridine dyes in the triplet state as reagents for the selective luminescence determination of polycyclic aromatic hydrocarbons

The possibility of the selective determination of several polycyclic aromatic hydrocarbons (PAH) by sensitized room-temperature phosphorescence (SRTP) in sodium dodecylsulfate (SDS) micelles was studied. Acridine dyes (trypaflavine, acridine yellow, and acridine orange) were used as triplet-energy donors. It was found that the presence of external heavy atoms of thallium(I) is a prerequisite to SRTP in the system of an acridine dye (donor) and a PAH (acceptor). The linear concentration ranges, detection limits, and selectivity factors for the determination of pyrene, anthracene, and 1,2-benzanthracene by fluorimetry, room-temperature phosphorescence (RTP), and proposed SRTP were compared.     

Search for solar neutrons using the data of neutron detector of the PAMELA spectrometer

The study is devoted to the development of the technique for searching for neutrons of solar origin during solar flares using the neutron detector of the PAMELA magnetic spectrometer onboard the RESURS-DK1 satellite. The study of the neutron detector counting rates showed that it operates properly and background conditions are stable in the geomagnetic equator region. 27 solar events from December 2006 to September 2014 were analyzed. Some events contain indications of solar neutron detection. The final conclusion on the nature of these neutrons requires an increase in statistics; to this end, background conditions in polar regions should be analyzed to increase the observation interval.     

Calcium carbonate microparticles with embedded silver and magnetite nanoparticles as new SERS-active sorbent for solid phase extraction

Microchimica Acta - The authors describe a dual-use sorbent for solid phase extraction (SPE) in combination with surface-enhanced Raman spectroscopy (SERS). The sorbent consists of calcium...     

Simultaneous determination of several mycotoxins by rapid immunofiltration assay

A method is developed for the simultaneous rapid determination of three mycotoxins, zearalenone (ZEN), ochratoxin A (OTA), and fumonisin B1 (Fum) by membrane immunofiltration analysis using a marker enzyme of alkaline phosphatase (AP) and two mycotoxins, deoxynivalenol (DON) and total T-2 toxin (T2) and HT-2 toxin (HT2) with horseradish peroxidase (HRP). The analysis is based on a competitive interaction between the antigene, free and bound to the enzyme, and antibodies immobilized on a membrane. The procedures of membrane fabrication and the conditions of mycotoxin to determination in model mixtures and extracts from wheat, corn, and silage are optimized. The influence of sample preparation on the results of analysis is studied. It is shown that the additives of polymers favor the reduction of the matrix effect in the analysis of complex matrixes using conjugated HRP. The methods developed allow the determination of mycotoxins at a level of the maximal permissible concentrations legislated by EU directives. The corresponding values (μg/kg) are 50, 2.5, and 500 in wheat; 100, 2.5, and 500 in corn; and 125, 25, and 1250 in silage for the simultaneous quantification of ZEN, OTA, and Fum (AP marker). For the determination of DON and total T2/HT2 with HRP, 1250 (1000) and 100 (500) in wheat and corn(silage). The procedures were validated by the analysis of spiked and naturally contaminated samples. The analysis of 10 samples takes 25 min.     

Surface-Enhanced Raman Spectroscopy for the Determination of Medical and Narcotic Drugs in Human Biofluids

Journal of Analytical Chemistry - The review is devoted to an analysis of the capabilities, limitations, and special features of the application of surface-enhanced Raman spectroscopy (SERS) to the...     

Photochemistry of Fe(III) complex with glyoxalic acid in aqueous solution

Nanosecond laser flash photolysis technique was used to study photochemistry of Fe(III) complex with glioxalic acid. The primary photochemical process was found to be inner-sphere electron transfer in the excited complex leading to formation of the long-lived radical complex [Fe^II … ^·OOC-C(O)H]²⁺. A number of important spectral-kinetic parameters of this species were determined and mechanism of photolysis of Fe(III)-glioxalate complex was proposed. 1 The article was translated by the authors.