Biosensor immunoassay of ivermectin in bovine milk

A rapid and sensitive biosensor immunoassay was developed for determination of ivermectin residues in bovine milk. A detection limit of 16.2 ng/mL was achieved. A Biacore optical biosensor based on surface plasmon resonance was used, and a range of extraction techniques was investigated. In the final assay procedure, ivermectin was extracted with acetonitrile followed by C8 solid-phase extraction cleanup. It was proven experimentally that 2 methods of milk storage, freezing or addition of mercury-containing compounds as preservatives, could be used without considerable change in detected concentrations (samples were fortified with ivermectin after storage). The average values for milk samples spiked at 100 and 50 ng/mL concentrations were 102.6 and 51.5 ng/mL, respectively. Extraction and analysis of 20 milk samples were performed within a single working day.     

Structure-based design of potent non-peptide MDM2 inhibitors

A successful structure-based design of a class of non-peptide small-molecule MDM2 inhibitors targeting the p53-MDM2 protein-protein interaction is reported. The most potent compound 1d binds to MDM2 protein with a Ki value of 86 nM and is 18 times more potent than a natural p53 peptide (residues 16-27). Compound 1d is potent in inhibition of cell growth in LNCaP prostate cancer cells with wild-type p53 and shows only a weak activity in PC-3 prostate cancer cells with a deleted p53. Importantly, 1d has a minimal toxicity to normal prostate epithelial cells. Our studies provide a convincing example that structure-based strategy can be employed to design highly potent, non-peptide, cell-permeable, small-molecule inhibitors to target protein-protein interaction, which remains a very challenging area in chemical biology and drug design.     

Study of sodium dodecyl sulfate-poly(propylene oxide) methacrylate mixed micelles

Sodium dodecyl sulfate (SDS)-poly(propylene oxide) methacrylate (PPOMA) (of molecular weight M(w) = 434 g x mol(-1)) mixtures have been studied using conductimetry, static light scattering, fluorescence spectroscopy, and 1H NMR. It has been shown that SDS and PPOMA form mixed micelles, and SDS and PPOMA aggregation numbers, N(ag SDS) and N(ag PPOMA), have been determined. Total aggregation numbers of the micelles (N(ag SDS) + N(ag PPOMA)) and those of SDS decrease upon increasing the weight ratio R = PPOMA/SDS. Localization of PPOMA inside the mixed micelles is considered (i) using 1H NMR to localize the methacrylate function at the hydrophobic core-water interface and (ii) by studying the SDS-PPO micellar system (whose M(w) = 400 g x mol(-1)). Both methods have indicated that the PPO chain of the macromonomer is localized at the SDS micelle surface. Models based on the theorical prediction of the critical micellar concentration of mixed micelles and structural model of swollen micelles are used to confirm the particular structure proposed for the SDS-PPOMA system, i.e., the micelle hydrophobic core is primarily composed of the C12 chains of the sodium dodecyl sulfate, the hydrophobic core-water interface is made up of the SDS polar heads as well as methacrylate functions of the PPOMA, the PPO chains of the macromonomer are adsorbed preferentially on the surface, i.e., on the polar heads of the SDS.     

Etude des volumes specifiques partiels de polystyrenes-modeles—Influence de la masse moleculaire et de la nature des groupements terminaux

It is well known that the apparent specific volume η₂ of a polymer may be expressed by the following relationship: $\text{η}{}_2\text{= η}{}_{\mathrm{m}}\text{+ K/}\text{M}{}_{\mathrm{n}}$ where M?_n is the number-average molecular weight of the polymer, η_m the specific volume of the infinite polymer, and K a constant. We have shown that this relationship is valid for low molecular weight polystyrenes ($\text{M}{}_{\mathrm{n}}\text{< 4·10}{}^4$) with different end-groups, independently of the nature of the solvent. The K values (and variations with the solvent and with the nature of the end-groups) may be predicted through simple calculations proposed here. We conclude that η_m does not represent the specific volume of the infinite polymer, since we observe a rapid decrease of η₂ for increasing M (when $\text{M}{}_{\mathrm{n}}\text{< 4·10}{}^4$). The decrease is much greater than expected from the relationship $\text{η}{}_2\text{= ? (1/}\text{M}\text{)}$.     

Determination of methyldibromoglutaronitrile in cosmetic products by high-performance liquid chromatography with electrochemical detection. Method validation

An increased frequency of contact allergy to methyldibromoglutaronitrile (MDBGN), a commonly used preservative in cosmetics and other consumer products, has been reported in recent years. A high-performance liquid chromatography (HPLC) method for the determination of MDBGN in cosmetic products has been validated in the present study. The identification is performed by reductive electrochemical detection of the bromine present in the molecule. The method is suitable for compliance testing of cosmetic products as well as for the research to support clinical and epidemiological studies.     

Theoretical chemical ionization rate constants of the concurrent reactions of hydronium ions (H3O+) and oxygen ions (O ) with selected organic iodides

Short chain volatile iodinated organic compounds (VIOCs) are of great importance in many fields that include atmospheric chemistry, agriculture, and environmental chemistry related to nuclear power plant safety. Proton‐transfer‐reaction mass spectrometry (PTR‐MS) allows for fast, sensitive, and online quantification of VIOCs if the chemical ionization (CI) reaction rate coefficients are known. In this work, the theoretical CI rate coefficients for the reactions of hydronium ions (H₃O⁺) and oxygen ions (O ) with selected atmospherically important short chain VIOCs are determined. The neutral CH₃I, CH₂I₂, C₂H₅I, iso‐C₃H₇I, n‐C₃H₇I, n‐C₄H₉I, 2‐C₄H₉I, n‐C₅H₁₁I, 2‐C₅H₁₁I, and 3‐C₅H₁₁I have been chosen because these compounds are of atmospheric and environmental importance in the field of safety of nuclear plant reactors. Theoretical ion‐molecule collision rate coefficients were determined using the Su and Chesnavich theory based on parametrized trajectory calculations. The proton affinity, ionization energy, dipole moment, and polarizability values of the neutral molecules were determined from density functional theory and coupled‐cluster calculations. The newly calculated rate constants facilitate the use of the CI mass spectrometry in the atmospheric quantification of selected VIOCs.     

On Bicategories of Relations and Pullback Spans

In this paper, we study relations in general categories. Our approach requires that these must have finite products and factorization systems. Klein [5] has obtained a condition for composition of relations to be strictly associative. Here we consider the possibility that associativity only holds up to a coherent isomorphism, in other words that the relations are the morphisms of a bicategory in the sense of Bénabou [2].