Deterministic solution of the kinetic theory model of colloidal suspensions of structureless particles

A direct modeling of colloidal suspensions consists of calculating trajectories of all suspended objects. Due to the large time computing and the large cost involved in such calculations, we consider in this paper another route. Colloidal suspensions are described on a mesoscopic level by a distribution function whose time evolution is governed by a Fokker–Planck-like equation. The difficulty encountered on this route is the high dimensionality of the space in which the distribution function is defined. A novel strategy is used to solve numerically the Fokker–Planck equation circumventing the curse of dimensionality issue. Rheological and morphological predictions of the model that includes both direct and hydrodynamic interactions are presented in different flows.     

How to confirm identified toxicants in effect-directed analysis

Due to the production and use of a multitude of chemicals in modern society, waters, sediments, soils and biota may be contaminated with numerous known and unknown chemicals that may cause adverse effects on ecosystems and human health. Effect-directed analysis (EDA), combining biotesting, fractionation and chemical analysis, helps to identify hazardous compounds in complex environmental mixtures. Confirmation of tentatively identified toxicants will help to avoid artefacts and to establish reliable cause–effect relationships. A tiered approach to confirmation is suggested in the present paper. The first tier focuses on the analytical confirmation of tentatively identified structures. If straightforward confirmation with neat standards for GC–MS or LC–MS is not available, it is suggested that a lines-of-evidence approach is used that combines spectral library information with computer-based structure generation and prediction of retention behaviour in different chromatographic systems using quantitative structure–retention relationships (QSRR). In the second tier, the identified toxicants need to be confirmed as being the cause of the measured effects. Candidate components of toxic fractions may be selected based, for example, on structural alerts. Quantitative effect confirmation is based on joint effect models. Joint effect prediction on the basis of full concentration–response plots and careful selection of the appropriate model are suggested as a means to improve confirmation quality. Confirmation according to the Toxicity Identification Evaluation (TIE) concept of the US EPA and novel tools of hazard identification help to confirm the relevance of identified compounds to populations and communities under realistic exposure conditions. Promising tools include bioavailability-directed extraction and dosing techniques, biomarker approaches and the concept of pollution-induced community tolerance (PICT). Figure Toxicity confirmation in EDA as a tiered approach     

Small camera as a handheld colorimetric tool in the analytical chemistry

Recently, there is an effort to introduce new types of analytical procedures and handheld assays to provide simple and reliable equipment for the field and household analyses. Development of diagnostic tools for self-diagnosis is another challenge in analytical chemistry. Digital cameras are widely available and cheap, hence they could be the sensor platform for construction of analytical and diagnostic methods. In general, good availability of cameras integrated into smartphones can be easily converted into an analytical tool. This review relates to the use of digital camera in analytical chemistry and there are introduced the facts how digital data can be processed and what the limits of digital photography are. Recent papers in this issue and discussion of development in camera based assays is also provided here.     

Gas separation properties of ultra-thin films based on fully cyclized polyimides

Fully cyclized polyimides based on octadecyl- or hexadecyl 3,5-diaminobenzoate and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride or 4,4′-oxydiphthalic anhydride were synthesized and deposited by the Langmuir-Schaefer technique onto a poly(1-trimethylsilylprop-1-yne) support. Composite membranes thus prepared show selective gas permeation for N₂, O₂, CO₂, H₂ with permeation rates in the range of 10⁻⁵ to 10⁻⁷ cm³ (STP)/(cm² · s · cmHg).     

A general synthesis of water soluble upper rim calix[n]arene guanidinium derivatives which bind to plasmid DNA

The reaction of O-alkylated p-aminocalix[n]arenes (n=4, 6, 8) with N,N′-di(tert-butoxycarbonyl)thiourea in the presence of HgCl₂ and subsequent removal of the protective groups with hydrochloric acid led to the new water soluble calix[n]guanidinium derivatives (p-guanidiniumcalix[n]arenes) 20-23. With the exception of tetraoctyl-p-guanidiniumcalix[4]arene 21, which forms a macroscopic gelatinous aggregate even at very low concentration, all the synthesised guanidinium calixarenes show good solubility in water and sharp NMR signals. Moreover, these compounds are not cytotoxic and bind to plasmid DNA.     

Fast and efficient separation of cytokinins from auxin and abscisic acid and their purification using mixed-mode solid-phase extraction

A method for separation of cytokinins from auxin and abscisic acid, which allows further separation of cytokinin ribotides from cytokinin bases, ribosides and glucosides and their purification on a single Oasis MCX column was developed. Due to the mixed reversed-phase and cation-exchange mode of the Oasis MCX sorbent the cationic cytokinin bases, ribosides and glucosides as well as the anionic auxin, abscisic acid and cytokinin ribotides are retained and can be sequentially eluted by solvents containing different concentrations of methanol and ammonium hydroxide. Characteristics of the method are high recoveries of analyzed phytohormones and their sufficient purity for quantification by HPLC–ELISA (RIA) or HPLC–MS.     

pH-Dependent Behavior of Hydrophobically Modified Polyelectrolyte Shells of Polymeric Nanoparticles

Summary: The self-assembled core-shell nanoparticles based on fluorescently double-tagged high-molar-mass polystyrene-block-poly(methacrylic acid), PS-PMA, were prepared in aqueous buffers by dialysis from 1,4-dioxane – water mixtures. The conformations of shell-forming PMA chains were studied using nonradiative excitation energy transfer measurements. The study shows that two populations of distinctly different conformations (collapsed and stretched) coexist in the shell and their ratio depends on pH.     

Wavelength-modulated femtosecond stimulated Raman spectroscopy-approach towards automatic data processing

A new wavelength modulator based on a custom-made chopper blade and a slit placed in the Fourier plane of a pulse shaper was used to detect explicitly the first derivative of the time-resolved femtosecond stimulated Raman spectroscopy (FSRS) signals. This approach resulted in an unprecedented reduction of the non-coherent background that results from population transfer by the Raman pump inherent to FSRS experiments. The method of Fourier peak filtering was implemented as a powerful tool for reducing both the remaining non-coherent and coherent background associated with FSRS experiments. The method was demonstrated on β-carotene and a similar synthetic aryl carotenoid. The experiments confirm earlier FSRS results on β-carotene but suggest some reinterpretation. Strong bleaching signals of ground state vibrations were observed and interpreted as an inseparable part of the time-resolved FSRS experiment. New long-lived Raman features were observed in β-carotene and the synthetic aryl carotenoid and assigned to a combination of conformational changes and solvent rearrangement. More complex wavelength modulation methods are proposed in the development of more robust FSRS experiments.     

Application of colloidal palladium nanoparticles for labeling in electron microscopy

The application of palladium nanoparticles as electron-dense markers for labeling in both transmission and scanning electron microscopy requires their conjugation to a specific protein. The conjugation protocol described here includes the dihydrolipoic acid (DHLA) capping of Pd nanoparticles (8 nm equivalent diameter) and their subsequent covalent attachment to functional protein molecules such as streptavidin, protein A, or avidin. The single-step reaction was mediated using the cross-linking agent ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The final Pd conjugates were fully functional, as demonstrated by labeling of ultrathin resin sections of either bovine serum albumin or secretory granules of the salivary gland isolated from the partially fed female Ixodes ricinus tick. The results of bovine serum labeling were quantified, statistically evaluated, and compared with results obtained using commercially available gold particle conjugates (10 nm diameter). The highest values of labeling density were achieved using both streptavidin-Pd (106 ± 7 particles/μm2) and protein A-Au conjugates (130 ± 18 particles/μm2) compared to a commercial streptavidin-Au (66 ± 16 particles/μm2) and protein A-Pd conjugates (70 ± 11 particles/μm2). The concentrations of both DHLA and EDC, pH during conjugation, and finally thorough washing away of unbound proteins crucially influenced conjugation.     

Self-organization of 1-methylnaphthalene on the surface of artificial snow grains: a combined experimental-computational approach

A combined experimental-computational approach was used to study the self-organization and microenvironment of 1-methylnaphthalene (1MN) deposited on the surface of artificial snow grains from vapors at 238 K. The specific surface area of this snow (1.1 × 10(4) cm(2) g(-1)), produced by spraying very fine droplets of pure water from a nebulizer into liquid nitrogen, was determined using valerophenone photochemistry to estimate the surface coverage by 1MN. Fluorescence spectroscopy at 77 K, in combination with molecular dynamics simulations, and density functional theory (DFT) and second-order coupled cluster (CC2) calculations, provided evidence for the occurrence of ground- and excited-state complexes (excimers) and other associates of 1MN on the snow grains' surface. Only weak excimer fluorescence was observed for a loading of 5 × 10(-6) mol kg(-1), which is ～2-3 orders of magnitude below monolayer coverage. However, the results indicate that the formation of excimers is favored at higher surface loadings (>5 × 10(-5) mol kg(-1)), albeit still being below monolayer coverage. The calculations of excited states of monomer and associated moieties suggested that a parallel-displaced arrangement is responsible for the excimer emission observed experimentally, although some other associations, such as T-shape dimer structures, which do not provide excimer emission, can still be relatively abundant at this surface concentration. The hydrophobic 1MN molecules, deposited on the ice surface, which is covered by a relatively flexible quasi-liquid layer at 238 K, are then assumed to be capable of dynamic motion resulting in the formation of energetically preferred associations to some extent. The environmental implications of organic compounds' deposition on snow grains and ice are discussed.