Spring-network model of red blood cell: From membrane mechanics to validation

Red blood cell membrane is highly elastic and proper modeling of this elasticity is essential for biomedical applications that involve computational experiments with blood flow. Inseparable and often some of the most difficult parts of modeling process are verification and validation. In this work, we present a revised model, which uses a spring network to represent the cell membrane immersed in a fluid and has been successfully used in blood flow simulations. We demonstrate the validation steps by first deriving the theoretical relations between the bulk properties of elastic membranes—shear modulus and area compressibility modulus—and parameters of the model that enter the nonlinear stretching and local area conservation computational moduli. We verify the theoretically derived relations using computer simulations of deformable triangular mesh. We calibrate the model by performing a computational version of the optical tweezers experiment. And finally, we validate the modeled cell behavior by investigating the cell rotation frequency when it is subjected to shear flow and cell deformation in narrow channels. The supplementary material contains an extensive dataset that can be used for setting different elastic properties for each cell in simulations of dense suspensions, while still conforming to the biological data. This work contains a complete model development process: From modelling of basic mechanical concepts (the spring network) and advanced biomechanical concepts (such as elasticity of the membrane), through calibration process towards the final stage of model validation.     

Measurement of hypoiodous acid concentration by a novel type iodide selective electrode and a new method to prepare HOI. Monitoring HOI levels in the Briggs-Rauscher oscillatory reaction

A new type of iodide selective electrode prepared by dipping a silver wire into molten silver iodide is reported. The electrode was calibrated for silver and iodide ions and the measured electromotive force for various Ag(+) and I(-) concentrations was close to the theoretical within a few millivolts. Besides Ag(+) and I(-) ions, however, the electrode also responds to hypoiodous acid. Thus, the electrode was calibrated for HOI as well, and for that purpose a new method of hypoiodous acid preparation was developed. To explain the close to Nernstian electrode response for HOI and also the effect of hydrogen ion and iodine concentration on that response, the corrosion potential theory suggested earlier by Noszticzius et al. was modified and developed further. Following oscillations in the Briggs-Rauscher reaction with the new electrode the potential crosses the "solubility limit potential" (SLP) of silver iodide. Potentials below SLP are controlled by the concentration of I(-), but potentials above SLP are corrosion potentials determined by the concentration of HOI. Finally, the measured HOI oscillations are compared with calculated ones simulated by a model by Furrow et al.     

Vibrational Spectroscopy of Intercalated Kaolinites. Part I.

Abstract

The industrial application of kaolinite is closely related to its reactivity and surface properties. The reactivity of kaolinite can be tested by intercalation; that is, via the insertion of low-molecular-weight organic compounds between the kaolinite layers resulting in the formation of a nano-layered organo-complex. Although intercalation of kaolinite is an old and ongoing research topic, there is limited knowledge available on the reactivity of different kaolinites and the mechanism of complex formation, as well as on the structure of the complexes formed. Grafting and incorporation of exfoliated kaolinite in polymer matrices and other potential applications can open new horizons in the study of kaolinite intercalation. This article attempts to summarize (without completion) the most recent achievements in the study of kaolinite organo-complexes obtained with the most common intercalating compounds such as urea, potassium acetate, dimethyl sulphoxide, formamide, and hydrazine using vibrational spectroscopy combined with X-ray powder diffraction and thermal analysis.     

A new methodology for the simulation of solid state phase transition kinetics by combination of nucleation and nuclei growth processes

A new methodology for the simulation of solid state phase transition kinetics has been developed by combining the influence of nucleation rate, nuclei growth rate and the power p characterizing the contact area between the growing particles. The equations used in this methodology were well known, and have been used previously for creating some of the most popular solid-state kinetic equations. The developed methodology made possible calculations of separate rate constants for two processes affecting the rate of phase transition—nucleation (described with K ₁) and nuclei growth (described with K ₂). Similar phase transitions were also approximated with the well-known single constant Avrami–Erofeev equation, but we successfully calculated both constants according to the new methodology, which allowed a separate evaluation of these two processes and explained the different induction periods. The effects of empirically adjusted constants on theoretically calculated kinetic curves were thus determined.     

Seasonal variation of bioactive alkaloid contents in Macleaya microcarpa (Maxim.) Fedde

Macleaya microcarpa (Maxim.) Fedde belongs to the genus Macleaya, family Papaveraceae. Together with the better known and more frequently studied species M. cordata (Willd.) R. Br. it is a main source of quaternary benzo[c]phenanthridine alkaloids. Using HPLC we determined the content of eight isoquinoline alkaloids in the aerial and underground parts of 1-, 2-, 12- and 13-year old plants and followed their changes during the vegetative period. The dominant alkaloid of all samples collected in the end of this period was allocryptopine (3.8-13.6 mg/g for aerial parts, 24.2-48.9 mg/g for underground parts). Chelerythrine, sanguinarine and protopine were also present in both parts of the plant. Additionally, measurable concentrations of chelilutine (CL), chelirubine (CR), macarpine (MA) and sanguirubine (SR) were detected in underground parts. The most important finding was that contents of CR, CL, SR and MA in the 12- and 13-year old plant roots were significantly higher (approximately 3-fold for CR, 6-fold for CL, 5-fold for SR, and at least 14-fold for MA) than in 1- or 2-year old plants. The proportion of individual alkaloids in aerial and underground parts thus changed significantly during the vegetative period.     

Thermal analysis of the structure of segmented polyurethane elastomers

Polyurethanes were prepared from 4,4′-methylenebis (phenyl isocyanate) (MDI), 1,4-butanediol (BD), and poly(tetrahydrofurane) polyether polyol (PTHF) by melt polymerization. The –OH functional group ratio of polyol/total diol was kept constant at 0.4, while the ratio of the isocyanate and hydroxyl groups (NCO/OH) changed between 0.940 and 1.150. The thermal analysis of the polymers by DSC and DMTA measurements indicated several transitions. The three glass transition temperatures observed were assigned to the relaxation of the aliphatic –CH₂– groups of the polyol, and to that of the soft and hard segments, respectively. The glass transition temperature of the soft and hard phase changed with the NCO/OH ratio indicating changes in phase structure and composition confirmed also by the maximum in the number of relaxing soft segments. Changes in the relatively small number of end-groups result in considerable modification of mechanical properties. Strength is determined by molecular mass and interactions, while stiffness depends mainly on phase structure. Surprisingly enough, –OH excess yields stiffer polymers, since the interaction of the –OH groups results in a decrease in the amount of the soft phase. A unique correlation was found between tensile modulus and the number of relaxing soft segments.     

Investigation of mandelic acid bonding on Pirkle type chromatographic stationary phases by Raman spectroscopy

The bonding of mandelic acid enantiomers has been studied on benzene-leucine, dinitrobenzene-leucine and dinitrobenzene-phenylalanine type chiral stationary phases connected to zeolite A supports. The pi-donor, pi-acceptor and H-bonding interactions responsible for diastereomer pair formations can be studied under quasi in situ chromatographic conditions by Fourier transform Raman and surface enhanced Raman spectroscopic techniques. Structural differences between diastereomer pairs result in observable spectral differences at a phase load of approx. 50%. It was shown that the decreasing pi-acceptor character of the phase is associated with its increasing capability of H-bond formation. Correlating spectral data to chromatographic results it can be concluded that, in addition to H-bonding as well as to pi-donor-pi-acceptor interactions, steric hindrances due to bulky moieties of either the stationary phase or the analyte molecules are of importance in successful separations.