Aggregation of polylactide with carboxyl groups at one chain end in the presence of metal cations

Polylactides with one or more carboxyl groups at one chain end were synthesized by cationic polymerization according to activated monomer mechanism and by application of “thiol-yne” click chemistry for subsequent functionalization. End groups of such obtained polylactides were converted into ionic groups by neutralization of polymer solutions with metal oxides, mainly calcium oxide, and the aggregation of individual stereoisomers as well as that of the mixture of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) was investigated. The extent and progress of the aggregation was followed by viscosity measurements, and aggregated polymers in the solid state were examined by SEM and DSC. Solution viscosity increase was observed upon the aggregation of individual PLA stereoisomers, whereas PLA stereocomplex precipitation occurred in the case of the aggregation of PLLA/PDLA/metal oxide mixture.     

Nanoscale Digital Devices Based on the Photoelectrochemical Photocurrent Switching Effect: Preparation,Properties and Applications

New materials and new phenomena which can be used for information processing always inspire great enthusiasm. On the other hand, silicon is still the main workhorse of modern electronics. Production of bulk quantities of ultrapure silicon is relatively cheap and the processing technologies are extremely sophisticated. Introduction of new materials and phenomena, on the other hand, requires an enormous amount of hard experimental and theoretical work. The photoelectrochemical photocurrent switching effect (PEPS) is one of the processes that, in principle, can evolve into new information processing technology. This review presents the effect itself, along with preparation of appropriate semiconducting materials, physical principles of semiconductor–molecule interactions, and finally some prototypical constructions of logic devices based on the PEPS effect.     

Lipid composition and cell surface hydrophobicity of Candida albicans influence the efficacy of fluconazole–gentamicin treatment

Adherence of the fungus, Candida albicans, to biotic (e.g. human tissues) and abiotic (e.g. catheters) surfaces can lead to emergence of opportunistic infections in humans. The process of adhesion and further biofilm development depends, in part, on cell surface hydrophobicity (CSH). In this study, we compared the resistance of C. albicans strains with different CSH to the most commonly prescribed antifungal drug, fluconazole, and the newly described synergistic combination, fluconazole and gentamicin. The hydrophobic strain was more resistant to fluconazole due to, among others, overexpression of the ERG11 gene encoding the fluconazole target protein (CYP51A1, Erg11p), which leads to overproduction of ergosterol in this strain. Additionally, the hydrophobic strain displayed high efflux activity of the multidrug resistance Cdr1 pump due to high expression of the CDR1 gene. On the other hand, the hydrophobic C. albicans strain was more susceptible to fluconazole–gentamicin combination because of its different effect on lipid content in the two strains. The combination resulted in ergosterol depletion with subsequent Cdr1p mislocalization and loss of activity in the hydrophobic strain. We propose that C. albicans strains with different CSH may possess altered lipid metabolism and consequently may differ in their response to treatment.     

Application of Multinomial Logistic Regression to Model the Impact of Rainfall Genesis on the Performance of Storm Overflows: Case Study

Water Resources Management - In this study, a mathematical model was proposed to analyze the performance of storm overflows. The model included the influence of rainfall genesis on the duration of...     

N-nitrosodimethylamine (NDMA) as a product of potassium permanganate reaction with aqueous solutions of dimethylamine (DMA)

The reactivity of permanganate with dimethylamine, as possible path of NDMA formation, has been investigated.The results have shown that potassium permanganate reaction with aqueous solutions of dimethylamine (DMA) leads to the formation of N-nitrosodimethylamine (NDMA). The contact time, the molar ratio of permanganate and DMA, pH and presence of nitrite are the key factors influencing the efficiency of NDMA formation. Significant conversion rates of DMA to NDMA were observed only for the high doses of permanganate, which were many times higher than those typically used in water treatment. This reaction however is of importance for water treatment technology, since it shows the possibility of NDMA formation as a result of oxidation of DMA.It is likely that nitrosation is the main path of the reaction. An important role of MnO₂ suspension, formed as a result of permanganate reduction in NDMA formation is emphasized. Significant influence of MnO₂ suspension on NDMA formation should draw our attention to the potential impact of MnO₂ activated filtration beds on NDMA formation.     

Enhanced multiple-point beam-to-beam frictionless contact finite element

In this paper a new contact finite element for beams with circular cross-sections is presented. The element is an enhancement of the previously formulated point-wise beam-to-beam contact finite elements to be used in cases when beams get in contact at very acute angles. In such situation, if beam deformations in the vicinity of the contact zone are taken into account, the contact is not point-wise but it extends to a certain area. To cover such a case in a more realistic way, two additional pairs of contact points are introduced to accompany the original single pair of contact points. The central pair is determined using the orthogonality conditions for the beam axes and the positions of two extra points are defined on one beam axis by a shift of the local co-ordinate. This shift depends on beams geometry and the current angle between tangent vectors at the central contact point. The appropriate kinematic variables for normal contact together with their finite element approximation are derived. Basing on the weak form for normal contact and its linearisation, the tangent stiffness matrix and the residual vector are derived. The new element is tested using author’s computer programs and comparisons with the point-wise contact elements are made.     

Acid-base catalysis of N-[(morpholine)methylene]daunorubicin

The stability of N-[(morpholine)methylene]-daunorubicin hydrochloride (MMD) was investigated in the pH range 0.44-13.54, at 313, 308, 303 and 298 K. The degradation of MMD as a result of hydrolysis is a pseudo-first-order reaction described by the following equation: ln c = ln c(0) - k(obs)? t. In the solutions of hydrochloric acid, sodium hydroxide, borate, acetate and phosphate buffers, k(obs) = k(pH) because general acid-base catalysis was not observed. Specific acid-base catalysis of MMD comprises the following reactions: hydrolysis of the protonated molecules of MMD catalyzed by hydrogen ions (k(1)) and spontaneous hydrolysis of MMD molecules other than the protonated ones (k(2)) under the influence of water. The total rate of the reaction is equal to the sum of partial reactions: k(pH) = k(1) ? a(H)+ ? f(1) + k(2) ? f(2) where: k(1) is the second-order rate constant (mol(-1) l s(-1)) of the specific hydrogen ion-catalyzed degradation of the protonated molecules of MMD; k(2) is the pseudo-first-order rate constant (s(-1)) of the water-catalyzed degradation of MMD molecules other than the protonated ones, f(1) - f(2) are fractions of the compound. MMD is the most stable at approx. pH 2.5.     

Thermal Properties and Wetting Behavior of High Temperature Zn-Al-In Solders

Solders for ultrahigh-temperature applications were defined by Vianco as those able to sustain working conditions with temperatures as high as 573 K, with momentary temperature rise up to 623 K. Zn-Al eutectic alloy (12 at.% Al) fits such defined criteria with respect to its melting temperature. It was found that small additions of indium to Zn-Al eutectic lower its melting temperature. The aim of this work is to assess if and to what extent thermal properties and wetting behavior are affected. It was found that addition of In increases electrical resistivity and coefficient of thermal expansion value. Wetting angles on Cu and Al substrates of liquid Zn-Al eutectic-based alloys containing up to 1.5 at.% of In were studied with the sessile drop method, after wetting at 773 K in the presence of flux. A decrease of apparent wetting angle was observed with increasing concentration of In. After wetting tests solidified alloy-substrate couples were cross-sectioned and examined with scanning electron microscopy coupled with electron dispersive X-ray analysis.