ESC resistance of commercial grade polycarbonates during exposure to butter and related chemicals

Three commercial grades of polycarbonates (Lexan^® 144, Lexan^® 104 and Makrolon Rx1805) were studied with respect to resistance to environmental stress cracking (ESC) when exposed to butter and related chemicals. The polycarbonates (PCs) were extensively characterised to determine whether differences in ESC resistance could be related to their structural or chemical properties. MALDI-TOF mass spectrometry revealed that Makrolon Rx1805 contains a low molar mass material characterised as poly(propylene glycol)p, which was confirmed by ATR-FTIR and ¹H NMR. Some “non-absorbing” chemicals, such as butter, cause the PCs to be less resistant to ESC under stress. The reason for this is that these chemicals and the PCs have sufficiently similar Hansen solubility parameters to allow surface conformational changes even though absorption is non-existent or extremely small. ATR-FTIR was used to detect changes in molecular structure in the PC surfaces.     

Maximizing field-effect mobility and solid-state luminescence in organic semiconductors

Conductive and emissive: organic transistors made from a simple styrylanthracene derivative have high charge mobility and high luminescence quantum yields. These properties are attributed to the lack of singlet fission, and challenge the idea that the efficient π interactions required for high mobility always lead to quenching of emission. The transistors emit blue electroluminescence and are stable during operation and storage.     

Synthesis of 1,2-dihydroquinolin-2-ylphosphonates and 1,2-dihydroisoquinolin-1-ylphosphonates via three-component reactions

Abstract  

A facile stereoselective synthesis of 1,2-dihydroquinolin-2-ylphosphonate and 1,2-dihydroisoquinolin-1-ylphosphonate derivatives by the three-component reactions of quinoline or isoquinoline, dialkyl acetylenedicarboxylates, and hydrogen phosphonates is described.     

On a graph of ideals

We associate a graph Γ₊(R) to a ring R whose vertices are nonzero proper right ideals of R and two vertices I and J are adjacent if I+J=R. Then we try to translate properties of this graph into algebraic properties of R and vice versa. For example, we characterize rings R for which Γ₊(R) respectively is connected, complete, planar, complemented or a forest. Also we find the dominating number of Γ₊(R).     

Stability-indicating high-performance thin-layer chromatographic determination of levonorgestrel and ethinyloestradiol in bulk drug and in low-dosage oral contraceptives

A stability-indicating high-performance thin-layer chromatography (HPTLC) method was developed and validated for simultaneous determination of steroidal hormones levonorgestrel and ethinyloestradiol both in bulk drug and in low-dosage oral contraceptives. Optimization of conditions for the spectrodensitometric procedure was reached by eluting HPTLC silica gel plates in a 10 cm × 10 cm horizontal chamber. The solvent system consisted of hexane-chloroform-methanol (1.0:3.0:0.25, v/v/v). This system was found to give compact, dense and typical peaks for both levonorgestrel (R_f = 0.65 ± 0.03) and ethinyloestradiol (R_f = 0.43 ± 0.02). Densitometric analysis of the drugs was carried out in the reflectance mode at 225 nm by using a computer controlled densitometric scanner. The calibration curves of levonorgestrel and ethinyloestradiol were linear in the range of 200-800 and 40-160 ng per spot, respectively. The method was validated for precision, robustness and recovery. As the proposed method can effectively separate the drugs from their degradation products, it can be employed as a stability-indicating method.     

Theoretical and computational investigations on thermodynamic properties, effective site diameters, and molecular free volume of carbon disulfide fluid

A newly proposed theory [R. Laghaei et al., J. Chem. Phys. 124, 154502 (2006)] was extended to polyatomics and applied to compute the density and temperature dependence of the effective site diameters of carbon disulfide fluids. The generic van der Waals (GvdW) theory was also extended to polyatomics in order to calculate the GvdW parameters and the molecular free volume using the effective site diameters as the repulsion-attraction separation distance. A three-site Lennard-Jones potential available in the literature was slightly modified and used in Monte Carlo simulations to obtain the functions appearing in the effective site diameter and GvdW expressions. The interaction potential was examined to reproduce the fluid phase thermodynamic properties using Gibbs ensemble Monte Carlo simulations and also the equation of state in the liquid phase using NVT Monte Carlo (NVT-MC) simulations. Comparison between the simulation results and experimental data shows excellent agreement for the densities of the coexisting phases, the vapor pressure, properties of the predicted critical point, and the equation of state. NVT-MC simulations were performed over a wide range of densities and temperatures in sub- and supercritical regions to compute the effective site diameters, the GvdW parameters, and the molecular free volume. The molecular structure in terms of the site-site pair correlation functions, the density dependence of the effective site diameters, and the density and temperature dependence of the GvdW parameters and molecular free volume were studied and discussed. The GvdW parameters were fitted to empirical expressions as a function of density and temperature. The computed molecular free volume will be used in future investigations to study the transport properties of carbon disulfide.     

Guided waves characteristics of multi-walled carbon nanotubes

The theoretical analysis of propagation of guided waves in the multi-walled carbon nanotubes is presented within the framework of the classical electrodynamics. Electronic excitations of each wall of the system are modeled as an infinitesimally thin cylindrical layer of the π-electrons, whose dynamics are described by means of the fluid theory. General expressions of dispersion relations are obtained for the electromagnetic wave with the transverse magnetic and transverse electric modes, respectively, by solving Maxwell and fluid equations with appropriate boundary conditions.     

Existence of Different Structural Intermediates and Aggregates on the Folding Pathway of Ovalbumin

Structural modifications of ovalbumin in presence of different concentration of guanidine hydrochloride (Gdn HCl) and glucose were investigated by using intrinsic fluorescence, Fourier transform infra-red spectroscopy, circular dichroism and 8-anilino-1-naphthalene-sulphonic acid, to confirm that partially folded intermediates of ovalbumin lead to aggregation. The two partially folded intermediates of ovalbumin were observed one at 1 M Gdn HCl and another in the presence of 20 mM glucose at 3 M Gdn HCl. Both intermediates exist as compact states with altered intrinsic fluorescence, prominent β-sheet secondary structure and enhanced ANS binding. Ovalbumin in the presence of glucose required more concentration of Gdn HCl (3 M) to exist as an intermediate state than control (1 M). Such alpha-helix/beta-sheet transition of proteins is a crucial step in amyloidogenic diseases and represents an internal rearrangement of local contacts in an already folded protein. Further, incubation for 24 h resulted in the formation of aggregates as detected by thioflavin T-assay. On further increasing the concentration of glucose to 50 mM and incubation time for various days resulted in the formation of molten globule state of ovalbumin at 6th day. Later on, at 10th day advanced glycated end products were observed.