Surface molecular degradation of selected high performance polymer composites under low earth orbit environmental conditions

Carbon fibre (CF), carbon nanotube (CNT), nano-clay (NanoC), and 3D-glass (3DG) reinforced polymer composites were selected to undergo treatment with an accelerated Low Earth Orbit (LEO) simulated space environment. Surface degradation mechanisms of the selected polymer composites with different types of reinforcements are discussed. The extent of the oxidation reaction at the surface as a result of LEO exposure was linked to the increase in the intensity of the oxygen-containing ions, as revealed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). X-ray photoelectron spectroscopy (XPS) indicated that an increasing duration of surface treatment correlates with increasing oxygen concentration and decreasing carbon concentration. The degraded CF composite showed the least amount of oxygen (15.6%) and nitrogen (2.5%) on the surface, likely indicating less surface degradation. Further, XPS high resolution region scans showed decreases in the overall carbon concentration accompanied increases in oxygen-containing carbon species C-O, CO and O-CO; functional groups which are attributed to the LEO treatment of the composite materials. All the sample surfaces were eroded upon exposure to LEO conditions with erosion mostly confined to encapsulating epoxy resin.     

Nanometer-sized,rod-like,ligand-containing tryptophan complexes: Anion influence–structural geometry–antitumor activity correlations

Matrix metalloproteinases (MMPs) are metal-dependent endopeptidases that are related to the initiation and progression of diseases and are involved in physiological processes such as angiogenesis, wound healing, and embryonic development. Synthetic inhibitors of MMPs are amino acid–based ligands as analyzed by the interactions between the enzyme and its natural substrate. Low production cost and low environmental toxicity of α-amino acid complexes resulted in a wide pharmacological spectrum, including the anti-inflammatory and anticonvulsant properties in addition to cytotoxic activities. These facts directed our search for the development of selective inhibitors that contain chemical entity. l -Tryptophan is a main component of proteins and is essential in human nutrition for establishing and sustaining positive nitrogen balance. Nanomaterials exhibited clinical influence in terms of delivery approaches on bioactive molecules as therapeutic and imaging contrast agents. In this article, we report the synthesis of nanometer rod-like 2,2′-(1,3,5,7-tetraoxopyrrolo[3,4-f]isoindole-2,6(1H,3H,5H,7H)-diyl)bis(3-(1H-indol-3-yl)propanoic acid) and its metal complexes. The effect of different anions on the geometrical structures and properties of several complexes was studied. Studies indicated that most complexes exhibited dinuclear octahedral or tetrahedral topologies with M–M interaction being absent, whereas mononuclear square planar or square pyramidal topologies were obtained for copper complexes containing chloride or nitrate anions. The ligand exhibited its activity solely against Bacillus subtilis. [Co₂(L)Cl₂(H₂O)₂] complex exhibited potent activity against various species of pathogenic microorganisms. The cytotoxicity against MCF-7 cell line demonstrated that the inhibitory effect is dose dependent. [Cu(HL)Cl.H₂O] complex exhibited an interesting cytotoxic activity in addition to copper anticancer analogues, the alternatives to cis-platin because of their biocompatibility and important roles in biological systems.     

Periodic solutions of nonlinear delay differential equations using spectral element method

We extend the temporal spectral element method further to study the periodic orbits of general autonomous nonlinear delay differential equations (DDEs) with one constant delay. Although we describe the approach for one delay to keep the presentation clear, the extension to multiple delays is straightforward. We also show the underlying similarities between this method and the method of collocation. The spectral element method that we present here can be used to find both the periodic orbit and its stability. This is demonstrated with a variety of different examples, namely, the delayed versions of Mackey–Glass equation, Van der Pol equation, and Duffing equation. For each example, we show the method’s convergence behavior using both p and h refinement and we provide comparisons between equal size meshes that have different distributions.     

Surface molecular characterisation of different epoxy resin composites subjected to UV accelerated degradation using XPS and ToF-SIMS

Epoxy resin composites reinforced with E-glass (E), 3D glass (3D) and carbon fibre (CF) were subjected to an intense UV and high temperature accelerated degradation environment. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to provide a molecular characterisation of the surface of the degraded composites. The response at the surface of the epoxy resin composites to oxidative degradation is influenced by the composite reinforcement type and characteristics. XPS results indicate that 3D resin composites exhibit more surface oxidation as a result of the accelerated degradation in comparison with E and CF composites. Principal components analysis (PCA) of the ToF-SIMS positive ion spectra showed that E and 3D resin composites suffered chain scission while CF composites suffered chain scission and cross-linking reactions as a result of the intense UV exposure. The extent of the surface oxidation, cross-linking/condensation reaction and loss of low molecular weight (lower than C₄H_x) aliphatic hydrocarbons may be indicated using PCA of both the ToF-SIMS positive and negative ion spectra. PCA also provides insight for proposing epoxy resin chain scission and oxidation reaction mechanisms.     

A Review of Analytical Methods for Codeine Determination

Codeine is derived from morphine, an opioid analgesic, and has weaker analgesic and sedative effects than the parent molecule. This weak opioid is commonly used in combination with other drugs for over-the-counter cough relief medication. Due to the psychoactive properties of opioid drugs, the easily obtained codeine often becomes subject to misuse. Codeine misuse has emerged as a concerning public health issue due to its associated adverse effects such as headache, nausea, vomiting, and hemorrhage. Thus, it is very important to develop reliable analytical techniques to detect codeine for both quality control of pharmaceutical formulations and identifying drug misuse in the community. This review aims to provide critical outlooks on analytical methods applicable to the determination of codeine.     

Inclusion Compound of Efavirenz and γ-Cyclodextrin: Solid State Studies and Effect on Solubility

Efavirenz is an antiretroviral drug of widespread use in the management of infections with human immunodeficiency virus type 1 (HIV-1). Efavirenz is also used in paediatrics, but due to its very poor aqueous solubility the liquid formulations available resort to oil-based excipients. In this report we describe the interaction of γ-cyclodextrin with efavirenz in solution and in the solid state. In aqueous solution, the preferential host–guest stoichiometry was determined by the continuous variation method using ¹H NMR, which indicated a 3:2 host-to-guest proportion. Following, the solid inclusion compound was prepared at different stoichiometries by co-dissolution and freeze-drying. Solid-state characterisation of the products using FT-IR, ¹³C{¹H} CP-MAS NMR, thermogravimetry, and X-ray powder diffraction has confirmed that the 3:2 stoichiometry is the adequate starting condition to isolate a solid inclusion compound in the pure form. The effect of γ-cyclodextrin on the solubility of efavirenz is studied by the isotherm method.     

On the comparison of semi-analytical methods for the stability analysis of delay differential equations

This paper provides the first comparison of the semi-discretization, spectral element, and Legendre collocation methods. Each method is a technique for solving delay differential equations (DDEs) as well as determining regions of stability in the DDE parameter space. We present the necessary concepts, assumptions, and equations required to implement each method. To compare the relative performance between the methods, the convergence rate and computational time for each method is compared in three numerical studies consisting of a ship stability example, the delayed damped Mathieu equation, and a helicopter rotor control problem. For each study, we present one or more stability diagrams in the parameter space and one or more convergence plots. The spectral element method is demonstrated to have the quickest convergence rate while the Legendre collocation method requires the least computational time. The semi-discretization method on the other hand has both the slowest convergence rate and requires the most computational time.     

Raft mediated surface grafting of t‐butyl acrylate onto an ethylene–propylene copolymer initiated by gamma radiation

RAFT mediated grafting of poly(t‐butyl acrylate) onto the surface of a commercial poly(ethylene‐co‐propylene), Elpro, has been carried out using initiation by ⁶⁰Co γ‐radiation at 298 and 273 K. The polymerizations were in bulk monomer and using the RAFT agent 1‐phenylethyl phenyldithioacetate. The rates of homopolymerization and grafting were found to decrease with increasing RAFT agent concentration, indicating that both polymerization processes involve participation of the RAFT agent. There was good agreement between the predicted and experimental molecular weights of the homopolymer that had a narrow polydispersity. The poly(t‐butyl acrylate) grafts were hydrolyzed by trifluoroacetic acid to form poly(acrylic acid) grafts, which could either be further functionalized or used to control the surface polarity of the Elpro. ATR‐FTIR spectroscopy was used to characterize the grafts and Raman spectroscopy was used to assess the depth of the grafts. The water contact angle for the Elpro surface grafted with poly(acrylic acid) was found to be linearly dependent on the amount of the graft present. The living nature of the grafted chains was demonstrated by the addition of a second block of polystyrene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1074–1083, 2007