Chemical composition and in vitro antioxidative activity of a lemon balm (Melissa officinalis L.) extract

The leaf material of lemon balm (Melissa officinalis L.) was extracted with 450 ml/l aqueous ethanol by medium pressure liquid-solid extraction. The total phenolic content of the extract was estimated as gallic acid equivalents by Folin-Ciocalteu reagent method and a qualitative-quantitative compositional analysis was carried out using high performance liquid chromatography coupled with photodiode array detection. The lemon balm extract contained hydroxycinnamic acid derivatives and flavonoids with caffeic acid, m-coumaric acid, eriodictyol-7-O-glucoside, naringin, hesperidin, rosmarinic acid, naringenin, hesperetin being identified based on their chromatographic behaviour and spectral characteristics. The extract was also investigated for potential in vitro antioxidant properties in iron(III) reduction, iron(II) chelation, 1,1-diphenyl-2-picrylhydrazyl, 2,2′-azinobis(3-ethylbenzothiazoline-6-sulphonate), superoxide anion and nitric oxide free-radical scavenging, and inhibition of β-carotene-linoleic acid bleaching assays. The extract demonstrated antioxidant activity in all the assays. However, it was not as potent as the positive controls except in the β-carotene-linoleic acid bleaching assay, where its activity was superior to that of gallic and caffeic acids and statistically indistinguishable from quercetin and BHA. The exceptionally high antioxidant activity and the fact that this assay is of biological relevance warrants further investigation of lemon balm extract in ex vivo and in vivo models of oxidative stress.     

Improvement of processability of poly(ε‐caprolactone) by radiation techniques

Improvement of processability of Poly(ε‐caprolactone) (PCL) was achieved by introduction of a branch structure using gamma‐irradiation from a ⁶⁰Co source. Irradiated PCL has higher molecular weight by producting a branch structure. Hence, the irradiation at a lower dose, such as 3 Mrad, leads to a higher melt viscosity. The branched structure gave improved properties for dynamic viscoelasticity and elongational viscosity. High elongational viscosity was observed by entanglement due to branch chain formed during irradiation, and the elongational viscosity for 3 Mrad is higher than 1.5 Mrad. Due to a higher elongational viscosity, PCL foam can be produced by a molding process. Foam produced from irradiated PCL pellets at 3 Mrad has honeycomb‐like structure, and the foam showed higher enzymatic degradation compared to film samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1815–1820, 1999     

The fabrication and characterization of poly(4-vinylpyridine)-based thin film transistors exhibiting enhanced ion modulation

Lithium perchlorate-doped hygroscopic poly(4-vinylpyridine)-based organic thin film transistors have been fabricated and characterized. More than one mechanism of current modulation is observed in these devices with the observed mechanism depending upon both the amount of added dopant and the operating voltage. At low gate voltages (0 to −0.8 V) the current modulation mechanism is dominated by ions intrinsic to the dielectric layer (due to its hygroscopic nature), while at higher gate voltages (−1 to −2 V) the device behavior is governed by the movement of the dopant ions. Most importantly, through careful control of dopant concentration, we show that it is now possible to fabricate all-solution processed devices with significantly enhanced current modulation. In particular, we demonstrate that current modulation ratios in excess of 10⁵ are possible with this device architecture.     

Synthesis,characterization and toxicological evaluation of pH-sensitive polyelectrolyte Nanogels

Nanogels are polymeric nanoparticles that have similar characteristic to hydrogels, but have the size in nano range. The pH-sensitive nanogel have gained much interest in the field of pharmaceutical nanotechnology as they have potential to be used as nanocarriers in drug delivery system. The aim of the present study was to synthesize pH-sensitive polyelectrolyte MMA/IA nanogels using free radical polymerization containing methyl methacrylate (MMA), itaconic acid (IA), and a crosslinker ethylene glycol dimethacrylate (EGDMA). In the synthesis of nanogels four parameters i.e. ethanol/water ratios (v/v), dilution volume using ethanol/water (v/v), crosslinker EGDMA concentration, and monomers MMA/IA ratios were optimized. Their effect on particle size, PdI, zeta potential and swelling ratio were evaluated. The swelling behaviour of the nanogels was studied by measuring swelling ratio using gravimetric method. The optimized nanogels were characterized by proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FTIR), liquid chromatography/time-of-flight/mass spectrometry (LC-TOF-MS), X-ray powder diffraction (X-RD) and transmission electron microscopy (TEM). Polyelectrolyte characteristic was confirmed by measuring isoelectric point using aqueous electrophoresis. The in-vitro and in-vivo toxicity studies were performed by MTT assays using Caco-2 cells and Limit test using female Sprague Dawly rats, respectively. The nanogels were amorphous in nature, exhibited pH-responsive property and polyelectrolyte characteristics, which showed an isoelectric point at pH 2.78. They had an average particle size <250 nm, narrow size distribution (PdI < 0.3), and negative zeta potential. The in-vitro MTT assays indicated that the nanogels had no sign of cytotoxicity. The in vivo Limit test showed that the LD50 was greater than 2000 mg/kg body weight. The necrospy, histopathology and hematological studies also revealed no sign of toxicity. These findings suggested that the MMA/IA nanogels are pH-sensitive, non-toxic and have potential to form a polyelectrolyte complex with oppositely charged of macromolecular drugs.     

Role of Morphology of Surfactant-Free Nanoparticles in Organic Photovoltaics

Journal of Electronic Materials - Nanoparticulate (NP) films and organic photovoltaic devices have been fabricated from poly(3-hexylthiophene):phenyl C61 butyric acid methyl ester (P3HT:PC61BM) NP...     

Heat resistance of radiation crosslinked poly(ε-caprolactone)

Polycaprolactone (PCL) was gamma-irradiated at different phases such as solid state at 30 to 55°C, molten state, and supercooled state, under vacuum or air atmosphere, to elucidate its crosslinking behavior. Irradiation in the molten state (80°C) gave higher gel content compared to room temperature. The resulting gel, however, contains many voids due to the gas evolved during irradiation. Conversely, irradiation of PCL in the supercooled state led to the highest gel content among the three irradiation conditions and it was free of voids. Based on these findings, to evaluate heat resistibility of crosslinked PCL prepared by irradiation in supercooled state, the crosslinked PCL was hot pressed at 200°C to form a film. Unirradiated PCL melted at 60°C. The film prepared from 160 kGy irradiated PCL (crosslinked sample) under an applied load of 0.667 MPa, at a temperature of 110°C did not break even after 3 h. At a temperature of 120°C, the film has a tensile strength of 3 MPa. Furthermore, the film extended by hot pressing is transparent and has high heat shrinkability. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 581–588, 1998     

Characterization of polymeric micelles for pulmonary delivery of beclomethasone dipropionate

The potential of using poly-(ethylene oxide)-block-distearoyl phosphatidyl-ethanolamine (mPEG-DSPE) polymer to prepare BDP-loaded micelles with high entrapment efficiency and mass median aerodynamic diameter of less than 5 microm demonstrating sustained release properties was evaluated. The result showed that lyophilized BDP-loaded polymeric micelles with entrapment efficiency of more than 96% could be achieved. Entrapment efficiency was affected by both the drug to polymer molar ratio and the amount of drug used. Investigation using FTIR and DSC confirmed that there was no chemical or physical interaction and the drug was molecularly dispersed within the micelles. TEM images showed that the drug-loaded polymeric micelles were spherical in shape with multivesicular morphology. Further analysis by photon correlation spectroscopy indicated that the particle size of the BDP-loaded micelles was about 22 nm in size. In vitro drug release showed a promising sustained release profile over six days following the Higuchi model. The mass median aerodynamic diameter and fine particle fraction were suitable for pulmonary delivery. Moreover, the small amount of deposited drug in the induction port (throat deposition) suggested possible reduction in incidence of oropharyngeal candidiasis, a side effect normally associated with inhaled corticosteroids therapy. The high encapsulation efficiency, comparable inhalation properties, sustained release behavior together with biocompatibility nature of the polymer support the potential of BDP-loaded polymeric micelles as a versatile delivery system to be used in the treatment of asthma and chronic obstructive pulmonary disease.     

Improvement of hot water resistance of poly(vinyl alcohol) hydrogel by acetalization and irradiation techniques

In order to improve the heat stability of poly(vinyl alcohol) (PVA) hydrogel, acetalized PVA was irradiated with electron beam irradiation. The acetalization was strongly affected by PVA water content. There is an optimum water content of 20–30% for acetalization of PVA. The PVA gave maximum tensile strength at a dose of 100 kGy before or after acetalization. The PVA hydrogel maintained tensile strength of 10 MPa, even after 90 min boiling (98°C) in water or autoclave sterilization (121°C). It was confirmed that irradiation after, or before, acetalization is effective for enhancing heat resistance of a PVA hydrogel. The hydrogel is transparent, soft, has high tensile strength, and high hot water resistance. © 1995 John Wiley & Sons, Inc.