Crystallization kinetics of PHB/PVAc blends using time resolved dielectric spectroscopy

Crystallization kinetics of poly(hydroxy butyrate), PHB, and its blends with poly(vinyl acetate), PVAc, have been thoroughly investigated using broadband dielectric technique over a wide range of frequencies (10⁻²-10⁵ Hz) as functions of crystallization temperature and blend composition. The dielectric strength of the amorphous segments, Δε, which is directly proportional to the volume fraction of the mobile amorphous phase in the blend decreases exponentially with increasing the crystallization time. However, on the other hand, the dielectric strength of the rigid amorphous segments, Δε_α′, which is related to the percentage of crystallinity in the blend increases dramatically with increasing crystallization time. A great variation in the dynamical constraints of relaxation segments with increasing crystallization time has been observed as a result of different environments, which would lead to a variation in the consistency of the cooperative regions. The value of the dielectric constant, ε′, decreases dramatically with increasing crystallization time, after that it reaches an equilibrium value at the end of the crystallization process. This dramatic decrease in the value of ε′ as a result of crystallization at a given crystallization temperature, was taken as an accurate evaluation for the amount of the amorphous phase that has undergone crystallization considering the theoretical approach of Avrami. The Avrami exponent, n, was found to be crystallization temperature, T_c, independent (n ∼ 3) indicating a three-dimensional crystal growth for pure PHB. The crystallization rate constant, k, increases greatly with increasing T_c due to the high crystallization rate. In the blend the value of n was found to be concentration dependent (n ∼ 1.8-3.2). The different values of n indicate that the shapes of the growing crystals are affected by blend concentration. For n ∼ 1.8, the crystals can either grow sporadically as rods or instantaneously as disks, while for n ∼ 3 a three-dimensional crystal growth takes place.     

Diazo Compounds and Phenyliodonium Ylides in Inter- and Intramolecular Cyclopropanations Catalyzed by Dirhodium(II). Synthesis and Chiral Resolution by GC versus HPLC

Summary. The dirhodium(II)-catalyzed intermolecular cyclopropanation of a set of olefins with either diazo free phenyliodonium ylides or diazo compounds afforded cyclopropanes derived from Meldrum’s acid, dimethyl malonate, (silanoxyvinyl)diazoacetates, 3,3,3-trifluoro-2-diazopropionate, ethyl diazo(triethyl)- and (dimethylphenyl)silylacetate with moderate to high yield in either racemic or enantio-enriched forms. The intramolecular cyclopropanation of triethylsilyl-substituted allyl diazoacetates in the presence of the chiral rhodium(II) catalyst [Rh₂(s-nttl)₄] in toluene afforded the corresponding cyclopropanes with up to 37% ee. An efficient chiral separation method based on enantioselective GC and HPLC was developed. The method provides information about the chemical yields of the cyclopropane products, enantioselectivity, substrate specifity, and catalytic activity of the chiral catalysts used in the inter- and intramolecular cyclopropanation reactions and avoids time-consuming work-up procedures.     

Corrosion studies of polyaniline/coconut oil poly(esteramide urethane) coatings

Advancements in the area of conducting polymers have been towards their application as effective corrosion protective coatings to replace the use of heavy metals as additives in the coatings industries, which are now considered to be an environmental as well as health hazard. With the aim to utilize a sustainable resource based polymer for the development of an anti‐corrosive conducting coating material, coconut oil based conducting blend coatings of polyaniline and poly(esteramide urethane) were prepared by loading different ratios (2, 4 and 8 wt%) of polyaniline in poly(esteramide urethane). Then their physico‐chemical, thermal, morphological, conductivity and anti‐corrosive coating characteristics were investigated. The effect of a 2 year environmental aging process on the coated samples was analyzed by thermal methods as well as by corrosion studies. Results showed that the corrosion protective performance of the blend coatings was far superior than that of plane poly(esteramide urethane). These coatings showed enhanced corrosion protection in acid as well as alkaline environments upto 360 and 192 hr respectively. Conductivity of the blends was found to be in the range 2.5 × 10^?5–5.7 × 10^?4 S/cm^?1. An increase in the thermal stability of the blend coatings and a decrease in their conductivity was noticed in the aged samples which was attributed to the crosslinking effect. The corrosion protective performance of the coatings remained almost unaffected even after 2 years of aging. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of pH on thermal- and chemical-induced denaturation of GFP

Green fluorescent protein (GFP) is an unusually stable autofluorescent protein that is increasingly being exploited for many applications. In this report, we have used fluorescence spectroscopy to study the effect of pH on the denaturation of GFP with sodium dodecyl sulfate (SDS), urea, and heat. Surprisingly, SDS (up to 0.5%) did not have any significant effect on the fluorescence of GFP at pH 7.5 or 8.5 buffers; however, at pH 6.5, the protein lost all fluorescence within 1 min of incubation. Similarly, incubation of GFP with 8 M urea at 50°C resulted in time dependent denaturation of GFP, but only in pH 6.5 buffer. At higher pH values (pH 7.5 and pH 8.5), the GFP was quite stable in 8 M urea at 50°C, showing only a slight decrease in fluorescence. Heat denaturation of GFP was found to be pH dependent as well, with the denaturation being fastest at pH 6.5 as compared to pH 7.5 or pH 8.5. Like the denaturation studies, renaturation of heat-denatured GFP was most efficient at pH 8.5, followed by pH 7.5, and then pH 6.5. These results suggests that GFP undergoes a structural/stability shift between pH 6.5 and pH 7.5, with the GFP structure at pH 6.5 being very sensitive to denaturation by SDS, urea, and heat.     

Seventeen new 14- and 15-crown-formazans: their synthesis and evaluation in spectrophotometric determination of lithium

A number of new crown-formazans with 14 and 15 membered rings have been synthesized, characterized and investigated as selective spectrophotometric chelating agents for lithium. The effect of sodium ion concentration on the background lithium signal was studied. A comparative study for the sensitivity of these new crown-formazans in spectrophotometric determinations was studied and compared with those reported previously. The three new 14- and 15-crown-formazans 4a–c containing the pyridyl N-oxide at the formazyl carbon showed the highest selectivity to lithium determination in the presence of sodium ion.     

On the Generalized Thermoelasticity Problem for an Infinite Fibre-Reinforced Thick Plate under Initial Stress

In this paper, the generalized thermoelasticity problem for an infinite fiber-reinforced transversely-isotropic thick plate subjected to initial stress is solved. The lower surface of the plate rests on a rigid foundation and temperature while the upper surface is thermally insulated with prescribed surface loading. The normal mode analysis is used to obtain the analytical expressions for the displacements, stresses and temperature distributions. The problem has been solved analytically using the generalized thermoelasticity theory of dual-phase-lags. Effect of phase-lags, reinforcement and initial stress on the field quantities is shown graphically. The results due to the coupled thermoelasticity theory, Lord and Shulman's theory, and Green and Naghdi's theory have been derived as limiting cases. The graphs illustrated that the initial stress, the reinforcement and phase-lags have great effects on the distributions of the field quantities.     

Radiative mixed convection flow of an Oldroyd-B fluid over an inclined stretching surface

A mixed convection flow of an Oldroyd-B fluid in the presence of thermal radiation is investigated. The flow is induced by an inclined stretching surface. The boundary layer equations of the Oldroyd-B fluid in the presence of heat transfer are used. Appropriate transformations reduce partial differential equations to ordinary differential equations. A computational analysis is performed for convergent series solutions. The values of the local Nusselt number are numerically analyzed. The effects of various parameters on velocity and temperature are discussed.     

A Brief Review on Fluorescent Copper Sensor Based on Conjugated Organic Dyes

The design and development of the fluorescence reporting molecules for the trace recognition of the metallic ions in the aqueous, mixed organic aqueous media, environmental specimen, living things e.g., body fluids, serum, urine etc is the evergreen research area. Among several methodologies utilized for these purposes, the fluorescent techniques have wonderful impact in the era of metal sensor development due to their acclamatory features of non-invasive detection process and appreciable sensitivity. The utilization of small organic molecules for the sensation of metallic ions through the fluorescent techniques harvested the wonderful results having some interesting features of chromogenic response on metal binding, robustness in the preparation and applicability to establish the metallic accumulation level inside the live cells via bioimaging studies. The detailed knowledge and background about the several reported chemosening strategies have the utmost importance in order to understand or to design the novel molecules for metal sensing purposes. The objective of the presents review was to compile the best ever used copper sensing strategies via fluorescent means in the running decade. We have summarized the values of optical positions of the spectral lines, spectral shifting upon metal binding, binding/association/dissociation constants, chromogenic changes in the reaction mixture, proposed complexation mechanism of the ligand with the copper, ligand sensitivities toward the copper recognition, binding stoichiometries and the detailed bioimaging results where applicable.