Study of optical band gap and carbon cluster sizes formed in 100 MeV Si8+ and 145 MeV Ne6+ ions irradiated polypropylene polymer

A wide variety of material modifications in polymers have been studied by using ion irradiation techniques. Extensive research has focused on to Swift Heavy Ions (MeV’s energy), probably because of good controllability and the large penetration length in polymers. High energy ion irradiation tends to damage polymers significantly by electronic excitation and ionization. It may result into the creation of latent tracks and can also cause formation of radicals such as ablation, sputtering, chain scission and intermolecular cross-linking, creation of triple bonds and unsaturated bonds and loss volatile fragments. Polypropylene polymer films of thickness 50 μm were irradiated to the fluences of 1 × 10¹⁰, 3 × 10¹⁰, 1 × 10¹¹, 3 × 10¹¹, 6 × 10¹¹ and 1 × 10¹² ions/cm² with Si⁸⁺ ions of 100 MeV energy from Pelletron accelerator at Inter University Accelerator Centre (IUAC), New Delhi and Ne⁶⁺ ions of 145 MeV to the fluences of 10⁸, 10¹⁰, 10¹¹, 10¹² and 10¹³ ions/cm³ from Variable Energy Cyclotron Centre, Kolkata. Optical modifications were characterized by UV towards the red end of the spectrum with the increase of the fluence. Value of optical band gap E _g shows a decreasing trend with ion fluence irradiated with both kinds of ions. Cluster size N, the number of carbon atoms per conjugation length increases with increasing ion dose. Cluster size also increases with the increase of electronic stopping power.      

Nucleophilic ring opening reactions of aziridines

Aziridine ring opening reactions have gained tremendous importance in the synthesis of nitrogen containing biologically active molecules. During recent years, a great effort has been put forward by scientists toward unique bond construction methodologies via ring opening of aziridines. In this regard, a wide range of chiral metal- and organo-catalyzed desymmetrization reactions of aziridines have been reported with carbon, sulfur, oxygen, nitrogen, halogen, and other nucleophiles. In this review, an outline of methodologies adopted by a number of scientists during 2013–2017 for aziridine ring opening reactions as well as their synthetic applications is described.     

Characterization of a planar NID chiral interface under negative and/or positive phase velocity conditions

Using positive and/or negative phase velocity conditions, characteristics of a planar non-integer dimensional (NID) chiral interface are explored for specific values of NID parameter. For this purpose, discussion is divided into four cases. It is noted how characteristics of the interface changes when the situation is changed from one case to another. Impact of variation of NID parameter on the reflected power is also noted for each case.     

Estimation of leaf transmittance in the near infrared region through reflectance measurements

A method, which allows one to compensate for the incomplete collection of transmitted light (T) by an integrating sphere, has recently been developed, and shown to be reliable provided that the absorptance (A) of the leaf in the NIR region (750-800 nm) can be neglected, allowing one to set R+T=1, where R denotes the reflectance; this implies that proper compensation can only be applied to healthy leaves, which do not absorb in the NIR region. To overcome this limitation, the feasibility of an alternative, requiring neither measurements of T nor an elaborate analysis of radiative transport through a leaf, is explored. Not surprisingly, this simplistic alternative provides results which (in general) do not agree with those found by using the compensation method, but the two approaches converge in the spectral regions where absorptance is low (that is, where R+T> or =0.9). The "T-through-R" method, as described here, thus provides an additional check on the correction factor used in conjunction with the integrating sphere, and extends the applicability of the compensation method to situations where NIR absorptance is not negligible, e.g., in the presence of 'browning' pigments produced upon the oxidation of polyphenols during leaf senescence.     

Brownian motion description of heat conduction by phonons

A non-Markovian partial differential equation, rooted in the theory of Brownian motion, is proposed for describing heat conduction by phonons. Although a finite speed of propagation is a built-in feature of the equation, it does not give rise to an inauthentic wave front that results from the application of Cattaneo's equation. Even a simplified, analytically tractable version of the equation yields results close to those found by solving, through more elaborate means, the equation of phonon radiative transfer.     

On recording the true absorption spectrum and the scattering spectrum of a turbid sample: application to cell suspensions of the cyanobacterium Anabaena variabilis

An integrating sphere is often used for recording the absorption spectrum of a turbid sample. If the sample is placed inside the sphere, scattering losses are eliminated, but the recorded spectrum suffers from other distortions. These distortions can be avoided by positioning the sample outside the sphere; but, since some of the scattered light escapes the detector, the recorded spectrum suffers from residual scattering losses. A method proposed by Latimer and Eubanks more than 30 years ago (Arch. Biochem. Biophys. 98 (1962) 274), is put to a quantitative examination, which has shown that one can obtain, by recording two spectra at different distances from the sphere, not only the true absorption spectrum but also the scattering spectra of the sample. Conditions for the validity of the basic assumption underlying the method are investigated by examining suspensions containing various concentrations of cells of the cyanobacterium Anabaena variabilis, and it is shown that the calculated absorbance is proportional to the number density of the cells. The application of the method for quantitative spectrophotometric analysis of pigments in cell suspensions is discussed.     

Preparation,characterization and biodistribution of salicylidene- and pyridoxylidene-thyroxine complexes of technetium-99m

New Schiff bases, salicylidene- and pyridoxylidene-thyroxine have been prepared and characterized. They were labeled with^99mTc. The labeling yield of the Schiff bases was over 95%. About 60% of the activity was bound to -globulin and albumin fractions when the labled compounds were incubated with a serum sample. The labeled compounds, after i.v. administration to rats, rapidly cleared from blood and excreted into the small intestine. They appeared to behave as hepatobiliary agents.     

Thermodynamic aspect: kinetics of the reduction of dicyanobis(phen)iron(III) by acetylferrocene and methylferrocenemethanol

Protonation plays an important role in the redox reactions. We observed this leading role during the reduction of [Fe^III(phen)₂(CN)₂]⁺ by FcCOMe and FcCHOHMe. The kinetic data showed that the reaction(s) followed a complex kinetics due to the formation of protonated acetylferrocene (FcC⁺OHMe), and or, protonated α-methylferrocenemethanol (FcCHO⁺H₂Me) in aqueous dioxane (80% v/v). Our results helped us to conclude that the reactions were completed in three phases. An overall zeroth order was observed in the first phase of the reactions. In the second phase, the kinetic data showed an overall second order reaction. The third phase was a complex phase where the rate of redox reactions and the insolubility of the neutral product ([Fe^II(phen)₂(CN)₂]) competed with each other. We studied the effect of different factors to identify the reacting entities, which take part in the rate-determining step of each reaction in the second phase. Consequently, we determined the effects of selected factors upon the observed pseudo-first order rate constant(s) (k′ _obs) of each reaction. The value of k′ _obs increased upon addition of protons in the reaction mixture in case of FcCOMe, and it decreased during the oxidation of FcCHOHMe. Meanwhile, upon enhancing the ionic strength, we observed an increase in k′ _obs for FcCOMe, and no change in the value of k′ _obs during the reaction of FcCHOHMe. However, a decrease in k′ _obs was noticed upon increasing the dielectric constant of the reaction mixture when the reductant was FcCOMe, and no effect was observed in case of FcCHOHMe. Together, these results suggested oxidation of FcC⁺OHMe and FcCHOHMe in the slow-step, and FcCOMe and FcCHO⁺H₂Me during the fast-step. We refined our results by estimating the thermodynamic parameters of activation. The low values of activation energy and enthalpy of activation confirmed that the reduction of [Fe^III(phen)₂(CN)₂]⁺ hardly depends upon temperature when the reducing agent is FcCOMe. The outcomes justified that the rate of reaction depends upon the unsaturated FcC⁺OHMe. This intermediate species contain a ‘carbonium ion’, which is very reactive and energetic. We obtained comparatively high values of the activation energy and enthalpy of activation for the reaction between [Fe^III(phen)₂(CN)₂]⁺ and FcCHOHMe. The results show that FcCHOHMe is a saturated and stable compound that leads the slow-step and controls the rate of reaction.     

Bacteriochlorophyll e monomers,but not aggregates,sensitize singlet oxygen: implications for a self-photoprotection mechanism in chlorosomes

Sensitization of singlet delta oxygen (O2(1delta(g))) by bacteriochlorophyll e (BChle) has been investigated to gain a better understanding of the photoprotection mechanism(s) operating in chlorosomes of green photosynthetic bacteria. The sensitization process has been studied in media where BChle forms monomers (acetone and aqueous solutions containing 0.5% Triton X-100 [TX]) and in systems where BChle aggregates, namely, aqueous solutions containing 0.003% monogalactosyl diglyceride (MGDG) and chlorosomes(control as well as hexanol perturbed) from Chlorobium phaeobacteroides strain CL1401. In Ar-purged acetone, BChle triplets (BChle triplets) have a lifetime of a few tens of microseconds; however, in air-saturated acetone, quenching of BChle triplets by ground-state oxygen (O2(3sigma(-)g)) and formation of O2(1delta(g)) take place. The O2(1delta(g)) so formed is susceptible to quenching by BChle0, a ground-state BChle molecule. A Stern-Volmer analysis reveals a linear fit between the decay rate of O2(1delta(g)) and the BChle concentration. The rate constants for the quenching of O2(1delta(g)) by BChle0 and for the deactivation of O2(1delta(g)) by the solvent come out to be kq = (1.4 +/- 0.1) x 10(9) M(-1) s(-1) and k0 = (18.5 +/- 0.7) x 10(3) s(-1), respectively. The absolute quantum yield of O2(1delta(g)) sensitization by BChle monomers is 0.65 +/- 0.15 in air-saturated acetone. In aqueous phase, the triplet lifetime of BChle aggregates in native or hexanol-perturbed chlorosomes shortens by more than two orders of magnitude when compared with the triplet lifetime of BChle monomers in 0.5% TX solution (a few hundreds of microseconds). Quenching by carotenoids (Car) makes only a minor contribution to the decay of BChle triplets in aggregates. Because O2(1delta(g)) sensitization by BChle triplets could be detected neither in MGDG aggregates nor in chlorosomes (control as well as hexanol perturbed), it is concluded that (1) this process is highly likely when BChle is present as a monomer but not when it is tightly packed in artificial aggregates or in chlorosomes; and (2) Car, though vital for the baseplate BChla, are dispensable for BChle.     

Measurements of sub-nanosecond lifetimes from biphotonic fluorescence produced by nanosecond laser pulses

When the absorption of light from nanosecond laser pulses gives rise to a short-lived biphotonic fluorescence the lifetime of the excited state can be derived from the dependence of the intensity of the fluorescence on the energy of the laser pulse. The results of investigations by Müller and Pflüger on cryptocyanine in methanol and glycerol are used to illustrate the principle of the method. An analysis of their data leads to a lifetime for the lowest singlet excited state of about 15 psec and 200 psec for methanol and glycerol, respectively.