Cyanobacteria as Natural Therapeutics and Pharmaceutical Potential: Role in Antitumor Activity and as Nanovectors

Cyanobacteria (blue-green microalgae) are ubiquitous, Gram-negative photoautotrophic prokaryotes. They are considered as one of the most efficient sources of bioactive secondary metabolites. More than 50% of cyanobacteria are cultivated on commercial platforms to extract bioactive compounds, which have bene shown to possess anticancer activity. The chemically diverse natural compounds or their analogues induce cytotoxicity and potentially kill a variety of cancer cells via the induction of apoptosis, or altering the activation of cell signaling, involving especially the protein kinase-C family members, cell cycle arrest, mitochondrial dysfunctions and oxidative damage. These therapeutic properties enable their use in the pharma and healthcare sectors for the betterment of future generations. This review provides a baseline overview of the anti-cancerous cyanobacterial bioactive compounds, along with recently introduced nanomaterials that could be used for the development of new anticancer drugs to build a healthy future for mankind.     

Positron annihilation spectroscopic studies of Mn substitution-induced cubic to tetragonal transformation in ZnFe2–xMnxO4 (x = 0.0–2.0) spinel nanocrystallites

The replacement of cations at the B-sites in the spinel ferrite ZnFe₂O₄ by Mn³⁺ ions brings in several interesting changes, the most striking among them being a transformation from the spinel cubic structure to a body-centered tetragonal one. Concomitantly, there are variations in the nanocrystallite sizes and also in the lattice parameters. These are examined through high-precision X-ray diffraction measurements and transmission electron microscopic analysis. A more interesting aspect is the success of positron annihilation spectroscopy comprising of the measurements of positron lifetime and coincidence Doppler broadening measurements in understanding the effects of cation replacement and the resultant generation of vacancy-type defects. There are definite changes in the positron lifetimes and intensities which show positron trapping in trivacancy-type defect clusters and the nanocrystallite surfaces. The presence of ortho-positronium atoms within the extended intercrystallite region is also identified, although in small concentrations. The cubic to tetragonal transformation is indicated through definite decrease in the values of the positron lifetimes. We also performed a model analysis to predict the expected effect of substitution on the positron lifetime in the bulk of the sample and the experimentally obtained positron lifetimes significantly differed, indirectly hinting at the possibility of a structural transformation. Finally, Mössbauer spectroscopic studies have indicated a ferromagnetic nature for one of the samples, i.e. the one with Mn³⁺ doping concentration x = 0.4, which incidentally had the lowest crystallite size ~10 nm.     

Ion-exchange studies on poly-o-anisidine Sn(IV) phosphate nano composite and its application as Cd(II) ion-selective membrane electrode

An organic-inorganic composite, poly-o-anisidine Sn(IV) phosphate, was chemically synthesized by mixing ortho-anisidine into gels of Sn(IV) phosphate with different mixing volume ratios. Studies on the effect of eluant concentration, elution behavior and separation of metal ions were carried out to understand the ion-exchange capabilities. Due to Cd(II) selective nature of composite, revealed by distribution studies, Cd(II) ion selective membrane electrode was fabricated. The analytical utility of the electrode was established by employing it as an indicator electrode in electrometric titrations having fast response time, 3–5s, and long life span of six months. Some physical parameters like self-diffusion coefficient (D₀), activation energy (E_a) and entropy of activation (ΔS₀) have been evaluated under conditions favoring a particle diffusion-controlled mechanism by studying ion-exchange kinetics.      

Renewable resource‐based poly (m‐phenylenevinylene)s and their statistical copolymers: Synthesis,characterization, and probing of molecular aggregation and Forster energy transfer processes

We report a novel poly (m‐phenylenevinylene)s and their copolymers based on renewable resource starting material 3‐pentadecylphenol to trace the Forster energy transfer process and molecular aggregation in the π‐conjugated polymers. The new bisylide monomer was polymerized with bisaldehyde (or benzaldehyde) under Wittig‐Horner reaction conditions to prepare poly [(4‐methoxy‐6‐pentadecyl‐1, 3‐phenylenevinylene)‐alt‐(1, 3‐phenylenevinylene)] (m‐PPV) and its para‐counterpart poly [(4‐methoxy‐6‐pentadecyl‐1, 3‐phenylenevinylene)‐alt‐(1, 4‐phenylenevinylene)] (p‐PPV) and oligo‐phenylenevinylene model compound 4‐methoxy‐6‐pentadecyl‐1, 3‐distyrylbenzene (OPV). A series of with m‐ or p‐conjugated segments were also prepared by varying the m‐ and p‐content from 0 to 100% in the feed. The selective excitation of m‐conjugated segments in the copolymer by 310 nm light showed emission properties of pure p‐conjugated segments indicating the efficient Forster energy transfer process in segmented copolymers. Both solution quantum yields and the emission intensities increase up to 75% of para‐content in the copolymers. In the solid state, the increase in the p‐incorporation in the copolymer decreases the photoluminescent intensity almost by four times as compared to that of pure meta‐substituted PPV. The excitation spectra of the polymers confirmed a new peak at 400 nm corresponding to the aggregated polymer chains in the film, which is absent in the solution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3241–3256, 2008     

Characterization of aging-induced microstructural changes in M250 maraging steel using magnetic parameters

The best combinations of mechanical properties (yield stress and fracture toughness) of M250 maraging steel is obtained through short-term thermal aging (3–10 h) at 755 K. This is attributed to the microstructure containing precipitation of intermetallic phases in austenite-free low-carbon martensite matrix. Over-aged microstructure, containing reverted austenite degrades the mechanical properties drastically. Hence, it necessitates identification of a suitable non-destructive evaluation (NDE) technique for detecting any reverted austenite unambiguously during aging. The influence of aging on microstructure, room temperature hardness and non-destructive magnetic parameters such as coercivity (H_c), saturation magnetization (M_s) and magnetic Barkhausen emission (MBE) RMS peak voltage is studied in order to derive correlations between these parameters in aged M250 maraging steel. Hardness was found to increase with precipitation of intermetallics during initial aging and decrease at longer durations due to austenite reversion. Among the different magnetic parameters studied, MBE RMS peak voltage was found to be very sensitive to austenite reversion (non-magnetic phase) as they decreased drastically up on initiation of austenite reversion. Hence, this parameter can be effectively utilized to detect and quantify the reverted austenite in maraging steel specimen. The present study clearly indicates that the combination of MBE RMS peak voltage and hardness can be used for unambiguous characterization of microstructural features of technological and practical importance (3–10 h of aging duration at 755 K) in M250 grade maraging steel.     

Two-dimensional angular optical scattering patterns of microdroplets in the mid infrared with strong and weak absorption

Two-dimensional angular optical scattering (TAOS) patterns of droplets composed of a mixture of H2O and D2O are detected in the mid infrared. First, a lens is used in the Abbé sine condition to collect a small solid angle of light, where the scattering pattern matches well numerical simulations based on Mie theory. Next, TAOS patterns from droplets spanning a large (approximately 27pi sr) solid angle are captured simultaneously at two wavelengths. The effects of absorption are evident in the patterns and are discernible without the need for curve matching by Mie theory.     

Asymmetric synthesis of an enantiomerically pure rivastigmine intermediate using ketoreductase

A novel chemo-enzymatic synthesis of (S)-rivastigmine using ketoreductases with NADH/NADPH as the proton donor has been demonstrated. An exclusive enzymatic process has been developed by exploring the possible ketoreductases by screening to identify enzymes useful for the preparation of the (S)-isomer intermediate, and scaling up of the enzymatic process for the production of an adequate, enantiomerically pure precursor of rivastigmine and for the total synthesis of (S)-rivastigmine.     

Inhomogeneous diophantine approximation with prime constraints

We study the problem of inhomogeneous diophantine approximation under certain primality restrictions.