Growth of Cyanobacteria: Optimization for Increased Carbohydrate Content

Growths of Lyngbya limnetica and Oscillatoria obscura were investigated at varying pH, light intensity, temperature, and trace element concentration with a view to optimize these parameters for obtaining the maximum carbohydrate content. The maximum growth for both strains was obtained at pH 9.0 and temperature 20 ± 3 °C using a light intensity of 68.0 μmol m^?2 s^?1 with continuous shaking. Growth under the nitrogen starvation condition affected the carbohydrate content more compared to the phosphorus starvation, and maximum concentrations were found as 0.660 and 0.621 g/g of dry biomass for L. limnetica and O. obscura, respectively. Under the optimized nitrogen-rich conditions, the specific growth rates for the two strains were found to be 0.187 and 0.215 day^?1, respectively. The two-stage growth studies under nitrogen-rich (stage I) followed by nitrogen starvation (stage II) conditions were performed, and maximum biomass and carbohydrate productivity were found as 0.088 and 0.423 g L^?1 day^?1 for L. limnetica. This is the first ever attempt to evaluate and optimize various parameters affecting the growth of cyanobacterial biomass of L. limnetica and O. obscura as well as their carbohydrate contents.     

Biological aspects of Schiff base–metal complexes derived from benzaldehydes: an overview

Schiff bases are stable imines containing C=N, where N is bonded to an alkyl or aryl group, but not with hydrogen and are prepared by condensation of aliphatic or aromatic primary amine with carbonyl compounds. They have the general formula R₁R₂C?=?NR₃, where R₃?≠?H. The presence of the basic donor N atom and the stability of the imine function render Schiff bases as the most favored ligands that have the ability to stabilize metal ions in different oxidation states. The chelating environment in a Schiff base profoundly influences the electron distribution in the coordination sphere of metal in a complex and thereby regulates the property of the compounds in a big way. The structural diversity in some of the metal complexes with multidentate Schiff base ligands has triggered a wide range of applications of this class of compounds in sensors, catalysis, biology, medicines, and photonics. This review compiles the synthesis and biological activities (antimicrobial, antioxidant, anticancer, antitubercular, DNA interaction studies) of benzaldehyde-based Schiff bases and their metal complexes.     

Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods

The self‐assembled structures of atomically precise, ligand‐protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding‐directed self‐assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p‐mercaptobenzoic acid (pMBA)‐protected atomically precise silver nanocluster, Na₄[Ag₄₄(pMBA)₃₀], and pMBA‐functionalized GNRs were used. High‐resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H‐bonding, leading to octahedral symmetry. The use of water‐dispersible gold nanoclusters, Au_≈250(pMBA)_n and Au₁₀₂(pMBA)₄₄, also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles are a new category of precision hybrids with diverse possibilities.     

Fungicidal and bactericidal activity of metal diethyldithiocarbamate fungicides

Copper diethyldithiocarbamate, cadmium diethyldithiocarbamate, lead diethyldithiocarbamate, nickel diethyldithiocarbamate and zinc diethyldithiocarbamate have been synthesized. They have been characterized using TG, DTA, IR spectroscopy, X-ray and atomic absorption spectrophotometry. The thermal conversion of the compounds is 54.36–88% at 1000°C. Their solubility in sodium hydroxide, mineral acids, organic solvents, distilled water and salts solution has been measured. Fungicidal activity of the dithiocarbamates has been tested by well or cup diffusion method using five fungi species. Their activity has also been tested by broth dilution method using six bacterial species. Minimum Inhibitory Concentration (bactericidal) is 6.25–25.00 μg mL⁻¹.     

Growth of anisotropic gold nanostructures on conducting glass surfaces

In this paper, we describe a method for the growth of gold nanowires and nanoplates starting from a bilayer array of gold seeds, anchored on electrically conducting indium tin oxide (ITO) substrates. This is based on a seed-mediated growth approach, where the nanoparticles attached on the substrate through molecular linkages are converted to nanowires and nanoplates at certain cetyltrimethylammonium bromide (CTAB) concentration. Our modified approach can be used to make nanowires of several tens of micrometers length at a lower CTAB concentration of 0.1 M. The length of the nanowires can be varied by adjusting the time of the reaction. As the concentration of CTAB was increased to 0.25 M, the nanoparticles got converted to nanoplates. These Au nanoplates are (111) oriented and are aligned parallel to the substrate.     

Computational studies on biosynthetic carbocation rearrangements leading to sativene, cyclosativene, alpha-ylangene, and beta-ylangene

In this paper, we describe theoretical studies, using gas-phase quantum chemical calculations, on carbocationic rearrangement pathways leading to the sesquiterpenes sativene, cyclosativene, alpha-ylangene, and beta-ylangene. For all four sesquiterpene natural products, viable pathways are presented, and these are compared both to mechanistic proposals found in the literature, and in certain cases to alternative stereochemical and rearrangement possibilities, thus providing a basis for comparison to experimental results. We find that these four sesquiterpenes likely arise from a common bicyclic intermediate and, furthermore, that the computed pathways are mostly in agreement with previous mechanistic proposals, although the few differences that we have uncovered are significant. Additionally, the potential energy profiles of the pathways are found to be very flat, supporting the notion that following the initial ionization of farnesyl diphosphate, minimal enzymatic intervention may be required for the generation of such sesquiterpenes.     

Synthetic Heparanase Inhibitors Can Prevent Herpes Simplex Viral Spread

Herpes simplex virus (HSV-1) employs heparan sulfate (HS) as receptor for cell attachment and entry. During late-stage infection, the virus induces the upregulation of human heparanase (Hpse) to remove cell surface HS allowing viral spread. We hypothesized that inhibition of Hpse will prevent viral release thereby representing a new therapeutic strategy for HSV-1. A range of HS-oligosaccharides was prepared to examine the importance of chain length and 2-O-sulfation of iduronic moieties for Hpse inhibition. It was found that hexa- and octasaccharides potently inhibited the enzyme and that 2-O-sulfation of iduronic acid is tolerated. Computational studies provided a rationale for the observed structure–activity relationship. Treatment of human corneal epithelial cells (HCEs) infected with HSV-1 with the hexa- and octasaccharide blocked viral induced shedding of HS which significantly reduced spread of virions. The compounds also inhibited migration and proliferation of immortalized HCEs thereby providing additional therapeutic properties.     

One-, two-, and three-dimensional superstructures of gold nanorods induced by dimercaptosuccinic acid

A method is described for assembling gold nanorods into one-, two-, and three-dimensional superstructures. The addition of dimercaptosuccinic acid (DMSA) into the nanorod solution was found to induce self-assembly of the latter to one-dimensional "tapelike", two-dimensional "sheetlike" and three-dimensional "superlattice-like" structures depending on the DMSA concentration. The assembly was found to follow a smectic structure, where the nanorod long axes are parallel to each other. The rods are spaced 8.5 +/- 0.3 nm apart in the resulting structures, which extend over several micrometers in length. Organizations perpendicular to the grid were also found. The nanorod tapes were found to bend, and they form circular assemblies as well. The assembly and morphology of the nanorod structures were characterized by transmission electron microscopy and UV-vis spectroscopy. The effect of the DMSA concentration as well as the pH of the medium was also studied. On the basis of several control experiments utilizing similar molecules, charge neutralization of the nanorods by the carboxylic group of DMSA was found to be the principal reason for such an assembly, while the mercapto groups render additional stability to its structure. A mechanistic model of the assembly is proposed. This type of assembly would plausibly function as a plasmonic waveguide in potential nanodevices.     

Robust stability analysis of stochastic neural networks with Markovian jumping parameters and probabilistic time‐varying delays

This article discusses the issue of robust stability analysis for a class of Markovian jumping stochastic neural networks (NNs) with probabilistic time‐varying delays. The jumping parameters are represented as a continuous‐time discrete‐state Markov chain. Using the stochastic stability theory, properties of Brownian motion, the information of probabilistic time‐varying delay, the generalized Ito's formula, and linear matrix inequality (LMI) technique, some novel sufficient conditions are obtained to guarantee the stochastical stability of the given NNs. In particular, the activation functions considered in this article are reasonably general in view of the fact that they may depend on Markovian jump parameters and they are more general than those usual Lipschitz conditions. The main features of this article are described in the following: first one is that, based on generalized Finsler lemma, some improved delay‐dependent stability criteria are established and the second one is that the nonlinear stochastic perturbation acting on the system satisfies a class of Lipschitz linear growth conditions. By resorting to the Lyapunov–Krasovskii stability theory and the stochastic analysis tools, sufficient stability conditions are established using an efficient LMI approach. Finally, two numerical examples and its simulations are given to demonstrate the usefulness and effectiveness of the proposed results. © 2014 Wiley Periodicals, Inc. Complexity 21: 59–72, 2016