Optimization of culture parameters for production of podophyllotoxin in suspension culture of Podophyllum hexandrum

The root explants of the germinated seedlings of Podophyllum hexandrum were grown in MS medium supplemented with indole acetic acid (IAA) (2 mg/L) and activated charcoal (0.5%), and healthy callus culture was obtained after incubation for 3 wk at 20°C. The cultivation of plant cells in shake flask was associated with problems such as clumping of cells and browning of media, which were solved by the addition of pectinase and polyvinylpyrrolidone. The effect of major media components and carbon source was studied on the growth and podophyllotoxin production in suspension culture. It was found that glucose was a better carbon source than sucrose and that NH₄ ⁺:NO₃ ⁻ ratio (total nitrogen concentration of 60 mM) and PO₄ ³⁻ did not have much effect on the growth and product formation. The relative effect of culture parameters (inoculum level, pH, IAA, glucose, NH₄ ⁺:NO₃ ⁻ ratio, and PO₄ ³⁻) on the overall growth and product response of the plant cell suspension culture was further investigated by Plackett-Burman design. This indicated that inoculum level, glucose, IAA, and pH had significant effects on growth and production of podophyllotoxin. To identify the exact optimum concentrations of these parameters on culture growth and podophyllotoxin production, central composite design experiments were formulated. The overall response equations with respect to growth and podophyllotoxin production as a function of these culture parameters were developed and used to determine the optimum concentrations of these parameters, which were pH 6.0, 1.25 mg/L of IAA, 72 g/L of glucose, and inoculum level of 8 g/L.     

Carbon nanotube salts. Arylation of single-wall carbon nanotubes

[reaction: see text] Carbon nanotube salts prepared by treating single-wall carbon nanotubes (SWNTs) with lithium in liquid ammonia react readily with aryl iodides to give SWNTs functionalized by aryl groups.     

A Stochastic Analysis of a Staffing Problem

Consider an organization with several categories of staff, each having a specified number of members. The age of entry into service and the age of retirement are both specified. Withdrawals occur at time-independent rates. Under this set-up, the authors have computed the maximum ages at which promotions should take place, assuming that the staff members continuing at various ages are random. Some illustrative calculations have been carried out.     

Noise Stability of SIS Receivers

There is a strong interest in the submillimeter astronomy community to increase the IF bandwidth of SIS receivers in order to better facilitate broad spectral linewidth and continuum observations of extragalactic sources. However, with an increase in receiver IF bandwidth there is a decrease in the mixer stability. This in turn effects the integration efficiency and quality of the measurement. In order to better understand the noise mechanisms responsible for reducing the receiver stability, we employed a technique first described by D.W. Allan and later elaborated upon by Schieder et al. In this paper we address a variety of factors that degrade the noise stability of SIS receivers. The goal of this exercise is to make recommendations aimed at maximizing SIS receiver stability.     

Propagation of arbitrary initial wave packets in a quantum parametric oscillator: Instability zones for higher order moments

We consider the dynamics of a particle in a parametric oscillator with a view to exploring any quantum feature of the initial wave packet that shows divergent (in time) behaviour for parameter values where the classical motion dynamics of the mean position is bounded. We use Ehrenfest's theorem to explore the dynamics of nth order moment which reduces exactly to a linear non autonomous differential equation of order $n+1$. It is found that while the width and skewness of the packet is unbounded exactly in the zones where the classical motion is unbounded, the kurtosis of an initially non-gaussian wave packet can become infinitely large in certain additional zones. This implies that the shape of the wave packet can change drastically with time in these zones.     

Unlocking the Chain-Walking Process in Gold Catalysis**

The successful realization of gold-catalyzed chain-walking reactions, facilitated by ligand-enabled Au(I)/Au(III) redox catalysis, has been reported for the first time. This breakthrough has led to the development of gold-catalyzed annulation reaction of alkenes with iodoarenes by leveraging the interplay of chain-walking and π-activation reactivity mode. The reaction mechanism has been elucidated through comprehensive experimental and computational studies.     

Au nanoparticles and polyaniline coated resin beads for simultaneous catalytic oxidation of glucose and colorimetric detection of the product

In this letter, we report the synthesis of Au nanoparticles (NPs) and polyaniline (PANI) on the same cation-exchange resin beads and demonstrate their use in catalyzing the oxidation of glucose to gluconic acid by Au NPs and simultaneously in detecting the formation of the acid by the color change of PANI. The synthesis was carried out by exchanging the cations of the resins with HAuCl4 and anilinuium chloride and then reducing the metal ions by NaBH4 to produce Au NPs followed by polymerization of aniline using H2O2. The green emeraldine salt form of PANI thus obtained was treated with NaOH to be converted to blue emeraldine base before use. The deposition of Au NPs was confirmed by a change in color of the bead, visible spectroscopy, X-ray diffraction, and scanning electron microscopic measurements. On the other hand, the presence of PANI was confirmed by Fourier transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopy. The formation of gluconic acid from glucose was confirmed by FTIR spectroscopy. We could detect the presence of glucose of a minimum 1.0 mM concentration in water, using the present method. Our experimental observations demonstrate the possibility of the incorporation of multifunctional components on the surfaces of resins for carrying out a chemical reaction as well as detection of the product.     

Determination of Thermal History by Photoluminescence of Core‐Shelled Quantum Dots Going Through Heating Events

A kind of novel thermal history nanosensors are theoretically designed and experimentally demonstrated to permanently record thermal events. The photoluminescence (PL) spectrum of core‐shelled quantum dots (QDs) CdSe/ZnS irreversibly shifts with heating histories (temperature and duration) of thermal events. The induced PL shift of the QDs CdSe/ZnS is employed to permanently record thermal histories. We further model a kind of thermal history nanosensor based on the thermal‐induced phenomena of core‐shelled QDs to permanently record thermal histories at microscale and demonstrate to reconstruct temperature and duration of heating events simultaneously from PL spectra of the QDs. The physical mechanism of the sensors is discussed.     

Phase diagram, crystal chemistry and thermoelectric properties of compounds in the Ca-Co-Zn-O system

In the Ca-Co-Zn-O system, we have determined the tie-line relationships and the thermoelectric properties, solid solution limits, and structures of two low-dimensional cobaltite series, Ca₃(Co, Zn)₄O_9−z and Ca₃(Co,Zn)₂O_6−z at 885 °C in air. In Ca₃(Co,Zn)₄O_9−z, which has a misfit layered structure, Zn was found to substitute in the Co site to a limit of Ca₃(Co_3.8Zn_0.2)O_9−z. The compound Ca₃(Co,Zn)₂O_6−z (n=1 member of the homologous series, Ca_n+2(Co,Z_n)_n(Co,Zn)′O_3n+3−z) consists of one-dimensional parallel (Co,Zn)₂O₆⁶⁻ chains that are built from successive alternating face-sharing (Co,Zn)O₆ trigonal prisms and ‘n’ units of (Co,Zn)O₆ octahedra along the hexagonal c-axis. Zn substitutes in the Co site of Ca₃Co₂O₆ to a small amount of approximately Ca₃(Co_1.95Zn_0.05)O_6−z. In the ZnO-CoO_z system, Zn substitutes in the tetrahedral Co site of Co₃O₄ to the maximum amount of (Co_2.49Zn_0.51)O_4−z and Co substitutes in the Zn site of ZnO to (Zn_0.94Co_0.06)O. The crystal structures of (Co_2.7Zn_0.3)O_4−z, (Zn_0.94Co_0.06)O, and Ca₃(Co_1.95 Zn_0.05)O_6−z are described. Despite the Ca₃(Co, Zn)₂O_6−z series having reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical resistivity values of its members are too high to achieve high figure of merit, ZT.     

Ternary copper complexes for photocleavage of DNA by red light: direct evidence for sulfur-to-copper charge transfer and d-d band involvement

A new class of ternary copper(II) complexes of formulation [Cu(L(n)B](ClO(4)) (1-4), where HL(n) is a NSO-donor Schiff base (HL(1), HL(2)) and B is a NN-donor heterocyclic base viz. 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmp), are prepared, structurally characterized, and their DNA binding and photocleavage activities studied in the presence of red light. Ternary complex [Cu(L(3))(phen)](ClO(4)) (5) containing an ONO-donor Schiff base and a binary complex [Cu(L(2))(2)] (6) are also prepared and structurally characterized for mechanistic investigations of the DNA cleavage reactions. While 1-4 have a square pyramidal (4 + 1) CuN(3)OS coordination geometry with the Schiff base bonded at the equatorial sites, 5 has a square pyramidal (4 + 1) geometry with CuN(3)O(2) coordination with the alcoholic oxygen at the axial site, and 6 has a square planar trans-CuN(2)O(2) geometry. Binding of the complexes 1-4 to calf thymus DNA shows the relative order: phen > dmp. Mechanistic investigations using distamycin reveal minor groove binding for the complexes. The phen complexes containing the Schiff base with a thiomethyl or thiophenyl moiety show red light induced photocleavage. The dmp complexes are essentially photonuclease inactive. Complexes 5 and 6 are cleavage inactive under similar photolytic conditions. A 10 microM solution of 1 displays a 72% cleavage of SC DNA (0.5 microg) on an exposure of 30 min using a 603 nm Nd:YAG pulsed laser (60 mJ/P) in Tris-HCl buffer (pH 7.2). Significant cleavage of 1 is also observed at 694 nm using a Ruby laser. Complex 1 is cleavage inactive under argon or nitrogen atmosphere. It shows a more enhanced cleavage in pure oxygen than in air. Enhancement of cleavage in D(2)O and inhibition with sodium azide addition indicate the possibility of the formation of singlet oxygen as a reactive intermediate leading to DNA cleavage. The d-d band excitation with red light shows significant enhancement of cleavage yield. The results indicate that the phen ligand is necessary for DNA binding of the complex. Both the sulfur-to-copper charge transfer band and copper d-d band excitations helped the DNA cleavage. While the absorption of a red photon induces a metal d-d transition, excitation at shorter visible wavelengths leads to the sulfur-to-copper charge transfer band excitation at the initial step of photocleavage. The excitation energy is subsequently transferred to ground state oxygen molecules to produce singlet oxygen that cleaves the DNA.