Triple minima in the free energy of semiflexible polymers

We study the free energy of the worm-like-chain model, in the constant-extension ensemble, as a function of the stiffness lambda for finite chains of length L. We find that the polymer properties obtained in this ensemble are qualitatively different from those obtained using constant-force ensembles. In particular, we find that as we change the stiffness parameter, t=L/lambda, the polymer makes a transition from the flexible to the rigid phase and there is an intermediate regime of parameter values where the free energy has three minima and both phases are stable. This leads to interesting features in the force-extension curves.     

Benzofuroxans in heterocyclic synthesis : Reaction of benzofuroxans with dienamines; synthesis of a novel class of quinoxaline nn'-dioxide enamines

Benzofuroxanes react with dienamines to give a novel class of quinoxaline NN'-dioxide enamines in good yields.     

Dehydration kinetics of an Indian clay

Decomposition of clay from Garo Hills of Meghalaya (India) was studied by dynamic thermogravimetry. A fourteen kinetic equation procedure was applied for analysis of non-isothermal weight change upto a temperature of 1223 K. Two stages of decomposition were clearly distinguised i.e. the initial dehydration period at temperature 373 K to 673 K and the dehydroxylation period in the temperature range 723 K to 1073 K. First order decomposition mechanism was found to be applicable to both dehydration and dehydroxylation steps. Activation energies of 67 kJ/mol and 278 kJ/mol are estimated for the first and second steps with frequency factors of 16.3 s^–1 and 5.16×10⁶s^–1 respectively. The weight loss relating to the steps in TG curves allows determination of the contents of the basic mineral in the clay. Percentages of Al₂O₃.SiO₂ and total volatiles as calculated from weight loss data are in accordance with the results of classical chemical analysis.

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Zusammenfassung Mittels DTG wurde die thermische Zersetung von Ton aus der Garo-Hills-Gegend bei Meghalaya (Indien) untersucht. Zur Analyse der nicht-isothermen Gewichtsveränderungen bis zu einer Temperatur von 1223 K wurde ein Verfahren mit vierzehn kinetischen Gleichungen angewendet. Zwei Teilschritte der Zersetzung können eindeutig unterschieden werden, nämlich die anfängliche Dehydratationsperiode bei Temperaturen von 373 bis 673 K und die Dehydroxylierungsperiode bei Temperaturen zwischen 723 K un 1073 K. Für beide Vorgänge konnte als Reaktionsmechanismus eine Zersetzung erster Ordnung angewendet werden. Für den ersten un zweiten Teilschritt konnten Aktivierungsenergien von 67 kJ/mol bzw. 278 kJ/mol un Frequenzfaktoren von 16.3s^–1 bzw. 5.16×10⁶s^–1 ermittelt werden. Der aus den TG-Kurven hervorgehende Gewichtsverlust läßt auf den Gehalt des Tones an Basismineral schließen. Der prozentuelle Gehalt an Al₂O₃, SiO₂ und der gesamten flüchtigen Bestandteile, berechnet aus den Gewichtsverlusdaten, stimmt mit den Ergebnissen aus herkömmlichen chemischen Analysen überein.

     

Banana pulp extract mediated synthesis of Cu2O nanoparticles: An efficient heterogeneous catalyst for the ipso-hydroxylation of arylboronic acids

A green and facile novel procedure has been developed for the synthesis of Cu₂O nanoparticles within a very short reaction time using banana pulp extract as a reducing agent. The synthesized nanoparticles are well characterized by SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope) and powder XRD (X-ray Diffraction) methods. An environmental benign and highly efficient protocol for the ipso-hydroxylation of aryl and hetero arylboronic acids using bio-fabricated Cu₂O nanoparticles as a catalyst and aqueous H₂O₂ as an oxidant has also been developed. The main advantages of this protocol are the base free reaction condition, reusable and heterogeneous catalytic system, and short reaction time with excellent yields.     

Unexpected cycloadducts from 1,3-dipolar cycloaddition of 3,4-dehydromorpholine N-oxide to N-cinnamoyl piperidines—first report of the novel formation of 2:1 cycloadducts

A series of unexpected cycloadducts along with normal cycloadducts have been isolated from the 1,3-dipolar cycloaddition of 3,4-dehydromorpholine N-oxide to piperidides of cinnamic acid and para-substituted cinnamic acids and these were analyzed by X-ray crystallography to reveal novel solid-state structures. At first, 1:1 cycloadducts were formed which underwent in situ nucleophilic attack by another reduced nitrone moiety. A plausible iminium-oxonium ion mechanism has been proposed.     

Facile synthesis of unusual glycosyl carbamates and amino acid glycosides from propargyl 1,2-orthoesters as glycosyl donors

Propargyl 1,2-O-orthoesters are exploited for the synthesis of 1,2-trans O-glycosides of protected amino acids. N-Fmoc- and N-Cbz protected serine/threonine - benzyl/methyl esters reacted well with glucosyl-, galactosyl-, mannosyl- and lactosyl- derived propargyl 1,2-orthoesters affording respective 1,2-trans glycosides in good yields under AuBr(3)/4 ? MS Powder/CH(2)Cl(2)/rt. t-Boc serine derivative gave serine 1,2-orthoester and glycosyl carbamate. Optimized conditions enabled preparation of new glycosyl carbamates from N-Boc protected amines in a single step using gold catalysts and propargyl 1,2-orthoesters in excellent yields.     

An Excursion-Theoretic Approach to Stability of Discrete-Time Stochastic Hybrid Systems

We address stability of a class of Markovian discrete-time stochastic hybrid systems. This class of systems is characterized by the state-space of the system being partitioned into a safe or target set and its exterior, and the dynamics of the system being different in each domain. We give conditions for L ₁-boundedness of Lyapunov functions based on certain negative drift conditions outside the target set, together with some more minor assumptions. We then apply our results to a wide class of randomly switched systems (or iterated function systems), for which we give conditions for global asymptotic stability almost surely and in L ₁. The systems need not be time-homogeneous, and our results apply to certain systems for which functional-analytic or martingale-based estimates are difficult or impossible to get.     

Asymmetric stochastic localization in geometry controlled kinetics

We consider the motion of Brownian particles confined in a two-dimensional symmetric bilobal enclosure with uneven cross section. Varying cross section of the confinement results in an effective entropic potential in reduced dimension. By employing two external noise forces, one additive and another multiplicative along x direction, we demonstrate that a correlation between them causes a symmetry breaking of entropic stability, i.e., a difference in relative stability of two lobes. This leads to an asymmetric localization of population in the stationary state. A two-state model is proposed to explain the asymmetric localization of population due to entropic diffusion.