Head-group size or hydrophilicity of surfactants: the major regulator of lipase activity in cationic water-in-oil microemulsions

To determine the crucial role of surfactant head-group size in micellar enzymology, the activity of Chromobacterium Viscosum (CV) lipase was estimated in cationic water-in-oil (w/o) microemulsions of three different series of surfactants with varied head-group size and hydrophilicity. The different series were prepared by subsequent replacement of three methyl groups of cetyltrimethylammonium bromide (CTAB) with hydroxyethyl (1-3, series I), methoxyethyl (4-6, series II), and n-propyl (7-9, series III) groups. The hydrophilicity at the polar head was gradually reduced from series I to series III. Interestingly, the lipase activity was found to be markedly higher for series II surfactants relative to their more hydrophilic analogues in series I. Moreover, the activity remained almost comparable for complementary analogues of both series I and III, though the hydrophilicity was drastically different. Noticeably, the head-group area per surfactant is almost similar for comparable surfactants of both series I and III, but distinctly higher in case of series II surfactants. Thus the lipase activity was largely regulated by the surfactant head-group size, which plays the dominant role over the hydrophilicity. The increase in head-group size presumably allows the enzyme to attain a flexible conformation as well as increase in the local concentration of enzyme and substrate, leading to the higher efficiency of lipase. The lipase showed its best activity in the microemulsion of 6 probably because of its highest head-group size. Furthermore, the observed activity in 6 is 2-3-fold and 8-fold higher than sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) and CTAB-based microemulsions, respectively, and in fact highest ever in any w/o microemulsions.     

Carbon-13 NMR spectra of kauranoid diterpenes

Carbon-13 NMR spectra of a number of (?)-ent-kauranoids have been studied. An unambiguous selfconsistent assignment of resonances has been made by considering the changes in chemical shifts produced by the change of substituent(s).     

Optical absorption and luminescence of n-irradiated Kbr

About ten minutes after reactor pneumatic tube irradiation (10–50 sec) of KBr samples, optical absorption and luminescence were studied during heating-cooling cycles. The induced radioactivity acting as an internal source of irradiation is found to play a dominant role and is responsible for some anomalous results.     

Ferromagnetic resonance in strained and strain-free single crystal nickel films

Ferromagnetic resonance measurements have been used to study the basic magnetic properties of nickel including the ratios of the magneto-striction coefficients (h₃/h₁ and h₄/h₁) over the temperature range 293°K to 132°K. A thermal cycling effect has been observed in the strained samples but not in the strain-free films.     

Carbon-13 NMR spectroscopy of some pentacyclic triterpenoids

Carbon-13 NMR signal assignment of a number of polyoxygenated triterpenes of the olean-12-ene and urs-12-ene series, carried out by considering the changes in chemical shift produced by the change of oxygenation pattern(s), and using methyl oleanolate as a model, are reported.     

Nonequilibrium quantum criticality in open electronic systems

A theory is presented of quantum criticality in open (coupled to reservoirs) itinerant-electron magnets, with nonequilibrium drive provided by current flow across the system. Both departures from equilibrium at conventional (equilibrium) quantum critical points and the physics of phase transitions induced by the nonequilibrium drive are treated. Nonequilibrium-induced phase transitions are found to have the same leading critical behavior as conventional thermal phase transitions.     

Identifiability issues in dynamic stress–strength modeling

In many real-life scenarios, system reliability depends on dynamic stress–strength interference, where strength degrades and stress accumulates concurrently over time. In some other cases, shocks appear at random time points, causing damage which is only effective at the instant of shock arrival. In this paper, we consider the identifiability problem of a system under deterministic strength degradation and stochastic damage due to shocks arriving according to a homogeneous Poisson process. We provide conditions under which the models are identifiable with respect to lifetime data only. We also consider current status data and suggest to collect additional information and discuss the issues of model identifiability under different data configurations.