Fabrication and structural characterization of the Langmuir–Blodgett films from a new chitosan derivative containing cinnamate chromophores

A new amphiphilic chitosan derivative, octanoylchitosan cinnamate (OCC) was synthesized through regioselective modifications of chitosan. A solution of OCC was spread to water to form a stable monolayer at the air/water interface. The surface pressure (π)–area (A) isotherm indicated that the polymer had a limiting area of about 100 Å² per repeat unit. YZ-type multilayers were deposited onto hydrophobic substrates through Langmuir–Blodgett (LB) technique. The structural features of the LB films were investigated by UV absorption, circular dichroism (CD) and linear dichroism (LD) spectroscopy. The results showed that the intrinsic chirality originating from the helical order of the OCC backbones was maintained in the LB films. Besides, the polymer backbones were uni-axially oriented in the LB film. The ordered structures of OCC assembled in a dilute solution and in a cast film were also investigated and the results were compared with that of the LB film.     

Second‐harmonic generation from Langmuir–Blodgett film of cyclic peptide carrying two disperse red 1 on fused quartz surface

Cyclic octapeptide carrying one or two nonlinear optical chromophores, disperse red 1 (DR‐1), was synthesized and immobilized on a substrate to attain an active surface for second‐harmonic generation (SHG). Each cyclic octapeptide was transferred on a fused quartz substrate by the Langmuir–Blodgett (LB) method to afford a uniform monolayer. Infrared reflection–absorption spectroscopy of the LB monolayer revealed that the cyclic skeleton lay roughly flat on the surface. The SHG intensity from the monolayer of the cyclic peptide with two DR‐1 units was stronger than that from that with one DR‐1 unit. The difference is discussed in terms of molecular orientation and surface density of the active chromophores. The cyclic peptide is shown here to be an effective scaffold to modify a substrate surface with functional groups of a monolayer with taking stability of the monolayer and orientation of the functional group into consideration. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.     

Unbinding free energy of acetylcholinesterase bound oxime drugs along the gorge pathway from metadynamics‐umbrella sampling investigation

Because of the pivotal role that the nerve enzyme, acetylcholinesterase plays in terminating nerve impulses at cholinergic synapses. Its active site, located deep inside a 20 Å gorge, is a vulnerable target of the lethal organophosphorus compounds. Potent reactivators of the intoxicated enzyme are nucleophiles, such as bispyridinium oxime that binds to the peripheral anionic site and the active site of the enzyme through suitable cation–π interactions. Atomic scale molecular dynamics and free energy calculations in explicit water are used to study unbinding pathways of two oxime drugs (Ortho‐7 and Obidoxime) from the gorge of the enzyme. The role of enzyme‐drug cation–π interactions are explored with the metadynamics simulation. The metadynamics discovered potential of mean force (PMF) of the unbinding events is refined by the umbrella sampling (US) corrections. The bidimensional free energy landscape of the metadynamics runs are further subjected to finite temperature string analysis to obtain the transition tube connecting the minima and bottlenecks of the unbinding pathway. The PMF is also obtained from US simulations using the biasing potential constructed from the transition tube and are found to be consistent with the metadynamics‐US corrected results. Although experimental structural data clearly shows analogous coordination of the two drugs inside the gorge in the bound state, the PMF of the drug trafficking along the gorge pathway point, within an equilibrium free energy context, to a multistep process that differs from one another. Routes, milestones and subtlety toward the unbinding pathway of the two oximes at finite temperature are identified. Proteins 2014; 82:1799–1818. © 2014 Wiley Periodicals, Inc.     

Lack of desensitization of muscarinic receptor–mediated second messenger signals in rat brain upon acute and chronic inhibition of acetylcholinesterase

We studied the effects of acute and chronic in vivo inhibition of acetylcholinesterase on both the density and function of brain muscarinic cholinergic receptors. Adult male rats were treated either once or multiple times over a period of 10 days with the irreversible acetylcholinesterase inhibitor diisopropylfluorophosphate (DFP). The concentration and affinity of muscarinic receptors in various brain regions were determined using radioligand binding techniques. Acute DFP treatment resulted in a significant reduction in receptor number only in the brain stem, while chronic treatment caused receptor downregulation in the brain stem, cerebral cortex, and striatum. There was no change in ligand affinity in any of the brain regions. In sharp contrast, muscarinic receptor function was fully preserved, in terms of coupling of the receptors to increased phosphoinositide hydrolysis in the cerebral cortex, hippocampus, and striatum, or inhibition of cyclic AMP formation in the cerebral cortex or striatum. Therefore, there is a marked lack or correlation between DFP-induced muscarinic receptor down-regulation and receptor desensitization.     

Comparative studies on species identification of Noctuoidea moths in two nature reserve conservation zones (Beijing,China) using DNA barcodes and thin‐film biosensor chips

Rapid and accurate identification of species is required for the biological control of pest Noctuoidea moths. DNA barcodes and thin‐film biosensor chips are two molecular approaches that have gained wide attention. Here, we compare these two methods for the identification of a limited number of Noctuoidea moth species. Based on the commonly used mitochondrial gene cytochrome c oxidase I (the standard DNA barcode for animal species), 14 probes were designed and synthesized for 14 species shared by two national nature reserves in Beijing and Hebei, China. Probes ranged in length from 18 to 27 bp and were designed as mismatch probes to guarantee that there were at least three base differences between the probe and nontarget sequences. The results on the chip could be detected by the naked eye without needing special equipment. No cross‐hybridizations were detected although we tested all probes on the 14 target and 24 nontarget Noctuoidea species. The neighbour‐joining tree of the 38 species based on COI sequences gave 38 highly supported independent groups. Both DNA barcoding and thin‐film biosensor chips, based on the COI gene, are able to accurately identify and discriminate the 14 targeted moth species in this study. Because of its speed, high accuracy and low cost, the thin‐film biosensor chip is a very practical means of species identification. Now, a more comprehensive chip will be developed for the identification of additional Noctuoidea moths for pest control and ecological protection.     

Hyposensitivity to the amnesic effects of scopolamine or amyloid β25–35 peptide in heterozygous acetylcholinesterase knockout (AChE) mice

We examined the sensitivity of AChE^+/− mice to the amnesic effects of scopolamine and amyloid β peptide. AChE^+/− and AChE^+/+ littermates, tested at 5–9 weeks of age, failed to show any difference in locomotion, exploration and anxiety in the open-field test, or in-place learning in the water-maze. However, when treated with the muscarinic receptor antagonist scopolamine (0.5, 5 mg/kg s.c.) 20 min before each water-maze training session, learning impairments were observed at both doses in AChE^+/+ mice, but only at the highest dose in AChE^+/− mice. The central injection of Aβ_25–35 peptide (9 nmol) induced learning deficits only in AChE^+/+ but not in AChE^+/− mice. Therefore, the hyper-activity of cholinergic systems in AChE^+/− mice did not result in increased memory abilities, but prevented the deleterious effects of muscarinic blockade or amyloid toxicity.