"Uncorking" of liposomes by matrix metalloproteinase-9

A triggered release methodology of liposomal contents via the enzyme MMP-9 is described.     

Electronic charge transport through ZnO nanoribbons

I–V characteristics of ZnO nanoribbons (NRs) have been investigated using density functional theory coupled to non-equilibrium Green’s Function. The current through the NRs drops with the increasing NR width, leveling off to 1.66 and 0.42 µA in zig-zag and arm-chair NRs respectively for widths ~20 Å at 3 V of electrical bias. The transconductance as well as the current flowing through the arm-chair NRs decays exponentially with NR width for both odd and even number of dimer lines traversed. The current through the zig-zag NRs falls off exponentially with NR width, being insensitive to the odd or even numbers of zig-zag lines appearing along the normal to the charge transport direction.     

Conformational dependence of tag induced intramolecular STM contrast in hexaphenylbenzene molecules

Chemically tagged hexaphenylbenzene molecules physisorbed on Au(1 1 1) surface display their tag differently under STM as compared to their physisorption on a Cu(1 1 1) surface. Our STM findings complemented by First Principles and Quantum Chemistry calculations have attributed this difference to two different conformations adopted by these molecules on Au(1 1 1) in comparison to its one conformation on Cu(1 1 1). The demonstration of the sensitivity of the tag to its electronic or chemical environment would have important implications in designing single molecule machinery where the motion of the molecule is to be discerned by tracking its tag induced intramolecular STM contrast.     

Ability of DFT to evaluate the torsional barriers in neutral and CO* protonated aromatic carbonyl compounds

Before the recent development of new functionals, the Density Functional Theory (DFT) was considered as a failing quantum chemical method in accurately computing the rotational barrier height of the gaseous benzaldehyde. Since the 2004 polemical Speakman's paper about the accuracy of microwave value of this quantity [L. D. Speakman, B. N. Papas, H. L. Woodcock, H. F. Schaefer, J. Chem. Phys. 2004, 120, 4247], the question is still relevant. This paper aims to display the ability of the DFT to evaluate the torsional barriers of a series of para‐substituted benzaldehydes in solution. The method is also tested in computing barriers of other solvated aromatic carbonyl compounds (in both neutral and carbonyl protonated forms) for which accurate experimental data are available. Computations have been carried out at two DFT methods using the popular hybrid generalized‐gradient‐approximation (GGA) density functional B3LYP and the global hybrid meta‐GGA Minnesota functional M06‐2X with a 6‐311++g (2d,2p) basis set. Solvent effects investigations were undertaken within the framework of the polarisable continuum model solvation approach. It has been concluded that the used computational methods are very satisfactory in predicting barriers of para‐substituted benzaldehydes in the liquid phase and less satisfactory for their CO*‐protonated forms. M06‐2X functional particularly leads to full agreement. For para‐substituted acetophenones, good agreement with experiment is observed only with M06‐2X applied to the CO*‐protonated forms. The present investigations have allowed to demonstrate that the Density Functional Theory does not constantly fail in accurately computing the rotational barrier heights of aromatic carbonyl compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

Self‐Consistent Theory of Structures and Transitions in Weak Polyampholytes

Weak polyampholytes are charged polymers, where the charge asymmetry can be tuned by varying the solution pH. We determine the size of a randomly charged weak polyampholyte in dilute solution as a function of charge asymmetry, Bjerrum length, salt concentration, pH, and degree of polymerization, using a self‐consistent method. It is known that in the limiting cases of low and high charge asymmetries, polyampholytes behave as neutral polyampholytes and polyelectrolytes, respectively. We explore in detail the regime of intermediate charge asymmetry where a polyampholyte show non‐monotonic change in the chain size as a function of Bjerrum length. A hierarchy of structures exists at different length scales, ranging from ideal coils at low Bjerrum length, extended rod‐like state at intermediate Bjerrum length to globular states at high Bjerrum length. The transition between ideal coil and rod‐like states is continuous, while that between rod‐like and globular states is discontinuous. The addition of salt changes the nature of the rod‐to‐globule transition from discontinuous to continuous. The effective free energy shows a double minimum at intermediate charge asymmetry, indicating the coexistence of globules and extended states. The size as a function of the solution pH shows a minimum at the isoelectric point. The size of neutral polyampholytes at the isoelectric pH increases with the increase in the salt concentration. The size of charge excess polyampholytes far away from the isoelectric pH decreases with the increase in the salt concentration.

     

First-principles study on the origin of ferromagnetism in n-type Cu-doped ZnO

Based on the density functional calculations with the GGA+U correction, we elucidate the origin of the experimentally reported ferromagnetism in n-type Cu-doped ZnO. Pure Cu-doped ZnO shows the unoccupied 3d states in the gap introduced by Cu, resulting in the insulating ground state and weak magnetic exchange interactions, in contrast to the half-metallic ground state and high ferromagnetic stability predicted by the calculations without U correction. However, the electron traps induced by Cu in n-type Cu-doped ZnO may lead to the partial occupancy of the Cu gap states, which stabilize the ferromagnetic ordering between two Cu atoms.     

Lipase-Catalyzed Condensation Reaction of 4-Nitrobenzaldehyde with Acetyl Acetone in Aqueous–Organic Cosolvent Mixtures and in Nearly Anhydrous Media

The nature of the product(s) in lipase-catalyzed reaction of acetyl acetone with 4-nitrobenzaldehyde was found to depend upon the source of lipase and the reaction medium. Mucor javanicus lipase was found to give 70% aldol with 80% enantiomeric excess in anhydrous t-amyl alcohol. A 2:2 adduct was formed by the dimerization of the aldol along with an unsaturated cyclic ether as the side products in varying proportions depending upon the reaction medium and the lipase used.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Synthesis of β‐Arylacyl/β‐Heteroarylacyl‐β‐alkylidene Malonates and Their Application in Substituted Pyridone Synthesis

A novel approach has been developed for the synthesis of β‐arylacyl/β‐heteroarylacyl‐β‐alkylidine malonates in moderate to good yields by the reaction of Stork aryl and heteroaryl enamine with β‐chloroalkylidene malonates. The reaction involves conjugate (Michael) addition of Stork enamine on β‐chloroalkylidene malonates and elimination of chloride ion. These Michael adducts were utilized as intermediates for the synthesis of highly substituted 1,4‐dialkyl‐2‐oxo‐6‐aryl/hetreoaryl‐1,2‐dihydro‐pyridine‐3‐carboxylic acid ethyl esters via 5 + 1 ring annulation protocol.     

Secretory Phospholipase A2 in Dromedary Tears: a Host Defense Against Staphylococci and Other Gram-Positive Bacteria

The best known physiologic function of secreted phospholipase A₂ (sPLA₂) group IIA (sPLA₂-IIA) is defense against bacterial infection through hydrolytic degradation of bacterial membrane phospholipids. In fact, sPLA₂-IIA effectively kills Gram-positive bacteria and to a lesser extent Gram-negative bacteria and is considered a major component of the eye’s innate immune defense system. The antibacterial properties of sPLA₂ have been demonstrated in rabbit and human tears. In this report, we have analyzed the bactericidal activity of dromedary tears and the subsequently purified sPLA₂ on several Gram-positive bacteria. Our results showed that the sPLA₂ displays a potent bactericidal activity against all the tested bacteria particularly against the Staphylococcus strains when tested in the ionic environment of tears. There is a synergic action of the sPLA₂ with lysozyme when added to the bacteria culture prior to sPLA₂. Interestingly, lysozyme purified from dromedary tears showed a significant bactericidal activity against Listeria monocytogene and Staphylococcus epidermidis, whereas the one purified from human tears displayed no activity against these two strains. We have also demonstrated that Ca²⁺ is crucial for the activity of dromedary tear sPLA₂ and to a less extent Mg²⁺ ions. Given the presence of sPLA₂ in tears and intestinal secretions, this enzyme may play a substantial role in innate mucosal and systemic bactericidal defenses against Gram-positive bacteria.