Direct evidence for CH···π interaction mediated stabilization of Pro-cisPro bond in peptides with Pro-Pro-aromatic motifs

Although weak interactions play subtle but important roles in dictating protein structures, their experimental detection is nontrivial. From NOE experiments we provide direct evidence for the presence of CH···π interaction, operational between the C(α)-H of the first Pro and the aromatic (Aro) side chain of Xaa, in a peptide series with the general sequence Ac-Pro-Pro-Xaa-NH(2). Indirect evidence of CH···π interaction is provided from ring current-induced upfield displacement of Pro(1) C(α)-H chemical shifts and restriction of side-chain (χ1) rotation of Xaa. A consequence of this interaction is the enhanced stability of the Pro-cisPro conformer in Ac-Pro-Pro-Xaa-NH(2) when Xaa is aromatic. The free energies associated with trans to cis transformation of the Pro-Pro moiety are 0.35, 0.59, 0.64, and 0.82 kcal/mol when Xaa is Tyr, Trp, Phe, and His (pH of 8.4), respectively. In comparison, the corresponding free energy is ～1.55 kcal/mol when Xaa is nonaromatic. The observed population of Pro-cisPro-His and the pH-induced perturbation of electron density of the His side chain were correlated, providing further evidence for a direct role of CH···π interaction in modulating the stability of Pro-cisPro population in Ac-Pro-Pro-Aro-NH(2). Our study establishes Pro-Pro-Aro to be a new sequence motif that can stabilize Pro-cisPro peptide bonds. This study not only identifies a new structurally biased sequence motif but also directly demonstrates the role played by CH···π interactions in subtly altering conformational preferences of three-residue peptide sequences with implications on the role played by cis-peptide bonds in unfolded proteins.     

Determination of the orientational order parameter of the homologous series of 4-cyanophenyl 4-alkylbenzoate (n.CN) by different methods

The orientational order parameters of a homologous series of 4-cyanophenyl 4-alkylbenzoates have been determined at different temperatures from (13)C-NMR, x-ray diffraction, optical birefringence, high resolution density and diamagnetic susceptibility anisotropy measurements. To determine the temperature dependence of the orientational order parameter from the (13)C chemical shift values, the two-dimensional polarization inversion spin exchange at the magic angle (PISEMA) method was also used for the measurement of (13)C-(1)H dipolar couplings at different sites in the oriented phase. The nematic order parameters determined from each of these methods have been compared. Apart from a slight shift in their values their trends with temperature are very similar. The differences among the results obtained by these five different methods have been discussed. From the high resolution density data, the values of the critical exponents near the T(N-I) transition are found to lie between the Ising model and tricritical behaviour.     

Switchgrass PviCAD1: Understanding Residues Important for Substrate Preferences and Activity

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the final step in monolignol biosynthesis. Although plants contain numerous genes coding for CADs, only one or two CADs appear to have a primary physiological role in lignin biosynthesis. Much of this distinction appears to reside in a few key residues that permit reasonable catalytic rates on monolignal substrates. Here, several mutant proteins were generated using switchgrass wild type (WT) PviCAD1 as a template to understand the role of some of these key residues, including a proton shuttling HL duo in the active site. Mutated proteins displayed lowered or limited activity on cinnamylaldehydes and exhibited altered kinetic properties compared to the WT enzyme, suggesting that key residues important for efficient catalysis had been identified. We have also shown that a sorghum ortholog containing EW, instead of HL in its active site, displayed negligible activity against monolignals. These results indicate that lignifying CADs require a specific set of key residues for efficient activity against monolignals.     

Study of participant-spectator matter,thermalization and other related phenomena for neutron-rich colliding pair

We study the participant-spectator matter, density and temperature reached in heavy-ion reactions of neutron-rich systems having N/Z ratio varying from 1.0 to 2.0 at 50 and 250MeV/nucleon. Our results show a weak dependence of these quantities on the neutron content of the colliding systems. We also shed light on the role of neutron content on the thermalization achieved in a reaction.     

Dielectric and magnetic properties of Bi1−xYxFeO3 ceramics

Y doped BiFeO₃ polycrystalline ceramics were prepared by sol–gel method. Crystal structure examined by X-ray diffraction indicates that the samples were single-phase and crystallize in rhombohedral structure. An anomaly in the dielectric constant and dielectric loss in the vicinity of the antiferromagnetic Neel temperature (T_N) was observed. Saturated magnetization loops were observed for all sample with saturated magnetization M_s=0.678 emu/g and remnant magnetization M_r=0.084 emu/g for x=0.3.     

Synthesis,Characterization, and Biological Evaluation of 10H‐Phenothiazines,Their Sulfones and Ribofuranosides

10H‐phenothiazines are synthesized via Smiles rearrangement. These prepared phenothiazines act as a base to prepare ribofuranosides by treating them with b‐D ‐ribofuranosyl‐1‐acetate‐2,3,5‐tribenzoate. 10H‐phenothiazines on refluxing with hydrogen peroxide in glacial acetic acid gave 10H‐phenothiazine‐5,5‐dioxides. The synthesized compounds were evaluated for their antioxidative properties through in vitro studies, and they are also screened for their antimicrobial activity. The structure of the synthesized compounds has been established by elemental analysis and spectroscopic data.     

Bilinear Fourier Restriction Theorems

We provide a general scheme for proving L ^p estimates for certain bilinear Fourier restrictions outside the local L ² setting. As an application, we show how such estimates follow for the lacunary polygon. In contrast with prior approaches, our argument avoids any use of the Rubio de Francia Littlewood?CPaley inequality.     

A projection method for phase field models in micromagnetics

Magnetic materials have been finding increasingly wider areas of application in industry and therefore, as indicated by the reviews [1], [2] and [3], there is an increased interest in the efficient modeling of such materials that have an inherent coupling between the magnetic and mechanical characteristics. A particular challenge in the modeling of such materials is the algorithmic preservation of the geometric constraint on the magnetization field, that remains constant in magnitude [4]. In earlier works, [5] and [6], we presented a phase field model within a geometrically exact incremental variational framework where the geometric property of the magnetization director is exactly preserved pointwise by nonlinear rotational updates at the nodes. In the current work however, we present an alternative approach that involves an operator split along with a projection step for the magnetization vector. This method provides significant advantages in terms of speed and ease of implementation at the cost of the maximum time step size used. The current work therefore presents comparative study of the the two methods. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase-conjugation in two-level atoms: comparison of quantum interference theory to exact results

The analytically derived predictions of a recently developed theory on phase conjugate four wave mixing (FWM) in two-level atoms [Phys. Rev. A 60, 1672 (1999)], which interprets many of the signal features as a consequence of quantum interference between the probability amplitudes for photon emission from relevant dressed states, is compared to the results that one obtains from a non-perturbative, numerical calculation of the density matrix equations. The results delineate the regimes and assumptions under which the perturbative results are valid, and it is shown that despite the simplifying assumptions that are invoked for the dressed state theory, many of its predictions are in qualitative agreement with the exact, numerical results.     

Macroporous oxide materials with three-dimensionally interconnected pores

Ordered mesoscale hollow spheres (1000 nm diameter) of binary oxides such as TiO₂ and ZrO₂ as well as of ternary oxides such as ferroelectric PbTiO₃ and Pb(ZrTi)O₃ have been prepared by templating against colloidal crystals of polystyrene, by adopting different procedures.