α/γ(4)-Hybrid peptide helices: synthesis, crystal conformations and analogy with the α-helix

Synthesis, crystal conformations of α/γ(4)-hybrid peptide helices containing proteinogenic amino acid side-chains, and the analogy with the α-helix are reported. Results suggest that α/γ(4)-hybrid peptides adopted helical conformations with 12-membered H-bond pseudocycles in single crystals.     

Experimental and computational insights into the stabilization of low-valent main group elements using crown ethers and related ligands

A series of tin(II) triflate and chloride salts in which the cations are complexed by either cyclic or acyclic polyether ligands and which have well-characterized single-crystal X-ray structures are investigated using a variety of experimental and computational techniques. M?ssbauer spectroscopy illustrates that the triflate salts tend to have valence electrons with higher s-character, and solid-state NMR spectroscopy reveals marked differences between superficially similar triflate and chloride salts. Cyclic voltammetry investigations of the triflate salts corroborate the results of the M?ssbauer and NMR spectroscopy and reveal substantial steric and electronic effects for the different polyether ligands. MP2 and DFT calculations provide insight into the effects of ligands and substituents on the stability and reactivity of the low-valent metal atom. Overall, the investigations reveal the existence of more substantial binding between tin and chlorine in comparison to the triflate substituent and provide a rationale for the considerably increased reactivity of the chloride salts.     

Perturbation of phospholipid bilayer properties by ethanol at a high concentration

Atomistic molecular dynamics (MD) simulations have been carried out at 30 degrees C on a fully hydrated liquid crystalline lamellar phase of dimyrystoylphosphatidylcholine (DMPC) lipid bilayer with embedded ethanol molecules at 1:1 composition, as well as on the pure bilayer phase. The ethanol molecules are found to exhibit a preference to occupy regions near the upper part of the lipid acyl chains and the phosphocholine headgroups. The calculations revealed that the phosphocholine headgroup dipoles (P- --> N+) of the lipids prefer to orient more toward the aqueous layer in the presence of ethanol. It is noticed that the ethanol molecules modify the dynamic properties of both lipids as well as the water molecules in the hydration layer of the lipid headgroups. Both the in-plane "rattling" and out-of-plane "protrusion" motions of the lipids have been found to increase in the presence of ethanol. Most importantly, it is observed that the water molecules within the hydration layer of the lipid headgroups exhibit faster translational and rotational motions in the presence of ethanol. This arises due to faster dynamics of hydrogen bonds between lipid headgroups and water in the presence of ethanol.     

Saradaferin, a new sesquiterpenoid coumarin from Ferula assafoetida

Phytochemical investigation of the gum resin of Ferula assafoetida resulted in the isolation and characterization of a new sesquiterpenoid coumarin, Saradaferin (1) named as [Decahydro-(3-alpha-hydroxy-4,4,10-trimethyl-8-methylene-9-naphthenyl)-alpha-hydroxymethyl] ether of umbelliferone.     

Coupling between hydration layer dynamics and unfolding kinetics of HP-36

We have performed atomistic molecular dynamics simulations of aqueous solutions of HP-36 at 300 K in its native state, as well as at high temperatures to explore the unfolding dynamics of the protein and its correlation with the motion of water around it. On increasing the temperature a partially unfolded molten globule state is formed where the smallest alpha helix (helix 2) unfolds into a coil. It is observed that the unfolding is initiated around the residue Phe-18 which shows a sharp displacement during unfolding. We have noticed that the unfolding of the protein affects the density of water near the protein surface. Besides, the dynamics of water in the protein hydration layer has been found to be strongly correlated with the time evolution of the unfolding process. We have introduced and calculated a displacement time correlation function to monitor the change in water motion relative to the protein backbone during unfolding. We find that the unfolding of helix 2 is associated with an increase in mobility of water around it as compared to water around the other two helices. We have also explored the microscopic aspects of secondary structure specific and site specific solvation dynamics of the protein. The calculations reveal that unfolding influences the solvation dynamics of the protein molecule in a heterogeneous manner depending on the location of the polar probe residues. This seems to be in agreement with recent experimental findings.     

Synthesis of 1,4-cyclohexadiene-based acetylenic macrocycles with Cadiot-Chodkiewicz coupling. Structure of a tub-shaped tetrameric container

The Cadiot-Chodkiewicz coupling of cis-1,4-diethynyl-1,4-dimethoxycyclohexa-2,5-diene and the corresponding ethynyl bromide gave a mixture of acetyenic macrocycles ranging from dimer to octamer in good isolable yields. The trimeric and tetrameric macrocycles have been structurally characterized by single-crystal X-ray crystallography. In the crystal structure of the trimeric macrocycle a molecule of benzene is sandwiched between a pair of macrocyles. The tetrameric macrocycle exhibited a tub-shaped conformation and encapsulated a molecule of ethyl acetate inside the tub.     

Cationic Crown Ether Complexes of Germanium(II)

Fit for a king : Cationic complexes of Ge^II can be prepared by using crown ethers to stabilize and protect the germanium center. Three different crown ethers were employed: [12]crown‐4 (see structure, Ge teal, O red, C gray), [15]crown‐5, and [18]crown‐6. The structures of the cationic complexes depend on the cavity size of the crown ether and on the substituent on germanium.

     

Nanomechanical properties inside the scratch grooves of soda–lime–silica glass

Zn_2?2x Mn_2x GeO₄ (x=0, 0.001, 0.01) phosphors were prepared by conventional solid state reaction technique. X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), diffuse reflection spectra, photoluminescence (PL), and cathodoluminescence (CL) spectroscopy were utilized to characterize the synthesized phosphors. The Mn²⁺-activated Zn₂GeO₄ phosphors exhibit narrow emission band at 532 nm under the excitation of ultraviolet light, which due to the ⁴T₁(⁴G)–⁶A₁(⁶S) transition of Mn²⁺ ions. Also it is observed that there exists energy transfer between the Zn₂GeO₄ host lattice and the activator (Mn²⁺). Under excitation of low-voltage electron beams, Zn₂GeO₄:Mn²⁺ shows strong green emission band dominating at 535 nm, corresponding to the ⁴T₁(⁴G)–⁶A₁(⁶S) emission of Mn²⁺ ions. The emission intensity and chromaticity coordinates of Zn₂GeO₄:Mn²⁺ as a function of accelerating voltage and the filament current were also investigated.     

Visible-light-switchable Chalcone-Flavylium Photochromic Systems in Aqueous Media

The chalcone-flavylium photochromic system switches in aqueous media. However, the chalcone→flavylium conversion requires detrimental ultra-violet (UV) light for the switching which deters their applications in the biological domain. To address this issue, we have synthesized strategically modified chalcone scaffolds that can be reversibly switched to the flavylium forms with visible light ranging from 456 nm (blue) to 640 nm (red).