An experimental study of a radial wall jet formed by the normal impingement of a round synthetic jet

The flow field of a radial wall jet created by the impingement of a round synthetic jet normal to a flat surface was characterized using hot-wire anemometry. In the synthetic wall jets the width of the outer layer was observed to increase linearly with the radial distance along the wall, while the local maximum velocity varied inversely. The synthetic wall jet exhibits self-similar behavior as distinguished by the collapse of the mean and rms velocity profiles when normalized by the outer layer scaling variables. Increasing the actuator driving amplitude at a fixed frequency (i) increased the growth rate of the outer layer, and (ii) decreased the decay rate of the local velocity maximum. The flow field of the synthetic wall jet was dominated by vortical structures associated with the actuator driving frequency, and harmonics connected with the interaction of the produced vortex structures. For the actuator conditions investigated, neither the classical laminar nor fully turbulent analytical solutions for continuous wall jets were amenable to modeling the synthetic wall jet profile due to the transitional and unsteady nature of the synthetic wall jet.     

Efficient Access to Enantiopure γ4‐Amino Acids with Proteinogenic Side‐Chains and Structural Investigation of γ4‐Asn and γ4‐Ser in Hybrid Peptide Helices

Hybrid peptides composed of α‐ and β‐amino acids have recently emerged as new class of peptide foldamers. Comparatively, γ‐ and hybrid γ‐peptides composed of γ⁴‐amino acids are less studied than their β‐counterparts. However, recent investigations reveal that γ⁴‐amino acids have a higher propensity to fold into ordered helical structures. As amino acid side‐chain functional groups play a crucial role in the biological context, the objective of this study was to investigate efficient synthesis of γ⁴‐residues with functional proteinogenic side‐chains and their structural analysis in hybrid‐peptide sequences. Here, the efficient and enantiopure synthesis of various N‐ and C‐terminal free‐γ⁴‐residues, starting from the benzyl esters (COOBzl) of N‐Cbz‐protected (E)‐α,β‐unsaturated γ‐amino acids through multiple hydrogenolysis and double‐bond reduction in a single‐pot catalytic hydrogenation is reported. The crystal conformations of eight unprotected γ⁴‐amino acids (γ⁴‐Val, γ⁴‐Leu, γ⁴‐Ile, γ⁴‐Thr(OtBu), γ⁴‐Tyr, γ⁴‐Asp(OtBu), γ⁴‐Glu(OtBu), and γ‐Aib) reveals that these amino acids adopted a helix favoring gauche conformations along the central C^γ? C^β bond. To study the behavior of γ⁴‐residues with functional side chains in peptide sequences, two short hybrid γ‐peptides P1 (Ac‐Aib‐γ⁴‐Asn‐Aib‐γ⁴‐Leu‐Aib‐γ⁴‐Leu‐CONH₂) and P2 (Ac‐Aib‐γ⁴‐Ser‐Aib‐γ⁴‐Val‐Aib‐γ⁴‐Val‐CONH₂) were designed, synthesized on solid phase, and their 12‐helical conformation in single crystals were studied. Remarkably, the γ⁴‐Asn residue in P1 facilitates the tetrameric helical aggregations through interhelical H bonding between the side‐chain amide groups. Furthermore, the hydroxyl side‐chain of γ⁴‐Ser in P2 is involved in the interhelical H bonding with the backbone amide group. In addition, the analysis of 87 γ⁴‐residues in peptide single‐crystals reveal that the γ⁴‐residues in 12‐helices are more ordered as compared with the 10/12‐ and 12/14‐helices.     

Spectroscopic investigations of nanohydroxyapatite powders synthesized by conventional and ultrasonic coupled sol-gel routes

In the present work, the synthesis and characterization of nano-HAP powders by a novel ultrasonic coupled sol-gel synthesis is reported. The obtained powders were sintered by conventional means at different temperatures. In addition to this, HAP powders prepared through the sol-gel method without the aid of the ultrasonic waves is also studied. The obtained nano-HAP powders were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopic (SEM) techniques. The results have proved that the nano-HAP powders synthesized by ultrasonic coupled sol-gel synthesis showed remarkable reduction in the particle size when compared with the conventional sol-gel method and hence these powders could be used as a coating material in biomedical applications.     

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.     

Ambidextrous α,γ‐Hybrid Peptide Foldamers

Molecular chirality is ubiquitous in nature. The natural biopolymers, proteins and DNA, preferred a right‐handed helical bias due to the inherent stereochemistry of the monomer building blocks. Here, we are reporting a rare co‐existence of left‐ and right‐handed helical conformations and helix‐terminating property at the C‐terminus within a single molecule of α,γ‐hybrid peptide foldamers composed of achiral Aib (α‐aminoisobutyric acid) and 3,3‐dimethyl‐substituted γ‐amino acid (Adb; 4‐amino‐3,3‐dimethylbutanoic acid). At the molecular level, the left‐ and right‐handed helical screw sense of α,γ‐hybrid peptides are representing a macroscopic tendril perversion. The pronounced helix‐terminating behaviour of C‐terminal Adb residues was further explored to design helix–Schellman loop mimetics and to study their conformations in solution and single crystals. The stereochemical constraints of dialkyl substitutions on γ‐amino acids showed a marked impact on the folding behaviour of α,γ‐hybrid peptides.     

β‐Hairpins Generated from Hybrid Peptide Sequences Containing both α‐ and β‐Amino Acids

The incorporation of the β‐amino acid residues into specific positions in the strands and β‐turn segments of peptide hairpins is being systematically explored. The presence of an additional torsion variable about the C(α) C(β) bond (θ) enhances the conformational repertoire in β‐residues. The conformational analysis of three designed peptide hairpins composed of α/β‐hybrid segments is described: Boc‐Leu‐Val‐Val‐^DPro‐β Phe ‐Leu‐Val‐Val‐OMe ( 1 ), Boc‐Leu‐Val‐β Val ‐^DPro‐Gly‐β Leu ‐Val‐Val‐OMe ( 2 ), and Boc‐Leu‐Val‐β Phe ‐Val‐^DPro‐Gly‐Leu‐β Phe ‐Val‐Val‐OMe ( 3 ). 500‐MHz ¹H‐NMR Analysis supports a preponderance of β‐hairpin conformation in solution for all three peptides, with critical cross‐strand NOEs providing evidence for the proposed structures. The crystal structure of peptide 2 reveals a β‐hairpin conformation with two β‐residues occupying facing, non‐H‐bonded positions in antiparallel β‐strands. Notably, βVal(3) adopts a gauche conformation about the C(α) C(β) bond (θ=+65°) without disturbing cross‐strand H‐bonding. The crystal structure of 2 , together with previously published crystal structures of peptides 3 and Boc‐β Phe ‐β Phe ‐^DPro‐Gly‐β Phe ‐β Phe ‐OMe, provide an opportunity to visualize the packing of peptide sheets with local ‘polar segments' formed as a consequence of reversal peptide‐bond orientation. The available structural evidence for hairpins suggests that β‐residues can be accommodated into nucleating turn segments and into both the H‐bonding and non‐H‐bonding positions on the strands.     

A domino palladium-catalyzed C-C and C-O bonds formation via dual O-H bond activation: synthesis of 6,6-dialkyl-6H-benzo[c]chromenes

An efficient Pd-catalyzed domino reaction of α,α-dialkyl-(2-bromoaryl)methanols to 6,6-dialkyl-6H-benzo[c]chromenes is presented. Their formation can be explained via a five membered Pd(II)-cycle that efficiently involves a domino homocoupling with the second molecule, β-carbon cleavage, and finally intramolecular Buchwald-Hartwig cyclization. This domino process effectively involves breaking of five σ-bonds (2C-Br, 2O-H, and a C-C) and formation of two new σ-bonds (C-C and C-O). This mechanistic pathway is unprecedented and further illustrates the power of transition metal catalysis.     

Preliminary investigation on biological possessions of Saquinavir-modified quinoline-derived azadipeptidomimetics

Herein, azadipeptidomimetic molecules were designed and synthesized using a quinoline-histidine-amino acid sequence with terminal amino acid modification. In-silico studies were carried out to evaluate the compound's HIV protease-1 inhibition temperament. In-vitro anti-proliferative possessions of the test compounds were studied by executing a series of experiments, namely DNA binding, bovine serum albumin (BSA) binding capability, and cytotoxicity assay on MCF-7 cells. The molecule 5j exhibited remarkable results in all experiments; it has an excellent DNA binding constant (3.76 × 10⁵), higher serum albumin unbound concentration of 5.96%, and a significant antiproliferative effect on MCF-7 cells with IC₅₀ value 0.31 nM.