PIV study of the influence of large-scale streamwise vortices on a turbulent boundary layer

Vortex generator jets were used to generate large-scale longitudinal vortices embedded in a flat-plate turbulent boundary layer. The investigation was performed in a water tunnel, measuring instantaneous flow fields in planes parallel and normal to the flat plate, using particle image velocimetry. The objective of the research was to observe the response of near-wall turbulence to the imposed perturbing flow. It was shown that a small-amplitude forcing vortical flow had significant influence on the mean and fluctuating velocity profiles. Moreover, particle image velocimetry permitted speculation upon the behaviour of the wall velocity streaks under the action of the perturbing forcing vortical flow.     

Turbulent boundary layer manipulation by outer-layer devices

A turbulent boundary layer manipulated by outer-layer devices has been studied. Experiments have been conducted in the 0.70 by 0.50 m² low speed wind tunnel of the Modesto Panetti Aeronautical Laboratory of the Politecnico di Torino. Mean values and turbulent quantities measured in the natural and manipulated boundary layers are shown for comparison. The mechanisms to explain the observed skin friction and turbulence reduction are discussed. The manipulator wake effect, consisting in decoupling the wall-region from the boundary layer outer-region, is stressed in the present results.

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Sommario Viene studiato uno strato limite turbolento manipolato, utilizzando la tecnica degli outer-layer devices. Gli esperimenti sono stati condotti nella galleria del vento 0.70×0.50 m² del Laboratorio di Aeronautica Modesto Panetti del Politecnico di Torino. Sono confrontati risultati relativi ai casi di flusso non manipolato e manipolato. Vengono discussi i meccanismi che conducono alla riduzione dello sforzo di attrito a parete e delle quantità turbolente; in particolare si punta l'attenzione sull'effetto decorrelante della scia del manipolatore.

     

Chloride‐Anion‐Templated Synthesis of a Strapped‐Porphyrin‐Containing Catenane Host System

The synthesis, structure and anion‐recognition properties of a new strapped‐porphyrin‐containing [2]catenane anion host system are described. The assembly of the catenane is directed by discrete chloride anion templation acting in synergy with secondary aromatic donor–acceptor and coordinative pyridine–zinc interactions. The [2]catenane incorporates a three‐dimensional, hydrogen‐bond‐donating anion‐binding pocket; solid‐state structural analysis of the catenane?chloride complex reveals that the chloride anion is encapsulated within the catenane’s interlocked binding cavity through six convergent CH????Cl and NH???Cl hydrogen‐bonding interactions and solution‐phase ¹H NMR titration experiments demonstrate that this complementary hydrogen‐bonding arrangement facilitates the selective recognition of chloride over larger halide anions in DMSO solution.     

A porphyrin fused to four anthracenes

We have synthesized a fused tetraanthracenylporphyrin by oxidation of a meso-anthracenyl nickel(II) porphyrin with FeCl(3). This compound exhibits an intense red-shifted absorption spectrum (λ(max) = 1417 nm; ε = 1.2 × 10(5) M(-1) cm(-1)) and a small electrochemical HOMO-LUMO gap (0.61 eV). The crystal structure shows that it forms π-stacked dimers with a short Ni···Ni distance (3.32 ?).     

Fluorescent properties of antioxidant cysteine ABZ analogue

The antioxidant properties of aminobenzamide cysteine (ABZ Cys) makes it a molecule that can potentially be used as a drug in oxidative stress related diseases and delivered in the form of a nanoparticles. Here we have studied the photo-physical properties of ABZ Cys, a fluorescent analogue of a popular antioxidant N-acetyl cysteine (NAC). We have compared ABZ Cys steady state and time-resolved fluorescence properties with its parent compounds anthranilic acid and anthranilamide in solution as well as in poly-vinyl alcohol (PVA) polymer films. ABZ Cys did not show any significant shift in absorption after entrapment in PVA film, but there was a shift towards shorter wavelengths in the emission peak compared to the phosphate buffer solution. Fluorescence lifetimes and quantum yields indicated a slight quenching of ABZ Cys fluorescence in comparison to the cysteine-less parent compounds. We also demonstrated that very low concentrations of ABZ Cys, such as 100 nM, are readily detected by a commercial spectrofluorometer. Hence we have established the possible use of ABZ Cys in biomedical applications.     

Pyrazole analogues of porphyrins and oxophlorins

A series of porphyrin analogues with pyrazole rings replacing one of the usual pyrrole subunits have been synthesized. This was accomplished by reacting 1-phenyl, 1-methyl and 1-ethyl pyrazole-1,3-dicarbaldehydes with a tripyrrane in the presence of TFA, followed by an oxidation step. The initially formed phlorin product was sufficiently stable for the N-phenyl system to be isolated and characterized, although the related N-alkyl phlorin analogues were less stable. Attempts to dehydrogenate the intermediary phlorins with DDQ resulted in decomposition, but the N-alkylphlorins could be oxidized with 0.2% aqueous ferric chloride solutions. Although the phenyl-substituted phlorin could not be oxidized under these conditions, it did afford the pyrazoloporphyrin upon treatment with silver acetate under acidic conditions. Oxidations with silver acetate also afforded oxophlorin analogues where the oxo-linkage was selectively formed at the 5-position. The pyrazole-containing porphyrin analogues are cross-conjugated and exhibit only a small degree of diatropic character. The internal CH resonances were observed between 5.27 and 5.87 ppm, while the external meso-protons fell into a range of 6.84-7.88 ppm. The borderline overall aromatic character was attributed to dipolar resonance contributors. Protonation considerably increased the diatropicity and the diprotonated dications formed from these porphyrin analogues gave the internal CH resonance at upfield values of 2.65-3.20 ppm. The aromatic character was enhanced by the presence of an electron-donating alkyl substituent on the nitrogen compared to the phenyl-substituted species. The pyrazoloporphyrins reacted with nickel(II) acetate in DMF, or palladium(II) acetate in acetonitrile, to give the corresponding organometallic derivatives. The metal complexes showed increased diatropic character but protonation afforded nonaromatic cations. The oxophlorin analogues were also nonaromatic in the free base and protonated forms. This work extends our understanding of carbaporphyrinoid systems and provides the first detailed studies on pyrazole-containing porphyrin analogues.     

Antimicrobial activities of essential oil and methanol extract of Coriaria nepalensis

Plant extracts and products have been used for centuries in traditional medicine; for most of them, in addition to the scant scientific credibility, the chemical composition and spectrum of activity are yet to be explored. To put forward this effort and to identify novel antimicrobial agents, the inhibitory activities of methanolic extract and essential oil from Coriaria nepalensis against various microorganisms including pathogenic yeast, and Gram-positive and negative bacteria were evaluated. Chemical compositions of C. nepalensis methanolic extract and essential oil were analysed by gas chromatography-mass spectrometry. In vitro susceptibility tests against all the tested isolates were performed in terms of minimum inhibitory concentration (MIC), and well diffusion assay using standard protocols. All microorganisms tested were profoundly found susceptible to both the C. nepalensis extract and oil with MIC values of 1.3-2.1?mg?mL?1 (Gram-positive bacteria), 1.4-2.2?mg?mL?1 (Gram-negative bacteria) and 0.9-1.6?mg?mL?1 (yeasts). The extent of inhibition was shown more by methanolic extract than by essential oil. This study is the first to report the antimicrobial activity of extracts obtained from the C. nepalensis. It can be concluded that the observed antimicrobial characteristics of C. nepalensis indicate that it might be a promising antimicrobial agent.     

A highly distorted open-shell endohedral Zintl cluster: [Mn@Pb12]3-

Reaction of an ethylenediamine (en) solution of K(4)Pb(9) and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) with a tetrahydrofuran (THF) solution of Mn(3)(Mes)(6) (Mes = 2,4,6-trimethylphenyl) yielded the anionic cluster [Mn@Pb(12)](3-). This species was observed in the positive and negative ion-mode electrospray mass-spectra of the crude reaction mixture. The crystalline samples obtained from such solutions allowed us to confirm the composition of the sample as [K(2,2,2-crypt)](3)[Mn@Pb(12)]·1.5en (1). Because of numerous issues related to crystal sample quality and crystallographic disorder a high-quality crystal structure solution could not be obtained. Despite this, however, the data collected permit us to draw reasonable conclusions about the charge and connectivity of the [Mn@Pb(12)](3-) cluster anion. Crystals of 1 were further characterized by elemental analysis and electron paramagnetic resonance (EPR). Density Functional Theory (DFT) calculations on such a system reveal a highly distorted endohedral cluster anion, consistent with the structural distortions observed by single crystal X-ray diffraction. The cluster anions are considerably expanded compared to the 36-electron closed-shell analogue [Ni@Pb(12)](2-) and, moreover, exhibit significant low-symmetry distortions from the idealized icosahedral (I(h)) geometry that is characteristic of related endohedral clusters. Our computations indicate that there is substantial transfer of electron density from the formally Mn(-I) center to the low-lying vacant orbitals of the [Pb(12)](2-) cage.