Numerical analysis of free convective flows in partially open enclosure

 Laminar steady state buoyancy induced flows in a two-dimensional, air filled partial open enclosure with a discrete flush mounted iso-flux heat source on one of its walls is investigated numerically. The transport equations for energy and vorticity are solved with the aid of the ADI finite difference scheme on uniform mesh. Because of the specific application of the present study in the air cooling of electronic equipments, results are obtained only for a Prandtl number of 0.71 with an aspect ratio of 1.0 for a range of Rayleigh numbers, Ra (≤10⁵), heat flux parameter, Q and opening parameter, A ₀ using constant properties and Boussinesq approximation by imposing approximate conditions at the opening. Results of flow and temperature patterns, velocity and temperature profiles shows that the outgoing flow is governed by strong characteristics of the cavity condition whereas the incoming flow influenced by outside conditions. It is observed that Rayleigh number considerably affects the flow and thermal fields within the open enclosure when compared with intensity of heat flux and size of the opening. Received on 22 January 2001 / Published online: 29 November 2001     

Steric and electronic effects in capsule-confined green fluorescent protein chromophores

The turn-on of emission in fluorescent protein chromophores sequestered in an "octaacid" capsule is controlled by stereoelectronic effects described by a linear free energy relationship. The stereochemical effects are governed by both the positions and volumes of the aryl substituents, while the electronic effects, including ortho effects, can be treated with Hammett σ parameters. The use of substituent volumes rather than A values reflects packing of the molecule within the confines of the capsule.     

Excited state chemistry of capsular assemblies in aqueous solution and on silica surfaces

Synthesis and encapsulation properties of two new water-soluble resorcinol-capped organic cavitands (tetra acid and octa acid; RTA and ROA) are reported in this Letter. Organic guest molecules template the formation of capsular assembly of the above cavitands in water. Depending upon the guest, either 1:2 (guest to host) or 2:2 capsular assemblies were formed. The excited state properties of guests such as anthracene, camphorthione, and 4,4'-dimethyl benzil were distinctly different within a capsular assembly from those when they were free in a solution. Importantly, the host-guest complexes of the above two hosts (RTA and ROA) as well as octa acid (OA) could be transferred to a silica surface. The excited state behavior of host-guest assemblies on silica surface resembled that in solution. The high cage effect in the decarbonylation products and high yield of rearrangement product obtained upon photolysis of 1-phenyl-3-tolyl-2-propanone included within RTA, ROA, and OA both in solution and on silica surface supported the conclusion that capsular assemblies of these hosts are stable on silica surface.     

Noscapine Prevents Rotenone-Induced Neurotoxicity: Involvement of Oxidative Stress,Neuroinflammation and Autophagy Pathways

Parkinson’s disease is characterized by the loss of dopaminergic neurons in substantia nigra pars compacta (SNpc) and the resultant loss of dopamine in the striatum. Various studies have shown that oxidative stress and neuroinflammation plays a major role in PD progression. In addition, the autophagy lysosome pathway (ALP) plays an important role in the degradation of aggregated proteins, abnormal cytoplasmic organelles and proteins for intracellular homeostasis. Dysfunction of ALP results in the accumulation of α-synuclein and the loss of dopaminergic neurons in PD. Thus, modulating ALP is becoming an appealing therapeutic intervention. In our current study, we wanted to evaluate the neuroprotective potency of noscapine in a rotenone-induced PD rat model. Rats were administered rotenone injections (2.5 mg/kg, i.p.,) daily followed by noscapine (10 mg/kg, i.p.,) for four weeks. Noscapine, an iso-qinulinin alkaloid found naturally in the Papaveraceae family, has traditionally been used in the treatment of cancer, stroke and fibrosis. However, the neuroprotective potency of noscapine has not been analyzed. Our study showed that administration of noscapine decreased the upregulation of pro-inflammatory factors, oxidative stress, and α-synuclein expression with a significant increase in antioxidant enzymes. In addition, noscapine prevented rotenone-induced activation of microglia and astrocytes. These neuroprotective mechanisms resulted in a decrease in dopaminergic neuron loss in SNpc and neuronal fibers in the striatum. Further, noscapine administration enhanced the mTOR-mediated p70S6K pathway as well as inhibited apoptosis. In addition to these mechanisms, noscapine prevented a rotenone-mediated increase in lysosomal degradation, resulting in a decrease in α-synuclein aggregation. However, further studies are needed to further develop noscapine as a potential therapeutic candidate for PD treatment.     

Water-soluble dendrimers as photochemical reaction media: chemical behavior of singlet and triplet radical pairs inside dendritic reaction cavities

Water-soluble poly(alkyl aryl ether) dendrimers have been explored for their use as hosts of organic substrates in aqueous media. Prototypical photoreactions, namely, photo-Fries reaction of (a) 1-naphthyl benzoate and (b) 1-naphthyl phenyl ester and alpha-cleavage reaction of (a) dibenzyl ketones and (b) benzoin alkyl ethers, have been examined. We find that a dendritic microenvironment not only restricts the mobility of radical intermediates but also rigidly encapsulates the substrate, intermediates, and products from "leaking" to the bulk environment. Comparative studies of the same photoreactions in micellar media demonstrate that dendritic media offer much better constrainment than the micelles.     

Influence of Meso Substituents on Electronic States of (Oxoferryl)porphyrin pi-Cation Radicals

A series of (oxoferryl)porphyrin pi-cation radicals generated from porphyrins substituted at the meso positions with highly electron-withdrawing aryl groups has been characterized: tetrakis-5,10,15,20-(2,6-dichlorophenyl)-, 5-(2-chloro-6-nitrophenyl)-10,15,20-tris(2,6-dichlorophenyl)-, and 5-(2,6-dinitrophenyl)-10,15,20-tris(2,6-dichlorophenyl)porphyrins (porphyrins 1-3, respectively). The physical-chemical properties of the oxidized complexes of 1-3 are compared to those of two (oxoferryl)porphyrin pi-cation radical complexes substituted with electron-releasing aryl groups: tetramesitylporphyrin (TMP) and 2-iodotetramesitylporphyrin (2-iodoTMP). While all of the complexes examined show close correspondance in a number of spectroscopic parameters, some significant differences were observed. In contrast to observations for the oxidized complexes of TMP and 2-iodoTMP, the resonance Raman marker bands nu(2) and nu(11), which are indicators of symmetry state of porphyrin pi-cation radicals of 1-3, do not show the expected downfrequency shifts for oxidation to compound I analogs in a(2u) symmetry states. The upfield hyperfine NMR shifts of the pyrrole beta-proton signals of the compound I analogs of 1-3 are much larger than those for TMP and 2-iodoTMP. These data may be explained by admixture of some a(1u) character into the ground state of radical cations of 1-3, consistent with the hypothesis that electron-withdrawing meso substituents lower the energy of the a(2u) molecular orbital, favoring an a(1u) admixture.