Magnetic circular dichroism of some benzene derivatives

The MCD spectra of phloroglucin, 1,3,5-trimethoxybenzene, 1,3,5-tricyanobenzene, 1,3,5-trinitrobenzene, 1,3,5-benzenetricarboxylic acid and 1,3,5-benzenetricarbonyl chloride were measured. For the ¹E′ ← ¹A′₁ transition of phloroglucin or 1,3,5-tricyanobenzene and the ¹E′ ← ¹A′ transition of 1,3,5-trimethoxybenzene, the Faraday A term was observed and the A/D value was extracted. However, 1,3,5-trinitrobenzene, 1,3,5-benzenetricarboxylic acid and 1,3,5-benzenetricarbonyl chloride showed no magnetic circular dichroism in this spectral region. The magnetic moments in the ¹E′ states of these molecules seem to be quenched by the effects of substituents. The magnetic moments in the ¹E′ states of benzene derivatives are sensitive to substitution in the benzene ring.     

Feedback control of vortex shedding from a circular cylinder by cross-flow cylinder oscillations

Feedback control of vortex shedding from a circular cylinder in a uniform flow at moderate Reynolds numbers is studied experimentally with the cylinder subjected to feedback cylinder oscillations in cross-flow direction. The cylinder oscillation is digitally phase shifted with respect to the shedding vortex and is controlled by velocity feedback from the shear layer of the cylinder wake. Possible attenuation of vortex shedding is demonstrated by hot-wire measurements of the flow field and its mechanisms are studied by simultaneous data sampling and flow visualization with the smoke wire method and a laser-sheet illumination technique. Measurement results reveal substantial reduction in the fluctuating reference velocity at the optimum phase control. Flow visualization study indicates that the shear layer roll-up and the eventual vortex formation are dynamically attenuated under the control which results in a modification of the near wake.List of symbols A amplitude of cylinder oscillation - D cylinder diameter - E _u power spectrum function for fluctuating velocity u - frequency - R radius of circular cylinder - t time - u streamwise mean velocity - u streamwise fluctuating velocity - U streamwise mean velocity of main flow - u _r mean reference velocity - u _r fluctuating reference velocity - u _rf fluctuating reference velocity after filtering - y _c cylinder displacement - x, y, z coordinates from the cylinder center (Fig. 1) - feedback coefficient - phase lag The authors would like to express thanks to Professor K. Nagaya for his advice for designing electromagnetic actuators in the present experiments.     

A new method for the stereoselective construction of angular methyl group of fuzed cyclic ethers

A convenient method for the stereoselective construction of angular methyl group of fuzed cyclic ethers is described. Reactions of mixed thioacetals with Me₂Zn/Zn(OTf)₂ afforded the corresponding methylated products in good yields. Various protective groups such as MOM ether, benzylidene acetal, TBS ether, and pivaloyl group were stable under the reaction conditions.     

Scanning liquid-crystal thermometry and stereo velocimetry for simultaneous three-dimensional measurement of temperature and velocity field in a turbulent Rayleigh-Bérnard convection

In this paper, we report on an experimental technique for the simultaneous measurement of temperature and three components of velocity in a three-dimensional thermal flow using scanning liquid-crystal thermometry and stereo velocimetry. The temperature is measured by the color image analysis of the liquid-crystal particles suspended in a fluid, while the three velocity components are measured by stereo particle image velocimetry (stereo PIV) with the aid of tracer particles. The measurement is carried out by scanning the light-sheet plane while capturing the sequential color images of the liquid crystals and tracer particles. This measurement allows the reconstruction of the three-dimensional distribution of temperature and full velocity field simultaneously. The present experimental technique is applied to the horizontal fluid layer of a turbulent Rayleigh-Bérnard convection and the three-dimensional structures of thermal plumes are evaluated. The experimental results indicate that the structures of plumes are often correlated with the vertical velocity of the fluid, but they behave randomly in space, influenced by the large-scale turbulence evident in the middle of the fluid layer.     

Theoretical calculation of the OH vibrational overtone spectra of 1-n alkane diols (n = 2-4): origin of disappearing hydrogen-bonded OH peak

In this theoretical study, we simulated the vibrational overtone spectrum of ethylene glycol (EG), 1-3 propanediol (PD), and 1-4 butanediol (BD). Using the local mode model along with the potential energy curve and dipole moment function calculated by B3LYP/6-31+G(d,p) and QCISD/6-311++G(3df,3pd), we obtained the theoretical peak position and integrated absorption coefficient. Furthermore, the vibrational spectra was simulated using a Voigt function using homogeneous and inhomogenous width obtained from quantum chemical calculation methods. Previously, Howard and Kjaergaard recorded the second and third overtone photoacoustic spectra of the three aforementioned alkane diols in the gas phase and observed that the intramolecular hydrogen bonded OH peak becomes difficult to observe as the intramolecular hydrogen bonding strength increased, that is, as the chain length was increased. In this paper we show that the disappearance of the hydrogen-bonded OH peak for the OH stretching overtone excitation for BD is partly due to the increase in homogeneous width due to the increase in the hydrogen bond strength and partly due to the decrease in the relative population of the intramolecular hydrogen-bonded conformers as the chain length is increased. This latter feature is a consequence of the unfavorable strained geometry needed to form the intramolecular hydrogen bond in longer alkane chains.     

Radical-scavenging activity of dietary phytophenols in combination with co-antioxidants using the induction period method

The radical-scavenging activity of dietary phytophenols has been investigated by many researches due to their antioxidant, anti-inflammatory and anticancer property but the radical-scavenging effect of 2-phytophenol and the phytophenol:co-antioxidants, vitamin C and thiol combination under nearly anaerobic conditions still remains unknown. The radical-scavenging activity for seventeen phytophenols and for six synthetic phenols (positive controls) was investigated using the induction period method in the polymerization of methyl methacrylates (MMA) initiated by thermal decomposition of benzoyl peroxide (BPO) by monitoring differential scanning calorimetery (DSC). The k(inh) for the phytophenols was likely with the range 0.5 × 103 M?1s?1-2.2 × 103 M?1s?1, whereas that for synthetic phenols, hydroquinone and galvinoxyl, was with the range 7 × 103 M?1s?1-8 × 103 M?1s?1. Also, the additive scavenging effect of the (-)-epigallocatechin (EGC):(-)-epicatechin (EC) and the (+)-catechin:epicatechin (EC) combination was observed at 1:1 molar ratio, whereas that of the EC:quercetin combination showed the cancel (prooxidative) effect. Furthermore, the EGC:ASDB (L-ascorbyl 2,6-dibutylate) or 2-ME (2-mercaptoethanol) combination showed the prooxidative effect. Such enhancement of prooxidation in the combination may increase their toxic effects due to their cooxidation. Also, the synergic, additive or cancel effects of the flavonoid:vitamins E combination on the induction period in the BPO (a PhCOO* radical) and 2,2'-azobisisobutyronitrile (AIBN, an R* radical) systems are discussed.     

Multinuclear magnetic resonance studies of five silver(I) trinuclear pyrazolate complexes

Structural Chemistry - Experimental multinuclear determination of the chemical shifts, especially 15N and 109Ag, of five silver(I) trinuclear pyrazolate complexes, (PzAg)3, coupled with ZORA...     

Formal total synthesis of enigmazole A

A stereoselective formal total synthesis of enigmazole A, a marine macrolide isolated from Cinachyrella enigmatica, is described. Lewis acid mediated intramolecular allylation of an α-acetoxy ether, prepared from alcohol and carboxylic acid fragments was carried out to construct the methylene THP ring with high stereoselectivity. The late-stage macrolactonization of the corresponding seco-acid provided a known synthetic intermediate of enigmazole A.