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A reusable, insoluble polystyrene-supported bis(oxazoline) was developed, affording e.e.s > 90% in the heterogeneous enantioselective cyclopropanation of styrene and 1,1-disubstituted alkenes with ethyl diazoacetate.
Neuroreceptor imaging by PET or SPECT has been widely applied in the field of neurobiology, from basic to clinical investigations, and has the potential to reveal the neurochemical basis of various neurological and psychiatric diseases as well as to provide new knowledge in the field of neuropharmacology. In contrast to the static nature of in vitro systems, neurotransmission systems in the intact brain constitute part of a dynamic and communicating environment. Thus, it is important to develop new functional imaging methods that reflect neural communications and the dynamism of signal transmission in the living brain. In vivo receptor binding can be altered not only by competitive inhibition by endogenous neurotransmitters but by trans-synaptic effects, and investigation of neural interactions by detection of changes in receptor binding therefore presents a potential method for studying this phenomenon. Recently, several PET studies on in vivo neural interactions using the D2 receptor ligand [11C]-raclopride concluded that the phenomenon was mediated by changes in synaptic endogenous dopamine concentrations that compete with [11C]-raclopride binding for neuroreceptor occupancy. However, a growing body of evidence indicates that these changes in in vivo receptor binding cannot be fully explained by competitive inhibition by endogenous ligand, and alternative mechanisms for the interneuronal modulation of receptor binding are addressed. This review highlights some of the discrepancies observed between in vitro and in vivo receptor binding studies with respect to a number of phenomena, including the heterogeneity of the reaction field surrounding receptors. Quantitative receptor binding studies are usually analyzed by using 'static' binding parameters, such as the Bmax, and KD, which are normally determined by in vitro assays. In addition to these parameters, the apparent association and dissociation rate constants (kon, koff) play equally significant roles in receptor binding in the intact brain is expected. The concepts of "diffusion boundary" and "reaction volume" are introduced, and discussions on some of the discrepancies between in vivo and in vitro receptor binding phenomena are presented.
Ozone oxidation combined with activated carbon adsorption (O(3)/AC) has recently started to be developed as a single process for water and wastewater treatment. While a number of aspects of aqueous ozone decomposition are well understood, the importance and relationship between aqueous ozone decomposition and organic contaminant degradation in the presence of activated carbon is still not clear. This study focuses on determining the contribution of homogeneous and heterogeneous reactions to organic contaminants removal in O(3)/AC system. Benzothiazole (BT) was selected as a target organic pollutant due to its environmental concern. A reactor system based on a differential circular flow reactor composed by a 19 cm(3) activated carbon fixed bed column and 1 dm(3) storage tank was used. Ozone was produced from pure and dry oxygen using an Ozocav ozone generator rated at 5 g O(3)h(-1). Experimental results show that BT removal rate was proportional to activated carbon dosage. Activated carbon surface contribution to BT oxidation reactions with ozone, increased with pH in absence of radical scavengers. The radical reaction contribution within the pH range 2-11 accounted for 67-83% for BT removal in O(3)/AC simultaneous treatment. Results suggest that at pH higher than the pH of the point of zero charge of the activated carbon dissociated acid groups such as carboxylic acid anhydrides and carboxylic acids present on activated carbon surface could be responsible for the observed increase in the ozone decomposition reaction rate. A simplified mechanism and a kinetic scheme representing the contribution of homogeneous and heterogeneous reactions on BT ozonation in the presence of activated carbon is proposed.
Self-propagating high temperature reaction waves, leading to the synthesis of advanced materials, are investigated in a variety of heterogeneous reaction systems by using a digital high-speed microscopic video recording technique. It is shown that, although on the macroscopic length and time scales, the reaction appears to move in a steady mode, on the microscopic level it has a complex character that is related to the reaction mechanism.
The effect of kinetics of chemical reactions in the gas-liquid interface between atmospheric gases and reactive solute in dilute aqueous aerosols is analysed in order to see if such processes will affect the overall uptake rate. Accordingly, a parameterization of such heterogeneous reactions was derived, taking into account interfacial reactions. Gibbs surface excess concentration of both reactive compounds and stable compounds leads to higher heterogeneous reaction rates in comparison to aqueous phase bulk reactions. An analytical formulation shows that the surface reactions may be of considerable importance for the uptake process in the case of small liquid aerosols even in the absence of organic film on the surface. In particular, we demonstrate that the uptake rate of atmospheric gas-phase oxidants (such as OH, NO(3) or O(3)) reacting with volatile organic compounds (such as ethanol or methanol) is increased by more than 10% for atmospheric aerosols with diameters lower than 0.1 microm. This effect is in addition intensified in the case of reactions of atmospheric oxidants with liquid aerosols containing organic surfactants, such as semi-volatile organic compounds, i.e., the chemical reactions at the gas-liquid interface may be dominant in the main uptake process for atmospheric submicron aerosols.
In this study, we examined the influence of the long-range transport of dust particles and air pollutants on the photochemistry of OH and NO3 on Jeju Island, Korea (33.17 degrees N, 126.10 degrees E) during the Asian-dust-storm (ADS) period of April 2001. Three ADS events were observed during the periods of April 10-12, 13-14, and 25-26. Average concentration levels of daytime OH and nighttime NO3 on Jeju Island during the ADS period were estimated to be about 1x10(6) and 2x10(8) moleculescm(-3) ( approximately 9 pptv), respectively. OH levels during the ADS period were lower than those during the non-Asian-dust-storm (NADS) period by a factor of 1.5. This was likely to result from higher CO levels and the significant loading of dust particles, reducing the photolysis frequencies of ozone. Decreases in NO3 levels during the ADS period was likely to be determined mainly by the enhancement of the N2O5 heterogeneous reaction on dust aerosol surfaces. Averaged over 24 h, the reaction between HO2 and NO was the most important source of OH during the study period, followed by ozone photolysis, which contributed more than 95% of the total source. The reactions with CO, NO2, and non-methane hydrocarbons (NMHCs) during the study period were major sinks for OH. The reaction of N2O5 on aerosol surfaces was a more important sink for nighttime NO3 during the ADS due to the significant loading of dust particles. The reaction of NO3 with NMHCs and the gas-phase reaction of N2O5 with water vapor were both significant loss mechanisms during the study period, especially during the NADS. However, dry deposition of these oxidized nitrogen species and a heterogeneous reaction of NO3 were of no importance.
Saponification of oils which is a commercially important heterogeneous reaction, can be speeded up by the application of ultrasound in the presence of phase-transfer catalyst (PTC). This paper focuses on the ability of ultrasound to cause efficient mixing of this liquid-liquid heterogeneous reaction. Castor oil was taken as a model oil and the kinetic of the reaction was followed by the extent of saponification. The hydrolysis of castor oil was carried out with different PTC such as cetyl trimethyl ammonium bromide (CTAB), benzyl triethyl ammonium chloride (BTAC) and tetrabutyl ammonium bromide (TBAB) in aqueous alkaline solution. As hydroxyl anion moves very slowly from aqueous to oil phase, the presence of a PTC is of prime importance. For this purpose, cationic surfactants are selected. The sonication of biphasic system were performed by 20 kHz (simple horn and cup horn) and 900 kHz. It was found that CTAB was better than the two others and this could be related to the molecular structure of the PTCs. The effect of temperature was also studied on the saponification process. By increasing the temperature, the yield was also increased and this could be explained by intermolecular forces, interfacial tension and mass transfer. Saponification of three different vegetable oils shows that the almond oil is saponified easier than the two others and this could be related to their properties such as surface tension, viscosity and density.
The MLL gene involved in 11q23 translocations found in the majority of infantile leukemias and some secondary leukemias makes fusion transcripts with genes such as LTG4 (chromosome 4), LTG9 (chromosome 9), and LTG19 (chromosome 19) as a result of reciprocal translocation. We have examined 25 cases of leukemias with 11q23 abnormalities by Southern blot analysis and the reverse transcriptase-polymerase chain reaction (RT-PCR). Using various primer pairs, chimeric mRNAs could be amplified in 6 of 7 leukemias with t(4;11), 6 of 8 leukemias with t(9;11) including secondary leukemia, 8 of 9 leukemias with t(11;19), and 1 with a deletion at 11q23. The chimeric mRNAs were heterogeneous and differential usage of the MLL exons was found, irrespective of the partner chromosomes. Sensitivity studies showed that a single clone with chimeric mRNA in 10(4) to 10(5) cells could be detected. These findings show that the present RT-PCR settings provide a rapid, accurate, and sensitive tool for diagnosing leukemias with 11q23 translocations and for monitoring response to therapy in these patients.
We examine the consequences of the eruption of the El Chichon volcano on the Earth's stratospheric chemistry. Formed after the eruption, the volcanic aerosol cloud, with a peak particle density at 27 km, was very efficient at altering the radiation field. The results of a one-dimensional radiative transfer model show that the total radiation increased by 8% within the aerosol layer longward of 3000 angstroms. At certain altitudes and wavelengths below 3000 angstroms, the total radiation decreased by 15%. Consequently, there are changes in the photolysis rates obtained with a one-dimensional photochemical model: for example, O2 photodissociation rate constants decrease by 10%, while O3 photodissociation rate constants increase by a comparable amount. A combination of this radiation change and the effect of a temperature variation of a few degrees causes the abundance of O3 to decrease by 7% at 24 km, in good agreement with the Solar Backscattered Ultraviolet experiment (SBUV) measurements of a 5-10% decrease. The combined radiative and thermal perturbations on the concentrations of O, O(1 D), OH, HO2, H2O2, NO, NO2, NO3, N2O5, HNO3, HO2NO2, Cl, ClO, ClO2, HOCl, ClNO3, and HCl are computed and presented in detail. However, these changes as calculated are insufficient to explain the observations of significant decreases in NO and NO2 and increases in HCl. A heterogeneous reaction catalyzed by aerosol surfaces which transforms ClNO3 into HCl provides a pathway for sequestering NOx, and at the same time reduces ClNO3 in favor of HCL. The inclusion of this reaction in the model leads to a satisfactory single-step explanation of the otherwise puzzling observations of NO, NO2, and HCl. The observed lack of change in HNO3 cannot be explained by this hypothesis. The effects of a number of heterogeneous reactions, some believed to be important for the Antarctic stratosphere, have been assessed with our model. We also examine the hypothesis of direct injection of gases from the volcano into the stratosphere. Only an unrealistically large injection (60% column increase above 12 km) results in an HCl increase in agreement with observations. An equally large water injection decreases HCl, and decreases the NO and NO2 by as much as 20%, but still does not simulate the observed NOx decrease.
Photoelectron resonance capture ionization (PERCI) is a soft and sensitive ionization method, based on the attachment of low-energy (<1 eV) photoelectrons to organic analyte molecules. PERCI has been developed in our laboratory for the real-time analysis of organic particles by mass spectrometry, and is employed here to monitor the heterogeneous reaction of ozone with oleic acid. Simplified identification of the reaction products is possible as a result of the soft nature of PERCI, giving predominantly the [M--H](-) ions. The major particle-phase products are identified as: 1-nonanal, nonanoic acid, 9-oxononanoic acid, and azelaic acid, consistent with proposed mechanisms. New insight into this well-studied heterogeneous reaction is gained as additional minor particle-phase products, consistent with the Criegee mechanism, are readily detected.
A nested chamber design was constructed for the purpose of studying parameters that affect indoor air chemistry. Experiments were conducted in this system to investigate the effects of three surface types (Teflon, wallpaper, and carpet) and two levels of relative humidity (50% and 70% RH) on the formation of gas-phase nitrous acid (HONO) through the heterogeneous reaction of nitrogen dioxide (NO2) with sorbed water vapor. The results of this investigation show that, compared with Teflon surfaces, carpet made of synthetic fibers increased the NO2 surface removal rate by nearly an order of magnitude and resulted in higher peak HONO concentrations. The results also suggest that the capacity of a surface to sorb water will determine if HONO is released from that surface after the NO2 source has been turned off and the heterogeneous reaction between NO2 and sorbed water is no longer significant. Vinyl-coated wallpaper was found to release HONO for prolonged periods of time after the NO2 source was turned off at both 50% and 70% RH whereas Teflon was found to do so only at 70% RH. The results of this investigation also demonstrate the utility of the nested chamber design in investigating indoor air chemistry.
Absorption of hydrogen sulfide in aqueous suspensions of biologically produced sulfur particles was studied in a batch stirred cell reactor, and in a continuous set-up, consisting of a lab-scale gas absorber column and a bioreactor. Presence of biosulfur particles was found to enhance the absorption rate of H(2)S gas in the mildly alkaline liquid. The mechanism for this enhancement was however found to depend on the type of particles used. In the gently stirred cell reactor only small hydrophilic particles were present (d(p) < 3 microm) and the enhancement of the H(2)S absorption rate can be explained from the heterogeneous reaction between dissolved H(2)S and solid elemental sulfur to polysulfide ions, S(x) (2-). Conditions favoring enhanced H(2)S absorption for these hydrophilic particles are: low liquid side mass transfer (k(L)), high sulfur content, and presence of polysulfide ions. In the set-up of gas absorber column and bioreactor, both small hydrophilic particles and larger, more hydrophobic particles were continuously produced (d(p) up to 20 microm). Here, observed enhancement could not be explained by the heterogeneous reaction between sulfide and sulfur, due to the relatively low specific particle surface area, high k(L), and low [S(x) (2-)]. A more likely explanation for enhancement here is the more hydrophobic behavior of the larger particles. A local increase of the hydrophobic sulfur particle concentration near the gas/liquid interface and specific adsorption of H(2)S at the particle surface can result in an increase in the H(2)S absorption rate.
Resorption rate of heterogeneous implants (lyophilized tissues of the rabbit liver and cerebriform cancer of the human stomach) has been studied 6, 24 h and 3, 7, 21, 30 days after their simultaneous implantation into the rat peritoneal cavity. The area of separate cellular zones, contents of granulocytes and immune-competent cells in the zone macrophage-fibroblasts, mitotic coefficient and index of 3H-thymidin-labelled fibroblast nuclei have been taken into consideration. Resorption and elimination rate of the protein implants applied, as well as proliferation of the connective tissue elements and maturation of the granulation tissue in the organization focus take place more quickly at implantation of the lyophilized tumoral tissue. Antigenic reaction to the native hepatic proteins and to the stomach cancer occurs in the same way as to alive cells. Its index is appearance of the zone consisting of lymphocytes with plasma cells in the periphery of the implants.
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The chemical reactivity of several minerals thought to be present in Martian fines is tested with respect to gases known in the Martian atmosphere. In these experiments, liquid water is excluded from the system, environmental temperatures are maintained below 0 degrees C, and the solar illumination spectrum is stimulated in the visible and UV using a Xenon arc lamp. Reactions are detected by mass spectrometric analysis of the gas phase over solid samples. No reactions were detected for Mars nominal gas over sulfates, nitrates, chloride, nontronite clay, or magnetitie. Oxidation was not observed for basaltic glass, nontronite, and magnetite. However, experiments incorporating SO2 gas--an expected product of volcanism and intrusive volatile release--gave positive results. Displacement of CO2 by SO2 occurred in all four carbonates tested. These reactions are catalyzed by irradiation with the solar simulator. A calcium nitrate hydrate released NO2 in the presence of SO2. These results have implications for cycling of atmospheric CO2, H2O, and N2 through the regolith.
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