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Steven L. Manley - One of the best experts on this subject based on the ideXlab platform.
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© 2002 Kluwer Academic Publishers. Printed in the Netherlands. Phytogenesis of Halomethanes: A product of selection or a metabolic accident?
2013Co-Authors: Steven L. ManleyAbstract:Abstract. Phytoplankton (microalgae), seaweeds (macroalgae), higher plants and fungi produce Halomethanes. Algae and fungi produce both methyl halides and polyHalomethanes, whereas plants are known to produce only methyl halides. Why these organisms produce Halomethanes is a question frequently asked by chemists and biologists. This question implies that Halomethanes have a function and have a selective value to the producing organism. Except for some fungi, the evolutionary advantage of producing Halomethanes may not presently exist. PolyHalomethanes are by-products of halogenation of certain organic compounds by haloperoxidases in marine algae and perhaps some fungi, and they may be indirectly produced in aquatic environments by algal release of oxidized halogen species. A main function of this enzyme is to rid the cell of harmful oxidants such as hydrogen peroxide. MonoHalomethanes (methyl halides) are products of methyltransferase activity. It has been proposed that methyl halide production may provide a mechanism to regulate chloride levels in halotolerant plants. The examination of halide cellular concentrations, Halomethane production rates, and enzyme characteristics raises questions about this possible function. In algae, plants and some fungi, methyl halides may be a result of the insertion of ubiquitous halides into the active site of numerous methyltransferases. Therefore, Halomethanes may be by-products or ‘accidents ’ of metabolism
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Phytogenesis of Halomethanes: A product ofselection or a metabolic accident?
Biogeochemistry, 2002Co-Authors: Steven L. ManleyAbstract:Phytoplankton (microalgae), seaweeds(macroalgae), higher plants and fungi produceHalomethanes. Algae and fungi produce bothmethyl halides and polyHalomethanes, whereasplants are known to produce only methylhalides. Why these organisms produceHalomethanes is a question frequently asked bychemists and biologists. This question impliesthat Halomethanes have a function and have aselective value to the producing organism.Except for some fungi, the evolutionaryadvantage of producing Halomethanes may notpresently exist. PolyHalomethanes areby-products of halogenation of certain organiccompounds by haloperoxidases in marine algaeand perhaps some fungi, and they may beindirectly produced in aquatic environments byalgal release of oxidized halogen species. Amain function of this enzyme is to rid the cellof harmful oxidants such as hydrogen peroxide.MonoHalomethanes (methyl halides) are productsof methyltransferase activity. It has beenproposed that methyl halide production mayprovide a mechanism to regulate chloride levelsin halotolerant plants. The examination of halidecellular concentrations, Halomethane productionrates, and enzyme characteristics raisesquestions about this possible function. Inalgae, plants and some fungi, methyl halidesmay be a result of the insertion of ubiquitoushalides into the active site of numerousmethyltransferases. Therefore, Halomethanes maybe by-products or `accidents' of metabolism.
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laboratory production of bromoform methylene bromide and methyl iodide by macroalgae and distribution in nearshore southern california waters
Limnology and Oceanography, 1992Co-Authors: Steven L. Manley, Kelly D Goodwin, Wheeler J NorthAbstract:Production rates of bromoform (CHBr,), methylene bromide (CH,Br,), and methyl iodide (CH31) were measured in the laboratory for 11 species of marine macroalgae. Production rates of the volatile bromomethanes extrapolated to a global scale suggest that marine macroalgae produce 2 x 10" g Br yr-I (1 x lo9 mol Br yr I), 98% of which is bromoform. Laminarians (kelps) produce 61% of this organic Br. These calculations suggest that marine macroalgae are important in the biogeochemical cycling of Br. Seawater concentrations of CHBr,, CH,Br,, and CH,I were deter- mined from various southern California coastal locales. High concentrations were measured in seawater from the canopy and the bottom of a dense bed of Macrocystis as compared to other sites. Surface seawater concentrations of these Halomethanes showed a strong cross-shore gradient with the highest concentration in the kelp canopy and the lowest at 5 km offshore. Seawater adjacent to decaying macroalgae on the bottom of a submarine canyon was not enriched in Halomethanes relative to- surface water. Water exiting a productive estuary was enriched only with CH,Br,, although two algal species that are abundant there (U/vu and Enteromorpha) showed high laboratory
Lorenzo Avaldi - One of the best experts on this subject based on the ideXlab platform.
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a joint theoretical and experimental study on diiodomethane ions and neutrals in the gas phase
Journal of Chemical Physics, 2015Co-Authors: M Satta, A R Casavola, Antonella Cartoni, P Bolognesi, Daniele Catone, Pal Markus, Lorenzo AvaldiAbstract:The chemical physics of Halomethanes is an important and challenging topic in several areas of chemistry in particular in the chemistry of the atmosphere. Among the class of Halomethanes, the diiodomethane molecule has attracted some interest in the last years, but despite this, the information on its radical cation [CH2I2]⋅+ is still limited. In this work, we measured and calculated the appearance energy (AE) of the ionic fragments I2⋅+ and CH2⋅+ and correlated the different fragmentation channels to the electronic states of the cation via photoelectron-photoion coincidence (PEPICO) experiments. In the case of the CH2/I2⋅+ channel, the experimentally determined AE is in excellent agreement with the adiabatic theoretical value while a discrepancy is observed for the CH2⋅+/I2 channel. This discrepancy can be understood accounting for a fragmentation involving the formation of two I atoms (CH2⋅+/2I channel), which, as explained by time dependent density functional theory (TD-DFT) calculations, occurs when [...
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vuv photofragmentation of ch2i2 the ch2i i iso diiodomethane intermediate in the i loss channel from ch2i2
Journal of Physical Chemistry A, 2015Co-Authors: Antonella Cartoni, A R Casavola, Stefano Borocci, Paola Bolognesi, Lorenzo AvaldiAbstract:Diiodomethane is an important halocarbon responsible for several atmospheric processes like ozone depletion and aerosol particle formation. Despite this, the thermochemical data and a detailed analysis of the pathways for the decomposition of this Halomethane and its molecular ion [CH2I2]•+ are scarce. In this paper an investigation of the photodissociation dynamics of the CH2I2 molecule focused on the I-loss channel by the photoelectron–photoion coincidence (PEPICO) technique and computational methods is reported. The experimental results show that upon VUV irradiation the dissociation of the lower electronic ionic states of diiodomethane leads only to the CH2I+ ion and the I atom. The theoretical calculations point out that isomerization of [CH2I2]•+ into iso-diiodomethane [CH2I–I]•+ may play an important role in the emission of iodine atom as compared to direct C–I bond breaking.
Italo Jose Da Cruz Rigotti - One of the best experts on this subject based on the ideXlab platform.
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Sintese de prolinas modificadas a partir de enecarbamato endociclico e estudo do equilibrio rotacional da ligação N-C(O) de seus derivados N-metoxicarbonilados por RMN 1H e calculos ab initio
2017Co-Authors: Italo Jose Da Cruz RigottiAbstract:Resumo: Uma série de 4,5-metanoprolinas foi preparada a partir da adição de espécies carbenóides ao N-carbometóxi-4,5-desidroprolinato de metila. Em condições de Simmons-Smith modificadas, obtiveram-se, após, 96 horas, dois produtos na proporção de 1:2 (determinado por CG) em 50% de rendimento. Sendo majoritário o produto que possui o grupamento metileno do ciclopropano cis ao éster do anel pirrolidínico. A adição de diclorocarbeno à olefina forneceu produtos com estereoquímica relativa cis e trans em razão 1:16 em 80% de rendimento. Apenas um produto, o trans, foi obtido em 50% de rendimento quando o dibromocarbeno foi adicionado à olefina. Além dos produtos finais e intermediários reacionais, uma série de N-carbometóxi-4-X-prolinatos de metila, em que X = -OH, -F e =O, tiveram a rotação da ligação N-C(O) estudada por RMN H. Não se observaram variações significativas no equilíbrio para os derivados das 4-X-prolinas quando comparados com o do da própria prolina, em contraste com as variações relatadas para a série das N-acetilprolinas. Por outro lado, para os derivados das hialometanoprolinas, houve um favorecimento do confôrmero Z, atribuído a interações dipolares desfavoráveis entre a carbonila do carbamato e os átomos de halogênio do confôrmero E. A barreira energética para a interconversão dos rotâmeros ficou na faixa de 16-18 kcal mol. As maiores barreiras foram observadas para os derivados das trans-dialometanoprolinas, e as menores para os derivados da desidroprolinae da cis-diclorometanoprolina. O estudo computacional desse processo por cálculos ab initio no nível HF/6-31G* permitiu, pela primeira vez, a observação dos quatro estados-de-transição possíveis para N-acilprolinas, e os valores determinados teoricamente se encontram em torno de 10% maior do que aqueles observados experimentalmente. A aplicação dos valores de energia das moléculas a reações isodésmicas permitiu inferir que o aumento da barreira nos derivados com estereoquímica trans se deve a uma maior desestabilização dos estados-de-transição que das geometrias de equilíbrio. Já a diminuição no caso do derivado cis, foi atribuído a uma maior desestabilização das geometrias de equilíbrio que dos estados-de-transição.Abstract: A series of 4,5-metanoprolines has been synthesized from the addition of carbenoid species to N-carbomethoxy-4,5-dehydroproline methyl ester. Under modified Simmons-Smith conditions, two products in a 1:2 ratio (as determined by GC) have been isolated in 50% yield after 96 hours. The major product has the cyclopropyl methylene cis to the pyrrolidine ester. Dichloromethane addition to the olefin furnished cis and trans products in a 1:16 ratio and 80% yield. Only one product was isolated when dibromocarbene was added to the olefine (50% yield). Moreover, a series of N-carbomethoxy-4-X-proline methyl esters, where X = -OH, -F and =O, had their N-C(O) bond rotational equilibrium studied by means of H NMR. Nosignificant variations in the equilibrium were observed for the 4-X-proline derivatives as compared to the proline derivative itself, in contrast to a previously reported variation for the N-acetyl-proline derivatives. ON the other hand, a preference for the Z conformer was observed for the di-Halomethane-proline derivatives. This was attributed to an unfavorable dipolar interaction between the carbonyl oxygen atom and the halogens in the E conformer. The barrier for conformer interconversion was determined to be around 16-18 kcal mol. The greatest barriers were observed for the trans-di-Halomethane-proline derivatives and the lowest for the dehydroproline and the cis-di-Halomethane ones. HF/6-31G* calculations for the topomerization allowed, for the first time, the observation of the four possible transition states for this process. The calculed barriers were overestimated by about 10% when compared to those obtained experimentally. The use of the molecular energies to isodesmic reactions allowed to infer that the rotational barrier increase observed for the trans-diHalomethane-proline derivatives is due to a greater destabilization of the transition states when compared to the equilibrium geometries, whereas the lowering in the barrier for the cis-di-Halomethane derivative is due to a greater destabilization of the ground state compared to the transition ones
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Sintese de prolinas modificadas a partir de enecarbamato endociclico e estudo do equilibrio rotacional da ligação N-C(O) de seus derivados N-metoxicarbonilados por RMN 1H e calculos ab initio
Universidade Estadual de Campinas . Instituto de Quimica, 2003Co-Authors: Italo Jose Da Cruz RigottiAbstract:Uma série de 4,5-metanoprolinas foi preparada a partir da adição de espécies carbenóides ao N-carbometóxi-4,5-desidroprolinato de metila. Em condições de Simmons-Smith modificadas, obtiveram-se, após, 96 horas, dois produtos na proporção de 1:2 (determinado por CG) em 50% de rendimento. Sendo majoritário o produto que possui o grupamento metileno do ciclopropano cis ao éster do anel pirrolidínico. A adição de diclorocarbeno à olefina forneceu produtos com estereoquímica relativa cis e trans em razão 1:16 em 80% de rendimento. Apenas um produto, o trans, foi obtido em 50% de rendimento quando o dibromocarbeno foi adicionado à olefina. Além dos produtos finais e intermediários reacionais, uma série de N-carbometóxi-4-X-prolinatos de metila, em que X = -OH, -F e =O, tiveram a rotação da ligação N-C(O) estudada por RMN H. Não se observaram variações significativas no equilíbrio para os derivados das 4-X-prolinas quando comparados com o do da própria prolina, em contraste com as variações relatadas para a série das N-acetilprolinas. Por outro lado, para os derivados das hialometanoprolinas, houve um favorecimento do confôrmero Z, atribuído a interações dipolares desfavoráveis entre a carbonila do carbamato e os átomos de halogênio do confôrmero E. A barreira energética para a interconversão dos rotâmeros ficou na faixa de 16-18 kcal mol. As maiores barreiras foram observadas para os derivados das trans-dialometanoprolinas, e as menores para os derivados da desidroprolinae da cis-diclorometanoprolina. O estudo computacional desse processo por cálculos ab initio no nível HF/6-31G* permitiu, pela primeira vez, a observação dos quatro estados-de-transição possíveis para N-acilprolinas, e os valores determinados teoricamente se encontram em torno de 10% maior do que aqueles observados experimentalmente. A aplicação dos valores de energia das moléculas a reações isodésmicas permitiu inferir que o aumento da barreira nos derivados com estereoquímica trans se deve a uma maior desestabilização dos estados-de-transição que das geometrias de equilíbrio. Já a diminuição no caso do derivado cis, foi atribuído a uma maior desestabilização das geometrias de equilíbrio que dos estados-de-transição.A series of 4,5-metanoprolines has been synthesized from the addition of carbenoid species to N-carbomethoxy-4,5-dehydroproline methyl ester. Under modified Simmons-Smith conditions, two products in a 1:2 ratio (as determined by GC) have been isolated in 50% yield after 96 hours. The major product has the cyclopropyl methylene cis to the pyrrolidine ester. Dichloromethane addition to the olefin furnished cis and trans products in a 1:16 ratio and 80% yield. Only one product was isolated when dibromocarbene was added to the olefine (50% yield). Moreover, a series of N-carbomethoxy-4-X-proline methyl esters, where X = -OH, -F and =O, had their N-C(O) bond rotational equilibrium studied by means of H NMR. Nosignificant variations in the equilibrium were observed for the 4-X-proline derivatives as compared to the proline derivative itself, in contrast to a previously reported variation for the N-acetyl-proline derivatives. ON the other hand, a preference for the Z conformer was observed for the di-Halomethane-proline derivatives. This was attributed to an unfavorable dipolar interaction between the carbonyl oxygen atom and the halogens in the E conformer. The barrier for conformer interconversion was determined to be around 16-18 kcal mol. The greatest barriers were observed for the trans-di-Halomethane-proline derivatives and the lowest for the dehydroproline and the cis-di-Halomethane ones. HF/6-31G* calculations for the topomerization allowed, for the first time, the observation of the four possible transition states for this process. The calculed barriers were overestimated by about 10% when compared to those obtained experimentally. The use of the molecular energies to isodesmic reactions allowed to infer that the rotational barrier increase observed for the trans-diHalomethane-proline derivatives is due to a greater destabilization of the transition states when compared to the equilibrium geometries, whereas the lowering in the barrier for the cis-di-Halomethane derivative is due to a greater destabilization of the ground state compared to the transition ones
Antonella Cartoni - One of the best experts on this subject based on the ideXlab platform.
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a joint theoretical and experimental study on diiodomethane ions and neutrals in the gas phase
Journal of Chemical Physics, 2015Co-Authors: M Satta, A R Casavola, Antonella Cartoni, P Bolognesi, Daniele Catone, Pal Markus, Lorenzo AvaldiAbstract:The chemical physics of Halomethanes is an important and challenging topic in several areas of chemistry in particular in the chemistry of the atmosphere. Among the class of Halomethanes, the diiodomethane molecule has attracted some interest in the last years, but despite this, the information on its radical cation [CH2I2]⋅+ is still limited. In this work, we measured and calculated the appearance energy (AE) of the ionic fragments I2⋅+ and CH2⋅+ and correlated the different fragmentation channels to the electronic states of the cation via photoelectron-photoion coincidence (PEPICO) experiments. In the case of the CH2/I2⋅+ channel, the experimentally determined AE is in excellent agreement with the adiabatic theoretical value while a discrepancy is observed for the CH2⋅+/I2 channel. This discrepancy can be understood accounting for a fragmentation involving the formation of two I atoms (CH2⋅+/2I channel), which, as explained by time dependent density functional theory (TD-DFT) calculations, occurs when [...
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vuv photofragmentation of ch2i2 the ch2i i iso diiodomethane intermediate in the i loss channel from ch2i2
Journal of Physical Chemistry A, 2015Co-Authors: Antonella Cartoni, A R Casavola, Stefano Borocci, Paola Bolognesi, Lorenzo AvaldiAbstract:Diiodomethane is an important halocarbon responsible for several atmospheric processes like ozone depletion and aerosol particle formation. Despite this, the thermochemical data and a detailed analysis of the pathways for the decomposition of this Halomethane and its molecular ion [CH2I2]•+ are scarce. In this paper an investigation of the photodissociation dynamics of the CH2I2 molecule focused on the I-loss channel by the photoelectron–photoion coincidence (PEPICO) technique and computational methods is reported. The experimental results show that upon VUV irradiation the dissociation of the lower electronic ionic states of diiodomethane leads only to the CH2I+ ion and the I atom. The theoretical calculations point out that isomerization of [CH2I2]•+ into iso-diiodomethane [CH2I–I]•+ may play an important role in the emission of iodine atom as compared to direct C–I bond breaking.
William R Dichtel - One of the best experts on this subject based on the ideXlab platform.
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resorcinarene cavitand polymers for the remediation of Halomethanes and 1 4 dioxane
Journal of the American Chemical Society, 2019Co-Authors: Luke P Skala, Anna Yang, Max J Klemes, Leilei Xiao, William R DichtelAbstract:Disinfection byproducts such as triHalomethanes are commonly found in drinking water. TriHalomethanes are formed upon chlorination of natural organic matter found in many drinking water sources. In...
