RESUMO
A polyhydroxamicalkanoate (PHA) polymer containing the functional groups hydroxamic acid and carboxylic acid with the ability to accelerate dephosphorylation reactions is proposed. The methodology used to prepare this polymer favored the position of the two functional groups next to each other, which allows for the cooperativity between these groups. This cooperative effect has an important role when one wants to mimic enzymes. The catalytic effect promoted by the polymer was evaluated on the cleavage of the bis(2,4-dinitrophenyl) phosphate (BDNPP) and diethyl 2,4-dinitrophenyl phosphate (DEDNPP) esters. Indeed, PHA was very efficient and promiscuous because it increased the rate of both reactions by a factor of up to 10(6)-fold. Isothermal titration calorimetry (ITC) experiments showed that the presence of PHA aids the formation of cetyltrimethylammonium bromide (CTABr) micelles. Thus, the effect of the cationic surfactant CTABr on the dephosphorylation of BDNPP by PHA was also investigated, and it was observed that, when CTABr is added to PHA, the reaction is ca. 15-fold faster compared to the reaction when only PHA is present.
Assuntos
Ácidos Carboxílicos/química , Ácidos Hidroxâmicos/química , Mimetismo Molecular , Nanotecnologia/métodos , Organofosfatos/metabolismo , Polímeros , Calorimetria , Catálise , Cetrimônio , Compostos de Cetrimônio/síntese química , Concentração de Íons de Hidrogênio , Hidrólise , Cinética , Espectrometria de Massas , Micelas , Monoéster Fosfórico Hidrolases/química , Monoéster Fosfórico Hidrolases/metabolismo , Polímeros/síntese química , Polímeros/metabolismo , Potenciometria , Especificidade por Substrato , Tensoativos/síntese químicaRESUMO
The aim of this study was to verify the duration of the development period, number of parasitoids produced per pupa, parasitism rate and sex ratio of Nasonia vitripennis (Hymenoptera, Pteromalidae), when they were exposed to a single host: Chrysomya megacephala (Diptera, Calliphoridae). One pupa was exposed in glass tubes to different numbers of female parasitoids (1, 3, 5, 7, 9 and 11) during 48 h. Twenty replications/treatment were used, under controlled conditions (T= 27 °C day/ 25 °C night, 60 ± 10 percent RH). Statistical analysis of the data was made using the ANOVA test and the "a posteriori" comparisons were made using the Tukey-HSD test (both tests with a significance level of 5 percent). The duration of the development period was longer in treatments where a higher density of females per host was used. When five females per host were used, the mean number of parasitoids that emerged per pupa was higher. The data showed a tendency to a decrease in the amount of parasitoids emerged per host, especially of female, when used high quantities of female per host. Higher parasitism rates were observed in the 3:1 and 5:1 treatments and an increase in the percentage of unviable pupae was observed, probably due to an increase of female densities in the treatments, possibly a consequence of superparasitism.
O objetivo deste estudo foi verificar a duração do período de desenvolvimento, número de parasitóides produzidos por pupa, a taxa de parasitismo e a razão sexual de Nasonia vitripennis (Hymenoptera, Pteromalidae), quando submetidas ao hospedeiro Chrysomya megacephala (Diptera, Calliphoridae). Uma pupa foi exposta, em tubos de ensaio, a diferentes quantidades de fêmeas parasitóides (1, 3, 5, 7, 9 e 11) por um período de 48 h. Foram realizadas 20 réplicas/ tratamento, sob condições controladas (T= 27 °C dia/ 25 °C noite, 60 ± 10 por cento UR). Foi utilizado ANOVA e teste Tukey-HSD para comparações posteriores (ambos com nível de significância 5 por cento). Foi observado um desenvolvimento mais lento nos tratamentos que utilizaram elevadas quantidades de fêmeas por hospedeiro. Quando utilizadas cinco fêmeas por hospedeiro, a média de parasitóides por pupa foi maior. Os dados mostraram que houve uma tendência para o decréscimo de parasitóides, especialmente de fêmeas, quando utilizadas elevadas quantidade de fêmeas por hospedeiro. As maiores taxas de parasitismo foram verificadas nos tratamentos 3:1 e 5:1, e foi observado um aumento na porcentagem de pupas inviáveis com a utilização de quantidades mais elevadas de fêmeas parasitóides por hospedeiro. Possivelmente causado pelo superparasitismo.
RESUMO
Mixed micelles of cetyltrimethylammonium bromide (CTABr) or dodecyltrimethylammonium bromide (DTABr) and the alpha-nucleophile, lauryl hydroxamic acid (LHA) accelerate dephosphorylation of bis(2,4-dinitrophenyl)phosphate (BDNPP) over the pH range 4-10. With a 0.1 mole fraction of LHA in DTABr or CTABr, dephosphorylation of BDNPP is approximately 10(4)-fold faster than its spontaneous hydrolysis, and monoanionic LHA(-) is the reactive species. The results are consistent with a mechanism involving concurrent nucleophilic attack by hydroxamate ion (i) on the aromatic carbon, giving an intermediate that decomposes to undecylamine and 2,4-dinitrophenol, and (ii) at phosphorus, giving an unstable intermediate that undergoes a Lossen rearrangement yielding a series of derivatives including N,N-dialkylurea, undecylamine, undecyl isocyanate, and carbamyl hydroxamate.
Assuntos
Ácidos Hidroxâmicos/química , Micelas , Organofosfatos/química , Tensoativos/química , Cátions , Cinética , Espectroscopia de Ressonância Magnética , Fosforilação , Potenciometria , Espectrometria de Massas por Ionização por ElectrosprayRESUMO
The reaction between the benzohydroxamate anion (BHO(-)) and bis(2,4-dinitrophenyl)phosphate (BDNPP) has been examined kinetically, and the products were characterized by mass and NMR spectroscopy. The nucleophilic attack of BHO(-) follows two reaction paths: (i) at phosphorus, giving an unstable intermediate that undergoes a Lossen rearrangement to phenyl isocyanate, aniline, diphenylurea, and O-phenylcarbamyl benzohydroxamate; and (ii) on the aromatic carbon, giving an intermediate that was detected but slowly decomposes to aniline and 2,4-dinitrophenol. Thus, the benzohydroxamate anion can be considered a self-destructive molecular scissor since it reacts and loses its nucleophilic ability.
Assuntos
2,4-Dinitrofenol/química , Benzeno , Ácidos Hidroxâmicos/química , Fosfatos/química , Ânions , Cinética , Espectroscopia de Ressonância Magnética , Estrutura MolecularRESUMO
The title mol-ecule (alternative name: pyridine-3-carbohydrazide; C(6)H(7)N(3)O) was obtained from the reaction of ethyl nicotinate with hydrazine hydrate in methanol. In the amide group, the C-N bond is relatively short, suggesting some degree of electronic delocalization in the mol-ecule. The stabilized conformation may be compared with those of isomeric compounds picolinohydrazide (pyridine-2-carbohydrazide) and isonicotinohydrazide (pyridine-4-carbohydrazide). In the title isomer, the pyridine ring forms an angle of 33.79â (9)° with the plane of the non-H atoms of the hydrazide group. This lack of coplanarity between the hydrazide functionality and the pyridine ring is considerably greater than that observed in isonicotinohydrazide (dihedral angle = 17.14°), while picolinohydrazide is almost fully planar. The title isomer forms inter-molecular N-Hâ¯O and N-Hâ¯N hydrogen bonds, which stabilize the crystal structure.