Resumo A atividade carrapaticida in vitro do extrato metanólico (EM) e da fração de alcaloides (FA) de Prosopis juliflora foi investigada, frente ao Rhipicephalus microplus, e relacionada com a inibição da enzima acetilcolinesterase (AChE). A predição in silico das interações de alcaloides dessa fração com a AChE1 de R. microplus (RmAChE1) foi realizada por acoplamento molecular. A atividade carrapaticida foi avaliada, utilizando-se os ensaios de imersão de adultos e larvas. Maior efeito sobre parâmetros reprodutivos de teleóginas foi verificado para a FA, com valor de Concentração Efetiva 50% (CE50) (31.6 mg/mL), quatro vezes menor do que o valor do EM (121 mg/mL). A FA induziu mortalidade de larvas (Concentração Letal de 50% - CL50 = 13,8 mg/mL). A inibição da atividade da AChE de larvas do carrapato foi observada para EM e FA, sendo a FA mais ativa (Concentração Inibitória 50%- CI50 de 0,041mg/mL). As análises químicas da FA permitiram a identificação dos alcaloides prosopina (1), juliprosinina (2) e juliprosopina (3). No ensaio in silico, observou-se que esses alcaloides podem interagir com o sítio ativo da RmAChE1, principalmente por ligações de hidrogênio e interações cátion-pi. Os alcaloides de P. juliflora têm atividade carrapaticida contra R. microplus, atuando através do mecanismo anticolinesterásico.

Abstract We investigated the in vitro acaricide activity of the methanolic extract (ME) and alkaloid-rich fraction (AF) of Prosopis juliflora on Rhipicephalus microplus and correlated this effect with acetylcholinesterase (AChE) inhibition. The acaricide activity was evaluated using adult and larval immersion tests. Also, we studied the possible interaction mechanism of the major alkaloids present in this fraction via molecular docking at the active site of R. microplus AChE1 (RmAChE1). Higher reproductive inhibitory activity of the AF was recorded, with effective concentration (EC50) four times lower than that of the ME (31.6 versus 121 mg/mL). The AF caused mortality of tick larvae, with lethal concentration 50% (LC50) of 13.8 mg/mL. Both ME and AF were seen to have anticholinesterase activity on AChE of R. microplus larvae, while AF was more active with half-maximal inhibitory concentration (IC50) of 0.041 mg/mL. The LC-MS/MS analyses on the AF led to identification of three alkaloids: prosopine (1), juliprosinine (2) and juliprosopine (3). The molecular docking studies revealed that these alkaloids had interactions at the active site of the RmAChE1, mainly relating to hydrogen bonds and cation-pi interactions. We concluded that the alkaloids of P. juliflora showed acaricide activity on R. microplus and acted through an anticholinesterase mechanism.

The combination of two low-cost classical procedures based on titrimetric techniques is presented for the determination of pyridoxine hydrochloride in pharmaceuticals samples. Initially some experiments were carried out aiming to determine both pKa1 and pKa2 values, being those compared to values of literature and theoretical procedures. Commercial samples containing pyridoxine hydrochloride were electrochemically analysed by exploiting their acid-base and precipitation reactions. Potentiometric titrations accomplished the reaction between the ionizable hydrogens present in pyridoxine hydrochloride, being NaOH used as titrant; while the conductimetric method was based on the chemical precipitation between the chloride of pyridoxine hydrochloride molecule and Ag+ ions from de silver nitrate, changing the conductivity of the solution. Both methods were applied to the same commercial samples leading to concordant results when compared by statistical tests (95 and 98% confidence levels). Recoveries ranging from 99.0 to 108.1% were observed, showing no significant interference on the results.