Preparation and Characterization of New Liposomes. Bactericidal Activity of Cefepime Encapsulated into Cationic Liposomes

Cefepime is an antibiotic with a broad spectrum of antimicrobial activity. However, this antibiotic has several side effects and a high degradation rate. For this reason, the preparation and characterization of new liposomes that are able to encapsulate this antibiotic seem to be an important research line in the pharmaceutical industry. Anionic and cationic liposomes were prepared and characterized. All cationic structures contained the same cationic surfactant, N,N,N-triethyl-N-(12-naphthoxydodecyl)ammonium. Results showed a better encapsulation-efficiency percentage (EE%) of cefepime in liposomes with phosphatidylcholine and cholesterol than with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). The presence of cholesterol and the quantity of egg-yolk phospholipid in the liposome increased the encapsulation percentage. The bactericidal activity against Escherichia coli of cefepime loaded into liposomes with phosphatidylcholine was measured. The inhibitory zone in an agar plate for free cefepime was similar to that obtained for loaded cefepime. The growth-rate constant of E. coli culture was also measured in working conditions. The liposome without any antibiotic exerted no influence in such a rate constant. All obtained results suggest that PC:CH:12NBr liposomes are biocompatible nanocarriers of cefepime that can be used in bacterial infections against Escherichia coli with high inhibitory activity

Activation Volumes for Peroxodisulphate Oxidation of Low-spin Iron(II) Complexes in Aqueous Salt Solutions

Activation volumes are reported for peroxodisulphate oxidation of the four complexes of the Fe2+-2,2′-bipyridyl-cyanide sequence, viz. [Fe(bipy)3]2+, [Fe(bipy)2(CN)2], [Fe(bipy)(CN)4]2- and [Fe(CN)6]4- (abbr. bipy for 2,2′-bipyridyl), in aqueous solutions of a selection of nitrate, sulphate, and perchlorate salts of Li+, Na+, K+, and Mg2+ containing up to 6 mol dm-3 of added salt. The dependences of activation volumes on the nature and concentration of the added salt, and on the nature of the iron(II) complex, are established and discussed. Ancillary information relevant to hydration of the substrate complexes in the initial state for peroxodisulphate oxidation has been obtained from solvatochromism (halochromism) of [Fe(bipy)2(CN)2] and of [Fe(bipy)(CN)4]2-, and from the solubility of [Fe(bipy)2(CN)2], in some of the electrolyte solutions used in the high pressure kinetic studies

Activation Volumes for Peroxodisulphate Oxidation of Low-spin Iron(II) Complexes in Aqueous Salt Solutions

Activation volumes are reported for peroxodisulphate oxidation of the four complexes of the Fe2+-2,2\u27-bipyridyl-cyanide sequence, viz. [Fe(bipy)3]2+, [Fe(bipy)2(CN)2], [Fe(bipy)(CN)4]2- and [Fe(CN)6]4- (abbr. bipy for 2,2\u27-bipyridyl), in aqueous Solutions of a selection of nitrate, sulphate, and perchlorate salts of Li+, Na+, K+, and Mg2+ containing up to 6 mol dm-3 of added salt. The dependences of activation volumes on the nature and concentration of the added salt, and on the nature of the iron(II) complex, are established and discussed. Ancillary information relevant to hydration of the substrate complexes in the initial state for peroxodisulphate oxidation has been obtained from solvatochromism (halochromism) of [Fe(bipy)2(CN)2] and of [Fe(bipy)(CN)4]2-, and from the solubility of [Fe(bipy)2(CN)2], in some of the electrolyte Solutions used in the high pressure kinetic studies

Influence of the surfactant degree of oligomerization on the formation of cyclodextrin: surfactant inclusion complexes

Supramolecular complexation is an attractive strategy to modulate the performance of surfactants, e.g., by host-guest interactions. Here, we investigate the interaction of single-chained, di-, tri-, and tetrameric cationic surfactants with cyclodextrins by conductivity and 1H NMR measurements, exploring the effect of increasing the number of the surfactant hydrophobic tails on the stability of cyclodextrin:surfactant inclusion complexes. The stoichiometry and the binding equilibrium constants of the different inclusion complexes were elucidated. Under the working conditions, the number of hydrophobic chains was found not to affect stoichiometry and 1:1 inclusion complexes were formed for all the surfactants investigated. The stability of the host-guest complexes decreases from single-chained to dimeric (“gemini”) surfactants, the binding following a non-cooperative mechanism. This result may be rationalized by taking into account steric constraints and electrostatic effects as well as the need to overcome the hydrophobic interactions between the chains of the same surfactant molecule. However, a further increase in the number of hydrophobic tails, from two to three to four, results in an increase in the equilibrium binding constant, K1. In this case, an increment in the number of chains capable of interaction with the cyclodextrin molecules seems to be the main factor responsible for the increase in K1. ROESY spectra show the coexistence of different types of 1:1 host-guest complexes for tri- and tetrameric surfactants.Consejería de Innovación, Ciencia y Empresa de la Junta de Andalucía P12-FQM- 1105, FQM-274 y FQM-206University of Seville 2017/1004FEDER fund

Spatio-temporal statistical analysis of PM1 and PM2.5 concentrations and their key influencing factors at Guayaquil city, Ecuador

Guayaquil, Ecuador, is in a tropical area on the equatorial Pacific Ocean coast of South America. Since 2008 the city has been increasing its population, vehicle fleet and manufacturing industries. Within the city there are various industrial and urban land uses sharing the same space. With regard to air quality there is a lack of government information on it. Therefore, the research’s aim was to investigate the spatio-temporal characteristics of PM1 and PM2.5 concentrations and their main influencing factors. For this, both PM fractions were sampled and a bivariate analysis (cross-correlation and Pearson's correlation), multivariate linear and logistic regression analysis was applied. Hourly and daily PM1 and PM2.5 were the dependent variables, and meteorological variables, occurrence of events and characteristics of land use were the independent variables. We found 48% exceedances of the PM2.5-24 h World Health Organization 2021 threshold’s, which questions the city’s air quality. The cross-correlation function and Pearson’s correlation analysis indicate that hourly and daily temperature, relative humidity, and wind speed have a complex nonlinear relationship with PM concentrations. Multivariate linear and logistic regression models for PM1-24 h showed that rain and the flat orography of cement plant sector decrease concentrations; while unusual PM emission events (traffic jams and vegetation-fires) increase them. The same models for PM2.5-24 h show that the dry season and the industrial sector (strong activity) increase the concentration of PM2.5-24 h, and the cement plant decrease them. Public policies and interventions should aim to regulate land uses while continuously monitoring emission sources, both regular and unusual.Peer ReviewedObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (published version

Binding of DNA by a dinitro-diester calix[4]arene: Denaturation and condensation of DNA

A study of a dinitro-diester calix[4]arene (5,17-(3-nitrobenzylideneamino)-11,23-di-tert-butyl-25,27-diethoxycarbonyl methyleneoxy-26,28-dihydroxycalix[4]arene) interaction with calf-thymus DNA was carried out using several techniques. The measurements were done at various molar ratios X=[calixarene]/[DNA]. Results show diverse changes in the DNA conformation depending on the X value. Thus, at low macrocycle concentrations, the calixarene binds to the polynucleotide. This interaction, mainly in groove mode, weakens the hydrogen bonds between base pairs of the helix inducing denaturation of the double strands, as well as condensation of the macromolecule, from an extended coil state to a globular state. An opposite effect is observed at X molar ratios higher than 0.07. The de-condensation of DNA happens, that is, the transition from a compact state to a more extended conformation, probably due to the stacking of calixarene molecules in the solution. Results also show the importance of making a proper choice of the system under consideration.Junta de Andalucía P08-FQM-03623, P12-FQM-110

Potentiometric study of carbon nanotube/surfactant interactions by ion-selective electrodes. Driving forces in the adsorption and dispersion processes

The interaction (adsorption process) of commercial ionic surfactants with non-functionalized and functionalized carbon nanotubes (CNTs) has been studied by potentiometric measurements based on the use of ion-selective electrodes. The goal of this work was to investigate the role of the CNTs' charge and structure in the CNT/surfactant interactions. Non-functionalized single- (SWCNT) and multi-walled carbon nanotubes (MWCNT), and amine functionalized SWCNT were used. The influence of the surfactant architecture on the CNT/surfactant interactions was also studied. Surfactants with different charge and hydrophobic tail length (sodium dodecyl sulfate (SDS), octyltrimethyl ammonium bromide (OTAB), dodecyltrimethyl ammonium bromide (DoTAB) and hexadecyltrimethyl ammonium bromide (CTAB)) were studied. According to the results, the adsorption process shows a cooperative character, with the hydrophobic interaction contribution playing a key role. This is made evident by the correlation between the free surfactant concentration (at a fixed [CNT]) and the critical micellar concentration, cmc, found for all the CNTs and surfactants investigated. The electrostatic interactions mainly determine the CNT dispersion, although hydrophobic interactions also contribute to this process.Fil: Ostos, Francisco José. Universidad de Sevilla; EspañaFil: Lebrón, José Antonio. Universidad de Sevilla; EspañaFil: Moyá, María Luisa. Universidad de Sevilla; EspañaFil: Bernal, Eva. Universidad de Sevilla; EspañaFil: Flores, Ana. Universidad de Huelva; EspañaFil: Lépori, Cristian Marcelo Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Maestre, Ángeles. Universidad de Huelva; EspañaFil: Sánchez, Francisco. Universidad de Sevilla; EspañaFil: López Cornejo, Pilar. Universidad de Sevilla; EspañaFil: López López, Manuel Carlos. Universidad de Huelva; Españ

Host-guest interactions between cyclodextrins and surfactants with functional groups at the end of the hydrophobic tail

The aim of this work was to investigate the influence of the incorporation of substituents at the end of the hydrophobic tail on the binding of cationic surfactants to α-, β-, and -cyclodextrins. The equilibrium binding constants of the 1:1 inclusion complexes formed follow the trend K1(α-CD)>K1(β-CD)>>K1(-CD), which can be explained by considering the influence of the CD cavity volume on the host-guest interactions. From the comparison of the K1 values obtained for dodecyltriethylammonium bromide, DTEAB, to those estimated for the surfactants with the substituents, it was found that the incorporation of a phenoxy group at the end of the hydrocarbon tail does not affect K1, and the inclusion of a naphthoxy group has some influence on the association process, slightly diminishing K1. This makes evident the importance of the contribution of hydrophobic interactions to the binding, the length of the hydrophobic chain being the key factor determining K1. However, the presence of the aromatic rings does influence the location of the host and the guest in the inclusion complexes. The observed NOE interactions between the aromatic protons and the CD protons indicate that the aromatic rings are partially inserted within the host cavity, with the cyclodextrin remaining close to the aromatic rings, which could be partially intercalated in the host cavity. To the authors´ knowledge this is the first study on the association of cyclodextrins with monomeric surfactants incorporating substituents at the end of the hydrophobic tai