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

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

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

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

Metallo-Liposomes Derived from the [Ru(bpy)3]2+ Complex as Nanocarriers of Therapeutic Agents

The obtaining of nanocarriers of gene material and small drugs is still an interesting research line. Side-effects produced by the toxicity of several pharmaceutics, the high concentrations needed to get therapeutic effects, or their excessive use by patients have motivated the search for new nanostructures. For these reasons, cationic metallo-liposomes composed by phosphatidylcholine (PC), cholesterol (CHO) and RuC1C19 (a surfactant derived from the metallic complex [Ru(bpy)3]2+) were prepared and characterized by using diverse techniques (zeta potential, dynamic light scattering and electronic transmission microscopy –TEM-). Unimodal or bimodal populations of spherical aggregates with small sizes were obtained depending on the composition of the liposomes. The presence of cholesterol favored the formation of small aggregates. ct-DNA was condensed in the presence of the liposomes investigated. In-vitro assays demonstrated the ability of these nanoaggregates to internalize into different cell lines. A positive gene transfection into human bone osteosarcoma epithelial cells (U2OS) was also observed. The RuC1C19 surfactant was used as sensor to quantify the binding of DNA to the liposomes. Doxorubicin was encapsulated into the metallo-liposomes, demonstrating their ability to be also used as nanocarriers of drugs. A relationship between then encapsulation percentage of the antibiotic and the composition of the aggregates has been established.Junta de Andalucía 2019/FQM-206, 2019/FQM-274Ministerio de Ciencia e Innovación RTI2018-100692-BI00, PI-0005-2018, P18-RT-127

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

Assessment of the denaturation of collagen protein concentrates using different techniques

The use of collagen and gelatin in the field of regenerative medicine is widely extended. However, most of the studies in this topic are focused on the scaffolds’ properties, but only a few are related to the properties of the raw material used. The raw material analysis not only consists of a study of the composition, but also of the denaturation degree that can influence the processing and properties of the structure of the scaffold. Thus, the denaturation degree analysis of different collagen proteins was performed and assessed by the comparison of four different methods: differential scanning calorimetry (DSC), Fourier transform Infrared Spectroscopy (FTIR) and circular dichroism (CD) spectra and sulfhydryls content analysis. DSC measurements put forward a glass transition between 88°C and 95°C as well as from the FTIR measurements; the characteristic peaks for proteins are evidenced. However, from the sulfur content, only a small proportion of free sulfhydryls are present with respect to their total amount. In addition, CD spectra allow to estimate the secondary structure of the protein by the analysis of the α-helix and β-strand and also quantify the denaturation degree with the ‘positive/negative ratio’ (RPN) from the CD profiles, obtaining values in the range between 25% and 100%.Ministerio de Economía y Competitividad (Spanish Government) / MINECO/FEDER (UE) CTQ2015-71164-

Metallo-Liposomes of Ruthenium Used as Promising Vectors of Genetic Material

Gene therapy is a therapeutic process consisting of the transport of genetic material into cells. The design and preparation of novel carriers to transport DNA is an important research line in the medical field. Hybrid compounds such as metallo-liposomes, containing a mixture of lipids, were prepared and characterized. Cationic metal lipids derived from the [Ru(bpy)3]2+ complex, RuC11C11 or RuC19C19, both with different hydrophobic/lipophilic ratios, were mixed with the phospholipid DOPE. A relation between the size and the molar fraction α was found and a multidisciplinary study about the interaction between the metallo-liposomes and DNA was performed. The metallo-liposomes/DNA association was quantified and a relationship between Kapp and α was obtained. Techniques such as AFM, SEM, zeta potential, dynamic light scattering and agarose gel electrophoresis demonstrated the formation of lipoplexes and showed the structure of the liposomes. L/D values corresponding to the polynucleotide's condensation were estimated. In vitro assays proved the low cell toxicity of the metallo-liposomes, lower for normal cells than for cancer cell lines, and a good internalization into cells. The latter as well as the transfection measurements carried out with plasmid DNA pEGFP-C1 have demonstrated a good availability of the Ru(II)-based liposomes for being used as non-toxic nanovectors in gene therapy.España Consejería de Educación y Ciencia de la Junta de Andalucía (Proyecto de Excelencia P12-FQM-1105, FQM-206 and FQM-274, and PI-0005-2018)España,, Universidad de Sevilla, VI Plan Propio Universidad de Sevilla (PP2018-10338)España Ministerio de Ciencia, Innovación y Universidades (RTI2018-100692-B-I00

Estudio de la reactividad química en sistemas micelares inversos

Desde hace ya varios años, nuestro grupo de investigación ha venido realizando estudios de los efectos del medio y salinos sobre las reacciones químicas. Con el fin de continuar en esta línea y dada la importancia que recientemente vienen presentando los sistemas micelares, en este trabajo hemos realizado un estudio sobre la influencia que pueden ejercer los sistemas micelares inversos del tipo AOT/fase orgánica/agua sobre diversas reacciones químicas, previamente estudiadas en disolución acuosa convencional, lo que nos permite comparar la velocidad de dichos procesos en disolución acuosa convencional y en sistemas micelares.Las reacciones elegidas han sido:1) 2Fe(CN)64- + S2O82- 2Fe(CN)63- + 2SO42-2) Fe(CN)5(4-CNpy)3- + CN- Fe(CN)64- + 4-CNpy3) 2Fe(CN)4(bpy)2- + S2O82- 2Fe(CN)4(bpy)- + 2SO42-4) 2cis-Fe(CN)2(bpy)2 + S2O82 2Fe(CN)2(bpy)2+ + 2SO42-5) 2Fe(bpy)32+ + S2O82 2Fe(bpy)33+ + 2SO42- La elección de estos sistemas reactivos se basó en una serie de puntos:I) El sistema Fe(CN)5(4-CNpy)3- + CN-, en presencia de suficiente exceso de ligando cianuro, transcurre siguiendo un mecanismo de reacción de verdadero primer orden, lo que nos va a permitir estudiar la influencia de los sistemas micelares inversos sobre una reacción sin necesidad de considera posibles cambios en las concentraciones efectivas de los reactivos. II) En cuanto al resto de los procesos, todos ellos de transferencia electrónica e independientes del pH del medio en un amplio intervalo se caracterizan por tener un reactivo común (el S2O82-) y por la variación de la magnitud y del signo de la carga del otro reactivo, así como su carácter polar. A este respecto pasamos de un reactivo muy hidrófilo y aniónico como es el ferrocianuro, a otro catiónico y de carácter hidrófobo como el Fe(bpy)32+. Esto, en principio, hace esperar que la reacción pueda transcurrir en diferentes zonas dentro del sistema micelar, lo que debería traducirse, como de hecho se verá, en una dependencia de la velocidad de reacción con los diferentes parámetros que caracterizan a las microemulsiones, bien diferenciados para los diferentes sistemas reactivos estudiados. Además, el presente estudio tiene el interés adicional de la escases de investigaciones existentes sobre reactividad química de procesos inorgánicos en sistemas microemulsiones