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Objective To estimate the incidence of falls and to know their characteristics in terms of location, temporality and injuries produced, and to analyse the sociodemographic and clinical characteristics of the patients who suffer falls. Methodology A retrospective observational cohort study was carried out in a level 2 hospital of the Madrid Health Service. Falls in hospitalized patients between July 1, 2018 and June 30, 2019 were studied. The incidence rate of falls per 1000 days of stay was estimated considering a Poisson distribution. The characteristics of the falls are described: temporality, injuries produced, location of the injuries and prescribed drugs. Sociodemographic and clinical characteristics of patients who suffered a fall were registered. A univariate analysis was performed to compare the results by gender. All data were obtained from the electronic medical record. Results One hundred and thirty-two falls were studied, which represent a rate of 1.61 falls per 1,000 days of stay. Men, older age, and admission to a medical specialty showed a significantly higher fall rate. The patients who suffered a fall had a mean age of 77.5 years (SD: 11.7), and had a median of 12.5 drugs prescribed (IQR: 9.25-15). Of the falls, 63.6% did not present any injury. Difference in gender was only found in the situation in which the fall occurred. Conclusions Our data report an incidence of falls similar to other institutions in our environment. The profile of the patient who suffers a fall is an older man, admitted under the charge of a medical specialty, with longer hospital stay, with associated comorbidity and polymedicated, without an obvious temporal feature.

Resumen Objetivo Estimar la incidencia de caidas y conocer sus caracteristicas en cuanto a localizacion, temporalidad y lesiones producidas, y analizar las caracteristicas sociodemograficas y clinicas de los pacientes que sufren caidas. Metodo Se llevo a cabo un estudio observacional de cohortes retrospectivo, en un hospital de nivel 2 del Servicio Madrileno de Salud. Se estudiaron las caidas de pacientes hospitalizados entre el 1 de julio de 2018 y el 30 de junio de 2019. Se estimo la tasa de incidencia de caidas por 1.000 dias de estancia considerando una distribucion de Poisson. Se describen las caracteristicas de las caidas: temporalidad, lesiones producidas, localizacion de las lesiones y pauta de farmacos. Se registraron caracteristicas sociodemograficas y clinicas de los pacientes que sufrieron una caida. Se realizo un analisis univariante para comparar los resultados por sexos. Todos los datos se han obtenido de registros de la historia clinica electronica. Resultados Se estudiaron 132 caidas, que suponen una tasa de 1,61 caidas por 1.000 dias de estancia. Hombres, edad avanzada e ingreso a cargo de una especialidad medica presentaron una tasa de caida significativamente mayor. Los pacientes que sufrieron una caida tienen una edad media de 77,5 anos (DE 11,7), y tuvieron pautados una mediana de 12,5 farmacos (RIC 9,25-15). El 63,6% de las caidas no presentan lesion alguna. Solo se encontro diferencia en cuanto al genero en la situacion en la que se produce la caida. Conclusiones Nuestros datos notifican una incidencia de caidas similar a la de centros de nuestro entorno. El perfil del paciente que sufre una caida es el de un hombre mayor, ingresado a cargo de una especialidad medica, con estancias hospitalarias mas largas, con alguna comorbilidad y polimedicado, sin una asociacion temporal evidente.

Embargado hasta 09/04/2023 Polymersomes and related self-assembled nanostructures displaying Aggregation-Induced Emission (AIE) are highly relevant for plenty of applications in imaging, biology and functional devices. Experimentally simple, scalable and universal strategies for on-demand self-assembly of polymers rendering well-defined nanostructures are highly desirable. A purposefully designed combination of amphiphilic block copolymers including tunable lengths of hydrophilic polyethylene glycol (PEGm) and hydrophobic AIE polymer poly(tetraphenylethylene-trimethylenecarbonate) (P(TPE-TMC)n) has been studied at the air/liquid interface. The unique 2D assembly properties have been analyzed by thermodynamic measurements, UV-vis reflection spectroscopy and photoluminescence in combination with molecular dynamics simulations. The (PEG)m-b-P(TPE-TMC)n monolayers formed tunable 2D nanostructures self-assembled on demand by adjusting the available surface area. Tuning of the PEG length allows to modification of the area per polymer molecule at the air/liquid interface. Molecular detail on the arrangement of the polymer molecules and relevant molecular interactions has been convincingly described. AIE fluorescence at the air/liquid interface has been successfully achieved by the (PEG)m-b-P(TPE-TMC)n nanostructures. An experimentally simple 2D to 3D transition allowed to obtain 3D polymersomes in solution. This work suggests that engineered amphiphilic polymers for AIE may be suitable for selective 2D and 3D self-assembly for imaging and technological applications.

The present work studies the stability of Langmuir organic-inorganic superlattice materials thin films consisting of layered perovskite-based films with controlled 2D framework as well as to design experimental conditions for increasing the efficiency of the organic-inorganic perovskite motif by mechanical stimulus. Therefore, a whole covering of the air/water interface by a compact and stable lead-based layered perovskite structure is pursued. A 2D layered perovskite-type hybrid structure of the form [(CH3(CH2)19NH3)2(PbX4)], X=Cl, and Br, in which, two-dimensional sheets stabilized by a inner bilayer of organic monoammonium cation matrix, is mechanically tailored by successive compression-expansion cycles. The formation of 2D molecular patterns has been characterized by ΔR, BAM, XRD and XPS.

Objective We report the findings from the Spanish Society of Neurology's NeuroCOVID-19 Registry. Methods We performed a multicentre study of patients with neurological manifestations of COVID-19. Participating physicians reported demographic, clinical, and paraclinical data and judged the involvement of COVID-19 in causing neurological symptoms. Results A total of 233 cases were submitted, including 74 different combinations of manifestations. The most frequently reported were stroke (27%), neuromuscular symptoms (23.6%), altered mental status (23.6%), anosmia (17.6%), headache (12.9%), and seizures (11.6%). The mean age of patients was 61.1 years, with 42.1% being women; a higher proportion of women was recorded among patients with altered mental status, anosmia, and headache. The onset of symptoms differed within categories. Onset of anosmia occurred a mean (standard deviation) of 2.9 (2.5) days after the first general symptom, whereas neuromuscular symptoms appeared after 13.9 (10.1) days. Neurological symptoms were persistent in 33% of patients. General symptoms were present in 97.7% of patients, and results from general laboratory studies were abnormal in 99.4% of patients. Cerebrospinal fluid analysis findings were abnormal in 62.7% of the cases in which this test was performed (n = 51), but positive results for SARS-CoV-2 were only found in one case. Conclusions The neurological manifestations of COVID-19 are diverse. Anosmia, myalgia, and headache occur earlier in the course of the disease. Altered mental status, neuromuscular symptoms, and stroke are associated with greater severity. COVID-19 must be incorporated into most clinical and radiological differential diagnoses. COVID-19 may cause persistent and disabling neurological symptoms., Highlights • NeuroCovid-19 is polymorph: Authors reported >70 different combinations of neurological syndromic presentations. • The timing of the neurological symptoms differ: from the early onset (anosmia, headache, myalgia) to later stages (altered mental status, seizures, stroke, neuromuscular symptoms). • Some neurological symptoms might persist, as headache or anosmia; while other may cause persistent disability, as stroke or polyneuropathies. • Cerebrospinal fluid was frequently abnormal but direct isolation of SARS-CoV-2 occurred only in 1/233 cases. • Neurologists must be prepared to face the various neurological syndromes that may be associated with Covid-19 infection.

A physical model of a batch aluminum degassing reactor equipped with the rotor-injector technique was used to measure deoxidation kinetics of water, assuming that this kinetics is similar to dehydrogenization of aluminum. Performances of three different impeller designs were tested with the model, two of them available commercially, while the third one is a design proposed in this work, which shows a better performance than the two commercial designs reducing the degassing time between 14% and 34%, the gas consumption between 14% and 32%, and an increment in gas efficiency between 22% and 49% compared with the commercial designs. Performance of the impellers in aluminum was tested in a pilot degassing unit, and again, the impeller design proposed showed a better performance by reducing the amount of hydrogen in liquid aluminum after 10 min of degassing 1/2 respect to the commercial design A and 2/3 respect to the design B.

Membranes are major targets to oxidative damage, particularly due to lipid oxidation, which has been associated to aging. The role, efficacy and membrane interaction of antioxidants is still unclear, requiring further understanding of molecular interaction. Hence, the objective of this work was to evaluate the interaction between antioxidants (α-tocopherol and its aqueous soluble analog Trolox) and the monolayer formed by phosphatidylcholine molecules at air/liquid interface upon peroxidation conditions, promoted by peroxyl radicals from thermal decomposition of 2,2′-azobis(2-methylpropionamidine) (AAPH). The interaction with three different monolayers, containing (i) 1,2-dihexadecanoyl-sn-glycero-3-phosphocholine (DPPC), (ii) DDPC + α-linolenic acid, or (iii) egg yolk l -α-phosphatidylcholine (EPC), was ascertain by surface pressure (π)–molecular area (A) isotherms and by monitoring monolayer features through Brewster angle microscopy (BAM). The interaction of antioxidants with DPPC monolayers was confirmed by modifications on DPPC domain shape for α-tocopherol and through the maintenance of typical multilobed domain shape during an extended surface pressure interval for Trolox. Under peroxidation conditions, BAM images showed a clear interaction between components of AAPH subphase with the monolayer through changes on DPPC domain shape and appearance of white dots, located mainly at the frontier between the condensed and expanded liquid phases. White branched structures were also observed whenever both α-linolenic acid and α-tocopherol were present, indicating the segregation of these components within the monolayer, which is highly significant in biological systems. For EPC monolayers, no information from BAM was obtained but π–A isotherms confirmed the existence of the same interactions observed within the other two monolayers.

In this work, the interactions of a novel rifabutin's analogue ( N ′-acetyl-rifabutin, RFB2) with two-dimensional (Langmuir monolayers) and three-dimensional (large unilamellar and multilamellar vesicles) membrane models of the pulmonary surfactant (PS) were evaluated. The main purpose of this study is to obtain detailed information at the molecular level between the interactions of RFB2 with the phospholipids of the PS, under physiological conditions. Therefore, the effects of RFB2 in the monolayer phase behaviour at the air–water interface and in the lipid bilayer of membrane models composed of 1,2-dipalmitoyl- sn -glycero-3-phosphocholine (DPPC) have been systematically compared. In this context, several biophysical techniques were carried out to establish the interactions of RFB2 with the two-dimensional membrane models of the PS: Langmuir isotherms, Brewster angle microscopy (BAM), and polarization-modulation infrared reflection–absorption spectroscopy (PM-IRRAS); and with three-dimensional membrane models of the PS: derivate spectrophotometry partition coefficient ( K p ), dynamic light scattering (DLS), small and wide angle X-ray scattering (SAXS and WAXS). The results gathered by the different biophysical techniques and the PS membrane model used provide detailed information about the strong interactions of RFB2 with the polar head groups of the PS phospholipids and permit to establish the impact of the RFB2-PS membrane interactions, justifying an often unexplored biophysical approach to the drug's pharmacokinetics and toxicological effect.

This work focuses on the interaction of mycolic acids (MAs) and two antimycobacterial compounds (Rifabutin and N′ -acetyl-Rifabutin) at the pulmonary membrane level to convey a biophysical perspective of their role in disease. For this purpose, accurate biophysical techniques (Langmuir isotherms, Brewster angle microscopy, and polarization-modulation infrared reflection spectroscopy) and lipid model systems were used to mimic biomembranes: MAs mimic bacterial lipids of the Mycobacterium tuberculosis (MTb) membrane, whereas Curosurf® was used as the human pulmonary surfactant (PS) membrane model. The results obtained show that high quantities of MAs are responsible for significant changes on PS biophysical properties. At the dynamic inspiratory surface tension, high amounts of MAs decrease the order of the lipid monolayer, which appears to be a concentration dependent effect. These results suggest that the amount of MAs might play a critical role in the initial access of the bacteria to their targets. Both molecules also interact with the PS monolayer at the dynamic inspiratory surface. However, in the presence of higher amounts of MAs, both compounds improve the phospholipid packing and, therefore, the order of the lipid surfactant monolayer. In summary, this work discloses the putative protective effects of antimycobacterial compounds against the MAs induced biophysical impairment of PS lipid monolayers. These protective effects are most of the times overlooked, but can constitute an additional therapeutic value in the treatment of pulmonary tuberculosis (Tb) and may provide significant insights for the design of new and more efficient anti-Tb drugs based on their behavior as membrane ordering agents.

π-A isotherms, ellipsometric measurements, Brewster angle microscopy (BAM) and reflection spectroscopy have been utilized to characterize the films of an amphiphilic porphyrin ((OD)(3)TPPS(3)) at the air-water interface as a function of pH. This porphyrin forms stable mono-molecular layers at such interfaces, and exhibits different J-aggregation as a function of pH. The J-aggregation of (OD)(3)TPPS(3) on neutral pH subphases is notable considering that the nitrogen atoms at the central macrocycle have a pK(a)≈4.9. The type of aggregates at neutral pH is like those detected at pH4, because the central porphyrin ring is already protonated. However at basic pH the aggregation happens without protonation of the central ring but can be instead controlled by application of the surface pressure. At the air-water interface, (OD)(3)TPPS(3) shows two bands, a red component and a blue component, which have characteristics of non-degenerate linear oscillators being perpendicularly polarized between each other. The spectral behavior observed on subphases at different pHs is qualitatively interpreted by means of exciton coupling theory, assuming that the degenerate transitions attributed to the Soret band are split. Additionally, highly oriented molecular films of these J-aggregates were deposited onto transparent quartz slides.

A blue organic light-emitting device, based on an iridium phosphorescent dopant in a polyvinylcarbazole host, has been modified by the addition of an external CaS:Eu inorganic phosphor layer. By incorporating a surfactant in the phosphor mixture, a uniform coating could be achieved by drop-casting. The resulting hybrid device exhibited white light emission, with Commission Internationale de l’Eclairage, CIE ( x , y ) coordinates of x = 0.32, y = 0.35. No significant change in these coordinates was observed for current densities in the range 25–510 A m −2 . The maximum power efficiencies of the white device was 2.3 lm W −1 at a brightness of 254 cd m −2 .

A series of semifluorinated thiols of the general formula CF(3)(CF(2))(m-1)(CH(2))(n)SH (abbreviated to FmHnSH) have been synthesized and the Langmuir monolayers thoroughly characterized using surface pressure (π) and electric surface potential (ΔV) measurements. These data have been complemented with Brewster angle microscopy (BAM) visualization of the monolayers structure and IR spectroscopy (PM-IRRAS) analysis of the alkyl chain conformation. The investigated thiols (namely F4H10SH, F8H6SH, F6H10SH, F10H6SH, F6H11SH, F8H10SH and F10H10SH) differ in the length of the hydrophobic chain as well as in the degree of fluorination. Although the -SH group cannot form strong hydrogen bonds with the water subphase, thereby causing only weak anchoring, it has been found that all the investigated thiols, except for F4H10SH, are capable of stable Langmuir monolayer formation. The investigated thiols can be divided into two categories - thiols with longer alkyl chain (F10H10SH, F10H6SH, F8H10SH) and compounds with shorter hydrophobic part (F6H10SH, F6H11SH, F8H6SH). The monolayers of the latter thiols have their equilibrium surface pressure (ESP) comparable with the collapse pressure (π(C)) of their monolayers; thus these films are stable within the whole range of compression. On the contrary, thiols with longer perfluorinated fragments have considerably lower ESP than the π(C) of their monolayers; therefore, both stable and metastable regions can be distinguished in their π-A isotherms. Interestingly, for F8H6SH, a smectic ordering of molecules can be observed in monolayers as visualized with BAM. By comparing film-forming properties of the studied semifluorinated thiols with previously studied semifluorinated alkanes it has been found that the presence of -SH group facilitates spreading at the free water surface. Semifluorinated thiols have been found to maintain their monomolecular ordering in the presence of heavy metal cations in the aqueous subphase, contrary to their hydrogenated analogues, which have been reported to crystallize under the same conditions.

In this work, ITO electrodes have been modified by means of the oxidative electrodeposition of two different cobalt porphyrins, CoTSPP and CoTMPyP, and the composition of such deposits have been studied by visible and reflection–FTIR spectroscopies. The data indicate that the porphyrin deposits are formed by a mixture of cobalt hydroxides, β-Co(OH) 2 and α-Co(OH) 2 , and the porphyrin ring as radical. Moreover, the porphyrin electrodeposits absorb molecular oxygen as peroxo species (O 2 2− ), which has been detected in the films by IR spectroscopy, and which acts as a bridge between Co atoms (Co–O–O–Co). Also, monolayers containing a viologen derivative have been transferred onto the porphyrin-MIE (MIE, modified ITO electrode) by using the LB technique, and its redox process has been investigated. The results show an excellent mediator character of both cobalt electrodeposits throughout the viologen redox processes. Furthermore, the Co–porphyrin electrodeposits store atmospheric oxygen in a ratio proportional to the deposited porphyrin amount. This oxygen can be totally released from the porphyrin film via the electrocatalytic action of the viologen monolayer on top.

El analisis citogenetico, junto a la citologia, los marcadores celulares y la biologia molecular, constituyen el conjunto de las pruebas diagnosticas esenciales en la leucemia linfoblastica aguda (LLA). Se presentan cariotipos alterados entre un 64 y un 85% de casos de LLA del adulto, y constituyen un factor pronostico independiente de primer orden, indicado por primera vez en el Third International Workshop on Chromosomes in Leukemia. Las alteraciones cromosomicas que se observan con frecuencia en la LLA del adulto son las translocaciones t(9;22)(q34;q11), t(4;11)(q21;q23), t(1;19)(q23;p13.3), t(8;14)(q24;q32), los reordenamientos 11q23, las deleciones del cromosoma 9p, 6q y 12p, los reordenamientos de los genes de los receptores de las celulas T (TCR) (14q11.2 [TCR-a y TCR-d], 7q35 [TCR-s] y 7p15 [TCR-?]), la hiperdiploidia superior a 50 cromosomas y la hipodiploidia de 30?39 cromosomas. En esta revision se describe la relevancia clinica de los principales trastornos citogeneticos en la LLA del adulto.

In this work, the mediator and/or catalytic properties of modified ITO electrodes by oxidative electrodeposition of Ni-porphyrins have been analyzed. Thus, monolayers containing viologen or azobenzene derivatives, have been transferred onto the porphyrin modified electrodes by using the Langmuir–Blodgett (LB) technique. Following, the redox processes of these compounds forming the LB films and deposited on the modified electrode and the bare ITO have been investigated. The obtained results reveal not only the excellent mediator character of the porphyrinic electrodeposit throughout the viologen redox processes, but also its the catalytic action over the azobenzene kinetics. Specifically, for the last case, the NiTMPyP films accelerate the azobenzene kinetics up to 100 times with respect to those results obtained in absence of porphyrin.

The oxidative electrodeposition of CoTSPP (tetrakis 4-sulfonatophenyl Co porphyrin) on ITO electrode from NaOH 0.1 M aqueoussolution has been studied, and cyclic voltammetry, spectroelectrochemistry, UV–Vis and reflection-FTIR spectroscopies have been usedto analyze the composition of such a film. Our experimental data lead us to propose that electrodeposited CoTSPP films are composed byðOHÞ 2 CoðIIIÞAO 2 and the porphyrin ring as radical cation. Futhermore, the Co(OH) 2 species is formed from the reduction of the film inoxygen absence. However, the properties of these films do not match with those corresponding to Co(II) hydroxide films, since the elec-trodeposited CoTSPP is able to absorb atmospheric oxygen to form CoðIIIÞAO 2 species. Moreover, in oxygen absence, the Co(II) mayinteract with the porphyrin radical cation to regenerate CoTSPP. 2006 Elsevier B.V. All rights reserved. Keywords: Cobalt porphyrin; Electrodeposition; Reversible dioxygen binding; Co a-hydroxide 1. IntroductionMetalloporphyrins and metallophthalocyanines havebeen increasingly explored, inter alia for their electrocata-lytic activity in processes as the oxygen reduction [1,2],the oxidation of hydrazines [3], thiols [4,5], etc. A proce-dure for the immobilization of these macro cycles ontoelectrodes consists in their electropolymerization, as soonas this method often increases the stability of the modifiedelectrode and also improves its catalytic activity [6].There are many studies related to the electropolymeriza-tion of CoAphtalocyanines [7–14], and CoAporphyrins[8,14–16], on different electrodes. In this paper the oxida-tive electrodeposition of CoTSPP (see inset in Fig. 1)onITO electrode from NaOH 0.1 M aqueous solution hasbeen studied, following the procedure previously describedby Bedioui et al. for Ni-porphyrins electrodeposition [17].In a previous work, this method has been utilized by usto electropolymerize NiTSPP [18], detecting the presenceof Ni(OH)

The properties of 4-methylbenzenethiol capped gold nanoparticles have been investigated at the air–water interface. Langmuir isotherms and compression cycles show that a stable monolayer is formed on the water surface. In situ UV-visible spectroscopy confirms that the plasmon absorption band is present which is characteristic of small metallic particles. The monolayer was imaged using real time Brewster Angle Microscopy (BAM). Above surface pressures of 5 mN m− 1 the monolayer was virtually homogeneous. During decompression, the monolayer fractured into rod-like structures. These rods were initially orientated parallel to the movable barriers containing the monolayer and as the area was increased, their orientation randomized. During subsequent compressions the rods recombined to recreate a homogeneous monolayer.

By using ellipsometry at the air–water interface, we determined the optical parameters of a mixed monolayer containing an anionic phospholipid matrix (DMPA), and a cationic porphyrin (Ni-TMPyP, Ni(II)-tetrakis(4-methylpyridyl) porphyrin) as large counter ion, in molar ratio Ni-TMPyP/DMPA=1:4 to further describe the organization of this film. The nulling ellipsometric measurements were done on two phases observed directly by Brewster angle microscopy, over specific regions with a size of few microns. Therefore, values of the ellipsometric angles for the different regions at the interface (domains and surrounding areas) have been obtained. The results have been interpreted applying the ‘‘one-layer’’ optical model being in good agreement with the predictions from the geometrical models. Further, the strong increase of the D ellipsometric angle with respect to the DMPA film has been interpreted as due, mostly, to the partial dehydration of the polar group whatever increase of the refractive index of the film. D 2005 Elsevier B.V. All rights reserved.

This paper reports new experimental evidence of the electrochemical formation of a 2D phase which, based on a recently developed model, takes place via a desorption-nucleation mechanism that includes the incorporation of adsorbed molecules into the condensed phase.

The formation of thin films of a new C60 derivative, C60-NaDDC (C60-sodium diethyldithiocarbamate), have been investigated at the air–water interface by using different surface methods. Thus, the surface pressure–surface area isotherm and the reflection spectra of the film at the air–water interface were measured and valuable information about the organization of the fullerene balls was achieved. The presence of the film and its state has been directly visualized at that interface by using Brewster angle microscopy (BAM). In addition, the ellipsometric angles, Δ and Ψ, were measured by nulling ellipsometric measurements at the air–water interface allowing us to obtain the thickness of the C60-NaDDC film. This value obtained from the combination of the reflection and nulling ellipsometry measurements is in a very good agreement with that expected from molecular models.

In this paper, we show that Langmuir–Blodgett (LB) film assemblies of 5,15-bis(4-aminophenyl)-10,20-bis[3,4-bis(2-ethylhexyloxi)phenyl]-21H,23H-porphine (CAH4) exhibit a fast, reversible and reproducible response to NO2 in the concentration range of 0.46–4.6 ppm. The monolayer behaviour at the air–water interface has been investigated by measuring the surface pressure–area isotherms as well as reflection spectroscopy (ΔR) and Brewster angle microscopy (BAM). It was found that intermolecular interaction between porphyrin rings directs the molecular organization even at submonolayer coverage. LB films of CAH4 were prepared using ultra-fast deposition. The high deposition rate employed (500 mm min−1) led to an inhomogeneous structure with high porosity. The LB film exposed to 4.6 ppm of NO2 showed a sensitivity of 60% relative absorbance change at 439 nm. The response was found to be faster than that measured in similar systems. Full recovery of the original spectrum after exposure to NO2 is obtained and can be dramatically accelerated with gentle heating (353 K). The fast response can be explained in terms of the molecular structure of the porphyrin as well as the enhanced surface area of the porous film.

In this work, mixed films of a tetra-cationic porphyrin, Ni(II)TMPyP, and an anionic phospholipid, DMPA, in molar ratio of 1:4, were formed at the air–water interface and transferred onto glass and optically transparent indium tin oxide (ITO) electrodes. Transmission spectroscopy (on glass and ITO) and cyclic voltammetry (on ITO) were used to infer the molecular organization and the electrochemical reduction of these LB films. Likewise, we compare the electrochemical reduction of the Ni(II)TMPyP in water solution with that in LB films. The porphyrin molecules in water solution show three two-electron reduction waves, which are related to the two-electron reduction of the central ring of the porphyrin and to the one-electron reductions of the four methyl–pyridyl groups of the molecule, respectively, while only two reversible one-electron reduction waves are observed in LB films corresponding to the reduction of the central ring of the porphyrin and to the Ni(II) to Ni(I) reduction, respectively. Keywords: Ni(II)Porphyrin, LB films, Modified ITO electrode, Cyclic voltammetry

In this work, the combination of the cyclic semi-integral voltammetry (CSIV) and cyclic semi-differential voltammetry (CSDV) methods with cyclic voltammetry (CV) has been used. Therefore, a quick and precise mechanistic interpretation of the experimental results is obtained. The procedure has been applied to the electrochemical reduction of Ni-meso-tetra(4-N-methylpyridyl) porphyrin (Ni–TMPyP) in acidic aqueous solution (pH 4.3), where this compound exhibits two reduction waves and one or two oxidation waves as a function of the scan rate in CV. Moreover, the electrode process is affected by the adsorption of an intermediate reduction product and by a chemical reaction following the first reduction wave. Finally, in order to confirm the proposed mechanism, numerical simulations of the CV and the CSDV were performed.

A new electrochemical double pulse potential technique called additive differential pulse voltammetry (ADPV) is proposed. This technique is inspired by the original idea of Birke et al. [Anal. Chem. 53 (1981) 852] of recording two differential pulse (DP) voltammograms and it consists of plotting the sum of these two signals versus the first pulse potential, although in this paper the proposal is to obtain the ADPV signal through just one experiment. ADPV behaves in an identical way to the triple-pulse technique double differential pulse voltammetry (DDPV) for reversible processes when diffusion coefficients are equal for spherical electrodes and for any value of diffusion coefficients in planar electrodes. In the case of reversible electrode processes with amalgamation of reaction product or other more complex processes, ADPV is more advantageous than DDPV. This is due, among other reasons, to the fact that, under these conditions, a double potential step is much simpler to analyse than a triple potential step. Keywords: Additive differential pulse voltammetry, Double differential pulse voltammetry, Reversible process

In aqueous media, the cation radical of heptyl viologen, HV +, forms a two-dimensional (2D) phase on a polycrystalline silver electrode. The phase results from the reduction of HV2+ molecules adsorbed on the electrode and consists of the cation radical salt and bromide as counterion; it is dissolved through gradual nucleation and growth of vacancies, which take place simultaneously with a Langmuir-type desorption process.

In this work, we propose a new general method based on the use of cubic spline functions, suitable for the numerical determination of extended semi integrals and semi differentials. The procedure combines these interpolation functions with different numerical integration and differentiation standard methods, including commercial software. The method has been applied to the electrochemical reduction of the meso-tetra(4-N-methylpyridyl)porphyrin in acidic aqueous solution, where this compound exhibits a two-electron wave in cyclic voltammetry. In this work, we determine the semi differential of the current and demonstrate that the signals obtained correspond to an EE process, where both electrochemical steps are reversible and their formal potentials are very close.

Non-faradaic peaks produced by the two-dimensional (2D) condensation of organic molecules on an electrode were studied theoretically by using cyclic voltammetry. Under limiting conditions of low scan rate and overpotential, the classical and atomistic theories of nucleation were found to predict the same behaviour for this type of process. The model developed from the previous study was also used to predict hysteresis in capacitance-potential curves for this type of process. With slight nomenclature changes, the ensuing mathematical expressions are also applicable to 2D phase transitions involving the simultaneous exchange of electrons between deposited molecules and the electrode.

In this work, isotherms for mixtures of methylene blue (MB+) and dimyristoyl phosphatidic acid (DMPA) were studied. Co-spreading techniques were used to spread a mixed solution of MB+ and DMPA in 3:1 CHCl 3 CH 3 OH at the air-water interface. This system exhibits markedly expanded isotherms at low π values. By using the Langmuir-Blodgett (LB) technique, a 1:1 DMPA MB + monolayer was transferred to an indium tin oxide electrode at π = 25 mN m−1. The presence of MB+ in LB films was detected by visible spectroscopy and electrochemical methods.

The theory corresponding to triple potential step chronoamperometry for a reversible charge transfer reaction in a static mercury drop electrode is presented. The equation for the current has been deduced assuming different diffusion coefficients for oxidized and reduced species and is valid when the reaction product is soluble in both the electrolytic solution and the electrode. The validity of equations proposed was verified by comparing theoretical i-t, double differential pulse and reverse differential pulse curves with those obtained experimentally for the system Cd2+Cd(Hg). It can be concluded that the double differential pulse and reverse differential pulse techniques are more sensitive to the presence or absence of amalgamation than double pulse techniques.

In an aqueous acid medium, 4,4′-bipyridine (BPH22+) may give up to five voltammetric reduction peaks, depending on its concentration and the presence or absence of a surfactant. This paper discusses such voltammetric peaks and assigns them to the electrode processes from which they originate. If the voltammetric scan is reversed when the most negative potential in the voltammogram is reached, only three of the previously observed peaks are reversible, depending on the final potential. Also, up to two inverted current peaks (ie, reduction peaks) are observed in the scan to positive potentials. Plausible mechanisms accounting for such inverted peaks are put forward in the paper.

In this paper, an experimental review of the isotherms of the metallotetraphenylporphyrin ( M -TPP) molecules has been carried out in the air-water interface. The isotherms are a function of the M -TPP concentration in the organic solvent used (chloroform) before spreading on the aqueous subphase. For very low M -TPP concentrations (10 -5 M ) in this solvent, isotherms whose extrapolated areas to π = 0 mN/m are on the order of 100-110 A 2 per molecule are obtained. This value is intermediate between those expected for a flat orientation of the molecules (160 A 2 ) and a perpendicular one (70 A 2 ). When a constant pressure is applied, such monolayers are initially not stable. However, after waiting sufficient time, one can observe a sudden condensation of this monolayer (decrease of the area at a constant pressure) which leads to the formation of a stable monolayer, with an area per molecule on the order of 67 A 2 for H 2 -TPP, 69 A 2 for Mg-TPP, and 86 A 2 for Zn-TPP (π = 7 mN/m). Monolayers were characterized by visible spectroscopy following transfer to glass slides. In this paper, a possible explanation for this phenomenon in relation to the molecular structure of the M -TPP is reached.

In this article we establish the necessary mathematical conditions for the superposition principle to be applicable to obtaining the faradaic response to a multipulse sequence on plane and spherical electrodes (whether increasing with time or not) and on cylindrical electrodes. These conditions have been partially established by some authors, but to date have not been derived in a rigorous and general form. The general expressions derived in this paper for the current Ij corresponding to any pulse j are much simpler than those obtained previously in the literature for some specific cases and can easily be used in practice. To illustrate this, we apply these solutions to staircase and square-wave voltammetry. The effect of the size of the electrode on the final solution is also analysed.

The reduction of 4,4′-bipyridine (BPH2+2) on mercury in an acid medium gives a very narrow sharp tail-less reversible voltammetric peak that can be ascribed to the formation of a two-dimensional (2D) phase of the cation radical BPH·+2 at the electrode according to the reaction BPH 2+ 2 + e − ⇌ |BPH ·+ 2 | 2 D The corresponding oxidation peak possesses similar properties and arises from the destruction (fusion) of the 2D phase. In this work we studied the influence of some experimental variables, namely the type of anion present in the medium, the concentration of 4,4′-bipyridine and temperature on the 2D phase transition peaks. Also, we tested various analytical criteria to validate this assignation and fitted both voltammetric peaks numerically to the theoretical model developed for this purpose.

A theoretical study of two-dimensional phase transitions taking place in electrode processes was carried out by using cyclic voltammetry. The equations derived are obeyed only at low to moderately high scan rates ( v ) depending on the particular experimental system. The treatment used was applied on the assumption that the nucleation rate for the process is a function only of the concentration of nuclei of a critical size which depends on the overpotential. This approximation holds whether nucleation at a constant potential is instantaneous or progressive. Consequently, neither has physical significance under variable-potential conditions, at least at low scan rates. Theoretical relationships between the peak current ( I p ) and v x ( x = 0.6), and also between both the peak half-width ( W ; the width, in mV, at the peak half-height) and the difference between the reduction and oxidation peak potential (Δ E p ) and v (1- x ), were found. Analytical criteria based on such relationships are put forward and the way they are affected by the number of molecules forming critically sized nuclei is discussed. While the effect is complex, exponent x in the above relationships increases with increase in the number of such molecules.

From the solution obtained in previous work for the faradaic response to a triple pulse of potentials, the double differential pulse technique can be defined through the equation I ddp = i 3 − 2 i 2 + i 1 , where i j ( j = 1, 2, 3) is the current corresponding to the potential E j . The solution to this equation, which is valid both for a static mercury drop electrode and for a dropping mercury electrode, was studied, and experimental conditions for the analysis of the corresponding curves are proposed. Likewise, approximate solutions and analysis criteria for completely reversible and irreversible processes are reported. The solutions were checked against experimental examples of well-known processes. The analytical and kinetic advantages of this technique are discussed.

We carried out a theoretical treatment of the reduction of α-keto acids, the limiting current of which typically reaches a maximum value at a given pH. Provided the protonated form of an α-keto acid is strongly hydrated in solution and the protonation equilibria involved are substantially faster than those of hydration, which is usually the case with these compounds, one can derive approximate expressions of the overall representative equations, which considerably simplified numerical fitting of experimental results. The treatment developed in this work was applied to the first reduction wave of glyoxylic acid and the rate constants of the process were calculated.

We studied the spontaneous formation of mixed monolayers of methylene blue (MB + ) and Triton X-100 (TX) from aqueous solutions containing both substances and a fixed concentration of MB + of c MB = 2.5 × 10 −6 M. The voltammetric peak obtained under these conditions was typical of redox sites immobilized at the electrode and was ascribed to the reduction of MB + molecules dissolved in the aliphatic subphase of the surface film formed by the TX molecules. This phenomenon arises from the hydrophobic character of MB + molecules and gives rise to strong interactions between such molecules and the hydrophobic moiety of TX molecules. The voltammetric peak of MB + in the surface film is of a quasi-reversible nature. The transfer coefficients of the reduction and oxidation processes were found to be aα f n ⋍ 1 and α b n ⋍ 1.5, with n = 2. A plausible mechanism to account for the relationship α f n + α b n ≠ 2 is put forward.

A single-step charge-transfer process with a very low coefficient of transfer and an adequate standard rate constant was theoretically found to yield curves made up of two current maxima or peaks seemingly corresponding to two different partly overlapping reduction processes in differential pulse polarography (DPP). The possible origin of this phenomenon is discussed, as are the reasons why it is more marked in DPP than in other electrochemical techniques. As an example, the phenomenon was studied in the well-known reductions of Cd2+ and Zn2+ in dimethylsulphoxide in the presence of tetrabutylammonium perchlorate and tetraethylammonium perchlorate respectively. The ease with which DPP solutions can be obtained allowed us to determine the kinetic parameters for both reduction processes by numerical fitting. The results in this respect were consistent with previously reported literature data.

We applied Matsuda's pulse polarography theory to the study of electrode processes under non-Nernstian conditions and coupled to very fast chemical steps by differential pulse polarography (reaction layer approximation). By way of example, the theory was applied to the CE mechanism in order to derive analytical criteria for very kinetic conditions and a completely irreversible transfer.

An experimental study was carried out on the inhibitory effect of a surfactant on the electrode reduction of cefazolin. The reduction potential was found to shift to more negative values with an increase in the surfactant concentration, while the transfer coefficient of the process remained unaltered. The inhibitory effect is accounted for on the basis of a model that takes account of the competitive adsorption of the two substances only. The variation of the rate constant of the process with the logarithm of the surfactant concentration allowed calculation of the ratio between the number of solvent molecules displaced by the reactant and the surfactant, respectively.

We have carried out a study on the reduction of cefsulodin by classic polarography (CP), linear sweep voltammetry (LSV) and chronocoulometry with voltammogram integration. The experimental conditions were chosen so as to ensure the exclusive reduction of the adsorbed cefsulodin molecules in LSV. The reduction process takes place via the isonicotinamide substituent of cefsulodin. In acid media, cefsulodin yields a four-electron signal in classic polarography and two two-electron signals in voltammetry — this latter result, however, depends on the sweep rate used. This effect is accounted for on the basis of an ECE mechanism, and some criteria are put forward for the determination of the intermediate rate constant of such a mechanism.

The polarographic waves yielded by the reduction of a radical in competition with a dimerization reaction are analyzed in order to distinguish between the different types of mechanism involved. The i-E relations for those cases involving competition with radical-substrate reactions are derived. The results of the logarithmic analysis of the dc polarographic waves are considered as diagnostic criteria.

This paper deals with the polarographic reduction of mesityl oxide as an example of an electrodimerization process which does not fit the classical mechanism involving radical-radical dimerization in the reaction layer. Various mechanisms are discussed on the basis of the experimental results found.

A method is proposed for the calculation of the rate constant of the intermediate chemical stage of an ECE mechanism, taking as a basis the study of the i–t curves obtained by dc polarography. This method has been applied to the electrochemical reduction of nitrophenols. The data obtained are in agreement with those determined by other techniques, thus showing the usefulness of dc polarography for this purpose.

A study of the electrochemical reduction of monoethyl maleate (MEM) on a mercury electrode has been carried out. Two waves were found by dc polarography and two peaks by dpp. The first wave or peak is due to the reduction of the protonated species whereas the second one owes its existence to the undissociated form. In contrast to monoethyl fumarate, no reduction wave corresponding to the dissociated form was observed. Tafel slopes and reaction orders were obtained at potentials corresponding to the foot of the wave. From these experimental data, the reaction mechanisms for the pH ranges 0–3, 4–5 and 6.5–7.5 are proposed for the zone of potentials where the Tafel law is fulfilled. The results obtained are compared with those corresponding to the reduction of monoethyl fumarate.

On the basis of i−t curves obtained, we propose some criteria to distinguish between various reaction mechanisms. These criteria have been deduced from implicit equations found in the bibliography, except for CEC mechanisms (pre-kinetic—reversible transfer—first and second-order post-kinetic) whose equations were obtained, for this work, from the concept of the reaction layer. In addition, we have studied some aspects of the experimental recording of i−t curves.