Alkylammonium Cation Affinities of Nitrogenated Organobases: The Roles of Hydrogen Bonding and Proton Transfer.

Alkylammonium cation affinities of 64 nitrogen-containing organobases, as well as the respective proton transfer processes from the alkylammonium cations to the base, have been computed in the gas phase by using DFT methods. The guanidine bases show the highest proton transfer values (191.9-233 kJ mol-1 ) whereas the cis-2,2'-biimidazole presents the largest affinity towards the alkylammonium cations (>200 kJ mol-1 ) values. The resulting data have been compared with the experimentally reported proton affinities of the studied nitrogen-containing organobases revealing that the propensity of an organobase for the proton transfer process increases linearly with its proton affinity. This work can provide a tool for designing senors for bioactive compounds containing amino groups that are protonated at physiological pH.

Lewis Acid-Mediated Formation of 1,3-Disubstituted Spiro[cyclopropane-1,2'-indanes]: The Activating Effect of the Cyclopropane Walsh Orbital.

By virtue of its alkylidenecyclopropane moiety, 2-(cyclopropylidenemethyl)benzaldehyde reacts with a range of amines and thiols under Lewis acid catalysis. These reactions yield 1,3-bis(arylamino) and 1,3-bis(arylthio and alkylthio)indanes, respectively, which are spirolinked to the cyclopropane ring at carbon 2. The reaction mechanism, and the peculiar contribution of the cyclopropane ring, have been scrutinized via DFT calculations.

On the Use of Popular Basis Sets: Impact of the Intramolecular Basis Set Superposition Error.

The magnitude of intramolecular basis set superposition error (BSSE) is revealed via computing systematic trends in molecular properties. This type of error is largely neglected in the study of the chemical properties of small molecules and it has historically been analyzed just in the study of large molecules and processes dominated by non-covalent interactions (typically dimerization or molecular complexation and recognition events). In this work we try to provide proof of the broader prevalence of this error, which permeates all types of electronic structure calculations, particularly when employing insufficiently large basis sets.

Chemodivergent Conversion of Ketenimines Bearing Cyclic Dithioacetalic Units into Isoquinoline-1-thiones or Quinolin-4-ones as a Function of the Acetalic Ring Size.

C-Alkoxycarbonyl- C-phenyl- N-aryl ketenimines bearing 1,3-dithiolan-2-yl or 1,3-dithian-2-yl substituents at ortho position of the C-phenyl ring, respectively, transform into isoquinoline-1-thiones and quinolin-4-ones under thermal treatment in toluene solution. The formation of isoquinolinethiones involves a rare degradation of the 1,3-dithiolane ring, whereas, in contrast, the 1,3-dithiane ring remains intact during the reaction course leading to quinolin-4-ones. Computational density functional theory results support that the kinetically favorable mechanism for the formation of isoquinoline-1-thiones proceeds through a [1,5]-hydride shift/6π-electrocyclization cascade, followed by a thiirane extrusion process. Alternative mechanistic paths showing interesting electronic reorganization processes have been also scrutinized but resulted not competitive on energetic grounds.

Lennard-Jones Intermolecular Potentials for the Description of 6-Membered Aromatic Heterocycles Interacting with the Isoelectronic CO2 and CS2.

We have generated Lennard-Jones potentials for the interaction between CX2 (X = O, S) and 11 nitrogen-doped benzene derivatives in different orientations at the M06-2X/def2-tzvpp level as tools to parametrize accurate force fields and to better understand the interaction of these greenhouse gases with heterocyclic building blocks used in the design of capture and detection systems. We find that the most favorable interactions are found between the carbon in CO2 and the main heterocycle in the ring in a parallel orientation, whereas the preferred interaction mode of CS2 is established between sulfur and the π density of the aromatic ring. The fact that the preferences for interaction sites and orientations of CO2 and CS2 are most of the times opposite helps in terms of ensuring the selectivity of these systems in front of these two isoelectronic compounds. The existence of very good linear correlations ( R2 values very close to one) between the number of nitrogen atoms in the heterocyclic ring and the depth of the interaction potential wells opens the door to the use of these results in generating coarse-grained potentials or models with predictive power for use in the design of larger systems.

Exploring the Conversion of Macrocyclic 2,2'-Biaryl Bis(thioureas) into Cyclic Monothioureas: An Experimental and Computational Investigation.

Macrocyclic bis(thioureas) derived from 2,2'-biphenyl and binaphthyl skeletons have been synthesized by reaction of 2,2'-diaminobiaryl and 2,2'-bis(isothiocyanato)biaryl derivatives. The splitting of these bis(thioureas) into two units of the respective cyclic monothioureas has been monitored by NMR, shedding some light on the factors that control these processes. Additionally, a computational study revealed up to three mechanistic paths for the conversion of the 2,2'-biphenyl-derived bis(thiourea) into the corresponding monothiourea. The proposed mechanisms account for the participation of a molecule of water as an efficient proton-switch as well as for different classes of putative intermediates. The computational study also supports the ability of the thiourea group to participate in a plethora of processes, such as prototropic equilibria, sigmatropic shifts, heteroene and retro-heteroene reactions, and cis ⇆ trans isomerizations.

Nitrogen doped nanohoops as promising CO2 capturing devices.

The impact of climate change in the face of steady or increasing emissions has made the capture and storage of CO2 a priority issue. Supramolecular chemistry is one of the tools that can be used for this task, due to the possibility of tuning intermolecular interactions for the capture of this gas in a selective and efficient way. In this context, this work presents a novel approach for the capture of CO2 based on n-cycloparaphenylenes ([n]-CPPs) doped with nitrogen atoms. This is the first time that the potential of these structures for the capture of polluting gases has been evaluated. Among all the structures analysed, the one yielding the best results (complexation energy of -32.80 kJ mol-1) contains 4 nitrogen atoms per monomer. The topology of the electron density of the host-guest complex and the nature of its non-covalent interactions have been analyzed in this work in order to explain this high binding energy and identify potential structural modifications to improve it. The capability of this system to be used as a sensing device for CO2 using vibrational spectroscopy is also explored.

Rational Design of Efficient Environmental Sensors: Ring-Shaped Nanostructures Can Capture Quat Herbicides.

The viability of using [n]-cycloparaphenylenes (CPPs) of different sizes to encapsulate diquat (DQ) pesticide molecules has been tested analyzing the origin of the host-guest interactions stabilizing the complex. This analysis provides rational design capabilities to construct ad hoc capturing systems tailored to the desired pollutant. All CPPs considered (n = 7-12) are capable of forming remarkably stable complexes with DQ, though [9]-CPP is the best candidate, where a fine balance is established between the energy penalty due to the deformation + repulsion of the pesticide molecule inside the cavity (larger in smaller CPPs) and the maximization of the favorable dispersion, electrostatic and induction contributions (which also decrease in larger rings). These encouraging results prompted us to evaluate the potential of using Resonance Raman spectroscopy on nanohoop complexes as a tool for DQ sensing. The shifts observed in the vibrational frequencies of DQ upon complexation allow us to determine whether complexation has been achieved. Additionally, a large enhancement of the signals permits a selective identification of the vibrational modes.

Lennard-Jones Potentials for the Interaction of CO2 with Five-Membered Aromatic Heterocycles.

We used M06-2X/Def2-TZVPP to calculate a broad set of rigid interaction profiles between CO2 and 30 different aromatic heterocycles, based on pyrrole, furan, and thiophene with ring positions subsituted with up to four nitrogens. For each system, several orientations of the fragments were explored to both find the preferred interaction mode and have information about other interaction modes that can contribute to the binding energy when CO2 is captured by complex systems. From these data, Lennard-Jones potentials were obtained, which can be used for the parametrization of force fields that correctly describe the multipolar and dispersion interactions at play between these kinds of fragments. These results are expected to contribute to the development of new force fields for the study of chemical systems for the capture and sequestration of CO2 and also directly for the design of such systems.

CO2 Complexes with Five-Membered Heterocycles: Structure, Topology, and Spectroscopic Characterization.

In a first step toward the rational design of macrocyclic structures optimized for CO2 capture, we systematically explored the potential of 30 five-membered aromatic heterocycles to establish coordinating complexes with this pollutant. The interactions between the two moieties were studied in several orientations, and the obtained complexes were analyzed in terms of electron density and vibrational fingerprint. The former is an aid to provide an in-depth knowledge of the interaction, whereas the latter should help to select structural motifs that have not only good complexation properties but also diagnostic spectroscopic signals.

Lewis acid catalyzed [3 + 2] annulation of ketenimines with donor-acceptor cyclopropanes: an approach to 2-alkylidenepyrrolidine derivatives.

The [3 + 2] annulation reaction of C,C,N-trisubstituted ketenimines with donor-acceptor cyclopropanes bearing aryl, styryl and vinyl substituents at the C2 position, triggered by the Lewis acid Sc(OTf)3, supplies highly substituted pyrrolidines. Activated cyclopropanes fused to naphthalene and [1]benzopyrane nuclei are also suitable substrates in similar transformations, yielding partially saturated benz[g]indoles and [1]benzopyran[4,3-b]pyrroles. An intramolecular version of this ketenimine/cyclopropane [3 + 2] annulation has also been developed leading to the pyrrolo[2,1-a]isoindole framework.

Tandem processes promoted by a hydrogen shift in 6-arylfulvenes bearing acetalic units at ortho position: a combined experimental and computational study.

6-Phenylfulvenes bearing (1,3-dioxolan or dioxan)-2-yl substituents at ortho position convert into mixtures of 4- and 9-(hydroxy)alkoxy-substituted benz[f]indenes as result of cascade processes initiated by a thermally activated hydrogen shift. Structurally related fulvenes with non-cyclic acetalic units afforded mixtures of 4- and 9-alkoxybenz[f]indenes under similar thermal conditions. Mechanistic paths promoted by an initial [1,4]-, [1,5]-, [1,7]- or [1,9]-H shift are conceivable for explaining these conversions. Deuterium labelling experiments exclude the [1,4]-hydride shift as the first step. A computational study scrutinized the reaction channels of these tandem conversions starting by [1,5]-, [1,7]- and [1,9]-H shifts, revealing that this first step is the rate-determining one and that the [1,9]-H shift is the one with the lowest energy barrier.

Acid-promoted cycloisomerizations of phenylallenes bearing acetalic functions at the ortho position: a stereocontrolled entry to indeno-fused dioxepanes, dioxocanes and thioanalogues.

The cycloisomerization reactions of allenes bearing cyclic acetal, thioacetal and dithioacetal subunits, when triggered either by the catalytic action of AgSbF6 or by one equiv. of CF3COOH, gave rise to four different classes of indeno-fused 1,4-dioxa, oxathia and dithia heterocycles, in most cases as a single diastereomer. Acyclic acetals and dithioacetals are also suitable starting materials in similar transformations yielding 1,2-disubstituted indenes and 1,3-disubstituted 2-alkylideneindanes.

DFT calculation of the potential energy landscape topology and Raman spectra of type I CH4 and CO2 hydrates.

CO2 and CH4 clathrate hydrates of type I were studied by means of DFT and QTAIM, in order to better understand their properties at the molecular level. Sub-cells of type I hydrates were modeled as independent rigid cages, both empty and containing guest molecules. Interaction potentials of guest molecules inside each cage, and moving from a cell to the adjacent one, were calculated using the DFT approximation B3LYP/6-311+g(d,p), considering the cases with and without long range Coulombic corrections. The selected theory level was validated by comparison of the simulated Raman spectra with the experimental ones, for the case of type I lattice at full occupation of CO2 and CH4, respectively. For this comparison, Fermi resonances of CO2 were taken into account by transforming experimental bands to the corresponding theoretical non-mixed states. On the one hand, our results confirm the validity of the theory level selected for the model. We have shown the high anisotropy of the guest-cell interaction potential of the molecules analyzed, which has implications in the formulation and use of equations of state, and in the study of transport properties as well. On the other hand, our results suggest that the concentration of guest species inside type I hydrates could be computed from the comparison of experimental and predicted Raman spectra, although there are non-trivial experimental limitations to get over for that purpose.

Thermal cyclization of phenylallenes that contain ortho-1,3-dioxolan-2-yl groups: new cascade reactions initiated by 1,5-hydride shifts of acetalic H atoms.

A series of 2-(1,3-dioxolan-2-yl)phenylallenes that contained a range of substituents (alkyl, aryl, phosphinyl, alkoxycarbonyl, sulfonyl) at the cumulenic C3 position were prepared by using a diverse range of synthetic strategies and converted into their respective 1-(2-hydroxy)-ethoxy-2-substituted naphthalenes by smooth thermal activation in toluene solution. Electron-withdrawing groups at the C3 position accelerated these tandem processes, which consisted of 1) an initial hydride-like [1,5]-H shift of the acetalic H atom onto the central cumulene carbon atom; 2) a subsequent 6π-electrocyclic ring-closure of the resulting reactive ortho-xylylenes; and 3) a final aromatization step with concomitant ring-opening of the 1,3-dioxolane fragment. If the 1,3-dioxolane ring of the starting allenes was replaced by a dimethoxymethyl group, the reactions led to mixtures of two disubstituted naphthalenes, which were formed by the migration of either the acetalic H atom or the methoxy group, with the latter migration occurring to a lesser extent. Two of the final 1,2-disubstituted naphthalenes were converted into their corresponding naphtho-fused dioxaphosphepine or dioxepinone through an intramolecular transesterification reaction. A DFT computational study accounted for the beneficial influence of the 1,3-dioxolane fragment on the carbon atom from which the H-shift took place and also of the electron-withdrawing substituents on the allene terminus. Remarkably, in the processes that contained a sulfonyl substituent, the conrotatory 6π-electrocyclization step was of lower activation energy than the alternative disrotatory mode.

De patito feo a cisne. Evolución para micro pymes en seguridad y salud laboral / From ugly duckling to swan. The way forward for micro and small enterprises in occupational health and safety

Cuando en Abril de 2011 obtuvimos nuestro primer Galardón Europeo a las Buenas Prácticas en la anterior Campaña sobre el Mantenimiento Seguro, la pregunta que más nos realizaron no fue en relación con los detalles de nuestro modelo de Coordinación Empresarial. La pregunta era: ¿Cómo una micro pyme de aquí ha conseguido ganar un premio europeo en Prevención de Riesgos? y la respuesta que dimos, un sencillo ejemplo, el nuestro, resultó ser para nuestra sorpresa nuevamente galardonado. Proponemos un modelo de Prevención de Riesgos aplicable a las pequeñas empresas, que suponen el mayor colectivo susceptible de padecer daños en la salud como consecuencia de su trabajo y que además, son las que disponen de menos recursos. Pretendemos obtener resultados excelentes con unos mínimos recursos utilizados con eficacia y eficiencia (AU)

When in April 2011 we got our first European Award for Best Practices in Campaign on Safe Maintenance, the most asked question was not about the details of our enterprises coordination model but how a micro establishment in Spain had managed to win a European award in Health and Safety. The answer that we have given is an explanation of our simple model of work. To our surprise turned out to be winning again. We propose a model of risk prevention to implement in small businesses. These enterprises are exposed to higher risks due to scarce resources. We aim to achieve excellent results despite limited financial resources (AU)

1,5-(H, RO, RS) shift/6π-electrocyclic ring closure tandem processes on N-[(α-heterosubstituted)-2-tolyl]ketenimines: a case study of relative migratory aptitudes and activating effects.

A number of N-aryl ketenimines, substituted at the ortho position either with different non-cyclic acetalic functions (acetals, monothioacetals, dithioacetals) or with only one alkoxymethyl or (alkylthio)methyl group, have been prepared and submitted to thermal treatment in toluene solution. Under smooth heating the ketenimines bearing non-cyclic acetals converted into 3,4-dihydroquinolines following two competitive tandem sequences that involve the alternative 1,5 migration of a hydride or alkoxy group as the first mechanistic step, followed by subsequent 6π electrocyclic ring closure. The heterocumulenes bearing acyclic monothioacetal and dithioacetal functions converted via a unique consecutive process involving the selective migration of the alkanethiolate group. Ketenimines bearing only one ether or thioether group transformed exclusively by the tandem sequence initiated by a 1,5 hydride shift. All these transformations provided as final reaction products a variety of quinoline derivatives with a range of substitution patterns. From these experiments the following order of propensity to migration can be extracted: RS > RO > H. It was also possible to estimate the following order of relative activating activities: RO > RS > H.

Anticuerpos séricos IgM e IgG anti-toxoplasma gondii en pacientes con abortos espontáneos: Barquisimeto Estado Lara / IgM and IgG serum antibodies anti-toxoplasma gonfii in patients with spontaneuos abortions: Barquisimeto Estado Lara

Evaluar la relación de abortos y la exposición a la infección toxoplasmósica, la serorreactividad contra Toxoplasma gondii y la exposición a factores de riesgo para toxoplasmosis, así como la presencia de signos o síntomas asociados a esta patología. Servicio de Obstetricia y Ginecología del Hospital "Dr. Pastor Oropeza Riera", Barquisimeto, Lara. Se estudiaron 51 pacientes con aborto y 51 en puerperio inmediato. Previo consentimiento informado, se les hizo entrevista, examen físico y toma de muestra sanguínea para determinación de anticuerpos IgM e IgG anti-Toxoplasma gondii por ELISA. Hubo serorreactividad general anti-Toxoplasma gondii en alrededor de 40 por ciento, encontrando IgM solo en una puérpera (1,96 por ciento) e IgG en 41,2 por ciento de las pacientes con aborto y 35,3 por ciento de las puérperas. No hubo relación entre infección toxoplasmósica y aborto, presencia de signos y/o síntomas de la enfermedad, ni con la ingesta de carnes crudas y el contacto con gatos, pero sí con la exposición a tierra.

To evaluate the relation of abortion and exposition to toxoplasmic infection, the seroreactivity anti-Toxoplasma gondii and exposition to toxoplasmic risk factors as well as, the presence of signs or symptoms associated to this pathology. Service of Gynecology and Obstetrics of the Hospital "Dr. Pastor Oropeza Riera", Barquisimeto, Lara. 51 abortion patients and 51 with inmediate puerperium were studied. With previous informed consent, they were interviewed, physical exam and blood samples taken in order to determine anti-Toxoplasma gondii IgM and IgG antibody by ELISA. There was general seroactivity anti-Toxoplasma gondii around 40 percent, finding IgM only in a puerperal patient (1.96 percent) and IgG in 41.2 percent of the abortion patients and 35.3 percent of the puerperal patients. Conclusions: There was not relation between toxoplasmic infection and abortion, no presence of signs and/or symptons of the disease, neither with the consumption of raw meat nor contact with cats, but yes with the exposure to soil.

Seroprevalencia contra toxocara canis en niños de 1 a 6 años con y sin síntomas respiratorios de barquisimeto, venezuela / Seroprevalence against Toxocara canis in children of 1-6 years without respiratory symptoms barquisimeto, Venezuela

Sabiendo la existencia de casos de Síndrome de Larva Migrans Visceral en Venezuela, es necesario conocer la seroprevalencia contra uno de sus agentes causales: Toxocara canis. Determinar la presencia de anticuerpos séricos IgG anti- Toxocara canis y su relación con síntomas respiratorios y factores de riesgo para Síndrome de Larva Migrans Visceral en niños de 1 a 6 años, que acudieron a dos ambulatorios urbanos de Barquisimeto-Venezuela. Se evaluaron 215 niños y niñas de 1 a 6 años de edad con y sin síntomas respiratorios. Previa información y solicitud del consentimiento informado de sus representantes, se les entrevistó y tomó muestra de sangre para determinar anticuerpos IgG séricos anti-Toxocara canis por ELISA, con el estuche DRG®. Se calcularon porcentajes y proporciones y se usaron Prevalencia Relativa (PR) y Chi Cuadrado con intervalo de confianza de 95%. Se detectaron anticuerpos en 34,4%. El mayor porcentaje de seroreactivos estuvo representado por los niños con síntomas respiratorios (83,8%), los del grupo de edad de 3 a 4 años (55,4%), el sexo masculino (54,1%), quienes refirieroncontacto con tierra y/o geofagia (95,9%) y contacto con cachorros caninos menores de 3 meses de edad (90,5%), quienes consumían agua de calidad inadecuada (85,1%) y quienes disponían inadecuadamente las excretas caninas (60,8%). La elevada seroprevalencia crea la necesidad de nuevos estudios para evaluar con precisión las características epidemiológicas de la infección por T. canis en Lara y Venezuela a fin de establecer planes adecuados de control

In view of the presence of Visceral Larva Migrans Syndrome in Venezuela, it is necessary to know the seroprevalence against one of its causal agents: Toxocara canis. A transversal study was performed to determine the presence of serum IgG anti-Toxocara canis antibodies and their relation with respiratory symptoms and risk factors for Visceral Larva Migrans Syndrome in patients from 1 to 6 years, who assisted to two urban outpatient clinics of Barquisimeto-Venezuela. 215 children 1 to 6 years old with and without respiratory symptoms were evaluated. Previous information on the investigation and request of the consent in writing of their care givers, an interview was withheld and a blood sample was drawn to determine serum IgG anti-Toxocara canis antibodies by the ELISA method, with DRG® commercial kit. Percentage and proportions were calculated and Relative Prevalence (RP) and x Squared used, with an interval of statistical confidence of 95%. Antibodies were detected in 34.4% of the children. The greater percentage of seroreactives was represented by children with respiratory symptoms (83.8%), those inthe age group of 3 to 4 years (55.4%), boys (54.1%), those who referred soil contact and/or geophagy (95.9%) and contact with puppies under three months of age (90.5%), that consumed water of inadequate quality (85.1%) and that had inadequate disposal of canine excretes (60.8%). The high seroprevalence creates the necessity of new studies to evaluate accurately the epidemiologic characteristics of the infection by T. canis in Lara and Venezuela in order to establish suitable control plans

Unprecedented intramolecular [3 + 2] cycloadditions of azido-ketenimines and azido-carbodiimides. Synthesis of indolo[1,2-a]quinazolines and tetrazolo[5,1-b]quinazolines.

N-(2-azidomethyl)phenyl ketenimines and N-(2-azidomethyl)phenyl-N'-alkyl(aryl) carbodiimides undergo, under mild thermal conditions, intramolecular [3 + 2] cycloaddition reactions between the azido group and either the C=C or the distal C=N double bonds of the ketenimine and carbodiimide functions respectively. The reaction products are indolo[1,2-a]quinazolines and/or indolo[2,1-b]quinazolines in the case of azido-ketenimines, and tetrazolo[5,1-b]quinazolines in the case of azido-carbodiimides. The formation of the two classes of indoloquinazolines implies the ulterior dinitrogen extrusion from the non-isolated, putative [3 + 2] cycloadducts between the azide and ketenimine functions, whereas in the case of azido-carbodiimides the initial cycloadducts, tetrazoloquinazolines, were cleanly isolated and further converted into 2-aminoquinazolines by thermally induced dinitrogen extrusion.