Search

Hydroxy-azirine (C2H3NO) is a -OH derivative of azirine (C2H3N), molecule that has been the subject of several unfruitful searches in space. Hydroxy-azirine is an isomer of the detected prebiotic species methyl isocyanate, CH3NCO, and glycolonitrile, HOCH2CN, as well as the yet undetected imine acetaldehyde, NHCHCHO. However, the lack of preliminary spectroscopic data on hydroxy-azirine has prevented its astronomical search. The aim of this study is to provide high-level theoretical spectroscopic signatures of the most stable hydroxy-azirine isomers to enable their eventual interstellar search. A total of 12 isomers have been characterized for hydroxy-azirine and their isomerization processes have been analysed at the CCSD(T)-F12/cc-pVTZ-F12 level. The most stable structures are 3-hydroxy-2H-azirine (I) and 2-hydroxy-2H-azirine (II) in their syn- and anti-configurations, which are suggested as the most relevant candidates for laboratory and interstellar detection. To ease their identification by means of rotational spectroscopy, we report a set of the required spectroscopic parameters using state-of-the-art composite and coupled-cluster approaches. For astronomical purposes, we provide a complete line list for I-syn and I-antihydroxy-azirine up to 50 GHz, which takes the hyperfine structure into account, and will be essential to hunt for these interstellar candidates experimentally. In addition, anharmonic vibrational frequencies and intensities are reported to predict a trustworthy vibrational spectra and to estimate the vibrational partition function. Finally, we analyse the possibility of formation of hydroxy-azirine from the reaction of azirine with the hydroxyl radical in the gas-phase and on the surface of ices, finding for the latter a feasible formation route under interstellar conditions.

Objetivo: Estudiar las diferentes maneras en que la Corte Constitucional de Colombia (1991-2020) ha venido fallando en casos donde estudiantes (o aspirantes a serlo) invocan el derecho a la libertad religiosa y de cultos en establecimientos educativos. Metodología: Desde una perspectiva cualitativa, se identifica la línea jurisprudencial relacionada con el tema, y se analizan los argumentos emitidos por la Corte en las sentencias que componen la línea. Resultados: Los argumentos de la Corte se dividen en dos tipos: uno que es categorizado como pluralista, en el cual se privilegia el derecho a la libertad religiosa de los individuos, y otro que es categorizado como uniformista, en el que se privilegian las normas institucionales independientemente de las creencias religiosas particulares. Conclusiones: La diversidad religiosa en establecimientos educativos revela algunos de los dilemas y tensiones existentes en la modernidad liberal, particularmente en lo concerniente al debate sobre el lugar de la religión en el espacio público y la posibilidad de que convivan diferentes sistemas de pensamiento y de valores en comunidades e instituciones que pretenden ser pluralistas.

ABRSTRACT. Objective/Context: This paper examines the arguments of the Constitutional Court of Colombia in a sentence declaring that Pentecostalism represents a threat to indigenous cultures and to the country’s cultural diversity. The sentence was issued in 1998, a few years after the political Constitution (1991) declared that Colombia is a pluralist nation that protects the cultural diversity of the country and the right to religious freedom. Methodology: A qualitative and hermeneutical study of the sentence was implemented to understand the arguments presented by the Court. Subsequently, a critical analysis of those arguments was carried out, questioning the pluralist presuppositions related to key categories such as “indigenous cultures,” “religion,” and “diversity.” Conclusions: The pluralist institution has been unable to recognize the dynamic and manifold realities of lived religion, as well as the problems related to the double marginalization of a religious minority within an ethnic minority. Furthermore, the pluralist imperative to protect cultural diversity places limits upon alterity and promotes new forms of exclusion. Originality: The jurisprudence under scrutiny is not studied in its legal or ethical dimensions-as it has been done in the past-but as the implementation of a pluralist ideology grounded in a certain worldview. Thus, pluralism is critically examined in its ontological, axiological, epistemological, and praxeological principles. RESUMEN. Objetivo/contexto: este trabajo examina los argumentos de la Corte Constitucional de Colombia en una sentencia que declaró que el pentecostalismo representa una amenaza para las culturas indígenas y para la diversidad cultural del país. La sentencia fue emitida en 1998, pocos años después de que la Constitución Política (1991) declarara que Colombia es una nación pluralista que protege la diversidad cultural del país y el derecho a la libertad religiosa. Metodología: se ha implementado un estudio cualitativo y hermenéutico de la sentencia con el fin de comprender los argumentos presentados por la Corte. Posteriormente, se ha realizado un análisis crítico de esos argumentos, cuestionando los presupuestos pluralistas relacionados con categorías clave como culturas indígenas, religión y diversidad. Conclusiones: la institución pluralista ha sido incapaz de reconocer las realidades dinámicas y múltiples de la religión vivida, así como los problemas relacionados con la doble marginación de una minoría religiosa dentro de una minoría étnica. Además, el imperativo pluralista de proteger la diversidad cultural pone límites a la alteridad y promueve nuevas formas de represión y exclusión. Originalidad: la jurisprudencia bajo escrutinio no se estudia en sus dimensiones legales o éticas -como se ha hecho en el pasado- sino como la implementación de una ideología pluralista basada en una determinada cosmovisión. El pluralismo se examina así críticamente en sus principios ontológicos, axiológicos, epistemológicos y praxeológicos. RESUMO. Objetivo/contexto: neste trabalho, examinam-se os argumentos do Tribunal Constitucional da Colômbia em uma decisão que declarou que o pentecostalismo representa uma ameaça às culturas indígenas e à diversidade cultural do país. A sentença foi emitida em 1998, poucos anos depois que a Constituição Política (1991) tivesse declarado que a Colômbia é uma nação pluralista que protege a diversidade cultural do país e o direito à liberdade religiosa. Metodologia: foi realizado um estudo qualitativo e hermenêutico da sentença para a compreensão dos argumentos apresentados pelo Tribunal. Posteriormente, procedeu-se a uma análise crítica desses argumentos, questionando os pressupostos pluralistas relacionados com categorias-chave como “culturas indígenas”, “religião” e “diversidade”. Conclusões: a instituição pluralista tem sido incapaz de reconhecer as realidades dinâmicas e múltiplas da religião vivida, bem como os problemas relacionados à dupla marginalização de uma minoria religiosa dentro de uma minoria étnica. Além disso, o imperativo pluralista de proteger a diversidade cultural limita a alteridade e promove novas formas de repressão e exclusão. Originalidade: a jurisprudência sob escrutínio não é estudada em suas dimensões jurídicas ou éticas -como se fazia no passado-, mas sim como a implementação de uma ideologia pluralista baseada em uma determinada cosmovisão. O pluralismo é, portanto, examinado criticamente em seus princípios ontológicos, axiológicos, epistemológicos e praxeológicos.

Herein, we report a computational investigation of the binding affinity of dexamethasone, betamethasone, chloroquine and hydroxychloroquine to SARS-CoV-2 main protease using molecular and quantum mechanics as well as molecular docking methodologies. We aim to provide information on the anti-COVID-19 mechanism of the abovementioned potential drugs against SARS-CoV-2 coronavirus. Hence, the 6w63 structure of the SARS-CoV-2 main protease was selected as potential target site for the docking analysis. The study includes an initial conformational analysis of dexamethasone, betamethasone, chloroquine and hydroxychloroquine. For the most stable conformers, a spectroscopic analysis has been carried out. In addition, global and local reactivity indexes have been calculated to predict the chemical reactivity of these molecules. The molecular docking results indicate that dexamethasone and betamethasone have a higher affinity than chloroquine and hydroxychloroquine for their theoretical 6w63 target. Additionally, dexamethasone and betamethasone show a hydrogen bond with the His41 residue of the 6w63 protein, while the interaction between chloroquine and hydroxychloroquine with this amino acid is weak. Thus, we confirm the importance of His41 amino acid as a target to inhibit the SARS-CoV-2 Mpro activity.

Metal cyanides and isocyanides play a relevant role in the metal chemistry of the carbon-rich circumstellar envelope IRC+10216. It is thought that hydrometal cyanides/isocyanides could also be present in these environments; in fact, HMgNC has been detected in the same source that MgCN, MgNC, and AlNC. The aim of this work is to provide information about hydroaluminum cyanide/isocyanide. For this goal, a comprehensive analysis of the doublet and quartet potential energy surfaces of the [Al, C, H, N] system has been carried out. Different quantum chemistry methodologies from density functional theory to ab initio have been employed. For the [Al, C, H, N] isomers, the stability against dissociation and their interconversion processes have been analyzed. Our results show that the most relevant isomers from an experimental point of view are HAlCN and HAlNC. HAlNC has been found to be the most stable isomer followed by HAlCN, which is located at 1.59 kcal mol−1 (0.0689 eV) at the composite level. The interconversion process between HAlCN and HAlNC presents an energy barrier of 10.0 kcal mol−1 (5032 K) that makes this process not viable in the interstellar medium. We provide a complete set of relevant spectroscopic parameters for rotational spectroscopy for both HAlCN and HAlNC isomers using state-of-the-art quantum chemical computations, mandatory to guide an eventual laboratory or interstellar detection. Moreover, both isomers present sizable μ a dipole moment components (3.7 and 3.3 D, respectively), which are large enough to enable a characterization by means of rotational spectroscopy, further increasing their interest as interstellar candidates.

21 p.-9 fig.-2 tab., Focal adhesion kinase (FAK) is a key component of the membrane proximal signaling layer in focal adhesion complexes, regulating important cellular processes, including cell migration, proliferation, and survival. In the cytosol, FAK adopts an autoinhibited state but is activated upon recruitment into focal adhesions, yet how this occurs or what induces structural changes is unknown. Here, we employ cryo-electron microscopy to reveal how FAK associates with lipid membranes and how membrane interactions unlock FAK autoinhibition to promote activation. Intriguingly, initial binding of FAK to the membrane causes steric clashes that release the kinase domain from autoinhibition, allowing it to undergo a large conformational change and interact itself with the membrane in an orientation that places the active site toward the membrane. In this conformation, the autophosphorylation site is exposed and multiple interfaces align to promote FAK oligomerization on the membrane. We show that interfaces responsible for initial dimerization and membrane attachment are essential for FAK autophosphorylation and resulting cellular activity including cancer cell invasion, while stable FAK oligomerization appears to be needed for optimal cancer cell proliferation in an anchorage-independent manner. Together, our data provide structural details of a key membrane bound state of FAK that is primed for efficient autophosphorylation and activation, hence revealing the critical event in integrin mediated FAK activation and signaling at focal adhesions., I.A. acknowledges support from the José Castillejo Mobility Grant issued by the Spanish Ministry of Education, Culture and Sports. R.D.R. acknowledges funding from the Fellowships for Excellence program sponsored by the Werner-Siemens Foundation and the University of Basel.H.S. acknowledges support by the Swiss National Science Foundation(grants 205320_166164 and 185544 (NCCR TransCure)). M.C.F., A.B., J.C., and C.S. were supported by a Cancer Research UK Programme Grant (C157/ A24837) to M.C.F. F.G. acknowledges funding by the Klaus Tschira Foundation, by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – 2082/1 –390761711, and the state of Baden-Württemberg through bwHPC and the DFG through grant INST 35/11341 FUGG.S.d.B. thanks the Carl Zeiss Foundation for financial support. D.L. acknowledges support from the Spanish Ministry of Economy, Industry and Competitiveness for the Retos Grant BFU2016-77665-R and the Ministry of Science, Innovation and Universities for the Spanish State Research Agency Retos Grant RTI2018-099318-B-I00,both co-funded by the European Regional Development Fund (FEDER) and from an intramural grant from the Spanish National Research Council(CSIC, Ref: 201820I124). O.L. is funded by SAF2017-82632-P grant from the Spanish Ministry of Science, Innovation and Universities (MCIU/AEI), cofunded by the European Regional Development Fund (ERDF), by the National Institute of Health Carlos III and by projects Y2018/BIO4747 and P2018/NMT4443 from the Autonomous Region of Madrid and co-funded by the European Social Fund and the European Regional Development Fund. C.F.R. is funded by a BES-2015-071348 PhD fellowship by the Spanish Ministry of Science, Innovation and Universities (MCIU/AEI).

Producción Científica, We present a computational study of the different conformers of amino acetaldehyde. This molecule is a precursor of glycine and also an isomer of the detected molecules acetaldehyde and methylformamide. In addition, a previous theoretical result shows that amino acetaldehyde could be formed from the gas phase reaction of formamide with CH+5⁠. Different computational approaches, going from density functional theory (DFT) to coupled cluster (CC) calculations, are employed for the characterization of the amino acetaldehyde conformers. We locate four low-lying conformation on the singlet potential energy surface (PES), two with a synperiplanar arrangement of the carboxylic oxygen atom and the NH2 group, and the other two conformers with an anticlinal disposition. All levels of theory predict the conformer with a synperiplanar arrangement and the H atoms of the NH2 group pointing in the direction of the oxygen, denoted as in-sp-amino acetaldehyde, as the most stable. The viability of the interconversion processes between the four conformers in space is analysed. Relevant spectroscopic parameters to rotational spectroscopy with ‘spectroscopic’ accuracy at the composite level are reported. Vibrational frequencies and infrared intensities are also computed at the CC with single and double excitations (CCSD) level including anharmonic corrections. This information could help in the experimental characterization of amino acetaldehyde that could be considered as a good candidate molecule to be searched for in space., Ministerio de Economía, Industria y Competitividad (Grant AYA2017-87515-P), Junta de Castilla y León (Ref. project VA010G18)

Producción Científica, Recently, the first Ca-bearing molecule discovered in space, calcium isocyanide, CaNC, has been detected in the IRC+10216 circumstellar envelope. Related to CaNC are closed-shell stable molecules of [C, Ca, H, N] composition. One of the isomers with this composition is hydrocalcium isocyanide, HCaNC, which belongs to the hydrometal isocyanide/cyanide group of compounds, among which hydromagnesium isocyanide, HMgNC, is, to date, the only one detected in space. In this work, we have performed a study of the [C, Ca, H, N] isomers that are systems of possible interstellar interest by using quantum theoretical methodologies. The analysis of the relative energies predicts three low-lying isomers: c-HCa–NC (1A'), hydrocalcium isocyanide, HCaNC (1Σ), and hydrocalcium cyanide, HCaCN (1Σ). At the composite level, HCaNC (1Σ) and HCaCN (1Σ) were located 0.87 and 4.84 kcal mol−1, respectively, above the c-HCa–NC (1Σ) isomer. Interconversion processes between these isomers have been studied to analyze their stability. Isomer HCaNC is characterized as a transition state and thus directly isomerizes to the c-HCa–NC minimum. The isomerization process of HCaCN → c-HCa–NC shows a small barrier of about 0.76 kcal mol−1 (~382 K) above HCaCN, at the highest level of theory employed in this work, suggesting that HCaCN could easily isomerize into the most stable isomer, c-HCa–NC. Our results predict two low-lying isomers, namely, c-HCa–NC (1A') and hydrocalcium cyanide, HCaCN (1Σ), as possible candidates for experimental or radioastronomical detection. For these isomers, we provide predictions for their vibrational and rotational spectroscopic parameters that could aid in their eventual characterization in the laboratory or in space., Ministerio de Economía, Industria y Competitividad (grant AYA2017-87515-P), Junta de Castilla y León (grant VA010G18)

Producción Científica, A computational kinetics study of the antioxidant activity of tryptamine toward HO• and HOO• radicals in water at 298 K has been carried out. Density functional methods have been employed for the quantum chemical calculations, and the conventional transition state theory was used for rate constant evaluation. Different mechanisms have been considered: radical adduct formation (RAF), single electron transfer (SET), and hydrogen atom transfer (HAT). For the reaction of tryptamine with the hydroxyl radical, nearly all channels are diffusion-controlled, and the overall rate constant is very high, 6.29 × 1010 M–1 s–1. The RAF mechanism has a branching ratio of 55%, followed by the HAT mechanism (31%), whereas the SET mechanism accounts just for 13% of the products. The less hindered carbon atom neighboring to the nitrogen of the indole ring seems to be the preferred site for the RAF mechanism, with a branching ratio of 16%. The overall rate constant for the reaction of tryptamine with the HOO• radical is 3.71 × 104 M–1 s–1, suggesting that it could be a competitive process with other reactions of hydroperoxyl radicals in biological environments. For this reaction only the HAT mechanism seems viable. Furthermore, only two centers may contribute to the HAT mechanism, the nitrogen atom of the indole ring and a carbon atom of the aminoethyl chain, the former accounting for more than 91% of the total products. Our results suggest that tryptamine could have a noticeable scavenging activity toward radicals, and that this activity is mainly related to the nitrogen atom of the indole ring, thus showing the relevance of their behavior in the study of aminoindoles., Universidad Nacional del Nordeste (grant F008-2013), Ministerio de Economía, Industria y Competitividad (grant AYA2017-87515-P)

A theoretical study of the monoboronyl compounds of second-row elements, [XBO] (X = Na, Si, P, S, Cl), has been carried out. It is observed that the preference for the XBO arrangement is higher when moving to the right of the period. In the case of sodium monoboronyl three minima were characterized, all lying rather close in energy: linear NaBO, linear NaOB, and an L-shaped structure. Linear NaBO and the L-shaped structure are nearly isoenergetic, whereas linear NaOB is located 2.11 kcal/mol above linear NaBO. The barrier for the conversion of the L-shaped structure into linear NaBO is about 5.1 kcal/mol, suggesting that both species could be potential targets for experimental detection. For silicon monoboronyl, two minima, linear SiBO and linear SiOB, are found, the latter lying about 13 kcal/mol above SiBO. The barrier for the isomerization of SiOB into SiBO is estimated to be 11.4 kcal/mol. For phosphorus, sulfur, and chlorine monoboronyls the linear XBO isomer is clearly the most stable one, and the barriers for the conversion into XOB species are relatively high, suggesting that quite likely the linear XBO isomer should be the main experimental target. All studied monoboronyls are relatively stable, with dissociation energies increasing from left to right of the second-row (69.8 kcal/mol for NaBO and 118.98 kcal/mol for ClBO). An analysis of the bonding for second-row monoboronyls has been carried out, emphasizing the different characteristics of the X-B and X-O bonds along the second row.

Theoretical methodologies have been employed to study [Mg,C,N,O] isomers, which are possible species of interstellar interest. It has been found that, at all levels of theory used, the most stable isomer is the magnesium isocyanate radical. The corresponding cyanate counterpart lies 15.8 kcal/mol, at the CCSD(T) level of theory, above MgNCO. Other isomers, such as the magnesium fulminate radical, MgCNO, the magnesium isofulminate radical, MgONC, and the two compounds that arise from the insertion of the magnesium atom between either O–N or O–C bonds, namely, OMgNC and OMgCN, are located clearly higher in energy than MgNCO. The barrier for the MgOCN → MgNCO process has been calculated to be 4.6 kcal/mol, suggesting a slow rate for the isomerization reaction. To examine the bonding interactions in the different [Mg,C,N,O] isomers, a natural bond orbital analysis, together with a topological analysis of the electron density in the framework of Bader’s quantum theory of atoms in molecules, has been carried ou...

Producción Científica, A theoretical study of the [C, Ti, H, N] isomers, which are species of possible interstellar interest, has been carried out. We have employed different ab initio and density functional theory methodologies. Eleven isomers on the singlet, triplet, and quintet potential energy surfaces (PES) are characterized. The three most stable isomers of this system are obtained on the 3A″ PES from the interaction of the titanium atom of TiH with the cyano radical, CN, giving the open chains hydrotitanium cyanide/isocyanide (HTiCN/HTiNC) and the cyclic arrangement HTi-CN. For the most stable isomers we apply a composite approach that considers the extrapolation to the complete basis set limit, relativistic, and core-valence electron correlation corrections at the coupled-cluster level, including single and double excitations and a perturbative treatment of triple excitations (CCSD(T)). The lowest-lying isomer, HTiNC, is predicted to lie about 3.67 kcal mol−1 and 3.86 kcal mol−1 below HTiCN and the cyclic structure HTi-CN, respectively. The isomerization processes between these isomers shows that the cyclic structure could easily isomerize into HTiNC (the energy barrier is estimated to be only 0.48 kcal mol−1). We report harmonic and anharmonic frequencies, infrared intensities, and rotational constants that could help in their experimental characterization., Ministerio de Economía, Industria y Competitividad ( grant AYA2017-87515-P ), Junta de Castilla y León (project VA010G18)

Producción Científica, A computational study of protonated glycine isomers with [H6C2O2N]+ molecular formula has been carried out. All of them are possible products of the reaction between protonated hydroxylamine and acetic acid. All reaction processes that could form the [H6C2O2N]+ isomers considered in this work are exothermic except for those initiated by the most stable isomer of protonated hydroxylamine which give CH3CONH2+OH and CH3COHNOH2+ isomers. The analysis of the potential energy surfaces corresponding to the reaction of protonated hydroxylamine and acetic acid has been focused on the most abundant products, namely, CH3CONH2+OH, CH3COONH3+, and CH3C(OH)+ONH2, obtained from a previous chemical dynamics simulations study. From this analysis we found that even if the reactions of formation of the CH3COONH3+ and the CH3C(OH)+ONH2 isomers are exothermic processes, significant activation barriers were found in the paths leading to these products. The only exothermic process (ΔE = −23.9 kcal mol–1 at the CCSD(T) level) with no net activation barrier was initiated by the high-energy isomer of protonated hydroxylamine, which leads to the CH3CONH2+OH isomer. Therefore, the formation of this isomer could be feasible under interstellar conditions from the reaction of the less stable isomer of protonated hydroxylamine and acetic acid. In addition, an analysis of their neutral counterparts, with [H5C2O2N] molecular formula, has been carried out. The relevant spectroscopic parameters for [H6C2O2N]+ and [H5C2O2N] isomers that could help in their laboratory or astronomical detection, by radioastronomy or infrared spectroscopy, are reported., Ministerio de Economía, Industria y Competitividad ( grant AYA2017-87515-P), Junta de Castilla y León (Grant VA010G18), Ministerio de Ciencia, Innovación y Universidades (Predoctoral FPU Grant FPU17/02987)

Tousled-like kinases (TLKs) are required for genome stability and normal development in numerous organisms and have been implicated in breast cancer and intellectual disability. In humans, the similar TLK1 and TLK2 interact with each other and TLK activity enhances ASF1 histone binding and is inhibited by the DNA damage response, although the molecular mechanisms of TLK regulation remain unclear. Here we describe the crystal structure of the TLK2 kinase domain. We show that the coiled-coil domains mediate dimerization and are essential for activation through ordered autophosphorylation that promotes higher order oligomers that locally increase TLK2 activity. We show that TLK2 mutations involved in intellectual disability impair kinase activity, and the docking of several small-molecule inhibitors of TLK activity suggest that the crystal structure will be useful for guiding the rationale design of new inhibition strategies. Together our results provide insights into the structure and molecular regulation of the TLKs., The Tousled-like kinase (TLKs) family belongs to a distinct branch of Ser/Thr kinases that exhibit the highest levels of activity during DNA replication. Here the authors present the crystal structure of the kinase domain from human TLK2 and propose an activation model for TLK2 based on biochemical and phosphoproteomics experiments.

The high DNA specificity of homing endonucleases makes them a powerful protein scaffold to engineer enzymes for genome manipulation. Understanding their molecular recognition of DNA is an important prerequisite to generate engineered enzymes able to cleave DNA in specific desired genome sites. Protein-DNA recognition studies have been mostly focused on specific direct contacts between amino acid side chains and bases to redesign the binding interface. However, the important role of indirect readout in the central region of the target DNA of the homing endonuclease I-CreI suggested that indirect readout may play a key role in the redesign of protein-DNA interactions. The sequences of the I-CreI central substrate region, 2NN, along with the adjacent 5NNN, are key for substrate cleavage. Here, we analyse the mechanism of target discrimination at the 5NNN region by the I-CreI protein, revealing its critical role in the location and occupancy of the catalytic metal ions, which is crucial for cleavage. Our data highlight the importance of indirect readout for target DNA cleavage, thus aiding I-CreI engineering when targeting new DNA sequences. e thank the Swiss Light Source (SLS) and ALBA beamline staff for their support. This work was supported by the Spanish MINECO (JCI-2011-09308 to R.M and CTQ2017-83810-R to F.J.B.), the Severo Ochoa Excellence Accreditation (SEV-2016-0644) and the Novo Nordisk Foundation (Grant NNF14CC0001 to G.M.), Sí

RESUMEN: Este artículo estudia el requisito de edad como condición para acceder a ciertos cargos y corporaciones públicas de elección popular en Colombia. Se plantea un recorrido por las normas constitucionales, las leyes y algunas jurisprudencias que se han producido sobre este tema. En particular, se investiga si el legislador está facultado para determinar la edad que deben ostentar los diputados del país, señalando, por ejemplo, la persistencia de interpretaciones erradas sobre las normas relativas al tema. Se evidencia, además, que en la práctica, algunas instituciones oficiales afirman públicamente que la edad mínima para acceder a la Asamblea Departamental es de 25 años, edad superior a la estipulada en la Constitución Política. El caso de los diputados es comparado con algunas controversias generadas a propósito de la edad en los concejales, lo cual permite problematizar la diversidad de perspectivas y la relatividad cultural de estos conceptos. Se concluye así que existen confusiones e irregularidades al nivel institucional sobre el requisito de edad, lo cual tiene graves consecuencias, ya que se están vulnerando los derechos políticos de los ciudadanos colombianos. ABSTRACT: This article examines the age requirement as a condition for access to certain public offices and public corporations of popular election in Colombia. A tour of the constitutional rules, laws and some jurisprudence that have been produced on this subject is proposed. In particular, it investigates whether the legislature has the power to determine the age of deputies in the country, noting, for example, the persistence of misinterpretation of the rules on the subject. It is also evident that, in practice, some official institutions publicly affirm that the minimum age for access to the Departmental Assembly is 25 years of age, which is higher than that stipulated in the Constitution. The case of deputies is compared to some controversies about the age of councillors, which allows problematizing the diversity of perspectives and cultural relativity of these concepts. This concludes that there are confusions and irregularities at the institutional level regarding the age requirement, which has serious consequences, since the political rights of Colombian citizens are being violated. RESUMO: Este artigo estuda o requisito de idade como condição para assumir certos cargos e corporações públicas de eleição popular na Colômbia. Apresenta-se um percorrido por normas constitucionais, leis e algumas jurisprudências produzidas sobre esse tema. Em particular, investiga-se se o legislador está facultado para determinar a idade que devem ostentar os deputados do país, indicando, por exemplo, a persistência de interpretações equivocadas sobre as normas relativas ao tema. Além disso, evidencia-se que, na prática, algumas instituições oficiais afirmam publicamente que a idade mínima para entrar na Assembleia Regional é de 25 anos, idade superior à estipulada na Constituição Política. O caso dos deputados é comparado com algumas controvérsias geradas sobre a idade dos vereadores, o que permite problematizar a diversidade de perspectivas e a relatividade cultural desses conceitos. Assim, conclui-se que existem confusão e irregularidades no contexto institucional sobre o requisito de idade, o que leva a graves consequências, já que estão sendo violados os direitos políticos dos cidadãos colombianos.

Homing endonucleases recognize and generate a DNA double-strand break, which has been used to promote gene targeting. These enzymes recognize long DNA stretches; they are highly sequence-specific enzymes and display a very low frequency of cleavage even in complete genomes. Although a large number of homing endonucleases have been identified, the landscape of possible target sequences is still very limited to cover the complexity of the whole eukaryotic genome. Therefore, the finding and molecular analysis of homing endonucleases identified but not yet characterized may widen the landscape of possible target sequences. The previous characterization of protein-DNA interaction before the engineering of new homing endonucleases is essential for further enzyme modification. Here we report the crystal structure of I-CvuI in complex with its target DNA and with the target DNA of I-CreI, a homologue enzyme widely used in genome engineering. To characterize the enzyme cleavage mechanism, we have solved the I-CvuI DNA structures in the presence of non-catalytic (Ca(2+)) and catalytic ions (Mg(2+)). We have also analyzed the metal dependence of DNA cleavage using Mg(2+) ions at different concentrations ranging from non-cleavable to cleavable concentrations obtained from in vitro cleavage experiments. The structure of I-CvuI homing endonuclease expands the current repertoire for engineering custom specificities, both by itself as a new scaffold alone and in hybrid constructs with other related homing endonucleases or other DNA-binding protein templates.

Sarcoidosis involves the lung in more than 90% of cases; skeletal involvement has been reported in 1% to 14%.

Situs inversus totalis is a congenital anatomic anomaly characterized by a complete inversion of thoracic and abdominal organs. We present a case of a 67 year-old patient diagnosed with situs inversus totals in his childhood who was referred for a two-month history of hematoquezia. Ascending colon cancer where found and he underwent a laparoscopic hemicolectomy with radical lymphadenectomy. An exhaustive preoperative study and a detailed planning of laparoscopic surgery including positions of operator and assistants and trocar sites have been performed to be aware of anatomic challenges. The operating time was 120 min and blood loss was minimal. Histologic examination showed a well-differentiated adenocarcinoma with serosal invasion and without lymph nodes metastasis (pT3N0). The patient was discharged on postoperative 6th day without complications. Laparoscopic surgery for colon cancer in patients with situs inversus totalis could be more difficult nevertheless a safe and feasible procedure should be performed successfully. Resumo: Situs inversus totalis é uma anomalia anatómica consistindo em um investimento de órgãos abdominais. Nesse estudo, descrevemos um paciente, homem 67 anos, que foi diagnosticado com situs inversus totalis na infância. Apresentava sintomas de sangramento retal e foi diagnosticado com câncer de cólon direito e tratado cirurgicamente com receção laparoscópica. Para a realização da colectomia laparoscopica precisamos de um estudo pré-operatória completa e um plano detalhado de cirurgia com localização do trocateres e cirurgiões. A cirurgia durou 120 minutos e perde de sangue foi mínima. O resultado do exame patológico relatou adenocarcinoma (T3N0). Nosso paciente foi admitido por 7 dias e não apresentaram complicações. Para os pacientes com situs inversus totalis e câncer colorretal a receção laparoscópica pode ser mais difícil mas eficaz e segura. Keywords: Colorectal cancer, Situs inversus totalis, Laparoscopic surgery, Laparoscopic hemicolectomy, Congenital anomaly, Palavras-chave: Câncer Colorretal, Situs inversus totalis, Cirurgia laparoscópica, Malformação congênita

The C-terminal kinase domain of TLK2 (a human tousled-like kinase) has been cloned and overexpressed in Escherichia coli followed by purification to homogeneity. Crystallization experiments in the presence of ATP-γ-S yielded crystals suitable for X-ray diffraction analysis belonging to two different space groups: tetragonal I4122 and cubic P213., Tousled-like kinases (TLKs) are an evolutionarily conserved family of serine/threonine protein kinases involved in chromatin dynamics, including DNA replication and repair, transcription and chromosome segregation. The two members of the family reported in humans, namely TLK1 and TLK2, localize to the cell nucleus and are capable of forming homo- or hetero-oligomers by themselves. To characterize the role of TLK2, its C-terminal kinase domain was cloned and overexpressed in Escherichia coli followed by purification to homogeneity. Crystallization experiments in the presence of ATP-γ-S yielded crystals suitable for X-ray diffraction analysis belonging to two different space groups: tetragonal I4122 and cubic P213. The latter produced the best diffracting crystal (3.4 Å resolution using synchrotron radiation), with unit-cell parameters a = b = c = 126.05 Å, α = β = γ = 90°. The asymmetric unit contained one protein molecule, with a Matthews coefficient of 4.59 Å3 Da−1 and a solvent content of 73.23%.

Homing endonucleases are highly specific DNA-cleaving enzymes that recognize long stretches of DNA. The engineering of these enzymes provides novel instruments for genome modification in a wide range of fields, including gene targeting, by inducing specific double-strand breaks. I-CvuI is a homing endonuclease from the green alga Chlorella vulgaris. This enzyme was purified after overexpression in Escherichia coli. Crystallization experiments of I-CvuI in complex with its DNA target in the presence of Mg2+ yielded crystals suitable for X-ray diffraction analysis. The crystals belonged to the orthorhombic space group P212121, with unit-cell parameters a = 62.83, b = 83.56, c = 94.40 Å. The self-rotation function and the Matthews coefficient suggested the presence of one protein–DNA complex per asymmetric unit. The crystals diffracted to a resolution limit of 1.9 Å using synchrotron radiation.

Thermodynamics and kinetics theoretical studies on the gas-phase reactions of fluoromethane with main fourth-period monocations (Ga(+), Ge(+), As(+), and Se(+)) have been carried out. Density functional theory (in particular mPW1K functional) was employed in the description of the potential energy surfaces, and refinement of the energies were done at the CCSD(T) level. The reaction rate constants were estimated using variational/conventional microcanonical transition state theory. From a thermodynamic viewpoint, the fluorine abstraction product is predicted for Ga(+) and Ge(+), whereas for As(+) and Se(+) the elimination product, MCH2(+) (M = As, Se) + HF, is the preferred one. Nevertheless, the most favorable channel for the reactions of CH3F with Ga(+) and Se(+) cations present a net activation barrier. In the case of Ga(+), the reaction proceeds via an addition channel forming the adduct complex, CH3FGa(+), whereas for Se(+) no reaction is found, in agreement with the experiments. The predicted reaction rate constants are in reasonable good agreement with the experimental values available. Apart from the harpoon-like mechanism, our results suggest that an oxidative addition mechanism seems to play a relevant role.

This pilot, double-blind, placebo-controlled, randomized, escalating dose trial explored the safety and efficacy of tideglusib, an inhibitor of glycogen synthase kinase-3, in Alzheimer's disease (AD) patients. Thirty mild-moderate AD patients on cholinesterase inhibitor treatment were administered escalating doses (400, 600, 800, 1,000 mg) of tideglusib or placebo (ratio 2 : 1) for 4, 4, 6, and 6 weeks, respectively. The primary objective was to evaluate the safety and tolerability of tideglusib with strict criteria for drug escalation or withdrawal. Mini-Mental Status Examination (MMSE), Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog+), word fluency, Geriatric Depression Scale (GDS), and a final Global Clinical Assessment (GCA) were assessed as secondary objectives. Treatment was well tolerated. Adverse events were as frequent in active and placebo groups, except for some moderate, asymptomatic, and fully reversible increases (>2.5 × ULN) of serum transaminases in 6 active cases (p = 0.001). Tideglusib produced positive trends in MMSE, ADAS-cog, GDS, and GCA without statistical significance in this small sample. Responders in MMSE were significantly higher in the active group (p = 0.05). Patients escalated up to 1000 mg/day had a benefit of 1.68 points in the MMSE and 4.72 points in the ADAS-cog+ when compared to placebo. This small pilot study provides valuable safety and efficacy estimates for the treatment of AD patients with tideglusib, currently being confirmed in a larger clinical trial. Due to escalating doses and the small sample size, this trial provides insufficient evidence to support or reject a benefit of tideglusib in AD.

Homing endonucleases are highly specific DNA-cleaving enzymes that recognize and cleave long stretches of DNA. The engineering of these enzymes provides instruments for genome modification in a wide range of fields, including gene targeting. The homing endonuclease I-SceI from the yeast Saccharomyces cerevisiae has been purified after overexpression in Escherichia coli and its crystal structure has been determined in complex with its target DNA. In order to evaluate the number of ions that are involved in the cleavage process, thus determining the catalytic mechanism, crystallization experiments were performed in the presence of Mn, yielding crystals that were suitable for X-ray diffraction analysis. The crystals belonged to the orthorhombic space group P212121, with unit-cell parameters a = 80.11, b = 80.57, c = 130.87 A, α = β = γ = 90°. The self-rotation function and the Matthews coefficient suggested the presence of two protein-DNA complexes in the asymmetric unit. The crystals diffracted to a resolution limit of 2.9 A using synchrotron radiation. From the anomalous data, it was determined that three cations are involved in catalysis and it was confirmed that I-SceI follows a two-metal-ion DNA-strand cleavage mechanism.

Producción Científica, Iron is the most abundant transition metal in space. Its abundance is similar to that of magnesium, and until today only, FeO and FeCN have been detected. However, magnesium-bearing compounds such as MgCN, MgNC, and HMgNC are found in IRC+10216. It seems that the hydrides of iron cyanide/isocyanide could be good candidates to be present in space. In the present work we carried out a characterization of the different minima on the quintet and triplet [C, Fe, H, N] potential energy surfaces, employing several theoretical approaches. The most stable isomers are predicted to be hydride of iron cyanide HFeCN, and isocyanide HFeNC, in their 5 states. Both isomers are found to be quasi-isoenergetics. The HFeNC isomer is predicted to lie about 0.5 kcal/mol below HFeCN. The barrier for the interconversion process is estimated to be around 6.0 kcal/mol, making this process unfeasible under low temperature conditions, such as those in the interstellar medium. Therefore, both HFeCN and HFeNC could be candidates for their detection. We report geometrical parameters, vibrational frequencies, and rotational constants that could help with their experimental characterization., Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13)

In this study, we asked whether CpG methylation could influence the DNA binding affinity and activity of meganucleases used for genome engineering applications. A combination of biochemical and structural approaches enabled us to demonstrate that CpG methylation decreases I-CreI DNA binding affinity and inhibits its endonuclease activity in vitro. This inhibition depends on the position of the methylated cytosine within the DNA target and was almost total when it is located inside the central tetrabase. Crystal structures of I-CreI bound to methylated cognate target DNA suggested a molecular basis for such inhibition, although the precise mechanism still has to be specified. Finally, we demonstrated that the efficacy of engineered meganucleases can be diminished by CpG methylation of the targeted endogenous site, and we proposed a rational design of the meganuclease DNA binding domain to alleviate such an effect. We conclude that although activity and sequence specificity of engineered meganucleases are crucial parameters, target DNA epigenetic modifications need to be considered for successful gene editions.

A theoretical study of the different isomers of neutral VCn (n = 1−8) clusters has been carried out. Predictions for their electronic energies, rotational constants, dipole moments, and vibrational frequencies have been made using the B3LYP method with different basis sets. For linear and cyclic VCn clusters, the lowest-lying states correspond to quartet states, with the only exception being VC, which has a 2Δ ground state. In the fan-type structures, the electronic ground state is found to be a quartet state for even n values, whereas for odd n values, the ground state is a doublet for VC3 and VC5 and a quartet for VC7. From the incremental binding energies, we can deduce an even−odd parity effect, with n-even clusters being more stable than n-odd ones in the linear and fan clusters. It was also found that neutral VCn clusters with n ≤ 6 prefer fan structures over linear and cyclic isomers, whereas cyclic ground states are predicted for the clusters with n > 6.

A theoretical study of neutral Zn[CN] n and Cu[CN] n complexes has been carried out, as representative examples of cyanide complexes of late transition metals. Both complexes prefer the cyanide arrangement over the isocyanide form, in agreement with the experimental evidence for the monocyanide compounds. The successive complexation energies suggest that the preferred complex in the case of copper is the monocyanide, CuCN, whereas for zinc the most favourable complex seems to be Zn(CN) 2 . Both Zn and Cu have preference for low coordination numbers, since mixed complexes with cyanide and cyanogen ligands are preferred over homoleptic M(CN) n complexes for n > 2.

Reactions of methyl fluoride with bare alkaline-earth metal monocations (Mg+, Ca+, Sr+, and Ba+) were studied using theoretical methods. Thermochemical data were calculated using density functional theory in conjunction with polarized 3-ζ and 4-ζ basis sets. Variational/conventional microcanonical transition state theory was used for the calculation of the reaction rate constants over a large range of temperatures. According to our calculations, the Ca+, Sr+, and Ba+ reactions with CH3F proceed to yield CaF+, SrF+, and BaF+, in agreement with the experimental observation. The theoretically predicted global rate constants are in reasonable agreement with the experimental data. In the case of Mg+, the large value of the computed energy barrier associated with the “inner” transition structure is fully consistent with the limited progress experimentally observed for this reaction. The importance of bottlenecks other than the “inner” transition state is highlighted and its mechanistic implications discussed. Particularly, our calculations suggest that the studied processes proceed through a “harpoon-like” mechanism.

Neutral iron-cyanide complexes have been studied through computational techniques. Fe[CN] n complexes are shown to prefer the cyanide arrangement. Only in the case of Fe[CN] the isocyanide isomer is found to lie slightly below the cyanide isomer. According to the complexation energies, Fe(CN) 2 seems to be the main target for possible experimental observation in the gas phase. Mixed complexes with cyanide and cyanogen ligands, Fe(CN) x (C 2 N 2 ) y , have also been studied. The balance between the stronger ligand character of CN and the preference for low coordination numbers, makes Fe(CN) 2 , Fe(CN)(C 2 N 2 ), Fe(CN) 2 (C 2 N 2 ), Fe(CN)(C 2 N 2 ) 2 , and Fe(CN) 2 (C 2 N 2 ) 2 the most stable complexes for each stoichiometry.

A theoretical study of the reactions of CH3NH2+/CH3NH3+ with formic acid has been carried out in order to clarify their role in the formation of glycine derivatives under the conditions of the interstellar medium. The possible intermediate species as well as the relevant transition states for these reactions were characterized at the MP2 level with the cc-pVTZ basis set. Energetic data were obtained at the CCSD(T) level employing the aug-cc-pVTZ basis set. Formation of protonated glycine is an exothermic process for the reaction of formic acid with CH3NH2+ (−2.5 kcal/mol at the CCSD(T) level) and a quasi-isoenergetic one for its reaction with CH3NH3+ (2.9 kcal/mol at the CCSD(T) level). However, in both cases a net activation barrier is found, suggesting that both processes are not allowed under interstellar conditions.

A computational study of arsenic dicarbide has been carried out. In agreement with the experimental evidence theoretical calculations predict a 2 Π ground state. However, a cyclic 2 B 2 species is found just about 3–4 kcal/mol higher in energy. The 2 B 2 species is shown to be a true minimum with a predicted barrier for isomerization around 7–8 kcal/mol. An analysis of the bonding suggests that the 2 B 2 state is a truly cyclic species. The preference for the linear arrangement appears to be due to weaker Pauli repulsion, since both electrostatic and orbital terms seem to favor the cyclic isomer.

The electronic and geometrical structures of the ground and excited states for the linear, fan and cyclic isomers of FeC n + and FeC n - ( n = 1–8) compounds are calculated using the B3LYP method. A comparison of these results with the previously obtained for TMC n + / TMC n - (TM = Sc, Ti, V, Co and Zn) systems, is carried out. Quartet and sextet states are found the most stables for FeC n + clusters. Linear FeC n - clusters prefer doublet and quartet ground states, whereas for cyclic and fan isomers the most stables are quartet and sextet ones. n -odd linear, fan, and cyclic FeC n + isomers are more stable than adjacent n -even ones. For FeC n - clusters the opposite trend is found for linear and fan structures, whereas for cyclic isomers the relative stability decreases along the series. In general linear isomers are the most stable conformations for FeC n + / FeC n - clusters. Systematic trends of different properties are analyzed for TMC n + / TMC n - clusters.

Sequence-specific endonucleases recognizing long target sequences are emerging as powerful tools for genome engineering. These endonucleases could be used to correct deleterious mutations or to inactivate viruses, in a new approach to molecular medicine. However, such applications are highly demanding in terms of safety. Mutations in the human RAG1 gene cause severe combined immunodeficiency (SCID). Using the I-CreI dimeric LAGLIDADG meganuclease as a scaffold, we describe here the engineering of a series of endonucleases cleaving the human RAG1 gene, including obligate heterodimers and single-chain molecules. We show that a novel single-chain design, in which two different monomers are linked to form a single molecule, can induce high levels of recombination while safeguarding more effectively against potential genotoxicity. We provide here the first demonstration that an engineered meganuclease can induce targeted recombination at an endogenous locus in up to 6% of transfected human cells. These properties rank this new generation of endonucleases among the best molecular scissors available for genome surgery strategies, potentially avoiding the deleterious effects of previous gene therapy approaches.

The stability of protonated and ionized hydroxylamine in relation to their reactivity with molecular hydrogen has been studied. All stationary points and transition states for the reactions of H2 with protonated and ionized hydroxylamine have been determined at the MP2(full) level with the cc-pVTZ basis set. Energetic data have been obtained at the CCSD(T) level employing the aug-cc-pVTZ basis set. The analysis of the potential energy surfaces corresponding to both reactions shows that molecular H2 cannot react either with protonated or ionized hydroxylamine under interstellar conditions. Therefore both ionized and protonated hydroxylamine may participate in synthetic routes of amino acids.

A theoretical study of the ion-molecule reaction, NH2(+) with acetic acid that could lead to precursors of glycine in the interstellar medium, has been carried out on the triplet and singlet potential energy surfaces. All stationary points and transition states on the (NO2C2H6)(+) triplet and singlet surfaces have been determined at the MP2(full) level with the cc-pVTZ basis set. Energetic data have been obtained at the CCSD(T) level employing the aug-cc-pVTZ basis set. The global minimum of the (NO2C2H6)(+) system is predicted to be protonated glycine in its singlet state, (1)A', and in general singlet states are more stable than the corresponding triplet ones. Formation of ionized glycine from this reaction is shown to be a feasible process under interstellar conditions, but the proton transfer channel and the formation of the compound CH2COOH(+) seem to be more favorable processes on the triplet and singlet potential surfaces, respectively.

The structures and molecular properties of open-chain and cyclic ZnC n +/− ( n = 1–8) clusters have been calculated by hybrid density functional theory. Equilibrium geometries, electronic energies, vibrational frequencies, dipole moments and rotational constants for individual species are provided. Some energetic aspects related to these clusters, such as their relative stabilities, are discussed in terms of the incremental binding energy, ionization energy and electron affinity. In addition, the competition between linear and cyclic structures is studied. In general, the incremental binding energy graphs show an even–odd parity effect with n -odd ZnC n + clusters being more stable than the adjacent n -even ones, while in anionic clusters the opposite tendency is found. Ionization energies and electron affinities also exhibit a parity alternation trend with n -even clusters having higher values than the adjacent n -odd ones. It is found that ZnC n +/− compounds prefer open-chain geometries over the cyclic ones with the only exception of ZnC 2 + .

The structure and properties of the different linear, fan and cyclic isomers of CoC n + and CoC n − ( n = 1–8) clusters have been calculated using the B3LYP method with the 6–311+G(d) basis set. The stability of clusters as a function of the size has been discussed in terms of the incremental binding energies. Linear, fan and cyclic structures of CoC n + clusters show a clear even–odd alternation in stability, n -odd members being more stable than the corresponding n -even ones. An opposite parity effect is found for linear and fan CoC n − clusters, whereas the relative stability of cyclic isomers decrease with n . Linear structures are the most stable CoC n + and CoC n − clusters, with the only exception of CoC 2 +/− and CoC 7 − where the fan and cyclic arrangements are slightly lower in energy. The computed ionization potentials for the three structures show a clear even–odd alternation, with higher values for n -even clusters than for n -odd ones. Electron affinities for CoC n clusters increase along the series.

The hyperthermophilic archaeon Desulfurococcus mobilis I-DmoI protein belongs to the family of proteins known as homing endonucleases (HEs). HEs are highly specific DNA-cleaving enzymes that recognize long stretches of DNA and are powerful tools for genome engineering. Because of its monomeric nature, I-DmoI is an ideal scaffold for generating mutant enzymes with novel DNA specificities, similarly reported for homodimeric HEs, but providing single chain endonucleases instead of dimers. However, this would require the use of a mesophilic variant cleaving its substrate at temperatures of 37 degrees C and below. We have generated mesophilic mutants of I-DmoI, using a single round of directed evolution that relies on a functional assay in yeast. The effect of mutations identified in the novel proteins has been investigated. These mutations are located distant to the DNA-binding site and cause changes in the size and polarity of buried residues, suggesting that they act by destabilizing the protein. Two of the novel proteins have been produced and analyzed in vitro. Their overall structures are similar to that of the parent protein, but they are destabilized against thermal and chemical denaturation. The temperature-dependent activity profiles for the mutants shifted toward lower temperatures with respect to the wild-type activity profile. However, the most destabilized mutant was not the most active at low temperatures, suggesting that other effects, like local structural distortions and/or changes in the protein dynamics, also influence their activity. These mesophilic I-DmoI mutants form the basis for generating new variants with tailored DNA specificities.

A theoretical study of the different linear, fan and cyclic CoCn (n = 1–8) clusters has been carried out. Predictions for their electronic energies, rotational constants, dipole moments, and harmonic vibrational frequencies have been made using the B3LYP method with the 6-311+G(d) basis set. Doublet and quartet lowest-lying states have been found for neutral CoCn clusters. The stability of linear, fan, and cyclic structures as a function of the size of the cluster has been discussed in terms of the incremental binding energies. Only fan structures show a clear even-odd alternation in stability. The incremental binding energies exhibit small changes along the series in the case of linear isomers, whereas for cyclic ones decrease along the series. It is also found that for the small CoCn clusters in general, the linear-type structures are more stable than the fan and cyclic ones. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

The structures and stabilities of TiCn+/− (n = 1–8) clusters have been studied by density functional theory (DFT) using the hybrid B3LYP functional. Molecular properties for three different isomers, linear, cyclic and fan species have been computed. The fan isomers, where the titanium atom interacts with the whole carbon chain, are predicted generally, to be more stable than both linear and cyclic structures. For linear and fan TiCn+/− isomers an even-odd alternation in stability is found, isomers with n-even being in general more stable than the adjacent n-odd numbered. The ionization potentials and electron affinities of linear and fan TiCn clusters also show an even–odd parity effect. Generally n-odd clusters have higher ionization potentials than the n-even ones whereas the electron affinities show an opposite alternation trend, n-even systems having higher values than the adjacent n-odd ones.

A theoretical study of the [FeCN]+ system has been carried out. Density functional methods, as well as single- and multi-reference techniques, were employed. Both cyanide and isocyanide isomers are very close in energy, with FeCN+ lying about 0.9 kcal mol−1 below FeNC+. A non-linear minimum, with iron formally bonded just to the nitrogen atom according to a topological analysis of the charge density, is also found just 1.3 kcal mol−1 above the cyanide isomer. The estimated energy barrier for the isomerization process is just 5 kcal mol−1, suggesting that rearrangement of [FeCN]+ should take place easily.

A theoretical study of the first-row transition metal dicarbide cations MC2+ (M=Sc-Zn) has been carried out. Predictions for different molecular properties that could help in their eventual experimental detection have been made. Most MC2+ compounds prefer a C2v symmetric arrangement over the linear geometry. In particular, the C2v isomer is specially favored for early transition metals. Only for CuC2+ is the linear isomer predicted to be the global minimum, although by only 1 kcal/mol. In all cases the isomerization barrier between cyclic and linear species seems to be very small (below 2 kcal/mol). The topological analysis of the electronic density shows that most C2v isomers are T-shaped structures. In general, MC2+ compounds for early transition metals have larger dissociation energies than those formed by late transition metals. In most cases the dissociation energies for MC2+ compounds are much smaller than those obtained for their neutral analogues. An analysis of the bonding in MC2+ compounds in terms of the interactions between the valence orbitals of the fragments helps to interpret their main features.

A theoretical study of the different fan and cyclic isomers of VCn+/− (n = 2–8) clusters has been carried out. Predictions for different molecular properties, such as electronic energies, harmonic vibrational frequencies or rotational constants, have been made using the B3LYP method with different basis set including effective core potentials, ECPs. In general, fan and cyclic structures have been predicted to prefer triplet ground states. The stability of fan and cyclic clusters as a function of the size has been discussed in terms of the incremental binding energies. For cationic systems a clear even–odd alternation in stability is found, n-even clusters being more stable than n-odd ones. This parity effect is also found for the first members of the fan isomers of VCn−, whereas for cyclic VCn− structures the stability decreases along the series. It is also found that VCn+ systems with n 5 n-even clusters prefer open-chain structures and for VC7− the cyclic structure is the most stable.

Meganucleases are sequence-specific endonucleases with large cleavage sites that can be used to induce efficient homologous gene targeting in cultured cells and plants. These enzymes open novel perspectives for genome engineering in a wide range of fields, including gene therapy. A new crystal structure of the I-CreI dimer without DNA has allowed the comparison with the DNA-bound protein. The C-terminal loop displays a different conformation, which suggests its implication in DNA binding. A site-directed mutagenesis study in this region demonstrates that whereas the C-terminal helix is negligible for DNA binding, the final C-terminal loop is essential in DNA binding and cleavage. We have identified two regions that comprise the Ser138-Lys139 and Lys142-Thr143 pairs whose double mutation affect DNA binding in vitro and abolish cleavage in vivo. However, the mutation of only one residue in these sites allows DNA binding in vitro and cleavage in vivo. These findings demonstrate that the C-terminal loop of I-CreI endonuclease plays a fundamental role in its catalytic mechanism and suggest this novel site as a region to take into account for engineering new endonucleases with tailored specificity.