Photochemical tyrosine oxidation with a hydrogen-bonded proton acceptor by bidirectional proton-coupled electron transfer

Amino acid radical generation and transport are fundamentally important to numerous essential biological processes to which small molecule models lend valuable mechanistic insights. Pyridyl-amino acid-methyl esters are appended to a rhenium(I) tricarbonyl 1,10-phenanthroline core to yield rhenium–amino acid complexes with tyrosine ([Re]–Y–OH) and phenylalanine ([Re]–F). The emission from the [Re] center is more significantly quenched for [Re]–Y–OH upon addition of base. Time-resolved studies establish that excited-state quenching occurs by a combination of static and dynamic mechanisms. The degree of quenching depends on the strength of the base, consistent with a proton-coupled electron transfer (PCET) quenching mechanism. Comparative studies of [Re]–Y–OH and [Re]–F enable a detailed mechanistic analysis of a bidirectional PCET process.National Institutes of Health (U.S.) (GM47274

Photoinitiated proton-coupled electron transfer and radical transport kinetics in class la ribonucleotide reductase

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.Cataloged from PDF version of thesis. Vita.Includes bibliographical references.Proton-coupled electron transfer (PCET) is a critical mechanism in biology, underpinning key processes such as radical transport, energy transduction, and enzymatic substrate activation. Ribonucleotide reductases (RNRs) rely on PCET to mediate the rate-limiting step in the synthesis of DNA precursors. E. coli class Ia RNR consists of two dimeric subunits: [alpha]₂ contains the active site, while [beta]₂ contains a stable diferric-tyrosyl radical cofactor. During turnover, transport occurs over 35 Ȧ, from Y₁₂₂ in [beta]₂ to C₄₃₉ in [alpha]₂) where an active-site thiyl radical mediates turnover. Radical transport is proposed to occur over a series of highly conserved redox-active amino acids, including Y₃₅₆ in [beta]₂,and Y₇₃₁ and Y₇₃₀ in [alpha]₂ . This thesis examines three subject areas of PCET that pertain to RNR: Small-molecule model systems provide insights into tyrosine oxidation and radical generation. Under physiological conditions, tyrosine oxidation is accompanied by deprotonation and occurs by PCET. A critical factor in PCET reactions is the nature ofthe proton acceptor and the presence ofhydrogen bonding. In a modular model system, pyridyl-amino acid-methyl esters are appended to rhenium(I) tricarbonyl phenanthroline to yield rhenium-amino acid complexes. In dichloromethane solution, bases coordinate to tyrosine by hydrogen bonding. Emission kinetics reveal base-dependent oxidation by PCET. A photopeptide composed of the 19 C-terminal residues of [beta]₂, fluorinated tyrosine in place of Y₃₅₆, and a rhenium(I) bipyridine photooxidant enables photoinitated radical transport into [alpha]₂. Transient absorption kinetics show rapid radical transport (10⁵ s-¹) that is only observed when both Y₇₃₁ and Y₇₃₀, are present, suggesting a critical role for the Y₇₃₁-Y₇₃₀, dyad for radical transport in RNR. An intact, photochemical [beta]₂ enables studies of an [alpha]₂:[beta]₂ complex. A bromomethylpyridine rhenium(I) phenanthroline photooxidant labels a single surface-cysteine mutant of [beta]₂ at position 355 to yield [Re]- [beta]₂. Under flash-quench conditions, transient absorption reveals a tyrosine radical. [Re] -[beta]₂ binds [alpha]₂ and is capable of light-initiated substrate turnover. Transient emission quenching experiments reveal Y₃₅₆ oxidation that is dependent on the presence of Y₇₃₁ in [alpha]₂. This result suggests that a Y₃₅₆-Y₇₃₁-Y₇₃₀ triad mediates radical transport across the subunit interface and into [alpha]₂.by Arturo A. Pizano.Ph.D

Application of the Trajectory Sensitivity Theory to Small Signal Stability Analysis

The security assessment of power systems represents one of the principal studies that must be carried out in energy control centers. In this context, small-signal stability analysis is very important to determine the corresponding control strategies to improve security under stressed operating conditions of power systems. This chapter details a practical approach for assessing the stability of power system’s equilibrium points in real time based on the concept of trajectory sensitivity theory. This approach provides complementary information to that given by selective modal analysis: it determines how the state variables linked with the critical eigenvalues are affected by the system’s parameters and also determines the way of judging how the system’s parameters affect the oscillatory behavior of a power system. The WSCC 9-bus and a 190-buses equivalent system of the Mexican power system are used to demonstrate the generality of the approach as well as how its application in energy management systems is suitable for power system operation and control

Simulación y revisión de un dispositivo de pequeña escala para la conversión de energía del oleaje

En este trabajo de investigación se aborda la exploración y el análisis del potencial energético undimotriz en la costa mexicana a través del análisis y la simulación electromagnética del dispositivo transductor, para la conversión de energía del oleaje en electricidad; un dispositivo que se desarrolló para este propósito es el generador eléctrico lineal (GEL) de imanes permanentes. El potencial energético del oleaje, obtenido en un trabajo preliminar, en diversos puntos en aguas costeras mexicanas, proporciona un panorama precedente para el diseño de estos dispositivos. La utilización de generadores eléctricos lineales para conseguir energía eléctrica por fuentes alternas es una temática que cada vez toma mayor fuerza para el progreso de nuevos sistemas de generación distribuida (microrredes), por lo que este trabajo, además de determinar el potencial energético a través de la simulación electromagnética del dispositivo, analiza el rendimiento y calidad energética proporcionada por GEL. El análisis de simulación desarrollado en este trabajo se fundamenta con base en la obtención del espectro de desplazamiento, en función de la altura significativa de las olas y su periodicidad en los puntos costeros mexicanos analizados en el trabajo preliminar. Además, se contribuye al diseño y desarrollo de dispositivos enfocados a la microgeneración por undimotriz, lo que abre el abanico de posibilidades para el modelado y desarrollo de convertidores de electrónica de potencia, para ayudar al control y la calidad energética de estos dispositivos generadores eléctricos lineales

Analysis of Optimal Steady-State Operation of Power Systems with Embedded FACTS Devices: A Matlab-Based Flexible Approach

This book chapter presents a flexible approach to incorporate mathematical models of FACTS devices into the Power Flow (PF) and the Optimal Power Flow (OPF) analysis tools, as well as into the standard OPF Market-Clearing (OPF-MC) procedure. The proposed approach uses the Matlab Optimization Toolbox because it allows to easily: (a) implement a given optimization model, (b) include different objective functions using distinct equality and inequality constraints and (c) modify and reuse an optimization model that has been previously implemented. The conventional OPF model is the main core of the proposed approach, which is easily implemented and adapted to include the mathematical models of FACTS devices. The resulting implementation of the OPF model featuring FACTS devices can be easily modified and adjusted to obtain the implementation of both the PF and the OPF-MC models which includes such devices. It should be mentioned that with the flexible approach proposed here, the complexity as well as the implementation time of optimized models featuring embedded FACTS devices is significantly reduced, since it is not necessary to define the expressions associated with the hessian matrix and the gradient vector. The flexibility and reliability of the proposed approach are demonstrated by means of several study cases using test as well as real power systems

Inflammaging as a link between autoimmunity and cardiovascular disease: The case of rheumatoid arthritis

Currently, traditional and non-traditional risk factors for cardiovascular disease have been established. The first group includes age, which constitutes one of the most important factors in the development of chronic diseases. The second group includes inflammation, the pathophysiology of which contributes to an accelerated process of vascular remodelling and atherogenesis in autoimmune diseases. Indeed, the term inflammaging has been used to refer to the inflammatory origin of ageing, explicitly due to the chronic inflammatory process associated with age (in healthy individuals). Taking this into account, it can be inferred that people with autoimmune diseases are likely to have an early acceleration of vascular ageing (vascular stiffness) as evidenced in the alteration of non-invasive cardiovascular tests such as pulse wave velocity. Thus, an association is created between autoimmunity and high morbidity and mortality rates caused by cardiovascular disease in this population group. The beneficial impact of the treatments for rheumatoid arthritis at the cardiovascular level has been reported, opening new opportunities for pharmacotherapy

Allergen sensitization linked to climate and age, not to intermittent-persistent rhinitis in a cross-sectional cohort study in the (sub)tropics

Background: Allergen exposure leads to allergen sensitization in susceptible individuals and this might influence allergic rhinitis (AR) phenotype expression. We investigated whether sensitization patterns vary in a country with subtropical and tropical regions and if sensitization patterns relate to AR phenotypes or age. Methods: In a national, cross-sectional study AR patients (2-70 y) seen by allergists underwent blinded skin prick testing with a panel of 18 allergens and completed a validated questionnaire on AR phenotypes. Results: 628 patients were recruited. The major sensitizing allergen was house dust mite (HDM) (56%), followed by Bermuda grass (26%), ash (24%), oak (23%) and mesquite (21%) pollen, cat (22%) and cockroach (21%). Patients living in the tropical region were almost exclusively sensitized to HDM (87%). In the central agricultural zones sensitization is primarily to grass and tree pollen. Nationwide, most study subjects had perennial (82.2%), intermittent (56.5%) and moderate-severe (84.7%) AR. Sensitization was not related to the intermittent-persistent AR classification or to AR severity; seasonal AR was associated with tree (p < 0.05) and grass pollen sensitization (p < 0.01). HDM sensitization was more frequent in children (0-11 y) and adolescents (12-17 y) (subtropical region: p < 0.0005; tropical region p < 0.05), but pollen sensitization becomes more important in the adult patients visiting allergists (Adults vs children + adolescents for tree pollen: p < 0.0001, weeds: p < 0.0005). Conclusions: In a country with (sub)tropical climate zones SPT sensitization patterns varied according to climatological zones; they were different from those found in Europe, HDM sensitization far outweighing pollen allergies and Bermuda grass and Ash pollen being the main grass and tree allergens, respectively. Pollen sensitization was related to SAR, but no relation between sensitization and intermittent-persistent AR or AR severity could be detected. Sensitization patterns vary with age (child HDM, adult pollen). Clinical implications of our findings are dual: only a few allergens –some region specific- cover the majority of sensitizations in (sub)tropical climate zones. This is of major importance for allergen manufacturers and immunotherapy planning. Secondly, patient selection in clinical trials should be based on the intermittent-persistent and severity classifications, rather than on the seasonal-perennial AR subtypes, especially when conducted in (sub)tropical countries

Expediciones Humboldt: Honda-Méndez, Tolima

Este informe presenta los resultados de la caracterización biológica de uno de los bosques secos con mejor estado de conservación en el departamento del Tolima, ubicado entre los municipio de Honda, Méndez y Armero-Guayabal. Estos bosques se encuentran en una matriz de ganadería y producción agropecuaria, donde las coberturas boscosas son conservadas por los propietarios, conscientes de la importancia de este ecosistema para la provisión de bienes y servicios ecosistémicos. Esperamos que esta información producto de la capacidad científica del Instituto Humboldt, sea relevante y útil en las decisiones de planificación estratégica tanto en el ordenamiento territorial de los municipios de Honda, Méndez y Armero-Guayabal, como para las decisiones de conservación que se tomen en la regiónBogotáCiencias Básicas de la Biodiversida

Taking the pulse of Earth's tropical forests using networks of highly distributed plots

Tropical forests are the most diverse and productive ecosystems on Earth. While better understanding of these forests is critical for our collective future, until quite recently efforts to measure and monitor them have been largely disconnected. Networking is essential to discover the answers to questions that transcend borders and the horizons of funding agencies. Here we show how a global community is responding to the challenges of tropical ecosystem research with diverse teams measuring forests tree-by-tree in thousands of long-term plots. We review the major scientific discoveries of this work and show how this process is changing tropical forest science. Our core approach involves linking long-term grassroots initiatives with standardized protocols and data management to generate robust scaled-up results. By connecting tropical researchers and elevating their status, our Social Research Network model recognises the key role of the data originator in scientific discovery. Conceived in 1999 with RAINFOR (South America), our permanent plot networks have been adapted to Africa (AfriTRON) and Southeast Asia (T-FORCES) and widely emulated worldwide. Now these multiple initiatives are integrated via ForestPlots.net cyber-infrastructure, linking colleagues from 54 countries across 24 plot networks. Collectively these are transforming understanding of tropical forests and their biospheric role. Together we have discovered how, where and why forest carbon and biodiversity are responding to climate change, and how they feedback on it. This long-term pan-tropical collaboration has revealed a large long-term carbon sink and its trends, as well as making clear which drivers are most important, which forest processes are affected, where they are changing, what the lags are, and the likely future responses of tropical forests as the climate continues to change. By leveraging a remarkably old technology, plot networks are sparking a very modern revolution in tropical forest science. In the future, humanity can benefit greatly by nurturing the grassroots communities now collectively capable of generating unique, long-term understanding of Earth's most precious forests. Resumen Los bosques tropicales son los ecosistemas más diversos y productivos del mundo y entender su funcionamiento es crítico para nuestro futuro colectivo. Sin embargo, hasta hace muy poco, los esfuerzos para medirlos y monitorearlos han estado muy desconectados. El trabajo en redes es esencial para descubrir las respuestas a preguntas que trascienden las fronteras y los plazos de las agencias de financiamiento. Aquí mostramos cómo una comunidad global está respondiendo a los desafíos de la investigación en ecosistemas tropicales a través de diversos equipos realizando mediciones árbol por árbol en miles de parcelas permanentes de largo plazo. Revisamos los descubrimientos más importantes de este trabajo y discutimos cómo este proceso está cambiando la ciencia relacionada a los bosques tropicales. El enfoque central de nuestro esfuerzo implica la conexión de iniciativas locales de largo plazo con protocolos estandarizados y manejo de datos para producir resultados que se puedan trasladar a múltiples escalas. Conectando investigadores tropicales, elevando su posición y estatus, nuestro modelo de Red Social de Investigación reconoce el rol fundamental que tienen, para el descubrimiento científico, quienes generan o producen los datos. Concebida en 1999 con RAINFOR (Suramérica), nuestras redes de parcelas permanentes han sido adaptadas en África (AfriTRON) y el sureste asiático (T-FORCES) y ampliamente replicadas en el mundo. Actualmente todas estas iniciativas están integradas a través de la ciber-infraestructura de ForestPlots.net, conectando colegas de 54 países en 24 redes diferentes de parcelas. Colectivamente, estas redes están transformando nuestro conocimiento sobre los bosques tropicales y el rol de éstos en la biósfera. Juntos hemos descubierto cómo, dónde y porqué el carbono y la biodiversidad de los bosques tropicales está respondiendo al cambio climático y cómo se retroalimentan. Esta colaboración pan-tropical de largo plazo ha expuesto un gran sumidero de carbono y sus tendencias, mostrando claramente cuáles son los factores más importantes, qué procesos se ven afectados, dónde ocurren los cambios, los tiempos de reacción y las probables respuestas futuras mientras el clima continúa cambiando. Apalancando lo que realmente es una tecnología antigua, las redes de parcelas están generando una verdadera y moderna revolución en la ciencia tropical. En el futuro, la humanidad puede beneficiarse enormemente si se nutren y cultivan comunidades de investigadores de base, actualmente con la capacidad de generar información única y de largo plazo para entender los que probablemente son los bosques más preciados de la tierra. Resumo Florestas tropicais são os ecossistemas mais diversos e produtivos da Terra. Embora uma boa compreensão destas florestas seja crucial para o nosso futuro coletivo, até muito recentemente os esforços de medições e monitoramento foram amplamente desconexos. É essencial formarmos redes para obtermos respostas que transcendem fronteiras e horizontes de agências financiadoras. Neste estudo nós mostramos como uma comunidade global está respondendo aos desafios da pesquisa de ecossistemas tropicais, com equipes diversas medindo florestas, árvore por árvore, em milhares de parcelas monitoradas à longo prazo. Nós revisamos as maiores descobertas científicas deste trabalho, e mostramos também como este processo está mudando a ciência de florestas tropicais. Nossa abordagem principal envolve unir iniciativas de base a protocolos padronizados e gerenciamento de dados a fim de gerar resultados robustos em escalas ampliadas. Ao conectar pesquisadores tropicais e elevar seus status, nosso modelo de Rede de Pesquisa Social reconhece o papel-chave do produtor dos dados na descoberta científica. Concebida em 1999 com o RAINFOR (América do Sul), nossa rede de parcelas permanentes foi adaptada para África (AfriTRON) e Sudeste asiático (T-FORCES), e tem sido extensamente reproduzida em todo o mundo. Agora estas múltiplas iniciativas estão integradas através de uma infraestrutura cibernética do ForestPlots.net, conectando colegas de 54 países de 24 redes de parcelas. Estas iniciativas estão transformando coletivamente o entendimento das florestas tropicais e seus papéis na biosfera. Juntos nós descobrimos como, onde e por que o carbono e a biodiversidade da floresta estão respondendo às mudanças climáticas, e seus efeitos de retroalimentação. Esta duradoura colaboração pantropical revelou um grande sumidouro de carbono persistente e suas tendências, assim como tem evidenciado quais direcionadores são mais importantes, quais processos florestais são mais afetados, onde eles estão mudando, seus atrasos no tempo de resposta, e as prováveis respostas das florestas tropicais conforme o clima continua a mudar. Dessa forma, aproveitando uma notável tecnologia antiga, redes de parcelas acendem faíscas de uma moderna revolução na ciência das florestas tropicais. No futuro a humanidade pode se beneficiar incentivando estas comunidades basais que agora são coletivamente capazes de gerar conhecimentos únicos e duradouros sobre as florestas mais preciosas da Terra. Résume Les forêts tropicales sont les écosystèmes les plus diversifiés et les plus productifs de la planète. Si une meilleure compréhension de ces forêts est essentielle pour notre avenir collectif, jusqu'à tout récemment, les efforts déployés pour les mesurer et les surveiller ont été largement déconnectés. La mise en réseau est essentielle pour découvrir les réponses à des questions qui dépassent les frontières et les horizons des organismes de financement. Nous montrons ici comment une communauté mondiale relève les défis de la recherche sur les écosystèmes tropicaux avec diverses équipes qui mesurent les forêts arbre après arbre dans de milliers de parcelles permanentes. Nous passons en revue les principales découvertes scientifiques de ces travaux et montrons comment ce processus modifie la science des forêts tropicales. Notre approche principale consiste à relier les initiatives de base à long terme à des protocoles standardisés et une gestion de données afin de générer des résultats solides à grande échelle. En reliant les chercheurs tropicaux et en élevant leur statut, notre modèle de réseau de recherche sociale reconnaît le rôle clé de l'auteur des données dans la découverte scientifique. Conçus en 1999 avec RAINFOR (Amérique du Sud), nos réseaux de parcelles permanentes ont été adaptés à l'Afrique (AfriTRON) et à l'Asie du Sud-Est (T-FORCES) et largement imités dans le monde entier. Ces multiples initiatives sont désormais intégrées via l'infrastructure ForestPlots.net, qui relie des collègues de 54 pays à travers 24 réseaux de parcelles. Ensemble, elles transforment la compréhension des forêts tropicales et de leur rôle biosphérique. Ensemble, nous avons découvert comment, où et pourquoi le carbone forestier et la biodiversité réagissent au changement climatique, et comment ils y réagissent. Cette collaboration pan-tropicale à long terme a révélé un important puits de carbone à long terme et ses tendances, tout en mettant en évidence les facteurs les plus importants, les processus forestiers qui sont affectés, les endroits où ils changent, les décalages et les réactions futures probables des forêts tropicales à mesure que le climat continue de changer. En tirant parti d'une technologie remarquablement ancienne, les réseaux de parcelles déclenchent une révolution très moderne dans la science des forêts tropicales. À l'avenir, l'humanité pourra grandement bénéficier du soutien des communautés de base qui sont maintenant collectivement capables de générer une compréhension unique et à long terme des forêts les plus précieuses de la Terre. Abstrak Hutan tropika adalah di antara ekosistem yang paling produktif dan mempunyai kepelbagaian biodiversiti yang tinggi di seluruh dunia. Walaupun pemahaman mengenai hutan tropika amat penting untuk masa depan kita, usaha-usaha untuk mengkaji dan mengawas hutah-hutan tersebut baru sekarang menjadi lebih diperhubungkan. Perangkaian adalah sangat penting untuk mencari jawapan kepada soalan-soalan yang menjangkaui sempadan dan batasan agensi pendanaan. Di sini kami menunjukkan bagaimana sebuah komuniti global bertindak balas terhadap cabaran penyelidikan ekosistem tropika melalui penglibatan pelbagai kumpulan yang mengukur hutan secara pokok demi pokok dalam beribu-ribu plot jangka panjang. Kami meninjau semula penemuan saintifik utama daripada kerja ini dan menunjukkan bagaimana proses ini sedang mengubah bidang sains hutan tropika. Teras pendekatan kami memberi tumpuan terhadap penghubungan inisiatif akar umbi jangka panjang dengan protokol standar serta pengurusan data untuk mendapatkan hasil skala besar yang kukuh. Dengan menghubungkan penyelidik-penyelidik tropika dan meningkatkan status mereka, model Rangkaian Penyelidikan Sosial kami mengiktiraf kepentingan peranan pengasas data dalam penemuan saintifik. Bermula dengan pengasasan RAINFOR (Amerika Selatan) pada tahun 1999, rangkaian-rangkaian plot kekal kami kemudian disesuaikan untuk Afrika (AfriTRON) dan Asia Tenggara (T-FORCES) dan selanjutnya telah banyak dicontohi di seluruh dunia. Kini, inisiatif-inisiatif tersebut disepadukan melalui infrastruktur siber ForestPlots.net yang menghubungkan rakan sekerja dari 54 negara di 24 buah rangkaian plot. Secara kolektif, rangkaian ini sedang mengubah pemahaman tentang hutan tropika dan peranannya dalam biosfera. Kami telah bekerjasama untuk menemukan bagaimana, di mana dan mengapa karbon serta biodiversiti hutan bertindak balas terhadap perubahan iklim dan juga bagaimana mereka saling bermaklum balas. Kolaborasi pan-tropika jangka panjang ini telah mendedahkan sebuah sinki karbon jangka panjang serta arah alirannya dan juga menjelaskan pemandu-pemandu perubahan yang terpenting, di mana dan bagaimana proses hutan terjejas, masa susul yang ada dan kemungkinan tindakbalas hutan tropika pada perubahan iklim secara berterusan di masa depan. Dengan memanfaatkan pendekatan lama, rangkaian plot sedang menyalakan revolusi yang amat moden dalam sains hutan tropika. Pada masa akan datang, manusia sejagat akan banyak mendapat manfaat jika memupuk komuniti-komuniti akar umbi yang kini berkemampuan secara kolektif menghasilkan pemahaman unik dan jangka panjang mengenai hutan-hutan yang paling berharga di dunia

“DETERMINATION OF STEADY Y-STAT AND TRANSIENTLY STABLE OP PTIMAL EQUILIBRIUM POINTS ELECTRIC POWER R SYSTEMS”

This research work focuses on the way of extending a conventional Newton-based Optimal Power Flow (OPF) approach to compute optimum steady state operating points under two important aspects in power systems operation. On the one hand, the conventional OPF approach is modified to consider a proposed steady state detailed model of a Voltage Source Converter-based High Voltage Direct Current (VSC-HVDC) system. The VSC-HVDC’s ability to provide independent control of the converters AC voltage magnitudes and phase angles relative to the system voltage, which allows the use of separate active and reactive power control loops for system regulation, is well represented by the proposed model. This development allows computing optimum steady state equilibrium points of power systems considering the operation of VSC-HVDC devices. On the other hand, the conventional OPF approach is modified to derive two new global Transient Stability Constrained-Optimal Power Flow (TSC-OPF) approaches. In both approaches, the SIngle Machine Equivalent (SIME) method is used to represent the multi- machine system dynamics by a corresponding One Machine Infinite Bus (OMIB) equivalent system. The multi-machine system transient stability is controlled by ensuring the transient stability of the corresponding OMIB equivalent system. Each one of the proposed TSC-OPF approaches formulates a corresponding new stability constraint in terms of the angular deviation of the OMIB equivalent rotor angle trajectory, at one specific integration time step of the interval to be considered into the TSC-OPF analysis. This formulation yields the following two main advantages: a substantial reduction of problem size and complexity related to the TSC-OPF global approaches and a non-heuristic representation of the system transient stability limits. Clearly, these advantages are the effect of using SIME salient parameters into the proposed TSC-OPF formulation, and allow the efficient and accurate computation of steady state operating points that ensure the system transient stability under credible contingency scenarios. The effectiveness and main characteristics of the two main aspects developed in this research work are illustrated by means of numerical examples