Search query: droxicam complexes

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abstract: A fundamental aim in the field of catalysis is the development of new modes of small molecule activation. One approach toward the catalytic activation of organic molecules that has received much attention recently is visible light photoredox catalysis. In a general sense, this approach relies on the ability of metal complexes and organic dyes to engage in single electron transfer (SET) processes with organic substrates upon photoexcitation with visible light. Many of the most commonly employed visible light photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2' bipyridine) ruthenium(II) or Ru(bpy)32+ (Figure 1) These complexes absorb light in the visible region of the electromagnetic spectrum to give stable, long lived photoexcited states.1,2 The lifetime of the excited species is sufficiently long (1100 ns for Ru(bpy)32+ that it may engage in bimolecular electron transfer reactions in competition with deactivation pathways.3 Although these species are poor single electron oxidants and reductants in the ground state, excitation of an electron affords excited states that are very potent single electron transfer reagents. Importantly, the conversion of these bench stable, benign catalysts to redox active species upon irradiation with simple household lightbulbs represents a remarkably chemoselective trigger to induce unique and valuable catalytic processes. Figure 1 Ruthenium polypyridyl complexes: versatile visible light photocatalysts. The ability of Ru(bpy)32+ and related complexes to function as visible light photocatalysts has been recognized and extensively investigated for applications in inorganic and materials chemistry. In particular, photoredox catalysts have been utilized to accomplish the splitting of water into hydrogen and oxygen4 and the reduction of carbon dioxide to methane.5 Ru(bpy)32+ and its analogues have been used (i) as components of dye sensitized solar cells6 and organic light emitting diodes,7 (ii) to initiate polymerization reactions,8 and (iii) in photo dynamic therapy.9 Until recently, however, these complexes had been only sporadically employed as photocatalysts in the area of organic synthesis. The limited exploration of this area is perhaps surprising, as single electron, radical processes have long been employed in C C bond construction and often provide access to reactivity that is complementary to that of closed shell, two electron pathways.10 In 2008, concurrent reports from the Yoon group and our own lab detailed the use of Ru(bpy)32+ as a visible light photoredox catalyst to perform a [2 2] cycloaddition11 and an a alkylation of aldehydes,12 respectively. Shortly thereafter, Stephenson and co workers disclosed a photoredox reductive dehalogenation of activated alkyl halides mediated by the same catalyst.13 The combined efforts of these three research groups have helped to initiate a renewed interest in this field, prompting a diversity of studies into the utility of photoredox catalysis as a conceptually novel approach to synthetic organic reaction development. Much of the promise of visible light photoredox catalysis hinges on its ability to achieve unique, if not exotic bond constructions that are not possible using established protocols. For instance, photoredox catalysis may be employed to perform overall redox neutral reactions. As both oxidants and reductants may be transiently generated in the same reaction vessel, photoredox approaches may be used to develop reactions requiring both the donation and the reception of electrons at disparate points in the reaction mechanism. This approach stands in contrast to methods requiring stoichiometric chemical oxidants and reductants, which are often incompatible with each other, as well as to electrochemical approaches, which are not amenable to redox neutral transformations. Furthermore, single electron transfer events often provide access to radical ion intermediates having reactivity patterns fundamentally different from those of their ground electronic or excited states.14 Access to these intermediates using other means of activation is often challenging or requires conditions under which their unique reactivity cannot be productively harnessed. At the same time, photoredox catalysts such as Ru(bpy)32+ may also be employed to generate radicals for use in a diverse range of established radical chemistries. Photoredox reactions occur under extremely mild conditions, with most reactions proceeding at room temperature without the need for highly reactive radical initiators. The irradiation source is typically a commercial household light bulb, a significant advantage over the specialized equipment required for processes employing high energy ultraviolet (UV) light. Additionally, because organic molecules generally do not absorb visible light, there is little potential for deleterious side reactions that might arise from photoexcitation of the substrate itself. Finally, photoredox catalysts may be employed at very low loadings, with 1 mole or less being typical. This Review will highlight the early work on the use of transition metal complexes as photoredox catalysts to promote reactions of organic compounds (prior to 2008) as well as cover the surge of work that has appeared since 2008. We have for the most part grouped reactions according to whether the organic substrate undergoes reduction, oxidation, or a redox neutral reaction and throughout have sought to highlight the variety of reactive intermediates that may be accessed via this general reaction manifold.15 Studies on the use of transition metal complexes as visible light photocatalysts for organic synthesis have benefited tremendously from advances in the related fields of organic and semiconductor photocatalysis. Many organic molecules may function as visible light photocatalysts; analogous to metal complexes such as Ru(bpy)32+ organic dyes such as eosin Y, 9,10 dicyanoanthracene, and triphenylpyrylium salts absorb light in the visible region to give excited states capable of single electron transfer. These catalysts have been employed to achieve a vast range of bond forming reactions of broad utility in organic synthesis.16 Visible light photocatalysis has also been carried out with heterogeneous semiconductors such as mesoporous carbon nitride17 and various metal oxides and sulfides.18 These approaches are often complementary to photoredox catalysis with transition metal polypyridyl complexes, and we have referred to work in these areas when it is similar to the chemistry under discussion. However, an in depth discussion of the extensive literature in these fields is outside the scope of this Review, and readers are directed to existing reviews on these topics.16 18
author_names: Christopher K Prier

Danica A Rankic

David W C MacMillan
title: Visible light photoredox catalysis with transition metal complexes: applications in organic synthesis.
venue: Chemical reviews
year: 2013

abstract: MicroRNAs (miRNAs) circulate in the bloodstream in a highly stable, extracellular form and are being developed as blood based biomarkers for cancer and other diseases. However, the mechanism underlying their remarkable stability in the RNase rich environment of blood is not well understood. The current model in the literature posits that circulating miRNAs are protected by encapsulation in membrane bound vesicles such as exosomes, but this has not been systematically studied. We used differential centrifugation and size exclusion chromatography as orthogonal approaches to characterize circulating miRNA complexes in human plasma and serum. We found, surprisingly, that the majority of circulating miRNAs cofractionated with protein complexes rather than with vesicles. miRNAs were also sensitive to protease treatment of plasma, indicating that protein complexes protect circulating miRNAs from plasma RNases. Further characterization revealed that Argonaute2 (Ago2) the key effector protein of miRNA mediated silencing, was present in human plasma and eluted with plasma miRNAs in size exclusion chromatography. Furthermore, immunoprecipitation of Ago2 from plasma readily recovered non vesicle associated plasma miRNAs. The majority of miRNAs studied copurified with the Ago2 ribonucleoprotein complex, but a minority of specific miRNAs associated predominantly with vesicles. Our results reveal two populations of circulating miRNAs and suggest that circulating Ago2 complexes are a mechanism responsible for the stability of plasma miRNAs. Our study has important implications for the development of biomarker approaches based on capture and analysis of circulating miRNAs. In addition, identification of extracellular Ago2 miRNA complexes in plasma raises the possibility that cells release a functional miRNA induced silencing complex into the circulation.
author_names: Jason D Arroyo

John R Chevillet

Evan M Kroh

Ingrid K Ruf

Colin C Pritchard

Donald F Gibson

Patrick S Mitchell

Christopher F Bennett

Era L Pogosova-Agadjanyan

Derek L Stirewalt

Jonathan F Tait

Muneesh Tewari
title: Argonaute2 complexes carry a population of circulating microRNAs independent of vesicles in human plasma
venue: Proceedings of the National Academy of Sciences
year: 2011

abstract: Most RNAs generated by the human genome have no protein coding ability and are termed non coding RNAs. Among these include circular RNAs, which include exonic circular RNAs (circRNA) mainly found in the cytoplasm, and intronic RNAs (ciRNA) predominantly detected in the nucleus. The biological functions of circular RNAs remain largely unknown, although ciRNAs have been reported to promote gene transcription, while circRNAs may function as microRNA sponges. We demonstrate that the circular RNA circ Foxo3 was highly expressed in non cancer cells and were associated with cell cycle progression. Silencing endogenous circ Foxo3 promoted cell proliferation. Ectopic expression of circ Foxo3 repressed cell cycle progression by binding to the cell cycle proteins cyclin dependent kinase 2 (also known as cell division protein kinase 2 or CDK2) and cyclin dependent kinase inhibitor 1 (or p21) resulting in the formation of a ternary complex. Normally, CDK2 interacts with cyclin A and cyclin E to facilitate cell cycle entry, while p21works to inhibit these interactions and arrest cell cycle progression. The formation of this circ Foxo3 p21 CDK2 ternary complex arrested the function of CDK2 and blocked cell cycle progression.
author_names: William Weidong Du

Weining Yang

Elizabeth Liu

Zhenguo Yang

Preet Dhaliwal

Burton B Yang
title: Foxo3 circular RNA retards cell cycle progression via forming ternary complexes with p21 and CDK2
venue: Nucleic acids research
year: 2016

abstract: Microtubule nucleation is regulated by the g tubulin ring complex (gTuRC) and related g tubulin complexes, providing spatial and temporal control over the initiation of microtubule growth. Recent structural work has shed light on the mechanism of gTuRC based microtubule nucleation, confirming the long standing hypothesis that the gTuRC functions as a microtubule template. The first crystallographic analysis of a non g tubulin gTuRC component (g tubulin complex protein 4 (GCP4) has resulted in a new appreciation of the relationships among all gTuRC proteins, leading to a refined model of their organization and function. The structures have also suggested an unexpected mechanism for regulating gTuRC activity via conformational modulation of the complex component GCP3. New experiments on gTuRC localization extend these insights, suggesting a direct link between its attachment at specific cellular sites and its activation.
author_names: Justin M Kollman

Andreas Merdes

Lionel Mourey

David A Agard
title: Microtubule nucleation by g tubulin complexes
venue: Nature Reviews Molecular Cell Biology
year: 2011

abstract: We introduce clustering with overlapping neighborhood expansion (ClusterONE) a method for detecting potentially overlapping protein complexes from protein protein interaction data. ClusterONE derived complexes for several yeast data sets showed better correspondence with reference complexes in the Munich Information Center for Protein Sequence (MIPS) catalog and complexes derived from the Saccharomyces Genome Database (SGD) than the results of seven popular methods. The results also showed a high extent of functional homogeneity.
author_names: Tamas Nepusz

Haiyuan Yu

Alberto Paccanaro
title: Detecting overlapping protein complexes in protein protein interaction networks
venue: Nature Methods
year: 2012

abstract: Subunits of mammalian SWI/SNF (mSWI/SNF or BAF) complexes have recently been implicated as tumor suppressors in human malignancies. To understand the full extent of their involvement, we conducted a proteomic analysis of endogenous mSWI/SNF complexes, which identified several new dedicated, stable subunits not found in yeast SWI/SNF complexes, including BCL7A, BCL7B and BCL7C, BCL11A and BCL11B, BRD9 and SS18. Incorporating these new members, we determined mSWI/SNF subunit mutation frequency in exome and whole genome sequencing studies of primary human tumors. Notably, mSWI/SNF subunits are mutated in 19.6% of all human tumors reported in 44 studies. Our analysis suggests that specific subunits protect against cancer in specific tissues. In addition, mutations affecting more than one subunit, defined here as compound heterozygosity, are prevalent in certain cancers. Our studies demonstrate that mSWI/SNF is the most frequently mutated chromatin regulatory complex (CRC) in human cancer, exhibiting a broad mutation pattern, similar to that of TP53. Thus, proper functioning of polymorphic BAF complexes may constitute a major mechanism of tumor suppression.
author_names: Cigall Kadoch

Diana C Hargreaves

Courtney Hodges

Laura Elias

Lena Ho

Jeffrey A Ranish

Gerald R Crabtree
title: Proteomic and bioinformatic analysis of mammalian SWI/SNF complexes identifies extensive roles in human malignancy
venue: Nature Genetics
year: 2013

abstract: The heterogeneous nature of mammalian PRC1 complexes has hindered our understanding of their biological functions. Here, we present a comprehensive proteomic and genomic analysis that uncovered six major groups of PRC1 complexes, each containing a distinct PCGF subunit, a RING1A/B ubiquitin ligase, and a unique set of associated polypeptides. These PRC1 complexes differ in their genomic localization, and only a small subset colocalize with H3K27me3. Further biochemical dissection revealed that the six PCGF RING1A/B combinations form multiple complexes through association with RYBP or its homolog YAF2, which prevents the incorporation of other canonical PRC1 subunits, such as CBX, PHC, and SCM. Although both RYBP/YAF2 and CBX/PHC/SCM containing complexes compact chromatin, only RYBP stimulates the activity of RING1B toward H2AK119ub1, suggesting a central role in PRC1 function. Knockdown of RYBP in embryonic stem cells compromised their ability to form embryoid bodies, likely because of defects in cell proliferation and maintenance of H2AK119ub1 levels.
author_names: Zhonghua Gao

Jin Zhang

Roberto Bonasio

Francesco Strino

Ayana Sawai

Fabio Parisi

Yuval Kluger

Danny Reinberg
title: PCGF homologs, CBX proteins, and RYBP define functionally distinct PRC1 family complexes.
venue: Molecular cell
year: 2012

abstract: A fundamental understanding of the luminescence of Au thiolate nanoclusters (NCs) such as the origin of emission and the size effect in luminescence, is pivotal to the development of efficient synthesis routes for highly luminescent Au NCs. This paper reports an interesting finding of Au(I) thiolate complexes: strong luminescence emission by the mechanism of aggregation induced emission (AIE) The AIE property of the complexes was then used to develop a simple one pot synthesis of highly luminescent Au thiolate NCs with a quantum yield of ~15% Our key strategy was to induce the controlled aggregation of Au(I) thiolate complexes on in situ generated Au(0) cores to form Au(0)@Au(I) thiolate core shell NCs where strong luminescence was generated by the AIE of Au(I) thiolate complexes on the NC surface. We were able to extend the synthetic strategy to other thiolate ligands with added functionalities (in the form of custom designed peptides) The discovery (e.g. identifying the source of emission and the size effect in luminescence) and the synthesis protocols in this study can contribute significantly to better understanding of these new luminescence probes and the development of new synthetic routes.
author_names: Zhentao Luo

Xun Yuan

Yue Yu

Qingbo Zhang

David Tai Leong

Jimmie Lee

Jianping Xie
title: From aggregation induced emission of Au(I) thiolate complexes to ultrabright Au(0)@Au(I) thiolate core shell nanoclusters.
venue: Journal of the American Chemical Society
year: 2012

abstract: Higher efficiency in the end use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid state electroluminescent materials and belong to the general area of solid state lighting (SSL) The two main technologies being developed in SSL are light emitting diodes (LEDs) and organic light emitting diodes (OLEDs) but in recent years, light emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition metal complexes (iTMCs) Cyclometalated complexes of Ir(III) are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn on time, stability, efficiency, and color is presented.
author_names: Ruben D Costa

Enrique Orti

Henk J Bolink

Filippo Monti

Gianluca Accorsi

Nicola Armaroli
title: Luminescent ionic transition metal complexes for light emitting electrochemical cells.
venue: Angewandte Chemie
year: 2012

abstract: A Lot of HOTAIR The roles of several classes of small <50 nucleotides) noncoding RNAs are beginning to be defined in molecular detail, whereas the function of most of the long ~200+ nucleotides) intergenic noncoding (linc)RNAs found in most eukaryotic genomes remains something of a mystery. The HOTAIR lincRNA, which is transcribed from the mouse HOXC locus, binds to the Polycomb Repressive Complex 2 (PRC2) and recruits it to HOXD and other genes, where its histone methylase activity acts to repress gene transcription. Tsai et al. (p. 689, published online 8 July) now show that HOTAIR also binds to a histone demethylase enzyme, LSD1, part of the CoREST/REST repressor complex. LSD1 acts to remove transcription activating histone marks, reinforcing the repressive activity of the PRC2 complex. HOTAIR thus functions as a platform for the coordinated binding of PRC2 and LSD1 containing complexes to genes, as revealed in a genome wide analysis of PRC1/CoREST/REST co regulated genes. The long noncoding RNA HOTAIR binds two distinct protein complexes that modify chromatin and repress transcription. Long intergenic noncoding RNAs (lincRNAs) regulate chromatin states and epigenetic inheritance. Here, we show that the lincRNA HOTAIR serves as a scaffold for at least two distinct histone modification complexes. A 5' domain of HOTAIR binds polycomb repressive complex 2 (PRC2) whereas a 3' domain of HOTAIR binds the LSD1/CoREST/REST complex. The ability to tether two distinct complexes enables RNA mediated assembly of PRC2 and LSD1 and coordinates targeting of PRC2 and LSD1 to chromatin for coupled histone H3 lysine 27 methylation and lysine 4 demethylation. Our results suggest that lincRNAs may serve as scaffolds by providing binding surfaces to assemble select histone modification enzymes, thereby specifying the pattern of histone modifications on target genes.
author_names: Miao-Chih Tsai

Ohad Manor

Yue Wan

Nima Mosammaparast

Jordon K Wang

Fei Lan

Yang Shi

Eran Segal

Howard Y Chang
title: Long Noncoding RNA as Modular Scaffold of Histone Modification Complexes
venue: Science
year: 2010