Publications by authors named "Maria A Lebedeva"

25 Publications

  • Page 1 of 1

Emergence and Rearrangement of Dynamic Supramolecular Aggregates Visualized by Interferometric Scattering Microscopy.

ACS Nano 2020 09 18;14(9):11160-11168. Epub 2020 Aug 18.

Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford, United Kingdom OX1 3TA.

Studying dynamic self-assembling systems in their native environment is essential for understanding the mechanisms of self-assembly and thereby exerting full control over these processes. Traditional ensemble-based analysis methods often struggle to reveal critical features of the self-assembly that occur at the single particle level. Here, we describe a label-free single-particle assay to visualize real-time self-assembly in aqueous solutions by interferometric scattering microscopy. We demonstrate how the assay can be applied to biphasic reactions yielding micellar or vesicular aggregates, detecting the onset of aggregate formation, quantifying the kinetics at the single particle level, and distinguishing sigmoidal and exponential growth of aggregate populations. Furthermore, we can follow the evolution in aggregate size in real time, visualizing the nucleation stages of the self-assembly processes and record phenomena such as incorporation of oily components into the micelle or vesicle lumen.
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http://dx.doi.org/10.1021/acsnano.0c02414DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7513470PMC
September 2020

Coupled Metabolic Cycles Allow Out-of-Equilibrium Autopoietic Vesicle Replication.

Angew Chem Int Ed Engl 2020 11 3;59(46):20361-20366. Epub 2020 Sep 3.

Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, UK.

We report chemically fuelled out-of-equilibrium self-replicating vesicles based on surfactant formation. We studied the vesicles' autocatalytic formation using UPLC to determine monomer concentration and interferometric scattering microscopy at the nanoparticle level. Unlike related reports of chemically fuelled self-replicating micelles, our vesicular system was too stable to surfactant degradation to be maintained out of equilibrium. The introduction of a catalyst, which introduces a second catalytic cycle into the metabolic network, was used to close the first cycle. This shows how coupled catalytic cycles can create a metabolic network that allows the creation and perseverance of fuel-driven, out-of-equilibrium self-replicating vesicles.
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http://dx.doi.org/10.1002/anie.202007302DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7692917PMC
November 2020

Cytokinin biosynthesis genes expressed during nodule organogenesis are directly regulated by the KNOX3 protein in Medicago truncatula.

PLoS One 2020 30;15(4):e0232352. Epub 2020 Apr 30.

Department of Genetics and Biotechnology, Saint Petersburg State University, Saint Petersburg, Russia.

Cytokinin is an important regulator of symbiotic nodule development. Recently, KNOTTED1-LIKE HOMEOBOX 3 transcription factor (TF) was shown to regulate symbiotic nodule development possibly via the activation of cytokinin biosynthesis genes. However, the direct interaction between the KNOX3 TF and its target genes has not been investigated up to date. Here, using EMSA analysis and SPR-based assay, we found that MtKNOX3 homeodomain directly binds to the regulatory sequences of the MtLOG1, MtLOG2, and MtIPT3 genes involved in nodulation in Medicago truncatula. Moreover, we showed that MtLOG2 and MtIPT3 expression patterns partially overlap with MtKNOX3 expression in developing nodules as it was shown by promoter:GUS analysis. Our data suggest that MtKNOX3 TF may directly activate the MtLOG1, MtLOG2, and MtIPT3 genes during nodulation thereby increasing cytokinin biosynthesis in developing nodules.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0232352PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7192382PMC
July 2020

Plant tumors: a hundred years of study.

Planta 2020 Mar 18;251(4):82. Epub 2020 Mar 18.

Department of Genetics and Biotechnology, Saint-Petersburg State University, Saint-Petersburg, Russia.

Main Conclusion: The review provides information on the mechanisms underlying the development of spontaneous and pathogen-induced tumors in higher plants. The activation of meristem-specific regulators in plant tumors of various origins suggests the meristem-like nature of abnormal plant hyperplasia. Plant tumor formation has more than a century of research history. The study of this phenomenon has led to a number of important discoveries, including the development of the Agrobacterium-mediated transformation technique and the discovery of horizontal gene transfer from bacteria to plants. There are two main groups of plant tumors: pathogen-induced tumors (e.g., tumors induced by bacteria, viruses, fungi, insects, etc.), and spontaneous ones, which are formed in the absence of any pathogen in plants with certain genotypes (e.g., interspecific hybrids, inbred lines, and mutants). The causes of the transition of plant cells to tumor growth are different from those in animals, and they include the disturbance of phytohormonal balance and the acquisition of meristematic characteristics by differentiated cells. The aim of this review is to discuss the mechanisms underlying the development of most known examples of plant tumors.
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http://dx.doi.org/10.1007/s00425-020-03375-5DOI Listing
March 2020

The Green Box: An Electronically Versatile Perylene Diimide Macrocyclic Host for Fullerenes.

J Am Chem Soc 2020 01 18;142(1):349-364. Epub 2019 Dec 18.

Chemistry Research Laboratory, Department of Chemistry , University of Oxford , Mansfield Road , Oxford OX1 3TA , United Kingdom.

The powerful electron accepting ability of fullerenes makes them ubiquitous components in biomimetic donor-acceptor systems that model the intermolecular electron transfer processes of Nature's photosynthetic center. Exploiting perylene diimides (PDIs) as components in cyclic host systems for the noncovalent recognition of fullerenes is unprecedented, in part because archetypal PDIs are also electron deficient, making dyad assembly formation electronically unfavorable. To address this, we report the strategic design and synthesis of a novel large, macrocyclic receptor composed of two covalently strapped electron-rich bis-pyrrolidine PDI panels, nicknamed the "Green Box" due to its color. Through the principle of electronic complementarity, the Green Box exhibits strong recognition of pristine fullerenes (C), with the noncovalent ground and excited state interactions that occur upon fullerene guest encapsulation characterized by a range of techniques including electronic absorption, fluorescence emission, NMR and time-resolved EPR spectroscopies, cyclic voltammetry, mass spectrometry, and DFT calculations. While relatively low polarity solvents result in partial charge transfer in the host donor-guest acceptor complex, increasing the polarity of the solvent medium facilitates rare, thermally allowed full electron transfer from the Green Box to fullerene in the ground state. The ensuing charge separated radical ion paired complex is spectroscopically characterized, with thermodynamic reversibility and kinetic stability also demonstrated. Importantly, the Green Box represents a seminal type of C host where electron-rich PDI motifs are utilized as recognition motifs for fullerenes, facilitating novel intermolecular, solvent tunable ground state electronic communication with these guests. The ability to switch between extremes of the charge transfer energy continuum is without precedent in synthetic fullerene-based dyads.
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http://dx.doi.org/10.1021/jacs.9b10929DOI Listing
January 2020

Identification and Expression Analysis of (s) Involved in Local and Systemic Control of Nodulation.

Front Plant Sci 2018 9;9:304. Epub 2018 Mar 9.

Department of Genetics and Biotechnology, Saint Petersburg State University, Saint Petersburg, Russia.

Cytokinins are essential for legume plants to establish a nitrogen-fixing symbiosis with rhizobia. Recently, the expression level of cytokinin biosynthesis s () genes was shown to be increased in response to rhizobial inoculation in and . In addition to its well-established positive role in nodule primordium initiation in root cortex, cytokinin negatively regulates infection processes in the epidermis. Moreover, it was reported that shoot-derived cytokinin inhibits the subsequent nodule formation through AON (autoregulation of nodulation) pathway. In gene was shown to be activated in the shoot phloem via the components of AON system, negatively affecting nodulation. However, in , the detailed analysis of s expression, both in roots and shoots, in response to nodulation has not been performed yet, and the link between s and AON has not been studied so far. In this study, we performed an extensive analysis of s expression levels in different organs, focusing on the possible role of s in nodule development. s expression dynamics in inoculated roots suggest that besides its early established role in the nodule primordia development, cytokinin may be also important for later stages of nodulation. According to expression analysis, , and are activated in the shoots in response to inoculation. Among these genes, is the only one the induction of which was not observed in leaves of the mutant defective in CLV1-like kinase, the key component of AON, suggesting that is activated in the shoots in an AON-dependent manner. Taken together, our findings suggest that s are involved in the nodule development at different stages, both locally in inoculated roots and systemically in shoots, where their expression can be activated in an AON-dependent manner.
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http://dx.doi.org/10.3389/fpls.2018.00304DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5855100PMC
March 2018

Anion-Mediated Photophysical Behavior in a C Fullerene [3]Rotaxane Shuttle.

J Am Chem Soc 2018 02 30;140(5):1924-1936. Epub 2018 Jan 30.

Chemistry Research Laboratory, Department of Chemistry, University of Oxford , Mansfield Road, Oxford OX1 3TA, United Kingdom.

By addressing the challenge of controlling molecular motion, mechanically interlocked molecular machines are primed for a variety of applications in the field of nanotechnology. Specifically, the designed manipulation of communication pathways between electron donor and acceptor moieties that are strategically integrated into dynamic photoactive rotaxanes and catenanes may lead to efficient artificial photosynthetic devices. In this pursuit, a novel [3]rotaxane molecular shuttle consisting of a four-station bis-naphthalene diimide (NDI) and central C fullerene bis-triazolium axle component and two mechanically bonded ferrocenyl-functionalized isophthalamide anion binding site-containing macrocycles is constructed using an anion template synthetic methodology. Dynamic coconformational anion recognition-mediated shuttling, which alters the relative positions of the electron donor and acceptor motifs of the [3]rotaxane's macrocycle and axle components, is demonstrated initially by H NMR spectroscopy. Detailed steady-state and time-resolved UV-vis-IR absorption and emission spectroscopies as well as electrochemical studies are employed to further probe the anion-dependent positional macrocycle-axle station state of the molecular shuttle, revealing a striking on/off switchable emission response induced by anion binding. Specifically, the [3]rotaxane chloride coconformation, where the ferrocenyl-functionalized macrocycles reside at the center of the axle component, precludes electron transfer to NDI, resulting in the switching-on of emission from the NDI fluorophore and concomitant formation of a C fullerene-based charge-separated state. By stark contrast, in the absence of chloride as the hexafluorophosphate salt, the ferrocenyl-functionalized macrocycles shuttle to the peripheral NDI axle stations, quenching the NDI emission via formation of a NDI-containing charge-separated state. Such anion-mediated control of the photophysical behavior of a rotaxane through molecular motion is unprecedented.
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http://dx.doi.org/10.1021/jacs.7b12819DOI Listing
February 2018

Detecting Mechanochemical Atropisomerization within an STM Break Junction.

J Am Chem Soc 2018 01 4;140(2):710-718. Epub 2018 Jan 4.

Department of Chemistry, Donnan and Robert Robinson Laboratories, University of Liverpool , Liverpool L69 7ZD, U.K.

We have employed the scanning tunneling microscope break-junction technique to investigate the single-molecule conductance of a family of 5,15-diaryl porphyrins bearing thioacetyl (SAc) or methylsulfide (SMe) binding groups at the ortho position of the phenyl rings (S2 compounds). These ortho substituents lead to two atropisomers, cis and trans, for each compound, which do not interconvert in solution under ambient conditions; even at high temperatures, isomerization takes several hours (half-life 15 h at 140 °C for SAc in CClD). All the S2 compounds exhibit two conductance groups, and comparison with a monothiolated (S1) compound shows the higher group arises from a direct Au-porphyrin interaction. The lower conductance group is associated with the S-to-S pathway. When the binding group is SMe, the difference in junction length distribution reflects the difference in S-S distance (0.3 nm) between the two isomers. In the case of SAc, there are no significant differences between the plateau length distributions of the two isomers, and both show maximal stretching distances well exceeding their calculated junction lengths. Contact deformation accounts for part of the extra length, but the results indicate that cis-to-trans conversion takes place in the junction for the cis isomer. The barrier to atropisomerization is lower than the strength of the thiolate Au-S and Au-Au bonds, but higher than that of the Au-SMe bond, which explains why the strain in the junction only induces isomerization in the SAc compound.
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http://dx.doi.org/10.1021/jacs.7b10542DOI Listing
January 2018

All-Fullerene-Based Cells for Nonaqueous Redox Flow Batteries.

J Am Chem Soc 2018 01 29;140(1):401-405. Epub 2017 Dec 29.

Institute of Process Research and Development, School of Chemistry, University of Leeds , Leeds, LS2 9JT, U.K.

Redox flow batteries have the potential to revolutionize our use of intermittent sustainable energy sources such as solar and wind power by storing the energy in liquid electrolytes. Our concept study utilizes a novel electrolyte system, exploiting derivatized fullerenes as both anolyte and catholyte species in a series of battery cells, including a symmetric, single species system which alleviates the common problem of membrane crossover. The prototype multielectron system, utilizing molecular based charge carriers, made from inexpensive, abundant, and sustainable materials, principally, C and Fe, demonstrates remarkable current and energy densities and promising long-term cycling stability.
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http://dx.doi.org/10.1021/jacs.7b11041DOI Listing
January 2018

Stop-Frame Filming and Discovery of Reactions at the Single-Molecule Level by Transmission Electron Microscopy.

ACS Nano 2017 03 8;11(3):2509-2520. Epub 2017 Mar 8.

School of Chemistry, University of Nottingham , Nottingham NG7 2RD, United Kingdom.

We report an approach, named chemTEM, to follow chemical transformations at the single-molecule level with the electron beam of a transmission electron microscope (TEM) applied as both a tunable source of energy and a sub-angstrom imaging probe. Deposited on graphene, disk-shaped perchlorocoronene molecules are precluded from intermolecular interactions. This allows monomolecular transformations to be studied at the single-molecule level in real time and reveals chlorine elimination and reactive aryne formation as a key initial stage of multistep reactions initiated by the 80 keV e-beam. Under the same conditions, perchlorocoronene confined within a nanotube cavity, where the molecules are situated in very close proximity to each other, enables imaging of intermolecular reactions, starting with the Diels-Alder cycloaddition of a generated aryne, followed by rearrangement of the angular adduct to a planar polyaromatic structure and the formation of a perchlorinated zigzag nanoribbon of graphene as the final product. ChemTEM enables the entire process of polycondensation, including the formation of metastable intermediates, to be captured in a one-shot "movie". A molecule with a similar size and shape but with a different chemical composition, octathio[8]circulene, under the same conditions undergoes another type of polycondensation via thiyl biradical generation and subsequent reaction leading to polythiophene nanoribbons with irregular edges incorporating bridging sulfur atoms. Graphene or carbon nanotubes supporting the individual molecules during chemTEM studies ensure that the elastic interactions of the molecules with the e-beam are the dominant forces that initiate and drive the reactions we image. Our ab initio DFT calculations explicitly incorporating the e-beam in the theoretical model correlate with the chemTEM observations and give a mechanism for direct control not only of the type of the reaction but also of the reaction rate. Selection of the appropriate e-beam energy and control of the dose rate in chemTEM enabled imaging of reactions on a time frame commensurate with TEM image capture rates, revealing atomistic mechanisms of previously unknown processes.
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http://dx.doi.org/10.1021/acsnano.6b08228DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5371926PMC
March 2017

Stabilising the lowest energy charge-separated state in a {metal chromophore - fullerene} assembly: a tuneable panchromatic absorbing donor-acceptor triad.

Chem Sci 2016 Sep 19;7(9):5908-5921. Epub 2016 May 19.

School of Chemistry , University of Nottingham , Nottingham , NG7 2RD , UK . Email:

Photoreduction of fullerene and the consequent stabilisation of a charge-separated state in a donor-acceptor assembly have been achieved, overcoming the common problem of a fullerene-based triplet state being an energy sink that prevents charge-separation. A route to incorporate a C-fullerene electron acceptor moiety into a catecholate-Pt(ii)-diimine photoactive dyad, which contains an unusually strong electron donor, 3,5-di--butylcatecholate, has been developed. The synthetic methodology is based on the formation of the aldehyde functionalised bipyridine-Pt(ii)-3,5-di--butylcatechol dyad which is then added to the fullerene cage a Prato cycloaddition reaction. The resultant product is the first example of a fullerene-diimine-Pt-catecholate donor-acceptor triad, Cbpy-Pt-cat. The triad exhibits an intense solvatochromic absorption band in the visible region due to catechol-to-diimine charge-transfer, which, together with fullerene-based transitions, provides efficient and tuneable light harvesting of the majority of the UV/visible spectral range. Cyclic voltammetry, EPR and UV/vis/IR spectroelectrochemistry reveal redox behaviour with a wealth of reversible reduction and oxidation processes forming multiply charged species and storing multiple redox equivalents. Ultrafast transient absorption and time resolved infrared spectroscopy, supported by molecular modelling, reveal the formation of a charge-separated state [C˙bpy-Pt-cat˙] with a lifetime of ∼890 ps. The formation of cat˙ in the excited state is evidenced directly by characteristic absorption bands in the 400-500 nm region, while the formation of C˙ was confirmed directly by time-resolved infrared spectroscopy, TRIR. An IR-spectroelectrochemical study of the mono-reduced building block (C-bpy)PtCl, revealed a characteristic C˙ vibrational feature at 1530 cm, which was also detected in the TRIR spectra. This combination of experiments offers the first direct IR-identification of C˙ species in solution, and paves the way towards the application of transient infrared spectroscopy to the study of light-induced charge-separation in C-containing assemblies, as well as fullerene films and fullerene/polymer blends in various OPV devices. Identification of the unique vibrational signature of a C-anion provides a new way to follow photoinduced processes in fullerene-containing assemblies by means of time-resolved vibrational spectroscopy, as demonstrated for the fullerene-transition metal chromophore assembly with the lowest energy charge-separated excited state.
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http://dx.doi.org/10.1039/c5sc04271bDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6024556PMC
September 2016

Direct Measurement of Electron Transfer in Nanoscale Host-Guest Systems: Metallocenes in Carbon Nanotubes.

Chemistry 2016 Sep 28;22(38):13540-9. Epub 2016 Jul 28.

School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.

Electron-transfer processes play a significant role in host-guest interactions and determine physicochemical phenomena emerging at the nanoscale that can be harnessed in electronic or optical devices, as well as biochemical and catalytic systems. A novel method for qualifying and quantifying the electronic doping of single walled carbon nanotubes (SWNTs) using electrochemistry has been developed that establishes a direct link between these experimental measurements and ab initio DFT calculations. Metallocenes such as cobaltocene and methylated ferrocene derivatives were encapsulated inside SWNTs (1.4 nm diameter) and cyclic voltammetry (CV) was performed on the resultant host-guest systems. The electron transfer between the guest molecules and the host SWNTs is measured as a function of shift in the redox potential (E1/2 ) of Co(II) /Co(I) , Co(III) /Co(II) and Fe(III) /Fe(II) . Furthermore, the shift in E1/2 is inversely proportional to the nanotube diameter. To quantify the amount of electron transfer from the guest molecules to the SWNTs, a novel method using coulometry was developed, allowing the mapping of the density of states and the Fermi level of the SWNTs. Correlated with theoretical calculations, coulometry provides an accurate indication of n/p-doping of the SWNTs.
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http://dx.doi.org/10.1002/chem.201602116DOI Listing
September 2016

Chemical reactions at the graphitic step-edge: changes in product distribution of catalytic reactions as a tool to explore the environment within carbon nanoreactors.

Nanoscale 2016 Jun;8(22):11727-37

School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. and Nanoscale and Microscale Research Centre, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.

A series of explorative cross-coupling reactions have been developed to investigate the local nanoscale environment around catalytically active Pd(ii)complexes encapsulated within hollow graphitised nanofibers (GNF). Two new fullerene-containing and fullerene-free Pd(ii)Salen catalysts have been synthesised, and their activity and selectivity towards different substrates has been explored in nanoreactors. The catalysts not only show a significant increase in activity and stability upon heterogenisation at the graphitic step-edges inside the GNF channel, but also exhibit a change in selectivity affected by the confinement which alters the distribution of isomeric products of the reaction. Furthermore, the observed selectivity changes reveal unprecedented details regarding the location and orientation of the catalyst molecules inside the GNF nanoreactor, inaccessible by any spectroscopic or microscopic techniques, thus shedding light on the precise reaction environment inside the molecular catalyst-GNF nanoreactor.
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http://dx.doi.org/10.1039/c6nr03360aDOI Listing
June 2016

Identification, expression, and functional analysis of CLE genes in radish (Raphanus sativus L.) storage root.

BMC Plant Biol 2016 Jan 27;16 Suppl 1. Epub 2016 Jan 27.

Department of Genetics and Biotechnology, Saint-Petersburg State University, Saint-Petersburg, 199034, Russia.

Background: Radish (Raphanus sativus L.) is a widespread agricultural plant forming storage root due to extensive secondary growth which involves cambium proliferation and differentiation of secondary conductive tissues. Closely related to the model object Arabidopsis thaliana, radish is a suitable model for studying processes of secondary growth and storage root development. CLE peptides are a group of peptide phytohormones which play important role in the regulation of primary meristems such as SAM, RAM, and procambium, as well as secondary meristems. However, the role of CLE peptides in lateral growth of root during storage root formation has not been studied to date.

Results: In present work we studied the role of CLE peptides in the development of storage root in radish. We have identified 18 CLE genes of radish (RsCLEs) and measured their expression in various plant organs and also at different stages of root development in R. sativus and Raphanus raphanistrum-its close relative which does not form storage root. We observed significant decline of expression levels for genes RsCLE1, 2, 11, 13, and 16, and also multifold increase of expression levels for genes RsCLE19, and 41 during secondary root growth in R. sativus but not in R. raphanistrum. Expression of RsCLE 2, 19, and 41 in R. sativus root was confined to certain types of tissues while RsCLE1, 11, 13, and 16 expressed throughout the root. Experiments on overexpression of RsCLE2, 19 and 41 or treatment of radish plants with synthetic CLE peptides revealed that CLE19 and CLE2 increase the number of xylem elements, and CLE41 induces the formation of extra cambium foci in secondary xylem. Expression levels of RsCLE2 and 19 strongly decrease in response to exogenous cytokinin, while auxin causes dramatic increase of RsCLE19 expression level and decrease of RsCLE41 expression.

Conclusions: Our data allow us to hypothesize about the role of RsCLE2, 19 and 41 genes in the development of storage root of Raphanus sativus, e.g. RsCLE19 may play a role in auxin-dependent processes of xylem differentiation and RsCLE41 stimulates cambium activity.
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http://dx.doi.org/10.1186/s12870-015-0687-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4895270PMC
January 2016

Harnessing the Synergistic and Complementary Properties of Fullerene and Transition-Metal Compounds for Nanomaterial Applications.

Chem Rev 2015 Oct 30;115(20):11301-51. Epub 2015 Sep 30.

School of Chemistry, University of Nottingham , Nottingham NG7 2RD, United Kingdom.

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http://dx.doi.org/10.1021/acs.chemrev.5b00005DOI Listing
October 2015

Tuning the interactions between electron spins in fullerene-based triad systems.

Beilstein J Org Chem 2014 5;10:332-43. Epub 2014 Feb 5.

School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, UK ; Nottingham Nanoscience & Nanotechnology Centre, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.

A series of six fullerene-linker-fullerene triads have been prepared by the stepwise addition of the fullerene cages to bridging moieties thus allowing the systematic variation of fullerene cage (C60 or C70) and linker (oxalate, acetate or terephthalate) and enabling precise control over the inter-fullerene separation. The fullerene triads exhibit good solubility in common organic solvents, have linear geometries and are diastereomerically pure. Cyclic voltammetric measurements demonstrate the excellent electron accepting capacity of all triads, with up to 6 electrons taken up per molecule in the potential range between -2.3 and 0.2 V (vs Fc(+)/Fc). No significant electronic interactions between fullerene cages are observed in the ground state indicating that the individual properties of each C60 or C70 cage are retained within the triads. The electron-electron interactions in the electrochemically generated dianions of these triads, with one electron per fullerene cage were studied by EPR spectroscopy. The nature of electron-electron coupling observed at 77 K can be described as an equilibrium between doublet and triplet state biradicals which depends on the inter-fullerene spacing. The shorter oxalate-bridged triads exhibit stronger spin-spin coupling with triplet character, while in the longer terephthalate-bridged triads the intramolecular spin-spin coupling is significantly reduced.
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http://dx.doi.org/10.3762/bjoc.10.31DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943482PMC
March 2014

Transition metal complexes of a salen-fullerene diad: redox and catalytically active nanostructures for delivery of metals in nanotubes.

Chemistry 2013 Sep 23;19(36):11999-2008. Epub 2013 Jul 23.

School of Chemistry, University of Nottingham, Nottingham NG7 2RD (UK).

A covalently-linked salen-C60 (H2L) assembly binds a range of transition metal cations in close proximity to the fullerene cage to give complexes [M(L)] (M=Mn, Co, Ni, Cu, Zn, Pd), [MCl(L)] (M=Cr, Fe) and [V(O)L]. Attaching salen covalently to the C60 cage only marginally slows down metal binding at the salen functionality compared to metal binding to free salen. Coordination of metal cations to salen-C60 introduces to these fullerene derivatives strong absorption bands across the visible spectrum from 400 to 630 nm, the optical features of which are controlled by the nature of the transition metal. The redox properties of the metal-salen-C60 complexes are determined both by the fullerene and by the nature of the transition metal, enabling the generation of a wide range of fullerene-containing charged species, some of which possess two or more unpaired electrons. The presence of the fullerene cage enhances the affinity of these complexes for carbon nanostructures, such as single-, double- and multiwalled carbon nanotubes and graphitised carbon nanofibres, without detrimental effects on the catalytic activity of the metal centre, as demonstrated in styrene oxidation catalysed by [Cu(L)]. This approach shows promise for applications of salen-C60 complexes in heterogeneous catalysis.
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http://dx.doi.org/10.1002/chem.201300872DOI Listing
September 2013

Cleavage of the C-S bond with the formation of a binuclear copper complex with 2-thiolato-3-phenyl-5-(pyridine-2-ylmethylene)-3,5-dihydro-4H-imidazole-4-one. A new mimic of the active site of N2O reductase.

Dalton Trans 2013 May;42(18):6290-3

Department of Chemistry, Lomonosov Moscow State University, Moscow, Russia.

The treatment of the ligands with copper(II) chloride dihydrate led to the formation of a binuclear copper complex with a [Cu(+1.5)Cu(+1.5)] redox state as a result of C-S bond cleavage in the course of the reaction. This complex catalyses the electrochemical reduction of nitrous oxide and triphenyl phosphine oxidation under N2O action.
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http://dx.doi.org/10.1039/c3dt50422kDOI Listing
May 2013

Loss of p53 causes mitochondrial DNA depletion and altered mitochondrial reactive oxygen species homeostasis.

Biochim Biophys Acta 2009 May 20;1787(5):328-34. Epub 2009 Jan 20.

Department of Pathology, Yale University School of Medicine, New Haven, CT 06520-8023, USA.

In addition to its central role in cellular stress signaling, the tumor suppressor p53 modulates mitochondrial respiration through its nuclear transcription factor activity and localizes to mitochondria, where it enhances apoptosis and suppresses mitochondrial DNA (mtDNA) mutagenesis. Here we demonstrate a new conserved role for p53 in mtDNA copy number maintenance and mitochondrial reactive oxygen species (ROS) homeostasis. In mammals, mtDNA is present at thousands of copies per cell and is essential for normal development and cell function. We show that p53 null mouse and p53 knockdown human primary fibroblasts exhibit mtDNA depletion and decreased mitochondrial mass under normal culture growth conditions. This is accompanied by a reduction of the p53R2 subunit of ribonucleotide reductase mRNA and protein and of mitochondrial transcription factor A (mtTFA) at the protein level only. Finally, p53-depleted cells exhibit significant disruption of cellular ROS homeostasis, characterized by reduced mitochondrial and cellular superoxide levels and increased cellular hydrogen peroxide. Altogether, these results elucidate additional mitochondria-related functions for p53 and implicate mtDNA depletion and ROS alterations as potentially relevant to cellular transformation, cancer cell phenotypes, and the Warburg Effect.
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http://dx.doi.org/10.1016/j.bbabio.2009.01.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2680458PMC
May 2009

The Kruppel-like factor KLF4 is a critical regulator of monocyte differentiation.

EMBO J 2007 Sep 30;26(18):4138-48. Epub 2007 Aug 30.

Department of Medicine, Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.

Monocyte differentiation involves the participation of lineage-restricted transcription factors, although the mechanisms by which this process occurs are incompletely defined. Within the hematopoietic system, members of the Kruppel-like family of factors (KLFs) play essential roles in erythrocyte and T lymphocyte development. Here we show that KLF4/GKLF is expressed in a monocyte-restricted and stage-specific pattern during myelopoiesis and functions to promote monocyte differentiation. Overexpression of KLF4 in HL-60 cells confers the characteristics of mature monocytes. Conversely, KLF4 knockdown blocked phorbol ester-induced monocyte differentiation. Forced expression of KLF4 in primary common myeloid progenitors (CMPs) or hematopoietic stem cells (HSCs) induced exclusive monocyte differentiation in clonogenic assays, whereas KLF4 deficiency inhibited monocyte but increased granulocyte differentiation. Mechanistic studies demonstrate that KLF4 is a target gene of PU.1. Consistently, KLF4 can rescue PU.1-/- fetal liver cells along the monocytic lineage and can activate the monocytic-specific CD14 promoter. Thus, KLF4 is a critical regulator in the transcriptional network controlling monocyte differentiation.
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http://dx.doi.org/10.1038/sj.emboj.7601824DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2230668PMC
September 2007

Cell cycle- and ribonucleotide reductase-driven changes in mtDNA copy number influence mtDNA Inheritance without compromising mitochondrial gene expression.

Cell Cycle 2007 Aug 7;6(16):2048-57. Epub 2007 Jun 7.

Department of Pathology, and Graduate Program in Genetics, Yale University School of Medicine, New Haven, Connecticut 06520, USA.

Most eukaryotes maintain multiple copies of mtDNA, ranging from 20-50 in yeast to as many as 10,000 in mammalian cells. The mitochondrial genome encodes essential subunits of the respiratory chain, but the number of mtDNA molecules is apparently in excess of that needed to sustain adequate respiration, as evidenced by the "threshold effect" in mitochondrial diseases. Thus, other selective pressures apparently have contributed to the universal maintenance of multiple mtDNA molecules/cell. Here we analyzed the interplay between the two pathways proposed to regulate mtDNA copy number in Saccharomyces cerevisiae, and the requirement of normal mtDNA copy number for mitochondrial gene expression, respiration, and inheritance. We provide the first direct evidence that upregulation of mtDNA can be achieved by increasing ribonucleotide reductase (RNR) activity via derepression of nuclear RNR gene transcription or elimination of allosteric-feedback regulation. Analysis of rad53 mutant strains also revealed upregulation of mtDNA copy number independent of that resulting from elevated RNR activity. We present evidence that a prolonged cell cycle allows accumulation of mtDNA in these strains. Analysis of multiple strains with increased or decreased mtDNA revealed that mechanisms are in place to prevent significant changes in mitochondrial gene expression and respiration in the face of approximately two-fold alterations in mtDNA copy number. However, depletion of mtDNA in abf2 null strains leads to defective mtDNA inheritance that is partially rescued by replenishing mtDNA via overexpression of RNR1. These results indicate that one role for multiple mtDNA copies is to ensure optimal inheritance of mtDNA during cell division.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2606055PMC
http://dx.doi.org/10.4161/cc.6.16.4572DOI Listing
August 2007

Kruppel-like factor 4 is a mediator of proinflammatory signaling in macrophages.

J Biol Chem 2005 Nov 16;280(46):38247-58. Epub 2005 Sep 16.

Program in Cardiovascular Transcriptional Biology, Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.

Activation of macrophages is important in chronic inflammatory disease states such as atherosclerosis. Proinflammatory cytokines such as interferon-gamma (IFN-gamma), lipopolysaccharide (LPS), or tumor necrosis factor-alpha can promote macrophage activation. Conversely, anti-inflammatory factors such as transforming growth factor-beta1 (TGF-beta1) can decrease proinflammatory activation. The molecular mediators regulating the balance of these opposing effectors remain incompletely understood. Herein, we identify Kruppel-like factor 4 (KLF4) as being markedly induced in response to IFN-gamma, LPS, or tumor necrosis factor-alpha and decreased by TGF-beta1 in macrophages. Overexpression of KLF4 in J774a macrophages induced the macrophage activation marker inducible nitric-oxide synthase and inhibited the TGF-beta1 and Smad3 target gene plasminogen activator inhibitor-1 (PAI-1). Conversely, KLF4 knockdown markedly attenuated the ability of IFN-gamma, LPS, or IFN-gamma plus LPS to induce the iNOS promoter, whereas it augmented macrophage responsiveness to TGF-beta1 and Smad3 signaling. The KLF4 induction of the iNOS promoter is mediated by two KLF DNA-binding sites at -95 and -212 bp, and mutation of these sites diminished induction by IFN-gamma and LPS. We further provide evidence that KLF4 interacts with the NF-kappaB family member p65 (RelA) to cooperatively induce the iNOS promoter. In contrast, KLF4 inhibited the TGF-beta1/Smad3 induction of the PAI-1 promoter independent of KLF4 DNA binding through a novel antagonistic competition with Smad3 for the C terminus of the coactivator p300/CBP. These findings support an important role for KLF4 as a regulator of key signaling pathways that control macrophage activation.
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http://dx.doi.org/10.1074/jbc.M509378200DOI Listing
November 2005

The conserved Mec1/Rad53 nuclear checkpoint pathway regulates mitochondrial DNA copy number in Saccharomyces cerevisiae.

Mol Biol Cell 2005 Jun 13;16(6):3010-8. Epub 2005 Apr 13.

Department of Pathology, Yale University School of Medicine, New Haven, CT 06520-8023, USA.

How mitochondrial DNA (mtDNA) copy number is determined and modulated according to cellular demands is largely unknown. Our previous investigations of the related DNA helicases Pif1p and Rrm3p uncovered a role for these factors and the conserved Mec1/Rad53 nuclear checkpoint pathway in mtDNA mutagenesis and stability in Saccharomyces cerevisiae. Here, we demonstrate another novel function of this pathway in the regulation of mtDNA copy number. Deletion of RRM3 or SML1, or overexpression of RNR1, which recapitulates Mec1/Rad53 pathway activation, resulted in an approximately twofold increase in mtDNA content relative to the corresponding wild-type yeast strains. In addition, deletion of RRM3 or SML1 fully rescued the approximately 50% depletion of mtDNA observed in a pif1 null strain. Furthermore, deletion of SML1 was shown to be epistatic to both a rad53 and an rrm3 null mutation, placing these three genes in the same genetic pathway of mtDNA copy number regulation. Finally, increased mtDNA copy number via the Mec1/Rad53 pathway could occur independently of Abf2p, an mtDNA-binding protein that, like its metazoan homologues, is implicated in mtDNA copy number control. Together, these results indicate that signaling through the Mec1/Rad53 pathway increases mtDNA copy number by altering deoxyribonucleoside triphosphate pools through the activity of ribonucleotide reductase. This comprises the first linkage of a conserved signaling pathway to the regulation of mitochondrial genome copy number and suggests that homologous pathways in humans may likewise regulate mtDNA content under physiological conditions.
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http://dx.doi.org/10.1091/mbc.e05-01-0053DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1142443PMC
June 2005

Transforming growth factor-beta1 inhibition of vascular smooth muscle cell activation is mediated via Smad3.

J Biol Chem 2004 Apr 1;279(16):16388-93. Epub 2004 Feb 1.

Division of Cardiovascular Medicine and Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.

Activation of vascular smooth muscle cells (VSMCs) by proinflammatory cytokines is a key feature of atherosclerotic lesion formation. Transforming growth factor (TGF)-beta1 is a pleiotropic growth factor that can modulate the inflammatory response in diverse cell types including VSMCs. However, the mechanisms by which TGF-beta1 is able to mediate these effects remains incompletely understood. We demonstrate here that the ability of TGF-beta1 to inhibit markers of VSMC activation, inducible nitric-oxide synthase (iNOS) and interleukin (IL)-6, is mediated through its downstream effector Smad3. In reporter gene transfection studies, we found that among a panel of Smads, Smad3 could inhibit iNOS induction in an analogous manner as exogenous TGF-beta1. Adenoviral overexpression of Smad3 potently repressed inducible expression of endogenous iNOS and IL-6. Conversely, TGF-beta1 inhibition of cytokine-mediated induction of iNOS and IL-6 expression was completely blocked in Smad3-deficient VSMCs. Previous studies demonstrate that CCAAT/enhancer-binding protein (C/EBP) and NF-kappaB sites are critical for cytokine induction of both the iNOS and IL-6 promoters. We demonstrate that the inhibitory effect of Smad3 occurs via a novel antagonistic effect of Smad3 on C/EBP DNA-protein binding and activity. Smad3 mediates this effect in part by inhibiting C/EBP-beta and C/EBP-delta through distinct mechanisms. Furthermore, we find that Smad3 prevents the cooperative induction of the iNOS promoter by C/EBP and NF-kappaB. These data demonstrate that Smad3 plays an essential role in mediating TGF-beta1 anti-inflammatory response in VSMCs.
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http://dx.doi.org/10.1074/jbc.M309664200DOI Listing
April 2004

Crossing over between regions of limited homology in Escherichia coli. RecA-dependent and RecA-independent pathways.

Genetics 2002 Mar;160(3):851-9

Rosenstiel Basic Medical Sciences Research Center and the Department of Biology, Brandeis University, Waltham, Massachusetts 02454-9110, USA.

We have developed an assay for intermolecular crossing over between circular plasmids carrying variable amounts of homology. Screens of Escherichia coli mutants demonstrated that known recombination functions can only partially account for the observed recombination. Recombination rates increased three to four orders of magnitude as homology rose from 25 to 411 bp. Loss of recA blocked most recombination; however, RecA-independent crossing over predominated at 25 bp and could be detected at all homology lengths. Products of recA-independent recombination were reciprocal in nature. This suggests that RecA-independent recombination may involve a true break-and-join mechanism, but the genetic basis for this mechanism remains unknown. RecA-dependent crossing over occurred primarily by the RecF pathway but considerable recombination occurred independent of both RecF and RecBCD. In many respects, the genetic dependence of RecA-dependent crossing over resembled that reported for single-strand gap repair. Surprisingly, ruvC mutants, in both recA(+) and recA mutant backgrounds, scored as hyperrecombinational. This may occur because RuvC preferentially resolves Holliday junction intermediates, critical to both RecA-dependent and RecA-independent mechanisms, to the noncrossover configuration. Levels of crossing over were increased by defects in DnaB helicase and by oxidative damage, showing that damaged DNA or stalled replication can initiate genetic recombination.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1462031PMC
March 2002