24 resultados para the major light harvesting complex of photosystem II (LHCIIb)


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A weekly paper that was published from 1805 to 1814. War related news includes: Page 95 - Weekly Retrospect: relief effort in London, England for those affected by the war in British North America; naval battles on Lake Ontario by Commodore Chauncey in late September; movements of Major Grant, De Rottenburgh's regiment, General Wilkinson, Commodore Yoe's fleet, General Hampton; the capture of Fort Malden by William Harrison. The rest of the newspaper contains literary works (poems and translations), marriages, deaths and other anecdotes. The motto on the front page states: "Visiting Every Flower with Labour Meet, and Gathering all its Treasures, Sweet by Sweet."

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This case study of curriculum at Dubai Women's College (DWC) examines perceptions of international educators who designed and implemented curriculum for female Emirati higher-educational students in the UAE, and sheds light on the complex social, cultural, and religious factors affecting educational practice. Participants were faculty and supervisors, mainly foreign nationals, while students at DWC are exclusively Emirati. Theories prominent in this study are: constructivist learning theory, trans formative curriculum theory, and sociological theory. Change and empowerment theory figure prominently in this study. Findings reveal this unique group of educators understand curriculum theory as a "contextualized" construct and argue that theory and practice must be viewed through an international lens of religious, cultural, and social contexts. As well, the study explores how mandated "standards" in education-in the form of the International English Language Testing System (IEL TS) and integrated, constructivist curriculum, as taught in the Higher Diploma Year 1 program-function as dual curricular emphases in this context. The study found that tensions among these dual emphases existed and were mediated through specific strategies, including the use of authentic texts to mirror the IEL TS examination during in-class activities, and the relevance of curricular tasks.

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Two classes of building blocks have been prepared and characterized and their coordination chemistry explored working towards the preparation of new molecule-based magnetic materials. In the first project, the amine functionality of 3,3'-diamino-2,2'- bipyridine was exploited for the preparation of a new family of ligands (H2L 1)-(H2L 4). The molecular structures of three ligands have been fully characterized by X-ray crystallography. [molecular structure diagram will not copy here, but is available in full pdf.] The coordination chemistry of these ligands with divalent first row transition metal ions was investigated. For ligand (H2L1), the molecular structures of four coordination complexes with stoichiometries [Zn2(Ll)(OAc)(MeO)]2 (I), [Cu2(L1)(OAc)2 (II), [Li(L1)]3 (III), and [Ni(L1)]3 (IV) were determined by X-ray crystallography. For ligand (H2L2), a Cu(II) complex of stoichiometry [Cu3(L2)(OAc)3MeO] (V) was determined by X-ray crystallography. The magnetic properties of complexes (II), (III), and (V) have been fully elucidated. In project two, synthetic strategies for the preparation of porphyrin molecules bearing triol substituents is presented. Following this approach, three new porphyrin derivatives have been prepared and characterized [Zn(HPTPP-CH2C(CH20H)3)] (VI), [P(TPP)(OCH2C(CH2)H)3)2]+CL- (VII), and [P(OEP)(C6H5)(OCH2C(CH2OH)3)]+Cl- (VIII). Attempts to exchange the labile methoxide bridges of a tetraironIIl single molecule magnet of stoichiometry [Fe4(OMe)6(dpm)6] (Hdpm = dipivaloylmethane) with the triol appended porphyrins will be discussed. [molecular structure diagram will not copy here, but is available in full pdf.]

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Scientists have overwhelmingly concluded that global warming occurs as a consequence of human activities and that climate change, combined with the depletion of resources, could have catastrophic consequences for the human civilization later this century. However, in political circles and in the public sphere these conclusions are not taken seriously, or they are laid aside for future generations to deal with; at the same time, significant efforts are being deployed to discredit the scientific evidence. In this thesis I have studied the positions of climate scientists as well as those of climate change deniers, and I also examined how their points of view are likely to impact the interests and habits of corporations and citizens. The work of Thomas Homer-Dixon was used as an important source for analyzing the complex interaction between our natural, economic, and social systems, and John Dewey's pattern of inquiry provided the theoretical foundation for an analysis of the current crisis and its possible solutions. No concerted action to deal with climate change has yet been taken by the leaders of the Western world; I corroborated data from four reliable sources (Hansen, 2009; IPCC, 2007; Lynas, 2007; Steffen, 2011) regarding several development scenarios and their likely consequences on greenhouse gas emissions, and I concluded that a future temperature increase of more than 2°C appears now as unavoidable. In the light of this conclusion I argue that education for increasing the resilience of smaller communities is a realistic alternative that can offer some hope in dealing with the challenges ahead.

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The synthesis and studies of two classes of poly dentate ligands are presented as two projects. In project 1, four new carboxamide ligands have been synthesised via the condensation of 2,2',6,6'-tetrachloroformyl-4,4'-bipyridine or 2,6-dichloroformyl pyridine together with heterocyclic amines containing pyridine or pyrazole substituents. The coordination chemistry of these ligands has been investigated and studies have shown that with a Cu(II) salt, two carboxamide ligands LJ and L2 afford large clusters with stoichiometries [Cu8(L1)4Cl16].CHCl3.5H2O.7CH3OH (I) and [Cu9(L2)6Cl6].CH3OH.5H2O.(C2H5)3N (II) respectively. [molecular diagram availabel in pdf]. X-ray diffraction studies of cluster (I) reveal that it has approximate S4 symmetry and is comprised of four ligands and eight copper (II) centers. Here, coordination takes place via amide 0 atoms, and pyrazole nitrogens. This complex is the first reported example of an octanuclear copper cluster with a saddle-shaped structure. The second cluster comprises nine copper ions that are arranged in a cyclic array. Each ligand coordinates three copper centers and each copper ion shares two ligands to connect six ligands with nine copper ions. The amide nitrogens are completely deprotonated and both amide Nand 0 atoms coordinate the metal centres. The cluster has three-fold symmetry. There are six chloride ions, three of which are bridging two neighbouring Cu(II) centres. Magnetic studies of (I) and (II) reveal that both clusters display weak antiferromagnetic interactions between neighbouring Cu(II) centers at low temperature. In the second project, three complexes with stoichiometries [Fe[N302](SCN)2]2 (III), R,R-[Fe[N3O2](SCN)2 (IV) and R,R-]Fe[N3O2](CN)2] (V) were prepared and characterized, where [N302] is a pentadentate macrocycle. Complex (III) was prepared via the metal templated Schiff-base condensation of 2,2',6,6'-tetraacetyl-4,4'-bipyridine together with 3,6-dioxaoctane-I,8-diamine and comprises of a dimeric macro cycle where the two Fe(II) centres are in a pentagonal-bipyramidal environment with the [N302] ligands occupying the equatorial plane and two axial NCS ligands. Complexes (IV) and (V) were prepared via the condensation of 2,6-diacetylpyridine together with a chiral diamine in the presence of FeCh. The synthetic strategy for the preparation of the chiral diamine (4R,5R)-4,5-diphenyl-3,6-dioxa-I,8-octane-diamine was elucidated. The chirality of both macrocycles (IV) and (V) was probed by circular dichroism spectroscopy. The crystal structure of (IV) at 200 K contains two independent molecules in the unit cell, both of which contain a hepta-coordinated Fe(II) and axial NCS ligands. Variable temperature magnetic susceptibility and structural studies are consistent with a high spin Fe(II) complex and show no evidence of any spin crossover behaviour. In contrast, the bis cyanide derivative (V) crystallizes with two independent molecules in the unit cell, both of which have different coordination geometries consistent with different spin states for the two Fe(II) centres. At 250 K, the molecular structure of (V) shows the presence of both 7- and a 6-coordinate Fe(II) complexes in the crystal lattice. As the temperature is lowered, the molecules undergo a structural change and at 100 K the structural data is consistent with a 6- and 5-coordinate Fe(II) complex in the unit cell. Magnetic studies confirm that this complex undergoes a gradual, thermal, spin crossover transition in the solid state. Photomagnetic measurements indicate this is the first chiral Fe (II) sea complex to exhibit a LIESST.

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The dependence of the electron transfer (ET) rate on the Photosystem I (PSI) cofactor phylloquinone (A1) is studied by time-resolved absorbance and electron paramagnetic resonance (EPR) spectroscopy. Two active branches (A and B) of electron transfer converge to the FX cofactor from the A1A and A1B quinone. The work described in Chapter 5 investigates the single hydrogen bond from the amino acid residue PsaA-L722 backbone nitrogen to A1A for its effect on the electron transfer rate to FX. Room temperature transient EPR measurements show an increase in the rate for the A1A- to FX for the PsaA-L722T mutant and an increased hyperfine coupling to the 2-methyl group of A1A when compared to wild type. The Arrhenius plot of the A1A- to FX ET in the PsaA-L722T mutant suggests that the increased rate is probably the result of a slight change in the electronic coupling between A1A- and FX. The reasons for the non-Arrhenius behavior are discussed. The work discussed in Chapter 6 investigates the directionality of ET at low temperature by blocking ET to the iron-sulfur clusters FX, FA and FB in the menB deletion mutant strain of Synechocyctis sp. PCC 6803, which is unable to synthesize phylloquinone, by incorporating the high midpoint potential (49 mV vs SHE) 2,3-dichloro-1,4-naphthoquinone (Cl2NQ) into the A1A and A1B binding sites. Various EPR spectroscopic techniques were implemented to differentiate between the spectral features created from A and B- branch electron transfer. The implications of this result for the directionality of electron transfer in PS I are discussed. The work discussed in Chapter 7 was done to study the dependence of the heterogeneous ET at low temperature on A1 midpoint potential. The menB PSI mutant contains plastiquinone-9 in the A1 binding site. The solution midpoint potential of the quinone measures 100 mV more positive then wild-type phylloquinone. The irreversible ET to the terminal acceptors FA and FB at low temperature is not controlled by the forward step from A1 to FX as expected due to the thermodynamic differences of the A1 cofactor in the two active branches A and B. Alternatives for the ET heterogeneity are discussed.

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Activated by elevations in myoplasmic calcium concentration, myosin light chain kinase (skMLCK) phosphorylates the regulatory light chains (RLCs) of fast muscle myosin. This covalent modification potentiates force production, but requires an investment of ATP. Our objective was to investigate the effect of RLC phosphorylation on the contractile economy (mechanical output:metabolic input) of fast twitch skeletal muscle. Extensor digitorum longus muscles isolated from Wildtype and skMLCK-/- mice mounted in vitro (25°C) were subjected to repetitive low-frequency stimulation (10Hz,15s) known to cause activation of skMLCK, and staircase potentiation of force. With a 3-fold increase in RLC phosphate content, Wildtype generated 44% more force than skMLCK-/- muscles over the stimulation period (P = .002), without an accompanied increase in energy cost (P = .449). Overall, the contractile economy of Wildtype muscles, with an intact RLC phosphorylation mechanism, was 73% greater than skMLCK /- muscles (P = .043), demonstrating an important physiological function of skMLCK during repetitive contractile activity.