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Britz, Alexander,Gawelda, Wojciech,Assefa, Tadesse A.,Jamula, Lindsey L.,Yarranton, Jonathan T.,Galler, Andreas,Khakhulin, Dmitry,Diez, Michael,Harder, Manuel,Doumy, Gilles,March, Anne Marie,Bajno American Chemical Society 2019 Inorganic chemistry Vol.58 No.14
<P>We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)<SUB>2</SUB>]<SUP>2+</SUP> (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising questions as to whether the ligand-field strength of dcpp had pushed this system beyond the <SUP>5</SUP>T<SUB>2</SUB>/<SUP>3</SUP>T<SUB>1</SUB> crossing point and stabilizing the latter as the lowest energy excited state. Kα and Kβ X-ray emission spectroscopies have been used to unambiguously determine the quintet spin multiplicity of the long-lived excited state, thereby establishing the <SUP>5</SUP>T<SUB>2</SUB> state as the lowest energy excited state of this compound. Geometric changes associated with the photoinduced ligand-field state conversion have also been monitored with extended X-ray absorption fine structure. The data show the typical average Fe-ligand bond length elongation of ∼0.18 Å for a <SUP>5</SUP>T<SUB>2</SUB> state and suggest a high anisotropy of the primary coordination sphere around the metal center in the excited <SUP>5</SUP>T<SUB>2</SUB> state, in stark contrast to the nearly perfect octahedral symmetry that characterizes the low-spin <SUP>1</SUP>A<SUB>1</SUB> ground state structure. This study illustrates how the application of time-resolved X-ray techniques can provide insights into the electronic structures of molecules-in particular, transition metal complexes-that are difficult if not impossible to obtain by other means.</P><P>Time-resolved X-ray emission and absorption spectroscopies have been used to probe the excited-state electronic and geometric structure of an Fe(II) polypyridyl complex. Analysis of the data revealed that the lowest energy excited state is high-spin (<I>S</I> = 2) in character. This determination had not been possible using other experimental techniques (e.g., time-resolved optical spectroscopy), demonstrating the potential for ultrafast X-ray methods to address scientific questions that are difficult to resolve by other means.</P> [FIG OMISSION]</BR>
Ahuja, Nidhi,Korkin, Dmitry,Chaba, Rachna,Cezairliyan, Brent O,Sauer, Robert T,Kim, Kyeong Kyu,Gross, Carol A American Society for Biochemistry and Molecular Bi 2009 The Journal of biological chemistry Vol.284 No.8
<P>The Escherichia coli envelope stress response is controlled by the alternative sigma factor, sigma(E), and is induced when unfolded outer membrane proteins accumulate in the periplasm. The response is initiated by sequential cleavage of the membrane-spanning antisigma factor, RseA. RseB is an important negative regulator of envelope stress response that exerts its negative effects onsigma(E) activity through its binding to RseA. In this study, we analyze the interaction between RseA and RseB. We found that tight binding of RseB to RseA required intact RseB. Using programs that performed global and local sequence alignment of RseB and RseA, we found regions of high similarity and performed alanine substitution mutagenesis to test the hypothesis that these regions were functionally important. This protocol is based on the hypothesis that functionally dependent regions of two proteins co-evolve and therefore are likely to be sequentially conserved. This procedure allowed us to identify both an N-terminal and C-terminal region in RseB important for binding to RseA. We extensively analyzed the C-terminal region, which aligns with a region of RseA coincident with the major RseB binding determinant in RseA. Both allele-specific suppression analysis and cysteine-mediated disulfide bond formation indicated that this C-terminal region of similarity of RseA and RseB identifies a contact site between the two proteins. We suggest a similar protocol can be successfully applied to pairs of non-homologous but functionally linked proteins to find specific regions of the protein sequences that are important for establishing functional linkage.</P>
Strain-induced indium clustering in non-polar <i>a</i>-plane InGaN quantum wells
Lee, Ja Kyung,Park, Bumsu,Song, Kyung,Jung, Woo Young,Tyutyunnikov, Dmitry,Yang, Tiannan,Koch, Christoph T.,Park, Chan Gyung,van Aken, Peter A.,Kim, Young-Min,Kim, Jong Kyu,Bang, Junhyeok,Chen, Long-Q Elsevier 2018 Acta materialia Vol.145 No.-
<P><B>Abstract</B></P> <P>In conventional light-emitting diodes the epitaxial strain and related piezoelectric polarization arising along the polar [0001] growth direction of the InGaN/GaN quantum wells (QWs) induce internal fields which adversely affect the radiative recombination of electron-hole pairs therein. Growing the quantum wells along a nonpolar orientation can, in principle, avoid this problem but seems to face with another problem associated with indium clustering. In this study, we present experimental evidence that supports the inhomogeneous distribution of indium in non-polar <I>a</I>-plane InGaN QWs by using dark-field inline electron holography as well as atom probe tomography measurements and discuss the possible origin by density functional theory calculation. A model non-polar <I>a</I>-plane QW structure with 10 nm-thick In<SUB>0.1</SUB>Ga<SUB>0.9</SUB>N double QWs was investigated and compared with the polar <I>c</I>-plane QWs with the same QW structure. Unlike the random distribution in the polar QWs, the indium atoms in the non-polar QW exhibit inhomogeneous distribution and show a tendency of periodic clustering. We suggest the dipole interaction energy and the strain energy associated with indium substitution could have a substantial influence on the local composition of strained InGaN QWs and, particularly, triggers In clustering in the non-polar <I>a</I>-plane QW structure. Accompanying phase field modeling rationalizes that In clustering can also modify the in-plane polarization through piezoelectric effects, preventing the electrostatic potential from diverging along the in-plane polar direction.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kudo, Masatoshi,Finn, Richard S,Qin, Shukui,Han, Kwang-Hyub,Ikeda, Kenji,Piscaglia, Fabio,Baron, Ari,Park, Joong-Won,Han, Guohong,Jassem, Jacek,Blanc, Jean Frederic,Vogel, Arndt,Komov, Dmitry,Evans, T Elsevier 2018 The Lancet Vol.391 No.10126
<P><B>Summary</B></P> <P><B>Background</B></P> <P>In a phase 2 trial, lenvatinib, an inhibitor of VEGF receptors 1–3, FGF receptors 1–4, PDGF receptor α, RET, and KIT, showed activity in hepatocellular carcinoma. We aimed to compare overall survival in patients treated with lenvatinib versus sorafenib as a first-line treatment for unresectable hepatocellular carcinoma.</P> <P><B>Methods</B></P> <P>This was an open-label, phase 3, multicentre, non-inferiority trial that recruited patients with unresectable hepatocellular carcinoma, who had not received treatment for advanced disease, at 154 sites in 20 countries throughout the Asia-Pacific, European, and North American regions. Patients were randomly assigned (1:1) via an interactive voice–web response system—with region; macroscopic portal vein invasion, extrahepatic spread, or both; Eastern Cooperative Oncology Group performance status; and bodyweight as stratification factors—to receive oral lenvatinib (12 mg/day for bodyweight ≥60 kg or 8 mg/day for bodyweight <60 kg) or sorafenib 400 mg twice-daily in 28-day cycles. The primary endpoint was overall survival, measured from the date of randomisation until the date of death from any cause. The efficacy analysis followed the intention-to-treat principle, and only patients who received treatment were included in the safety analysis. The non-inferiority margin was set at 1·08. The trial is registered with ClinicalTrials.gov, number NCT01761266.</P> <P><B>Findings</B></P> <P>Between March 1, 2013 and July 30, 2015, 1492 patients were recruited. 954 eligible patients were randomly assigned to lenvatinib (n=478) or sorafenib (n=476). Median survival time for lenvatinib of 13·6 months (95% CI 12·1–14·9) was non-inferior to sorafenib (12·3 months, 10·4–13·9; hazard ratio 0·92, 95% CI 0·79–1·06), meeting criteria for non-inferiority. The most common any-grade adverse events were hypertension (201 [42%]), diarrhoea (184 [39%]), decreased appetite (162 [34%]), and decreased weight (147 [31%]) for lenvatinib, and palmar-plantar erythrodysaesthesia (249 [52%]), diarrhoea (220 [46%]), hypertension (144 [30%]), and decreased appetite (127 [27%]) for sorafenib.</P> <P><B>Interpretation</B></P> <P>Lenvatinib was non-inferior to sorafenib in overall survival in untreated advanced hepatocellular carcinoma. The safety and tolerability profiles of lenvatinib were consistent with those previously observed.</P> <P><B>Funding</B></P> <P>Eisai Inc.</P>