scholarly journals Experimental and computational evaluation of the barrier to torsional rotation in a butadiyne-linked porphyrin dimer

2016 ◽  
Vol 18 (7) ◽  
pp. 5264-5274 ◽  
Author(s):  
Martin D. Peeks ◽  
Patrik Neuhaus ◽  
Harry L. Anderson
Keyword(s):  
Absorption Spectrum ◽  
Energy Barrier ◽  
Temperature Dependent ◽  
Computational Evaluation ◽  
Nir Absorption ◽  
Torsional Rotation ◽  
Porphyrin Dimer

Temperature-dependent changes in the UV-vis-NIR absorption spectrum of a butadiyne linked porphyrin dimer have been used to determine the height of the energy barrier to torsional rotation.

A study of conformation about the aryl C-N bonds in N-aryl imides by dynamic N.M.R. spectroscopy

1976 ◽  
Vol 29 (2) ◽  
pp. 295 ◽  
Author(s):  
SM Verma ◽  
NB Singh
Keyword(s):  
Energy Barrier ◽  
Phenyl Group ◽  
Spectral Studies ◽  
Free Rotation ◽  
Conformational Study ◽  
Temperature Dependent ◽  
Restricted Rotation ◽  
Planar Conformation

A series of α, β-(9,10-dihydroanthracene-9,10-diyl)-N-arylsuccinimide derivatives has been prepared and their N.M.R. spectral studies are reported. The effect of the substituents at the N-phenyl group on the conformational process about the aryl C-N bond has been investigated.The asymmetric cage moiety present in this system was employed for the conformational study.� The N.M.R. spectra provided evidence for the non-planar conformation and restricted rotation about the aryl C-N bond in the case of ortho-substituted derivatives. Electronegative substituents were found to have a preferred conformation (anti to the cage moiety). The energy barrier (ΔGt) of the order of 86 kJ/mol has been determined by their temperature-dependent spectra. Free rotation about the aryl C-N bond was observed for the meta- and para-substituted derivatives. No buttressing effect by meta substituents has been noticed.

Temperature-dependent absorption spectrum of betaine-30 in methanol

2002 ◽  
Vol 356 (3-4) ◽  
pp. 214-220 ◽  
Author(s):  
Xihua Zhao ◽  
Fritz J. Knorr ◽  
Jeanne L. McHale
Keyword(s):  
Absorption Spectrum ◽  
Temperature Dependent ◽  
Dependent Absorption

Low Temperature GaN Growth on Nitridated Sapphire Using Remote Plasma Enhanced Ultrahigh Vacuum Chemical Vapor Deposition

1997 ◽  
Vol 482 ◽  
Author(s):  
Dong-Jun Kim ◽  
Kyoung-Kook Kim ◽  
Jong-Sik Paek ◽  
Min-Su Yi ◽  
Do-Young Noh ◽  
...  
Keyword(s):  
Absorption Spectrum ◽  
Chemical Vapor Deposition ◽  
Low Temperature ◽  
Vapor Deposition ◽  
Ultrahigh Vacuum ◽  
Chemical Vapor ◽  
Rocking Curve ◽  
X Ray ◽  
Nitridation Time ◽  
Nir Absorption

AbstractGaN epitaxial thin films were grown on a nitridated sapphire at low temperature (550°C) using remote plasma enhanced ultrahigh vacuum chemical vapor deposition system and these films were investigated by Rutherford backscattering spectroscopy (RBS), X-ray diffraction(XRD) θ-rocking technique and the Ultraviolet-Visible-Nearinfrared (UV-VIS-NIR) absorption spectrum. The FWHM of the X-ray θ-rocking curve was about 0.4 degree using the (0002) reflection from the GaN layer with 5000Å thickness grown on the nitridated sapphire. An analysis of XRD and the UV-VIS-NIR absorption spectrum showed that the crystalline and optical qualities of GaN are dependent on the nitridation time of the sapphire even at low temperature when a plasma source is used for nitridation. This means that the density of protrusion, which is formed by a relaxation of the elastic energy caused by the lattice difference between the sapphire and AlxO1-xN, with the sapphire nitridation time plays a key role in the crystalline and optical properties of grown GaN films. The RBS channeling data and the FWHM value of the θ-rocking curve for GaNr(0002) also indicated that the truncated hexagonals are tilted towards each other. These results showed that the GaN epitaxial film can be successfully grown on nitridated sapphire by RPE-UHVCVD even at low temperature.

scholarly journals Enhancing the Inhomogeneonus Photodynamics of Canonical Bacteriophytochrome

2021 ◽  
Author(s):  
Jakub Rydzewski ◽  
Katarzyna Walczewska-Szewc ◽  
Sylwia Czach ◽  
Marco Caricato ◽  
Sijin Ren ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Deinococcus Radiodurans ◽  
Metastable States ◽  
Signal Transduction Pathways ◽  
Nanometer Scale ◽  
Thermal Transition ◽  
Enhanced Sampling ◽  
Temperature Dependent ◽  
Dark Reversion ◽  
First Time

The ability of phytochromes to act as photoswitches in plants and microorganisms depends on interactions between a bilin-like chromophore and a protein. The interconversion occurs between the spectrally distinct red (Pr) and far-red (Pfr) conformers. This conformational change is triggered by the photoisomerization of the chromophore D-ring pyrrole. In this study, as a representative example of a phytochrome-bilin system, we take biliverdin IXα (BV) bound to bacteriophytochrome (BphP) from Deinococcus radiodurans. In the absence of light, we use an enhanced sampling molecular dynamics (MD) method to overcome the photoisomerization energy barrier. We find that the calculated free energy (FE) barriers between essential metastable states agree with spectroscopic results. We show that the enhanced dynamics of the BV chromophore in BphP triggers nanometer-scale conformational movements that propagate by two experimentally determined signal transduction pathways. Most importantly, we describe how the metastable states enable a thermal transition known as the dark reversion between Pfr and Pr, through a previously unknown intermediate state of Pfr. Here, for the first time, the heterogeneity of temperature-dependent Pfr states is presented at the atomistic level. This work paves a way toward understanding the complete mechanism of the photoisomerization of a bilin-like chromophore in phytochromes.

Interaction Potentials of Hg-Ar from Temperature Dependent Absorption Spectra

1978 ◽  
Vol 33 (12) ◽  
pp. 1461-1468 ◽  
Author(s):  
H. C. Petzold ◽  
W. Behmenburg
Keyword(s):  
Absorption Spectrum ◽  
Thermal Energy ◽  
Short Wavelength ◽  
Line Broadening ◽  
Vibrational States ◽  
Temperature Dependent ◽  
Satellite Structure ◽  
Lennard Jones ◽  
Dependent Absorption ◽  
Short Wavelength Side

Abstract The temperature dependence of the absorption spectrum k(v̄) of Hg-Ar-mixtures in the range 30-1000 cm-1 about the center of the Hg-line at v̄0 = 39425 cm-1 (λ0 = 2536.5 Å) has been investigated in the temperature interval 473 -1273 K. The measurements were carried out at number densities 1.0 x 1017-9.1 X 1018 cm-3 for Hg and 9.4 x 1018-9.7 x 1018 cm-3 for Ar. Potentials for the Hg-Ar-system in the thermal energy range originating from the Hg-states 61S0 and 63P1 have been deduced from the data. It turned out that they differ considerably from Lennard-Jones-functions. By comparison of the observed spectra with calculations on the basis of quantummechanical theory of collisional line broadening it is concluded that transitions from free translational states of Hg-Ar-pairs as well as bound and quasi-bound vibrational states of the Hg-Ar-molecule contribute to the formation of the satellite structure on the short wavelength side of the Hg-line.

scholarly journals Enhancing the Inhomogeneonus Photodynamics of Canonical Bacteriophytochrome

2021 ◽  
Author(s):  
Jakub Rydzewski ◽  
Katarzyna Walczewska-Szewc ◽  
Sylwia Czach ◽  
Wiesław Nowak ◽  
Krzysztof Kuczera
Keyword(s):  
Energy Barrier ◽  
Deinococcus Radiodurans ◽  
Metastable States ◽  
Signal Transduction Pathways ◽  
Nanometer Scale ◽  
Thermal Transition ◽  
Enhanced Sampling ◽  
Temperature Dependent ◽  
Dark Reversion ◽  
First Time

The ability of phytochromes to act as photoswitches in plants and microorganisms depends on interactions between a bilin-like chromophore and a protein. The interconversion occurs between the spectrally distinct red (Pr) and far-red (Pfr) conformers. This conformational change is triggered by the photoisomerization of the chromophore D-ring pyrrole. In this study, as a representative example of a phytochrome-bilin system, we take biliverdin IXα (BV) bound to bacteriophytochrome (BphP) from Deinococcus radiodurans. In the absence of light, we use an enhanced sampling molecular dynamics (MD) method to overcome the photoisomerization energy barrier. We find that the calculated free energy (FE) barriers between essential metastable states agree with spectroscopic results. We show that the enhanced dynamics of the BV chromophore in BphP triggers nanometer-scale conformational movements that propagate by two experimentally determined signal transduction pathways. Most importantly, we describe how the metastable states enable a thermal transition known as the dark reversion between Pfr and Pr, through a previously unknown intermediate state of Pfr. Here, for the first time, the heterogeneity of temperature-dependent Pfr states is presented at the atomistic level. This work paves a way toward understanding the complete mechanism of the photoisomerization of a bilin-like chromophore in phytochromes.

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