scholarly journals Quantum Chemistry of in situ Retinal: Study of the Spectral Properties and Dark Adaptation of Bacteriorhodopsin

1996 ◽  
pp. 235-256
Author(s):  
I. Logunov ◽  
K. Schulten
Keyword(s):  
Quantum Chemistry ◽  
Dark Adaptation ◽  
Spectral Properties

Subcellular localization of phosducin in rod photoreceptors

2005 ◽  
Vol 22 (1) ◽  
pp. 19-25 ◽  
Author(s):  
JING CHEN ◽  
TATSURO YOSHIDA ◽  
KOICHI NAKANO ◽  
MARK W. BITENSKY
Keyword(s):  
Subcellular Localization ◽  
Dark Adaptation ◽  
Outer Segment ◽  
Photoreceptor Cells ◽  
Immunogold Labeling ◽  
Synaptic Function ◽  
Immunogold Electron Microscopy ◽  
Rod Photoreceptors ◽  
Relative Paucity

Phosducin (Pd) is a 28-kD phosphoprotein whose expression in retina appears limited to photoreceptor cells. Pd binds to the β,γ subunits of transducin (Gt). Their binding affinity is markedly diminished by Pd phosphorylation. While Pd has long been regarded as a candidate for the regulation of Gt, the molecular details of Pd function remain unclear. This gap in understanding is due in part to a lack of precise information concerning the total amount and subcellular localization of rod Pd. While earlier studies suggested that Pd was a rod outer segment (ROS) protein, recent findings have demonstrated that Pd is distributed throughout the rod. In this report, the subcellular distribution and amounts of rat Pd are quantified with immunogold electron microscopy. After light or dark adaptation, retinal tissues were fixedin situand prepared for ultrathin sectioning and immunogold labeling. Pd concentrations were analyzed over the entire length of the rod. The highest Pd labeling densities were found in the rod synapse. Less intense Pd staining was observed in the ellipsoid and myoid regions, while minimal labeling densities were found in the ROS and the rod nucleus. In contrast with rod Gt, no evidence was found for light-dependent movement of Pd between inner and outer segments. There is a relative paucity of Pd in the ROS as compared with the large amounts of Gtfound there. This does not support the earlier idea that Pd could modulate Gtactivity by controlling its concentration. On the other hand, the presence of Pd in the nucleus is consistent with its possible role as a regulator of transcription. The functions of Pd in the ellipsoid and myoid regions remain unclear. The highest concentration of Pd was found at the rod synapse, consistent with a suggested role for Pd in the regulation of synaptic function.

2-(3-Acylselenoureido)benzonitriles and 2-(3-Acylselenoureido)thiophene-3-carbonitriles. Preparation, Structure Elucidation, Cyclization and Retrocyclization Reactions

1999 ◽  
Vol 64 (10) ◽  
pp. 1673-1695 ◽  
Author(s):  
Jiří Šibor ◽  
Dalimil Žůrek ◽  
Radek Marek ◽  
Michal Kutý ◽  
Otakar Humpa ◽  
...  
Keyword(s):  
Quantum Chemistry ◽  
Ab Initio ◽  
Potassium Hydroxide ◽  
Potassium Hydroxide Solution ◽  
Quantum Chemistry Calculation ◽  
Potassium Salts ◽  
X Ray ◽  
Chemistry Calculation ◽  
Acid Cyclization

Synthesis of 2-(3-acylselenoureido)benzonitriles and 2-(3-acylselenoureido)thiophene- 3-carbonitriles 5a-5f by addition of 2-aminonitriles 4a-4c to benzoyl- or 2,2-dimethyl- propanoylisoselenocyanate and their cycloaddition reactions are described. Structures of compounds 5a-5f were supported by CIMS, FTIR, 1H, 13C, 77Se and 15N NMR spectra. The parameters of 15N and 77Se nuclei were obtained from inverse 1H-X 2D HMBC and GSQMBC correlation experiments at natural abundance. Structure of compound 5b was confirmed by X-ray analysis. The geometry of 5b was optimized by ab initio RHF/DZVP quantum chemistry calculation. A very good correlation between the calculation and experimental data was found. The geometry of 5e was optimized by ab initio DFT/VWN/DZVP quantum chemistry calculation. It was found that title compounds 5a-5f do not undergo isomerization to acylisoselenoureas, in contrast to analogous ester derivatives. Fused 6-imino-6H-1,3- selenazinium salts (chlorides 6a-6f, hydrogensulfates 7a-7f and tetrafluoroborates 8a-8f) were prepared by an acid cyclization of 5a-5f. It was found that neutralization of 6a-6f, 7a-7f and 8a-8f led to their retrocyclization to 5a-5f. Selenoureas 5a-5f with equimolar amounts of methanolic potassium hydroxide afforded potassium salts 9a-9f. Only the salts 9b, 9c, 9e and 9f of the thiophene series were isolated. Their heating in methanol solution led to deacylation of isoselenoureas 10b and 10c. The in situ prepared compounds 9a and 9d cyclized and deacylated to 4-aminoquinazoline-2-selenole 11a under the same conditions. The compounds 5a-5f and 10a-10c cyclized to fused 4-aminopyrimidine-2-selenols 11a, 11b and 4-aminopyrimidine-2-selenone 12c by boiling in methanolic potassium hydroxide solution.

scholarly journals Characterisation and improvement of <i>j</i>(O<sup>1</sup>D) filter radiometers

2016 ◽  
Author(s):  
Birger Bohn ◽  
Dwayne E. Heard ◽  
Nikolaos Mihalopoulos ◽  
Christian Plass-Dülmer ◽  
Rainer Schmitt ◽  
...  
Keyword(s):  
Cross Sections ◽  
Spectral Properties ◽  
Solar Spectrum ◽  
Field Measurements ◽  
Correction Method ◽  
Quantum Yields ◽  
Photolysis Frequencies ◽  
Filter Radiometer ◽  
Improved Performance

Abstract. Atmospheric O3 → O(1D) photolysis frequencies j(O1D) are crucial parameters for atmospheric photochemistry because of their importance for primary OH formation. Filter radiometers have been used for many years for in-situ field measurements of j(O1D). Typically the relationship between the output of the instruments and j(O1D) is non-linear because of changes in the shape of the solar spectrum dependent on solar zenith angles and total ozone columns. These non-linearities can be compensated by a correction method based on laboratory measurements of the spectral sensitivity of the filter radiometer and simulated solar actinic flux density spectra. Although this correction is routinely applied, the results of a previous field comparison study of several filter radiometers revealed that some corrections were inadequate. In this work the spectral characterisations of seven instruments were revised and the correction procedures were updated and harmonized considering recent recommendations of absorption cross sections and quantum yields of the photolysis process O3 → O(1D). Previous inconsistencies were largely removed using these procedures. In addition, optical interference filters were replaced to improve the spectral properties of the instruments. Successive determinations of spectral sensitivities and field comparisons of the modified instruments with a spectroradiometer reference confirmed the improved performance. Overall, filter radiometers remain a low-maintenance alternative of spectroradiometers for accurate measurements of j(O1D) provided their spectral properties are known and potential drifts in sensitivities are monitored by regular calibrations with standard lamps or reference instruments.

scholarly journals Characterisation and improvement of <i>j</i>(O<sup>1</sup>D) filter radiometers

2016 ◽  
Vol 9 (7) ◽  
pp. 3455-3466 ◽  
Author(s):  
Birger Bohn ◽  
Dwayne E. Heard ◽  
Nikolaos Mihalopoulos ◽  
Christian Plass-Dülmer ◽  
Rainer Schmitt ◽  
...  
Keyword(s):  
Cross Sections ◽  
Spectral Properties ◽  
Solar Spectrum ◽  
Field Measurements ◽  
Correction Method ◽  
Quantum Yields ◽  
Photolysis Frequencies ◽  
Filter Radiometer ◽  
Improved Performance

Abstract. Atmospheric O3 →  O(1D) photolysis frequencies j(O1D) are crucial parameters for atmospheric photochemistry because of their importance for primary OH formation. Filter radiometers have been used for many years for in situ field measurements of j(O1D). Typically the relationship between the output of the instruments and j(O1D) is non-linear because of changes in the shape of the solar spectrum dependent on solar zenith angles and total ozone columns. These non-linearities can be compensated for by a correction method based on laboratory measurements of the spectral sensitivity of the filter radiometer and simulated solar actinic flux density spectra. Although this correction is routinely applied, the results of a previous field comparison study of several filter radiometers revealed that some corrections were inadequate. In this work the spectral characterisations of seven instruments were revised, and the correction procedures were updated and harmonised considering recent recommendations of absorption cross sections and quantum yields of the photolysis process O3 →  O(1D). Previous inconsistencies were largely removed using these procedures. In addition, optical interference filters were replaced to improve the spectral properties of the instruments. Successive determinations of spectral sensitivities and field comparisons of the modified instruments with a spectroradiometer reference confirmed the improved performance. Overall, filter radiometers remain a low-maintenance alternative of spectroradiometers for accurate measurements of j(O1D) provided their spectral properties are known and potential drifts in sensitivities are monitored by regular calibrations with standard lamps or reference instruments.

scholarly journals Spectral Properties of Coniferous Forests: A Review of In Situ and Laboratory Measurements

2018 ◽  
Vol 10 (2) ◽  
pp. 207 ◽  
Author(s):  
Miina Rautiainen ◽  
Petr Lukeš ◽  
Lucie Homolová ◽  
Aarne Hovi ◽  
Jan Pisek ◽  
...  
Keyword(s):  
Spectral Properties ◽  
Coniferous Forests ◽  
Laboratory Measurements
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