Phosphorescence, hydration

Room temperature phosphorescence can be observed from dried proteins. Sheep wool keratin(47) has a phosphorescence lifetime of 1.4 s. Six lyophilized proteins were shown to exhibit phosphorescence at room temperature.(48) The spectra were diffuse, and the lifetime was non-single-exponential, which the authors interpreted as due to inhomogeneous distribution of tryptophans. As the protein was hydrated, the phosphorescence lifetime decreased. This decrease occurred over the same range of hydration where the tryptophan fluorescence becomes depolarized. Hence, these results are consistent with the idea that rigidity of the site contributes to the lifetimes. 

The water lattice may be an important element in forming the ordered thymine structure necessary for dimerization, as pointed out by Beukers and Berends.37 Thymine can crystallize from solution as a monohydrate (a real hydrate)38 in whose crystal lattice one thymine is directly above another. The influence of humidity upon dimer yield in dry films may be connected with monohydrate formation, and monohydrate formation in frozen solutions may be the reason for the almost theoretically maximum quantum yields for dimer formation.31 The possible existence of aggregates in frozen aqueous solutions is supported by a tenfold increase in purine phosphorescence at 44°K produced by the presence of 1% ethanol and by a blue shift of excitation and emission spectra.39... 

The fluorescence polarization excitation spectrum has been measured for thymine in aqueous solution. " The depolarization at the red edge is attributed to the hidden n, ir transition. Ionization of the lowest excited singlet and triplet states have been determined by the effect of pH on the absorption, fluorescence, and phosphorescence spectra of purines and pyrimidines. " Spectral, polarization, and quantum yield studies of cytidylyl-(3, 5 )-adenosine have also been published. Intermediates in the room-temperature flash photolysis of adenine and some of its derivatives have been identified hydrated electron, radical cations and anions, and neutral radicals resulting from their reactions have been assigned. Photoionization occurs via the triplet state. FMN encapsulated in surfactant-entrapped water pools interacts with polar head groups, entrapped water molecules, and outer apolar solvent. ... 

Properties A natural hydrated double chloride of potassium and magnesium, white, brownish, and reddish streak white shining, greasy luster strongly phosphorescent bitter taste. Deliquescent, d 1.62, Mohs hardness 1. 

The phosphorescence of biacetyl (2,3-butadione) can be sensitized by chlorobenzene in the aqueous media and biacetyl Inhibits the photohydrolysis of chlorobenzene (19). Blacetyl in water is hydrated in the proportion of 73.5% ( ) according to the reaction ... 

Naphtalides, alkalides, and alkali metals are sufficiently powerful to reduce Ge and Si salts to the elements. Si nanocrystals have been prepared in solution by the reduction of the halides with Na, Li naphthalide, and hydride reagents [216-219]. Similarly, Ge nanocrystals have been made by the reduction of GeCL with Li naphthalide in THF [217]. TEOS (Si(OEt)4) is readily reduced by sodium to yield Si nanocrystals. Si and Ge nanocrystals are frequently covered by an oxide layer. Y2O3 nanocrystals have been made by the alkalide reduction of YCI3 followed by oxidation by exposure to ambient conditions [220]. Yittria nanocrystals could be doped with Eu to render them phosphorescent [221]. ZnO nanoparticles have been prepared from zinc acetate in 2-propanol by the reaction with water [222]. Pure anatase nanocrystals are obtained by the hydrolysis of TiCL with ethanol at 0°C followed by calcination at 87° C for 3 days [223]. The growth kinetics and the surface hydration chemistry in this reaction have been investigated. 

Activation parameters associated with k were determined at pH 10, 12, and high [OH ], but no dissection into values for the elementary steps was attempted/ The complete thermal, photophysical, and photochemical pathways are summarized in Scheme 1. Very similar results have been obtained for [Cr(bipy)3] " using laser flash photolysis with conductivity and visible spectral detection. However, the pKa of the aquointermediate was found to be less than 2, and it is suggested that this may indicate that this intermediate has a Gillard-type covalent hydrate structure rather than a seven-coordinate chromium(III) structure. The preference, however, is for a seven-coordinate intermediate. Energy transfer from the Eg excited state of [Cr(bipy)3] to a series of cobalt(III) complexes has also been studied. The wavelength dependence of the phosphorescence yields of [Cr(en)3] is also available. ... 

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