GAMMA RAY THERMOLUMINESCENCE IN NUCLEIC ACID CONSTITUENTS

Abstract— The phenomenon of gamma ray thermoluminescence has been studied in DNA, RNA, and their various constituents. Single peaks in the glow curves have been usually observed at 110–120°K except in cytosine which shows two peaks at 135°K and 180°K. Adenine and cytosine show very intense thermoluminescence whereas the intensity of light emitted from thymine, uracil and guanine is very small. The addition of sugar and sugar-phosphate groups to the base-molecules affects only the amount of light emitted. The thermoluminescence emission spectra lie in the same wavelength region as the u.v. induced phosphorescence, suggesting a triplet-singlet transition. The spectral content of DNA thermoluminescence seems to be superposition of contributions from its constituents. An attempt is made to explain the phenomenon as a result of electron-cation recombination.     

Thermoluminescence from photoexcited polyethylene terephthalate

Thermoluminescence from polyethylene terephthalate (PET) has been investigated. A correlation was found between thermoluminescence (TL) and thermally stimulated current (TSC). The apparent activation energy was estimated at 0.23–0.50 eV for both TSC and TL from ?170 to 0°C. This activation energy presumably indicates the trap depth, which is decreased by molecular motions, since both TSC and TL are quenched efficiently with visible light, but not with infrared light of energy of the magnitude of thermal activation energy. The spectrum of TL glow curves agrees with the photoluminescence spectrum at ?185°C, which is composed of an excimer and a monomer fluorescence and also a structured phosphorescence at wavelengths longer than 400 nm.     

ISOTHERMAL LUMINESCENCE AND THERMO-LUMINESCENCE OF NUCLEIC ACID BASES FOLLOWING γ-IRRADIATION

Abstract— The emission spectra of radiation induced isothermal luminescence (ITL) and the thermolu-minescence (TL) of purines and pyrimidines of nucleic acids and analogue 6-azauracil in the form of pellets of dry polycrystalline powders have been studied at 77 K, and compared with their low temperature fluorescence and phosphorescence spectra. The qualitative and quantitative measurements of isothermal luminescence and thermoluminescence show that the two result from the same radiative transitions. The thermoluminescence emission was observed to coincide with the phosphorescence emission of the compounds in all the cases. The thermoluminescence of the pyrimidines and their analogue, however, have shown an additional component corresponding to their fluorescence in the ultraviolet region. An extension of the Weissbluth model based on the location of the electron traps in relation to the excited states of the compounds is proposed to explain their thermoluminescence emission.     

ON THE ORIGIN OF LOW TEMPERATURE THERMOLUMINESCENCE IN NUCLEIC ACID BASES: EXCITATION AND EMISSION SPECTRAL STUDIES

Abstract. Thermoluminescence excitation spectra of adenine, guanine, thymine and 1,3-dimethyluracil were observed to be similar to their phosphorescence excitation spectra. Intensity dependence studies of thermoluminescence induced by ultraviolet light suggest that thermoluminescence could not be due to biphotonic ionisation of the molecule by UV. Evidence is presented which demonstrates that the fluorescence component observed in thermoluminescence of some compounds may not be due to triplet-triplet fusion. Further, phosphorescence and thermoluminescence measurements following excitation with monochromatic light at very low intensities and short durations have shown for both a linear dependence on excitation intensity. It thus appears that direct entry of the electrons from the traps into the singlet manifold is necessary for explaining the fluorescence component of thermoluminescence.     

TRYPTOPHAN PHOSPHORESCENCE AT ROOM TEMPERATURE AS A TOOL TO STUDY PROTEIN STRUCTURE AND DYNAMICS

Fluorescence and phosphorescence resemble each other and in many ways can give the same type of information. Both originate from a dipolar interaction between light and the molecule. In this regard, both are polarized and subject to the same type of quenching phenomena. In other respects the information which they divulge are complementary. The fluorescence quantum yield is higher for exposed tryptophans and this is expressed in longer lifetime (Grinvald and Steinberg, 1976); in contrast long lifetime of phosphorescence appears to correlate with burial. Phosphorescence, spin-disallowed, is much longer lived than fluorescence. This allows the structural/dynamic characterization of proteins to be studied on a new time regime. A really remarkable finding of studies of protein phosphorescence is that there is such variability both in phosphorescence lifetime and quenchability. We would interpret this to indicate that the tryptophan environment can range from essentially a crystal, almost comparable in rigidity as found at 77 K, to tryptophans in a flexible environment, almost as flexible as free in solution. An interesting task will be to examine the relationship between the yield and lifetime of phosphorescence and details of the tryptophan environment in terms of rigidity and adjacent amino acids among the proteins with known three dimensional structure.     

Phosphorescence from pyrimidine vapor

The phosphorescence from pyrimidine vapor has been observed by a method of time-resolved laser spectroscopy. The phosphorescence spectrum commences at 350.5 nm and consists mainly of three totally symmetric vibrations in the ground state, v_6a, v₁₂ and v_9a as in the case of the zero-point vibrational level fluorescence of pyrimidine vapor. The phosphorescence quantum yield and lifetime are found to be about 1 × 10^?4 and 50 μs.     

Phosphorescence and its characteristics in pyridine vapor

The phosphorescence emission of pyridine-d₀ and -d₅ has been observed in the vapor phase by means of time-resolved spectroscopy. The results of the experiments, which are described in full detail in this paper, on the phosphorescence spectrum, the excitation spectrum, the phosphorescence decay and sensitization of biacetyl phosphorescence indicate that the emission concerned is the genuine phosphorescence of the pyridines. For pyridine-d₀ (-d₅), the wavelength of the phosphorescence maximum is 450 nm (440 nm), the phosphorescence quantum yield 1.5 × 10^?6) (1.7 × 10^?6) and the phosphorescence lifetime is 1.2 μs (2.1 μs), the values for pyridine-d₅ being given in parentheses. The phosphorescence characteristics of pyridine are compared with those of other related molecules. The nature of the phosphorescent triplet state of pyridine is discussed with particular regard to the exceptionally fast non-radiative decay from that state.     

Tict fluorescence in rigid matrices: α-delayed fluorescence

The observation of the dual fluorescence of 4-N,N-dimethylaminobenzonitrile (DMABN) in polyvinylalcohol has been extended to other matrices able to act as hydrogen-bond donors (nylon and polyurethane) and to related molecules. A model of α-delayed fluorescence is proposed to account for the properties of the luminescence in rigid matrices. This proposal is consistent with: the positive polarization of the anomalous fluorescence (room temperature) while the polarization of phosphorescence is negative (at 77 K); the quenching of the anomalous fluorescence by lowering the temperature; the very long lifetime (τ ≈ 1 s) of the anomalous fluorescence, in the same range as the phosphorescence lifetime.     

The nature of the lowest triplet configuration of flavins

Abstract— The phosphorescence spectrum of riboflavin has been reexamined at 77°K in an ethylene glycol: water matrix. The phosphorescence occurs at approximately the 605 nm (ca. 2-·05 eV) region, in reasonable agreement with the theoretical calculations of 1·6–1·8 eV [21]. The emission was found to be negatively polarized, and to have a relatively long lifetime (0·56 sec). On the basis of this data and additional theoretical results, it is concluded that the lowest triplet of riboflavin is of ³(τ,τ*) type. Upon addition of potassium iodide, the phosphorescence emission is enhanced through spin-orbit perturbation. The presence of oxygen (atmospheric pressure) in the frozen glass apparently has no effect on the emission. The phosphorescence spectra of alloxazine are also presented. Results of the present work have been applied to the photodephosphorylation of menadiol diphosphate in elucidating its mechan ism involving the riboflavin triplet and singlet oxygen.     

Excitation pulse deconvolution in luminescence lifetime analysis for oxygen measurements in vivo

Oxygen-dependent quenching of phosphorescence has been proven to be a valuable tool for the measurement of oxygen concentrations both in vitro and in vivo. For biological measurements the relatively long lifetimes of phosphorescence have promoted time-domain-based devices using xenon arc flashlamps as the most common excitation light source. The resulting complex form of the excitation pulse leads to complications in the analysis of phosphorescence lifetimes and ultimately to errors in the recovered pO2 values. Although the problem has been recognized, the consequences on in vivo phosphorescence lifetime measurements have been neglected so far. In this study, the consequences of finite excitation flash duration are analyzed using computer simulations, and a method for the recovery of phosphorescence decay times from complex photometric signals is presented. The analysis provides an explanation as to why different calibration constants are reported in the literature and presents a unified explanation whereby calibration constants are not solely a property of the dye but also of the measuring device. It is concluded that complex excitation pulse patterns without appropriate analysis methods lead to device-specific calibration constants and nonlinearity and can be a potent source of errors when applied in vivo. The method of analysis presented in this article allows reliable phosphorescence lifetime measurements to be made for oxygen pressure measurements and can easily be applied to existing phosphorimeters.     

沉淀法合成蓝色长余辉发光材料Sr_2MgSi_2O_7:Eu~(2+),Dy~(3+)

采用沉淀法制备了高亮度的长余辉发光材料Sr_2MgSi_2O_7:Eu~(2+),Dy~(3+).通过XRD、荧光光谱和热释光谱对其进行表征.XRD测试表明所制备的Sr_2MgSi_2O_7:Eu~(2+),Dy~(3+),四方晶.荧光光谱测试表明,λ_(em)=467 nm作为监控波长,在275～450 nm之间有宽的激发光谱,峰值位于399 nm.用λ=399 nm激发样品,其发射光谱为一宽带,峰值位于467 nm.1050℃煅烧前躯体所制备的Sr_2MgSi_2O_7:Eu~(2+),Dy~(3+)发光性能最好.热释光谱峰值位于357 K,适合长余辉现象的产生.对Sr_2MgSi_2O_7:Eu~(2+),Dy~(3+)长余辉发光机理进行了讨论.     

Room-temperature metal-activator-free phosphorescence from mesoporous silica

Room-temperature phosphorescence has been observed and studied on metal-activator-free mesoporous silica. The mesoporous silica was prepared using a nonionic triblock copolymer as the mesostructure-directing agent. The as-calcined products have a well-ordered porous structure and exhibit strong phosphorescence under ultraviolet light excitation. The luminescence spectra are featured with several peaks in the visible region. The luminescence intensity is found to vary as a function of the calcination temperature and reach a maximum around 500-600 °C, but the peak positions remain nearly unchanged. The average luminescence lifetime is several hundred microseconds, and the luminescence can persist for seconds after the excitation is switched off. In addition, due to the moderate calcination temperature, phosphorescent mesoporous silica monoliths with controllable sizes and shapes have been fabricated. Such mesoporous silica materials, including both powders and monoliths, with strong phosphorescence could find promising applications as low-density and eco-friendly phosphors and optically detectable drug carriers.     

Self-Assembled Helical Arrays for the Stabilization of the Triplet State

Room-temperature phosphorescence of metal and heavy atom-free organic molecules has emerged as an area of great potential in recent years. A rational design played a critical role in controlling the molecular ordering to impart efficient intersystem crossing and stabilize the triplet state to achieve room-temperature ultralong phosphorescence. However, in most cases, the strategies to strengthen phosphorescence efficiency have resulted in a reduced lifetime, and the available nearly degenerate singlet-triplet energy levels impart a natural competition between delayed fluorescence and phosphorescence, with the former one having the advantage. Herein, an organic helical assembly supports the exhibition of an ultralong phosphorescence lifetime. In contrary to other molecules, 3,6-phenylmethanone functionalized 9-hexylcarbazole exhibits a remarkable improvement in phosphorescence lifetime (>4.1 s) and quantum yield (11 %) owing to an efficient molecular packing in the crystal state. A right-handed helical molecular array act as a trap and exhibits triplet exciton migration to support the exceptionally longer phosphorescence lifetime.     

Time-resolved fluorescence spectra using time-correlated photon counting: Picosecond fluorescence in aqueous solutions of Cr(III) complexes at room temperature

A new procedure for measuring time-resolved emission spectra has been implemented. This technique has subnanosecond time resolution combined with the sensitivity and dynamic range needed to cope with extremely weak luminescence. Using this method the emissions of Cr(NH₃)₂ (NCS)₄^? and Cr(NCS)₆^3- in aqueous solution at room temperature have each been analyzed into two components. The fast component has a broad spectrum and is assigned to prompt fluorescence with lifetime below 100 ps. The slow component is dominated by phosphorescence but may include some delayed fluorescence. The phosphorescence lifetime is 5.5 ± 0.5 ns in Cr(NH₃)₂ (NCS)₄^? and 1.65 ± 0.1 ns in Cr(NCS)₆^3-. Order of magnitude estimates have been derived for other photophysical parameters.     

Self‐Assembled Helical Arrays for the Stabilization of the Triplet State

Room‐temperature phosphorescence of metal and heavy atom‐free organic molecules has emerged as an area of great potential in recent years. A rational design played a critical role in controlling the molecular ordering to impart efficient intersystem crossing and stabilize the triplet state to achieve room‐temperature ultralong phosphorescence. However, in most cases, the strategies to strengthen phosphorescence efficiency have resulted in a reduced lifetime, and the available nearly degenerate singlet‐triplet energy levels impart a natural competition between delayed fluorescence and phosphorescence, with the former one having the advantage. Herein, an organic helical assembly supports the exhibition of an ultralong phosphorescence lifetime. In contrary to other molecules, 3,6‐phenylmethanone functionalized 9‐hexylcarbazole exhibits a remarkable improvement in phosphorescence lifetime (>4.1 s) and quantum yield (11 %) owing to an efficient molecular packing in the crystal state. A right‐handed helical molecular array act as a trap and exhibits triplet exciton migration to support the exceptionally longer phosphorescence lifetime.     

Effect of pH on the absorption and emission characteristics of di(3-pyridyl)ketone

The absorption and emission properties of di(3-pyridyl)ketone have been studied in aqueous solution as a function of pH and the pKs of the nitrogen protonated mono- and di-cations have been spectrophotometrically determined. This molecule exhibits room temperature and low temperature phosphorescence emission of n, π* character in the whole acidity range explored [pH 9/(H₀ − 9)]; triplet lifetime has been measured from the phosphorescence intensity decay.An unusual trend of phosphorescence intensity and lifetime as a function of pH was found and was interpreted as due to hydrogen bond formation with the solvent, whose entity is influenced by both structure breaking of water and protonation of the nitrogen atoms caused by decreasing pH. Experiments carried out in the presence of sodium acetate are described which support this hypothesis.Comparison of the results obtained with those for benzophenone and phenyl(3-pyridyl)ketone allows some generalizations to be drawn about the influence of the heteroatom on the photophysics of ketones.     

Multivalent supramolecular assembly with ultralong organic room temperature phosphorescence,high transfer efficiency and ultrahigh antenna effect in water

Multivalent supramolecular assemblies have recently attracted extensive attention in the applications of soft materials and cell imaging. Here, we report a novel multivalent supramolecular assembly constructed from 4-(4-bromophenyl)pyridine-1-ium bromide modified hyaluronic acid (HABr), cucurbit[8]uril (CB[8]) and laponite® clay (LP), which could emit purely organic room-temperature phosphorescence (RTP) with a phosphorescence lifetime of up to 4.79 ms in aqueous solution via multivalent supramolecular interactions. By doping the organic dyes rhodamine B (RhB) or sulfonated rhodamine 101 (SR101) into the HABr/CB[8]/LP assembly, phosphorescence energy transfer was realized with high transfer efficiency (energy transfer efficiency = 73–80%) and ultrahigh antenna effect (antenna effect value = 308–362) within the phosphorescent light harvesting system. Moreover, owing to the dynamic nature of the noncovalent interactions, a wide-range spectrum of phosphorescence energy transfer outputs could be obtained not only in water but also on filter paper and a glass plate by adjusting the donor–acceptor ratio and, importantly, white-light emission was obtained, which could be used in the application of information encryption.

An ultralong lifetime supramolecular assembly was constructed via multivalent supramolecular interactions and achieved phosphorescence light harvesting. Multicolor (including white) broad-spectrum outputs could be achieved in water and also on filter paper and a glass plate.     

Differentiation of the local structure around tryptophan 51 and 64 in recombinant human erythropoietin by tryptophan phosphorescence

Abstract Recombinant human erythropoietin is a 4-helix bundle, glycosylated cytokine containing three tryptophan residues at positions 51, 64 and 88 whose phosphorescence emission may represent a sensitive probe of the structure at multiple sites near or at the protein surface. This report characterizes the phosphorescence properties (spectral energy, thermal spectral relaxation and phosphorescence lifetime), from low temperature glasses to ambient temperature, of the native protein plus that of three single point mutation analogs where each Trp was replaced by Phe. The structural information inferred from the phosphorescence parameters was essentially in good agreement with the structure of the Escherichia coli-produced nonglycosylated protein determined by nuclear magnetic resonance (Cheetham et al., Nat Struct Biol [1998] 5:861). The results showed that the fluorescence and phosphorescence spectra of the native protein were entirely due to independent contributions of Trp51 and Trp64 and that Trp88 was quenched under all conditions. The phosphorescence emissions of Trp51 and Trp64 were differentiated by their unique spectra at 77 K with Trp64 exhibiting an unusually blueshifted spectrum likely due to the attractive interaction of Arg110 and Lys116 with the ground state dipole of Trp64. In the native protein the room temperature phosphorescence lifetime of Trp64 was relatively short with a time of 1.62 ms whereas the lifetime of Trp51 was five-fold longer. Characterization of the single point mutation analogs showed that each lifetime was composed of multiple components revealing the presence of multiple stable conformations of the protein at these surface sites.     

ROOM-TEMPERATURE PHOSPHORESCENCE FROM AZURIN DERIVATIVES. PHOSPHORESCENCE QUENCHING IN OXIDIZED NATIVE AZURIN

The tryptophan phosphorescence from a series of derivatives of Pseudomonas aeruginosa azurin has been monitored at 30 degrees C in pH 8.5 buffer solution. The phosphorescence lifetimes fall in the range of 230-270 ms for deoxygenated solutions of derivatives containing Cd(II), Cu(I), Co(II), Ni(II), Hg(II) or apoazurin. A weak signal with a lifetime of ca 130 ms is observed from solutions of oxidized native azurin, but this component is ascribed to a modified form of azurin in solution, i.e. protein heterogeneity, on the basis of the unique sensitivity to quenching by dioxygen. Aside from this minor component, the tryptophan phosphorescence in the Cu(II) protein appears to be fully quenched. The quenching is assigned an electron-transfer mechanism involving transient reduction of the metal center. The same mechanism is deemed to be responsible for fluorescence quenching in oxidized native azurin as well. These observations are of interest because aromatic groups like tryptophan may be conduits for physiological electron-transfer processes involving the copper center.     

ZnO-B2O3∶Tb3+长余辉玻璃的发光性质

通过还原方法制备了Tb³⁺离子掺杂的硼酸锌玻璃，并观察到在254 nm紫外光激发后有明亮的绿色长余辉发光现象，余辉时间达6 h。通过激发与发射光谱、余辉光谱、余辉衰减曲线、热释光谱、热释光释出速率衰减曲线等得到的信息，研究了Tb³⁺离子掺杂的硼酸锌玻璃的发光性质。