COMPARISON OF THE SOLID-MATRIX LUMINESCENCE PROPERTIES AND PHOTOPHYSICAL PARAMETERS OF TWO PRODUCTS FROM BENZO(a)PYRENE-DNA ADDUCTS

Abstract: The solid-matrix luminescence properties and several calculated photophysical parameters of two important products from the benzo(a)pyrene-DNA adducts were compared. The products were benzo(a)pyrene-r-7,t-8,9,c-10-tetrahydrotetrol (I-1) and 7R,8S,9S-trihydroxy-10-( N ²-deoxyguanosyl-3'-phosphate)-7,8,9,10-tetrahydroben-zo(a)pyrene (BPDE-dG). The solid-matrix luminescence data were obtained for I-1 and BPDE-dG adsorbed on two different solid matrices, namely, 1%α-cyclodextrin (CD)/NaCl and 25% trehalose/NaCl and at two different temperatures (93 K and 296 K). The 25% trehalose/NaCl gave higher fluorescence and phosphorescence quantum yields from both I-1 and BPDE-dG in contrast to the 1%α-CD/NaCl matrix. The BPDE-dG showed lower fluorescence quantum yields on the solid matrices compared to I-1. The lower fluorescence quantum yields for BPDE-dG were attributed to a photoinduced electron transfer mechanism. In contrast to the room-temperature solution fluorescence of BPDE-dG, BPDE-dG gave rather high fluorescence quantum yields at room temperature when adsorbed on the two solid matrices. From solid-matrix luminescence quantum yields and solid-matrix luminescence lifetimes, many photophysical parameters were calculated and compared. Several differences among the rate constants were noted with the two solid matrices for BPDE-dG and I-1. For example, BPDE-dG showed internal conversion at 296 K with 25% trehalose/NaCl, but no internal conversion was observed at 93 K with this solid matrix. Also, for BPDE-dG the phosphorescence rate constants at 296 K and 93 K were very small with 25% trehalose/NaCl, but the intersystem crossing rate constants from the triplet state to the ground state were very large. The results from this work show how solid-matrix luminescence can be employed to obtain unique luminescence information from the I-1 and BPDE-dG systems.     

COMPARISON OF THE SOLID-MATRIX LUMINESCENCE PROPERTIES OF BENZO(a)PYRENE-DNA ADDUCTS ON α-CYCLODEXTRIN/NaCl and TREHALOSE/NaCl MATRICES

Abstract— The solid-matrix luminescence properties of (±)- trans -7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene-DNA ([±]-anti-BPDE-DNA) adducts were compared on α-cyclo-dextrin (CD)/NaCl and trehalose/NaCl solid matrices. Both the optimum composition for the solid matrices and the best solvent system were obtained experimentally for acquiring the maximum room-temperature fluorescence (RTF) and room-temperature phosphorescence (RTP) signals for the (±)- anti -BPDE-DNA. Most of the solid-matrix RTF and RTP data were obtained at 296 K and 93 K for (±)-anti-BPDE-DNA adducts adsorbed on 1%α-CD/NaCl and 80% trehalose/NaCl. The RTF signals were strong for (±)-BPDE-DNA adducts on both solid matrices, but RTP was only obtained on the trehalose/NaCl solid matrices with the 80% trehalose yielding the strongest RTP signal for (±)-anti-BPDE-DNA. The fluorescence lifetime data for (±)-anti-BPDE-DNA gave two components on 1 %α-CD/NaCl. For 80% trehalose/NaCl, three components were revealed, but two components were obtained with 80% trehalose/NaCl after ether extraction of the solid matrix. The third component was ascribed to the formation of the tetrols from (±)- anti -BPDE-DNA adducts during the drying step in the sample preparation of 80% trehalose/NaCl. The results give the first reported data on the solid-matrix luminescence of the (±)- anti -BPDE-DNA adducts. These results should be of considerable interest not only from an analytical viewpoint but as a new means of studying the luminescence characteristics of the adducts.     

Luminescence Properties and Analytical Figures of Merits of Benzo(a)Pyrene Guanosine Adduct Adsorbed on α- β- and γ-Cyclodextrin/NaCl,and Trehalose/NaCl Solid Matrices

Abstract

Several cyclodextrin/NaCl and trehalose/NaCl mixtures were investigated as solid matrices for obtaining room-temperature luminescence from a benzo(a)pyrene (B(a)P) guanosine adduct. Room-temperature fluorescence (RTF) and room-temperature phosphorescence (RTP) intensities from the B(a)P-guanosine adduct were compared for different solid matrices. These results showed that 25% trehalose/NaCl, 1% α-cyclodextrin/NaCl, and 1% γ-cyclodextrin/NaCl solid matrices yielded strong fluorescence signals and moderately strong phosphorescence signals at room temperature from the B(a)P-guanosine adduct. In addition, the luminescence properties of pyrene, guanosine, guanosine 3′ -monophosphate free acid and guanosine 3′-monophosphate sodium salt on 1% α-, β-, and γ- cyclodextrin/NaCl solid matrices were obtained.     

Luminescence Properties and Analytical Figures of Merit of the Tetrols of Benzo(A)Pyrene-Dna Adducts Adsorbed on α-, β- and γ- Cyclodextrin/Nacl Mixtures

Abstract

Several cyclodextrin/NaCl mixtures were investigated as solid matrices for obtaining room-temperature phosphorescence (RTP) and room-temperature fluorescence (RTF). The optimum experimental conditions for obtaining both RTF and RTP for the four tetrols were explored. Also, luminescence spectra, limits of detection, and linear ranges for calibration curves were acquired. This is the first report of the solid-matrix luminescence analytical figures of merit for the tetrols on cyclodextrin solid matrices.     

Solid-Phase microextraction with Whatman 1PS paper and direct room-temperature solid-matrix luminescence analysis

Solid-phase microextraction has been combined with solid-matrix luminescence for the detection of a variety of compounds at sub-nanogram levels for the first time. Whatman 1PS paper was placed in water solutions of polar and nonpolar compounds for the selective removal of the nonpolar compounds such as benzo(a)pyrene. Distribution constants were obtained for 4-phenylphenol, benzo(f)quinoline, benzo(h)quinoline, phenanthrene, and benzo(a)pyrene. The distribution constants showed that phenanthrene and benzo(a)pyrene in water had a very strong affinity for the 1PS paper. Once the solutes were extracted for a fixed period of time, the 1PS paper was dried, and either the solid-matrix fluorescence or solid-matrix phosphorescence was detected from the adsorbed lumiphors by using the appropriate excitation wavelengths. It was a simple matter to detect at least three adsorbed compounds on the 1PS paper by solid-matrix luminescence. Benzo(a)pyrene was easily detected at a level of 0.02 ng ml⁻¹ in water.     

The solid-matrix room-temperature luminescence detection and characterization of polyaromatic hydrocarbons without a heavy atom

A selective and sensitive method to detect polyaromatic hydrocarbons (PAH) using a new solid-matrix room-temperature luminescence technique is presented. The solid-matrix room-temperature fluorescence (SMRTF) and phosphorescence (SMRTP) of PAH can be readily obtained by adsorbing a PAH on Whatman 1PS filter paper. Strong phosphorescence can be detected without adding a heavy atom. Detection limits, ranging from 0.12 to 18 ng, were obtained for several PAH.     

Analytical and mechanistic aspects of the room-temperature fluorescence and phosphorescence of benzo(f)quinoline adsorbed on silica gel chromatoplates with humidified gases

The solid-matrix room-temperature fluorescence and room-temperature phosphorescence properties of benzo(f)quinoline adsorbed on silica gel chromatoplates were investigated over a wide range of humidities in N(2), air and O(2). Both neutral and acidic conditions were used and even at the highest relative humidity used, 93% relative humidity, the room-temperature fluorescence and phosphorescence intensities from benzo(f)quinoline were not totally quenched. However, in all experiments, the room-temperature phosphorescence was much more sensitive to humidity quenching than the room-temperature fluorescence. The results gave rather detailed information on quenching of the room-temperature fluorescence and phosphorescence in the different gases at a variety of humidities. It was possible to calculate the contribution to the percent decrease in luminescence due to moisture or a quenching gas. Thus, a more detailed assessment could be made about the quenching of moisture and individual quenching gases on the solid-matrix fluorescence and phosphorescence.     

Comparison of the Solution Luminescence Properties and Solid-Matrix Luminescence Properties of 2-Amino-1-Methyl-6-Phenylimidazo[4,5-B]Pyridine

Abstract

The solution fluorescence properties of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were compared with the solid-matrix luminescence properties of PhIP. The fluorescence properties were obtained in ethanol and several binary solutions of ethanol:water. An ethanol solution of PhIP gave a very strong fluorescence signal and the ethanol:water solutions only showed a small increase in the fluorescence signal. Acidic solutions of PhIP in ethanol:water (7:3) showed a major decrease in fluorescence intensity with at HCl of 10^?4 M and greater, but NaOH solutions of PhIP did not affect the fluorescence intensity to any great extent. Both acidic and basic solutions gave fluorescence emission spectra that were shifted to longer wavelengths. Solid-matrix room-temperature fluorescence (SMRTF) and solid-matrix room-temperature phosphorescence (SMRTP) were readily obtained on filter paper. SMRTP showed some distinct advantages over SMRTF and gave a limit of detection of 0.2 ng on filter paper. Several aspects of both solution luminescence and solid-matrix luminescence of PhIP are discussed.     

Solution interactions and solid-matrix interactions in beta-cyclodextrin solid-matrix luminescence

A variety of liquid chromatographic, solution fluorescence, and extraction data were obtained in an attempt to correlate solution interactions with solid-matrix interactions for solute-beta-cyclodextrin complexes. From the chromatographic data, dissociation constants were calculated for the complexes. Fluorescence spectral characteristics were obtained for sodium chloride, glucose, and beta-cyclodextrin solutions of several solutes. In addition, extraction experiments were performed in an attempt to remove the solutes from the beta-cyclodextrin solid matrix. Generally, the results revealed that there were no simple correlations between the solution data and solid-matrix luminescence data. However, the extraction results yielded important information related to the solute interactions in the solid matrix.     

Separation and characterization of tetrol metabolites of benzo[a]pyrene-DNA adducts using HPLC and solid-matrix room temperature luminescence

Four tetrols of benzo[a]pyrene-DNA adducts were separated using reversed-phase high performance liquid chromatography. Chromatographic fractions containing a given tetrol were readily characterized with solid-matrix room temperature luminescence techniques. Solid-matrix fluorescence and phosphorescence spectra at picogram amounts of a tetrol were easily obtained. Tetrol fractions collected based on retention times, but with no response from the ultraviolet detector, were characterized by solid-matrix luminescence spectra at very small quantities.     

The Effects of Salts on the Room-Temperature Fluorescence and Room-Temperature Phosphorescence of Tetrols on Filter Paper and Filter Paper with Silicone

Abstract

Several salts were investigated to enhance the room-temperature solid-matrix phosphorescence of the four stereoisomeric tetrols on filter paper. Thallium acetate was found to enhance the phosphorescence to the greatest extent, but it was necessary to prepare the thallium acetate in an acetic acid solution to achieve the maximum phosphorescence from the solid matrix. Also, thallium acetate essentially quenched the solid-matrix fluorescence of the tetrols. Without thallium acetate adsorbed on filter paper, strong room-temperature fluorescence signals were observed from the tetrols adsorbed on filter paper. With a new solid matrix, filter paper which contained silicone, no heavy-atom was needed to obtain strong phosphorescence from the adsorbed tetrols. In fact, the room-temperature fluorescence from the tetrols adsorbed on this type of filter paper was very strong. The room-temperature fluorescence gave a limit of detection in the sub-picogram range for one of the tetrols with the silicone treated filter paper.     

Hydrogen bonding-induced oxygen clusters and long-lived room temperature phosphorescence from amorphous polyols

Developing non-conjugated luminescent polymers (NCLPs) with fluorescence and long-lived room-temperature phosphorescence is of great significance for revealing the essence of NCLPs luminescence, which has gradually attracted the attention of researchers in recent years. Herein, polymethylol (PMO) and poly(3-butene-1,2-diol) (PBD) with polyhydroxy structures were prepared and their luminescence behaviors were investigated to reveal the clusteroluminescence (CL) mechanism. Compared with polyvinyl alcohol with non-luminescent behavior, PMO and PBD exhibit cyan-blue fluorescence with quantum yields of ca. 12% and green room-temperature phosphorescence with lifetimes of ca. 89 ms in the solid state. Both fluorescence and phosphorescence exhibit typical excitation-dependent CL behavior. Experimental and theoretical analyses show that the strong hydrogen-bonding interaction of PMO and PBD greatly promotes the formation of oxygen clusters and the through-space n-n interaction of oxygen atoms, enabling fluorescence and phosphorescence emission. Our results have enormous implications for understanding the CL mechanism of NCLPs and provide a new polymer design strategy for the rational design of novel NCLPs materials.     

Electronic spectra and luminescence properties of 1,2-benzotetraphene in crystalline matrices at 77 K

Quasilinear absorption and luminescence spectra of 1,2-benzotetraphene were obtained in polycrystalline matrices at 77 K. Tne energies of successive excited singlet states as well as the energy of the lowest excited triplet state were found experimentally and compared with those calculated by the PPP CI method. The fluorescence lifetime and quantum yield were determined experimentally. Moreover, the radiationless transition probabilities, lifetime of triplet state and phosphorescence quantum yield were estimated employing the Siebrand-Williams model. The results obtained suggest that radiationless ISC processes are the main deactivation channel of the S₁ and T₁ states. The vibrational analysis of quasilinear absorption and luminescence spectra was performed and fundamental frequencies of ground and first excited singlet states were determined.     

FLUORESCENT TAUTOMERS AND THE APPARENT PHOTOPHYSICS OF ADENINE AND GUANINE

Abstract— Fluorescence, absorption and fluorescence excitation spectra, and quantum yields of 0.02 mM solutions of adenine, 7-methyladenine (7-MA), guanine and 7-melhylguanine (7-MG) are presented for excitation with240–300 nm light. The solvent is neutral ethylene glycol-water (70:30 v/v) in the temperature range140–165 K. Phosphorescence spectra of adenine and 7-MA at 140 K are also presented. The excitation spectrum of adenine shows vibrational structure, whereas the absorption does not. However, the fluorescence of adenine shows the vibrational structure, as do the absorption, fluorescence and excitation spectra of 7-MA. The results confirm (and reinforce) the notion that luminescence from adenine under these conditions is from the N₇–H tautomer, instead of the more abundant N₉–H form. In a similar fashion, the data from guanine and 7-MG strongly suggest that the luminescence from guanine is also mostly from the N₇–H tautomer.     

Excited state properties of oligophenyl and oligothienyl swivel cruciforms

A comprehensive study has been undertaken of the electronic spectral and photophysical properties of two oligophenyl (BPH and BPHF) and one oligothienyl (BTF) swivel cruciforms involving measurements of absorption, fluorescence, and phosphorescence spectra, quantum yields of fluorescence (phiF), phosphorescence (phiPh) and triplet formation (phiT), lifetimes of fluorescence (tauF) and of the triplet state (tauT), and quantum yields of singlet oxygen production (phiDelta). From these, all radiative kF and radiationless rate constants, kIC and kISC, have been obtained in solution. The energies of the lowest lying singlet and triplet excited states were also determined at 293 K. Several of the above properties have also been obtained at low temperature and in the solid state (thin films). In general, for the phenyl oligophenyl (BPH) and for the oligothienyl (BTF) compounds, the radiationless decay channels (phiIC+phiISC) are the dominant pathway for the excited-state deactivation, whereas with the fluorene based oligophenyl BPHF the radiative route prevails. In contrast to the general rule found for related oligomers (and polymers) where radiative emission from T1 is absent, with the compounds studied, phosphorescence has been observed for all of the compounds, indicating that this type of functionalization can lead to emissive triplets. Time-resolved fluorescence decays with picosecond resolution revealed multiexponential (bi- and triexponential) decay laws compatible with the existence of more than one species or conformation in the excited state. These results are discussed on the basis of conformational flexibility in the excited state.     

THE PHOTOCHEMISTRY OF RIBOFLAVIN—VI. THE PHOTOPHYSICAL PROPERTIES OF ISOALLOXAZINES

Abstract— Many of the photophysical properties of riboflavin and several other N-10 substituted isoal-loxazines have been measured and these include: quantum yields of fluorescence at 77 K and 298 K, φ, quantum yields of phosphorescence at 77 K, φ_P, lifetimes of the triplet state by electron spin resonance and phosphorescence at 77 K, φp,. and the quantum yield of intersystem crossing. φ_isc. For riboflavin in an alcoholic matrix at 77 K the limiting values were: φ _J = 0.32, φ_P= 0.007, φp = 0.20s and φ_isc= 0.7. At 298 K, φ _f for riboflavin in water and alcohol were 0.25 and 0.32, respectively. The results for the photophysical processes are compared with several photochemical processes known to involve the triplet state of riboflavin in aqueous solution. It is concluded that the φ _isc decreases from 0.7 in alcohol to 0.6 in water at 298 K.     

A simple route to incorporate redox mediator into carbon nanotubes/Nafion composite film and its application to determine NADH at low potential

Several new sugar glasses were investigated for their potential in solid-matrix luminescence. Both solid-matrix fluorescence (SMF) and solid-matrix phosphorescence (SMP) properties were obtained, and two heterocyclic aromatic amines were employed as model compounds. In addition to glucose glasses, which were investigated previously, fructose, ribose, xylose, galactose, maltose, and glucose with poly(acrylic acid) (PAA) were studied. Detailed experimental conditions were obtained for each sugar-glass system. In addition, NaI was investigated as a heavy-atom salt in the sugar-glass systems to enhance the SMP of the heterocyclic aromatic amines. The SMF intensity was the strongest in maltose and glucose with PAA for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and in maltose for 2-amino-9H-pyrido[2,3-b]indole (AαC). The largest SMP signals for PhIP with and without NaI were acquired in glucose with PAA. For AαC with NaI, the strongest SMP signal was obtained in maltose. Limits of detection were obtained for PhIP in the several sugar-glass systems, and the lowest limit of detection was 0.04 pmol/mg of PhIP in maltose with NaI present. An extensive study was carried out using both SMF and SMP to determine if neutral and/or protonated species of PhIP and AαC were in the sugar-glass systems. General guidelines such as glass transition temperature and solubility are discussed for selecting a sugar glass as a solid matrix.     

ON THE LUMINESCENCE OF L-TRYPTOPHANE AND l-TYROSINE IN AQUEOUS SOLUTION AT 77dK INDUCED BY X-RAYS AND U.V.-LIGHT

Abstract— The lumincscence arising from L-tryptophane and L-tyrosine in aqueous solutions at 77K during irradiation with u.v.-light and with X-rays has been studied. The spectra obtained with the two types of radiation were largely similar, differing only in that the yields of phosphorescence relative to fluorescence were considerably enhanced in the case of X-irradiation. The decay times observed for the exponentially decaying phosphorescence, being 6.6 sec and 2.7 sec for tryptophane and tyrosine respectively, were the same for both kinds of irradiation. The G-value of the X-ray induced luminescence was about 10 for both tryptophane and tyrosine. Thus, about 30 per cent of the total energy absorbed from X-rays in these compounds was re-emitted as light.
It was concluded that the X-ray induced fluorescence and phosphorescence originate from the same levels as does the luminescence caused by u.v.-light, i.e. the lowest excited singlet and the lowest triplet level of the aromatic structure of these compounds. In the case of X-irradiation the enhanced ratios between the yields of phosphorescence and fluorescence indicated that some process other than excitation directly from the ground state contributed considerably to the luminescence yields. Assuming this process to be a recombination between the ionized molecule and its electron, it was calculated that the contribution to the luminescence yield from excitations directly from the ground state relative to that from ionizations, was negligible for both compounds.     

Luminescence and Stability of 1,4,5-Triaryl-1,2,3-Triazoles

The fluorescence, phosphorescence, and photochemical properties of di- and triaryl-substituted-1,2,3-triazoles are reported in this work. The ease of synthesis of regioisomers of substituted triazoles enables a systematic study on the correlation between regiochemistry and excited state properties, which include the solvent dependence of fluorescence, energy gap between singlet and triplet emitters, and propensity to photon-triggered transformations. The triazoles that carry electron (e)-donor and e-acceptor aryl substituents show high fluorescence quantum yields in weakly polar solvents and exhibit solvent-dependent fluorescence. The luminescence properties of these compounds in glass matrices at 77 K are characterized. The thermal and photo-stability, two parameters that are crucial to their potential utilities in optical devices, of these compounds are determined. The position of the e-donor substituent has a significant impact on the fluorescence emission energy and solvent sensitivity, singlet-triplet energy gap, and photochemical reactivity and stability. The experimental observations on the structural correlation with the photophysical and photochemical properties are explained by quantum chemical calculations. This study provides a rationale on the placement of substituent on a donor-acceptor type fluorophore to maneuver a range of photo-related properties.     

Photophysics of boron difluoride chelates with dihalogenated tetraphenyl-<Emphasis Type="Italic">ms</Emphasis>-azadipyrromethenes

Spectral, luminescent, and photophysical properties of the BF₂ chelates with dichloroand dibromotetraphenyl-ms-azadipyrromethene (derivatives of tetraphenyl-aza-BODIPY) have been studied experimentally and theoretically by quantum chemistry methods. The positions of fluorescence bands, quantum yields, and lifetimes were measured experimentally. The rate constants of intramolecular photophysical processes have been estimated, and the quantum yields of fluorescence and phosphorescence and the lifetimes of excited states have been calculated. Complete energy schemes of electronically excited states and photophysical processes in the molecules of the compounds under study have been built on the basis of calculation results. The decrease in the fluorescence quantum yields upon excitation into the second absorption band and the absence of the phosphorescence of the chelates have been explained.