Photosensitizing properties and subcellular localisation of 3,4-dihydro-β-carbolines harmaline and harmalol

Harmaline (1) and harmalol (2) represent two 3,4-dihydro-β-carboline (DHβCs) most frequently reported in a vast number of living systems. Fundamental aspects including the photosensitizing properties, cellular uptake, as well as the cyto- and phototoxicity of 1 and 2 were investigated herein. The molecular basis underlying the investigated processes are elucidated. Data reveal that both alkaloids show a distinctive pattern of extracellular DNA photodamage. Compound 1 induces a DNA photodamage profile dominated by oxidised purines and sites of base loss (AP sites), whereas 2 mostly induces single-strand breaks (SSBs) in addition to a small extent of purine oxidative damage. In both cases, DNA oxidative damage would occur through type I mechanism. In addition, a concerted hydrolytic attack is suggested as an extra mechanism accounting for the SSBs formation photoinduced by 2. Subcellular internalisation, cyto- and phototoxicity of 1 and 2 and the corresponding full-aromatic derivatives harmine (3) and harmol (4) also showed quite distinctive patterns in a structure-dependent manner. These results are discussed in the framework of the potential biological, biomedical and/or pharmacological roles reported for these alkaloids.

Graphical abstract

The subtle structural difference (i.e., the exchange of a methoxy group for a hydroxyl substituent at C(7)) between harmaline and harmalol, gives rise to distinctive photosensitizing and subcellular localisation patterns.

Self-Assembled Lanthanide Antenna Glutathione Sensor for the Study of Immune Cells

The small molecule 8-methoxy-2-oxo-1,2,4,5-tetrahydrocyclopenta[de]quinoline-3-carboxylic acid (2b) behaves as a reactive non-fluorescent Michael acceptor, which after reaction with thiols becomes fluorescent, and an efficient Eu³⁺ antenna, after self-assembling with this cation in water. This behavior makes 2b a highly selective GSH biosensor, which has demonstrated high potential for studies in murine and human cells of the immune system (CD4⁺ T, CD8⁺ T, and B cells) using flow cytometry. GSH can be monitored by the fluorescence of the product of addition to 2b (445 nm) or by the luminescence of Eu³⁺ (592 nm). 2b was able to capture baseline differences in GSH intracellular levels among murine and human CD4⁺ T, CD8⁺ T, and B cells. We also successfully used 2b to monitor intracellular changes in GSH associated with the metabolic variations governing the induction of CD4⁺ naïve T cells into regulatory T cells (T_REG).

Studying the reactivity of alkyl substituted BODIPYs: first enantioselective addition of BODIPY to MBH carbonates

The first enantioselective addition of alkyl BODIPYs to Morita-Baylis-Hillman (MBH) carbonates is reported. This is the first reported enantioselective methodology using the methylene position of BODIPYs as a nucleophile. The reaction is efficiently catalyzed by cinchona alkaloids, achieving high enantioselectivities and total diastereoselectivity. The use of cinchona alkaloid pseudo enantiomers (chinine/cinchonine) allows us to obtain both pairs of enantiomers in similar yields and enantioselectivities, a common issue in this type of reaction. The photophysical study of these dyes (absorption and fluorescence) has been performed in order to determine their parameters and explore future possible application in bioimaging. In addition, electronic circular dichroism (ECD) studies supported by time-dependent density functional theory (TD-DFT) calculations were also performed.

N-Methyl-β-carboline alkaloids: structure-dependent photosensitizing properties and localization in subcellular domains

N-Methyl-β-carboline (βC) alkaloids, including normelinonine F (1b) and melinonine F (2b), have been found in a vast range of living species playing different biological, biomedical and/or pharmacological roles. Despite this, molecular bases of the mechanisms through which these alkaloids would exert their effect still remain unknown. Fundamental aspects including the photosensitizing properties and intracellular internalization of a selected group of N-methyl-βC alkaloids were investigated herein. Data reveal that methylation of the βC main ring enhances its photosensitizing properties either by increasing its binding affinity with DNA as a biomolecular target and/or by increasing its oxidation potential, in a structure-dependent manner. As a general rule, N(9)-substituted βCs showed the highest photosensitizing efficiency. With the exception of 2-methyl-harminium, all the N-methyl-βCs investigated herein induce a similar DNA photodamage profile, dominated largely by oxidized purines. This fact represents a distinctive behavior when comparing with N-unsubstituted-βCs. On the other hand, although all the investigated compounds might accumulate mainly into the mitochondria of HeLa cells, methylation provides a distinctive dynamic pattern for mitochondrial uptake. While rapid (passive) diffusion is most probably reponsible for the prompt uptake/release of neutral βCs, an active transport appears to mediate the (reatively slow) uptake of the quaternary cationic βCs. This might be a consequence of a distinctive subcellular localization (mitochondrial membrane and/or matrix) or interaction with intracellular components. Biomedical and biotechnological implications are also discussed herein.

Synthesis, Photophysics, and Solvatochromic Studies of an Aggregated-Induced-Emission Luminogen Useful in Bioimaging

Biological samples are a complex and heterogeneous matrix where different macromolecules with different physicochemical parameters cohabit in reduced spaces. The introduction of fluorophores into these samples, such as in the interior of cells, can produce changes in the fluorescence emission properties of these dyes, caused by the specific physicochemical properties of cells. This effect can be especially intense with solvatofluorochromic dyes, where changes in the polarity environment surrounding the dye can drastically change the fluorescence emission. In this article, we studied the photophysical behavior of a new dye and confirmed the aggregation-induced emission (AIE) phenomenon with different approaches, such as by using different solvent proportions, increasing the viscosity, forming micelles, and adding bovine serum albumin (BSA), through analysis of the absorption and steady-state and time-resolved fluorescence. Our results show the preferences of the dye for nonpolar media, exhibiting AIE under specific conditions through immobilization. Additionally, this approach offers the possibility of easily determining the critical micelle concentration (CMC). Finally, we studied the rate of spontaneous incorporation of the dye into cells by fluorescence lifetime imaging and observed the intracellular pattern produced by the AIE. Interestingly, different intracellular compartments present strong differences in fluorescence intensity and fluorescence lifetime. We used this difference to isolate different intracellular regions to selectively study these regions. Interestingly, the fluorescence lifetime shows a strong difference in different intracellular compartments, facilitating selective isolation for a detailed study of specific organelles.

O–H and (CO)N–H bond weakening by coordination to Fe(ii)

Coordination of hydroxyl/amide groups to Fe(ii) diminishes BDFEs of O–H and (CO)N–H bonds down to 76.0 and 80.5 kcal mol⁻¹ respectively.

Versatile synthesis and enlargement of functionalized distorted heptagon-containing nanographenes

Highly distorted polycyclic aromatic hydrocarbons (PAHs) are predicted to be attractive goals in nanoscience owing to the new properties they can exhibit. We have shown that a variety of functionalized distorted heptagon-containing nanographenes can be easily prepared from simple building blocks by a sequence of Co-catalyzed cyclotrimerization and cyclodehydrogenation reactions. The versatility of this strategy allows easy subsequent enlargement of these nanostructures by Ni-catalyzed cross-coupling and final cyclodehydrogenation reactions. Soluble extended distorted nanographenes 1 and 2 containing heptagon and an edge-shared pentagon-heptagon combination have been synthesized. High distortion of the polycyclic backbone of 2 caused by non-hexagonal rings and a helicene moiety was confirmed by X-ray crystallography. Experimental data reveal promising optical and electronic properties for distorted PAHs with long fluorescence lifetimes (up to 14.5 ns) and low band gaps (down to 2.27 eV). This straightforward and versatile synthetic strategy, the observed long fluorescence lifetimes and the small optical and electrochemical band gaps for the presented compounds may promote the future implementation of distorted graphene molecules in electronic devices.

Stapled helical o-OPE foldamers as new circularly polarized luminescence emitters based on carbophilic interactions with Ag(i)-sensitivity

ortho-Oligo(phenylene)ethynylenes (o-OPEs) stapled with enantiopure 2,3-dihydroxybutane diethers have highly intense circular dichroism (CD) spectra and excellent circular polarized luminescence (CPL) responses (glum values up to 1.1 × 10-2), which are consistent with homochiral helically folded structures. In the presence of Ag(i), a change in the CPL emission is observed, representing the first example of CPL active small organic molecular emitters, which can be modulated by carbophilic interactions in a reversible manner.

Effect of the substitution position (2, 3 or 8) on the spectroscopic and photophysical properties of BODIPY dyes with a phenyl, styryl or phenylethynyl group

Understanding the spectroscopic properties of BODIPY dyes for a rational design of tailored fluorescent probes.

Unusual spectroscopic and photophysical properties of meso-tert-butylBODIPY in comparison to related alkylated BODIPY dyes

meso-t-Bu-BODIPY produces unusual spectroscopic and photophysical characteristics in comparison to those of related alkylated BODIPY dyes.

Fluorescence enhancement of a fluorescein derivative upon adsorption on cellulose

9-[1-(2-Methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (2-Me-4-OMe TG) is a fluorescein derivative dye whose photophysical properties show a remarkable pH dependence. In aqueous solution the fluorescence quantum yield (Φf) of its anionic species is nearly a hundred times higher than that of its neutral species. Such a large difference in Φf makes 2-Me-4-OMe TG useful as an "on-off" pH indicator. Here we report that adsorption on the surface of microcrystalline cellulose exerts a profound effect upon the photophysical properties of 2-Me-4-OMe TG. On the solid only the dye neutral species is observed and its Φf is 0.31 ± 0.10, which is approximately thirty times higher than the value found for the neutral species in aqueous solution (Φf = 0.01). 2-Me-4-OMe TG and Dabcyl (DB) were co-adsorbed on the surface of microcrystalline cellulose to study the transfer of excitation energy from the former to the latter. In the absence of the dye, the formation of DB aggregates is observed at concentrations greater than 0.34 μmol per gram of cellulose, while in the presence of 2-Me-4-OMe TG the formation of DB aggregates is thoroughly inhibited. The quenching of fluorescence of 2-Me-4-OMe TG by DB reaches efficiencies as high as 90% for the most concentrated samples.

Rational design of a new fluorescent ‘ON/OFF’ xanthene dye for phosphate detection in live cells

A new fluorescein derivative with ON/OFF features, 9-[1-(4-tert-butyl-2-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (Granada Green, GG), was designed and synthesised.

Effects of the anion salt nature on the rate constants of the aqueous proton exchange reactions

The proton-transfer ground-state rate constants of the xanthenic dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II), recovered by Fluorescence Lifetime Correlation Spectroscopy (FLCS), have proven to be useful to quantitatively reflect specific cation effects in aqueous solutions (J. M. Paredes, L. Crovetto, A. Orte, J. M. Alvarez-Pez and E. M. Talavera, Phys. Chem. Chem. Phys., 2011, 13, 1685-1694). Since these phenomena are more sensitive to anions than to cations, in this paper we have accounted for the influence of salts with the sodium cation in common, and the anion classified according to the empirical Hofmeister series, on the proton transfer rate constants of TG-II. We demonstrate that the presence of ions accelerates the rate of the ground-state proton-exchange reaction in the same order than ions that affect ion solvation in water. The combination of FLCS with a fluorophore undergoing proton transfer reactions in the ground state, along with the desirable feature of a pseudo-dark state when the dye is protonated, allows one unique direct determination of kinetic rate constants of the proton exchange chemical reaction.

Dynamics of water-in-oil nanoemulsions revealed by fluorescence lifetime correlation spectroscopy

The size, diffusional properties, and dynamics of reverse water-in-oil nanoemulsions, or reverse micelles (RMs), have been widely investigated because of interest in this system as a model for biological compartmentalization. Here, we have employed fluorescence lifetime correlation spectroscopy (FLCS) to reveal the dynamics and sizes of aerosol-OT (AOT)/isooctane RMs using a fluorescent xanthene derivative called Tokyo Green II (TG-II). The dye undergoes a partition and a shift in its tautomeric equilibrium such that the TG-II anion remains in the inner micellar aqueous core, and the neutral quinoid form lies in the interfacial region. By applying FLCS, we specifically obtained the lifetime filtered autocorrelation curves of the anionic TG-II, which shows a characteristic lifetime of approximately 4 ns. Analysis of the FLCS curves provides the diffusion coefficient and hydrodynamic radius of the RMs as well as micelle dynamics in the same experiment. The FLCS curves show dynamics in the microsecond time range, which represents an interconversion rate that changes the distribution of the TG-II neutral and anionic forms in the hydrophobic interface and the water core.

Photophysics of the interaction between a fluorescein derivative and Ficoll

Ficoll has been widely used as a crowding agent to mimic intracellular media because it is believed to be noninteracting and is composed of mixed sizes such that smaller and larger diffusing solutes can be studied. Due to the interest that the fluorescent dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II) as a fluorometric probe of phosphate ions in intracellular media could generate, we describe the spectral characteristics of the system TG-II-Ficoll in aqueous solution by means of absorption spectroscopy, steady-state fluorescence, time-resolved fluorescence, time-resolved emission spectroscopy, and fluorescence lifetime correlation spectroscopy. The spectral characteristics found are consistent with the formation of an adsorption complex on the surface of Ficoll, probably due to hydrogen bonding between TG-II and Ficoll. In addition, the diffusion coefficient calculated for the association was similar to the diffusion coefficient previously recovered for Ficoll in the same experimental conditions. Therefore, our overall data clearly demonstrate that Ficoll is not an inert crowding agent when in the presence of fluorescein derivative dyes.

Photophysics and binding constant determination of the homodimeric dye BOBO-3 and DNA oligonucleotides

The interactions between single- and double-stranded DNA and the trimethine cyanine homodimer dye, BOBO-3 (1,1'-(4,4,7,7-tetramethyl-4,7-diazaundecamethylene)-bis-4-[3-methyl-2,3-dihydro-(benzo-1,3-thiazole)-2-methylidene]pyridinium tetraiodide), have been investigated in detail using absorption and steady-state and time-resolved fluorescence spectroscopy. The dye interacts with both single-stranded and double-stranded DNA, under a variety of conditions, with changes in its spectral characteristics. Our results indicated that the complex formed between BOBO-3 dye and DNA oligonucleotides could not be explained with a simple, single intercalation mechanism; therefore, different modes of interaction were proposed. By using time-resolved fluorescence methodology and in-depth analysis of the fluorescence decay traces, we obtained the contribution of the different forms of BOBO-3: free in solution, a low affinity, electrostatically driven interaction with DNA, and a full bis-intercalation mechanism within the DNA double helix. With this information, we applied the McGhee-Von Hippel theory for two overlapping, noncooperative binding modes to obtain equilibrium binding constants and the number of sites occupied for each binding mode. Binding constants for dye/dsDNA complexes in complete bis-intercalation and externally bound were (8.8 +/- 1.1) x 10(5) and (2.6 +/- 0.3) x 10(5) M(-1), respectively. The corresponding recovered number of base pairs covered were 5.9 +/- 0.2 and 3.5 +/- 0.5 sites for each mode.

Tuned lifetime, at the ensemble and single molecule level, of a xanthenic fluorescent dye by means of a buffer-mediated excited-state proton exchange reaction

The photophysical behaviour of the new fluorescein derivative 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one has been explored by using absorption, and steady-state, time-resolved and single-molecule fluorescence measurements. The apparent ground-state acidity constant of the dye determined by both the absorbance and steady-state fluorescence is almost independent of the added buffer and salt concentrations. The excited-state proton exchange reaction around the physiological pH becomes reversible upon addition of phosphate buffer, inducing a pH-dependent change of the steady-state fluorescence and decay times. Fluorescence decay traces, collected as a function of total buffer concentration and pH, were analyzed by global compartmental analysis (GCA) to elucidate the values of the excited-state rate constants. The features of this system make the fluorescence decays monoexponential at pH values and phosphate buffer concentrations higher than 6.10 and 0.2 M respectively, with the possibility of tuning the fluorescence lifetime value by changing pH or buffer concentrations. The tuned lifetimes obtained by means of phosphate concentration at constant pH have also been recovered at the single-molecule level.

Photoinduced Electron Transfer from Tetrasulfonated Porphyrin to Benzoquinone Revisited. The Structural Volume-Normalized Entropy Change Correlates with Marcus Reorganization Energy

Time-resolved laser-induced optoacoustic spectroscopy was used for the determination of the enthalpy, DeltaTH, and structural volume changes, DeltaTV, concomitant with triplet state formation upon excitation of meso-tetrakis(4-sulfonatophenyl)porphyrin, TSPP(4-), as well as with the triplet state electron-transfer (ET) quenching by benzoquinone, BQ (DeltaRH and DeltaRV). The values of DeltaTH and DeltaTV for (3)TSPP(4-) formation in the presence of different cations (Li+, Na+, K+, NH4+, and Cs+) correlated with each other and afforded a value of DeltaTG = 140 +/- 20 kJ mol(-1), equal to the value of E+ at 77 K, but much larger than the DeltaTH values in solution at room temperature, due to the large entropic factor in solution. The influence of the cations on DeltaTH and DeltaTV (a contraction ranging from 5.4 to 3.8 cm3 mol(-1)) is attributed to changing chromophore-water interactions in the ground and triplet states. Upon quenching of 3TSPP(4-) by BQ, the quantum yield of free radical formation, PhiR = 0.66 +/- 0.04, is the same in the solutions of the five cations. The values of DeltaRH and DeltaRV are small and have a large error. The energy level of the free radicals formed is thus very similar to that of 3TSPP(4-). TDeltaRS and X = TDeltaRS/DeltaRV, i.e., the structural volume change-normalized entropy change for free radicals formation, were derived using average values of DeltaRH and DeltaRV together with the calculated DeltaRG degrees . The measured Marcus reorganization energy, lambda, and X fall into the lambda vs X linear dependence we previously found for the radical formation upon ET quenching of triplet flavins (3FMN and 3FAD) by amines and amino acids. Thus, X = TDeltaRS/DeltaRV in aqueous solutions is a property of the particular donor-acceptor pair linearly correlated to the corresponding Marcus reorganization energy. The value of X is much larger than the predicted value applying the electrostriction concepts in view of the noncontinuum nature of the aqueous solutions.

Entropy changes drive the electron transfer reaction of triplet flavin mononucleotide from aromatic amino acids in cation-organized aqueous media. A laser-induced optoacoustic study

The thermodynamic parameters for the formation of the free radicals upon electron transfer quenching of the flavin triplet state (3FMN) by tryptophan and tyrosine, Delta(FR)H and Delta(FR)V, were obtained in aqueous solution by the application of laser-induced optoacoustic spectroscopy at various temperatures. The Delta(FR)H and Delta(FR)V values include the electron transfer and charge separation steps plus the protonation of the FMN anion radical and the deprotonation of the amino-acid cation radical. A linear correlation was found between the Delta(FR)H and Delta(FR)V values for each of the amino acids in phosphate buffers of [CH3(CH2)3]4N+, Li+, NH4+, K+ and Cs+. The compensation between Delta(FR)H and Delta(FR)V within the salt series, and the independent evaluation of the Gibbs energy for electron transfer Delta(ET)G(o) afforded the entropy change, Delta(FR)S, for the reaction, different for the two amino acids. The values of Delta(FR)H, Delta(FR)V and Delta(FR)S in each buffer are mainly determined by the changes in strength and probably number of hydrogen bonds between the reacting partners and water produced along all steps leading to the radicals FMNH* and A*. The Delta(FR)V values linearly correlate with the tabulated entropy of organization of the water structure for the five cations, DeltaS(o)(cat). The entropy change upon formation of the free radicals, Delta(FR)S, quantitatively correlated to the Delta(FR)V value, drives the separation of the ion pair after the electron transfer reaction in the case of highly organizing cations. The ratio X = T Delta(FR)S/Delta(FR)V = (55 +/- 9) kJ cm(-3) for Trp as 3FMN quencher is smaller than X = (83 +/- 9) kJ cm(-3) for Tyr as quencher. These values are discussed in conjunction with the Marcus reorganization energy, as calculated from the Gibbs activation energy of the electron transfer process, which is independent of the salt present but different for each of the two quenchers.

Photoinduced Electron Transfer to Triplet Flavins. Correlation between the Volume Change-Normalized Entropic Term and the Marcus Reorganization Energy†

The data obtained through the application of nanosecond laser-induced optoacoustic spectroscopy (LIOAS) to several electron donor-acceptor pairs in aqueous solution were analyzed together with the respective experimentally determined Marcus reorganization energy. Acceptors were the flavin mononucleotide and flavin-adenine dinucleotide triplet states (3FMN and 3FAD) and donors were tryptophan, tyrosine, histidine, triethanolamine, and ethylenediaminetetraacetic acid. The respective calculated Gibbs energy for electron transfer, Delta(ET)G degrees , was used together with the enthalpy change for the formation of free radicals, Delta(FR)H, obtained from the LIOAS data, to derive the entropy change for the formation of the radicals, Delta(FR)S. In all cases, variation of the monovalent cations, i.e., [CH3(CH2)3]4N+, Li+, NH4+, K+, and Cs+, resulted in variation of the enthalpy change, Delta(FR)H, and in the structural volume change, Delta(FR)V, for the free-radical production, both derived from LIOAS. Delta(FR)H and Delta(FR)V linearly correlated with each other within the cation series. From this correlation the respective entropic term TDelta(FR)S was derived as well as the ratio X = TDelta(FR)S/Delta(FR)V for each of the pairs. X linearly correlated with the respective total Marcus reorganization energy, lambda, for all systems analyzed. This observation underlines the concept that both lambda and Delta(FR)V respond to the same phenomena. The correlation also offers an experimental approach for the understanding at a molecular level of the origin of the lambda values as well as for their evaluation.

2‘,7‘-Difluorofluorescein Excited-State Proton Reactions: Correlation between Time-Resolved Emission and Steady-State Fluorescence Intensity

The presence of excited-state buffer-mediated proton exchange reactions influences the steady-state fluorescence signals from dyes in solution. Since biomolecules in general have some chemical groups that can act as proton acceptors/donors and are usually dissolved in buffer solutions which can also behave as appropriate proton acceptors/donors, the excited-state proton exchange reactions may result in distorted steady-state fluorescence signals. In a previous paper (J. Phys. Chem. A 2005, 109, 734-747), we evaluated kinetic and other pertinent parameters for the excited-state proton reactions of the prototropic forms of 2',7'-difluorofluorescein (Oregon Green 488, OG488), recording a fluorescence decay surface at different pH values and acetate buffer concentrations, analyzed by means of global compartmental analysis. In this article we use the rate constants and the corrected pre-exponential factors from the previously recorded fluorescence decay traces to simulate the decay times and associated pre-exponentials at different acetate buffer concentrations and constant pH and compare these theoretically calculated values with new experimental data. We also calculate the steady-state fluorescence intensity vs pH and vs acetate buffer concentration (at constant pH) and compare these calculated emission values with the experimental data previously published. The agreement between the experimental and simulated data is excellent.

Initial experience with gamma knife surgery for endocrine ophthalmopathy

OBJECT

The aim of this study was to evaluate both the effectiveness and safety of the treatment of endocrine ophthalmopathy with gamma knife surgery (GKS).

METHODS

Five patients were included in a prospective study designed to assess the results of GKS of endocrine ophthalmopathy secondary to Graves disease. All the patients completed a 2-year follow-up period. During this period, the patients were evaluated both clinically and by means of additional methods, including computerized tomography and magnetic resonance imaging studies. The minimum dose delivered to the 50% isodose line was 6.5 Gy in all the patients. In all cases, a clinical improvement was observed. The best effect was seen in symptom regression related to soft-tissue involvement. No treatment-related side effects were detected.

CONCLUSIONS

In light of the results obtained the authors consider that GKS may be a safe and effective way to treat endocrine ophthalmopathy.

Absorption and Emission Study of 2‘,7‘-Difluorofluorescein and Its Excited-State Buffer-Mediated Proton Exchange Reactions

2',7'-Difluorofluorescein (Oregon Green 488) is a new fluorescein-based dye, which has found many applications, above all in biochemistry and neurosciences, and its use has become very popular in the last years. In recent years, we have been investigating the excited-state proton exchange reactions of fluorescein and the effect of suitable proton acceptors and donors which promote these reactions. The excited-state proton transfer reactions may appreciably influence the fluorescence results when using these dyes. We present steady-state emission evidence that acetate buffer species promote an excited-state proton transfer between neutral, monoanionic, and dianionic forms of 2',7'-difluorofluorescein. The time course of the excited species in this reaction was characterized through time-resolved fluorescence measurements, and the kinetics of the reaction was solved by using the global compartmental analysis. A previous identifiability study on the compartmental system set the conditions to design the fluorescence decay surface. This is the first experimental system, studied within this kinetic model, solved under identifiability conditions through global compartmental analysis. The recovered rate constant values for deactivation were 2.94 x 10(8) s(-1) for the monoanion and 2.47 x 10(8) s(-1) for the dianion, whereas the rate constant values of the buffer-mediated excited-state reaction were 9.70 x 10(8) and 1.79 x 10(8) M(-1) s(-1) for the deprotonation and protonation, respectively. With these values, a pK(a) = 4.02 was obtained. In this work, we additionally provide an absorption study, including acid-base equilibria, determination of ground-state pK(a) values (1.02, 3.61, and 4.69), and recovery of molar absorption coefficients of every prototropic species, including absorption and NMR evidence for the existence of three tautomers in neutral species. Steady-state emission spectra of 2',7'-difluorofluorescein in aqueous solution are also described, where the strong photoacid behavior of the cation is noteworthy.

Initial experience with gamma knife surgery for endocrine ophthalmopathy

Object. The aim of this study was to evaluate both the effectiveness and safety of the treatment of endocrine ophthalmopathy with gamma knife surgery (GKS).

Methods. Five patients were included in a prospective study designed to assess the results of GKS of endocrine ophthalmopathy secondary to Graves disease. All the patients completed a 2-year follow-up period. During this period, the patients were evaluated both clinically and by means of additional methods, including computerized tomography and magnetic resonance imaging studies. The minimum dose delivered to the 50% isodose line was 6.5 Gy in all the patients.

In all cases, a clinical improvement was observed. The best effect was seen in symptom regression related to soft-tissue involvement. No treatment-related side effects were detected.

Conclusions. In light of the results obtained the authors consider that GKS may be a safe and effective way to treat endocrine ophthalmopathy.

Fluorescence energy transfer between fluorescein label and DNA intercalators to detect nucleic acids hybridization in homogeneous media

A general approach to detecting nucleic acid sequences in homogeneous media by means of steady-state fluorescence measurements is proposed. The methodology combines the use of a fluorescence-labeled single-strand DNA model probe, the complementary single-strand DNA target, and a DNA intercalator. The probe was fluorescein labeled to a spacer arm at the N4 position of the cytosine amino groups in polyribocytidylic acid (5'), poly(C), which acts as a model DNA probe. The complementary strand was polyriboinosinic acid (5'), poly(I), as a model of the target, and the energy transfer acceptor was an intercalator, either ethidium bromide or ethidium homodimer. In previous papers we have shown that the fluorescence intensity of the fluorescein label decreases when labeled poly(C) hybridizes with poly(I), and this fluorescence quenching can be used to detect DNA hybridization or renaturation in homogeneous media. In this paper we demonstrate that fluorescence resonance energy transfer (FRET) between fluorescein labeled to poly(C) and an intercalator agent takes place when single-stranded poly(C) hybridizes with poly(I), and we show how the fluorescence energy transfer further decreases the steady-state fluorescence intensity of the label, thus increasing the detection limit of the method. The main aim of this work was to develop a truly homogeneous detection system for specific nucleic acid hybridization in solution using steady-state fluorescence and FRET, but with the advantage of only having to label the probe with the energy donor since the energy acceptor is intercalated spontaneously. Moreover, the site label is not critical and can be labeled randomly in the DNA strand. Thus, the method is simpler than those published previously based on FRET. The experiments were carried out in both direct and competitive formats.

Single fiber electromyography of extraocular muscles: a sensitive method for the diagnosis of ocular myasthenia gravis

We performed single fiber electromyography (SFEMG) in the superior rectus and levator palpebralis (SR-LP) muscles of 17 patients with pure ocular myasthenia gravis (MG) and 9 controls. Thirteen patients were also assessed with SFEMG in the orbicularis oculi (OO) muscle. All the MG patients but none of the control subjects showed abnormal SFEMG jitter in the SR-LP muscles. On the other hand, only 62% of the MG patients had abnormal SFEMG jitter in the OO muscle. The procedure was well tolerated by the patients, and complications were minor. We conclude that SFEMG of the SR-LP muscles is a safe and highly sensitive technique for the diagnosis of ocular MG.

Vertical ocular motor apraxia

We report a case of vertical ocular motor apraxia in a 4-year old boy whom we have followed for 2 years. The patient had no upward and downward voluntary movements of the eyes since birth, but horizontal movements were normal. He achieved gaze changes in the vertical plane by combined blinks and head movements. Magnetic resonance imaging demonstrated bilateral lesions at the mesencephalic-diencephalic junction.

Hydatid cysts of the orbit. A review of 35 cases

The authors reviewed 35 cases of orbital hydatid cysts, which represented 5% of orbital surgical cases seen from 1944 to 1985. The average age was 16 years (range, 2-57 years). Slowly progressive unilateral exophthalmos, with or without pain, was the most frequent clinical manifestation. Computed tomography (CT) of the orbit demonstrated a well-circumscribed mass. Ultrasonography showed an anechoic cystic mass. The parasitic membrane and contents were surgically removed through an orbital approach. Hydatid cysts should be included in the differential diagnosis of unilateral exophthalmos in patients from countries where echinococcosis is endemic. Preoperative recognition is important for planning an appropriate surgical treatment in avoiding complications.

Angle closure glaucoma as initial manifestation of melanocytoma of the optic disc

A 44-year-old man had progressive visual loss and pain due to angle-closure glaucoma associated with a papillary pigmented lesion. The eye was enucleated because of intractable pain and the suspicion of a malignant tumor. Histologic and electron microscopic examination of the enucleated eye revealed a partially necrotic melanocytoma of the optic nerve. There was histologic evidence of vaso-occlusive disease within the optic nerve that resulted in ischemic necrosis of the tumor, hypoxic retinopathy and neovascular glaucoma. This report emphasizes that significant complications may occur in otherwise typical intraocular nevi.