Study on the interaction between erythrosine B and the cardiac drug amiodarone using fluorescence, scattering, and absorbance spectra and their analytical application.

In an acidic buffered solution, erythrosine B can react with amiodarone to form an association complex, which not only generates great enhancement in resonance Rayleigh scattering (RRS) spectrum of erythrosine B at 346.5 nm but also results in quenching of fluorescence spectra of erythrosine B at λemission = 550.4 nm/λexcitation = 528.5 nm. In addition, the formed erythrosine B-amiodarone complex produces a new absorbance peak at 555 nm. The spectral characteristics of the RRS, absorbance, and fluorescence spectra, as well as the optimum analytical conditions, were studied and investigated. As a result, new spectroscopic methods were developed to determine amiodarone by utilizing erythrosine B as a probe. Moreover, the ICH guidelines were used to validate the developed RRS, photometric, and fluorimetric methods. The enhancements in the absorbance and the RRS intensity and the decrease in the fluorescence intensity of the used probe were proportional to the concentration of amiodarone in ranges of 2.5-20.0, 0.2-2.5, and 0.25-1.75 µg/mL, respectively. Furthermore, limit of detection values were 0.52 ng/mL for the spectrophotometric method, 0.051 µg/mL for the RRS method, and 0.075 µg/mL for the fluorimetric method. Moreover, with good recoveries, the developed spectroscopic procedures were applied to analyze amiodarone in its commercial tablets.

Integration of a facile sustainable resonance Rayleigh scattering switchable-based system for feasible determination of centrophenoxine, a nootropic and antioxidant agent; application to crude materials and dosage forms.

The proposed research adheres to a certain methodology to ensure that the technique used for analyzing the centrophenoxine drug is sustainable and green. It is important to highlight that several tools that have been recently developed were utilized as potential indicators of environmental sustainability and applicability. The present research presents a novel and entirely innovative method utilizing ultrasensitive spectrofluorimetry for the detection of centrophenoxine (CPX) drug. The employed methodology in this study involved the utilization of one-step, one-pot, and direct spectrofluorimetric technique, which was found to be both efficient and environmentally sustainable in the validation and assessment of the drug. Simply, when CPX and erythrosine B reagent were combined in an acidic environment, the highly resonance Rayleigh scattering product was immediately produced. The sensitivity limits were observed to be within the range of 15-47 ng mL-1, whereas the linearity was assessed to be in the range of 50-2000 ng mL-1. The optimal settings for all modifiable parameters of the system were ascertained through an analysis of centrophenoxine-erythrosine B complexes. Moreover, the system demonstrated compliance with International Council for Harmonization (ICH) specifications without encountering any issues. The suggested process was then rated on different recent environmental safety measuring metrics to see how good it was for the environment. Fortunately, the WAC standards that combine ecological and functional elements utilizing the Green/Red/Blue (RGB 12) design also acclaimed the current analytical technique as a white one. Additionally, a new applicability evaluation tool (BAGI) was employed to estimate the practicability of the planned method in the analytical chemistry field.

Utility of the food colorant erythrosine B as an effective green probe for quantitation of the anticancer sunitinib. Application to pharmaceutical formulations and human plasma.

Sunitinib is a tyrosine kinase inhibitor used for the treatment of renal cell carcinoma and gastrointestinal stromal tumors. In this study, two spectroscopic methods, spectrofluorometric and spectrophotometric, were utilized to quantify sunitinib in different matrices. In method I, the native fluorescence of erythrosine B was quenched by forming ion-pair complex with increasing quantities of sunitinib. This approach was utilized for measuring sunitinib in its dosage forms and spiked plasma. After excitation at 528 nm, the quenching of fluorescence is linearly related to the concentration across the range of 0.05-0.5 µg mL-1 at 550 nm in Britton-Robinson buffer (pH 4.0), with a correlation value of 0.9999 and a high level of sensitivity with detection limit down to 10 ng mL-1 . Method II relies on spectrophotometric measurements of the produced complex at 550 nm across a range of 0.5-10.0 µg mL-1 , with good correlation value of 0.9999. This method has a detection limit down to 0.16 µg mL-1 . The proposed methodologies were validated according to International Conference on Harmonization (ICH) guidelines with satisfactory results. The stoichiometry of the reaction was determined through the application of Job's method, while the mechanism of quenching was investigated by employing the Stern-Volmer plot. The designated methods were used to estimate sunitinib in its capsules and in spiked human plasma. Additionally, the statistical analysis of the data revealed no substantial differences when compared to previous reported spectroscopic method. Green assessment tools provide further details about the eco-friendly nature of the methods.

Utility of a xanthene-based dye for determination of nilotinib using two spectroscopic approaches. Applications to bulk powder, capsules, and spiked human plasma.

Novel, selective, facile, and precise spectroscopic approaches were validated to determine nilotinib hydrochloride, a tyrosine kinase inhibitor used to treat patients with chronic myeloid leukemia. These approaches depend on the reaction of the tertiary amine group of nilotinib with erythrosine B in the Britton-Robinson buffer at pH 4. Method I, depends on measuring the absorbance of the formed complex at 551 nm. The absorbance concentration plot showed linearity over the concentration range of 1.0 to 9.0 µg/ml. Method II, involved the measurement of the quenching of the native fluorescence of erythrosine B by adding nilotinib in an acidic medium. The fluorescence quenching of erythrosine B was measured at 549 nm after excitation at 528 nm. This approach showed excellent linearity in the concentration range of 0.04 to 0.7 µg/ml. The limit of detection values for Method I and Method II were 0.225 and 0.008 µg/ml, respectively, while the limit of quantitation values for Method I and Method II were 0.68 and 0.026 µg/ml, respectively. To get the optimal conditions, factors that may affect the formation of the ion-pairing complex were thoroughly examined. The two approaches were carefully validated following the International Conference of Harmonization (ICH Q2R1) guidelines. Statistical assessment of the results achieved using the suggested and previously published comparison approaches showed no significant difference. The approaches were successful in determining nilotinib in a pharmaceutical dosage form as well as spiked human plasma samples. The eco-friendly properties of the methods were evaluated by three different tools.

Novel approaches of erythrosine B as a food dye-derived spectroscopic probe for assessing trospium chloride in raw material and dosage form.

Two facile spectroscopic methodologies were designed for estimating trospium chloride (TPM) in raw material and tablets with high operational reliability and selectivity. The methods were based on using erythrosine B (EB) as a spectroscopic tool for ion-pair complex formation with the drug. In a mild acidic medium of Britton Robinson buffer (pH 4.0), the ionized hydroxyl group in the reagent interacted with the ionized amine in the studied drug. Method I was based on the spectrophotometric measuring of the absorbance of the reaction product at 557 nm. Method II was based on spectrofluorimetric measurement of the quenching effect of TPM on the inherent fluorescence of EB at 550 nm (λex. = 528 nm). The two methods showed linearity through ranges 1.0-10.0 and 0.5-10.0 µg/ml for Methods I and II, respectively. The suggested methods were exploited for analyzing TPM in Trospamexin® tablets and showed good applicability. The designed systems were validated as per International Conference on Harmonization guidelines. Experimental conditions were modulated to obtain the best sensitivities. The quenching mechanism was investigated and the quenching constant was computed relying on the Stern-Volmer equation. Environmental impact was appraised using novel metric green tools, GABI, and AGREE. The suggested systems excelled over other reported methods in terms of greenness, sensitivity, and cost-effectiveness.

Resonance Rayleigh scattering approach based on association complex formation with erythrosine B for determination of venlafaxine, application to the dosage form and spiked human plasma.

The interaction of venlafaxine hydrochloride (VLX) with erythrosine B was investigated using a resonance Rayleigh scattering (RRS) spectroscopic technique. In acetate buffer (pH 3.4), erythrosine B reacted with VLX to form a 1:1 ion-pair complex with concomitant enhancement in RRS intensity that was measured at 330 nm. In addition, the stability constant and the change in free energy of the reaction were estimated. Based on this interaction a new method was developed for a sensitive VLX analysis using erythrosine B as a probe. The results indicated that this method had good selectivity in the presence of coexisting compounds. The scattering intensity (ΔIRRS ) was linearly dependent on VLX concentration over the range 0.04-1.0 µg ml-1 with a determination coefficient (r) of 0.9998. The limit of detection and limit of quantitation were 0.01 and 0.03 µg ml-1 , respectively. This method could be suitably used for analysis of VLX in pharmaceutical capsules and human plasma.

Plasma membrane permeabilization to explain erythrosine B phototoxicity on in vitro breast cancer cell models.

Lipid oxidation is ubiquitous in cell life under oxygen and essential for photodynamic therapy (PDT) of carcinomas. However, the mechanisms underlying lipid oxidation in rather complex systems such as plasma membranes remain elusive. Herein, Langmuir monolayers were assembled with the lipid extract of glandular breast cancer (MCF7) cells and used to probe the molecular interactions allowing adsorption of the photosensitizer (PS) erythrosine B and subsequent photooxidation outcomes. Surface pressure (π) versus area (cm2/mL) isotherms of MCF7 lipid extract shifted to larger areas upon erythrosine incorporation, driven by secondary interactions that affected the orientation of the carbonyl groups and lipid chain organization. Light-irradiation increased the surface area of the MCF7 lipid extract monolayer containing erythrosine owing to the lipid hydroperoxidation, which may further undergo decomposition, resulting in the chain cleavage of phospholipids and membrane permeabilization. Incorporation of erythrosine by MCF7 cells induced slight toxic effects on in vitro assays, differently of the severe phototoxicity caused by light-irradiation, which significantly decreased cell viability by more than 75% at 2.5 × 10-6 mol/L of erythrosine incubated for 3 and 24 h, reaching nearly 90% at 48 h of incubation. The origin of the phototoxic effects is in the rupture of the plasma membrane shown by the frontal (FSC) and side (SSC) light scattering of flow cytometry. Consistent with hydroperoxide decomposition, membrane permeabilization was also confirmed by cleaved lipids detected in mass spectrometry and subsidizes the necrotic pathway of cell death.

Inhibitory Effects of Erythrosine/Curcumin Derivatives/Nano-Titanium Dioxide-Mediated Photodynamic Therapy on Candida albicans.

This study focuses on the role of photosensitizers in photodynamic therapy. The photosensitizers were prepared in combinations of 110/220 µM erythrosine and/or 10/20 µM demethoxy/bisdemethoxy curcumin with/without 10% (w/w) nano-titanium dioxide. Irradiation was performed with a dental blue light in the 395-480 nm wavelength range, with a power density of 3200 mW/cm2 and yield of 72 J/cm2. The production of ROS and hydroxyl radical was investigated using an electron paramagnetic resonance spectrometer for each individual photosensitizer or in photosensitizer combinations. Subsequently, a PrestoBlue® toxicity test of the gingival fibroblast cells was performed at 6 and 24 h on the eight highest ROS-generating photosensitizers containing curcumin derivatives and erythrosine 220 µM. Finally, the antifungal ability of 22 test photosensitizers, Candida albicans (ATCC 10231), were cultured in biofilm form at 37 °C for 48 h, then the colonies were counted in colony-forming units (CFU/mL) via the drop plate technique, and then the log reduction was calculated. The results showed that at 48 h the test photosensitizers could simultaneously produce both ROS types. All test photosensitizers demonstrated no toxicity on the fibroblast cells. In total, 18 test photosensitizers were able to inhibit Candida albicans similarly to nystatin. Conclusively, 20 µM bisdemethoxy curcumin + 220 µM erythrosine + 10% (w/w) nano-titanium dioxide exerted the highest inhibitory effect on Candida albicans.

Development and characterization of regenerable chitosan-coated nickel selenide nano-photocatalytic system for decontamination of toxic azo dyes.

In this investigation, chitosan-coated nickel selenide nano-photocatalyst (CS-NiSe) was successfully prepared through the chemical reduction method. FTIR spectroscopy confirmed the synthesis of CS-NiSe nano-photocatalyst. Further, XRD analysis exhibited a monoclinic crystalline phase of photocatalyst with a crystallite size of 32 nm based on Scherer's equation. The SEM micrographs showed that the photocatalyst has an average particle size of 60 nm. The bandgap of CS-NiSe was (2.85 eV) in the visible region of the spectrum. Due to this reason, the CS-NiSe was applied under solar light illumination for the photocatalytic activity of Erythrosine and Allura red dyes. The CS-NiSe presented the highest degradation efficiency of 99.53% for Erythrosine dye in optimized experimental conditions of 100 min at 30 °C, 30 ppm concentration, pH 5.0, and 0.14 g catalyst dose. For Allura red dye, a high degradation of 96.12% was attained in 120 min at pH 4.0, 100 ppm initial dye concentration, 35 °C temperature, and 0.1 g catalyst dose. The CS-NiSe showed excellent degradation efficiency and reduced to (95% for Erythrosine and 91% for Allura red dye) after five consecutive batches. Moreover, the statistical and neural network modelling analysis showed the significant influence of all studied variables on dyes degradation performance. The results demonstrated that CS-NiSe exhibited excellent photocatalytic performances for Erythrosine and Allura red dyes and could be a better photocatalyst for removing these dyes from industrial effluents.

Metabolic labeling of Escherichia coli genomic DNA with erythrosine-11-dUTP for functional imaging via correlative microscopy.

The fluorescent metabolic labeling of microorganisms genome is an advanced imaging technique to observe and study the native shapes, structural changes, functions, and tracking of nucleic acids in single cells or tissues. We have attempted to visualize the newly synthesized DNA within the intact nucleoid of ice-embedded proliferating cells of Escherichia coli K-12 (thymidine-requiring mutant, strain N4316) via correlative light-electron microscopy. For that purpose, erythrosine-11-dUTP was synthesized and used as a modified analog of the exogenous thymidine substrate for metabolic incorporation into the bacterial chromosome. The formed fluorescent genomic DNA during in cellulo polymerase reaction caused a minimal cellular arrest and cytotoxicity of E. coli at certain controlled conditions. The stained cells were visualized in typical red emission color via an epifluorescence microscope. They were further ice-embedded and examined with a Hilbert differential contrast transmission electron microscopy. At high-resolution, the ultrastructure of tagged nucleoid appeared with significantly higher electron dense in comparison to the unlabeled one. The enhanced contrast areas in the chromosome were ascribed to the presence of iodine contents from erythrosine dye. The presented labeling approach might be a powerful strategy to reveal the structural and dynamic changes in natural DNA replication including the relationship between newly synthesized in vivo nucleic acid and the physiological state of the cell.

Erythrosin B: a versatile colorimetric and fluorescent vital dye for bacteria.

Rapidly assaying cell viability for diverse bacteria species is not always straightforward. In eukaryotes, cell viability is often determined using colorimetric dyes; however, such dyes have not been identified for bacteria. We screened different dyes and found that erythrosin B (EB), a visibly red dye with fluorescent properties, functions as a vital dye for many Gram-positive and -negative bacteria. EB worked at a similar concentration for all bacteria studied and incubations were as short as 5 min. Given EB's spectral properties, diverse experimental approaches are possible to rapidly visualize and/or quantitate dead bacterial cells in a population. As the first broadly applicable colorimetric viability dye for bacteria, EB provides a cost-effective alternative for researchers in academia and industry.

A novel spectral method for determination of trace malathion using EryB as light scattering probe by resonance Rayleigh scattering technique.

A convenient and sensitive spectrophotometric methods was proposed for determination of Malathion (Mala) using Erythrosin B (EryB) as a probe through the Resonance Rayleigh scattering (RRS) technique. The interaction between EryB, Pd2+and malathion in the system was investigated by fluorescence, RRS and UV-Vis spectroscopy. Under the optimum conditions, the RRS intensity of EryB, Pd2+ and malathion was weak when exist in alone or any two kinds, however, the RRS intensity of the EryB-Pd2+-Mala system had an obvious enhancement due to Pd2+ could interact with the hydrolysis products of Mala and EryB each other form a new complexes. At the same time, the fluorescence intensity of EryB was decreased significantly in the presence of Pd2+, and the fluorescence intensity of EryB-Pd2+ system further decreased when Mala added, interestingly. So it was further proved that there was a forming complex in EryB-Pd2+-Mala system. Under the optimal conditions, the RRS enhanced intensity of the system was linearly proportional to the Mala's concentration in the range of 0.012-0.8 µg/mL, and the LOD was 1.7 ng/mL, with the correlation coefficient was R2 = 0.9960. So, a new method for determination of Mala was established and this method has been demonstrated in real sample with satisfactory results.

PEG-coated vesicles from Pluronic/lipid mixtures for the carrying of photoactive erythrosine derivatives.

Liposomes are very attractive membrane models and excellent drug delivery systems. Concerning their drug delivery aspects, the mixing liposomes with biocompatible copolymers allows for stability and the incorporation of several drugs. We developed PEG coated vesicles from the mixture of DPPC and F127 Pluronic copolymer to obtain long-circulating nanoparticles (mixed vesicles). We employed an innovative process previously developed by us: a small amount of F127 mixed in DPPC, thin film preparation, followed by hydration (lipids plus F127) using a bath sonicator cleaner type, forming unilamellar spherical vesicles with diameter ∼100 nm. The formed PEG coated vesicles were incorporated with the xanthene dye Erythrosine B (ERY), and its ester derivatives as photosensitizers (PS) for photodynamic proposes. The F127/DPPC mixed vesicles promoted a higher PS incorporation, and with better thermal and kinetic stability, at least 60 days, when compared to conventional DPPC liposome. The binding constant and quenching analysis revealed that with a higher PS hydrophobicity, PS affinity increases toward the nanoparticle and results in a deeper PS location inside the lipid bilayer. An increment in the fluorescence quantum yield was observed, while the PS singlet oxygen generations remained high. Dialysis studies demonstrated that PS were released based on their hydrophobicity. Permeation analysis showed that all PS can reach the deeper regions of the skin. The Decyl Ester derivative/nanoparticle exhibited high photoactivity against Caco-2 cancer cells (in vitro studies). The PEG coated from F127/DPPC mixed vesicles are very promising nanocarriers for erythrosine and its derivatives.

High-performance liquid chromatography study of gatifloxacin and sparfloxacin using erythrosine as post-column resonance Rayleigh scattering reagent and mechanism study.

Herein, a highly selective high-performance liquid chromatography (HPLC) coupled with resonance Rayleigh scattering (RRS) method was developed to detect gatifloxacin (GFLX) and sparfloxacin (SPLX). GFLX and SPLX were first separated by HPLC, then, in pH 4.4 Britton-Robinson (BR) buffer medium, protonic quaternary ammonia cation of GFLX and SPLX reacted with erythrosine (ERY) to form 1:1 ion-association complexes, which resulted in a significant enhancement of RRS signal. The experimental conditions of HPLC and post-column RRS have been investigated, including detection wavelength, flow rate, pH, reacting tube length and reaction temperature. Reaction mechanism were studied in detail by calculating the distribution fraction. The maximum RRS signals for GFLX and SPLX were recorded at λex  = λem  = 330 nm. The detection limits were 3.8 ng ml-1 for GFLX and 17.5 ng ml-1 for SPLX at a signal-to-noise ratio of 3. The developed method was successfully applied to the determination of GFLX and SPLX in water samples. Recoveries from spiked water samples were 97.56-98.85%.

Erythrosin B is a potent and broad-spectrum orthosteric inhibitor of the flavivirus NS2B-NS3 protease.

Many flaviviruses, such as Zika virus (ZIKV), Dengue virus (DENV1-4) and yellow fever virus (YFV), are significant human pathogens. Infection with ZIKV, an emerging mosquito-borne flavivirus, is associated with increased risk of microcephaly in newborns and Guillain-Barré syndrome and other complications in adults. Currently, specific therapy does not exist for any flavivirus infections. In this study, we found that erythrosin B, an FDA-approved food additive, is a potent inhibitor for flaviviruses, including ZIKV and DENV2. Erythrosin B was found to inhibit the DENV2 and ZIKV NS2B-NS3 proteases with IC50 in low micromolar range, via a non-competitive mechanism. Erythrosin B can significantly reduce titers of representative flaviviruses, DENV2, ZIKV, YFV, JEV, and WNV, with micromolar potency and with excellent cytotoxicity profile. Erythrosin B can also inhibit ZIKV replication in ZIKV-relevant human placental and neural progenitor cells. As a pregnancy category B food additive, erythrosin B may represent a promising and easily developed therapy for management of infections by ZIKV and other flaviviruses.

FRET Sensor for Erythrosine Dye Based on Organic Nanoparticles: Application to Analysis of Food Stuff.

An aqueous suspension of fluorescent nanoparticles (PHNNPs) of naphthol based fluorescent organic compound 1-[(Z)-(2-phenylhydrazinylidene) methyl] naphthalene -2-ol (PHN) were prepared using reprecipitation method shows bathochromically shifted aggregation induced enhanced emission (AIEE) in the spectral region where erythrosine (ETS) food dye absorbs strongly. The average size of 72.6 nm of aqueous suspension of PHNNPs obtained by Dynamic light scattering results shows a narrow particle size distribution. The negative zeta potential of nano probe (-22.6 mV) responsible to adsorb oppositely charged analyte on its surface and further permit to bind nano probe and analyte within the close distance proximity required for efficient fluorescence resonance energy transfer (FRET) to take place from donor (PHNNPs) to acceptor (ETS). Systematic FRET experiments performed by measuring fluorescence quenching of PHNNPs with successive addition of ETS solution exploited the use of the PHNNPs as a novel nano probe for the detection of ETS in aqueous solution with extremely lower limit of detection equal to 3.6 nM (3.1 ng/mL). The estimation of photo kinetic and thermodynamic parameters such as quenching rate constant, enthalpy change (∆H), Gibbs free energy change (∆G) and entropy change (∆S) was obtained by the quenching results obtained at different constant temperatures which were found to fit the well-known Stern-Volmer relation. The mechanism of binding and fluorescence quenching of PHNNPs by ETS food dye is proposed on the basis of results obtained in photophysical studies, thermodynamic parameter, energy transfer efficiency, critical energy transfer distance (R0) and distance of approach between donor-acceptor molecules (r). The proposed FRET method based on fluorescence quenching of PHNNPs was successfully applied to develop an analytical method for estimation of ETS from food stuffs without interference of other complex ingredients. Graphical Abstract A fluorescent organic nanoprobe developed for the detection of erythrosine (ETS) food dye in aqueous medium based on fluorescence resonance energy transfer (FRET). The FRET process between donor (nanoparticles) and acceptor (ETS dye) arises due to oppositely charge attraction through hydrophobic interactions. The proposed method was successfully applied to quantitative determination of ETS dye in food stuff sample collected from local market.

Double-wavelength overlapping resonance Rayleigh scattering technique for the simultaneous quantitative analysis of three ß-adrenergic blockade.

Four simple and accurate spectrophotometric methods were proposed for the simultaneous determination of three ß-adrenergic blockade, e.g. atenolol, metoprolol and propranolol. The methods were based on the reaction of the three drugs with erythrosine B (EB) in a Britton-Robinson buffer solution at pH4.6. EB could combine with the drugs to form three ion-association complexes, which resulted in the resonance Rayleigh scattering (RRS) intensity that is enhanced significantly with new RRS peaks that appeared at 337 nm and 370 nm, respectively. In addition, the fluorescence intensity of EB was also quenched. The enhanced scattering intensities of the two peaks and the fluorescence quenched intensity of EB were proportional to the concentrations of the drugs, respectively. What is more, the RRS intensity overlapped with the double-wavelength of 337 nm and 370 nm (so short for DW-RRS) was also proportional to the drugs concentrations. So, a new method with highly sensitive for simultaneous determination of three bisoprolol drugs was established. Finally, the optimum reaction conditions, influencing factors and spectral enhanced mechanism were investigated. The new DW-RRS method has been applied to simultaneously detect the three ß-blockers in fresh serum with satisfactory results.

Investigation of the effect of erythrosine B on amyloid beta peptide using molecular modeling.

Neurotoxic plaques composed of 39 to 42 residue-long amyloid beta peptides (Aßs) are copiously present in the brains of patients with Alzheimer's disease (AD). Erythrosine B (ER), a xanthene food dye, inhibits the formation of Aß fibrils and Aß-associated cytotoxicity in vitro. Here, in an attempt to elucidate the inhibition mechanism, we performed molecular dynamics (MD) simulations to demonstrate the conformational change of Aß40 induced by ER molecules in atomistic detail. During the simulation, the ER bound to the surfaces of both N-terminus and C-terminus regions of Aß40. Our result shows that ER interacts with the aromatic side chains at the N-terminus region resulting in destabilization of the inter-chain stacking of Aß40. Moreover, the stablility of the helical structures at the residues from 13 to 16 suggests that ER disturbs conformational transition of Aß40. At the C-terminus region, the bound ER blocks water molecules and stabilizes the α-helical structure. Regardless of the number of ER molecules used, the interruption of the formation of the salt-bridge between aspartic acid 23 and lysine 28 occurred. To further validate our analysis, binding free energies of ER at each binding site were evaluated. The finding of stronger binding energy at the N-terminus region supports an inhibition mechanism induced by stacking interaction between ER and phenylalanine. These findings could aid present and future treatment studies for AD by clarifying the inhibition mechanism of ER on the conformational transition of Aß40 at the molecular level.

Molecular-Level Modifications Induced by Photo-Oxidation of Lipid Monolayers Interacting with Erythrosin.

Incorporation into cell membranes is key for the action of photosensitizers in photomedicine treatments, with hydroperoxidation as the prominent pathway of lipid oxidation. In this paper, we use Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as cell membrane models to investigate adsorption of the photosensitizer erythrosin and its effect on photoinduced lipid oxidation. From surface pressure isotherms and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) data, erythrosin was found to adsorb mainly via electrostatic interaction with the choline in the head groups of both DOPC and DPPC. It caused larger monolayer expansion in DOPC, with possible penetration into the hydrophobic unsaturated chains, while penetration into the DPPC saturated chains was insignificant. Easier penetration is due to the less packed DOPC monolayer, in comparison to the more compact DPPC according to the monolayer compressibility data. Most importantly, light irradiation at 530 nm made the erythrosin-containing DOPC monolayer become less unstable, with a relative surface area increase of ca. 19%, in agreement with previous findings for bioadhesive giant vesicles. The relative area increase is consistent with hydroperoxidation, supporting the erythrosin penetration into the lipid chains, which favors singlet oxygen generation close to double bonds, an important requirement for photodynamic efficiency.

Application of a non-hazardous vital dye for cell counting with automated cell counters.

Recent advances in automated cell counters enable us to count cells more easily with consistency. However, the wide use of the traditional vital dye trypan blue (TB) raises environmental and health concerns due to its potential teratogenic effects. To avoid this chemical hazard, it is of importance to introduce an alternative non-hazardous vital dye that is compatible with automated cell counters. Erythrosin B (EB) is a vital dye that is impermeable to biological membranes and is used as a food additive. Similarly to TB, EB stains only nonviable cells with disintegrated membranes. However, EB is less popular than TB and is seldom used with automated cell counters. We found that cell counting accuracy with EB was comparable to that with TB. EB was found to be an effective dye for accurate counting of cells with different viabilities across three different automated cell counters. In contrast to TB, EB was less toxic to cultured HL-60 cells during the cell counting process. These results indicate that replacing TB with EB for use with automated cell counters will significantly reduce the hazardous risk while producing comparable results.