Dibromofluorescein Research Articles

Roles of breast cancer resistance protein and organic anion transporting polypeptide 2B1 in gastrointestinal toxicity induced by SN-38 under inflammatory conditions

Drug transporters are among the factors that determine the pharmacokinetic profiles after drug administration. In this study, we investigated the roles of drug transporters involved in transport of SN-38, which is an active metabolite of irinotecan, in the intestine under inflammatory conditions in vitro and determined their functional consequences. The expression alterations of breast cancer resistance protein (BCRP) and organic anion transporting polypeptide (OATP) 2B1 were determined at the mRNA and protein levels, and the subsequent functional alterations were evaluated via an accumulation study with the representative transporter substrates [prazosin and dibromofluorescein (DBF)] and SN-38. We also determined the cytotoxicity of SN-38 under inflammatory conditions. Decreased BCRP expression and increased OATP2B1 expression were observed under inflammatory conditions in vitro, which led to altered accumulation profiles of prazosin, DBF, and SN-38, and the subsequent cytotoxic profiles of SN-38. Treatment with rifampin or novobiocin supported the significant roles of BCRP and OATP2B1 in the transport and cytotoxic profile of SN-38. Collectively, these results suggest that BCRP and OATP2B1 are involved in the increased cytotoxicity of SN-38 under inflammatory conditions in vitro. Further comprehensive research is warranted to completely understand SN-38-induced gastrointestinal cytotoxicity and aid in the successful treatment of cancer with irinotecan.

G45 and V386 in Transmembrane Domains 1 and 8 Are Critical for the Activation of OATP1B3-Mediated E17βG Uptake by Clotrimazole.

Organic anion-transporting polypeptides (OATPs) 1B1 and 1B3 are two highly homologous transport proteins. However, OATP1B1- and 1B3-mediated estradiol-17β-glucuronide (E17βG) uptake can be differentially affected by clotrimazole. In this study, by functional characterization on chimeric transporters and single mutants, we find that G45 in transmembrane domain 1 (TM1) and V386 in TM8 are critical for the activation of OATP1B3-mediated E17βG uptake by clotrimazole. However, the effect of clotrimazole on the function of OATP1B3 is substrate-dependent as clotrimazole does not stimulate OATP1B3-mediated uptake of 4',5'-dibromofluorescein (DBF) and rosuvastatin. In addition, clotrimazole is not transported by OATP1B3, but it can efficiently permeate the plasma membrane due to its lipophilic properties. Homology modeling and molecular docking indicate that E17βG binds in a substrate binding pocket of OATP1B3 through hydrogen bonding and hydrophobic interactions, among which its sterol scaffold forms hydrophobic contacts with V386. In addition, a flexible glycine residue at position 45 is essential for the activation of OATP1B3. Finally, clotrimazole is predicted to bind at an allosteric site, which mainly consists of hydrophobic residues located at the cytoplasmic halves of TMs 4, 5, 10, and 11.

Intracellular RNA Labeling Technologies for the Analysis of RNA Biology†

Comprehensive SummaryAs a cornerstone of the central dogma of molecular biology, RNA plays vital roles in living organisms. Over the past few decades, many RNA labeling technologies have been developed to elucidate the biological function of RNA. These technologies have significantly advanced our understanding of RNA secondary structure, localization, and turnover. Additionally, taking advantage of these innovative RNA labeling approaches, plenty of tool kits have been devised for the regulation of RNA‐related biological process, such as gene expression and gene editing. In this review, we primarily focus on an array of intracellular RNA labeling methods, encompassing chemical probes‐based labeling, metabolic labeling, and proximity‐dependent labeling. We also provide a brief overview of their applications in the research of RNA biology. Finally, the perspectives of RNA labeling are also discussed.Key Scientists4SU was first used in1978 as a safer way to directly examine RNA synthesis. However, the enrichment of 4SU‐labeled RNA seriously relied on mercurated cellulose columns, which are toxic. In 2005, Boothroyd et al. introduced a novel covalent‐modification method of 4SU based on thiol exchange reaction. Then, Salic et al. applied 5EU, which is clickable, for RNA metabolic labeling in animals. Later, Spitale et al. designed 5EC and 2’AzU, which enabled cell specific RNA metabolic labeling under the help of specific enzyme. In 2013, directly chemical RNA labeling in living cell for RNA structure mapping was realized by Chang and Kool et al. using SHAPE reagent, which was further modified with an azide handle in 2015. Weissman, Bevilacqua and Assmann et al. introduced DMS probe that targets adenine and cytosine of RNA for RNA structure mapping in 2014. Then, Chang et al. exploited psoralen for RNA duplex mapping in 2016. Later, He, Zhou and Zhang et al. described another clickable probe N3‐kethoxal targeting guanine for RNA secondary structure mapping. Besides, Chang and Ting et al. described a proximity‐dependent RNA labeling method based on APEX in 2019, revealing subcellular RNA localization. Meanwhile, Zou and Wang et al. achieved proximity‐dependent RNA labeling using miniSOG oxidase, which provided an alternative method to investigate the spatial transcriptome. Spitale et al. utilizing photosensitizer dibromofluorescein (DBF) to realize proximity‐dependent RNA labeling and sequencing.

Antigen-Specific T Cell Detection via Photocatalytic Proximity Cell Labeling (PhoXCELL).

Quantitative detection and characterization of antigen-specific T cells are crucial to our understanding of immune responses as well as the development of new immunotherapies. Herein, we report a spatiotemporally resolved method for the detection and quantification of cell-cell interactions via Photocatalytic proXimity CELl Labeling (PhoXCELL). The biocompatible photosensitizer dibromofluorescein (DBF) was leveraged and optimized as a nongenetic alternative of enzymatic approaches for efficient generation of singlet oxygen upon photoirradiation (520 nm) on the cell surface, which allowed the subsequent labeling of nearby oxidized proteins with primary aliphatic amine-based probes. We demonstrated that DBF-functionalized dendritic cells (DCs) could spatiotemporally label interacting T cells in immune synapses via rapid photoirradiation with quantitatively discriminated interaction strength, which revealed distinct gene signatures for T cells that strongly interact with antigen-pulsed DCs. Furthermore, we employed PhoXCELL to simultaneously detect tumor antigen-specific CD8+ as well as CD4+ T cells from tumor-infiltrating lymphocytes and draining lymph nodes in murine tumor models, enabling PhoXCELL as a powerful platform to identify antigen-specific T cells in T cell receptor (TCR)-relevant personal immunotherapy.

3D-Non-destructive Imaging through Heavy-Metal Eosin Salt Contrast Agents.

Conventional histology is a destructive technique based on the evaluation of 2D slices of a 3D biopsy. By using 3D X‐ray histology these obstacles can be overcome, but their application is still restricted due to the inherently low attenuation properties of soft tissue. In order to solve this problem, the tissue can be stained before X‐ray computed tomography imaging (CT) to enhance the soft tissue X‐ray contrast. Evaluation of brominated fluorescein salts revealed a mutual influence of the number of bromine atoms and the cations applied on the achieved contrast enhancement. The dibromo fluorescein barium salt turned out to be the ideal X‐ray contrast agent, allowing for 3D imaging and subsequent complementing counterstaining applying standard histological techniques.

Functional Characterization Reveals the Significance of Rare Coding Variations in Human Organic Anion Transporting Polypeptide 2B1 (SLCO2B1).

The organic anion transporting polypeptide 2B1 (OATP2B1), which is encoded by the SLCO2B1 gene, plays important roles in the absorption and disposition of its substrate drugs. Nonsynonymous variations of SLCO2B1 change its amino acid sequence and may alter its function. However, so far, very few genetic variants of SLCO2B1 have been functionally characterized. In the present study, first of all, 14 nonsynonymous single nucleotide variants (SNVs) of SLCO2B1 have been identified from the dbSNP database. Then, human embryonic kidney (HEK293) cells were employed as the expression system and functional studies were carried out for these 14 SNVs using substrates 4',5'-dibromofluorescein (DBF), estrone-3-sulfate (E3S), atorvastatin, and rosuvastatin. Our results showed that four nonsynonymous rare variants, namely, SLCO2B1 c.332G > A (p.R111Q), c.1184C > A (p.P395H), c.1624G > A (p.V542M), and c.1998C > A (p.F666L), have great effect on the function of OATP2B1. Surface biotinylation and immunoblot analysis indicated that the variant c.1184C > A (p.P395H) almost completely disrupted OATP2B1's expression on the plasma membrane. According to the three-dimensional structural model of OATP2B1 we developed, these four mutated residues are not located at the substrate binding region of OATP2B1. Their significant effect on the function of OATP2B1 could probably be attributed to jeopardizing OATP2B1's surface expression as exemplified by c.1184C > A (p.P395H), altering the transporter's overall structure and affecting its interactions with other proteins or the lipid bilayer. Taken together, our results demonstrated that rare coding variants could have a great impact on the function and expression of OATP2B1.

Investigation of Fluorescent Substrates and Substrate-Dependent Interactions of a Drug Transporter Organic Anion Transporting Polypeptide 2B1 (OATP2B1).

In this study, we investigated organic anion transporting polypeptide 2B1 (OATP2B1)-mediated uptake of fluorescent anions to better identify fluorescent substrates for in vitro OATP2B1 assays. The OATP2B1 is involved in the intestinal absorption and one of the pharmacokinetic determinants of orally administered drugs. A microplate reader was used to determine the cellular accumulation of the fluorescent compounds into the OATP2B1 or the empty vector-transfected HEK293 cells. Two types of derivatives were found to be OATP2B1 substrates: heavy halogenated derivatives, such as 4',5'-dibromofluorescein (DBF), and carboxylated derivatives, such as 5-carboxyfluorescein (5-CF). The DBF and 5-CF were transported in a time and concentration-dependent manner. The DBF was transported at a broad pH (pH6.5-8.0) while 5-CF was transported at an acidic pH (pH5.5-6.5). The Km values were 0.818 ± 0.067μM at pH7.4 for DBF and 8.56 ± 0.41μM at pH5.5 for 5-CF. The OATP2B1 inhibitors, including atorvastatin, bromosulfophthalein, glibenclamide, sulfasalazine, talinolol, and estrone 3-sulfate, inhibited the DBF and the 5-CF transport. Contrastively, testosterone, dehydroepiandrosterone sulfate, and progesterone inhibited the DBF transport but stimulated the 5-CF transport. Natural flavonoid aglycones, such as naringenin and baicalein, also exhibited substrate-dependent effects in this manner. We found two fluorescein analogs, DBF and 5-CF as the OATP2B1 substrates that exhibited substrate-dependent interactions.

Clinically Relevant OATP2B1 Inhibitors in Marketed Drug Space.

OATP2B1 is an intestinal and hepatic drug uptake transporter. Intestinal OATP2B1 has been elucidated as the mechanism of unexpected clinical drug-drug interactions (DDIs), where drug exposure was unexpectedly decreased with unchanged half-life. Hepatic OATP2B1 may be an understudied clinical DDI mechanism. The aim of the present work was to understand the prevalence of clinically relevant intestinal and hepatic OATP2B1 inhibitors in marketed drug space. HEK293 cells stably overexpressing human OATP2B1 or vector control were generated and cultured for 72 h in a 96-well format. OATP2B1-mediated uptake of dibromofluorescein (DBF) was found to be optimal at 10 μM concentration and 30 min incubation time. A total of 294 drugs (top 300 marketed drugs, excluding biologics and restricted drugs, supplemented with ∼100 small-molecule drugs) were screened for OATP2B1 inhibition at 10 μM. Drugs demonstrating ≥50% inhibition in this screen were advanced for IC50 determination, which was extrapolated to clinical intestinal and hepatic OATP2B1 inhibition as per 2017 FDA DDI guidance. Of the 294 drugs screened, 67 elicited ≥50% inhibition of OATP2B1-mediated DBF uptake at 10 μM screening concentration. For the 67 drugs flagged in the single-concentration inhibition screen, upon evaluation of a full concentration range, IC50 values could be determined for 58 drugs. OATP2B1 IC50 values established for these 58 drugs were extrapolated as potentially clinically relevant at the intestinal level for 38 orally administered drugs (Igut/IC50 ≥ 10), and 17 were flagged as potential clinical inhibitors of hepatic OATP2B1 uptake (1 + Iin,max,u/IC50 ≥ 1.1). This analysis of 294 drugs demonstrated prevalence of clinically relevant intestinal and hepatic OATP2B1 inhibitors to be 13 and 6%, respectively. As OATP2B1-inhibitor drugs are not exceedingly rare, these results suggest that clinical OATP2B1 DDIs have been rarely observed because OATP2B1 is uncommonly the predominant determinant of drug disposition.

An ultrasensitive stain for negative protein detection in SDS-PAGE via 4′,5′-Dibromofluorescein

A highly sensitive method for brief and economical staining of proteins in 1-D and 2-D sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) by 4′,5′-Dibromofluorescein (DBF) was developed in this study. Down to 0.025–0.05ng protein could be detected within 10min (only 2 steps) by DBF stain, which is approximately 10-fold more sensitive than those of Eosin Y (EY) and SYPRO Ruby stains, and 20-fold more sensitive than that of imidazole-zinc (IZ) negative stain. In addition, the LC-MS/MS results indicated that the newly developed staining method is compatible with the downstream protein identification. Moreover, the mechanism of DBF stain was investigated by molecular docking.

Investigation of Fluorescein Derivatives as Substrates of Organic Anion Transporting Polypeptide (OATP) 1B1 To Develop Sensitive Fluorescence-Based OATP1B1 Inhibition Assays.

Organic anion transporting polypeptide (OATP) 1B1 plays an important role in the hepatic uptake of various drugs. Because OATP1B1 is a site of drug-drug interactions (DDIs), evaluating the inhibitory potential of drug candidates on OATP1B1 is required during drug development. For establishing a highly sensitive, high-throughput fluorescence-based OATP1B1 inhibition assay system, the present study focused on fluorescein (FL) and its derivatives and evaluated their uptake via OATP1B1 as well as OATP1B3 and OATP2B1 using the transporter-expressing human embryonic kidney 293 cells. We identified 2',7'-dichlorofluorescein (DCF), 4',5'-dibromofluorescein (DBF), and Oregon green (OG) as good OATP1B1 substrates with Km values of 5.29, 4.16, and 54.1 μM and Vmax values of 87.9, 48.1, and 187 pmol/min/mg protein, respectively. In addition to FL, fluo-3, and 8-fluorescein-cAMP, OG, and DBF were identified as OATP1B3 substrates. FL, OG, DCF, and DBF were identified as OATP2B1 substrates. Among the FL derivatives, DCF displayed the highest OATP1B1-mediated uptake. The Ki values of 14 compounds on OATP1B1 determined with DCF as a probe exhibited good agreement with those obtained using [(3)H]estradiol-17β-glucuronide (E2G) as a substrate, whereas [(3)H]estrone-3-sulfate and [(3)H]sulfobromophthalein yielded higher Ki values for all inhibitors than DCF. Mutually competitive inhibition observed between DCF and E2G suggested that they share the same binding site on OATP1B1. Therefore, DCF as well as E2G can be used as sensitive probes for in vitro OATP1B1 inhibition assays, which will help mitigate the risk of false-negative DDI predictions potentially caused by substrate-dependent Ki variations.

Supramolecular Networks of Hyperbranched Poly(ether amine) (hPEA) Nanogel/Chitosan (CS) for the Selective Adsorption and Separation of Guest Molecules

Supramolecular networks with selective adsorption for guest molecules were formed via dynamic hydrogen-bonding interactions between the carboxyl group-containing hyperbranched poly(ether amine) nanogels (hPEA-NG) and chitosan (CS). The hPEA-NG/CS supramolecular networks were physically cross-linked and were composed of hPEA-NGs dispersed within a crystallized CS matrix. An increasing CS content enhanced the mechanical properties of the hPEA-NG/CS supramolecular networks. The transparent hPEA-NG supramolecular networks did not disassemble in aqueous solutions with different pH values and organic solvents and were swollen with high weight fractions of water (WH2O = 0.95) in less than 30 s. The adsorptive behavior of seven fluorescein dyes and five azobenzene (azo) dyes onto the hPEA-NG/CS supramolecular networks was investigated. These hPEA-NG/CS supramolecular networks showed rapid adsorption for Rose Bengal (RB), Erythrosin B (ETB), Eosin B (EB), 4′,5′-dibromofluorescein (DBF), Ponceau S (PS) and Evans blue (EVB) dyes with high adsorption capacities (Qeq). The networks showed very low adsorption for calcein (Cal), fluorescein (FR), 4,5,6,7-tetrachlorofluorescein (TCF), and Bismarck brown (BBY) dyes. The adsorption process was found to follow pseudo-second-order kinetics. The different adsorptive behaviors for different dyes indicated the selective adsorption of the hPEA-NG/CS supramolecular networks for the azo and fluorescein dyes despite similar backbone structures and charge states. On the basis of the unique selective adsorption, the separation of mixtures of fluorescein dyes, such as RB/Cal, RB/FR, and PS/MR, was achieved using the hPEA-NG/CS supramolecular network as an adsorbent.

One-pot synthesis of fluorescent and cross-linked polyphosphazene nanoparticles for highly sensitive and selective detection of dopamine in body fluids

Highly cross-linked and monodisperse polyphosphazene (PZS) nanoparticles exhibiting strong fluorescence were prepared by the facile one-pot polycondensation of hexachlorocyclotriphosphazene and 4′,5′-dibromofluorescein (DBF).

Hyperbranched Poly(ether amine) (hPEA)/Poly(vinyl alcohol) (PVA) Interpenetrating Network (IPN) for Selective Adsorption and Separation of Guest Homologues

We here reported that hyperbranched poly(ether amine) (hPEA) and poly(vinyl alcohol) (PVA) interpenetrating network (hPEA/PVA-IPN) can be used for the selective adsorption and separation of guest homologues. A series of hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks (hPEA/PVA-IPNs) were fabricated by introducing poly(vinyl alcohol) chains into network of hyperbranched poly(ether amine), in which two independent networks of hyperbranched poly(ether amine) and poly(vinyl alcohol) were cross-linked through photodimerization of coumarin groups of hyperbranched poly(ether amine) and aldol condensation reaction between hydroxyl groups of poly(vinyl alcohol) and glutaraldehyde, respectively. The mechanical strength of interpenetrating networks can be enhanced by the introduction of poly(vinyl alcohol), and the tensile strength of interpenetrating networks increased with tens of times in compared with the pure hyperbranched poly(ether amine) network. The adsorption behavior of seven fluorescein dyes sharing with the same backbone and charge state onto hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks was then investigated in detail. Regardless of their charge states, these interpenetrating networks exhibited the quick adsorption to Rose Bengal (RB), Erythrosin B (ETB), Eosin B (EB), 4',5'-dibromofluorescein (DBF), and 4,5,6,7-tetrachlorofluorescein (TCF), with high adsorption capacity (Qeq) and very low adsorption of Calcein (Cal) and fluorescein (FR). The adsorption process was found to follow the pseudo-second-order kinetics, and the introduction of poly(vinyl alcohol) has no obvious effect on the adsorption behavior in this study. The big difference in the adsorption is indicative of the selective adsorption of hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks to fluorescein dyes. Based on the unique selective adsorption, the separation of several mixtures of fluorescein dyes such as RB/Cal, RB/FR, ETB/FR, and ETB/Cal was achieved by using hPEA/PVA-IPN as adsorbent.

Ultrafast Hole- and Electron-Transfer Dynamics in CdS–Dibromofluorescein (DBF) Supersensitized Quantum Dot Solar Cell Materials

Ultrafast charge-transfer (CT) dynamics has been demonstrated in CdS quantum dot (QD)–4′,5′-dibromofluorescein (DBF) composite materials, which form a strong CT complex in the ground state. Charge separation in the CdS–DBF composite was found to take place in three different pathways, by transferring the photoexcited hole of CdS to DBF, electron injection from photoexcited DBF to the CdS QD, and direct electron transfer from the HOMO of DBF to the conduction band of the CdS QD. CT dynamics was monitored by direct detection of the DBF cation radical and electron in the QD in the transient absorption spectra. Electron injection and the electron-transfer process are found to be pulse-width-limited (<100 fs); however, the hole-transfer time was measured to be 800 fs. Charge recombination dynamics has been found to be very slow, confirming spatial charge separation in the CdS–DBF supersensitized quantum dot system. Grand charge separation process suggests that the CdS–DBF supersensitized quantum dot system can be used as superior materials for quantum dot solar cells (QDSCs).

Determination of torasemide by fluorescence quenching method with some dihalogenated fluorescein dyes as probes

A novel fluorescence quenching method for the determination of torasemide (TOR) with some dihalogenated fluorescein dyes as fluorescence probes was developed. In acidulous medium, TOR could interact with some dihalogenated fluorescein dyes such as dichlorofluorescein (DCF), dibromofluorescein (DBF) and diiodofluorescein (DIF) to form binary complexes, which could lead to fluorescence quenching of above dihalogenated fluorescein dyes. The maximum fluorescence emission wavelengths were located at 532nm (TOR–DCF), 535nm (TOR–DBF) and 554nm (TOR–DIF). The relative fluorescence intensities (ΔF=F0−F) were proportional to the concentration of TOR in certain ranges. The detection limits were 4.8ngmL−1 for TOR–DCF system, 9.8ngmL−1 for TOR–DBF system and 35.1ngmL−1 for TOR–DIF system. The optimum reaction conditions, influencing factors were studied; and the effect of coexisting substances was investigated owing to the highest sensitivity of TOR–DCF system. In addition, the reaction mechanism, composition and structure of the complex were discussed by quantum chemical calculation and Job’s method. The fluorescence quenching of dihalogenated fluorescein dyes by TOR was a static quenching process judging from the effect of temperature and the Stern–Volmer plots. The method was satisfactorily applied to the determination of TOR in tablets and human urine samples.

Ecotoxicity of xanthene dyes and a non-chlorinated bisphenol in soil

Soil eco-toxicity testing was conducted in support of Canada’s Chemical Management Plan (CMP) to fill data gaps for organic chemicals known to primarily partition to soil, and of which the persistence and inherent toxicity are uncertain. Two compounds representative of specific classes of chemicals: non-chlorinated bisphenols containing an –OH group (4,4′-methylenebis(2,6-di-tert-butylphenol (Binox)) and xanthene dyes (2′,4′,5′,7′-tetrabromo-4,5,6,7-tetrachloro-3′,6′-dihydroxy-, disodium salt (Phloxine B), 2′,4′,5’,7′-tetrabromofluorescein (TBF), 4′,5′-dibromofluorescein (DBF), and 4,5,6,7-tetrachlorofluorescein (TCF)) were evaluated. The effect of these substances on plant growth (Elymus lanceolatus and Trifolium pratense) and soil invertebrate survival and reproduction (Folsomia candida and Eisenia andrei) were assessed using a field-collected sandy soil. Binox was persistent throughout testing (up to 63d) with an average recovery of 77±2.9% at test end. Binox was not toxic to plants (IC50s>1076mgkg−1) or E. andrei (IC50s>2651mgkg−1); however, a significant reduction in F. candida adult survival and reproduction (IC50=89 (44–149) mgkg−1) was evident. Phloxine B was also persistent throughout testing, with an average recovery of 82±3.0% at test end. Phloxine B was significantly more toxic than Binox, with significant reductions in plant root growth (IC50s⩾11mgkg−1) and invertebrate reproduction (IC50s⩾22mgkg−1). DBF toxicity was not significantly different from that of Phloxine B for plant root growth (IC50s⩾30mgkg−1), but was significantly less toxic for shoot growth (IC50s⩾1758mgkg−1), and invertebrate adult survival (IC50s⩾2291mgkg−1) and reproduction (IC50s⩾451mgkg−1). A comparison between all four xanthene dyes was completed using F. candida, with the degree of toxicity in the order of Phloxine B⩾TBF∼DBF>TCF. The results from these studies will contribute to data gaps for poorly understood chemicals (and chemical groupings) under review for environmental risk assessments, and will aid in the validation of model predictions used to characterize the fate and effects of these substances in soil environments.

Study on the ternary ion-association complex nanoparticles of palladium(II)-famotidine and halogen-fluorescein dyes by the resonance Rayleigh scattering and their application

In pH 3.5-4.7 NaAc-HAc buffer medium,famotidine(FMTD)reacted with palladium(Ⅱ)(Pd(Ⅱ))to form chelate cation,which further reacted with halogen-fluorescein dyes(HF)such as dichlorofluorescein(DCF),dibromofluorescein(DBF),diiodofluorescein(DIF),Erythrosine(ER),eosine(EY)and eosin(EE)to form ternary ion-association complexes[Pd(FMTD)]·(HF)2.It further aggregated to form average diameter of about 9 nm nanoparticles by hydrophobic forces and Van der Waals forces.As a result,the absorption bands of DCF,DBF,DIF,ER,EY,EE were shifted,the fluorescences of them were quenched and the resonance Rayleigh scattering(RRS) were enhanced greatly.The maximum absorption wavelengths of[Pd(FMTD)·(HF)2]were located at 476 nm(DCF system),540 nm(DBF system),553 nm(DIF system),560 nm(ER system),547 nm(EY system),549 nm(EE system)and the maximum RRS wavelengths of those were located at 302-361 nm.The ΔI was proportional to the FMTD concentration in a certain range and the detection limit was 1.0-2.6 ng/L.Based on it,a high sensitive,good selective,rapid and new molecular spectrum method had been proposed to determine FMTD.It could be applied to determine FMTD in pharmaceutical preparation such as tablets,gelatin capsule and injection.In this work,the optimum reaction conditions,the influences of coexisting substances and the properties of analytical chemistry were investigated.Moreover,the mechanism of ion-association reaction and the reasons of enhancement for RRS were also discussed by the change of absorption,fluorescence and the formation of nanoparticles.

Dual wavelength excitation fluorescence detector for capillary electrophoresis using a pulsed bi-colour light emitting diode

A simple and novel two-colour fluorescence detector for capillary electrophoresis was created using a single bi-colour light emitting diode (LED), multi-band pass excitation and emission filters and a single detector. Excitation light from a blue/red (470/635 nm) bi-colour LED was filtered through a 390/482/563/640 nm multi-band bandpass filter, with emitted light filtered through a 446/523/600/677 nm multi-band bandpass filter before being detected using a photon counting detector. Sequential pulsing of the blue/red LED and deconvolution of the collected fluorescence data allowed extracted electropherograms to be obtained corresponding to excitation with the blue and red LEDs. Optimisation of the pulsed LED conditions revealed an optimum LED on-time of 50 ms, off-time of 30 ms with a pulsed current of 40 mA, giving an effective data acquisition rate of 6.25 Hz. The characteristics of this system were validated by the simultaneous separation and determination of six fluorescent dyes: fluorescein, FITC, coumarin 334, dibromo(R)fluorescein (Ex/Em 470/525 nm), and Cy 5 and the Agilent Bioanalyser DNA dye (Ex/Em 635/670 nm). Under optimum conditions, the detection limits for FITC, fluorescein and Cy 5 were 69 nM, 42 nM and 289 nM (S/N = 3), respectively. These were lower than those obtained with continuous operation of the individual wavelengths at a constant current of 20 mA, but were slightly higher than those obtained using dedicated single wavelength filter combinations designed specifically for use with these fluorophores. The intraday repeatability (n = 6) of migration times was less than 1.0% and less than 3.4% for peak areas, while interday (n = 3) migration time and peak area reproducibility were less than 0.9% and 3.6%, respectively. This simple detector is capable of performing quantitative two-wavelength excitation without the need for complex optics and light source configurations.

Effect of Surface Modification on Back Electron Transfer Dynamics of Dibromo Fluorescein Sensitized TiO2 Nanoparticles

Electron injection and back electron transfer (BET) dynamics have been carried out for dibromo fluorescein (DBF) sensitized TiO2 nanoparticles capped (modified) with sodium dodecyl benzene sulfonate using transient absorption techniques in picosecond and microsecond time domain. BET dynamics have been compared with bare (unmodified) nanoparticles for the same DBF/TiO2 system. It has been observed that BET reaction is slow on the modified surface compared to a bare surface in earlier time domain (picosecond). This observation has been explained by the fact that on surface modification the energy levels of the semiconductor nanoparticles are pushed up in energy. As a result, the free energy of reaction (-deltaG zero) for BET reaction of a dye/SM-TiO2 system increases as compared to the dye/bare TiO2 system. High exoergic BET reaction in dye-sensitized TiO2 nanoparticles surfaces fall in the Marcus inverted regime, so with increasing free energy of reaction, BET rate decreases on the modified surface. However, a reversible trend in BET dynamics has been observed for the above systems in the longer time domain (microsecond). In microsecond time domain BET reaction is faster on the modified surface as compared to on the bare surface. Modification of this surface reduces the density of deep trap states. Recombination dynamics between deep-trapped electron and parent cation is slow due to low coupling strength of BET reaction. As the density of deep-trapped electrons is high in bare particles, BET reaction is slow in longer time domain.