How Graphene Oxide Quenches Fluorescence of Rhodamine 6G

We investigate the fluorescence quenching of Rhodamine 6G (R6G), a well known laser dye with a high fluorescence quantum yield, by as-synthesized graphene oxide (GO) in aqueous solution, which is found to be rather efficient. By means of steady-state and time-resolved fluorescence spectroscopy combined with detailed analysis about the linear absorption variation for this R6G-GO system, the pertinent quenching mechanism has been elucidated to be a combination of dynamic and static quenching. Possible ground-state complexes between R6G and GO during the static quenching have also been suggested. Furthermore, the direction of photoinduced electron transfer between R6G and GO has been discussed.     

Fluorescence quenching of dyes by tryptophan: interactions at atomic detail from combination of experiment and computer simulation

Fluorescence spectroscopy and molecular dynamics (MD) simulation are combined to characterize the interaction of two organic fluorescent dyes, rhodamine 6G (R6G) and an oxazine derivative (MR121), with the amino acid tryptophan in aqueous solution. Steady-state and time-resolved fluorescence quenching experiments reveal the formation of essentially nonfluorescent ground-state dye/Trp complexes. The MD simulations are used to elucidate the molecular interaction geometries involved. The MD-derived probability distribution of the distance r between the centers of geometry of the dye and quencher ring systems, P(r), extends to higher distances for R6G than for MR121 due to population in the R6G/Trp system of fluorescent interaction geometries between Trp and the phenyl ring and ester group of the dye. The consequence of this is the experimental finding that under the conditions used in the simulations about 25% of the R6G dye is fluorescent in comparison with 10% of the MR121. Combining the above findings allows determination of the "quenching distance", r, above which no quenching occurs. r is found to be very similar (approximately 5.5 A) for both dye/Trp systems, corresponding to close to van der Waals contact. Both experimental dynamic Stern-Volmer analysis and the MD trajectories demonstrate that the main determinant of the fluorescence intensity is static quenching. The approach presented is likely to be useful in the structural interpretation of data obtained from fluorescent conjugates commonly used for monitoring the binding and dynamics of biomolecular systems.     

Solvent Effects on the Spectral Properties of Rhodamine 6G: Estimation of Ground and Excited State Dipole Moments

Spectroscopic and photophysical behavior of Rhodamine 6G (R6G) in seven solvents are reported in this work. R6G monomers exhibit strong electronic absorptions (due to π*←π transitions) in the 529–539-nm region, and the band positions were shown to depend on the refractive indices of the respective solvents. The Stokes’ shifts displayed a linear dependence on solvent polarity, with values ranging between 19 nm (in benzene) and 28 nm (in water). R6G’s fluorescence quantum yields (Φ_F) are generally high (> 0.90), and this was ascribed to structural features (rigidity, planarity and presence of condensed rings) in the R6G molecule. These Φ_F values are shown to vary with solvent viscosity in accordance with the Förster–Hoffmann model. Fluorescence quenching of R6G by 1,4-benzoquinone was diffusion controlled and occurred via an electron transfer mechanism. Theoretical treatment of the fluorescence quenching data yielded fluorescence lifetime values, which were also shown to be solvent viscosity dependent. Ground-state and excited-state dipole moments of R6G were obtained semi-empirically via the analysis of solvatochromic data, and the values are found to be 0.69 D and 1.97 D, respectively.     

能量转移荧光猝灭法测定加替沙星

在λ_(ex)/λ_(em)=470/566 nm、BR缓冲溶液(pH=5.72)、十二烷基苯磺酸钠介质中,吖啶橙(AO)与罗丹明6G(R6G)间能发生有效的能量转移,使R6G的荧光强度显著增强;加替沙星的加入,使R6G的荧光发生猝灭.应用AO-R6G能量转移荧光猝灭法测定加替沙星含量,提高了测定的灵敏度和选择性.加替沙星的浓度在0.6～9.0 μmol·L~(-1)范围内与R6G荧光猝灭程度呈线性关系;方法检出限为0.52 μmol·L~(-1);平行6次测定样品相对标准偏差为0.62%～0.84%;回收率为90.0%～105%.常见金属离子及药物敷料对测定无干扰,不经分离直接用于药物中加替沙星的测定.     

Silver Nanostructures on Graphene Oxide as the Substrate for Surface-Enhanced Raman Scattering (SERS)

Nanosized surface-enhanced Raman scattering (SERS) substrates fabricated by the controlled growth of metal nanostructures on water-dispersed two-dimensional nanomaterials can open a new avenue for SERS analysis of liquid samples in biological fields. In this work, regular and uniform Ag nanostructures were grown on the surface of graphene oxide (GO) through a microwave-assisted hydrothermal method. Polyamidoamine (PAMAM) dendrimers were assembled on the surface of GO to form GO/PAMAM templates for growing Ag nanostructures, which are primarily comprised of Ag dimers and trimers. The prepared Ag/GO nanocomposites are highly dispersed and stable in aqueous solution and may be used as substrates for enhanced Raman detection of rhodamine 6?G (R6G) in aqueous solution. This special substrate provides high-performance SERS and suppresses R6G fluorescence in aqueous solution and is promising as a nanosized material for the enhanced Raman detection of liquid samples in biological diagnostics.     

吖啶橙-罗丹明6G荧光共振能量转移及其罗丹明6G荧光猝灭法测定蛋白质

研究了吖啶橙(AO)与罗丹明6G(R6G)之间能量转移的最佳条件。在pH=7．20的Tirs-HCl缓冲溶液,十二烷基苯磺酸钠介质中,AO-R6G能够发生有效能量转移,使R6G荧光增强。蛋白质的加入使R6G荧光猝灭,以此建立了利用AO-R6G荧光共振能量转移间接测定蛋白质的新方法。牛血清白蛋白、人血清白蛋白工作曲线线性范围分别为1．0～31和1．0—30mg／L;检出限分别为0．32和0．33mg／L;平行6次测定相对标准偏差为1．1％～2．0％;回收率为96．7％～103．2％。此方法的稳定性好,选择性高,用于人血清试样中总蛋白含量的测定,与常用的双缩脲法基本一致。     

Quenching mechanism of Zn(salicylaldimine) by nitroaromatics

Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N'-phenylene-bis-(3,5-di- tert-butylsalicylideneimine); ZnL(R)) complexes. A structurally related family of ZnL(R) complexes (R = OMe, di-tBu, tBu, Cl, NO2) were prepared, and the mechanisms of fluorescence quenching by nitroaromatics were studied by a combined kinetics and spectroscopic approach. The fluorescent quantum yields for ZnL(R) were generally high (Phi approximately 0.3) with sub-nanosecond fluorescence lifetimes. The fluorescence of ZnL(R) was quenched by nitroaromatic compounds by a mixture of static and dynamic pathways, reflecting the ZnL(R) ligand bulk and reduction potential. Steady-state Stern-Volmer plots were curved for ZnL(R) with less-bulky substituents (R = OMe, NO2), suggesting that both static and dynamic pathways were important for quenching. Transient Stern-Volmer data indicated that the dynamic pathway dominated quenching for ZnL(R) with bulky substituents (R = tBu, DtBu). The quenching rate constants with varied nitroaromatics (ArNO2) followed the driving force dependence predicted for bimolecular electron transfer: ZnL* + ArNO2 --> ZnL(+) + ArNO2(-). A treatment of the diffusion-corrected quenching rates with Marcus theory yielded a modest reorganization energy (lambda = 25 kcal/mol), and a small self-exchange reorganization energy for ZnL*/ZnL(+) (ca. 20 kcal/mol) was estimated from the Marcus cross-relation, suggesting that metal phenoxyls may be robust biological redox cofactors. Electronic structure calculations indicated very small changes in bond distances for the ZnL --> ZnL(+) oxidation, suggesting that solvation was the dominant contributor to the observed reorganization energy. These mechanistic insights provide information that will be helpful to further develop ZnL(R) as sensors, as well as for potential photoinduced charge transfer chemistry.     

芦丁对罗丹明6G的荧光猝灭机理研究及其含量测定

根据Stem - Volmer方程和罗丹明6G吸收光谱的变化研究了芦丁对其荧光猝灭的类型及机理,结果表明,芦丁与罗丹明6G作用,形成一种稳定的复合物,而发生荧光静态猝灭,求得复合物的结合常数K=5.55×105L/mol,结合点数n=1.26.芦丁含量在0.92～137.8μg/mL范围内与F0/F成正比,检出限为0....     

Studies on the Spectra of 4,5‐Dibromofluorescein with Proteins and its Analytical Application

4,5‐Dibromofluorescein(R) binding to proteins causes a decrease in the fluorescence maximum of R at 530 nm; the intensity of fluorescence quenching is directly proportional to protein content, Based on this, a new fast and simple fluorescence quenching method for the determination of proteins was developed. Under experimental conditions, the linear range of this assay is 0?15 mg/L and the detection limit is 40 μg/L. The method has been applied to the analysis of human serum samples and gave values close to those obtained by the Coomassie brilliant blue G‐250 (CBB G‐250) method, which indicated that the method is not only high in sensitivity but also reliable.     

Fluorescence resonance energy transfer between acridine orange and rhodamine 6G and its analytical application for vitamin B12 with flow-injection laser-induced fluorescence detection

By coupling flow-injection with laser-induced fluorescence detection, a setup was developed and a novel method combining fluorescence resonance energy transfer (FRET) and flow-injection analysis (FIA) was proposed for the determination of vitamin B₁₂ (VB₁₂) based on its fluorescence quenching on the system of acridine orange (AO)/rhodamine 6G (R6G). The effective energy transfer could occur between AO and R6G in the dodecyl benzene sodium sulfonate (DBS) while 454 nm argon laser was used as the excitation source, and as a result, the fluorescence emission of R6G has been increased significantly. It was found that the fluorescence of the above system could be sharply diminished by VB₁₂. By using the mixed solution AO-R6G-DBS and the same solution containing VB₁₂ as the carrier and sample, respectively, a series of negative peaks which could be applied for the quantification of VB₁₂ were obtained. The detection limit for VB₁₂ was 1.65 × 10⁻⁶ mol/L. The linear range for determining VB₁₂ was 4 × 10⁻⁴ to 2 × 10⁻⁶ mol/L (correlation coefficient, r = 0.9923). The method was applied to measure VB₁₂ injections with satisfactory results.     

醇存在下R,S-1,1′-2-联萘酚对映体的环糊精手性识别研究

以R,S-1,1′-2-联萘酚对映体为手性客体分子, 采用荧光探针法详细研究了各种醇对β-环糊精/(R或S)-1,1′-2-联萘酚对映体的手性包络和手性荧光猝灭等性质的影响, 结果表明, 醇的存在可显著影响R,S-1,1′-2-联萘酚对映体与β-环糊精形成包络物的包络形式和包络常数. 通过与该对映体的β-环糊精手性固定相高效液相色谱拆分法比较研究结果表明, 醇等第三客体分子可显著影响环糊精对对映体化合物的手性选择性和分离度.     

茉莉酸甲酯和超氧化物歧化酶相互作用的光谱法研究

通过荧光光谱法和紫外吸收光谱法研究了超氧化物歧化酶和茉莉酸甲酯之间的相互作用。经过荧光光谱法的研究表明,超氧化物歧化酶和茉莉酸甲酯的相互作用是一个静态猝灭的过程,它们之间是以氢键和范德华力结合的,同时得到超氧化物歧化酶和茉莉酸甲酯的结合位点数n,表观结合常数K和热力学参数ΔH,ΔG,ΔS。而根据非放射性能量转移的F rster理论和同步荧光光谱证明茉莉酸甲酯和超氧化物歧化酶的相互作用位点同时接近超氧化物歧化酶色氨酸(Trp)和酪氨酸(Tyr)残基。     

Interaction of Bovine Serum Albumin with N‐(4‐Ethoxyphenyl)‐N′‐(4‐Antipyrinyl)Thiourea (EPAT) Using Spectroscopies

The interaction between N‐(4‐ethoxyphenyl)‐N′‐(4‐antipyrinyl)thiourea (EPAT) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy in combination with UV absorption spectroscopy. The intrinsic fluorescence of bovine serum albumin was quenched by EPAT through a static quenching procedure. The binding constants of EPAT with BSA were estimated according to the fluorescence quenching results at different temperatures. The thermodynamic parameters: enthalpy change (ΔH) and entropy change (ΔS) were calculated to be ?10.69 kJ/mol and 42.64 J·mol^?1·K^?1 according to thermodynamic equations, respectively, and indicating that the binding force was suggested to be mainly a hydrophobic force. The effect of common ions on the binding constant was also investigated. A new fluorescence spectroscopy assay of the proteins was presented in this paper. The determination results of the proteins in bovine serum by means of this method were very close to those obtained using Coomassie Brilliant Blue G‐250 colorimetry.     

Stabilization of Aqueous Graphene Oxide with Acetone under \begin{document}$\gamma$\end{document}-Ray/UV Irradiation

Graphene oxide (GO) is a kind of water soluble two-dimensional materials containing a large amount of oxygen-containing groups which infuse GO with water solubility, biocompatibility and functionality, etc. But GO can be easily reduced by losing oxygen-containing groups under some circumstances such as irradiation of \begin{document}$\gamma$\end{document}-ray or ultraviolet (UV). In this work, we found that acetone can significantly slow down the reduction process of GO under the irradiation of either \begin{document}$\gamma$\end{document}-ray or UV, which was supported by analysis results with UV-visible (UV-Vis) absorption spectra, X-ray photoelectron spectroscopy, etc. Acetone can capture and remove strongly reducible hydrated electrons generated under \begin{document}$\gamma$\end{document}-irradiation. GO reduction by UV also involves electron transfer process which can be affected by the presence of acetone. Hence, acetone can be used to stabilize, adjust the radiation reduction process of GO. This would be interesting not only in radiation and radiation protection, but also in understanding the redox properties of GO.     

Highly fluorescence quenching graphene oxide-based oligodeoxynucleotide hairpin systems for probing CNG DNA repeat sequences

In this study we synthesized a novel graphene-oxide (GO) based CNG repeat hairpin probing system capable of detecting target CAG and CTG DNA repeat sequences. The fluorescence of the 30-mer CNG repeat hairpin structure was quenched dramatically by GO in the absence of the target sequence, with a high quenching constant [K = 0.030 (mg/mL)^?1]. We optimized the quenching behavior of this probing system by using graphene oxide (GO) to induce a high degree of discrimination factor (44.6 times) between the fluorescence of the target sequence and that of other non-target sequences. All detection process is explained by displacement mechanism using adsorption, desorption, and hybridization of probe with target DNA sequence on the GO. Graphene-oxide (GO) based CNG repeat hairpin probing system exhibited high sensitivity and selectivity to the target CNG repeat sequence and its detection process is so simple and quick.     

香豆素类中药有效成分与牛血清白蛋白结合的构效关系

本文主要用荧光光谱(FS)、 紫外光谱(UV)从药物分子结构角度研究五种香豆素类中药有效成分CⅠ~CⅤ与牛血清白蛋白(Bovine Serum Albumin, BSA)结合时的构效关系.     

Photoinduced Electron Transfer in Host-Guest Complexes of 2-Naphthyl-O(CH2) n -adamantanamines with Mono-6-O-p-nitrobenzoyl-β-cyclodextrin and Mono-6-O-m-nitrobenzoyl-β-cyclodextrin

A number of naphthalene derivatives containing adamantanamine binding moiety and an (CH₂) _n (n=2, 3, 4, 5, 6) spacer were prepared as the electron donor. A supramolecular assembly was fabricated by the inclusion between the donor substrates and the host molecules, i.e., mono-6-O-p-nitrobenzoyl-β-cyclodextrin (pNBCD) and mono-6-O-m-nitrobenzoyl-β-cyclodextrin (mNBCD), in water. The fluorescence quenching in these systems was studied in detail. It revealed efficient photoinduced electron transfers (PET) between the naphthalene donors and the cyclodextrin acceptors. This PET process was partitioned into a dynamic quenching component caused by bimolecule collision reactions and a static quenching component due to hydrophobic binding between the donor and acceptor molecules. Detailed Stern–Volmer constants were measured and they were partitioned into dynamic Stern–Volmer quenching constants (dynamic quenching) and static binding constants (static quenching). In these two pathways, the static quenching was found to be highly efficient and dominant in the presence of NBCD.     

Theoretical Investigating Mechanisms of Drug-Resistance Generated by Mutation-Induced Changes in Influenza Viruses

Influenza A (A/H\begin{document}$ x $\end{document}N\begin{document}$ y $\end{document}) is a significant public health concern due to its high infectiousness and mortality. Neuraminidase, which interacts with sialic acid (SIA) in host cells, has become an essential target since its highly conserved catalytic center structure, while resistance mutations have already generated. Here, a detailed investigation of the drug resistance mechanism caused by mutations was performed for subtype N9 (A/H7N9). Molecular dynamics simulation and alanine-scanning-interaction-entropy method (ASIE) were used to explore the critical differences between N9 and Zanamivir (ZMR) before and after R294K mutation. The results showed that the mutation caused the hydrogen bond between Arg294 and ZMR to break, then the hydrogen bonding network was disrupted, leading to weakened binding ability and resistance. While in wild type (A/H7N9\begin{document}$ ^{ \rm{WT}} $\end{document}), this hydrogen bond was initially stable. Meanwhile, N9 derived from A/H11N9 was obtained as an R292K mutation. Then the relative binding free energy of N9 with five inhibitors (SIA, DAN, ZMR, G28, and G39) was predicted, basically consistent with experimental values, indicating that the calculated results were reliable by ASIE. In addition, Arg292 and Tyr406 were hot spots in the A/H11N9\begin{document}$ ^{ \rm{WT}} $\end{document}-drugs. However, Lys292 was not observed as a favorable contributing residue in A/H11N9\begin{document}$ ^{ \rm{R292K}} $\end{document}, which may promote resistance. In comparison, Tyr406 remained the hotspot feature when SIA, ZMR, and G28 binding to A/H11N9\begin{document}$ ^{ \rm{R292K}} $\end{document}. Combining the two groups, we speculate that the resistance was mainly caused by the disruption of the hydrogen bonding network and the transformation of hotspots. This study could guide novel drug delivery of drug-resistant mutations in the treatment of A/H\begin{document}$ x $\end{document}N9.     

Synthesis,crystal structure,DNA/bovine serum albumin binding and antitumor activity of two transition metal complexes with 4‐acylpyrazolone derivative

Two new complexes, namely [Cu₆L₆] ( 1 ) and [Zn(HL)₂] ( 2 ) (H₂L = N‐(1‐phenyl‐3‐methyl‐4‐propenylidene‐5‐pyrazolone)‐2‐furancarboxylic acid hydrazide), have been synthesized and characterized. Single crystal X‐ray analysis indicates that complex 1 has a hexanuclear structure and complex 2 exhibits a mononuclear structure. The DNA/bovine serum albumin (BSA) binding properties of complexes 1 and 2 were investigated by absorption spectroscopy and fluorescence quenching. Both complexes could effectively intercalate to DNA with calculated quenching constants of 2.6 × 10⁵ and 1.25 × 10⁵ M^?1, respectively. The quenching mechanism of the intrinsic fluorescence of BSA by the complexes was found to be a static one. The cytotoxicities of 1 and 2 were investigated in two human tumor cell lines, human esophageal cancer cells (Eca‐109) and cervical cancer cells (HeLa). Complex 1 exhibits higher antitumor activity than 2 . Furthermore, 1 can inhibit HeLa cells by inducing apoptosis and G0/G1 phase cell cycle arrest. All results demonstrate that 1 and 2 both have DNA/BSA binding capacity and antitumor activity.     

Fluorescent Property of Gold Nanoparticles with Different Surface Structures

"?Fluorescence spectra of naked gold nanoparticles, triphenylphosphine stabled gold nanoparticles, and 3-mercaptopropionic acid substituted gold nanoparticles were studied. It was found that fluorescence intensities of gold nanoparticles were highly sensitive to surface molecules. The fluorescence quenching effect of these gold nanoparticles on CdSe nanoparticles was also investigated. This quenching effect was related to the overlap degree between the absorption spectra of gold nanoparticles and the emission spectrum of CdSe nanoparticles, and was surface-dependent as well. "