Junfen Li

Synthesis and spectral characteristics of two novel intramolecular charge transfer fluorescent dyes

The synthesis and absorption/fluorescence properties of two novel intramolecular charge transfer (ICT) compounds of (fluorene-2-yl)-(9-ethylcarbazole-3-yl) ketene and 1-phenyl-3-(fluorenone-2-yl)-5-(9-ethylcarbazole-3-yl)-2-pyrazoline were reported. The primary structure of the target compounds was characterized by IR and (1)H NMR. The systems contained a fluorenone or a propenon group as an electron acceptor (A) and an N-ethylcarbazole and a pyrazoline group as electron donors (D). From the emissive properties it was concluded that the electronic coupling between D and A was sufficient to allow charge transfer in these molecules. The ICT maximal emission displayed a large wavelength shift and Stokes shifts increased in response to the increase of the solvent polarity. The highly solvatochromic properties made the two compounds of great interest as new classes of fluorescent probes, electroluminescent and electrofax materials.

Luminescence and binding properties of two isoquinoline alkaloids chelerythrine and sanguinarine with ctDNA.

The binding mode and mechanism of the interactions between two planar cationic alkaloids chelerythrine (Che) and sanguinarine (San) with calf thymus DNA (ctDNA) were systematically investigated at pH 5.40 using UV-vis absorption spectroscopy, fluorescence spectroscopy and cyclic voltammetry. Che and San show strong fluorescence at 570 and 589 nm, respectively. Che displays fluorescence enhancement with ctDNA whereas the fluorescence of San is quenched on interaction with ctDNA. In addition, UV-vis spectra of both alkaloids show apparent hypochromicity and are bathochromic shifted, indicating that they could intercalate into ctDNA bases. The fluorescence polarization of Che and San increases in the presence of ctDNA, again implying the intercalation of two alkaloids with ctDNA. This conclusion was also supported by the results obtained from anion quenching and cyclic voltammetry. The binding constants of both alkaloids with ctDNA were calculated in the order of 10(5)L/mol. San binds with ctDNA 3-fold stronger than Che. The stoichiometric bindings are five nucleotides per Che or San. Electrostatic binding also exists between the alkaloids and DNA helix. Finally, theoretical calculations show that only certain parts of Che and San molecules intercalate into the DNA helix.

Study on the phosphorescence characterizations of palmatine chloride on the solid substrate and its interaction with ctDNA

The spectroscopic characterizations of solid substrate room temperature phosphorescence (SS-RTP) of palmatine (Pal) have been studied. Strong RTP signal at 615nm can be induced on filter paper in the presence of TIAc. The interaction between calf thymus DNA (ctDNA) and Pal has been investigated at pH 6.90 using fluorescence, UV-vis, SS-RTP and cyclic voltammogram spectroscopy. Strong binding affinity of Pal with DNA is revealed from the absorption and fluorescence studies in the liquid state. With the addition of ctDNA, the fluorescence intensity of Pal is enhanced greatly and UV-vis spectra show no apparent hypochromicity and red shift, which indicates that Pal intercalates into ctDNA bases. However, this conclusion could not explain the phenomena from fluorescence polarization and denatured DNA measurements, which indicate that groove binding is at least the main binding mode. Binding constant and binding site size have been calculated to be 2.57x10(4)L/mol and 0.16 based on Scatchard plot from fluorescence titration data. Groove binding has also been supported by phosphorescence lifetime and anion quenching experiments. Above studies demonstrate that there should exist intercalative binding and groove binding in the interaction of Pal and DNA. Furthermore, cyclic voltammogram study suggests that electrostatic binding exists at the same time exactly. Taken together, the binding model obtained in this study is mixed-mode.

Synthesis of 1-phenyl-3-biphenyl-5-(N-ethylcarbazole-3-yl)-2-pyrazoline and its use as DNA probe

A novel pyrazoline derivative, named 1-phenyl-3-biphenyl-5-(N-ethylcarbazole-3-yl)-2-pyrazoline, was synthesized, and its structure was confirmed by means of IR, (1)H NMR, and elementary analysis. The compound emits strong yellow fluorescence. Decrease of fluorescence intensity of the pyrazoline derivative in the presence of calf thymus DNA (ct DNA) is observed, and the quenching obey Stern-Volmer equation. There is a single quenching mechanism for the complex, which belongs to static quenching. KI quenching study shows that the magnitude of K(SV) of the bound pyrazoline is lower than that of the free one. It is also found that ionic strength could affect the interaction. Binding constants for pyrazoline with ct DNA and salmon sperm DNA (ss DNA) are in the same order of 10(4) molL(-1), and binding site size are about 1 per base pairs. Experimental results indicate that the new compound might insert into DNA base pairs by intercalative binding mode.

Study on the inclusion complexes of cryptotanshinone with β-cyclodextrin and hydroxypropyl-β-cyclodextrin

The inclusion complexes of β-cyclodextrin (β-CD) and HP-β-cyclodextrin (HP-β-CD) with a kind of tanshinone, cryptotanshinone (CTan) were investigated by using spectrophotometry. Stable inclusion complexes were established in solution and in solid state and were characterized by UV, IR and 1H NMR spectra, respectively. The optimum pH for inclusion is about 7.5. Stoichiometry of the inclusion complex is 1:1. The stabilities of β-CD and HP-β-CD to CTan were in the order: β-CD<HP-β-CD. The effect of temperature on the inclusion interaction was examined and the thermodynamic parameters of inclusion process, ΔG, ΔH, ΔS were determined. The experimental results indicated that the inclusion process was an exothermic and enthalpy-driven process. Special configuration of the inclusion complexes was proposed by 1D, 2D NMR.

Photophysical processes of an intramolecular charge transfer fluorescent dye with carbazole units

A carbazole-based compound with intramolecular charge transfer (ICT) characteristics, 3,6-bis-((N-ethylcarbazole-3-)-propene-1-keto)-N-ethylcarbazole (BCzPCz) was synthesized by N-alkylation, acetylation and aldol condensation. BCzPCz was further confirmed by IR and (1)H NMR. The central N-ethylcarbazole was connected with two N-ethylcarbazole units through the propenone group in BCzPCz. N-ethylcarbazole and carbonyl groups were electron donors (D) and acceptors (A), respectively. The UV-vis absorption and fluorescence characteristics of BCzPCz were also investigated in different solvents. Solvatochromism was attributed to ICT complex formation in singlet excited state. Magnitude of the change in the dipole moment was 24.78 D according to Lippert-Mataga equation. Fluorescence of BCzPCz was significantly affected by pH and was quenched in acidic medium. Fluorescence quantum yield of BCzPCz was 0.516 in ethanol. Experimental results showed its potential use as a fluorescence probe and as two-photon absorption material.

Studies on the spectroscopic behavior of cryptotanshinone, tanshinone IIA, and tanshinone I

A comparative study on the spectroscopic behavior of cryptotanshinone (CTan), tanshinone IIA (Tan IIA), and tanshinone I (Tan I) has been investigated, including UV-Vis absorption, low temperature phosphorescence (LTP), low temperature fluorescence (LTF), paper substrate-room temperature phosphorescence (PS-RTP), paper substrate-room temperature fluorescence (PS-RTF) and fluorescence in liquid (LF). The effect of pH on the luminescence intensity is discussed. Lifetime and polarization of the LTP and RTP have been examined with phosphorescence lifetime in the range of 0.6-0.9s and polarization in the range of 0.10-0.27. Analytical characteristics of LF, PS-RTF and PS-RTP of CTan, Tan IIA, and Tan I have been studied.

An Analytical Application of Ofloxacin by Solid‐Substrate Room Temperature Phosphorescence

ABSTRACT This article presents a new determination method for the analysis of ofloxacin (OFLX) by solid‐substrate room temperature phosphorescence (SS‐RTP) with filter paper as solid substrate and CdCl2 as heavy‐atom salt. Various factors affecting RTP intensity of OFLX, such as heavy‐atom effect, pH, and drying time of the sample, were studied in detail. The linear dynamic range (LDR), limit of detection, and RSD were: 1.03 to 411 ng/spot, 0.123 ng/spot and 1.7% for OFLX, respectively. The method was applied to determine OFLX in urine successfully. The recoveries of OFLX in urine were from 94.60% to 105.4%. The pharmacokinetic of OFLX was studied in urine as well. Mean accumulative excretion rate was 77.69%.

Immobilization of uricase-gold nanoparticles composite nanomaterial on a biofilm and its application to determination of uric acid

The uricase-gold nanoparticles (AuNPs) composite nanomaterial was covalently immobilized on a biofilm, eggshell membrane. The uric acid biosensor was constructed by positioning the immobilized biofilm on the surface of a Clark dissolved oxygen electrode. The scanning electron micrograph revealed that the uricase-AuNPs composite nanomaterial was successfully immobilized. The effects of enzyme loading, pH, concentration of phosphate buffer and temperature on the biosensor response have been studied in detail. The results showed that response time of the biosensor was 60 s, the linear range for the detection of uric acid varied from 1.0 µM to ~1.0 mM with a detection limit of 0.8 µM (S/N = 3) and relative standard deviation of 2.6% for 0.1 mM uric acid (n = 6). Some common potential interferents in samples demonstrated no interferences. The biosensor has been successfully applied to determine the uric acid level in urine and serum samples.

The Solid Surface Room Temperature Phosphorescence of Three Purine Compounds and Analytical Application

Abstract Solid surface room temperature phosphorescence (SS‐RTP) of 6‐mercaptopurine (6‐MP), azathiopurine (BAN), and 8‐azaguanine (8‐Azan) was investigated. Various factors affecting the SS‐RTP signal were discussed in detail. The corresponding analytical determination methods were established. The linear dynamic range (LDR) was 2.00 × 10−3 mmol/L–0.401 mmol/L for 6‐MP, 2.01 × 10−3 mmol/L–0.600 mmol/L for BAN, 1.09 × 10−3 mmol/L–0.218 mmol/L for 8‐Azan, respectively. The limit of detection (LOD) was 1.30 µmol/L for 6‐MP, 1.21 µmol/L for BAN, 7.35 × 10−2 µmol/L for 8‐Azan, respectively. Average recoveries in urine sample were 97.1%–99.9% for 6‐MP, 95.4%–101.7% for BAN, 96.2%–101.3% for 8‐Azan. The recovery of 6‐MP added to pharmaceutical preparation was 99.6%–100.5%.