Synthesis and photophysical behaviors of temperature/pH-sensitive polymeric materials. I. Vinyl monomer bearing 9-aminoacridine and polymers

A novel acrylic monomer bearing acridinyl group, acridine-9-N-acrylamide (Ac-9AA) was synthesized from 9-aminoacridine (9AA) and acryloyl chloride in the presence of triethylamine in dry dichloromethane (CCl₂) at room temperature. The synthesized Ac-9AA was identified by IR, MS and ¹H NMR spectra. Homopolymer of Ac-9AA was obtained using AIBN as a thermal initiator in THF under 65-70 °C and the average molecular weights (M_w) of poly(Ac-9AA) obtained was very low, being in the order of ca. 10³. Copolymer of Ac-9AA and acrylamide was synthesized with thermal initiator and poly(Ac-9AA-co-AM) was characterized by the method of IR, UV-vis and DSC. The photophysical behaviors of Ac-9AA and its polymers were explored by recording the fluorescence spectra in solution, solid and film. In addition, the pH and temperature dependence on fluorescence of the water-soluble poly(Ac-9AA-co-AM) were investigated in detail. The results showed that the relative fluorescence intensity of poly(Ac-9AA-co-AM) had an excellent linear response to temperature in the range of 0-60 °C. Moreover, the fluorescence intensity increased continuously from low pH to high pH while the excitation maxima at 388 nm and emission maxima at 400 nm had redshift after the addition of HCl or NaOH, which results from the fact that the predominance of tautomeric forms of Ac-9AA changed at different medium. This investigation may provide a convenient way to prepared multifunctional macromolecule biomaterial bearing aminoacridine to probe pH and temperature in biological system.     

Spectrofluorimetric determination of aliphatic amines using a new fluorigenic reagent: 2,6-dimethylquinoline-4-(N-succinimidyl)-formate

A new amino fluorescence probe, 2,6-dimethylquinoline-4-(N-succinimidyl) formate (DMQF-OSu) has been synthesized. Based on the selective reaction of DMQF-OSu with primary and secondary aliphatic amines to yield strong fluorescence, a new spectrofluorimetric method for the determination of total aliphatic amines has been developed. At λ_ex/λ_em=324.4/416 nm, the linear calibration range was 6×10⁻⁸-6×10⁻⁶ mol l⁻¹ with the detection limit (3σ) of 1.94×10⁻¹⁰ mol l⁻¹ for the determination of aliphatic amines in weak basic media. The proposed method has been applied to the determination of aliphatic amines in tap water and lake water with the recoveries of 99-104%. Compared with the reported methods, the method presented here is rapid, simple, sensitive and feasible.     

Synthesis and nonlinear optical properties of new symmetrically substituted stilbenes

Three new chromophores and trans-4-(N-(ethyl 4″-nitrobenzoate)-N-ethyl amino)-4′-(dimethyl amino) stilbene (DMANHAS) have been synthesized and whose chemical structures have been characterized by ¹H NMR, IR, and elemental analyses. Linear absorption, single-photon-induced fluorescence and two-photon-induced fluorescence are experimentally studied. Trans-4-(N-2-hydroxyethyl-N-ethyl amino)-4′-(dimethyl amino)stilbene (DMAHAS) and trans-4-(N-2-hydroxyethyl-N-ethyl amino)-4′-(diethyl amino)stilbene (DEAHAS) have effective two-photon absorption cross-sections of σ₂=0.91×10⁻⁴⁶ cm⁴ s/photon and σ₂=1.19×10⁻⁴⁶ cm⁴ s/photon at 532 nm by using an open aperture Z-scan technique, respectively. When pumped with 800 nm laser irradiation, DMAHAS and DEAHAS indicate strong two-photon-induced blue fluorescence of 436 and 440 nm, respectively, while trans-4-(N-(ethyl 4″-nitrobenzoate)-N-ethyl amino)-4′-(diethyl amino) stilbene (DEANHAS) and DMANHAS exhibit no fluorescence.     

Vanillin-coumarin hybrid molecule as an efficient fluorescent probe for trace level determination of Hg(II) and its application in cell imaging

An efficient Hg²⁺ selective fluorescent probe (vanillin azo coumarin, VAC) was synthesized by blending vanillin with coumarin. VAC and its Hg²⁺ complex were well characterized by different spectroscopic techniques like ¹H NMR, QTOF-MS ES⁺, FTIR and elemental analysis as well. VAC could detect up to 1.25 μM Hg²⁺ in aqueous methanol solution through fluorescence enhancement. The method was linear up to 16 μM of Hg²⁺. Negative interferences from Cu²⁺, Ni²⁺, Fe³⁺, and Zn²⁺ were eliminated using EDTA as a masking agent. VAC showed a strong binding to Hg²⁺ ion as evident from its binding constant value (2.2 × 10⁵), estimated using Benesi-Hildebrand equation. Mercuration assisted restricted rotation of the vanillin moiety and inhibited photoinduced electron transfer from the O, N-donor sites to the coumarin unit are responsible for the enhancement of fluorescence upon mercuration of VAC. VAC was used for imaging the accumulation of Hg²⁺ ions in Candida albicans cells.     

Development of a fluorescent probe for nitric oxide detection based on difluoroboradiaza-s-indacene fluorophore

Nitric oxide (NO) is an important mediator involved in various physiological phenomena. To obtain direct evidence for NO functions in vivo, a novel fluorescent probe for NO, 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s-indacence (TMDABODIPY) was designed and synthesized, which features high photostability and no pH dependency over a wide pH range. The fluorescence of 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s-indacence is very strong, however, when the reagent traps NO in the presence of dioxygen, the weakly fluorescent triazole form is obtained, which offers the advantages of specificity and sensitivity for direct detection of NO. Calibration for NO showed the response has good linearity (0.01-0.4 μmol l⁻¹) and its detection limit is 2.5 nmol l⁻¹ (s/n=3). The proposed method has been used to monitor the release of NO from S-nitrosocysteine, a NO-releasing agent.     

Ultrasensitive and selective determination of trace amounts of nitrite ion with a novel fluorescence probe mono[6-N(2-carboxy-phenyl)]-β-cyclodextrin

A novel fluorescence probe, mono[6-N(2-carboxy-phenyl)]-β-cyclodextrin (OACCD), has been developed for the determination of trace nitrite, In dilute HCl medium, the fluorescence intensity of the newly synthesized fluorescence probe OACCD was quenched in presence of trace nitrite at room temperature. Based on this, a simple, sensitive, and selective method for rapid determination of nitrite was described. Furthermore, common ions do not interfere the determination of trace amounts of nitrite. The fluorescence quenching intensity was linear over a nitrite concentration of 0.02-1.7 μmol l⁻¹ with a detection limit of 0.2 nmol l⁻¹ (S/N = 3). The method was applied to the determination of nitrite in different water samples, soil samples, and food samples with satisfactory results.     

Fluorescence detection of total count of Escherichia coli and Staphylococcus aureus on water-soluble CdSe quantum dots coupled with bacteria

The aim of this paper was to demonstrate a fluorescence measurement method for rapid detection of two bacterial count by using water-soluble quantum dots (QDs) as a fluorescence marker, and spectrofluorometer acted as detection apparatus, while Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were as detection target bacteria. Highly luminescent water-soluble CdSe QDs were first prepared by using thioglycolic acid (TGA) as a ligand, and were then covalently coupled with target bacteria. The bacterial cell images were obtained using fluorescence microscopy. Our results showed that CdSe QDs prepared in water phase were highly luminescent, stable, and successfully conjugated with E. coli and S. aureus. The fluorescence method could detect 10²-10⁷ CFU/mL total count of E. coli and S. aureus in 1-2 h and the low detection limit is 10² CFU/mL. A linear relationship of the fluorescence peak intensity and log total count of E. coli and S. aureus have been established using the equation Y = 118.68X − 141.75 (r = 0.9907).     

Novel water-soluble fluorescent polymer containing recognition units: Synthesis and interactions with PC12 cell

New water-soluble fluorescent poly(N-vinylpyrrolidone) (PVP) containing carbonylhydrazide recognition units was synthesized by free radical polymerization of N-vinylpyrrolidone in the presence of mercaptoacetic acid as chain transfer agent and then being modified by 1-pyrenebutyric acid hydrazide. FT-IR, ¹H NMR, gel permeation chromatography-multi-angle laser light scattering and fluorescence spectroscopy were used to characterize these polymers. Results of fluorescence measurements show that these polymers have a good affinity for deoxyribonucleic acid (DNA). The interactions with PC12 cell results indicated that the polymer with suitable molecular weight could penetrate into PC12 cell and emit fluorescence. This water-soluble polymer with recognition units and high luminescence can be used as a promising fluorescent probe for measurements of biomacromolecules and cells.     

Effects of synthesis-solvent on swelling and elastic properties of poly(N-isopropylacrylamide) hydrogels

Thermosensitive N-isopropylacrylamide (NIPA) hydrogels were synthesized by a free radical copolymerization with N,N′-methylenebisacrylamide (MBAA) in four solvents: water, ethanol, acetone and N,N-dimethylformamide. The swelling and elastic properties of the hydrogels were affected by the synthesis-solvents; the hydrogels (e.g. NIPA/MBAA = 1000/50 mol/m³-pre-gel solution) synthesized in water have smaller swelling volume and larger shear modulus at 10 °C than those synthesized in amphiphilic solvents. The network structure of hydrogels was estimated in terms of the conversion and two sorts of effective crosslinking density based on the Flory theory and the concentration of crosslinker. The hydrogels synthesized in water can have the microscopic inhomogeneous network arising from the entanglement of polymer chains, while the hydrogels synthesized in amphiphilic solvents can have the homogeneous network arising from the polymer concentration lower than the pre-gel solution and can be similar in network structure to the lightly crosslinked hydrogel synthesized in water.     

Fluorimetric determination of ascorbic acid with o-phenylenediamine

A simple and sensitive fluorimetric method for the determination of ascorbic acid (AA) is described. The method is based on the condensation reaction between AA and o-phenylenediamine (OPDA) in the absence of the oxidant. The fluorescence intensity is measured at excitation and emission wavelengths of 360 and 430 nm, respectively. Under optimum condition, a linear relationship is obtained between the fluorescence intensity and the concentration of AA in the range of 0.05-40 μg ml⁻¹. The detection limit is 0.006 μg ml⁻¹, which is obviously lower than that of other fluorimetric methods reported.     

Sensitive fluorimetric flow injection analysis for fluoride ion with a novel reagent, 2',7'-dichlorofluorescein di-tert-butyldimethylsilyl ether

A novel reagent, 2′,7′-dichlorofluorescein di-tert-butyldimethylsilyl ether (FCl₂TBS), was synthesized for fluoride ion and used for a sensitive fluorimetric flow injection analysis by detecting the recovery of fluorescence due to cleavage of Si-O bond. Four kinds of fluorescein di-tert-butyldimethylsilyl ether (FTBS) analogues were synthesized and FCl₂TBS was the best. By introducing chlorine to FTBS, stability of the reagent, reactivity and the baseline signals were improved. The FIA system was three lines. The sample solution (aqua medium) was injected in the carrier solution (water) and merged with the reagent solution (2.0 × 10⁻⁵ M FCl₂TBS acetone solution), then mixed with phosphate buffer solution (pH 7.5). The fluorescence intensities were measured at λ_ex 503 nm and λ_em 527 nm. The calibration graph had linear relationship between (1.0-50.0) × 10⁻⁶ M and the determinable limit was 1.0 × 10⁻⁶ M. The relative standard deviation of 12 measurements with 1.0 × 10⁻⁵ M F⁻ solution was 1.0% and the sample throughput was 13 h⁻¹. The developed method was successfully applied to river and tap water samples.     

A new fluorescent turn-on chemodosimeter for mercury ions in solution and its application in cells and organisms

Using the Hg²⁺-induced desulfurization reaction of thiosemicarbazide derivative, we designed and synthesized a novel “turn on” coumarin-based fluorescent probe L with a simple structure for detecting mercury ion (II). Spectroscopy revealed that the probe responds selectively to mercury ions over other metal ions with marked fluorescence enhancement. Detection of Hg²⁺ was effective at pH 7.0–9.5, with high selectivity and significant effect in HeLa cells, human umbilical vein endothelial cells and Escherichia coli, but no cytotoxicity. This probe could be an ideal and practical Hg²⁺ probe with important biological significance.     

Synthesis and binding properties of carboxylphenyl-modified calix[4]arenes and cytochrome c

Two novel carboxylphenyl-modified calix[4]arenes, tetrakis-carboxylphenylcalix[4]arene (TCPC) and 1,3-bis-carboxylphenylcalix[4]arene (BCPC), as well as a corresponding analogue for comparison, tetrakis-phenylcalix[4]arene (TPC), have been synthesized by palladium-catalyzed Suzuki cross-coupling of arylboronic acid and tetrabromocalix[4]arene as a key step. The binding properties of these calix[4]arene derivatives with bovine heart cytochrome c (cyt c) in dimethylformamide (DMF) was investigated by fluorescence spectroscopy. The binding affinity in the order of TCPC > BCPC ? TPC reflects a clear dependence on the number of carboxyl ligating groups attached onto a receptor and suggests the electrostatic force may be the predominant factor driving the complexing process. The stable 1:1 complexes of TCPC and BCPC with cyt c were evidenced with the binding constants of 3.15 × 10⁶ and 5.85 × 10⁵ L mol⁻¹, respectively. Due to a large overlap between the emission spectrum of TCPC and the absorption spectrum of cyt c, and a short interaction distance (estimated to be 5.6 nm) between them, the fluorescence quenching of TCPC upon complexation with cyt c is attributed to an efficient energy transfer.     

Simultaneous amperometric determination of lignin peroxidase and manganese peroxidase activities in compost bioremediation using artificial neural networks

High-performance liquid chromatography (HPLC) and fluorescence derivatization were applied for a nanogram-level N-nitrosodimethylamine (NDMA) analysis of water samples. For the analysis of N-nitrosodimethylamine, samples were first denitrosated by a mixed solution of hydrobromic acid and acetic acid to produce dimethylamine, which was derivatized with dansyl chloride for HPLC fluorescence detection. Fluorescence detection was optimized with excitation and emission wavelengths of 340 and 530 nm, respectively. pH adjustment after denitrosation was necessary to maximize fluorescence intensity with pHs in the range of 9-12. A dansyl chloride concentration of 500 mg l⁻¹ was found to be optimal for measuring a fluorescence signal. An instrumental detection limit of 0.1 ng of NDMA was possible with fluorescence derivatization. The NDMA in water samples was extracted by continuous solid-phase extraction using Ambersorb 572. Although the determination of NDMA was variable at lower concentrations (less than 200 ng l⁻¹), it was observed that the NDMA detection limit with this method could be lowered to a concentration of 10 ng l⁻¹. Another benefit of this method can be found in its selectivity for NDMA. Unlike gas chromatographic (GC) methods, this method generates a distinct peak for NDMA without interference even in the complex matrix of wastewater effluents. The HPLC with fluorescence derivatization method may be applicable for determining NDMA in water and wastewater samples for various research purposes and for screening environmental samples.     

One-pot synthesis of strongly fluorescent DNA-CuInS2 quantum dots for label-free and ultrasensitive detection of anthrax lethal factor DNA

Herein, high quality DNA-CuInS₂ QDs are facilely synthesized through a one-pot hydrothermal method with fluorescence quantum yield as high as 23.4%, and the strongly fluorescent DNA-CuInS₂ QDs have been utilized as a novel fluorescent biosensor for label-free and ultrasensitive detection of anthrax lethal factor DNA. L-Cysteine (L-Cys) and a specific-sequence DNA are used as co-ligands to stabilize the CuInS₂ QDs. The specific-sequence DNA consists of two domains: phosphorothiolates domain (sulfur-containing variants of the usual phosphodiester backbone) controls the nanocrystal passivation and serves as a ligand, and the functional domain (non-phosphorothioates) controls the biorecognition. The as-prepared DNA-CuInS₂ QDs have high stability, good water-solubility and low toxicity. Under the optimized conditions, a linear correlation was established between the fluorescence intensity ratio I/I₀ (I₀ is the original fluorescence intensity of DNA-CuInS₂ QDs, and I is the fluorescence intensity of DNA-CuInS₂ QDs/GO with the addition of various concentrations of anthrax lethal factor DNA) and the concentration of anthrax lethal factor DNA in the range of 0.029–0.733 nmol L⁻¹ with a detection limit of 0.013 nmol L⁻¹. The proposed method has been successfully applied to the determination of anthrax lethal factor DNA sequence in human serum samples with satisfactory results. Because of low toxicity and fine biocompatibility, DNA-CuInS₂ QDs also hold potential applications in bioimaging.     

Synthesis of oligo(p-phenylene vinylene)-porphyrin-oligo(p-phenylene vinylene) triads as antenna molecules for energy transfer

The oligo(p-phenylene vinylene)-porphyrin-oligo(p-phenylene vinylene) (P-OPVn, n=2, 4, where n is the number of phenyl rings) and the complex with Zn²⁺ based on P-OPVn were synthesized for investigating their photophysical properties via UV-vis, voltammetry, steady-state and time-resolved fluorescence spectra. In these molecules two OPV moieties as energy donors were linked to porphyrin center by virtue of Wittig reaction. The detailed studies of photophysical properties indicate that OPV group can act as an antenna unit for effective intramolecular energy transfer.     

Spectrofluorometric determination and chemical speciation of trace concentrations of chromium (III & VI) species in water using the ion pairing reagent tetraphenyl-phosphonium bromide

A highly selective, and low cost extractive spectrofluorometric method has been developed for determination of trace concentrations of chromium (III & VI) in water samples using the fluorescent reagent tetraphenylphosphonium bromide (TPP⁺·Br⁻). The method was based upon solvent extraction of the produced ion associate [TPP⁺·CrO₃Cl⁻] of TPP⁺·Br⁻ and halochromate in aqueous HCl and measuring the fluorescence quenching of TPP⁺·Br⁻ in chloroform at λ_ex/em = 242/305 nm. The fluorescence intensity of TPP⁺Br⁻ decreased linearly on increasing the chromium (VI) concentration in the range of 1-114 μg L⁻¹. The limits of detection (LOD) and quantification (LOQ) of chromium (VI) were 0.43 and 1.42 μg L⁻¹, respectively. Chromium (III) species after oxidation to chromium (VI) with H₂O₂ in alkaline solution were also determined. Chemical speciation of chromium (III & VI) species at trace levels was achieved. The method was applied for analysis of chromium in certified reference material (IAEA Soil-7) and in tap- and wastewater samples and compared successfully (>95%) with the inductively coupled plasma-mass spectrometry (ICP-MS) results.     

First observation of intra-5f fluorescence from an actinyl center: Np(VI) near-IR emission in Cs2U(Np)O2Cl4

Fluorescence from an excited 5f state of Np(VI) has been observed in the doped impurity system Cs₂U(Np)O₂Cl₄. This is the first intra-5f fluorescence transition that has been detected at room temperature in a condensed-phase system with an actinyl (An(VI)O₂²⁺) core, and it is a rare example of fluorescence of any kind from non-uranyl ions of this type. The emission originates from an excited state approximately 6890 cm⁻¹ above the ground state. Its emission spectrum and fluorescence lifetime at 295 K will be discussed. Vibronic structure in the emission spectrum is assigned based on comparison with the detailed analysis of the absorption spectra published by Denning et al.     

Selective fluorescence sensing of cyanide with an o-(carboxamido)trifluoroacetophenone fused with a cyano-1,2-diphenylethylene fluorophore

A novel fluorescence probe has been synthesized, which consists of o-(carboxamido)trifluoroacetophenone moiety as the recognition element and cyano-1,2-diphenylethylene moiety as the signaling unit. Fluorescence titrations of the probe with anions such as F⁻, Cl⁻, I⁻, CN⁻, SCN⁻, AcO⁻, , , and as their Bu₄N⁺ salts in acetonitrile show that CN⁻ is the most efficient quencher, AcO⁻ and F⁻ follow it, and other anions show little changes. In an aqueous medium, MeOH-water (9:1), the probe shows fluorescence quenching only toward cyanide and no changes toward the other anions.     

Synthesis and structural characterization of a dichloro zinc complex of N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane: Application to ring opening polymerization of rac-lactide

A novel dichloro zinc complex (L¹)ZnCl₂, where L¹ is N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane, has been synthesized and characterized. The dimethyl derivatives, generated in situ from the well characterized dichloro zinc complexes (L¹)ZnCl₂ and (L²)ZnCl₂, where L² is N,N′-bis-(benzyl)-(R,R)-1,2-diaminocyclohexane, were employed as initiators for the ring opening polymerization (ROP) of rac-lactide (rac-LA). The complexes were found to be highly efficient initiators yielding the polylactide (PLA) with a narrow molecular weight distribution. The catalytic activity and heterotactic selectivity of the Zn(II) complexes were affected by the substituents on the phenyl groups of benzyl moieties in (R,R)-1,2-diaminocyclohexane. The dimethyl derivative of (L²)ZnCl₂ produced highly stereocontrolled PLA with P_r = 0.75 at −25 °C.