Changes In Fluorescence Spectra Research Articles

Effect of pressure on structure and fluorescence of phthalocyanine

Phthalocyanine (Pc) is a kind of important photoelectric material, but a lot of questions remain to be clarified, like the relationship between the structure of Pc and its photoelectric property. High pressure is a powerful tool to study the structure transformation. High pressure study on piezochromic materials, which shows color change under high pressure due to structure changing, serves as an effectively way of studying the relationship between materials’ structure and photoelectric property. In this work Raman spectrum is employed to study the phase change of α phase metal-free Pc (α-H<sub>2</sub>Pc) under high pressure, meanwhile the effect of pressure on fluorescence (FL) is also studied to show how the Pc’s structure affects the photoelectric property. The diamond anvil cell is employed to achieve the high pressure condition, by using NaCl as a pressure transmitting medium. And Raman and FL measurements are performed by using a LabRam HR Evolution spectrometer equipped with a 473 nm laser. The Raman spectra of α-H<sub>2</sub>Pc show to slightly change during compression to 12.0 GPa. The main Raman peaks remain at highest pressure, including the Raman peak from macrocyclic of Pc molecules, which shows the stability of Pc molecules. Note that an enhancement of Raman peak at 623 cm<sup>–1</sup> can be found with the pressure increasing, which appears only in the Raman spectrum of χ phase metal-free Pc (χ-H<sub>2</sub>Pc), showing that α-H<sub>2</sub>Pc is converted into χ-H<sub>2</sub>Pc under pressure. The curve for Raman frequency as a function of pressure shows that no obvious evidence related to bonding or structure transition can be observed, which means that α-H<sub>2</sub>Pc is transformed into χ-H<sub>2</sub>Pc gradually. For FL spectrum, only the FL of excimer can be found in α-H<sub>2</sub>Pc at atmosphere pressure. When the solid α-H<sub>2</sub>Pc is compressed, the FL intensity is found to decrease as pressure increases, and it is quenched at 3.0 GPa. The FL of Pc molecule, which is not found in α-H<sub>2</sub>Pc at ambient pressure, appears at 0.7 GPa. As the pressure increases, the FL intensity ratio between Pc molecule and excimer is enhanced. Considering the pressure induced phase transition from α-H<sub>2</sub>Pc to χ-H<sub>2</sub>Pc gradually, the change in FL spectrum should be due to the structure transformation. It is proved that the degree of overlapping between Pc molecules in α-H<sub>2</sub>Pc is larger than that in χ-H<sub>2</sub>Pc. We think, the degree of overlapping decreases under high pressure, which hinders the formation of excimer. It makes the excimer emission decrease and the FL of Pc molecules appear under high pressure. Our work can explain the relationship between Pc crystal structure and its fluorescence, reveals the kinetic behavior of macromolecules similar to Pc system under high pressure, and provides a new possibility of designing the photoelectric materials with excellent performances.

Effect of anions on fluorescence quenching of Rhodamine B–Pluronic F127 complex

ABSTRACTPluronic F127 has been widely used for controlled release of drugs. The aggregation behaviour and solubilisation properties of pluronics can be affected by addition of salts. This work reports the studies on the changes in micellar assemblies of F127 due to addition of inorganic anions (KCl, KBr, KI and KNO3) in Pluronic F127–Rhodamine B system. This was monitored by using UV–vis spectroscopy, fluorescence spectroscopy and fluorescence lifetime spectra. The change in fluorescence spectrum due to the presence of quenchers was attributed to the change in microenvironment of the micelle. The quenching depends on the ability of the fluorophore to transfer energy to the quencher. Out of all four salts, KI was observed to be the best quencher for the above system.

Study of the binding interactions between uric acid and bovine serum albumin using multiple spectroscopic techniques

The binding interactions between bovine serum albumin (BSA) and a large excess of uric acid (UA) have been analyzed in aqueous solution at pH = 7.4, using UV–vis absorption and steady-state, time-resolved, synchronous and three-dimensional fluorescence spectra techniques. The observed effects verify the formation of π-π stacked non-covalent and non-fluorescent complexes in the system BSA-UA. All the calculated parameters, the binding, fluorescence quenching and bimolecular quenching rate constants, as well as the measurements of fluorescence decay times and Förster resonance energy transfer parameters validate the mechanism of static quenching. The changes in the synchronous fluorescence spectra indicate that the BSA fluorescence quenching originates both from Trp and Tyr residues, but their involvement is not equivalent. The interaction with UA induces the diverse alterations of BSA tertiary structure: folding of the polypeptide chains around Trp residues and concurrently their extension around Tyr residues. The obtained outcomes suggest that the presence of the excessive amount of UA in blood could interfere with the physiological functions of serum albumin, especially in case of UA overproduction.

Chlorophyll degradation by tetracycline and cadmium in spinach (Spinacia oleracea L.) leaves

Degradation of chlorophyll was studied in leaves of spinach grown in soil containing cadmium and tetracycline, based on spectroscopic measurements and biochemical analyses of plant extracts. It was shown that plant exposure to the highest levels of tetracycline and cadmium resulted in 64% and 68%, respectively, reduction in chlorophyll content. The chlorophyll degradation rate constants were determined, and they were found to increase with increasing doses of tetracycline and cadmium. The rate constant of chlorophyll degradation by tetracycline ranged from k = 960 M−1 day−1 to k = 2180 M−1 day−1, and the rate constant of chlorophyll degradation by cadmium ranged from k = 1130 M−1 day−1 to k = 2580 M−1 day−1, depending on dose. Plant stress responses to tetracycline are much stronger than to cadmium, as is visible from the activity of guaiacol peroxidase and catalase. However, phytotoxicity of cadmium, measured by the rate of chlorophyll degradation and enzyme activities, is much higher compared to tetracycline. The spectroscopic measurements were taken 10 days after tetracycline and cadmium were added to the reagent grade chlorophyll which was used at the concentration of chlorophyll in plants. Changes in absorption and fluorescence spectra are likely to result from removal of magnesium from the chlorophyll molecule, and thus they indicate the formation of pheophytin. Cadmium, on the other hand, is probably bound into the chlorophyll molecule, substituting its magnesium.

A two-step heat treatment of cell disruption supernatant enables efficient removal of host cell proteins before chromatographic purification of HBc particles

The thermal stability of HBc particles was systematically investigated for efficient removal of host cell proteins (HCP) by heat treatment before chromatographic step. The HBc particles were found stable up to 80°C for 30 min without any noticeable change in circular dichroism spectra, fluorescence spectra and transmission electron microscope observation. When heating was applied to precipitate the HCP in the cell disruption supernatant of HBc fermentation, the HCP removal effect was more obvious as the temperature went higher. However, a phenomenon was found beyond 70°C where the recovered HBc particles had larger than normal size and molecular weight as observed by dynamic light scattering and multi-angle laser light scattering. Analysis found that the HBc particles possess nanopores which expand with temperature. When the temperature was above 70℃, the pores were large enough for some HCP to penetrate in, but not being able to get out after cooling down. To fully utilize the thermal stability and avoid the interference of HCP entering, a two-step heat treatment strategy was designed. The supernatant was firstly heated up to 60°C for 30 min to precipitate most HCP, then another 30 min at 70°C was used to remove the rest impurities. The two-step heat treatment effectively avoided the HCP entering problem, achieving 85.8% particle recovery and 74.7% purity. With further one-step hydrophobic interaction chromatography, the purity was increased to 99.0% with overall process recovery of 77.7%, considerably higher than those reported in the literature. The same process design was applied to purify three HBc-related products, including OVA-HBc, M2e-HBc and NP-HBc. All recoveries were higher than 50% with purity greater than 97%.

Effect of bovine serum albumin on the photodynamic activity of sulfonated tetrapyrazinoporphyrazine

We synthesized water-soluble zinc(II) complex of octa(p-sulfonatophenyl)tetrapyrazinoporphyrazine (TPyzPz), which is monomeric above pH 2.5 up to micromolar concentration. Significant aggregation occurs at lower pH as a consequence of losing repulsion forces after protonation of sulfonate groups. Changes in both absorption and fluorescence spectra indicated strong interaction of TPyzPz and bovine serum albumin (BSA) with a maximum at 3:1 ratio (dye: BSA). Binding to the BSA leads to significant quenching of the singlet excited state of the photosensitizer and to longer triplet states lifetimes as a consequence of limited diffusion of oxygen to the excited TPyzPz. The photodynamic activity of this TPyzPz was also strongly influenced by binding to BSA; it was lower in the cell culture medium containing serum (EC50 = 99.8 ± 23.5 μM) than in the medium without the proteins (EC50 = 0.83 ± 0.31 μM). The compound was of minimal dark toxicity without irradiation (TC50 > 1000 μM). Fluorescence microscopy revealed lysosomes as the localization site of the TPyzPz, their rupture after irradiation and subsequent relocalization of TPyzPz to the cytoplasm with predominantly necrotic mode of cell death.

A Study of the Structure of Trypsin-Like Serine Proteinases: 1. Study of Mini-Plasminogen Activation Using Tryptophan Fluorescence

Abstract—It has been shown that the curve of the time dependence of tryptophan fluorescence during plasminogen activation by urokinase is well correlated with kinetic curves of activation, which were plotted according to both direct measurements of amidolytic activity of the forming plasmin and the analysis of the plasminogen cleavage products. Three curves represent the intercorrelation within a wide range of the pH and temperature change. We hypothesized that the fluorescence shift is caused by the changes in the Trp215 (Chymotrypsin numbering) side chain environment of activated plasmin. Plasmin activation via proteolytic cleavage of plasminogen induces rotation of the Trp215 side chain with subsequent translocation of the benzene ring of Trp215 from negatively charged (Asp194 and Glu143) to positively charged (Arg175) neighborhood. Our findings show that this rotation is not caused by the indol ring displacement from the substrate recognition pocket, which is provoked by the inhibitor or substrate binding. It has also been demonstrated that the conformation of plasminogen (at least relevant to Trp215 in the substrate recognition pocket) is not sensitive to the pH or temperature changes, while changes in fluorescence spectrum of plasmin correlate with its amidolytic activity.

Synthesis of pyrenocrown ethers as fluorescent sensors and their recognition ability of metal ions

Novel pyrenocrown ethers having different ring sizes were synthesized, and change of fluorescence spectra was investigated upon addition of metal ions. By the addition of Li+ and Na+ ions to 10–2 M CH3CN solutions of pyreno-15-crown-5 ether (3), excimer/monomer ratio decreased with 3–4 nm longer wavelength shift. Upon addition of Mg2+ and Ba2+ ions to the solution of 3, excimer emission increased with 11–25 nm longer wavelength shift. On the other hand, when these metal ions were added to pyreno-18-crown-6 ether (4), the excimer/monomer ratio monotonically decreased. Addition of Pb2+ ion to solutions of 3 and 4 caused dramatic decrease of both monomer and excimer fluorescence intensity. Inspection of these results indicates that 3 forms 1:1 and 2:1 complexes with respective monovalent and divalent metal ions, whereas 4 forms 1:1 complexes with both monovalent and divalent metal ions. The 1:1 complexes of 3 with monovalent and divalent metal ions emit respective excimer and monomer fluorescence, whereas the 2:1 complexes of 3 emit excimer fluorescence. Monotonical decrease of fluorescence intensity by the addition Pb2+ is attributed to heavy atom effect.

Synthesis and fluorescence spectral studies of novel quinolylbenzothiazole-based sensors for selective detection of Fe3+ ion

Four novel fluorescence sensors bearing a quinolylbenzothiazole platform were synthesized and characterized. The sensors displayed excellent selectivity and highly sensitive fluorescence response to Fe3+ ion in H2O/DMSO buffer solution (1:4 volume ratio; Tris-HCl, 0.01 mol/L; pH = 7.40) at 500 nm originating from quinolylbenzothiazole fluorophore group. Other cations, namely Li+, Na+, K+, Mg2+, Ca2+, Co2+, Ni2+, Cd2+, Cu2+, Zn2+, Mn2+, Ba2+, Pb2+, Hg2+, Al3+, and Eu3+, showed no appreciable change in fluorescence spectrum. The binding stoichiometry between sensors L1, L2, L3, or L4 and Fe3+ was observed to be 1:1 based on fluorescence titration and Jobs plot analysis. The detection limits of L1, L2, L3, and L4 for Fe3+ were found to be 0.155, 0.362, 0.249, and 0.517 μmol/L, respectively. Furthermore, possible utilization of sensors to detect Fe3+ in living HeLa cells was also investigated by confocal fluorescence microscopy.

Soluble Zwitterionic Poly(sulfobetaine) Destabilizes Proteins.

The widespread interest in neutral, water-soluble polymers such as poly(ethylene glycol) (PEG) and poly(zwitterions) such as poly(sulfobetaine) (pSB) for biomedical applications is due to their widely assumed low protein binding. Here we demonstrate that pSB chains in solution can interact with proteins directly. Moreover, pSB can reduce the thermal stability and increase the protein folding cooperativity relative to proteins in buffer or in PEG solutions. Polymer-dependent changes in the tryptophan fluorescence spectra of three structurally-distinct proteins reveal that soluble, 100 kDa pSB interacts directly with all three proteins and changes both the local polarity near tryptophan residues and the protein conformation. Thermal denaturation studies show that the protein melting temperatures decrease by as much as ∼1.9 °C per weight percent of polymer and that protein folding cooperativity increases by as much as ∼130 J mol-1 K-1 per weight percent of polymer. The exact extent of the changes is protein-dependent, as some proteins exhibit increased stability, whereas others experience decreased stability at high soluble pSB concentrations. These results suggest that pSB is not universally protein-repellent and that its efficacy in biotechnological applications will depend on the specific proteins used.

Irreversible solvent-assisted structural transformation in 3D metal-organic frameworks: Structural modification and enhanced iodine-adsorption properties

In this work, we demonstrate a solvent-assisted structural transformation between two 3D metal-organic frameworks (MOFs) ([Zn4(α-bptc)2(H2O)3]n (1) → {[Zn2(α-bptc)(H2O)4]·(pra)}n (2)) (α-H4bptc = 2,3,3′,4′-biphenyl tetra-carboxylic acid and pra = pyridin-2-amine) at room temperature by immersing complex 1 in a mother solution. The structural transformation involves not only solvent exchange but also the cleavage and formation of coordination bonds, which is confirmed by infrared spectroscopy, single-crystal X-ray diffraction analysis, powder X-ray diffraction patterns, and thermogravimetric analysis. Structural analyses revealed that significant modifications occurred during the transformation including the changes in lattice parameters, unit cell volume, space group, coordination number, secondary building units, and topological type. In the case of drastic structural transitions, significant changes in properties were also observed. Complex 2 displayed the interesting uptake and release of iodine with the changes in visible color, UV and fluorescence spectra, and fully reversible I2 uptake of 8.5 mg g−1, which further suggested about its future application as iodine absorbing material.

Excimer Emission of Acridine Orange Adsorbed on Gadolinium-Yttrium Orthovanadate Nanoparticles.

Studying the complexes of inorganic nanoparticles - organic dye molecules is of great importance for their theranostics application. In this paper, we report gadolinium-yttrium orthovanadate nanoparticles (VNPs) - Acridine Orange (AO) complex formation in water solutions. To study the interactions between VNPs and AO, the methods of steady-state and time-resolved spectroscopy were used. It was shown that in aqueous solutions containing VNPs, AO aggregation takes place with a sandwich-like stacking of AO molecules in the near-surface layer of VNPs. The VNPs-AO complex formation causes significant changes in the AO fluorescence spectrum, namely, the appearance of a new broad, structureless band in the long-wavelength spectral edge, which was not observed in AO spectrum in a pure water solution. By analyzing of the absorption, fluorescence excitation spectra and fluorescence decay, the static excimer origin of the long-wavelength fluorescence band has been established.

Fluorinated coumarin silicon(IV) / zinc(II) phthalocyanines: Synthesis, photophysical properties and photoinduced intramolecular energy transfer

A novel series of fluorinated coumarin substituted zinc (II) /silicon (IV) phthalocyanines were synthesized. Their structures were characterized by FT-IR, 1H NMR, ESI methods as well as elemental analysis. Their photophysical and photochemical properties were investigated by UV–Vis and fluorescence spectroscopic methods. The effects of the central ions and the substitution positions of fluorinated coumarin on the photophysical and photochemical properties of phthalocyanine rings were studied. The photoinduced intramolecular energy transfer between the phthalocyanine and fluorinated coumarin evidenced the fluorescence spectra changes. The above results demonstrated that newly synthesized phthalocyanines could be good candidates for photodynamic therapy of cancer.

Absorption and fluorescence spectral studies of the interaction of sulpha drugs with α-cyclodextrin

ABSTRACTThe spectral characteristics of different drugs i.e. sulfanilamide, sulfanilic acid, sulfosalicylic acid dihydrate (SSAD) and sulfamethoxazole in aqueous α-cyclodextrin (CD) have been investigated at neutral pH. The formation of inclusion complexes of sulfa drugs with α-CD leads to the changes in fluorescence and absorption spectra which further enable the calculation of association constant of the bind processes by implementing the non-linear regression on the experimental data. The standard Gibbs energy ΔG was also calculated for the systems in which complex formation was observed. The α-CD study indicates that the sulpha drugs form 1:1 inclusion complex with α-CD.

Reaction-based fluorescent sensor for detection of bisulfite through 1,4-addition reaction in water

Reaction-based fluorescent sensor (L) based upon a conjugated benzothiazol structure was synthesized and used for detection of bisulfite (HSO3−) in water. L displayed large change in both fluorescence and absorption spectra immediately after the addition of HSO3−. It can be easily observed about the fading of the solution’s color through the naked eye. The HSO3− underwent a 1,4-addition reaction with the C-4 atom in the ethylene group. The detection limit of L for HSO3− was measured to be 0.45 μmol/L. The live cell fluorescent experiments proved the potential application of the L in tracing the HSO3− in future biological systems.

Development of Acridine‐Derived “Turn On” Al3+ Fluorescent Sensors and Their Imaging in Living Cells

AbstractTwo novel highly selective fluorescent sensors L‐1 and L‐2 for the determination of Al3+ ion were synthesized and characterized. The sensors acridine‐4,5‐diylbismethyl(bis(oxy))bis(2,1‐phenylene))bis‐(methylene))bis(azanediyl))bis(3‐phenylpropan‐1‐ol) (L‐1) and 2,2′‐acridine‐4,5‐diylbis(methylene(bis(oxy))bis(2,1‐phenylene))bis‐(methylene))bis(azanediyl))bis(propan‐1‐ol) (L‐2) showed “turn on” fluorescence response in the presence of Al3+ ion in DMSO/tris‐HCl (1:1, v:v, pH=7.2) buffer solution. Other cations viz. Li+, Na+, K+, Mg2+, Ca2+, Fe2+, Co2+, Ni2+, Cd2+, Cu2+, Zn2+, Mn2+, Ba2+, Pb2+, Hg2+, Fe3+ and Eu3+ ions showed no appreciable change in fluorescence spectrum. The detection limits of L‐1 and L‐2 for Al3+ ion were at the parts per billion level. In addition, possible utilization of sensors as bio‐imaging fluorescent sensors to detect Al3+ in human cervical HeLa cells was also investigated by confocal fluorescence microscopy.

A novel PBT-based fluorescent probe for hydrazine detection and its application in living cells

A new 2-phenyl-benzothiazole (PBT) based fluorescent probe (AcO-PBT-CHO) was designed and synthesized for the detection of hydrazine. The aldehyde and acetyl ester groups were used as the recognition units. Upon the treatment of the probe with hydrazine, the emission at 505 nm decreased while the emission at 430 nm increased. Accordingly, the fluorescent color changed from green to blue. The aldehyde and acetyl ester groups exerted additive effect on the fluorescence spectrum changes of the probe. The probe could selectively identify hydrazine over other related interfering species. The probe could detect hydrazine quantitatively in the range of 20–40 μM with the detection limit of 2.80 ppb. Furthermore, the probe was successfully applied to detect hydrazine in living cells.

A 3-hydroxyflavone derivative as fluorescence chemosensor for copper and zinc ions

A 3-hydroxyflavone derivative as fluorescence chemosensor for copper and zinc ions has been synthesized. Its recognition properties for copper and zinc ions in aqueous solution were investigated based on UV-vis absorption and fluorescence spectra change. The compound exhibits color change from colorless to yellow and quenching of green fluorescence in the presence of copper ions in aqueous solution due to coordination reaction. In turn, the addition of zinc ions induces the color change from colorless to green and fluorescence enhancement of the compound. The complex ratios between the sensor molecule and copper(zinc) ions are 1:1 and 1:2, respectively, based on the Job's plots and in situ mass spectra. Thus, this compound can selectively recognize copper and zinc ions, and the recognition also can be observed by naked eye.

Impact of Temperature Cycling and Isothermal Storage on the Quality of Acidic and Neutral Shelf-Stable Dairy Desserts Packaged in Flexible Pouches

The aims of the present study were, first, to identify the quality changes occurring in sterilized vanilla and strawberry pudding during storage at 20 °C; second, to understand the effect of storage temperature on aging; and, third, to determine if temperature could be used as an accelerating factor for shelf life or stability studies. Shelf-stable pudding was produced industrially and packaged in flexible pouches. Different ingredients were used to produce strawberry and vanilla pudding, and the resulting pH was 4.1 and 6.5, respectively. Pudding pouches were kept for 7 days at 20 °C and stored for up to 112 days at − 18, 4, 20, and 30 °C, or cycled repeatedly between − 18 and 20 °C, 4 and 20 °C, and 30 and 20 °C with a frequency of two cycles per week. Color, pH, apparent viscosity, flow behavior, and fluorescence spectra measurements were conducted up to 112 days of storage. The most relevant indicators to monitor quality changes in vanilla pudding were η, pH, b*, and tryptophan emission spectra, and in strawberry pudding, a*, b*, and riboflavin, tryptophan, and vitamin A emission spectra. Indeed, the temperature of 30 °C was identified as the most suitable accelerating factor for accelerated aging tests regarding changes in pH, color, riboflavin, and tryptophan fluorescence spectra of pudding, while cycles of 4/20 °C and isothermal storage at 4 °C were the most appropriate tests to accelerate changes in apparent viscosity of pudding.

Real-Time Tracking the Synthesis and Degradation of Albumin in Complex Biological Systems with a near-Infrared Fluorescent Probe.

In this study, a novel fluorescent detection system for biological sensing of human albumin (HA) was developed on the basis of the pseudoesterase activity and substrate preference of HA. The designed near-infrared (NIR) fluorescent probe (DDAP) could be effectively hydrolyzed by HA, accompanied by significant changes in both color and fluorescence spectrum. The sensing mechanism was fully investigated by fluorescence spectroscopy, NMR, and mass spectra. DDAP exhibited excellent selectivity and sensitivity toward HA over a variety of human plasma proteins, hydrolases, and abundant biomolecules found in human body. The probe has been successfully applied to measure native HA in diluted plasma samples and the secreted HA in the hepatocyte culture supernatant. DDAP has also been used for fluorescence imaging of HA reabsorption in living renal cells, and the results show that the probe exhibits good cell permeability, low cytotoxicity and high imaging resolution. Furthermore, DDAP has been successfully used for real-time tracking the uptaking and degradation of albumin in ex vivo mouse kidney models for the first time. All these results clearly demonstrated that DDAP-based assay held great promise for real-time sensing and tracking HA in complex biological systems, which would be very useful for basic researches and clinical diagnosis of HA-associated diseases.