Synthesis of a cysteine-linked cyclophane dimer having two rhodamine moieties and its reduction-responsive degradation as studied by fluorescence spectroscopy

Cysteine-linked cyclophane dimer having two rhodamine moieties (2) was synthesized as a reduction-responsive host. Owing to self-quenching property of the two rhodamine moieties, cyclophane dimer 2 showed weak fluorescence intensity relative to that of the rhodamine B moiety itself. The cleavage of disulfide bond of 2 was performed by a treatment with reducing agents such as dithiothreitol, to give the corresponding monomeric cyclophanes having a rhodamine moiety. Such reductive degradation of 2 was detected by the increase on fluorescence intensity. As a host, cyclophane dimer 2 was found to show a stronger guest-binding affinity than the monomeric cyclophanes due to concentration effects of the macrocycles. In addition, reduction-responsive release of entrapped guest molecules by 2 was also monitored by fluorescence spectroscopy.     

Dynamic light scattering from concentrated colloidal dispersions

From the scattered intensity as a function of scattering wave number, local ordering in concentrated latex dispersions in benzene is found. From the combination of intensity and photon correlation experiments follows the existence of strong hydrodynamic interactions between the dispersed particles.     

Determination of DNA based on localized surface plasmon resonance light scattering using unmodified gold bipyramids

The DNA was determined based on resonance light scattering (RLS) spectrometry and the localized surface plasmon resonance. The gold bipyramids were used as the probes and synthesized by a seed-mediated method. Cetyltrimethylammonium bromide was used as stabilizing agent. DNA can be bound to the gold bipyramids due to electrostatic interaction and aggregates, which results in a strong enhancement of the RLS intensity. Under the optimal conditions, the intensity of RLS is directly proportional to the concentration of DNA in the range from 0.1 to 2.0 μg mL(-1).     

Anguler-resolved raman spectroscopy of pyridine on copper and gold electrodes

The surface enhanced Raman scattering from pyridine molecules adsorbed on smooth copper or gold electrodes exhibits a similar strong enhancement as for pyridine on Ag. The intensity is very sensitive to the angle of incidence, and the signal is detectable only in a narrow angular range, when only monolayer amounts of the metals have been dissolved and redeposited electrochemically.     

基于分子内电荷转移机制的巯基荧光比色化学传感器

设计并合成了以香豆素为荧光发色团的多氰基分子化合物TCC。分子内强烈的电荷转移效应使得其本身荧光较弱。巯基化合物如半胱氨酸（Cys）、高半胱氨酸（Hcy）和还原型谷胱甘肽（GSH）的加入能与TCC中的三氰基乙烯基进行加成反应从而破坏分子内电荷转移,使分子内电荷转移吸收峰消失,颜色由紫色变成黄绿色,最大吸收波长由560 nm移至380 nm。并且化合物的荧光也随着巯基化合物的加入逐渐增强,荧光的强度与巯基化合物的浓度有很好的线性关系,检测限可以达到10^-5 mol/L。其它离子与不含巯基的氨基酸则不会与化合物TCC发生上述反应,也就不会对体系的吸收和荧光光谱产生明显的影响,从而实现高效、专一的识别巯基化合物。     

Unique fluorescence behavior of perylenetetracarboxydiimides in polyimide systems

Perylenetetracarboxydiimide (PEDI) molecularly dispersed in polyamic acid (PAA) and polyimide (PI) films has unique fluorescence properties. An originally strong fluorescence of PEDI is efficiently quenched in the PAA films. The systematic variation of the chain structure of the PAA matrices revealed that the aromatic amide groups in the PAA chains function as a quencher. When a PAA derived from 3,4,3′4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA), BPDA/PDA, was used as a matrix polymer, the fluorescence of the dye dispersed in the film increased abruptly as imidization of the matrix proceeds. But annealing at temperatures higher than 320°C in the step-heating process caused a gradual decrease in the fluorescence intensity. The decreased intensity results from the dye–PDA units interactions intensified by the denser molecular packing of the matrix polymer chains. PEDI shows significant dependence of the fluorescence intensity on the chain structure of the PI matrices. In the various PI films containing a fixed diamine component, the dye fluorescence intensity reduces linearly with an increase in the intramolecular charge transfer ability of the PI matrices. From the result, we propose a fluorescence quenching mechanism through multistep electron transfer processes. The BPDA/PDA polyimide matrix leads to a strong PEDI fluorescence whereas the pyromellitic dianhydride (PMDA)-based PI matrices do not. For the blends composed of these PIs, the fluorescence of PEDI bound into the main chains provides a valuable indicator of the miscibility on the molecular level. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 827–840, 1998     

The luminescence of NaI:Tl for excitation in the vacuum ultraviolet (12–66 eV)

The excitation spectrum (luminescence intensity vs energy of exciting photon) of NaI:Tl is studied for excitation energies in the range 12–66 eV. When the exciting radiation is of low intensity only a prompt fluorescence is observed which shows a structured excitation spectrum. This is interpreted by the assumption of secondary excitations by energetic electrons which have been raised into the conduction band. The energy of these electrons depends on the level from which they were raised. For high illumination intensities an additional, strong, slowly rising luminescence is observed, the intensity and rise time of which depends on the energy as well as on the intensity of the exciting radiation. These results are interpreted by the assumption of trapping of electrons from the conduction band. These electrons may be raised again into the conduction band by interaction with energetic conduction band electrons. The rate for the thermal release of the trapped electrons is independent of the excitation energy. A detailed model is presented which permits the calculation of the various rate parameters from the experimental results.     

The mass spectra of 1- and 2-alkylbenzotriazoles

The fragmentation patterns of a series of 1- and 2-alkylbenzotriazoles are recorded and interpreted in comparison with available literature data. 1- and 2-Substituted benzotriazoles are readily differentiated on the basis of the relative ease with which a 1-substituted isomer loses nitrogen compared with the corresponding 2-isomer, resulting in generally weak parent ions for the former and strong parent ions for the latter. This loss of nitrogen in the 1-isomer ultimately gives rise to a strong peak at m/z 104, which is small or absent in the 2-isomer. In addition, examination of the intensity and distribution of peaks clustered around m/z 118 reveals that weak signals with a maximum intensity at m/z 117 or 118 are indicative of the 1-isomers, while strong signals with a maximum intensity at 119 or 120 are typical of the 2-isomers. Thus, isomers are distinguished by analysis of mass spectral cracking patterns. © 1997 John Wiley & Sons, Inc. Heteroatom Chem. 8: 459–464, 1997     

Amphiphilic Inclusion Spaces for Various Guests and Regulation of Fluorescence Intensity of 1,8‐Bis(4‐aminophenyl)anthracene Crystals

A host framework for inclusion of various guest molecules was investigated by preparation of inclusion crystals of 1,8‐bis(4‐aminophenyl)anthracene (1,8‐BAPA) with organic solvents. X‐ray crystallographic analysis revealed construction of the same inclusion space incorporating 1,8‐BAPA and eight guest molecules including both non‐polar (benzene) and polar guests (N,N‐dimethylformamide, DMF). Fluorescence efficiencies varied depending on guest molecule polarity; DMF inclusion crystals exhibited the highest fluorescence intensity (Φ_F=0.40), four times as high as that of a benzene inclusion crystal (Φ_F=0.10). According to systematic investigations of inclusion phenomena, strong host–guest interactions and filling of the inclusion space led to a high fluorescence intensity. Temperature‐dependent fluorescence spectral measurements revealed these factors effectively immobilised the host framework. Although hydrogen bonding commonly decreases fluorescence intensity, the present study demonstrated that such strong interactions provide excellent conditions for fluorescence enhancement. Thus, this remarkable behaviour has potential application toward sensing of highly polar molecules, such as biogenic compounds.     

雌二醇的流动注射阻抑化学发光法测定

基于碱性介质中雌二醇对N-溴代丁二酰亚胺-钙黄绿素化学发光体系的阻抑作用,建立了雌二醇的流动注射化学发光分析新方法,优化了其分析条件,并初步探讨了该化学发光反应的机理。该方法测定雌二醇的线性范围为0.02~0.1、0.1~8.0 mg/L,检出限为0.008 5 mg/L。对0.1 mg/L的雌二醇标准溶液进行11次平行测定,相对标准偏差为1.2%。将该法用于注射液中雌二醇的测定,结果满意。     

On studies of spontaneously emitted Cd I and Cd II lasing transitions

The effect of spatial variation with respect to metal surface, buffer gas (helium) pressure, temporal behavior on the intensity of spontaneously emitted Cd I and Cd II lasing transitions is reported. A strong dependence of intensity of the emitted spectrum on pressure of helium gas, indicating electron-ion recombination is observed. An estimate of temperature corresponding to recombination laser for Cd I and Cd II transitions is presented.     

Non-perturbative theory of four-wave light scattering in strong fields

Nonlinear four-wave light scattering (FWLS) on a three-level system is analyzed, adopting the density operator approach. A strong field Ω₁ is mixed by the material system with two fields Ω₂ and Ω₃ to yield an output field peaked at the frequency Ω₄ = Ω₁ + Ω₃ - Ω₂. The theory is developed within the dipole and Markov approximations. The strong resonant field is treated “exactly”, while the other fields are regarded as perturbations. The generated intensity is obtained as the expectation value of the photon number operator, estimated at the sixth order in the weak-field expansion. The generation of a coherent field at the frequency Ω₄ is due to processes where either a single molecule or a couple of molecules are involved. The total intensity is interpreted as the superposition of four contributions: a four-photon scattering process (FPS), a three-photon process (TPS), and two more processes related to resonance Raman scattering (RRS) and resonance fluorescence (RF). The method allows the deduction of nonlinearities in the generated intensity which are not included in fully perturbative treatment, and which, in the strong-field limit, originate the Rabi intensity dip of the lines.     

Optical Diagnostics of the Effect of Oxygen on Bi-Level Contact Etch

The effect of oxygen flow rate on bi-level contact etch was studied by observing uv-visible emission from the plasma, during CHF₃/CO/O₂ etching of di-electric layers consisting of SiO₂ and SiN_x. The emission intensity of CN at 387 nm drifted progressively from wafer to wafer during plasma etch. Such a phenomenon became more obvious when using low or high oxygen flow rate, whereas for intermediate flow rates, no significant drift of emission intensity was observed. The critical dimension (CD) bias of each wafer showed a strong correlation with CN emission intensity. Possible mechanisms for such an intensity drift phenomenon are proposed. The drift of emission intensity indicates that the contribution of chamber wall polymers in wafer etching is non-negligible. The CN emission intensity is an indication of the magnitude of etching rate. Our results suggest that the variation of plasma emission intensity might be used as an index for in-line monitoring of CD bias fluctuation.     

A simple coumarin-based fluorescent probe for specific detection of cysteine over homocysteine and glutathione

In this work, we designed and synthesized 3-cyano-2-oxo-2H-chromen-7-yl acrylate as a simple and effective probe 1, which is capable of detecting cysteine (Cys) over other biothiols, such as homocysteine and glutathione. Remarkably, with the addition of cysteine, the 125-fold increase in fluorescence intensity of probe 1 was observed at 450 nm with excitation at 413 nm and 5 min incubation time. Furthermore, it is more important that probe 1 possesses the detection limit of 80 nM, and there is good linear relationship between fluorescence intensity and concentration of Cys from 0 to 100 μM. Thus, these made a powerful safeguard for the detection of Cys in the biological system. Simultaneously, probe 1 showed low toxicity and could be used in living cell imaging.     

Fabrication of acrylate monolith using photopolymerization: Effect of light intensity on electrochromatographic performance

A hexyl acrylate monolith was prepared via photopolymerization into a cyclic olefin copolymer micro-device for reversed-phase electrochromatography purposes. This work deals with the influence of the irradiation conditions (irradiation time and light intensity) used during synthesis on the electrochromatographic performances of the monolithic column obtained. Up to day, the monolith structure was often controlled by means of irradiation time at constant light intensity, but the effect of light intensity (irradiance) on the monolith structure was scarcely considered. This study shows a strong effect of light intensity on electrochromatographic efficiency. Using an optimal light intensity of 4.7 mW/cm(2) and an irradiation time of a few minutes allows obtaining heights equivalent to a theoretical plate reaching down to 5 μm for the reversed-phase separation of six polycyclic aromatic hydrocarbons.     

An optical ionic-strength sensor based on polyelectrolyte association and fluorescence energy transfer

The optical ionic-strength sensor is based on an indicator phase consisting of an aqueous solution of fluorescein-labelled dextran and polyethyleneimine labelled with Sulforhodamine 101 (Texas Red), confined behind a dialysis membrane. At low ionic strength the polymers associate and the average distance between the fluorescein and Texas Red is short enough for efficient energy transfer to occur. With increasing ionic strength the polymers dissociate and the efficiency of energy transfer decreases. The measured parameter is the ratio of the emission intensity at 520 nm, where fluorescein fluorescence is maximal, to the intensity at 620 nm, where the Texas Red emission is strong. The increase in the intensity ratio as a function of ionic strength is similar but not quite the same for different ions, suggesting that the mechanism of response involves more than a simple ionic strength effect.     

Dipyrrolyl quinoxalines with extended chromophores are efficient fluorimetric sensors for pyrophosphate

2,3-Di(pyrrole-2-yl)quinoxaline anion sensors with extended chromophores display dramatic enhancement in fluorescence intensity (sensing output), increased affinity for inorganic anions as well as strong selectivity for pyrophosphate over phosphate anion.     

Influence of substitution pattern on the benzenoid transitions: Quantitative evaluation of the electronic and vibrational components from new experimental polarization data

The influence of substitution on the benzenoid ¹L_b, ¹L_a and ¹B transitions is studied by the technique of linear dichroism in stretched polyethylene films.The total intensity of the ¹L_b system is resolved into induced and vibrational components and the influence of various substitution patterns on the magnitude and polarization of both components is analyzed quantitatively. As expected from theoretical considerations, the vibrational components like the induced intensity are found to be strongly affected by the substituent strength and the symmetry of substitution pattern. The previously accepted assumption, according to which the vibrational intensity is regarded as a constant, appears to be completely unrealistic when dealing with cases of strong substituents. A satisfactory quantitative treatment of both weak and strong substituents using the same simple theoretical approach seems possible only if the systematic variations observed in the vibrational intensity are not neglected.A qualitative analysis is given for the ¹L_a, and ¹B systems. The results are compared with available theoretical predictions and previous experimental data.Practical implications of the present new experimental information to the study of aromatic optical activity are discussed.     

Radiative and Nonradiative Lifetimes of Band Edge States and Deep Trap States of CdS Nanoparticles Determined by Time-correlated Single Photon Counting

Emission lifetimes of band edge and deep trap states of CdS nanoparticles with different surface capping were measured using time-resolved single-photon-counting^[1]. For unpassivated nanoparticles with low fluorescence yield, the emission is dominated by deep trap states and the decay can be fit to a single exponential with a time constant of 5 ns that is independent of excitation intensity. For surface passivated nanoparticles with strong luminescence, the emission is dominated by band edge states and the decay is fit to a double exponential with time constants of a few ns and 50 ns. While the 50 ns decay is independent of excitation intensity, the fast component is strongly dependent on intensity. For the fast decay component, the amplitude decreases non-linearly and the time constant becomes longer (from 2.5 to 7.9 ns) as the intensity decrease. The results support the model of exciton-exciton annihilation^[2] upon trap state saturation at high excitation intensities.