Enhanced fluorescence detection of metal ions using light-harvesting mesoporous organosilica

Enhanced fluorescence detection of metal ions was realized in a system consisting of a fluorescent 2,2′‐bipyridine (BPy) receptor and light‐harvesting periodic mesoporous organosilica (PMO). The fluorescent BPy receptor with two silyl groups was synthesized and covalently attached to the pore walls of biphenyl (Bp)‐bridged PMO powder. The fluorescence intensity from the BPy receptor was significantly enhanced by the light‐harvesting property of Bp‐PMO, that is, the energy funneling into the BPy receptor from a large number of Bp groups in the PMO framework which absorbed UV light effectively. The enhanced emission of the BPy receptor was quenched upon the addition of a low concentration of Cu²⁺ (0.15–1.2×10^?6 M ), resulting in the sensitive detection of Cu²⁺. Upon titration of Zn²⁺ (0.3–6.0×10^?6 M ), the fluorescence excitation spectrum was systematically changed with an isosbestic point at 375 nm through 1:1 complexation of BPy and Zn²⁺ similar to that observed in BPy‐based solutions, indicating almost complete preservation of the binding property of the BPy receptor despite covalent fixing on the solid surface. These results demonstrate that light‐harvesting PMOs have great potential as supporting materials for enhanced fluorescence chemosensors.     

Phenanthroline method for quantitative determination of surface carboxyl groups on carboxylated polystyrene particles with high sensitivity

This study developed a phenanthroline method for quantitative determination of surface carboxyl groups on carboxylated polystyrene (PS‐COOH) particles based on the coordination between the carboxyl groups and Fe²⁺. The ratio of the carboxyl groups, which is determined by conductometric titration method, to Fe²⁺ coordinated with the particles, which is determined by phenanthroline method, is 4.7, i.e. n_COOH = 4.7 × Δn_Fe²⁺. The Lambert–Beer law is obeyed in the range of 0–60 × 10^?9 mol/ml for the amount of surface carboxyl on the particles. The detection limit of the method is 2 nmol COOH/ml. The average standard deviation of the experiments is 4.4%. The relative deviation of the data obtained with this method is lower than 7% compared with that obtained with the conductometric titration method. The weight of the sample necessary for phenanthroline method is only about 0.1% of that necessary for conductometric titration method. It has been demonstrated that the phenanthroline method is suitable for quantitative determination of low amount of surface carboxyl groups on PS‐COOH particles due to its high sensitivity. Copyright © 2009 John Wiley & Sons, Ltd.     

Studies on the non‐covalent interactions between cyclodextrins and aryl alkanol piperazine derivatives by mass spectrometry and fluorescence spectroscopy

The non‐covalent complexes of α‐ and β‐cyclodextrins (α‐, β‐CDs) with two aryl alkanol piperazine derivatives (Pipe I and Pipe II) have been studied by electrospray ionization mass spectrometry (ESI‐MS) and fluorescence spectroscopy. The ESI‐MS experimental results demonstrated that Pipe I can conjugate to β‐CD and form 1:1 or 1:2 stoichiometric non‐covalent complexes, and Pipe II can only form 1:1 complexes with α‐ or β‐CD. Fluorescence spectra indicated that the fluorescence intensities of Pipe I and Pipe II can be enhanced by increasing the content of β‐CD. The mass spectrometric titration experiments showed that the dissociation constants K_d1 were 5.77 and 9.52 × 10^?4 mol L^?1 for the complexes of α‐CD with Pipe I and Pipe II, respectively, revealing that the binding of α‐CD‐Pipe I was stronger than α‐CD‐Pipe II. The K_d1 and K_d2 values were 9.81 × 10^?4 mol L^?1 and 1.11 × 10^?7 (mol L^?1)² for 1:1 and 1:2 complexes of Pipe I with β‐CD, respectively. The K_d values obtained from fluorescence spectroscopy were in agreement with those from ESI‐MS titration. Copyright © 2010 John Wiley & Sons, Ltd.     

A Five‐layer π‐Aromatic Structure Formed through Self‐assembly of a Porphyrin Trimer and Two Aromatic Guests

In this study we synthesized two‐ and four‐armed porphyrins – bearing two carboxyl and four 2‐aminoquinolino functionalities, respectively, at their meso positions – as a complementary hydrogen bonding pair for the self‐assembly of a D₂‐symmetric porphyrin trimer host. Two units of the two‐armed porphyrin and one unit of the four‐armed porphyrin self‐assembled quantitatively into the D₂‐symmetric porphyrin trimer, stabilized through ammidinium‐carboxylate salt bridge formation, in CH₂Cl₂ and CHCl₃. The porphyrin trimer host gradually bound two units of 1,3,5‐trinitrobenzene between the pair of porphyrin units, forming a five‐layer aromatic structure. At temperatures below ?40 °C, the rates of association and dissociation of the complexes were slow on the NMR spectroscopic time scale, allowing the 1 : 1 and 1 : 2 complexes of the trimer host and trinitrobenzene guest(s) to be detected independently when using less than 2 eq of trinitrobenzene. Vis titration experiments revealed the values of K₁ (2.1±0.4×10⁵ M^?1) and K₂ (2.2±0.06×10⁴ M^?1) in CHCl₃ at room temperature.     

Energy transfer from chemically attached rhodamine 101 to adsorbed methylene blue on microcrystalline cellulose particles

Rhodamine 101 (R101) was chemically attached onto microcrystalline cellulose and methylene blue (MB) was adsorbed to a sample bearing nearby 6 × 10^?7 mol R101 (g cellulose)^?1. The system was studied by reflectance and emission spectroscopy in the solid state. R101 shows no aggregation in these conditions and, while pure MB builds up dimers on cellulose even at 2 × 10^?8 mol g^?1, in the presence of R101 no evidence on selfaggregation or heteroaggregation is found up to around 10^?6 mol g^?1. No exciplex formation is found as well. The overall fluorescence quantum yield measured on thick layers, once re‐absorption effects are accounted for, amounts to 0.80 ± 0.07 for pure R101 and decreases steadily on increasing the concentration of MB. Results demonstrate the occurrence of radiative and nonradiative singlet energy transfer from R101 to MB. For thick layers of particles, the combined effect of both kinds of energy transfer amounts to nearly 80% at the highest acceptor concentration, while nonradiative transfer reaches 60% both for thin and optically thick layers. The dependence of nonradiative energy transfer efficiencies on the acceptor concentration is analyzed and the origin of departures from Förster behavior at low acceptor concentration is discussed.     

Focused ion beam implantation of Ga in Si and Ge: fluence‐dependent retention and surface morphology

Focused ion beam implantation of 30‐keV Ga⁺ ions in single‐crystalline Si and Ge was investigated by SIMS, using Cs⁺ primary ions for sputtering. Nine different implantation fluences ranging from 1 × 10¹³ to 1 × 10¹⁷ Ga⁺‐ions/cm² were used, with implanted areas of 40 × 40 µm². The Ga concentration distributions of these implants were determined by SIMS depth profiling. Such 30‐keV Ga implantations were also simulated by a dynamic Monte‐Carlo code that takes into account the gradual change of the near‐surface composition due to the Ga incorporation. In both approaches, an essentially linear increase of the Ga peak concentrations with fluence is found up to ～1 × 10¹⁶cm^?2; for higher fluences, the Ga content approaches a saturation level which is reached at about (1–2) × 10¹⁷cm^?2. The measured and simulated peak concentrations of the Ga distributions are in good agreement. The most probable ranges obtained from the experiments correspond closely with the respective values from the simulations. The surface morphology caused by Ga⁺ implantation was investigated by atomic force microscopy (AFM). The AFM data indicate that for low fluences (<3 × 10¹⁵cm^?2) the surface within the implanted areas is growing outward (i.e. is swelling). For increasingly higher fluences, sputter‐induced erosion of the surface becomes dominant and distinct craters are formed for fluences above ～1 × 10¹⁶cm^?2. At the boundary of the implanted region a wall‐like structure is found to form upon Ga implantation; its height is growing with increasing fluence, reaching a value of ～15 nm at 1 × 10¹⁷ Ga⁺‐ions/cm². Copyright © 2008 John Wiley & Sons, Ltd.     

Selective Detection of Hg2+ Ions with Boron Dipyrromethene‐Based Fluorescent Probes Appended with a Bis(1,2,3‐triazole)amino Receptor

By using a copper‐promoted alkyne–azide cycloaddition reaction, two boron dipyrromethene (BODIPY) derivatives bearing a bis(1,2,3‐triazole)amino receptor at the meso position were prepared and characterized. For the analogue with two terminal triethylene glycol chains, the fluorescence emission at 509 nm responded selectively toward Hg²⁺ ions, which greatly increased the fluorescence quantum yield from 0.003 to 0.25 as a result of inhibition of the photoinduced electron transfer (PET) process. By introducing two additional rhodamine moieties at the termini, the resulting conjugate could also detect Hg²⁺ ions in a highly selective manner. Upon excitation at the BODIPY core, the fluorescence emission of rhodamine at 580 nm was observed and the intensity increased substantially upon addition of Hg²⁺ ions due to inhibition of the PET process followed by highly efficient fluorescence resonance energy transfer (FRET) from the BODIPY core to the rhodamine moieties. The Hg²⁺‐responsive fluorescence change of these two probes could be easily seen with the naked eye. The binding stoichiometry between the probes and Hg²⁺ ions in CH₃CN was determined to be 1:2 by Job′s plot analysis and ¹H NMR titration, and the binding constants were found to be (1.2±0.1)×10¹¹ m ^?2 and (1.3±0.3)×10¹⁰ m ^?2, respectively. The overall results suggest that these two BODIPY derivatives can serve as highly selective fluorescent probes for Hg²⁺ ions. The rhodamine derivative makes use of a combined PET‐FRET sensing mechanism which can greatly increase the sensitivity of detection.     

Self‐Healing Supramolecular Materials Constructed by Copolymerization via Molecular Recognition of Cavitand‐Based Coordination Capsules

The repeating guest units of poly‐(R)‐ 2 were selectively encapsulated by the self‐assembled capsule poly‐ 1 possessing eight polymer side chains to form the supramolecular graft polymer (poly‐ 1 )_n?poly‐(R)‐ 2 . The encapsulation of the guest units was confirmed by ¹H NMR spectroscopy and the DOSY technique. The hydrodynamic radius of the graft polymer structure was greatly increased upon the complexation of poly‐ 1 . The supramolecular graft polymer (poly‐ 1 )_n?poly‐(R)‐ 2 was stably formed in the 1:1 host–guest ratio, which increased the glass transition temperature by more than 10 °C compared to that of poly‐ 1 . AFM visualized that (poly‐ 1 )_n?poly‐(R)‐ 2 formed the networked structure on mica. The (poly‐ 1 )_n?poly‐(R)‐ 2 gelled in 1,1,2,2‐tetrachloroethane, which led to fabrication of distinct viscoelastic materials that demonstrated self‐healing behavior in a tensile test.     

Determination of Butylated Hydroxyanisole by Briggs‐Rauscher Oscillating Reaction Catalyzed by a Macrocyclic Nickel (II) Complex

A novel analytical approach for quantitative measurement of butylated hydroxyanisole (BHA) is dis‐ cussed in this paper. Such a method depends on the inhibitory effect of BHA on a Briggs‐Rauscher (B‐R) oscillating reaction. Unlike the classical B‐R system which involves Mn²⁺ as the catalyst, such a B‐R sys‐ tem is catalyzed by a macrocyclic nickel (II) complex [NiL](ClO₄)₂, where L in the complex is an unsatu‐ rated ligand 5,7,7,12,14,14‐hexemethyl‐1,4,8,11‐tetraazacyclotetradeca‐4,11‐diene. By perturbation of BHA on the system, the oscillation was inhibited in the presence trace amounts of BHA and the inhibition time was found to be proportional to the concentration of BHA over the range 1.00×10^?7–1.20×10^?4 mol/L. Two calibration curves were obtained: the first linear regression is over the range of 1.00×10^?7–2.00×10^?6 mol/L, and the second linear regression is over the range between 2.00×10^?6 and 1.20×10^?4 mol/L, with a lowest limit of detection of 4.00×10^?8 mol/L. UV spectra measurements were employed to clarify the possible perturbation mechanism caused by BHA on the B‐R oscillating reaction.     

N‐Annulated Perylene‐Substituted and Fused Porphyrin Dimers with Intense Near‐Infrared One‐Photon and Two‐Photon Absorption

Fusion of two N‐annulated perylene (NP) units with a fused porphyrin dimer along the S₀–S₁ electronic transition moment axis has resulted in new near‐infrared (NIR) dyes 1 a / 1 b with very intense absorption (ε>1.3×10⁵ M ^?1 cm^?1) beyond 1250 nm. Both compounds displayed moderate NIR fluorescence with fluorescence quantum yields of 4.4×10^?6 and 6.0×10^?6 for 1 a and 1 b , respectively. The NP‐substituted porphyrin dimers 2 a / 2 b have also been obtained by controlled oxidative coupling and cyclodehydrogenation, and they showed superimposed absorptions of the fused porphyrin dimer and the NP chromophore. The excited‐state dynamics of all of these compounds have been studied by femtosecond transient absorption measurements, which revealed porphyrin dimer‐like behaviour. These new chromophores also exhibited good nonlinear optical susceptibility with large two‐photon absorption cross‐sections in the NIR region due to extended π‐conjugation. Time‐dependent density functional theory calculations have been performed to aid our understanding of their electronic structures and absorption spectra.     

Polyelectrolyte titration using fluorescent indicator. II. Analysis of cationic starches and flocculants

In the conventional polyelectrolyte titration, toluidine blue (TB) has been used exclusively as an indicator. This is a very convenient method for analyses of polyelectrolytes with fairly high charge density, but it is very difficult, or impossible, to analyze samples with low charge density such as commercial cationic starches because of the unclear color change of TB at the end point. Also analyses of polyelectrolytes with ultrahigh molecular weights over 10⁷ (such as common flocculants) are often accompanied by serious errors. Usually, the concentration of standard titrant is around 0.2 × 10^?3 N. On the other hand, the standard titrant with very dilute concentration such as 1 × 10^?4 N can be used in the polyelectrolyte titration using a fluorescent indicator because the sensitivity of fluorescence detection is extremely high. It has been elucidated that this method can be employed for accurate analyses of cationic starches, cationic and anionic flocculants, and also for determination of sulfonic and carboxyl groups contained in the same molecule by the titration at pH 2.8 and 9.5, respectively. © 1993 John Wiley & Sons, Inc.     

铜（II）离子对脱镁叶绿素-a荧光猝灭的研究

本文介绍了一种利用荧光熄灭定量的测定铜（II）的新方法。从新鲜菠菜中提取叶绿素-a,用高氯酸溶液处理,制得脱镁叶绿素-a。测量脱镁叶绿素-a的紫外-可见吸收光谱,观测到505和535nm处有特征吸收峰。在60 ℃水浴中,脱镁叶绿素-a的丙酮溶液与铜（II）离子水溶液混合,5分钟后发现混合液颜色变绿,505和535 nm处吸收峰消失。铜（II）离子水溶液与脱镁叶绿素-a的丙酮溶液混合后发生荧光猝灭现象,而类似浓度的其它生理离子在相同反应条件下对脱镁叶绿素-a的荧光猝灭现象不明显。 研究了铜（II）离子与脱镁叶绿素-a的反应时间,反应温度对荧光强度衰减的影响。并通过阿累尼乌斯经验关系估算铜（II）离子与脱镁叶绿素-a反应的活化能约为10 ±1kJ·mol-1。研究了铜（II）离子的浓度对脱镁叶绿素-a的丙酮溶液荧光强度的影响,在8.0×10-5 ～8.0×10-7 mol·dm-3范围内,铜（II）离子的浓度与混合液的荧光强度成线性衰减关系,检测限可达8.0×10-7 mol·dm-3。利用脱镁叶绿素-a的丙酮溶液的荧光强度变化测量,有望发展成为一种检测铜（II）离子的新方法。     

Hybridization of Long Pyridine‐Dicarboxamide Oligomers into Multi‐Turn Double Helices: Slow Strand Association and Dissociation,Solvent Dependence,and Solid State Structures

Oligoamides of 2,6‐diaminopyridine and 2,6‐pyridinedicarboxylic acid comprised of 5, 7, 9, 11, or 13 units and bearing 4‐isobutoxychains on all pyridine rings and tert‐butyl‐carbamate terminal groups have been synthesized stepwise, along with an 11 mer having benzyl‐carbamate terminal groups. The crystal structure of all five Boc‐terminated compounds has been obtained and shows a highly regular and conserved double helical hybridization motif of up to 3 complete turns for the 13 mer. Four pyridine units span one helical turn and define a helix pitch of ca 7 Å. Solution studies in CDCl₃ demonstrated that the Boc‐terminated oligomers strongly hybridize in this solvent, and that K_dim values increase with oligomer length. The K_dim values are 31000 and 7×10⁵ L mol^?1 for the 7 mer and the 9 mer, respectively, and are too high to be measured by NMR for the 11 mer and the 13 mer. Hybridization and dissociation kinetics at 2 mM proceed at decreasing rates upon increasing oligomer length. The rate was faster than minutes for the 7 mer, of the order of hours for the 9 mer, and days for the 11 mer and 13 mer. The same trend was observed in [D₅]pyridine but with considerably lower K_dim values and faster kinetics. The benzylcarbamate 11 mer was also found to hybridize into a double helix but with reduced K_dim values and faster kinetics compared to its Boc‐terminated analogue. Combined with previous studies, the results presented here frame a global understanding of the hybridization of these pyridinecarboxamide oligomers and provide useful guidelines for the design of other artificial double helices.     

Phthalocyanine-based fluorescent chemosensor for the sensing of Zn (II) in dimethyl sulfoxide-acetonitrile

A tetra-substituted phthalocyanine based on 4-[2-(4-nitrophenoxy)ethoxy]phthalonitrile carrying nitrophenyl group for the sensing of Zn²⁺ has been prepared and characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR, and MS spectral data. The sensing of Zn²⁺ is based on the fluorescence quenching of Pc. Both absorbance and fluorescence spectra of ZnPc exhibit distinct changes in visible region in response to treatment with Zn²⁺ ion in dimethyl sulfoxide. The fluorescence spectrum of the ligand showed quenching in the intensity of the signal at 688?nm for Zn²⁺. The complex composition of ZnPc was found 1:1 by means of spectrophotometric and spectrofluorimetric titration data. The spectrofluorimetric method showed good sensitivity for Zn²⁺ with linear range and detection limit of 4.0?×?10^?6–4.4?×?10^?5 and 2.4×10^?7?M, respectively.     

Graphite Electrode Coated with a 7,16‐Dibenzyl‐1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane‐Multiwalled Carbon Nanotube Composite as Sensor For Detection of Samarium

A composite multiwalled carbon nanotube polyvinyl chloride electrode based on 7,16‐dibenzyl‐1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane (DBDA18C6) as Sm³⁺ ionophore is reported. This potentiometric sensor showed a wide linear working range, 1×10^?2–1×10^?8 M, Nernstian slope, 20.2±0.48 mV per decade and a limit of detection, 6.3±0.36×10^?9 M. It works in the pH range 2.5–8.5 and shows a good selectivity over a number of metal ions. It has been found suitable for the analysis of ores and industrial effluents. The electrode surface is characterized by FRA and AFM.     

Novel Ytterbium(III) Selective Membrane Sensor Based on N‐(2‐Pyridyl)‐N′‐(2‐Methoxyphenyl)‐Thiourea as an Excellent Carrier and Its Application to Determination of Fluoride in Mouth Wash Preparation Samples

The construction, performance, and applications of a novel ytterbium(III) sensor based on N‐(2‐pyridyl)‐N′‐(2‐methoxyphenyl)‐thiourea (PMT), as an excellent carrier, in plasticized poly(vinyl chloride) PVC matrix, is described. The influences of membrane composition and pH on the potentiometric response of the sensor were investigated. The sensor exhibits a nice Nernstian response for Yb(III) ion over a wide concentration range of 4 decades of concentration (1.0×10^?6–1.0×10^?2 M), and a detection limit of 5.0×10^?7 M. The response time of the electrodes is between 8 and 10 s, depending on the concentration of ytterbium(III) ions. The proposed sensor can be used for about 8 weeks without any considerable divergence in potential. The sensor revealed very good selectivity for Yb(III) in the presence of several metal ions. The best performance was observed for the membrane containing; 30% PVC, 59% o‐nitrophenyloctyl ether (NPOE) as solvent mediator, 7% PMT, and 4% sodium tetraphenyl borate (NaTPB). It was successfully applied as indicator electrodes in the potentiometric titration of Yb(III) with EDTA and for the determination of fluoride ion in two mouth wash formulations. The proposed La(III) sensor was found to work well under laboratory conditions. It was also used as an indicator electrode in titration of a 1.0×10^?4 M of Yb(III) with a standard EDTA solution (1.0×10^?2 M). It was also used for determination of Yb(III) ion in Xenotime .     

Electroanalytical Studies of Chromone Based Ionophores for the Selective Determination of Arsenite Ion

Two chemosensors 4H‐1‐benzopyran‐3‐carboxaldehyde, 4‐oxo‐, 3‐(2‐phenylhydrazone), [I₁] and 4H‐1‐benzopyran‐3‐carboxaldehyde, 4‐oxo‐, 3‐[2‐(2,4‐dinitrophenyl)hydrazone], [I₂] with hydrazone‐NH group as binding site have been shown excellent selectivity for arsenite ion. It is confirmed by the UV‐vis titration that I₂ is more selective than I₁. The performance of the coated graphite electrode (CGE) was found to be better than polymeric membrane electrode (PME) in terms of linear range of 4.89×10^?7–1.0×10^?1 mol L^?1, low detection limit of 8.31×10^?8 mol L^?1 and short response time. The proposed sensors were also used to determine the arsenite ion in different water samples.     

健那绿B的荧光猝灭研究及作为核酸测定探针的应用

用紫外可见光谱、稳态荧光发射及荧光寿命测定研究了核酸猝灭十二烷基磺酸钠胶束中的健那绿荧光。水溶液中弱的健那绿荧光在十二烷基磺酸钠胶束中被大大加强，其最大发射从425纳米移至410纳米，核酸的加入将猝灭健那绿的荧光，当健那绿浓度为2.5×10^–5 mol•L^-1时，荧光猝灭(F₀/F)分别与小牛胸腺DNA及鱼精DNA在2.4×10^–8 到 1.08×10^–7及 1.9×10^–8 到 3.8×10^–8 mol•L^-1范围内成正比, 检测限分别为1.3×10^–8 mol•L^-1 (小牛胸腺DNA)及6.3×10^–9 mol•L^-1 (鱼精DNA)。当DNA浓度较高时, 将系统偏离Stern-Volmer方程。这是因为动态猝灭和静态猝灭同时存在。方法已应用于鸡血提取液中DNA的测定, 测定结果与紫外法一致。     

A Novel PVC‐Membrane‐Coated Graphite Sensor Based on an Anthraquinone Derivative Membrane for the Determination of Lead

A highly selective membrane electrode for the determination of ultratrace amounts of lead was prepared. The PVC membrane electrode based on 2‐(2‐ethanoloxymethyl)‐1‐hydroxy‐9,10‐anthraquinone (AQ), directly coated on graphite, exhibits a good Nernstian response for Pb(II) ions over a very wide concentration range (1.0×10^?7–1.0×10^?2 M) with a limit of detection of 8.0×10^?8 M. It has a fast response time of ca. 10 s and can be used over a period 2 months with good reproducibility (SD=±0.2 mV). The electrode revealed a very good selectivity respect to common alkali, alkaline earth, transition and heavy metal ions and could be used in the pH range of 3.5–6.8. It was used as an indicator electrode in potentiometric titration of lead ions with chromate and oxalate, and in indirect determination of lead in spring water samples.