新型三脚架苯甲醛苯腙醋酸根选择性比色化学传感器

本文合成了一个新的基于三脚架苯甲醛苯腙的能够选择地检测醋酸根离子的比色化学传感器1。用紫外可见吸收光谱证实了受体1在二甲基亚砜溶液中对醋酸根离子高选择的键合能力超越了其它阴离子。和其他所研究的阴离子相比,其在二甲基亚砜中紫外可见吸收光谱对具有高选择性醋酸根离子的存在显示了应答,当存在（2´10^-5mol·dm^-3）醋酸根离子时其溶液的颜色也由黄色变化到蓝色。当用其他不同的客体阴离子（F^-, Cl^-, Br^-, I^-, H₂PO₄ ^–和 OH^-）处理受体1时,仅出现了很小的紫外可见吸收光谱变化。受体1对醋酸根的结合常数 K_ass为1.69´ 10⁴。     

pH sensor based on polyaniline and aniline–anthranilic acid copolymer films using quartz crystal microbalance and electronic absorption spectroscopy

The pH sensitivity based on conducting polyaniline (PANI) and copolymer of aniline and o‐anthranilic acid (AA) films were studied using quartz crystal microbalance (QCM) technique and UV–Vis spectroscopy. The sensor was constructed from these polymer films coated on the electrode of the QCM. The resonant frequency changes as a function of pH in the range of 2–12 were measured. These changes are quantitative indication of the degree of dedoping or redoping of the polymer films upon the subsequent exposure of the electrode to 0.25 M sulfuric acid and different pH solutions. There are two linear regressions between the frequency change and pH with two different and opposite slopes in the regions from 2 to 9 and 9 to 12. The pH sensitivity of the copolymer film was found to be less than using the PANI film. Thin films of PANI and copolymer, which were chemically polymerized in a sulfuric acid solution, were deposited onto the inner walls of the quartz cuvettes. The UV–Vis absorption spectra of these films were measured in different pH solutions. Relations between the maximum absorption and its wavelength versus pH were constructed. The copolymer film shows some advantages over the PANI film. The difference between the PANI and copolymer films as pH sensors using the QCM and electronic absorption extends from the determination of pK_a for both films. Copyright © 2008 John Wiley & Sons, Ltd.     

A novel indicator series for measuring pKa values in acetonitrile

A series of substituted azobenzene dyes was found to span a range of 8 pK_a units in acetonitrile. The UV absorption spectra of the dyes are responsive to protonation, changing in both absorption maximum and intensity. These characteristics make the dyes useful as indicators for the measurement of pK_a values of neutral organic bases that absorb in the visible region of the spectrum.     

1H NMR,IR and UV/VIS Spectroscopic Studies of Some Schiff Bases Derived from 2‐Aminobenzothiazole and 2‐Amino‐3‐Hydroxypyridine

By condensing 2‐aminobenzothiazole with 2‐hydroxy‐1‐naphthaldehyde, 2‐hydroxybenzaldehyde, 4‐methoxybenzaldehyde, 4‐hydroxybenzal‐dehyde, benzaldehyde and 4‐dimethylaminobenzaldehyde, and five Schiff bases Ia‐Ie are prepared. Also, two Schiff bases IIa and IIb are prepared by condensation of 2‐amino‐3‐hydroxypyridine with 2‐hydroxy‐1‐naphthaldehyde and 2‐hydroxybenzaldehyde. The ¹H NMR, IR and UV/Vis spectra of these seven Schiff bases are investigated. The signals of the ¹H NMR spectra as well as the important bands in the IR spectra are considered and discussed in relation to molecular structure. The UV/Vis absorption bands in ethanol are assigned to the corresponding electronic transitions and the electronic absorption spectra of Schiff bases Ib and IIb are studied in organic solvents of different polarities. The UV/Vis absorption spectra of 2‐amino‐3‐hydroxypyridine Schiff bases IIa and IIb are investigated in buffer solutions of different pH values containing 5% (v/v) methanol, and the results are utilized for the determination of pK_a and ΔG^* of the ionization of the phenolic OH‐groups. The fluorescence spectra of IIa and IIb are studied in organic solvents of different polarities. The obtained spectral results are confirmed by some molecular calculations using the atom super position and electron delocalization molecular orbital theory for the Schiff base IIb.     

2‐Nitro‐1,4‐diaminobenzene‐Functionalized Poly(vinyl amine)s as Water‐Soluble UV‐Vis‐Sensitive pH Sensors

Summary: Nucleophilic aromatic substitution of 2,6‐O‐dimethyl‐β‐cyclodextrin (β‐DMCD)‐complexed 4‐fluoro‐3‐nitroaniline derivatives with poly(vinyl amine) (PVAm) in water results in 2‐nitro‐1,4‐benzenediamine‐functionalized water‐soluble PVAms in one step. The 2‐nitro‐1,4‐benzenediamine moiety linked to the polymer is solvatochromic and undergoes protonation and deprotonation as function of pH as shown by UV‐Vis spectroscopy. The occurrence of an isosbestic point in the UV‐Vis spectrum is suitable to directly determine the pK_a value using the Henderson‐Hasselbalch equation. The influence of the methyl group substitution of the polymer and the 2‐nitro‐1,4‐benzenediamine moiety on the pK_a is discussed.

Structure of the 4‐N,N‐dimethyl‐2‐nitro‐1,4‐benzenediamine‐functionalized PVAm and its solution in water at varying pH.     

Bis-ratiometric absorbance detection of Al(III) in the rhodamine B-functionalized bis-polydiacetylene film

A rhodamine B-functionalized bis-polydiacetylene (RB/bis-PDA) film sensor was prepared. Rhodamine B derivatives as the ion-recognition elements were embedded in the bis-polydiacetylene matrix through the hydrolysis/condensation process of organic silicon. The as-prepared blue-phase RB/bis-PDA film could transfer to yellow phase at high temperatures. Upon dipping the blue and yellow RB/bis-PDA films into various metal ion solutions, respectively, only Al³⁺ could induce remarkable changes in absorption and color signals. The UV–Vis absorption spectrum of the Al³⁺-containing film showed two separate absorption peaks at 556 nm and at another wavelength (617 or 470 nm), corresponding to ring opening of the spirolactam structure in rhodamine moiety and PDA (blue- or yellow-phase PDA), respectively. Utilizing the different intensity ratios of the two absorption signals (A₅₅₆/A₆₁₇ or A₅₅₆/A₄₇₀), the RB/bis-PDA system could be used as a bis-ratiometric absorbance sensor for Al³⁺. The reusable and free-standing films have great potential in environmental and biological sensing fields as they are more convenient to achieve real-time sensing than the conventional probes dissolved in aqueous or organic solvents.     

Host–Guest Interactions of Phosphorescent Molecular Tweezers Based on an Alkynylplatinum(II) Terpyridine System with Polyaromatic Hydrocarbons

Host–guest interactions of a molecular tweezer complex 1 with various planar organic molecules including polyaromatic hydrocarbons (PAHs) were investigated by 1D and 2D ¹H NMR spectroscopy, UV/Vis absorption and emission titration studies. 2D and DOSY NMR spectroscopies support the sandwiched binding mode based on 1:1 host–guest interactions. The binding constants (K_S) of complex 1 for various PAHs were determined by NMR titration studies and the values were found to span up to an order of 10⁴ M ^?1 for coronene to no observable interaction for benzene, indicating that the π‐surface area is important for such host–guest interactions. The substituent effect on the host–guest interaction based on the guest series of 9‐substituted anthracenes was also studied. In general, a stronger interaction was observed for the anthracene guest with electron‐donating groups, although steric and π‐conjugation factors cannot be completely excluded. The photophysical responses of complex 1 upon addition of various PAHs were measured by UV/Vis and emission titration studies. The UV/Vis absorption spectra were found to show a drop in absorbance of the metal‐to‐ligand charge‐transfer (MLCT) and ligand‐to‐ligand charge‐transfer (LLCT) admixture band upon addition of various guest molecules to 1 , whereas the emission behavior was found to change differently depending on the guest molecules, showing emission enhancement and/or quenching. It was found that emission quenching occurred either via energy transfer or electron transfer pathway or both, while emission enhancement was caused by the increase in rigidity of complex 1 as a result of host–guest interaction.     

Synthesis,Crystal Structure,Spectral and Thermodynamic Properties of One Benzoindole Pentamethine Cyanine Dye

One benzoindole pentamethine cyanine dye was synthesized and characterized by ¹H NMR, IR, MS and UV‐Vis spectra. The UV‐Vis absorption and fluorescence spectra of the dye in chloroform, dimethyl sulfoxide, acetone, ethanol and methanol were investigated, and the λ_max of the dye was in the region 682.0–689.0 nm with large molar extinction coefficients (? > 10⁵ M^?1cm^?1) in different solvents. The structure of the dye was also characterized and analyzed by X‐ray diffraction. Crystallographic data revealed that the dye belonged to orthorhombic, with space group P2₁2₁2₁, a = 10.059(2) Å, b = 15.098(4) Å, c = 24.989(6) Å, V = 3794.8(15) ų, Z = 4. The C‐H···F intermolecular hydrogen bonds were displayed in the molecular system, which were effective in the molecular packing. The aggregation behavior and thermodynamic properties of the dye in aqueous methanol solution were also studied by means of UV‐Vis spectroscopy methods. The results indicated that the dye existed monomer‐dimer equilibrium in aqueous methanol solutions. The fundamental properties of the dye, such as the dimeric association constant K_D, the dimeric free energy ΔG_D, the dimeric entropy ΔS_D, and the dimeric enthalpy ΔH_D were determined. The ΔH_D of the dye was –46.0 kJ mol^?1.     

Synthesis of TiO2/CNT Composites and its Photocatalytic Activity Toward Sudan (I) Degradation

Semiconductor photocatalysis has the potential for achieving sustainable energy generation and degrading organic contaminants. In TiO₂, the addition of carbonaceous nanomaterials has attracted extensive attention as a means to increase its photocatalytic activity. In this study, composites of TiO₂ and carbon nanotubes (CNT) in various proportions were synthesized by the hydrothermal method. The crystalline structures, morphologies, and light absorption properties of the TiO₂/CNT photocatalysts were characterized by PXRD, TEM and UV–Vis absorption spectra. The photocatalytic efficiency of the composites was evaluated by the degradation of Sudan (I) in UV–Vis light. Introducing 0.1–0.5 wt% CNT was shown to substantially improve the photoactivity of TiO₂. The composite with 0.3 wt% CNT showed the best catalytic activity, and its reaction activation energy was calculated as 39.57 kJ mol^?1 from experimental rates. The degradation products of Sudan (I) with different irradiation durations were characterized by Fourier transform infrared spectroscopy, and a degradation reaction process was proposed.     

Study on Synthesis and Binding Ability of a New Anion Receptor Containing NH Binding Sites

A new colorimetric recognition receptor 1 based on the dual capability containing NH binding sites of selectively sensing anionic guest species has been synthesized. Compared with other halide anions, its UV/Vis absorption spectrum in dimethyl sulfoxide showed the response toward the presence of fluoride anion with high selectivity, and also displayed dramatic color changes from colorless to yellow in the presence of TBAF （5 × 10^-5 mol/L）. The similar UV/Vis absorption spectrum change also occurred when 1 was treated with AcO^- while a little change with H2PO^-4 and OH^-. Receptor 1 has almost not affinity abilities to Cl^-, Br^- and I^-. The binding ability of receptor 1 to fluoride with high selectivity over other halides contributes to the anion size and the ability of forming hydrogen bonding. While the different ability of binding with geometrically triangular （AcO^-）, tetrahedral （H2PO^-4 ） and linear （OH^-） anions maybe result from their geometry configuration.     

Silane grafting of TiO2 nanoparticles: dispersibility and photoactivity in aqueous solutions

Titania nano‐sized particles were treated by various amounts of tetraethyl orthosilicate precursor. The extent of grafting was characterized using Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐Vis) spectroscopy techniques, thermal gravimetric analysis, X‐ray fluorescence and zeta potential measurements. Sedimentation behaviour of titanium dioxide (TiO₂) nanoparticles in aqueous solutions was evaluated visually and using a separation analyser. Photocatalytic activity of nanoparticles was studied by photo‐activated degradation reaction of Rhodamine B dyestuff in aqueous solutions. The results showed that grafted particles had acquired enhanced dispersion stability and lower photocatalytic activity in aqueous solutions. Untreated TiO₂ dispersions settled rapidly and sedimentation completed within 24 h through the coagulation mechanism, whereas that of the silica‐treated nanoparticles, depending on the silica content, showed different degrees of stability by flocculation mechanism. Photodebleaching of Rhodamine B in the presence of treated nanoparticles is evident by weaker intensity of UV absorption peak of 554 nm due to lowering concentration of Rhodamine B accompanied with the blue shift in UV absorption peaks. However, untreated TiO₂ nanoparticles showed only weaker intensity of UV absorption peak. Copyright © 2011 John Wiley & Sons, Ltd.     

The green synthesis of fine particles of gold using an aqueous extract of <Emphasis Type="Italic">Monotheca buxifolia</Emphasis> (Flac.)

This study deals with the synthesis and physicochemical investigation of gold nanoparticles using an aqueous extract of Monotheca buxifolia (Flac.). On the treatment of aqueous solution of tetrachloroauric acid with the plant extract, gold nanoparticles were rapidly fabricated. The synthesized particles were characterized by UV–Vis spectrophotometry (UV), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray (EDX) and Scanning electron microscopy (SEM). The formation of AuNPs was confirmed by noting the change in color through visual observations as well as via UV–Vis spectroscopy. UV?Vis spectrum of the aqueous medium containing gold nanoparticles showed an absorption peak at around 540 nm. FTIR was used to identify the chemical composition of gold nanoparticles and Au-capped plant extract. The presence of elemental gold was also confirmed through EDX analysis. SEM analysis of the gold nanoparticles showed that they have a uniform spherical shape with an average size in the range of 70–78 nm. This green system showed to be better capping and stabilizing agent for the fine particles. Further, the antioxidant activity of Monotheca buxifolia (Flac.) extract and Au-capped with the plant extract was also evaluated using FeCl₃/K₃[Fe(CN)]₆ in vitro assay.     

Multi-Color Fluorescent Carbon Dots: Graphitized sp2 Conjugated Domains and Surface State Energy Level Co-Modulate Band Gap Rather Than Size Effects

Four types of carbon dots (CDs) with various color (blue, green, yellow, and red) emissions have been synthesized under solvent-free conditions from citric acid and different nitrogen sources (DMF, urea, ethanamide, and formamide). By detailed characterization and comparison, it is confirmed that the graphitized sp² conjugated domain and surface functional groups such as C−O and C=N play synergetic roles in adjusting the fluorescence properties. Notably, the size effect is not the dominant mechanism to achieve multi-color fluorescence emissions in this work. The structural configuration of the carbon dots further influences the energy band structure, as demonstrated in simplified energy level diagrams. An absorption peak at approximately 560 nm appears in the visible light region for red-emitting CDs, assigned to an n→π* transition of the aromatic structure, thus introducing a new surface state energy level, resulting in a reduction in the energy of electron transition and the expansion into the visible region of the UV/Vis spectrum. Taking advantage of the diverse absorption and emission properties, different CDs/TiO₂ binary composites are obtained for photocatalytic degradation of organic dyes, and it is found that the absorption range in terms of visible light and the band gap of the carbon dots make a difference to the photocatalytic performance of the composites.     

Synthesis,photophysical, electrochemical,and ion-binding properties of Ru(II) polypyridyl complexes containing benzo-15-crown-5

Two polypyridyl ligands, 5-(4′-ethynylbenzo-15-crown-5)-2,2′-bipyridine (L¹) and 3-bromo-8-(4′-ethynylbenzo-15-crown-5)-1,10-phenanthroline (L²), and their Ru(II) complexes [(bpy)₂RuL](PF₆)₂ have been prepared and characterized. Both complexes exhibit metal-to-ligand charge transfer absorption at around 452 nm and emission at around 640 nm in MeCN solution. Electrochemical studies of the complexes reveal a Ru(II)-centered oxidation at around 1.31 V and three ligand-centered reductions. The binding ability of the complexes with Na⁺ has been investigated by UV/Vis absorption, emission, and electrochemical titrations. Addition of Na⁺ to MeCN solutions of both complexes results in a progressive enhancement of the emission, a red-shift of the UV/Vis absorption, and a progressive cathodic shift of the Ru(II)-centered E _1/2 couple. The stability constants for the 1:1 stoichiometry adducts of the complexes with Na⁺ have been obtained from the UV/Vis absorption titrations.     

Two-photon Dissociation Study of Carbon Disulfide in Acetonitrile at 266 nm

Using laser flash photolysis/transient absorption technique for the study of two photon photodissociation of carbon disulfide in acetonitrile solution at 266 nm, the transient UV-Vis absorption spectrum of Rydberg state CS2 （6sσg） within 240-370 nm and subsequent dissociation product CS （α^3П） with the maximum absorption at 260 nm were directly observed. The lifetime of CS （α^3П） in the nitrogen and oxygen saturated solution is also studied in our experiment.     

Multiwalled carbon nanotubes covalently functionalized with poly(N‐vinylcarbazole) via RAFT polymerization: Synthesis and nonliner optical properties

The poly(N‐vinylcarbazole)‐grafted MWNTs (MWNT‐PVK) hybrid materials were synthesized in the presence of S‐1‐Dodecyl‐S′‐(α, α′‐dimethyl‐α″‐acetic acid) trithiocarbonate (DDAT)‐covalently functionalized multiwalled carbon nanotubes (MWNT‐DDAT) as reversible addition–fragmentation chain transfer (RAFT) agent. Incorporation of the PVK moieties onto the MWNTs surface can considerably improve the solubility and processability of MWNTs. For all MWNT‐PVK hybrid materials, they are soluble in some common organic solvents such as toluene, THF, chloroform, DMF and others. In contrast to the UV/Vis spectrum of DDAT‐PVK, which was synthesized by use of DDAT as RAFT agent under the same synthetic condition, in the visible region, the absorption spectrum of MWNT‐PVK exhibited a typical electronic absorption characteristics of solubilized carbon nanotubes, in which the absorbance decreases gradually in the range of 350–600 nm. At the same level of linear transmission the MWNT‐PVK with 79.2% PVK moieties in the material structure possesses best optical limiting performance in comparison with the other MWNT‐PVK composites, MWNTs and C₆₀. The significant NLO responses manifest the MWNT‐PVK materials suitable candidate for viable optical limiting devices. Light scattering, originating from the thermal‐induced microplasmas and/or microbubbles, is responsible for the optical limiting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3161–3168, 2010     

Theoretical Study of Firefly Luciferin pKa Values—Relative Absorption Intensity in Aqueous Solutions

Ground‐state vibrational analyses of firefly luciferin and its conjugate acids and bases are performed. The Gibbs free energies obtained from these analyses are used to estimate pK_a values for phenolic hydroxy and carboxy groups and the N–H⁺ bond in the N‐protonated thiazoline or benzothiazole ring of firefly luciferin. The theoretical pK_a values are corrected using the experimental values. The concentrations of these chemical species in solutions with different pH values are estimated from their corrected pK_a values, and the pH dependence of their relative absorption intensities is elucidated. With the results obtained we assign the experimental spectra unequivocally. Especially, the small peak near 400 nm at pH 1–2 in experimental absorption spectra is clarified to be due to the excitation of carboxylate anion with N‐protonated thiazoline ring of firefly luciferin. Our results show that the pK_a values of chemical species, which are contained in the aqueous solutions, are effective to assign experimental absorption spectra.     

Microscopic Protonation/Deprotonation Equilibria of the Anti-Inflammatory Agent Piroxicam

The microscopic ionization behavior of piroxicam was investigated using two different approaches, i.e., direct UV spectroscopy and an indirect analogue approach (deductive method). The best microscopic pK_a values (pK_a12 = 4.60, pK_a21 = 5.40, pK_a22 = 2.72, and pK_a11 = 1.92) were obtained by the deductive method using as pK_a22 the pK_a of the enolic O-methylated piroxicam 2 . The results show remarkable electrostatic effects in the protonation/deprotonation equilibria, a marked increase in the acidity of the enolic function (2.68 pK_a units) being caused by the pyridinium group. The electronic structure of piroxicam was studied based on ¹H-NMR chemical shifts at various ionization states, indicating an extended electron conjugation through the molecule. The partition measurements in octan-1-ol/H₂O of zwitterionic compound 3 (the pyridyl N-methyl derivative of piroxicam ( 1 )) suggest that the two opposite charges in zwitterionic piroxicam are indeed in a close intramolecular proximity.     

A New Samarium(III) Complex of Liriodenine: Synthesis,Crystal Structure,Antitumor Activity,and DNA Binding Study

A novel Sm^III complex [Sm^III(LA)₂(pic)₃] (Hpic = picric acid), in which LA is a natural‐derived alkaloid, liriodenine, was synthesized and characterized by IR, elemental analysis, and single‐crystal X‐ray diffraction analysis. This complex showed enhanced solubility compared with liriodenine and its metal complexes that have been previously reported. The interaction of the Sm^III complex with ct‐DNA was further investigated by various spectroscopic techniques, such as UV/Vis spectroscopy, fluorescence spectroscopy, circular dichroism spectroscopy (CD), and viscosity measurement. The results showed that the intrinsic binding constant K_b of the Sm^III complex with ct‐DNA was calculated to be 5.03 × 10³ L·mol^–1 by UV/Vis absorption spectral analysis. The thermodynamic fluorescent spectral analysis suggested that the fluorescence intensity of the Sm^III complex was weakened by ct‐DNA mainly through a dynamic quenching mechanism. The presence of Sm complex could increase the viscosity of DNA solution, so it was concluded that the complex bound with ct‐DNA via a moderate intercalative mode. Furthermore, this Sm^III complex exhibited significant growth inhibition on the three typical tumor cell lines, HepG2, T‐24, and SK‐OV‐3, with the corresponding IC₅₀ values, 10.76 ± 0.19, 8.85 ± 1.12, and 10.01 ± 0.55 μM, respectively. The in vitro antitumor activity was comparable with LA and cisplatin, which suggested that it might be a new broad spectrum antitumor agent with more satisfying solubility.     

Supramolecular array of imizazolylethynyl-zinc-porphyrin

Novel imidazolylethynyl-zinc-porphyrin 1a and its meso,meso-linked bisporphyrin 5M were synthesized effectively by the reaction of the corresponding bromoporphyrins and 2-imidazolylethyne in the presence of palladium-arsenic catalyst. The complementary coordination of monomer 1a into dimer 2a was observed by ¹H NMR and UV–Vis spectroscopy. Self-association constant of 1a to 2a in CHCl₃ (including 0.5% ethanol) was determined as 1.84 × 10⁷ M⁻¹ by UV–Vis titration of 2a with N-methylimidazole. UV–Vis absorption and fluorescence spectra of 1a, 2a, monomer 5M, and its polymer 5P were compared.