Solid-State Photochemical [2+2] Cycloaddition Reaction of MnII Complexes

Three Mn^II complexes have been synthesized under similar experimental conditions. Of these [Mn₂(benzoate)₄(L)₂] (where L=4-styrylpyridine or 4spy, 1 and 2-fluoro-4′-styrylpyridine or 2F-4spy, 3 ) are paddlewheel complexes, but crystallized in different space groups. Whereas [Mn₂(benzoate)₄(3F-4spy)₄] (3F-4spy=3-fluoro-4′-styrylpyridine), 4 is a dinuclear complex having different stoichiometry from 1 and 3 with two pairs of 3F-4spy ligands aligned in face-to-face manner. An irreversible phase transition occurs from the space group P2₁/c to C2/c when 1 was heated up to 125 °C to 2 in a single-crystal-to-single-crystal fashion or when ground 1 to powder. 2 is isomorphous and isostructural to 3 . Complimentary π–π interactions in head-to-tail alignment of the styrylpyridine ligands furnishes 1D aggregates in 1 – 3 which are congenial to undergo [2+2] cycloaddition reaction under UV light. Whereas, face-to-face alignment of the 4spy pairs in 4 is expected to provide a head-to-head photoproduct. All the Mn^II complexes are indeed found to be photoreactive. To our surprise, contrary to their Zn^II analogues, 2 and 3 were not found to be photosalient. The percentage volume expansion during the photoreaction as determined from the density measurements, was found to be too low (3.2 and 4.6 % respectively for 2 and 3 ) to have this behavior.     

Self-organization of crown-containing hetarylphenylethenes,phthalic acid,and potassium cations into supramolecular assemblies

Multicomponent molecular assemblies of 15-crown-5-containing 4-styrylpyridine with phthalic acid in the presence of potassium perchlorate were studied. The structure of the obtained complicated assemblies was determined by ¹H and ¹³C NMR spectroscopy, UV spectroscopy, and X-ray analysis. The composition of the supramolecular complexes was established by spectrophotometric titration, and the stability constants were calculated. The quantum yields of fluorescence for the ligand and its complexes of various nature were determined.     

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.     

In‐situ Synthesis and Photoluminescence of a Europium Porphyrin Complex Incorporated in the Silica Matrix

A practicable synthesis method is explored to synthesize a europium porphyrin complex in which a water‐soluble positively charged 5,10,15,20‐tetrakis(4‐trimethylammoniophenyl)porphyrin iodide, H₂TMePPI, is immobilized into the sol‐gel silica matrix and then in‐situ metallized with the Eu³⁺ ion. The product is characterized by means of the solid UV diffusion reflection spectra, fluorescence spectra, and thermal gravimetric analysis (TG). The solid UV diffusion reflection spectra show that the number of Q bands in the product is less than that of the H₂TMePPI ligand, which is one of the important characteristics of porphyrin metallization. The fluorescence spectra of the product are different from that of the silica doped with free Eu³⁺ ions, implying the different function of Eu³⁺ ions in the product. The TG curves show that the thermal stability of the Eu(III)TMePPI entrapped into silica is higher than that of the H₂TMePPI. The effect of a heat treatment and an UV‐light irradiation on the photoluminescence properties of the composite is investigated in details. The stronger interaction between Eu(III)TMePPI and SiO₂ in the composite is responsible for the different spectra.     

Synthesis and characterization of a new 4-styrylpyridine based square planar copper(II) complex: exploration of phenoxazinone synthase-mimicking activity and DFT study

Abstract

A new 4-styrylpyridine (4-spy)-based square planar copper(II) complex, [Cu(4-spy)₂(NCS)₂] {4-spy = 4-styrylpyridine} (1), has been synthesized and characterized by elemental analysis and single-crystal X-ray diffraction study. The complex crystallizes in triclinic space group Pī and forms square planar geometry. Complex 1 is self-assembled to construct 3D supramolecular architecture via π–π interactions. Complex 1 exhibits strong biomimetic phenoxazinone synthase-like activity under mild conditions for the aerial oxidation of o-aminophenol to amino phenoxazinone, i.e. modeling the catalytic function of the copper-containing enzyme phenoxazinone synthase. The turnover number (k_cat) for the process in methanol is 50.13?×?10^?2 s^?1. The mechanism of phenoxazinone synthase-like activity has been proposed for the Cu(II) catalyst with the help of mass spectral analysis. Density functional theory study has also been explored to corroborate the experimental findings.     

Carbon-13 chemical shift assignment of some N substituted derivatives of (E)-hydroxyazastilbenes

Carbon-13 NMR spectra of 24 new N-carboxyalkyl- and N-alkoxycarbonylalkylsubstituted derivatives of (E)-4-styrylpyridine and (E)-4-o(m- or p)hydroxystyrylpyridine bromides have been calculated and fully assigned. The Ai and AiK empirical parameters of the N-carboxyalkyl, N-alkoxycarbonylalkyl, N-carboxyalkyl-4-vinylpyridyl and N-alkoxycarbonylalkyl-4-vinylpyridyl groups were calculated for the prediction of the chemical shifts of substituted stytylpyridines.     

Photochromic and molecular switching behaviour of Schiff base-containing pyrazolone ring

A new Schiff base compound, 4-[[(5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)methylidene] amino]-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-one (I), was synthesised and characterised by elemental analysis and LC-MS, FTIR and ¹H NMR spectra. The photochromic property of the synthesised compound investigated under 365 nm UV irradiation can be observed by solid state absorption and fluorescence spectra. The kinetic study showed that the photochromic reaction was of the pseudo-first-order. The photo-isomerisation was due to photo-induced intermolecular hydrogen bonding, which resulted in enol to keto transformation. The molecular switching behaviour was studied in solution with two inputs in three different systems (OH^? and Ag⁺), (OH^? and Cd²⁺) and (OH^? and Th⁴⁺) based on the UV absorption spectra. It exhibited the logic behaviour of XNOR, AND and NOR for Ag⁺,Cd²⁺ and Th⁴⁺ in alkaline media, respectively.     

Benzindoles XII. Spectra and three-dimensional structures of [6,7]- and [4,5]benzoskatolideneacetones

It was found by means of their ER, UV, and PMR spectra that [6,7]benzoskatolideneacetones have a side chain in the trans-s-cis form, whereas the [4, 5] isomers have a side chain in the cis-s-cis form. It was concluded from the integral intensities of the bands of the vibrations of the double bond (A_C=C)) and the parameters of the UV spectra that the investigated molecules have a planar structure. The A_C=C) integral intensities in the IR spectra exceed the previously observed values and, in the case of [6,7]benzoskatolideneacetones, reach ～6· 10⁴ mole^?1liter·cm^?2.     

Synthesis and different substituent effects on spectral and electrochemical properties of porphyrin nicotinic acid binary compounds

The porphyrin nicotinic acid binary compounds with different substituents in porphine rings (5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-triphenylporhyrin 2a, 5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-tri(4-chlorophenyl)porphyrin 2b and 5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-tri(4-methoxyphenyl)porphyrin 2c) were synthesized. All of them have been characterized, assigned and analyzed by UV–vis, IR, MS and ¹H NMR spectra. Their electrochemical and spectroscopic properties were studied by using cyclic voltammetry, fluorescence spectra and Resonance Raman spectra. Different substituents have a little influence on electrochemical behavior and fluorescence spectra. In the Resonance Raman spectra, the substituent has little influence on the skeleton vibration of porphyrin and has much influence on the vibration of phenyl.     

Homoleptic Zinc(II) Complexes Based on 4′‐(2‐Thienyl)‐terpyridine: Preparation,Structures, and Properties

The homoleptic complexes Zn^II(4′‐(2‐(5‐R‐thienyl))‐terpyridine)₂(ClO₄)₂ [R = hydrogen ( 1 ), bromo ( 2 ), methyl ( 3 ), and methoxy ( 4 )] were prepared. Their structures were determined by single‐crystal X‐ray diffraction analyses, and further characterized by high resolution mass, infrared spectra (IR), and elemental analyses. Single crystal X‐ray diffraction analysis showed that Zn^II ions in the complexes are both six‐coordinate with N₆ coordination sphere, displaying distorted octahedral arrangements. The absorption and emission spectra of the homoleptic Zn^II complexes were investigated and compared to those of the parent complex Zn^II(4′‐(2‐thienyl))‐terpyridine)₂(ClO₄)₂. The UV/Vis absorption spectra showed that the complexes all exhibit strong absorption component in UV region, moreover, complex 4 has an absorption component in the visible region. Thus, the photocatalytic activities of the complexes in degradation of organic dyes were investigated under UV and visible irradiation.     

Syntheses,characterizations and properties of boronoalkylalkoxycalix[4]arenes

Some new calixarenes bearing boronic acid moieties, boronoalkylalkoxycalix[4]arenes, were synthesized by allylation, Claisen's rearrangement, alkylation, hydroboration and hydrolysis from 25,26,27,28-tetrahydroxycalix[4]arene and their structures were identified by elemental analysis, IR, ¹H NMR, ¹³C NMR, ¹¹B NMR, MS and UV spectra. The UV data showed that tetraalkoxycalix[4]arene tetraalkyltriboronic acid could coordinate significantly with carbohydrates.     

Ultraviolet Spectral Energy Differences Affect the Ability of Sunscreen Lotions to Prevent Ultraviolet-Radiation-Induced Immunosuppression*

Acute exposure to UV radiation causes immunosuppression of contact hypersensitivity (CH) responses. Past studies conducted with unfiltered sunlamps emitting nonsolar spectrum UV power (wavelengths below 295 nm) or using excessive UV doses have suggested sunscreens may not prevent UV-induced immunosuppression in mice. This study was thus designed to evaluate critically the effects of different UV energy spectra on the immune protection capacity of sunscreen lotions. Minimum immune suppression doses (MISD), i.e. the lowest UV dose to cause~50% suppression of the CH response to dinitrofluorobenzene in C3H mice, were established for three artificial UV sources. The MISD for each UV source was 0.25 kJ/m² for unfiltered FS20 sunlamps (FS), 0.90 kJ/m² for Kodacel-filtered FS20 sunlamps (KFS), which do not emit UV power at wavelengths <290 nm, and 1.35 kJ/m² for a 1000 W filtered xenon arc lamp solar simulator. Using MISD as baseline, sunscreens with labeled sun protection factors (SPF) of 4, 8, 15 and 30 were tested with each UV source to establish their relative immune protection factors. The immune protection factor of each sunscreen exceeded its labeled SPF in tests conducted with the solar simulator, which has a UV power spectrum (295–400 nm) similar to that of sunlight. Conversely, sunscreen immune protection factors were significantly less than the labeled SPF in tests conducted with FS and KFS. Comparison of the immunosuppression effectiveness spectra showed that relatively small amounts of nonsolar spectrum UV energy, i.e. UVC (200–290 nm) and/or shorter wavelength UVB (between 290 and 295 nm), produced by FS and KFS contributes significantly to the induction of immunosuppression. For example, 36.3% and 3.5% of the total immunosuppressive UV energy from FS and KFS, respectively, lies below 295 nm. Sunscreen absorption spectra showed that transmission of immunosuppressive UV energy below 295 nm for FS was at least eight-fold higher than that for KFS. Compared to the solar simulator UV spectrum the transmission of nonsolar immunosuppressive UV energy through sunscreens was >15-fold higher for FS and ≥1.5-fold higher for KFS. These data demonstrate that relevant evaluations of sunscreen immune protection can only be obtained when tests are conducted with UV sources that produce UV power spectra similar to that of sunlight and UV doses are employed that are based on established MISD.     

Solvatochromic responses and pH effects on the electronic spectra of some azo derivatives of 1-amino-2-hydroxy-4-naphthalenesulfonic acid

Synthesis and characterization of five arylazo derivatives of 1-amino-2-hydroxy-4-naphthalenesulfonic acid (H₂L¹) are reported. The UV/Vis absorption spectra of the parent compound (H₂L¹) and its arylazo derivatives (H₂L²–H₄L⁶) have been measured at room temperature in seven solvents of different polarities and with variable parameters. The electronic transitions were analyzed using SPSS program, linear regression technique and Kamlet–Taft’s equation to permit a good understanding of solvent-induced spectral shifts. The electronic absorption spectra of the prepared compounds containing different substituents were studied in aqueous solutions at different pH values. The pK values of the investigated compounds were evaluated spectrophotometrically. The prevailing acid species present at any pH range are judged from the constructed distribution diagrams.     

Structure and optical properties of cerium(III)-doped PbWO4 micro-crystals synthesized by a facile wet chemical method

Cerium(III) doped PbWO₄ micro-crystals with different doping contents were synthesized via a facile wet chemical method in air atmosphere at room temperature. X-ray diffraction patterns of as-synthesized powders revealed that these micro-crystals were pure scheelite PbWO₄, without any impurities such as Ce₂(WO₄)₃ and PbO, and Ce³⁺ could enter into Pb²⁺ sites, which would induce the formation of lead vacancies in the PbWO₄ crystal lattice. The UV–vis diffuse reflection spectra, Raman spectra and photoluminescence (PL) spectra of doped and pure PbWO₄ micro-crystals were studied in detail, which indicated that optical properties of doped PbWO₄ were greatly changed. The adsorption edge of Ce(III)-doped PbWO₄ micro-crystals would shift toward high wavelength (red-shift) with gradually increasing Ce³⁺ doping concentration. It shows an obvious decrease in blue emission band which made the shape of the whole emission band remodeled with the Ce³⁺ doping.     

新型间苯二酚杯芳烃硫脲衍生物对阴离子的识别

通过间苯二酚杯芳烃连续三步反应, 以较高产率合成了分子中连有8个和12个硫脲端基的间苯二酚杯芳烃的酰胺衍生物. 用紫外可见光谱法研究了两个代表性化合物4,6,10,12,16,18,22,24-八[6-(苯基硫脲基)-己氨甲酰基甲氧基]-2,8,14,20-四苯基杯[4]间苯二酚芳烃(THBC)和4,6,10,12,16,18,22,24-八[2-(苯基硫脲基)-1-甲基乙基-1-氨甲酰基甲氧基]-2,8,14,20-四苯基杯[4]间苯二酚芳烃(TPBC), 对各种阴离子(AcO^－, H₂PO₄^－, HSO₄^－, H₂PO₄^2－, C₁₂H₂₅-C₆H₄-SO₃^－, Cr₂O₇^2－, B₄O₇^2－, Cl^－, Br^－)的识别性能, 结果表明它们对AcO^－, H₂PO₄^－, HSO₄^－等阴离子有较好的配位作用, 能形成1∶3的配合物.     

Substituted pyridines. 2, 5-dimethyl-4-styryl- and -4-phenylethy-nylpyridines

2, 5-Dimethyl-4-styrylpyridine and 2,5-dimethyl-4-phenylethynylpyridine are prepared from 2, 5-dimethyl-4-β-phenylethylpyridine. Hydration of the second of these compounds gives gw-(2,5-dimethylpyridyl-4)acetophenone.     

Understanding and improving direct UV detection of monosaccharides and disaccharides in free solution capillary electrophoresis

Direct UV detection of carbohydrates in free solution capillary electrophoresis at 270 nm is made possible by a photo-oxidation reaction. Glucose, rhamnose and xylose were shown to have unique UV absorption spectra hypothesizing different UV absorbing intermediates for their respective photo-oxidation. NMR spectroscopy of the photo-oxidation end products proved they consisted of carboxylates and not malondialdehyde as previously theorized and that oxygen thus plays a key role in the photo-oxidation pathway. Adding the photo-initiator Irgacure^® 2959 in the background electrolyte increased sensitivity by 40% at an optimum concentration of 1 × 10⁻⁴ mM and 1 × 10⁻⁸ mM for conventional 50 μm i.d. capillaries and for the corresponding extended light path capillaries, respectively.     

Hydrogen bonding interactions between ethylene glycol and water: density,excess molar volume,and spectral study

Studies of the density and the excess molar volume of ethylene glycol (EG)-water mixtures were carried out to illustrate the hydrogen bonding interactions of EG with water at different temperatures. The re-sults suggest that a likely complex of 3 ethylene glycol molecules bonding with 4 water molecules in an ethylene glycol-water mixture (EGW) is formed at the maximal excess molar volume,which displays stronger absorption capabilities for SO2 when the concentration of SO2 reaches 400×10?6 (volume ratio) in the gas phase. Meanwhile,FTIR and UV spectra of EGWs were recorded at various EG concentra-tions to display the hydrogen bonding interactions of EG with water. The FTIR spectra show that the stretching vibrational band of hydroxyl in the EGWs shifts to a lower frequency and the bending vibra-tional band of water shifts to a higher frequency with increasing the EG concentration,respectively. Furthermore,the UV spectra show that the electron transferring band of the hydroxyl oxygen in EG shows red shift with increasing the EG concentration. The frequency shifts in FTIR spectra and the shifts of absorption bands in UV absorption spectra of EGWs are interpreted as the strong hydrogen bonding interactions of the hydrogen atoms in water with the hydroxyl oxygen atoms of EG.     

Alkylation des «malonyl-α-aminopyridines»

The alkylation of the ‘malonyl-α-aminopyridines’ ( 4 ) gives mixtures of substitution products, mainly the N¹-and O²-alkyl derivatives. The IR., UV. and NMR. spectra are discussed.     

Luminescence of Fe3+ in AIPO4

Emission and excitation spectra for Fe³⁺ in AIPO₄ single crystals are reported and discussed. With excitation in the near UV emission bands originating from higher exicted states are observed in addition to weak bands between 13 300 and 14 800 cm^?1.