Fluorimetric determination of cyclofenil using photochemical derivatization

In this work, a fluorimetric approach for the determination of cyclofenil, 4-4′-(cyclohexylidenemethylene)bis(phenylacetate), is presented. The method was based on the intense fluorescence (250/410 nm) observed after a UV photochemical treatment of cyclofenil. The influence of the pH and solvent system and UV exposure time on the fluorescence magnitude was studied. Optimization of parameters was made using experimental design (factorial design and central composite design). Limit of detection (3S_b/m) were estimated to be 1.1 × 10⁻⁸ mol L⁻¹ with the linear dynamic range extending up to 8 × 10⁻⁵ mol L⁻¹. This analytical approach was tested through the analysis of a commercial pharmaceutical formulation. In this case, tests enabled an average recovery of 98.3 ± 3.9% (for n = 9) using the analytical curve. The identification of the fluorescent derivative is proposed based on results achieved from GC-MS.     

Iron pentacarbonyl assisted photochemical route to 2,5- and 2,6-divinyl-substituted 1,4-benzoquinones from 1-ene-3-ynes

Photochemical reaction between the enynes, (Z)-1-methoxybut-1-ene-3-yne, 1 or isopropenyl acetylene, 2 with CO in presence of Fe(CO)₅ yields the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones: 2,6-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (3, 42%), 2,5-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (4, 31.5%), [{η²,η²:2,6-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (5, 45%), and {η²,η²:2,5-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (6, 65%).     

Photochemical degradation of environmentally persistent perfluorooctanoic acid (PFOA) in the presence of Fe(III)

Environmentally persistent and bioaccumulative perfluorooctanic acid (PFOA) was difficult to be decomposed under the irradiation of 254 nm UV light. However, in the presence of 80μmol /L Fe(III), 80% of PFOA with initial concentration of 48μmol/L (20 mg/L) was effectively degraded and 47.8% of fluorine atoms in PFOA molecule were transformed into inorganic fluoride ion after 4 h reaction. Shorter chain perfluorocarboxylic acids bearing C3-C7 and fluoride ion were detected and identified by LC/MS and IC as the degradation products in the aqueous solution. It was proposed that complexes of PFOA with Fe(III) initiated degradation of PFOA irradiated with 254 nm UV light.     

Photochemical reaction between magnesium tetraphenyl porphyrin and oxygen

The photochemical reaction of magnesium tetraphenyl porphyrin （MgTPP） with O2 was studied in CH2Cl2 by steady-state fluorescence, UV-vis absorption, FTIR and MALDI-TOF MS measurements. These spectra indicate that O2 can react with MgTPP excited by irradiation, forming the stable 1：1 coordinated adduct of MgTPP-O2. In the adduct, the oxygen atoms of O2 may insert in the Mg-N bonds in MgTPP and bind with the nitrogen atoms of MgTPP to form N-O-Mg bonds.     

基于磺胺掺杂氮硫的碳点制备及对Hg2+的光化学识别

为提高碳点对汞离子光化学识别的选择性及检测方法的可行性,以柠檬酸和磺胺为原材料采用热解法制备一种新型氮、硫共掺杂碳点（NS-CDs）。用红外光谱仪、紫外-可见光吸收光谱仪、透射电镜、元素分析仪和荧光光谱仪等对其结构和光学性能进行表征。结果表明：该量子点水溶性和分散性高,平均粒径4.78 nm左右,具有类石墨结构;其在3 446和3 261 cm-1处存在N-C和O-H键振动吸收峰;2 966和2 923 cm-1处为C-H键振动吸收带;1 630和1 570 cm-1处吸收峰归属于苯环骨架C═C双键振动;1 388 cm-1处为-CH₃剪式振动峰;1 268,1 192,1 146及1 071 cm-1处的振动吸收峰表明存在为C-N,C-S,C-O,C-O-C及-SO-₃键,912 cm-1处为环氧基的特征吸收峰,739 cm-1处吸收带归属于N-H键变形振动,可见,该碳点不仅含有苯环骨架结构,还有N和S等元素参与的成键结构存在。其在21.4°处出现一个明显且宽的(002)晶面衍射特征峰,晶格间距为0.41 nm,稍大于石墨晶格间距（0.34 nm）。NS-CDs的C,N,S和O元素含量分别为68.72%,7.37%,6.24%及17.67%,与红外分析结果吻合。NS-CDs在309 nm处有一个由C═C键的π→π*电子跃迁产生的较强吸收峰,且在可见光区域内有一个很长的拖尾;同时在335 nm处出现了一个由C═O键的n→π*电子跃迁而产生的吸收肩峰。当激发波长小于390 nm时,NS-CDs原液荧光发射峰值随激发波长增大而逐渐增大,且在390 nm时,荧光强度最强;大于390 nm时,随激发波长增大而逐渐减弱。同时发现随激发波长增加,发射峰逐渐红移。当NS-CDs溶液逐渐稀释时,其最佳激发峰也由390 nm蓝移至360 nm;当pH值＜11.0时,NS-CDs的荧光强度变化很小,在pH值为7.0时荧光峰最强;在pH＞12.0时,荧光强度急剧下降,故选用PBS缓冲溶液（pH 7）进行金属离子检测实验。在16种金属离子中只有Hg2+对NS-CDs荧光强度具有极其显著的影响,使碳点荧光完全猝灭,基于NS-CDs对Hg2+具有高选择性及Hg2+对NS-CDs强荧光猝灭作用,建立了其对Hg2+的荧光化学识别方法。该识别方法的线性方程为y=5.559 02x-13.860 39,其线性范围为1×10-3~1×10-9 mol·L-1,R2为0.9947,检出限为7.11×10-3 nmol·L-1,相对标准偏差小于2.5%,对实际样品检测精度和回收率高,可用于实际水样中Hg2+的检测,在生物和环境分析领域具有良好的应用前景。     

Photo-oxidation of Isoprene with Organic Seed: Estimates of Aerosol Size Distributions Evolution and Formation Rates

ondary organic aerosol (SOA) formation from OH-initiated photo-oxidation of isoprene in the presence of organic seed aerosol. The dependence of the size distributions of SOA on both the level of pre-existing particles generated in situ from the photo-oxidation of trace hydrocarbons of indoor atmosphere and the concentration of precursor, has been investi-gated. It was shown that in the presence of high-level seed aerosol and low-level isoprene (typical urban atmospheric conditions), particle growth due to condensation of secondary organic products on pre-existing particles dominated; while in the presence of low-level seed aerosol and comparatively high-level isoprene (typical atmospheric conditions in rural re-gion), bimodal structures appeared in the size distributions of SOA, which corresponded to new particle formation resulting from homogeneous nucleation and particle growth due to condensation of secondary organic products on the per-existing particles respectively. The effects of concentrations of organic seed particles on SOA were also investigated. The particle size distributions evolutions as well as the corresponding formation rates of new particles indifferent conditions were also estimated.     

吡啶气相光氯化反应机理的理论研究──夺氢机理过渡态和IRC解析

氯自由基与吡啶分子发生夺氢反应生成2-氯吡啶、3-氯吡啶和4-氯吡啶等不同产物主要由两个连续的基元反应组成.研究了生成不同氯代产物的每一个基元反应过渡态,计算比较了不同反应路径活化能的高低,结果表明,不同产物以生成2-氯吡啶的活化能最低,生成2-氯吡啶两个连续基元反应的活化能分别为8.33kJ/mol和1.51kJ/mol,反应优先生成2-氯吡啶,并对邻位反应路径进行了键级、净电荷密度和IRC解析.     

硅锑钼三元杂多酸光化学光度法测定痕量硅

在０．０３ｍｏｌ／Ｌ ＨＣｌ－８％甲醇介质中,Ｓｉ（Ⅳ）、Ｓｂ（Ⅲ）、Ｍｏ（Ⅵ）形成三元杂多酸,再将ＨＣｌ浓度调至０．４３ｍｏｌ／Ｌ,用紫外光照射后生成ＳｉＳｂＭｏ三元杂多蓝（λｍａｘ＝７６０ｎｍ）。据此建立了一个测定０．０６～１．０μｍＬＳｉ的光化学分光光度分析新方法。该法具有灵敏度高,选择性好,操作简便等特点。     

用核磁共振成象研究大白鼠的光化学反应脑缺血模型

用不同权重的核磁共振T₂加权成象数据在采样过程中完成叠加,所得到的核磁共振T₂加权图象清晰地显示出大白鼠大脑中缺血损伤区域的位置和大小.用该方法研究大白鼠的光化学反应局部脑缺血模型,在大白鼠脑缺血发生后大约一小时即可以用T₂加权的MRI图象发现缺血区,证明该种方法有很大的应用潜力.     

Formal Syntheses of (±)‐Methylenomycins A and B

The syntheses of methyl ester of (±)‐desepoxy‐4,5‐didehydromethylenomycin A ( 4 ) and 2,3‐dimethyl‐5‐methoxycarbonyl‐2‐cyclopentenone ( 5 ) were accomplished from a common starting material, 2,3‐dimethyl‐4‐methoxyphenol (8), in only four and two steps in 35% and 53% overall yields, respectively. Photochemical rearrangements of masked p‐benzoquinones in methanol are the key steps.