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191.
Jiyun Hu Hamed Mehrabi Yin-Shan Meng Maddison Taylor Jin-Hui Zhan Qigeng Yan Mourad Benamara Robert H. Coridan Hudson Beyzavi 《Chemical science》2021,12(22):7930
Metalation of covalent organic frameworks (COFs) is a critical strategy to functionalize COFs for advanced applications yet largely relies on the pre-installed specific metal docking sites in the network, such as porphyrin, salen, 2,2′-bipyridine, etc. We show in this study that the imine linkage of simple imine-based COFs, one of the most popular COFs, readily chelate transition metal (Ir in this work) via cyclometalation, which has not been explored before. The iridacycle decorated COF exhibited more than 10-fold efficiency enhancement in (photo)catalytic hydrogen evolution from aqueous formate solution than its molecular counterpart under mild conditions. This work will inspire more functional cyclometallated COFs to be explored beyond catalysis considering the large imine COF library and the rich metallacycle chemistry.This study describes cyclometallation as a new metal binding mode for imine-based COFs. The iridacycle decorated COF could be used for catalytic hydrogen evolution from aqueous formate solution with high stability and high efficacy. 相似文献
192.
Brunner H Cattey H Meier W Mugnier Y Stückl AC Wachter J Wanninger R Zabel M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(16):3796-3802
The reaction of the cluster salts [Cp(2*) Nb(CO)(2)](n)[Co(11)Te(7)(CO)(10)] (Cp*=C(5)Me(5); n=1, 2) with excess PMe(2)Ph gave the neutral, dark brown clusters [Co(11)Te(7)(CO)(6)(PMe(2)Ph)(4)] (5) and [Co(11)Te(7)(CO)(5)(PMe(2)Ph)(5)] (6) with 147 metal valence electrons. The new compounds were characterized by IR spectroscopy, elemental analyses, and mass spectrometry. The molecular structure of 6 was determined by X-ray crystallography. Like its precursor anion, it consists of a pentagonal-prismatic [Co(11)Te(7)] core, but with a ligand sphere composed of five CO and five PMe(2)Ph ligands. Detailed electrochemical studies of both reactions reveal that a stepwise substitution of CO ligands in the initial cluster anions takes place leading to intermediate [Co(11)Te(7)(CO)(10-m)(PMe(2)Ph)(m)](n-) ions (m=1-5; n=1, 2). Each of these intermediates is distinguished by at least one oxidation and two reduction waves, giving rise to a total of 21 redox couples and 27 electroactive species. The electron sponge character of the new compounds is particularly pronounced in 5, which exhibits charges n between +1 and -4 corresponding to metal valence electron counts of between 146 and 151. 相似文献
193.
Groothaert MH Smeets PJ Sels BF Jacobs PA Schoonheydt RA 《Journal of the American Chemical Society》2005,127(5):1394-1395
This work reports on the capability of the O2-activated Cu-ZSM-5 and Cu-MOR zeolites to selectively convert methane into methanol at a temperature of 398 K. A strong correlation between (i) the activity and (ii) the intensity of the 22 700 cm-1 UV-vis band, assigned to the bis(mu-oxo)dicopper core, is found (i) as a function of the reaction temperature, (ii) as a function of the Cu loading of the zeolite, and (iii) in comparison to other Cu materials. These three lines of evidence firmly support the key role of the bis(mu-oxo)dicopper core in this selective, low-temperature hydroxylation of methane. 相似文献
194.
Sammelson RE Gurusinghe CD Kurth JM Olmstead MM Kurth MJ 《The Journal of organic chemistry》2002,67(3):876-882
An efficient and selective method for the synthesis of spiro-fused (C5)-isoxazolino-(C4)-pyrazolones (C) is reported. The process consists of utilizing the Baylis-Hillman reaction-or a quicker, stepwise MAC procedure-to give I followed by 1,3-dipolar cycloaddition and Swern oxidation to give beta-ketoesters H, which were condensed with hydrazine derivatives to provide hydrazones that underwent cycloelimination. These novel spiro-fused (C5)-isoxazolino-(C4)-pyrazolones were confirmed by spectroscopic analysis as well as single-crystal X-ray of 5. We also concluded that all condensations/cycloeliminations, except with hydrazine itself, were more effective with catalysts or higher reaction temperatures. For example, TiCl(4) was an efficient catalyst for hydrazone formation and cycloelimination with methylhydrazine, while phenyl-, benzyl-, and (4-methoxyphenyl)hydrazine reacted effectively without catalyst in refluxing xylene. 相似文献
195.
Linda B. Whittall Robert R. Whittle Grayson W. Stowell 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):o525-o527
Two unique conformational polymorphic forms of the compound 6‐[4‐(1‐cyclohexyl‐1H‐tetrazol‐5‐yl)butoxy]‐3,4‐dihydroquinolin‐2(1H)‐one (cilostazol), C20H27N5O2, have been discovered and characterized using single‐crystal X‐ray structural analysis. A third polymorph also exists, but acceptable crystals could not be obtained. Features of both reported polymorphic structures include a chair conformation of the cyclohexyl ring and puckering in the quinolinone ring. The major feature distinguishing the two polymorphic forms is a rotational twisting of the butoxy chain between the tetrazole and quinolinone rings. This difference in conformation influences the intermolecular forces, and hence the packing of the two molecules during crystallization. 相似文献
196.
Bergen HR Abraham RS Johnson KL Bradwell AR Naylor S 《Biomedical chromatography : BMC》2004,18(3):191-201
Primary systemic amyloidosis (AL) is characterized by the overproduction of immunoglobulin light chain proteins by a monoclonal, terminally differentiated B-lymphocyte or plasma cell clone. The free immunoglobulin light chains are deposited in an abnormal conformation as amyloid in a variety of organs in the body. The mechanism of amyloid formation is not well understood, but appears to be associated with some form of cleavage of the immunoglobulin light chain with subsequent aggregate formation. In an attempt to characterize the structure of amyloid-forming light chain proteins we developed an on-line immunoaffinity purification and subsequent characterization of free kappa and free lambda immunoglobulin light chains by electrospray ionization mass spectrometry. The methodology is totally automated and requires 20 micro L of serum. Mass spectral analysis of Bence Jones proteins under non-denaturing conditions was also utilized to examine the tertiary and quaternary structure of light chain proteins and clearly shows covalent dimer formation of lambda type light chain. This type of on-line assay may prove helpful in elucidating distinguishing features capable of discriminating AL from benign monoclonal gammopathies of undetermined significance as well as diagnosing AL. 相似文献
197.
Lydia J. Martinez Robert H. Sik Colin F. Chignell† 《Photochemistry and photobiology》1998,67(4):399-403
The fluoroquinolone antibacterial agents possess photo-sensitizing properties that lead to phototoxic responses in both human and animal subjects. The phototoxicity order reported in humans is: fleroxacin > lomefloxacin, pefloxacin > ciprofloxacin ? enoxacin, norfloxacin and ofloxacin. Studies both in vivo and in vitro have related this phototoxicity to the generation of reactive oxygen species including hydrogen peroxide and the hydroxyl radical. We determined the quantum yields of singlet oxygen generation (φΔ,) by detection of the singlet oxygen (1O2) luminescence at 1270 tun for several fluoroquinolones, naphthyridines and other structurally related compounds. All the fluoroquinolones examined have low φΔ values ranging from 0.06 to 0.09 in phosphate buffer at pD 7.5. We also determined the 1O2 quenching constants for these compounds and their values were on the order of 106M?1 s1, except for lomefloxacin whose rate constant was 1.8 × 107M?1 s?1. The φΔ values were significantly decreased in a solvent of lower polarity such as methanol (0.007 ≤φΔ≤ 0.02). The production of 1O2 by these antibiotics did not correlate with the order reported for their phototoxicity. We also measured the photogeneration (λ > 300 nm) of superoxide by these antibacterials in dimethylsulfoxide using electron paramagnetic resonance and the spin trap 5,5-dimethyl-l-pyrroiine N-oxide. Although there is not a one-to-one correspondence between the relative rates of superoxide generation and the phototoxicity ranking of the fluoroquinolones, the more phototoxic compounds tended to produce superoxide at a faster rate. Nevertheless, the magnitudes of the observed differences do not appear sufficient to explain the range of fluoroquinolone phototoxicity potencies in human and animal subjects in general and the high activity of fleroxacin and lomefloxacin in particular. For these latter drugs the photoinduced loss of the F8 atom as fluoride and the concomitant generation of a highly reactive carbene at C-8 provide a more plausible mechanism for their potent phototoxic and photocarcinogenic properties. 相似文献
198.
Leavitt AJ Wyrwas RB Wallace WT Serrano DS Arredondo MG Leslie LM Khan FA Whetten RL 《The journal of physical chemistry. A》2005,109(28):6218-6222
Carbon-cluster anions, CN-, are very reactive toward SO2 (sticking probability of 0.012 +/- 0.005 for C27- at 25 degrees C), in contrast to their inertness toward other common atmospheric gases and pollutants. In flow reactor experiments at ambient temperature and near atmospheric pressure, primary adsorption of SO2 by the carbon cluster anions, N = 4-60, yields CNSO2- or CN-1S-. The inferred elimination of neutral CO2 is also detected as meta-stable decay in collision-induced dissociation. At higher temperatures, the reaction of SO2 with nascent carbon clusters yields CN-1SO- as well as undetected CO. The size-dependent initial reactivity reflects the previously established structural transitions (i.e., from chain to cyclic to cage structures). Such carbon clusters are formed in sooting flames and may act as nuclei for the formation of primary soot particles and serve as models for the local structural features of active soot particle sites for black-carbon soot. The facile generation of reactive carbon-sulfide and -sulfinate units may therefore have implications for understanding the health and environmental effects attributed to the coincidence of soot and SO2. 相似文献
199.
The base hydrolysis and spontaneous water hydrolysis of the phosphonate ester 2,4-dinitrophenyl ethyl methylphosphonate (DNPEMP) has been studied in detail and the activation parameters for these processes determined. The catalytic effect of a series of 19 oxygen and nitrogen bases and metal hydroxo complexes has been studied. The Brønsted plot of pK versus logkN has a slope (β) of 0.47, which is fairly typical for phosphate and phosphonate esters. alpha-Effect nucleophiles such as 2-iodosobenzoate, hypochlorite and the hydroperoxide ion (HO-2) exhibit enhanced reactivity, as does fluoride ion and the bifunctional metal complex [Cu(tmen) (OH2)(OH)]+ (tmen = N,N,N',N',-tetramethylethylenediamine). Reactions involving these species appear to take place by a nucleophilic pathway, while the other oxygen and nitrogen bases act as general base catalysts. The solvent deuterium isotope effect for Et3N catalysis, kH2O/kD2O=1.3, is consistent with general base catalysis. The mechanisms of these reactions are discussed in detail. 相似文献
200.
Colin F. Chignell Ann G. Motten Robert H. Sik Carol E. Parker Krzysztof Reszka 《Photochemistry and photobiology》1994,59(1):5-11
The photochemistry of 5,5-dimethyl-l-pyrroline N -oxide (DMPO) has been studied in benzene, cyclohexane and aqueous buffer solutions (pH 7.4) by means of electron paramagnetic resonance (EPR) and the spin trapping technique. Ultraviolet irradiation of DMPO in aqueous buffer with unfiltered UV radiation from a Xe arc lamp results in photoionization of the spin trap and the generation of the DMPO cation radical, DMPO+ . The aqueous electron, eaq − , was trapped by DMPO and detected as the DMPO/H adduct. The DMPO+ - reacted with the water to yield the DMPO/OH adduct. Ultraviolet irradiation of DMPO in nitrogen-saturated benzene gave an unidentified carbon-centered DMPO adduct that was replaced by hydroperoxyl and alkoxyl adducts of DMPO when oxygen was present. Experiments employing 17 O2 gas indicated that the oxygen in the DMPO alkoxyl adduct was derived from molecular oxygen. However, UV irradiation of DMPO in cyclohexane yielded the cyclohexyl and cyclohexyloxyl adducts of DMPO in nitrogen-saturated and air-saturated solutions, respectively. These observations suggest that in aprotic solvents UV irradiation of DMPO generates a carbon-centered radical (R− ), derived from the trap itself, which in benzene reacts with oxygen to yield an alkoxyl radical (RO− ), possibly via a peroxyl radical (ROO− ) intermediate. In cyclohexane R− abstracts a hydrogen atom from the solvent to yield the cyclohexyl radical in the absence of oxygen and the cyclohexyloxyl radical in the presence of oxygen. These findings indicate that when DMPO is used as a spin trap in studies employing short-wavelength UV radiation (λ < 300 nm) the photochemistry of DMPO cannot be ignored. 相似文献