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211.
阳离子表面活性剂存在下卟啉聚集的光谱研究 总被引:8,自引:0,他引:8
报导在阳离子表面活性剂溴化十六烷基三甲铵(CTMAB)存在下mcso-四(对-磺基苯基)卟啉(TPPS_4)发生聚集的电子吸收光谱、荧光光谱和共振光散射光谱特性.结果表明:CTMAB低于1.0×10~(-5)mol·L~(-1)时TPPS_4发生J-型聚集,形成一种交错卡迭式二聚体。在1.0×10~(-5)~1.0×10~(-4)mol·L~(-1)时,J-型聚集产物仍然存在,但TPPS_4的Soret蜂蓝移.如果CTMAB浓度高于1.0×10~(-4)mol·L~(-1),J-型聚集产物消失,出现游离碱卟啉的D_(2h)。吸收特征.相对于水介质,游离碱卟啉的Soret带在CTMAB胶束中红移. 相似文献
212.
Multidentate organosiloxane thin films were prepared on SiO2/Si surfaces by solution phase deposition of carbosilane dendrons containing a bromophenyl group at the focal point and 3 (Br-G0), 9 (Br-G1), and 27 (Br-G2) SiCl3 groups at the periphery. The films were characterized by contact angle goniometry, ellipsometry, and X-ray photoelectron spectroscopy (XPS). The results indicated that about six Br-G0 molecules covered the same surface area as three Br-G1 molecules and one Br-G2 molecule. Hence, the density of the bromophenyl groups in the films could be defined by the size (generation) of the dendron adsorbates. We also demonstrated that the bromophenyl groups on the film surfaces could serve as a handle for attaching conjugated molecules via formation of C-C bonds. Thus, upon treatment of the films with 4-fluorostyrene under Heck reaction conditions, XPS analysis showed that about 90, 66, and 51% of the bromine atoms in the films prepared from Br-G0, Br-G1, and Br-G2 were consumed, and 94, 82, and 58% of the consumed bromine atoms were replaced by fluorostyryl groups. The remaining bromophenyl groups were probably not accessible to the reactants because of their unfavorable orientation. The overall yields for the surface Heck reaction were estimated to be 84, 54, and 30% for the films prepared from Br-G0, Br-G1, and Br-G2, respectively. 相似文献
213.
Dupradeau FY Case DA Yu C Jimenez R Romesberg FE 《Journal of the American Chemical Society》2005,127(44):15612-15617
2-(2'-Hydroxyphenyl)benzoxazole (HBO) may be used as a model base pair to study solvation, duplex environment, and tautomerization within the major and minor groves of DNA duplexes. In its ground state, HBO possesses an enol moiety which may be oriented syn or anti relative to the imino nitrogen of the benzoxazole ring. In the absence of external hydrogen-bond donors and acceptors HBO exists as the internally hydrogen-bonded syn-enol, a mimic of the rare base pair tautomer found in DNA, which may be photoinduced to tautomerize and form the keto tautomer, a mimic of the dominant base pair tautomer. Previously, we demonstrated that when incorporated into DNA such that the enol moiety is positioned in the major groove, HBO is not solvated, exists exclusively as the internally hydrogen-bonded syn-enol which is efficiently photoinduced to tautomerize, and the corresponding keto tautomer is preferentially stabilized. In stark contrast, we now show that when HBO is incorporated in DNA such that the enol moiety is positioned in the minor groove, the enol tautomer is preferentially stabilized. Molecular dynamics simulations suggest that this results from the formation of a stable hydrogen-bond between the HBO enol and the O4' atom of an adjacent nucleotide, an H-bond acceptor that is only available in the minor groove. The differential stabilization of the enol and keto tautomers in the major and minor grooves may reflect the functions for which these environments evolved, including duplex replication, stability, and recognition. 相似文献
214.
meso—四(4—磺基苯基)卟啉双波长分光光度法测定阳离子表面活性剂 总被引:10,自引:0,他引:10
在酸性条件下,阳离子表面活性剂使meso-四(4-磺基苯基)卟啉(TPPS4)发生J-型聚合,在490nm处出现J-型聚集吸收并导致位于434nm的Soret吸收带降低。阴离子表面活性剂如十二烷基硫酸钠(SDS)使聚集更一步增强,据此建立起水中痕量阳离子表面活性剂的双波长分光光度测定,方法成功地应用于合成和实际水样分析。 相似文献
215.
Rational Design of Cyclometalated Iridium(III) Complexes for Three‐Photon Phosphorescence Bioimaging
Chengzhi Jin Fengyin Liang Jinquan Wang Lili Wang Jiangping Liu Xinxing Liao Thomas W. Rees Bo Yuan Hui Wang Yong Shen Zhong Pei Liangnian Ji Hui Chao 《Angewandte Chemie (International ed. in English)》2020,59(37):15987-15991
Compared to 2PE (two‐photon excitation) microscopy, 3PE microscopy has superior spatial resolution, deeper tissue penetration, and less defocused interference. The design of suitable agents with a large Stokes shift, good three‐photon absorption (3PA), subcellular targeting, and fluorescence lifetime imaging (FLIM) properties, is challenging. Now, two IrIII complexes (3PAIr1 and 3PAIr2) were developed as efficient three‐photon phosphorescence (3PP) agents. Calculations reveal that the introduction of a new group to the molecular scaffold confers a quadruple promotion in three‐photon transition probability. Confocal and lifetime imaging of mitochondria using IrIII complexes as 3PP agents is shown. The complexes exhibit low working concentration (50 nm ), fast uptake (5 min), and low threshold for three‐photon excitation power (0.5 mW at 980 nm). The impressive tissue penetration depth (ca. 450 μm) allowed the 3D imaging and reconstruction of brain vasculature from a living specimen. 相似文献
216.
In [1] S.-N. Chow and J. A. Sanders proved that the period function is monotone for elliptic Hamiltonian of degree 3. In this paper we significantly simplify their proof, and give a new way to prove this fact, which may be used in other problems. 相似文献
217.