排序方式: 共有44条查询结果,搜索用时 0 毫秒
41.
Dalavoy TS Wernette DP Gong M Sweedler JV Lu Y Flachsbart BR Shannon MA Bohn PW Cropek DM 《Lab on a chip》2008,8(5):786-793
Due to the numerous toxicological effects of lead, its presence in the environment needs to be effectively monitored. Incorporating a biosensing element within a microfluidic platform enables rapid and reliable determinations of lead at trace levels. A microchip-based lead sensor is described here that employs a lead-specific DNAzyme (also called catalytic DNA or deoxyribozyme) as a recognition element that cleaves its complementary substrate DNA strand only in the presence of cationic lead (Pb(2+)). Fluorescent tags on the DNAzyme translate the cleavage events to measurable, optical signals proportional to Pb(2+) concentration. The DNAzyme responds sensitively and selectively to Pb(2+), and immobilizing DNAzyme in the sensor permits both sensor regeneration and localization of the detection zone. Here, the DNAzyme has been immobilized on a PMMA surface using the highly specific biotin-streptavidin interaction. The strategy includes using streptavidin physisorbed on a PMMA surface to immobilize DNAzyme both on planar PMMA and on the walls of a PMMA microfluidic device. The immobilized DNAzyme retains its Pb(2+) detection activity in the microfluidic device and can be regenerated and reused. The DNAzyme shows no response to other common metal cations and the presence of these contaminants does not interfere with the lead-induced fluorescence signal. While prior work has shown lead-specific catalytic DNA can be used in its solubilized form and while attached to gold substrates to quantitate Pb(2+) in solution, this is the first use of the DNAzyme immobilized within a microfluidic platform for real time Pb(2+) detection. 相似文献
42.
Magnetic Anisotropy of Mononuclear NiII Complexes: On the Importance of Structural Diversity and the Structural Distortions 下载免费PDF全文
Saurabh Kumar Singh Tulika Gupta Prashi Badkur Prof. Dr. Gopalan Rajaraman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(33):10305-10313
Mononuclear NiII complexes are particularly attractive in the area of single‐molecule magnets as the axial zero‐field splitting (D) for the NiII complexes is in the range of ?200 to +200 cm?1. Despite this advantage, very little is known on the origin of anisotropy across various coordination ligands, coordination numbers, and particularly what factors influence the D parameter in these complexes. To answer some of these questions, herein we have undertaken a detailed study of a series of mononuclear NiII complexes with ab initio calculations. Our results demonstrate that three prominent spin‐conserved low‐lying d–d transitions contribute significantly to the D value. Variation in the sign and the magnitude of D values are found to correlate to the specific structural distortions. Apart from the metal–ligand bond lengths, two different parameters, namely, Δα and Δβ, which are correlated to the cis angles present in the coordination environment, are found to significantly influence the axial D values. Developed magneto–structural D correlations suggest that the D values can be enhanced significantly by fine tuning the structural distortion in the coordination environment. Calculations performed on a series of NiII models with coordination numbers two to six unfold an interesting observation—the D parameter increases significantly upon a reduction in coordination number compared with a reference octahedral coordination. Besides, if high symmetry is maintained, even larger coordination numbers yield large D values. 相似文献
43.
Single‐Molecule Magnetism,Enhanced Magnetocaloric Effect,and Toroidal Magnetic Moments in a Family of Ln4 Squares 下载免费PDF全文
Chinmoy Das Shefali Vaidya Tulika Gupta Jamie M. Frost Mattia Righi Prof. Dr. Euan K. Brechin Prof. Dr. Marco Affronte Prof. Dr. Gopalan Rajaraman Prof. Dr. Maheswaran Shanmugam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15639-15650
Three cationic [Ln4] squares (Ln=lanthanide) were isolated as single crystals and their structures solved as [Dy4(μ4‐OH)(HL)(H2L)3(H2O)4]Cl2?(CH3OH)4?(H2O)8 ( 1 ), [Tb4(μ4‐OH)(HL)(H2L)3(MeOH)4]Cl2?(CH3OH)4?(H2O)4 ( 2 ) and [Gd4(μ4‐OH)(HL)(H2L)3(H2O)2(MeOH)2]Br2?(CH3OH)4?(H2O)3 ( 3 ). The structures are described as hydroxo‐centered squares of lanthanide ions, with each edge of the square bridged by a doubly deprotonated H2L2? ligand. Alternating current magnetic susceptibility measurements show frequency‐dependent out‐of‐phase signals with two different thermally assisted relaxation processes for 1 , whereas no maxima in χM“ appears above 2.0 K for complex 2 . For 1 , the estimated effective energy barrier for these two relaxation processes is 29 and 100 K. Detailed ab initio studies reveal that complex 1 possesses a toroidal magnetic moment. The ab initio calculated anisotropies of the metal ions in complex 1 were employed to simulate the magnetic susceptibility by using the Lines model (POLY_ANISO) and this procedure yields J1=+0.01 and J2=?0.01 cm?1 for 1 as the two distinct exchange interactions between the DyIII ions. Similar parameters are also obtained for complex 1 (and 2 ) from specific heat measurements. A very weak antiferromagnetic super‐exchange interaction (J1=?0.043 cm?1 and g=1.99) is observed between the metal centers in 3 . The magnetocaloric effect (MCE) was estimated by using field‐dependent magnetization and temperature‐dependent heat‐capacity measurements. An excellent agreement is found for the ?ΔSm values extracted from these two measurements for all three complexes. As expected, 3 shows the largest ?ΔSm variation (23 J Kg?1 K?1) among the three complexes. The negligible magnetic anisotropy of Gd indeed ensures near degeneracy in the (2S+1) ground state microstates, and the weak super‐exchange interaction facilitates dense population of low‐lying excited states, all of which are likely to contribute to the MCE, making complex 3 an attractive candidate for cryogenic refrigeration. 相似文献
44.
Saracoside: a new lignan glycoside from Saraca indica, a potential inhibitor of DNA topoisomerase IB
Mukherjee T Chowdhury S Kumar A Majumder HK Jaisankar P Mukhopadhyay S 《Natural product communications》2012,7(6):767-769
Chemical investigation of the stem bark of Saraca indica has resulted in the isolation of a new lignan glycoside, saracoside, along with four known lignan glycosides lyoniside, icariside E3, (+)5'-methoxyisolarciresinol-9'-O-beta-D-glucopyranoside and nudiposide, and a phenolic glucopyranoside, 3,4,5-trimethoxyphenyl-beta-D-glucopyranoside, which has been isolated for the first time from this species. The isolated lignan glycosides exhibit potent DNA topoisomerase IB inhibitory activity. 相似文献