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191.
Madwar C Kwan WC Deng L Ramström O Schmidt R Zou S Cuccia LA 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):16677-16680
The versatility of perfluorophenyl azide (PFPA) derivatives makes them useful for attaching a wide variety of biomolecules and polymers to surfaces. Herein, a single molecule force spectroscopy (SMFS) study of the concanavalin A/mannose interaction was carried out using PFPA immobilization chemistry. SMFS of the concanavalin A/mannose interaction yielded an average unbinding force of 70-80 pN for loading rates between 8000 and 40,000 pN/s for mannose surfaces on aminated glass, and an unbinding force of 57 ± 20 pN at 6960 pN/s for mannose surfaces on gold-coated glass. Dynamic force spectroscopy was used to determine the dissociation rate constant, k(off), for this interaction to be 0.16 s(-1). 相似文献
192.
Seung Tae Hong Jin-Woo Kim Won-Ho Jang Jong Sung Lim Hyung Sang Park Ki-Pung Yoo Carolin Apfel Wolfgang Arlt 《Research on Chemical Intermediates》2009,35(2):197-207
The transesterification of palm oil in supercritical methanol has been investigated without using any catalyst. HCFC-141b
was used as co-solvent to reduce the molar ratio of methanol to palm oil under the milder conditions. The reaction was carried
out in a flow-type tubular reactor. The residence time was fixed at 40 min. When the molar ratio of methanol to palm oil was
set to 20:1 at 325 °C and 35 MPa, the optimum molar ratio of methanol to co-solvent was found to be 20:1. Addition of HCFC-141b
increased FAME production even at the lower molar ratio of methanol to palm oil. In addition, a similar FAME content was obtained
under the milder conditions (5 MPa lower pressure) compared with conditions without co-solvent at higher pressure. The role
of HCFC-141b in the transesterification reaction under supercritical conditions was investigated. 相似文献
193.
Ute Pyell Wendelin Bücking Carolin Huhn Barbara Herrmann Alexey Merkoulov Joachim Mannhardt Hartmut Jungclas Thomas Nann 《Analytical and bioanalytical chemistry》2009,395(6):1681-1691
Although colloidal nanoparticles show an electrophoretic heterogeneity under the conditions of capillary electrophoresis,
which can be either due to the particle-size distribution and/or the particle shape distribution and/or the zeta-potential
distribution, they can form correct isotachophoretic zones with sharp-moving boundaries. Therefore, the technique of isotachophoresis
permits to generate plugs in which the co-ions and counter ions of the original colloidal solution are removed and replaced
by the buffering counter ions of the leading electrolyte. It is shown that analytical isotachophoresis can be used to measure
directly, without calibration, the molar (particle) concentration of dispersed ionic colloids provided that the transference
number and the mean effective charge number of the particles (within the isotachophoretic zone) can be determined with adequate
accuracy. The method can also be used to measure directly the effective charge number of biomacromolecules or colloidal particles,
if solutions with known molar (particle) concentration can be prepared. The validity of the approach was confirmed for a model
solution containing a known molar concentration of bovine serum albumin.
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195.
Wolf R Finger M Limburg C Willis AC Wild SB Hey-Hawkins E 《Dalton transactions (Cambridge, England : 2003)》2006,(6):831-837
The borane complexes cyclo-1,4-(BH3)2(P4Ph4CH2) (3) and cyclo-1,2-(BH3)2(P5Ph5) (4) were prepared by reaction of cyclo-(P4Ph4CH2) and cyclo-(P5Ph5) with BH3(SMe2). Only the 2:1 complexes 3 and 4 were isolated, even when an excess of the borane source was used. In solution, 3 exists as a mixture of the two diastereomers (R(P)*,S(P)*,S(P)*,R(P)*)-(+/-)-3 and (R(P)*,R(P)*,R(P)*,R(P)*)-(+/-)-3. However, in the solid state the (R(P)*,S(P)*,S(P)*,R(P)*)-(+/-) diastereomer is the major stereoisomer. Similarly, while only one isomer of 4 is observed in its X-ray structure, NMR spectroscopic investigations reveal that it forms a complex mixture of isomers in solution. 3 may be deprotonated with tBuLi to give the lithium salt cyclo-1,4-(BH3)2(P4Ph4CHLi) (3 x Li), though this could not be isolated in pure form. 相似文献
196.
Sensitivity to local dipole fields in the CRAZED experiment: an approach to bright spot MRI 总被引:1,自引:0,他引:1
Faber C Heil C Zahneisen B Balla DZ Bowtell R 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,182(2):315-324
Local dipole fields such as those created by small iron-oxide particles are used to produce regions of low intensity (dark contrast) in many molecular magnetic resonance imaging applications. We have investigated, with computer simulations and experiments at 17.6 T, how the COSY revamped with asymmetric z-gradient echo detection (CRAZED) experiment that selects intermolecular double-quantum coherences can also be used to visualize such local dipole fields. Application of the coherence-selection gradient pulses parallel to the main magnetic field produced similar, dark contrast as conventional gradient echo imaging. Application of the gradient along the magic angle leads to total loss of signal intensity in homogeneous samples. In the presence of local dipole fields, the contrast was inverted and bright signals from the dipoles were observed over a very low background. Both simulations and experiments showed that the signal strongly decreased when a phase-cycle suppressing single-quantum coherences was employed. Therefore, we conclude that most of the signal comes from directly refocused magnetization or intermolecular single-quantum coherences. Finally, we demonstrate that bright contrast from local dipole fields can also be obtained, when the pair of coherence-selection gradient pulses is deliberately mismatched. Both methods allowed visualization of local dipole fields in phantoms in experimental times of about 3 min. 相似文献
197.
Huhn C Ruhaak LR Mannhardt J Wuhrer M Neusüß C Deelder AM Meyer H 《Electrophoresis》2012,33(4):563-566
The combination of optical detection techniques like photometry (UV) or laser-induced fluorescence (LIF) with mass spectrometry for capillary electrophoresis offers advantages, both for later use of stand-alone CE-UV or CE-LIF systems and for combined CE-UV-MS or CE-LIF-MS analysis. Faster method development is enabled, the identification of analytes is facilitated, and it allows christian the optical detection scheme to be used for more precise quantification. However, shortcomings of current methodology and equipment hindered the broader use of such detection combinations mainly due to the long distance between the detection points (at least 20 cm). Large shifts in migration times and changes in resolution are visible between the detection traces hindering their straightforward comparison. We present here novel equipment for a robust coupling of CE-LIF-MS with the shortest possible distance between detection points (12 cm) determined by the length of the electrospray needle. In addition, we encourage the use of a normalization of detection traces using a scale of effective electrophoretic mobility to obtain the same x-scale for both detection traces. As an example, the proposed methodology is applied to a mixture of labeled as well as non-labeled N-glycans. 相似文献
198.
In this study we show that a nonaqueous capillary electrophoresis mass spectrometry (NACE-MS) method carefully optimized by a design of experiment can be applied to a very large number of alkaloids in different plant extracts. It is possible to characterize the pattern of the psychoactive alkaloids in several plant samples and preparations thereof, each presenting different challenges in their analysis. The method is shown to be able to separate structurally closely related substances, diastereomers and further isobaric compounds, to separate members of different alkaloid classes within one run and to tolerate significant matrix load. A comparison with methods presented in the literature reveals that a near-generic NACE-MS method for the fast profiling of alkaloids in forensically relevant plant samples has been developed. 相似文献
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