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11.
12.
Stacchiola D Burkholder L Zheng T Weinert M Tysoe WT 《The journal of physical chemistry. B》2005,109(2):851-856
The chemisorptive enantioselectivity of propylene oxide is examined on Pd(111) surfaces templated by chiral 2-methylbutanoate and 2-aminobutanoate species. It has been found previously that chiral propylene oxide is chemisorbed enantiospecifically onto Pd(111) surfaces modified by either (R)- or (S)-2-butoxide. The enantiomeric excess (ee) varied with template coverage, reaching a maximum of approximately 31%. Templating the surface using 2-methylbutanoate, where the chiral center is identical to that in the 2-butoxide species, but is now anchored to the surface by a carboxylate rather than an alkoxide linkage, shows no enantiospecificity. The enantioselectivity is restored when the methyl group is replaced by an amine group, where a maximum ee value of approximately 27% is found. DFT calculations and infrared measurements suggest that the structures of the butyl group on the surface are similar for both 2-butoxide and 2-methylbutanoate species, implying that gross conformational changes are not responsible for differences in chemisorptive enantioselectivity. There is no clear correlation between the location of the chiral center and enantioselectivity, suggesting that differences in the template adsorption site are also not responsible for the lack of enantioselectivity. It is proposed that the 2-butyl group in 2-methylbutanoate species is less rigidly bonded to the surface than that in 2-butoxides, allowing the chiral center to rotate azimuthally. It is postulated that the role of the amino group in 2-aminobutanoate species is to anchor the chiral group to the surface to inhibit azimuthal rotation. 相似文献
13.
Arena DA Bartynski RA Nayak RA Weiss AH Hulbert SL Weinert M 《Physical review letters》2003,91(17):176403
The Pd M4VV and M5VV Auger spectra of the 0.1 ML Pd/Ag(100) dilute surface alloy have been measured using Auger-photoelectron coincidence spectroscopy. The M4VV spectrum indicates that Pd 3d(3/2) core holes have a Coster-Kronig decay rate that is approximately 10 times that of Pd metal. Our calculations show that this giant enhancement arises from the local electronic structure of excited Pd atoms at the surface. Anomalous features in the Auger line shape are similar to those seen in dilute bulk PdAg alloys, and these features in the M5VV and M4VV lines are in good agreement with theoretical predictions. 相似文献
14.
Regulating Molecular Recognition with C‐Shaped Strips Attained by Chirality‐Assisted Synthesis
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Dr. Xiaoxi Liu Zackariah J. Weinert Mona Sharafi Dr. Chenyi Liao Prof. Jianing Li Prof. Severin T. Schneebeli 《Angewandte Chemie (International ed. in English)》2015,54(43):12772-12776
Chirality‐assisted synthesis (CAS) is a general approach to control the shapes of large molecular strips. CAS is based on enantiomerically pure building blocks that are designed to strictly couple in a single geometric orientation. Fully shape‐persistent structures can thus be created, even in the form of linear chains. With CAS, selective recognition between large host and guest molecules can reliably be designed de novo. To demonstrate this concept, three C‐shaped strips that can embrace a pillar[5]arene macrocycle were synthesized. The pillar[5]arene bound to the strips was a better host for electron‐deficient guests than the free macrocycle. Experimental and computational evidence is provided for these unique cooperative interactions to illustrate how CAS could open the door towards the precise positioning of functional groups for regulated supramolecular recognition and catalysis. 相似文献
15.
Schrick AC Rheingold AL Weinert CS 《Dalton transactions (Cambridge, England : 2003)》2011,40(25):6629-6631
The reaction of the germylene Ge[N(SiMe(3))(2)](2) with calix[5]arene yields the first example of a group 14 calix[5]arene complex. The crystal structure of this material has been obtained and contains two calix[5]arene macrocycles held together by a Ge(2)O(2) rhombus. 相似文献
16.
McCrane MP Weinert EE Lin Y Mazzola EP Lam YF Scholl PF Rokita SE 《Organic letters》2011,13(5):1186-1189
Selective oxidation by bis[(trifluoroacetoxy)iodo]benzene (BTI) provides an effective trap for quenching adducts formed reversibly between dC and an ortho-quinone methide (QM) under physiological conditions. A model adduct generated by 4-methyl-o-QM and 2'-deoxycytidine is rapidly converted by intramolecular cyclization and loss of aromaticity to a characteristic product for quantifying QM alkylation. However, BTI induces a surprising rearrangement driven by overoxidation of a derivative lacking an alkyl substituent at the 4-position of the QM. 相似文献
17.
Gursharan S. Sidhu Howard L. Weinert 《Journal of Mathematical Analysis and Applications》1984,101(2):380-396
In the first paper of this series, Lg-spline theory was extended to the vector-valued interpolating case. Here this work is complemented by giving the extension for smoothing splines. The problem is formulated as a constrained minimum norm problem in a reproducing kernel Hilbert space, and solved recursively using a congruent stochastic estimation model. 相似文献
18.
H. J. Weinert 《Acta Mathematica Hungarica》1964,15(3-4):309-323
Ohne ZusammenfassungVorgelegt vonL. Rédei 相似文献
19.
H. L. Weinert R. H. Byrd G. S. Sidhu 《Journal of Optimization Theory and Applications》1980,30(2):255-268
Many of the optimal curve-fitting problems arising in approximation theory have the same structure as certain estimation problems involving random processes. We develop this structural correspondence for the problem of smoothing inaccurate data with splines and show that the smoothing spline is a sample function of a certain linear least-squares estimate. Estimation techniques are then used to derive a recursive algorithm for spline smoothing. 相似文献
20.