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71.
Senge MO Hatscher SS Wiehe A Dahms K Kelling A 《Journal of the American Chemical Society》2004,126(42):13634-13635
Vilsmeier formylation is one of the most widely used substitution reactions for the functionalization of porphyrins. However, its utility is limited by the electrophilic/acidic reaction conditions, deactivation of the aromatic system and regiochemical problems, the requirement for metal complexes and necessity for subsequent demetalation under harsh conditions, and low functional group tolerance. To overcome these limitations, the dithianyl group has been utilized as a latent formyl synthon in porphyrin chemistry. 2-Formyl-1,3-dithiane can be used directly in pyrrole condensation reactions to regioselectively yield porphyrins with up to four dithianyl residues. Likewise, 5-dithianyldipyrromethane could be prepared quantitatively as a key building block for various porphyrin condensation reactions yielding the respective free base formylporphyrins after deprotection. Additionally, dithianyllithium can be used as a reagent for the direct aromatic substitution of metallo- and free base porphyrins under nucleophilic conditions. 相似文献
72.
Kristian Syberg Maria Bille Nielsen Lauge Peter Westergaard Clausen Geert van Calster Annemarie van Wezel Chelsea Rochman Albert A. Koelmans Richard Cronin Sabine Pahl Steffen Foss Hansen 《Current Opinion in Green and Sustainable Chemistry》2021
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73.
74.
Robert Blank Karl-Heinz Muth Sabine Proske-Gerhards Eberhard Staude 《Colloids and surfaces. A, Physicochemical and engineering aspects》1998,140(1-3):3-11
Asymmetric ultrafiltration membranes were prepared from fully aromatic polyamides differing in the diamine monomers of the polymeric backbone and from polysulfone. Nanofiltration membranes were made from polysulfone and polyethersulfone. The polysulfone as well as the polyethersulfone were chemically modified to change the surface charges of the membranes that were made from these polymers. This means neutral, positively as well as negatively charged membranes could be employed for the measurements. The surface properties of the membranes as a function of pH were determined by measuring the streaming potential in a perpendicular and horizontal mode. Applying proteins the values of the streaming potential changed depending on the original charges of the membranes as well as on the pH of the solution. The values shifted to either higher or lower absolute values. Thus, characterization of unused and used membranes can be carried out by electrokinetic measurements. This was also demonstrated using a membrane fitted out with invertase. The zeta potential of nanofiltration membranes, however, was only evaluated from the results obtained with the horizontally run cell. 相似文献
75.
Recent data from deep inelastic scattering experiments atx10–2 are used to fix the parton distributions down tox10–4 andQ
20.3 GeV2. The predicted extrapolations are uniquely determined by the requirement of avalence-like structure ofall parton distributions at some low resolution scale and are furthermore shown to be insensitive in the small-x region, 10–4x10–2, to the detailed experimental input at the presently accessiblex>10–2. Simple parameterizations of the resulting parton distributions are presented in the range 10–5x<1 and=">1>Q
2108 GeV2 as obtained from the leading- and higher-order evolution equations. 相似文献
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79.
R. M. Vogt 《manuscripta mathematica》1982,38(1):21-39
The n-fold free loop space nSnX is for connected spaces X weakly equivalent to a simpler space CnX, which has a natural filtration Finr CnX. It is well known that there is a splitting StFr(CnX) V
m=1
p
St(Fm(CnX)¦Fm–1(CnX) inducing a stable splitting of CnX. We give a simple construction for such a splitting with comparatively low estimates for the number t of necessary suspension coordinates. 相似文献
80.
Badham NF Mendelson WL Allen A Diederich AM Eggleston DS Filan JJ Freyer AJ Killmer LB Kowalski CJ Liu L Novack VJ Vogt FG Webb KS Yang J 《The Journal of organic chemistry》2002,67(15):5440-5443
A convenient two-step homologation of both aliphatic and aromatic ketones to the corresponding carboxylic acid has been developed. First ketones were converted to epoxynitriles with the Darzens reaction. Second, a Lewis acid mediated rearrangement of these epoxynitriles with lithium bromide was achieved to give homologated secondary alkanoic acids (as well as aryl-alkanoic) in good yields. The mechanism and the scope of the rearrangement reaction were investigated. This strategy constitutes a two-step homologation of ketones to secondary carboxylic acids. 相似文献