Naphthalene linker

In the cases of catalysts containing the naphthalene linker (30-35), the 1,4-, 1,5-, and 2,7-substituted catalysts 30, 31 and 35 gave good enantioselectivities [13], Whereas, the 2,6-substituted catalyst 34 yielded a moderate result, the sterically hindered catalysts 32 and 33 showed poor enantioselectivities. Especially, the 2,7-naphthalene-linked catalyst 35 was found to possess excellent catalytic activity for this alkylation from the viewpoints of enantioselectivity and chemical yield. 

Interestingly, the molecular structure of the 2,7-naphthyl catalysts 39 and 40 markedly resembles that of the 1,3-phenyl catalysts 37 and 38, respectively the only difference is the distance between the two cinchona alkaloid units. The naphthalene linker is about 2.4 A longer than the benzene linker. The Park-Jew group proposed that the reason for the higher enantioselectivity of the 2,7-naphthyl catalyst was that the 2,7-naphthalene linker might confer a spatial benefit to form a more favorable conformation by decreasing the steric hindrance between the two cinchona units compared to that in the 1,3-benzene linker. 

Reported structures for homobifunctional aryl azides include a biphenyl derivative and a naphthalene derivative (Mikkelsen and Wallach, 1976), a biphenyl derivative containing a central, cleavable disulfide group (Guire, 1976), and a compound containing a central l,3-diamino-2-propanol bridge between phenyl azide rings that are nitrated (Guire, 1976). The only commercially available homobifunctional photoreactive cross-linker is BASED. 

Ueno et al. also prepared the b i s (2 - n ap h t h y I s u I fe n y 1) - y - CD series in which the naphthyl moieties are very limited in their movement because the linker between naphthalene and CD is only sulfur [37], All isomers of 12(AB), 13(AC), 14(AD), and 15(AE) exhibit only monomer fluorescence due to the rigid linker. It means that the two naphthalene moieties cannot take face-to-face orientation because of the limited flexibility. Although the excimer cannot be used for sensing molecules, Ueno et al. found that the monomer fluorescence intensity increases with increasing guest concentration. Thus, this modified CD series can be used as chemosensors of a different type. 

From the systematic investigation of the Park and Jew group, several highly efficient and practical polymeric cinchona PTCs were developed (Scheme 6.6). Interestingly, polymeric catalysts with a specific direction of attachment between aromatic linkers (e.g., benzene or naphthalene) and each cinchona unit were found to be effective in the asymmetric alkylation of 4b. The phenyl-based polymeric PTCs with the meta-relationship between cinchona units such as 14, 15, and 18 showed their high catalytic efficiencies. Furthermore, the 2,7-dimethylnaphthalene moiety as in 16 and 17 was ultimately found to be the ideal spacer for dimeric cinchona PTC for this asymmetric alkylation. For example, with 5 mol% of 16, the benzylation of 4b was completed within a short reaction time of 30 min at 0 ° C, affording (S)-5a in 95% yield with 97% ee. Almost optically pure (>99% ee) (S)-5a was obtained at lower reaction temperature (—40 °C) with 16, and moreover, even with a smaller quantity (1 mol%), its high catalytic efficiency in terms of both reactivity and enantioselectivity was well conserved. 

A set of fluorophores derived from naphthalene, phenanthrene, pyrene, phenazine and fluorene have been conjugated to the 5 -ends of DNA and RNA to compare their physico-chemical properties. Decreasing the Ji-electron density led to an enhancement in thermal stability, attributable to more favourable Jt-Ji interactions. Stability is further enhanced by using nitrated fluorophores. Fluorescent labelling of ODNs using oxyamino modified fluorescein has been reported by the incorporation into DNA of aldehyde functions. The aldehyde function was attached either at the 5 -end via a phosphate linker or internally via 8-mercaptobutanal. Reduction of the resulting oxime was not necessary. 

The receptor 73, based on an azaferrocenophane structure bearing two urea groups as linkers between the redox active (ferrocene) and fluorescent (naphthalene) signalling subimits, also shows both fluorescent and electrochemical sensing of fluoride [51]. On addition of excess fluoride it displays an enhancement factor of 13 in the naphthalene emission bands at 362 and 380 nm in DMF solution and a cathodic shift of the ferrocene/ferrocenium couple of 190 mV in DMSO electrolyte solution. 

The complex in Figure 11.18 successfully induces photoinduced proton reduction, hut with very low activities. Provide two reasons why using naphthalene monoimide dithiolates as the linker between the photosensitizer and the active site for proton reduction was considered desirable. What spectral argument was used to reason that the ground state zinc porphyrin moiety does not interact electronically with the diiron portion of this complex ... 

A few other examples of chain-forming coordination polymers are mentioned. A polymer 31 was obtained under inert conditions by the reaction of 4,4, 5,5 -tetramethyl-2,2 -bisphosphinine with naphthalene/Na in dimethoxy-ethane [85]. The bisphosphinine is reduced two-fold. In the deep purple oxygen-sensitive crystals the chain is held together by electrostatic interactions through alternation between three and one Na(I) cations. The reaction of pentaphosphaferrocene with CuX (X = Cl, Br, I) was used to prepare yellow-brown crystals of one- and two-dimensional poljmiers in which the phospha-ferrocene units are connected by CuX units [86]. One-, two- and three-dimensional tubes were prepared by employing dimetal building units [87]. For example, a one-dimensional tube was obtained from a Rh2 compound with malonic acid and linkers such as tra 5-l,2-bis(4-pyridyl)ethylene. 

The folding of a protein explained in the Introduction to this chapter creates an intertwined chemical structure. Ponnuswamy et al. (2012) fabricated knotted molecules, similar to protein structure, which took advantage of hydrophobic interactions. The molecular structure was comprised of three hydrophobic naphthalene diimides held together with alanine linkers and anchored at both ends with cysteine amino acid. 

Figure 6.8 Synthesis of different tetragonal 2D COFs by co-condensation of phthalocyanine with various linkers [ly, pyrene NDI, naphthalene diimide PPE, poly(phenylene ethynylene)].

The sensitivity can be further enhanced by incorporating various polymer linker molecules. Different terminal groups incorporated into the linker molecules can be utilized to achieve enhanced sensitivity. For example, Chen and Lu (2010) have shown that the functionalization of Ag and Au nanoparticles by decanethiol, naphthalene thiol, and 2-mercaptobenzothiazole makes it possible to... 

Beyond RCM and CM strategies, Craig has reported cleavage using Diels-Alder reactions (Scheme 1.16). ° [4 + 2] Cycloaddition (with concomitant aromatization) of the o-quinodimethane precursor (52) with dimethylacetylene dicarboxylate (DMAD), trichlor-oacetonitrile, and benzoquinone provided dimethyl naphthalene-2,3-dicarboxylate (53), 3-(trichloromethyl)isoquinoline (54), and 2,3-naphthoquinone (55), respectively. The diverse products from a single polymer-supported intermediate, such as the bismuth linkers discussed previously, make Craig s multifunctional linker unit attractive for approaches toward diversity-oriented synthesis. 

Fig. 2 shows the simulated methane adsorption isotherms for a variety of IRMOF materials. In order to judge the performance of the materials, both the amount adsorbed per volume and per mass are shown. The materials with the best volumetric performances are the ones with the smallest linker molecules and therefore the smallest cavities (see Fig. 1 and Table 1). Within the group of the smaller IRMOFs, materials that consist of linker molecules with more carbon atoms (e.g. the dicarboxylate naphthalene linka- of lRMOF-7 compared to the dicarboxylate benzene linker of IRMOF-1) show a better performance, as the additional carbon atoms result not only in an increased surface area but also in strongs interactions between the methane molecules and the cavities. Fig. 2 a also illustrates that the interpenetrated IRMOFs, which have comparable (in the case of IRMOF-15) or even smaller cavities (IRMOF-9), show a similar performance. At higji pressures the differences between the absolute and the excess amount adsorbed become apparent. Whereas the absolute adsorption isotherms start to level off, the excess adsorption isotherms show a maximum, which is expected for any gas above its critical temperature when the increase of the bulk gas density is larger than the increase in the density of the adsorbate (see Eq. (1)). 

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