Alkyl spacer

S. Hana, T. Yoshida, and T. Uryu, Synthesis of a new polylysine-dendritic oligosaccharide with alkyl spacer having peptide linkage, Carbohydr. Polym., 69 (2007) 436 144. 

Increasing the length of the alkyl spacer in such a way as to yield 1,4-bis(tetrazol-l-yl)butane (abbreviated as btzb) (Fig. 16), changes the dimensionality of the Fe(II) spin crossover material [89]. In fact, [Fe(btzb)3] (C104)2 is the first highly thermochromic Fe(II) spin crossover material with a supramolecular catenane structure consisting of three interlocked 3-D networks [89]. Unfortunately, only a tentative model of the 3-D structure of [Fe(btzb)3](Cl04)2 could be determined based on the x-ray data collected at 150 K (Fig. 20). 

Flexible and semiflexible chains for the connection of carbazole units have been used by Braun et al. [43, 44]. However, it can clearly be seen that introducing longer alkyl spacers lowers the Tg. In addition to carbazoles, the... 

Yet hands-on experience with 1 and other related compounds showed that free malonic acid groups on fullerenes are rather unstable even under physiological conditions and readily decarboxylate into side products, some of which may show toxicity under certain circumstances (Beuerle et al., 2007). To avoid these potential side effects new polar derivatives of 1 like 3, 4 and 5 have been synthesized (Beuerle et al., 2005 Witte et al., 2007). In these trisadducts the polar endgroups are attached via alkyl spacers to the fullerene core and thus no unwanted decarboxylation... 

These systems possess the simplest possible variation in that only one parameter, i.e., the fluorescence quantum yield is proton-controlled. The insulation of the fluor and receptor modules in the ground state by the alkyl spacer leads to essentially pH-invariant absorption (position, shape, and intensity) and fluorescence spectra (shape and position only). The same pKa values are obtained from fluorimetry or absorption spectroscopy so that the detection sensitivity of excited state experiments can be used for the measurement of binding constants of the ground state. 

Auer et al. [134] presented an example for multilayer formation and controlled deposition of functionalized nanoparticles on SAM of mercaptohexadecanoic acid (MHA) using electrostatic interactions. As a pH-sensitive switchable linker between the SAM of MHA and negatively charged gold nanoparticles, bis-benzami-dine bolaamphiphiles having different alkyl spacers were used [135]. This strategy resulted in a potentially tunable and switchable property of the entire assembly. For example, the kinetics of adsorption as well as the final particle layer thickness can be controlled by the kind of bis-benzamidine used as the linker (Fig. 9.16). 

The syntheses of the methyl esters 116-118 from 115 and hydroxamic acids 119-121 were carried out via a typical alkylation of the hydroxy function of methyl 4-hydroxyben-zoate 116 followed by either reaction with hydroxylamine to provide bishydroxamic acids 119-121 containing an alkyl spacer between two aromatic rings. 

In a subsequent paper, the authors developed another type of silica-supported dendritic chiral catalyst that was anticipated to suppress the background racemic reaction caused by the surface silanol groups, and to diminish the multiple interactions between chiral groups at the periphery of the dendrimer 91). The silica-supported chiral dendrimers were synthesized in four steps (1) grafting of an epoxide linker on a silica support, (2) immobilization of the nth generation PAMAM dendrimer, (3) introduction of a long alkyl spacer, and (4) introduction of chiral auxiliaries at the periphery of the dendrimer with (IR, 2R)-( + )-l-phenyl-propene oxide. Two families of dendritic chiral catalysts with different spacer lengths were prepared (nG-104 and nG-105). 

The reactions with nG-105 dendrimers show a different trend. Enhanced catalytic performance was observed with increasing dendrimer generation (77.3% yield, 97.2% selectivity, 15.5% ee for Gl 85% yield, 98% selectivity, 37% ee for G4). This comparison indicates that the introduction of an alkyl spacer not only facilitates the access of reactant to the catalytic active sites but also prevents the formation of frozen-in conformations and thus different chiral active sites. However, when the fifth-generation dendrimer is reached, the multiple interactions between end groups become more pronounced, which leads to a decrease in the catalyst performance (68% yield, 95.3% selectivity, 17.6% ee). 

From a series of sulfated bis-aldonic acid amides with different alkyl spacer length, compound 34 was chosen for further evaluation as an antithrombotic. This compound was synthetically available in four steps from lactobionic acid (Scheme 7). Compound 34 had relatively high APTT values (42 U/mg) and antithrombotic activity, both of which decreased gradually when the number of methylene groups in the spacer was increased. It was thought to act via HCII and multiple sites in the intrinsic pathway of the coagulation cascade [64]. 

The simplest approach to isosteric replacement of one or both sulfur atoms of the cystine disulfide with a methylene or ethylene moiety is given for natural bioactive peptides when one cysteine residue is located in the N-terminal sequence position and the related amino group or peptide extension is not involved in the bioactivity. This allows for direct side chain to backbone (N-terminus) cyclization via amide bonds with suitable 5-carboxyalkyl derivatives of the second cysteine residue, or with the oo-carboxy group of aminodicarboxylic adds containing an alkyl side chain that mimics the Ca to Ca spacer in cystine. Thereby, the length and degree of branching of the sulfide or alkyl spacer can additionally be varied. 

AuC14 ions have been stabilized by organically modified sol-gel monomers of the type (MeO)3Si-X-NH2 (X = alkyl spacer) containing amine functional groups. The... 

Figure 10 Plot of rate constants for back electron transfer from Sn02 to electrostatically bound ruthenium ( ) and osmium ( ) complexes as a function of the number of carbon atoms comprising alkyl spacers. Within experimental error, the driving force for each series of reactions is unaffected by changing the size of the alkyl spacer.

Table 3 Kinetic Parameters for Back Electron Transfer from Colloidal SnC>2 to Several Dyes Featuring Peripheral Alkyl Spacer Groups...

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