Trifunctional crosslinker

In the case of (Ala-Gly-Pro)n with n = 5-15, the tripeptide chains were synthesized by the liquid-solid phase technique. As mentioned above, the coupling of longer preformed peptide chains was difficult and the yield of the trimer was low. Therefore, a liquid-solid phase technique was applied in which a trimer was grown in a stepwise manner, beginning from a trifunctional crosslinked base A. 

Substituted aziridines have been used to form homobifunctional and trifunctional crosslinking agents, although their use has been limited (Ross, 1953 Alexander, 1954). The functional group has found use, however, in the design of the fluorescent probe dansyl aziridine (5-dimethylaminonaphthalene-2-sulfonyl aziridine) (Johnson et al., 1978 Grossman et al., 1981). 

Figure 6.1 The Wedekind trifunctional crosslinker can react with amine groups via its p-nitrophenyl ester to form amide bond linkages. The phenyl azide group then can be photoactivated with UV light to generate covalent bond formation with a second molecule. The biotin side chain provides binding capability with avidin or streptavidin probes.

MTS-ATF-biotin and MTS-ATF-LC-biotin are trifunctional crosslinkers similar in design to sulfo-SBED discussed previously, but in addition to the biotin handle, they contain a... 

Suyama K, Yamazaki K and Nakamura P (1995) Gyclopentenosine, trifunctional crosslinking amino acid of elastin and collagen, characterization and distribution. Spec Publ - R Soc Chem 151, 425. 

Tropoelastin molecules are crosslinked in the extracellular space through the action of the copper-dependent amine oxidase, lysyl oxidase. Specific members of the lysyl oxidase-like family of enzymes are implicated in this process (Liu etal, 2004 Noblesse etal, 2004), although their direct roles are yet to be demonstrated enzymatically. Lysyl oxidase catalyzes the oxidative deamination of e-amino groups on lysine residues (Kagan and Sullivan, 1982) within tropoelastin to form the o-aminoadipic-6-semialdehyde, allysine (Kagan and Cai, 1995). The oxidation of lysine residues by lysyl oxidase is the only known posttranslational modification of tropoelastin. Allysine is the reactive precursor to a variety of inter- and intramolecular crosslinks found in elastin. These crosslinks are formed by nonenzymatic, spontaneous condensation of allysine with another allysine or unmodified lysyl residues. Crosslinking is essential for the structural integrity and function of elastin. Various crosslink types include the bifunctional crosslinks allysine-aldol and lysinonorleucine, the trifunctional crosslink merodes-mosine, and the tetrafunctional crosslinks desmosine and isodesmosine (Umeda etal, 2001). 

Figure 3.16 shows the evolution of trifunctional and tetrafunctional crosslinks for an A4 homopolymerization. While the fraction of trifunctional crosslinks goes through a maximum, the fraction of tetrafunctional crosslinks increases continuously. At full conversion all A4 molecules are converted into tetrafunctional crosslinks. 

By plotting (Tg-Tg,)/veT gi versus F, one must obtain a straight line of slope Kdm. This approach was tested on about 100 systems of Tg values ranging from 270 to 520 K, and crosslink densities ranging from 0 to about 10 mol kg-1. We obtained excellent results with KDM = 2.91, when the crosslink density was expressed in terms of crosslink concentration (for trifunctional crosslinks). This leads to KDM 2, when the crosslink density is expressed in chain concentration. 

In the case where D is a small group - e.g., a single rotatable unit such as a methylene or a phenylene - is it pertinent to consider that the CRU is composed of two trifunctional crosslinks... 

We lack a rigorous demonstration, but we find empirically that better results were obtained taking the first option (trifunctional crosslinks). 

Cyanuric chloride was described as a potent trifunctional crosslinking agent for both model compounds and sulfonated lignins (27) (Figure 5). A healthy incorporation of triazine functionality produced homogeneous network gels. 

Sinz, A. Kalkhof, S. Ihling, C. Mapping protein interfaces by a trifunctional crosslinker combined with MALDI-TOF and ESI-FTICR mass spectrometry. J. Am. Soc. Mass Spectrom. 2005,16, 1921-1931. 

Results similar to the ones described above are also obtained for the V3-crosslinked side-chain LCEs, i.e. LCEs with different crosslinker geometry and functionality. The measurements of these LCEs showed that the critical point is shifted to essentially lower crosslinking densities in the case of flexible trifunctional crosslinkers, as significantly smaller latent-heat values have been observed already at lower V3 densities [4] (See Eig. 21). 

Small angle neutron scattering (SANS) measurements were performed on poly(isoprene) networks at different uniaxial strains, i.e., 1,0 < X (extension ratio) <2.1. The networks were prepared from anionically polymerized, a, oo-dihydroxy-poly(isoprene) precursors (H-chains) and the corresponding poly(isoprene-dg) isotopic counterparts (D-chains), crosslinked in concentrated tetrahydrofuran solutions by trifunctional crosslinkers, tri-isocyanates. The two components of the radius of gyration of elastic strands, parallel and perpendicular to the strain axis, were determined from the vSANS data of the networks with 8% and 15% D-chains. Two molecular weights of D-chains, 26,000 and 64,000, crosslinked with approximately the same molecular weight H-chains (29,000 and 68,000 respectively) were examined for the deformation behaviors. 

Some authors consider four chains (as opposed to three chains) to emanate from a crosslink, regarding a trifunctional crosslink as merely a junction point. 

Optimization of the trifunctional crosslinker (Pluracol) was performed first using combinatorial libraries such as that depicted in Figure I. Pluracol composition was varied while PCL-to-PEG weight ratio was kept constant throughout at 0.2. The desired result was minimum weight loss at less than 10% of initial weight upon immersion into aqueous solution for 3 days. This minimum weight loss area corresponds to an optimal formation of PEG crosslinks, and the ability to control PCL microdomain shape and size. 

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