Capped amines

Scheme 3.10 Synthesis of gold (I) amine precursors [AuCI(NH2R)] and amine-capped Au NPs.

The amine-capping reagents 4-cyano- and 4-nitro-2,6-bis(bromomethyl)pyridine were synthesized in three steps from 2,6-lutidine <03JOC7661>. 

The very first report of two-dimensional arrays was of Fe304 nanocrystals [128]. Bentzon et al. observed that the ferrofluid obtained by thermolysis of iron penta-carbonyl upon drying (over a period of several weeks) yielded well ordered two-dimensional arrays of Fe304 nanocrystals. Since then, easier methods have been devised to obtain arrays of Fc304 nanocrystals [129]. Two-dimensional arrays of amine-capped metal oxide nanocrystals such as C03O4 have been obtained by start-... 

Fig. 5.2. Transmission electron micrographs of maghemite > -Fe203 nanoparticles prepared by hydrolysis of Fe(lll) salts in refluxing propylene glycol in the presence of amine capping agents. The nanoparticles are soluble in toluene solutions of n-octylamine and, as a result, display a tendency for superlattice self-...

Table 3.1 The energies of HOMO and LUMO, and energy gaps (AE) between HOMO and LUMO, the absorption (Eabs) and emission (Eemi) energies of SiQDs with different diameters (denoted by do in nanometers) in their ground and first singlet excited states [25]. Reprinted with permission from (Li QS, Zhang RQ, Lee ST, Niehaus TA, Frauenheim T (2008) Amine-capped silicon quantum dots, Appl Phys Lett 92 053107). Copyright (2008), American Institute of Physics...

Amine not only affects the fundamental optical gaps but also produces a significant enhancement of absorbance and fluorescence, as indicated by an enhancement in the oscillator strengths of the amine-capped SiQDs relative to the H-SiQDs. In small clusters, the Si-N bonds most likely act, at least, in two different ways (a) to reduce the optical gap and (b) to enhance the light absorption and emission. Amine is hydrophilic and the produced amine-capped surfaces are expected to be useful for solution phase sequential reactions with various aldehydes and carboxylic acids. Therefore, H2N-SiQDs may play an important role in fabricating hybrid devices and sensors. 

Li QS, Zhang RQ, Lee ST, Niehaus TA, Erauenheim T (2008) Amine-capped silicon quantum dots. Appl Phys Lett 92 053107... 

The reaction takes place in dilute THF solutions (2-3 w/v %) at 70 C for several days using an excess of the sultone over the amine groups (sultone/amine = 10/1). For the PBd samples inert atmosphere was used. Under these conditions this postpolymerization reaction is free of side reactions (crosslinking, degradation etc.) as was verified by SEC. Similar peaks with the corresponding amine-capped polymers were observed in CHCI3 in all cases. 

The amine-capped samples behave more or less as conventional polyisoprenes indicating that only weak association may exist in the melt state. The situation is very... 

Viscosity measurements were also performed to complement the DLS data. The [r ] values for the zwitterionic samples are considerably higher than those for the amine-capped samples and the reduced viscosity vs concentration plots are not always... 

The presence of the polar groups introduces another factor capable to enhance the aggregation numbers for the zwitterionic samples in n-decane. Much lower Nw values were observed for the amine-capped copolymers, meaning that the amine groups are not polar enough to enhance the association process. Typical LALLS plots are given in figure 12. 

In both cases the plots are curves. For the amine-capped copolymers negative A2 values are obtained meaning that the equilibrium is not completely shifted towards the micelles. 

From DLS measurements negative ko values were obtained for the amine-capped polymers as expected having in mind the negative A2 values. For the zwitterionic samples the ko values were positive meaning that the equilibrium is shifted in favor of the micelles. 

Viscometry measurements were also conducted. The Huggins coefficients increase with increasing molecular weight for the amine-capped polymers. This behavior is consisted with a star-like structure. For the zwitterionic samples constant kn values, around 1.1 were obtained, meaning that rather compact structures exist in solution. 

Star Shaped Polybutadienes with End-Functional Groups. The amine-capped star polymers provide no evidence of association in cyclohexane, whereas strong association is observed in the case of zwitterionic samples. It is evident that (a) among the different series of polymers the aggregation number decreases with increasing number of functional groups and (b) among the samples with the same... 

The conclusions drawn by DLS are verified by viscometry for the amine-capped polymers. The zwiterionic trifimctional samples have lower intrinsic viscosities than their precursors but the kn values are extremely high, indicating the presence of strong hydrodynamic interactions. This behavior implies that in very dilute solutions compact structures are formed through intramolecular association. This result is in agreement with LALLS and DLS data. 

Working in the area of elastomers, Itovaclc (U. S. Patent 2,818,407 Dec. 31, 1957) reported the Michael addition of amine capped prepolymers to bls-maleimides. Similarly, Sheremeteva euid co-workers found that reaction of stoichiometric amounts of bls-maleimides and primary aromatic diamines in refluxing ethanol afforded polymers, vAiich thermally degraded so rapidly that they could not be considered heat resistant. 

Thiol addition enhances the emission properties of already highly fluorescent amine-capped CdSe/ZnS core-shell QDs... 

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