Pyrenes attached

The (3-CD derivative bearing two pyrenes attached at one appending chain (75) was also prepared [72]. It exhibits both monomer and excimer emissions even though the excimer emission is remarkable in a 20% DMSO aqueous solution. This system is also responsive to guest compounds, and a remarkable decrease in the excimer emission was observed when lithocholic acid was added. 

Excimer fluorescence of pyrene attached to synthetic polymer chains can be used to study polymer conformation in solution and on particle surfaces. In this case, fluorescence spectroscopy involves the measurement of the emission intensity of monomer (/ , observed at 375 mn) and excimer (/ at 480 nm). The ratio of f to I is related to coiling/stretching behavior of a labeled polymer and we have called it the coiling index. In the absence of intermolecular interactions (the polymer concentration used is usually below this limit), a high value of IJI can be considered the result of a coiled conformation whereas a low value is associated with a stretched conformation. 

In addition to energy transfer, pyrene excimer formation has also been used to detect DNA hybridization. In this case DNA probes were synthesized with pyrene attached to the S and 3 ends (Figure 21.22). It is wdl known that one excited pyrene molecule can form an excited-state complex with anotho- ground-state [ rene. This com dex is called an excimer and rliqrlays an unstructured emission near SOO nm as compared to the structured emission of pyrene imnomer near 400 nm. 

Figure 15.9 Fluorescence spectra of pyrene attached to silylated graphite oxide containing perfluoroalkyl groups reacted with N-(3-triethoxysilylpropane)-1-pyrenemethaneimineof(A) 10 and (B) 100 mmol/L at85°C for 1 h. (unpublished data)...

Brown, G.O., Guardala, N.A., Price, J.L., and Weiss, RG., Selectivity and efficiency of pyrene attachment to polyethylene films by bombardment with MeV range protons, /. Phys. Chem. B, 106, 3375, 2002. 

The attachment of pyrene or another fluorescent marker to a phospholipid or its addition to an insoluble monolayer facilitates their study via fluorescence spectroscopy [163]. Pyrene is often chosen due to its high quantum yield and spectroscopic sensitivity to the polarity of the local environment. In addition, one of several amphiphilic quenching molecules allows measurement of the pyrene lateral diffusion in the mono-layer via the change in the fluorescence decay due to the bimolecular quenching reaction [164,165]. 

It is interesting to note that recent evidence shows that even extra-terrestrially formed hydrocarbons can reach the Earth. The Earth continues to receive some 40,000 tons of interplanetary dust every year. Mass-spectrometric analysis has revealed the presence of hydrocarbons attached to these dust particles, including polycyclic aromatics such as phenanthrene, chrysene, pyrene, benzopyrene, and pentacene of extraterrestrial origin indicated by anomalous isotopic ratios. 

In an effort to understand how actin-actin interactions might be affected by the binding of the myosin head, and in order to gain more insight into the nature of the actin-myosin interface, we have investigated the nature of the kinetic actin-myosin intermediates involved in the process of S)-induced polymerization of G-actin. For this purpose, a variety of fluorescent probes (e.g., pyrene, NBD, AEDANS) have been covalently attached to the C-terminus of G-actin to probe the G-actin-S] interaction under conditions of tightest binding, i.e., in the absence of ATP. 

Smalley MK, Silverman SK (2006) Fluorescence of covalently attached pyrene as a general RNA folding probe. Nucleic Acids Res 34 152-166... 

Compounds 42 and 43 are based on the PBI acceptor, made soluble by a C19 swallowtail attached to one imide nitrogen The donor is attached through the other imide nitrogen. In 42, the moderate donor pyrene is separated from the PBI by a Ci ct bridge that holds the donor and acceptor close to perpendicular, with limited motion possible. Nonetheless, 42 has a persistent, small RR (Fig. 18g) [106]. In 43, the good donor ferrocene is separated from the PBI by a more flexible C2 a bridge. It has an IVT band that peaks at 595 nm and forms a rectifier with a persistent RR between 25 and 35 (Fig. 18h) [106]. 

In order to study the molecular dynamics of the outer segments of a dendrimer, one pyrene moiety was selectively and covalently attached to one dendron of poly(aryl ester) dendrimers by Adams (in total three pyrene molecules per dendrimer) [24]. The fluorescence decay of pyrene in the THF solution of the labeled dendrimers provided details of the pyrene excimer formation, such as the excimer formation rate, the excimer decomposition rate constant and the equilibrium constant of the excimer formation. These parameters were utilized to evaluate the diffusional mobility of the dendrimer branches. 

Recent literature contains many examples of the construction of cascades [56], Usually they are made by the covalent linking of monomer dyes, which allows strict control of their stoichiometry. The pyrene-Bodipy molecular dyads and triads are examples [57]. Efficient energy flow was reported in a purpose-built cascade molecule bearing three distinct chromophores attached to the terminal acceptor [58]. A combinatorial approach with the selection of the best hits can be applied using the assembly of fluorescent oligonucleotide analogs [59]. 

In compound 28,(59) the conformational change induced by sodium binding reduces the probability of collision between the pyrene fluorophore and the nitrobenzene quencher, both attached to the calixarene ring. 

One of the approaches to attach a biomolecule to CNTs is to introduce a functional group that can noncovalently bind the graphene motif via n-n stacking. As in the case of polymers discussed previously, pyrene moieties proved to be very effective and they are in most cases the anchor group of choice [72]. 

Pyrenes appear to be once again amongst the most useful linkers, and the attachment of metal-complexed porphyrins has already been discussed in the section on small aromatic molecules. Porphyrin rings bearing a metal center can also be directly adsorbed on the CNTs sidewalls, and they have been shown to exhibit an increased charge transfer from the metal to the tubes, presumably mediated by the aromatic moieties [100]. A similar behavior is exhibited by the phthalocyanine-based complexes [101]. Other aromatic molecules can be used for appendages, including triphenylphos-... 

The most common linker molecules are pyrene derivatives, which have been used, for example, to link Au [64,65] and Pd [66] NPs, as well as QDs [67] to CNTs. Martin et al. chemically attached a n-extended tetrathiafulvalene (exTFF) group to pyrene prior to n-n hybridization on SWCNTs in order to investigate donor-acceptor interactions between the SWCNT and electron rich exTFF [68], More recently, the same group has synthesized a complex molecule consisting of two exTFF anchors connected via a flexible linkage that also consists of a second generation carboxylic terminated den-dron [69]. Here, n interactions between the exTFF anchors and the SWCNTs lead to hybridization while the carboxylic acid groups of the dendron (when de-protonated) lead to increased solubility in aqueous solutions [69]. 

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