Biomimetic features

BIOMIMETIC FEATURES OF FeZSM-5 ZEOLITE 3.1. a-Oxygcn methane oxidation... 

At the present time, "interest in reversed micelles is intense for several reasons. The rates of several types of reactions in apolar solvents are strongly enhanced by certain amphiphiles, and this "micellar catalysis" has been regarded as a model for enzyme activity (. Aside from such "biomimetic" features, rate enhancement by these surfactants may be important for applications in synthetic chemistry. Lastly, the aqueous "pools" solubilized within reversed micelles may be spectrally probed to provide structural information on the otherwise elusive state of water in small clusters. 

Fig. 25 A sample of synthetic routes (a-c) to the staurosporine aglycone (I) with biomimetic features ...

The emphasis taken here to achieve these desired tissue microenvironments is through use of novel membrane systems designed to possess unique features for the specific apphcation of interest, and in many cases to exhibit stimulant/response characteristics. These so-called intelligent or smart membranes are the result of biomimicry, that is, they have biomimetic features. Through functionalized membranes, typically in concerted assembhes, these systems respond to external stresses (chemical and physical in nature) to eliminate the threat either by altering stress characteristics or by modifying and protecting the ceU/tissue microenvironment. An example (discussed further later in this chapter), is a microencapsulation motif for beta ceU islet clusters to perform as an artificial pancreas. This system uses multiple membrane materials. 

The first examples of macrocyclization by enyne RCM were used in Shair s impressive biomimetic total synthesis of the cytotoxic marine natural product longithorone A (429) [180]. This unique compound features an unusual hep-tacyclic structure which, in addition to the stereogenic centers in rings A-E, is also chiral by atropisomerism arising from hindered rotation of quinone ring G through macrocycle F (Scheme 85). It was assumed that biosynthesis of 429 could occur via an intermolecular Diels-Alder reaction between [12]paracy-... 

A biomolecular system of glycoproteins derived from bacterial cell envelopes that spontaneously aggregates to form crystalline arrays in the mesoscopic range is reviewed in Chapter 9. The structure and features of these S-layers that can be applied in biotechnology, membrane biomimetics, sensors, and vaccine development are discussed. 

Results discussed above show in several lines a distinct biomimetic-type activity of iron complexes stabilized in the ZSM-S matrix. The most important feature is their unique ability to coordinate a very reactive a-oxygen form which is similar to the active oxygen species of MMO. At room temperature a-oxygen provides various oxidation reactions including selective hydroxylation of methane to methanol. Like in biological oxidation, the rate determining step of this reaction involves the cleavage of C-H bond. 

Conventional MS in the energy domain has contributed a lot to the understanding of the electronic ground state of iron centers in proteins and biomimetic models ([55], and references therein). However, the vibrational properties of these centers, which are thought to be related to their biological function, are much less studied. This is partly due to the fact that the vibrational states of the iron centers are masked by the vibrational states of the protein backbone and thus techniques such as Resonance Raman- or IR-spectroscopy do not provide a clear picture of the vibrational properties of these centers. A special feature of NIS is that it directly reveals the fraction of kinetic energy due to the Fe motion in a particular vibrational mode. 

A breakthrough was reported by Stack and co-workers in 1998 (212) who reported the first biomimetic catalytic system for the oxidation of primary alcohols by air. Independently, in the same year Chaudhuri, et al. (216) reported efficient aerobic oxidation of primary and secondary alcohols by the dinuclear catalyst [Cu2 2(Ls )2]C12 (216). Next, we will briefly review the salient features of these two systems. 

The quest for nanostructures and devices based on the biomimetic premise of architectural and functional precision is intense and remains an ultimate challenge. One must ask - what new options or unique properties does the dendritic state offer to meet the needs of nanoscale science and technology The rest of this chapter will attempt to overview key features of the dendritic state that address these and other issues. 

In the first place, the structure of the target molecule is submitted to a rational analysis in order to perceive the most significant structural features, and it may be useful to use different types of molecular models at this point. It should be remembered that a molecular structure has "thousand faces" and finding the most convenient perspective may greatly simplifly the synthetic problem. The synthesis of opium alkaloids, for instance, is much simplified if one realises that they are, in fact, derivatives of benzyltetrahydroisoquinoline (18) (see Scheme 3.8). This was indeed the inspired intuition of Sir Robert Robinson which led to the structural elucidation of morphine (19) and to a first sketch of the biogenetic pathway [22], and later on to the biomimetic synthesis of thebaine 20 [23] [24]. 

Both the face-to-face dimers and the T- and L-shaped dimers have relevance to biomimetic systems, especially in light of the work on the x-ray structure of the R. Viridis reaction center ill). As will be discussed in the following, the results obtained for the face-to-face dimer with an interplanar spacing of 5.35 A is prototypical of the results obtained for almost all the dimers investigated, and thus it provides a reasonable basis for illustrating a number of important features that arise from the calculations. However, it should be noted that the lack oP covalent links in our model dimers precludes the possibility of "through-bond" effects. 

A unique feature of the biomimetic approach is the ability to construct model compounds that combine all the required parameters gained over time in a single molecule and to examine to which extent the new structures sustain bioactivity. Motifs that have not been incorporated in the assembled structures will be exposed, either by reduced bioactivity or by the lack of it altogether, thus providing an indication that some parameters have been omitted, and should be searched for and introduced. 

A study of biomimetic oxygenations of phenol and indol derivatives has featured theoretical investigation of the charge-transfer complexes formed between carbanions and molecular oxygen (organodioxide anions).20... 

MIP features down to 1.5 pm on 4-in silicon wafers was reached (Fig. 6). A wide range of micrometric patterns with different geometries can be obtained, such as lines, spirals, circle matrices, and circular, squared, or hexagonal patterns (Fig. 6 bottom). Multiplexed chips containing three different polymers were also fabricated, paving the road to mass production of biomimetic chips. Fluorescence microscopy was used to test for the binding of fluorescent model analyte to the micropattems. 

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