Molecular architectures, derived from

Figure 1.2 Four major small molecular architectures derived from the hybridization states of carbon...

A major barrier to understanding fundamental relationships between molecular architecture, electronic structure, and charge transport in molecular metals derives from our inability to introduce poten-... 

The next phase in this evolutionary sequence involved the natural combination of these reactive elements to produce a bewildering array of simple molecular combinations derived from these coreshell atomic spheroids (i.e., NH3, CH4, urea, etc.) followed by the formation of more complex, but yet small molecules that included o -amino acids, nucleic acids, sugars, hydrocarbons, etc. Combinations and permutations of specific CADPs at the atomic level articulated molecular level architectures and... 

The essential distinction between the approaches used to formulate and evaluate proteins, compared with conventional low molecular weight drugs, lies in the need to maintain several levels of protein structure and the unique chemical and physical properties that these higher-order structures convey. Proteins are condensation polymers of amino acids, joined by peptide bonds. The levels of protein architecture are typically described in terms of the four orders of structure [23,24] depicted in Fig. 2. The primary structure refers to the sequence of amino acids and the location of any disulfide bonds. Secondary structure is derived from the steric relations of amino acid residues that are close to one another. The alpha-helix and beta-pleated sheet are examples of periodic secondary structure. Tertiary... 

Porphyrazines (pz), or tetraazaporphyrins, are compounds that can be viewed as porphyrin variants in which the meso carbon atoms are replaced with nitrogen atoms, as Fig. 1 shows (1). This difference intrinsically gives porphyrazines discrete physiochemical properties from the porphyrins. In addition, despite their similar molecular architecture, porphyrazines are prepared by an entirely different synthetic route than porphyrins—by template cyclization of maleonitrile derivatives, as in Fig. 2, where the open circle with the A in it represents the peripheral substituent of the pz—rather than by the condensation of pyrrole and aldehyde derivatives (1). The pz synthetic route allows for the preparation of macrocycles with chemical and physical properties not readily accessible to porphyrins. In particular, procedures have been developed for the synthesis of porphyrazines with S, N, or O heteroatom peripheral functionalization of the macrocycle core (2-11). It is difficult to impossible to attach the equivalent heteroatoms to the periphery of porphyrins (12). In addition, the preparation and purification of porphyrazines that bear two different kinds of substituents is readily achievable through the directed cocyclization of two different dinitriles, Fig. 3 (4, 5, 13). 

It is clear that the combination of different architectures and the precise localization of functionalities within a single macromolecule provide unique opportunities for the control of molecular shape as well as molecular, optical, and electronic properties. A significant hurdle that still remains today is the relatively demanding multistep process used to prepare dendrons and hybrids. This, in turn, translates into limited availability but, as high added-value applications emerge, it is clear that current, as well as yet-to-be-developed, syntheses will be used to prepare specialty materials that benefit from the unique properties derived from the combination of dendritic and linear architectures. 

The universal calibration, derived from GPC viscosimetry online coupling, has further confirmed the predicted molecular weights. Absolute verification of this calibration principle, which neglects differences in viscosity of molecules of equal molecular weight but with different architectures, is still underway [16]. 

It was envisioned that the addition of an indole derived from a tryptamine to the activated iminium ion, arising from imidazolidinone catalyst 3 and an a,p-unsaturated aldehyde, would generate a C(3)-quaternary carbon-substituted indo-lium ion. As a central feature this intermediate cannot undergo re-aromatization by means of proton loss, in contrast to the analogous 3-H indole addition pathway. As a result, 5-exo-heterocyclization of the pendant ethylamine would provide the corresponding pyrroloindoline compounds. In terms of molecular complexity, this cascade sequence should allow the rapid and enantioenriched formation of stereochemically defined pyrroloindoline architecture from tryptamines and simple a,/i-unsaturated aldehydes. 

Since the term cryptand only refers to crown ether derived polycyclic receptors, polycyclic systems deriving from other structural motifs are commonly termed molecular cages or molecular capsules, although other names such as nanospheres, nanoflasks, temple-type receptors, etc., can also be found. The word cage well illustrates the overall architecture of many of these receptors, consisting of a floor and a roof connected by at least three bars.1 For self-assembled receptors, on the other hand, the term molecular capsule is often more appropriate. 

Poly(ethylenimine) (PEI) has been examined extensively both in its classical, random branched topology [125] and in its linear form [126]. The various architectural and topological forms of PEI have been reviewed recently [127], Here we describe the first example of this polymer system as an ideal, hyper-branched molecular assembly. Synthesis of a tri-dendron poly(ethyleneimine) dendrimer derived from an ammonia core involved, first the selective alkylation of diethylenetriamine (DETA) with aziridine to produce a symmetrical core cell, namely tris-(-2-aminoethyl)amine. Subsequent exhaustive alkylations of the terminal amino moieties with activated aziridines [2, 127, 128], such as IV-tosyl- or N-mesylaziridine gave very good conversions to the first-generation protected... 

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