Modified precursors

Polymer films may also be synthesized by direct chemical routesT 101. These chemical synthesis routes generally involve some form of electrophilic substitution using Grignard reagents or other modified precursors. The purity and electrical properties of the films produced from the chemical route are generally poorer than... 

Add Precursor Modify Precursor Synthetic sequence v Unique numbering flCTIUE... 

The option "Modify precursor" (Process menu) permits you to modify the position of the atoms in any precursor on the synthesis tree. It has been introduced because, when the program disconnects a molecule, partially overlapping atoms may appear, or the precursor generated may come up in an impossible conformation. 

Since the drawing resulting from the "Wharton-Grob reconnections" appears in the screen completely distorted, correct it as shown in B by the "Modify Precursor" option. 

Unsubstituted 4//-pyran (5) and 4//-thiopyran (7) with 2,4-dinitrophenyl-hydrazine afford identical bishydrazones 503.18,19 Analogous product 504 was obtained from 4//-pyran derivative 68 (X = EtO, Y = Me), whereas a slightly modified precursor possessing Y = Ph provided monohydrazone 505.86... 

VI. Enzymic Synthesis of Bacterial Polysaccharides from Modified Precursors... 

The compounds most characteristic of the phylum are the saponins, glycosolated sterols, most of which are sulfated. The suite of secondary metabolites produced by the classes Asteroidea, Ophiuroidea, and Holothuroidea are dominated by these sterols. It is believed that echinoderms do not generally undertake de novo synthesis of these sterols, but create them by modifying precursors obtained through feeding.90... 

Lantibiotics are secreted out of the cell by the LanT ATP-binding cassette transporters. These enzymes are transmembrane, homodimeric proteins that use the energy of ATP hydrolysis to secrete either the mature lantibiotic or a fully modified precursor peptide with the leader sequence still attached. A second type of LanT transporter is found in the... 

Hybrid, chelate, or molecularly modified precursor routes also utilize alkoxide compounds for the B-site species. Unlike true sol-gel processes, these routes rely on molecular modification of alkoxide compounds through reactions with other reagents, namely chelating ligands, such as acetic acid, acetylacetone, or amine compounds. Despite this difference, chelate processes stiU share several common attributes with methoxyethanol-based sol-gel processes, most importantly, the formation of oligomeric species during solution synthesis. 

In these and other studies, the initial sticking coefficient for molecular adsorption could be as high on the alloys as on the clean Pt surfaces, even though adsorption did not occur at Sn sites. The existence of a modifier precursor state was postulated and its importance was discussed for understanding adsorption kinetics on alloys and other modified surfaces [24, 35]. 

Xu C, Koel BE (1994) Probing the modifier precursor state adsorption of CO on Sn/Pt(lll) surface alloys. Surf Sci 304 L505... 

An example related to the polymeric route has been given by Roger et al. [72] in which a tin alkoxide is modified in order to create a residual porosity in the matrix formed from this modified precursor. These compounds were prepared from a tin (IV) alkoxide modified with difunctional carboxylate ligands. Formation of the final porous material is obtained through a two step process. The first... 

Ormosils are prepared in a manner very similar to conventional sol-gel solutions, except that in addition to the conventional alkoxide precursor, another organically modified precursor is added [50], For example, ormosils have been... 

Halliday, D.A., et al. 1993. Extended TT-conjugation in poly(p-phenylenevinylene) from a chemically modified precursor polymer. Synth Met 55 954. 

Many types of triblock copolymers of the ABA sequence have been synthesized to study the behavior of finally modified precursors by hydrogenation of the PBd-1,4 segments to crystallizable polyethylene (PE) in combination with superhydrophobic middle blocks such as PDMS. ... 

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