Colouring Matters Derived from Pyrroles. Part I I .

The proton-coupled uptake of di- and tri-peptides is the major route of dietary nitrogen absorption in the intestine and of reabsorption of filtered protein in the kidney. In addition, the transporters involved, PepT1 (SLC15a1) and PepT2 (SLC15a2), are responsible for the uptake and tissue distribution of a wide range of pharmaceutically important compounds, including beta-lactam antibiotics, angiotensin-converting enzyme inhibitors, anti-cancer and anti-viral drugs. PepT1 and PepT2 are large proteins, with over 700 amino acids, and to date there are no reports of their crystal structures, nor of those of related proteins from lower organisms. Therefore there is virtually no information about the protein 3-D structure, although computer-based approaches have been used to both model the transmembrane domain (TM) layout and to produce a substrate binding template. These models will be discussed, and a new one proposed from homology modeling rabbit PepT1 to the recently crystallized bacterial transporters LacY and GlpT. Understanding the mechanism by which PepT1 and PepT2 bind and transport their substrates is of great interest to researchers, both in academia and in the pharmaceutical industries.

A thiodipeptide carrier system is shown to be effective at enabling a range of covalently bound molecules, including benzyl, benzoyl and ibuprofen conjugates, to be transported via the intestinal peptide transporter PepT1, demonstrating its potential as a rational drug delivery target.

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The ratio of the nascent population of C 2 (X 1 ⌺ g ϩ ) to C 2 (A 1 ⌸ u ) to C 2 (BЈ 1 ⌺ g ϩ ) produced from the photodissociation of C 2 H at 193 nm has been measured using laser induced fluorescence. This technique is typically used to measure rotational and vibrational distributions in a given electronic state. Here, we have extended the technique to measure the relative electronic distributions in the C 2 photofragment. From the simultaneous measurement of the Mulliken (X 1 ⌺ g ϩ -D 1 ⌺ u ϩ ) and Freymark (A 1 ⌸ u -E 1 ⌺ g ϩ ) systems, the nascent population ratio of C 2 (A 1 ⌸ u ) to C 2 (X 1 ⌺ g ϩ ) molecules was determined. Similarly, from the measurement of the Deslandres-D'Azumbuja (A 1 ⌸ u -C 1 ⌸ g ) and the LeBlanc (BЈ 1 ⌺ g ϩ -D 1 ⌺ u ϩ ) systems, the nascent population ratio of C 2 (A 1 ⌸ u ) to C 2 (BЈ 1 ⌺ g ϩ ) was determined. The overall ratio for the production of C 2 in the X:A:BЈ electronic states was found to be 1:19:1.4. These results along with the results of high quality ab initio calculations of Cui and Morokuma ͑unpublished͒ are used to discuss the photodissociation dynamics of C 2 H at 193 nm. Furthermore, these results should aid in the analysis and modeling of cometary spectra of C 2 .