Short chain length monomers

PHAscl (short chain length monomer unit consisting of up to five carbon atoms)... 

Each type of PHA generally consists of 1000-10000 monomers, but most are synthesised by short chain length monomers. 

Fig. 2 Common PHA monomer structures. Short-chain-length monomers 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV). Medium-chain-length monomers 3-hydroxyhexanoate (3HHx), 3-hydroxyoctanoate (3HO), 3-hydroxydecanoate (3HD), 3-hydroxydodecanoate (3HDD)...

The enzymes and their structural genes for the three key reactions for the synthesis of PHAs of short-chain-length monomers (three to five carbon atoms) have been extensively studied, and their salient features are summarized below. 

In R. eutropha, acetoacetyl-CoA reductase is encoded by the phbB gene (Peoples and Sinskey 1987). The phb biosynthesis operon in R. eutropha consists of the phbC (encoding PHA polymerase), phbA (encoding 3-ketothiolase), and phbB genes in that order. The three enzymes encoded by the R. eutropha phb operon are sufficient for the synthesis of PHAs consisting of short-chain-length monomers (3-hydroxyacyl-CoAs with 3-5 carbon atoms). 

The FT-IR spectra of pure PHA containing short-chain-length monomers, such as hydroxybutyrate (HB), medium-chain-length hydroxyalkanoate (mclHA) monomers including hydroxyoctanoate (HO) and hydroxy-decanoate (HD), or both HB and mclHA monomers, show their strong characteristic band at 1728, 1740, and 1732 cm respectively. Other accompanying bands near 1280 and 1165 cm help identify the types of PHA. The intensity of the methylene band near 2925 cm" provides additional information for PHA characterization. In comparison, bacterial... 

A particularly simple lattice model has been utilized by Harris and Rice [129] and subsequently by Stettin et al. [130] to simulate Langmuir mono-layers at the air/water interface chains on a cubic lattice which are confined to a plane at one end. Haas et al. have used the bond-fluctuation model, a more sophisticated chain model which is common in polymer simulations, to study the same system [131]. Amphiphiles are modeled as short chains of monomers which occupy a cube of eight sites on a cubic lattice and are connected by bonds of variable length [132], At high surface coverage, Haas et al. report various lattice artefacts. They conclude that the study... 

There have been notable successes in the replacement of individual peptide residues by peptoid monomers with retention of in vitro activity and enhancement of specificity. Unfortunately, attempts to completely transform those bioactive peptides that function via specific peptide-protein binding events into entirely pep-toid-based ohgomers have so far proven successful only at short chain lengths (e.g. [23]). It remains to be seen whether any general strategy can be developed in... 

Fig. 5.3. Log-log plot of the self-diffusion constant D of polymer melts vs. chain length N. D is normalized by the diffusion constant of the Rouse limit, DRoUse> which is reached for short chain lengths. N is normalized by Ne, which is estimated from the kink in the log-log plot of the mean-square displacement of inner monomers vs. time [gi (t) vs. t]. Molecular dynamics results [177] and experimental data on PE [178] are compared with the MC results [40] for the athermal bond fluctuation model. From [40]...

It is important to note that, in most cases, the DP remained low and did not complement the previous studies on the SPG protocol referred to above [6]. A logical explanation for this discrepancy is as follows. Dendronized macromonomers for all the discussed polymers are relatively complex, requiring multistep synthetic procedures, and this limits both the amounts and the level of purity of the prepared macromonomers. As monomer purity and the scale of the reaction are two key factors (to ensure sufficient stoichiometry control) in SPG [5], it is reasonable to assume that those polymers with higher molar masses would be accessible if additional efforts had been undertaken to satisfy these stringent requirements. On the other hand, an effective conjugation length for such polymers is reached already at short chain lengths hence, it is understandable that further efforts towards molar mass improvement were not pursued. 

There are four classes of PhaC reported so far. PhaC belonging to the first class utilise (R)-3-hydroxy fatty acids with 3-5 carbon atoms and produce short-chain-length (sc/)-monomers this type of PhaC can be found in Cupriavidus necator [2, 7]. Class II PhaC can be found in Pseudomonas aeruginosa, catalyse medium-chain-length... 

However, PHA polymers are also classified according to monomers carbon units. Short-chain-length (SCL) PHAs consist of 3-5 carbon units monomers, whilst medium-chain-length (MCL) PHAs have 6-14 carbon units monomers (Lee and Park, 2005). The most representative polymer belonging to this family is poly-3-hydroxybutyrate (P3HB), whose main component is R-3-hydroxybutanoic acid, a metabolite found also in human blood (Fig. 1.3). 

Based on the monomer structures, PHA have been classified into short-chain length (SCL) ones consisting of monomers of 3-5 carbon-chain lengths (C3-C5), medium-chain length (MCL) ones containing C6-C14 monomers, and random copolymers of SCL and MCL monomers. ... 

Two major classes of PHAs are known to exist. PHAs whose polymeric units are predominantly five carbons or less are classified as short-chain-length PHAs (SCL PHAs) while all others are referred to as medium-chain-length PHAs (MCL PHAs). The term MCL was coined because the number of carbons in the monomers roughly corresponds to those of medium-chain-length carboxylic acids. PHA nomenclatme may still be in a state of flux as new stnictmes continue to be discovered. 

---