Structural Characterization of α-Terminal Group of Natural Rubber. 2. Decomposition of Branch-Points by Phospholipase and Chemical Treatments

Abstract

The treatment of deproteinized natural rubber (DPNR) latex with phospholipases A(2), B, C, and D decreased significantly the long-chain fatty acid ester contents in DPNR and also the molecular weight and Higgins' k' constant, except for phospholipase D treatment. This indicates the presence of phospholipid molecules in NR, which combine rubber molecules together. Transesterification of DPNR resulted in the decomposition of the functional group at the terminal chain-end (alpha-terminal), including phospholipids and formed linear rubber molecules. The addition of small amounts of ethanol into the DPNR solution reduced the molecular weight and shifted the molecular weight distribution (MWD) comparable to that of transesterified DPNR (TE-DPNR). The addition of diammonium hydrogen phosphate into DPNR-latex in order to remove Mg2+ ions yielded a slight decrease in molecular weight and a slight shift in MWD. The phospholipids are expected to link with mono- and diphosphate groups at the alpha-terminal by hydrogen bonding and/or ionic linkages. The decrease in the molecular weight and Huggins' k' constant of DPNR demonstrates the formation of linear molecules after decomposition of branch-points by this treatment, showing that phospholipids participate in the branching formation of NR. The branch-points formed at the alpha-terminus are postulated to originate predominantly by the association of phospholipids via micelle formation of long-chain fatty acid esters and hydrogen bonding between polar headgroups of phospholipids.

Nitric oxide release using natural rubber latex as matrix

“…One of the most important of the non-hydrocarbon group's presents in NRL is the aldehyde group, which is thought to be responsible for crosslinking between the chains in NRL 27 and their concentration varying from clone to clone 28 . Other compounds, such as lipids, neutral glycolipids and phospholipids, amount to 1.4-3.2%.…”

Molecular Structure of Natural Rubber and Its Characteristics Based on Recent Evidence

“…Therefore, the formation of gel in NR during SH is presumed to compose of two types of branching points; the first one is expected to originate from phospholipids, which are associated to rubber chains and/or free phospholipid molecules. The phospholipids are associated together by the formation of micelle structure mainly via hydrogen bonding between polar groups in phospholipids molecules as reported (Tarachiwin et al, 2005a(Tarachiwin et al, , 2005b. The other crosslinking point is due to proteins, which can be formed via hydrogen bonding.…”

“…These groups can be removed by transesterification or saponification. These findings suggest that most of the chain-ends of NR consist of a phosphate group belonging long-chain fatty acid ester (Tangpakdee & Tanaka, 1997a;Eng et al, 1994a), which corresponds to phospholipids as follows (Figure 7 (Tangpakdee & Tanaka, 1997a) The new information of structure of α-terminal group in NR was analyzed recently by selective decomposition of the branch-points followed by structural characterization by using high resolution 1 H-, 13 C-and 31 P-NMR, FTIR, and GPC techniques as well as diluted solution viscometry for highly purified NR (Tarachiwin et al, 2005a(Tarachiwin et al, , 2005b. The selective decomposition of branch-points was carried out by using lipase, phosphatase, and phospholipases A 2 , B, C, and D. The 1 H-NMR spectrum of acetone-extracted deproteinized NR (AE-DPNR) at 750 MHz ( Figure 8) shows not only the signals derived from phospholipids, but also two small triplet signals due to mono-and diphosphate groups (Tarachiwin et al, 2005a).…”

“…13. Change of molecular weight and gel content of NR after the first tapping of virgin tree Recently, as mentioned above, the structure of α-terminal group of NR was proposed to consist of two kinds of functional group, i.e., monophosphate and diphosphate groups, which are linked with phospholipids via hydrogen bonding as a predominant linkage and some parts via ionic linkage (Tarachiwin et al, 2005a(Tarachiwin et al, , 2005b. Here, it is postulated that the branch-points in NR are formed by aggregation of the phospholipids which are linked to phosphate or diphosphate groups at the α-terminal.…”

Effect of rubber polarity on selective wetting of carbon nanotubes in ternary blends

“…As discussed in our previous work [20] a strong rubber-filler interaction between NR and CNTs was proposed by comparing the CNT localization in SBR/NR and SBR/isoprene (IR) blend. The solid NR was proposed to consist of (-terminal, two trans-1,4 isoprene units, about 1000-3000 cis-1,4 isoprene units, and "-terminal [25,26]. The (-terminal of the rubber molecule was postulated to be a modified dimethylallyl group linking to a functional group, which is associated with the proteins as cross-linking points in NR.…”