Cuticular waxes

The surface of the green coffee contains a cuticular wax layer (0.2—0.3% db) for both varieties. The wax contains insoluble hydroxytryptamides derived from 5-hydroxytryptamine [61 7-2] and saturated C18—C22 fatty acids. 

Terrestrial BMOs have also been widely used for monitoring environmental contaminants. In particular, the lipid-like waxy cuticle layer of various types of plant leaves has been used to monitor residues of HOCs in the atmosphere. However, some of the problems associated with aquatic BMOs apply to terrestrial BMOs as well. For example, Bohme et al. (1999) found that the concentrations of HOCs with log KoaS < 9 (i.e., those compounds that should have attained equilibrium) varied by as much as 37-fold in plant species, after normalization of residue concentrations to levels in ryegrass (Lolium spp.). These authors suggested that differences in cuticular wax composition (quality) were responsible for this deviation from equilibrium partition theory. Other characteristics of plant leaves may affect the amount of kinetically-limited and particle-bound HOCs sampled by plant leaves but to a lesser extent (i.e., <4-fold), these include age, surface area, topography of the surface, and leaf orientation. 

Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic compounds which are absorbed by the cuticular wax layer, which acts as a trap for these pollutants. Plants experiencing PAEI exposure (for example, on the verges of roads carrying heavy traffic) often show an increased level of wax... 

Examples are the benefits in the area of extraction of vegetable cuticular waxes being separated from the more valuable essential oils, using supercritical CO2 (Stassi and Schiraldi, 1994). A molecular understanding of how a phenomenon like supercritical behavior affects solvent properties is important (Kazarian and Poliakoff, 1995). 

Lipids are essential plant components as they are constituents of membranes and cuticular waxes as well as being major seed storage... 

A non-volatile contact pheromone contained in the cuticular wax of females elicits a wing-raising courtship response from males (Roth and Wilhs, 1952 Ishii, 1972). Nishida and co-workers obtained three active chromatographic fractions from hexane extracts of 224000 females. The major active component was identified as... 

In general, volatile components can be extracted from the dried raw materials under conditions close to the critical point of carbon dioxide. Temperatures should be within the range of 32 to 60°C. However, some heat-sensitive components may decompose, even below this range. Extraction pressures should be between 74 and 120 bar, since at higher pressures the increased solvent power of CO2 also increases the solubility of unwanted components. The yields obtained by SFE are very similar to those found by steam distillation. However, even under mild extraction conditions, some small amount of cuticular waxes is co-extracted with the volatiles. The major constituents of the waxes are -paraffins, ranging from C25 to... 

The extraction, in combination with fractional separation of extracts in a multi-stage separation system, results in high-quality volatile oils [42,44]. Recently, this fractional separation technique has been refined by Reverchon and co-workers for selective precipitation of cuticular waxes and volatile oils [43,56],... 

The Paleosoil of Mangrove. The GC trace of the saturated/unsaturated hydrocarbons of the extract from the buried soil of mangrove is dominated by odd n-alkanes probably derived from cuticular waxes (Figure 6A). The "intermediate" fraction of the same extract is poor in sulfur compounds (Figure 6B) only a C29 sterane thiol previously identified in the Rozel Point oil (18). and by a C30 n-alkylthiophene. The former compound might be related to the C29 sterene dominantly present in the saturated/unsaturated fraction (Figure 6A). 

The other long understood and, indeed, fundamental function of insect cuticular lipids is to restrict water loss to prevent a lethal rate of desiccation (Hadley, 1984 Noble-Nesbitt, 1991 Nelson and Blomquist, 1995). Conservation of water is a primary challenge faced by terrestrial animals with high surface area to volume ratio such as insects. The anti-desiccatory function of the cuticular waxes is crucial in meeting this need, and makes them a focused target for insect control. 

The ability of insects to withstand desiccation was recognized in the 1930s to be due to the epicuticular layer of the cuticle. Wigglesworth (1933) described a complex fatty or waxy substance in the upper layers of the cuticle which he called cuticulin . The presence of hydrocarbons in this wax of insects was suggested by Chibnall et al. (1934) and Blount et al. (1937), and over the next few decades the importance of hydrocarbons in the cuticular wax of insects was established (Baker et al., 1963 and references therein). The first relatively complete chemical analyses of the hydrocarbons from any insect, the American cockroach, Periplaneta americana (Baker et al., 1963), occurred after the development of gas-liquid chromatography (GLC). The three major components of the hydrocarbons of this insect, //-pen taco sane, 3-methylpentacosane and (Z,Z)-6,9-heptacosadiene, represent the three major classes of hydrocarbons on insects, n-alkanes, methyl-branched alkanes and alkenes. Baker and co-workers (1963) were able to identify n-pentacosane by its elution time on GLC to a standard and its inclusion in a 5-angstrom molecular sieve. 3-Methylpentacosane... 

Baker, G., Pepper, J.H., Johnson, L.H. and Hastings, E. (1960). Estimation of the composition of the cuticular wax of the Mormon cricket, Anabrus simplex Hald. 

Blomquist, G.J., Soliday, C.L., Byers, B.A., Brakke, J. W. and Jackson, L.L. (1972). Cuticular lipids of insects V. Cuticular wax esters of secondary alcohols from the grasshoppers Melanoplus packardii and Melanoplus sanguinipes. Lipids, 7, 356-362. 

Genin, E., Jullien, R. and Fuzeau-Braesch, S. (1987). New natural aliphatic ethers in cuticular waxes of gregarious and solitary locusts Locusta migratoria cinerascens (II). J. Chem. Ecol., 13, 265-282. 

Southwell, I. A. and Stiff, I. A. (1989). Presence of long-chain dialkyl ethers in cuticular wax of the Australian chrysomelid beetle Monolepta australis. J. Chem. Ecol., 15, 255-263. 

Table 16.7 Determination of cuticular waxes of the two scorpion species (t traces).

Methylfurolabdane containing a 2,3-disubstituted furan substructure, isolated from the cuticular wax of the leaves of Nicotiana tabacum, was synthesized from (+)-sclareolide. The furan ring was formed from a P,y-unsaturated ketone via an oxidation-cyclization procedure <02EJO4169>. 

There is evidence suggesting that many of the thiocarbamates reduce the production of cuticular wax and interference with lipid biosynthesis which probably represents the primary mode of action of these herbicides. 

Tobacco leaf has a complicated chemical composition including a variety of polymers and small molecules. The small molecules from tobacco belong to numerous classes of compounds such as hydrocarbons, terpenes, alcohols, phenols, acids, aldehydes, ketones, quinones, esters, nitriles, sulfur compounds, carbohydrates, amino acids, alkaloids, sterols, isoprenoids [48], Amadori compounds, etc. Some of these compounds were studied by pyrolysis techniques. One example of pyrolytic study is that of cuticular wax of tobacco leaf (green and aged), which was studied by Py-GC/MS [49]. By pyrolysis, some portion of cuticular wax may remain undecomposed. The undecomposed waxes consist of eicosyl tetradecanoate, docosyl octadecanoate, etc. The molecules detected in the wax pyrolysates include hydrocarbons (Cz to C34 with a maximum of occurrence of iso-Czi, normal C31 and anti-iso-C32), alcohols (docosanol, eicosanol), acids (hexadecanoic, hexadecenoic, octadecanoic, etc ). The cuticular wax also contains terpenoids such as a- and p-8,13-duvatriene-1,3-diols. By pyrolysis, some of these compounds are not decomposed and others generate closely related products such as seco-cembranoids (5-isopropyl-8,12-dimethyl-3E,8E,12E,14-pentadecatrien-2-one, 3,7,13-trimethyl-10-isopropyl-2,6,11,13-tetradecatrien-1al) and manols. By pyrolysis, c/s-abienol, (12-Z)- -12,14-dien-8a-ol, generates mainly frans-neo-abienol. 

Phenolics can exhibit simple structures such as arbutin, or complex ones such as those characteristic of the tannin class. They are most frequently linked to sugars, which render themselves polar compounds, or they can be permethylated or methoxylated, becoming nonpolar compounds as what happens with flavonoids found in cuticular waxes. 

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