Synthesis serpentine

The geological process of the formation of serpentine from peridotite probably involves the synthesis of carbon compounds under FTT conditions (see Sect. 7.2.3). The hydrogen set free in the serpentinisation process can react with CO2 or CO in various ways. The process must be quite complex, as CO2 and CO flow through the system of clefts and chasms in the oceanic crust and must thus pass by various mineral surfaces, at which catalytic processes as well as adsorption and desorption could occur. 

The aqueous chemistry of chromium(in) above 100 °C has been investigated with particular reference to corrosion phenomena and the possibility of hydro-thermal synthesis of chromite in serpentine rocks. Isotopic exchange studies have indicated that the CrO unit exchanges intact between [Cr(H20)6] and [CrMo6024H6] . This appears to be the first established exchange of such a unit. ° [CrlHjOljlEtOH)] has a stability constant of 6.5 x 10" and is only stable in perchlorate solutions with >80% EtOH. ... 

Ajmalicine, 19-epi-ajmalicine and tetrahydroalstonine are formed from 4,21-dehydrogeissoschizine via cathenamine (Fig. 2.9). The enzymatic synthesis of these corynanthe-type alkaloids has been investigated using C. roseus cell suspension cultures, and the enzymes involved have been reviewed by De Luca (1993) and Ziegler and Facchini (2008). Ajmalicine can be oxidized by POD to serpentine. This reaction may take in the vacuole. 

C. roseus is, therefore, an amazing chemical factory, which produces more than 100 different monoterpenoid indole alkaloids, many of them possessing notable pharmacological activity [158-159]. The main alkaloids present in C. roseus plants are catharanthine, vindoline and a-3 ,4 -anhydrovinblastine. Ajmalicine and serpentine are also present in significant amounts in the plant [160-165]. Class III plant peroxidases have been involved in the synthesis of many of these monoterpenoid indole alkaloids. 

Artificial synthesis of smectites, especially those with Mg in the octahedral sheet, is relatively easy. A solution saturated with monomeric silica, to which an equal number of moles of MgCl has been added, is adjusted to pH 11 with NaOH. This yields a crystalline precipitate of trioctahedral smectite at room temperature. Magnesium silicate with the 1 1 layer structure (serpentine) results if the Si/Mg mole... 

The synthesis of indole alkaloids from the common precursors tryptamine and secologanin by cell cultures of C, roseus has been studied in detail (IT). Cells entrapped in agar, agarose, or carrageenan produce ajmalicine isomers at about the same rate as the freely suspended cells, while cells entrapped in alginate showed up to 160 fold increased synthesis. A major reason for this increased synthesis is believed to be the restricted growth of the entrapped cells, as has been discussed above for Capsiaum. The yield of ajmalicine is above 12 times as much product formed from added precursors as by de novo synthesis. In this case too, alginate entrapped cells were much more productive than freely suspended cells (140% increase), and were also used to synthesize the related alkaloid serpentine in a batch procedure (17). 

The influence of phosphate and sucrose on the production of serpentine in steady-state chemostat cultures was examined by Balague and Wilson (603). Alkaloid synthesis continued during phosphate but not during su ... 

Natural clays of TOT (2 1) or TO (1 1) structure are constituted of layers of Si04 tetrahedra (T) and NiOe octahedra (O) [15]. Synthetic clays corresponding to Si4Ni30io (OH)2(Ni talc, TOT phyllosilicate) and Si2Ni305(0H)4 (Ni serpentine referred to as nepouite, TO phyllosilicate) respectively, were hydrothermally synthesized in the 25-250 C range acconling to a procedure already described [16, 17]. These samples are referred to as Ta-x and Ne-x where Ta, Ne and x stand for talc, nepouite and the temperature of synthesis respectively. 

H. P. Eugster and D. R. Wones Synthesis and Stability of Micas J. J. Fawcett Synthesis and Stability of Chlorite and Serpentine... 

Ring Oxygen Heterocycles. The isomeric bases ajmalicine and tetrahydroalstonine (along with their tetradehydro compounds, serpentine and alstonine) are the most well known members of this group and had to be closely related to the seco compounds since upon dehydrogenation they yielded alstyrine. From the empirical formulae, absence of an isolated double bond, presence of C-methyl and a /3-oxyacrylic ester moiety (saponification and ultraviolet absorption spectra) the structures of ajmalicine and alstonine were derived. The stereochemical problems were not completely resolved until the total synthesis of ajmalicine was accomplished. 

Segnit [1963] has extended the range of synthesis of clinochlore up to 20 kbar by utilizing a piston-anvil apparatus. Between 10 and 20 kbar, aluminian serpentine was found to form below 600°C and clinochlore above 780°C. Evidence for a metastable mixed-layer phase was found between 600° and 780°C. 

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