Photometric synthesis control system

Fig. 39. The recording of the continuously operating photometric synthesis control system shows the course of the proceeding Merrifield synthesis...

To date there have been hardly any experiences concerning the efficiency of ammo-nolytic detachment of peptides Unked to the support by phenacyl groupings. For analytical purposes, in our laboratory we detected, by the aid of our photometric synthesis control system, the release of hpophilic peptide amides within 24 hours of ammonolysis. The reagent we are utilizing is 10% (w) ammonia in dioxane/methanol 9 1 (v v), with renewal of the mixture delivered to the centrifugal reactor every 2 hours. It should be recalled, however, that in most of the cases when peptide amides are to be built up, the target sequences are synthesized on a benzhydrylamine support [171], which by HF-cleavage directly releases the entirely deprotected amide (see p. 64). 

Fig. 61. The photometric synthesis control system in cooperation with the centrifugal reactor to monitor the Merrifleld process...

Fig. 62. The recordings from the individual operations in the Merrifield synthesis by the photometric synthesis control system depend upon the absorbance of the Ddz-amino acids used...

In our laboratory this principle of photometric synthesis control is already in use, yet man s decision in judging the recording of the synthesis has to be substituted in the future by a computer system. 

The utilization of the photometric synthesis control [95] was already mentioned in Sect. 3.1.3, 3.2.4, and 3.3.6 (Fig. 61). The system consists of a two-channel flow photometer with reference cell technique operating on two wavelengths. It is connected to a continuous line recorder with fifteen times automatic scale expansion at constant sensitivity and a graphic integration supplement. The photometer reference flow cell of a wide inner diameter has an optical path of 5 mm. It is inserted between the metering system of the synthesizer and the centrifugal reactor and allows a flow rate of 5 to 10 liters/hour. 

The completion of the wash-out operations should be checked as carefully as the chemical transformations on polymer, since remaining by-products would cause side reactions in subsequent steps of the synthesis. In our group, this is simply and sensitively performed by the continuously monitoring control system, which operates during the whole Merrifield synthesis. On the recordings, completed wash-out operations after each chemical reaction on polymer are indicated by a straight zero curve, since reference and sample flow cell of the photometric unit in this situation contain nothing but pure solvent. 

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