Development of a universal ellipsoidal mirror device for fluorescence detected circular dichroism: elimination of polarization artifacts

We have developed an ellipsoidal mirror fluorescence detected circular dichroism (FDCD) device with enhanced detection sensitivity that eliminates the polarization artifact; this is applicable to samples with strongly polarized fluorescence. The device, JASCO FDCD465, has an ellipsoidal mirror structure with a framework consisting of three mirrors (one elliptical and two plane mirrors) that maximally collects light in the FDCD. All assemblies on the device including the ellipsoidal mirror, cylindrical cell, and photomultiplier tube (PMT) are aligned on the chamber-fitting sample mount as an attachment compatible with a standard CD spectropolarimeter. The new FDCD465 device eliminates the polarization artifact caused by anisotropic distribution of the emitted light. It represents a convenient, reliable, and sensitive FDCD attachment to the JASCO J-800 CD spectrometer series that can be used under both isotropic and photoselected conditions.

(6R)-5,6,7,8-tetrahydro-L-monapterin from Escherichia coli, a novel natural unconjugated tetrahydropterin

The structure of the major tetrahydropterin in Escherichia coli was determined as (6R)-5,6,7,8-tetrahydro-L-monapterin, i. e. (6R)-2-amino-5,6,7,8-tetrahydro-6-[(1S,2S)-1,2,3-trihydroxypropyl]pteridin-4(3H)-one. Although the stereochemical structure of the trihydroxypropyl side chain has been determined previously by fluorescence detected circular dichroism analysis on its aromatic derivative, the most important configuration at C(6) has not been clarified. The major difficulties for the determination of the chirality were instability toward air oxidation and very low concentration of the tetrahydropterin derivative. In the present study, the C(6)-configuration was determined as R by comparing its stable hexaacetyl derivative with authentic (6R)- and (6S)-hexaacetyl-5,6,7,8-tetrahydro-L-monapterins by high performance liquid chromatography (HPLC) and HPLC-mass spectrometry (LC-MS). (6R)-5,6,7,8-Tetrahydro-L-monapterin is a new unconjugated tetrahydropterin from natural sources.