> Summary of important facts about the Olis dual-beam CDs

Summary of important facts about the Olis dual-beam CDs

The remainder of this document offers 'sole source justification' points which many labs have used to specify the Olis dual-beam CDs over single-beam CD spectrophotometers. This list is also a comprehensive and succinct tally of important facts to know over single-beam CD spectrophotometers.


The Olis RSM CD spectrophotometer use the patented DeSa dual-beam, double-grating monochromator with a scan rate of 1,000 scans/second [1.4 x 107 nm/min]. Only with this design can photometrically accurate millisecond 2D data points be acquired for correct and complete capture of a fast reaction for the purpose of understanding the kinetics and identifying spectral intermediates. A dual-beam spectrophotometer presents `true' absorbance spectra, not `difference' spectra.


The Olis dual-beam CD spectrophotometers are phase- coherent, in which both beams of light produced by the polarizer pass through the CD cuvette; the beams are identical except their state of polarization, which toggles from left to right (or parallel to perpendicular) at a rate of 50 modulations per millisecond. Two `piles' of data, 50% from one photomultiplier tube and 50% from the other PMT, are created and their ratio is calculated. In this way, "first principle" CD information is collected. The optional Olis USA CD stopped-flow has a cylindrical cuvette observation cell with a pathlength of 1 mm; both beams of light will pass through this observation window to ensure that the dual-beam, phase-coherent CD detection principle will apply to the stopped-flow applications.


The Olis dual-beam CDs support single-beam CD and simultaneously dual-beam absorbance.


The Olis dual-beam CDs support dual-beam absorbance spectroscopy measurements with no hardware changes between CD and absorbance work. Moving between absorbance stopped- flow and CD stopped- flow will involve exchanging one observation cell for another. The exchange will take no more than 5-10 minutes.


The DeSa monochromator is a subtractive double design to produce a homogeneous output beam. This output beam is homogeneous (all the same color), independent of the bandwidth. The subtractive design recombines the light which passes from the first monochromator into the second; an additive monochromator [the alternative] further disperses the light which passes from the first monochromator to the second.


No optical components move during rapid-scanning. The 50-mm2 gratings used in the DeSa monochromator are stationary during fast scanning. Their center wavelength position is selectable by the user through the software; the two gratings are moved in synchrony by means of a stepper motor-driven coupling bar. The gratings move in a conventional way when slow scanning is performed, i.e., when the fixed slit cartridge (static ScanDisk) is in place and the software is instructed to move gratings in the conventional wavelength-by-wavelength mode.


All Olis CD spectrophotometers are usable in a fixed-wavelength, dual-beam mode with collection rates to 2 MHz [2 x 106 readings/second; 1.2 x 108 readings/ minute].


The DeSa monochromator is usable over the spectral range of approximately 167-1180 nm with appropriately blazed gratings and light sources; these gratings and light sources are easily accessible by owners of the instrument for quick and fail-safe exchanges. The lowest UV CD obtained at Olis as of March 1998 is 167 nm.


The Olis RSM CD is configurable for luminescence, fluorescence emission and excitation, anisotropy, polarization of fluorescence, and flash photolysis with reasonably priced and easy to implement accessories. Fixed-wavelength excitation and fixed-wavelength emission work can be done immediately. Fixed- wavelength excitation and rapid- scanning emission work can be done after the addition of the "Full Fluorescence Optimization."


In future, time-resolved FDCD and time- resolved CPL (circular polarized luminescence or the CD of the excited state) will be supported.


The Olis RSM CD is mounted on a TMC honeycombed optical table for maximum stability and ease in moving from one table or bench to another.


All electronics are external to the optical bench, ensuring that diagnosis and repair are as simple and economical as possible.


The bandwidth is selectable from 0.5 to 20 nm with the DeSa monochromator and fully variable to 0.1 nm with the Carys.


The controlling computer hardware system includes a computer at least as modern as a Pentium II 350. The printer will be an HP LaserJet 1100L or HP DeskJet 683C color printer.


The software supports collection and analysis of data as a function of wavelength, time, and temperature.


The software includes two schemes for secondary structure protein determinationú┐that of Chang and Yang, and that of Compton, et al.


The software includes SVD algorithms which are primarily used in the Olis program to calculate the number of components that caused the data. These algorithms incidentally reduce the size of the raw data files by 40 fold while losing none of the information in the data files, e.g., from 0.8 Mbyte to 32 Kbytes. (Word processor-type compression algorithms cannot work on 'real data' since every datum may be unique.)


The software supports a dynamic, interactive 3D display of the data for graphical interpretation of the kinetic process.


The software supports extraction of kinetics from any wavelength collected during the spectral acquisition.


The software supports ASCII file creation of any selected scans or kinetic traces; default storage format is binary, for maximum utilization of disk space.


The 2D and 3D kinetic fitting algorithms include the Method of Successive Integration, which is entirely objective, requiring no starting value guesstimates.


The software requires single-keystroke entries and is fully menu-driven.


All tools for taking apart the instrument are provided at installation.


Support for the instrument is free for period of time not less than three years. Repair or replacement of defective components is done at cost.


The workstation is delivered fully operational, and an on-site verification is made by qualified Olis staff.