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Summary of important facts about the Olis
dual-beam CDs
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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.
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1.
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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.
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2.
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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. |
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3.
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The
Olis dual-beam CDs support single-beam
CD and simultaneously dual-beam
absorbance.
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4.
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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.
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5.
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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.
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6.
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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.
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7.
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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].
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8.
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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.
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9.
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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."
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10.
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In
future, time-resolved FDCD and
time- resolved CPL (circular
polarized luminescence or the
CD of the excited state) will
be supported.
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11.
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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.
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12.
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All
electronics are external to
the optical bench, ensuring
that diagnosis and repair are
as simple and economical as
possible.
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13.
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The
bandwidth is selectable from
0.5 to 20 nm with the DeSa monochromator
and fully variable to 0.1 nm
with the Carys.
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14.
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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.
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15.
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The
software supports collection
and analysis of data as a function
of wavelength, time, and temperature.
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16.
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The
software includes two schemes
for secondary structure protein
determination？that of Chang
and Yang, and that of Compton,
et al.
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17.
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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.)
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18.
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The
software supports a dynamic,
interactive 3D display of the
data for graphical interpretation
of the kinetic process.
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19.
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The
software supports extraction
of kinetics from any wavelength
collected during the spectral
acquisition.
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20.
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The
software supports ASCII file
creation of any selected scans
or kinetic traces; default storage
format is binary, for maximum
utilization of disk space.
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21.
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The
2D and 3D kinetic fitting algorithms
include the Method of Successive
Integration, which is entirely
objective, requiring no starting
value guesstimates.
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22.
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The
software requires single-keystroke
entries and is fully menu-driven.
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23.
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All
tools for taking apart the instrument
are provided at installation.
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24.
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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.
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25.
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The
workstation is delivered fully
operational, and an on-site
verification is made by qualified
Olis staff.
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