A solid-state dedicated circular dichroism spectrophotometer: Development and application

Abstract

A solid-state dedicated circular dichroism (CD) spectrophotometer (J-800KCM) was designed and constructed. As a CD spectrophotometer is a polarization–modulation instrument, CD spectra are necessarily accompanied by artifacts due to macroscopic anisotropies such as linear birefringence (LB) and linear dichroism (LD) which are unique to the solid state. A photomultiplier with the least polarization characteristics and a photoelastic modulator (PEM) with the least residual static birefringence were selected for the new instrument, which was based on the electrical and optical systems of a commercially available spectrophotometer. A phased-locked loop circuit was introduced to a PEM driver, and a sample rotation holder, a stage controller, and an analyzer were installed. We have designed and built a special solid-state sample holder to enable the cancellation of artifact CD, and a lens unit for smaller samples. A set of procedures for obtaining true CD has been devised based on the Mueller matrix method, and a program was written to facilitate the otherwise cumbersome measurements. Using the J-800KCM instrument and this approach, we could obtain nearly zero CD for achiral polyvinyl alcohol (PVA) film dyed with achiral Congo Red by cancelling the substantial apparent CD arising from large macroscopic anisotropies. Experiments on chiral single crystals of α-Ni(H2O)6⋅SO4, one with larger and one with smaller LB, have established that, by our method, we could also eliminate parasitic artifacts to obtain the true CD.

Experimental aspects of solid state circular dichroism

“…The target was achieved by a dedicated spectrometer (J-800KCM) based on an extensively modified commercial unit, 10,11 which is suitable only for relatively large sized crystals.…”

“…86 Surface pressure effects in LB protein films were studied by CD and other techniques by Nicolini et al 87 A tendency to increase b-sheet structure in proteins' films dried on a thin quartz window compared to solution phase samples was observed by Hu et al, 88 whose results were however criticized by Harada and Kuroda 89 using the dedicated J-800KCM instrument. 10 Nakagawa et al studied amino acid films prepared with vacuum sublimation technique. 90 A far more detailed article on CD of polymethyl-glutamate LB films deposited on a quartz window, with care to avoid linear orientation artifacts and employing long accumulation times to be able to obtain the weak signal, was published by Nordé n group.…”

CD measurements of β‐amyloid (1–40) and (1–42) in the condensed phase

“…Solid-state CD and circular birefringence (CB) spectroscopy requires special knowledge and skill, as CD and CB spectra in the solid phase are necessarily accompanied by artifacts which originate from the macroscopic anisotropies of a sample such as linear birefringence (LB) and linear dichroism (LD), and the coupling between the macroscopic anisotropies and the non-ideal characteristics of polarization-modulation instruments. [10][11][12][13][14][15][16][17][18][19] Thus, we have developed UCS-1 (J-800KCM) 10 as well as the measurement and analytical methods based on the Stokes-Mueller matrix analyses, and their integrity has been already proven. 10,11,19 As for protein samples, we warned 11 that careless chiroptical measurements of peptides/proteins in the solid state might lead to erroneous conclusions such as conversion to a b-sheet structure during the solution to solid-state phase transition, as reported in literature for Bovine Serum Albumin (BSA) cast films.…”

Layered and cubic cobaltites grown by floating zone, structural and magnetic properties study

“…They can be used as new functional materials for electron, ion, or molecular transportation, sensory, catalytic, optical, and bio-active materials [1,2]. Herein, we describe new approaches to functionalization of liquid crystals and show how the design of liquid-crystalline structures formed by supramolecular assembly and nano-segregation leads to the formation of a variety of new functional soft materials.…”