PubMed · 6855515
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R I Shmurun, A I Shmurun. [Device for measuring microscopic objects].. https://pubmed.ncbi.nlm.nih.gov/6855515/
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The concentration distribution across a zone of iodine migrating along a column made of glass, packed with C18-bonded silica, and eluted with carbon tetrachloride was derived from a quantitative analysis of the photographs of the zone. The photographs were scanned and turned into digital images. The intensity distributions obtained from the measurement of the grayscale intensity were converted into concentration profiles using a calibration method. This procedure is illustrated and suitable corrections are introduced to account for the transverse variation of the optical path length, as a result of using a cylindrical detector cell (the column itself), and for the refraction of light due to the differences between the refraction indices of the glass wall and the liquids involved. An error analysis is also reported. It shows that the method can reliably produce results with a precision of a few percent, allowing on-column evaluation of column performance and the derivation of the radial distributions of the column efficiency, the migration velocity of the zone, and the sample distribution at the head of the column.
A quantitative on-column visualization technique for evaluating solute migration in liquid chromatography columns was described. This technique employed a matched refraction index phase system in high-pressure glass columns. In this case, the mobile phase was carbon tetrachloride and the stationary phase was a C18 silica. Because the refractive indexes of the two phases were the same, the column bed, otherwise opaque, was transparent to the eye. Zones of colored solutes could be injected (iodine for instance) and their migration studied along the column. Photographing the sample band during its migration allowed chromatographic information to be extracted using digital technology. As an example of applications for this technique, we show the sample entry through various inlet fittings. The results demonstrate that chromatographers should pay more attention to the selection of inlet frits. Importantly, the frit porosity should be matched to the particle size of the packing.
A low-resolution molecular model, which combines the known mechanical properties of protein-free DNA with the accumulating picture of chromatosome structure, has been developed to account for the stretching of single chromatin fibers by an imposed external force. Force-extension characteristics of sets of chains accumulated by Monte Carlo sampling are consistent with recently observed findings in the non-destructive regime (<20 pN imposed force), where the structure of the chromatosome remains intact. The correspondence between simulation and the relaxation phase of the experiment limits the equilibrium entry-exit angle of linker DNA on the chromatosome to W=50(+/-10) degrees and the effective DNA linker length to L(eff)=40(+/-5) bp. The computed force-extension characteristics are relatively insensitive to other parameters of the model, precluding their accurate estimation. The introduction of an attractive potential between closely spaced nucleosomes reproduces the added initial resistance of single fibers to extension at high salt conditions. The consideration of elastic linkers also improves the fitting of assorted classical measurements of unstressed chromatin structure in solution. The overall picture of chromatin that emerges is an irregular, fluctuating, three-dimensional, zig-zag structure with intact, mechanically stable chromatosome units and deformable linkers. The modeled fiber undergoes large-scale configurational rearrangements without significant perturbation of the constituent chromatosome beads, collapsing into a highly condensed form in response to small (<2kT) inter-nucleosomal attractions.