A New, Small-color-difference Equation for Dental Shades

Traditionally, dental-shade-guide standards are designated in terms of Munsell hue (H), value (V), and chroma (C). However, ΔE color differences proposed as ADA tolerances for shade guides are in the CIE L*a*b* system. The purpose of this study was to evaluate a new color-difference equation, for estimation of small color differences by Munsell parameters. The published values of the Bioform shade-guide tooth colors determined with a Beckman spectrophotometer were used. Color differences among 276 combinations of the 24 Bioform shade-guide colors were calculated with Eq. 1, with use of the Munsell notation, and also with the CIE L*a*b* equation for ΔE. An estimate of the accuracy of Eq. 1 was 0.41 ΔE units when ΔE CIE was below 4.0. The Vita shade-guide colors were determined with a Beckman spectrophotometer. This data set contained 16 samples, and 120 combinations were used for calculation of color difference. An estimate of the accuracy for this set of data was 0.35 ΔE units when ΔE CIE was less than 4.0. The new color-difference equation provides a means for estimation of AE CIE L*a*b* color difference between dental shades with Munsell notation. This equation will be useful for estimation of small AE CIE L*a*b* values for shade-guide teeth that are designated in terms of Munsell notation.

Analysis of the Mechanism of Unfolding of Foot-and-Mouth Disease Virus-RNA During Heat and Chemical Denaturation

Two different approaches were used to examine the mechanism of unfolding of foot-and-mouth disease virus (FMDV) RNA. In the first procedure, we prepared single stranded 37S virion RNA by extracting purified virus with phenol and sedimenting the RNA through a 5 to 25% sucrose gradient. The purified RNA was then dissolved in NT buffer (10mM Tris-HCl, pH 7.4, 100 mM NaCl) containing either 1 mM EDTA or 1 mM Mg and absorbed onto Formvar-coated, carton shadowed, glow-discharged 200 mesh copper grids. In the second procedure, we heat denatured intact viral capsids in 0.05 M K2HPO4, 0.2 M KCl buffer (pH 7.0) in a thermostatically controlled Beckman spectrophotometer. We measured viral uncoating and the controlled release of the RNA by increased absorbancy at 260 nm. Samples taken at various temperatures were added to an equal volume of 20% formaldehyde and quick-frozen in covered BEEM capsules in liquid nitrogen. The heat-denatured formaldehyde-fixed virus was then spread onto grids using the BAC-formamide procedure of Vollenweider.

THE ESTIMATION OF CRUDE PROTEIN IN RAPESEED MEAL BY A DYE-BINDING METHOD

The relationships between Kjeldahl protein content and the dye-binding capacity (DBC) with Orange G and Acid Orange 12 of 15 rapeseed meals were studied. The unbound dyes were measured with a Beckman spectrophotometer and also by the Udy colorimeter in the case of Acid Orange 12. The correlation between DBC and Kjeldahl protein content or total basic amino acids was highly significant. The results favored the Udy method with Acid Orange 12.

Differential Spectrophotometric Determination of Calcium

The appearance of kits for the determination of micro amounts of calcium stimulated our interest in the use of Eriochrome Blue SE for this analysis. A study of spectrophotometric curves indicates that, at pH values above 13.7, calcium will complex and cause a change of dye absorbance while magnesium does not complex with the dye. A differential spectrophotometric technic is described in this paper in which the spectrophotometer is set at zero absorbance with a dye-calcium standard solution or a dye-calcium sample solution as reference and the absorbance of the dye solution then measured. For a set of standards the absorbance-calcium relationship is linear. With the Beckman spectrophotometer, Model DU, it has been found that 1 part of serum to 100 parts of alkaline dye solution (100 λ of serum to 10 ml. alkaline dye solution) can be used. The technic shows greater sensitivity and accuracy than do previous methods using Eriochrome Blue SE.

Straylight Error in a Spectrophotometer

A method is described for arriving at a calibration equation expressing concentration in terms of absorbancy. This equation is based on the assumption of a constant stray radiant energy or a constant dark current compensation error. The deviation from linearity was found to correspond to 0.1 per cent stray radiant energy at 273 mµ in a Beckman spectrophotometer.

Effect of Synthetic Detergents on the Swelling and the ATPase of Mitochondria Isolated from Rat Liver

A study was made of the effects of various types of detergents on the swelling of isolated mitochondria and on mitochondrial ATPases which are activated by Mg or DNP respectively. The rate of swelling was measured in the Beckman spectrophotometer by following the decrease in turbidity of dilute suspensions of these organelles. It was found that non-ionic detergents containing a nonyl phenoxy side chain or anionic detergents caused swelling of the mitochondria and activation of Mg-ATPase. On the other hand, cationic detergents promoted the clumping of mitochondria and did not activate Mg-ATPase. DNP-ATPase was inhibited by all of the detergents tested. It would appear from these observations that the inhibition of DNP-ATPase is not related to a gross change in the morphology of the organelles; in contrast, the activation of Mg-ATPase definitely is correlated with swelling of the isolated mitochondria. These data also suggest that the ionic detergents combine with charged sites on the protein moiety of the lipoprotein in the mitochondrial surface, whereas the non-ionic detergents form inclusion compounds with the lipide moiety, thereby altering the mitochondrial structure and permeability.