A Gallery of Tetramethyldiaminodiphenylmethane Photomicrographs

(using a variety of illumination techniques)

by Brian Johnston   (Canada)

As you can see from the title, organic (carbon based) chemical names can be tongue-twisters!  The name of this compound is pronounced as tetra-methyl-di-amino-di-phenyl-methane.  It is commonly used as a universal reagent in thin layer chromatography to identify drugs.  During the production of many dyes,  the compound acts as an intermediate.  Historically, it was used in analytical chemistry for the identification of lead.

Tetramethyldiaminodiphenylmethane  is a solid consisting of pale yellow leaflets or plates with a melting point of about 90 degrees Celsius.  This very low melting temperature permits a melt specimen to be prepared by heating a small quantity between a microscope slide and cover-glass.  Note that the MSDS safety document for this compound states:

Clear evidence of carcinogenic properties in animals. Anticipated to be a human carcinogen. May cause reproductive damage. Harmful if inhaled, swallowed or absorbed through skin. Irritant.

May cause methemoglobinemia, which is characterized by chocolate-brown colored blood, headache, weakness, dizziness, breath shortness, cyanosis (bluish skin due to deficient oxygenation of blood), rapid heart rate, unconsciousness and possible death. Animal inhalation studies have reported the development of tumors. Effects may be delayed. Laboratory experiments have resulted in mutagenic effects.

The three melt specimens used in this article were prepared in the fume-hood of my lab while I was still teaching chemistry.  (I am now retired.)

Tetramethyldiaminodiphenylmethane’s structural formula and molecular shape are shown below.  Both images were produced using HyperChem Pro software.  Notice that the molecule has two benzene rings bonded to a central carbon.  A nitrogen-based amino group is attached to each benzene ring.

The first image in the article shows the distinctive feather-shaped forms that often occur in melt specimens of the compound.  (Unless otherwise stated, polarized light is used for illumination.)  Two higher magnification images of these feathery areas are shown below.

Compensators can be used to alter the colouration of a particular field.  In the two images following, lambda and lambda/4 plates were used, and the lambda/4 plate was rotated to produce the colour difference.

If pressure is applied to one area of the cover-glass as the melt cools, the resulting crystal layer will be thinner.  Under polarized light, this often results in images that are shades of gray rather than brilliantly coloured.

The image on the left, below, utilized two lambda/4 compensators, while the one on the right utilized lambda/4 and lambda compensators.

Below is a higher magnification photomicrograph of an area shown in the right hand image above.

The use of compensators can completely change the appearance of a particular field.

You may have to take a second look before you realize that all three images below are of exactly the same field!

The first three images use polarized light and compensators.  The fourth image was produced by using a phase-contrast condenser instead of a polarizing one.  However, instead of fitting a phase-contrast objective, a normal objective was used.  Doing this sometimes results in images with a distinctive three-dimensional appearance.

A similar field, (at lower magnification), using a dark-ground condenser resulted in the following image.

Here again, a phase-contrast condenser coupled with a non-phase objective were utilized to form the images.

As mentioned before, by choosing the right annular stop of the phase-contrast condenser, and the right non-phase objective, very 3-D-like images can be produced.

The final two images show one particular field.  Both use the same non-phase objective.  A different annular stop was used in the second image.  Although both photomicrographs show three-dimensional characteristics, these seem to be more enhanced in the second image.

Photomicrographic Equipment

The images in the article were photographed using a Nikon Coolpix 4500 camera attached to a Leitz SM-Pol polarizing microscope.  Images were produced using several illumination techniques: dark-ground, phase contrast and polarized light.  Crossed polars were used in all polarized light images.  Compensators, ( lambda and lambda/4 plates ), were utilized to alter the appearance in some cases.  A 2.5x, 6.3x, 16x or 25x flat-field objective formed the original image and a 10x Periplan eyepiece projected the image to the camera lens.

All comments to the author Brian Johnston are welcomed.

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