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Administrator<br />

Chem3D provides two overlay techniques.<br />

“Tutorial 6: Overlaying Models” on page 39<br />

describes the Fast Overlay method. This section<br />

uses the same example—superimposing a molecule<br />

of Methamphetamine on a molecule of<br />

Epinephrine (Adrenalin) to demonstrate their<br />

structural similarities—to describe the<br />

Minimization Method.<br />

1. From the File menu, choose New Model.<br />

2. Select the Text Building tool and click in the<br />

model window.<br />

A text box appears.<br />

3. Type Epinephrine and press the Enter key.<br />

A molecule of Epinephrine appears.<br />

4. Click in the model window, below the<br />

Epinephrine molecule.<br />

A text box appears.<br />

5. Type Methamphetamine and press the Enter<br />

key.<br />

A molecule of Methamphetamine appears<br />

beneath the Epinephrine molecule.<br />

6. From the Model Display submenu of the View<br />

menu, deselect Show Hs and Lps.<br />

The hydrogen atoms and lone pairs in the<br />

molecule are hidden.<br />

The two molecules should appear as shown in<br />

the following illustration. You may need to<br />

move or rotate the models to display them as<br />

shown.<br />

TIP: To move only one of the models, select an atom<br />

in it before rotating.<br />

7. From the Model Display submenu of the View<br />

menu, select Show Atom Labels and Show Serial<br />

Numbers.<br />

The atom labels and serial numbers appear for<br />

all the visible atoms.<br />

To perform an overlay, you must first identify atom<br />

pairs by selecting an atom in each fragment, and<br />

then display the atom pairs in the Measurements<br />

table.<br />

Atom Pair —an atom in one fragment which has a<br />

distance specified to an atom in a second fragment.<br />

1. Select C(9) in the Epinephrine molecule.<br />

2. Shift+click C(27) in the Methamphetamine<br />

molecule.<br />

3. From the Structure menu, point to<br />

Measurements and choose Set Distance.<br />

The Measurements table appears. The Actual<br />

cell contains the current distance between the<br />

two atoms listed in the Atom cell.<br />

4. For an acceptable overlay, you must specify at<br />

least three atom pairs, although it can be done<br />

with only two pairs. Repeat steps 1 to 3 to<br />

create at least three atom pairs.<br />

5. The optimal distances for overlaying two<br />

fragments are assumed to be zero for any atom<br />

pair that appears in the Measurements table.<br />

For each atom pair, type 0 into the Optimal<br />

column and press the Enter key.<br />

106•Inspecting Models<br />

<strong>CambridgeSoft</strong><br />

<strong>Com</strong>paring Models by Overlay

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