3

I'm using chemfig to create a structural formula of a reaction. I'm showing two alpha-amino acids that are reacting and generating a 2-residue peptide when loosing a molecule of water and I want to show the reverse reaction, i.e., adding one water to obtain two separate the amino acids.

This is my code.

\begin{equation}
    \begin{array}{c}
        \chemfig{
            H_{3}\chemabove{N}{\scriptstyle+}- 
            CH(
                -[:90,,1,1]R^{1}
            )- 
            C(
                =[:-90]O
            )- 
            OH
            \qquad
            +
            \qquad
            H-
            N(
                -[:90]H
            )-
            CH(
                -[:90,,1,1]R^{2}
            )- 
            COO^{-}
        }
        \\
        \chemfig{
            \schemestart \arrow{-U>[*{0}H\textsubscript{2}O]}[90] \schemestop
            \quad
            \schemestart \arrow{-U>[][*{0}H\textsubscript{2}O]}[270] \schemestop
        }
        \\
        \chemfig{
            H_{3}\chemabove{N}{\scriptstyle+}- 
            CH(
                -[:90,,1,1]R^{1}
            )- 
            C(
                =[:-90]O
            )- 
            N(
                -[:90]H
            )-
            CH(
                -[:90,,1,1]R^{2}
            )- 
            COO^{-}
        }
    \end{array}
    \label{fe:exemploLigacaoPeptidica}
\end{equation}

That generates this:

enter image description here

But I want to generate this:

enter image description here

In chemfig there isn't a arrow of type " < U-" like, for exemple, "<-" and "->", so I need to rotate an "-U>" arrow, but it rotates using the start of the line as center. So, my question is, how to get something like the second image.

1
  • I am really displeased the way how these arrows rendered.
    – Matsmath
    Jun 22, 2016 at 18:29

1 Answer 1

0

Here is my kludge to solve this:

\begin{equation}
    \begin{array}{c}
        \chemfig{
            H_{3}\chemabove{N}{\scriptstyle+}- 
            CH(
                -[:90,,1,1]R^{1}
            )- 
            C(
                =[:-90]O
            )- 
            OH
            \qquad
            +
            \qquad
            H-
            N(
                -[:90]H
            )-
            CH(
                -[:90,,1,1]R^{2}
            )- 
            COO^{-}
        }
        \\
        \\
        \begin{tikzpicture}
            \node[anchor=south west,inner sep=0] at (0,0) {\includegraphics[scale=0.15]{images/arrowsReacaoPeptideo}};
            \node at (-0.5,0.5) {H\textsubscript{2}O};
            \node at (1.8,0.5) {H\textsubscript{2}O};
        \end{tikzpicture}
        \\
        \\
        \chemfig{
            H_{3}\chemabove{N}{\scriptstyle+}- 
            CH(
                -[:90,,1,1]R^{1}
            )- 
            C(
                =[:-90]O
            )- 
            N(
                -[:90]H
            )-
            CH(
                -[:90,,1,1]R^{2}
            )- 
            COO^{-}
        }
    \end{array}
    \label{fe:exemploLigacaoPeptidica}
\end{equation}

And I got this:

enter image description here

I used a tikzpicture to draw the arrows, that were created as an png image called setaReacaoBidirecional:

enter image description here

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