salve a tutti,
scusate il ritardo,
alla fine ho risolto così…
`
\documentclass[11pt,a4paper,oneside,openright,titlepage]{book}
\usepackage[italian]{babel}
\usepackage[utf8]{inputenc}
\usepackage{chemfig}
\usepackage{amsmath}
\usepackage{array,booktabs}
\newcolumntype{P}[1]{>{\raggedright\arraybackslash}p{#1}}
\newlength{\mngsp}
\usepackage{stmaryrd}
\usepackage{textcomp}
\usepackage{colortbl}
\usepackage{booktabs}
\usepackage[version=3]{mhchem}
\usepackage{tikz}
\newcommand{\blocknewline}{\\[3pt]\hspace{0pt}}
\usetikzlibrary{positioning,shapes,shadows,arrows,patterns,shadings}
\usepackage{pgfplots}
\pgfplotsset{/pgf/number format/use comma,compat=newest}
\usepackage{pdflscape}
\usepackage{subfig}
\usepackage[round,sort]{natbib}
\usepackage{hyperref}
\makeatletter
\renewcommand\hyper@natlinkbreak[2]{#1}
\makeatother
\usepackage[font=footnotesize, labelfont=bf]{caption}
\usepackage{siunitx}
\usepackage[Lenny]{fncychap}
\ChNameVar{\fontsize{16}{18}\usefont{T1}{phv}{m}{n}\selectfont}
\ChNumVar{\fontsize{80}{84}\usefont{T1}{ptm}{m}{n}\selectfont}
\usepackage{fancyhdr}
\newcommand{\fncyblank}{\fancyhf{}}
\newenvironment{abstract}%
{\cleardoublepage \fncyblank \null \vfill \begin{center}
\bfseries \abstractname \end{center}}%
{\vfill \null}
\usepackage{newfloat,caption}
\DeclareFloatingEnvironment[
name=Formula,
fileext=loc,
listname=Elenco delle formule,
placement=htbp,
within=chapter,
]{chemenvinn}
\newenvironment{chemenv}
{\begin{center}
\renewcommand\chemname[3][]{##2\captionof{chemenvinn}{##3}}}
{\end{center}}
\let\listofformulas\listofchemenvinns
\usepackage{minitoc}
\renewcommand\mtctitle{Sezioni}
\renewcommand\mlftitle{Figure}
\renewcommand\mlttitle{Tabelle}
\usepackage{makeidx}
\makeindex
\setcounter{tocdepth}{3}
\setcounter{secnumdepth}{3}
\begin{document}
\frontmatter{\tableofcontents\listoffigures\listoftables\listofformulas}
\mainmatter
\begin{center}
\setatomsep{0.7cm}
\schemestart
\chemname{\chemfig{*6(-=*5(-N=(-*5(-S–(<:(=[2]O)-[8]O^{-})=N-))-S-)-=-(-[3]OH)=)}}{luciferina}
\arrow{->[ATP]}
\schemestop
\par
\schemestart
\chemname{\chemfig{*6(-=*5(-N=(-*5(-S-(<:(=[6]O)-[8]O-[8]P(=[2]O)(-[6]O)-[8]O-[8]*5(-(-OH)-(-OH)-(-N*5(-(*6(-N=-N=-=))--N=-))--))--N=))-S-)-=-(-[3]OH)=)}}{luciferina-AMP}
\arrow{->[*{0}\textcolor{red}{\ce{O_2}}][*{0}$-$\ce{H+}$-$\ce{AMP}$-$\ce{CO_2}]}[-90]
\schemestop
\par
\schemestart
\chemname{
\chemfig{*6(-=*5(-N=(-*5(-S-=(-OH)-N=))-S-)-=-(-[3]OH)=)}}{ossiluciferina}
\chemsign{+}
\chemfig{PPi}
\chemsign{+}
\chemfig{\textcolor{red}{Luce}}
\schemestop
\begin{chemenv}
\chemname{}{Reazione catalizzata dall'enzima luciferasi}
\label{luciferina}
\end{chemenv}
\end{center}
\end{document}
`