What I found is:
Peter Mykolayovych Kapnist, Colonel in the Imperial Russian Guard, no noble title noted
married
Catherine d'Allonville, born after 1804 in Russia
daughter of Armand-Francois d'Allonville, Marquis d'Allonville, and Countess Catherine de Munnich (They were married in Russia in 1804)
From http://racineshistoire.free.fr/
Maybe it helps....