Can a Plan purchase an investment from an IRA?

I have been asked by a client, can my wife (who is a single member business and sponsors a 401(k) plan)... can her 401(k) purchase an investment from my IRA?  He has an investment that has a capital call and he doesn't have the $ to cover it.  His wife's 401(k) is flush with cash.   Can the do this?  Would it be a prohibited transaction? 

Thanks for any thoughts.

Extremely likely this is a 4975(c)(1)(D) prohibited transaction. See also DOL Opinion Letter 2011-4A.

Advisory Opinion 2000-10A might be relevant as well.