These are my meta-tags:
$("meta[name='og:title']").attr('content', 'my new title');
Using "property=" does not work in Chrome
You could give each meta element an ID or Class.
$('#metaelement').attr('content', 'my new meta description');
Make sure your quotes are like this:
$('meta[property="og:description"]').attr('content',"$modified_desc" );
I think you should escape :
look at the documentation
$("meta[property='og\\:title']").attr("content", result.title);