alternate method for openssl_public_encrypt in C#

I am completely new to encryption and C#. I have public.key file which contain public key. using php i can use the key to encrypt the data and send to thirdparty.

$publicKey = openssl_pkey_get_public('public.key'); //open public key file

//encryot the data

if (!openssl_public_encrypt($plaintect, $encryptdata, $publicKey))

$encrypted = base64_encode($encryptdata);

I used libraries from http://openssl-net.sourceforge.net/ but I cannot find anything similar to php above

any help would ne really appreciated

thank you