You may want to try the Heavy-atom Database System http://hatodas.harima.riken.go.jp/
Version 2 (http://hatodas.harima.riken.go.jp/hatodas_v2/query/queryheavy.jsp) allows for pH as a search option. http://hatodas.harima.riken.go.jp/hatodas_v2/query/queryheavy.jsp Hope that helps, Sean