# Tip from an email in: http://tolstoy.newcastle.edu.au/R/help/06/07/30469.html

formatEng <- function(x) {
   s<-as.numeric(strsplit(format(x, scientific=T),"e")[[1]])
   return(paste(s[1]*10^(s[2]%%3),as.integer(s[2]-(s[2]%%3)),sep="e"))
} 

# Use with sapply on dataframe elements
sapply(x$col, formatEng)