[R] Relocating Axis Label/Title

[Lorenzo Isella]

Dear All,
I am experiencing some problems with relocating an axis title.
I visited the following link before posting:

http://tolstoy.newcastle.edu.au/R/help/05/05/5283.html

But this is not entirely what I would like to do
Consider the example below:

rm(list=ls())
D_mean<-seq(-5,5,length=100)
y<-exp(-D_mean^2/5)
pdf("my.pdf")
plot(D_mean,y,type="l",yaxt="n",lty=2,lwd=2,col="black",
ylab = list(expression(paste(dN/dlogD[agg]," ["*cm^-3*"]"))),
xlab = expression(paste(D[agg]," [nm]")),
cex.lab=1.2
)
title(2, mgp=c(0, .3, 0))
dev.off()

I have the problem that the "3" in cubic centimeters (on the y axis)
is somehow "cut" in the pdf file I generate. Everything would be fine
if I could shift a bit the title of the y axis.
It must be trivial, but so far I have not managed to do it.
Any suggestions?
Many thanks

Lorenzo
I tried playing with the mgp parameter, but I managed to move the