I wish for entries in my bibliography to be set in sentence case. To do so I have been using `\DeclareFieldFormat{titlecase}{\MakeSentenceCase*{#1}}` in my preamble. I then use curly braces in my entries to preserve capitalisation for proper nouns and other words. However, this protection does not seem to effect single letters. Consider the following MWE:

```
\documentclass{article}

\usepackage{filecontents}
\usepackage[backend=biber, style=authoryear, maxbibnames=10]{biblatex}

\DeclareFieldFormat{titlecase}{\MakeSentenceCase*{#1}}

\begin{filecontents}{\jobname.bib}
@Article{     creutz88,
  Title     = {Global Monte Carlo algorithms for many-fermion systems},
  Author    = {Creutz, Michael},
  Journal   = {Physical Review {D}},
  Volume    = {38},
  Number    = {4},
  Pages     = {1228--1238},
  Year      = {1988},
  Publisher = {APS}
}
@Article{     metropolis49,
  Title     = {The monte carlo method},
  Author    = {Metropolis, Nicholas and Ulam, Stanislaw},
  Journal   = {Journal of the {American} Statistical Association},
  Volume    = {44},
  Number    = {247},
  Pages     = {335--341},
  Year      = {1949},
  Publisher = {Taylor \& Francis}
}
\end{filecontents}

\addbibresource{\jobname}

\begin{document}

Stanislaw Ulam was one of the original pioneers of Monte Carlo methods
\parencite{metropolis49}.

With a problem of dimension $d$, the computational expense of a random-walk
sampler is $O(d^2)$, whereas the cost of Hamiltonian Monte Carlo is roughly
$O(d^{5/4})$ \parencite{creutz88}.

\printbibliography

\end{document}

```

This produces the bibliography:

```
Creutz, Michael (1988). “Global monte carlo algorithms for many-fermion sys-
tems”. In: Physical review d 38.4, pp. 1228–1238.
Metropolis, Nicholas and Stanislaw Ulam (1949). “The monte carlo method”.
In: Journal of the American statistical association 44.247, pp. 335–341.

```

The entries are in sentence case as desired. And the capitalisation of `American` has been preserved, as intended. However, the capitalisation in `Physical Review {D}` has not been preserved.

So, how do I protect capitalisation of single letters in my bibliography? Or what is it that I'm misunderstanding in my current approach?