purchased from Sigma-Aldrich (St. Louis, MO). Nitric acid was purchased from
MilliporeSigma (Burlington, MA). V2O5 nanoparticles were
purchased from US Research Nanomaterials, Inc. (Houston, TX). An internal
standard mixture for mass spectral analysis consisted of
[13C6]-D-glucose, [15N]-indole,
[2-15N]-L-lysine dihydrochloride,
[13C5]-L-glutamic acid,
[13C7]-benzoic acid,
[3,4-13C2]-cholesterol, [15N]-L-tyrosine,
[trimethyl-13C3]-caffeine,
[15N2]-uracil, [3,3-13C2]-cystine,
[1,2-13C2]-palmitic acid, [15N ,
13C5]-L-methionine, [15N]-choline chloride,
and
2’-deoxyguanosine-15N2,13C10-5’-monophosphate,
all from Cambridge Isotope Laboratories, Inc (Andover, Pennsylvania). Ultra-pure
water (Milli-Q; Sigma-Aldrich, St. Louis, MO) was used as indicated. All
reagents were analytical grade or better unless otherwise stated.