Table 2.

Physicochemical property trends of small molecules stratified into lower (<500 Daltons) and higher (>500 Daltons) molecular weight categories, and associated with various subcellular localizations. For each localization class, Z-scores were used to compare differences in molecular properties of localizing vs. non-localizing molecules. Z-scores with an absolute value greater than 3.1 were highlighted in bold, indicating a significant trend associated with a specific localization. Z-scores with absolutes value greater than 3.1 and with a different sign from the Z-score of molecular weight were underscored. Z-scores for molecular descriptors that exhibited consistent (same sign) and significant differences between localizing vs. non-localizing compounds in both lower and higher MW groups were shaded in grey. Chemicals with reported ER/Golgi and Cyto localization were excluded from this analysis due to the small number of chemicals.

Lower MW molecules	Number (%)	difference of targeting from non-targeting small molecules (Z-scores)
		weight	a_don	b_rotR	charge	dipole	glob	logP_ow
Endo-lysosomes	148 (65.5)	−8.8	−2.1	2.2	5.3	−1.4	5.3	−8.4
Mitochondria	164 (63.3)	3.6	−0.8	−2.6	−3.1	−3.7	−0.2	3.1
Nuclei	64 (52.0)	4.6	4.7	−3.9	3.8	−0.9	−4.7	−1.6
Plasma membrane	61 (37.7)	6.2	−6.9	4.6	−2.7	7.0	−8.8	10.4

Higher MW molecules	Number (%)	difference of targeting from non-targeting large molecules (Z-scores)
		weight	a_don	b_rotR	charge	dipole	glob	logP_ow
Endo-lysosomes	78 (34.5)	4.6	3.9	−3.5	2.6	3.4	2.9	0.6
Mitochondria	95 (36.7)	−3.8	−0.9	−1.2	1.3	−4.5	−0.9	−1.6
Nuclei	59 (48)	0.4	1.9	−4.0	0.4	−0.7	−0.4	−5.7
Plasma membrane	101 (62.3)	−7.0	−9.6	8.4	−3.9	1.6	−3.2	8.0