These morphological changes must likewise reflect the death processes of cells, i. All the RED values of the nontoxic test solvents Fig. The RED values of some cytotoxic test solvents Fig. Therefore, only the 5 cytotoxic test solvents S2, S5, S11, S17 and S18 excluding S24 should be tentatively considered as anomalies and explored to clarify their potential secondary cytotoxic factors. Retesting with S2, S5 and S17 provided essentially the same results as the first test, i.
In contrast, retesting with S11 and S18 showed reduced cytotoxicity compared to the first test. As shown in the inset photos for S2 Fig. This detachment is attributed to both the high specific gravity and the high hydrophobicity of S2. The hydrophobicity of S2 could result in solvent infiltration into the interface between the cells and the underlying polystyrene of the test well; in addition, the high specific gravity of S2 could result in cells floating due to buoyancy, resulting in the cells detaching from the well surface.
This would result in underestimation of the survival rate of cells treated with S2 and assessed by the WST-8 assay. Therefore, we conclude that the moderate cytotoxicity of S2 was a false-positive, i. Cell detachment is also a potential factor affecting the reproducibility of the test with S11 because phase contrast observation Fig. Therefore, we also conclude that the moderate cytotoxicity of S11 in the first test was a false-positive, i.
On the other hand, the reduced cytotoxicity of S18 in the repeat test should be attributed to an artifact due to non-contact of the test solvent with cells around the periphery of the test wells due to the residual culture medium blocking the cells from the test solvent. The inset photos of cells treated with S18 Fig. Hence, S18 remained categorized as a cytotoxic solvent and as an anomaly.
As confirmed above, S2 and S11 were non-toxic and not anomalies, while S5, S17 and S18 were cytotoxic and anomalies. We suspect the chemical stability of the cytotoxic test solvents to act as a secondary cytotoxic factor: specifically, the degradation products due to hydrolysis of the test solvents caused false cytotoxicity. S5, S17 and S18 generate alcohols and diols as hydrolytic products, 18,20,24 and HSPs indicate that these products are generally considered to be cytotoxic. Therefore, the false cytotoxicity must originate from the hydrolytic products of S5, S17 and S As discussed above, since all the anomalies were excluded as false-positive inherently nontoxic or false-cytotoxic solvents, our hypothesis is highly probable.
Furthermore, we propose that the hydrolytic instability of solvents is the secondary cytotoxic false-cytotoxic factor. Cytotoxic test solvents predicted as being nontoxic based on HSP consideration, i. The hydrolytic instability of these solvents and the toxicity of their products were identified as giving rise to secondary cytotoxicity and causing the observed anomalies. The identified nontoxic solvents and the proposed screening method based on HSPs will contribute to a wide range of applications such as 3D cell printing and cell sheet fabrication.
DOI: Received 23rd February , Accepted 10th March Abstract Nontoxicities of organic solvents were predicted using Hansen solubility parameters and various truly nontoxic solvents were identified according to the prediction.
Polar reactants will dissolve in polar solvents. For our purposes there are three measures of the polarity of a solvent:. Molecules with large dipole moments and high dielectric constants are considered polar. Those with low dipole moments and small dielectric constants are classified as non-polar. On an operational basis, solvents that are miscible with water are polar, while those that are not are non-polar; remember the saying " Oil and water don't mix ".
Let's start with the meaning of the adjective protic. In the context used here, protic refers to a hydrogen atom attached to an electronegative atom. For our purposes that electronegative atom is almost exclusively oxygen. In other words, polar protic solvents are compounds that can be represented by the general formula ROH. The polarity of the polar protic solvents stems from the bond dipole of the O-H bond. The large difference in electronegativities of the oxygen and the hydrogen atom, combined with the small size of the hydrogen atom, warrant separating molecules that contain an OH group from those polar compounds that do not.
Here the key word is aprotic. In the context used here, aprotic describes a molecule that does not contain an O-H bond. Solvents in this class all contain a bond that has a large bond dipole.
Typically this bond is a multiple bond between carbon and either either oxygen or nitrogen. Most dipolar aprotic solvents contain a C-O double bond. Non-polar solvents are compounds that have low dielecrtic constants and are not miscible with water. Table 1 presents a list of solvents that are commonly used in chemical reactions. The boiling point, dipole moment, and dielectric constant of each solvent is included.
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