## Results and Discussion
### Relative Quantification
(2010) where they found the methanol extracts  
Figure 3: Relative quantification of the identified compounds (**A**) chlorophyll-c1, chlorophyll-a, arachidonic acid, \(\alpha\)-linolenic acid, astaxanthin, cantaxanthin, cantaxanthin, lutein, sucrose, palmitic acid and fucoxanthin, (**B**) stearic acid, isoleucine, violaxanthin, zeaxanthin, cholesterol, leucine, glucose, proline, myo-inositol and glycine of different extraction solvents from _Chaetoceros calcitrans_ based on the mean peak area of \({}^{1}\)H NMR signals. Chemical shifts (ppm) used for the relative quantification are chlorophyll c1 (9.82), chlorophyll a (9.5), arachidonic acid (1.26), \(\alpha\)-linolenic acid (1.3), astaxanthin (1.34), canthaxanthin (2.02), lutein (0.86), sucrose (5.38), palmitic acid (1.66), fucoxanthin (1.22), stearic acid (1.78), isoleucine (0.94), violaxanthin (0.98), zeaxanthin (1.1), cholesterol (0.7), leucine (1.7), glucose (3.5), proline (4.1), myo-inositol (3.62) and glycine (3.54). Data presented are based on the mean of six replicates each of the solvent systems (acetone, chloroform, hexane, methanol, 70% ethanol) \(\pm\) standard deviation (SD). exhibited better free radical scavenging activity in comparison to the other solvent systems. This contradictory result on scavenging activity may vary the metabolites' yield due to different microalgae growth conditions, origin of the strains, methods during microalgal cultivation and harvesting, as well as temperature and time for extraction [20; 33]. The results of DPPH radical scavenging activity showed almost the same par with TPC for the different solvent extractions (Figure 4B). It was observed that acetone possessed high total phenolic content with 30.79 mg GAE/g dw extract compared to chloroform with 25.41 mg GAE/g dw extract. When comparing 70% ethanol and methanol extracts of _C. calcitrans_, 70% ethanol contained higher TPC with a value of 19.34 mg GAE/g dw extract. Hexane extract had the lowest TPC value of 9.95 mg GAE/g dw extract compared to the other solvent extractions. Statistically, there were significant differences (\(P<0.05\)) in all solvent systems. In addition to having activity for DPPH free radical scavenging and the presence of phenolic compounds, the results also demonstrated that the extracts of _C. calcitrans_ showed the inhibitory effects of NO, as shown in Figure 4C. The IC50 values of some of the extracts indicated higher activity than cucurmin. However, unlike the results of TPC and DPPH scavenging activity, the chloroform, methanol, acetone and 70% ethanol extracts exhibited stronger NO inhibitory activity with IC50 values of 3.46, 3.83, 15.35, 17.94 g/mL compared to the hexane extract with a IC50 value of 187.7 g/mL. There was no significant difference (\(P>0.05\)) between these four  
Figure 4: Total phenolic content (**A**), percentage of DPPH free radical scavenging activity (**B**), and NO inhibitory IC50 (**C**) of the diatom _Chuetocros calcitrans_. Values are the mean of 6 replicates \(\pm\) SD. Means with different letters indicate the significant differences (\(P<0.05\); \(n=6\)) differences. IC50 Quercetin = 4.73 g/mL. IC50 Curcumin = 6.10 g/mL. extracts but higher significant difference (\(P<0.05\)) for hexane extracts. The inhibition was not caused by the toxicity as the values of cell viability for all extracts were more than 80%.