Thi Hai Huynh

Glucose, Galactose and Mannose

In this study, we could identify the anomeric configurations (i.e., α and β form) of glucose, galactose and mannose based on their mass spectrum and computational results at B3LYP/6-311+G(d,p) level of  theory based on the difference in intensity/activation energy between dehydration and cross-ring channels. The TS initial guesses were automatically generated, hence the computational process was accelerated with high success rate of the number of TS found (> 80% on average).

N-acetyl glucosamine and N-acetyl galactosamine

Following the same idea from our previous study of hexoses, in this study we also search TSs for N-acetyl glucosamine and N-acetyl galactose (HexNAcs) at the same level of theory (i.e., B3LYP/6-311+G(d,p)) as in hexoses. Unlike hexoses, the most challenge part of HexNAcs is the mechanistic search of dehydration channel which was suggested as the dominant loss fragment from mass spectrometry (MS). After many tested mechanisms, the most suitable mechanism of dehydration was not a single step in ring form as in hexoses, but a multiple-step mechanism in linear form of HexNAcs instead. The corresponding computational result of activation energy for this channel was aslo the lowest, thus agreed with experimental results. In addition, our proposed mechanism of dehydration and computational results can also explain why there was no difference in mass spectrum between α and β-anomers of the same HexNAc.

Glucosamine and Galactosamine

After obtaining better understanding from Hexoses and HexNAcs, we continued to work on glucosamine and galactosamine (HexNs). Unlike Hexoses, we could not distinguish the anomeric configurations of HexNs from experimental observation. Besides that, the major product was not dehydration as in HexNAcs, but the cross-ring channels instead. The mechanism of the dominant channel of cross-ring (0,2A cleavage) of HexNs was the same as in Hexs and HexNAcs; however, the mechanism of the other channel of cross-ring (0,3A/X cleavage) in glucosamine was slightly different from galactosamine. As a result, one can distinguish both considered HexNs based on these two channels. Moreover, our computational and mechanistic study well explained the experimental result. Unlike both Hexoses and HexNAcs, in this study the computation at B3LYP cheap level was not consistent to experimental results, hence we switched to MP2 level.  Besides that, in order to obtain high success rate for TSs search of the low-lying pathways of dissociation channels, we employed the climbing image nudge elastic band (CI-NEB) method. The more effective ways for TSs search will be applied and the effects of the chosen functional (either B3LYP or MP2) will be tested carefully in our next studies.

Publications

1.   C.-c. Chiu, H.T. Huynh, S.-T. Tsai, H.-Y. Lin, P.-J. Hsu, H.T. Phan, A. Karumanthra, H. Thompson, Y.-C. Lee, J.-L. Kuo, C.-K. Ni, “Toward Closing the Gap between Hexoses and N-Acetlyhexosamines: Experimental and Computational Studies on the Collision-Induced Dissociation of Hexosamines”, J Phys Chem A, 2019, 123, 6683-6700. 

DOI: 10.1021/acs.jpca.9b04143

2.   C.-c. Chiu, S.-T. Tsai, P.-J. Hsu, H.T. Huynh, J.-L. Chen, H.T. Phan, S.-P. Huang, H.-Y. Lin, J.-L. Kuo, C.-K. Ni, “Unexpected Dissociation Mechanism of Sodiated N-Acetylglucosamine and N-Acetylgalactosamine”, J Phys Chem A, 2019, 123, 3441-3453. 

DOI: 10.1021/acs.jpca.9b00934

3.  H.T. Huynh, H.T. Phan, P.J. Hsu, J.L. Chen, H.S. Nguan, S.-T. Tsai, T. Roongcharoen, C.Y. Liew, C.-K. Ni and J.-L. Kuo, “Collision-induced dissociation of sodiated glucose, galactose, and mannose, and the identification of anomeric configurations”, Phys Chem Chem Phys, 2018, 20, 19614-19624.

DOI: 10.1039/c8cp03753a

4.  J. A. Tan, J.-W. Li, C.-c. Chiu, H.-Y. Liao, H.T. Huynh, and J.-L. Kuo, “Tuning the Vibrational Coupling of H3O+ by Changing Its Solvation Environment”, Phys Chem Chem Phys, 2016, 18, 30721-30732

            DOI: 10.1039/C6CP06326H