Weak interactions between molecules have always been a particular concern in the field of chemistry. Almost all chemical processes involve the participation of weak interactions between molecules, especially in the fields of supramolecular self-assembly and enzyme catalysis, where weak interaction between molecules plays an irreplaceable role. Hydrogen bond and halogen bond are two common weak interactions between molecules. Similar to chemical bonds (covalent bonds), they have directionality and saturation. However, bond energy of them is much smaller than common chemical bonds, and the bond formation mechanism is also different from that of chemical bonds (covalent bonds). The formation of hydrogen bonds and halogen bonds involves electron donors and electron acceptors. The electron acceptor of the hydrogen bond is a positively charged hydrogen atom, while the electron acceptor in the halogen bond is an electronegative halogen atom. Scientists use quantum chemistry calculations and wave function analysis to fully study the nature of hydrogen bonds and halogen bonds.
Figure 1. Characterisation of 1:1 and 2:1 binding of (a) 1a' and (b) 1b' to chloride. Enthalpies, entropies and free energies of binding were calculated at the [SMD(CHCl3)-DLPNO-CCSD(T)/def 2-TZVP (ma-def 2-TZVP on Cl, I)//ωB97X-D3/def2-SVP (ma-def2-SVP on Cl, I)] level of theory. (Bickerton, L. E.; et al. 2020)
At Alfa Chemistry, our scientists are capable of conducting MP2 method, density functional theory, coupled-cluster singles and doubles method, atoms-in-molecules theory and molecular tailoring approach method. Our fast and high-quality services include the following:
1. MP2 method
Hydrogen bond and halogen bond are investigated by constructing their potential energy surfaces using computational quantum mechanics method, thereby performing calculation of weak interactions between molecules. Our calculation process using MP2 method is as follows:
- Build hydrogen and halogen bond models.
- Apply the formula to calculate the bond energy of hydrogen bond and halogen bond at the theoretical level of MP2/6-311++G (3d, 2p).
- Calculate the potential energy surface of the hydrogen bond and halogen bond system.
2. Density functional theory (DFT)-B3LYP
Alfa Chemistry supports the application of counterpoise (CP) correction to correct the Basis Set Superposition Error (BSSE), aiming to obtain more accurate interaction energy.
- Firstly, the structures of two independent molecules and complex molecules are established and optimized.
- We then use the optimized molecule as the initial structure, and B3LYP method is applied to calculate the single point energy of two independent molecules.
- Our scientists perform BSSE calculation and CP correction on complex molecules to validate the calculation.
- Finally, the results obtained are analyzed to get the final hydrogen bond energy and halogen bond energy.
3. Coupled-cluster singles and doubles (CCSD(T))
We apply CCSD(T)/jul-cc-pVTZ method to calculate the binding energy (BE), and use the high-order SAPT method (SAPT2+(3)δMP2 combined with aug-cc-pVTZ basis set) to conduct energy decomposition and obtain the binding energy.
- Atoms-in-molecules (AIM) theory
AIM theory uses the properties of the position of the bond critical point (BCP) of the hydrogen bond to investigate the characteristics of the hydrogen bond. This method has better accuracy than other prediction formulas based on hydrogen bond descriptors. We have developed formulas to fit intermolecular hydrogen bonds and predict internal hydrogen bonds.
- Molecular tailoring approach (MTA) method
MTA method calculates the internal hydrogen bond energy. At Alfa Chemistry, we combine the MTA method with empirical prediction methods based on descriptors such as BCP properties, vibration frequency changes, and hydrogen NMR chemical shift changes to predict hydrogen bond bonds and intramolecular halogen bonds.
Why Choose Us?
- With many years of experience in molecular calculations, we can select the most suitable method for the calculation of intramolecular/intermolecular hydrogen bonds and halogen bonds.
- We provide a variety of software and programs to achieve fast and accurate calculations.
Hydrogen bonds and halogen bonds calculation provides an effective way to optimize the chemical process. Our hydrogen bonds and halogen bonds calculation services remarkably reduce the cost, promote further experiments, and enhance the understanding of chemical process for customers worldwide. Our personalized and all-around services will satisfy your innovative study demands. If you are interested in our services, please don't hesitate to contact us. We are glad to cooperate with you and witness your success!
- Sinha, V.; et al. Accurate and rapid prediction of pKa of transition metal complexes: semiempirical quantum chemistry with a data-augmented approach. Physical Chemistry Chemical Physics. 2021, 23: 2557-2657.
- Bickerton, L. E.; et al. Transmembrane anion transport mediated by halogen bonding and hydrogen bonding triazole anionophores. Chemical Science. 2020, 11: 4722-4729.