Simulation method for predicting directional arrangement of chiral influence surfactant on fluid interface

Abstract

The invention discloses a simulation method for predicting directional arrangement of a chiral influence surfactant on a fluid interface. Aiming at a surfactant with a hydrophilic head group containing four chiral centers, a molecular model library covering all chiral configurations is established, and the oriented arrangement rule of different chiral surfactants on a gas-liquid interface is studied by molecular dynamics simulation. According to the method, head group spatial configuration characteristics, hydrogen bond number distribution rules and radial distribution function peak value changes of different chiral molecules are systematically analyzed, and a regulation and control mechanism of chiral configuration on surfactant molecular interface orientation and intermolecular interaction is clarified. In combination with a chemical flooding tertiary oil recovery technology, the mechanism can optimize the interfacial behavior of the surfactant in an oil reservoir through chiral design, and a new theoretical and technical approach is provided for improving the crude oil recovery rate.

Description

Technical Field

[0001] This invention belongs to the field of colloidal interface technology, specifically relating to a simulation method for predicting the influence of chirality on the directional distribution of surfactants at fluid interfaces. Background Technology

[0002] With the increasing depletion of petroleum resources, biomass-based surfactants have become an important development direction for green chemical flooding in tertiary oil recovery due to their renewability and environmental friendliness. Biomass-based surfactants, derived from natural chiral molecules such as glycosyl groups and amino acids, often contain multiple chiral centers. The spatial configuration differences of their chiral carbons can significantly alter hydroxyl orientation and hydrogen bond networks, thereby affecting interfacial adsorption structure and stability. This is both a structural characteristic that distinguishes them from petroleum-based products and a new challenge for regulating interfacial behavior.

[0003] While current research in surfactant molecular design has focused on hydrophobic chain modification and head group polarity regulation, it has severely neglected the influence of chiral spatial configuration on the directional arrangement of surfactant molecules at the interface. Traditional experimental methods struggle to observe the dynamic processes of molecular arrangement at the nanoscale in real time, and molecular dynamics simulations often overlook the regulatory mechanisms of chiral configuration on hydrogen bond networks and interfacial adsorption structures. Therefore, establishing a precise predictive method that correlates chiral configuration with interfacial directional arrangement is a key breakthrough in unlocking the interfacial regulation potential of biomass-based surfactants, providing crucial theoretical basis and technical support for the design of efficient and green enhanced oil recovery agents in the field of tertiary oil recovery. Summary of the Invention

[0004] To address the aforementioned technical bottlenecks, this invention provides a simulation method for predicting the influence of chiral configuration on the directional arrangement of surfactants at fluid interfaces. This method reveals the influence of chiral configuration on the arrangement of surfactant molecules at the fluid interface at the microscopic scale, elucidating the regulatory mechanism of chiral configuration on the interfacial arrangement and intermolecular interactions of surfactant molecules. Ultimately, it achieves accurate prediction of the interfacial behavior of chiral surfactants, providing a theoretical tool for the targeted design of highly efficient biomass-based oil displacement agents and promoting the improvement of tertiary oil recovery rates.

[0005] To achieve the above objectives, the technical solution adopted by the present invention includes:

[0006] This invention discloses a simulation method for predicting the influence of chirality on the directional distribution of surfactants at fluid interfaces, the specific steps of which include:

[0007] Step 1: Construct single-molecule structural models of surfactants with different chiral configurations as basic molecular units for constructing multi-molecule system models;

[0008] Step 2: Optimize the initial topology of the surfactant to obtain the charge parameters of the all-atomic structure, and generate the corresponding force field parameters from the Amber molecular force field;

[0009] Step 3: Construct a multi-molecule model of the air / surfactant / water system for simulation calculations;

[0010] Step 4: Perform energy minimization and NVT ensemble molecular dynamics simulations on the multi-molecular system model in sequence to determine the air / surfactant / water three-phase system model under steady state, so as to obtain the dynamic trajectory under equilibrium state;

[0011] Step 5: Based on the kinetic trajectory, calculate the head group configuration, number of hydrogen bonds, and radial distribution function of surfactants with different chiral configurations.

[0012] Preferably, the specific steps of step one of the method are as follows:

[0013] Using GaussView software, the geometric structures of surfactant molecules with different chiral configurations were constructed and saved as coordinate files in .gjf format.

[0014] Preferably, in the method, step two specifically comprises the following steps:

[0015] The initial configuration of the surfactant was geometrically optimized using the Gaussian 09 software package at the B3LYP / 6-31+g(d) computational level.

[0016] Using the Amber Tools 19 program's General Amber Force Field (GAFF), combined with the atomic charge of the confined electrostatic potential (RESP) calculated by the B3LYP / 6-311+g(d) method, the van der Waals parameters and bonding parameters of each atom can be directly obtained from the Amber molecular force field.

[0017] The potential energy function used in the Amber molecular force field is in the form of:

[0018]

[0019] Where K r K θ V n These are the force constants for the bond, bond angle, and dihedral angle, respectively; r eq and θ eq These represent the balanced bond length and bond angle, respectively; n is a multiple. ε is the phase angle; q is the atomic charge; ε0 is the vacuum permittivity; ε ij and σ ij is the Lennard-Jones parameter for the two-atom non-bonding term.

[0020] Preferably, in the method described in step three, the method for constructing the multi-molecule structure model is as follows:

[0021] Using Packmol software, system models of air / surfactant / water / surfactant / air were constructed for the surfactants and saved as .gro files.

[0022] Preferably, in the method, the molecular dynamics simulation method in step four is:

[0023] Using Gromacs software, the steepest descent method was employed to minimize the energy of the multi-molecule structure model, eliminating unreasonable contacts caused by model building. Subsequently, a 15ns NVT ensemble simulation was performed, and the dynamic trajectory of the last 5ns was collected for subsequent analysis.

[0024] Preferably, the method uses a V-rescale temperature control method to control the system temperature, with the system temperature selected as 298.15K and the coupling time constant set to 0.1ps.

[0025] Preferably, in the method, the geometric standard for the existence of hydrogen bonds in step five is that the distance between the donor (D) and the acceptor (A) is less than 0.35 nm and the angle HDA is less than 30°.

[0026] The expression for the radial distribution function is:

[0027]

[0028] Wherein, N represents the oxygen atoms (O) in the water within the range of nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant. W The total number of oxygen atoms in the aqueous phase, ρ is the number density of oxygen atoms in the aqueous phase, and r represents the number of oxygen atoms (O2) in the aqueous phase. W The distance from the oxygen atom to the nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant is given by g(r), which is the radial distribution function of the oxygen atom relative to the nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant.

[0029] Preferably, in the method, the surfactant is a sorbitol-based surfactant (SAAS-C12) with a hydrophilic head containing four chiral carbon atoms.

[0030] The beneficial effects of this invention are as follows:

[0031] This invention provides a simulation method for predicting the influence of chiral configuration on the directional arrangement of surfactant molecules at fluid interfaces. This method systematically reveals the influence of chiral configuration on the directional arrangement of surfactant molecules at fluid interfaces at the microscopic level, clarifies the unique mechanism of chirality as a key factor in the interfacial behavior of surfactants, elucidates the regulatory mechanism of chiral configuration on the interfacial adsorption structure and stability of chiral surfactants, provides a theoretical basis for accurately predicting the interfacial behavior of chiral surfactants, and lays a solid theoretical foundation for the targeted design of efficient biomass-based oil displacement agents. This powerfully promotes the advancement of tertiary oil recovery technology towards higher recovery rates and provides key technical support for achieving efficient crude oil extraction. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the sorbitol-based surfactant molecule (SAAS-C12) in an embodiment of the present invention;

[0033] Figure 2 This is a simulated structural model of the air / surfactant / water system in the embodiments of the present invention;

[0034] Figure 3 This is the density distribution curve of each component of the air / surfactant / water system along the z-axis in an embodiment of the present invention;

[0035] Figure 4 The following figures represent the ascent height of the hydrophilic head chain of molecules with different chiral configurations and the average number of hydrogen bonds formed between each hydroxyl group and water in the embodiments of the present invention: (A) RRRR; (B) RRRS; (C) RRSR; (D) RRSS; (E) RSRR; (F) RSRS; (G) RSRR; (H) RSSS.

[0036] Figure 5 This diagram illustrates the formation of intramolecular and intermolecular hydrogen bonds, as well as surfactant-water hydrogen bonds, in the SAAS-C12 molecule in this embodiment of the invention.

[0037] Figure 6 The average number of hydrogen bonds formed within molecules, between molecules, and between surfactant and water for molecules with different chiral configurations in the embodiments of the present invention.

[0038] Figure 7 This is the radial distribution function of each hydroxyl group and O atoms in water when the chiral configuration of the SAAS-C12 molecule is RRRR in the embodiments of the present invention. Detailed Implementation

[0039] Example

[0040] This experimental example involves the study of the interfacial behavior of a sorbitol-based surfactant with a hydrophilic head containing four chiral carbon atoms at the gas-liquid interface. Specifically, it includes the following steps:

[0041] Step 1: Construct single-molecule structural models of surfactants with different chiral configurations as the basic molecular units for constructing multi-molecule system models.

[0042] (1) Using GaussView software, the geometric structures of surfactant molecules with different chiral configurations were constructed and saved as coordinate files in .gjf format. The surfactant molecule structures are shown below. Figure 1 As shown, C2, C3, C4, and C5 are chiral carbon atoms, and their corresponding chirality is shown in Table 1.

[0043] Table 1. Chiral types of carbon atoms in SAAS-C12

[0044]

[0045]

[0046] Step 2: Optimize the initial topology of the surfactant to obtain the charge parameters of the all-atom structure. Generate the corresponding force field parameters from the Amber molecular force field. (1) Use the Gaussian 09 software package to perform geometric optimization on the initial configuration of surfactants with different chiral configurations at the B3LYP / 6-31+g(d) calculation level and save it as a coordinate file in .pdb format. The force field parameters used in the simulation are from the general Amber force field (GAFF) of the AmberTools19 program, and the confined electrostatic potential (RESP) atomic charge is calculated by the B3LYP / 6-311+g(d) method. The van der Waals parameters and bonding parameters of each atom are directly obtained from the Amber molecular force field. The surfactant molecule uses an all-atom model, and the water molecule uses the SPC / E three-point water model.

[0047] The potential energy function used in the Amber molecular force field is in the form of:

[0048]

[0049] Where K r K θ V n These are the force constants for the bond, bond angle, and dihedral angle, respectively; r eq and θ eq These represent the balanced bond length and bond angle, respectively; n is a multiple. ε is the phase angle; q is the atomic charge; ε0 is the vacuum permittivity; ε ij and σ ijis the Lennard-Jones parameter for the two-atom non-bonding term.

[0050] Step 3: Construct a multi-molecular system model of air / surfactant / water for simulation calculations.

[0051] (1) Import the coordinate file of the optimized surfactant molecules from step two and construct the initial system using Packmol software. Set the periodic box size to 5.0nm × 5.0nm × 40.0nm (x, y, and z directions, respectively), where the z-axis direction is the interface normal. In the central region of the box, based on the actual density of pure water corresponding to the simulation conditions, accurately place a water box composed of 6660 water molecules, with a size of 5.0nm × 5.0nm × 8.0nm. On the two outer sides of this water box (along the z-axis direction), 35 surfactant molecules are symmetrically arranged, for a total of 70. During the arrangement, ensure that the hydrophilic head group of each surfactant molecule is close to the adjacent water layer, while the two hydrophobic tail chains extend away from the water layer and into the air. Finally, obtain the air / surfactant / water / surfactant / air two-layer interface model, and save it as a .gro file, such as... Figure 2 As shown.

[0052] Step 4: Perform energy minimization and NVT ensemble molecular dynamics simulations sequentially on the multi-molecular system model to determine the air / surfactant / water three-phase system model under steady-state conditions, thereby obtaining the dynamic trajectory under equilibrium conditions.

[0053] (1) Using Gromacs 2018.1 software, with the .gro file obtained in step three as the input structure, the steepest descent method was used to minimize energy and eliminate unreasonable atomic contacts within the system. The system energy convergence criterion was less than 100 kJ / mol. In the calculation, the Verlet cutoff scheme was used to process the neighboring atom list. Long-range electrostatic interactions were calculated using the particle mesh (PME) method. The cutoff radius for nonbonded interactions was set to 1.4 nm, and van der Waals forces were calculated using the cutoff method.

[0054] (2) The structure file obtained by successfully converging the energy to less than 100 kJ / mol was used as the input file for a 15 ns NVT ensemble simulation. The dynamic trajectory in the last 5 ns was collected for subsequent analysis. The simulation settings were as follows: periodic boundary conditions were applied in the x, y, and z directions; the LINCS algorithm was used to constrain all bonds connected to hydrogen atoms; the simulation time step was 2 fs, and trajectory data was output every 500 steps. Temperature control was achieved using a V-rescale thermostat, with a target temperature of 298.15 K and a coupling time constant of 0.1 ps. The non-bonded interaction treatment was consistent with the energy minimization described above.

[0055] Step 5: Based on the described kinetic trajectory, calculate the head group configuration, number of hydrogen bonds, and radial distribution function of surfactants with different chiral configurations.

[0056] (1) The density of the system was analyzed. Using the `gmx density` command in Gromacs, the mass density distribution of water, surfactant, and the two hydrophobic tail chains (C1 and C2 chains) and one hydrophilic chain (N1-N2 chain) along the z-axis was obtained. Figure 3 As shown in the figure. The effectiveness of the simulation system is verified by comparing the density of the aqueous phase with that of actual water. At the same time, the relative positions of each component in space are analyzed based on the density distribution diagram: hydrophilic groups are mainly enriched in the aqueous phase region, while hydrophobic tail chains tend to extend towards the air.

[0057] (2) The rise height of each atom in the hydrophilic head group of surfactant molecules with different chiral configurations along the z-axis was analyzed, such as... Figure 4 As shown. First, the N, C, and O atoms on each hydrophilic head group chain were extracted using the `gmx make_ndx` command in Gromacs. The N1 atom was set as the reference point, and the perpendicular distance between each atom and the reference point in the z-direction was calculated. Then, the distance was calculated using the `gmx distance` command in Gromacs. It was found that the head group configurations of surfactant molecules with different chiral configurations are different, indicating the influence of chiral configuration on the SAAS-C12 interface arrangement. Simultaneously, the rising height of the chiral carbon atom is positively correlated with the rising height of the oxygen atom on the hydroxyl group it is connected to, suggesting that its interface arrangement may be affected by the hydrogen bonds formed between the hydroxyl groups and water.

[0058] (3) The number of hydrogen bonds formed between each hydroxyl group and water on surfactant molecules with different chiral configurations was analyzed, such as... Figure 4 The criteria for defining the existence of hydrogen bonds are that the distance between the donor (D) and acceptor (A) is less than 0.35 nm and the angle HDA is less than 30°. First, the hydroxyl groups were placed in separate index groups using the `gmx make_ndx` command in Gromacs, and then the values ​​were calculated using the `gmx hbond` command in Gromacs. The results show that the average number of hydrogen bonds formed by the oxygen atoms of hydroxyl groups with different chiral configurations differs significantly, and the number of hydrogen bonds is negatively correlated with the height of the oxygen atom.

[0059] Simultaneously, using the aforementioned commands, the number of intramolecular and intermolecular hydrogen bonds, as well as the number of surfactant-water hydrogen bonds, formed by surfactant molecules with different chiral configurations are analyzed. A schematic diagram of the hydrogen bonds is shown below. Figure 5 As shown, the analysis results are as follows: Figure 6As shown, there are significant differences in the number of various hydrogen bonds formed by surfactant molecules with different chiral configurations, further illustrating the influence of chiral configuration.

[0060] (4) Analyze the radial distribution function of each hydroxyl group on surfactant molecules with O atoms in water for different chiral configurations. The results were calculated using the gmx rdf command in Gromacs, as shown below. Figure 7 As shown. The expression for the radial distribution function is:

[0061]

[0062] Wherein, N represents the oxygen atoms (O) in the water within the range of nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant. W The total number of oxygen atoms in the aqueous phase, ρ is the number density of oxygen atoms in the aqueous phase, and r represents the number of oxygen atoms (O2) in the aqueous phase. W The distance from the oxygen atom to the nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant is given by g(r), which is the radial distribution function of the oxygen atom relative to the nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant.

[0063] Analysis revealed that the number of hydrogen bonds formed between each hydroxyl group and water, and the number of hydrogen bonds formed with O in water... W The peak value of the radial distribution function of atoms is positively correlated; that is, the more hydrogen bonds formed, the higher the peak value of the radial distribution function.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A simulation method for predicting the influence of chirality on the directional distribution of surfactants at fluid interfaces, characterized in that, The specific steps include: Step 1: Construct single-molecule structural models of surfactants with different chiral configurations as basic molecular units for constructing multi-molecule system models; Step 2: Optimize the initial topology of the surfactant to obtain the charge parameters of the all-atomic structure, and generate the corresponding force field parameters from the Amber molecular force field; Step 3: Construct a multi-molecule model of the air / surfactant / water system for simulation calculations; Step 4: Perform energy minimization and NVT ensemble molecular dynamics simulations on the multi-molecular system model in sequence to determine the air / surfactant / water three-phase system model under steady state, so as to obtain the dynamic trajectory under equilibrium state; Step 5: Based on the kinetic trajectory, calculate the head group configuration, number of hydrogen bonds, and radial distribution function of surfactants with different chiral configurations.

2. The simulation method for predicting the chiral influence of surfactants on the directional distribution at a fluid interface according to claim 1, characterized in that, The specific steps of step one are as follows: Using GaussView software, the geometric structures of surfactant molecules with different chiral configurations were constructed and saved as coordinate files in .gjf format.

3. The simulation method for predicting the chiral influence of surfactants on the directional distribution at a fluid interface according to claim 1, characterized in that, The specific steps for step two are as follows: The initial configuration of the surfactant was geometrically optimized using the Gaussian 09 software package at the B3LYP / 6-31+g(d) computational level. Using the Amber Tools 19 program's General Amber Force Field (GAFF), combined with the atomic charge of the confined electrostatic potential (RESP) calculated by the B3LYP / 6-311+g(d) method, the van der Waals parameters and bonding parameters of each atom can be directly obtained from the Amber molecular force field. The potential energy function used in the Amber molecular force field is in the form of: Where K r K θ 、V n These are the force constants for the bond, bond angle, and dihedral angle, respectively; r eq and θ eq These represent the balanced bond length and bond angle, respectively; n is a multiple. ε is the phase angle; q is the atomic charge; ε0 is the vacuum permittivity; ε ij and σ ij is the Lennard-Jones parameter for the two-atom non-bonding term.

4. The simulation method for predicting the chiral influence of surfactants on the directional arrangement of surfactants at a fluid interface according to claim 1, characterized in that, The method for constructing the multi-molecule system model described in step three is as follows: Using Packmol software, system models of air / surfactant / water / surfactant / air were constructed for the surfactants and saved as .gro files.

5. The simulation method for predicting the chiral influence of surfactants on the directional distribution at a fluid interface according to claim 1, characterized in that, The molecular dynamics simulation method described in step four is: Using Gromacs software, the steepest descent method was employed to minimize the energy of the multi-molecule system model, eliminating unreasonable contacts caused by model construction. A 15ns NVT ensemble simulation was then performed, and the dynamic trajectory of the last 5ns was collected for subsequent analysis.

6. The simulation method for predicting the chiral influence of surfactants on the directional arrangement of surfactants at a fluid interface according to claim 5, characterized in that, The V-rescale temperature control method was used to control the system temperature, which was set to 298.15K, and the coupling time constant was set to 0.1ps.

7. The simulation method for predicting the chiral influence of surfactants on the directional arrangement at a fluid interface according to claim 1, characterized in that, The geometric standard for the existence of hydrogen bonds described in step five is that the distance between the donor (D) and the acceptor (A) is less than 0.35 nm and the angle HDA is less than 30°. The expression for the radial distribution function is: Wherein, N represents the oxygen atoms (O) in the water within the range of nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant. W The total number of oxygen atoms in the aqueous phase, ρ is the number density of oxygen atoms in the aqueous phase, and r represents the number of oxygen atoms (O2) in the aqueous phase. W The distance from the nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant, g(r) represents the distance from the oxygen (O) atoms in the water. W Radial distribution function of nitrogen (N) and oxygen (O) atoms on the polar head group of the surfactant.

8. The simulation method for predicting the chiral influence of surfactants on the directional arrangement at a fluid interface according to claim 1, characterized in that, The surfactant is a sorbitol-based surfactant (SAAS-C12) with a hydrophilic head containing four chiral carbon atoms.

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