Integrating statistical and experimental protocols to model and design novel Gemini surfactants with promising critical micelle concentration and low environmental risk

QSPR for the prediction of critical micelle concentration of different classes of surfactants using machine learning algorithms

The determination of the critical micelle concentration (CMC) is a crucial factor when evaluating surfactants, making it an essential tool in studying the properties of surfactants in various industrial fields. In this present research, we assembled a comprehensive set of 593 different classes of surfactants including, anionic, cationic, nonionic, zwitterionic, and Gemini surfactants to establish a link between their molecular structure and the negative logarithmic value of critical micelle concentration (pCMC) utilizing quantitative structure-property relationship (QSPR) methodologies. Statistical analysis revealed that a set of 14 significant Mordred descriptors (SlogP, GATS6d, nAcid, GATS8dv, GATS4dv, PEOE_VSA11, GATS8d, ATS0p, GATS1d, MATS5p, GATS3d, NdssC, GATS6dv and EState_VSA4), along with temperature, served as appropriate inputs. Different machine learning methods, such as multiple linear regression (MLR), random forest regression (RFR), artificial neural network (ANN), and support vector regression (SVM), were employed in this study to build QSPR models. According to the statistical coefficients of QSPR models, SVR with Dragonfly hyperparameter optimization (SVR-DA) was the most accurate in predicting pCMC values, achieving (R2 = 0.9740, Q2 = 0.9739, r‾m2 = 0.9627, and Δrm2 = 0.0244) for the entire dataset.

The critical aggregation concentration of peptide surfactants is predictable from dynamic hydrophobic property

Peptide surfactants are a kind of newly emerged functional materials, which have a variety of applications such as building nanoarchitecture, stabilizing membrane proteins and controlling drug release. In the present study, we report the modelling and prediction of critical aggregation concentration (CAC), an important parameter that characterizes the self-assembling behaviour of peptide surfactants through the use of statistical modelling and quantitative structure-property relationship (QSPR) approaches. In order to accurately describe the structural and physicochemical properties of the highly flexible peptide molecules, a new method called molecular dynamics-based hydrophobic cross-field (MD-HCF) is proposed to capture both the hydrophobic profile and dynamic feature of 32 surface-activity, structure-known peptides. A number of statistical models are then developed using partial least squares (PLS) regression with or without improvement by genetic algorithm (GA). We demonstrate that MD-HCF performs much better than the widely used CODESSA method in both its predictability and interpretability. We also highlight the importance of dynamic hydrophobic property in accurate prediction and reasonable explanation of peptide self-assembling behaviour in solution, albeit which is exhaustive to compute compared with those derived directly from peptide static structure. To the best of our knowledge, this study is the first to computationally model and predict the self-assembling behaviour of peptide surfactants.

Enhanced aqueous solubility of naphthalene and pyrene by binary and ternary Gemini cationic and conventional nonionic surfactants

A systematic study has been carried out to get insight into the micellar behavior of Gemini cationic and conventional nonionic in their single as well as equimolar bi and ternary mixed state using the technique of tensiometry. The models proposed by Clint, Rubingh and Motomura et al. have been employed to interpret the formation of mixed micelles and find out synergism. The obtained experimental CMCs are lower than the ideal CMCs, indicating negative deviation from ideal behavior for all multi-component mixed micelles formation. The solubilization capacities of selected equimolar bi and ternary surfactant systems towards polycyclic aromatic hydrocarbons (PAHs), naphthalene and pyrene, have been evaluated from measurements of the molar solubilization ratio (MSR), the micelle-water partition coefficient (K(m)), the deviation ratio (R) and the free energy of solubilization (ΔG(s)(0)) of PAHs. The results show that the solubility of naphthalene and pyrene over that in water in case of Gemini cationic surfactant is dramatically enhanced by adding equimolar nonionic surfactant in both bi and ternary mixed surfactant systems. The studied equimolar ternary surfactant system shows higher solubilizing efficiency than Gemini cationic binary system but lower than their cationic-nonionic counterpart. In addition, the solubilizing power of multi-component mixed surfactants towards naphthalene and pyrene increases with increasing logK(ow) of PAHs. Certainly, the solubilization abilities of the selected surfactants not only depend on their structure and mixing effect but also associate with solubilizing microenvironment and chemical nature of organic solutes.

Ecotoxicity and biodegradability of antielectrostatic dicephalic cationic surfactants

Four series of dicephalic cationic surfactants, considered as new antielectrostatic agents have been investigated in order to establish their toxicity and biodegradability. Among them N,N-bis[3,3'-(dimethylamine)propyl]alkylamides, N,N-bis[3,3'-(dimethylamine)propyl]alkylamide dihydrochlorides, N,N-bis[3,3'-(trimethylammonio)propyl]alkylamide dibromides and N,N-bis[3,3'-(trimethylammonio)propyl]alkylamide dimethylsulphates with different hydrophobic chain length (n-C(9)H(19) to n-C(15)H(31)) and type of counterion (chloride, bromide and methylsulfate) have been studied. The inhibitory effect against microorganisms has been examined using model gram-positive and gram-negative bacteria, and yeasts. None of the tested surfactants have shown antimicrobial activity against gram-negative bacteria (Escherichia coli, Pseudomonas putida) and yeasts (Saccharomyces cerevisiae, Rhodotorula glutinis) at a concentration below 1000 μg mL(-1), however some of them were moderately active against gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis). The Microtox® test was successfully applied to measure EC(50) values of the studied dicephalic cationic surfactants. Their toxicity to Vibrio fischeri depended upon the alkanoyl chain length with the EC(50) values in a range of 2.6-980 mg L(-1). N,N-bis[3,3'-(dimethylamine)propyl]alkylamide dihydrochlorides 2a-b and N,N-bis[3,3'-(trimethylammonio)propyl]alkylamide dibromides 3a-b comprising n-decanoyl and n-dodecanoyl hydrophobic tails appeared to be the least toxic. Furthermore, the biodegradability under aerobic conditions of 2a-b, 3a-b was evaluated using OECD Method 301F. According to the obtained results 2a, 3a-3b can be considered as almost readily biodegradable and they are not expected to be persistent in the environment. Additionally, partial biodegradation was observed for 2b, indicating its possible biodegradation in wastewater treatment systems.