Decrease In Surface Tension Research Articles

Functional, physicochemical properties of sodium carbonate-soluble polysaccharides from the bulbs and foliage leaves of yellow and red onion

The oil and water holding capacities, surface activity, and gelling ability of sodium carbonate-soluble pectin (NSP) extracted from the cell wall of bulb and foliage leaves of yellow and red onion (Allium cepa L.) were investigated and compared with those of commercial citrus pectin. Pectin chemical composition and properties its aqueous dispersions (e.g. the viscosity, pH) were studied. Homogalacturonan was the main component of the low-methoxylated pectin, with a small amount of rhamnogalacturonan I (more branched in the bulb pectin). Both the oil (35–41 g/gd.m.) and water (20 g/gd.m) holding capacities of NSP were higher than citrus pectin (1 and 17 g/gd.m, respectively). The surface activity of NSP was comparable (foliage leaves; surface tension (γ) decrease to 62 mN/m) or higher (bulb; γ decrease to 56 mN/m) than commercial pectin. The ability of NSP, especially extracted from the bulb, to form larger structures with increasing viscosity and neutralizing the negative surface charge, was significantly higher than that of citrus pectin. Therefore, NSP of bulb and foliage leaves may be useful as a carrier of oil- or water-soluble substances, a surface active agent, texturizer and gelling agent in the food, pharmaceutical, cosmetic and agricultural branches of industry.

Study on the relationship between surface tension and dilational visco‐elasticity with foam stability

AbstractThe replacement of fluorine‐free foam is imminent, but to date, no fluorine‐free foam has reached comparable fire extinguishing performance to AFFF (aqueous film forming foam). The stability of firefighting foam significantly affects its extinguishing performance. In order to better understand the influence of foam formulation physical properties on foam stability, we correlate the foam stability with surface tension and dilational visco‐elasticity based on the AFFF formulation. The results show that, the foam stability rising steadily with the decrease of surface tension, which indicates that low surface tension favors the improvement of foam stability. However, when at the studied highest surface tension, the foam stability elevates slightly instead, demonstrating the surface tension is not the determinant of foam stability. By contrast, the dilational visco‐elasticity shows a closer correlation with foam stability for the consistent tendency. In the case of constantly changing disturbance frequency, the interface dilational elasticity shows a trend of first increasing and then decreasing with the rise of disturbance frequency, whereas the interface dilational viscosity is completely opposite. Different relaxation processes show up for different samples. More attention can be paid to the regulation of dilational visco‐elasticity in the development of fluorine‐free foams, so as to improve their extinguishing ability.

Chitosan solutions and films properties obtained using electromagnetic-activated water

Purpose of research: to obtain chitosan films with improved performance properties by using water activated by an electromagnetic field of the radio frequency range as a solvent. Objects of research: water activated by an electromagnetic field of the radio frequency range (90-200 MHz), as well as chitosan solutions and films obtained using it. Methods of research: conductometry, potentiometry, densitometry, viscometry, turbidimetry, gravimetry, IR spectroscopy are used in the work. To determine the deformation and strength characteristics of the films, a universal testing machine with an electromechanical drive УТС-110M was used. Main results of research: The effect of pretreatment of water with an electromagnetic field of various frequencies on the properties of acetic acid (2 %) chitosan solutions in the concentration range of 0.1-2.0% has been studied. A decrease in surface tension by 2.0–5.2 % was found, as well as an increase in light transmission by 10-30 % and viscosity of solutions by 24-37 % at a chitosan concentration of 1.0-2.0 %. These effects are most pronounced for frequencies of 70, 90, 110 and 130 MHz. Films were prepared from 2 % chitosan solutions and their deformation-strength and sorption characteristics with respect to water vapor were determined. The greatest increase in tensile strength was found for chitosan films obtained from solutions prepared on water activated by an electromagnetic field with frequencies of 70 and 110 MHz (38 and 23 %, respectively). A decrease in the hygroscopicity of films and an increase in the intensity of bands in the IR spectra of films obtained using activated water were found.

Structure, orientation, and dynamics of per- and polyfluoroalkyl substance (PFAS) surfactants at the air-water interface: Molecular-level insights

HypothesisUnderstanding the intricate molecular-level details of toxic per- and polyfluoroalkyl substances (PFAS) partitioning to the air–water interface holds paramount importance in evaluating their fate and transport, as well as for finding safer alternatives for various applications, including aqueous film forming foams. The behavior of these substances at interfaces strongly depends on molecular architecture, chemistry, and concentration, which define molecular packing, self-assembly, interfacial diffusion, and the surface tension. SimulationsModeling of three PFAS surfactants, namely, longer-tail (perfluorooctanoate (PFOA)) and shorter-tail (perfluorobutanoate (PFBA) and 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy) propanoate (GenX)) has been conducted using atomistic molecular dynamics simulations. A systematic comparison between these representative PFAS of different sizes and structure reveals factors influencing their association behavior, mechanism of surface tension reduction, and interfacial mobility as a function of surface coverage. FindingsShorter-chain PFAS surfactants (GenX or PFBA) require lower surface coverage compared to longer chain (PFOA) PFAS to achieve the same decrease in surface tension. However, a higher concentration of GenX and PFBA is necessary in the bulk aqueous solution to achieve the same surface coverage as PFOA, due to their higher solubility in water. The PFAS molecular orientation and mobility at the interface are found to be vastly influenced by the length and architecture of the hydrophobic fluorocarbon tail. A significant ordering of the water dipole moment near the anionic headgroup is apparent at high surface concentration. A direct correlation is established between the PFAS interfacial properties and PFAS-PFAS, PFAS-counterion, and PFAS-water interactions.

Investigation of Sulfur Influence on the Atomization of Stainless Steels

In this study, the alloying of stainless steels with various sulfur contents is investigated to obtain steel powders with significantly reduced mean diameters without changing the operational parameters of the atomizing unit. The steels are produced in a VIM12 furnace and atomized on a VIGA‐1B setup with high‐pressure argon. The desired reduction in the mean diameter is attributed to the decrease in surface tension with increasing sulfur content, which is in good agreement with previous findings. A transition from a positive to a negative thermal gradient of the surface tension is observed, along with a shift to higher temperatures with increasing sulphur concentration. In addition, the chemical assessment of the powders reveals a lower evaporation of manganese and a reduced increase in nitrogen content with increasing sulfur content. The sphericity and flowability are not affected by the addition of sulfur. Viscosity and density measurements are also conducted to characterize the steels thoroughly. Scanning electron microscopy reveals the presence of manganese sulfide, which was submicron in size and well distributed. Iron sulfides, mostly attributed to hot shortness, were not observed, which was also confirmed by thermodynamic modeling using Thermo‐Calc software.

Experimental study of foam stability and interfacial behaviour of cellulose nanocrystals-enhanced C22-tailed zwitterionic betaine surfactant

The intrinsic thermodynamic instability of foam systems significantly constrains their effectiveness in enhancing oil and gas recovery from unconventional reservoirs. This study investigated the foam properties and interfacial rheological characteristics of the EDAB/CNC/APG system, analyzing the influence of various factors including temperature, pH, and inorganic salts. The results indicated that the optimal concentration ratio for CNC-surfactant system consists of 0.3 % EDAB, 1.5 % CNC and 0.5 % APG by mass fraction. In this system, the addition of CNC forms a three-dimensional network structure at the gas–liquid continuous interface, significantly extending the drainage half-life of the system. At elevated temperatures, the intense molecular thermal motion disrupts the interactions between CNC and EDAB. This disruption leads to a decrease in surface tension and the viscoelastic modulus of interfacial expansion, resulting in an increase of foam volume but a decline in foam drainage half-life. Foam performance and interfacial rheological characteristics are optimal under neutral pH conditions and manifest higher stability in alkaline conditions compared to acidic conditions. In highly mineralized reservoirs (≥5.0 % salt concentration), inorganic salt ions shield the attraction between CNC and oppositely charged surfactants. This shielding weakens the cross-linking within CNC-surfactant systems, altering the structure of the liquid film interface and causing a sharp decrease in foam half-life. The C22-tailed zwitterionic betaine surfactant EDAB, enhanced by CNC, provides a novel, environmentally friendly, efficient, and safe approach to the exploitation of complex, low-permeability oil and gas reservoirs.

Quantitative Structure Photovoltaic Properties Relationship of Coumarin Dyes Derived

The performance of an organic solar cell is strongly influenced by the structure of the photosensitizer. In this work, the open-circuit voltage (<I>V<SUB>OC</SUB></I>) and conversion efficiency (<i>η</i>) of a series of coumarin dyes are quantitatively related to the structure of nine coumarin derivatives. The Quantitative Structure Property Relationship (QSPR) is performed using the statistical method of multiple linear regression. In addition, descriptors determined from the ground state at the Cam_B3lyp/6-31G(d, p) level of theory and from the 2D structure of the molecules are mathematically related to the photovoltaic properties. These VOC and <i>η </i>models are accredited with very good statistical indicators (<I>R<sup>2</sup></I> = 0.906 and 0.918; Q<sub>cv</sub><sup>2</sup>= 0.845 and 0.849; S= 0.045 and 0.112; F = 14.524 and 16.846). These statistical indicators confirm the robustness and performance of the models developed. The results show that Voc improves with decreasing surface tension (<i>ts</i>) and increasing number of cycles (<i>cycle</i>). As for the conversion efficiency of light radiation into electrical energy, it is optimal when the light harvesting efficiency (<i>LHE<sub>th</sub></i>) and the excited state lifetime (<i>τ<sub>th</sub></i>) are high. In conclusion, these models have good predictive capabilities and can be used to predict and explain the open-circuit voltage and efficiency of coumarin derivatives that belong to the same field of application.

An experimental study on the wettability of nanofluids

The wettability of nanofluid is a key factor affecting oil recovery and fluid heat transfer. However, the traditional wettability measurement method consisting in determining the contact angle enables to assess the wettability at a solid–liquid contact point only and not within the continuous detection range. Therefore, in this work, a lateral friction detection system is used to continuously measure the wettability of hydroxylated multi-walled carbon nanotubes/deionized water (MWCNT-OH/DIW) nanofluids on polydimethylsiloxane surfaces. Specifically, MWCNT-OH/DIW nanofluids with various mass fractions are configured, and different surfactants are introduced to regulate the dispersion in deionized water. The results reveal that the surface tension and contact angle decrease simultaneously with the increase in MWCNT-OH/DIW mass fraction. Meanwhile, this change also causes an increase in the lateral friction at the nanofluid/PDMS interface. Furthermore, both sodium dodecyl sulfate and cetyltrimethylammonium bromide (CTAB) as surfactants can effectively reduce its surface tension. Notably, when CTAB is added, the maximum static friction (132.62 μN) exceeds that of SDS (113.13 μN). Therefore, the proposed method opens up new prospects in wettability detection of nanofluids.

Exploring the role of aspartic acid in modulating micellization behavior of cationic cetyltrimethylammonium bromide

The study of the interaction between aspartic acid (Asp) and cetyltrimethylammonium bromide (CTAB) reveals important information about surfactant organization, surface tension, critical micelle concentration (CMC), and surface pressure. Because of enhanced surfactant solubility brought about by electrostatic interactions, Asp’s ionization lowers CTAB’s CMC. The maximal surface excess concentration falls with increasing Asp concentration, suggesting competition for surface adsorption. The minimum occupied area per surfactant molecule increases at the same time, indicating changed surfactant activity at the interface between air and water. Higher CTAB concentrations are associated with a decrease in surface tension, which suggests that when Asp concentration rises, micelle formation would be promoted. Saturation effects, on the other hand, happen at high Asp concentrations and interfere with micelle formation. These tendencies are supported by surface pressure measurements, highlighting the significance of ionic interactions in micelle behavior.Moreover, surfactant structuring is impacted by the packing parameter decreasing as Asp concentration increases. The changing balance between hydrophilic and hydrophobic interactions within the CTAB/Asp micellar complexes is further explained by variations in degree of counterion dissociation of micelles (α) values. The complex dynamics of ionic interactions and their impact on surfactant behavior in CTAB/Asp systems are highlighted by these studies.

Enhancing Understanding of Siloxane Surface Properties and Functional Group Effects on Water Deoxygenation

The deoxygenation process in water used in well injection operations is an important matter to eliminate corrosion in the petroleum industry. This study used molecular dynamics simulations to understand the behavior of siloxane surfaces by studying the surface properties with two functional groups attached to the end of siloxane and their effect on the deoxygenation process. The simulations were performed using LAMMPS to characterize surface properties. Jmol software version 14 was used to generate siloxane chains with (8, 20, and 35) repeat units. We evaluated properties such as total energy, surface tension, and viscosity. Then, we used siloxane as a membrane to compare the efficiency of deoxygenation for both types of functional groups. The results indicated that longer chain lengths increased the total energy and viscosity while decreasing surface tension. Replacing methyl groups with trifluoromethyl (CF3) groups increased all the above mentioned properties in varying proportions. Trifluoromethyl (CF3) groups showed better removal efficiency than methyl (CH3) groups but allowed more water to pass. Furthermore, the simulations were run using the class II potential developed by Sun, Rigby, and others within an explicit-atom (EA) model. This force field is universally applicable to the atomistic simulation of polymers, inorganic small molecules, and common organic molecules.

Physical Properties of Cellulose Derivative-Based Edible Films Elaborated with Liposomes Encapsulating Grape Seed Tannins.

Combined use of edible films (EF) with nanoencapsulation systems could be an effective alternative for improving the films' physical properties and maintaining bioactive compounds' stability. This research work focuses on the combined use of EF of cellulose-derived biopolymers enriched with liposomes that encapsulate grape seed tannins and on the subsequent evaluation of the physical properties and wettability. Tannin-containing liposomal suspensions (TLS) showed 570.8 ± 6.0 nm particle size and 99% encapsulation efficiency. In vitro studies showed that the release of tannins from liposomes was slower than that of free tannins, reaching a maximum release of catechin of 0.13 ± 0.01%, epicatechin of 0.57 ± 0.01%, and gallic acid of 3.90 ± 0.001% over a 144 h period. Adding liposomes to biopolymer matrices resulted in significant decrease (p < 0.05) of density, surface tension, tensile strength, elongation percentage, and elastic modulus in comparison to the control, obtaining films with greater flexibility and lower breaking strength. Incorporating TLS into EF formulations resulted in partially wetting the hydrophobic surface, reducing adhesion and cohesion compared to EF without liposomes. Results indicate that the presence of liposomes improves films' physical and wettability properties, causing them to extend and not contract when applied to hydrophobic food surfaces.

Effect of oxygen in shielding gas on weldability in plasma-GMA hybrid welding process of high-tensile strength steel

This study aims to clarify the effect of oxygen in shielding gas on weldability in the plasma-GMA (Gas Metal Arc) hybrid welding process of high-tensile strength steel plates. The difference in keyhole profile and bead formation, when the GMA shielding gas was pure Ar, Ar + 2% O2, or Ar + 20% CO2, was investigated for plate thicknesses of 6 and 9 mm for the first time. It was found that the weld beads were in good condition for 6 mm thickness plates for all shielding gases, which implied that the window of welding conditions for this thickness is wide. In contrast, for 9 mm thickness plates, a fully penetrated weld bead was achieved only in Ar + 20% CO2, and weld bead penetration in Ar + 20% CO2 is higher than in pure Ar and Ar + 2% O2 in the same welding condition. Due to decreased surface tension caused by sufficiently increased oxygen absorbed into the weld pool, the keyhole diameter increased to penetrate the bottom side of the plate, and the depressing weld pool surface under GMA allowed the heat input from the GMA to be directly applied to a deeper position. Consequently, the plasma-GMA hybrid welding process with Ar + 20% CO2 achieved a complete penetration for a plate of 9 mm thickness, owing to the effects of both phenomena. It proved a potential to increase penetrability in welding thicker plates by controlling oxygen content in shielding gas of GMA adequately.

Quantitative characterization of bubble stability of foam concrete throughout extrusion process: From yield stress, viscosity and surface tension point of view

Foam concrete (FC) is suitable to be used as printing ink for drones in extreme environment because of its light weight, it can reduce the load of drones and improve printing efficiency. Furthermore, since the FC density and thermal insulation performance can be flexibly changed by changing the bubble content, it can be used to print functional gradient components and special-shaped insulation walls. The stability of bubbles is crucial as it directly impacts the performance of 3D printed FC (3DPFC). Here, we examined the bubble destabilization and deformation of FC throughout the mixing process, resting period prior to extrusion, and extrusion process based on three parameters, i.e., yield stress, viscosity, and surface tension. The results indicate that increasing the yield stress from 1406 Pa to 13379 Pa of the precursor leads to a decrease in bubble volume fraction after mixing from 38.26 % to 27.24 %, while increasing viscosity from 2.16 Pa s to 6.65 Pa s and decreasing surface tension from 72.4 mN/m to 33.5 mN/m are favorable for improving the sphericity of bubbles with the diameter between 300 and 800 μm in FC. In the resting stage, the yield stress of the interstitial paste is the primary factor controlling bubble stability. When the initial yield stress of the equivalent interstitial paste is 5212 Pa, the bubble volume fraction decreases by only 0.8 % within 60 min. During extrusion, high yield stress leading to bubble deformation and instability, whereas viscosity and pore solution surface tension act as sources of bubble compression resistance. There exists a suitable diameter interval for bubble pressure-bearing limit under different paste environment during extrusion.

Increase proportion of di‐rhamnolipids biosynthesized from Pseudomonas aeruginosa and evaluation of relationship between activity and di‐rhamnolipids proportion

AbstractRhamnolipids, simply divided into mono‐rhamnolipids and di‐rhamnolipids, their physicochemical properties are structure‐dependent. This study explored to increase the proportion of di‐rhamnolipids biosynthesized from Pseudomonas aeruginosa and evaluate the relationship between activity and di‐rhamnolipids proportions. P. aeruginosa SGrhlC was constructed by increasing the rhlC gene in P. aeruginosa SG. HPLC‐MS results indicated that SGrhlC produced more di‐rhamnolipids (62.32%) than that of the wild‐type strain SG (45.24%). Both the species and proportion of di‐rhamnolipids were increased, mainly Rha‐Rha‐C8‐C10 and Rha‐Rha‐C10‐C10. The rhamnolipids produced by SGrhlC was thermostable and salt‐tolerant. The SGrhlC rhamnolipids decreased surface tension of water to 27.0 mN/m with a critical micelle concentration (CMC) of 50 mg/L and emulsified crude oil with an emulsification index of 66.9 ± 1.5%. The SGrhlC rhamnolipids exhibited antimicrobial activity against Staphylococcus aureus and Cladosporium sp. with IC50 (half maximal inhibitory concentration) values less than 15 mg/L, and washed 73.02% ± 1.77% of oil from petroleum‐contaminated soil. Physicochemical activities of three bacterial rhamnolipids varied with their di‐rhamnolipids proportions. Results indicated that the higher proportions of di‐rhamnolipids were, the lower CMC, better surface activity and higher washing oil rate were, while the weaker emulsifying activity and lower antimicrobial activity were. The SGrhlC rhamnolipids showed better surface activity and a lower critical micelle concentration, which was superior for wetting, foaming, desorbing and dispersing. This study revealed that P. aeruginosa can be genetically regulated to biosynthesize rhamnolipids with specific structure. Perspectives of the customized biosynthesis and applications of rhamnolipids were also discussed.

From Agriculture to Clinics: Unlocking the Potential of Magnetized Water for Planetary and Human Health.

Magnetized water (MW) is a form of liquid water that has been exposed to a magnetic field to alter its hydrogen bonding structure, resulting in the formation of water molecule clusters of various sizes and configurations connected by hydrogen bonds. This magnetization process induces several changes in the physicochemical properties of water, such as increased pH, electrical conductivity, and dissolved oxygen content, as well as decreased surface tension, density, and evaporation temperature compared to untreated water. In this narrative review, we explore the effective utilization of MW in agriculture, where it has a well-established history of applications, and its potential for direct applications in the medical field, which are currently at the forefront of research. MW is one of the most promising innovations for facilitating the transition from unsustainable to sustainable agriculture, which is expected to yield positive human health outcomes by promoting the consumption of less processed foods and reducing resource consumption. In addition to these indirect effects on human health, preclinical research utilizing animal models has demonstrated that water magnetization exerts beneficial effects on diabetes, renal function, bone health, and fertility. These health benefits appear to stem from the ability of MW to increase the activity of antioxidant enzymes while decreasing lipid peroxidation and inflammatory markers. In terms of direct human applications, MW has been primarily studied in the fields of dentistry and dermatology. MW mouthrinse has consistently shown efficacy against Streptococcus mutans, with studies reporting comparable effects to chlorhexidine. In dermatology, the topical application of MW has demonstrated improvements in skin biophysical parameters, increased hair count and hair mass index, and promoted the healing of challenging wounds. Intriguingly, these effects on human skin seem to be mediated by local activation of autophagy, potentially through mild alkaline stress. In conclusion, this review underscores the promising role of MW in promoting a holistic approach to planetary and human health. Future studies should focus on standardizing the magnetization process, exploring the molecular mechanisms underlying MW-induced autophagy, and investigating the potential of MW as a complementary strategy for treating human diseases characterized by impaired autophagy.

Studies on wetting behaviour of pure and aqueous protic ionic liquids (PIL) solutions on different surfaces: ILphobicity to ILphilicity

In this study, the wetting behaviour of pure protic ionic liquids (PILs) and their mixture with water was studied at ambient conditions. Ethanolammonium acetate [EAAc], ethanolammonium butyrate [EABu], and ethanolammonium hexanoate [EAHx] were used as PILs for the wetting studies on various surfaces. The contact angle and wetting area of pure and mixed PIL solutions were determined on superhydrophobic, hydrophilic, and total wetting surfaces. Smaller alkyl chain PIL, ethanolammonium acetate (EAAc) displayed the highest contact angle (CA) of 141° on superhydrophobic surfaces. On hydrophilic polycarbonate (PC), shorter anionic chain PILs demonstrated CA < 90°, showing the ILphilic behaviour, and the variation of CA was PIL anionic chain length dependent. Total wetting glass exhibited the lowest CA for [EAAc], which increased with the PIL anionic chain. A binary mixture of PIL with water demonstrated unique wetting behaviour on the total wetting surface. The aqueous drops of EAHx exhibited a dynamic contact line on the glass surface, showing the greatest expansion in wetting area compared to drops of aqueous EAAc or aqueous EABu. This occurrence could be ascribed to the substantial decrease in water surface tension induced by the hydrophobic hexanoate anion, potentially leading to improved spreading characteristics.

Density and surface tension of liquid Al, V and their binary alloys measured by electromagnetic levitation

Both density and surface tension were systematically investigated over a wide temperature and compositional range for the liquid Al–V alloy system. The thermophysical properties were measured in an electromagnetic levitation device. A linear decrease in surface tension and density with increasing temperature was observed for every alloy composition investigated. Additionally, a decrease in density and surface tension was observed for increasing aluminum content among the different probed samples. This decrease is, a strong deviation from an ideal mixing behavior which was experienced for both properties. Different models, including variants of the well-established Butler model, were employed to better describe the compositional dependence of density and surface tension in the liquid Al–V system. The advantages and disadvantages were discussed for each model describing the measured thermophysical property data. Strong similarities were observed when comparing the mixing behavior and segregation effects of the investigated Al–V system with already established works for the liquid Al–Ti system. The results suggest that both vanadium and titanium show similar mixing behavior when alloyed with aluminum.

Influence of Tramp Elements on Surface Properties of Liquid Medium‐Carbon Steels

The transformation of the steel industry is inevitably linked to increased recycling rates of steel. However, end‐of‐life scrap is often contaminated with tramp elements like copper, molybdenum, and tin and while their influence on mechanical properties of steels is well described, their effect on nonmetallic inclusions remains largely unknown. Therefore, herein, two medium‐carbon steels are alloyed with up to 1 wt% of the listed tramp elements. The influence these elements have on the inclusion behavior in liquid steel is investigated using the sessile drop method in contact with alumina and zirconia as well as in steel/slag melting experiments to evaluate the formation and separation of new inclusions. Additionally, a semiempirical approach using CALPHAD to model the surface tension of steels with tramp elements is done. Copper and tin decrease the surface tension, while molybdenum increases the surface tension. It is demonstrated that most investigated alloys lead to a decrease of wetting angle as compared to the nonalloyed steels. The shown trends in the sessile drop experiments are lower contact angles with increased surface tension while a higher number of inclusions occurs with a decrease in surface tension. Thus, this study demonstrates that tramp elements affect the oxidic cleanness of steels.

Dual function surfactants for pharmaceutical formulations: The case of surface active and antibacterial 1-tolyl alkyl biguanide derivatives

One interesting field of research in the view of developing novel surfactants for pharmaceutical and cosmetic applications is the design of amphiphiles showing further bioactive properties in addition to those commonly displayed by surface-active compounds. We propose here the chemical synthesis, and characterization of 1-o-tolyl alkyl biguanide derivatives, having different lengths of the hydrocarbon chain (C3, C6, and C10), and showing surface active and antibacterial/disinfectant activities toward both Gram-positive and Gram-negative bacteria. Both surface active properties in terms of critical micelle concentration (CMC) and surface tension at CMC (γCMC), as well as the antimicrobial activity in terms of minimum inhibitory concentrations (MICs), were strongly dependent on the length of the hydrocarbon chain. Particularly, the C6 and C10 derivatives have a good ability to decrease surface tension (γCMC <40 mN/m) at low concentrations (CMC < 12 mM) and a satisfactory antibacterial effect (MIC values between 0.230 and 0.012 mM against S. aureus strains and between 0.910 and 0.190 against P.aeruginosa strains). Interestingly, these compounds showed a disinfectant activity at the tested concentrations that was comparable to that of the reference compound chlorhexidine digluconate. All these results support the possible use of these amphiphilic compounds as antibacterial agents and disinfectants in pharmaceutical or cosmetic formulations.

Effect of surfactants on lactate dehydrogenase aqueous solutions: A comparative study of poloxamer 188, polysorbate 20 and 80

The effect of three commonly used surfactants, poloxamer 188 (P188), polysorbate 20 and 80 (PS20 and PS80), on the stability of a model protein, lactate dehydrogenase (LDH), was compared in aqueous solutions. In the absence of a surfactant, protein solution revealed a gradual decrease in surface tension as a function of time. The addition of surfactant resulted in a rapid decrease in the surface tension. This suggested that the surface behavior was dictated by the surfactant. PS20 and PS80 were more effective than P188 in preventing LDH adsorption on the solution surface. The advantage of polysorbates over P188 was also evident from the higher LDH tetramer recovery after shaking (room temperature, 30 h), especially when the surfactants were used at concentrations ≤ 0.01% w/v. However, PS20 and PS80 accelerated protein unfolding during quiescent storage at 40 °C. Based on circular dichroism results, polysorbates perturbed the tertiary structure of LDH but not the secondary structure, while P188 did not impact the protein structure and stability. Polysorbates were more effective in stabilizing LDH against mechanical stress (shaking), but their adverse effects on protein conformational stability need to be carefully evaluated.