Spacer Length Research Articles

Comparative Evaluation of Sealing Ability of Moisture-tolerant Sealant and Glass Ionomer Sealant Using Stereomicroscope: An In Vitro Study.

The preventive benefits of pit and fissure sealants rely on their retention and sealing ability. The drawback of the conventional pit and fissure sealant is its poor retention due to the presence of moisture. Among the numerous pit and fissure sealants available, newer hydrophilic sealants are ideal for children. This study evaluates and compares the sealing ability of hydrophilic sealant Embrace WetBond with conventionally used glass ionomer sealant under a stereomicroscope. A total of 48 extracted human premolars were randomly divided into two groups (N = 24) and sealed with Embrace WetBond and GC Fuji VII as per manufacturers' instructions. Following thermocycling, the sectioned samples were evaluated for sealant penetration, unfilled space, and total length of fissure under a stereomicroscope at magnifications 2.5×, 4×, and 5×. The values were measured in microns and in various fissure types using the "ImageJ app" to measure the sealant penetrability and sealing ability. The data recorded were statistically evaluated. The penetrability of moisture-tolerant sealant was better (87.8 ± 10.7) compared to that of glass ionomer sealant (73.8 ± 15.5) (p = 0.002). Among the samples, U-type fissure patterns displayed greater penetrability (94.2 ± 6.2), whereas IK-type fissures revealed the lowest degree of penetrability (67.5 ± 7.3). Embrace WetBond is better than glass ionomer sealant with respect to penetrability and sealing ability under stereomicroscope hence recommended as a better sealant for pediatric clinical practice. Priscilla S, Shivashankarappa PG, Mohandoss S, et al. Comparative Evaluation of Sealing Ability of Moisture-tolerant Sealant and Glass Ionomer Sealant Using Stereomicroscope: An In Vitro Study. Int J Clin Pediatr Dent 2023;16(S-1):S67-S71.

Targeted large fragment deletion in plants using paired crRNAs with type I CRISPR system.

The CRISPR-Cas systems have been widely used as genome editing tools, with type II and V systems typically introducing small indels, and type I system mediating long-range deletions. However, the precision of type I systems for large fragment deletion is still remained to be optimized. Here, we developed a compact Cascade-Cas3 Dvu I-C system with Cas11c for plant genome editing. The Dvu I-C system was efficient to introduce controllable large fragment deletion up to at least 20 kb using paired crRNAs. The paired-crRNAs design also improved the controllability of deletions for the type I-E system. Dvu I-C system was sensitive to spacer length and mismatch, which was benefit for target specificity. In addition, we showed that the Dvu I-C system was efficient for generating stable transgenic lines in maize and rice with the editing efficiency up to 86.67%. Overall, Dvu I-C system we developed here is powerful for achieving controllable large fragment deletions.

Development and optimization of an in-house heterologous ELISA for detection of prednisolone drug in enzyme conjugates using spacers.

The introduction of spacers in coating steroid protein complexes and/or enzyme conjugates or immunogens is known to exert an influence on the sensitivity of steroid enzyme immunoassays. We investigated the impact of different homobifunctional spacers, ranging in atomic length from 3 to 10, on the sensitivity and specificity of prednisolone (PSL) enzyme immunoassays. In this study, four homo-bifunctional spacers, namely, carbohydrazide (CH), adipic acid dihydrazide (ADH), ethylene diamine (EDA), and urea (U), were incorporated between PSL and horseradish peroxidase (HRP) for preparing the enzyme conjugate with an aim to improve the sensitivity of the assay without compromising assay specificity. The assays were developed using these enzymes conjugated with antibodies raised against the PSL-21-HS-BSA immunogen. The sensitivity of the PSL assays after insertion of a bridge in the enzyme conjugate was 1.22 ng/mL, 0.59 ng/mL, 0.48 ng/mL, and 0.018 ng/mL with ADH, CH, EDA, and urea as a spacer, respectively. Among the four combinations, the PSL-21-HS-BSA-antibody with PSL-21-HS-U-HRP-enzyme conjugate gave better sensitivity and less cross-reaction. The percent recovery of PSL from the exogenously spiked human serum pools was in the range of 88.32%-102.50%. The intra and inter-assay CV% was< 8.46%. The PSL concentration was estimated in the serum samples of patients on PSL treatment. The serum PSL values obtained by this method correlated well with the commercially available kit (r2 = 0.98). The present study suggests that the nature of the spacer is related to assay sensitivity and not the spacer length.

Optimization of Process Parameters and Mechanical Properties of 316L Stainless Steel Block via Arc Additive Manufacturing

_ A study was conducted on the influence of current, spacing, current mode, and arc length on the formation of adjacent weld overlays in the 316L stainless steel block melting process using an extremely inert gas-shielded arc additive manufacturing method. The main defect observed during the formation of adjacent weld overlays was the incomplete fusion at the bottom. When using direct current, low current and short arc length could ensure the flatness of the overlay surface, and the fusion at the bottom of the adjacent weld overlays was improved, but the problem of incomplete fusion remained unresolved. When using pulse current, low current, short arc length, and continuous welding method could solve the problem of bottom fusion of adjacent weld overlays. Due to the thermal influence during the accumulation of adjacent weld overlays, the microstructure inside the weld overlay was uneven, and the crystallographic texture in the entire weld overlay was not formed. With a pulse current of 80 A, adjacent weld overlay spacing of 4.5 mm, travel speed of 200 mm/min, dry elongation of 10 mm, and arc length of 2 mm, the tensile strengths of the block in the X, Y, and Z directions were 568.5, 570.3, and 550.7 MPa, respectively, and the fracture elongations were 46%, 48%, and 43.3%, respectively. The strength and plasticity in the Z-direction were lower than those in the X and Y directions. Keywords 316L stainless steel; arc additive manufacturing; incomplete fusion; pulse current

IDeLUCS: a deep learning interactive tool for alignment-free clustering of DNA sequences.

We present an interactive Deep Learning-based software tool for Unsupervised Clustering of DNA Sequences (iDeLUCS), that detects genomic signatures and uses them to cluster DNA sequences, without the need for sequence alignment or taxonomic identifiers. iDeLUCS is scalable and user-friendly: its graphical user interface, with support for hardware acceleration, allows the practitioner to fine-tune the different hyper-parameters involved in the training process without requiring extensive knowledge of deep learning. The performance of iDeLUCS was evaluated on a diverse set of datasets: several real genomic datasets from organisms in kingdoms Animalia, Protista, Fungi, Bacteria, and Archaea, three datasets of viral genomes, a dataset of simulated metagenomic reads from microbial genomes, and multiple datasets of synthetic DNA sequences. The performance of iDeLUCS was compared to that of two classical clustering algorithms (k-means++ and GMM) and two clustering algorithms specialized in DNA sequences (MeShClust v3.0 and DeLUCS), using both intrinsic cluster evaluation metrics and external evaluation metrics. In terms of unsupervised clustering accuracy, iDeLUCS outperforms the two classical algorithms by an average of ∼20%, and the two specialized algorithms by an average of ∼12%, on the datasets of real DNA sequences analyzed. Overall, our results indicate that iDeLUCS is a robust clustering method suitable for the clustering of large and diverse datasets of unlabeled DNA sequences. iDeLUCS is available at https://github.com/Kari-Genomics-Lab/iDeLUCS under the terms of the MIT licence.

Design Rules for Binary Bisamide Gelators: toward Gels with Tailor-Made Structures and Properties.

This study intends to develop design rules for binary mixture of gelators that govern their assembly behavior and subsequently explore the impact of their supramolecular assembly patterns on the gels' rheological properties. To achieve these goals, nBA gelators with odd and even parities [n-methylene spacers between the amide groups (n = 5-10) and 17 carbons at each end] were blended at different ratios. Such bisamides with simple structures were selected to study because their different spacer lengths offer the possibility to have matching or non-matching hydrogen bonds. The results show that the assembly behavior of binary mixtures of bisamide gelators is the same in the solid and gel states. Binary mixtures of gelators, which only differ two methylene moieties in the spacer length, form compounds and co-assemble into fibers and sheets observed for (5BA)1(7BA)1 and (6BA)1(8BA)1 mixtures, respectively. Binary gelator mixtures of the same parity and a larger spacer length difference still lead to mixing for the odd parity couple (5BA)1(9BA)1), but to partial phase separation for the even parity mixture (6BA)1(10BA)1. Binary mixtures of gelators of different parities gave complete phase separation in the solid state, and self-sorted gels consisting of discrete fibers and sheets in the gels of (5BA)3(6BA)1 and (5BA)3(10BA)1. The even-even binary gels (20 wt %) consisting of co-assembled sheets show higher G' than odd-odd binary gels (20 wt %) consisting of co-assembled fibers. In general, the self-sorting of odd and even molecules into the separate primary structures results in a dramatic decrease of G' compared to the co-assembled gels (20 wt %), except for (5BA)1(9BA)1 gel (20 wt %). It might be due to larger woven spheres in (5BA)1(9BA)1 gel (20 wt %), which probably have a less entangled gel network.

Self-aggregation of cationic gemini surfactants with amide groups in the spacer and variable alkyl chain length

AbstractSynthesis, aggregation parameters and antimicrobial activity of novel cationic gemini surfactants with two amide groups in gemini spacer structure and a variable number of carbon atoms in alkyl tails ranging from 12 to 15 are reported. The critical micelle concentration of gemini surfactants was determined using surface tension and electrical conductivity methods. The cmc values were found in the range 0.83 to 0.06 mM. The interfacial area, micelle ionisation degree and the Gibbs free energy per molecule and alkyl chain were calculated from the surface tension and conductivity curves. Particle size analysis using the dynamic light scattering method confirmed the formation of small spherical micelles 6–7 nm large in size for gemini surfactants with 12 and 13 carbon atoms in the alkyl chain. A large size above 50 nm was found for the aggregates composed of long-chain gemini molecules with 14 and 15 carbon atoms. The zeta potential of gemini surfactants shows a continuous increase with the increasing alkyl chain length. Micelle aggregation number of gemini surfactants correlates well with the hydrodynamic size data. Small aggregation number values were found for short-chain gemini molecules with 12 and 13 carbon atoms in the alkyl chain. Long-chain gemini molecules with 14 and 15 carbon atoms exhibit aggregate growth represented by an increase in the aggregation number values while maintaining the spherical or spheroidal shape of micelles. The investigations of antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria and yeast indicate the increasing antimicrobial efficiency towards the short-chain surfactant with 12 carbon atoms in the alkyl chain. A possible cut-off effect presence is proposed to explain the dependence of antimicrobial activity on the surfactant alkyl tail length.

The Development and Investigation of the Diffusion-Stabilizing Burner with the Niche

The article presents the results of researches of the development and field tests in bench conditions of the microdiffusion stabilizer burner device of a rectangular slot type with a niche deepening along the entire perimeter of the burner. The air passes through a rectangular slot, gaseous fuel for combustion is supplied to the recirculation zone through a system of holes in the end wall of the stabilizer. On the side of the output end of the stabilizer, there is a niche deepening. As studies have shown, the niche deepening is an additional source of stabilization and intensification of torch burning. The experimental data and calculated dependences on the stabilization of the torch in the modes of “poor” disruption are obtained. It is shown that the stable operation of the burner on the lean limit expands – the coefficient of excess air increases with an increase in the width of the stabilizer, the diameter of the gas distribution holes, the coefficient of shading of the burner and air temperature, as well as with a decrease in the speed of the air flow. The research results showed that “rich” flame failure – flame failure with a gradual increase in gas flow occurs at air excess ratios less than unity. This ensures the reliable operation of the burner at the calculated operating modes with respect to the coefficient of excess air a = 1.15 – 6.0 and the air flow speed Wp = 12.0 m/s. A dependence was obtained that determines the influence of regime and design factors on the characteristics of a rich flare failure. The sustainability of the burner operation on the rich limit increases – the coefficient of excess air decreases, with an increase in the width of the stabilizer, the shading coefficient of the burner, air temperature and a decrease in air velocity. The experimental data and calculated dependences on the length of the combustion zone in the burner device are obtained. It was established that at the calculated coefficient of excess air a = 2.0 and higher coefficients, complete combustion of fuel occurs on the length of the combustion space X = 1000 mm. The relative length of the flame decreases when the shading coefficient of the burner and the air temperature increases. Measurements of harmful nitrogen oxides showed that the maximum content of oxides is observed at the coefficient of excess air a = 1.0 and is 125 mg/m3, which is less than the limit values which allowed by regulatory documents.

Three-dimensional laser scanning and numerical investigation on the influence of freeze-thaw and hang-wall mining on the instability of an open-pit slope

The instability of the open-pit slope and associated disasters of complex orebodies such as hanging-wall mining are the key problems to be solved urgently in the development of western resources. In this work, taking the hanging-wall mining in the open-pit mine of Hejing iron mine, for example, the disaster mechanism influenced by the coupling freeze-thaw and hanging-wall mining is systematically studied by 3D laser scanning and numerical simulation. Firstly, the rock mass structure information such as dip, dip angle, spacing, and equivalent trace length characteristics was obtained using 3D intelligent recognition technology. Then, numerical simulation is employed to reveal the influence of freeze-thaw and excavation sequences on the overall stability of the open-pit slope. The stress, displacement, plasticity zone, and maximum shear strain patterns are revealed in detail. The results show that the excavation engineering will lead to frequent increase and unloading of the internal stress of the rock mass, and the gradual increase of the goaf area will cause great damage to the rock mass. The slope failure mode is strongly impacted by freeze-thaw weathering and orebody excavation.

Rotational mechanism for stability analysis of slopes reinforced with piles

The installation of stabilizing piles has significant effects on the failure characteristics of slopes. A kinematical mechanism composed of rotational blocks is proposed for analyzing the stability of reinforced slopes. The plastic failure of the soil surrounding piles is considered by introducing velocity discontinuities on the pile plane. Objective functions are derived to determine the needed resisting forces or safety factors. Several example validations are conducted, and the effectiveness of the proposed method has been proven. The critical slip surface determined by the proposed method agrees well with the plastic region obtained through numerical analysis, particularly the plastic failure on the pile plane. Parametric studies indicate that local slope failure will occur when piles have close spacing and sufficient length. The optimal position of piles depends on the object to be determined, but it is generally recommended to place them between the toe and the middle-upper part of the slope. Additionally, the proposed mechanism is utilized to generate stability charts for quick evaluation of slope stability.

Heat Transfer and Friction Correlations for R134a With Offset Strip Fin Surface

Single phase heat transfer analysis of R134a refrigerant (liquid phase) has been carried out using Computational Fluid Dynamics (CFD) approach for offset strip fin. Colburn j factor and Fanning friction factor are predicted for offset strip fin. The correlations are developed at Reynolds number range of 100-15000. The effect of fin geometry (fin spacing, fin height, fin thickness and lance length) on the enhanced heat transfer and pressure drops were investigated. Colburn j factor and fanning friction factor f, correlations have proposed in terms Re and geometry parameters (h/s, t/s, t/l) for liquid refrigerant R134a in the present study. Two separate correlations have proposed for the low and high Re regions i.e. Between Re of 100-1000 and Re of 1000-15000. The numerical results are validated with experimental results, results are found in good agreement with experimental results. Variation is found less than 5%.

Prevalence of Fecal Incontinence in Normal Pressure Hydrocephalus: A Prospective Evaluation of 100 Patients

Normal pressure hydrocephalus (NPH) is a frequent disease in elderly patients. The main symptoms are gait disturbance, urine incontinence, and cognitive decline. Fecal urgency and incontinence are described as rare additional symptoms; however, no exact numbers are known. The aim of this study was to investigate the prevalence of fecal disturbances in NPH patients. Patients who presented to our department with confirmed diagnosis of NPH between January and December 2021 were interviewed prospectively about fecal function. Additionally, the extent of gait disturbance, cognitive decline, ventriculomegaly (EvansIndex), disproportionate enlarged subarachnoid space hydrocephalus (DESH presence), age, gender, and length of history were documented. In those who were operated with a hydrocephalus shunt postoperative development of stool incontinence was followed up. One hundred patients were evaluated (67 males, 33 females, medium age 77.5years, medium Evans Index: 0.37; 87 with disproportionate enlarged subarachnoid space hydrocephalus). 97 patients showed gait disturbance, 84 cognitive decline, and 87 bladder dysfunctions. 78 patients had the complete Hakim triad. 32 patients complained about fecal incontinence (20 with urge incontinence, 12 with complete incontinence). Twenty nine patients were shunted, of which 17 (57%) recovered completely, 9 (31%) partially, and 3 (10%) did not show any change. Fecal urgency and incontinence is a frequent finding in NPH (32%) and is essential for the quality of life. In the general population, fecal incontinence in elderly is found in up to 15%. The more than two-fold higher prevalence in NPH patients and the high percentage of postshunted improvement suggests that NPH causes often directly fecal disturbance.

Enhancement Design and Quasi‐Static Crushing Response of Novel Star‐Rhombus Honeycombs

To enhance the load‐bearing capacity and energy absorption capacity of the honeycomb, three kinds of star‐rhombus honeycombs (SRHs) are proposed by adding rhombic parts to the traditional star‐shaped honeycomb (TSH). The quasi‐static crushing responses of SRHs, including deformation mechanism, crushing stress, specific energy absorption (SEA), and Poisson's ratio, are studied based on the finite‐element (FE) method. The introduction of rhombic parts increases the number of plastic hinges, resulting in significantly higher crushing stress and SEA of the SRHs than that of the TSH. Among the SRHs, SRH‐A has the largest energy absorption, and the SEA value of SRH‐A is 98.2% higher than TSH. Then, parametric studies including wall thickness, cell wall angle, and spacing length between the vertices of the star‐shaped part and the rhombic part are carried out. The wall thickness and cell wall angle have the greatest influence on the crushing response of SRHs. Crushing stress and Poisson's ratio of SRHs can be adjusted by changing the wall thickness of the rhombic part. The configurations and geometric parameters of the rhombic part determine the Poisson's ratio of SRHs. This study provides effective guidance for designing star‐shaped honeycombs with enhanced load‐bearing capacity and energy absorption capacity.

Unveiling the Significance of Correlations in K-Space and Configuration Space for Drift Wave Turbulence in Tokamaks

Turbulence and transport phenomena play a crucial role in the confinement and stability of tokamak plasmas. Turbulent fluctuations in certain physical quantities, such as density or temperature fluctuations, can have a wide range of spatial scales, and understanding their correlation length is important for predicting and controlling the behavior of the plasma. The correlation length in the radial direction is identified as the critical length in real space. The dynamics in real space are of significant interest because transport in configuration space is primarily focused on them. When investigating transport caused by the E×B drift, the correlation length in real space represents the size of E×B whirls. It was numerically discovered that in drift wave turbulence, this length is inversely proportional to the normalized mode number of the fastest growing mode relative to the drift frequency. Considerable time was required before a proper analytical derivation of this condition was accomplished. Therefore, a connection has been established between phenomena occurring in real space and those occurring in k-space. Although accompanied by a turbulent spectrum in k-space with a substantial width, transport in real space is uniquely determined by the correlation length, allowing for accurate transport calculations through the dynamics of a single mode. Naturally, the dynamics are subject to nonlinear effects, with resonance broadening in frequency being the most significant nonlinear effect. Thus, mode number space is once again involved. Resonance broadening leads to the detuning of waves from particles, permitting a fluid treatment. It should be emphasized that the consideration here involves the total electric field, including the induction part, which becomes particularly important at higher beta plasmas.

Rational design of hairpin aptamer using intrinsic disorder mechanism to enhance sensitivity of aptamer folding-based electrochemical sensor for tobramycin

Folding-based electrochemical sensors employing electrode-immobilized, structure-switching aptamers represent a promising platform for rapid and selective detection of a variety of target analytes. Sensitivity of this class of sensors usually needs, however, to be improved through re-engineering the parent aptamer probes to undergo large conformation change upon target binding. Here, we report the development of a sensitive folding-based electrochemical sensor for tobramycin by re-engineering a DNA hairpin aptamer based on the concept of intrinsic disorder. Through incorporating disordered poly-thymine base spacers of various lengths into the loop of the parent hairpin aptamer, structure-switching aptamers exhibiting large target binding-induced conformation change for high signal sensitivity were re-engineered and an optimal hairpin aptamer containing a disordered spacer of 24 thymine bases (probe T24) was obtained. Folding-based electrochemical sensor modified with the probe T24 is sensitive for tobramycin with a maximum percent signal change of 767.1% for signal-saturating target concentration compared to 54.7% obtained using the parent aptamer. This sensor is also selective enough and applicable to detection of tobramycin in real samples with satisfactory results. We believe that the intrinsic disorder-based concept for re-engineering of structure-switching aptamers will help guide further design and application of highly sensitive aptamer folding-based electrochemical sensors.

Contact-Biocide TiO2 Surfaces by Surface-Initiated Atom Transfer Radical Polymerization with Chemically Stable Phosphonate Initiators.

Surface-initiated atom transfer radical polymerization (SI-ATRP) is a powerful tool for grafting functional polymers from metal surfaces. It depends on the immobilization of suitable initiators on the surface before radical polymerization. Herein, we report a set of bifunctional initiators bearing a phosphonic acid group for surface binding and a bromoisobutyramide moiety for SI-ATRP. We have analyzed the impact of the connecting alkyl spacers on the grafting process of (vinylbenzyl)trimethylammonium chloride (VBTAC) from titanium as a base material. The thickness of the grafted polymer increased with the spacer length of the initiator. We obtained chemically stable polycationic surfaces with high charge densities of ∼1016 N+/cm2 leading to efficient contact activity of modified titanium coupons against S. aureus. Notably, SI-ATRP grafting was efficient with VBTAC as a styrene-derived ammonium compound. Thus, the reported protocol avoids post-grafting quaternization with toxic alkylating reagents.

Validation of high-resolution satellite precipitation products over West Africa for rainfall monitoring and early warning

Satellite rainfall estimation products (SRPs) can help overcome the absence of rain gauge data to monitor rainfall-related risks and provide early warning. However, SRPs can be subject to several sources of errors and need to be validated before specific uses. In this study, a comprehensive validation of nine high spatial resolution SRPs (less than 10 km) was performed on monthly and dekadal time scales for the period 2001–2015 in West Africa. Both SRPs and reference data were remapped to a spatial resolution of 0.1 ° and the validation process was carried out on a grid scale, with 1,202 grids having at least one rain gauge throughout West Africa. Unconditional statistical metrics, such as mean absolute error, Pearson correlation, Kling-Gupta efficiency and relative bias, as well as the reproducibility of rainfall seasonality, were used to describe the agreement between SRPs and reference data. The PROMETHEE II multi-criteria decision analysis (MCDA) method was employed to rank SRPs by considering criteria encompassing both their intrinsic characteristics and performance metrics. Overall, IMERGv6-Final, MSWEPv2.2, RFE2, ARC2, and TAMSATv3.1, performed reasonably well, regardless of West African climate zones and rainy season period. Given the performances displayed by each of these SRPs, RFE2, ARC2, and MSWEPv2.2 would be suitable for drought monitoring. TAMSATv3.1, IMERGv6-Final, RFE2, ARC2, and MSWEPv2.2 are recommended for comprehensive basin water resources assessments. TAMSATv3.1 and MSWEPv2.2 would be of interest for the characterization of variability and long-term changes in precipitation. Finally, TAMSATv3.1, ARC2, and MSWEPv2.2, could be good alternatives to observed data as predictants in West African Regional Climate Outlook Forum (RCOF) process.

Kinetics of Polycycloaddition of Flexible α-Azide-ω-Alkynes Having Different Spacer Length.

Two flexible α-azide-ω-alkynes differing in the length of the hydrocarbon spacers (C8 vs. C12) between functional groups are synthesized. Their bulk polymerization kinetics is studied by differential scanning calorimetry (DSC) and parameterized with the aid of isoconversional methodology. The monomer with a shorter hydrocarbon spacer has somewhat greater reactivity. The effect is traced to a moderate increase in the effective value of the preexponential factor that arises from the fact that the respective monomer has a higher initial molar concentration in itself. The techniques of GPC and NMR provide additional kinetic and mechanistic insights into the studied reaction.

Synthesis, physical properties and cytotoxic assessment of ester-terminated gemini imidazolium surfactants

Ester-functionalized gemini imidazolium amphiphiles appended with different spacers have been developed. The desired structures were confirmed using mass spectroscopy and NMR techniques. With the help of tensiometry, conductometry, and spectrofluorometry, the investigated amphiphiles have been characterized for a variety of physical properties including Gibbs free energy of adsorption (ΔG0ads), C20 (surfactant concentration required to reduce the surface tension of the solvent by 20 mN•m−1), maximum surface excess (Ʈmax), critical micelle concentration (cmc), Gibbs free energy of the micellization (ΔG0mic) and Amin (minimum surface area/molecule). Dynamic light scattering (DLS) measurements were taken to examine aggregate size distribution and zeta potential. Thermal decomposition temperature of investigated amphiphiles was determined from thermogravimetric analysis (TGA) analysis. By using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, the toxicity of examined amphiphiles towards the C6 glioma cell line was assessed. The physicochemical study of these surfactants revealed that varying spacer length considerably affects the properties.

Self-Aggregation, Antimicrobial Activity and Cytotoxicity of Ester-Bonded Gemini Quaternary Ammonium Salts: The Role of the Spacer.

Five ester-bonded gemini quaternary ammonium surfactants C12-En-C12 (n = 2, 4, 6), with a flexible spacer group, and C12-Bm-C12 (m = 1, 2), with rigid benzene spacers, were synthesized via a two-step reaction and analyzed. Furthermore, the effects of the spacer structure, spacer length and polymerization degree on the self-aggregation, antimicrobial activity and cytotoxicity of C12-En-C12 and C12-Bm-C12 and their corresponding monomer N-dodecyl-N,N,N-trimethyl ammonium chloride DTAC were investigated. The results showed that C12-En-C12 and C12-Bm-C12 had markedly lower critical micellar concentration (CMC) values and lower surface tension than DTAC. Moreover, the CMC values of C12-En-C12 and C12-Bm-C12 decreased with increasing spacer length. In the case of equivalent chain length, the rigidity and steric hindrance of phenylene and 1,4-benzenediyl resulted in larger CMC values for C12-Bm-C12 than for C12-En-C12. The antibacterial ability of C12-En-C12 and C12-Bm-C12 was assessed using Escherichia coli (E. coli) and Staphylococcus albus (S. aureus) based on minimum inhibitory concentrations (MICs). Furthermore, C12-En-C12 and C12-Bm-C12 exhibited higher antimicrobial activity than DTAC and had stronger function toward S. aureus than E. coli. The antimicrobial activity was enhanced by increasing the spacer chain length and decreased with the increased rigidity of the spacers. The cytotoxic effects of C12-En-C12 and C12-Bm-C12 in cultured Hela cells were evaluated by the standard CCK8 method based on half-maximal inhibitory concentration (IC50). The cytotoxicity of C12-En-C12 and C12-Bm-C12 was significantly lower than alkanediyl-α,ω-bis(dimethyldodecylammonium) bromide surfactants and DTAC. The spacer structure and the spacer length could induce significant cytotoxic effects on Hela cells. These findings indicate that the five ester-bonded GQASs have stronger antibacterial activity and lower toxicity profile, and thus can be used in the pharmaceutical industry.