Increase In Solution Viscosity Research Articles

Target-Triggered Ultrafast Chondroitin Gelation Enabled Power-Free and Point-of-Care Bioassays.

Point-of-care (POC) tests increasingly highlight the importance of portable, cost-effective, and visually quantitative detection of biomarkers. Herein, we developed a power-free and visual signal-readout POC sensor based on the target-triggered ultrafast gelation process. In the gelation process, the target triggered the cascade reaction catalyzed by oxidase and ferrous glycinate to produce carbon radicals that immediately initiated the rapid polymerization and cross-linking of acryloylated chondroitin sulfate and dimethylacrylamide. This highly efficient enzymatic polymerization process contributed to the ultrafast generation of chondroitin hydrogel within 1 min at 25 °C. The increase in viscosity of aqueous solution resulted from hydrogel formation was then visually measured according to the distance of solution migration on a tick-labeled pH test strip, which thus realized the quantification of a target. By utilizing glucose oxidase as an oxidase model during the gelation process, this POC sensor was successfully employed in the rapid quantitative detection of glucose without the need for any auxiliary instruments. Benefiting from the specificity and stability of the enzymatic polymerization reaction, the sensor exhibited excellent performance in the detection of glucose in clinical blood samples. Moreover, the sensor was further extended to uric acid detection and enabled accurate assay in clinical urine samples, which indicated the versatility and practicability of this sensor in the POC test.

Exploring the impact of cresols on aggregation characteristics of non-linear PEO-PPO-PEO block copolymers in aqueous solution

The present research investigates the intricate interplay between some industrially essential compounds, viz. 2-methylphenol (o-cresol, OC), 4-methylphenol (p-cresol, PC), 4-n-Butylphenol (BP) and non-linear ethylene oxide-propylene oxide (EO-PO) type block copolymers (Tetronics®) in aqueous solutions by employing an array of physico-chemical techniques. Each examined Tetronic® possesses 40% EO segments in its molecular structure. The study delves into the interaction and structural modifications that occur when cresols are doped into the copolymer solutions. The added cresols disrupt the hydrophilic-hydrophobic balance of Tetronics® depending on their hydrophobicities. The lowering of the cloud point (CP) is accompanied by a corresponding increase in solution viscosity. Doping of OC and PC has a dissimilar effect on viscosity compared to BP. The intermicellar interactions are adjudged to be probable cause of the unusual viscosity trend. Scattering techniques (DLS and SANS) confirm the morphology of aggregates. The results are interpreted in terms of H-bonding.

Preparation and overall water-splitting performance study of amorphous nickel-copper-phosphide

Hydrogen energy is one of the most important vehicles for energy development in China. One of the effective hydrogen production pathways is overall water-splitting, which is considered as one of the most promising technologies for large-scale hydrogen production. However, its stability, activity, and selectivity still need to be improved. Therefore, in this article, amorphous nickel-copper phosphide was prepared by solvothermal method. Increasing the concentration of ethylene glycol in the solvent makes the solution viscosity increase, which inhibits the nucleation process of the crystal and causes structural distortion, leading to complete amorphization of the nickel-copper phosphide. After the analysis of physical phase and electrocatalytic properties, it can be concluded that the performance of the catalyst is optimal when completely amorphous. When the current density is 10 mA·cm−2, the overpotential of HER and OER are 140.5 and 232.65 mV respectively, and the overall water-splitting overpotential is 1.6404 V. Theoretical calculations indicate that the amorphous phase can optimize the electronic structure, thereby endowing the catalyst with excellent overall water-splitting catalytic activity and stability. This article demonstrates that the formation of an amorphous phase increases the number of active sites on the catalyst, enhancing its catalytic activity, and provides an explanation for the mechanism behind the catalytic performance. This research provides a theoretical foundation for the development of hydrogen production through electrochemical water splitting and expands the design strategies for catalysts.

Structurally tuned polyamide membranes via the polyvinylpyrrolidone-modulated interfacial polymerization reaction for enhanced forward osmosis performance

Controllable interfacial polymerization (IP) reaction is an important strategy to fabricate high-performance polyamide (PA) thin-film composite (TFC) membranes. In this work, a new TFC membrane was successfully fabricated by incorporating polyvinylpyrrolidone (PVP) with different molecular weights (K15, K30 and K60) at different concentrations into the aqueous phase of IP process. Due to an increased solution viscosity and interaction between PVP and amine monomers, the lower diffusion rate of amine monomers resulted into a thin (the thinnest basal PA layer of approximately 30 nm) and smooth PA layer with a high crosslinking degree. Among, the optimum PVP K60–0.25 TFC membranes with the highest molecular weights and lower incorporating concentrations had a more positive effect on forward osmosis performance, which presented a pure water flux of 11.2 L m−2 h−1, 25 % higher, and a specific salt flux of 0.04 g L−1, 43 % lower than the original membrane. Our work provides a low-cost and simple approach to obtain high-performance TFC membrane with an improved trade-off effect, and helps to deeply understand the role played by additives in PA layer modulation.

Elevated water transport of polyamide nanofiltration membranes via aqueous organophosphorus mediated interfacial polymerization

As interfacial polymerization (IP) is a reaction-diffusion process, rational regulation of diamine diffusion rate is effective to heighten the nanofiltration (NF) performance of polyamide (PA) membranes. Herein, we propose an aqueous organophosphorus-regulated IP strategy that promotes the formation of thinner and moderately crosslinked films toward improved water transport. Two similar compounds tetrakis (hydroxymethyl) phosphonium chloride (THPC) and tetrakis (hydroxymethyl) phosphonium sulfate (THPS) were utilized as functional additives to physically interact with piperazine via hydrogen bonding and thus retard piperazine diffusion rate during an IP process. The resultant polyamide membranes have been analyzed in terms of surface morphologies, chemical structures, hydrophilicity, and separation performance in detail. Surface temperature monitoring results revealed that heat release from regulated IP was less than that from unmodified IP, which was ascribed to retard monomer diffusion toward organic boundary in the presence of THPC or THPS. Molecular dynamics simulation further confirmed that the addition of THPC and THPS could efficiently decline the monomer diffusion rate via hydrogen bonds and increased solution viscosity. The modified PA membranes exhibited a reduced film thickness, moderate crosslinking degree, as well as increased average pore size, as revealed by a series of characterizations. Furthermore, the incorporation of THPC or THPS resulted the PA membranes with higher surface hydrophilicity and stronger negative charges. These improved physicochemical features synergically conferred a two-fold water permeance while maintaining a high divalent salt rejection (THPC-0.01: 18.3 L m-2 h−1 bar−1, 99.0 %, THPS-0.015: 20.2 L m−2 h−1 bar−1, 98 %). This aqueous organophosphorus regulated IP offers a simple and feasible approach to the preparation of low-transport-resistance PA membranes for enhanced NF performance.

The search for novel proline analogs for viscosity reduction and stabilization of highly concentrated monoclonal antibody solutions

Administration of monoclonal antibodies (mAbs) is currently focused on subcutaneous injection associated with increased patient adherence and reduced treatment cost, leading to sustainable healthcare. The main bottleneck is low volume that can be injected, requiring highly concentrated mAb solutions. The latter results in increased solution viscosity with pronounced mAb aggregation propensity because of intensive protein-protein interactions. Small molecule excipients have been proposed to restrict the protein-protein interactions, contributing to reduced viscosity. The aim of the study was to discover novel compounds that reduce the viscosity of highly concentrated mAb solution. First, the chemical space of proline analogs was explored and 35 compounds were determined. Viscosity measurements revealed that 18 proline analogs reduced the mAb solution viscosity similar to or more than proline. The compounds forming both electrostatic and hydrophobic interactions with mAb reduced the viscosity of the formulation more efficiently without detrimentally effecting mAb physical stability. A correlation between the level of interaction and viscosity-reducing effect was confirmed with molecular dynamic simulations. Structure rigidity of the compounds and aromaticity contributed to their viscosity-reducing effect, dependent on molecule size. The study results highlight the novel proline analogs as an effective approach in viscosity reduction in development of biopharmaceuticals for subcutaneous administration.

Hysteresis-Free and Bias-Stable Organic Transistors Fabricated by Dip-Coating with a Vertical-Phase-Separation Structure.

The morphology of organic films plays a pivotal role in determining the performance of transistor devices. While the dip-coating technique is capable of producing highly oriented organic films, it often encounters challenges such as limited coverage and the presence of defects in gaps between strips, adversely affecting device performance. In this study, we address these challenges by increasing solution viscosity through the incorporation of a substantial proportion of dielectric polymers, thereby enhancing the participation of additional molecules during the film formation process when pulled up. This method produces continuous and oriented organic films with a notable absence of gaps, significantly improving the carrier mobility of transistor devices by more than twofold. Importantly, the fabricated devices exhibit remarkable reliability, showing no hysteresis even after 200 cycles of measurement. Furthermore, the current and threshold voltages of the devices demonstrate exceptional stability, maintaining steady after 10,000 s of bias measurement. This approach provides a solution for the cost-effective and large-scale production of organic transistors, contributing significantly to the advancement of organic electronics.

Self-assembling and foaming properties of nonionic, cardanol-based surfactants in aqueous solutions

Surfactants from renewable sources have gained attention due to their potential as substituents for petroleum-based chemicals. In this sense, surfactants based on cardanol, a compound abundant in the cashew nutshell liquid, have been proposed as suitable candidates for this purpose. However, their application is hindered by the lack of quantitative and reliable information about their bulk and surface properties in aqueous solutions. In this work, for the first time, three nonionic, cardanol-derived surfactants (7EO, 9EO, and 12EO), with different number of ethylene oxide (EO) units in the polar headgroup, had their foaming performances analyzed and correlated with their respective surface (equilibrium and dynamic surface tension and surface viscoelasticity) and bulk (cloud points, critical micelle concentration, micelle diameter, and viscosity) properties. Depending on the EO number, different scenarios were seen. Solutions containing the 7EO surfactant were below the cloud point at room temperature and presented antifoaming properties. Aqueous solutions of 9EO and 12EO displayed foamability comparable to solutions prepared with a traditionally employed anionic surfactant (sodium dodecyl sulfate, SDS) at the same concentrations. The surfactant 12EO presented a rapid surface adsorption, thus favoring the formation of large amounts of foam during aeration. Furthermore, solutions of 9EO resulted in foams that were considerably more stable than the ones formed by SDS. Such an enhanced stability was attributed to the presence of elongated micelles, formed at the vicinity of the cloud point, that increased solution viscosity and delayed the liquid drainage in the foams. This surfactant also promoted the formation of highly viscoelastic surface films that contributed to foam stabilization. The obtained results suggest that these surfactants can be used in the formulation of new products with a more sustainable character and with improved properties. Moreover, they indicate the important interchange among bulk aggregates, surface properties and foam stability in aqueous surfactant systems.

Single-Walled (Magnetic) Carbon Nanotubes in a Pectin Matrix in the Design of an Allantoin Delivery System.

Single-walled carbon nanotubes (SWCNTs) outperform other materials due to their high conductivity, large specific surface area, and chemical resistance. They have numerous biomedical applications, including the magnetization of the SWCNT (mSWCNT). The drug loading and release properties of see-through pectin hydrogels doped with SWCNTs and mSWCNTs were evaluated in this study. The active molecule in the hydrogel structure is allantoin, and calcium chloride serves as a cross-linker. In addition to mixing, absorption, and swelling techniques, drug loading into carbon nanotubes was also been studied. To characterize the films, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, surface contact angle measurements, and opacity analysis were carried out. Apart from these, a rheological analysis was also carried out to examine the flow properties of the hydrogels. The study was also expanded to include N-(9-fluorenyl methoxycarbonyl)glycine-coated SWCNTs and mSWCNTs as additives to evaluate the efficiency of the drug-loading approach. Although the CNT additive was used at a 1:1000 weight ratio, it had a significant impact on the hydrogel properties. This effect, which was first observed in the thermal properties, was confirmed in rheological analyses by increasing solution viscosity. Additionally, rheological analysis and drug release profiles show that the type of additive causes a change in the matrix structure. According to TGA findings, even though SWCNTs and mSWCNTs were not coated more than 5%, the coating had a significant effect on drug release control. In addition to all findings, cell viability tests revealed that hydrogels with various additives could be used for visual wound monitoring, hyperthermia treatment, and allantoin release in wound treatment applications.

Ovalbumin amyloid-like fibrils/resveratrol self-assembling hydrogel: Preparation, characterization and formation mechanism

Food protein amyloid-like fibrils can significantly increase solution viscosity and promote the formation of entangled gel network due to its high stiffness and extreme aspect ratios. In this study, the ability of hydrophobic resveratrol (RES) deposited on the surface of the ovalbumin (OVA) amyloid-like fibrils (OVAF) to form a new self-assembling hydrogel was explored. The results showed that the simple mixing of RES and OVAF at pH 6.5 can successfully drive the formation of hybrid hydrogels through molecular self-assembly. The interactions between OVAF and RES were confirmed by the results of transmission electron microscope and fluorescence spectra. Non-covalent interactions including hydrophobic interactions and hydrogen bonds played an important role in the formation of the OVAF/RES self-assembling hydrogels. Furthermore, the OVAF/RES hydrogel showed a dense structure, high water holding capacity and remarkable rheological properties. The viscosity and storage modulus of the hybrid hydrogels increased with the increase of the RES and OVAF concentrations. After gastrointestinal digestion, some fibrous structures in the OVAF/RES hydrogels remained, which allowed for continuous release of RES. In summary, the OVAF/RES hybrid hydrogels with tunable structures, encapsulation ability and self-assembly characteristics are expected to be candidates for the delivery of hydrophobic active polyphenols in the food industry.

The characteristics and flocculation performance of hydrophobic association poly‐(3‐methacryloylamido propyl trimethyl ammonium chloride)

AbstractThe cationic polymer plays a crucial role in the flocculation process for solid–liquid separation. A hydrophobic‐associated cationic polymer was prepared through micellar free‐radical polymerization of cationic monomer 3‐methyl acrylamide propyl trimethyl ammonium chloride (MAPTAC) and hydrophobic monomer Poly (ethylene glycol) Octadecyl methacrylate (OEMA). The Poly‐MAPTAC‐OEMA can form network structure through intermolecular hydrophobic association in aqueous solution, which leads to the solution viscosity increase and the salt thickening property. The critical associating concentrations (CACs) of Poly‐MAPTAC‐OEMA are 5818–6992 mg/L in aqueous solution. For the diatomite suspensions, at the dosage above about 5 mg/L, the Poly‐MAPTAC‐OEMA can show higher flocculation efficiency compared with Poly‐MAPTAC. Specifically, at the dosage of 8 mg/L, the enhancement rate of sedimentation rate can reach 7.27%–32.31%. Meanwhile, the hydrophobic association mainly enhances the bridging ability but has no significant effect on the improvement of the electric neutralization ability of Poly‐MAPTAC‐OEMA. The flocculation performance‐enhanced dosage of Poly‐MAPTAC‐OEMA is obviously lower than the CAC of Poly‐MAPTAC‐OEMA; this may be because during the flocculation process, the Poly‐MAPTAC‐OEMA first absorb and deeply concentrate on the particle surface, and then the hydrophobic association and bridging enhancement of Poly‐MAPTAC‐OEMA can occur more easily on the particle surface.

Destabilization mechanism of acid aluminum phosphate solution: Effects of P/Al ratio, concentration and boron doping

The poor long-term stability of acid aluminum phosphate (AAP) solutions limits their industrial application. To understand its destabilization mechanism, the effects of phosphorus to aluminum ratio, concentration, and boron doping on the stability of the AAP solution are investigated. The destabilization mechanism involves polymerizing the aluminum phosphate species to form insoluble aluminum phosphate compounds. The solution concentration controls the polymerization kinetics, and reducing the concentration can improve the stability of the AAP solution. Boron introduction improves solution stability by reducing the number of active sites on the aluminum phosphate species available for polymerization and by increasing solution viscosity to restrict the movement of the aluminum phosphate species.

Effect of small molecular crowders on dynamics of kinesin molecular motors

Kinesin is a motor protein that can convert chemical energy of ATP hydrolysis into mechanical energy of moving processively on microtubules. Apart from the load and ATP concentration affecting the dynamics of the motor such as velocity, run length, dissociation rate, etc., the increase of solution viscosity by supplementing crowding agents of low molecular weight into the buffer can also affect the dynamics. Here, based on our proposed model for the chemomechanical coupling of the kinesin motor, a systematically theoretical study of the motor dynamics under the variation of the viscosity and load is presented. Both the load on the motor’s stalk and that on one of the two heads are considered. The theoretical results provide a consistent explanation of the available contradictory experimental results, with some showing that increasing viscosity decreases sensitively the velocity whereas others showing that increasing viscosity has little effect on the velocity. The theoretical results reproduce quantitatively the puzzling experimental data showing that under different directions of the load on the stalk, increasing viscosity has very different effects on the change of run length or dissociation rate. The theoretical results predict that in both the pure and crowded buffers the dependence of the run length on the load acting one of the two heads has very different feature from that on the load acting on the stalk.

ITC study on the interaction of some bile salts with tragacanth, Arabic, and guar gums with potential cholesterol-lowering ability.

The urge of designing new safe and natural functional foods to control blood lipids and dispensable without the need of physician supervision, has increased especially after the coming into effect of the recent EU Commission regulation 2022/860, that regulates the consumption of "red yeast rice," made by fermentation of rice with Monascus purpureus, and perceived as a natural functional food, due to a health risk for frail consumers. The results of the present work are a part of the systematic study we are carrying out of the binding ability of some soluble dietary fibers (SDF) from different natural sources toward selected bile salts (BS). Measurements were carried out by isothermal titration calorimetry (ITC) with the idea to shed light on the mechanism, if any, by which they show cholesterol-lowering activity. Epidemiological studies are sometimes conflicting and offer only hypothesis about the mechanism of action, the most accredited being the reduction of reabsorption of BS in the gut. Previous measurements done on negatively charged pectin and alginate, showed specific binding interaction with monomer NaDC for pectin and no interaction at all for alginate. Chitosan, positively charged and soluble only at low pH, in 100 mM acetate buffer at pH = 3 shows strong exothermic interactions with NaTC and NaTDC. Here we considered two plant exudates (Arabic gum and tragacanth gum) and guar gum, extracted from guar beans, and their interaction with the same bile salts. ITC measurements do not evidence specific interactions between gums and the studied BS, so that their cholesterol lowering ability, if any, is due to a different mechanism very probably bound to the viscosity increase. Moreover, the addition of NaC, the most abundant BS in the bile, at very low concentration (under the cmc) causes a structural change of the solution. The obtained results seem to corroborate the hypothesis that the cholesterol lowering activity is related to the increase in viscosity of guar solution favored by NaC, the major component of the bile.

Non-Covalent Interactions between Polyvinyl Chloride and Conjugated Polymers Enable Excellent Mechanical Properties and High Stability in Organic Solar Cells.

The incorporation of insulating polymers into conjugated polymers has been widely explored as a strategy to improve mechanical properties of flexible organic electronics. However, phase separation due to the immiscibility of these polymers has limited their effectiveness. In this study, we report the discovery of multiple non-covalent interactions that enhances the miscibility between insulating and conjugated polymers, resulting in improved mechanical properties. Specifically, we have added polyvinyl chloride (PVC) into the conjugated polymer PM6 and observed a significant increase in solution viscosity, indicative of favorable miscibility between these two polymers. This phenomenon has been rarely observed in other insulating/conjugated polymer composites. Thin films of PM6/PVC exhibit a much-improved crack-onset strain of 19.35 %, compared to 10.12 % for pristine PM6 films. Analysis reveal that a "cyclohexyl-like" structure formed through dipole-dipole interactions and hydrogen bonding between PVC and PM6 acted as a cross-linking site in the thin films, leading to improved mechanical properties. Moreover, PM6/PVC blend films have demonstrated excellent thermal and bending stability when applied as an electron donor in organic solar cells. These findings provide new insights into non-covalent interactions that can be utilized to enhance the properties of conjugated polymers and may have potential applications in flexible organic electronics.

Non‐Covalent Interactions between Polyvinyl Chloride and Conjugated Polymers Enable Excellent Mechanical Properties and High Stability in Organic Solar Cells

AbstractThe incorporation of insulating polymers into conjugated polymers has been widely explored as a strategy to improve mechanical properties of flexible organic electronics. However, phase separation due to the immiscibility of these polymers has limited their effectiveness. In this study, we report the discovery of multiple non‐covalent interactions that enhances the miscibility between insulating and conjugated polymers, resulting in improved mechanical properties. Specifically, we have added polyvinyl chloride (PVC) into the conjugated polymer PM6 and observed a significant increase in solution viscosity, indicative of favorable miscibility between these two polymers. This phenomenon has been rarely observed in other insulating/conjugated polymer composites. Thin films of PM6/PVC exhibit a much‐improved crack‐onset strain of 19.35 %, compared to 10.12 % for pristine PM6 films. Analysis reveal that a “cyclohexyl‐like” structure formed through dipole‐dipole interactions and hydrogen bonding between PVC and PM6 acted as a cross‐linking site in the thin films, leading to improved mechanical properties. Moreover, PM6/PVC blend films have demonstrated excellent thermal and bending stability when applied as an electron donor in organic solar cells. These findings provide new insights into non‐covalent interactions that can be utilized to enhance the properties of conjugated polymers and may have potential applications in flexible organic electronics.

Investigating the effects of solution viscosity on the stability and success rate of SECCM imaging

Due to the capability of simultaneously detecting the morphology and electrochemical information of samples and limiting the electrochemical reaction to a range approximately the size of the inner diameter of the pipette tip opening, scanning electrochemical cell microscopy (SECCM) enables higher precision local electrochemical measurement and surface material delivery and has been demonstrating unique advantages and broad application prospects. However, the meniscus droplet at the pipette tip of SECCM is equivalent to the opening radius of the pipette tip, which is usually tens of nanometers to hundreds of nanometers. The tiny meniscus droplet makes it susceptible to evaporation and crystallization, which increases the likelihood of the pipette colliding with the sample during the scanning process, resulting in the failure of scanning. In this paper, the influence of solution viscosity on the shape variation of the droplet at the tip during the movement of the pipette of SECCM was studied by finite element analysis. It is proved that the increase of solution viscosity is helpful in reducing the shape variation of the droplet at the tip during the movement of the pipette. Then scanning experiments were carried out using a flat Au substrate and Au substrates with rounded triangle and rounded rectangular convex structures as the samples. According to the experimental results, increasing solution viscosity improves scanning success rates and scanning quality and effectively lowers the MSE of the scanning results. The experimental results also show that SECCM can image at a higher speed when the solution's viscosity increases since the deformation of the droplet at the tip is less than with a typical solution.

Self-assembly modulation in star block copolymers by amphiphilic diol: A scattering insight

The present study offers a better insight into the alteration in the aggregation characteristics of ethylene oxide-propylene oxide (EO-PO)-based star block copolymers Tetronics® T1304 and T1307 induced by an amphiphilic diol Surfynol® 104 (hereafter C14 diol) using scattering (dynamic light scattering and small angle neutron scattering) with complementary physical property measurement viz. solution viscosity and cloud point (CP). It is the hydrophobic interaction that drives C14 diol molecules to penetrate inside copolymer micelles resulting in dehydration that lowered the CP and markedly increase in solution viscosity. Quite interestingly, initial lowering in CP is followed by sudden increase at higher level of solubilization. A significant increase in the apparent hydrodynamic diameter (Dh) divulges the growth of micelles which is equally supported by SANS measurements. The micellar parameters obtained from SANS analysis for T1304 and T1307 in the presence of C14 diol are described. The preferential partitioning of C14 diol into the copolymer micelles is the driving force for morphological changes from spherical to unilamellar vesicles. Also, the effect of temperature and NaCl was examined with the aim to observe various micellar transitions. The observed changes are clarified in terms of the hydrophobic interaction of C14 diol with Tetronic® micelles and HLB value of copolymers. The perception of C14 diol stabilised Tetronic® micelles is anticipated and correlated with optimal parameters obtained from computational simulation approach, providing a clear understanding of the correlation between the molecular orbital energy levels of Tetronic® and C14 diol. The present manuscript thus sheds light on C14 diol induced dehydration causing the micelle growth for both Tetronics® with varied hydrophobicity. Such hydrophobic diol-induced spherical to vesicular transition is observed for the first time in Tetronic®-diol mixed system.

DNA binding properties and cytotoxic effects of two double rollover cycloplatinated (II) complexes on cancer cell lines

In this study, the DNA binding capacity and cytotoxic effects of two double rollovers cycloplatinated complexes, [Pt2(μ-bpy-2H)(CF3COO)2(PPh3)2] and [Pt2(μ-bpy-2H)(I)2(PPh3)2] denoted as C1 and C2, respectively, were evaluated. By using UV–Visible spectroscopy the intrinsic binding constant (Kb) of C1 and C2 to DNA were determined as 2.9 × 105 M−1, and 5.4 × 105 M−1, respectively. Both the compounds were able to quench the fluorescence of ethidium bromide as a well known DNA intercalator. The calculated Stern-Volmer quenching constants (Ksv) for C1 and C2 were 3.5 × 103 M−1, and 1.2 × 104 M−1, respectively. Upon interaction of both the compounds with DNA, increase in viscosity of DNA solution were observed, further confiming the involvement of intercalative interactions between the complexes and DNA. The cytotoxic effects of complexes in compare to cisplatin were evaluated on different cancer cell lines by MTT assay. Interestingly, C2 showed the highest cytotoxicity on A2780R, a cisplatin resistant-cell line. Induction of apoptosis by the complexes was proved by flowcytometry. In all the studied cell lines, the extent of apoptosis induced by C2 was comparable or higher than cisplatin. Cisplatin induced more necrosis in all the cancer cell lines in the tested concentration.

Fabrication of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Fibers Using Centrifugal Fiber Spinning: Structure, Properties and Application Potential

Biobased and biodegradable polyhydroxyalkanoates (PHAs) are currently gaining momentum. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) polymer has a useful processing window for extrusion and injection molding of packaging, agricultural and fishery applications with required flexibility. Processing PHBHHx into fibers using electrospinning or centrifugal fiber spinning (CFS) can further broaden the application area, although CFS remains rather unexplored. In this study, PHBHHx fibers are centrifugally spun from 4-12 wt.% polymer/chloroform solutions. Beads and beads-on-a-string (BOAS) fibrous structures with an average diameter (ϕav) between 0.5 and 1.6 µm form at 4-8 wt.% polymer concentrations, while more continuous fibers (ϕav = 3.6-4.6 µm) with few beads form at 10-12 wt.% polymer concentrations. This change is correlated with increased solution viscosity and enhanced mechanical properties of the fiber mats (strength, stiffness and elongation values range between 1.2-9.4 MPa, 11-93 MPa, and 102-188%, respectively), though the crystallinity degree of the fibers remains constant (33.0-34.3%). In addition, PHBHHx fibers are shown to anneal at 160 °C in a hot press into 10-20 µm compact top-layers on PHBHHx film substrates. We conclude that CFS is a promising novel processing technique for the production of PHBHHx fibers with tunable morphology and properties. Subsequent thermal post-processing as a barrier or active substrate top-layer offers new application potential.