Anionic Biopolymers Research Articles

Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy of Staphylococcus aureus Biofilms.

Understanding the dynamics of biofilm formation and its elemental composition is crucial for developing effective strategies against biofilm-associated infections. In this study, we employed scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to investigate the morphological changes and elemental compositions of Staphylococcus aureus biofilms. SEM images revealed distinct stages of biofilm development, from initial aggregation to the formation of mature and aged biofilms. EDS analysis consistently showed elevated levels of sodium (Na), oxygen (O), and phosphorus (P) in the biofilm matrix, indicating its high negative charge and the presence of anionic biopolymers. The incorporation of extracellular DNA (eDNA) into the biofilm matrix, leading to significant retention of sodium ions, underscored the importance of electrostatic interactions in biofilm formation and stability. Our findings highlight the potential of EDS analysis in quantifying elemental compositions and elucidating the role of anionic biopolymers in biofilm development.

Facile Preconcentration of Cell-Free DNA in Human Plasma by Ion-Specific Poly Ionic Sorbents Featuring an Anion Exchange Mechanism.

The expanding horizon of diagnostic and therapeutic applications involving nucleic acids (NA) requires novel tools for purification, including minimal sample preparation. In this work, thin-film microextraction devices featuring five poly ionic sorbents were examined as anion exchange extraction phases for the rapid purification of NAs. Each sorbent is composed of a nonionic cross-linker and a methacrylate monomer containing a core tetra-alkyl ammonium moiety with an alkyl, anionic, or cationic residue. Extraction devices were produced through the application of the prepolymer sorbent mixture onto a functionalized nitinol metal support followed by photoinduced free-radical polymerization. The miniaturized extraction devices (10 mm × 3.5 mm) were directly immersed into aqueous samples to isolate NAs via electrostatic interactions with the polycation. The ammonium methacrylate (AMA) monomer containing a propyl trimethylammonium group (AMA-C3N(CH3)3) exhibited the highest affinity for DNA, with 80 ± 10% of DNA being isolated. Recovery of DNA from the sorbents required the introduction of ions in an aqueous solution to exchange the anionic biopolymer from the polycationic moiety. An investigation of three anion species revealed that the AMA-C3N(CH3)3 sorbent showed the highest recoveries, with the perchlorate anion producing a preconcentration factor of 4.36 ± 0.86 while requiring only 250 mM NaClO4. A directly compatible quantitative polymerase chain reaction assay was developed to quantify the recovery of spiked DNA with lengths of 830, 204, and 98 base pairs in heat-treated human plasma. The AMA-C3N(CH3)3 sorbent was uninhibited by the complex human plasma matrix and enabled high preconcentration factors for the spiked DNA at a biologically relevant concentration of 10 pg/mL. While Qiagen's circulating cell-free DNA MinElute extraction kit enabled higher preconcentration of all analytes, the methodology described in this work requires fewer steps, less user intervention, and minimal equipment requirements to isolate DNA, making it more amenable for high-throughput and low resource applications.

Charge-Patterned Disordered Peptides Tune Intracellular Phase Separation in Bacteria.

Subcellular phase-separated compartments, known as biomolecular condensates, play an important role in the spatiotemporal organization of cells. To understand the sequence-determinants of phase separation in bacteria, we engineered protein-based condensates in Escherichia coli using electrostatic interactions as the main driving force. Minimal cationic disordered peptides were used to supercharge negative, neutral, and positive globular model proteins, enabling their phase separation with anionic biomacromolecules in the cell. The phase behavior was governed by the interaction strength between the cationic proteins and anionic biopolymers, in addition to the protein concentration. The interaction strength primarily depended on the overall net charge of the protein, but the distribution of charge between the globular and disordered domains also had an impact. Notably, the protein charge distribution between domains could tune mesoscale attributes such as the size, number, and subcellular localization of condensates within E. coli cells. The length and charge density of the disordered peptides had significant effects on protein expression levels, ultimately influencing the formation of condensates. Taken together, charge-patterned disordered peptides provide a platform for understanding the molecular grammar underlying phase separation in bacteria.

Mechanical, durability, and microstructure of soft clay stabilised with anionic biopolymer

This study examines the impact of incorporating sodium alginate (SA) biopolymer into soft clay using the deep soil mixing method (DSM). SA-stabilised samples were tested under high-moisture (A) and low-moisture (B) conditions to assess their mechanical properties, chemical attributes, freeze-thaw resistance, and microstructure. Results indicate that samples cured under condition A outperformed those in condition B, primarily due to enhanced biopolymer gel formation. In both conditions, increasing the SA content and curing time led to higher peak strength, stiffness, and pH. The higher SA ratio improved ductility in condition A but increased brittleness in condition B. At the 28-day mark, a 1.0% SA ratio and a pH range of 8.2–8.4 were crucial for specimen strength increase. Freeze-thaw cycles had minimal impact, with a modest reduction in compressive strength observed. Scanning electron microscopy showed face-to-face bonding between clay particles and the gel-like materials due to electrostatic attraction. After 14 days, ramifications occurred around the core structure, and after 28 days, high agglomeration structures appeared, attributed to clay particle flocculation. Energy-dispersive X-ray (EDX) analysis indicated an increase in the Si/Al ratio boosted sample strength, while X-ray diffraction (XRD) results showed no crystalline phase in SA-stabilised samples due to encapsulating clay minerals with gel-like materials. In summary, this study suggests that SA biopolymer offers an eco-friendly, sustainable option for enhancing soft clay with DSM.

Liquid-Liquid Phase Separation (LLPS)-Driven Fibrilization of Amyloid-β Protein.

Amyloid-β [Aβ(1-40)] aggregation into a fibrillar network is one of the major hallmarks of Alzheimer's disease (AD). Recently, a few studies reported that polyphosphate (polyP), an anionic biopolymer that participates in various cellular physiological processes in humans, induces fibrilization in many amyloidogenic proteins [ 2020 Alzheimer's Disease Facts and Figures; John Wiley and Sons Inc., 2020; Tanzi, R. E.; Bertram, L. Cell 2005, 120, 545-555; Selkoe, D. J. Proc. Natl. Acad. Sci. U.S.A. 1995, 275, 630-631; and Rambaran, R. N.; Serpell, L. C. Prion 2008, 2, 112-117]. However, the role of polyP in Aβ(1-40) fibrilization and the underlying mechanism are unclear. In this study, we report experimental investigations on the role of polyP in the fibrilization kinetics of Aβ(1-40). It is found that polyP exhibits a dual effect depending upon the pH value. At pH = 7 (neutral), polyP inhibits amyloid fibrilization in a dose-dependent manner similar to negatively charged nanoparticles. On the contrary, at pH = 3 (acidic), polyP accelerates amyloid fibrilization kinetics via liquid-liquid phase separation (LLPS), wherein the protein-rich droplets contain mature fibrils. In the parameter space spanned by concentrations of Aβ(1-40) and polyP, a phase diagram is constructed to demark the domain where LLPS is observed at pH = 3. Characterization of the protein aggregates, secondary structure content in the aggregates, and cell viability studies in the presence of aggregates are discussed at both pH values. This study reveals that anionic biopolymers can modulate amyloid fibrilization kinetics, linked to neurodegenerative diseases, depending upon their local concentrations and pH.

Alginates as Green Flocculants for Metal Oxide Nanoparticles

AbstractFlocculation is used for the removal or separation of colloids, e.g. in water treatment and mineral processing. Alginates are linear, anionic biopolymers composed of mannuronic (M) and guluronic (G) acids. The relative amount and distribution of M and G impact the ion-binding and gel-forming properties of the polymer, but still no one has yet addressed the impact of alginate composition on flocculation of nanoparticles or mineral particles. Our results showed that the distribution of G was important for flocculation, especially when Ca2+ was used as activating ion. With Ce3+ as activating ion, the shape and size of flocs were affected by alginate acetylation. This work expands the knowledge about the flocculation behavior of alginates and demonstrates that both bacteria- and algae-derived alginates can be potential biodegradable flocculants of ultrafine particles for mineral processing industry.

Enhanced anticancer activity of siRNA and drug codelivered by anionic biopolymer: overcoming electrostatic repulsion.

Aim: To codeliver an anticancer drug (doxorubicin) and siRNA in the form of nanoparticles into CD44-overexpressing colon cancer cells (HT-29) using an anionic, amphiphilic biopolymer comprisingmodified hyaluronic acid (6-O-[3-hexadecyloxy-2-hydroxypropyl]-hyaluronic acid). Materials & methods: Characterization of nanoparticles was performed using dynamic light scattering, scanning electron microscopy, transmission electron microscopy, molecular docking, in vitro drug release and gel mobility assays. Detailed in vitro experiments, including a gene silencing study and western blot, were also performed. Results: A 69% knockdown of the target gene was observed, and western blot showed 5.7-fold downregulation of the target protein. The repulsive forces between siRNA and 6-O-(3-hexadecyloxy-2-hydroxypropyl)-hyaluronic acid were overcome by hydrogen bonding and hydrophobic interactions. Conclusion: The authors successfully codelivered a drug and siRNA by anionic vector.

Implication of organic solvents in the precipitation of γ-polyglutamic acid for application as a sustainable flocculating agent

γ-Polyglutamic (γ-PGA) acid is a homopolyamide composed of D- and l-glutamic acid units. It is an anionic biopolymer that has properties such as water solubility, non-toxicity, and biodegradability. γ-PGA, has many environmental applications, including use as an increment to the flocculation process in water treatment. This study evaluated the extraction and quantification of γ-PGA using different organic solvents, following by application as a sustainable flocculating agent. The results demonstrate that the use of methanol was able to precipitate 6.83 mg γ-PGA g−1 natto, followed by 5.44 and 4.24 mg γ-PGA g−1 natto, respectively for ethanol and acetone. The adoption of refrigeration (12 h) is an advantage to increase the yield of the biopolymer for methanol (46.27%), ethanol (52.25%), and acetone (14.25%) as a precipitating agent. The γ-PGA yield increased in overnight extraction with ethanol, enabling the use of ethanol as an alternative to methanol. Due to steric stabilization, it was observed that increasing the γ-PGA concentration resulted in a reduction in the flocculation rate. The highest flocculation rate (92.9%) was achieved at 10 mg L−1 of γ-PGA extracted with methanol, followed by acetone at 10 mg L−1 of γ-PGA (92.43%) and ethanol at 5 mg L−1 of γ-PGA (92.2%).

Elucidating the mechanism of polyphosphate granule consolidation in bacteria.

Synthesis of polyphosphate (polyP), an ancient anionic biopolymer composed of phosphoryl groups, is universally conserved in the kingdom of life. PolyP has been implicated in promoting fitness under starvation conditions in diverse bacteria, and it has been associated with pleiotropic effects on biofilm formation, motility, cell cycle and oxidative stress resistance. The molecular mechanisms underpinning these effects have traditionally been difficult to explain. In many bacteria, polyP chains come together to form membrane-less superstructures, termed polyP granules. Some bacterial species regulate the organization of these granules. Despite the critical role of polyP in starvation fitness, the composition of these structures and the mechanism(s) underpinning their organization are poorly understood. Our previous work identified polyP-granule associated proteins in opportunistic human pathogen Pseudomonas aeruginosa. However, the mechanism(s) of polyP granule maturation and subcellular organization are not well understood. To understand the fundamental properties of polyP granules, we use in vitro reconstitution to study a simplified multicomponent system of polyP, inorganic multivalent cations, the granule-associated protein AlgP, and DNA. Using light and fluorescence microscopy, our preliminary results suggest that these ternary systems can undergo heterotypic phase transitions. Additionally, the material properties of these condensates are tunable and sensitive to environmental conditions. Interestingly, we also observe that these condensates exhibit unique sub-structure. These studies will inform future efforts to understand the basis of polyP granule composition and consolidation, as well as its functional significance to cellular fitness during starvation stress in diverse bacteria.

Effect of Sulfation on the Conformational Dynamics of Dermatan Sulfate Glycosaminoglycan: A Gaussian Accelerated Molecular Dynamics Study.

Glycosaminoglycans (GAGs) are anionic biopolymers present on cell surfaces as a part of proteoglycans. The biological activities of GAGs depend on the sulfation pattern. In our study, we have considered three octadecasaccharide dermatan sulfate (DS) chains with increasing order of sulfation (dp6s, dp7s, and dp12s) to illuminate the role of sulfation on the GAG units and its chain conformation through 10 μs-long Gaussian accelerated molecular dynamics simulations. DS is composed of repeating disaccharide units of iduronic acid (IdoA) and N-acetylgalactosamine (N-GalNAc). Here, N-GalNAc is linked to IdoA via β(1-4), while IdoA is linked to N-GalNAc through α(1-3). With the increase in sulfation, the DS structure becomes more rigid and linear, as is evident from the distribution of root-mean-square deviations (RMSDs) and end-to-end distances. The tetrasaccharide linker region of the main chain shows a rigid conformation in terms of the glycosidic linkage. We have observed that upon sulfation (i.e., dp12s), the ring flip between two chair forms vanished for IdoA. The dynamic cross-correlation analysis reveals that the anticorrelation motions in dp12s are reduced significantly compared to dp6s or dp7s. An increase in sulfation generates relatively more stable hydrogen-bond networks, including water bridging with the neighboring monosaccharides. Despite the favorable linear structures of the GAG chains, our study also predicts few significant bendings related to the different puckering states, which may play a notable role in the function of the DS. The relation between the global conformation with the micro-level parameters such as puckering and water-mediated hydrogen bonds shapes the overall conformational space of GAGs. Overall, atomistic details of the DS chain provided in this study will help understand their functional and mechanical roles, besides developing new biomaterials.

Ecotoxicity of polyelectrolyte formulations in water and soil matrices.

Interpolyelectrolyte complexes (IPECs) formed by the interaction of two oppositely charged polyelectrolytes have been proposed as soil structure stabilizers. However, little is known about the environmental safety of IPECs. The goal of this study was to investigate the toxicity of a positively charged IPEC formed by two commercial polymers, namely the cationic biopolymer poly(diallyldimethylammonium chloride) (PDDA) and the anionic biopolymer lignohumate (LH), a humic-based plant growth promoter. Toxicity was assessed using cultures of the bacteria Escherichia coli, the ciliate Paramecium caudatum, mammalian (Bos taurus) spermatozoa in vitro, and three plant species (Sinapis alba, Raphanus sativus, and Triticum durum). The responses of test organisms were evaluated in contact with (1) polymer and water and (2) polymer and soil. In water, PDDA and IPEC were highly toxic to bacteria and ciliates at all concentrations and less toxic to mammalian cells. Higher plants were less sensitive to the polymers, and the toxicity progressively decreased in the order PDDA > IPEC > LH. In soil matrices; the phytotoxicity of PDDA and IPEC was found to be quite low, and none of the polymers was toxic to plants at concentrations that allowed the formation of polymeric soil crusts against erosion. This is because the toxicity of cationic polymers decreases as they enter the soil matrix and bind to organic matter and minerals.

An anionic biopolymer γ-polyglutamate enhanced the microbially induced carbonate precipitation for soil improvement: mechanical behaviors and underlying mechanism

An anionic biopolymer γ-polyglutamate enhanced the microbially induced carbonate precipitation for soil improvement: mechanical behaviors and underlying mechanism

Adsorption capacity of composite bio-modified geopolymer for multi-component heavy metal system: optimisation, equilibrium and kinetics study.

Industrialisation and urbanisation contribute greatly to the deposition of toxic waste and metalloids to the environment. Therefore, the use of efficient and eco-friendly materials such as geopolymers and biopolymers is essential for the adsorption of the toxic metals. The implementation of these low-cost sorbents has fascinated a great deal of interest owing to effectiveness, ease of operation, less environmental impact, etc. In this study, biocomposites were synthesised from bio-treatment of geopolymer (kaolin and palm oil fuel ash) using an anionic biopolymer. The biocomposites were utilised as biosorbent for removal of Cu, Fe and Zn in a multi-component system, with the process parameters optimised. FTIR and SEM/EDX outcomes clearly denoted the microporous framework of geopolymer structures and the presence of bio-molecules from the biopolymer. XRD and XRF techniques on the precursors described suitability for geopolymerisation due to the rich aluminate-silicate content. Based on response surface methodology, the adsorption capacities for Cu, Fe and Zn are 35.01mg/g, 45.175mg/g and 44.630mg/g at optimal conditions of pH (7.5), time (40.5min), metal ion concentration (80mg/l), biosorbent dosage (0.2g) and biopolymer concentration (0.75g in 50ml). The multi-component system was apt with the modified competitive Langmuir isotherm which described the homogeneity of the prominent sites of the biocomposites. Based on the adsorption kinetics, Cu was only dominated by the pseudo-first-order reaction (PFOR) while Fe and Zn were influenced by both PFOR and intra-particle diffusion processes. The result obtained from the synthesised biocomposites recommends application to actual wastewater systems.

Hybrid polymer/lipid vesicle synthesis: Association between cationic liposomes and lipoplexes with chondroitin sulfate

The association of cationic carriers with different anionic mucoadhesive biopolymers has been widely explored as an alternative to improve their delivery routes and specific targeting. This work presents a complete analysis of the association between chondroitin sulfate (CS) and cationic liposomes (CLs)/lipoplex (CL-pDNA). In this study, plasmid DNA (pDNA) was used as a genetic cargo for association with carriers. Firstly, we measured the stoichiometry of pseudo complexes and evaluated their colloidal properties, structural and morphological characteristics. Optimized CL-pDNA lipoplexes (positive z-potential) and CL-CS / CL-pDNA-CS (negative z-potential with CS mass ratio of 9% (w/w)) were further studied in detail. Small-angle X-ray scattering analysis and cryo-transmission electron microscopy micrographs revealed that the electrostatic interaction between CS and CL / CL-pDNA easily reorganized the lipid bilayers resulting in nanoscale uni/multilamellar vesicles. A high CS mass ratio (9% (w/w)) led to the reassembly of liposomal structure, wherein the pDNA was easily exchanged for CS chains, forming more than 50% of dense multilamellar vesicles. This data evidenced that the association between CS and CLs is not a conventional coating process since it generates complex and hybrid structures. We believe that these obtained colloidal data may be used in the future to investigate polymer-tailored nanocarriers and their production process. In brief, the colloidal study of hybrid structures may open interesting perspectives for developing novel carriers for drug and gene delivery applications.

Modeling the drying kinetics of alginate particles considering shrinkage

AbstractAlginate is an anionic and biodegradable biopolymer of natural occurrence, typically obtained from brown algae, being studied, and used in several applications in biomedicine and food industry by its low toxicity, low cost, and its gelification obtained by the addition of bivalent cations (Ca2+), besides being able to storage large amounts of liquid in its structure. In this context, this work aims to study the drying and shrinkage kinetics of this biomaterial. Microparticles of alginate were synthesized by the ionic gelification method using calcium chloride as reticulant agent. These microparticles were submitted to drying experiments conducted at 40, 50, and 60°C. A mathematical model which considers the microparticles moisture and volume change with time was proposed to model the drying process. Considering that the radius depends on time as Page and Sigmoid equations, two mathematical models were obtained. Both models were able to describe the experimental data and the kinetic parameters were adjusted as an exponential function of temperature (R2 = 0.99). The statistical analysis of the residues between calculated and experimental data indicates an adequate prediction, with Page's model fitting more accurately to the data sets. Akaike's test also indicated the coupled Page model as the most adequate.Practical ApplicationsThe results presented in this paper provide mathematical methods of modelling the hydration kinetics of alginate particles and fitting the parameters which can help understanding the mass transfer and shrinkage phenomena during drying. Those characteristics are essential in describing alginate particles due to the high amount of water that they contain. Describing the drying kinetics of such particles may help to project and optimize equipment involved in alginate particles production process.

Unique Actions of GABA Arising from Cytoplasmic Chloride Microdomains.

Developmental, cellular, and subcellular variations in the direction of neuronal Cl- currents elicited by GABAA receptor activation have been frequently reported. We found a corresponding variance in the GABAA receptor reversal potential (EGABA) for synapses originating from individual interneurons onto a single pyramidal cell. These findings suggest a similar heterogeneity in the cytoplasmic intracellular concentration of chloride ([Cl-]i) in individual dendrites. We determined [Cl-]i in the murine hippocampus and cerebral cortex of both sexes by (1) two-photon imaging of the Cl--sensitive, ratiometric fluorescent protein SuperClomeleon; (2) Fluorescence Lifetime IMaging (FLIM) of the Cl--sensitive fluorophore MEQ (6-methoxy-N-ethylquinolinium); and (3) electrophysiological measurements of EGABA by pressure application of GABA and RuBi-GABA uncaging. Fluorometric and electrophysiological estimates of local [Cl-]i were highly correlated. [Cl-]i microdomains persisted after pharmacological inhibition of cation-chloride cotransporters, but were progressively modified after inhibiting the polymerization of the anionic biopolymer actin. These methods collectively demonstrated stable [Cl-]i microdomains in individual neurons in vitro and in vivo and the role of immobile anions in its stability. Our results highlight the existence of functionally significant neuronal Cl- microdomains that modify the impact of GABAergic inputs.SIGNIFICANCE STATEMENT Microdomains of varying chloride concentrations in the neuronal cytoplasm are a predictable consequence of the inhomogeneous distribution of anionic polymers such as actin, tubulin, and nucleic acids. Here, we demonstrate the existence and stability of these microdomains, as well as the consequence for GABAergic synaptic signaling: each interneuron produces a postsynaptic GABAA response with a unique reversal potential. In individual hippocampal pyramidal cells, the range of GABAA reversal potentials evoked by stimulating different interneurons was >20 mV. Some interneurons generated postsynaptic responses in pyramidal cells that reversed at potentials beyond what would be considered purely inhibitory. Cytoplasmic chloride microdomains enable each pyramidal cell to maintain a compendium of unique postsynaptic responses to the activity of individual interneurons.

Anionic Biopolymer Assisted Preparation of MoO2@C Heterostructure Nanoparticles with Oxygen Vacancies for Ambient Electrocatalytic Ammonia Synthesis.

Recently, Mo-based metal catalysts are widely applied in the electrocatalytic nitrogen reduction reaction (NRR) due to the lower binding energy between the Mo atom and N atom. The design of a Mo-based catalyst@carbon heterostructure and the introduction of anion vacancies are effective measures to improve their NRR performance. In this research, the cross-linked Vo-MoO2@C (Vo means oxygen vacancies) heterostructure nanoparticles with rich oxygen vacancies are first synthesized via pectin assisted hydrothermal reaction followed by calcination and treating with NaBH4 solution. Vo-MoO2@C exhibits good electrocatalytic NRR performance with an ammonia yield rate of 9.75 μg h-1 mg-1 at -0.5 V (RHE) and a Faraday efficiency (FE) of 3.24% at -0.3 V (RHE) under ambient conditions.

Watson-Crick versus Hoogsteen Base Pairs: Chemical Strategy to Encode and Express Genetic Information in Life.

Nucleic acids typically form a double helix structure through Watson-Crick base-pairing. In contrast, non-Watson-Crick base pairs can form other three-dimensional structures. Although it is well-known that Watson-Crick base pairs may be more unstable than non-Watson-Crick base pairs under some conditions, the importance of non-Watson-Crick base pairs has not been widely examined. Hoogsteen base pairs, the non-Watson-Crick base pairs, contain important hydrogen-bond patterns that form the helices of nucleic acids, such as in Watson-Crick base pairs, and can form non-double helix structures such as triplexes and quadruplexes. In recent years, non-double helix structures have been discovered in cells and were reported to considerably influence gene expression. The complex behavior of these nucleic acids in cells is gradually being revealed, but the underlying mechanisms remain almost unknown.Quantitatively analyzing the structural stability of nucleic acids is important for understanding their behavior. A nucleic acid is an anionic biopolymer composed of a sugar, base, and phosphoric acid. The physicochemical factors that determine the stability of nucleic acid structures include those derived from the interactions of nucleic acid structures and those derived from the environments surrounding nucleic acids. The Gibbs free energy change (ΔG) of structure formation is the most commonly used physicochemical parameter for analyzing quantitative stability. Quantitatively understanding the intracellular behavior of nucleic acids involves describing the formation of nucleic acid structures and related reactions as ΔG. Based on this concept, we quantitatively analyzed the stability of double helix and non-double helix structures and found that decreased water activity, an important factor in crowded cellular conditions, significantly destabilize the formation of Watson-Crick base pairs but stabilizes Hoogsteen base pairs.Here, we describe a physicochemical approach to understand the regulation of gene expressions based on the stability of nucleic acid structures. We developed new methods for predicting the stability of double and non-double helices in various molecular environments by mimicking intracellular environments. Furthermore, the physicochemical approach used for analyzing gene expression regulated by non-double helix structures is useful for not only determining how gene expression is controlled by cellular environments but also for developing new technologies to chemically regulate gene expression by targeting non-double helix structures. We discuss the roles of Watson-Crick and Hoogsteen base pairs in cells based on our results and why both types of base pairing are required for life. Finally, a new concept in nucleic acid science beyond that of Watson and Crick base pairing is introduced.

Water softening using graphene oxide/biopolymer hybrid nanomaterials

There is a growing interest in developing more environmentally friendly softeners for hardness reduction of water supplied for domestic consumption. This work focuses on exploring biopolymer-based softeners, through the surface modification of graphene oxide (GO) with the anionic biopolymer κ-carrageenan (GO-Si(κ)CRG). The performance of the modified GO to decrease the hardness of natural waters containing high levels of Ca2+ was assessed. The sorption efficiency was dependent on the initial Ca2+ concentration and on the sorbent dose, with 8–34% removal for GO and 21–100% for GO-Si(κ)CRG. The surface modification considerably improved the adsorptive efficiency and under certain experimental conditions, it was possible to convert very hard water (300 mg L−1 CaCO3) to soft water. Importantly, the performance was not affected by the presence of other ions typically found in natural bottled waters. The kinetics was well described by pseudo-first-order and diffusion models. The multi-linear nature observed in Boyd’s and Webber’s plots suggested that both film diffusion and pore diffusion controlled the sorption rate. The maximum Ca2+ sorption capacity at monolayer coverage of GO-Si(κ)CRG was 47.6 ± 3.2 mg g−1. The electrostatic attraction between sulfonate groups and calcium cations is likely to be the main mechanism involved in the sorption process of Ca2+ by GO-Si(κ)CRG. Overall, the results indicate good prospects for the development of a new class of softeners based on the GO modification described.

Strategies to Functionalize the Anionic Biopolymer Na-Alginate without Restricting Its Polyelectrolyte Properties.

The natural anionic polyelectrolyte alginate and its derivatives are of particular interest for pharmaceutical and biomedical applications. Most interesting for such applications are alginate hydrogels, which can be processed into various shapes, self-standing or at surfaces. Increasing efforts are underway to functionalize the alginate macromolecules prior to hydrogel formation in order to overcome the shortcomings of purely ionically cross-linked alginate hydrogels that are hindering the progress of several sophisticated biomedical applications. Particularly promising are derivatives of alginate, which allow simultaneous ionic and covalent cross-linking to improve the physical properties and add biological activity to the hydrogel. This review will report recent progress in alginate modification and functionalization with special focus on synthesis procedures, which completely conserve the ionic functionality of the carboxyl groups along the backbone. Recent advances in analytical techniques and instrumentation supported the goal-directed modification and functionalization.