Phosphate Chains Research Articles

Monodisperse Chemical Oligophosphorylation of Peptides via Protected Oligophosphorimidazolide Reagents

Protein poly‐ and oligophosphorylation are recently discovered post‐translational modifications that remain poorly characterized due to (1) the difficulty of extracting endogenously polyphosphorylated species without degradation and (2) the absence of synthetic and analytical tools to prepare and characterize poly‐ and oligophosphorylated species in biochemical contexts. Herein, we report a methodology for the selective oligophosphorylation of peptides with monodisperse phosphate chain lengths (Pn = 3–6). A library of oligophosphorimidazolide (oligoP‐imidazolide) reagents featuring benzyl and o‐nitrophenylethyl protecting groups were synthesized in moderate‐to‐good yields (65–93%). These oligoP‐imidazolide reagents enabled the selective and simultaneous conjugation of multiple phosphate units to phosphoryl nucleophiles, circumventing tedious iterative processes. The generalizability of this approach is illustrated by a substrate scope study that includes several biologically relevant phosphopeptide sequences, culminating in the synthesis of >60 examples of peptide oligophosphates (Pn = 2–6). Moreover, we report the preparation of oligoP‐diimidazolides (Pn = 3–5) and discuss their application in generating unique condensed phosphate‐peptide conjugates. We also demonstrate that human phospho‐ubiquitin (pS65‐Ub) is amenable to functionalization by our reagents. Overall, we envision the methods described here will enable future studies that characterize these newly discovered but poorly understood phosphorylation modes.

Monodisperse Chemical Oligophosphorylation of Peptides via Protected Oligophosphorimidazolide Reagents.

Protein poly- and oligophosphorylation are recently discovered post-translational modifications that remain poorly characterized due to (1) the difficulty of extracting endogenously polyphosphorylated species without degradation and (2) the absence of synthetic and analytical tools to prepare and characterize poly- and oligophosphorylated species in biochemical contexts. Herein, we report a methodology for the selective oligophosphorylation of peptides with monodisperse phosphate chain lengths (Pn = 3-6). A library of oligophosphorimidazolide (oligoP-imidazolide) reagents featuring benzyl and o-nitrophenylethyl protecting groups were synthesized in moderate-to-good yields (65-93%). These oligoP-imidazolide reagents enabled the selective and simultaneous conjugation of multiple phosphate units to phosphoryl nucleophiles, circumventing tedious iterative processes. The generalizability of this approach is illustrated by a substrate scope study that includes several biologically relevant phosphopeptide sequences, culminating in the synthesis of >60 examples of peptide oligophosphates (Pn = 2-6). Moreover, we report the preparation of oligoP-diimidazolides (Pn = 3-5) and discuss their application in generating unique condensed phosphate-peptide conjugates. We also demonstrate that human phospho-ubiquitin (pS65-Ub) is amenable to functionalization by our reagents. Overall, we envision the methods described here will enable future studies that characterize these newly discovered but poorly understood phosphorylation modes.

Characterization of the α-relaxation and gel-like dynamics in mixed network forming (GeO2)x(NaPO3)100-x glass melts by photon correlation spectroscopy

Dynamic light scattering investigations of the α-relaxation in network-forming (GeO2)x(NaPO3)100-x glass melts is reported for x = 0 to 40 mol% GeO2. Addition of GeO2 results in an increased density of bridging oxygen bonds. This monotonically increases the glass transition temperature but generates complex changes to the glass forming fragility which initially decreases with increasing GeO2 but increases again at higher GeO2 contents. A resolution to this odd fragility behavior is obtained by applying a coarse-graining procedure used previously in sodium germanate melts to arrive at a topological network connectivity for which fragility exhibits a universal dependence. Also observed in the light scattering measurements is a secondary relaxation, several orders of magnitude slower than that of the α-relaxation, which we tentatively attribute to gel-like anomalous diffusion of Ge crosslinks formed between phosphate chains.

Phosphoric acid salts of amino acids as a source of oligopeptides on the early Earth

Because of their unique proton-conductivity, chains of phosphoric acid molecules are excellent proton-transfer catalysts. Here we demonstrate that this property could have been exploited for the prebiotic synthesis of the first oligopeptide sequences on our planet. Our results suggest that drying highly diluted solutions containing amino acids (like glycine, histidine and arginine) and phosphates in comparable concentrations at elevated temperatures (ca. 80 °C) in an acidic environment could lead to the accumulation of amino acid:phosphoric acid crystalline salts. Subsequent heating of these materials at 100 °C for 1–3 days results in the formation of oligoglycines consisting of up to 24 monomeric units, while arginine and histidine form shorter oligomers (up to trimers) only. Overall, our results suggest that combining the catalytic effect of phosphate chains with the crystalline order present in amino acid:phosphoric acid salts represents a viable solution that could be utilized to generate the first oligopeptide sequences in a mild acidic hydrothermal field scenario. Further, we propose that crystallization could help overcoming cyclic oligomer formation that is a generally known bottleneck of prebiotic polymerization processes preventing further chain growth.

Antioxidant and Emulsifying Activity of the Exopolymer Produced by Bacillus licheniformis.

The exopolymer (ESPp) was obtained from Bacillus licheniformis IDN-EC, composed of a polyglutamic acid and polyglycerol phosphate chain O-substituted with αGal moieties (αGal/αGlcNH2 3:1 molar ratio) and with a 5000 Da molecular weight. The cytotoxicity activity of EPSp was determined by reducing the MTT (3-[4,5-dimethyl-thiazol-2-yl]-2,5-diphenyltetrazolium bromide) to formazan on HeLa cells. This EPS did not show cytotoxicity against the tested cell line. The ESPp presented great advantages as an antioxidant with free radical scavenging activities (1,1-diphenyl-2-picryl-hydrazyl radical (DPPH),hydroxyl radical (OH), and superoxide anion (O2-)) (65 ± 1.2%, 98.7 ± 1.9%, and 97 ± 1.7%), respectively. Moreover, EPSp increased the enzyme activity for catalase (CAT) and glutathione peroxidase (GSH-Px) in HeLa cells (CAT, 2.6 ± 0.24 U/mL; and GSH-Px, 0.75 ± 0.3 U/L). The presence of ESPp showed a significant protective effect against H2O2 in the cell line studied, showing great viability (91.8 ± 2.8, 89.9 ± 2.9, and 93.5 ± 3.6%). The EPSp presented good emulsifying activity, only for vegetable oils, olive oil (50 ± 2.1%) and sesame (72 ± 3%). Sesame was effective compared to commercials products, Triton X-100 (52.38 ± 1.6%), Tween 20 (14.29 ± 1.1%), and sodium dodecyl sulphate (SDS) (52.63 ± 1.6%). Furthermore, the EPS produced at 0.6 M has potential for environmental applications, such as the removal of hazardous materials by emulsification whilst resulting in positive health effects such as antioxidant activity and non-toxicity. EPSp is presented as a good exopolysaccharide for various applications.

Atomistic insights into the reentrant phase-transitions in polyuracil and polylysine mixtures.

The phase separation of protein and RNA mixtures underpins the assembly and regulation of numerous membraneless organelles in cells. The ubiquity of protein-RNA condensates in cellular regulatory processes is in part due to their sensitivity to RNA concentration, which affects their physical properties and stability. Recent experiments with poly-cationic peptide-RNA mixtures have revealed closed-loop phase diagrams featuring lower and upper critical solution temperatures. These diagrams indicate reentrant phase transitions shaped by biomolecular interactions and entropic forces such as solvent and ion reorganization. We employed atomistic simulations to study mixtures with various RNA-polylysine stoichiometries and temperatures to elucidate the microscopic driving forces behind reentrant phase transitions in protein-RNA mixtures. Our findings reveal an intricate interplay between hydration, ion condensation, and specific RNA-polylysine hydrogen bonding, resulting in distinct stoichiometry-dependent phase equilibria governing stabilities and structures of the condensate phase. Our simulations show that reentrant transitions are accompanied by desolvation around the phosphate groups of RNA, with increased contacts between phosphate and lysine side chains. In RNA-rich systems at lower temperatures, RNA molecules can form an extensive pi-stacking and hydrogen bond network, leading to percolation. In protein-rich systems, no such percolation-induced transitions are observed. Furthermore, we assessed the performance of three prominent water force fields-Optimal Point Charge (OPC), TIP4P-2005, and TIP4P-D-in capturing reentrant phase transitions. OPC provided a superior balance of interactions, enabling effective capture of reentrant transitions and accurate characterization of changes in solvent reorganization. This study offers atomistic insights into the nature of reentrant phase transitions using simple model peptide and nucleotide mixtures. We believe that our results are broadly applicable to larger classes of peptide-RNA mixtures exhibiting reentrant phase transitions.

Potassium-based emulsifying salts in processed cheese: A rheological, textural, tribological, and thermal approach

The aim of the study was to investigate the impact of potassium-based emulsifying salts (ES; 2% wt/wt concentration) with different phosphate chain lengths [dipotassium hydrogenphosphate (K2HPO4; DKP), tetrapotassium diphosphate (K4P2O7; KTPP), pentapotassium triphosphate (K5P3O10; TKPP)] on the physicochemical, viscoelastic, textural, tribological, thermal, and sensory properties of processed cheese (PC; 40% wt/wt dry matter, 50% wt/wt fat in dry matter) during a 60d storage period (6 ± 2°C). On the whole, the hardness of all PC samples increased with the increasing chain length of ES (DKP < TKPP < KTPP) and the prolonging storage period. Moreover, the hardness results were in accordance with those of the rheological analysis. All PC samples exhibited a more elastic character (G' > G"; tan δ < 1). The type of potassium-based ES affected the binding of water into the structure of the PC. Furthermore, the study confirmed that the manufactured PCs received optimal sensory scores, without any excessive bitterness. It could be concluded that the type of applied ES and storage length affected the functional properties of PC. Finally, the information provided in this study could serve as a tool for the dairy industry to help appropriately select potassium-based ES for PC manufacture with desired properties.

How Does Mg2+(aq) Interact with ATP(aq)? Biomolecular Structure through the Lens of Liquid-Jet Photoemission Spectroscopy.

Liquid-jet photoemission spectroscopy (LJ-PES) allows for a direct probing of electronic structure in aqueous solutions. We show the applicability of the approach to biomolecules in a complex environment, exploring site-specific information on the interaction of adenosine triphosphate in the aqueous phase (ATP(aq)) with magnesium (Mg2+(aq)), highlighting the synergy brought about by the simultaneous analysis of different regions in the photoelectron spectrum. In particular, we demonstrate intermolecular Coulombic decay (ICD) spectroscopy as a new and powerful addition to the arsenal of techniques for biomolecular structure investigation. We apply LJ-PES assisted by electronic-structure calculations to study ATP(aq) solutions with and without dissolved Mg2+. Valence photoelectron data reveal spectral changes in the phosphate and adenine features of ATP(aq) due to interactions with the divalent cation. Chemical shifts in Mg 2p, Mg 2s, P 2p, and P 2s core-level spectra as a function of the Mg2+/ATP concentration ratio are correlated to the formation of [Mg(ATP) 2]6-(aq), [MgATP]2-(aq), and [Mg2ATP](aq) complexes, demonstrating the element sensitivity of the technique to Mg2+-phosphate interactions. The most direct probe of the intermolecular interactions between ATP(aq) and Mg2+(aq) is delivered by the emerging ICD electrons following ionization of Mg 1s electrons. ICD spectra are shown to sensitively probe ligand exchange in the Mg2+-ATP(aq) coordination environment. In addition, we report and compare P 2s data from ATP(aq) and adenosine mono- and diphosphate (AMP(aq) and ADP(aq), respectively) solutions, probing the electronic structure of the phosphate chain and the local environment of individual phosphate units in ATP(aq). Our results provide a comprehensive view of the electronic structure of ATP(aq) and Mg2+-ATP(aq) complexes relevant to phosphorylation and dephosphorylation reactions that are central to bioenergetics in living organisms.

Synthesis, kinetic studies, and QSAR of dinucleoside polyphosphate derivatives as human AK1 inhibitors

Adenylate kinase (AK) plays a crucial role in the metabolic monitoring of cellular adenine nucleotide homeostasis by catalyzing the reversible transfer of a phosphate group between ATP and AMP, yielding two ADP molecules. By regulating the nucleotide levels and energy metabolism, the enzyme is considered a disease modifier and potential therapeutic target for various human diseases, including malignancies and inflammatory and neurodegenerative disorders. However, lacking approved drugs targeting AK hinders broad studies on this enzyme's pathological importance and therapeutic potential.In this work, we determined the effect of a series of dinucleoside polyphosphate derivatives, commercially available (11 compounds) and newly synthesized (8 compounds), on the catalytic activity of human adenylate kinase isoenzyme 1 (hAK1). The tested compounds belonged to the following groups: (1) diadenosine polyphosphates with different phosphate chain lengths, (2) base-modified derivatives, and (3) phosphate-modified derivatives. We found that all the investigated compounds inhibited the catalytic activity of hAK1, yet with different efficiencies. Three dinucleoside polyphosphates showed IC50 values below 1 µM, and the most significant inhibitory effect was observed for P1-(5′-adenosyl) P5-(5′-adenosyl) pentaphosphate (Ap5A). To understand the observed differences in the inhibition efficiency of the tested dinucleoside polyphosphates, the molecular docking of these compounds to hAK1 was performed. Finally, we conducted a quantitative structure–activity relationship (QSAR) analysis to establish a computational prediction model for hAK1 modulators. Two PLS-regression-based models were built using kinetic data obtained from the AK1 activity analysis performed in both directions of the enzymatic reaction. Model 1 (AMP and ATP synthesis) had a good prediction power (R2 = 0.931, Q2 = 0.854, and MAE = 0.286), while Model 2 (ADP synthesis) exhibited a moderate quality (R2 = 0.913, Q2 = 0.848, and MAE = 0.370). These studies can help better understand the interactions between dinucleoside polyphosphates and adenylate kinase to attain more effective and selective inhibitors in the future.

The Influence of Sodium Hexametaphosphate Chain Length on the Physicochemical Properties of High-Milk Protein Dispersions.

Protein-protein and protein-mineral interactions can result in defects, such as sedimentation and age gelation, during the storage of high-protein beverages. It is well known that age gelation can be delayed by adding cyclic polyphosphates such as sodium hexametaphosphate (SHMP). This study aims to assess the influence of different phosphate chain lengths of SHMP on the physicochemical properties of high-protein dispersions. The effect of adding different SHMP concentrations at 0%, 0.15%, and 0.25% (w/w) before and after heating of 6%, 8%, and 10% (w/w) milk protein concentrate dispersions was studied. The phosphate chain lengths of SHMPs used in this study were 16.47, 13.31, and 9.88, and they were classified as long-, medium-, and short-chain SHMPs, respectively. Apparent viscosity, particle size, heat coagulation time (HCT), color, and turbidity were evaluated. It was observed that the addition of SHMP (0.15% and 0.25%) increased the apparent viscosity of MPC dispersions. However, the chain length and the concentration of the added SHMP had no significant (p > 0.05) effect on the apparent viscosity after heating the dispersions. The HCT of a dispersion containing 6%, 8%, and 10% protein with no SHMP added was 15.28, 15.61, and 11.35 min, respectively. The addition of SHMP at both levels (0.15% and 0.25%) significantly increased the HCT. Protein dispersions (6%, 8%, and 10%) containing 0.25% short-chain SHMP had the highest HCT at 19.29, 19.61, and 16.09 min, respectively. Therefore, the chain length and concentration of added SHMP significantly affected the HCT of unheated protein dispersion (p < 0.05).

Compelling DNA intercalation through 'anion-anion' anti-coulombic interactions: boron cluster self-vehicles as promising anticancer agents.

Anticancer drugs inhibit DNA replication by intercalating between DNA base pairs, forming covalent bonds with nucleotide bases, or binding to the DNA groove. To develop safer drugs, novel molecular structures with alternative binding mechanisms are essential. Stable boron hydrides offer a promising alternative for cancer therapy, opening up additional options like boron neutron capture therapy based on 10B and thermal neutron beams or proton boron fusion therapy using 11B and proton beams. These therapies are more efficient when the boron compound is ideally located inside cancer cells, particularly in the nucleus. Current cancer treatments often utilize small, polycyclic, aromatic, planar molecules that intercalate between ds-DNA base pairs, requiring only a spacing of approximately 0.34 nm. In this paper, we demonstrate another type of intercalation. Notably, [3,3'-Fe(1,2-C2B9H11)2]-, ([o-FESAN]-), a compact 3D molecule measuring 1.1 nm × 0.6 nm, can as well intercalate by strong non-bonding interactions preferentially with guanine. Unlike known intercalators, which are positive or neutral, [o-FESAN]- is a negative species and when an [o-FESAN]- molecule approaches the negatively charged DNA phosphate chain an anion-anion interaction consistently anti-electrostatic via Ccluster-H⋯O-P bonds occurs. Then, when more molecules approach, an elongated outstandingly self-assembled structure of [o-FESAN]--[o-FESAN]- forms moving anions towards the interthread region to interact with base pairs and form aggregates of four [o-FESAN]- anions per base pair. These aggregates, in this environment, are generated by Ccluster-H⋯O-C, N-H⋯H-B and Ccluster-H⋯H-B interactions. The ferrabis(dicarbollide) boron-rich small molecules not only effectively penetrate the nucleus but also intercalate with ds-DNA, making them promising for cancer treatment. This amphiphilic anionic molecule, used as a carrier-free drug, can enhance radiotherapy in a multimodal perspective, providing healthcare professionals with improved tools for cancer treatment. This work demonstrates these findings with a plethora of techniques.

Self-association as a solubility limiting factor of riboflavin in aqueous media.

Single crystal X-ray diffraction analysis of needle shaped riboflavin (RF) crystals revealed π-stacking of RF's isoalloxazine units (distance: 3.643-3.313 Å) with syn-orientated ribityl chains. In line with this, classical molecular dynamics (MD) (400 ns) using an isobaric-isothermal (NPT) ensemble of eight RF in a water box (〈V〉 ∼ 508.62 nm3, 〈p〉 = 1.11 bar) revealed anti-aligned aggregation of RF in water (COM-distance: 4 Å). Comparing umbrella sampling for the separation of two RF molecules to the separation of two lumichrome molecules, the similar mean potential force for the separation of RF and lumichrome (22.8 kJ mol-1; 24.4 kJ mol-1) proved dispersive interactions as the origin of RF's aggregation. Though stacking of RF is the major water-solubility limiting factor, the conformation of RF's ribityl chain may alter the solubility in water. Both, MD (in water) and COSMO-RS (in water continuum) predicted that conformations of RF with an extended ribityl chain are thermodynamically preferred over any conformations with internal hydrogen bonds between hydroxyl groups and nitrogen/oxygen atoms of the pyrimidine moiety of the flavin ring. Interestingly, COSMO-RS predicted the solubility of the extended conformation to be significantly lower than the latter leading to the very low average solubility of RF. Nuclear Overhauser effect measurements (NOESY) of the structurally related sodium riboflavin 5'-monophosphate (RF-PO4) in deuterium oxide confirmed π-stacking of the isoalloxazine rings. In conformity with the 350 times higher water-solubility of RF-PO4, NOESY also indicated a contorted conformation of the ribityl phosphate chain, whereas, for RF, indications for a contorted chain were not observed.

Advancing controlled-release phosphate glasses as sustainable fertilizers: Microelement-enhanced formulations and dissolution behavior analysis

In this study, we explore the potential of phosphate glasses as controlled-release fertilizers, addressing the need for sustainable nutrient management in agriculture. Our approach involves the systematic incorporation of microelements (Fe, Mn, Zn, B, Cu, Mo) into phosphate glasses to assess their impact on the glass's physicochemical properties. For this, seven phosphate glasses were synthesized using a combination of raw materials, and a series of experiments to analyze their thermal properties, structural characteristics, and dissolution behaviors were conducted. Results from the thermal analysis revealed an increase in glass transition, crystallization, and melting temperatures with progressively incorporating microelements indicating an enhancement in thermal stability. Structural characterizations unveiled a prevalent presence of Q2 units in the phosphate network, with discernible Q1 units existing as shorter phosphate chains within the matrix. The inclusion of microelements enhances the chemical durability of the glasses, with specific elements like iron and manganese significantly reducing dissolution rates. This enhanced chemical stability aligns with the requirements for controlled-release fertilizers as defined by ISO 18,644 standards. This study offers valuable insights into the interactions of microelements within phosphate glass matrices, highlighting their potential as effective and environmentally friendly controlled-release fertilizers. By meeting the ISO 18,644 criteria for controlled-release fertilizers, these glasses hold promise for sustainable agriculture practices.

Theoretical insights into phosphate chains: Density functional theory study and Zinc ion insertion reaction

The present research delves into a theoretical examination of phosphate chains using the density functional theory method with the RB3LYP/6-311G model. The geometry of the studied chains was optimized and their atomic charge densities were evaluated. Various parameters, such as HOMO and LUMO energies, energy difference (ΔE), chemical hardness, chemical potential, softness, and global electrophilicity index were thoroughly investigated. Moreover, vibrational frequencies were explored, highlighting both symmetric and asymmetric vibrations in the chains based on the computed IR and Raman spectra. Subsequently, an investigation into the Zinc ion insertion reaction in the studied phosphate chains was carried out. Several parameters were calculated to determine the electrophilic/nucleophilic character of these two constituents. The outcomes revealed that the phosphate chains display nucleophilic behavior and tend to release electrons, while the Zinc ion exhibits electrophilic tendencies and retains electrons. Notably, electron transfer occurs from the chains to the Zinc ion, with the chains acting as electron donors and the Zinc ion as an electron acceptor. The smaller overall electrophilicity gap between chain III and Zn2+ indicates the weak polar character of this reaction. Furthermore, favorable nucleophilic sites for the attack of the Zinc ion (Zn2+) on chain III were identified using the FUKUI indexes.

Development of charge-transfer interatomic potential for O-Fe-P-Zn systems and its application to tribochemical reactions between ZnDTP-derived tribofilm and iron oxide

ZnDTP (zinc dialkyl-dithiophosphate) is added to lubricants to reduce wear in automobile engines. However, the atomistic understanding of its formation and effect on wear resistance remains incomplete. We have developed a charge-transfer interatomic potential for O-Fe-P-Zn systems to reproduce the tribochemical reactions between zinc phosphate and iron oxide. Since our potential function can handle a mixed system of covalent and ionic bonds, it can successfully reproduce structural changes in phosphate chains at the interface. To increase the potential’s accuracy and robustness, we employ three types of training data: target structures of stable crystalline and molecular structures, standard structures of various crystal structures covering a wide range of coordination numbers and bond angles, and annealed random structures with various compositions. The developed potential well reproduces energies, forces, and atomic charges for O-Fe and O-P-Zn systems as well as polyphosphate chain structures. We then apply this developed potential to ZnDTP-derived tribofilm on iron oxide, revealing that the long-chain phosphate turns into a dense network of short chains under high shear and normal stress conditions. Fe atoms are incorporated into the zinc metaphosphate network, creating a hard Fe/Zn mixed layer. Our results indicate that the short-chain layer acts as an easily sheared lubricant while the Fe/Zn mixed layer prevents wear on the iron oxide substrate.

Entropy of Charge Inversion in DNA including One-Loop Fluctuations.

The entropy and charge distributions have been calculated for a simple model of polyelectrolytes attached to the surface of DNA using a field-theoretic method that includes fluctuations to the lowest one-loop order beyond mean-field theory. Experiments have revealed correlation-driven behavior of DNA in charged solutions, including charge inversion and condensation. In our model, the condensed polyelectrolytes are taken to be doubly charged dimers of length comparable to the distance between sites along the phosphate chains. Within this lattice gas model, each adsorption site is assumed to have either a vacancy or a positively charged dimer attached with the dimer oriented either parallel or perpendicular to the double-helix DNA chain. We find that the inclusion of the fluctuation terms decreases the entropy by ∼50% in the weak-binding regime. There, the bound dimer concentration is low because the dimers are repelled from the DNA molecule, which competes with the chemical potential driving them from the solution to the DNA surface. Surprisingly, this decrease in entropy due to correlations is so significant that it overcompensates for the entropy increase at the mean-field level, so that the total entropy is even lower than in the absence of interactions between lattice sites. As a bonus, we present a transparent exposition of the methods used that could be useful to students and others wishing to use this formulation to extend this calculation to more realistic models.

The influence of Bi2O3 on structural and enhancing physical properties of Li2O–Fe2O3–In2O3–P2O5 glasses

Glasses based on the Li2O–Fe2O3–In2O3–Bi2O3–P2O5 system were prepared as potential low-melting sealing glasses. The modifications of the glass structure were characterized by means of XRD and FTIR spectroscopy as a function of Bi2O3/P2O5 substitutions. The bulk density, together with other parameters, was also calculated. The amorphous nature was observed for all glass samples except the highest Bi-content. FTIR and Raman spectrum reveal that the prompt polymerization of the phosphate chains by increasing the Bi2O3 content and forming P–O–Bi bonds and the existence of different structural groups FeO6, FeO4, BiO6, PO4, PO3 and PO. The dilatometry measurements showed an increase in both transition (Tg) and softening (Ts) temperatures with Bi-content. Conversely, coefficients of thermal expansion decreased from 120 × 10−7/°C to 80 × 10−7/°C. The dissolution rate of the prepared glasses was tested, and the results showed significantly improved glass stability. Finally, the obtained glasses have a suitable working temperature, suitable thermal expansion values, and good thermal and chemical stability, making them a prospective candidate for low-temperature sealing materials.

Influence of the type of phosphate additive and its concentration on the setting kinetics of CA cement bonded refractory castables with special regard to the resulting pH value

During the hydration of CA cement exists a dormant period, which is responsible for the setting kinetics of CA cement bonded refractory castables. The dormant period is believed to be caused by an Al–O–H passivation layer on the CA cement particles. Recent publications indicate that the dissolution (aging) of the passivation layer is closely connected to the prevailing pH value of the pore solution during setting. The higher the pH value, the faster the dissolution of the passivation layer.As phosphate additives, frequently used as dispersing agent, differ in their pH value when dissolved in water it is reasonable that they change the setting kinetics of CA cement bonded refractory castables. Commonly used sodium polyphosphate (S-PP, special case S-TPP for sodium tripolyphosphate) dispersing agents mainly differ in chain length, and therefore in Na+ and phosphate concentration, with different setting kinetics as a result.To investigate the influence of S-(T)PP on setting kinetics, sonic velocity and pH measurements were conducted on S-(T)PP/citric acid dispersed and CA cement bonded refractory castables during their setting. Different phosphates, differing in portion of Na+ to phosphate and medium chain length of the phosphate molecules, were used in varied concentrations within refractory castables to quantify the shift in setting kinetics and verify the role of the pH value during the hydration of CA cement.It was found that the chain length of the phosphate molecule of S-(T)PP influences the setting kinetics, and especially the length of the dormant period of the hydration of CA cement, in an indistinct way. Minor differences within the Na+ concentration at differing chain length S-(T)PP showed a comparable tendency to influence the hydration kinetics of CA cement as the chain length of the phosphate molecule was varied. However, an increase of the concentration of the applied S-(T)PP, which goes along with a distinctly increased Na+ concentration, resulted in a significant shorter dormant period and correspondingly an accelerated main hydration of CA cement. The corresponding pH value during the dormant period of the hydration of CA cement increased concurrently to the increase of the S-(T)PP and Na+ concentration.It is discussed that this increase of the pH value of the pore solution of the refractory castable results from an increase of the Na+ concentration from the S-(T)PP, while phosphate molecules are precipitated as Ca-phosphate. This indicates that the dissolution of the Al–O–H passivation layer accelerates with an increasing Na+ concentration (equivalent to increasing pH value) in the pore solution. Thereby, the dormant period is shorter and the hydration of CA cement starts earlier.The general tendency that additives of alkaline nature are accelerating the setting kinetics could be linked to the pH value during the dormant period. Therefore, the theory of the pH dependent aging of the Al–O–H passivation layer on CA cement particles was confirmed. As a directly applicable result, S-(T)PP may be used as accelerator (accelerating the CA cement hydration) beside their dispersing effect.

Structural studies of the deacylated glycolipids and lipoteichoic acid of Lactococcus cremoris 3107

Lactococcus cremoris and Lactococcus lactis are among the most extensively exploited species of lactic acid bacteria in dairy fermentations. The cell wall of lactococci, like other Gram-positive bacteria, possesses a thick peptidoglycan layer, which may incorporate cell wall polysaccharides (CWPS), wall teichoic acids (WTA), and/or lipoteichoic acids (LTA).In this study, we report the isolation, purification and structural analysis of the carbohydrate moieties of glycolipids (GL) and LTA of the L. cremoris model strain 3107. Chemical structures of these compounds were studied by chemical methods, NMR spectroscopy and positive and negative mode ESI MS. We found that the LTA of strain 3107 is composed of short chains of 1,3-polyglycerol phosphate (PGP), attached to O-6 of the non-reducing glucose of the kojibiose-Gro backbone of the glycolipid anchor. Extraction of cells with cold TCA afforded the detection of 1,3-glycerol phosphate chains randomly substituted at O-2 of glycerol by D-Ala. Unlike the LTA of L. lactis strains studied to date, the PGP backbone of the LTA of L. cremoris 3107 did not carry any glycosyl substitution. The deacylated glycolipid fraction contained the free kojibiose-Gro oligosaccharide, identical to the backbone of the GL anchor of LTA, and its shorter fragment α-Glc-1-Gro. These OS may have originated from the GL precursors of LTA biosynthesis.

#6348 HFR USING A HIGH-FLUX DIALYZER (SUPRA-H) AS NEW EFFECTIVE ALTERNATIVE TO ON-LINE HEMODIAFILTRATION: A SINGLE SESSION ANALYSIS

Abstract Background and Aims Hemodiafiltration with regeneration of the ultrafiltrate (HFR) is a highly biocompatible dialysis technique that combines convection, diffusion, and adsorption. SUPRA-H is a new HFR system which uses a high-flux dialyzer in the diffusive stage to improve large uremic toxin removal. The aim of our study was to compare the toxin removal of the SUPRA-H system with high-volume online-hemodiafiltration (OL-HDF). Method In an open, randomized, cross-over, single-center, controlled study, 16 adult chronic hemodialysis patients were treated with SUPRA-H or OL-HDF. Hemodialysis sessions were delivered with Flexya dialysis monitor (Medtronic) in the middle-week session, lasting four hours. OL-HDF session was performed in post-dilution mode with the same high-flux dialyzer (Phylter HF17G, Medtronic) as that used in the diffusive stage of the SUPRA-H system. All other dialysis parameters were kept constant in both study arms. The reduction rate (RR) of urea, creatinine, phosphate, β2-microglobulin (β2mglob), kappa (κFLC) and lambda (λFLC) free light chains, interleukin-6 (IL-6) p-Cresyl sulfate, indoxyl sulfate and albumin, was intraindividually compared for the two dialysis types with linear mixed models. Results Whereas urea RR was significantly lower, SUPRA-H had significantly higher RR for κFLC (Median: 58.63%, IQR: 49.91-70.24) than those obtained with OL-HDF (Median: 51.97%, IQR: 37.12-62.71); p = 0.03). The RRs for the other large and protein-bound uremic toxins tended to be higher with the SUPRA-H system (Figure 1). There were no significant differences in the RRs for creatinine, phosphate, IL-6, and albumin. Conclusion The new HFR system SUPRA-H, appears to be a potential technologic step ahead in terms of improved large molecule removal for dialysis patients, and might contribute to a more adequate dialysis therapy.