Riboflavin Crystals with Extremely High Water Solubility.

New insights into the unique biochemical properties of riboflavin (Rf), also known as vitamin B2, are leading to the development of its use not only as a vitamin supplement but also as a potential anti-inflammatory, immunomodulatory, antioxidant, anticancer, and antiviral agent, where it may play a role as an inhibitor of viral proteinases. At the same time, the comparison of the pharmacoactivity of Rf with its known metabolites, namely, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is very complicated due to its poor water solubility: 0.1-0.3 g/L versus 67 g/L for FMN and 50 g/L for FAD, which is the limiting factor for its administration in clinical practice. In this study, we report the recrystallization procedure of the type A Rf crystals into the slightly hydrophobic type B/C and a new hydrophilic crystal form that has been termed the P type. Our method of Rf crystal modification based on recrystallization from dilute alkaline solution provides an unprecedented extremely high water solubility of Rf, reaching 23.5 g/L. A comprehensive study of the physicochemical properties of type P riboflavin showed increased photodynamic therapeutic activity compared to the known types A and B/C against clinical isolates of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Salmonella typhimurium. Importantly, our work not only demonstrates a simple and inexpensive method for the synthesis of riboflavin with high solubility, which should lead to increased bioactivity, but also opens up opportunities for improving both known and new therapeutic applications of vitamin B2.

Resolving the Seeming Contradiction between the Superior Rate Capability of Prussian Blue Analogues and the Extremely Slow Ionic Diffusion.

The superior rate capabilities of metal ion battery materials based on Prussian blue analogues (PBAs) are almost exclusively ascribed to the extremely fast solid-state ionic diffusion, which is possible due to structural voids and spacious three-dimensional channels in PBA structures. We performed a detailed electroanalytical study of alkali ion diffusivities in nanosized cation-rich and cation-poor PBAs obtained as particles or electrodeposited films in both aqueous and non-aqueous media, which resulted in a solid conclusion about the exceptionally slow ionic transport. We show that the impressive rate capability of PBA materials is determined solely by the small size of the primary particles of PBAs, while the apparent diffusion coefficients are 3-5 orders of magnitude lower than those reported in earlier studies. Our finding calls for a reconsideration of the apparent facility of ionic transport in PBA materials and deeper analysis of the charge carrier-host interactions in PBAs.

The Misconception of Mg2+ Insertion into Prussian Blue Analogue Structures from Aqueous Solution.

Prussian blue analogues (PBAs) are commonly believed to reversibly insert divalent ions, such as calcium and magnesium, rendering them as perspective cathode materials for aqueous magnesium-ion batteries. In this study, the occurrence of Mg2+ insertion into nanosized PBA materials is shown to be a misconception and conclusive evidence is provided for the unfeasibility of this process for both cation-rich and cation-poor nickel, iron, and copper hexacyanoferrates. Based on structural, electrochemical, IR spectroscopy, and quartz crystal microbalance data, the charge compensation of PBA redox can be attributed to protons rather than to divalent ions in aqueous Mg2+ solution. The reversible insertion of protons involves complex lattice water rearrangements, whereas the presence of Mg2+ ion and Mg salt anion stabilizes the proton (de)insertion reaction through local pH effects and anion adsorption at the PBA surface. The obtained results draw attention to the design of proton-based batteries operating in environmentally benign aqueous solutions with low acidity.

Disruption of Cationic/Anionic Viscoelastic Surfactant Micellar Networks by Hydrocarbon as a Basis of Enhanced Fracturing Fluids Clean-Up.

Studies of the effects produced by the solubilization of hydrophobic substances by micellar aggregates in water medium are quite important for applications of viscoelastic surfactant solutions for enhanced oil recovery (EOR), especially in hydraulic fracturing technology. The present paper aims at the investigation of the structural transformations produced by the absorption of an aliphatic hydrocarbon (n-decane) by mixed wormlike micelles of cationic (n-octyltrimethylammonium bromide, C8TAB) and anionic (potassium oleate) surfactants enriched by C8TAB. As a result of contact with a small amount (0.5 wt%) of oil, a highly viscoelastic fluid is transformed to a water-like liquid. By small-angle neutron scattering (SANS) combined with cryo-TEM, it was shown that this is due to the transition of long wormlike micelles with elliptical cross-sections to ellipsoidal microemulsion droplets. The non-spherical shape was attributed to partial segregation of longer- and shorter-tail surfactant molecules inside the surfactant monolayer, providing an optimum curvature for both of them. As a result, the long-chain surfactant could preferably be located in the flatter part of the aggregates and the short-chain surfactant-at the ellipsoid edges with higher curvature. It is proven that the transition proceeds via a co-existence of microemulsion droplets and wormlike micelles, and upon the increase of hydrocarbon content, the size and volume fraction of ellipsoidal microemulsion droplets increase. The internal structure of the droplets was revealed by contrast variation SANS, and it was shown that, despite the excess of the cationic surfactant, the radius of surfactant shell is controlled by the anionic surfactant with longer tail. These findings open a way for optimizing the performance of viscoelastic surfactant fluids by regulating both the mechanical properties of the fluids and their clean-up from the fracture induced by contact with hydrocarbons.

The antibacterial efficacy of a foam mouthwash and its ability to remove biofilms.

OBJECTIVES/AIMS: To evaluate the antimicrobial activity of a newly developed foam mouthwash containing a modified lactoperoxidase system in vitro. MATERIALS AND METHODS: Biofilms of five bacterial species were developed on hydrophobic and hydrophilic surfaces whilst salivary-based biofilm was grown on tooth enamel. Each surface was exposed to the foam mouthwash or saline in vitro. Optical density and scanning electron microscopy (SEM) was used to determine retention of the biofilm following 5 or 30 s exposure time. RESULTS: The foam mouthwash was active against biofilms formed by S. aureus, K. rhizophila, M. thailandicus, E. coli, and C. violaceum and eliminated significant amount of biofilm from each surface; immature 4 h biofilm was less resistant than 24 h biofilm. A 30 s rinse showed best performance, with removal of up to 66% of biofilm from the hydrophilic surface. SEM imaging confirmed oral biofilm removal from the enamel surface after a 5 s rinse with the foam mouthwash. DISCUSSION: Foam mouthwash demonstrated a significant impact on growing biofilm when compared against saline solution. Growing biofilms were more susceptible to the action of the foam mouthwash, which justifies after-meal use of the mouthwash when traditional dentifrices may not be accessible. CONCLUSIONS: Foam mouthwash can be a convenient on-the-go format of oral care products that can be used after meals or when needed to reduce the risk of biofilm-associated oral conditions.

Transmission electron microscopy of Ca oxide nano- and microcrystals in alpha-tricalcium phosphate prepared by sintering of beta-tricalcium phosphate.

Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to study the porous and non-porous alpha-tricalcium phosphate (alpha-Ca3(PO4)2, alpha-TCP) prepared through a sintering procedure at 1200-1400 degrees C of beta-tricalcium phosphate (beta-Ca3(PO4)2, beta-TCP). The interpretation of experimental and calculated X-ray and electron diffraction patterns showed that the final product at 1400 degrees C was primarily alpha-TCP but roughly 3.0-8.0 wt.% of the starting beta-TCP phase and up to 8.0 wt.% of CaO were in the final product. TEM images and electron diffraction patterns showed that the CaO phase--formed by decomposition of TCP--exists as micron-sized areas of various oriented nanocrystals embedded into the bulk alpha-TCP material and also as self-standing spherulite particles of a few microns in size. Surprisingly, formation of CaO from TCP decomposition occurred at temperatures below those predicted from the phase diagram of the CaO-P2O5 system.