Formation of carbonated apatite particles from a supersaturated inorganic blood serum model

Selective anions mediated fluorescence "turn-on", aggregation induced emission (AIE) and lysozyme targeting properties of pyrene-naphthalene sulphonyl conjugate

We have designed and synthesized a novel pyrene-naphthalene sulphonyl conjugate, 1-((1Z)-(4-((Z)-4-(pyrene-1-yl)methyleneamino)phenylsulfonyl)phenylimino)methyl)naphthalene-2-ol (PSN) through a facile two-step reactions. It was characterized by various spectral techniques. Fluorescence spectral studies showed that compound PSN featured fluorescence enhancement upon increasing the water content in THF. This can be attributed to the phenomena of aggregated induced emission (AIE), which is confirmed by SEM and AFM studies, due to the restriction of CHN isomerization of PSN. The anion sensing of PSN was examined with various anions. Among these anions, H₂PO₄^- and F^- ions were selectively sensing with a low detection limit of 3.52 × 10^-7 M and 7.23 × 10^-7 M, respectively, and an obvious color change from yellow to orange was observed by the naked eye. The mechanism of sensing involved the formation of hydrogen bonding interaction between O-H group of PSN and H₂PO₄^-/ F^- ions. The binding of PSN with LYZ was also examined by docking studies, which shows that H-bonding and hydrophobic interactions play crucial roles for the interaction of LYZ toward PSN.

A review of phosphate mineral nucleation in biology and geobiology

Relationships between geological phosphorite deposition and biological apatite nucleation have often been overlooked. However, similarities in biological apatite and phosphorite mineralogy suggest that their chemical formation mechanisms may be similar. This review serves to draw parallels between two newly described phosphorite mineralization processes, and proposes a similar novel mechanism for biologically controlled apatite mineral nucleation. This mechanism integrates polyphosphate biochemistry with crystal nucleation theory. Recently, the roles of polyphosphates in the nucleation of marine phosphorites were discovered. Marine bacteria and diatoms have been shown to store and concentrate inorganic phosphate (Pi) as amorphous, polyphosphate granules. Subsequent release of these P reserves into the local marine environment as Pi results in biologically induced phosphorite nucleation. Pi storage and release through an intracellular polyphosphate intermediate may also occur in mineralizing oral bacteria. Polyphosphates may be associated with biologically controlled apatite nucleation within vertebrates and invertebrates. Historically, biological apatite nucleation has been attributed to either a biochemical increase in local Pi concentration or matrix-mediated apatite nucleation control. This review proposes a mechanism that integrates both theories. Intracellular and extracellular amorphous granules, rich in both calcium and phosphorus, have been observed in apatite-biomineralizing vertebrates, protists, and atremate brachiopods. These granules may represent stores of calcium-polyphosphate. Not unlike phosphorite nucleation by bacteria and diatoms, polyphosphate depolymerization to Pi would be controlled by phosphatase activity. Enzymatic polyphosphate depolymerization would increase apatite saturation to the level required for mineral nucleation, while matrix proteins would simultaneously control the progression of new biological apatite formation.

A red herring in vascular calcification: 'nanobacteria' are protein-mineral complexes involved in biomineralization

Biomineralization at pathological extraosseous sites (i.e. vasculature and soft tissues) is associated with increased morbidity and mortality. So-called 'nanobacteria' have been described as pathogenic agents causing many diseases including calcification. Initially, their appearance, and having a content consisting of nucleic acids plus proteins and properties of growing structures, suggested that they were living organisms. However, it could be demonstrated that the so-called nanobacteria were in fact mineralizing nanoparticles that contain mineral and non-mineral compounds, that these particles bind to charged molecules and that supersaturation enables in vitro growth of these nanoparticles. Recent data indicate that nanoparticles consisting of protein-mineral complexes can be seen both in vitro and in vivo as precursors of matrix calcification.

Polyphosphates affect biological apatite nucleation

While biological apatite (bone mineral) resorption is understood, from the perspective of crystallization theory, nucleation is not. The degree of saturation (Ω) describes the chemical driving force for mineral dissolution (Ω <1) or formation (Ω > 1). Ω is the ratio of the ion activity product (IAP) of free apatite (available for reaction) component ion concentrations (predominately [Ca²⁺] and [PO¾⁻)] for apatite) and its solubility product (K(sp)). Free ion concentrations can be less than total ion concentrations if the ions form complexes, or if the ion speciation changes. Within the acidic bone resorption pit, free [PO¾⁻] is reduced due to speciation into H₂PO₄⁻. This reduces IAP(bio-Ap), and Ω(bio-Ap); at Ω(bio-Ap) <1, apatite dissolves. Apatite nucleation requires Ω(bio-Ap) >1, and bioaccumulation of molar total [Ca²⁺] and [PO¾⁻] to form the 60-70 weight percent mineral in bone tissue. This is possible with the polymerization of PO¾⁻ into polyphosphate [polyP: (PO₃⁻)(n)] which reduces free [PO¾⁻] while leaving total [P] unchanged. polyP forms neutral complexes by chelation with Ca²⁺, which further reduces free [Ca²⁺] and Ω(bio-Ap), yet total [Ca²⁺] is unchanged. In vitro experiments demonstrate reduction in free [Ca²⁺], free [PO¾⁻], and Ω(bio-Ap) by Ca-polyP formation, while total [Ca²⁺] and total [P] are constant. polyP depolymerization restores free [Ca²⁺] and [PO¾⁻] to total [Ca] and [P], and increases Ω(bio-Ap), favouring apatite nucleation.

Ultrastructural analysis of vascular calcifications in uremia

Accelerated intimal and medial calcification and sclerosis accompany the increased cardiovascular mortality of dialysis patients, but the pathomechanisms initiating microcalcifications of the media are largely unknown. In this study, we systematically investigated the ultrastructural properties of medial calcifications from patients with uremia. We collected iliac artery segments from 30 dialysis patients before kidney transplantation and studied them by radiography, microcomputed tomography, light microscopy, and transmission electron microscopy including electron energy loss spectrometry, energy dispersive spectroscopy, and electron diffraction. In addition, we performed synchrotron x-ray analyses and immunogold labeling to detect inhibitors of calcification. Von Kossa staining revealed calcification of 53% of the arteries. The diameter of these microcalcifications ranged from 20 to 500 nm, with a core-shell structure consisting of up to three layers (subshells). Many of the calcifications consisted of 2- to 10-nm nanocrystals and showed a hydroxyapatite and whitlockite crystalline structure and mineral phase. Immunogold labeling of calcification foci revealed the calcification inhibitors fetuin-A, osteopontin, and matrix gla protein. These observations suggest that uremic microcalcifications originate from nanocrystals, are chemically diverse, and intimately associate with proteinaceous inhibitors of calcification. Furthermore, considering the core-shell structure of the calcifications, apoptotic bodies or matrix vesicles may serve as a calcification nidus.