Structural features of two novel alluaudite-like arsenates Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5.

Two new compounds, Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 (1) and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5 (2), have been prepared hydrothermally. Their crystal structures consist of chains of edge-sharing M1O4(OH0.5)2, M1aO4(OH0.5)2, M2O5(OH0.5), and M2aO5(OH0.5) octahedra (M1, M1a = Zn, Cd; M2, M2a = Zn for 1, and M1, M1a = Mg, Cd; M2, M2a = Mg for 2) that are stacked parallel to (1 0 1) and are connected by the [(AsO4)0.5(AsO3(OH))0.5]2.5- and [(AsO4)0.5(AsO2(OH)2)0.5]2- tetrahedra. These chains produce two types of channels parallel to the c-axis. Cd atoms are located in channels 2, while in channels 1 are situated hydrogen atoms of OH groups. The infrared spectra clearly show the presence of broad O-H stretching and bending vibrations centred at 3236, 2392 1575 and 1396 cm-1 in (1), and 3210, 2379 1602 and 1310 cm-1 in (2). The O-H stretching frequency is in good agreement with O⋯O distances. Furthermore, structural characteristics of compounds with similar alluaudite-like structures were discussed.

Influence of selective acid-etching on functionality of halloysite-chitosan nanocontainers for sustained drug release.

The functionality of halloysite (Hal) nanotubes as drug carriers can be improved by lumen enlargement and polymer modification. This study investigates the influence of selective acid etching on Hal functionalization with cationic biopolymer chitosan. Hal was subjected to lumen etching under mild conditions, loaded under vacuum with nonsteroidal antiinflammatory drug aceclofenac, and incubated in an acidic solution of chitosan. The functionality of pristine and etched Hal before and upon polymer functionalization was assessed by ζ-potential measurements, structural characterization (FT-IR, DSC and XRPD analysis), cell viability assay, drug loading and drug release studies. Acid etching increased specific surface area, pore volume and pore size of Hal, decreased ζ-potential and facilitated binding of the cationic polymer. XRPD and DSC analysis revealed crystalline structure of etched Hal. Successful chitosan binding and drug entrapment were further confirmed by FT-IR and DSC studies. XRPD showed surface polymer binding. DSC and FT-IR analyses confirmed the presence of the entrapped drug in its crystalline form. Drug loading was increased for ≈81% by selective lumen etching. Slight decrease of drug content occurred during chitosan functionalization due to aceclofenac diffusion in the polymer solution. The drug release was more sustained from etched Hal nanocomposites (up to ≈87% for 12 h) than from pristine Hal (up to ≈97% for 12 h) due to more intensive chitosan binding. High human fibroblast survival rates upon exposure to pristine and etched Hal before and after chitosan functionalization (>90% in the concentration of 1000 µg/mL) confirmed that both lumen etching under mild conditions and polymer functionalization had no significant effect on cytocompatibility. Based on these findings, selective lumen etching in combination with polycation modification appears to be a promising approach for improvement of Hal nanotubes functionality by increasing payload, polymer binding capacity, and sustained release properties with no significant effect on their cytocompatibility.

[Zn3(PO4)2(H2O)(0.8)(NH3)(1.2)].

The structure of the title compound, ammineaquadi-mu(5)-phosphato-trizinc(II), [Zn(3)(PO(4))(2)(H(2)O)(0.8)(NH(3))(1.2)], consists of two parts: (i) PO(4) and ZnO(4) vertex-sharing tetrahedra arranged in layers parallel to (100) and (ii) ZnO(2)(N/O)(2) tetrahedra located between the layers. Elemental analysis establishes the ammine-to-water ratio as 3:2. ZnO(2)(N/O)(2) tetrahedra are located at special position 4e (site symmetry 2) in C2/c. The two O atoms of ZnO(2)(N/O)(2) are bonded to neighbouring P atoms, forming two Zn-O-P linkages and connecting ZnO(2)(N/O)(2) tetrahedra with two adjacent bc plane layers. A noteworthy feature of the structure is the presence of NH(3) and H(2)O at the same crystallographic position and, consequently, qualitative changes in the pattern of hydrogen bonding and weaker N/O-H...O electrostatic interactions, as compared to two closely related structures.

Zn(1.86)Cd(0.14)(OH)VO(4).

The title compound, dizinc cadmium hydroxide tetraoxido-vanadate, Zn(1.86)Cd(0.14)(OH)VO(4), was prepared under low-temperature hydro-thermal conditions. It is isostructural with Zn(2)(OH)VO(4) and Cu(2)(OH)VO(4). In the crystal structure, chains of edge-sharing [ZnO(6)] octahedra are inter-connected by VO(4) tetra-hedra (site symmetries of both V atoms and their coordination polyhedra are .m.) to form a three-dimensional [Zn(OH)VO(4)](2-) framework with channels occupied by Zn and Zn/Cd cations adopting trigonal-bipyramidal and distorted octa-hedral coordinations, respectively. Zn(1.86)Cd(0.14)(OH)VO(4) is topologically related to adamite-type phases, and descloizite- and tsumcorite-type structures.

Antibacterial graphene-based hydroxyapatite/chitosan coating with gentamicin for potential applications in bone tissue engineering.

Electrophoretic deposition process (EPD) was successfully used for obtaining graphene (Gr)-reinforced composite coating based on hydroxyapatite (HAP), chitosan (CS), and antibiotic gentamicin (Gent), from aqueous suspension. The deposition process was performed as a single step process at a constant voltage (5 V, deposition time 12 min) on pure titanium foils. The influence of graphene was examined through detailed physicochemical and biological characterization. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, Raman, and X-ray photoelectron analyses confirmed the formation of composite HAP/CS/Gr and HAP/CS/Gr/Gent coatings on Ti. Obtained coatings had porous, uniform, fracture-free surfaces, suggesting strong interfacial interaction between HAP, CS, and Gr. Large specific area of graphene enabled strong bonding with chitosan, acting as nanofiller throughout the polymer matrix. Gentamicin addition strongly improved the antibacterial activity of HAP/CS/Gr/Gent coating that was confirmed by antibacterial activity kinetics in suspension and agar diffusion testing, while results indicated more pronounced antibacterial effect against Staphylococcus aureus (bactericidal, viable cells number reduction >3 logarithmic units) compared to Escherichia coli (bacteriostatic, <3 logarithmic units). MTT assay indicated low cytotoxicity (75% cell viability) against MRC-5 and L929 (70% cell viability) tested cell lines, indicating good biocompatibility of HAP/CS/Gr/Gent coating. Therefore, electrodeposited HAP/CS/Gr/Gent coating on Ti can be considered as a prospective material for bone tissue engineering as a hard tissue implant.

Assessing the Bioactivity of Gentamicin-Preloaded Hydroxyapatite/Chitosan Composite Coating on Titanium Substrate.

The electrophoretic deposition process (EPD) was utilized to produce bioactive hydroxyapatite/chitosan (HAP/CS) and hydroxyapatite/chitosan/gentamicin (HAP/CS/Gent) coatings on titanium. The bioactivity of newly synthesized composite coatings was investigated in the simulated body fluid (SBF) and examined by X-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy. The obtained results revealed carbonate-substituted hydroxyapatite after immersion in SBF, emphasizing the similarity of the biomimetically grown HAP with the naturally occurring apatite in the bone. The formation of biomimetic HAP was confirmed by electrochemical impedance spectroscopy and polarization measurements, through the decrease in corrosion current density and coating capacitance values after 28-day immersion in SBF. The osseointegration ability was further validated by measuring the alkaline phosphatase activity (ALP) indicating the favorable osseopromotive properties of deposited coatings (significant increase in ALP levels for both HAP/CS (3.206 U mL-1) and HAP/CS/Gent (4.039 U mL-1) coatings, compared to the control (0.900 U mL-1)). Drug-release kinetics was investigated in deionized water at 37 °C by high-performance liquid chromatography coupled with mass spectrometry. Release profiles revealed the beneficial "burst-release effect" (∼21% of gentamicin released in the first 48 h) as a potentially promising solution against the biofilm formation in the initial period. When tested against human and mice fibroblast cells (MRC-5 and L929), both composite coatings showed a noncytotoxic effect (viability >85%), providing a promising basis for further medical application trials.

Cd2Cu(PO4)2.

During an investigation of the insufficiently known system M1O-M2O-X(2)O(5)-H(2)O (M1 = Cd(2+), Sr(2+) and Ba(2+); M2 = Cu(2+), Ni(2+), Co(2+), Zn(2+) and Mg(2+); X = P(5+), As(5+) and V(5+)), single crystals of the novel compound dicadmium copper(II) bis[phosphate(V)], Cd(2)Cu(PO(4))(2), were obtained. This compound belongs to a small group of compounds adopting a Cu(3)(PO(4))(2)-type structure and having the general formula M1(2)M2(XO(4))(2) (M1/M2 = Cd(2+), Cu(2+), Mg(2+) and Zn(2+); X = As(5+), P(5+) and V(5+)). The crystal structure is characterized by the interconnection of infinite [Cu(PO(4))(2)](n) chains and [Cd(2)O(10)](n) double chains, both extending along the a axis. Exceptional characteristics of this structure are its novel chemical composition and the occurrence of double chains of CdO(6) polyhedra that were not found in related structures. In contrast to the isomorphous compounds, where the M1 cations are coordinated by five O atoms, the Cd atom is coordinated by six. The dissimilarity in the geometry of M1 coordination between Cd(2)Cu(PO(4))(2) and the isomorphous compounds is mostly due to the larger ionic radius of the Cd cation in comparison with the Cu, Mg and Zn cations. Sharing a common edge, two CdO(6) polyhedra form Cd(2)O(10) dimers. Each such dimer is bonded to another dimer sharing common vertices, forming [Cd(2)O(10)](n) double chains in the [100] direction. The Cu atoms, located on an inversion centre (site symmetry \overline{1}), form isolated CuO(4) squares interconnected by PO(4) tetrahedra, forming [Cu(PO(4))(2)](n) chains similar to those found in related structures. Conversely, the [Cd(2)O(10)](n) double chains, which were not found in related structures, are an exclusive feature of this structure.

Sr, Ba and Cd arsenates with the apatite-type structure.

X-ray diffraction analysis of single crystals of three new arsenates adopting apatite-type structures yielded formula Sr(5)(AsO(4))(3)F for strontium arsenate fluoride, (I), (Sr(1.66)Ba(0.34))(Ba(2.61)Sr(0.39))(AsO(4))(3)Cl for strontium barium arsenate chloride, (II), and Cd(5)(AsO(4))(3)Cl(0.58)(OH)(0.42) for cadmium arsenate hydroxide chloride, (III). All three structures are built up of isolated slightly distorted AsO(4) tetrahedra that are bridged by Sr(2+) in (I), by Sr(2+)/Ba(2+) in (II) and by Cd(2+) in (III). Compounds (I) and (II) represent typical fluorapatites and chlorapatites, respectively, with F(-) at the 2a (0, 0, {1/4}) site and Cl(-) at the 2b (0, 0, 0) site of P6(3)/m. In contrast, in (III), due to the requirement that the smaller Cd(2+) cation is positioned closer to the channel Cl(-) anion (partially substituted by OH(-)), the anion occupies the unusual 2a (0, 0, {1/4}) site. Therefore, Cl(-) is similar to F(-) in (I), coordinated by three A2 cations, unlike the octahedrally coordinated Cl(-) in (II) and other ordinary chlorapatites. Furthermore, in (III), using FT-IR studies, we have inferred the existence of H(+) outside the channel in oxyhydroxyapatites and provided possible atomic coordinates for a H atom in HAsO(4)(2-), leading to a proposed formulation of the compound as Cd(5)(AsO(4))(3-x)(HAsO(4))(x)Cl(0.58)(OH)(0.42-x-(y/2))O(x+(y/2))(y/2).

Gentamicin-Loaded Bioactive Hydroxyapatite/Chitosan Composite Coating Electrodeposited on Titanium.

Composite coating of antibiotic gentamicin (Gent), natural polymer chitosan (CS), and hydroxyapatite (HAP) was successfully assessed by applying the electrophoretic deposition (EPD) technique. EPD was performed under optimized deposition conditions (5 V, 12 min) on pure titanium plates, to obtain HAP/CS and HAP/CS/Gent composite coatings in a single step from three-component aqueous suspension, with favorable antibacterial properties. Composite coatings were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron analysis, confirming the formation of composite HAP/CS and HAP/CS/Gent coatings on the titanium surface, which is due to intermolecular hydrogen bonds. Employing the XRD technique, HAP was detected by obtaining the characteristic diffraction maximums. Good antibacterial activity of the composite coating loaded with antibiotic (HAP/CS/Gent) was confirmed against Staphylococcus aureus and Escherichia coli, pointing to the high potential for bioapplication. Introduction of gentamicin in HAP/CS/Gent coating caused very mild cytotoxicity in the tested cell lines MRC-5 and L929. MTT testing was used to evaluate cell viability, and HAP/CS was classified as noncytotoxic.