Multicomponent periodic nanoparticle superlattices

In this article, we review the state-of-the-art in the preparation and characterization of multicomponent self-assembled superlattices of colloidal nanoparticles with core sizes in the range of 2–20 nm and interparticle spacing less than 2 nm down to intimate contact stemming from sintering. Several aspects of the field are discussed, including: structural organization, the role of particle size distribution, key interparticle forces at play, and methods of investigation of the structures. Contrary to the extensively studied colloidal crystals composed of microscale particles, the nanoparticles possess unique size-dependent properties, such as electronic, optical, or magnetic, which when combined into periodic structures can potentially lead to new collective states stemming from precise positioning of the nanocolloids. As such, we examine a number of emerging applications of this new class of metamaterials. Finally, we speculate on the potential impact of these materials, the new directions, and the challenges for the researchers.     

Layer-by-layer assembly of nacre-like nanostructured composites with antimicrobial properties

In a recent report, we have presented the layer-by-layer (LBL) assembly of a biomimetic nanostructured composite from Na(+)-montmorillonite clay nanosheets and poly(diallylmethylammonium chloride) (Tang, Z.; Kotov, N.; Magonov, S.; Ozturk, B. Nat. Mater. 2003, 2, 413). The structure, deformation mechanism, and mechanical properties of the material are very similar to those of natural nacre and lamellar bones. This fact prompts further investigation of these composites as potential bone implants. LBL assembly affords preparation of multifunctional composites, and here we demonstrate that not only mechanical strength, but also antibacterial activity, can be introduced in these implantable materials by alternating clay layers with starch-stabilized silver nanoparticles. The resulting composite showed excellent structural stability with no detectable levels of silver lost over a 1 month period. Evaluation of the antibacterial properties showed almost complete growth inhibition of E. coli over an 18 h period. The amount of silver eluted from the LBL composite over a 1 month period was determined to be only 0.5-3.0 microg/L. This concentration of silver did not prevent the growth of the mammalian tissue cultures. The LBL composite has shown biocompatibility with the human osteoblast cell line.     

Phase equilibria in ternary system PbO-P2O5-PbCl2 Part I. Partial system Pb3(PO4)2-Pb8P2O13-Pb10(PO4)6Cl2

In ternary system PbO-P₂O₅-PbCl₂, the Pb₃(PO₄)₂-Pb₈P₂O₁₃-Pb₁₀(PO₄)₆Cl₂ partial ternary system has been examined by the thermal, microscopic, X-ray and dilatometric analyses, and its phase diagram provided. The components do not form any new chemical compounds.

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Zusammenfassung Mittels Thermo-, mikroskopischer, röntgenographischer und dilatometrischer Analyse wurde im ternÄren System PbO-P₂O₅-PbCl₂ das ternÄre Teilsystem Pb₃(PO₄)₂-Pb₈P₂O₁₃-Pb₁₀(PO₄)₆C₁₂ untersucht und ein Phasendiagramm erstellt. Die Komponenten bilden keinerlei neue chemische Verbindungen.

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The paper was financed by the Ministry of National Education.     

Lattice parameters and anisotropic thermal expansion of hexagonal boron nitride in the 10–297.5 K temperature range

Lattice parameters for hexagonal boron nitride (hBN) were determined using X-ray powder diffraction at a synchrotron-radiation source (beamline B2, Hasylab/DESY, Hamburg) in the previously uninvestigated temperature range from 10 K up to 297.5 K. The relative change of a and c with rise of temperature in the studied range is anisotropic and amounts to about -0.05% and +0.82%, respectively. The corresponding increase of the unit-cell volume is 0.73%. The evaluated values of thermal expansion coefficients derived from the lattice-parameter dependences on temperature are generally consistent with earlier data determined by interferometryfor T≥82 K. Received: 25 July 2001 / Accepted: 9 August 2001 / Published online: 17 October 2001     

Formation and thermal decomposition of silicon oxynitride compounds I

The existence of formerly unknown compounds of the type M ₃ ¹ SiNO₂, suggested in previous papers, has been confirmed in reactions of lithium and sodium oxides with silicon oxynitride, Si₂N₂O.     

Gold nanoparticles enhance the anti-leukemia action of a 6-mercaptopurine chemotherapeutic agent

6-mercaptopurine and its riboside derivatives are some of the most widely utilized anti-leukemic and anti-inflammatory drugs. Their short biological half-life and severe side effects limit their use. A new delivery method for these drugs based on 4-5 nm gold nanoparticles can potentially resolve these issues. We have found substantial enhancement of the antiproliferative effect against K-562 leukemia cells of Au nanoparticles bearing 6-mercaptopurine-9-beta-d-ribofuranoside compared to the same drug in typically administered free form. The improvement was attributed to enhanced intracellular transport followed by the subsequent release in lysosomes. Enhanced activity and nanoparticle carriers will make possible the reduction of the overall concentration of the drug, renal clearance, and, thus, side effects. The nanoparticles with mercaptopurine also showed excellent stability over 1 year without loss of inhibitory activity.     

Reversible loading and unloading of nanoparticles in "exponentially" growing polyelectrolyte LBL films

The exponentially growing layer-by-layer (LBL) films made from poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA) were used to load and unload the CdTe nanoparticles (NPs). The reversible loading of NPs were investigated through UV-vis studies and further confirmed by confocal microscopy. In addition the LBL films were also compared for the release kinetics for pH 9 and 7 and films capped with (PDDA-PSS)10 layers. The amount of released particles at pH 9 was found to be at least 2 orders of magnitude higher than those at pH 7 and with (PDDA-PSS)10 capped layers after 25 h. This variation in film response for CdTe-particle release presents a route for studies in which highly swollen exponentially growing LBL films can be loaded with functionalized NPs for biological applications and explored as carriers to hold the NPs inside the films for self-assembly.     

Polymorphic transitions in the binary system lead fluorapatite [Pb10(PO4)6F2] - calcium fluorapatite [Ca10(PO4)6F2]

The phase diagram of the binary system lead fluorapatite [Pb₁₀(PO₄)₆F₂] - calcium fluorapatite [Ca₁₀(PO₄)₆F₂] was determined over the whole composition and temperature range. Special attention was paid to the polymorphic transitions of the initial compounds and their behaviour in the investigated system. The two apatites form continuous solid solutions. Examinations were performed by means of thermal, microscopic, X-ray and dilatometric analyses.     

Dilatometric examinations of the compounds 14PbO·P2O5·2PbCl2 (R) and 29PbO·3P2O5·6PbCl2 (S)

The ternary compounds 14PbO·P₂O₅·2PbCl₂ (R) and 29PbO·3P₂O₅·6PbCl₂ (S), which are formed in the ternary system PbO-P₂O₂-PbCl₂, were examined by dilatometry. Numerous, previously undescribed thermal and dilatational effects were observed to occur in these compounds under the influence of temperature.     

Phase equilibria in the ternary system PbO-P2O5-PbCl2

In the ternary system PbO-P₂O₅-PbCl₂, the partial system PbO-Pb₅Cl₂O₄-Pb₁₀(P04)₆Cl₂-14PbO·P₂O₅·2PbCl₂ has been examined by thermal, microscopic, X-ray, dilatometric and IR absorption analyses, and its phase diagram is reported. A new ternary compound with the formula 29PbO·3P₂O₅·6PbCl₂ has been found to occur, which is formed peritectically in the system Pb₅Cl₂O₄-Pb₁₀(PO₄)₆Cl₂ making a pseudobinary section here. X-ray identification data on the newly discovered phase are presented.

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Zusammenfassung Im ternären System PbO-P₂O₅-PbCl₂ wurde mittels thermischer, mikroskopischer, röntgenografischer, dilatometrischer und IR-Absorptionsanalyse das Teilsystem PbO-Pb₅Cl₂O₄-Pb₁₀(PO₄)₆Cl₂-d14PbO·P₂O₅·2PbCl₂ untersucht und sein Phasendiagramm erstellt. Es wurde die Existenz einer neuen ternären Verbindung mit der Formel 29PbO·3P₂O₅·6PbCl₂ gefunden, die peritektisch im System Pb₅Cl₂O₄-Pb₁₀(PO₄)₆Cl₂ geformt wird und dort einen pseudobinären Bereich bildet. Zur Identifizierung werden hier die Röntgenangaben der neu entdeckten Phase veröffentlicht.

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The author is deeply grateful to Dr. Janusz Matuszewski for his help during the X-ray examinations.