Elemental analysis of a single-wall carbon nanotube candidate reference material

A material containing single-wall carbon nanotubes (SWCNTs) with other carbon species, catalyst residues, and trace element contaminants has been prepared by the National Institute of Standards and Technology for characterization and distribution as Standard Reference Material SRM 2483 Carbon Nanotube Soot. Neutron activation analysis (NAA) and inductively coupled plasma mass spectrometry (ICP–MS) were selected to characterize the elemental composition. Catalyst residues at percentage mass fraction level were determined with independent NAA procedures and a number of trace elements, including selected rare earth elements, were determined with NAA and ICP–MS procedures. The results of the investigated materials agreed well among the NAA and ICP–MS procedures and good agreement of measured values with certified values was found in selected SRMs included in the analyses. Based on this work mass fraction values for catalyst and trace elements were assigned to the candidate SRM.     

Hexanuclear dysprosium(III) compound incorporating vertex- and edge-sharing Dy3 triangles exhibiting single-molecule-magnet behavior

A unique hexanuclear dysprosium(III) compound with a new polydentate Schiff-base ligand shows complex slow relaxation of the magnetization most likely associated with the single-ion behavior of individual Dy(III) ions as well as the possible weak coupling between them.     

Reversible capture of small molecules on bimetallaborane clusters: synthesis, structural characterization, and photophysical aspects

Metallaborane compounds containing two adjacent metal atoms, [(PMe(2)Ph)(4)MM'B(10)H(10)] (where MM' = Pt(2), 1; PtPd, 7; Pd(2), 8), have been synthesized, and their propensity to sequester O(2), CO, and SO(2) and to then release them under pulsed and continuous irradiation are described. Only [(PMe(2)Ph)(4)Pt(2)B(10)H(10)], 1, undergoes reversible binding of O(2) to form [(PMe(2)Ph)(4)(O(2))Pt(2)B(10)H(10)] 3, but solutions of 1, 7, and 8 all quantitatively take up CO across their metal-metal vectors to form [(PMe(2)Ph)(4)(CO)Pt(2)B(10)H(10)] 4, [(PMe(2)Ph)(4)(CO)PtPdB(10)H(10)] 10, and [(PMe(2)Ph)(4)(CO)Pd(2)B(10)H(10)] 11, respectively. Crystallographically determined interatomic M-M distances and infrared CO stretching frequencies show that the CO molecule is bound progressively more weakly in the sequence {PtPt} > {PtPd} > {PdPd}. Similarly, SO(2) forms [(PMe(2)Ph)(4)(SO(2))Pt(2)B(10)H(10)] 5, [(PMe(2)Ph)(4)(SO(2))PtPdB(10)H(10)] 12, and [(PMe(2)Ph)(4)(SO(2))Pd(2)B(10)H(10)] 13 with progressively weaker binding of the SO(2) molecule. The uptake and release of gas molecules are accompanied by changes in their absorption spectra. Nanosecond transient absorption spectroscopy clearly shows that the O(2) and CO molecules are liberated from the bimetallic binding site with high quantum yields of about 0.6. For 3, in addition to dioxygen release in the triplet ground state, singlet oxygen O(2)((1)Δ(g)) was also detected with a quantum yield <0.01. In most cases, the release and rebinding of the gas molecules can be cycled with little photodegradation of the compounds. Femtosecond transient absorption spectroscopy further reveals that the photorelease of the O(2) and CO molecules, from 3 and 4 respectively, is an ultrafast process taking place on a time scale of tens of picoseconds. For SO(2), the release is even faster (<1 ps), but only in the case of mixed metal PtPd adducts, most probably because of the metal-metal bonding asymmetry in the mixed metal clusters; for the corresponding symmetric Pt(2) and Pd(2) adducts, 5 and 13, the release of SO(2) is significantly slower (>1 ns). All these compounds may have potential to serve as light-triggered local and instantaneous sources of the studied gases.     

Layered zinc hydroxide salts: delamination, preferred orientation of hydroxide lamellae, and formation of ZnO nanodiscs

Herein, we report our analysis of the surface modification of polystyrene (PS) when treated under ambient conditions with a common biological buffer such as phosphate buffered saline (PBS) or aqueous solutions of the ionic constituents of PBS. Attenuated total reflection Fourier transform infrared spectroscopy was used for the analysis because the resultant spectra are very sensitive to minor changes in the chemical and structural properties of PS films. In addition, ultraviolet-visible spectroscopy was applied to characterize the surface modifications of PS. Treatment with PBS resulted in the most significant chemical and structural surface modifications of the PS films, as compared with each of the solutions of the constituents of PBS, which were tested separately. A multistep mechanism for the wet modification of PS is discussed. We postulate that the observed surface modifications are the result of photo-oxidation/reduction, swelling, and conformational changes and re-arrangement of the polymer chain. The resultant surface modifications could be similar to those produced by commonly used dry processes such as plasma treatments and electron, ion or ultraviolet irradiation. We found that the modifications that occurred in PBS were more stable than those initiated by dry processes. The formation of active groups on the surface of PS can be controlled by adsorption of bovine serum albumin or thermal annealing of PS before PBS treatment. This approach provides a simple and efficient method for the surface modification of PS for biomedical applications.     

Heat capacity studies of the iron oxyhydroxides akaganéite (β-FeOOH) and lepidocrocite (γ-FeOOH)

The iron oxides and iron oxyhydroxides exist as several different polymorphs, and a thermodynamic understanding of these polymorphs can provide us with an understanding of their relative stability and chemical reactivity. This study provides heat capacity measurements for lepidocrocite (γ-FeOOH) over the temperature range (0.8 to 38) K and akaganéite (β-FeOOH) over the range (0.7 to 302) K. Fits of the heat capacity of the two samples below T = 15 K showed similar behavior to previously published fits of goethite (α-FeOOH), which required a linear term and an anisotropic gap parameter to model accurately the antiferromagnetic spin–wave contributions. The akaganéite measurements were compared to previously reported measurements all of which showed significant disagreement. It is believed that the measurements reported here are the most reliable. Also, the presence of adsorbed water contributes significantly to the heat capacity of akaganéite, and the standard molar entropy at T = 298.15 K of the hydrated form was calculated to be (81.8 ± 2) J · mol^?1 · K^?1.     

Preparation of poly(methyl methacrylate) grafted hydroxyapatite nanoparticles via reverse ATRP

Surface-initiated reverse atom transfer radical polymerization (reverse ATRP) technical was successfully employed to modify hydroxyapatite (HAP) nanoparticles with poly(methyl methacrylate) (PMMA). The peroxide initiator moiety for reverse ATRP was covalently attached to the HAP surface through the surface hydroxyl groups. Reverse ATRP of methyl methacrylate (MMA) from the initiator-functionalized HAP was carried out, and the end bromide groups of grafted PMMA initiated ATRP of MMA subsequently. Fourier transformation infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM) were employed to confirm the grafting and to characterize the nanoparticle structure. The grafted PMMA gave HAP nanoparticles excellent dispersibility in MMA monomer. As the amount of grafted PMMA increased, the dispersibility of surface-grafted HAP and the compressive strength of HAP/PMMA composites were improved.     

Charge transfer in porphyrin-calixarene complexes: ultrafast kinetics, cyclic voltammetry, and DFT calculations

Transient absorption spectroscopy, cyclic voltammetry, and DFT calculations were used to describe charge transfer processes in a series of 5,10,15,20-tetrakis(N-methylpyridinium-n-yl) porphyrins (TMPyPn, n = 4,3,2) and TMPyPn/p-sulfonatocalix[m]arene (clxm, m = 4,6,8) complexes. Excitation of TMPyPn is accompanied by an increasing electron density at the methylpyridinium substituents in the order TMPyP2 < TMPyP3 < TMPyP4. The quenching of the excited singlet states of the complexes increases with the number of ionized phenolic groups of clxm and can be correlated with the partial transfer of the electron density from O(-) to the peripheral methylpyridinium substituents rather than to the porphyrin ring.     

A microfluidic system with optical laser tweezers to study mechanotransduction and focal adhesion recruitment

We present a new method to locally apply mechanical tensile and compressive force on single cells based on integration of a microfluidic device with an optical laser tweezers. This system can locate a single cell within customized wells exposing a square-like membrane segment to a functionalized bead. Beads are coated with extracellular matrix (ECM) proteins of interest (e.g. fibronectin) to activate specific membrane receptors (e.g. integrins). The functionalized beads are trapped and manipulated by optical tweezers to apply mechanical load on the ECM-integrin-cytoskeleton linkage. Activation of the receptor is visualized by accumulation of expressed fluorescent proteins. This platform facilitates isolation of single cells and excitation by tensile/compressive forces applied directly to the focal adhesion via specific membrane receptors. Protein assembly or recruitment in a focal adhesion can then be monitored and identified using fluorescent imaging. This platform is used to study the recruitment of vinculin upon the application of external tensile force to single endothelial cells. Vinculin appears to be recruited above the forced bead as an elliptical cloud, centered 2.1 ± 0.5 μm from the 2 μm bead center. The mechanical stiffness of the membrane patch inferred from this measurement is 42.9 ± 6.4 pN μm(-1) for a 5 μm × 5 μm membrane segment. This method provides a foundation for further studies of mechanotransduction and tensile stiffness of single cells.     

A diabolo-shaped Dy9 cluster: synthesis, crystal structure and magnetic properties

The reaction of Dy(NO(3))(3)·6H(2)O with the ligand 2-((1-hydroxybutan-2-ylimino)methyl)phenol (H(2)L, ) generates the nonanuclear compound [Dy(9)L(8)(μ(3)-OH)(8)(μ(4)-OH)(2)(CH(3)OH)(8)](OH)(CH(3)OH)(3) (Dy(9)), whose single-crystal X-ray structure reveals the presence of two square pyramidal pentanuclear units assembled via the apical metal center. The square pyramidal core of a previously reported [Dy(5)(μ(4)-OH)(μ(3)-OH)(4)(μ-η(2)-Ph(2)acac)(4)(η(2)-Ph(2)acac)(6)] (Dy(5); Ph(2)acac = dibenzoylmethanide), is structurally related to those herein described; however, the magnetic properties of Dy(9) and Dy(5) are drastically different. Indeed, Dy(5) shows slow relaxation of magnetization while no out-of-phase ac signal is noticed for Dy(9). The underlying mechanism is not clear due to the complexity of such systems; however, the different anisotropy of the respective structures, which is dictated by the combination of the metal topology, the ligands involved and the structural parameters of the molecule, is mostly responsible for the distinctive relaxation dynamics observed.