Magnetocaloric effect in Gd-based Gd60FexCo30−xAl10 metallic glasses

Magnetocaloric effect and refrigerant capacity of Gd-based Gd₆₀Fe_xCo_30−xAl₁₀ metallic glasses are investigated for x = 0, 10 , 20 and 30. It is found that the non-linearity of saturation magnetization in crystalline Co-Fe binary alloys can be transferred to the quaternary metallic glass. Whereas the magnetocaloric specific values of Gd₆₀Co₃₀Al₁₀ are comparable in magnitude with those of other Gd-based metallic glasses, Fe addition leads to an increase of the saturation magnetization and refrigerator capacity with a maximum for x = 20. Simultaneously, the temperature of maximum isothermal change of magnetic entropy T_ΔSmax increases from 145 to 200 K with increasing Fe-content and also the halfwidth ΔT_Smax/2 of the ΔS-T-curve is considerably broadened. Furthermore, the effect of thermal treatment slightly above the first crystallization event on the magnetocaloric effect are investigated, showing a lowering of the working temperature in the first place.     

Structural and Electronic Properties of Ultrathin Tin–Phthalocyanine Films on Ag(111) at the Single‐Molecule Level

Heads or tails? The evolution of structural and electronic properties of tin–phthalocyanine films has been analyzed for sub‐monolayer to multilayer coverage using low‐temperature scanning tunneling microscopy. Two molecular conformations are observed: randomly dispersed for the first layer, and islands with a single conformation in subsequent layers.

     

Patterned Monolayers of Neutral and Charged Functionalized Manganese Arene Complexes on a Highly Ordered Pyrolytic Graphite Surface

Complex patterns : The arene manganese tricarbonyl complexes [Mn(η⁵‐2,5‐didodecoxy‐1,4‐semiquinone)(CO)₃] and [Mn(η⁶‐1,4‐dioctyloxybenzene)(CO)₃] BF₄ form patterned monolayers on the surface of highly ordered pyrolytic graphite (HOPG), as a result of hydrogen‐bonding, hydrophobic, and electrostatic interactions, leading to an ordered 2D array of manganese atoms or ions.

     

Robust Supramolecular Network on Ag(111): Hydrogen‐Bond Enhancement through Partial Alcohol Dehydrogenation

Alcohol oxidation and self‐assembly: the in situ oxidation of hydroxyl functional groups to quinone groups promotes the formation of enhanced hydrogen bonds and allows reorganization of the resulting supramolecular self‐assemblies, which evolve from a weakly bound dense phase to a strongly bound nanoporous open structure (see picture).

     

Effects of Fullerenes on Phospholipid Membranes: A Langmuir Monolayer Study

We investigate two‐component Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC)/C₆₀ by recording surface pressure/area (π/A) and surface potential/area (ΔV/A) isotherms and by direct Brewster angle microscopy (BAM) imaging. Atomic force microscopy (AFM) is employed to study morphologies of the mixed monolayers transferred to a solid substrate by the Langmuir–Blodgett technique. C₆₀ is shown to have little influence on isotherms of the DPPC/C₆₀ monolayers even at a molar fraction as high as X_C60=0.3. The elastic modulus ( ) versus π curves of the DPPC/C₆₀ monolayers almost overlay each other, as well as that of pure DPPC, that is, the elasticities of pure DPPC monolayers and DPPC/C₆₀ monolayers are remarkably similar. AFM studies reveal that fullerene flocs form at low surface pressures (π≤15 mN m^?1), are gradually disaggregated and dispersed in the DPPC monolayer with increasing surface pressure up to 35 mN m^?1, and are then progressively squeezed out to form protruded islands as the surface pressure increases up to 65 mN m^?1. Our work provides experimental support to the computational result that C₆₀ can dissolve in lipid bilayers without significantly compromising their mechanical properties, a finding which has important implications for the toxicity and development of drug vehicles from fullerene materials.     

Adsorption of Large Organic Molecules on Clean and Hydroxylated Rutile TiO2(110) Surfaces

Behavior of large organic molecules equipped with spacer groups (Violet Landers, VL) on the TiO₂(110)‐(1×1) surfaces is investigated by means of high‐resolution scanning tunneling microscopy (STM). Two distinct adsorption geometries are observed. We demonstrate that the molecule adsorption morphology can be alternated by well‐controlled STM tip‐induced manipulation. It is used to probe the mobility of molecules and reveals locking in one of the analyzed adsorption sites, thus allow to enhance or reduce the mobility along the [001] direction. Field induced hydrogen desorption is used to perform lateral STM manipulation on a hydroxyl‐free surface, which provides insight into the influence of surface hydroxyl groups on the molecule behavior. The ability to image with submolecular resolution both the central board and the spacer groups of the VL molecule is demonstrated.     

AFM‐Correlated CSM‐Coupled Raman/Fluorescence Studies on Selective Interactions of Water Soluble Porphyrins with DNA

The Raman and fluorescence spectroscopic properties of water‐soluble oxo‐titanium(IV) mesotetrakis (1‐methyl pyridium‐4‐yl) porphyrin (O=Ti(TMPyP)⁴⁺) bound with calf thymus DNA and artificial DNAs such as double stranded poly[d(A‐T)₂] and poly[d(G‐C)₂] have been investigated on the single DNA molecule basis by AFM‐correlated confocal scanning microscope (CSM)‐coupled Raman and fluorescence spectroscopic techniques as well as the ensemble‐averaged spectroscopy. The ensemble‐averaged spectroscopic studies imply that the porphyrin interacts with DNA in different groove binding patterns depending on the base pairs. AFM‐images of the different DNAs bound with O=Ti(TMPyP)⁴⁺ were measured, and their morphologies are found to depend on kind of base pairs interacting with O=Ti(TMPyP)⁴⁺. Being correlated with the AFM images, the CSM‐coupled Raman and fluorescence spectral properties of the three different single O=Ti(TMPyP)⁴⁺‐DNA complexes were observed to be highly resolved and sensitive to base pair‐dependent axial ligation of Ti‐O bond as compared to the corresponding ensemble‐averaged spectral properties, which affect the groove binding and its strength of the O=Ti(TMPyP)⁴⁺ with DNA. The axial ligation was found to be accompanied by vibration structural change of the porphyrin ring, leading to keep the shape of double stranded poly[d(A‐T)₂] rigid while poly‐[d(G‐C)₂] and calf thymus DNA flexible after binding with the oxo‐titanyl porphyrin. The base pair dependence of the fluorescence decay times of the DNA‐bound porphyrins was also observed, implying that an excited‐state charge transfer takes place in the G‐C rich major groove in calf thymus DNA. These results suggest that binding of O=Ti(TMPyP)⁴⁺ is more preferential with the G‐C rich major groove than with the A‐T rich minor groove in calf thymus DNA so that the morphology of DNA is changed.     

Determination of marker pteridins and biopterin reduced forms, tetrahydrobiopterin and dihydrobiopterin, in human urine, using a post-column photoinduced fluorescence liquid chromatographic derivatization method

A liquid chromatographic method for the simultaneous analysis of marker pteridins and biopterin reduced forms, in urine samples is proposed. A Zorbax Eclipse XDB-C18 column was used for the chromatographic separation, using a 98/2 (v/v), citrate buffer (pH 5.5)-acetonitrile mobile phase, in isocratic mode. A post-column photoderivatization was carried out with an on-line photoreactor, located between a diode array detector (DAD) and a fast scanning fluorescence detector (FSFD). Neopterin (NEO), biopterin (BIO), pterin (PT) and dihydrobiopterin (BH2) were determined by measuring native fluorescence, using the photoreactor in OFF-mode, and tetrahydrobiopterin (BH4) was determined by measuring of the induced fluorescence of the generated photoproducts, using the photoreactor in ON-mode. In addition, Creatinine (CREA), as a reference of metabolites excrection in urine, was simultaneously determined using the DAD detector. Detection limits were 0.2, 13.0, 0.3, 0.3 and 3.5 ng mL⁻¹, for NEO, BH2, BIO, PT and BH4, respectively, and 0.4 μg mL⁻¹ for CREA. Ratio values for NEO/CREA, PT/CREA, BH4/CREA, BH2/CREA, NEO/BIO and BIO_total/CREA, in urine samples, of healthy children and adults, phenylketonuric children and infected mononucleosis children, are reported. A comparative study, about the mean values obtained for each of the compounds, by the present procedure and by the classical iodine oxidation method (Fukushimás method), has been performed, in urine samples belonging to healthy volunteers. The values obtained were BH4/CREA: 0.41, BH2/CREA: 0.31 and BIO_total/CREA: 0.73, by the proposed method, and BH4/CREA: 0.35, BH2/CREA: 0.20 and BIO_total/CREA: 0.48, by iodine oxidation method.     

Purity determination and uncertainty evaluation of theophylline by mass balance method, high performance liquid chromatography and differential scanning calorimetry

Purity determination of pure organic substance is essential for the establishment of traceability to SI units. A mass balance method was employed to determine the purity of theophylline certified reference materials (CRM), compared with high performance liquid chromatography (HPLC) and differential scanning calorimetry (DSC). In the approach of the mass balance, the impurities were identified by ion trap time-of-flight mass spectrometer (IT-TOF-MS) and quantified by HPLC. The purity of theophylline CRM determined by mass balance method was 99.82% with an extended uncertainty of 0.1% (k = 2). The uncertainty evaluation of purity demonstrated that the accuracy of the mass balance method is better than that of HPLC and DSC. It indicated that the mass balance is suitable for the CRM and pharmaceutical standards.     

Thermodynamics of BaNd2Fe2O7(s) and BaNdFeO4(s) in the system BaNdFeO

Two compounds, BaNd₂Fe₂O₇(s) and BaNdFeO₄(s) in the quaternary system BaNdFeO were prepared by citrate-nitrate gel combustion route and characterized by X-ray diffraction analysis. Heat capacities of these two oxides were measured in two different temperature ranges: (i) 130-325 K and (ii) 310-845 K, using a heat flux type differential scanning calorimeter. Two different types of solid-state electrochemical cells with CaF₂(s) as the solid electrolyte were employed to measure the e.m.f. as a function of temperature. The standard molar Gibbs energies of formation of these quaternary oxides were calculated as a function of temperature from the e.m.f. data. The standard molar enthalpies of formation from elements at 298.15 K, ΔfHm° (298.15 K) and the standard entropies, Sm° (298.15 K) of these oxides were calculated by the second law method. The values of ΔfHm° (298.15 K) and Sm° (298.15 K) obtained for BaNd₂Fe₂O₇(s) are: −2756.9 kJ mol⁻¹ and 234.0 J K⁻¹ mol⁻¹ whereas those for BaNdFeO₄(s) are: −2061.5 kJ mol⁻¹ and 91.6 J K⁻¹ mol⁻¹, respectively.