Improved analysis of melamine-formaldehyde resins by capillary zone electrophoresis-mass spectrometry using ion-trap and quadrupole-time-of-flight mass spectrometers

An improved method based on capillary zone electrophoresis (CZE) coupled to either ion-trap (IT) mass spectrometry (MS) or quadrupole-time-of-flight (Q-TOF) MS for the analysis of melamine-formaldehyde condensates is presented. Employing a formic acid-based electrolyte containing 50% acetonitrile (ACN) and MS detection up to 13 compounds could be determined in lab-made resins, synthesized by mixing formaldehyde and melamine in different ratios ranging from 1:1.5 to 1:4. The use of a Q-TOF-MS for detection allowed the assignment of molecular formulas for all 13 substances with high accuracy.     

New insights into urea action on proteins: a SANS study of the lysozyme case

We present a study on lysozyme dissolved in mixtures of water and urea, which is ubiquitously used as a protein denaturant. Despite the wide use of urea, the basic molecular mechanisms inducing protein unfolding are not still clarified. Small-angle neutron scattering (SANS) experiments have been performed using little amounts of denaturant in solutions in order to investigate the urea effect on lysozyme preceding the unfolding process. A global fit strategy, applied to analyze SANS experiments, provides an estimation of the average composition of the solvent in the close vicinity of the protein surface and the change of the protein-protein interactions due to the presence of urea. In particular, the thermodynamic equilibrium constant responsible for cosolvent balancing between the bulk and solvation layer has been determined. It turns out that urea is preferentially driven to the protein surface, confirming literature results at infinite dilute conditions. SANS data also reveal a possible variation of the protein net charge as a function of urea concentration, opening new perspectives and questions about the protein surface architecture at the first stages of unfolding processes.     

The coordination behaviour of ferrocene-based pyridylphosphine ligands towards Zn(II), Cd(II) and Hg(II)

The reaction of Group 12 metal dihalides MX(2) with the P,N-ligands [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-2-py)] (1) (2-py = pyrid-2-yl), [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-CH(2)-2-py)] (2) and [Fe(C(5)H(4)-PPh(2))(C(5)H(4)-3-py)] (3) (3-py = pyrid-3-yl) was investigated. For a 1 : 1 molar ratio of MX(2) and the respective ligand, three structure types were found in the solid state, viz. chelate, cyclic dimer and chain-like coordination polymer. The M(II) coordination environment is distorted pseudo-tetrahedral in each case. The P-M-N angle is much larger in the chelates (≥119°) than in the ligand-bridged structures (≤109°). 1 prefers the formation of chelates [MX(2)(1-κ(2)N,P)]. 3 forms coordination polymers [MX(2)(μ-3)](n). With the more flexible 2 all three structure types can occur. Dynamic coordination equilibria were observed in solution for the molecular complexes obtained with 1 and 2. NMR data indicate that the N- and P-donor sites interact most strongly with Zn(II) and Hg(II), respectively. While the formation of bis(phosphine)mercury complexes (soft-soft) was easily achieved, no bis(pyridine)zinc complex (borderline-borderline) could be obtained, which is surprising in view of the HSAB principle.     

2′-O-Lysylaminohexyladenosine modified oligonucleotides

Abstract  

Development of therapeutically active oligonucleotides for sequence-specific gene knockdown relies on chemical modifications that confer high stability and target affinity and ideally enable cellular uptake. 2′-O-Lysylaminohexyluridine-containing antisense and siRNA oligonucleotides have been shown to be well suited for gene knockdown. They are highly resistant to enzymatic degradation while having good affinity for the targeted RNA strand and efficiently down-regulate their target in cell culture tumor models. The 2′-O-lysylaminohexyl modification was expanded to adenosine nucleosides. The corresponding phosphoramidite building block was prepared in a straightforward procedure comprising six steps starting from adenosine. After 2′-O-alkylation with N-(6-bromohexyl)phthalimide and removal of the N-protecting group, the protected lysine was specifically attached to the alkylamino group. Incorporation of 2′-O-lysylaminohexyladenosine nucleotides in a test sequence confirmed that the cationic chains lead only to minor duplex destabilization and do not disturb the duplex structure. Results further emphasize the advantageous properties of 2′-O-lysylaminohexyl modified oligonucleotides for therapeutic applications.     

Synthesis and characterization of the La1−xSrxFeO3−δ system and the fluorinated phases La1−xSrxFeO3−xFx

The oxyfluorides La_1−xSr_xFeO_3−xF_x have been prepared by fluorination of the precursor oxides La_1−xSr_xFeO_3−δ via a low temperature route using poly(vinylidene fluoride) (PVDF). The structures of the oxides and oxyfluorides were investigated in detail by the Rietveld analysis of powder diffraction data. The oxyfluorides crystallize in the space group Pnma for 0<x≤0.9 (SrFeO₂F itself is cubic, space group Pm-3m) and show a sort of two-step structural distortion for decreasing x. Furthermore, a structural comparison of the oxyfluorides with the oxides is given, revealing an increase of the volume per La_1−xSr_xFeX₃ unit during fluorination, of which the magnitude highly depends on the value of x.     

Ru9Zn7Sb8: a structure with a 2 × 2 × 2 supercell of the half-Heusler phase

The title compound Ru(9)Zn(7)Sb(8) was synthesized via a high-temperature reaction from the elements in a stoichiometric ratio, and its structure was solved by a single-crystal X-ray diffraction method. The structure [cubic, space group Fm3m, Pearson symbol cF96, a = 11.9062(14) ? (293 K), and Z = 4] adopts a unique 2a(hh) × 2a(hh) × 2a(hh) supercell of a normal half-Heusler phase and shows abnormal features of atomic coordination against the Pauling rule. The formation of this superstructure was discussed in light of the valence electron concentration per unit cell. It is a metallic conductor [ρ(300 K) = 16 μΩ·m], and differential scanning calorimetry revealed that Ru(9)Zn(7)Sb(8) undergoes a transformation at 1356(1) K and melts, by all indications, congruently at 1386 K. At room temperature, its thermal conductivity is about 3 W/m·K, which is only one-quarter of that of most normal half-Heusler phases. Ru(9)Zn(7)Sb(8) as well as its analogues of iron-, cobalt-, rhodium-, and iridium-containing compounds are expected to serve as a new structure type for exploring new thermoelectric materials.     

Local structure of amorphous ice as revealed by O K-edge EXAFS.

The oxygen K-edge extended X-ray absorption fine structure (EXAFS) spectrum of an ice film prepared by deposition of water vapor on a substrate at 100 K was measured in the surface-sensitive Auger yield mode. Five distinct peaks are revealed in the Fourier transform spectrum of the EXAFS data. The peaks are attributed to O-H bonds (with overlapping contributions from intramolecular covalent and intermolecular hydrogen bonds) as well as to intermolecular O...O scattering paths in the distance range of 1-7 A. The pattern of the longer O...O distances resembles that of a high-pressure crystalline modification of ice (ice II).     

Structure and spacing of cellulose microfibrils in woody cell walls of dicots

The structure of cellulose microfibrils in situ in wood from the dicotyledonous (hardwood) species cherry and birch, and the vascular tissue from sunflower stems, was examined by wide-angle X-ray and neutron scattering (WAXS and WANS) and small-angle neutron scattering (SANS). Deuteration of accessible cellulose chains followed by WANS showed that these chains were packed at similar spacings to crystalline cellulose, consistent with their inclusion in the microfibril dimensions and with a location at the surface of the microfibrils. Using the Scherrer equation and correcting for considerable lateral disorder, the microfibril dimensions of cherry, birch and sunflower microfibrils perpendicular to the [200] crystal plane were estimated as 3.0, 3.4 and 3.3 nm respectively. The lateral dimensions in other directions were more difficult to correct for disorder but appeared to be 3 nm or less. However for cherry and sunflower, the microfibril spacing estimated by SANS was about 4 nm and was insensitive to the presence of moisture. If the microfibril width was 3 nm as estimated by WAXS, the SANS spacing suggests that a non-cellulosic polymer segment might in places separate the aggregated cellulose microfibrils.     

Stereo‐ and Regioselective Phyllobilane Oxidation in Leaf Homogenates of the Peace Lily (Spathiphyllum wallisii): Hypothetical Endogenous Path to Yellow Chlorophyll Catabolites

In senescent leaves, chlorophyll typically is broken down to colorless and essentially photo‐inactive phyllobilanes, which are linear tetrapyrroles classified as “nonfluorescent” chlorophyll catabolites (NCCs) and dioxobilane‐type NCCs (DNCCs). In homogenates of senescent leaves of the tropical evergreen Spathiphyllum wallisii, when left at room temperature and extracted with methanol, the major endogenous, naturally formed NCC was regio‐ and stereoselectively oxidized (in part) to a mixture of its 15‐hydroxy and 15‐methoxy derivative. In the absence of methanol in the extract, only the 15‐OH‐NCC was observed. The endogenous oxidation process depended upon molecular oxygen. It was inhibited by carbon monoxide, as well as by keeping the leaf homogenate and extract at low temperatures. The remarkable “oxidative activity” was inactivated by heating the homogenate for 10 min at 70 °C. Upon addition of a natural epimeric NCC (epiNCC) to the homogenate of senescent or green Sp. wallisii leaves at room temperature, the exogenous epiNCC was oxidized regio‐ and stereoselectively to 15‐OH‐epiNCC and 15‐OMe‐epiNCC. The identical two oxidized epiNCCs were also obtained as products of the oxidation of epiNCC with dicyanodichlorobenzoquinone (DDQ). Water elimination from 15‐OH‐epiNCC occurred readily and gave a known “yellow” chlorophyll catabolite (YCC). The endogenous oxidation process, described here, may represent the elusive natural path from the colorless NCCs to yellow and pink coloured phyllobilins, which were found in (extracts of) some senescent leaves.     

Semiconductor quantum dots for photodynamic therapy

The applicability of semiconductor QDs in photodynamic therapy (PDT) was evaluated by studying the interaction between CdSe QDs with a known silicon phthalocyanine PDT photosensitizer, Pc4. The study revealed that the QDs could be used to sensitize the PDT agent through a fluorescence resonance energy transfer (FRET) mechanism, or interact directly with molecular oxygen via a triplet energy-transfer process (TET). Both mechanisms result in the generation of reactive singlet oxygen species that can be used for PDT cancer therapy.