Chemical, structural, and thermal properties of Zn(II)-Cr(III) layered double hydroxides intercalated with sulfated and sulfonated surfactants

Zn(II)-Cr(III)-LDHs (layered double hydroxides) containing sulfated or sulfonated surfactants as the interlamellar anion were synthesized by the coprecipitation method. The syntheses were conducted under various different experimental conditions, such as the Zn : Cr ratio, pH, and aging time. In each of the prepared materials, unlike previously reported data, the interlayer anion arrangement did not change, being consistent with a perpendicular monolayer. The thermal decomposition process of the prepared materials was studied by a set of analysis methods, such as TG/DTA, TG/MS, PXRD, and FT-IR. From the results obtained it was possible to conclude that, in an air atmosphere, the anions decomposed by a partial combustion, leading to the formation of sulfide. The results also showed that sulfonated surfactants containing LDHs are much more stable than those containing sulfated surfactants. A mechanism was proposed for the thermal decomposition of such LDHs based on the experimental results.     

Water adsorption in disordered mesoporous silica (Vycor) at 300 K and 650 K: a Grand Canonical Monte Carlo simulation study of hysteresis

This numerical simulation paper focuses on the adsorption/desorption of water in disordered mesoporous silica glasses (Vycor-like). The numerical adsorbent was previously obtained by off lattice method, and was shown to reproduce quite well the micro- and mesotextural properties of real Vycor, as well as morphological (pore size distribution) and topological (pore interconnections) disorder. The water-water interactions are described by the SPC model while water-silica interactions are calculated in the framework of the PN-TrAZ model. The water adsorption/desorption isotherms and the configurational energies are calculated by the Grand Canonical Monte Carlo simulation method. The low pressure results compare well with experiments, showing the good transferability of the intermolecular potential. It is shown that if the hysteresis loop observed in the adsorption/desorption isotherm is considered as a true phase transition (which is actually still an open question in the case of disordered porous materials), then it is possible to calculate the grand potential by applying the thermodynamic integration scheme. The grand potential is shown to be multivalued for low (subcritical) temperature, and continuous for high (supercritical) temperature. A coexistence point is found within the hysteresis loop, actually close to the vertical desorption line. Below the equilibrium chemical potential, the gaslike branch is stable whereas the liquidlike branch is metastable. The situation is reversed above the coexistence point.     

Evaluation of the immobilized artificial membrane phosphatidylcholine: Drug discovery column for high-performance liquid chromatographic screening of drug–membrane interactions

Chromatographic retention factors (k′) of a series of eight β-adrenoceptor antagonist compounds (β-adrenolytic drugs) were determined employing an immobilized artificial membrane column (IAM.PC.DD). The influence of mobile phase pH, ionic strength, and organic modifier composition was studied in order to examine column performance. After the IAM.PC.DD columns were exposed to approximately 7000 column volumes of a 0.01 M PBS mobile phase, five out of six columns tested showed significant peak broadening and decreased k′ values indicative of premature column failure. The data suggested that the immobilized phospholipids stationary phase was removed by the 0.01 M PBS mobile phase. The β-adrenolytic drug's log k′_IAM values obtained with an IAM.PC.DD column were compared to an ^esterIAM.PC.MG column for predicting drug membrane interactions. For the linear regression analysis between log k′_IAM and the logarithm of the n-octanol–water partition coefficients (r_IAM.PC.DD=0.8710 vs. r_IAM.PC.MG=0.9538), the C₁₈ HPLC retention factors (r_IAM.PC.DD=0.8408 vs. r_IAM.PC.MG=0.9380), the liposome partition coefficients (r_IAM.PC.DD=0.8887 vs. r_IAM.PC.MG=0.9187), and various pharmacokinetic parameters, significantly better correlations were obtained with the ^esterIAM.PC.MG column than the IAM.PC.DD column.     

Optimization of matrix-assisted laser desorption/ionization time-of-flight collision-induced dissociation using poly(ethylene glycol)

Details of the optimization of the collision-induced dissociation (CID) process, using a collision cell on a matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer, are described using poly(ethylene glycol) 1000 (PEG 1000) as a model analyte. The effects of collision gas identity (helium, air, and argon), as well as collision gas pressure, on the resulting MS/MS data were investigated. With PEG 1000, helium was found to give the best results with respect to signal-to-noise (S/N) ratio. The optimum pressure for each gas was found to be in the range where the precursor ion signal was attenuated to approximately 30-50% for helium and 40-60% for argon. The effect of cation choice (Li, Na, and K) on the CID of PEG was also studied. CID spectra were produced for each, but PEG cationized with lithium was found to produce the spectra with the highest S/N ratio. The MALDI-TOF CID spectra that were generated for PEG were compared with the high-energy and low-energy MS/MS spectra obtained from a sector mass spectrometer and from a triple quadrupole mass spectrometer, respectively. The results observed for PEG confirm that CID on a MALDI-TOF mass spectrometer is a high-energy MS/MS technique.     

Channel flow cell studies on the evaluation of surface pretreatments using phosphoric acid or polymaleic acid for calcite stone protection

The dissolution kinetics of surface-pretreated and weathered calcite was investigated in dilute acid using a channel flow cell with microdisk detection. Two pretreatments were studied, polymaleic acid and phosphoric acid. Treatment with polymaleic acid was shown to significantly passivate calcite but to a lesser extent than the phosphoric acid and the former coating was found to be less effective for protection of calcite from acid attack. However, treatment of calcite with phosphoric acid resulted in the passivation of calcite from acid attack which strongly inhibited dissolution, an effect that was enhanced even further after exposure to the environment.     

S1P1-selective in vivo-active agonists from high-throughput screening: off-the-shelf chemical probes of receptor interactions, signaling, and fate

The essential role of the sphingosine 1-phosphate (S1P) receptor S1P(1) in regulating lymphocyte trafficking was demonstrated with the S1P(1)-selective nanomolar agonist, SEW2871. Despite its lack of charged headgroup, the tetraaromatic compound SEW2871 binds and activates S1P(1) through a combination of hydrophobic and ion-dipole interactions. Both S1P and SEW2871 activated ERK, Akt, and Rac signaling pathways and induced S1P(1) internalization and recycling, unlike FTY720-phosphate, which induces receptor degradation. Agonism with receptor recycling is sufficient for alteration of lymphocyte trafficking by S1P and SEW2871. S1P(1) modeling and mutagenesis studies revealed that residues binding the S1P headgroup are required for kinase activation by both S1P and SEW2871. Therefore, SEW2871 recapitulates the action of S1P in all the signaling pathways examined and overlaps in interactions with key headgroup binding receptor residues, presumably replacing salt-bridge interactions with ion-dipole interactions.     

Selective cleavage of P-N bonds and the conversion of rhodium N-pyrrolyl phosphine complexes into diphosphoxane-bridged dimers

Rhodium(I) complexes trans-[RhCl(CO)(PR(2)[NC(4)H(3)C(O)Me-2])(2)] (R = Ph, NC(4)H(4)) react with water to give the diphosphoxane-bridged dimers [Rh(2)Cl(2)(CO)(2)(mu-PR(2)OPR(2))(2)] following cleavage of the P-N bonds to the 2-acetyl-N-pyrrolyl groups. The two dimers have been crystallographically characterized and show a number of structural differences, with the PPh(2)OPPh(2) compound possessing semibridging chloride and carbonyl ligands whereas the P(NC(4)H(4))(2)OP(NC(4)H(4))(2) compound contains only terminal chlorides and carbonyls. No evidence for cleavage of the P-N bonds involving the unfunctionalized N-pyrrolyl groups in trans-[RhCl(CO)(P[NC(4)H(4)](2)[NC(4)H(3)C(O)Me-2])(2)] was observed.     

Solid-phase synthesis of amidines by the reduction of amidoximes

Amidines can be prepared on a solid support by reducing polymer-bound amidoximes with SnCl₂·2H₂O. The method has proved to be straightforward and highly efficient. Amidoximes attached to the solid support are readily available by treating resin-bound nitriles with hydroxylamine.     

Toward a microchip-based solid-phase extraction method for isolation of nucleic acids

A silica-based solid-phase extraction system suitable for incorporation into a microchip platform (nu-total analytical system; nu-TAS) would find utility in a variety of genetic analysis protocols, including DNA sequencing. The extraction procedure utilized is based on adsorption of the DNA onto bare silica. The procedure involves three steps: (i) DNA adsorption in the presence of a chaotropic salt, (ii) removal of contaminants with an alcohol/water solution, and (iii) elution of the adsorbed DNA in a small volume of buffer suitable for polymerase chain reaction (PCR) amplification. Multiple approaches for incorporation of this protocol into a microchip were examined with regard to extraction efficiency, reproducibility, stability, and the potential to provide PCR-amplifiable DNA. These included packing microchannels with silica beads only, generating a continuous silica network via sol-gel chemistry, and combinations of these. The optimal approach was found to involve immobilizing silica beads packed into the channel using a sol-gel network. This method allowed for successful extraction and elution of nanogram quantities of DNA in less than 25 min, with the DNA obtained in the elution buffer fraction. Evaluation of the eluted DNA indicated that it was of suitable quality for subsequent amplification by PCR.     

Rhodium(II)-Catalyzed CH Insertions with {[(4-Nitrophenyl)sulfonyl]imino}phenyl-λ3-iodane

The [Rh₂(OAc)₄]-catalyzed decomposition of {[(4-nitrophenyl)sulfonyl]imino}phenyl-λ³-iodane (NsN?IPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by O-substituents. Scope and limitations of the reaction were investigated. Yields of up to 84% were achieved in the most favorable cases. Yields were enhanced by electron-releasing substituents and decreased by steric hindrance. Aziridination competed with allylic insertion with olefinic substrates. The insertion reaction proceeded with retention of configuration. With chiral Rh^II catalysts, a modest asymmetric induction was observed. A mechanism involving direct insertion by a Rh-complexed nitrene into the CH bond is proposed.