Monitoring the coordination of aluminium during microporous oxide crystallisation by in situ soft X-ray absorption spectroscopy

An in situ cell, which is capable of obtaining time resolved soft X-ray data (200 eV < E < 3000 eV) under hydrothermal conditions has been developed and used to study the self-assembly processes occurring during microporous aluminophosphate crystallization.     

Synthesis of the ester side chains of some potently antileukemic harringtonia alkaloids from chiral citrates

The selective reduction of one of the three carboxyl groups of two chiral citric acid derivatives to the corresponding aldehydes, under Rosenmund conditions, are reported together with the application of these aldehydes to the syntheses of the ester side chains of some potently antileukemic Cephalotaxus alkaloids e.g. anhydroharringtonine.     

New insights into the coordination chemistry and molecular structure of copper(II) histidine complexes in aqueous solutions

Aqueous solutions of Cu2+/histidine (his) (1:2) have been analyzed in parallel with infrared, Raman, ultraviolet/visible/near-infrared, electron spin resonance, and X-ray absorption spectroscopy in the pH range from 0 to 10. Comprehensive interpretation of the data has been used to extract complementary structural information in order to determine the relative abundance of the different complexes. The formation of six different, partly coexisting species is proposed. Structural proposals from literature have been unambiguously confirmed, refined, or, in several cases, corrected. At highly acidic conditions, Cu2+ and his are present as free ions, but around pH = 2, coordination starts via the deprotonated carboxylic acid group. This results in the intermediate species Cu2+[H3his+(Oc)] and Cu2+[H3his+(Oc)]2. The coordination via Oc is attended with a drop in the pKa value of the other receptor groups resulting in a concomitant conversion to the bidentates Cu2+[H2his0(Oc,Nam)] and Cu2+[H2his0(Oc,Nam)]2, with the latter being dominant at pH = 3.5. Coordination of the imidazole ring begins around pH = 3 and leads to the formation of the mixed ligand complexes Cu2+[H2his0(Oc,Nam)][Hhis-(Oc,Nam,Nim)] and Cu2+[Hhis-(Nam,Nim)][Hhis-(Oc,Nam,Nim)] around pH = 5. It is demonstrated that coordination of the imidazole ring occurs predominantly via the N(pi) atom. At pH > 7, the double-tridentate ligand complex Cu2+[Hhis-(Oc,Nam,Nim)]2 is the major species with the N atoms in the equatorial plane and the O atoms in the axial position. This complex decomposes at pH > 10 into a copper oxide/hydroxide precipitate. The overall results provide a consistent picture of the mechanism that drives the coordination and complex formation of the Cu2+/his system.     

Detection of s-triazine pesticides in natural waters by modified large-volume direct injection HPLC

There is a need for simple and inexpensive methods to quantify potentially harmful persistent pesticides often found in our water-ways and water distribution systems. This paper presents a simple, relatively inexpensive method for the detection of a group of commonly used pesticides (atrazine, simazine and hexazinone) in natural waters using large-volume direct injection high performance liquid chromatography (HPLC) utilizing a monolithic column and a single wavelength ultraviolet-visible light (UV-vis) detector. The best results for this system were obtained with a mobile phase made up of acetonitrile and water in a 30:70 ratio, a flow rate of 2.0 mL min⁻¹, and a detector wavelength of 230 nm. Using this method, we achieved retention times of less than three minutes, and detection limits of 5.7 μg L⁻¹ for atrazine, 4.7 μg L⁻¹ for simazine and 4.0 μg L⁻¹ for hexazinone. The performance of this method was validated with an inter-laboratory trial against a National Association of Testing Authorities (NATA) accredited liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method commonly used in commercial laboratories.     

Total syntheses of the bromotyrosine-derived natural products ianthelline, 5-bromoverongamine and JBIR-44

The total syntheses of the bromotyrosine-derived natural products ianthelline, 5-bromoverongamine and JBIR-44 are described and their cytotoxic activity in a cervical cancer (HeLa) cell line and human umbilical vein endothelial cells (HUVECs) are reported.     

Luminescence Characterization of a Novel, Hydrophobically Modified and Heavy Atom-Functionalized, Water-Soluble Polymer

A hydrophobically modified water-soluble polymer, based upon acrylic acid and styryl derivatives, was synthesized. A proportion (ca. 75 mol%) of the styryl residues in the copolymer contain a bromine substituent as a heavy-atom functionality. It has been shown that room-temperature phosphorescence (RTP) can be induced in an acenaphthylene (ACE) label, covalently bound to the polymer chain, through intramacromolecular interactions in dilute solutions of the copolymer. This is the first instance in which RTP has been generated in either label or solubilized guest, in such a fashion. The conformational behavior of the functionalized copolymer, BrSTY/STY/AA, has been studied using RTP, fluorescence lifetime, and time-resolved anisotropy measurements and compared to that of both its unbrominated, styrene-modified analogue, STY/AA, and poly(acrylic acid) PAA itself. The conformation transition which accompanies conversion of each polyacid into the corresponding fully neutralized polysalt is much more dramatic in either hydrophobically modified species than in poly(acrylic acid). Intramacromolecular aggregation leading to the creation of hydrophobic domains within the coils of the macromolecules is enhanced at a low pH and severely impedes segmental motion in the two styrene-modified polyacids. The effect is greater in the bromine-containing polymer, which suggests that more densely packed domains are formed in this species than in STY/AA. In addition to altering the magnitude of the effect that neutralization has upon the molecular dynamics of the polyacid in aqueous media, hydrophobic modification raises the pH range over which the change in conformational behavior of the macromolecule is apparent.     

Computational Estimation of the Acidities of Pyrimidines and Related Compounds

Pyrimidines are key components in the genetic code of living organisms and the pyrimidine scaffold is also found in many bioactive and medicinal compounds. The acidities of these compounds, as represented by their pK_as, are of special interest since they determine the species that will prevail under different pH conditions. Here, a quantum chemical quantitative structure–activity relationship (QSAR) approach was employed to estimate these acidities. Density-functional theory calculations at the B3LYP/6-31+G(d,p) level and the SM8 aqueous solvent model were employed, and the energy difference ∆E_H2O between the parent compound and its dissociation product was used as a variation parameter. Excellent estimates for both the cation → neutral (pK_a1, R² = 0.965) and neutral → anion (pK_a2, R² = 0.962) dissociations were obtained. A commercial package from Advanced Chemical Design also yielded excellent results for these acidities.     

Pressure–heat release measurements during start-up conditions in a pulse combustor

An experimental study focusing on the temporal evolution of the global OH heat release (q′) and dynamic pressure (p′) from ignition to limit cycle conditions in an aerovalved pulse combustor has been carried out. The motivation of the work was to investigate how the thermo-acoustic relationships evolve, as very little is understood regarding how pressure and heat release couplings develop prior to establishing limit cycle conditions. The start-up experiments demonstrated that the total start-up sequences occurred within 100 ms and can be subdivided into three regimes: (i) ignition and decay; (ii) instability growth; and (iii) onset of limit cycle operation. The main results showed that upon ignition the high amplitude impulse pressure wave corresponded to the natural frequency of the pulse combustor at ambient gas temperature and was verified by an acoustic model. The pressure field over the growth period exhibited two main trends, either steady amplitude growth or a short delay interval followed by steady amplitude growth to limit cycle conditions. Overall, no reproducibility in frequency or phase during the growth period was observed pointing to the influence of strong non-linear interactions. When operating under limit cycle conditions, the heat release and pressure oscillations were in phase, possessed high levels of coherence, and exhibited narrow band frequency response at the operating frequency and several harmonics.