The Li2CrO4---CaCrO4 binary phase diagram

Phase equilibria in the Li₂CrO₄---CaCrO₄ system were determined by differential thermal analysis and X-ray powder diffraction. The phase diagram is characterized by a eutectic reaction at 489°C and 5 mole% CaCrO₄, and a monotectic reaction at 570°C and 80 mole% CaCrO₄. The solubility of Li₂CrO₄ in CaCrO₄ was ≈15 mole% at the eutectic temperature and declined to <5 mole% at the monotectic temperature. No double salt was formed between the end members. The immiscibility observed in the system is rationalized in terms of the cation coordination polyhedra.

Thermal events indicative of a solid state phase change in Li₂CrO₄ as reported in some references are judged to be the result of a Li₂CO₃ impurity.     

The influence of the adsorbent amount on the changes in molecular mass distribution of polymers under adsorption from mixtures

Changes in the molecular mass distribution (MMD) for polymer as a result of adsorption from binary and ternary solutions have been studied by the exclusion chromatography method. It was found that the affinity of polymer components to a surface has a crucial influence on the changes in MMD of polymers. The diminution of polydispersity in solutions after adsorption was observed for two polymers. In the case of the polar polymer poly(butyl methacrylate) (PBMA) the diminution of polydispersity is caused mainly by the preferential adsorption of low-molecular-mass fractions, whereas in the case of the nonpolar polymer polystyrene (PS) it is caused by the transition of the high-molecular-mass fractions onto the adsorbent surface. The analysis of experimental results indicates that the quantity of the adsorbent affects the composition of the adsorption layer formed by polymers of different chemical nature.     

IMPROVED SURVIVAL FROM INTRACAVITARY PHOTODYNAMIC THERAPY OF RAT GLIOMA

The effectiveness of intratumoral photoradiation in photodynamic therapy (PDT) using a polyporphyrin photosensitizer was studied in the RT-2 rat glioma model. One week after intracerebral implantation of RT-2 cells, experimental rats received a single i.p. injection of 2 mg/kg of Photofrin. After administration of the photosensitizer (48 h), the tumors were partially resected and the exposed cavity was irradiated with 15 J of laser light at a wavelength of 630 nm. Further treatment with a large craniectomy significantly enhanced rat survival. Control rats which received no photosensitizer but were treated with surgery, alone or in combination with laser irradiation, succumbed from early tumor recurrence. Photodynamic therapy without decompressive surgery resulted in hemorrhagic infarction of residual tumor and adjacent brain with focal cerebral edema which resulted in cerebral herniation and early death. Our results indicate that photodynamic therapy is effective in treating residual brain tumor but at the expense of brain tissue surrounding the tumor. Unless relieved, intracranial pressure from photodynamic therapy-associated cerebral edema in this animal model resulted in shortened survival.     

Reaction of β-keto ethyleneacetals with hydroxylamine: A correction

A reaction of 2-(2-nitrobenzoylmethyl)-1,3-dioxolane ( 3 ) with hydroxylamine, followed by acid catalyzed cyclization, produced 5-(2-nitrophenyl)isoxazole ( 5 ) as the only isolable product, whereas 2-(benzoylmethyl)-1,3-dioxolane ( 9 ) under identical conditions produced a 2.5:1 mixture of 3-phenyl and 5-phenylisoxazoles 10 and 11 . These findings contradict the literature report that β-keto ethyleneacetals on treatment with hydroxylamine produce exclusively 3-substituted isoxazoles. As an additional proof, 3-(2-nitrophenyl)isoxazole ( 8 ) was prepared by an unambiguous method via the nitrile oxide route for comparison. The intermediate obtained on treatment of 2-(2-nitrobenzoylmethyl)-1,3-dioxolane ( 3 ) with hydroxylamine was found to be an isomeric mixture of 5-hydroxy-5-(2-nitrophenyl)-2-isoxazoline ( 4 ) and the syn and anti mono-oximes 19 (at least in solution), either of which could give 5-(2-nitrophenyl)isoxazole ( 5 ) on acid treatment. A mechanistic rationale is provided to explain the anomalous results.     

Design, formation and properties of tetrahedral M(4)L(4) and M(4)L(6) supramolecular clusters

The rigid tris- and bis(catecholamide) ligands H(6)A, H(4)B and H(4)C form tetrahedral clusters of the type M(4)L(4) and M(4)L(6) through self-assembly reactions with tri- and tetravalent metal ions such as Ga(III), Fe(III), Ti(IV) and Sn(IV). General design principles for the synthesis of such clusters are presented with an emphasis on geometric requirements and kinetic and thermodynamic considerations. The solution and solid-state characterization of these complexes is presented, and their dynamic solution behavior is described. The tris-catecholamide H(6)A forms M(4)L(4) tetrahedra with Ga(III), Ti(IV), and Sn(IV); (Et(3)N)(8)[Ti(4)A(4)] crystallizes in R3(-)c (No. 167), with a = 22.6143(5) A, c = 106.038(2) A. The cluster is a racemic mixture of homoconfigurational tetrahedra (all Delta or all Lambda at the metal centers within a given cluster). Though the synthetic procedure for synthesis of the cluster is markedly metal-dependent, extensive electrospray mass spectrometry investigations show that the M(4)A(4) (M = Ga(III), Ti(IV), and Sn(IV)) clusters are remarkably stable once formed. Two approaches are presented for the formation of M(4)L(6) tetrahedral clusters. Of the bis(catecholamide) ligands, H(4)B forms an M(4)L(6) tetrahedron (M = Ga(III)) based on an "edge-on" design, while H(4)C forms an M(4)L(6) tetrahedron (M = Ga(III), Fe(III)) based on a "face-on" strategy. K(5)[Et(4)N](7)[Fe(4)C(6)] crystallizes in I43(-)d (No. 220) with a = 43.706(8) A. This M(4)L(6) tetrahedral cluster is also a racemic mixture of homoconfigurational tetrahedra and has a cavity large enough to encapsulate a molecule of Et(4)N(+). This host-guest interaction is maintained in solution as revealed by NMR investigations of the Ga(III) complex.     

Elucidating the Origin of Conformational Energy Differences in Substituted 1,3-Dioxanes: A Combined Theoretical and Experimental Study

13C NMR spectroscopy, ab initio quantum mechanics, and molecular mechanics have been used to investigate the trans-4-(trifluoromethyl)-2,2,6-trimethyl-1,3-dioxane chair/twist-boat equilibrium. The molecular mechanics calculations were based upon the MM3 and AMBER force fields. A 6-31G basis set was used for the ab initio calculations, and MP2 correlation corrections were applied. Both the ab initio and AMBER molecular mechanics calculations are consistent with the (13)C NMR chemical shift differences for the trans-4-(trifluoromethyl)-2,2,6-trimethyl-1,3-dioxane conformers. The predicted chair to twist-boat equilibrium suggested by the MM3 calculations is not consistent with the experimental data. These results support the suggestion by Howard et al. (Howard, A. E.; Cieplak, P.; Kollman, P. A. J. Comput.Chem. 1995, 16, 243-261) on the critical role of electrostatic interactions in determining the chair/twist-boat equilibrium.     

Parallel determination of multiple protein metabolite interactions using cell extract, protein microarrays and mass spectrometric detection

Analysis of interactive networks between proteins and other molecular constituents is of paramount importance to delineate complex cellular processes. In order to facilitate this process, new technologies that allow rapid, high-throughput parallel screening, as well as identification of constituents, are necessary. A particularly powerful combination in this regard could be the use of multiprotein microarrays coupled with mass spectrometry (MS). In the initial step of the method development we applied MS to single-protein microarrays. We demonstrated that even a simplified version of the method allows rapid parallel label-free assay of specific protein interactions with multiple metabolites derived from complex artificial and natural mixtures. The microarrays fabricated by the electrospray deposition technique and cross-linked in glutaraldehyde vapor were brought into contact with droplets of solution containing either a natural extract of baker's yeast cells or an artificial cocktail of metabolites. After washing, the microarrays were placed into 75% methanol to denature proteins and release specifically bound metabolites. The eluates were then analyzed by electrospray ionization mass spectrometry (ESI-MS) to simultaneously detect all the metabolites bound. Such a procedure applied to ten different proteins demonstrated that 50-400 ng of cross-linked protein is enough to obtain ion intensities from metabolites that are well distinguishable above noise. The compatibility of microplates and different microarray designs with MS detection is discussed.     

Epigenetic Anti-Cancer Treatment With a Stabilized Carbocyclic Decitabine Analogue

5-Aza-2’-deoxycytidine (Decitabine, AzadC) is a nucleoside analogue, which is in clinical use to treat patients with myelodysplastic syndrome or acute myeloid leukemia. Its mode of action is unusual because the compound is one of the few drugs that act at the epigenetic level of the genetic code. AzadC is incorporated as an antimetabolite into the genome and creates covalent, inhibitory links to DNA methyltransferases (DNMTs) that methylate 2’-deoxycytidine (dC) to 5-methyl-dC (mdC). Consequently, AzadC treatment leads to a global loss of mdC, which presumably results in a reactivation of silenced genes, among them tumor suppressor and DNA damage response genes. Because AzadC suffers from severe instability, which limits its use in the clinic, a more sophisticated AzadC derivative would be highly valuable. Here, we report that a recently developed carbocyclic AzadC analogue (cAzadC) blocks DNMT1 in the AML cell line MOLM-13 as efficient as AzadC. Moreover, cAzadC has a surprisingly strong anti-proliferative effect and leads to a significantly higher number of double strand breaks compared to AzadC, while showing less off-target toxicity. These results show that cAzadC triggers more deleterious repair and apoptotic pathways in cancer cells than AzadC, which makes cAzadC a promising next generation epigenetic drug.     

Confinement of polystyrene at interfaces: Consequences on chain orientation

The knowledge of the structure and orientation of polymer chains adsorbed at an interface could be of major importance to predict the level of interfacial interactions and adhesion that depend strongly on the properties of the interface formed between the two materials (polymer and substrate) brought into contact. In this work, we were interested to study thin films of atactic polystyrene after adsorption (spin‐coating) on two chemically different substrates (inert and OH‐grafted gold substrates). The main aim is to analyze the resulting anisotropy due to the confinement in a quasi‐bidimensional geometry, as well as to investigate the incidence of the interfacial interactions, potentially established between the polymer and the surface, on the chain organization. Our infrared spectroscopy results allowed us to access the adsorption model of polystyrene chains and to highlight the relation between chain orientation and interfacial acid–base interactions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1268–1276, 2006     

Mechanism ofb-picoline oxidation to nicotinic acid on V-Ti-O catalyst as studied by in situFTIR

Summary In situFTIR spectroscopy was used to study the interaction of<span style='font-family:Symbol;mso-bidi-font-family:Symbol'>b-picoline with the surface of a V-Ti-O catalyst in the temperature range of 120-300°C.b-picoline was found to react with the Lewis acid sites of the catalyst to form a nitrogen-coordinated complex. This complex turns into an aldehyde-like complex at</o:p>150-250°C and then into a nicotinate, which is a direct precursor of nicotinic acid.</o:p>