Coherent waves in a multiply scattering poro-elastic medium obeying Biot's theory

Twersky's theory is generalized to multiple scattering by a uniform random distribution of cylinders in a poro-elastic medium. The high-frequency regime only, where no dispersion effects occur in the absence of scatterers, is investigated in the frame of Biot's theory. The scatterers lie within a slab of the host medium, and an incident wave gives rise to a fast longitudinal coherent wave, a slow longitudinal one, as well as a shear one in the slab. The dispersion equations of those three coherent waves are derived. The shear coherent wave propagates independently of the other two, while the longitudinal coherent waves obey a coupled dispersion equation involving conversion terms. Numerically speaking, coupling effects are significant only when forward scattering by a single cylinder of the fast wave into the slow one (or the slow wave into the fast) is larger than forward scattering with no conversion.     

Crystal structure, vibrational spectra and thermal decomposition of a new tetrazinc(II) dipyrophosphate decahydrate, Zn4(P2O7)2 < eqid1 > ?10H2O

A new zinc(II) pyrophosphate, Zn₄(P₂O₇)₂ < eqid1 > 10H₂O, has been synthesized and characterized by single-crystal X-ray diffraction [orthorhombic space group Pnma, with unit cell parameters of a = 9.1508(2) A, b = 25.5271(5) Å, c = 8.3574(2) Å, Z = 4]. All the pyrophosphate anions show nonlinear P–O–P bonds with an average angle of 126.5. The framework of this new pyrophosphate is made up of packed layers of ZnO₆ octahedra connected by double-tetrahedra P₂O₇ groups and a layer of Zn(H₂O)₆ units. The [P₂O₇]^4– anions adopt a bent, near-staggered conformation. The absence of coincidences for the majority of the IR and Raman bands is in accord with the centrosymmetric structure of the material. The vibrational spectra have been interpreted in part on the basis of factor group effects. The structural changes occurring during heating have been investigated by TG-DSC, powder X-ray diffraction, and IR and Raman spectroscopy. When Zn₄(P₂O₇)₂ 10H₂O is gradually heated, it decomposes and -Zn₂P₂O₇ is formed at 481C. On further heating, -Zn₂P₂O₇ is transformed into -Zn₂P₂O₇ at 750C. The conversion between the and -Zn2P2O7 forms is irreversible and, on cooling -Zn2P2O7 to room temperature, it reverts back to -Zn2P2O7. The crystal structure of the new zinc(II) pyrophosphate material is compared with the known structures of the related anhydrous products -, -, and -Zn2P2O7.     

1-(4-Nitrophenoxycarbonyl)-7-pyridin-4-yl indolizine: a new versatile fluorescent building block. Application to the synthesis of a series of fluorescent β-cyclodextrins

The synthesis of a series of new fluorescent building blocks 1a-d incorporating a pyridinoindolizine unit and two potentially reactive sites is described. The reaction of 1a-d with the mono-6-amino-6-deoxy-β-cyclodextrin provides the corresponding fluorescent water soluble hosts 2a-d in good yield. The sensor properties of 2a-d in the presence of 1-adamantanol is described.     

PHOTODYNAMIC INHIBITION OF ESCHERICHIA COLI DNA POLYMERASE I BY 8-METHOXYPSORALEN PLUS NEAR ULTRAVIOLET IRRADIATION

Abstract— Morphological abnormality due to the UV irradiation of sperm and its modification by photoreactivation (PR) were studied in the sea urchin, Hemicentrotus pukherrimus. When sperm was UV-irradiated and allowed to fertilize unirradiated eggs, the effect of the UV was manifested as an abnormal morphology of embryos in the gastrula or later stages. The UV-induced morphological abnormality was prevented by photoreactivation when the fertilized eggs were illuminated with visible light. In the experiments on a stage-dependent change of PR effectiveness, it was found that an illumination sufficed to effect a nearly complete PR when applied up to the onset of the first DNA synthetic phase, while the PR effectiveness declined thereafter. Illumination after the completion of DNA synthesis had little effect for PR.     

Assessment of the stereoselective metabolism of methaqualone in man by capillary electrophoresis

Methaqualone (MQ) and its hydroxylated metabolites are quinazoline derivatives that exhibit atropisomerism. As a continuation of our previous work with these compounds (Electrophoresis 2001, 22, 3270-3280), chiral capillary zone electrophoresis with hydroxypropyl-beta-cyclodextrin as buffer additive and multiwavelength absorbance detection is shown to be an effective tool to provide insight into the stereoselectivity of the MQ metabolism. The five major monohydroxy MQ metabolites formed during biotransformation do not show enantiomerization at temperatures up to 85 degrees C. Enzymatic and acidic hydrolysis of urines that were collected after concomitant administration of 250 mg of MQ and 25 mg diphenhydramine (DH) chloride are both shown to provide stereoselective metabolic patterns with 4'-hydroxymethaqualone, the major urinary metabolite, being excreted almost exclusively as a single enantiomer. A stereoselectivity in the formation of 2'-hydroxymethaqualone and 2-hydroxymethaqualone was also observed in vitro using human liver microsomes and preparations containing the cytochrome P450 enzyme (CYP) CYP3A4 only. The presence of DH during incubation with human liver microsomes did not reveal a difference in the metabolic pattern obtained. Furthermore, CYP2D6 and CYP2C19 do not significantly contribute to the metabolism of MQ. This was independently observed in vitro and via analysis of urines of individuals that are either efficient metabolizer phenotypes or poor metabolizer phenotypes for the two polymorphic enzymes. Although interindividual differences in the monitored metabolic patterns were noted, no marked difference could be related to a CYP2D6 or CYP2C19 polymorphism.     

Chiral tetrathiafulvalene based phosphine- and thiomethyl-oxazoline ligands. Evaluation in palladium catalysed asymmetric allylic alkylation

New chiral redox active ligands based on ethylenedithio-tetrathiafulvalene (EDT-TTF) bearing racemic or optically pure oxazolines have been synthesised. These auxiliaries possess an additional functionality on the TTF unit, namely a thiomethyl residue or a diphenylphosphino moiety. All ligands have been tested in asymmetric allylic substitutions. The enantioselectivity reached is 85% ee.     

Synthesis, structure and spectroscopic study of Rh polypyridine complexes with phenylcyanamide derivative ligands

Several new Rh^III complexes, [Rh(tpy)(bpy)L](PF₆)₂ (tpy=2,2′:6′,2″-terpyridine, bpy=2,2′-bipyridine, and L=monoanions of phenylcyanamide(pcyd)), 4-methylphenylcyanamide (4-MePcyd), 2,4-dimethylphenylcyanamide (2,4-Me₂pcyd), 4-methoxyphenylcyanamide (4-MeOPcyd), 2-chlorophenylcyanamide (2-Clpcyd) and 2,5-dichlorophenylcyanamide (2,5-Cl₂pcyd) have been synthesized and characterized by elemental analysis, IR, ¹H NMR and electronic absorption spectroscopies. ORTEP drawing of [Rh(tpy)(bpy)(2,5-Cl₂pcyd)](PF₆)₂·1/2CH₃CN shows three pyridyl rings of the tpy ligand that are nearly coplanar, as are the two rings of bpy. The anionic cyanamide group is coordinated end-on by the nitrile nitrogen to the Rh^III. The Rh^III–NCN bond is bent, having an angle of 125.4°. This bent bond is largely determined by the σ-bonding interaction of a cyanamide non-bonding electron pair in a sp² hybrid orbital.     

PHOTOCHEMICAL REACTIONS OF THYMINE WITH CARBOXYLIC ACIDS. A MODEL FOR NUCLEIC ACID-PROTEIN PHOTOCROSSLINKING

When nucleic acid bases are UV-irradiated in the presence of carboxylic acids or carboxylate anions new photoproducts are formed as compared to the bases irradiated in the absence of carboxylic acids. The behavior of thymine and thymidine has been examined in detail. At least four photoproducts are formed in the presence of propionic acid and three in the presence of butyric acid. None of them appears to be a cyclobutyl dimer. From the concentration dependence of the rate of photoproduct formation it is concluded that the reactive excited species is the first excited singlet state of thymine. When ¹⁴C-labelled thymine is irradiated in the presence of polyglutamic acid an important part of the radioactive material is covalently linked to the polymer. Photochemical reaction of thymine with glutamic (or aspartic) acid could thus induce crosslinks between proteins and nucleic acids. It is also shown that these photoproducts are stable under usual conditions of acidic hydrolysis of UV-irradiated DNA.     

A highly stereoselective route to substituted bis-tetrahydrofurans from 1,5-dienes.

Bis-tetrahydrofurans $\text{1a}$ and $\text{1b}$, containing four chiral centers, are obtained with a 90 % isomeric purity from geranyl and neryl chlorides in four steps including two stereoselective cyclizations.     

Identification of diphenhydramine metabolites in human urine by capillary electrophoresis-ion trap-mass spectrometry

The identification of diphenhydramine (DH) metabolites that are frequently observed in the capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MEKC) analyses of alkaline liquid/liquid and solid-phase extracts of patient urines is demonstrated. Having standards for DH and diphenhydramine-N-oxide (DHNO), the presence of these two compounds could be confirmed in urines that were collected overnight after administration of 25 mg DH chloride. Using CZE coupled to ion-trap mass spectrometry (CE-MS(n)) with positive electrospray ionization and an acetate buffer at pH 5.6, the [M+H](+) ions of DH (m/z = 256), DHNO (m/z = 272), and nordiphenhydramine (NDH, m/z = 242) and their fragmentation to a common m/z 167 product ion (diphenylcarbinol moiety) was monitored. The data indicate that all three compounds are cations in an acidic environment, the migration order being NDH, DH, and DHNO. Data obtained under negative electrospray ionization conditions suggest the presence of diphenylmethoxyacetic acid-glycine amide ([M-H](-) ion of m/z 298 and fragmentation to m/z 254, loss of CO(2)), a metabolite that could tentatively be assigned to a characteristic peak observed in the MEKC electropherogram at alkaline pH. The data presented in this paper illustrate the value of using CE-MS(n) for identification of urinary drug metabolites for which no standards are available.