摘要:

Spiro-fused &bgr; -lactam oxadiazoline2awas prepared from acetone semicarbazone in five steps. Thermolysis of2aat 100°C in benzene led to carbene3a, which cyclized to the benzo-fused oxapenem derivative4via intramolecular OH insertion. Compound10, with a &bgr; -lactam ring linked to an azetidinedione ring, was a minor product.Key words: benzoxapenem, carbene, &bgr; -lactam-4-ylidene, OH insertion.

ISSN:0008-4042    

DOI:10.1139/v98-016

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

(L-L)W(CO)3I2(L-L = (CH3)2AsC(CF3)== C(CF3)As(CH3)2) reacts with the monodentate phosphite P(OC6H5)3and (L-L)W(CO)3Br2reacts with L-L to form new seven-coordinate complexes (L-L)W(CO)2I2P(OC6H5)3and (L-L)2W(CO)Br2. Low-temperature X-ray diffraction analyses show the tungsten atom to be seven coordinate in both complexes, with the geometry most closely approximated by a monocapped octahedral environment, the capping group being a carbonyl in the dicarbonyl complex; the geometry is most closely approximated by a pentagonal bipyramidal environment in the monocarbonyl complex. The1H,13C, and19F NMR data indicate that the dicarbonyl complex is stereochemically nonrigid at 298 K and rigid at lower temperatures, while the monocarbonyl is nonrigid both at 298 K and at lower temperatures. &Dgr;Gnot equalvalues calculated at coalescence temperatures are consistent with an intramolecular rearrangement process for both complexes. The13C chemical shifts and2J(13C-31P) values provide important structural considerations in the assignment of a seven-coordinate geometry. Spectroscopic properties for the related seven-coordinate dicarbonyl complexes (L-L)W(CO)2PX2(P = P(OC6H5)3; X = Br; P = P(OCH3)3, P(C6H5)3; X = Br, I) and monocarbonyl complexes (L-L)2W(CO)I2and (L-L)W(CO)X2[P(OCH3)3]2(X = Br, I) are presented and compared to those of the two title complexes.Key words: seven-coordination, X-ray, NMR analysis.

ISSN:0008-4042    

DOI:10.1139/v98-008

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A sensor system based on the optical phenomenon of surface plasmon resonance (SPR), which employs either photothermal deflection spectroscopy (PDS) or a photodiode array (PDA) for detection, was developed to use molecularly imprinted (MI) polymethacrylic acid - ethylene glycol dimethacrylates (PMAA-EDMA) as the sensing element. The MI polymers were first processed by Soxhlet extraction to remove the print molecules (theophylline, caffeine, and xanthine), yielding the specificanti-polymers. Eachanti-polymer was layered over a silver film to serve as the analysis surface for the molecularly imprinted sorbent assay (MIA) of one target drug. This surface was exposed for 60 min to an aqueous standard drug solution, dried in air, and the uptake of the print molecule into theanti-polymer was monitored by shifts in the SPR angle θr(and hence the SPR-PDS signal measured at constant θ ). The linear dynamic range of the MIA was found to extend up to 6 mg/mL, with a concentration detection limit estimated at 0.4 mg/mL for theophylline in aqueous solution. A cross-reactivity study of theanti-theophylline andanti-caffeine polymers, using eight other drugs structurally similar to theophylline and caffeine, showed none or very slight shifts in θr. This implies that theanti-polymers were selective only for their original print molecules and had no affinity for the other drug molecules. Similar molecular recognition characteristics were observed for theanti-xanthine polymer.Key words: surface plasmon resonance, molecular imprinting, theophylline, caffeine, xanthine, sensor.

ISSN:0008-4042    

DOI:10.1139/v98-007

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

We report the experimental and predicted absorption and vibrational circular dichroism (VCD) spectra of (1S, 2R, 5S)-(+)-menthol. The harmonic force fields and atomic polar tensors (APTs) were obtained for 10 conformers using density functional theory (DFT) with the Becke3LYP functional and the 6-31G** basis set. The atomic axial tensors (AATs) were obtained with restricted Hartree-Fock (RHF) theory and a 6-31G basis set. VCD intensities were predicted from vibronic coupling theory (VCT). The predicted absorption and VCD spectra based on an equilibrium mixture of conformers corresponded well with the experimental spectra, indicating a reasonable geometry and frequency analysis for each of the conformers. The largest contributions towards the equilibrium population derive from conformers in which the cyclohexane ring occupies a chair conformation, the isopropyl group is directed away from the hydroxyl group, and only the hydroxyl group assumes different conformations.Key words: vibrational circular dichroism (VCD), menthol, conformational analysis.

ISSN:0008-4042    

DOI:10.1139/v98-014

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper delineates and illustrates an important physical consequence of the Heisenberg equation of motion governing the expectation value of an observable for a proper open system, one whose basin is bounded by a surface of zero flux in the gradient vector field of the electron density. For a system in a stationary state, this theorem derives from the variation of Schrödinger's energy functional over an open system. The variation demonstrates that the surface of theopensystem, as well as the wave function and energy of thetotalsystem, are simultaneously stationary with respect to any and all variations &dgr; ψ , corresponding to a stationarity with respect to any and all physical perturbations -(i&egr;/ Planck's constant) G caret ψ caused by a generator G caret. Thus the properties of a proper open system are dependent upon its surface and vice versa, the theorem equating the expectation value of the commutator of the Hamiltonian and a generator G caret for the open system to the flux in the current density for G caret through its surface. The criticisms of the interdependence of the basin and surface properties of a proper open system that appeared recently in this journal are refuted, including the argument that mutiplication of an electron density by a constant factor yields a density for a different system. The consequences of this interdependence in the construction of a polypeptide through the use of amino acid residues defined as proper open systems is discussed and illustrated through the explicit calculation of the properties of the C|N interatomic surfaces of the amidic bonds. It is demonstrated that the the degree of transferability of a residue is determined by the degree of similarity in the properties of its two bounding amidic surfaces.Key words:electron density, ransferability of density, atoms in molecules, zero flux surface.

ISSN:0008-4042    

DOI:10.1139/v98-011

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Two series ofS-alkyl trithiocarbonate derivatives of imethylgermane, Me2Ge[S2CSR]2, and halodiphenylgermane, Ph2GeX[S2CSR], where R = Me,i-Pr,n-Pr,n-Bu and X = Cl, Br, and three series ofO-alkyl monothiocarbonate derivatives of triphenylgermane, Ph3Ge[SCO2R], diphenylgermane, Ph2Ge[SCO2R], and trimethylgermane, me3Ge[SCO2R], where R = Me,i-Pr, andn-Pr, have been prepared in 73-92% yields by the reaction of the potassium or sodium salt of the appropriate tri- or monothiocarbonic acid with dichlorodimethyl-, chlorotriphenyl-, dichlorodiphenyl-, and chlorotrimethylgermane. The compounds were principally characterized by infrared, Raman, and1H and13C NMR spectroscopy, including some variable temperature studies, as well as by mass spectrometry. Me2Ge[S2CSEt]2,1:P21/m(No. 11) with cell parametersa= 6.647(4) Å,b= 7.423(2) Å,c= 16.290(4) Å,&bgr;= 91.07(3)°,V= 803.6(4) Å3,Z= 2,R= 0.0484,Rw= 0.0485. Ph3Ge[SCO2Me],13: P1bar (No. 2) with cell parametersa= 9.970(4) Å,b= 10.660(3) Å,c= 9.853(2) Å,&agr;= 101.78(2)°,&bgr;= 109.98(2)°,&ggr;= 89.76(3)°,V= 961.0(5) Å3,Z= 2,R= 0.0534,Rw= 0.0451. Ph3Ge[SCO2(i-Pr)],14: P 1bar (No. 2) with cell parametersa= 14.386(7) Å,b= 18.598(6) Å,c= 9.223(3) Å,&agr;= 102.85(3)°,&bgr;= 94.58(3)°,&ggr;= 108.13(3)°,V= 2256(1) Å3,Z= 2,R= 0.0545,Rw= 0.0552. Ph2Ge[SCO2Me]2,16:Cc, (No. 9) with cell parametersa= 11.790(4) Å,b= 13.696(5) Å,c= 23.232(6) Å,&bgr;= 92.26(3)°,V= 3748(2) Å3,Z= 8,R= 0.0563,Rw= 0.0512. The immediate environment about Ge is that of tetrahedral but the orientations of the thiocarbonate groups display interesting features.Key words: structure, germanium, phenyl, methyl, thiocarbonates.

ISSN:0008-4042    

DOI:10.1139/v98-026

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The intriguing gas-phase ion chemistry of &bgr;-hydroxypyruvic acid (HPA), HOCH2C(==O)COOH, has been investigated using tandem mass spectrometry (metastable ion (MI) and (multiple) collision-induced dissociation (CID) experiments, neutralization-reionization mass spectrometry (NRMS),18O and D isotopic labelling on both the acid and its methyl ester) in conjunction with computational chemistry (ab initio MO and density functional theories). HPA does not enolize upon evaporation, but it retains its keto structure. When ionized, decarbonylation occurs and, depending on the internal-energy content, this dissociation reaction proceeds via two distinct routes. The source-generated, high-energy ions lose the keto C==O, not via a least-motion extrusion into ionized glycolic acid, HOCH2COOH.+, but via a rearrangement that yields the title H-bridged radical cation CH2==O...H...O==C-OH.+for which &Dgr;Hf0= 99 ± 3 kcal/mol. The long-lived low-energy ions enolize prior to decarbonylation and lose the carboxyl C==O. Again, this is not a least-motion extrusion (which would produce the most stable isomer, HOC(H)==C(OH)2.+&Dgr;Hf0= 73 kcal/mol) but a rearrangement yielding the ion-dipole complex HOC(H)C==C==O.+/H2O. The methyl ester of HPA behaves analogously, yielding CH2==O...H...O==C-OCH3.+and HOC(H)C==C==O.+/ CH3OH upon decarbonylation of the high- and low-energy ions, respectively. Decarboxylation into the ylidion CH2OH2.+characterizes the dissociation chemistry of both the title H-bridged ion and its glycolic acid isomer HOCH2COOH.+. A computational analysis of this reaction (which satisfies the experimental observations) leads to the proposal that the decarboxylation of the acid occurs via CH2-O(H)...H...==C==O.+as the key intermediate, whereas the title H-bridged ion follows a higher energy route that involves ion-dipole rotations leading to the ionized carbene HO(H2)CO-C-OH.+and the distonic ion H2O-C(H2)-O-C==O.+as key intermediates.Key words: tandem mass spectrometry, hydrogen-bridged radical cation, hydroxypyruvic acid, ab initio calculations, keto-enol tautomerization,18O labelling.

ISSN:0008-4042    

DOI:10.1139/v98-022

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Equilibrium studies show that in aqueous solutions containing excess 1,10-phenanthroline (phen) in the range pH 3-9, the complex ion [Fe2III( &mgr;-O)(phen)4(H2O)2]4+(1) undergoes rapid but partial hydrolysis and coexists with [Fe2III( &mgr;-)(phen)3(H2O)4]4+(1d),[Fe2III( &mgr;-O)(phen)4(H2O)(OH)]3+(2), and [Fe2III( &mgr;-O)(phen)4(OH)2]2+(3). The solution oxidizes hydroxylamine quantitatively to N2O and is itself reduced to [Fe(phen)3]2+. The reactions in the range pH 3-6 are first-order in concentrations of complex and hydroxylamine but exhibits complex [H+] dependence, suggesting kinetic contributions from1,1d, and2but not from3. Rapid formation of inner-sphere adducts between NH2OH and different {Fe2O}4+species followed by rate-determining one-electron transfer to produce NHOH and {Fe2O}3+is proposed. All subsequent steps are rapid. Ambient light does not affect kinetics and reaction products.Key words: kinetics, equilibrium, oxo bridge, iron (III), hydroxylamine.

ISSN:0008-4042    

DOI:10.1139/v98-004

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Using ab initio molecular orbital theory mainly at the 3-21+G level, intramolecular SN2 methyl transfer between two oxygens confined within a rigid template is found to proceed exclusively by a high energy retention mechanism when the oxygens are separated by three or four bonds, and by a high energy inversion mechanism when the oxygens are separated by six bonds. Both mechanisms exist when the oxygens are separated by five bonds. The CH3/CD3kinetic isotope effects are normal (1.21-1.34) in the retention processes and inverse (0.66-0.81) in the inversion reactions. In the case of inversion, compression of C-H bonds of the transition state by structural effects in the plane perpendicular to the O-C-O plane increases the inverse isotope effect. The retention barriers are high because retention is inherently unfavorable, even when pericyclic stabilization of the transition state is possible. The inversion barriers are high because a rigid template cannot accommodate a linear O-CH3-O structure, and the O-C-O bending vibration is stiff (the Eschenmoser effect). Using a novel design strategy, a nonrigid template has been found in which the barrier and the CH3/CD3kinetic isotope effect are the same as in an intermolecular reaction.Key words: Eschenmoser effect, isotope effect, compression, SN2, sigmatropic rearrangement.

ISSN:0008-4042    

DOI:10.1139/v98-090

出版商:NRC Research Press    

年代:1998

数据来源: NRC