Synthesis of 4-alkyl-4H-benzo[e]- and 4H-pyrido[2,3-e]-1,2,4-triazin-3-one 1-oxides for potential anticancer activity

Alkylation of the sodium salt of 4H-benzo[e]-1,2,4-triazin-3-one 1-oxide and its 7-methyl homolog with benzyl bromide and chloromethoxyethyl acetate gave the 4-substituted products. Alkylation with aceto-bromoglucose formed the 3-ether. Alkylation of 4H-pyrido[2,3-e]-1,2,4-triazin-3-one 1-oxide gave the 4-substi-tuted products with both benzyl bromide and acetobromoglucose. Deacetylation of both the tetra-O-acetyl-glucosyl and acetoxyethoxymethyl derivatives was accompolished was accompolished. Antileukemia tests for several of the 4-alkyl derivatives showed no activity.     

What is the enthalpy of formation of acrylic acid?

Acrylic acid is a key industrial compound with numerous uses. Despite its importance, its enthalpy of formation is still contentious—even ignoring “ancient” determinations, there is a 12 kJ mol⁻¹ range of values reported for the gas phase quantity, −320 to −332 kJ mol⁻¹. Our quantum chemical calculations using current methodology suggest the value of −321 ± 3 kJ mol⁻¹.     

Enthalpy of formation of triphenylphosphine sulfide

The first measurements of the enthalpies of combustion, sublimation, and fusion of an organo-phosphorus sulfide, triphenylphosphine sulfide, are reported: _c H _m ^o (C₁₈H₁₅PS, cr)=–(10752.58 ±2.90), _sub H _m ^o (C₁₈H₁₅PS, 403 K)=(136.80±6.09), and _fus H _m ^o (C₁₈H₁₅PS, T_m=435.92 K) =(30.53±0.21) kJ·mol^–1. Correction of the phase change enthalpies toT=298.15K and p^o =0.1 MPa results in the standard phase change enthalpy values of _sub H _m ^o (298.15 K)=(142.8 ±6.8) and _fus H _m ^o (298.15 K)=(19.28±0.21) kj·mol^–1. Accordingly, the enthalpies of formation of solid, liquid, and gaseous triphenylphosphine sulfide are derived: _f H _m ^o (C₁₈H₁₅PS, cr) =(63.20±2.56), _fH _m ^o (C₁₈H₁₅PS, l)=(82.48±2.57), and _fH _m ^o (C₁₈H₁₅PS, g)=(206.0±7.3) kJ·mol^–1. From these ancillary data, the P=S double-bond enthalpy is 394 kJ-mol^–1 and in good agreement with earlier reaction calorimetry results. These phosphorus sulfide values are compared with those for the arsenic sulfides. Plausibility arguments are given for our results.     

Rotational cooling of rigid rotors desorbed from flat surfaces

A simple model is presented for predicting the final rotational state distribution of an initially physisorbed rigid rotor. Based on the assumptions that the adsorbed rotor is freely rotating and that desorption occurs by a weak coupling between the rotational and desorbing degrees of freedom, a significant rotational “cooling” is predicted.     

Reaction pathways leading to arylene ethynylene macrocycles via alkyne metathesis

Mechanistic studies on the direct formation of arylene ethynylene macrocycles via alkyne metathesis catalyzed by a molybdenum complex are reported. Gel permeation chromatography (GPC) and matrix-assisted laser desorption ionization (MALDI) mass spectrometry on the products from metathesis of monomer 1 show the initial formation of linear oligomers and large macrocycles (n > 6), followed by their transformation into the thermodynamically most stable product distribution-mainly the cyclic hexamer. Variable temperature and scrambling experiments reveal the reversibility of macrocycle formation. Nearly identical product distributions are observed from the cross metathesis of hexacycle 2 with diphenylacetylene and from the metathesis of bis(phenylethynyl) substituted monomer 4, demonstrating that macrocycle formation is thermodynamically rather than kinetically controlled. The metathesis byproduct, 3-hexyne, is shown to inhibit the catalyst. It is suggested that the relative metathesis rates of dialkylalkynes versus diarylalkynes trap the catalyst in a nonproductive manifold, rendering it unavailable for the productive metathesis of aryl alkylalkyne substrates. This finding indicates that dialkyl-substituted alkyne byproducts should be avoided (or efficiently removed) if the metatheses of aryl substrates, especially those with electron-withdrawing groups, are to proceed to high conversion.     

Resonance in aromatic and heteroaromatico-dicarboxylic acids,their anhydrides and imides

It is found thato-dicarboxylic acids derived from pyrrole and 1,2,5-thiadiazole do not form cyclic anhydrides as readily as phthalic acid. This is discussed in terms of ionic resonance structures and derived stabilization of the anhydrides and acids.     

Gamma radiation-initiated polymerization of styrene at high pressure. I. Kinetic parameters with intermittent irradiation

By adapting the rotating sector technique to provide an intermittent source of cobalt-60 radiation the activation volumes for all reaction steps of the bulk polymerization of styrene have been shown to be independent of pressure up to 208 MPa. The activation volumes determined for polymerization, initiation, propagation and termination were, respectively, ΔV^≠_pol = ?20.5 ± 0.22, ΔV^≠_i = +2.0 ± 0.18, ΔV^≠_p = ?18.6 ± 0.44, and ΔV^≠_t = +5.8 ± 0.55 cm³ mol^?. The values for the effect of pressure on the degree of polymerization ΔDP and the radical lifetime Δτ were, respectively, ?22.6 ± 0.16 and ?3.9 ± 0.29. The average radical lifetime increased from 4.5 s at atmospheric pressure to 6.3 s at 208 MPa. Because ΔV^≠_t is less than ΔV^≠_t and both are positive, the molecular weight increased with pressure at a faster rate than the polymerization rate. Although fewer radical chains were initiated per second under pressure the macroradical concentration increased with pressure because of the longer average lifetime of the radicals.     

计算机在化学教育中的应用——美国Seraphim计划简介

计算机辅助教学的重要性 Seraphim (Systems Engineering respective acguisition and propagation of Heuristic instructional materials的简称)计划是关于收集及传播启发性教学材料的系统工程计划。我们相信,计算机辅助数学法无论对于低年级还是高年级均具有很大意义。如果一个学生在学习化学课程时没有使用计算机,也没有借助于计算机去学习化学,那就不能说他受到了全面的教育。     

Magnetic circular dichroism and cobalt(II) binding equilibrium studies of Escherichia coli methionyl aminopeptidase

Equilibrium dialysis of methionyl aminopeptidase from Escherichia coli (EcMetAP) monitored by atomic absorption spectrometry and magnetic circular dichroism (MCD) shows that the enzyme binds up to 1.1 +/- 0.1 equiv of Co(2+) in the metal concentration range likely to be found in vivo. The dissociation constant, K(d), is estimated to be between 2.5 and 4.0 microM. Analysis of the temperature and magnetization behavior of the two major peaks in the MCD spectrum at 495 and 567 nm suggests that these transitions arise from Co(2+) with different ground states. Ligand field calculations using AOMX are used to assign the 495 nm peak to Co(2+) in the 6-coordinate binding site and the 567 nm peak to Co(2+) in the 5-coordinate site. This is further supported by the fact that the binding affinity of the Co(2+) associated with the 567 nm peak is enhanced when the pH is increased from 7.5 to 9.0, consistent with having an imidazole ligand from a histidine amino acid residue. On the basis of the MCD intensities, it is estimated that, when the 5-coordinate site is fully occupied, 0.1 equiv of cobalt is in the 6-coordinate site. Even when the cobalt concentration is very low, there is a small fraction of binuclear sites in EcMetAP formed through cooperative binding between the 5- and 6-coordinate Co(2+) ions. The magnetization behavior of the 6-coordinate Co(2+) MCD peak is consistent with an isolated pseudo-Kramer doublet ground state, suggesting that the cobalt ions in the binuclear sites are not magnetically coupled.     

Interference effects in resonance raman spectroscopy

We show that resonance Raman excitation profiles are not generally expected to superimpose on the profile of the absorption spectrum. The discrepancy is due to interference between transition amplitudes of preresonant and more nearly resonant states. Two cases are outlined: in the first the amplitudes have similar magnitudes, and in the second they are quite different. Examples discussed include hemeproteins, visual pigments and resonant scattering from triplet states of molecules. A main point is that qualitative aspects of these interferences may be used to assign states and vibrations. Some new experiments are reported for ferrocytochrome-c scattering.