Lithiation of 2-Alkyl-3-amino- and 2-Alkyl-3-(methylamino)-4(3H)-quinazolinones(1)

3-Amino-2-methyl-4(3H)-quinazolinone has been doubly lithiated, on nitrogen and in the 2-methyl group, with n-butyllithium. The lithium reagent thus obtained reacts with a variety of electrophiles (D(2)O, benzophenone, cyclohexanone, cyclopentanone, acetophenone, benzaldehyde, tetraisopropylthiuram disulfide (TITD)) to give the corresponding 2-substituted derivatives in very good yields. Reactions of the dilithio reagent with 2 molar equiv of methyl iodide or phenyl isocyanate give disubstituted derivatives. Double lithiation of the 2-ethyl and 2-propyl analogues have been achieved using LDA, and subsequent reactions with most electophiles are then similar. In the reaction of the dianion of the 2-ethyl compound with TITD, deamination from position 3 takes place with the formation of the 2-substituted derivative. In reactions with prochiral ketones, the dianion of the 2-ethyl compound gives very high diastereoselectivity. Lithiation and subsequent reactions of 3-(methylamino) analogues take place in a similar manner, thus providing access to a range of substituted 3-(methylamino)-2-alkyl-4(3H)-quinazolinones by a general procedure. Lithiation of 3-(dimethylamino)-2-ethyl-4(3H)-quinazolinone did not take place under similar conditions. Lithiation of 3-amino-2-unsubstituted-4(3H)-quinazolinone was also unsuccessful.     

Relative molecular mass information from aliphatic nitro compounds: A chemical ionization study

The mass spectra of a number of aliphatic nitro compounds have been studied using electron Ionization (EI) and a variety of chemical Ionization (CI) techniques in attempts to obtain relative molecular mass information. The use of positive ion ammonia chemical Ionization techniques gave very satisfactory results, providing abundant [M + NH4]⁺ ions, not only from both primary and secondary nitro compounds, but also from the much more labile tertiary nitro compounds. However, the use of methane and isobutane positive ion CI or EI conditions resulted in facile fragmentation with little relative molecular mass information being made available. Negative ion CI using methane, isobutane or ammonia as moderating gases all gave abundant [M ? 1]^? ions with primary and secondary nitro compounds but at much reduced sensitivity.     

Preparation of a thermally phase-separating copolymer,poly(N-isopropylacrylamide-co-N-acryloxysuccinimide), with a controlled number of active esters per polymer chain

N-isopropylacrylamide and N-acryloxysuccinimide have been copolymerized in various mixtures of terrahydrofuran and toluene using azobisisobutyronitrile as initiator. Polymerization has been conducted for 24 h at 50°C under a slightly positive pressure of nitrogen. The copolymers were assayed for active ester content by measuring the UV absorbance (259 nm) of N-hydroxysuccinimide anion, generated by reacting the copolymers with N-isopropylamine in dimethylformamide and dissolving the resulting mixture in 0.1M HEPES buffer, pH 7.5. The molecular weight and its distribution have been estimated by gel permeation chromatography. The active ester content was found to be equivalent to the comonomer feed ratio, and the major factor controlling the molecular weight was the ratio of tetrahydrofuran to toluene. Thus, the number of active esters per polymer chain could be controlled by adjustment of the comonomer feed ratio and the ratio of tetrahydrofuran to toluene. Monomer reactivity ratios for copolymerization of N-isopropylacrylamide with N-acryloxysuccinimide were also estimated. These copolymers are useful for immobilizing binding ligands such as antibodies for subsequent thermally induced precipitation immunoassays and bioseparation processes.     

Acidity functions of aqueous fluorinated acid solutions by differential pulse polarography

The acidity functions of aqueous trifluoroacetic and trifluoromethanesulphonic acid mixtures, and aqueous hexafluoropropane-2, 2-diol solutions, have been determined by differential pulse polarography. The apparent shift of the half-wave potential for the ferrocene—ferricinium couple, as the solvent composition is changed, is used to indicate the change in potential of a glass electrode; acidity is measured as the H_GF acidity function. The densities of two of these solvent systems as a function of composition are also reported. Trifluoromethanesulphonic acid—water mixtures represent the strongest aqueous acid solvent system so far studied.     

Reactions of organoboranes and 2-lithio-2-alkyl-1,3-benzodithioles. A new,improved synthesis of ketones

Reactions of trialkylboranes with 2-lithio-2-alkyl-1,3-benzodithioles followed by oxidation give ketones in good yields. This method is far less subject to steric hindrance than the analogous reactions using anions derived from bis(phenylthio)alkanes.     

Analysis of insecticidal proteins from Bacillus thuringiensis and recombinant Escherichia coli by capillary electrokinetic chromatography

Bacillus thuringiensis and recombinant Escherichia coli proteinaceous protoxins were subject to proteolysis and analyzed by capillary electrokinetic chromatography. Three resulting toxins (65 kDa) were baseline-resolved within 22 min using a 10 mM borate, pH 11 separation buffer consisting of 25 mM sodium dodecyl sulfate (SDS) and 30 mM phytic acid. The toxins displayed differential interactions with the SDS and phytic acid phases to effect their separation. The ion-pairing interaction between the analyte and phytic acid was also useful in preventing adsorption to the capillary walls and thus enhanced separation resolution and efficiency. The use of electrokinetic chromatography allows achievement of the separation in a significantly shorter time than conventional high-performance liquid chromatography (HPLC) using a diethylaminoethyl (DEAE) weak-anion exchanger.     

Investigating bidentate and tridentate carbamoylmethylphosphine oxide ligand interactions with rare-Earth elements using electrospray ionization quadrupole ion trap mass spectrometry

Electrospray ionization (ESI) quadrupole ion trap mass spectrometry (QIT-MS) and collisionally activated dissociation (CAD) were used to evaluate the rare-earth binding properties of two hydrophobic carbamoylmethylphosphine oxide (CMPO) ligands, the normal bidentate variety, (t-BuC6H4)2P(O)CH2C(O)N(i-Bu)2 (A), a new potentially tridentate extractant, (t-BuC6H4)2P(O)CH[CH2C(O)N(i-Bu)2]C(O)N(i-Bu)2 (B), and tributyl phosphate. The mass spectral results obtained from analysis of 1% HNO3/methanol solution containing the ligands and dissolved lanthanide salts reveal that the favorable stoichiometries of the ligand/metal/nitrate complexes are 2:1:2 for the bidentate ligand A, 1:1:2 for the tridentate ligand B, and 3:1:2 for the monodentate tributyl phosphate. These observed stoichiometries correlate with the number of available binding sites on each ligand as well as with potential steric effects. Energy-variable collisionally activated dissociation experiments showed that for the 2:1:2 complexes involving ligand A or B, as the ionic radius of the bound metal decreased, the removal of nitric acid required less energy and resulted in less extensive spontaneous solvent coordination. This experimental trend suggests that, as the ionic radius of the lanthanide ion decreases, a pair of the carbamoylmethylphosphine ligands is able to more completely solvate the bound metal ion thereby weakening the nitrate-metal interaction.     

Theoretical Definition of a Functional Group and the Molecular Orbital Paradigm

It is the purpose of this review to demonstrate that the empirical classification of the observations of chemistry in terms of the properties assigned to functional groups is a consequence of and is predicted by physics. This is accomplished by showing that the atoms and functional groups of chemistry can be identified with bounded space-filling objects whose properties are defined by quantum mechanics. The quantum mechanical definition of a group is combined with a new pictorial representation of its form to obtain a unified picture which should make it eminently recognizable to chemists. This picture, when combined with the demonstrated ability of these groups to recover the measured properties of atoms in molecules, is offered as one which meets the expectations a chemist associates with the concept of a functional group. The manner in which this physical definition of a group differs fundamentally from models of functional groups based upon molecular orbital theory is discussed.     

The [4Fe-4S](2+) cluster in reconstituted biotin synthase binds S-adenosyl-L-methionine

The combination of resonance Raman, electron paramagnetic resonance and M?ssbauer spectroscopies has been used to investigate the effect of S-adenosyl-l-methionine (SAM) on the spectroscopic properties of the [4Fe-4S]2+ cluster in biotin synthase. The results indicate that SAM interacts directly at a unique iron site of the [4Fe-4S]2+ cluster in BioB and support the hypothesis of a common inner-sphere mechanism for the reductive cleavage of SAM in the radical SAM family of Fe-S enzymes.     

Analysis of pseudopartial and partial wetting of various substrates by lead

Lead drops exhibit partial wetting on some substrates and pseudopartial wetting on others. In pseudopartial wetting, a film is in equilibrium with a capillary body with a nonzero contact angle. Using a free energy formulation appropriate for the experiments, we show the conditions under which minimization of the system energy is accurately achieved by minimizing the energy of the film alone. Using a set of simple surface energy isotherms, we explain the various wetting behaviors of lead. We contrast isotherms for autophobing systems and the metallic systems considered here.