Spectrophotometric determination of vanadium in natural waters and rocks after selective adsorption on sephadex gel

Vanadium(V) ions are strongly adsorbed on Sephadex G-25 gel at pH 4.2, and are desorbed reversibly into 0.1 M acids. Vanadium present in rocks and in natural waters at μg l⁻¹ levels can be separated and concentrated by means of a gel column at pH 6 (in order to avoid the interference of molybdenum(VI)) and determined spectrophotometrically with 4-(2-pyridylazo)resorcinol. Interference by iron(III) can be suppressed by adding copper(II)—CyDTA. Large amounts of sodium chloride and potassium nitrate have little effect on the adsorption.     

Chemical conversion of humulene to dactylol. Biomimetic,apparent 1,2-shift of a methyl group

Africanol, which had been previously derived from humulene, was converted to dactylol through a formal 1,2-shift of a methyl group, which involved a cyclopropane sliding reaction and subsequent cyclopropane ring opening.     

Reactions of cyclic disulfides with carbenes; desulfurization and insertion

Reactions of several cyclic disulfides with carbenes generated by catalytic and photochemical decompositions of diazo compounds have been studied. Carbenes reacted with cyclic disulfides yielding 1,3-dithiane quantitatively as S-S insertion reaction, while the selective desulfurization results in the reaction of disulfides with bulky substituents. The carbene reaction is sensitive to bulkiness of disulfides.     

Fabrication of a novel immunosensor using functionalized self-assembled monolayer for trace level detection of TNT by surface plasmon resonance

We have developed a new immunosensor based on self-assembly chemistry for highly sensitive and label-free detection of 2,4,6-trinitrotoluene (TNT) using surface plasmon resonance (SPR). A monolayer of amine terminated poly(ethylene glycol) hydrazinehydrochloride (PEG-NH₂) thiolate was constructed on an activated gold surface and immobilized with trinitrophenyl-β-alanine (TNPh-β-alanine) by amide coupling method. The binding interaction of a monoclonal anti-TNT Ab (M-TNT Ab) with TNPh-β-alanine immobilized thiolate monolayer surface was monitored and evaluated for detection of TNT based on the principle of indirect competitive immunoreaction. Here, the competition between the self-assembled TNT derivative and the TNT in solution for binding with antibody yields in the response signal that is inversely proportional to the concentration of TNT in the linear detection range. With the present immunoassay format, TNT could be detected in the concentration range from 0.008 ng/ml (8 ppt) to 30 ng/ml (30 ppb). The response time for an immunoreaction was 2 min and one immunocycle could be done with in 4 min including surface regeneration. Bound antibodies could be easily eluted from the self-assembled immunosurface at high recoveries (more than 100 cycles) using pepsin solution without any damage to the TNT derivatives immobilized on the surface. The compact self-assembled monolayer was highly stable and prevented the non-specific adsorption of proteins on the surface favoring error free measurement.     

Convergent synthesis of the FGHI ring segment of yessotoxin

A convergent synthesis of the FGHI ring segment of yessotoxin was achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis.     

An investigation of the mechanism of single and double hydrogen atom transfer reactions in alkyl benzoates by the ortho effect

Single and double hydrogen atom transfers in reactions (1) and (2) in the mass spectra of ethyl benzoate, isopropyl benzoate, and isobutyl benzoate have been investigated with reference to the ortho effect: (1) [C₆H₅CO₂R]⁺? → [C₆H₅CO₂H]⁺? (m/z 122) + (R-H); (2) [C₆H₅CO₂R]⁺? → [C₆H₅CO₂H₂]⁺ (m/z 123) + · (R-2H). It is demonstrated that the intermediate ion [C₆H₅CO₂H₂]⁺ has the protonated benzoic acid structure with the hydrogen atom on the carbonyl group.     

Electron-transfer-induced substitution of alkylated C60 chlorides with proton sponge

A series of alkylated C(60) chlorides 1,4-RC(60)Cl (1) were found to undergo nucleophilic substitution with 1,8-bis(dimethylamino)naphthalene (2), affording 1,4-RC(60)Ar [3, Ar = 4,5-bis(dimethylamino)-1-naphthyl] in good yields. An S(RN)1 mechanism, initiated by a single-electron transfer from 2 to 1, is proposed on the basis of the enhanced rates compared with the rate of the S(N)1 reaction of 1 with anisole. The involvement of free radicals in the reaction is supported by the formation of a small amount of dimer RC(60)-C(60)R (4) as a byproduct. The enhanced ability of C(60) chlorides 1 to accept an electron, attributable to the inductive effect of the directly attached chlorine atom, was demonstrated by its reduction potential and calculated LUMO energy.     

In situ chemical aminoacylation with amino acid thioesters linked to a peptide nucleic acid

tRNA-specific chemical aminoacylation was achieved with nonnatural amino acids. A nonnatural amino acid was activated as a thioester derivative, and the latter was linked through a spacer to the N-terminal of a 9-mer peptide nucleic acid that is complementary to the 3'-terminal region of yeast phenylalanine tRNA. Efficient aminoacylation was observed when the amino acid thioester-spacer-PNA conjugate was mixed with the tRNA. The PNA-assisted aminoacylation was also successful in an Escherichia coli in vitro protein synthesizing system that contained an orthogonalized tRNA. The in situ aminoacylation/in vitro translation gave a mutant protein in which the nonnatural amino acid was incorporated into the position directed by a CGGG 4-base codon/anticodon pair.     

Iron twin-coronet porphyrins as models of myoglobin and hemoglobin: amphibious electrostatic effects of overhanging hydroxyl groups for successful CO/O2 discrimination

Inspired by the observation of polar interactions between CO and O(2) ligands and the peptide residues at the active site of hemoglobin and myoglobin, we synthesized two kinds of superstructured porphyrins: TCP-IM, which contains a linked imidazole ligand, and TCP-PY, which contains a linked pyridine ligand, and examined the thermodynamic, kinetic, and spectroscopic (UV/Vis, IR, NMR, and resonance Raman) properties of their CO and O(2) complexes. On both sides of each porphyrin plane, bulky binaphthyl bridges form hydrophobic cavities that are suitable for the binding of small molecules. In the proximal site, an imidazole or pyridine residue is covalently fixed and coordinates axially to the central iron atom. In the distal site, two naphtholic hydroxyl groups overhang toward the center above the heme. The CO affinities of TCPs are significantly lower than those of other heme models. In contrast, TCPs have moderate O(2) binding ability. Compared with reported model hemes, the binding selectivity of O(2) over CO in TCP-IM and TCP-PY complexes is greatly improved. The high O(2) selectivity of the TCPs is mainly attributable to a low CO affinity. The comparison of k(on)(CO) values of TCPs with those of unhindered hemes indicates the absence of steric hindrance to the intrinsically linear CO coordination to Fe(II) in TCP-IM and TCP-PY. The abnormally large k(off)(CO) values are responsible for the low CO affinities. In contrast, k(off)(O(2)) of TCP-PY is smaller than those of other pyridine-coordinated model hemes. For the CO adducts of TCPs, unusually low nu(Fe-CO) and unusually high nu(C-O) frequencies are observed. These results can be ascribed to decreased back-bonding from the iron atom to the bound CO. The lone pairs of the oxygen atoms of the hydroxyl groups prevent back-bonding by exertion of a strong negative electrostatic interaction. On the other hand, high nu(Fe-O(2)) frequencies are observed for the O(2) adducts of TCPs. In the resonance Raman (RR) spectrum of oxy-TCP-IM, we observed simultaneous enhancement of the Fe-O(2) and O-O stretching modes. Furthermore, direct evidence for hydrogen bonding between the hydroxyl groups and bound dioxygen was obtained by RR and IR spectroscopy. These spectroscopic data strongly suggest that O(2) and CO binding to TCPs is controlled mainly by the two different electrostatic effects exerted by the overhanging OH groups: destabilization of CO binding by decreasing back-bonding and stabilization of O(2) binding by hydrogen bonding.