Complete N-1 regiocontrol in the formation of N-arylimidazoles. Synthesis of the active site His-Tyr side chain coupled dipeptide of cytochrome c oxidase

Under catalysis by copper(II) acetate, complete regiocontrol (N-1 versus N-3) was obtained in the arylation of substituted imidazoles with aryllead(IV) reagents. The mildness of the reaction conditions (rt, no added base) allows for the first synthesis of the histidine-tyrosine side chain coupled dipeptide found in the active site of cytochrome c oxidase.     

Vibrational relaxation of HF(υ = 3,4)

The vibrational relaxation of pure HF(υ = 3 and υ = 4) has been studied by pumping HF directly from υ = 0 to υ = 4. The relaxation rates of υ = 3 and υ = 4 were determined to be k³_T = (2.8 ± 0.4) × 10^?11 cm³ molecule^?1 s^?1 and k⁴_T = (7.2. ± 0.5) × 10^?11 cm³ molecule^?1 s^?1 at 293 K. It is shown that sigle quantum energy transfer can account for all the vibrational relaxation.     

Syntheses and stereochemistry of 4-hydroxy tetrahydroisoquinolines in the 1-benzyl and 1-phenethyl series. Efficient routes to isopavines and homoisopavines

The title compounds have been prepared in high yield $\text{via}$ cyclisation of urethane acetals.     

The synthesis of organo-imido complexes of Cr(IV) and Fe(III)

The reaction of p-tolylazide with (5,10,15,20- tetraphenylporphyrinato) chromium(II) (Cr(TPP)) yields the high spin chromium(IV) organo-imido complex, CH₃C₆H₄N=Cr(TPP). N,N′-ethylene- bis-(salicylideneiminato)iron(II), (Fe(salen)), however reacts with arylazides to produce iron(III) organo-imido-bridged compounds of general formula, [Fe(salen)]₂NR showing magnetic coupling between the Fe(III) centres.     

Kinetics of phase-transfer-catalyzed oxidations ofp-substituted benzyl alcohols with aqueous hypochlorite

A series ofp-substituted benzyl alcohols have been oxidized to their corresponding aldehydes using aqueous hypochlorite and phase-transfer catalyst (PTC) conditions. The reaction constant, p, has been determined to be +1.03. Possible mechanisms are suggested.     

Molecular recognition of trigonal oxyanions using a ditopic salt receptor: evidence for anisotropic shielding surface around nitrate anion

A ditopic, macrobicyclic receptor with adjacent anion and cation binding sites is able to extract a range of monovalent salts into chloroform solution. The structures of the receptor complexed with KAcO, LiNO(3), NaNO(3), KNO(3), and NaNO(2) are characterized in solution by NMR spectroscopy and in the solid state by X-ray crystallography. The sodium and potassium salts are bound to the receptor as contact ion-pairs, with the metal cation located in the receptor's crown ether ring and the trigonal oxyanion hydrogen bonded to the receptor NH residues. The solid-state structure of the LiNO(3) complex has a bridging water molecule between the cation and anion. In all solid-state structures, the trigonal oxyanion is not located symmetrically inside the receptor cavity. It appears that anion orientation is controlled by a complex interplay of steric factors, coordination bonding to the metal cation, and hydrogen bonding with the receptor NH residues. An important feature with this latter effect is the fact that hydrogen bonds directed toward the oxygen lone pairs on a trigonal oxyanion are stronger than hydrogen bonds to the pi-electrons. In solution, the (1)H NMR spectra of the nitrate and nitrite salt complexes are noteworthy because several receptor signals, including the NH protons, undergo unusual upfield movements in chemical shift upon complexation. This is a reflection of the diamagnetic anisotropy of these trigonal oxyanions. The magnetic shielding surface for the NO(3)(-) anion is calculated using density functional theory and shown to have a shielding region directly above the central nitrogen.     

Patenting computer-designed peptides

The problem of designing new peptides that possess specific properties, such as bactericidal activity, is of wide interest. Recently, attention has focused on the use of Computer-Aided Molecular Design techniques in parallel with more traditional 'synthesise and test' methods. These techniques may typically use Genetic Algorithms to optimise molecules based on Neural Network models that predict activity. In this paper we describe a successful application of this Molecular Design methodology that has resulted in novel bactericidal peptides of real value. A key issue for commercial utilisation of such results is the ability to protect the intellectual property rights associated with the discovery of new molecules. Typically peptide patents use structural templates of amino acid hydrophobicity-hydrophilicity that define highly regular peptide patent spaces. In an extension of established patenting practice we describe a patent application that uses a Neural Net predictive model to define the regions of peptide space that we claim within the patent. This formalism makes no a priori assumptions about the regularity of the patent space. A preliminary comparative investigation of the shape and size of this and other bactericidal peptide patent spaces is conducted.     

Picosecond measurements of 3,3′-diethyloxadicarbocyanine iodide and photoisomer fluorescence

Fluorescence spectra of DODCI photoisomer, created by laser microsecond and picosecond excitation, have been recorded. The fluorescence lifetimes of the normal and photoisomer forms of this mode-locking dye have been measured directly with a picosecond streak camera and shown to both have the same value of ≈330 psec. These results are related to the evolution of mode-locking in rhodamine dye lasers.     

Tervalent conducting polymers with tailor-made work functions: preparation, characterization, and applications as cathodes in electroluminescent devices

A series of conducting polymers have been prepared through thermal polymerization of transition-metal diimine complexes. The as-polymerized material is electrochemically converted into its formally zerovalent form. Due to the proximity of the half-wave potentials of the formal 1+/0 and 0/1- couples, there is substantial disproportionation of the redox sites at room temperature, resulting in a conductive tervalent mixed-valent material. The redox processes that give rise to this mixed-valent material are predominantly ligand-based, and therefore are highly sensitive to substitution on the ligand periphery. Solution redox chemistry of the monomer can be used to accurately predict the work function of the corresponding zerovalent conducting polymer, which has been verified by ultraviolet photoelectron spectroscopy. Many of these materials have especially low work functions (<3.6 eV) making them appropriate materials to use as cathode materials in organic light-emitting devices (OLEDs). Working examples of tris(8-hydroxyquinoline)aluminum(III)-based OLEDs have been fabricated using one of these polymers as a cathode.