Electron capture dissociation of peptide hormone changes upon opening of the tocin ring and complexation with transition metal cations

Electron capture dissociation (ECD) is an analytical technique in mass spectrometry (MS) that allows detailed structural study of biomolecules to gain insight in their function. In this work the ECD behavior of two peptide hormones oxytocin (OT1) and vasopressin (VP1) was studied. The results of OT1 and VP1 were compared to structural analogues OT2 and VP2, which have similar amino acid sequences but lack the tocin ring. The ECD results showed that both the fragment type (c/z versus b/y) and the cleavage sites (ring versus tail) changed upon opening of the tocin ring. All four peptides were complexed with three different transition metal cations (Zn²⁺, Ni²⁺ and Cu²⁺) and the ECD results were compared to those obtained from the doubly protonated species. The use of various metal ions yielded different cleavages sites within the same peptide. This can be an effect of the metal ion itself, or a consequence of a change in conformation as was suggested earlier. In addition, the type of fragment ion varied for each metal‐complexed peptide, which is in agreement with previous observations. Copyright © 2008 John Wiley & Sons, Ltd.     

Regioselective photoamination of 4-nitroveratrole upon cyclodextrin complexation

Photoamination of 4-nitroveratrole in cyclodextrins with the nucleophiles ammonia, methylamine and hexylamine provides a new route to regioselectivity. This method gives a displaced product para to the nitro group as the predominant product, in contrast to the solution reaction wherein the meta-displaced product predominates. This is due to the change in the mechanistic shift fromS _N2Ar*, wherein the nitro group is meta-directing, to a mechanism involving electron transfer from the nucleophile to the excited aromatic substrate(S _N (ET)Ar*) to give the para-displaced product     

One-dimensional transition metal-benzene sandwich polymers: possible ideal conductors for spin transport

We investigate the electronic and magnetic properties of the proposed one-dimensional transition metal (TM = Sc, Ti, V, Cr, and Mn) -benzene (Bz) sandwich polymers by means of density functional calculations. [V(Bz)](infinity) is found to be a quasi-half-metallic ferromagnet, and half-metallic ferromagnetism is predicted for [Mn(Bz)](infinity). Moreover, we show that stretching the [TM(Bz)](infinity) polymers could have dramatic effects on their electronic and magnetic properties. The elongated [V(Bz)](infinity) displays half-metallic behavior, and [Mn(Bz)](infinity) stretched to a certain degree becomes an antiferromagnetic insulator. The possibilities to stabilize the ferromagnetic order in [V(Bz)](infinity) and [Mn(Bz)](infinity) polymers at finite temperatures are discussed. We suggest that the hexagonal bundles composed by these polymers might display intrachain ferromagnetic order at finite temperatures by introducing interchain exchange coupling.     

Spirometallodendrimers: terpyridine-based intramacromolecular cyclization upon complexation

The first examples of metallodendritic spiranes have been obtained via incorporation of single terpyridine units within each dendritic quadrant.     

Fluorescent ratiometry of tetrahomodioxacalix[4]arene pyrenylamides upon cation complexation

[structure: see text] C-1,2-alternate tetrahomodioxacalix[4]arene pyreneamides were synthesized. Pb(2+) coordination gave a quenched monomer and excimer fluorescence emission, while upon Ca(2+) ion binding, the receptor provides an enhanced excimer and declined monomer emission with ratiometric response. The excimer emission spectra changes are rationalized by frontier molecular orbitals that the effective Py-Py interaction induces emission intensity increases upon Ca(2+) ion complexation, whereas there is no such interaction observed upon Pb(2+) binding.     

Thermochemistry of adducts of some bivalent transition metal bromides with 4-chloroaniline

The compounds [MBr₂(p-clan)₂] (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or Zn(II); p-clan = 4-chloroaniline) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of solution of the adducts, metal(II) bromides and 4-chloroaniline in methanol, 1.2 M aqueous HCl or 25% (v/v) 1.2 M aqueous HCl in methanol were measures and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH°), the standard enthalpies of formation (Δ_fH°), the standard enthalpies of decomposition (Δ_DH°), the lattice standard enthalpies (Δ_MH°) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH°(g)). The mean bond dissociation enthalpies of the metal(II)-nitrogen coordinated bonds and the enthalpies of adduct formation in the gaseous phase have been estimated.     

UV band Splitting of chromogenic azo-coupled calix[4]crown upon cation complexation

Calixcrown-6 compounds carrying a pair of phenylazo moieties on the upper rim and two OH groups, one OH group, and two OR groups on the lower rim have been prepared in both the cone and partial cone conformations. UV/vis spectral measurements showed a red shift upon the addition of Ca2+ to the calixcrown carrying two OH groups and a blue shift for the calixcrown carrying two OR groups. For the compounds with two OR groups on the lower rim and a fixed partial cone conformation, a blue shift caused by electrostatic interaction between the oxygen atoms of OR and the metal ion as well as a red shift caused by the pi-metal complexation between the rotated calix benzene and the metal ion were observed.     

Multifunctionalised cationic fullerene adducts for gene transfer: design, synthesis and DNA complexation

Cationic poly-N,N-dimethylfulleropyrrolidinium derivatives have been designed and synthesised to complex plasmid DNA for gene delivery.     

Calix[4]arenes with carboxamide and sulfonamide groups and their complexation with transition metal salts

Calix[4]arene derivatives functionalized by ester and carboxamide groups on the lower rim and sulfonamide groups on the upper rim were synthesized, and their complexing properties toward transition metal salts (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺) were studied by extraction in chloroform-water system. The presence of carboxamide and sulfonamide fragments in the ligand was shown to considerably enhance binding of transition metal cations.     

Reorganization of highly preorganized hosts upon cation complexation: Ab initio study of fluorospherands

Fluorospherands (F‐spherands) are highly preorganized hosts composed of fluorobenzene or 4‐methylfluorobenzene units attached to one another at their 2,6‐positions. To understand the intrinsic factors affecting cation complexation, we investigated the complexation behavior between F‐spherands and cations using density functional theory (DFT) at the level of B3LYP/6‐31G**. The F6‐spherand (C₆H₃F)₆, ( 1 ) has a highly preorganized spherical cavity, which can encapsulate Li⁺ and Na⁺. Its cavity is not big enough for K⁺ and NH, which prefer external binding. Plausible conformations were studied for F8‐spherand (C₆H₃F)₈. Conformer of D_2d symmetry ( 2b ) is more stable than that of D_4d ( 2a ), in agreement with NMR experiments. The cavity size of F8‐spherand is big enough to encapsulate all cations studied. However, the cavity size of 2b is smaller than that of 2a , which resulted in the guest selectivity. Upon complexation, 2b conformation is more stable for Li⁺ and Na⁺, while 2a conformation is preferred for larger cations such as K⁺ and NH. Thus, the ab initio calculations over these highly preorganized fluorospherands give important insights into their host–guest chemistry. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Reduction and reconstruction of Co3O4 nanocubes upon carbon deposition

We describe a synthetic investigation on the formation of carbon nanofibers using a preshaped free-standing metal-oxide catalyst (single-crystal cobalt oxide (Co(3)O(4)) nanocubes). In reacting with acetylene (C(2)H(2)) vapor, Co(3)O(4) nanocubes are reduced and reconstructed into metallic cobalt. The resultant metal catalyst with a 2-fold symmetry leads to a bilateral base growth for carbon nanofibers. Our findings indicate that an understanding of catalyst-assisted chemical vapor deposition (CVD) mechanisms can be acquired, when the shape, size, and crystal orientation of pristine metal catalysts are made known to the CVD process. By tracing their evolutional changes in structure and composition, the shape-designed model catalysts may offer new opportunities for mechanistic investigations on the chemical reactivity of nanoparticles, general catalyst-assisted material synthesis, and metal intercalation chemistry.     

Metal Complexes with Macrocyclic Ligands. X. On the metal complexation kinetics of two N4-macrocycles containing a pyridine ring

The complexation kinetics of the two macrocycles 1 and 2 with Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ have been measured by pH-stat techniques. The rates are first order in metal and ligand concentration and depend upon the pH. This results from the different reactivities of the various protonated species of the macrocyclic tetraamines. The resolved rate constants are given in Table 2. In comparison with other 14-membered cyclic aliphatic tetraazasystems 1 and 2 react more slowly with metal ions. This might be a consequence of the more rigid structure induced by the pyridine ring.     

Anion-arene adducts: C-H hydrogen bonding, anion-pi interaction, and carbon bonding motifs

This article summarizes experimental and theoretical evidence for the existence of four distinct binding modes for complexes of anions with charge-neutral arenes. These include C-H hydrogen bonding and three motifs involving the arene-pi system-the noncovalent anion-pi interaction, weakly covalent sigma interaction, and strongly covalent sigma interaction.     

Aziridinium ring opening: a simple ionic reaction pathway with sequential transition states

Most organic reactions go from a starting material to an intermediate or a product after crossing one transition state. We report calculations that show a simple ionic reaction, aziridinium ring opening, proceeds through sequential transition states without an intervening intermediate.     

Group 4 Metal-Containing Polymers: An Overview

This review describes the recent advances in the chemistry of titanium-, zirconium-, and hafnium-containing polymers. The paper does not focus on the catalytic role of molecules including metal in their structure, but instead, on the different ways to incorporate these group 4 metals in macromolecular structures. The synthetic approaches of these structures are exposed, according to the three different routes listed, which are the blending, the chemical modification, and the direct polymerization. A particular interest is accorded to the applications of these group 4 metal-containing polymers, which impact various fields such as ceramic, biomedical, and photovoltaic materials.     

Mobility of the ring structure and the characteristics of crosslinked polymers: The structural effect of the eleven-membered ring and its homologs upon the dynamic mechanical properties and glass transition temperature of crosslinked diallyl succinate polymers

Dynamic mechanical properties and glass transition temperatures were measured for crosslinked polymers derived from diallyl succinate monomers. The mobility of the diester having an eleven-membered ring and of homologous structures which are introduced in the crosslinked polymer system, is discussed on the basis of the parameter for cyclization polymerization of a monomer, dynamic mechanical properties, and glass transition temperature. Control of the mobility of the ring structure and its homologous structures involved in the crosslinked polymers was attempted by modification of the substituent at the 1- or 1,2-position of diallyl succinate, and the diallyl succinate monomers were derived from the succinic acid and its derivatives: succinic acid, methyl succinic, ethyl succinic, and chlorosuccinic acids; cis-1,2-dicarboxylic acids of cyclopropane, cyclobutane, cyclopentane, and cyclohexane; cis-1,3- and 1,4-dicarboxylic acids of cyclohexane, and phthalic acid. The results obtained are explained well on the basis of the mobility of the ring and homologous structures.     

The synthesis and transition temperatures of ester derivatives of 2-fluoro-4-hydroxy- and 3-fluoro-4-hydroxybenzonitriles also incorporating aliphatic ring systems

The synthesis and liquid-crystal transition temperatures of forty ester derivatives of 2-fluoro-4-hydroxybenzonitrile and 3-fluoro-4-hydroxybenzonitrile are reported. The esters contain the trans-1,4-disubstituted cyclohexane or the 1,4-disubstituted bicyclo[2.2.2]octane rings (some contain an additional phenyl ring). Many of the novel F-substituted esters exhibit substantially higher nematic-isotropic transition temperatures than the corresponding unsubstituted esters. The order of clearing points of these laterally substiuted esters differing only in the presence of a benzene ring and the above-mentioned rings id established.     

Restricted rotation involving the tetrahedral carbon—VI : Some Diels-Alder adducts derived from 2-t-butylfuran

1 - t - Butyl - 1,4 - dihydronaphthalene 1,4 - endoxide derivatives were prepared by treating 2 -t- butylfuran with some benzynes to see the effect of the bulkiness on the barrier to rotation. The NMR signals of the t-Bu group of these compounds split at low temperature, showing that the rotation about the C^Bu-C₁ bond was frozen on the NMR time scale. Activation parameters for rotation were obtained by the total line shape analysis. On further lowering of the temperature, the restricted rotation of the Me in t-Bu group was observed. The signals of the Me groups were assigned by taking the chemical shifts and the through-space H-F couplings into consideration.