Identification of arginine analogues as antagonists and agonists for the melanocortin-4 receptor

In the present study, conducted to explore potent and small molecular melanocortin-4 (MC4) receptor ligands, we found that tripeptide 3a, containing a D-Phe-Arg-2-Nal (Nal; naphthylalanine) sequence, exhibited a moderate affinity for the MC4 receptor. Structural optimization led to the identification of a compound with a high affinity for the MC4 receptor, namely, tripeptide 3e, which showed a 70-fold higher affinity for the MC4 receptor than the lead compound 3a. Moreover, in an effort to further reduce the peptidic characters of tripeptide 3e, we found that dipeptide 3g exhibited a relatively high affinity for the MC4 receptor. Furthermore, in these analogues, the substituted position (1' vs. 2') of the naphthyl ring of Nal residue at position 7 was found to be important for the differentiation of agonist and antagonist activity. The synthesis and structure-activity relationships of the arginine analogues as MC4 receptor ligands were described in this paper.     

Photochemical ligand substitution reactions of fac-[Re(bpy)(CO)3Cl] and derivatives

Excitation by high-energy light, such as that of 313 nm wavelength, induces a photochemical ligand substitution (PLS) reaction of fac-[Re(bpy)(CO)3Cl] (1a) to give the solvento complexes (OC-6-34)- and (OC-6-44)-[Re(bpy)(CO)2(MeCN)Cl] (2 and 3) in good yields. The disappearance quantum yield of 1a was 0.01+/-0.001 at 313 nm. The products were isolated, and X-ray crystallographic analysis was successfully performed for 2. Time-resolved IR measurements clearly indicated that the CO ligand dissociates with subpicosecond rates after excitation, leading to vibrationally hot photoproducts, which relax within 50-100 ps. Detailed studies of the reaction mechanism show that the PLS reaction of 1a does not proceed via the lowest vibrational level in the 3MLCT excited state. The PLS reaction gives 2 and (OC-6-24)-[Re(bpy)(CO)2(MeCN)Cl] (5) as primary products, and one of the products, 5, isomerizes to 3. This type of PLS reaction is more general, occurring in various fac-rhenium(I) diimine tricarbonyl complexes such as fac-[Re(X2bpy)(CO)3Cl] (X2bpy=4,4'-X2-bpy; X=MeO, NH2, CF3), fac-[Re(bpy)(CO)3(pyridine)]+, and fac-[Re(bpy)(CO)3(MeCN)]+. The stable photoproducts (OC-6-44)- and (OC-6-43)-[Re(bpy)(CO)2(MeCN)(pyridine)]+ and (OC-6-32)- and (OC-6-33)-[Re(bpy)(CO)2(MeCN)2]+ were isolated. The PLS reaction of rhenium tricarbonyl-diimine complexes is therefore applicable as a general synthetic method for novel dicarbonyls.     

Fourier transform microwave spectrum of CO-dimethyl ether

Two sets of 32 rotational transitions were observed for the carbon monoxide-dimethyl ether (CO-DME) complex and two sets of 30 transitions for both (13)CO-DME and C(18)O-DME, in the frequency region from 3.5 to 25.2 GHz, with J ranging from 1<--0 up to 7<--6, by using a Fourier transform microwave spectrometer. The splittings between the two sets of the same transition varied from 2 to 15 MHz, and the two components were assigned to the two lowest states of the internal rotation of CO with respect to DME governed by a twofold potential. A preliminary analysis carried out separately for the two sets of the observed transition frequencies by using an ordinary asymmetric-rotor Hamiltonian indicated that the heavy-atom skeleton of the complex was essentially planar, as evidenced by the "pseudoinertial defects," i.e., the inertial defects, which involve the contributions of the out-of-plane hydrogens of the two methyl groups, I(cc)-I(aa)-I(bb) of -5.764(23) and -5.753(16) uA(2) for the symmetric and antisymmetric states, respectively. All of the observed transition frequencies were subsequently analyzed simultaneously, by using a phenomenological Hamiltonian which was described in a previous paper on Ar-DME and Ne-DME [Morita et al., J. Chem. Phys. 124, 094301 (2006)]. The rotational constants thus derived were analyzed to give the distance between the centers of gravity of the two component molecules, DME and CO, to be 3.682 A and the angle between the CO and the a-inertial axes to be 75.7 degrees ; the C end of the CO being closer to the DME. Most a-type transitions were observed as closely spaced triplets, which were ascribed to the internal rotation of the two methyl tops of DME. The V(3) potential barrier was obtained to be 772(2) cm(-1) from the first-order Coriolis coupling term between the internal rotation and overall rotation, which is about 82% of V(3) for the DME monomer, whereas the second-order contribution of the coupling to the B rotational constant led to V(3) of 705(3) cm(-1). By assuming a Lennard-Jones-type potential, the dissociation energy was estimated to be E(B)=1.6 kJ mol(-1), to be compared with 1.0 and 2.5 kJ mol(-1) for Ne-DME and Ar-DME, respectively.     

Observation of free-electron-laser-induced collective spontaneous emission (superfluorescence)

We have observed and characterized 501.6 nm collective spontaneous emission (superfluorescence) following 1s(2) → 1s3p excitation of helium atoms by 53.7 nm free-electron laser radiation. Emitted pulse energies of up to 100 nJ are observed, corresponding to a photon number conversion efficiency of up to 10%. We observe the peak intensity to scale as ρ(2) and the emitted pulse width and delay to scale as ρ(-1), where ρ is the atom number density. Emitted pulses as short as 1 ps are observed, which corresponds to a rate around 75,000 times faster than the spontaneous 1s3p → 1s2s decay rate. To our knowledge, this is the first observation of superfluorescence following pumping in the extreme ultraviolet wavelength region, and extension of the technique to the generation of extreme ultraviolet and x-ray superfluorescence pulses should be straightforward by using suitable atomic systems and pump wavelengths.     

Phosphorylation of Amine Compounds with Sodium Cyclo-triphosphate

Abstract

Among inorganic linear and cyclic phosphates, cyclo-triphosphate has drawn special attention for its high reactivity with various amine compounds. A ring opening reaction to produce N-alkylamidotriphosphate derivatives proceeds under moderate conditions, e.g., at room temperature in aqueous solution. In spite of its potentiality as a phosphorylating agent for amino groups, a systematic investigation on the reaction mechanism has not fully carried out. This may be due to the lack of analytical methods which allow the quantitative examination of the reactions. In this work, HPLC with an anion-exchanger column developed for phosphate compounds together with ³¹P-NMR were applied to a kinetic study. It has been clarified that; 1) the reactivity of amine compounds is primarily correlated with the basisity of the amino groups, i.e., pKa values of its conjugate acids, though, branching at α carbon of the amino group greatry retards the reaction rate because of steric hindrance, and 2) some bifunctional reagents, such as ethylenediamine, propanediamine, ethanol-amine, and some α-amino acids produce heterocycles which contain P-N bond through an intramolecular reaction following the ring opening of cyclo-triphosphate. Ba or Mg salts of N-alkylamidotriphosphate derivatives have been prepared from mono amines, diamines, aminoalcohols, and aminoacids.     

Tolerance to Solar Ultraviolet‐B Radiation in the Citrus Red Mite,An Upper Surface User of Host Plant Leaves

Plant‐dwelling mites are potentially exposed to solar ultraviolet‐B (UVB) radiation that causes deleterious and often lethal effects, leading most mites to inhabit the lower (underside) leaf surfaces. However, in species of spider mite belonging to the Genus Panonychus, a substantial portion of individuals occur on upper leaf surfaces. We investigated whether the upper leaf surfaces of citrus trees are favorable for P. citri, and to what extent they are tolerant to UVB radiation. If eggs are not adequately protected from UVB damage, females may avoid ovipositing on the upper surfaces of sunny leaves. To test this, we conducted laboratory experiments using a UVB lamp, and semioutdoor manipulative experiments. As a result, P. citri eggs are tolerant to UVB. Field studies revealed that the ratio of eggs and adult females on upper leaf surfaces were larger for shaded than for sunny leaves. However, 64–89% of eggs hatched successfully even on sunny upper leaf surfaces. Nutritional evaluation revealed that whether on sunny or shaded leaves, in fecundity and juvenile development P. citri reaped the fitness benefits of upper leaf surfaces. Consequently, P. citri is tolerant to UVB damage, and inhabiting the upper surfaces of shaded leaves is advantageous to this mite.     

Constructing non-Abelian vortices with arbitrary gauge groups

We construct the general vortex solution in the color–flavor-locked vacuum of a non-Abelian gauge theory, where the gauge group is taken to be the product of an arbitrary simple group and U(1)$U(1)$. Use of the holomorphic invariants allows us to extend the moduli-matrix method and to determine the vortex moduli space in all cases. Our approach provides a new framework for studying solitons of non-Abelian varieties with various possible applications in physics.     

Right handed or left handed? Forbidden x-ray diffraction reveals chirality

Enantiomers, or stereoisomers, have crystal structures that are mirror images of each other and are thus handed, like our right and left hands. The physical properties of enantiomers are identical except for optical activity, which rotates linearly polarized light by equal amounts but in opposite directions. While conventional x-ray Bragg diffraction can determine crystal structures, it does not distinguish between right- and left-handed crystals. We show resonant Bragg diffraction using circularly polarized x rays reveals the handedness of crystals by coupling x-ray helicity to a crystal screw axis. The intensity of resonantly allowed reflection of alpha-quartz is well described by an admixture of a parity-even and a parity-odd process. Our results are of general importance and demonstrate a new method to directly study chiral motifs in structures that include biomaterials, liquid crystals, magnets, multiferroics, etc.     

Coherent and Incoherent Excitations of Electron-Doped SrTiO3

Resonant photoemission at the Ti 2p and O 1s edges on a Nb-doped SrTiO(3) thin film revealed that the coherent state (CS) at the Fermi level (E(F)) had a mainly Ti 3d character whereas the incoherent in-gap state (IGS) positioned approximately 1.5 eV below E(F) had a mixed character of Ti 3d and O 2p states. This indicates that the IGS is formed by a spectral-weight transfer from the CS and subsequent spectral-weight redistribution through d-p hybridization. We discuss the evolution of the excitation spectrum with 3d band filling and rationalize the IGS through a mechanism similar to that proposed by Haldane and Anderson.