Updated Nucleosynthesis Constraints on Unstable Relic Particles

We revisit the upper limits on the abundance of unstable massive relic particles provided by the success of Big-Bang Nucleosynthesis calculations. We use the cosmic microwave background data to constrain the baryon-to-photon ratio, and incorporate an extensively updated compilation of cross sections into a new calculation of the network of reactions induced by electromagnetic showers that create and destroy the light elements deuterium, he3, he4, li6 and li7. We derive analytic approximations that complement and check the full numerical calculations. Considerations of the abundances of he4 and li6 exclude exceptional regions of parameter space that would otherwise have been permitted by deuterium alone. We illustrate our results by applying them to massive gravitinos. If they weigh ~100 GeV, their primordial abundance should have been below about 10^{-13} of the total entropy. This would imply an upper limit on the reheating temperature of a few times 10^7 GeV, which could be a potential difficulty for some models of inflation. We discuss possible ways of evading this problem.Comment: 40 pages LaTeX, 18 eps figure

PREDICTIONS AND METHODS OF SEPARATION OF RACEMIC BIDENTATE LIGANDS VIA STEREOSELECTIVE LIGAND-EXCHANGE REACTIONS

The technique of molecular mechanics has been applied to the prediction of isomer distributions of several complexes of chiral quadridentate amine ligands in conjunction with some optically active bidentate substrates. Specifically, the systems reported comprise the cobalt(III) and nickel(II) complexes of N,N'-bis[2(S)-2-pyrrolidinylmethyl]ethane-1,2-diamine (S,S-epm) and N,N'-bis[2(S)-2-pyrrolidinylmethyl]propane-1,3-diamine (S,S-ppm) in combination with the chiral bidentate ligands propane-1,2-diamine, (pn) 2-pyrrolidinylmethanamine (pam), and alanine (ala). Agreement between all predicted and observed isomer ratios was within 5%. The experimentally determined enantiomer ratios were as follows: [Co(S,S-ppm)(pn)]3+, 49/51 R-pn/S-pn; [Ni(S,S-ppm)(pn)]2+, 57/43 R-pn/S-pn; [Ni(S,S-ppm)(pam)]2+, 44/56 R-pam/S-pam; [Ni(S,S-epm)(pn)]2+, 43/57 R-pn/S-pn; [Ni(S,S-epm)(pam)]2+, 70/30 R-pam/S-pam. Various experimental methods are reported for the determination of chiral separation

RESOLUTION OF RACEMIC AMINO-ACIDS VIA STEREOSELECTIVE LIGAND-EXCHANGE REACTIONS ON AN OPTICALLY PURE NICKEL(II) COMPLEX

Racemic amino acids (Ala, Val, Leu) co-ordinate steroselectively to the square-planar chiral matrix complex [Ni{(S,S)-L)}]2+ {(S,S)-L = N,N'-bis[(2S)-pyrrolidin-2-yl]propane-1,3-diamine}.The stereoselectivities [Ala, 60% (S), 40% (R); Val, 75% (S), 25% (R); Leu, 68% (S), 32% (R)] have been predicted by molecular mechanics calculations and determined experimentally by potentiometric titrations. The structure of the chiral matrix complex has also been determined: orthorhombic, space group P2(1)2(1)2(1), a = 8.298 (3), b = 13.51 3 (4), c = 18.293 (7) angstrom. Z = 4, R' = 0.051

ISOLATION AND COMPLEXATION OF THE CIS ISOMER OF THE PENDANT ARM MACROCYCLE 6,13-DIMETHYL-1,4,8,11-TETRAAZACYCLOTETRADECANE-6,13-DIAMINE

The cis isomer of the pendant arm macrocyclic hexaamine 6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L2) has been isolated for the first time. The ligand has been complexed with cadmium(II) and characterised structurally. The complex [CdL2][ClO4]2 crystallises in the monoclinic space group P2(1)/n, a = 10.238(1), b = 16.445(2), c = 13.106(2) angstrom, beta = 103.33(1)-degrees, and Z = 4. The Cd-N bond lengths are not unusual by comparison with those exhibited by typical CdN62+ complexes, compared with the generally short M-N bond lengths that have been observed in sexidentate co-ordinated complexes of the trans isomer L1. Reaction of L1 with cadmium(II) does not yield a hexaamine complex, instead the pendant primary amines are not co-ordinated and the four secondary amines encircle the metal centre

CHIRAL TETRAAMINES BASED ON (S)-2-(AMINOMETHYL)PYRROLIDINE - TEMPLATE SYNTHESIS AND PROPERTIES OF COPPER(II) COMPLEXES

The template reaction of {bis[(S)-2-(aminomethyl)pyrrolidine]}copper(II) with formaldehyde, nitroethane, and base in MeOH yields optically pure {1,7-bis[(S)-pyrrolidin-2-yl]-4-methyl-4-nitro-2,6-diazaheptane}-copper(II) ([Cu((S,S)-mnppm)]2+) in high yield. The same reaction with rac-2-(aminomethyl)pyrrolidine is also described. Preparative details and spectroscopic and electrochemical properties of the Cu(II) complexes and of the free ligands are reported and compared with structural, spectroscopic, and electrochemical data of the Cu(II) complex of the unsubstituted parent ligand 1,7-bis[(S)-pyrrolidin-2-yl]-2,6-diazaheptane (ppm). The crystal structure of [CU(PPM)]Cl.ClO4 has been determined by X-ray diffraction methods

TRANSITION-METAL COMPLEXES OF THE NOVEL TRIDENTATE DI-2-PYRIDYLMETHANAMINE (DIPA)

The first row transition metal complexes [M(dipa)2]n+ (dipa = di-2-pyridylmethanamine, M = Fe(III), Fe(II), Co(III), Ni(II) and Cu(II)) have been synthesized in generally high yields. Stability constants for the labile Co(II), Ni(II), and Cu(II) complexes have been determined by potentiometric titrations and are as follows (log K1, log K2): 7.63 (1), 6.57 (1); 8.55 (1), 8.25 (1); and 8.89 (1), 7.94 (1). A rather large degree of steric strain within the complexes is evident from the X-ray crystal structures of rac-[Fe(dipa)2](ClO4)2.2H2O (monoclinic, P2(1)/n, a = 9.392 (3) angstrom, b = 16.749 (3) angstrom, c = 17.131 (14) angstrom, beta = 96.62 (5)-degrees, Z = 4) rac-[Co(dipa)2](ClO4)3 (orthorhombic, Pcca, a = 17.574 (5) angstrom, b = 8.568 (2) angstrom, c = 19.159 (3) angstrom, Z = 4), meso-[Ni(dipa)2](S2O6).4H2O (triclinic, P1BAR, a = 7.903 (3) angstrom, b = 9.810 (3) angstrom c = 10.900 (2) angstrom, alpha = 113.10 (3)-degrees, beta = 106.01 (3)-degrees, gamma = 96.93 (4)-degrees, Z = 1), and meso- [Cu(dipa)2] (ClO4)2 (monoclinic, P2(1)/n, a = 7.964 (3) angstrom, b = 10.1 54 (2) angstrom, c = 16.842 (4) angstrom, beta = 100.12 (4)-degrees, Z = 2). Molecular mechanics calculations indicate that the formation of rac-[Co(dipa)2]3+ in preference to the meso isomer is dominant, and this is in agreement with experimental results based on NMR spectra of equilibrated solutions. In the case of Cu(II), formation of the meso isomer is not selective, and this was confirmed by the successful Cu(II)-directed template condensation of the rac isomer with formaldehyde and nitroethane. Calculations also indicate that the rac isomer of the Ni(II) complex is more stable than the crystallized meso isomer

CHIRAL QUADRIDENTATE LIGANDS BASED ON AMINO-ACIDS - TEMPLATE SYNTHESES AND PROPERTIES OF THE FREE LIGANDS AND THEIR TRANSITION-METAL COMPLEXES

The copper(II)-directed condensation of amino acids with formaldehyde and nitroethane has produced new open-chain quadridentate ligands stereoselectively and in generally high yield. The free ligands with pendant amine substituents may be isolated by zinc reduction of the copper(II) complexes. The reactions studied employed optically pure L-amino acids with non-co-ordinating side chains, racemic amino acids with non-co-ordinating side chains, amino acid mixtures and beta-amino acids. The quadri- and quinquedentate ligands form very stable complexes with transition-metal ions, with their copper(II) complexes being generally stable down to pH almost-equal-to 1. The isolation and spectroscopic properties (UV/VIS, IR, NMR and EPR) of cobalt(III) and copper(II) complexes of some of the amino acid-based ligands are reported. Condensation of racemic and mixed amino acids led to one out of three possible quadridentate ligands, and this stereoselectivity is interpreted based on a model involving the co-ordination of an organic nitro group. This mechanism is supported by qualitative molecular mechanics calculations. The crystal structures of the condensation products with beta-alanine, ([Cu(mnp-beta-ala)].5H2O (mnp-beta-ala = 6-methyl-6-nitro-4,8-diazaundecanedioate), and the Zn-HCI reduction product of the condensation with glycine [Cu(Hampgly)Cl].2H2O (ampgly = 5-amino-5-methyl-3,7-diazanonanedioate), have been determined. In the former structure the Cu(II) is in a distorted trigonal-bipyramidal environment with the fifth site being a co-ordinated carboxylate oxygen from an adjacent molecule, while in the latter Cu(II) has a square-pyramidal co-ordination with an apical chloride ligand