Organometallic compounds containing a guanidinium group. Phenylmercury(II) derivatives of creatine and creatinine

Abstract: Structural studies of mercury compounds are evaluated to providing definite evidence that the van der Waals radius of mercury is in the range 1.7-2.0 A. A general value for the radius should lie at the conservative end of the range, hence 1.73 A, conveniently corresponding to Grdenic’s largely neglected upper limit for any form of bonding, is proposed.

Abstract: Dimethylcyanamide (N identical withCNMe(2)) has been coordinated to both hard and soft electrophiles ((NH(3))(5)Co(3+), (NH(3))(5)Os(3+), (dien)Pt(2+)) which activate ( approximately x10(6)) the nitrile toward attack by nucleophiles such as ammonia and hydroxide. Amination with liquid ammonia gave a rare coordinated guanidine (N,N-dimethylguanidine) ligand, which NMR spectra and X-ray crystal structures show to be charge neutral rather than anionic. Crystals of [(NH(3))(5)CoNH=C(NH(2))NMe(2)](S(2)O(6))(3/2).H(2)O, CoC(3)H(26)N(8)O(10)S(3), were triclinic, space group Po, a = 11.565(2) A, b = 10.629(5) A, c = 8.026(1) A, alpha = 84.93(3) degrees, beta = 76.01(1) degrees, gamma = 73.82(3) degrees, V = 919.2(5) A(3), Z = 2, and R(F)() (R(w)(F)()) = 0.038 (0.047) for 3262 observed reflections (I > 3.0 sigma(I)). Crystals of [(dien)PtNH=C(NH(2))NMe(2)](CF(3)SO(3))(2), PtC(9)H(22)N(6)O(6) S(2)F(6), are monoclinic, space group P2(1)/c, a = 13.857(4), b = 14.748(4) A, c = 22.092(4) A, beta = 105.38(2) degrees, V = 4353(2) A(3), Z = 8, and R(F)() (R(w)(F)()) = 0.034 (0.038) for 6778 reflections. Coordination geometries around the metals are octahedral and square planar, respectively, the guanidine skeletons being planar with bond angles and lengths characteristic of the metal-imino (rather than metal-amino) tautomer. The complexes are very stable in coordinating solvents (DMSO; water, pH 3-11) indicating high affinity of guanidine ligands for metal ions. Hydration of the dimethylcyanamide ligand is base-catalyzed, and first-order in [OH(-)] (0.05-0.5 M NaOH; k = k(s) + k(OH)[OH(-)], k(OH) = 2-5 M(-)(1) s(-)(1), 25 degrees C), in each case producing coordinated N,N-dimethylurea ([dienPtNHCONMe(2)](+), [(NH(3))(5)CoNHCONMe(2)](2+), [(NH(3))(5)OsNHCONMe(2)](2+)). Hydration rates are surprizingly similar despite differing radial extensions of the metal d-orbitals, a finding consistent with their comparable polarizing powers but contrary to expectation from other work. The relevance of metal activation of nitriles to biological systems is discussed.

Abstract: Fourier-transform infrared (FT-IR), Raman (RS), and surface-enhanced Raman scattering (SERS) spectra of β-hydroxy-β-methylobutanoic acid (HMB), L-carnitine, and N-methylglycocyamine (creatine) have been measured. The SERS spectra have been taken from species adsorbed on a colloidal silver surface. The respective FT-IR and RS band assignments (solid-state samples) based on the literature data have been proposed. The strongest absorptions in the FT-IR spectrum of creatine are observed at 1398, 1615, and 1699 cm−1, which are due to νs(COOH) + ν(CN) + δ(CN), ρs(NH2), and ν(CO) modes, respectively, whereas those of L-carnitine (at 1396/1586 cm−1 and 1480 cm−1) and HMB (at 1405/1555/1585 cm−1 and 1437–1473 cm−1) are associated with carboxyl and methyl/methylene group vibrations, respectively. On the other hand, the strongest bands in the RS spectrum of HMB observed at 748/1442/1462 cm−1 and 1408 cm−1 are due to methyl/methylene deformations and carboxyl group vibrations, respectively. The strongest Raman band of creatine at 831 cm−1 (ρw(RNH2)) is accompanied by two weaker bands at 1054 and 1397 cm−1 due to ν(CN) + ν(RNH2) and νs(COOH) + ν(CN) + δ(CN) modes, respectively. In the case of L-carnitine, its RS spectrum is dominated by bands at 772 and 1461 cm−1 assigned to ρr(CH2) and δ(CH3), respectively. The analysis of the SERS spectra shows that HMB interacts with the silver surface mainly through the COO−, hydroxyl, and CH2 groups, whereas L-carnitine binds to the surface via COO− and N+(CH3)3 which is rarely enhanced at pH = 8.3. On the other hand, it seems that creatine binds weakly to the silver surface mainly by NH2, and CO from the COO− group. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract: The nature of the peptide seems to be a very important factor for the reactivity of copper(II) peptide complexes with bioligands. Thus, although we have tried to obtain all the ternary complexes derived from the dipeptides l -ala-gly, gly- l -tyr and gly- l -trp with benzimidazole and creatinine, only four new ternary Cu(II) peptide complexes have been obtained: [Cu(gly- l -tyr)(benzimidazole)] · H2O (1), [Cu( l -ala-gly)(benzimidazole)] · 3H2O (2), [Cu(gly- l -trp) (creatinine)] · 1.25H2O (4) and [Cu( l -ala-gly)(H2O)(creatinine)] · 2H2O (5). Compounds 1, 2 and 4 exist as slightly distorted square planar complexes with the four coordination sites occupied by the tridentate peptide dianion and a nitrogen of the ligand, while compound 5 present a square pyramidal co-ordination in which the axial position is occupied by a water molecule. In the ternary benzimidazole complexes the lateral chain of the peptide moiety seems to determine the relative orientation of the ligand. In contrast, in the creatinine complexes the presence of two important intramolecular hydrogen bonds, involving the exocyclic NH2 and CO groups of the creatinine molecule, yield a nearly co-planar system which is independent of the nature of the peptidic lateral chain. These compounds do not present catalase-like activity nor remarkable SOD-like activity but the values of IC50 permit to distinguish a different behavior between benzimidazole and creatinine ternary complexes. Thus, benzimidazole compounds show lower IC50 (similar to free Cu(II)) values than creatinine ones.