[No Value] Huo Wen

Bio: [No Value] Huo Wen is an academic researcher from University College West. The author has contributed to research in topics: Stability constants of complexes & Cis–trans isomerism. The author has an hindex of 3, co-authored 4 publications receiving 69 citations.

Models for Arginine-Metal Binding. Synthesis of Guanidine and Urea Ligands through Amination and Hydration of a Cyanamide Ligand Bound to Platinum(II), Osmium(III), and Cobalt(III).

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.

Selection of metal ions by geometric isomers of a polyamine macrocycle with pendant donors

Abstract: The syn and anti isomers of 6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L1 and L2 respectively) have distinctly different shapes for binding metal ions. This is reflected in part in the stability constants for complexation (log K, 25°C, 1:1 complex), which have been determined for the d10 metal ions Zn2+(syn, 16.1; anti, 14.9), Cd2+(syn, 12.1; anti, 10.6), Hg2+(syn, 12.2; anti, 10.5), and Pb2+(syn, 11.8; anti, 10.8), none of which involves ligand-field stabilization contributions to the stability of complexes. The syn isomer, with its sterically undemanding ‘nest’ shape, displays higher K values than the anti isomer irrespective of metal ion size. Selection of the small zinc(II) ion compared to the larger cadmium(II) ion by both isomers is significant (Δ log K syn 4.0, anti 4.6). The syn isomer accommodates the large lead(II) ion, the [PbL1(H2O)][ClO4]2 complex crystallizing in the monoclinic P21/c space group, Z= 4, a= 8.774(3), b= 17.794(6), c= 15.738(5)A, β= 109.67(3)°. The lead(II) ion is co–ordinated by all six amines [Pb–N range 2.505(5)–2.809(7)A], the water molecule [Pb–O 3.098(6)A] and weakly chelated by a perchlorate ion [Pb–O 3.24(1), 3.298(9)A]. By contrast, the slightly smaller mercury(II) ion is not accommodated in the cavity of the anti isomer, the isolated complex [(H2L2)(HgCl3)2][L2(HgCl2)2]·2H2O crystallizing in the triclinic P space group, Z= 1, a= 14.321(4), b= 10.317(2), c= 8.246(2)A, α= 95.19(2), β= 96.24(2), γ= 97.68(2)°. Two separate molecular units co-exist in equal amounts in the structure, the first with mercury(II) ions bound to each pendant amine in a unidentate manner, whereas the second has two mercury ions chelated at opposite sides of the macrocycle to, in each case, the pendant amine and one secondary amine. In each unit, chloride ions complete the tetrahedral environment for the metal ion, with variable Hg–N [range 2.279(7)–2.364(7)A] and Hg–Cl [range 2.370(3)–2.535(2)A] distances.

Structural Study of an ent-Kaurane Lactone

Abstract: The structure of the methyl ester derivative (2) of ent-20-hydroxy-16βH-kaurane-17,19-dioic acid 19,20-lactone has been determined by X-ray crystallographic methods. The δ-lactone ring adopts the chair conformation both in the solid state and in solution.

Structural Study of an ent-Kaurane Lactone.

Abstract: The structure of the methyl ester derivative (2) of ent-20-hydroxy-16βH-kaurane-17,19-dioic acid 19,20-lactone has been determined by X-ray crystallographic methods. The δ-lactone ring adopts the chair conformation both in the solid state and in solution.

Crystal structure of biotin synthase, an S-adenosylmethionine-dependent radical enzyme.

Abstract: The crystal structure of biotin synthase from Escherichia coli in complex with S-adenosyl-L-methionine and dethiobiotin has been determined to 3.4 angstrom resolution. This structure addresses how "AdoMet radical" or "radical SAM" enzymes use Fe4S4 clusters and S-adenosyl-L-methionine to generate organic radicals. Biotin synthase catalyzes the radical-mediated insertion of sulfur into dethiobiotin to form biotin. The structure places the substrates between the Fe4S4 cluster, essential for radical generation, and the Fe2S2 cluster, postulated to be the source of sulfur, with both clusters in unprecedented coordination environments.

Application of neutral amidines and guanidines in coordination chemistry

Abstract: The aim of this perspective is to highlight the continued development and application of amidines and guanidines as neutral, N-based donor ligands in coordination chemistry. From a sporadic interest dating back to the 1980s, work on these two closely related classes of compounds has steadily grown, with examples of evermore sophisticated substitution about the common ligand framework being developed to address specific problems in a number of fields of chemistry. These compounds have shown varied coordination modes at metals from across the periodic table, and examples of their application in a number of catalytic processes are emerging as the field matures.

Electronic tuning of the lability of Pt(II) complexes through π-acceptor effects. Correlations between thermodynamic, kinetic, and theoretical parameters

Abstract: π-Acceptor effects are often used to account for the unusual high lability of [Pt(terpy)L](2-n)+ (terpy = 2,2‘:6‘,2‘ ‘-terpyridine) complexes. To gain further insight into this phenomenon, the π-acceptor effect was varied systematically by studying the lability of [Pt(diethylenetriamine)OH2]2+ (aaa), [Pt(2,6-bis-aminomethylpyridine)OH2]2+ (apa), [Pt(N-(pyridyl-2-methyl)-1,2-diamino-ethane)OH2]2+ (aap), [Pt(bis(2-pyridylmethyl)amine)OH2]2+ (pap), [Pt(2,2'-bipyridine)(NH3)(OH2)]2+ (app), and [Pt(terpy)OH2]2+ (ppp). The crystal structure of the apa precursor [Pt(2,6-bis-aminomethylpyridine)Cl]Cl·H2O was determined. The substitution of water by a series of nucleophiles, viz. thiourea, N,N-dimethylthiourea, N,N,N‘,N‘-tetramethylthiourea, I-, and SCN-, was studied under pseudo-first-order conditions as a function of concentration, pH, temperature, and pressure, using stopped-flow techniques. The data enable an overall comparison of the substitution behavior of these complexes, emphasizing the role played by the...