1,721,125 research outputs found
Conformation-directing chiral groups in bis(naphthaldiminato)nickel(ii) complexes: A rare example with 16 crystallographically independent units (: Z′)
No full textConformational distortions in bis-chelating nickelIJII) complexes
with naphtholate Schiff base ligands bearing an alkyl chiral group
at the imino nitrogen atoms are described. The single crystal X-ray
analysis at 100 K by using synchrotron radiation of bisij1-((((R)-
1,2,2-trimethylpropyl)imino)methyl)-2-naphtholato]nickelIJII) shows
an umbrella shape of sizeable bending. In addition, the unit cell of
this complex contains 16 crystallographically independent units, a
rare example of high Z′ value
Investigation of 2-Fold Disorder of Inhibitors and Relative Potency by Crystallizations of HIV-1 Protease in Ritonavir and Saquinavir Mixtures
No full textInvestigation of 2-Fold Disorder of Inhibitors and Relative Potency by Crystallizations of HIV-1 Protease in Ritonavir and Saquinavir Mixtures
No full textHIV-1 protease (PR) was cocrystallized in competitive mixtures of saquinavir (SQV) and ritonavir (RTV) in an attempt to compare the relative potencies of inhibitors using a crystallographic approach. The mixture ratio of RTV/SQV was in the range of 1:1 to 50:1. The crystal form obtained with 1:1 and 5:1 ratios of RTV/SQV was monoclinic, while ratios 15:1 and 50:1 gave orthorhombic crystal form. The four crystal structures of PR/RTV/SQV were solved at 1.03, 1.12, 1.25, and 1.72 Å resolutions. The X-ray crystal structures reveal that the crystal forms are dependent on the occupancy of either SQV or RTV in the active site of PR. At low RTV/SQV concentrations, PR/SQV complex is dominant, and at higher ratios, PR/RTV is found. The absence of a crystal structure having both inhibitors statistically disordered in the catalytic site of PR suggests that the two protein complexes are sufficiently different in properties to be discriminated in crystal growth process. The X-ray structures of the dimeric enzyme with C2 pseudosymmetry show a 2-fold-disorder phenomenon for the SQV, while the RTV inhibitor is detected in a single orientation. The dominancy of PR/SQV crystal form at an equimolar mixture of inhibitor and the presence/absence of the 2-fold disorder of inhibitors have given new insight into the relative potency of these drugs and both suggest a higher potency of SQV with respect to RTV
New Insight into a Deceptively Simple Reaction: The Coordination of bpy to RuII-Carbonyl Precursors - The Central Role of thefac-[Ru(bpy)Cl(CO)3]+Intermediate and theChloride Rebound Mechanism
Full text linkThis work demonstrates how a careful reexamination of well-trodden fields can fill conceptual gaps that previously escaped full understanding. The coordination of 2,2'-bipyridine (bpy) to the known Ru(II)-chlorido-carbonyl precursors – the dinuclear [RuCl2(CO)3]2 (P1) and the polymeric [RuCl2(CO)2]n (P2) – has been investigated by several groups in the past, and a remarkably large number of ruthenium mono(bpy) carbonyls were identified and fully characterized. Many were investigated as catalysts or key intermediates for the photochemical, electrochemical, and photo-electrochemical reduction of CO2, and for the water–gas shift reaction. Nevertheless, even though most – if not all – the reaction products are known already, a careful exam of the literature led us to believe that a convincing general scheme interconnecting them all was still missing and important questions remained unanswered. For this reason, we investigated the reactivity of two mononuclear Ru(II)-carbonyl-dmso precursors, trans,cis,cis-[RuCl2(CO)2(dmso-O)2] (P3) and fac-[RuCl2(CO)3(dmso-O)] (P4) – that can be considered as ‘activated forms’ of P2 and P1, respectively – towards the coordination of bpy. Compounds P3 and P4, allowed us to gain new mechanistic insight and a deeper level of understanding. In particular, we found that coordination of bpy to P4 (or P1) generates first the tricarbonyl cation fac-[Ru(bpy)Cl(CO)3]+.This key intermediate undergoes the facile and selective nucleophilic attack on the CO trans to Cl (by RO– in alcoholic solvents or OH– from adventitious water in other solvents), leading to all other species. We also demonstrated that Cl– – even when in large excess – is unable to replace a carbonyl on fac-[Ru(bpy)Cl(CO)3]+. However, the chloride set free from the precursor, competes efficiently with bpy for the coordination to Ru(II) (chloride rebound mechanism)
Reactivity of a fluorine-containing dirhodium tetracarboxylate compound with proteins
No full text: Dirhodium complexes of general formula [Rh2(O2CR)4]L2 are a well-known class of bimetallic compounds that are used as efficient catalysts for a variety of reactions and have been shown to be potent antibacterial and anticancer agents. The catalytic and biological properties of these complexes largely depend on the nature of the bridging carboxylate ligands. Trifluoroacetate (tfa)-containing dirhodium compounds have been used to build artificial metalloenzymes upon reaction with peptides and have been shown to be more cytotoxic than dirhodium tetraacetate. However, there is no structural information on the interaction between these compounds and proteins. Here, cis-Rh2(μ-O2CCH3)2(μ-O2CCF3)2 ([cis-Rh2(OAc)2(tfa)2]) has been synthesized and its reaction with bovine pancreatic ribonuclease (RNase A) and hen egg white lysozyme (HEWL) was analyzed using a combination of different techniques, including Fluorine-19 nuclear magnetic resonance spectroscopy and macromolecular X-ray crystallography, with the aim to unveil the differences in the reactivity of tfa-containing dihrodium complexes with proteins when compared to [Rh2(OAc)4]. [cis-Rh2(OAc)2(tfa)2] and [Rh2(OAc)4] bind the N atoms of His side chains of RNase A at the axial position; however the fluorine-containing compound rapidly loses its tfa ligands, while [Rh2(OAc)4] can retain the acetate ligands upon protein binding. The reactivity of [cis-Rh2(OAc)2(tfa)2] with HEWL is slightly distinct when compared to that of [Rh2(OAc)4] under the same experimental conditions; however, both [cis-Rh2(OAc)2(tfa)2] and [Rh2(OAc)4] degrade when soaked within HEWL crystals. These results provide a structural-based guide for the design of new heterogenous chiral dirhodium/peptide and dirhodium/protein adducts with application in the fields of organic synthesis and asymmetric catalysis
Isolation and characterization of major diterpenes from C. canephora roasted coffee oil
Full text linkA simple laboratory procedure for the isolation of pure cafestol and 16-O-methylcafestol together with beta-sitosterol from coffee is disclosed. Cafestol and 16-O-methylcafestol have been exhaustively characterized through 1D and 2D H-1, C-13 NMR, CD and X-ray diffraction. For the first time, the molecular structure of cafestol is reported and the assignment of the absolute configuration is unequivocally given by exploiting anomalous scattering of a brominated derivative
Synthesis and Anticancer Activity of Palladium‐Butadienyl Complexes Bearing Picolyl‐NHC and Phosphine Ligands
No full textThis work presents the synthesis and full characterization of Pd(II)-butadienyl complexes incorporating picolyl-NHC or phosphine ligands (PPh3 or PTA). These complexes were evaluated against four different cancer cell lines and human lung fibroblasts. Our findings indicate a slightly lower antiproliferative activity of picolyl-NHC Pd(II)-butadienyl complexes compared to recently published ones featuring N−N, P−P, and C−C ligands but, above all, they exhibited selectivity for ovarian cancer cells. Additionally, trans-[PdX (phosphine)2C4(COOMe)4Y)] derivatives (X=Br, Cl and Y=CH3, Br) proved excellent anticancer activity across all tested cancer cell lines, especially the bisPTA complexes. Importantly, the IC50 values suggest minimal impact from the halide coordinated to palladium or that present in the butadienyl terminal position. Furthermore, the low activity observed towards non-cancerous cells underscores the potential of these synthesized Pd(II)-butadienyl compounds as promising candidates for further investigation in anticancer research
Neutral 1,3,5-Triaza-7-phosphaadamantane-Ruthenium(II) Complexes as Precursors for the Preparation of Highly Water-Soluble Derivatives
Full text linkThe monodentate phosphane ligand 1,3,5-triaza-7-phosphaadamantane (PTA) imparts excellent water solubility to its complexes. We aimed to prepare precursors with one or more PTA coligands for solubility and one or more labile ligands for facile replacement by a linker. For this purpose, we investigated the reactivity of the neutral isomers trans- and cis-RuCl2(PTA)4 (1 and 2) towards 2,2′-bipyridine (bpy), as a model chelating diimine linker. The new derivatives mer-[Ru(bpy)Cl(PTA)3]Cl (9) and fac-[Ru(bpy)Cl(PTA)3]Cl (10) were prepared and characterized. We also found that PTA reacts rapidly with cis,fac-RuCl2(dmso-O)(dmso-S)3 (11) and trans-RuCl2(dmso-S)4 (13) under mild conditions through the replacement
of pairs of mutually trans dmso ligands with high selectivity, even when in stoichiometric defect. Thus, 11 affords cis,cis,trans-RuCl2(dmso-S)2(PTA)2 (12), whereas 13 gives 1. The two dmso ligands of 12 can be replaced selectively by chelating diimines such as bpy to afford the less symmetrical all-cis product cis,cis-Ru(bpy)Cl2(PTA)2 (16)
Gabrielsonite revisited: crystal-structure determination and redefinition of chemical formula
Full text linkA reinvestigation of gabrielsonite from the holotype specimen from Långban, central Sweden, using single-crystal
synchrotron diffraction, electron-microprobe techniques and Fourier-transform infrared (FTIR) spectroscopy, Raman and Mo ̈ssbauer
spectroscopies show that the mineral is an anhydrous Fe3+-bearing arsenite and not a hydrous Fe2+-bearing arsenate, as originally
proposed. The revised ideal chemical formula of gabrielsonite is PbFe3+(As3+O3)O. The mineral is related to the descloizite
supergroup, but it differs through the valencies of the non-Pb cations Fe (M3+ vs. M2+) and As (3 + vs. 4 +) and through lower
coordination of Pb (4 vs. 7–8) and As (3 vs. 4). The redefinition of gabrielsonite (proposal 17-G) has been approved by the
Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association
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