Luminescent Di‐ and Polynuclear Organometallic Gold(I)–Metal (Au2, {Au2Ag}n and {Au2Cu}n) Compounds Containing Bidentate Phosphanes as Active Antimicrobial Agents

The reaction of new dinuclear gold(I) organometallic complexes containing mesityl ligands and bridging bidentate phosphanes [Au₂(mes)₂(μ‐LL)] (LL=dppe: 1,2‐bis(diphenylphosphano)ethane 1 a , and water‐soluble dppy: 1,2‐bis(di‐3‐pyridylphosphano)ethane 1 b ) with Ag⁺ and Cu⁺ lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au₂M(μ‐mes)₂(μ‐LL)][A] (M=Ag, A=ClO₄^?, LL=dppe 2 a , dppy 2 b ; M=Ag, A=SO₃CF₃^?, LL=dppe 3 a , dppy 3 b ; M=Cu, A=PF₆^?, LL=dppe 4 a , dppy 4 b ). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au₂(mes)₂(μ‐dppy)] ( 1 b ) and [Au₂Ag(μ‐mes)₂(μ‐dppe)][SO₃CF₃] ( 3 a ) were determined by a single‐crystal X‐ray diffraction study. 3 a in solid state is not a cyclic trinuclear Au₂Ag derivative but it gives an open polymeric structure instead, with the {Au₂(μ‐dppe)} fragments “linked” by {Ag(μ‐mes)₂} units. The very short distances of 2.7559(6) Å (Au? Ag) and 2.9229(8) Å (Au? Au) are indicative of gold–silver (metallophilic) and aurophilic interactions. A systematic study of their luminescence properties revealed that all compounds are brightly luminescent in solid state, at room temperature (RT) and at 77 K, or in frozen DMSO solutions with lifetimes in the microsecond range and probably due to the self‐aggregation of [Au₂M(μ‐mes)₂(μ‐LL)]⁺ units (M=Ag or Cu; LL=dppe or dppy) into an extended chain structure, through Au? Au and/or Au? M metallophilic interactions, as that observed for 3 a . In solid state the heterometallic Au₂M complexes with dppe ( 2 a – 4 a ) show a shift of emission maxima (from ca. 430 to the range of 520‐540 nm) as compared to the parent dinuclear organometallic product 1 a while the complexes with dppy ( 2 b–4 b ) display a more moderate shift (505 for 1 b to a max of 563 nm for 4 b ). More importantly, compound [Au₂Ag(μ‐mes)₂(μ‐dppy)]ClO₄ ( 2 b ) resulted luminescent in diluted DMSO solution at room temperature. Previously reported compound [Au₂Cl₂(μ‐LL)] (LL dppy 5 b ) was also studied for comparative purposes. The antimicrobial activity of 1–5 and Ag[A] (A=ClO₄^?, SO₃CF₃^?) against Gram‐positive and Gram‐negative bacteria and yeast was evaluated. Most tested compounds displayed moderate to high antibacterial activity while heteronuclear Au₂M derivatives with dppe ( 2 a – 4 a ) were the more active (minimum inhibitory concentration 10 to 1 μg mL^?1). Compounds containing silver were ten times more active to Gram‐negative bacteria than the parent dinuclear compound 1 a or silver salts. Au₂Ag compounds with dppy ( 2 b , 3 b ) were also potent against fungi.     

Conformation of glycomimetics in the free and protein-bound state: structural and binding features of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man

The conformational properties of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man in solution have been carefully analyzed by a combination of NMR spectroscopy and time-averaged restrained molecular dynamics. It has been found that both the alpha-1,3- and the alpha-1,6-glycosidic linkages show a major conformational averaging. Unusual Phi ca. 60 degrees orientations for both Phi torsion angles are found. Moreover, a major conformational distinction between the natural compound and the glycomimetic affects to the behavior of the omega(16) torsion angle around the alpha-1 --> 6-linkage. Despite this increased flexibility, the C-glycosyl analogue is recognized by three mannose binding lectins, as shown by NMR (line broadening, TR-NOE, and STD) and surface plasmon resonance (SPR) methods. Moreover, a process of conformational selection takes place, so that these lectins probably bind the glycomimetic similarly to the way they recognize the natural analogue. Depending upon the architecture and extension of the binding site of the lectin, loss or gain of binding affinity with respect to the natural analogue is found.     

Formation of the unusual alkynyl carboxamide complex, C2H5N(H)C(O)CC[Co2(CO)6]CCo3(CO)9

The reaction of the cluster complex HCC[Co₂(CO)₆]CCo₃(CO)₉ with (or without) BrCCo₃(CO)₉ under Cadiot-Chodkiewicz coupling conditions gave the unusual alkynyl carboxamide complex C₂H₅N(H)C(O)CC[Co₂(CO)₆]CCo₃(CO)₉ rather than a coupled product containing two tricobalt cluster units. Steric demands imposed by the Co₃ cluster allow attack at the least hindered alkyne carbon and stabilise the formed ynamine, so allowing subsequent CO insertion. The product has been characterised by X-ray crystallography.     

Determination of rotenone residues in raw honey by solid-phase extraction and high-performance liquid chromatography

A method for determining residues of the insecticide rotenone in raw-honey by high-performance liquid chromatography (HPLC) is described. To extract the residues, organic solvents such as ethyl acetate, n-hexane/dichloromethane and solid-phase extraction with octadecylsilane cartridges or Florisil packed columns were tested. Determination was carried out by reversed-phase HPLC using acetonitrile-buffer phosphate (pH 7) (60:40, v/v) as mobile phase and detection at 210 nm. Although the data showed that the two extraction methods were able to isolate the pesticide residues, the extraction on octadecylsilane cartridges was preferred due to its simplicity and higher recovery. Recoveries depended strongly on the fortification level for the two extraction procedures. Practical determination limits of 0.015 mg/kg were obtained. In the analysis of honeys, from beehives treated with rotenone at therapeutical doses for 1 month, residual amounts below 0.2 mg/kg were found.     

Engineering strategy to improve peptide analogs: from structure-based computational design to tumor homing

We present a chemical strategy to engineer analogs of the tumor-homing peptide CREKA (Cys-Arg-Glu-Lys-Ala), which binds to fibrin and fibrin-associated clotted plasma proteins in tumor vessels (Simberg et al. in Proc Natl Acad Sci USA 104:932–936, 2007) with improved ability to inhibit tumor growth. Computer modeling using a combination of simulated annealing and molecular dynamics were carried out to design targeted replacements aimed at enhancing the stability of the bioactive conformation of CREKA. Because this conformation presents a pocket-like shape with the charged groups of Arg, Glu and Lys pointing outward, non-proteinogenic amino acids α-methyl and N-methyl derivatives of Arg, Glu and Lys were selected, rationally designed and incorporated into CREKA analogs. The stabilization of the bioactive conformation predicted by the modeling for the different CREKA analogs matched the tumor fluorescence results, with tumor accumulation increasing with stabilization. Here we report the modeling, synthetic procedures, and new biological assays used to test the efficacy and utility of the analogs. Combined, our results show how studies based on multi-disciplinary collaboration can converge and lead to useful biomedical advances.     

Innovations in high-pressure liquid injection technique for gas chromatography: pressurized liquid injection system

In gas chromatography (GC), highly volatile liquefied hydrocarbons are commonly injected using devices such as high-pressure syringes, piston valves, liquid rotary sampling valves, or vaporizing regulators. Although these techniques are adequate in some cases, there are known deficiencies. A new generation of sampling valve has been recently innovated and commercialized. Some of the highlights of the pressurized liquid injection system (PLIS) include compact size, the capability to directly couple to an injection port without the need for preinjection vaporization and transfer lines, and sample sizes ranging from 0.2 to 2.0 micro L. Although the valve has a specification of helium leak-free rating of 82.7 bar (1200 psig), the valve passes a hydrostatic pressure test of up to 414 bar (6000 psig). In the unheated version of PLIS, vaporization of solutes occur mainly because of the sheering effect of carrier gas in combination with thermal energy drawn from an injection port or a heated adaptor. This was found to be adequate for solutes with high to medium volatility of up to nC14 hydrocarbon. A higher molecular weight range of up to nC44 hydrocarbon can be achieved with the implementation of a heated version of PLIS, in which the channel of the shaft can be resistively heated at a rate of up to 400 degrees C/s. With its first introduction in May 2002, PLIS has gained acceptance amongst practitioners in GC because it addresses a key unarticulated need in sample introduction/enrichment and by specifically targeting many deficiencies encountered in contemporary high-pressure injection devices. In this paper, the design and performance of the various valve systems of PLIS, as well as industrial chromatographic applications, is presented.     

Tentoxin as a scaffold for drug discovery. Total solid-phase synthesis of tentoxin and a library of analogues

[reaction: see text] A solid-phase method for the synthesis of tentoxin has been developed. Two key steps-dehydration and N-alkylation-are carried out while the peptide is anchored to the resin. The method, which has been validated by the preparation of a library of tentoxin analogues, should be applicable to the generation of further libraries that have the tentoxin scaffold structure, as well as other structures containing N-alkylated didehydroamino acids.     

The Plasticity of the Carbohydrate Recognition Domain Dictates the Exquisite Mechanism of Binding of Human Macrophage Galactose-Type Lectin

The human macrophage galactose-type lectin (MGL), expressed on macrophages and dendritic cells (DCs), modulates distinct immune cell responses by recognizing N-acetylgalactosamine (GalNAc) containing structures present on pathogens, self-glycoproteins, and tumor cells. Herein, NMR spectroscopy and molecular dynamics (MD) simulations were used to investigate the structural preferences of MGL against different GalNAc-containing structures derived from the blood group A antigen, the Forssman antigen, and the GM2 glycolipid. NMR spectroscopic analysis of the MGL carbohydrate recognition domain (MGL-CRD, C181-H316) in the absence and presence of methyl α-GalNAc (α-MeGalNAc), a simple monosaccharide, shows that the MGL-CRD is highly dynamic and its structure is strongly altered upon ligand binding. This plasticity of the MGL-CRD structure explains the ability of MGL to accommodate different GalNAc-containing molecules. However, key differences are observed in the recognition process depending on whether the GalNAc is part of the blood group A antigen, the Forssman antigen, or GM2-derived structures. These results are in accordance with molecular dynamics simulations that suggest the existence of a distinct MGL binding mechanism depending on the context of GalNAc moiety presentation. These results afford new perspectives for the rational design of GalNAc modifications that fine tune MGL immune responses in distinct biological contexts, especially in malignancy.