Iron Speciation in Fram Strait and Over the Northeast Greenland Shelf: An Inter-Comparison Study of Voltammetric Methods

Competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV) is a widely used technique to determine dissolved iron (Fe) speciation in seawater, and involves competition for Fe of a known added ligand (AL) with natural organic ligands. Three different ALs were used, 2-(2-thiazolylazo)-p-cresol (TAC), salicylaldoxime (SA) and 1-nitroso-2-napthol (NN). The total ligand concentrations ([Lt]) and conditional stability constants (log K′Fe’L) obtained using the different ALs are compared. The comparison was done on seawater samples from Fram Strait and northeast Greenland shelf region, including the Norske Trough, Nioghalvfjerdsfjorden (79N) Glacier front and Westwind Trough. Data interpretation using a one-ligand model resulted in [Lt]SA (2.72 ± 0.99 nM eq Fe) > [Lt]TAC (1.77 ± 0.57 nM eq Fe) > [Lt]NN (1.57 ± 0.58 nM eq Fe); with the mean of log K′Fe’L being the highest for TAC (log ′KFe’L(TAC) = 12.8 ± 0.5), followed by SA (log K′Fe’L(SA) = 10.9 ± 0.4) and NN (log K′Fe’L(NN) = 10.1 ± 0.6). These differences are only partly explained by the detection windows employed, and are probably due to uncertainties propagated from the calibration and the heterogeneity of the natural organic ligands. An almost constant ratio of [Lt]TAC/[Lt]SA = 0.5 – 0.6 was obtained in samples over the shelf, potentially related to contributions of humic acid-type ligands. In contrast, in Fram Strait [Lt]TAC/[Lt]SA varied considerably from 0.6 to 1, indicating the influence of other ligand types, which seemed to be detected to a different extent by the TAC and SA methods. Our results show that even though the SA, TAC and NN methods have different detection windows, the results of the one ligand model captured a similar trend in [Lt], increasing from Fram Strait to the Norske Trough to the Westwind Trough. Application of a two-ligand model confirms a previous suggestion that in Polar Surface Water and in water masses over the shelf, two ligand groups existed, a relatively strong and relatively weak ligand group. The relatively weak ligand group contributed less to the total complexation capacity, hence it could only keep part of Fe released from the 79N Glacier in the dissolved phase.

Featuring Xantphos

This review highlights the use of the bisphosphine ligand group in homogeneous catalysis.

Binding Site Extraction by Similar Subgraphs Mining from Protein Molecular Surfaces and Its Application to Protein Classification

Most proteins express their functions by binding with other proteins or molecular compounds (ligands). Since the characteristics of the local portion involved in binding (binding site) often determine the function of the protein, clarifying the location of the binding site of the protein helps analyze the function of proteins. Binding sites that bind to similar ligands often have common surface structures (surface motifs). Extracting the surface motifs among several proteins with similar functions improves binding site prediction. We propose a method that predicts binding sites by extracting the surface motifs that are frequently observed in only a specific set of proteins that bind to the same ligand (group). Since most binding sites have concave structures (pockets), the pockets are compared and common structures are searched for to extract the surface motifs by applying similar graph mining to the pocket data, which are represented as graphs. Common binding sites across several groups can be predicted in such a way to integrate more than one group. We also proposed a method of protein classification, in which the surface motifs extracted using the above method are evaluated on the assumption that a protein belongs to each one of the groups.

Tris[3,6-di-tert-butyl-1-(isoquinolin-1-yl)naphthalen-2-olato-κ2N,O]aluminium(III) toluene sesquisolvate

The central AlIIIatom of the title compound, [Al(C27H28NO)3]·1.5C7H8, has octahedral geometry in which the three N atoms are arranged in a meridional fashion. One of the toluene solvent molecules is located on a general position, while the second is disordered around a centre of inversion. The ligand molecule has axial chirality, and two of the three ligands in the complex exhibit the same stereochemistry. The three independent chelate rings exhibit significantly different bite angles at the metal atom, with one [83.72 (8)°] notably smaller than the other two [87.22 (8) and 87.13 (8)°]. Calculation of the solid angle covered by the ligands at the metal atom reveals that coverage is greatest for the ligand group with the shortest Al—O bond distance.

Survival Difference of AML Patients Receiving HLA Matched Sibling Allogeneic Bone Marrow Transplants (ABMT) Correlates with HLA-Cw Ligand Groups for Killer Immunoglobulin-Like Receptors (KIRs).

The reactivity of NK cells and some T cell populations is regulated by the interaction of KIRs with target cell HLA class I molecules. KIR interactions have been suggested to influence outcomes of haploidentical and HLA-identical allogeneic hematopoietic stem cell transplants, particularly for AML patients. We analyzed the KIR ligand phenotypes of 60 AML patients who received HLA-identical sibling myeloablative ABMT from 4/9/97-11/5/03. The median age was 45 yrs (range 8–62). At the time of transplant 24 patients (40%) were in CR. All patients received a busulfan/cyclophosphamide-based preparative regimen and all received bone marrow (T-cell replete) as their stem cell source. Patient HLA KIR ligands were categorized as: 1) HLA-Cw groups C1/C1, C2/C2, C1/C2; 2) HLA-Bw4 (+ or −); 3) HLA-A3 or A11 (+ or −) (as reviewed in Farag et al Blood100:1935,2002). Recursive partitioning analysis for post-transplant time-related outcomes (acute GVHD, grade 3/4 acute GVHD, chronic GVHD, extensive chronic GVHD, freedom from relapse and survival) was performed for each KIR ligand group. Patients with C1/C1 or C2/C2 (n=26) had improved survival compared to the C1/C2 group (n=34) (median survival 43.5 months vs. 5.8 months, respectively, p=0.018), as shown below: Figure Figure This survival difference was associated with more relapse in the C1/C2 group (p=0.048), but not with incidence or severity of acute or chronic GVHD, age, infection or pretransplant disease status. There were 26/34 (76%) deaths in the C1/C2 group with 15 (58%) due to relapse as compared to 13/26 (50%) deaths in the C1/C1 + C2/C2 group where 4/13 (31%) were due to relapse. The median follow up of survivors was 36.3 mos (range 7.8–72.4 mos). No significant differences in outcomes were observed when patients were analyzed for the presence or absence of HLA-Bw4 or A3/11. The majority of patients had KIR genotyping performed for those KIRs with established HLA ligands. Among those tested there were no cases in which the donor did not have at least one inhibitory KIR gene specific for a Cw ligand present in the patient or donor. This may suggest that KIR expression at the cellular level rather than KIR genotype alone should be investigated. In conclusion, AML patients undergoing matched sibling donor ABMT who were heterozygous for HLA-Cw KIR ligand groups (C1/C2) had reduced survival compared to patients homozygous for these groups. The higher relapse rate observed in the heterozygous ligand group may suggest a less effective graft-versus-leukemia (GVL) response. Since C1/C2 heterozygotes have a greater opportunity to engage inhibitory KIRs than do C1 or C2 homozygotes, they may more effectively inhibit KIR-positive NK and T cell populations involved in GVL responses.