Nonmagnetic J=0 State and Spin-Orbit Excitations in K_{2}RuCl_{6}.

Spin-orbit Mott insulators composed of t_{2g}^{4} transition metal ions may host excitonic magnetism due to the condensation of spin-orbital J=1 triplons. Prior experiments suggest that the 4d antiferromagnet Ca_{2}RuO_{4} embodies this notion, but a J=0 nonmagnetic state as a basis of the excitonic picture remains to be confirmed. We use Ru L_{3}-edge resonant inelastic x-ray scattering to reveal archetypal J multiplets with a J=0 ground state in the cubic compound K_{2}RuCl_{6}, which are well described within the LS-coupling scheme. This result highlights the critical role of unquenched orbital moments in 4d-electron compounds and calls for investigations of quantum criticality and excitonic magnetism on various crystal lattices.

Spin waves and spin-state transitions in a ruthenate high-temperature antiferromagnet.

Ruthenium compounds serve as a platform for fundamental concepts such as spin-triplet superconductivity1, Kitaev spin liquids2-5 and solid-state analogues of the Higgs mode in particle physics6,7. However, basic questions about the electronic structure of ruthenates remain unanswered, because several key parameters (including Hund's coupling, spin-orbit coupling and exchange interactions) are comparable in magnitude and their interplay is poorly understood, partly due to difficulties in synthesizing large single crystals for spectroscopic experiments. Here we introduce a resonant inelastic X-ray scattering (RIXS)8,9 technique capable of probing collective modes in microcrystals of 4d electron materials. We observe spin waves and spin-state transitions in the honeycomb antiferromagnet SrRu2O6 (ref. 10) and use the extracted exchange interactions and measured magnon gap to explain its high Néel temperature11-16. We expect that the RIXS method presented here will enable momentum-resolved spectroscopy of a large class of 4d transition-metal compounds.

Correction: Rapid biocompatible macrocyclization of peptides with decafluoro-diphenylsulfone.

[This corrects the article DOI: 10.1039/C5SC03856A.].

Rapid biocompatible macrocyclization of peptides with decafluoro-diphenylsulfone.

In this manuscript, we describe modification of Cys-residues in peptides and proteins in aqueous solvents via aromatic nucleophilic substitution (SNAr) with perfluoroarenes (fAr). Biocompatibility of this reaction makes it attractive for derivatization of proteins and peptide libraries comprised of 20 natural amino acids. Measurement of the reaction rates for fAr derivatives by 19F NMR with a model thiol donor (ß-mercaptoethanol) in aqueous buffers identified decafluoro-diphenylsulfone (DFS) as the most reactive SNAr electrophile. Reaction of DFS with thiol nucleophiles is >100 000 faster than analogous reaction of perfluorobenzene; this increase in reactivity enables application of DFS at low concentrations in aqueous solutions compatible with biomolecules and protein complexes irreversibly degraded by organic solvents (e.g., bacteriophages). DFS forms macrocycles when reacted with peptides of the general structure X n -Cys-X m -Cys-X l , where X is any amino acid and m = 1-15. It formed cyclic peptides with 6 peptide hormones-oxytocin, urotensin II, salmon calcitonin, melanin-concentrating hormone, somatostatin-14, and atrial natriuretic factor (1-28) as well as peptides displayed on M13 phage. Rates up to 180 M-1 s-1 make this reaction one of the fastest Cys-modifications to-date. Long-term stability of macrocycles derived from DFS and their stability toward oxidation further supports DFS as a promising method for modification of peptide-based ligands, cyclization of genetically-encoded peptide libraries, and discovery of bioactive macrocyclic peptides.

Hyperhoneycomb Iridate ß-Li2IrO3 as a platform for Kitaev magnetism.

A complex iridium oxide ß-Li(2)IrO(3) crystallizes in a hyperhoneycomb structure, a three-dimensional analogue of honeycomb lattice, and is found to be a spin-orbital Mott insulator with J(eff)=1/2 moment. Ir ions are connected to the three neighboring Ir ions via Ir-O(2)-Ir bonding planes, which very likely gives rise to bond-dependent ferromagnetic interactions between the J(eff)=1/2 moments, an essential ingredient of Kitaev model with a spin liquid ground state. Dominant ferromagnetic interaction between J(eff)=1/2 moments is indeed confirmed by the temperature dependence of magnetic susceptibility χ(T) which shows a positive Curie-Weiss temperature θ(CW)∼+40 K. A magnetic ordering with a very small entropy change, likely associated with a noncollinear arrangement of J(eff)=1/2 moments, is observed at T(c)=38 K. With the application of magnetic field to the ordered state, a large moment of more than 0.35 µ(B)/Ir is induced above 3 T, a substantially polarized J(eff)=1/2 state. We argue that the close proximity to ferromagnetism and the presence of large fluctuations evidence that the ground state of hyperhoneycomb ß-Li(2)IrO(3) is located in close proximity of a Kitaev spin liquid.

Pharmacophore-guided lead optimization: the rational design of a non-zinc coordinating, sub-micromolar inhibitor of the botulinum neurotoxin serotype a metalloprotease.

Botulinum neurotoxins, responsible for the neuroparalytic syndrome botulism, are the deadliest of known biological toxins. The work described in this study was based on a three-zone pharmacophore model for botulinum neurotoxin serotype A light chain inhibition. Specifically, the pharmacophore defined a separation between the overlaps of several different, non-zinc(II)-coordinating small molecule chemotypes, enabling the design and synthesis of a new structural hybrid possessing a Ki=600 nM (+/-100 nM).

Current therapies and emerging targets for the treatment of diabetes.

Concurrent with the spread of the western lifestyle, the prevalence of all types of diabetes is on the rise in the world's population. The number of diabetics is increasing by 4-5% per year with an estimated 40-45% of individual's over the age of 65 years having either type II diabetes or impaired glucose tolerance. Since the signs of diabetes are not immediately obvious, diagnosis can be preceded by an extended period of impaired glucose tolerance resulting in the prevalence of beta-cell dysfunction and macrovascular complications. In addition to increased medical vigilance, diabetes is being combatted through aggressive treatment directed at lowering circulating blood glucose and inhibiting postprandial hyperglycemic spikes. Current strategies to treat diabetes include reducing insulin resistance using glitazones, supplementing insulin supplies with exogenous insulin, increasing endogenous insulin production with sulfonylureas and meglitinides, reducing hepatic glucose production through biguanides, and limiting postprandial glucose absorption with alpha-glucosidase inhibitors. In all of these areas, new generations of small molecules are being investigated which exhibit improved efficacy and safety profiles. Promising biological targets are also emerging such as (1) insulin sensitizers including protein tyrosine phosphatase-1B (PTP-1B) and glycogen synthase kinase 3 (GSK3), (2) inhibitors of gluconeogenesis like pyruvate dehydrogenase kinase (PDH) inhibitors, (3) lipolysis inhibitors, (4) fat oxidation including carnitine palmitoyltransferase (CPT) I and II inhibitors, and (5) energy expenditure by means of beta 3-adrenoceptor agonists. Also important are alternative routes of glucose disposal such as Na+-glucose cotransporter (SGLT) inhibitors, combination therapies, and the treatment of diabetic complications (eg. retinopathy, nephropathy, and neuropathy). With may new opportunities for drug discovery, the prospects are excellent for development of innovative therapies to effectively manage diabetes and prevent its long term complications. This review highlights recent (1997-2000) advances in diabetes therapy and research with an emphasis on small molecule drug design (275 references).

An improved synthesis of 1,2,4-oxadiazoles on solid support.

The use of tetra-N-butylammonium fluoride (TBAF) as a mild and efficient reagent for the cyclodehydration of O-acyl amidoximes has been extended to the synthesis of 1,2,4-oxadiazoles on solid support. Argopore MB-CHO resin (Argonaut Technologies) was reductively aminated and subsequently acylated with 4-cyanobenzoyl chloride. Conversion of the nitrile to the amidoxime and acylation with a range of acid chlorides in parallel followed by treatment with TBAF under ambient conditions afforded a library of 3,5-disubstituted 1,2,4-oxadiazoles.

Characterization of novel antimicrobial peptoids.

Peptoids differ from peptides in that peptoids are composed of N-substituted rather than alpha-carbon-substituted glycine units. In this paper we report the in vitro and in vivo antibacterial activities of several antibacterial peptoids discovered by screening combinatorial chemistry libraries for bacterial growth inhibition. In vitro, the peptoid CHIR29498 and some of its analogues were active in the range of 3 to 12 microg/ml against a panel of gram-positive and gram-negative bacteria which included isolates which were resistant to known antibiotics. Peptoid antimicrobial activity against Staphylococcus aureus was rapid, bactericidal, and independent of protein synthesis. beta-Galactosidase and propidium iodide leakage assays indicated that the membrane is the most likely target of activity. Positional isomers of an active peptoid were also active, consistent with a mode of action, such as membrane disruption, that does not require a specific fit between the molecule and its target. In vivo, CHIR29498 protected S. aureus-infected mice in a simple infection model.

First Report on Natural Occurrence of Tomato Spotted Wilt Tospovirus in Basil (Ocimum basilicum).

Virus-like symptoms were observed on basil plants (Ocimum basilicum L. 'Mrs. Burns Lemon' [MBL]) growing in containers and a demonstration plot at the Louisiana State University Burden Research Plantation, Baton Rouge, during July 1998. Symptoms consisted of ring spots, leaf distortion, and severe mosaic. Mechanical transmission of the suspect virus by sap inoculation from infected MBL to basil cvs. MBL, Aussie Sweet, Cinnamon, Siam Queen, and Sweet Dani was successful. Symptoms were similar to those on infected MBL. Nicotiana benthamiana Domin. reacted with local chlorotic spots followed by severe yellows, necrosis, and death. Electron microscopy of thin sections of infected basil revealed virus inclusions but no virus particles. However, infected N. benthamiana revealed the presence of 82-nm membrane-bound particles in the cytoplasm. The virus was identified from basil and N. benthamiana as the common strain of tomato spotted wilt tospovirus (TSWV) by enzyme-linked immunosorbent assay (Agdia, Elkhart, IN). An outbreak of thrips insects during the summer drought in 1998 was probably responsible for the occurrence of TSWV in basil. This is the first report of the occurrence of TSWV in basil (1). Reference: (1) A. A. Brunt et al., eds. 1996. Plant Viruses Online: Descriptions and Lists from the VIDE Database. Published online by Australian National University, Canberra.

Advances in solid-supported organic synthesis methods, 1998 to 1999.

Combinatorial chemistry is now regarded as an important component of the drug discovery process and is increasingly having an impact in other areas of the chemical sciences, such as catalysis and materials science. Solid-supported organic synthesis continues to be an integral component in the efficient assembly of combinatorial libraries. This review attempts to describe some of the most important recent developments in solid-supported organic synthesis during the period 1998 to 1999. Particular emphasis is placed on the development of novel, efficient methods for the synthesis of diverse, non-oligomeric libraries and structurally complex molecules.

The histrionicotoxin-sensitive ethidium binding site is located outside of the transmembrane domain of the nicotinic acetylcholine receptor: a fluorescence study.

A novel, relatively photostable, long-wavelength fluorescent membrane probe, N-(Texas Red sulfonyl)-5(and 6)-dodecanoylamine (C12-Texas Red), was synthesized and used as an electronic energy acceptor for Förster fluorescence resonance energy transfer (FRET) between ethidium bound to a histrionicotoxin-sensitive binding site on the Torpedo nicotinic acetylcholine receptor (AChR) and the lipid membrane surface. FRET from membrane-partitioned 5-(N-dodecanoylamino)fluorescein (C12-fluorescein) to the membrane-partitioned C12-Texas Red was also determined with a parallel set of cuvettes to (1) compare FRET results with a donor in a known position in the membrane and (2) assess the surface density of the membrane-partitioned C12-Texas Red. Stern-Volmer analysis of the FRET results showed that C12-Texas Red quenched membrane-partitioned C12-fluorescein fluorescence 2.9 times more effectively than it quenched the receptor-bound ethidium fluorescence even though the Förster critical distances for the two donor-acceptor pairs were very similar (49.9 and 54.3 A, respectively). Analysis of the ethidium to C12-Texas Red FRET as a function of acceptor surface density with the assumptions that the donor is attached along the major axis of symmetry of a cylindrical protein embedded perpendicularly into the membrane (On-Axis FRET model) suggested that the distance of closest approach between the receptor-bound ethidium and the membrane surface was approximately 52 A. Because the minimum distance between the surface of the lipid-membrane domain and the major symmetry axis of the AChR is approximately 28 A, the FRET results strongly suggest that the ethidium binding site is not located near the entrance of the luminal transmembrane domain is generally assumed.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet thrombus formation and hemostasis are delayed in the microcirculation of copper-deficient rats.

The role of dietary copper in platelet thrombus formation and hemostasis was studied in the cremaster muscle microcirculation. Male weanling Sprague-Dawley rats were fed purified diets that were either copper-adequate (94 mumol Cu/kg diet) or copper-deficient (0 mumol Cu/kg diet) for 1, 3 or 5 wk. The rats were anesthetized with pentobarbital, and the cremaster was spread in a Krebs-filled tissue bath. Fluorescein isothiocyanate tagged to bovine serum albumin (FITC-BSA) was injected intra-arterially. After a 20-min equilibration, blue light (1.8 W/cm2, 450-490 nm) was used to activate the FITC-BSA and induced platelet thrombus formation within the vasculature. In vivo television microscopy was used to quantify the thrombus formation. In rats fed the copper-deficient diet for 3 or 5 wk, platelet thrombus formation induced by photoactivation was significantly (P < 0.05) delayed and prothrombin time was significantly longer but the number of circulating platelets was significantly greater than in age-matched rats fed the copper-adequate diet. Bleeding time, measured after micropuncture of a second-order venule, was significantly longer but hematocrit was significantly lower in rats fed the copper-deficient diet than in those fed the copper-adequate diet. The results demonstrate that platelet-mediated hemostasis is depressed in dietary copper deficiency and that this may be due to a decrease in hematocrit, a decrease in the activity of a coagulation factor and/or an alteration of platelet function.

Defining the requirements for an antibody epitope on influenza virus neuraminidase: how tolerant are protein epitopes?

To determine the conformational requirements for antibody recognition and extent of flexibility within a protein epitope, a chimeric influenza A virus neuraminidase (NA) has been constructed in which five discontinuous polypeptide segments from a subtype N9 NA, which comprise the monoclonal antibody NC41 epitope, have been grafted onto a subtype N2 NA. The resulting chimeric NA was expressed, assembled as a tetramer, and transported to the cell surface, but was not recognized by NC41 in immunoprecipitation experiments or by surface immunofluorescence. Although the N2 and N9 protein folds are identical and this chimera contains all the antibody contacts as defined by the crystal structure of the complex, NC41 binding was not achieved. Modeling studies suggest that at least one polypeptide segment is displaced from its normal position which would account for the observed lack of enzyme activity as well as lack of antibody binding. This implies that in addition to the specific critical interactions between NA and Fab residues required for antibody binding, the overall arrangement of amino acids within an epitope must be in a specific orientation that is necessary for initial antibody recognition.

Identification of critical contact residues in the NC41 epitope of a subtype N9 influenza virus neuraminidase.

We have examined amino acids on influenza virus neuraminidase (NA) subtype N9 (A/tern/Australia/G70c/75) which are in contact with monoclonal antibody NC41 to analyze individual interactions important for antibody recognition. The crystal structure of NA complexed with NC41 Fab1 shows antibody contacts at 19 amino acid residues on the NA surface which are localized on five polypeptide loops surrounding the enzyme active site. Fifteen mutant NA genes were constructed to encode a protein which contained a single amino acid substitution and these were tested for effects of the replacement on NC41 binding. Our data revealed that NAs with changes at 368, 400, and 434 completely lost NC41 recognition. NAs with side chains replaced at residues 346 and 373 exhibited binding reduced to less than 50% of wild-type binding. Changes in seven other contacting residues, including substituted side chains which differed considerably from wild-type NA in size and charge, had no significant effect on NC41 binding. These results indicate that only a few of the many residues which make up an epitope are crucial for interaction and provide the critical contacts required for antibody recognition. This implies that antibody escape mutants are selected only if they contain changes at these crucial sites, or changes which introduce bulky side chains that sterically prevent antibody attachment.

[Comparative study of two methods of arterialization of foot veins in ischemic crisis]. / Etude comparative de deux modalités d'artérialisation des veines du pied en ischémie critique.

Between February 1974 and December 1991, a total of 28 arterializations of the venous network of foot were performed in patients with stage IIIB or IV arteriopathies presenting disseminated femoropopliteal and more distal lesions excluding revascularization by conventional arterial shunt operations. Two groups of patients could be distinguished. The first group, of 8 patients, underwent arterialization by shunt operation with end to end fistula at the distal part of leg and return blood emptying at the dorsal surface of foot (3 cases). The procedure was successful in 50% of cases after a mean follow up of 76 months. The intervention in the second group, of 20 patients, was by end to side fistula of foot after preoperative countercurrent phlebography and the use of a material better adapted for the destruction of the valves. Results were evaluated as successful in 70% of cases at 31 month follow up. After spontaneous closure of the fistula, the collateral circulation provoked by it was sufficient to conserve the acquired benefit. No deaths or cases of cardiac overload were reported as a result of the intervention. Comparative analysis of results showed that the use of the second procedure allowed amputation to be avoided in more than 2/3rds of cases, provided relief from pain, provoked healing of necrosed areas and permitted renewal of walking. The results of this study have demonstrated that venous arterialization of the foot by this method represents an interesting alternative in the saving of a limb destined for amputation.

Transfer of the hemagglutinin activity of influenza virus neuraminidase subtype N9 into an N2 neuraminidase background.

It has previously been shown that influenza virus neuraminidase (NA) of the N9 subtype is unusual in that it possesses hemagglutinin activity as well as NA activity. Loss of red cell binding in certain escape mutants suggested that the hemagglutinating site is separate from the NA active site and involves at least two of the polypeptide loops found on the surface of the molecule (Webster et al., 1987. J. Virol. 61, 2910-2916). We have used site-directed mutagenesis to transfer the amino acids in these loops at positions 368-370 and 399-403 of N9 NA (A/tern/Australia/G70c/75), separately and together, into subtype N2 NA (A/Tokyo/3/67). The three mutant proteins were expressed from an SV40 transient expression system (Fuerst et al., 1986. Proc. Natl. Acad. Sci. USA. 83, 8122-8126). The mutant which contained both loops of N9 NA had acquired the hemagglutinin activity of N9. The agglutinated red cells are released by the enzyme activity of N9 NA, indicating that the agglutination involves binding to sialic acid in the same configuration as does the parental N9 NA, and an inhibitor of NA did not affect hemagglutination, indicating that this site is separate from the NA site as in parental N9.

[Treatment of fractures of the clavicle by closed pinning inside-out without back-and-forth]. / Traitement des fractures de la clavicule par embrochage à foyer fermé de dedans en dehors sans va-et-vient.

Pinning of fractures of the clavicle is easily and safely done by introducing the pin through the medial fragment. The pointed tip is embedded into the cortex of the lateral fragment and the inner end of the pin is bent at a right angle to fix it to the bone. Insertion is made with image intensification to avoid vascular damage and to guide the passage of the pin through the medial fragment without danger. Of 25 fractures treated in this way, only two, treated at the beginning of the series, required open reduction. No other immobilisation was necessary. All the fractures united uneventfully.

Arterialization of the venous network of the foot through a bypass in severe arteriopathic ischemia.

With the object of saving a very ischemic extremity, when the classic procedures have been unsuccessful or impossible, the authors are using a modification of San Martin's operation. At present, we are making an A-V fistula with a graft interposed between the femoral or popliteal artery and the peripheral long saphenous vein at the foot or near to it. The distal valves are ruptured. In order to prevent the noxious venous overloading resulting from the distal end-to-end anastomosis, it is important to replace it by an end-to-side anastomosis. Eight patients with intense continuous rest pain and necrotic lesions of the toes and heel have been operated on: 3 failures in spite of well functioning A-V fistula; 2 temporary improvements lasted 7 and 16 months when distal thrombosis of the A-V fistula occurred; 3 good results, maintained during 5 months, 4 3/4 years and 9 1/2 years respectively. Postoperative angiography and scintillography reveal a satisfactory retrograde distribution of blood in the fore foot except in the necrotic tissues.

Effect of post-mortem storage temperatures on isometric tension, pH, ATP, glycogen and glucose-6-phosphate for selected bovine muscles.

Relationships between isometric tension development and pH, ATP, glucose-6-phosphate and glycogen levels as a function of post-mortem storage temperature were examined for three bovine muscles. Tension responses in the range of 5-37°C were similar for B. femoris, Vastus lateralis and outer M. semitendinosis. At 0°C, the three muscles developed considerably higher tension than at 5°C. Cold shortening developed only in the outer M. semitendinosis strips at 0°C. At low temperatures the drop in pH lagged compared to the decline in ATP and glycogen and maximum tension was attained several hours after ultimate pH and minimum levels of ATP and glycogen were reached. Glucose-6-phosphate was found to accumulate rapidly at 0°C in both outer M. semitendinosis and B. femoris, being more pronounced in the latter muscle. The responses of glucose-6-phosphate levels suggest that the relative activities of glycolytic enzymes in muscle stored at 0°C are altered compared to those in muscle stored at higher temperatures.