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We present a method for computing sample size for cluster-randomized studies involving a large number of clusters with relatively small numbers of observations within each cluster. For multivariate survival data, only the marginal bivariate distribution is assumed to be known. The validity of this assumption is also discussed.
Glyceryl trinitrate (GTN) is known to induce single extra attacks of cluster headache (CH) during active cluster periods, most probably via actions of nitric oxide (NO). Induction of whole periods of CH by organic nitrates has, however, attracted little attention in the literature. We report on eight patients with episodic CH and coexistent effort-induced angina pectoris. Cases 1-6 had been free of their headaches for many years but got recurrence of CH within a few weeks after the administration of long-acting organic nitrates (isosorbide-dinitrate, isosorbide-5-mononitrate or slow-release GTN) aimed at treating their chest pains. These nitrate-induced headache periods were more severe and had a longer duration than the previous spontaneous ones. Furthermore, one of the subjects and two additional cases experienced a marked reduction of their anginal attacks during successive CH periods. Exercise time to effort-induced angina was increased in all three patients and one of them revealed a markedly elevated threshold for eliciting ischaemic cardiac symptoms by standardized physical exercise on a cycle ergometer. We hypothesize whether extra CH periods elicited by sustained nitrate therapy and remission of angina pectoris during active clusters are caused by central mechanisms involving inhibition of sympathetic tone and effects on both cranial vessels and cardiac functions.
The cyclic nature of cluster headache warranted a study of the 24-hour rhythms of serum cortisol and melatonin. They were both altered during cluster periods as compared with periods of remission and healthy controls. The 24-hour mean and maximal cortisol levels were higher and the timing of the cortisol minimum was delayed as compared to the same patients in remission. Although there was no relation between the cortisol and melatonin levels and headaches, the rise of cortisol following many attacks might in part represent an adaptive response to pain. The nocturnal melatonin maximum was lower during cluster periods than in remission. This finding, and the dysautonomic signs during attacks, may reflect a change of the vegetative tone in a hyposympathetic direction.
In September 2003, a scientific meeting was held in Rome to revive the International Cluster Headache Research Group (or "Cluster Club") tradition. This group of specialists was originally formed in the late 1970s by Ottar Sjaastad in order to promote research ideas, and to generate papers and other important information in this field. Its meetings, the last of which had taken place in 1994, had been informal events at which there was ample time for lively discussion. The last decade of the 20th century brought a significant increase in clinical and experimental research into cluster headache (CH), and this review summarizes some of the results of this research. The male preponderance of CH has been shown to be progressively decreasing over the years. Revised clinical criteria and a modern classification have been presented. First-degree relatives of probands with CH have been shown to have an increased risk of suffering from CH compared with the general population. Genetic analysis suggests that an autosomal dominant gene plays a role in some families. Functional neuroimaging has contributed to a better understanding of the pathophysiology of the condition. Positron emission tomography during provoked attacks has shown activation of the ipsilateral inferior posterior hypothalamus and it has been suggested that CH might be a functional neurovascular disorder of pacemaker or circadian regions in the hypothalamic grey matter. Subcutaneously administered sumatriptan has emerged as a highly effective acute treatment, but, in our opinion, the emphasis should be on attack prevention. Deep brain stimulation of the inferior posterior hypothalamic grey matter seems to be very promising as a novel treatment targeting the presumed central origin of pain attacks.
A basic problem of cluster analysis is the determination or selection of the number of clusters evinced in any set of data. We address this issue with multinomial data using Akaike's information criterion and demonstrate its utility in identifying an appropriate number of clusters of tumor types with similar profiles of cell surface antigens.
Reactions of MS4(2-) (M = Mo, W) with M'(PCy3)X (M'=Ag/Au, X= ClO4/Cl) and [Cu2(dcpm)2(MeCN)2](ClO4)2 (dcpm = bis(dicyclohexylphosphino)methane) afforded heterometallic sulfido clusters [M'2(PCy3)2(MS4)] (M=Mo, M'=Au: 2; M=W, M'=Ag: 3, Au: 4) and [Cu4(dcpm)4(MS4)](ClO4)2 (M=Mo: 5 x (ClO4)2, W: 6 x (ClO4)2), all of which, except 4, have been characterized by X-ray structure determination. Clusters 5 x(ClO4)2 and 6 x (ClO4)2 feature unusual 16-membered [Cu4P5C4] metallamacrocycles formed on the respective tetrathiometalate anion templates and have unusually long Cu-S bonds and Cu...M distances for metal sulfur clusters that contain a saddle-shaped [Cu4MS4] core. Low-energy absorption bands are observed in their electronic spectra at approximately 562 and 467 nm, respectively, assignable to MMCT transitions; quasireversible reduction waves are observed with E(1/2) = -1.43 (52+) and -1.78 V (62+) versus FeCp2(0/+); and they are emissive either in the solid state or in solution. The emission of 6(2+) can be quenched by both electron acceptors, such as methylviologen, or electron donors, such as aromatic amines, with the excited state reduction potential E(62+*/6+) estimated to be approximately 1.13V versus a normal hydrogen electrode.
The syntheses, structures and magnetic properties of three new MnIII clusters, [Mn26O17(OH)8(OMe)4F10(bta)22(MeOH)14(H2O)2] (1), [Mn(0O6(OH)2(bta)8(py)8F8] (2) and [NHEt3]2[Mn3O(bta)6F3] (3), are reported (bta=anion of benzotriazole), thereby demonstrating the utility of MnF3 as a new synthon in Mn cluster chemistry. The "melt" reaction (100 degrees C) between MnF(3) and benzotriazole (btaH, C6H5N3) under an inert atmosphere, followed by dissolution in MeOH produces the cluster [Mn26O17(OH)8(OMe)4F10(bta)22(MeOH)14(H2O)2] (1) after two weeks. Complex 1 crystallizes in the triclinic space group P1, and consists of a complicated array of metal tetrahedra linked by mu3-O2- ions, mu3- and mu2-OH- ions, mu2-MeO- ions and mu2-bta- ligands. The "simpler" reaction between MnF3 and btaH in boiling MeOH (50 degrees C) also produces complex 1. If this reaction is repeated in the presence of pyridine, the decametallic complex [Mn10O6(OH)2(bta)8(py)8F8] (2) is produced. Complex 2 crystallizes in the triclinic space group P1 and consists of a "supertetrahedral" [Mn(III)10] core bridged by six mu3-O2- ions, two mu3-OH- ions, four mu2-F- ions and eight mu2-bta- ions. The replacement of pyridine by triethylamine in the same reaction scheme produces the trimetallic species [NHEt3]2[Mn3O(bta)6F3] (3). Complex 3 crystallises in the monoclinic space group P2(1)/c and has a structure analogous to that of the basic metal carboxylates of general formula [M3O(RCO2)6L3]0/+, which consists of an oxo-centred metal triangle with mu2-bta- ligands bridging each edge of the triangle and the fluoride ions acting as the terminal ligands. DC magnetic susceptibility measurements in the 300-1.8 K and 0.1-7 T ranges were investigated for all three complexes. For each, the value of chi(M)T decreases with decreasing temperatures; this indicates the presence of dominant antiferromagnetic exchange interactions in 1-3. For complex 1, the low-temperature value of chi(M)T is 10 cm(3) K mol(-1) and fitting of the magnetisation data gives S=4, g=2.0 and D=-0.90 cm(-1). For complex 2, the value of chi(M)T falls to a value of approximately 5.0 cm(3) K mol(-1) at 1.8 K, which is consistent with a small spin ground state. For the triangular complex 3, the best fit to the experimental chi(M)T versus T data was obtained for the following parameters: Ja = -5.01 cm(-1), Jb = +9.16 cm(-1) and g=2.00, resulting in an S=2 spin ground state. DFT calculations on 3, however, suggest an S=1 or S=0 ground state with J(a)=-2.95 cm(-1) and J(b)=-2.12 cm(-1). AC susceptibility measurements performed on 1 in the 1.8-4.00 K range show the presence of out-of-phase AC susceptibility signals, but no peaks. Low-temperature single-crystal studies performed on 1 on an array of micro-SQUIDS show the time- and temperature-dependent hysteresis loops indicative of single-molecule magnetism behaviour.
The exponential increase in expressed sequence tag (EST) sequence data amplifies the computational cost of clustering sequences such that new algorithms are required to analyze data at a greater rate. We have parallelized d2_cluster on a SGI Origin 2000 multiprocessor and observed a speedup of approximately 100x on 126 processors when processing a 15,876 EST dataset. The parallelized d2_cluster code is obtainable from the SANBI website (http://www.sanbi.ac.za/CODES).
For accurate mass measurements and identification of atomic and molecular species precise mass calibration is mandatory. Recent studies with laser desorption/ionization and time-of-flight analysis of cluster ion production by use of fullerene and gold targets demonstrate the generation of atomic clusters for calibration purposes. Atomic ion results from the Penning trap mass spectrometer ISOLTRAP, in which a carbon cluster ion source has recently been installed, are presented as an application in the field of precision mass spectrometry.
Statistical clustering was performed on flow cytometry data generated from the reactivities of 189 mAbs with 56 cell preparations or cell lines (targets). Six targets were excluded from the statistical clustering because of non-reproducibility of data from the internal controls. Thirty-six temporary clusters (TC) were formed which were subjected to further examination in the second phase of the workshop.
Analysis of flow cytometric staining of 50 target cells resulted in five monoclonal antibodies (mAbs) forming two adjacent clusters called temporary cluster (TC) 2. The five mAbs gave similar immunostaining of frozen sections, but flow cytometric analysis and the M(r) of molecules indicated that they comprised two distinct specificities. Mabs CC98, IL-A114 and IL-A53 all immunoprecipitated a molecule of 210 kDa that preclearing experiments with mAbs to the leukocyte common antigen (CD45) showed did not recognize isoforms within the CD45R family of molecules. The 210 kDa molecule was present on all CD2+ cells and B cells, but not expressed by WC1+ gamma/delta T cells. mAbs TH1A and TH18A precipitated molecules of 69 and 62 kDa which were present on cells expressing CD2, WC3 (B cells) and WC1 (gamma/delta T cells). It is proposed that these five mAbs should be considered as comprising two new bovine lymphocyte differentiation clusters, WC6 (mAbs CC 98, IL-A114 and IL-A53) and WC7 (TH18A and TH1A).
The static and magic angle spinning NMR solid-state spectra of Re6Te15 and a series of Re(6)-Te cluster compounds demonstrate the positive and negative 125Te NMR chemical shifts indicating that the [Re6] cluster distorts strongly magnetic field at the neighboring Te sites. The local magnetic field is decreased at the facial tellurium sites (Teface) and enhanced at the apexial tellurium sites (Teapex). The facial and sagittal sections of the Re(6)-Te clusters were reconstructed from analysis of Teface and Teapex NMR spectra, respectively.
The roles of aromatic core residues in regulating the reduction potential, the enthalpy and entropy of reduction, and the self-exchange rate constants for electron-transfer reactions for the prosthetic [Fe4S4]3+/2+ cluster of Chromatium vinosum high potential iron protein (HiPIP) have been addressed by a combination of site-directed mutagenesis, high field NMR (EXSY) experiments, and variable temperature spectrochemical redox titration measurements. Minimal changes are observed following nonconservative mutation of residues Tyr19, Phe48, and Phe66. Apparently these hydrophobic residues play only a minor role in defining the electronic properties of the cluster. These data support a model, first defined from results obtained on Tyr19 mutant HiPIP's [Agarwal, A., Li, D., & Cowan, J.A. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 9440-9444], in which the aromatic core restricts solvent accessibility and thereby stabilizes the oxidized [Fe4S4]3+ cluster.
By reacting 1-aminoethylammonium (H2NCH2CH2NH3+ = enH+) salts of [Sn2E6]4- anions (E = S, Se), [enH]4[Sn2S6] (1) and [enH]4[Sn2Se6] x en (2), with FeCl2/LiCp, three novel (partly) oxidized, Cp* ligated iron chalcogenide clusters were synthesized. Two of them, [(CpFe)3(mu3-S)2] (3) and [(Cp*Fe)3(mu3-Se)2] (4), contain formally 47 valence electrons. [(Cp*Fe)3(SnCl3)(mu3-Se)4] x DME (5) represents the first known mixed metal Fe/Sn/Se heterocubane type cluster. Compounds 3-5 were structurally characterized by single-crystal X-ray diffraction, and the odd valence electron number of the [Fe3E2] clusters (E = S, Se) was confirmed by density functional (DFT) investigations, mass spectrometry, cyclic voltammetry and a susceptibility measurement of 3.
Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge(11)(z) (z = -6, -4, -2, 0, +2, +4, +6) starting from eight different initial configurations. The global minimum within the Ge(11)(2-) set is an elongated pentacapped trigonal prism distorted from D(3)(h) to C(2v) symmetry. However, the much more spherical edge-coalesced icosahedron, also of C(2v) symmetry, expected by the Wade-Mingos rules for a 2n + 2 skeletal electron system and found experimentally in B(11)H(11)(2-) and isoelectronic carboranes, is of only slightly higher energy (+5.2 kcal/mol). Even more elongated D(3)(h) pentacapped trigonal prisms are the global minima for the electron-rich structures Ge(11)(4-) and Ge(11)(6-). For Ge(11)(4-) the C(5v) 5-capped pentagonal antiprism analogous to the dicarbollide ligand C(2)B(9)H(11)(2-) is of significantly higher energy (approximately 28 kcal/mol) than the D(3h) global minimum. The C(2v) edge-coalesced icosahedron is also the global minimum for the electron-poor Ge(11) similar to its occurrence in experimentally known 11-vertex "isocloso" metallaboranes of the type (eta(6)-arene)RuB(10)H(10). The lowest energy polyhedral structures computed for the more hypoelectronic Ge(11)(4+) and Ge(11)(6+) clusters are very similar to those found experimentally for the isoelectronic ions E(11)(7-) (E = Ga, In, Tl) and Tl(9)Au(2)(9-) in intermetallics in the case of Ge(11)(4+) and Ge(11)(6+), respectively. These DFT studies predict an interesting D(5h) centered pentagonal prismatic structure for Ge(11)(2+) and isoelectronic metal clusters.
A novel series of fully reduced heteropolyoxovanadium(IV) compounds, [MVIV6O6[(OCH2CH2)2N(CH2CH2OH)]6]X (1, M = Li, X = Cl x LiCl; 2, M = Na, X = Cl x H2O; 3, M = Mg, X = 2Br x H2O; 4, M = Mn, X = 2Cl; 5, M = Fe, X = 2Cl; 6, M = Co, X = 2Cl x H2O; 7, M = Ni, X = 2Cl x H2O), have been synthesized and characterized by FT-IR and UV-vis spectroscopies, thermogravimetric analysis, elemental analysis, manganometric titration, temperature-dependent magnetic susceptibility measurements, bond valence sum calculations, X-ray powder diffraction, and single-crystal X-ray diffraction analyses. The structures of the crystals are comprised of discrete units of fully reduced cluster cations, [MVIV6O6[(OCH2CH2)2N(CH2CH2OH)]6]n+, counterions (chloride or bromide), and water of crystallization (in the case of 2, 3, 6, 7). In each case the cluster ion is composed of a fully reduced cyclic [MV6N6O18] (M = Li, Na, Mg, Mn, Fe, Co, Ni) framework decorated with six triethanolamine ligands. Two arms of each triethanolamine ligand are coordinated to the metallacycle, and the third arm projects outward from the hexagonal ring. The [MV6N6O18] core adopts the Anderson-type structure. The cyclic core is comprised of a ring of six edge-sharing [VO5N] octahedra linked to a central [MO6] unit. The hexametalate ring contains six d1 ions [VIV] and shows remarkable flexibility to encapsulate a variety of metal centers Mn+ (Mn+ = Li+, Na+, Mg2+, Mn2+, Fe2+, Co2+, Ni2+) with different (dn) spins. The compounds show good thermal stability and exhibit interesting magnetic properties that make these magnetic clusters promising building blocks for constructing supramolecular structures and extended structure magnetic solids. Crystal data for 1; C36H78Cl2N6Li2O24V6, trigonal space group R, a = 13.7185(3) angstroms, c = 24.8899(8) angstroms, Z = 3. Crystal data for 2: C36H80ClN6NaO25V6, triclinic space group P, a = 11.1817(5) angstroms, b = 12.1612(5) angstroms, c = 21.5979(10) angstroms, alpha = 75.8210(10), beta = 78.8270(10), gamma = 71.1400(10), Z = 2. Crystal data for 4: C36H78Cl2N6MnO24V6, monoclinic, space group P2(1), a =11.2208(5) angstroms, b = 21.5041(9) angstroms, c = 11.8126(5), beta = 111.2680, Z= 2. Crystal data for 5: C36H78Cl2N6FeO24V6, monoclinic, space group P2(1), a = 11.3057(7) angstroms, b = 21.4372(13) angstroms, c = 11.8167(7) angstroms, beta = 111.4170, Z = 2.
The reaction of lead acetate with (CO)(9)Co(3)(&mgr;(3)-CCOOH) leads to the formation of [Pb{(CO)(9)Co(3)(&mgr;(3)-CCO(2))}(2)](n)(), I, in high yield. The structure of I exhibits unusual six-coordinate Pb(II) centers with two asymmetrical chelating cluster carboxylates (C(22)Co(6)PbO(22); triclinic P&onemacr;; a = 8.119(1), b = 14.346(2), c = 14.660(2) Å; alpha = 102.18(1), beta = 99.01(1), gamma = 97.30(1) degrees; Z = 2). One oxygen of each cluster carboxylate ligand bridges between adjacent lead atoms such that a chainlike extended structure is found in the solid state without the presence of solvent or water. I is converted stepwise on pyrolysis into two metastable forms of solid materials (designated LT and HT), each of which has been characterized spectroscopically. The hydrogenation of 2-butenal as a test reaction shows that the LT catalyst exhibits selectivities similar to previous LT materials derived from other cobalt cluster metal carboxylates and that the HT material is totally inactive. The observed release of the lead core metal under HT activation conditions totally inactivates the catalyst and demonstrates exposure of the core metal in the HT form of these novel catalysts.
The cluster [Fe(5)RhN(CO)(15)](2)(-) was synthesized in 40% yield from [Fe(4)N(CO)(12)](-) and [Rh(CO)(4)](-) in refluxing tetrahydrofuran, whereas the analogous anion [Fe(5)IrN(CO)(15)](2)(-) was prepared in CH(3)CN at room temperature from [Fe(6)N(CO)(15)](3)(-) and [Ir(C(8)H(14))(2)Cl](2); the yields are higher than 60%. The monoanion [Fe(4)Rh(2)N(CO)(15)](-) was obtained in 70% yield from [Fe(5)RhN(CO)(15)](2)(-) and hydrated RhCl(3). The solid-state structures of the three anions were determined on their [PPh(4)](+) salts: the six metal atoms are arranged in octahedral cages and are coordinated to 3 edge-bridging and 12 terminal carbonyl ligands and to a &mgr;(6)-N ligand. The Rh and Ir atoms have less terminal COs than Fe, in order to equalize the excess electrons at the d(9) metal centers. The two rhodium atoms in [Fe(4)Rh(2)N(CO)(15)](-) are directly bound. The (15)N NMR spectra of the three compounds have been recorded; the signals of the nitride ligands were found at delta = 514 ppm for the dianions and 470 ppm for [Fe(4)Rh(2)N(CO)(15)](-); any group 9 atom shifts the resonance of nitrogen to higher fields. The coupling constants J((15)N-(103)Rh) are 8-9 Hz. The vibrational patterns of the metal cores have been interpreted on the basis of an idealized M(6) octahedral arrangement, subsequently modified by the perturbations given by different atomic masses and M-M stretching force constants. The motions of the nitrogen are related to the idealized symmetry of the cage; the M-N force constant values depend on the type of metal and on the charge of the anion. The dianions [Fe(5)MN(CO)(15)](2)(-) can be electrochemically oxidized at -20 degrees C to their short-lived monoanions, which can be characterized by EPR spectroscopy. In contrast, the cluster [Fe(4)Rh(2)N(CO)(15)](-) undergoes a single-step 2-electron reduction to the partially stable trianion [Fe(4)Rh(2)N(CO)(15)](3)(-), which was also characterized by EPR spectroscopy. The Fe-Rh nitride clusters are active catalysts for the hydroformylation of 1-pentene, but display low selectivity (35-65%) in n-hexanal and are demolished under catalytic conditions.