Triangular Complex Research Articles

Traitement arthroscopique des lésions traumatiques récentes et chroniques du complexe triangulaire du poignet

Lesions of the triangular fibrocartilage complex of the wrist (TFCC) have perfectly been dismembered by Andrew Palmer and have largely benefited from progress of arthroscopy of the wrist. One distinguishes thus traumatic lesions (class 1) individualized according to their localization, central (1-A), ulnar (1-B), radial (1-D) or distal (1-C). Central lesions are classically associated to a positive ulnar variance. The clinical symptomatology evokes a meniscal like syndrome of the wrist. In case of failure of the medical treatment, it will be necessary to propose a surgical procedure guided by histopathology of the triangular complex. Thus, ulnar peripheral richly vascularized lesions (1-B) could therefore potentially heal and will have to benefit by an attempt of surgical reattachment (arthroscopic technique of Whipple, Poehling or other techniques) or by an osteosynthesis in case of fracture on the basis on the ulnar styloid process. Central fibrocartilage lesions (1-A) or radial avulsions (1-D) are less vascularized and have therefore little probability to heal; they will benefit then ideally from the endoscopic debridement of unstable flaps of the central portion of TFCC. No immobilization is required and rehabilitation is immediately undertaken. Less frequent class 1-C lesions justify in our practice a simple arthroscopic regularization, alone complete ruptures could have necessitate a direct suture. Class 2 degenerative lesions are graduated (A to E) according to evolution of the chondromalacia of the ulnar head and carpal bone, perforation of the central disc and lunotriquetral ligament degeneration. They are usually associated with a constitutional or an acquired ulnar plus variance syndrome, for example after a distal radius fracture malunion. The clinical symptomatology needs to differentiate them from the simple frequent physiological perforations after the age of 50 years. Arthroscopy will allow to regularize unstable non-vascularized lesions and to perform a wafer procedure through the large hole of the central disc. Alone lesions with very positive ulnar variance or fail of minimally invasive procedures, justify, in our experience, a shortening osteotomy of the ulna.

Condensation of Rare Earth Pyrazolates: The Dimeric, Trimeric and Polymeric Units [Gd2(Pz)6(PzH)4], [Nd3(Pz)9(PzH)2] and

Solvent free high-temperature oxidations of rare earth metals with the heterocycle pyrazole as well as in low to non-coordinating solvents were investigated to isolate intermediate stages between monomeric and polymeric pyrazolates of the lanthanides. Reaction conditions were tuned according to simultaneous DTA/TG and temperature dependent X-ray powder diffraction experiments on known monomeric and polymeric pyrazolates, that gave rise to the idea that further structure intermediates could be isolated. Reactions in 1,2,3,4-tetrahydroquinoline gave the dimeric complex [Gd2(Pz)6(PzH)4](PzH)(Tech) (1) as well as the triangular complex [Nd3(Pz)9(PzH)2](PzH)(Tech)2 (2). The solvent free melt synthesis resulted in a new polymeric form of (3) (pyrazole, PzH = C3H3NNH; pyrazolate anion, Pz− = C3H3NN−; 1,2,3,4-tetrahydroquinoline, Tech = C9H13N). All three compounds contain coordinating pyrazolate amide groups and pyrazole molecules the latter decreasing in numbers upon condensation of the building units. According to simultaneous DTA/TG/MS investigations the condensation process can be identified with the release of pyrazole molecules.1 consists of dimeric molecules containing trivalent gadolinium with a C.N. of eight. The two gadolinium atoms show different coordination polyhedra. Only σ coordination and bridging is found for 1. 2 consists of trimeric molecules containing trivalent neodymium. The neodymium atoms also exhibit different coordination polyhedra with C.N.s of eight and nine. Both π and σ coordination is found for 2, the π coordinating pyrazolate ligands acting as lids of the triangular units. Topological analysis of the electron localization function (ELF) for 2 calculated at the scalar-relativistic DFT level reveals only weakly covalent π donor η5-Pz–Nd interactions compared to the stronger covalent σ donor Pz–Nd interactions. The topological analysis of both, the ELF and the electron density reveals no significant differences of the respective charges of the Nd atoms. 3 exhibits a one-dimensional chain structure with EuII and a C.N of ten. It can thus be addressed the β form of the referring formula with a new arrangement of the coordinating ligands. Like the α form 3 shows σ and π coordination of pyrazole and pyrazolate ligands. Simultaneous DTA/TG analysis reveals that the low-temperature α form shows a phase transition into the β form between 110 °C and 130 °C. The three compounds were investigated by low-temperature single crystal X-ray analysis, Mid IR and Far IR spectroscopy.

Syntheses, Structures, and Magnetic Properties of Unusual Nonlinear Polynuclear Copper(II) Complexes Containing Derivatives of 1,2,4-Triazole and Pivalate Ligands

Novel polynuclear Cu(II) complexes containing derivatives of 1,2,4-trizaole and pivalate ligands, [Cu(3)(mu(3)-OH)(mu-adetrz)(2)(piv)(5)(H(2)O)].6.5H(2)O (1) (adetrz = 4-amino-3,5-diethyl-1,2,4-triazole, piv = pivalate), [Cu(4)(mu(3)-OH)(2)(mu-atrz)(2)(mu-piv)(4)(piv)(2)].2MeOH.H(2)O (2) (atrz = 4-amino-1,2,4-triazole), [Cu(4)(mu(3)-OH)(2)(mu-tbtrz)(2)(mu-piv)(2)(piv)(4)].4H(2)O (3) (tbtrz = 4-tert-butyl-1,2,4-trizaole), and [Cu(4)(mu(3)-O)(2)(mu-admtrz)(4)(admtrz)(2)(mu-piv)(2)(piv)(2)].2[Cu(2)(mu-H(2)O)(mu-admtrz)(piv)(4)].13H(2)O [4 = 4a.2(4b).13H(2)O; admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole], have been prepared and structurally characterized. 1 is an asymmetrical triangular complex containing a [Cu(3)(mu(3)-OH)] core with two Cu---Cu edges spanned by bridging adetrz ligands. 2, 3, and 4a are novel tetranuclear compounds containing a [Cu(4)(mu(3)-O)(2)] or [Cu(4)(mu(3)-OH)(2)] core with Cu---Cu edges spanned by bridging 1,2,4-triazole or pivalate ligands. 4b is a dinuclear compound with one admtrz and one water bridge, and it is the first dinuclear Cu(II) triazole complex with one bridging water molecule. 1 is one of few reported triangular Cu(II) complexes with derivatives of 1,2,4-triazole, while 2, 3, and 4a are the first group of the nonlinear tetranuclear Cu(II) compounds with derivatives of 1,2,4-triazole. Variable-temperature magnetic susceptibility studies on the powder samples of 1-3 reveal the overall antiferromagnetic coupling between Cu(II) ions with J values of -55.6 to -12.8 cm(-1) (1), -216.4 to 0 cm(-1) (2), and -259.8 to 4.8 cm(-1) (3).

Non-trivial behavior of palladium(ii) acetate

Reaction of activated palladium metal with a HNO3/acetic acid mixture produces both orange Pd3(OAc)6, 1, and purple Pd3(OAc)5(NO2), 2. Compound has a trinuclear structure derived from that of the well-known triangular complex 1 in which one acetate group has been replaced by a nitrite group which is bonded to one palladium atom by the nitrogen atom and to another Pd atom using one of the oxygen atoms. Highly pure 1 can be made by continuous removal of the nitric oxides from the reaction mixture using a flow of N2. 1H NMR spectra of solutions of 1 in CDCl3 and C6D6 show several signals of various intensities when a small amount of water is present in the deuterated solvents but only one signal when the solvents are thoroughly dried. These results are consistent with the occurrence of one or more hydrolysis processes when the solvents contain water and suggest that hypotheses about various [Pd(OAc)2]n aggregates that have previously been brought forward in the literature to explain the complexity of the spectrum of 1 are unnecessary, especially for nonpolar solvents. Compound 2 does not hydrolyze, and in wet or dried solvents shows a 1H NMR spectrum that consists of five equal-intensity signals due to the five nonequivalent acetate groups.

New routes to polymetallic clusters: fluoride-based tri-, deca-, and hexaicosametallic MnIII clusters and their magnetic properties.

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.

Les lésions ligamentaires intracarpiennes associées aux fractures du poignet: Étude prospective radio-clinique sur 40 cas

Purpose of the study We performed a prospective study to search for arthrographic signs in favor of intracarpal ligament lesions occurring concomitantly with wrist fractures. We looked for a relationship between type of fracture and displacement and examined their impact on early functional outcome. Material and methods The series included 40 patients treated over a 1-year period. All 40 patients had a displaced wrist fracture requiring surgical treatment. A three-phase arthrography was performed during the initial operation in order to search for injuries involving the scapho-lunate, luno-pyramidal or triangular complex ligaments. A second arthrography was performed at the time the osteosynthesis material was removed. All patients were followed one year postperatively. Functional outcome was recorded at one year. Results Abnormal images were found in 57% of the patients at the first arthrography. Injury to the triangular complex predominated, followed by combined injuries. There was no statistical correlation between type of fracture, degree of displacement, and presence of ligament lesions (p > 0.05). Lesions of the triangular fibrocartilaginous complex (TFCC) were significantly increased (p = 0.04) in the event of intra-articular fracture. Age and gender did not influence ligament injury. At one year, the functional outcome was statistically comparable between patients with and without ligament injury. At the second arthrography, we observed only five cases where cure of the luno-pyramidal ligament had been achieved. Discussion Intracarpal ligament injuries associated with wrist fractures are frequent. Age had no effect on occurrence of ligament injury in our series, similar to findings reported by others. Likewise, the type of fracture had no effect. Data in the literature show that intra-articular fractures and highly-displaced fractures aggravate ligament injury. Our functional results at one year did not demonstrate any significant difference in patients with and without ligament injury. A 3 or 5-year follow-up might provide further insight. Nevertheless, neglected scapho-lunate lesions still have a bad reputation in the literature, leading us to search for such lesions and to provide adapted treatment in all patients aged less than 50 years presenting a displaced fracture of the wrist.

Born charge differences ofTiO2polytypes: Multipole expansion of Wannier charge densities

The bonding Wannier functions (WF's) associated with the O 2s/2p valence states of TiO 2 have been calculated for both the futile and the anatase forms. They are similar in the two polymorphs, and correspond to three distorted O sp 2 -like hybrids in the plane of the Ti 3 coordination triangle, and one p-like orbital perpendicular to this plane. For both structures, the WF's show that the OTi 3 triangular complex is the relevant structural unit for understanding TiO 2 electronic properties. WF's differences between the two phases are quantitatively measured with a multipole expansion of the static charge density of the fourfold WF complex. These differences reflect the opposite distortion from equilateral shape that the isosceles Ti 3 triangle has in the two structures, and correlate quantitatively with the opposite anisotropy of the dynamical Bom charge tensors calculated for the two polytypes.

First example of mu(3)-sulfido bridged mixed-valent triruthenium complex triangle Ru(III)(2)Ru(II)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-S) (1) incorporating simultaneous O,O- and gamma-C-bonded bridging acetylacetonate units. Synthesis, crystal structure, and spectral and redox properties.

The reaction of mononuclear ruthenium precursor [Ru(II)(acac)(2)(CH(3)CN)(2)] (acac = acetylacetonate) with the thiouracil ligand (2-thiouracil, H(2)L(1) or 6-methyl -2-thiouracil, H(2)L(2)) in the presence of NEt(3) as base in ethanol solvent afforded a trinuclear triangular complex Ru(3)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-sulfido) (1). In 1, each ruthenium center is linked to one usual O,O-bonded terminal acetylacetonate molecule whereas the other three acetylacetonate units act as bridging functions: each bridges two adjacent ruthenium ions through the terminal O,O-donor centers at one end and via the gamma-carbon center at the other end. Moreover, there is a mu(3)-sulfido bridging in the center of the complex unit, which essentially resulted via the selective cleavage of the carbon-sulfur bond of the thiouracil ligand. In diamagnetic complex 1, the ruthenium ions are in mixed valent Ru(III)Ru(III)Ru(II) state, where the paramagnetic ruthenium(III) ions are antiferromagnetically coupled. The single crystal X-ray structure of 1 showed two crystallographically independent C(3)-symmetric molecules, Ru(3)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-S) (1), in the asymmetric unit. Bond distances of both crystallographically independent molecules are almost identical, but there are some significant differences in bond angles (up to 6 degrees ) and interplanar angles (up to 8 degrees ). Each ruthenium atom exhibits a distorted octahedral environment formed by four oxygen atoms, two from each of the terminal and bridging acetylacetonate units, one gamma-carbon of an adjacent acetylacetonate ligand, and the sulfur atom in the center of the complex. In agreement with the expected 3-fold symmetry of the complex molecule, the (1)H and (13)C NMR spectra of 1 in CDCl(3) displayed signals corresponding to two types of ligand units. In dichloromethane solvent, 1 exhibited three metal center based successive quasireversible redox processes, Ru(III)Ru(III)Ru(III)-Ru(III)Ru(III)Ru(II) (couple I, 0.43 V vs SCE); Ru(III)Ru(III)Ru(IV)-Ru(III)Ru(III)Ru(III) (couple II, 1.12 V); and Ru(III)Ru(III)Ru(II)-Ru(III)Ru(II)Ru(II) (couple III, -1.21 V). However, in acetonitrile solvent, in addition to the three described couples [(couple I), 0.34 V; (couple II), 1.0 V; (couple III), -1.0], one irreversible oxidative response (Ru(III)Ru(III)Ru(IV) --> Ru(III)Ru(IV)Ru(IV) or oxidation of the coordinated sulfide center) appeared at E(pa), 1.50 V. The large differences in potentials between the successive couples are indicative of strong coupling between the ruthenium ions in the mixed-valent states. Compound 1 exhibited a moderately strong charge-transfer (CT) transition at 654 nm and multiple ligand based intense transitions in the UV region. In the Ru(III)Ru(III)Ru(III) (1(+)) state, the CT band was slightly blue shifted to 644 nm; however, the CT band was further blue shifted to 520 nm on two-electron oxidation to the Ru(III)Ru(III)Ru(IV) (1(2+)) state with a reduction in intensity.

Molecular triangle of palladium(II) and its anion binding properties.

The ligand 4(3H)-pyrimidone (Hpm) forms the complexes trans-[PdCl(2)(Hpm)(2)] and [Pd(PP)(Hpm)(2)](CF(3)SO(3))(2) (PP = Ph(2)PCH(2)PPh(2) or Ph(2)P(CH(2))(3)PPh(2)), with the neutral ligand (Hpm), and a bowl-like molecular triangle, [(Pd(bu(2)bipy)(mu-pm))(3)](3+) (bu(2)bipy = 4,4'-di-tert-butyl-2,2'-bipyridine), with the deprotonated ligand (pm). This triangular complex acts as a host for binding of several anionic guests.

Synthesis and crystal structure of a triangular nickel(ii) complex with the shortest imine-based rigid ligand

A novel triangular complex [Ni(SCN)2L]3 was generated via self-assembly from Ni(SCN)2 and the readily prepared imine-based ligand L, (C5H4N)–CHN–NCH–(C5H4N), by appropriately adjusting the coordination conditions of the metal center.

Synthesis, Crystal and Molecular Structures, and Properties of Optically Active Copper(II) Complexes with 3-N,N-Dimethylaminocaran-4-one-oxime

Copper(II) complexes with 3-N,N-dimethylaminocaran-4-one-oxime (HL) were synthesized and characterized by X-ray diffraction analysis, photoelectronic, IR, and EPR spectroscopy, magnetic susceptibility, and thermal analysis methods, and their optical activities were studied. The [Cu2(HL)2Cl4] complex is a dimer with weak exchange interactions between unpaired electrons of the Cu(II) ions. The [Cu3L3(OH)Cl]Cl · 8H2O structure is composed of triangular trinuclear complex cations, outer-sphere Cl–anions, and water molecules. The exchange parameter Jfor the trinuclear exchange cluster is –190 cm–1. The title complexes are optically active in the visible range of the spectrum.

The Lateral Rhinopexy

Correction of the collapsing nasal valve is often a surgical challenge. The surgical procedures suggested so far do not always show satisfactory results. In a nonrandomized pilot study, 8 patients were operated with a new technique. The technique uses a permanent fixation of the nasal valve at the piriform aperture (lateral rhinopexy) with simultaneous lateralization of the triangular complex. This was performed through a sublabial (external) approach (lateral rhinopexy). On average, patients had had 3.2 times previous nose surgery, including procedures at the nasal valve. The surgical technique is introduced. Follow-up periods ranged from 14 to 34 months. Functional results were verified by rhinomanometry 1 year after surgery. At that time, the nasal flow was on average more than doubled. Besides the functional improvement, the cosmetic results were satisfactory. Lateral rhinopexy proved to be a safe and effective procedure for the treatment of nasal valve collapse.

Arthroscopically assisted osteosynthesis of distal intraarticular radius fractures

Closed reduction and internal fixation of intraarticular distal radial fractures under direct vision of the articular surfaces. Concomitant control of additional carpal injuries and, if necessary, minimally invasive treatment. Distal, intraarticular radial fractures, particularly of group B and C according to the AO fracture classification. Fractures of group A with marked displacement with probable suspected additional carpal injuries, such as of scapholunar and lunotriquetral ligaments, triangular fibrocartilaginous complex. Open fractures, polytrauma patients, comminuted intraarticular fractures. Closed reduction of fracture. Arthrography of the wrist. Exact reduction of the fragments under arthroscopic control. Stabilization of fragments with the help of percutaneously introduced Kirschner wires and/or cannulated screws. If required, temporary arthrodesis of the scapholunar joint, or resection or reattachment of the articular disc. Thirty patients were treated with the described method, 23 of them showed additional injuries. Twenty-three patients who had surgery at least a year before were followed up at an average of 32.5 months (12 to 48) and were assessed according to the point score of Cooney. An excellent or good result was seen in 16 patients, a satisfactory result in 4 and a poor result in 3 patients. A transient paresthesia was noted in 3 patients, in 1 patient we observed an irritation of the extensor pollicis longus. Two patients required revision surgery: 1 shortening of the ulna, 1 plate fixation of the radius.

Design of a shaped beam cylindrical dipole array for cellular base stations

A linear dipole array mounted on a finite solid conducting cylinder is analysed by the method of moments with piecewise overlapping triangular functions and complex Fourier mode expansions. The port-current vector is obtained by the shaped beam pattern synthesis procedure, and the port voltage vector is computed with mutual coupling included. Currents along the dipoles and the current density on the cylindrical surface are calculated. Active input impedance at each dipole port is evaluated accordingly. The antenna has potential application for mobile communications in urban terrain.

Gold(I) Compounds without Significant Aurophilic Intermolecular Interactions: Synthesis, Structure, and Electronic Properties of Ph(3)PAuC(O)NHMe and Au(3)(PhCH(2)N=COMe)(3): Comparative Monomeric and Trimeric Analogues of the Solvoluminescent Trimer, Au(3)(MeN=COMe)(3).

The preparations of Ph(3)PAuC(O)NHMe( )()and Au(3)(PhCH(2)N=COMe)(3) are reported. In solution Ph(3)PAuC(O)NHMe is unstable and readily deposits metallic gold. Colorless needles of the monomeric complex, Ph(3)PAuC(O)NHMe, crystallize in the monoclinic space group P2(1)/c, with a = 8.993(2) Å, b = 22.583(5) Å, c = 8.932(2) Å, beta = 98.22(2) degrees, at 123 K with Z = 4. Refinement of 2609 reflections and 114 parameters yielded R = 0.0455. A hydrogen-bonded intermolecular network links molecular units through N-H.O hydrogen bonds. No aurophilic interactions are present in this solid. The crystal structure of the cyclic trinuclear organogold compound, Au(3)(PhCH(2)N=COMe)(3), reveals that the complex does not associate into a trigonal prismatic array via intermolecular interactions of gold(I) centers as is seen in the triangular complex, Au(3)(MeN=COMe)(3). Rather, the complex packs in a stair-step fashion with eight discrete molecules in the asymmetric unit. Additionally, the solvent-stimulated emission (solvoluminescence) associated with Au(3)(MeN=COMe)(3) is not observed for this complex. Colorless needles of Au(3)(PhCH(2)N=COMe)(3) crystallize in the monoclinic space group P2(1), with a = 17.311(6) Å, b = 34.761(10) Å, c = 18.052(6) Å, beta = 94.73(2) degrees, at 133 K with Z = 16. Refinement of 16 250 reflections and 985 parameters yielded R = 0.0735.

An unprecedented trinucleating bridging mode (μ3-η1∶η1∶η1) of a tris(pyrazolyl)borate ligand in a trinuclear silver(I) complex

The crystal structure of [Ag3(TpAn)2][ClO4], where TpAn is tris[3-(2-methoxyphenyl)pyrazol-1-yl]hydroborate, shows a unique trinucleating bridging coordination mode for the tris(pyrazolyl)borate: each of the two ligands coordinates one pyrazolyl donor to each of the three two-coordinate Ag(I) ions, affording a triangular complex in which each face is capped by a µ3-η1∶η1∶η1-tris(pyrazolyl)borate.

An Ultrastructural Characterization of in Vitro-Assembled hnRNP C Protein-RNA Complexes

In mammalian cells approximately 700 nucleotide lengths of pre-mRNA are packaged during transcription by a unique group of abundant nuclear proteins to form a repeating array of regular ribonucleoprotein complexes termed 30-40S heterogeneous nuclear ribonucleoprotein particles (hnRNP particles). We have used electron microscopy to examine complexes that form when in vitro-transcribed RNA is bound by one of the purified native core-particle proteins which comprise the 40S monoparticle (the C protein tetramer). Negatively stained images of the C protein tetramer bound to particle-length RNA (700 nt) demonstrate that three tetramers bind each RNA molecule to form a stable closed triangular complex. The triangular complexes have an isosceles shape with a base of 18.0 nm and sides of 23.0 nm. When RNA molecules of 230 nt are used as substrates single tetramers bind to form complexes that appear as small rounded structures with an average diameter of 9.7 nm. Twice this length of RNA (456 nt) supports the assembly of mostly bilobed complexes that are 20.4 nm long and 11.8 nm wide. Images of the C protein-RNA complexes which assemble on 1400-nucleotide lengths of RNA (two particle lengths of RNA) clearly show complexes composed of two triangles while three-triangle complexes are seen when 2100-nt lengths of RNA are used as the assembly substrate. These ultrastructural results demonstrate that groups of three C protein tetramers combine with the length of RNA packaged in monoparticles to form a discreet triad structure. This interaction establishes a structural basis for the RNA length requirement in monoparticle assembly and a mechanism for the packaging of nascent transcripts into a repeating array of regular structures.

Synthesis and structure of a seven electron triangular cluster complex [Mo3S4Cl3(dppe)2(PEt3

Synthesis and structure of a seven electron triangular cluster complex [Mo3S4Cl3(dppe)2(PEt3

Ab Initio Molecular Dynamics Investigation of Singlet C2H2Li2: Determination of the Ground State Structure and Observation of LiH Intermediates

The structural, electronic, and dynamic properties of the organolithium compd. C2H2Li2 were studied via ab initio mol. dynamics simulations based on the Car-Parrinello method. Dynamic simulated annealing techniques applied to search for the low-energy configurations resulted in a structure that is not a dilithioethylene isomer as suggested by the stoichiometric formula but an acetylenic deriv. that can be visualized geometrically as a complex of lithioacetylene with Li hydride HC2Li.HLi. However, the ground state electronic structure is more suggestive of an ionic complex (H-C:C)-.(Li+H-Li+) in which the linear anion HCC- binds to the two Li cations in the triangular complex Li+H-Li+. Several ethylene-like isomers were identified via high-temp. quenches, but these invariably turned out to lie at high energies (.apprx.>30 kcal/mol). Anal. of the high-temp. dynamics indicated that ethylene-like isomers are always unstable toward an intramol. H migration mediated via a Li hydride unit. The direct observation of these intramol. rearrangement reactions revealed the role of the Li atoms as H transfer reagents and confirmed the importance of Li hydride as an intermediate species. [on SciFinder (R)]

The C-protein tetramer binds 230 to 240 nucleotides of pre-mRNA and nucleates the assembly of 40S heterogeneous nuclear ribonucleoprotein particles.

A series of in vitro protein-RNA binding studies using purified native (C1)3C2 and (A2)3B1 tetramers, total soluble heterogeneous nuclear ribonucleoprotein (hnRNP), and pre-mRNA molecules differing in length and sequence have revealed that a single C-protein tetramer has an RNA site size of 230 to 240 nucleotides (nt). Two tetramers bind twice this RNA length, and three tetramers fold monoparticle lengths of RNA (700 nt) into a unique 19S triangular complex. In the absence of this unique structure, the basic A- and B-group proteins bind RNA to form several different artifactual structures which are not present in preparations of native hnRNP and which do not function in hnRNP assembly. Three (A2)3B1 tetramers bind the 19S complex to form a 35S assembly intermediate. Following UV irradiation to immobilize the C proteins on the packaged RNA, the 19S triangular complex is recovered as a remnant structure from both native and reconstituted hnRNP particles. C protein-RNA complexes composed of three, six, or nine tetramers (one, two, or three triangular complexes) nucleate the stoichiometric assembly of monomer, dimer, and trimer hnRNP particles. The binding of C-protein tetramers to RNAs longer than 230 nt is through a self-cooperative combinatorial mode. RNA packaged in the 19S complex and in 40S hnRNP particles is efficiently spliced in vitro. These findings demonstrate that formation of the triangular C protein-RNA complex is an obligate first event in the in vitro and probably the in vivo assembly the 40S hnRNP core particle, and they provide insight into the mechanism through which the core proteins package 700-nt increments of RNA. These findings also demonstrate that unless excluded by other factors, the C proteins are likely to be located along the length of nascent transcripts.