Synthesis, structures and magnetic properties of [(η9-C9H9)Ln(η8-C8H8)] super sandwich complexes.

Sandwich complexes are an indispensable part of organometallic chemistry, which is becoming increasingly important in the field of lanthanide-based single molecule magnets. Herein, a fundamental class of pure sandwich complexes, [(η9-C9H9)Ln(η8-C8H8)] (Ln=Nd, Sm, Dy, Er), is reported. These neutral and sandwiched lanthanide compounds exclusively contain fully π-coordinated coplanar eight and nine membered CH rings. The magnetic properties of these compounds are investigated, leading to the observation of slow relaxation of the magnetization, including open hysteresis loops up to 10 K for the Er(III) analogue. Fast relaxation of the magnetization is likewise observed near zero field, a highly important characteristic for quantum information processing schemes. Our synthetic strategy is straightforward and utilizes the reaction of [(η8-C8H8)LnI(thf)n] complexes with [K(C9H9)]. Although all compounds are fully characterized, structural details of the title compounds can also be deduced by Raman spectroscopy only.

The boron-boron triple bond? A thermodynamic and force field based interpretation of the N-heterocyclic carbene (NHC) stabilization procedure.

Recently, the NHC→B[triple bond, length as m-dash]B←NHC molecule 1 has been published in Science where it is described as a stabilized B2 molecule in its 1Σ excited state (B2*) (NHC = N-heterocyclic carbene C3N2H2(C6H3Pri 2-2,6)2). The bonding of 1 based on sophisticated calculations and the BB distances of the solid compound was discussed as the first example of a B2 triple bond in a stable molecule. Now we present an only experimentally based interpretation of 1 via detailed thermodynamic considerations, including its fragmentation to B2 molecules. Furthermore, from the vibrational spectrum force constants (f BB for the BB bond and f BC for the BC bond) were extracted, which are classical examples to indicate single, double and triple CC bonds in organic chemistry. The consequence of both properties of 1 (ΔE and f) generates a new interpretation which is in contrast to the triple bond donor-acceptor description visualized by arrows and which casts a critical light on the interpretation of any NHC "stabilized" molecule.

PS2Br and AsS2X (X = Br, I): similar molecules with completely different shapes--a combined experimental and theoretical study.

By the reaction of solid As(4)S(4) with gaseous Br(2) at a temperature of 410 K gaseous AsSBr and AsS(2)Br are formed; the reaction with gaseous I(2) at 468 K leads to the formation of AsSI, AsS(2)I, As(2)S(2)I(2) and As(2)S(3)I(2). Thermodynamic data on these novel species are obtained by mass spectrometry. The experimental findings are extended and confirmed by ab initio quantum chemical calculations. Undoubtedly the molecules AsSX (X = Br, I) and As(2)S(2)I(2) contain As-atoms in the formal oxidation state III. Unexpectedly, in AsS(2)X arsenic is not of formal oxidation state +V but +III: due to the absence of As-S π-bonding, the molecular structure of AsS(2)X is arranged as a dithia-arsirane with an AsS(2) three-membered ring. For comparison with AsS(2)X, PS(2)Br is investigated for the first time. This high temperature species is planar with symmetry C(2v) and phosphorus of the formal oxidation state +V in which the two P=S π-bonds are realized due to their strength over one S-S σ-bond. As(2)S(3)I(2) contains a five-membered As(2)S(3)-ring with one S-S-bond. The ionization energies are determined and compared with those obtained from calculations; they serve as a further indication for the structures realized in these molecules.

AsS2Cl-an Arsenic(V) compound? Formation, stability and structure of gaseous AsSCl and AsS2Cl--a combined experimental and theoretical study.

By reaction of solid As(4)S(4) with gaseous Cl(2) at a temperature of 410 K gaseous AsSCl and AsS(2)Cl are formed. Unexpectedly in AsS(2)Cl the arsenic is not of formal oxidation state +V but +III: the molecular structure of AsS(2)Cl is arranged as a 1-chloro-dithia-arsirane and comprises an hitherto unknown AsS(2) three-membered ring. Thermodynamic data on AsSCl and AsS(2)Cl are obtained by mass spectrometry (MS). The experimental data are extended and confirmed by ab initio quantum chemical calculations (QC). The following values are given: Δ(f)H(0)(298)(AsSCl) = -5.2 kJ mol(-1) (MS), Δ(f)H(0)(298)(AsSCl) = 1.7 kJ mol(-1) (QC), S(0)(298)(AsSCl) = 296.9 J K(-1) mol(-1) (QC) and c(p)(0)(T)(AsSCl) = 55.77 + 3.97 × 10(-3)T- 4.38 × 10(5)T(-2)- 1.83 × 10(-6)T(2) and Δ(f)H(0)(298)(AsS(2)Cl) = -39.0 kJ mol(-1) (MS), Δ(f)H(0)(298)(AsS(2)Cl) = -20.2 kJ mol(-1) (QC), S(0)(298)(AsS(2)Cl) = 321.3 J K(-1) mol(-1) (QC) and c(p)(0)(T)(AsS(2)Cl) = 80.05 + 5.09 × 10(-3)T- 7.61 × 10(5)T(-2)- 2.35 × 10(-6)T(2) (298.15 K < T < 1000 K) (QC). The ionization energies are determined (IP(AsSCl) = 10.5, IP(AsS(2)Cl) = 10.2 eV). The IR spectrum of AsSCl is detected by means of matrix isolation spectroscopy. The estimated force constant f(As=S) = 4.47 mdyn·Å(-1) gives rise to an As=S double bond.

Molecular lattice fragment of LiI. Crystal structure and ab initio calculations of [LiI(NEt3)]4.

Numerous crystal structures of donor-stabilized LiX species are known, but only two of them show a heterocubane arrangement [LiX(Do)]4 (X = Cl, Br; Do = donor) in the solid state. Herein we report the X-ray crystal structure of [LiI(NEt3)]4 (1), obtained by the reaction of LiN(SiMe3)2 with either GaI or All in the presence of NEt3. The structural backbone of 1 is a [LiI]4 heterocubane core, which is compared to [LiX]4 (X = Cl, Br) as well as to [Li(CH3)]4. The energetics of the formation of 1 and its stability with respect to solid LiI is rationalized and additionally supported by DFT (density functional theory) calculations.

[Al]

A "naked" aluminum atom links two aluminum tetrahedra in the [Al(7){N(SiMe(3))(2)}(6)](-) ion (see picture), which results from the reaction of a metastable AlCl solution with LiN(SiMe(3))(2) and crystallizes with [Li(OEt(2))(3)](+) as cation. This unique structure among molecular metal atom clusters represents a small but characteristic section of cubic close-packed aluminum.

Three-dimensional reconstruction of high contrast objects using C-arm image intensifier projection data.

The reconstruction of three-dimensional (3D) objects from 2D X-ray cone-beam projections using a circular source path is most commonly done with an algorithm according to Feldkamp et al. [Feldkamp LA, Davis LC, Kress JW. Practical cone-beam algorithms. J Opt Soc Am A 1984;6:612-619]. An adaptation of this so-called Feldkamp method to cone-beam projections acquired with a C-arm system is presented here. In a phantom study, reconstruction results obtained along real source-detector trajectories of a C-arm system are compared to reconstruction results obtained from projections acquired from a full-circular trajectory and from one consisting of two full orthogonal circles, which fulfills Tuy's sufficiency condition. The straightforward application of Feldkamp's method adapted to projection data obtained with a C-arm system illustrates the 3D imaging potential of image intensifier based cone-beam computed tomography. Reconstruction results from projection data of different patients acquired with a motorized C-arm system such as vessel structures filled with contrast agent and bones are presented.

Structure and developmental expression of troponin I isoforms. cDNA clone analysis of avian cardiac troponin I mRNA.

We isolated avian (chicken and quail) cardiac troponin I (TnIcardiac) cDNA clones for studies of Tn-Icardiac protein structure/evolution and developmental gene regulation. Comparison of the cDNA-predicted avian TnIcardiac amino acid sequences with known TnI sequences indicated 1) that the presence of an N-terminal extension sequence carrying a dual protein kinase A phosphorylation target site and an adjacent proline-rich segment is an ancient cardiac-specific feature of TnI which has been conserved since the bird/mammal divergence, 2) that features of the near-N-terminal troponin C (TnC)-binding site sequence suggest isoform-specific adaptation of TnI and TnC, and 3) that the avian TnIcardiac internal actin/TnC-binding, actomyosin-inhibitory, domain shows significant sequence divergence from mammalian TnIcardiac sequences, including the absence of a protein kinase C target site which is a cardiac-specific feature of TnI in mammals. Use of the cDNA clones to probe TnIcardiac mRNA expression during striated muscle development showed active expression in cardiac muscle from early developmental times (day 4 in ovo), but not in embryonic or adult skeletal muscle or in embryonic skeletal muscle cell cultures. Transcriptional run-on analysis showed that the heart-specific expression of TnIcardiac mRNA in embryonic striated muscle reflects transcriptional control of TnIcardiac gene expression. In many other contractile protein gene families, genes encoding cardiac isoforms are expressed early in skeletal muscle development and are later repressed. Thus, the restriction of active TnIcardiac gene expression to the cardiac muscle cell lineage is an unusual expression pattern for cardiac contractile protein genes and indicates that diverse gene regulatory mechanisms direct the differential expression of cardiac and skeletal muscle isoforms in different muscle gene families.

Real-time distortion correction of digital X-ray II/TV-systems: an application example for digital flashing tomosynthesis (DFTS).

In X-ray image intensifier (II)/TV-camera systems geometric distortions occur, e.g. due to the curved input screen of the II. For methods which are based on a pixelwise comparison of images, e.g. digital angio-tomosynthesis, an accurate correction of these geometric distortions is absolutely necessary. For the application of tomosynthesis to coronary angiography the correction in addition has to be done in real-time, because the reconstruction of the three dimensional structure of the blood vessels has to be done while the patient is undergoing catheterization. This paper describes a digital correction unit which allows a large variety of geometric distortions to be corrected. It consists of an input memory for storing the distorted image, an output memory for storing the corrected image and a special address memory which will serve as an address table during the correction step. For each element of the output image the location of the corresponding element of the distorted input image is determined in a preprocessing step and stored in the address memory. The actual correction of an image is then done while the image is copied from the input into the output memory. In this way 512 x 512 images can be corrected in real-time by a 32-bit 680X0-based microprocessor system. Presented as Poster at the 3rd International Symposium CAR '89 Computer Assisted Radiology, Berlin, June 25-28, 1989.

Ambiguous genitalia associated with skeletal abnormalities, cutis laxa, craniostenosis, psychomotor retardation, and facial abnormalities (SCARF syndrome).

We describe 2 male maternal first cousins, 7 years and 7 months old, with a previously unreported pattern of malformations including lax skin, joint hyperextensibility, umbilical and inguinal herniae, craniosynostosis, pectus carinatum, several abnormally shaped vertebrae, enamel hypoplasia and hypocalcification of the teeth, facial abnormalities and wide webbed neck, ambiguous genitalia, multiple nodular liver tumors, and mild psychomotor retardation. The occurrence of 2 male children related through their mothers suggests the possibility of X-linked recessive inheritance. It is proposed to call this disorder the SCARF syndrome (skeletal abnormalities, cutis laxa, craniostenosis, ambiguous genitalia, retardation, facial abnormalities).

cDNA clone and expression analysis of rodent fast and slow skeletal muscle troponin I mRNAs.

We have characterized the structure and expression of rodent mRNAs encoding the fast and slow skeletal muscle isoforms of the contractile regulatory protein, troponin I (TnIfast and TnIslow). TnIfast and TnIslow cDNA clones were isolated from mouse and rat muscle cDNA clone libraries and were used as isoform-specific probes in Northern blot and in situ hybridization studies. These studies showed that the TnIfast and TnIslow mRNAs are expressed in skeletal muscle, but not cardiac muscle or other tissues, and that they are differentially expressed in individual muscle fibers. Fiber typing on the basis of in situ hybridization analysis of TnI isoform mRNA content showed an excellent correlation with fiber type as assessed by myosin ATPase histochemistry. These results directly demonstrate that the differential expression of skeletal muscle TnI isoforms in the various classes of vertebrate striated muscle cells is based on gene regulatory mechanisms which control the abundances of specific TnI mRNAs in individual muscle cells. Both TnIfast and TnIslow mRNAs are expressed, at comparable levels, in differentiated cultures of rat L6 and mouse C2 muscle cell lines. Thus, although neuronal input has been shown to be an important factor in determining fast versus slow isoform-specific expression in skeletal muscle, both TnIfast and TnIslow genes can be expressed in muscle cells in the absence of nerve. Comparison of the deduced rodent TnI amino acid sequences with previously determined rabbit protein sequences showed that residues with potential fast/slow isoform-specific function are present in several discrete clusters, two of which are located near previously identified actin and troponin C binding sites.

Digital flashing tomosynthesis (DFTS)--a technique for three-dimensional coronary angiography.

Digital Flashing Tomosynthesis (DFTS) represents a technique for three-dimensional (3D) coronary angiography. Four ECG-gated simultaneously flashed X-ray tubes generate a multiperspective digital substraction image as DFTS multiangiogram for 3D reconstruction and visualization. Computerized morphologic and morphometric quantitative analysis can be performed including videodensitometry. Postmortem coronary angiography of 30 human hearts with suspected coronary artery disease was performed by 35-mm cine technique and by DFTS. The results of angiographic measurements in 50 stenotic arterial segments were compared with the histologic reference and show excellent regression results with correlation coefficients of more than 0.95 (p less than or equal to 0.0001). No significant differences in standard errors of estimates between the techniques were found. DFTS yields an accuracy in depiction of the coronary arteries and angiographic estimation of arterial lumen equivalent to 35-mm cineangiography. DFTS images can be directly used for visual interpretation and for computerized morphologic and morphometric quantitative analysis. DFTS technology reduces the amount of radiation exposure, the amount of contrast medium, and the time of the procedure. DFTS offers the possibility to obtain 3D images of the coronary artery tree.

Generation of a subtraction mask for digital angiography based on the movement of the coronary arteries.

A synthetic mask technique for angiography of coronary arteries was experimentally studied, using conventional 35 mm film sequences of coronary arteries. The method makes use of the fact that because of the movement of the heart vessels different parts of the background will be hidden. The background is extracted from two or more neighbouring frames by computer assistance and afterwards used for a subtraction mask. The experiments showed that the synthetic masks are of a good accuracy, the background anatomy is markedly reduced and the contrast is increased.

First clinical results with digital flashing tomosynthesis in coronary angiography.

Digital flashing tomosynthesis (D-FTS) investigations have been performed using a new nonlinear reconstruction algorithm. It is called extreme-value decoding and produces significantly less artefact than back projection used commonly in tomosynthesis. The reduction of artefact allows the use of tomosynthesis based on only four projections in the case of dilute objects, i.e. objects with only a small number of high absorbing voxels. This condition can be realized in angiography by cancelling soft-tissue and bones by subtraction (e.g. DSA technique). The new technique has been carried out in 10 patients with coronary artery disease after investigation with standard 35 mm cineangiography. For the recording step of the D-FTS images we have used a multiple X-ray source. For the digital nonlinear reconstruction step we have used a VAX 11/780 computer. The estimated degree of stenosis found by D-FTS tomograms shows good accordance with the cineangiographic studies. The amount of contrast medium, the X-ray dose, and the investigation time are significantly reduced, because D-FTS requires only a single pre- and post-injection multiple perspective-image for each coronary artery.

A new digital tomosynthesis method with less artifacts for angiography.

A new nonlinear reconstruction method for tomosynthesis is described. This method is suited for "dilute" objects, i.e., objects in which most of the voxels have negligibly small absorption. Images of blood vessels filled with contrast material approximate this condition if the background is subtracted. The technique has been tested experimentally using a wire phantom and a prepared human heart. The results show significantly less artifacts than the well-known back projection. It is possible to get diagnostic image quality with a few projections. The reconstruction algorithm can be realized with dedicated real-time hardware.