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PubMed1997

[Preserving and improving the profile in primary and secondary orbital reconstruction].

Computed tomographies in 15 patients following reconstruction of multiple-wall defects of the orbit following trauma and tumor demonstrate a correlation between moderate overcorrection of the orbital bony frame and a good aesthetic profile. Reconstruction of the deep orbital cone, the transition level between the orbital floor and medial orbital wall, as well as the convex shape of the medial orbital wall, are of great importance for good results.

Adult↗
PubMed2003

Differential connections of the temporal pole with the orbital and medial prefrontal networks in macaque monkeys.

Previous studies indicate that the orbital and medial prefrontal cortex (OMPFC) is organized into "orbital" and "medial" networks, which have distinct connections with cortical, limbic, and subcortical structures. In this study, retrograde and anterograde tracer experiments in monkeys demonstrated differential connections between the medial and orbital networks and the dorsal and ventral parts of the temporal pole. The dorsal part, including dysgranular and granular areas (TGdd and TGdg), is reciprocally connected with the medial network areas on the medial wall and gyrus rectus (areas 10m, 10o, 11m, 13a, 14c, 14r, 25, and 32) and on the lateral orbital surface (areas Iai and 12o). The strongest connections are with areas 10m (caudal part), 14c, 14r, 25, 32, and Iai. The agranular temporal pole (TGa) is connected with several areas, but most strongly with medial network area 25. The granular area around the superior temporal sulcus (TGsts) and the ventral dysgranular and granular areas (TGvd and TGvg) are reciprocally connected with the orbital network (especially areas 11l, 13b, 13l, 13m, Ial, Iam, and Iapm). TGsts is strongly connected with the entire orbital network, whereas areas TGvd and TGvg have lighter and more limited connections. Intrinsic connections within the temporal pole are also restricted to dorsal or ventral parts. Together with evidence that the dorsal and ventral temporal pole are differentially connected to auditory and visual areas of the superior and inferior temporal cortex, the results indicate separate connections between these systems and the medial and orbital prefrontal networks.

Animals↗
PubMed2006

Highly anisotropic orbitally dependent superexchange in cyano-bridged clusters containing Mn(III) and Mn(II) ions.

We study the orbitally dependent magnetic exchange in cyanide-based clusters as a source of the barrier for reversal magnetization. We consider the Mn(III)-CN-Mn(II) dimer and linear Mn(II)-NC-Mn(III)-CN-Mn(II) trimer containing octahedrally coordinated Mn(III) and Mn(II) ions with special emphasis on the magnetic manifestations of the orbital degeneracy of the Mn(III) ion. The kinetic exchange mechanism involves the electron transfer from the single occupied t(2) orbitals of the Mn(II) ion [6A1(t2(3)e2) ground state] to the singly occupied t(2) orbitals of the Mn(III) ion [3T1(t2(4)) ground state] resulting in the charge-transfer 5T2(t2(2)e2)Mn(III) - 2T2(t2(5))Mn(II) state of the pair. The deduced effective exchange Hamiltonian that takes into account orbital degeneracy leads to an essentially non-Heisenberg energy pattern. The energy levels are shown to be dependent on both spin and orbital quantum numbers, thus providing direct information about the magnetic anisotropy of the system. Along with the magnetic exchange, the model includes an axial component of the crystal field and spin-orbit coupling operating within the ground 3T1(t2(4)) cubic term of the Mn(III) ion. We have shown that under certain conditions both named interactions lead to the occurrence of the barrier for the reversal of magnetization, which significantly increases when passing from the dimer to the trimer. This provides a possible way for raising the magnetic barrier in the family of cyano-bridged manganese clusters.

Journal Article↗
PubMed2002

Spin-orbit coupling of DFT/MRCI wavefunctions: method, test calculations, and application to thiophene.

During the past decade the one-center mean-field approximation has proven to be a very appropriate framework for the accurate description of spin-orbit effects at the correlated all-electron level. Here, a new efficient code, SPOCK, is introduced that calculates spin-orbit matrix elements in the one-center mean-field approximation for multireference CI wave functions. For the first time, the computation of spin-dependent interactions within a Kohn-Sham orbital based CI (DFT/MRCI) scheme1 is made possible. The latter approach is suitable for large scale systems with up to 100-200 valence electrons. Test calculations are performed on well-known diatomic molecules and the thiocarbonyl pyranthione. Spin-orbit matrix elements show good agreement with their Hartree-Fock orbital based counterparts but are obtained at considerably lower expense, thus demonstrating the power of the method. As an application singlet-triplet couplings in thiophene are investigated that are important for the photophysics and photochemistry. Spin-orbit matrix elements between all pi --> pi* excited states are found to be small. Considerably larger spin-orbit matrix elements are observed only for cases in which pi --> sigma* excited configurations are involved.

Journal Article↗
PubMed2006

On the suitability of strictly localized orbitals for hybrid QM/MM calculations.

In the QM/MM method we have developed (LSCF/MM), the QM and the MM parts are held together by means of strictly localized bonding orbitals (SLBOs). Generally these SLBOs are derived from localized bond orbitals (LBOs) that undergo tails deletion, resulting in a nonpredictable change of their properties. An alternative set of SLBOs is provided by the extremely localized molecular orbitals (ELMOs) approach, where the orbitals are rigorously localized on some prefixed atoms without tails on the other atoms of the molecule. A comparative study of SLBOs arising from various localization schemes and ELMOs is presented to test the reliability and the transferability of these functions within the Local Self-Consistent Field (LSCF) framework. Two types of chemical bonds were considered: C--C and C--O single bonds. The localized functions are obtained on the ethane and the methanol molecules, and are tested on beta-alanine and diethyl ether molecules. Moreover, the various protonation forms of beta-alanine have been investigated to illustrate how well the polarity variation of the chemical bond can be handled throughout a chemical process. At last, rotation energy profiles around C--C and C--O bonds are reproduced for butane and fluoromethanol. Energetic, geometric, as well as electronic factors all indicate that ELMO functions are much more transferable from one molecule to another, leading to results closer to the usual SCF reference than any other calculations involving any other localized orbitals. When the shape of the orbital is the most important factor then ELMO functions will perform as well as any other localized orbital.

Butanes↗
PubMed2001

Ribozyme catalysis via orbital steering.

Orbital steering is invoked to explain how the three-dimensional structure of a small self-cleaving RNA, the hammerhead ribozyme, both prevents and enhances RNA autocatalysis. Within the conserved catalytic core of the ribozyme, the position of the 2' oxygen atom of the G8 ribose is observed to be aligned almost perfectly with the phosphorus atom and the 5' oxygen atom of the adjacent A9 phosphate group for self-cleavage via an in-line attack mechanism. Despite this apparent near-perfect atomic positioning, no cleavage takes place. The explanation proposed is that a network of hydrogen bonds in the ribozyme core orients or steers the orbitals containing the electron lone pairs of the attacking nucleophile (the 2' oxygen atom) away from the A9 phosphorus atom, eliminating overlap with the vacant phosphorus d-orbitals despite the near-perfect in-line positioning of the oxygen atom, thus preventing catalysis. Because of the near-perfect atomic positioning of the 2' oxygen atom relative to the phosphate group, orbital steering effects in this case are fortuitously uncoupled from conformational, distance and orientation effects, allowing an assessment of the catalytic power due purely to orbital steering. In contrast, a conformational change at the cleavage site is required to bring the 2' oxygen atom and the scissile phosphate group into atomic positions amenable to an in-line attack mechanism. In addition, the conformationally changed structure must then steer the lone-pair orbitals of the correctly positioned 2' oxygen atom toward the scissile phosphorus atom in order for cleavage to take place. We estimate that fulfillment of each of these two required changes may contribute separately an approximately 1000-fold rate enhancement, potentially accounting for a significant fraction of the catalytic power of this ribozyme. Orbital steering therefore appears to be a general phenomenon that may help to explain catalysis in both ribozymes and protein enzymes in a unified manner.

Base Sequence↗
PubMed1995

Different metabolic pathways of 2,5-difluoronitrobenzene and 2,5-difluoroaminobenzene compared to molecular orbital substrate characteristics.

The in vivo metabolite patterns of 2,5-difluoroaminobenzene and of its nitrobenzene analogue, 2,5-difluoronitrobenzene, were determined using 19F NMR analysis of urine samples. Results obtained demonstrate significant differences between the biotransformation patterns of these two analogues. For the aminobenzene, cytochrome P450 catalysed aromatic hydroxylation presents the main metabolic pathway. 2,5-Difluoronitrobenzene was predominantly metabolised through glutathione conjugation leading to excretion of 5-fluoro-2-(N-acetylcysteinyl)-nitrobenzene and fluoride anions, and, to a minor extent, through cytochrome P450 catalysed hydroxylation and nitroreduction. Pretreatment of the rats with various inducers of cytochrome P450 enzymes, known also to influence glutathione S-transferase enzyme patterns, followed by exposure to the 2,5-difluoroamino- or 2,5-difluoronitrobenzene, generally resulted in metabolite patterns that varied only to a small (< or = 12%) extent. Based on these results it was concluded that the biotransformation enzyme pattern is not the predominant factor in determining the metabolic route of these two model compounds. Additional in vitro microsomal and cytosolic incubations with 2,5-difluoroaminobenzene and 2,5-difluoronitrobenzene qualitatively confirmed the in vivo results. NADPH/oxygen supported microsomal cytochrome P450 catalysed hydroxylation was observed only for 2,5-difluoroaminobenzene whereas cytosolic GSH conjugation occurred only in incubations with 2,5-difluoronitrobenzene as the substrate. Outcomes from molecular orbital calculations provided a working hypothesis that can explain the difference in metabolic pathways of the nitro- and aminobenzene derivative on the basis of their chemical characteristics. This hypothesis states that the chances for a nitro- or aminobenzene derivative to enter either a cytochrome P450 or a glutathione conjugation pathway are determined by the relative energy levels of the frontier orbitals of the compounds. The aminobenzene derivative has relatively high energy molecular orbitals leading to an efficient reaction of its highest occupied molecular orbital (HOMO) with the singly occupied molecular orbital of the cytochrome P450 (FeO)3+ intermediate, but a low reactivity of its lowest unoccupied molecular orbital (LUMO) with the HOMO of glutathione. The nitrobenzene, on the other hand, has molecular orbitals of relatively low energy, explaining the efficient interaction, and, thus, reaction between its LUMO and the HOMO electrons of glutathione, but resulting in low reactivity with the SOMO electron of the cytochrome P450 (FeO)3+ reaction intermediate.

Aniline Compounds↗
PubMed2003

Early social deprivation alters monoaminergic afferents in the orbital prefrontal cortex of Octodon degus.

The influence of early parental deprivation on the development of tyrosine hydroxylase- and 5-hydroxytryptamine-immunoreactive fiber innervation of subregions of the orbital prefrontal cortex (ventrolateral orbital, lateral orbital and agranular insular cortex) was quantitatively investigated in the precocious lagomorph Octodon degus. Forty-five-day-old degus from two groups were compared: 1) degus which were repeatedly separated from their parents during the first three postnatal weeks, and after weaning they were reared in social isolation; and 2) degus which were reared undisturbed in their families. Compared with the normal control animals the ventrolateral orbital prefrontal cortex and agranular insular cortex of the deprived animals displayed significantly increased density of tyrosine hydroxylase-immunoreactive fibers (up to 172% in the ventrolateral orbital prefrontal cortex and up to 143% in the agranular insular cortex). The lateral orbital prefrontal cortex showed increased 5-hydroxytryptamine-positive fiber densities (up to 118%). This altered balance between the serotonergic and dopaminergic cortical innervation in the orbital prefrontal cortex may reflect an anatomical and functional adaptation, which may be triggered by an altered activity of these transmitter systems during the phases of parental separation and social isolation.

Afferent Pathways↗
PubMed2001

Core molecular orbital contribution to N2O isomerization as studied using theoretical electron momentum spectroscopy.

Core molecular orbital contribution to the electronic structure of N2O isomers has been studied using quantum mechanical density functional theory combined with a plane wave impulse approximation method. Momentum distributions of wave functions for inner shell molecular orbitals of the linear NNO, cyclic and linear NON isomers of N2O are calculated through the (e, 2e) differential cross sections in momentum space. This is possible because this momentum distribution is directly proportional to the modulus squared of the momentum space wave function for the molecular orbital in question. While the momentum distributions of the NNO and cyclic N2O isomers demonstrate strong atomic orbital characteristics in their core space, the outer core molecular orbitals of the linear NON isomer exhibit configuration interactions between them and the valence molecular orbitals. It is suggested that the frozen core approximation breaks down in the prediction of the electronic structure of such an isomer. Core molecular orbital contributions to the electronic structure can alter the order of total energies of the isomers and lead to incorrect conclusions of the stability among the isomers. As a result, full electron calculations should be employed in the study of N2O isomerization.

Electrons↗
PubMed2005

Mössbauer, electron paramagnetic resonance, and crystallographic characterization of a high-spin Fe(I) diketiminate complex with orbital degeneracy.

The synthesis and X-ray structure of the low-coordinate, high-spin Fe(I) compound LFe(HCCPh) (L = HC(C[tBu]N[2,6-diisopropylphenyl])2]-), 1, are reported. Low-temperature Mössbauer and electron paramagnetic resonance (EPR) spectroscopies reveal that the electronic ground state is a Kramers doublet with uniaxial magnetic properties (effective g values g(x) = 8.9, 0 < g(y), g(z) < 0.3) that is well isolated from the excited states. The observation of a large and positive magnetic hyperfine field, B(int) = +68.8(3) T, demonstrates that the orbital angular moment is essentially unquenched along one spatial direction. Relaxation rates obtained from variable-temperature Mössbauer spectra were fit to an Orbach process, yielding delta = 130-190 cm(-1) for the energy gap ("zero-field splitting") between the two Kramers doublets of the S = 3/2 multiplet. Density functional theory (DFT) and time-dependent DFT calculations give insight into the electronic structures of the ground and excited states. The oxidation state of the iron and the bond order of the phenylacetylene ligand in complex 1 are analyzed using DFT, showing a substantial back-bonding interaction. Spin-orbit coupling acting in the subspace of quasi-degenerate z2 and yz orbitals provides a consistent description of both the zero-field splitting and magnetic hyperfine parameters that fits the EPR and Mössbauer data for 1. Interestingly, the spin-orbit coupling involves the same two orbitals (z2, yz) as in the analogous three-coordinate Fe(II) compounds, because back-bonding significantly lowers the energy of the xy orbital, making it the lowest doubly occupied d orbital. Despite the different oxidation state and different number of atoms in the first coordination sphere, the electronic structure of LFe(I)(HCCPh) can be interpreted similarly to that of three-coordinate Fe(II) diketiminate complexes, but with a substantial effect of back-bonding. To our knowledge, this is the first detailed Mössbauer and EPR study of a structurally characterized high-spin Fe(I) complex.

Journal Article↗
PubMed2006

Octahedral and tetrahedral coinage metal clusters: is three-dimensional d-orbital aromaticity viable?

The first quantitative evidence for the viability of three-dimensional aromatic clusters involving d-orbitals in pseudo-octahedral coinage metal cages M(6)Li(2) (M = Cu, Ag, Au) as well as in tetrahedral coinage metal cages M'(4)Li(4) (M' = Cu, Ag) was obtained computationally. These cages exhibit many features similar to those of their square planar M(4)Li(2) analogues. The large negative nucleus-independent chemical shifts (NICS) at the cage centers indicate three-dimensional delocalization. This diatropic character arises mostly from d-orbital delocalization combined with substantial contributions from the lowest-valence orbitals. The bonding molecular orbitals of the pseudo-octahedral clusters M(6)Li(2) (M = Cu, Ag, Au) are analogous to those in similar octahedral clusters involving p-orbital delocalization (e.g., B(6)H(6)(2-)). The M'(4)Li(4) clusters exhibit two isomeric forms: metal tetrahedral cages tetracapped by lithium cations on the outside [(M'(4)).4Li] and lithium tetrahedra on the inside capped by coinage metal atoms on each of the four faces [(Li(4)).4M]. Whereas the (M'(4)).4Li type structure is preferred for copper, gold and silver favor the (Li(4)).4M arrangement. NBO-NICS analysis shows that the large diatropic character in (M'(4)).4Li structures is due to the favorable contribution from both s- and d-orbitals, whereas the small NICS values in the center of (Li(4)).4M are due only to the diatropic contributions from the s-orbitals.

Journal Article↗
PubMed2005

Role of Hartree-Fock and Kohn-Sham orbitals in the basis set superposition error for systems linked by hydrogen bonds.

In this work the effect of the basis set superposition error (BSSE) is explored with the counterpoise method on the occupied and unoccupied Hartree-Fock (HF) and Kohn-Sham (KS) orbitals. Three different systems linked by hydrogen bonds, H(2)O...FH, H(2)O...H(2)O, and H(2)O...CFH(3), were studied by using the basis set families cc-pVXZ and aug-cc-pVXZ (X = D, T, Q). The basis sets were tested with the HF method and two approximations for the exchange-correlation functional of KS: a generalized gradient approximation and a hybrid approach. In addition to these methods, the second-order Møller-Plesset perturbation theory, MP2, was considered. It was found that the presence of the "ghost" basis set affects the orbitals in two ways: (1) The occupied KS orbitals are more sensitive to the presence of this "ghost" basis set than the occupied HF orbitals. For this reason the BSSE observed in HF is less than that obtained with KS. (2) The unoccupied HF orbitals are more sensitive to the presence of the "ghost" basis set than their corresponding occupied orbitals. Because the MP2 method uses both, occupied and unoccupied HF orbitals, to compute the total energy, the contribution of the BSSE is bigger than that obtained with HF or KS methodologies.

Journal Article↗
PubMed2000

Origin of the Moon's orbital inclination from resonant disk interactions

The Moon is generally believed to have formed from the debris disk created by a large body colliding with the early Earth. Recent models of this process predict that the orbit of the newly formed Moon should be in, or very near, the Earth's equatorial plane. This prediction, however, is at odds with the known history of the lunar orbit: the orbit is currently expanding, but can be traced back in time to reveal that, when the Moon formed, its orbital inclination relative to the Earth's equator was I approximately = 10 degrees. The cause of this initial inclination has been a mystery for over 30 years, as most dynamical processes (such as those that act to flatten Saturn's rings) will tend to decrease orbital inclinations. Here we show that the Moon's substantial orbital inclination is probably a natural result of its formation from an impact-generated disk. The mechanism involves a gravitational resonance between the Moon and accretion-disk material, which can increase orbital inclinations up to approximately 15 degrees.

Journal Article↗
PubMed2001

Discovery of 12 satellites of Saturn exhibiting orbital clustering.

The giant planets in the Solar System each have two groups of satellites. The regular satellites move along nearly circular orbits in the planet's orbital plane, revolving about it in the same sense as the planet spins. In contrast, the so-called irregular satellites are generally smaller in size and are characterized by large orbits with significant eccentricity, inclination or both. The differences in their characteristics suggest that the regular and irregular satellites formed by different mechanisms: the regular satellites are believed to have formed in an accretion disk around the planet, like a miniature Solar System, whereas the irregulars are generally thought to be captured planetesimals. Here we report the discovery of 12 irregular satellites of Saturn, along with the determinations of their orbits. These orbits, along with the orbits of irregular satellites of Jupiter and Uranus, fall into groups on the basis of their orbital inclinations. We interpret this result as indicating that most of the irregular moons are collisional remnants of larger satellites that were fragmented after capture, rather than being captured independently.

Journal Article↗
PubMed2004

Stellar encounters as the origin of distant Solar System objects in highly eccentric orbits.

The Kuiper belt extends from the orbit of Neptune at 30 au to an abrupt outer edge about 50 au from the Sun. Beyond the edge is a sparse population of objects with large orbital eccentricities. Neptune shapes the dynamics of most Kuiper belt objects, but the recently discovered planet 2003 VB12 (Sedna) has an eccentric orbit with a perihelion distance of 70 au, far beyond Neptune's gravitational influence. Although influences from passing stars could have created the Kuiper belt's outer edge and could have scattered objects into large, eccentric orbits, no model currently explains the properties of Sedna. Here we show that a passing star probably scattered Sedna from the Kuiper belt into its observed orbit. The likelihood that a planet at 60-80 au can be scattered into Sedna's orbit is about 50 per cent; this estimate depends critically on the geometry of the fly-by. Even more interesting is the approximately 10 per cent chance that Sedna was captured from the outer disk of the passing star. Most captures have very high inclination orbits; detection of such objects would confirm the presence of extrasolar planets in our own Solar System.

Journal Article↗
PubMed2005

Origin of the orbital architecture of the giant planets of the Solar System.

Planetary formation theories suggest that the giant planets formed on circular and coplanar orbits. The eccentricities of Jupiter, Saturn and Uranus, however, reach values of 6 per cent, 9 per cent and 8 per cent, respectively. In addition, the inclinations of the orbital planes of Saturn, Uranus and Neptune take maximum values of approximately 2 degrees with respect to the mean orbital plane of Jupiter. Existing models for the excitation of the eccentricity of extrasolar giant planets have not been successfully applied to the Solar System. Here we show that a planetary system with initial quasi-circular, coplanar orbits would have evolved to the current orbital configuration, provided that Jupiter and Saturn crossed their 1:2 orbital resonance. We show that this resonance crossing could have occurred as the giant planets migrated owing to their interaction with a disk of planetesimals. Our model reproduces all the important characteristics of the giant planets' orbits, namely their final semimajor axes, eccentricities and mutual inclinations.

Journal Article↗
PubMed2000

Accessing the Orbital Roof via an Eyelid Incision: The Transpalpebral Approach.

THIS ARTICLE OUTLINES A NEW SURGICAL TECHNIQUE FOR ACCESSING THE ORBITAL ROOF: the transpalpebral approach. It involves making an incision on the double fold of the upper eyelid, then dissecting the orbital septum and the orbicular muscle of the eye. This exposes the orbital roof and enables the surgeon to approach without a coronal incision of the scalp; the direct eyelid incision provides adequate workspace. We use this approach in three orbital roof fractures and one orbital hemangioma. This orbital approach offers a simpler surgical technique, a less invasive one, and still provides excellent exposure of the superior orbital cavity.

Journal Article↗
PubMedDate not supplied

[Orbital myopathy in metastatic malignant paraganglioma: a paraneoplastic syndrome?].

BACKGROUND: Several disease entities of the orbit are known which display an autoimmunological pathogenesis. Among these disease entities the thyroid-related immune orbitopathy and the idiopathic orbital inflammatory syndrome (orbital pseudotumor). The pathogenesis of these diseases is not well understood; however, an autoimmune inflammatory reaction histologically characterized by a chronic inflammatory cell infiltrate has been suggested. One care of orbital pseudotumor presumably of paraneoplastic origin occurring in a patient with a non-Hodgkin's lymphoma has been reported. We report a patient with a metastatic paraganglioma and a proptosis secondary to enlargement of all extraocular muscles. CASE REPORT: A 52-year-old woman presented with a recent decline in visual clarity of her left eye and diplopia. Two years ago, the diagnosis of a hormonally inactive paraganglioma has been made. Ophthalmologic examination displayed a lagophthalmos caused by a right-sided facial paralysis secondary to a cerebral metastasis and a bilateral enlargement of all extraocular muscles. Curative therapy for the paraganglioma was not available. Palliative therapy as well as a high-dose corticosteroid therapy for the orbitopathy was refused by the patient. The patient died 18 months later. DISCUSSION: Our patient developed orbital changes similar to thyroid-related immune orbitopathy; however, there was no dysfunction of the thyroid. We believe that the orbital changes were a paraneoplastic immune reaction caused by the metastatic paraganglioma. We recommend that in patients who do not conform to the prototypical profile of well-known orbital disease entities should undergo further testing to exclude a remote neoplasm.

Autoimmune Diseases↗