N-Heterocyclic Carbene Stabilized Digermanium(0) Sidiropoulos, Anastas; Jones, Cameron; Stasch, Andreas ...
Angewandte Chemie (International ed.),
December 14, 2009, Volume:
48, Issue:
51
Journal Article
Peer reviewed
Zero Ge! Reductions of an N‐heterocyclic carbene (NHC) adduct of GeCl2 with magnesium(I) dimers afford a dimeric compound (see picture), which structural and theoretical studies show to contain a ...singlet digermanium(0) fragment :GeGe: datively coordinated by two NHC ligands.
Quantum‐chemical calculations using DFT and ab initio methods have been carried out for fourteen divalent carbon(0) compounds (carbones), in which the bonding situation at the two‐coordinate carbon ...atom can be described in terms of donor–acceptor interactions L→C←L. The charge‐ and energy‐decomposition analysis of the electronic structure of compounds 1–10 reveals divalent carbon(0) character in different degrees for all molecules. Carbone‐type bonding L→C←L is particularly strong for the carbodicarbenes 1 and 2, for the “bent allenes” 3 a, 3 b, 4 a, and 4 b, and for the carbocarbenephosphoranes 7 a, 7 b, and 7 c. The last‐named molecules have very large first and large second proton affinities. They also bind two BH3 ligands with very high bond energies, which are large enough that the bis‐adducts should be isolable in a condensed phase. The second proton affinities of the complexes 5, 6, and 8–10 bearing CO or N2 as ligand are significantly lower than those of the other molecules. However, they give stable complexes with two BH3 ligands and thus are twofold Lewis bases. The calculated data thus identify 1–10 as carbones L→C←L in which the carbon atom has two electron pairs. The chemistry of carbones is different from that of carbenes because divalent carbon(0) compounds CL2 are π donors and thus may serve as double Lewis bases, while divalent carbon(II) compounds are π acceptors. The theoretical results point toward new directions for experimental research in the field of low‐coordinate carbon compounds.
Carbene or carbone? Quantum‐chemical studies on dicoordinated carbon compounds with various mono‐ and bidentate ligands (see picture) show that there is a gliding scale between the bonding situation of carbenes RCR, in which the carbon atom has one electron pair, and carbones L→C←L, in which the carbon atom has two electron pairs. Divalent carbon(0) compounds (carbones) CL2 are π donors, whereas divalent carbon(II) compounds (carbenes) CR2 are π acceptors.
Quantum chemical calculations using DFT (BP86, M05‐2X) and ab initio methods (CCSD(T), SCS‐MP2) have been carried out on the borylene complexes (BH)L2 and nitrogen cation complexes (N+)L2 with the ...ligands L=CO, N2, PPh3, NHCMe, CAAC, and CAACmodel. The results are compared with those obtained for the isoelectronic carbones CL2. The geometries and bond dissociation energies of the ligands, the proton affinities, and adducts with the Lewis acids BH3 and AuCl were calculated. The nature of the bonding has been analyzed with charge and energy partitioning methods. The calculated borylene complexes (BH)L2 have trigonal planar coordinated boron atoms which possess rather short BL bonds. The calculated bond dissociation energies (BDEs) of the ligands for complexes where L is a carbene (NHC or CAAC) are very large (De=141.6–177.3 kcal mol−1) which suggest that such species might become isolated in a condensed phase. The borylene complexes (BH)(PPh3)2 and (BH)(CO)2 have intermediate bond strengths (De=90.1 and 92.6 kcal mol−1). Substituted homologues with bulky groups at boron which protect the boron atom from electrophilic attack might also be stable enough to become isolated. The BDE of (BH)(N2)2 is much smaller (De=31.9 kcal mol−1), but could become observable in a low‐temperature matrix. The proton affinities of the borylene complexes are very large, particularly for the bulky adducts with L=PPh3, NHCMe, CAACmodel and CAAC and thus, they are superbases. All (BH)L2 molecules bind strongly AuCl either η1 (L=N2, PPh3, NHCMe, CAAC) or η2 (L=CO, CAACmodel). The BDEs of H3B(BH)L2 adducts which possess a hitherto unknown boron→boron donor–acceptor bond are smaller than for the AuCl complexes. The strongest bonded BH3 adduct that might be isolable is (BH)(PPh3)2BH3 (De=36.2 kcal mol−1). The analysis of the bonding situation reveals that (BH)L2 bonding comes mainly from the orbital interactions which has three major contributions, that is, the donation from the symmetric (σ) and antisymmetric (π||) combination of the ligand lone‐pair orbitals into the vacant MOs of BH L→(BH)←L and the L←(BH)→L π backdonation from the boron lone‐pair orbital. The nitrogen cation complexes (N+)L2 have strongly bent LNL geometries, in which the calculated bending angle varies between 113.9° (L=N2) and 146.9° (L=CAAC). The BDEs for (N+)L2 are much larger than those of the borylene complexes. The carbene ligands NHC and CAAC but also the phosphane ligands PPh3 bind very strongly between De=358.4 kcal mol−1 (L=PPh3) and De=412.5 kcal mol−1 (L=CAACmodel). The proton affinities (PA) of (N+)L2 are much smaller and they bind AuCl and BH3 less strongly compared with (BH)L2. However, the PAs (N+)L2 for complexes with bulky ligands L are still between 139.9 kcal mol−1 (L=CAACmodel) and 168.5 kcal mol−1 (L=CAAC). The analysis of the (N+)L2 bonding situation reveals that the binding interactions come mainly from the L→(N+)←L donation while L←(N+)→L π backdonation is rather weak.
Quantum chemical calculations suggest that the bonding model for carbones CL2 in terms of donor–acceptor interactions L→C←L is also valid for the isoelectronic systems (BH)L2 and (N+)L2. The nature of the donor–acceptor bonds and the theoretically predicted equilibrium geometries and bond dissociation energies of (BH)L2, (N+)L2 and CL2 with L=CO, N2, PPh3 and the carbene ligands NHCMe, CAACmodel, and CAAC are discussed (see figure). NHC=N‐heterocyclic carbene; CAAC=cyclic alkyl amino carbene.
On 17 May 1861, James Clerk Maxwell delivered a lecture at the Royal Society where he demonstrated, using a lantern slide projection, his theory for colour perception in the human eye via the ...additive colour process known today as RGB. Three images from three separate lantern slide projectors were projected onto a surface. The same colour filters with which the object had been photographed where then placed in front of each projection lens, carefully realigned, and what has been called “the first colour photograph” was supposed to have been created. It was a series of happy accidents, during capture and exposure, and a misinterpretation of the results—mostly long after the event itself—that has invented this commonly referred to fictional “First Ever” title. In the following retelling of the historical details in their chronological order and through a series of experiments with historically correct emulsions, we will clearly outline the errors and where they occurred.
The Woodburytype is a 19th century photomechanical technique capable of producing high-quality continuous-tone prints. It uses pigment dispersed in gelatin to produce a 2.5D print, in which the ...effect of varying tone is produced by a variation in the print height. We propose a method of constructing full colour prints in this manner, using a CMY colour model. This involves the layering of multiple translucent pigmented gelatin films and tracking how the perceived colour of these stacks changes with varying height. A set of CMY inks is constructed, taking into account the optical properties of both the pigment and gelatin, and a method of translating images into these prints is detailed.
Introduction
Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a curative approach for multiple hematologic diseases. The success of alloHSCT is evaluated by analyzing the proportion ...of living donor cells in blood and bone marrow samples of the recipient (chimerism analysis). To monitor the engrafted cells, donor's individual genetic markers are analyzed in peripheral blood and bone marrow samples, usually by using short tandem repeat (STR) analysis. An alternative method to measure chimerism is based on insertion and deletion markers (InDels) analyzed by digital droplet PCR (ddPCR); however, this approach is rarely evaluated in clinical practice.
Methods
In this study, we examined the usefulness of ddPCR‐based chimerism analysis against the standard STR analysis in samples around day+30 after alloHSCT in clinical practice using peripheral blood and bone marrow samples.
Results
The median absolute difference between ddPCR and STR analysis was 0.55% points for bone marrow chimerisms and 0.25% points for peripheral blood chimerisms, respectively, including variation in the range of maximum 2% for both methods. The results of every single sample gave the same clinical message.
Conclusion
According to our data, chimerism analysis by ddPCR has an excellent correlation with STR‐based analyses. Due to its fast and easy applicability, the ddPCR technique is suitable for chimerism monitoring in clinical practice.
This article reviews the empirical evidence for psychodynamic therapy for specific mental disorders in adults. According to the results presented here, there is evidence from randomized controlled ...trials (RCTs) that psychodynamic therapy is efficacious in common mental disorders, including depressive disorders, anxiety disorders, somatoform disorders, personality disorders, eating disorders, complicated grief, posttraumatic stress disorder (PTSD), and substance-related disorders. These results clearly contradict assertions repeatedly made by representatives of other psychotherapeutic approaches claiming that psychodynamic psychotherapy is not empirically supported. However, further research is required, both on outcome and processes of psychodynamic psychotherapy. There is a need, for example, for RCTs of psychodynamic psychotherapy of PTSD. Furthermore, research on long-term psychotherapy for specific mental disorders is required.
Unlike regular pigments based on selective light absorption, the so-called “effect pigments″ are based on the phenomena of structural color, or selective reflectance. Structural color has appealing ...aesthetic qualities, such as angle-dependent hue, and is able to produce lightfast colors. When used as a pigment, however, the gamut of the print is more limited, the color is difficult to measure, and therefore color management and preprint process become challenging. The aim of this paper is to compare the behavior of effect pigments in the processes of lithographic and screen printing with standard pigments used in so-called process inks, and to analyze their optical properties when used on their own or in combination with absorption pigments. An image of amber beads was printed as screen prints and lithographs. Three sets of inks were used: Set one: Standard process inks in the colors cyan, magenta, yellow and black (CMYK); set two: RGB inks formulated with Merck Spectraval™ pearlescent pigments which allow additive red, green, blue printing on a black substrate; and set three: golden inks formulated with pigments from the Merck Iriodin™ and Pyrisma™ effect pigment range. The image was printed on white and black paper. The optical appearance was assessed visually, and spectra and color coordinates were measured.
Two of the most significant cases of extant 16th-century featherwork from Mexico are the so-called Moctezuma’s headdress and the Ahuizotl shield. While the feathers used in these artworks exhibit ...lightfast colors, their assembly comprises mainly organic materials, which makes them extremely fragile. Printed media, including books, catalogs, educational materials, and fine copies, offer an accessible means for audiences to document and disseminate visual aspects of delicate cultural artifacts without risking their integrity. Nevertheless, the singular brightness and iridescent colors of feathers are difficult to communicate to the viewer in printed reproductions when traditional pigments are used. This research explores the use of effect pigments (multilayered reflective structures) and improved halftoning techniques for additive printing, with the objective of enhancing the reproduction of featherwork by capturing its changing color and improving texture representation via a screen printing process. The reproduced images of featherwork exhibit significant perceptual resemblances to the originals, primarily owing to the shared presence of structural coloration. We applied structure-aware halftoning to better represent the textural qualities of feathers without compromising the performance of effect pigments in the screen printing method. Our prints show angle-dependent color, although their gamut is reduced. The novelty of this work lies in the refinement of techniques for printing full-color images by additive printing, which can enhance the 2D representation of the appearance of culturally significant artifacts.
PDF
