N-benzoylimido complexes of palladium. Synthesis, structural characterisation and structure-reactivity relationship

Benzoyl azides, ArC(O)N3, 2, (Ar = phenyl or substituted phenyl), react with [Pd2Cl2(dppm)2], 1, [dppm = bis(diphenylphosphino)methane] with the formation of novel [Pd2Cl2(mu-NC(O)Ar)(dppm)2], 3, benzoylnitrene complexes that were structurally characterised by multinuclear magnetic resonance and IR spectroscopy and, in several instances, by single crystal X-ray diffraction. As shown by crystallographic studies, the C2P4Pd2 rings adopt extended twist-boat conformations with methylene groups bending towards the bridging benzoylimido moieties. X-ray diffraction studies have revealed the chiral nature of the imido complexes, the chiral element being the propeller-like C2P4Pd2 ring. Structural data accumulated on complexes 3 such as short C-N distances (1.32 A), elongated C=O bonds (1.30 A) as well as the outstandingly high barrier to internal rotation around the N-C(O) linkage (88.3 kJ mol(-1)) are in line with extensive ppi-ppi interaction between the bridging nitrogen and the carbonyl carbon atoms. Theoretical calculations indicate an electron shift from the dimer towards the apical nitrogen atom, which, in turn, facilitates the donation of electrons towards the carbonyl moiety. To elucidate the structure-reactivity relationship of benzoyl azides towards 1, crystallographic and solution IR spectroscopic studies were carried out on a series of para-substituted benzoyl azides. The reaction obeys the Hammett equation. The large positive value of the reaction constant indicates that the azides act as electrophiles in the reaction studied. The enhanced reactivity of 2-nitrobenzoyl azide has been attributed to a decreased conjugation of the phenyl and carbonyl moieties in this reagent.     

Description of chemical ordering in amorphous alloys

Partial coordination numbers $\text{Z}{}_{\mathrm{ij}}{}^1$ for a chemically disordered binary amorphous alloy A_XAB_XB are obtained in terms of total coordination numbers Z_i and average coordination numbers 〈Z〉 $\text{Z}{}_{\mathrm{ij}}{}^1\text{=x}{}_{\mathrm{j}}\text{Z}{}_{\mathrm{i}}\text{Z}{}_{\mathrm{j}}\text{/〈Z〉}$. Departures from complete chemical disorder are characterized by a short-range order coefficient with η_AB^max=x_BZ_B/x_AZ_A for X_BZ_B<x_AZ_A and η_AB^max=x_AZ_A/x_BZ_B for x_BZ_B>x_AZ_A.For complete chemical disorder ν_AB⁰ = 0; for complete chemical order, i.e. with chemical preference for AB nearest neighbor pairs, ν_AB⁰ = 1. For departures from chemical disorder associated with clustering, i.e. chemical preference against AB nearest neighbor pairs, ν_AB⁰ < 0. Experimental results for several amorphous alloys are used to demonstrate the usefulness of these results. A more precise calculation of η_AB^max is necessary to compare the degree of ordering in the metal-metalloid and metal-metal alloys.     

Study on the Existence of Hydrogen Bonds in Ammonium Permanganate

The crystal structures of ammonium permanganate and ammonium perchlorate at 293 K were determined and compared. X‐ray and vibrational spectroscopic data confirmed the existence of weak hydrogen bonds in NH₄MnO₄. These hydrogen bonds proved to be slightly stronger than H‐bonds in ammonium perchlorate. Difference between the results of diffuse reflectance and KBr matrix pellet IR spectra of NH₄MnO₄ has been explained.     

EXAFS studies of arsenic in amorphous silicon

Extended X-ray absorption fine structure measurements were used to determine nearest neighbor coordination numbers and distances for As in amorphous Si prepared by 100 keV As ion-implantation of single crystal Si. In the limit of low As concentration, the average As---Si coordination number was 3.2±0.1 and the As-to-Si distance was 2.37±0.02 Å, compared with 4 and 2.41±0.02 Å, respectively, for As in crystalline Si. It is concluded that 20% of the As atoms are fourfold coordinated and 80% are threefold coordinated in the amorphous Si, and that the lack of electrical doping by the fourfold coordinated As results from electron trapping by dangling bonds or other structural defects.     

Age at developmental cortical injury differentially Alters corpus callosum volume in the rat

Background  

Freezing lesions to developing rat cortex induced between postnatal day (P) one and three (P1 – 3) lead to malformations similar to human microgyria, and further correspond to reductions in brain weight and cortical volume. In contrast, comparable lesions on P5 do not produce microgyric malformations, nor the changes in brain weight seen with microgyria. However, injury occurring at all three ages does lead to rapid auditory processing deficits as measured in the juvenile period. Interestingly, these deficits persist into adulthood only in the P1 lesion case [1]. Given prior evidence that early focal cortical lesions induce abnormalities in cortical morphology and connectivity [1–4], we hypothesized that the differential behavioral effects of focal cortical lesions on P1, P3 or P5 may be associated with underlying neuroanatomical changes that are sensitive to timing of injury. Clinical studies indicate that humans with perinatal brain injury often show regional reductions in corpus callosum size and abnormal symmetry, which frequently correspond to learning impairments [5–7]. Therefore, in the current study the brains of P1, 3 or 5 lesion rats, previously evaluated for brain weight, and cortical volume changes and auditory processing impairments (P21-90), were further analyzed for changes in corpus callosum volume.     

A rapid,chromatography-free route to substituted acridine–isoalloxazine conjugates under microwave irradiation

Microwave irradiation was applied to a sequence of condensation reactions from readily available 9-chloroacridines to provide a range of novel acridine–isoalloxazine conjugates. The combination of these two moieties, both of biological interest, was achieved by a chromatography-free route.     

Quantification of insulin-like growth factor-1 in dried blood spots for detection of growth hormone abuse in sport

There is significant evidence that athletes are using recombinant human growth hormone (rhGH) to enhance performance, and its use is banned by the World Anti-Doping Agency and professional sports leagues. Insulin-like growth factor-1 (IGF-1) is the primary mediator of growth hormone action and is used as a biomarker for the detection of rhGH abuse. The current biomarker-based method requires collection and expedited shipment of venous blood which is costly and may decrease the number of tests performed. Measurement of GH biomarkers in dried blood spots (DBS) would considerably simplify sample collection and shipping methods to allow testing of a greater number of samples regardless of location. A method was developed to quantify intact IGF-1 protein in DBS by liquid chromatography–tandem mass spectrometry. A step-wise acid–acetonitrile extraction was optimized to achieve a sensitive assay with a lower limit of quantification of 50 ng/mL. IGF-1 remained stable at room temperature for up to 8 days, which would allow shipment of DBS cards at ambient temperature. In a comparison between plasma concentrations of IGF-1 and concentrations measured from venous and finger prick DBS, there was good correlation and agreement, r ² of 0.8551 and accuracy of 86–113 % for venous DBS and r ² of 0.9586 and accuracy of 89–122 % for finger prick DBS. The method is intended for use as a rapid screening method for IGF-1 to be used in the biomarker method of rhGH abuse detection.