Bulky 4-phosphacyclohexanones: diastereoselective complexations, orthometallations and unprecedented [3.1.1]metallabicycles

The 4-phosphacyclohexanones, 2,2,6,6-tetramethyl-1-phenyl-4-phosphorinanone (La), 1,2,6-triphenyl-4-phosphorinanone ((Ph)Lb), 1-cyclohexyl-2,6-diphenyl-4-phosphorinanone ((Cy)Lb) and 1-tert-butyl-2,6-diphenyl-4-phosphorinanone ((Bu)Lb) have been made by modifications of literature methods. Phosphines (R)Lb are each formed as mixtures of meso- and rac-diastereoisomers. Isomerically pure rac-(Ph)Lb, rac-(Cy)Lb and meso-(Bu)Lb can be isolated by recrystallisation from MeCN. Heating mixtures of isomers of (R)Lb with TsOH leads to isomerisations to give predominantly the meso-(R)Lb. The complex trans-[PdCl2(La)2] (1) is readily made from [PdCl2(NCPh)2] but the analogous platinum complex 2 has not been detected and instead, cyclometallation at the 3-position (alpha to the ketone) in the phosphacycle occurs to give trans-[PtCl(La)(La-3H)] (3) (where La-3H = La deprotonated at the 3-position) featuring a [3.1.1]metallabicycle as confirmed by X-ray crystallography. The analogous palladabicycle 4 has been detected upon treatment of 1 with Et3N in refluxing toluene. The type of complex formed by (R)Lb depends on which diastereoisomer (meso or rac) is involved. rac-(Ph)Lb (a mixture of R,R- and S,S-enantiomers, labelled alpha and beta) forms trans-[MCl2(rac-(Ph)Lb)2], M = Pd (5) or Pt (6), as mixtures of diastereoisomers (alphaalpha/betabeta and alphabeta forms). The structure of alphaalpha-6 has been determined by X-ray crystallography. Ligand competition experiments monitored by 31P NMR showed that Pd(II) and Pt(II) have a significant preference to bind rac-(Ph)Lb over meso-(Ph)Lb. meso-(Bu)Lb reacts with [PtCl2(NCBu(t))2] under ambient conditions to give the binuclear complex [Pt2Cl2(meso-(Bu)Lb-2'H)2] (7) where orthometallation has occurred on one of the exocyclic phenyl substituents as confirmed by X-ray crystallography. rac-(Bu)Lb reacts with [PtCl2(NCBu(t))2] to give a mononuclear cyclometallated species assigned the structure trans-[PtCl(rac-(Bu)Lb-2'H)((Bu)Lb)] (8) on the basis of its 31P NMR spectrum. rac-(Cy)Lb reacts with [PtCl2(NCBu(t))2] in refluxing toluene to give trans-[PtCl2(rac-(Cy)Lb)2] (9) and the crystal structure of alphabeta-9 has been determined.     

Identification of a set of genes showing regionally enriched expression in the mouse brain

Background

We have recorded responses from single neurons in murine visual cortex to determine the effectiveness of the input from the two murine cone photoreceptor mechanisms and whether there is any unique selectivity for cone inputs at this higher region of the visual system that would support the possibility of colour vision in mice. Each eye was stimulated by diffuse light, either 370 (strong stimulus for the ultra-violet (UV) cone opsin) or 505 nm (exclusively stimulating the middle wavelength sensitive (M) cone opsin), obtained from light emitting diodes (LEDs) in the presence of a strong adapting light that suppressed the responses of rods.

Results

Single cells responded to these diffuse stimuli in all areas of striate cortex. Two types of responsive cells were encountered. One type (135/323 – 42%) had little to no spontaneous activity and responded at either the on and/or the off phase of the light stimulus with a few impulses often of relatively large amplitude. A second type (166/323 – 51%) had spontaneous activity and responded tonically to light stimuli with impulses often of small amplitude. Most of the cells responded similarly to both spectral stimuli. A few (18/323 – 6%) responded strongly or exclusively to one or the other spectral stimulus and rarely in a spectrally opponent manner.

Conclusion

Most cells in murine striate cortex receive excitatory inputs from both UV- and M-cones. A small fraction shows either strong selectivity for one or the other cone mechanism and occasionally cone opponent responses. Cells that could underlie chromatic contrast detection are present but extremely rare in murine striate cortex.     

Optimised Desorption Electrospray Ionisation Mass Spectrometry Imaging (DESI-MSI) for the Analysis of Proteins/Peptides Directly from Tissue Sections on a Travelling Wave Ion Mobility Q-ToF

Desorption electrospray ionisation mass spectrometry imaging (DESI-MSI) is typically known for the ionisation of small molecules such as lipids and metabolites, in singly charged form. Here we present a method that allows the direct detection of proteins and peptides in multiply charged forms directly from tissue sections by DESI. Utilising a heated mass spectrometer inlet capillary, combined with ion mobility separation (IMS), the conditions with regard to solvent composition, nebulising gas flow, and solvent flow rate have been explored and optimised. Without the use of ion mobility separation prior to mass spectrometry analysis, only the most abundant charge series were observed. In addition to the dominant haemoglobin subunit(s) related trend line in the m/z vs drift time (DT) 2D plot, trend lines were found relating to background solvent peaks, residual lipids and, more importantly, small proteins/large peptides of lower abundance. These small proteins/peptides were observed with charge states from 1+ to 12+, the majority of which could only be resolved from the background when using IMS. By extracting charge series from the 2D m/z vs DT plot, a number of proteins could be tentatively assigned by accurate mass. Tissue images were acquired with a pixel size of 150 μm showing a marked improvement in protein image resolution compared to other liquid-based ambient imaging techniques such as liquid extraction surface analysis (LESA) and continuous-flow liquid microjunction surface sampling probe (LMJ-SSP) imaging.

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Graphical Abstract ?

     

A simple entry into nido-C2B10 clusters: HCl promoted cleavage of the C-C bond in ortho-carboranyl diphosphines

Treatment of the diphosphines ortho-B10H10C(P(t)Bu2)C(PR2) (R = Et, Cy, Ph) with HCl gives the zwitterionic, nido-12-vertex species B10H10C(PH(t)Bu2)C(PClR2); these reactions are reversed by the addition of NEt3.     

Evaluating the utility of ion mobility separation in combination with high-pressure liquid chromatography/mass spectrometry to facilitate detection of trace impurities in formulated drug products

Many formulated products contain complex polymeric excipients such as polyethylene glycols (PEGs). Such excipients can be readily ionized by electrospray and may be present at very high concentrations, thus making it very difficult to identify trace level impurities such as degradants in samples, even if hyphenated techniques such as liquid chromatography/mass spectrometry (LC/MS) are used. Ion mobility (IM) spectrometry is a very rapid gas-phase separation technique and offers additional separation capability within the LC timeframe. This work investigates the use of an IM separator in combination with high-pressure liquid chromatography (HPLC) and MS, to improve the separation of drug-related materials from excipients, thus aiding the identification of trace-level impurities in an anti-HIV medication, Combivir.     

A Mössbauer effect study of the interstitial hydrides and nitride of Nd2Fe17

The Mössbauer effect spectra of Nd₂Fe₁₇H₃, Nd₂Fe₁₇H₅, and Nd₂Fe₁₇N₃ have been measured at several temperatures between 85 and 295 K and fitted with a model which is similar to that used for the analysis of the Mössbauer effect spectra of Nd₂Fe₁₇ and Nd₂Fe₁₇N_2.6. The weighted average isomer shift increases in going from Nd₂Fe₁₇ to its hydrides and nitride, an increase which results mainly from the lattice expansion. The changes in the individual isomer shifts upon hydrogenation may be understood in terms of the expansion of the Wigner-Seitz cell volume and the presence of hydrogen or nitrogen near neighbors at a specific site. The 295 K weighted average hyperfine field increases from 157 kOe in Nd₂Fe₁₇ to 243 kOe in Nd₂Fe₁₇H₃, 280 kOe in Nd₂Fe₁₇H₅, and 318 kOe in Nd₂Fe₁₇N₃, a sequence determined by the Curie temperatures. In contrast, the weighted average hyperfine field at 85 K and the saturation magnetization at 5 K for Nd₂Fe₁₇H₃ are lower than those of Nd₂Fe₁₇, presumably because of thec-axis lattice contraction which occurs upon hydrogenation of this compound. The main difference between the effect of hydrogenation and nitrogenation resides in the substantial increase observed for the 9d and 18h hyperfine fields upon nitrogenation.     

连续波锁模Pr3+:YLF激光器

本文报导了采用氩离子激光器来泵浦Pr³⁺:YLF晶体,应用声光调制器实现了主动锁模;同时应用振动─高反射平面镜也实现了被动锁模,两种锁模均得到了ps光脉冲.据作者了解这是这种晶体材料的第一次锁模运转.     

Solution of sparse quasi-square rectangular systems by Gaussian elimination

We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of A^T. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included.