Multinuclear (P, Pt) magnetic resonance and electrospray mass spectrometric studies of the reactions between platinum bis(dithiolates) and two potentially tetradentate phosphine ligands

The reactions of platinum(II) bis(dithiolates) Pt(S---S)₂ ((S---S)=S₂P(OEt)₂ (dtp), S₂COⁿPr (xan), S₂CNEt₂ (dtc)) with two potentially tetradentate phosphine ligands have been investigated by multinuclear magnetic resonance spectroscopy and electrospray mass spectrometry (ESMS). The phosphines used were P(CH₂CH₂PPh₂)₃ (P₃P′) and Ph₂PCH₂CH₂P(Ph)CH₂CH₂P(Ph)CH₂CH₂PPh₂ (P₂P′₂). ³¹P and ¹⁹⁵Pt NMR spectroscopies show that P₃P′ reacts in dichloromethane solution with Pt(dtp)₂ and Pt(xan)₂ to give five-coordinate [(η⁴-P₃P′)Pt(η¹-S---S)]⁺ and with Pt(dtc)₂ to give a temperature dependent mixture of [(η⁴-P₃P′)Pt(η¹-dtc)]⁺ and [(η³-P₃P′)Pt(η²-dtc)]⁺. All these formulations were confirmed by observation of the intact ions in the ES mass spectra directly from the solutions. [(η⁴-P₃P′)Pt(η¹-xan)]⁺ slowly reacts with the free xan ion to give the dithiocarbonate complex (η³-P₃P′)Pt(η²-S₂CO). The pendant phosphine in [(η³-P₃P′)Pt(η²-dtc)]⁺ undergoes various chemical reactions such as methylation and reaction with sulfur, and the cation behaves as a monodentate phosphine towards Pt(dtp)₂ to give [(η¹-dtp)(η²-dtp)Pt(η¹-μ²-η³-P₃P′)Pt(η²-dtc)]⁺ which was fully characterised by multi-NMR spectroscopy and confirmed by observation of the intact ion by ESMS. P₂P′₂ reacts with Pt(dtp)₂ to give [(P₂P′₂)Pt]²⁺, but with Pt(xan)₂ and Pt(dtc)₂ the products are [(η⁴-P₂P′₂)Pt(η¹-S---S)]⁺, but the xanthate complex slowly de-alkylates to give (η³-P₂P′₂)Pt(η²-S₂CO). The identities of the cationic P₂P′₂ species in solution were confirmed by direct observation of the intact ion by ESMS.     

Blockade of hyperbaric oxygen induced seizures by excitatory amino acid antagonists

The effectiveness of several excitatory amino acid antagonists to delay or block seizures induced by oxygen at high pressure was examined in mice. Of the antagonists tested, namely, L-proline, DL-alpha-aminoadipate, DL-2-amino-5-phosphonovalerate, and L-glutamic acid diethyl ester, DL-2-amino-5-phosphonovalerate was the most effective in delaying or preventing seizures. L-Glutamic acid diethylester was also effective but at significantly higher doses, which were also associated with marked sedation.     

Chemical synthesis and characterisation of the complement C5 inhibitory peptide zilucoplan

The complement component C5 inhibitory peptide zilucoplan is currently in phase III clinical trials for myasthenia gravis (MG). Despite being at an advanced stage of clinical development, there have been no published reports in the literature detailing its chemical synthesis. In this work, we describe an approach for the chemical synthesis of zilucoplan and validate that the synthesised compound blocks LPS-induced C5a production from human blood.

     

REVIEWS

Avian remains from the Early Miocene (～17 Ma) Moghra Formation of Egypt include new records of ‘waterbirds’ (storks, herons, pelicans and allies) and a ratite. Only a single avian fossil has been previously reported from Wadi Moghra and, thus, additional knowledge of the avifauna complements previously documented faunal and floral assemblages and provides a more complete picture of the Early Miocene ecosystem of that locality. The presence of ciconiiforms and pelecaniforms is consistent with the relatively abundant records of ‘waterbirds’ from other African freshwater fossil localities. Moreover, avian fossils from Wadi Moghra provide new insight into the avifaunal composition of the Early Miocene in Africa, a period that is relatively underrepresented in the avian fossil record of that continent.     

ALLELOPATHIC MECHANISMS OF VELVETLEAF (ABUTILON THEOPHRASTI MEDIC., MALVACEAE) ON SOYBEAN

Sampling in a soybean field established that presence of velvetleaf (A. theophrasti) weeds interfered with soybean production. Number of soybean pods and number of pods/stem were significantly lower in transect segments adjacent to velvetleaf plants. In bioassays for phytotoxicity of velvetleaf, several dilutions of aqueous extracts from fresh field-collected leaves depressed germination of radish seeds and inhibited growth of soybean seedlings. Seed germination bioassays from eluates of chromatograms developed in one dimension showed that two of three bands containing phenolic compounds were inhibitory to radish seed germination. Soybeans inhibited by aqueous velvetleaf extracts had increased diffusive resistance, suggesting partial stomatal closure. Inhibited plants also gave evidence of water stress, with leaf water potentials often as low as –20 bars and reduced water content, when compared with controls. Quantification of chlorophyll on a leaf area basis showed that chlorophyll of inhibited plants was below controls. These data demonstrate the allelopathic potential of velvetleaf and suggest that interference with water balance and chlorophyll content may be two mechanisms of inhibitory action of toxins present in the leaves of velvetleaf.     

Topographical mapping of sites of enhanced HRP permeability in the normal rabbit aorta.

The spatial distribution of sites of enhanced permeability to the macromolecule horseradish peroxidase (HRP) in the normal rabbit aorta after one min circulation was studied using image analysis. These sites, referred to as "HRP spots," exhibit a nonuniform distribution that is qualitatively similar in all rabbits studied. The density of HRP spots is highest in the aortic arch, decreases distally, reaches a minimum in the lower descending thoracic aorta, and then increases again in the abdominal aorta. The region of highest spot density follows a clockwise helical pattern in the aortic arch and outside the arch occurs in streaks largely oriented in the bulk flow direction. The streaks in the abdominal aorta localize along the anatomical right lateral wall and occasionally along the left lateral wall proximal to the celiac artery and along the ventral wall between the celiac and superior mesenteric arteries. The density of spots is high in the immediate vicinity of aortic ostia with the most elevated density being distal to ostia in most cases. At a short distance from the ostium edge of the celiac and superior mesenteric branches the proximal density is comparably high, and no preferred spot orientation is observed around the brachiocephalic vessel. These results are consistent with an influence of localizing factors such as detailed hemodynamic phenomena and/or arterial wall structural and/or functional variations.     

The development of an implantable electrochemical glucose sensor: response to glucose in bovine serum ultrafiltrate.

A glucose sensor based on organic oxidation reactions at a platinum electrode is being developed as the key component for an implantable artificial beta cell for diabetic patients. Sensitivity of a membrane-covered platinum electrode to changing glucose concentration in bovine serum ultrafiltrate has been demonstrated, with current response as high as 60 microamperes per 100 mg/dl change in glucose concentration. Reproducibility of measurements probably will depend on satisfactory mechanical assembly of the membrane-electrode combination. An approach to selectivity based on multiple current measurements is suggested.