Simon Svane

Charge inversion of phospholipids by dimetal complexes for positive ion-mode electrospray ionization mass spectrometry analysis.

Phospholipids are vital constituents of living cells, as they are involved in signaling and membrane formation. Mass spectrometry analysis of many phospholipids is preferentially performed in the negative ion-mode because of their acidic nature. Here we have studied the potential of a digallium and dizinc complex to charge-invert a range of different types of phospholipids and measured their ion yield and fragmentation behavior in positive ion-mode tandem mass spectrometry. The dimetal complexes bind specifically the phosphate groups of phospholipids and add an excess of up to three positive charges per phosphate group. Three different phosphoinositide phosphates (mono-, di-, and triphosphorylated inositides), a phosphatidic acid, a phosphatidylcholine, a phosphatidylethanolamine, and a phosphatidylglycerol were investigated. The intensities obtained in positive ion-mode of phosphoinositide phosphates and phosphatidic acid bound to {LGa2}(5+) were between 2.5- and 116-fold higher than that of the unmodified lipids in the negative ion-mode. Native phosphoinositide ions yielded upon CID in the negative ion-mode predominantly product ions due to losses of H3PO4, PO3(-) and H2O. In comparison, CID spectra of {LGa2}(5+)-bound phosphoinositides generally resulted in fragment ions corresponding to loss of the full diglyceride chain as well as the remaining headgroup bound to {LGa2}(5+) as the most abundant peaks. A number of signature fragment ions of moderate abundance were observed that allowed for distinction between the three regioisomers of 1,2-di(9Z-octadecenoyl)-sn-glycero-3-[phosphoinositol-x,y-bisphosphate] (PI(3,4)P2, PI(3,5)P2, PI(4,5)P2).

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

Ammonia emissions from the agricultural sector give rise to numerous environmental and societal concerns and represent an economic challenge in crop farming, causing a loss of fertilizer nitrogen. Ammonia emissions from agriculture originate from manure slurry (livestock housing, storage, and fertilization of fields) as well as urea-based mineral fertilizers. Consequently, political attention has been given to ammonia volatilization, and regulations of ammonia emissions have been implemented in several countries. The molecular cause of the emission is the enzyme urease, which catalyzes the hydrolysis of urea to ammonia and carbonic acid. Urease is present in many different organisms, encompassing bacteria, fungi, and plants. In agriculture, microorganisms found in animal fecal matter and soil are responsible for urea hydrolysis. One strategy to reduce ammonia emissions is the application of urease inhibitors as additives to urea-based synthetic fertilizers and manure slurry to block the formation of ammonia. However, treatment of the manure slurry with urease inhibitors is associated with increased livestock production costs and has not yet been commercialized. Thus, development of novel, environmentally friendly and cost-effective technologies for ammonia emission mitigation is important. This mini-review describes the challenges associated with the volatilization of ammonia in agriculture and provides an overview of the molecular processes of urea hydrolysis and ammonia emissions. Different technologies and strategies to reduce ammonia emissions are described with a special focus on the use of urease inhibitors. The mechanisms of action and efficiency of the most important urease inhibitors in relation to agriculture will be briefly discussed.

Dimetallic functionalities in liposome bilayers

A dicopper(II) complex can be covalently linked to palmitate/palmitoyl-oleoyl-phosphatidylcholine (PA/POPC) liposomes using the following one-pot strategy: preformed [Cu2(bpbp)(PA)](ClO4)2 (bpbp− = 2,6-bis((N,N′-bis(2-picolyl)amino)methyl)-4-tertbutylphenolato) was incorporated into POPC liposomes with a loading of up to 10 mol%. Despite its shape and charge, the decoration of PA/POPC liposomes with {Cu2(bpbp)}3+ did not disrupt the liposome structure; however, the mean liposome diameter increased from about 130 nm (0 mol% dicopper complex) to about 150 nm (10 mol% dicopper complex). Single-crystal X-ray structures furnish ‘snapshots’ of the pH-dependent solution state derivatives of {Cu2(bpbp)}3+, and model the structure of the [Cu2(bpbp)(PA)]2+ head group at the surface of the liposomes. An impressive plasticity in the intramolecular non-bonded Cu….Cu distance for these ions, ranging from 3 to 4 Å, in [Cu2(bpbp)OH]2+, [Cu2(bpbp)(OAc)(H2O)]2+ and [Cu2(bpbp)(H2O)2]3+ allows for their utility as labile reagents in water. Remarkably, the flexible dicopper site is selective for a single carboxylate ligand, so that [Cu2(bpbp)(PA)]2+ is favoured even in the presence of other chemically similar oxoanions, such as CO32 − , HCO3− , NO3− , ClO4− , ReO4− and CF3SO3− .