On molecular chirality within naturally occurring secondary organic aerosol particles from the central Amazon Basin

In this perspectives article, we reflect upon the existence of chirality in atmospheric aerosol particles. We then show that organic particles collected at a field site in the central Amazon Basin under pristine background conditions during the wet and dry seasons consist of chiral secondary organic material. We show how the chiral response from the aerosol particles can be imaged directly without the need for sample dissolution, solvent extraction, or sample preconcentration. By comparing the chiral-response images with optical images, we show that chiral responses always originate from particles on the filter, but not all aerosol particles produce chiral signals. The intensity of the chiral signal produced by the size resolved particles strongly indicates the presence of chiral secondary organic material in the particle. Finally, we discuss the implications of our findings on chiral atmospheric aerosol particles in terms of climate-related properties and source apportionment.     

Organic constituents on the surfaces of aerosol particles from southern Finland, amazonia, and california studied by vibrational sum frequency generation

This article summarizes and compares the analysis of the surfaces of natural aerosol particles from three different forest environments by vibrational sum frequency generation. The experiments were carried out directly on filter and impactor substrates, without the need for sample preconcentration, manipulation, or destruction. We discuss the important first steps leading to secondary organic aerosol (SOA) particle nucleation and growth from terpene oxidation by showing that, as viewed by coherent vibrational spectroscopy, the chemical composition of the surface region of aerosol particles having sizes of 1 μm and lower appears to be close to size-invariant. We also discuss the concept of molecular chirality as a chemical marker that could be useful for quantifying how chemical constituents in the SOA gas phase and the SOA particle phase are related in time. Finally, we describe how the combination of multiple disciplines, such as aerosol science, advanced vibrational spectroscopy, meteorology, and chemistry can be highly informative when studying particles collected during atmospheric chemistry field campaigns, such as those carried out during HUMPPA-COPEC-2010, AMAZE-08, or BEARPEX-2009, and when they are compared to results from synthetic model systems such as particles from the Harvard Environmental Chamber (HEC). Discussions regarding the future of SOA chemical analysis approaches are given in the context of providing a path toward detailed spectroscopic assignments of SOA particle precursors and constituents and to fast-forward, in terms of mechanistic studies, through the SOA particle formation process.     

Amenability,Kazhdan’s property and percolation for trees,groups and equivalence relations

We prove amenability for a broad class of equivalence relations which have trees associated to the equivalence classes. The proof makes crucial use of percolation on trees. We also discuss related concepts and results, including amenability of automorphism groups. A second main result is that no discrete subgroup of the automorphism group of a tree is isomorphic to the fundamental group of any closed manifoldM admitting a nontrivial connection-preserving, volume-preserving action of a noncompact, simply connected, almost simple Lie group having Kazhdan’s property (T). The technique of proof also shows that M does not admit a hyperbolic structure. The research of both authors was supported by NSF Postdoctoral Fellowships. The second author was also supported by an Alfred P. Sloan Foundation Research Fellowship.     

Betti numbers of congruence groups

It is shown that, for certain congruence families of Galois coverings of a manifold, the individual Betti numbers are polynomial periodic functions of the level. Similar results are proved for the dimensions of other spaces of automorphic forms.     

Cu(I)(bpp)]BF4: the first extended coordination network prepared solvothermally in an ionic liquid solvent

Use of an ionic liquid [bmim][BF4] (bmim = 1-butyl-3-methylimidazolium) as solvent has resulted in the first extended coordination structure, the two-dimensional network [Cu(bpp)]BF4 [bpp = 1,3-bis(4-pyridyl)propane], produced via a solvothermal route.     

Induction of Geometric Actions

We prove that, in some situations, an induced action from a normal subgroup preserves a geometric structure. Combined with known geometric rigidity results, this result implies certain rigidity statements concerning the full diffeomorphism group of a manifold. It also provides many examples of actions on Lorentz manifolds. Combining these with a small number of well-known actions, we get the full list of connected, simply connected Lie groups admitting a locally faithful, orbit nonproper action by isometries of a connected Lorentz manifold. We give an example of a connected nilpotent Lie group with no complicated action on a Lorentz manifold. We show that, if a connected Lie group has a normal closed subgroup isomorphic to a (two-dimensional) cylinder, then it admits a locally faithful, orbit nonproper action by isometries of a connected Lorentz manifold.     

Driving parts of Krebs cycle in reverse through mineral photochemistry

Scenarios for driving the Krebs cycle in reverse in the absence of enzymatic networks have received much attention in the literature of prebiotic evolution because repeated cycling provides a core mechanism for the synthesis of useful biomolecules from carbon dioxide. Here, we show that three of the five reductive steps in the cycle can be driven photochemically at high yield by a ZnS colloid. The results show the conversion of oxaloacetate to malate, fumarate to succinate, and oxoglutarate to oxalosuccinate. The experimental conditions of circumneutral pH and 288 K, as well as the ZnS semiconductor photocatalyst particles (sphalerite), are believed to have been prevalent in the waters of early Earth. These findings therefore both establish and constrain the plausibility of the occurrence of heretofore difficult chemical conversions in prebiotic metabolic systems.     

Dynamics of Simple Lie Groups on Lorentz Manifolds

We give an alternate proof of N. Kowalsky's theorem describing the collection of connected simple Lie groups with finite center which admit a nontrivial, nonproper action by isometries of a connected Lorentz manifold.