Nanoparticles are an essential component in the emerging field of nanomedical imaging and therapy. When deployed in vivo, these materials are typically protected from the immune system by polyethylene glycol (PEG). A wide variety of strategies to coat and characterize nanoparticles with PEG has established important trends on PEG size, shape, density, loading level, molecular weight, charge and purification. Strategies to incorporate targeting ligands are also prevalent. This article presents a background to investigators new to stealth nanoparticles, and suggests some key considerations needed prior to designing a nanoparticle PEGylation protocol and characterizing the performance features of the product.

The Yen−Mullins model, also known as the modified Yen model, specifies the predominant molecular and colloidal structure of asphaltenes in crude oils and laboratory solvents and consists of the following: The most probable asphaltene molecular weight is ∼750 g/mol, with the island molecular architecture dominant. At sufficient concentration, asphaltene molecules form nanoaggregates with an aggregation number less than 10. At higher concentrations, nanoaggregates form clusters again with small aggregation numbers. The Yen−Mullins model is consistent with numerous molecular and colloidal studies employing a broad array of methodologies. Moreover, the Yen−Mullins model provides a foundation for the development of the first asphaltene equation of state for predicting asphaltene gradients in oil reservoirs, the Flory−Huggins− Zuo equation of state (FHZ EoS). In turn, the FHZ EoS has proven applicability in oil reservoirs containing condensates, black oils, and heavy oils. While the development of the Yen−Mullins model was founded on a very large number of studies, it nevertheless remains essential to validate consistency of this model with important new data streams in asphaltene science. In this paper, we review recent advances in asphaltene science that address all critical aspects of the Yen−Mullins model, especially molecular architecture and characteristics of asphaltene nanoaggregates and clusters. Important new studies are shown to be consistent with the Yen−Mullins model. Wide ranging studies with direct interrogation of the Yen−Mullins model include detailed molecular decomposition analyses, optical measurements coupled with molecular orbital calculations, nuclear magnetic resonance (NMR) spectroscopy, centrifugation, direct-current (DC) conductivity, interfacial studies, small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS), as well as oilfield studies. In all cases, the Yen−Mullins model is proven to be at least consistent if not valid. In addition, several studies previously viewed as potentially inconsistent with the Yen−Mullins model are now largely resolved. Moreover, oilfield studies using the Yen−Mullins model in the FHZ EoS are greatly improving the understanding of many reservoir concerns, such as reservoir connectivity, heavy oil gradients, tar mat formation, and disequilibrium. The simple yet powerful advances codified in the Yen−Mullins model especially with the FHZ EoS provide a framework for future studies in asphaltene science, petroleum science, and reservoir studies.

Flower-shaped inorganic nanocrystals have been used for applications in catalysis and analytical science, but so far there have been no reports of 'nanoflowers' made of organic components. Here, we report a method for creating hybrid organic-inorganic nanoflowers using copper (II) ions as the inorganic component and various proteins as the organic component. The protein molecules form complexes with the copper ions, and these complexes become nucleation sites for primary crystals of copper phosphate. Interaction between the protein and copper ions then leads to the growth of micrometre-sized particles that have nanoscale features and that are shaped like flower petals. When an enzyme is used as the protein component of the hybrid nanoflower, it exhibits enhanced enzymatic activity and stability compared with the free enzyme. This is attributed to the high surface area and confinement of the enzymes in the nanoflowers.

Protein molecules were directly embedded in metal-organic frameworks (MOFs) by a coprecipitation method. The protein molecules majorly embedded on the surface region of MOFs display high biological activities. As a demonstration of the power of such materials, the resulting Cyt c embedded in ZIF-8 showed a 10-fold increase in peroxidase activity compared to free Cyt c in solution and thus gave convenient, fast, and highly sensitive detection of trace amounts of explosive organic peroxides in solution.

G protein-coupled receptors (GPCRs) respond to a diverse array of ligands, mediating cellular responses to hormones and neurotransmitters, as well as the senses of smell and taste. The structures of the GPCR rhodopsin and several G proteins have been determined by x-ray crystallography, yet the organization of the signaling complex between GPCRs and G proteins is poorly understood. The observations that some GPCRs are obligate heterodimers, and that many GPCRs form both homo-and heterodimers, has led to speculation that GPCR dimers may be required for efficient activation of G proteins. However, technical limitations have precluded a definitive analysis of G protein coupling to monomeric GPCRs in a biochemically defined and membrane-bound system. Here we demonstrate that a prototypical GPCR, the ␤2-adrenergic receptor (␤2AR), can be incorporated into a reconstituted highdensity lipoprotein (rHDL) phospholipid bilayer particle together with the stimulatory heterotrimeric G protein, Gs. Single-molecule fluorescence imaging and FRET analysis demonstrate that a single ␤2AR is incorporated per rHDL particle. The monomeric ␤2AR efficiently activates Gs and displays GTP-sensitive allosteric ligandbinding properties. These data suggest that a monomeric receptor in a lipid bilayer is the minimal functional unit necessary for signaling, and that the cooperativity of agonist binding is due to G protein association with a receptor monomer and not receptor oligomerization.␤2-adrenergic receptor ͉ single-molecule spectroscopy ͉ oligomerization

The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

We present a framework, which we call Molecule Deep Q -Networks (MolDQN), for molecule optimization by combining domain knowledge of chemistry and state-of-the-art reinforcement learning techniques (double Q -learning and randomized value functions). We directly define modifications on molecules, thereby ensuring 100% chemical validity. Further, we operate without pre-training on any dataset to avoid possible bias from the choice of that set. MolDQN achieves comparable or better performance against several other recently published algorithms for benchmark molecular optimization tasks. However, we also argue that many of these tasks are not representative of real optimization problems in drug discovery. Inspired by problems faced during medicinal chemistry lead optimization, we extend our model with multi-objective reinforcement learning, which maximizes drug-likeness while maintaining similarity to the original molecule. We further show the path through chemical space to achieve optimization for a molecule to understand how the model works.

Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.