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Ultrasmall iron oxide nanoparticles have recently attracted much attention as T1 (positive) contrast agents for magnetic resonance imaging to serve as safer alternatives to gadolinium-based T1 contrast agents. This review will discuss several key aspects regarding this newly developed contrast agent, including synthetic strategies, parameters affecting T1 signal (e.g., size, surface, and environment), and emerging applications. The integration with other imaging modalities will be discussed as well, such as dual T1/T2 imaging, positron emission tomography, and computed tomography. Finally, perspectives and outlook about the future development and concerns will be included. [ABSTRACT FROM AUTHOR]

Nanomaterials have many advanced applications, from bio-medicine to flexible electronics to energy storage, and the broad interest in graphene-based materials and devices means that high annual tonnages will be required to meet this demand. However, manufacturing at the required scale remains unfeasible until economic and environmental obstacles are resolved. Liquid exfoliation of graphite is the preferred scalable method to prepare large quantities of good quality graphene, but only low concentrations are achieved and the solvents habitually employed are toxic. Furthermore, good dispersions of nanomaterials in organic solvents are crucial for the synthesis of many types of nanocomposites. To address the performance and safety issues of solvent use, a bespoke approach to solvent selection was developed and the renewable solvent Cyrene was identified as having excellent properties. Graphene dispersions in Cyrene were found to be an order of magnitude more concentrated than those achieved in N-methylpyrrolidinone (NMP). Key attributes to this success are optimum solvent polarity, and importantly a high viscosity. We report the role of viscosity as crucial for the creation of larger and less defective graphene flakes. These findings can equally be applied to the dispersion of other layered bi-dimensional materials, where alternative solvent options could be used as drop-in replacements for established processes without disruption or the need to use specialized equipment. Thus, the discovery of a benign yet high performance graphene processing solvent enhances the efficiency, sustainability and commercial potential of this ever-growing field, particularly in the area of bulk material processing for large volume applications. [ABSTRACT FROM AUTHOR]

Cross-coupling and cascade reactions typically rely on unsustainable and toxic volatile organic solvents. 2,2,5,5-Tetramethyloxolane (TMO) and 2,5-diethyl-2,5-dimethyloxolane (DEDMO) are both inherently non-peroxide forming ethers, and have been used in this work as effective, more sustainable, and potentially bio-based alternative solvents for Suzuki-Miyaura and Sonogashira reactions. Suzuki-Miyaura reactions demonstrated good yields for a range of substrates, 71-89% in TMO and 63-92% in DEDMO. In addition, a Sonogashira reaction exhibited the excellent yields of 85-99% performed in TMO, which was significantly higher than traditional volatile organic solvents, THF or toluene, and higher than those reported for another non-peroxide forming ether, namely eucalyptol. Cascade Sonogashira reactions utilizing a simple annulation methodology were particularly effective in TMO. Furthermore, a green metric assessment confirmed that the methodology employing TMO was more sustainable and greener than the traditional solvents THF and toluene, thereby demonstrating the promise of TMO as an alternative solvent for Pd-catalyzed cross-coupling reactions.

Methylation of acetoin with dimethyl carbonate was performed in a sustainable one-step process, with improved process mass intensity (PMI) and atom economy compared to previously published methods. The resulting product, 3-methoxybutan-2-one (MO) was successfully evaluated as a bio-based solvent, while both Kamlet-Taft solvatochromic parameters and Hansen solubility parameters demonstrate its potential viability in the substitution of chlorinated solvents. MO exhibited a low peroxide forming potential and a negative Ames mutagenicity test and was successfully used as a solvent in a Friedel-Crafts acylation (79% yield compared to 77% in dichloromethane) and for N -alkylations. MO is a renewable oxygenated solvent, with the potential ability to substitute carcinogenic halogenated solvents in some applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

With increased awareness of environmental issues caused by traditional petrochemical processes, both academia and industry are making enormous efforts towards the development of sustainable practices using renewable biomass as a feedstock. In this work, the biocatalyzed synthesis of polyesters derived from renewable monomers was performed in safer, bio-derivable organic solvents. Candida antarctica lipase B (CaLB), an enzyme belonging to the Ser-hydrolase family (adsorbed on methacrylic resin, also known as Novozym 435) was tested for its performance in the synthesis of adipate- and furandicarboxylate-based polyesters. In addition, the traditional solvents toluene and tetrahydrofuran were compared with a series of green solvents, 2,2,5,5-tetramethyloxolane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran and pinacolone for the enzymatic polymerizations. We can conclude that the monomer conversions and molecular masses of the obtained polyesters in all the tested alternative solvents were suitable, and in some cases superior, with CaLB immobilized via physisorption on acrylic resin being the optimal biocatalyst for all reactions. Strikingly, it was found that for the majority of the new solvents, lower reaction temperatures gave comparable monomer conversions and polymers with similar molecular weights whilst pinacolone yielded better polymers with M n > 2000 Da and conversions of over 80%.

Dihydrolevoglucosenone (Cyrene) is a bio-based molecule, derived in two simple steps from cellulose, which demonstrates significant promise as a dipolar aprotic solvent. The dipolarity of dihydrolevoglucosenone is similar to NMP, DMF and sulpholane. Dihydrolevoglucosenone demonstrates similar performance to NMP in a fluorination reaction and the Menschutkin reaction.

Hyper-Rayleigh scattering is revealed as a very sensitive monitor of cluster formation in solution, and as a means of studying the mechanism of crystal nucleation in molecular species. Two compounds are selected with particularly high second harmonic generation (SHG) powers in the crystalline state and experimental conditions are defined allowing the measurement of the beta value for one of these as 18+/-1x10(-30) esu. It is found to agree with current theoretical prediction of 20x10(-30) esu. In the more powerful of these, two photon induced fluorescence is found to be partly responsible for the SHG. The solubilities of both compounds in methanol are measured and it is observed that these differ by a factor of ten. When the solution concentration is increased beyond 45% of the saturation value, the quadratic coefficient exhibits non-linear behaviour with respect to concentration. Additionally, the widths of the distributions of the HRS signals increase initially with concentration as expected, but, beyond 45% saturation concentrations, these narrow again. These phenomena are interpreted as indicators of cluster formation in these solutions well below saturation concentrations. A future experimental design is proposed in which the coherent component will yield information on the organisation of the molecules in such clusters.