Microbial community structure mediates response of soil C decomposition to litter addition and warming

Microbial activity has been highlighted as one of the main unknowns controlling the fate and turnover of soil organic matter (SOM) in response to climate change. How microbial community structure and function may (or may not) interact with increasing temperature to impact the fate and turnover of SOM, in particular when combined with changes in litter chemistry, is not well understood. The primary aim of this study was to determine if litter chemistry impacted the decomposition of soil and litter-derived carbon (C), and its interaction with temperature, and whether this response was controlled by microbial community structure and function. Fresh or pre-incubated eucalyptus leaf litter (13C enriched) was added to a woodland soil and incubated at 12, 22, or 32 �C. We tracked the movement of litter and soilderived C into CO2, water-extractable organic carbon (WEOC), and microbial phospholipids (PLFA). The litter additions produced significant changes in every parameter measured, while temperature, interacting with litter chemistry, predominately affected soil C respiration (priming and temperature sensitivity), microbial community structure, and the metabolic quotient (a proxy for microbial carbon use efficiency [CUE]). The direction of priming varied with the litter additions (negative with fresh litter, positive with pre-incubated litter) and was related to differences in the composition of microbial communities degrading soil-C, particularly gram-positive and gram-negative bacteria, resulting from litter addition. Soil-C decomposition in both litter treatments was more temperature sensitive (higher Q10) than in the soil-only control, and soil-C priming became increasingly positive with temperature. However, microbes utilizing soil-C in the litter treatments had higher CUE, suggesting the longer-term stability of soil-C may be increased at higher temperature with litter addition. Our results show that in the same soil, the growth of distinct microbial communities can alter the turnover and fate of SOM and, in the context of global change, its response to temperature

Nanopod Formation through Gold Nanoparticle Templated and Catalyzed Cross-linking of Polymers Bearing Pendant Propargyl Ethers

A novel method for synthesizing polymer nanopods from a linear polymer bearing pendant propargyl ether groups, using gold nanoparticles as both the template and the catalyst for the crosslinking reaction, is reported. The transformations involved in the cross-linking process are unprecedented on the surface of a gold particle. A tentative cross-linking mechanism is proposed. Includes Supporting Information

Spherical Nucleic Acids

A historical perspective of the development of spherical nucleic acid (SNA) conjugates and other three-dimensional nucleic acid nanostructures is provided. This Perspective details the synthetic methods for preparing them, followed by a discussion of their unique properties and theoretical and experimental models for understanding them. Important examples of technological advances made possible by their fundamental properties spanning the fields of chemistry, molecular diagnostics, gene regulation, medicine, and materials science are also presented

Nucleic Acid–Metal Organic Framework (MOF) Nanoparticle Conjugates

Nanoparticles of a metal–organic framework (MOF), UiO-66-N₃ (Zr₆O₄OH₄(C₈H₃O₄–N₃)₆), were synthesized. The surface of the MOF was covalently functionalized with oligonucleotides, utilizing a strain promoted click reaction between DNA appended with dibenzyl­cyclo­octyne and azide-functionalized UiO-66-N₃ to create the first MOF nanoparticle–nucleic acid conjugates. The structure of the framework was preserved throughout the chemical transformation, and the surface coverage of DNA was quantified. Due to the small pore sizes, the particles are only modified on their surfaces. When dispersed in aqueous NaCl, they exhibit increased stability and enhanced cellular uptake when compared with unfunctionalized MOF particles of comparable size

The sequence-specific cellular uptake of spherical nucleic acid nanoparticle conjugates

The sequence-dependent cellular uptake of spherical nucleic acid nanoparticle conjugates (SNAs) is investigated. This process occurs by interaction with class A scavenger receptors (SR-A) and caveolae-mediated endocytosis. It is known that linear poly(guanine) (poly G) is a natural ligand for SR-A, and it has been proposed that interaction of poly G with SR-A is dependent on the formation of G-quadruplexes. Since G-rich oligonucleotides are known to interact strongly with SR-A, it is hypothesized that SNAs with higher G contents would be able to enter cells in larger amounts than SNAs composed of other nucleotides, and as such, cellular internalization of SNAs is measured as a function of constituent oligonucleotide sequence. Indeed, SNAs with enriched G content show the highest cellular uptake. Using this hypothesis, a small molecule (camptothecin) is chemically conjugated with SNAs to create drug-SNA conjugates and it is observed that poly G SNAs deliver the most camptothecin to cells and have the highest cytotoxicity in cancer cells. Our data elucidate important design considerations for enhancing the intracellular delivery of spherical nucleic acids

Stepwise and epitaxial growth of DNA-programmable nanoparticle superlattices

Many researchers are interested in developing methods for rationally assembling nanoparticle building blocks into periodic lattices. These superlattices could in principle be used to create designer materials with unique properties, useful in optics, biomedicine, energy, and catalysis. DNA is a particularly attractive ligand for the programmable assembly of nanoparticles, as synthetically tunable variations in nucleotide sequence allow for precise engineering of the nanoparticle hydrodynamic radius and hybridization properties. These factors, in turn, dictate the crystallog. symmetry and lattice parameter of the assembly. Although superlattices with diverse geometries can be assembled in soln., the incorporation of specific bonding interactions between particle building blocks and a substrate would significantly enhance control over the crystal growth process. Herein, we use a stepwise growth process to systematically study and control the evolution of a bcc cryst. thin-film comprised of DNA-functionalized nanoparticle building blocks on a complementary DNA substrate. We examine crystal growth as a function of temp., no. of layers, and substrate-particle bonding interactions. Importantly, the judicious choice of DNA interconnects allows one to tune the interfacial energy between various crystal planes and the substrate, and thereby control crystal orientation and size in a stepwise fashion using chem. programmable attractive forces. We further demonstrate that such assemblies can be grown epitaxially on lithog. patterned templates, eliminating grain boundaries and enabling fine control over orientation and size of assemblies up to thousands of square micrometers. The effects of drying on the superlattice structure are examd.; surprisingly, this allows for a reversible contraction and expansion of the colloidal crystal with a greater than 60% decrease in the vol. of the lattice. Ultimately, this work will be important for the development of on-chip material platforms that take advantage of the periodicity and/or controlled d. of the inorg. core, such as optical metamaterials, photonic crystals and heterogeneous catalysts

Role of Modulators in Controlling the Colloidal Stability and Polydispersity of the UiO-66 Metal–Organic Framework

Nanoscale UiO-66 Zr₆(OH)₄O₄(C₈O₄H₄)₆ has been synthesized with a series of carboxylic acid modulators, R-COOH (where R = H, CH₃, CF₃, and CHCl₂). The phase purity and size of each MOF was confirmed by powder X-ray diffraction, BET surface area analysis, and scanning transmission electron microscopy (STEM). Size control of UiO-66 crystals from 20 nm to over 1 μm was achieved, and confirmed by STEM. The colloidal stability of each MOF was evaluated by dynamic light scattering and was found to be highly dependent on the modulator conditions utilized in the synthesis, with both lower p<i>K</i>a and higher acid concentration resulting in more stable structures. Furthermore, STEM was carried out on both colloidally stable samples and those that exhibited a large degree of aggregation, which allowed for visualization of the different degrees of dispersion of the samples. The use of modulators at higher concentrations and with lower p<i>K</i>_as leads to the formation of more defects, as a consequence of terephthalic acid ligands being replaced by modulator molecules, thereby enhancing the colloidal stability of the UiO-66 nanoparticles. These findings could have a significant impact on nanoscale MOF material syntheses and applications, especially in the areas of catalysis and drug delivery

Reconstitutable Nanoparticle Superlattices

Colloidal self-assembly predominantly results in lattices that are either: (1) fixed in the solid state and not amenable to additional modification, or (2) in solution, capable of dynamic adjustment, but difficult to transition to other environments. Accordingly, approaches to both dynamically adjust the interparticle spacing of nanoparticle superlattices and reversibly transfer superlattices between solution-phase and solid state environments are limited. In this manuscript, we report the reversible contraction and expansion of nanoparticles within immobilized monolayers, surface-assembled superlattices, and free-standing single crystal superlattices through dehydration and subsequent rehydration. Interestingly, DNA contraction upon dehydration occurs in a highly uniform manner, which allows access to spacings as small as 4.6 nm and as much as a 63% contraction in the volume of the lattice. This enables one to deliberately control interparticle spacings over a 4–46 nm range and to preserve solution-phase lattice symmetry in the solid state. This approach could be of use in the study of distance-dependent properties of nanoparticle superlattices and for long-term superlattice preservation