Glucose hydrochar consists of linked phenol, furan, arene, alkyl, and ketone structures revealed by advanced solid-state nuclear magnetic resonance.

The molecular structure of hydrochars produced from C-enriched glucose under various conditions has been elucidated based on advanced one- and two-dimensional (2D) H-C and C-C solid-state nuclear magnetic resonance (NMR) with spectral editing. Regardless of synthesis conditions, hydrochars consist mostly of oxygen-substituted arene rings (including diphenols) and furans connected by alkyl linkers rich in ketones. Cross-linking nonprotonated and methyne (C-H) alkyl carbons have been identified through spectrally edited 2D NMR.

A specialized metabolic pathway partitions citrate in hydroxyapatite to impact mineralization of bones and teeth.

Citrate is a critical metabolic substrate and key regulator of energy metabolism in mammalian cells. It has been known for decades that the skeleton contains most (>85%) of the body's citrate, but the question of why and how this metabolite should be partitioned in bone has received singularly little attention. Here, we show that osteoblasts use a specialized metabolic pathway to regulate uptake, endogenous production, and the deposition of citrate into bone.

Polymer Chains Fold Prior to Crystallization.

There are long-standing debates in crystallization mechanism of polymer chains at the molecular levels: Which comes first, chain folding or lamellae formation during crystallization? In this study, we report the local chain trajectory of C-labeled semicrystalline polymer in an extreme case of rapidly quenched glassy state as well as thermodynamically stable crystals formed via different pathways from glass and melt. Magnetically dipole interactions do not require a long-range order of molecular objects and thus enable us to trace the local chain trajectory of polymer chains even in a glassy state. To accurately characterize the local chain trajectory of polymer glass, the natural abundance effect on C-C double-quantum (DQ) nuclear magnetic resonance (NMR) signal is re-examined using extended chain conformation.

The role of foreign capital and economic freedom in sustainable food production: Evidence from DLD countries.

In many developing countries, the deficiency in public and private investment has resulted in lower growth rates and stagnation in productivity. The need for a new paradigm of foreign investment and aid in agricultural production is becoming exigent in developing countries. Given the decline in per capita arable land, the rise in production costs, and the increase in population and urbanization, major changes in agriculture have been proposed to boost agricultural production.

Perfect and Defective C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by C NMR.

The molecular structure of nanothreads produced by the slow compression of C-furan was studied by advanced solid-state NMR. Spectral editing showed that >95% of carbon atoms were bonded to one hydrogen (C-H) and that there were 2-4% CH, 0.6% C═O, and <0.

Immobilized C-labeled polyether chain ends confined to the crystallite surface detected by advanced NMR.

A comprehensive C nuclear magnetic resonance (NMR) approach for characterizing the location of chain ends of polyethers and polyesters, at the crystallite surface or in the amorphous layers, is presented. The OH chain ends of polyoxymethylene are labeled with COO-acetyl groups and their dynamics probed by C NMR with chemical shift anisotropy (CSA) recoupling. At least three-quarters of the chain ends are not mobile dangling cilia but are immobilized, exhibiting a powder pattern characteristic of the crystalline environment and fast CSA dephasing.

Structure of the Polymer Backbones in polyMOF Materials.

The molecular connectivity of polymer-metal-organic framework (polyMOF) hybrid materials was investigated using density functional theory calculations and solid-state NMR spectroscopy. The architectural constraints that dictate the formation of polyMOFs were assessed by examining poly(1,4-benzenedicarboxylic acid) (pbdc) polymers in two archetypical MOF lattices (UiO-66 and IRMOF-1). Modeling of the polyMOFs showed that in the IRMOF-1-type lattice, six, seven, and eight methylene (-CH-) groups between 1,4-benzenedicarboxylate (terephthalate, bdc) units can be accommodated without significant distortions, while in the UiO-66-type lattice, an optimal spacing of seven methylene groups between bdc units is needed to minimize strain.

Novel Lewis Base Cyclam Self-Passivation of Perovskites without an Anti-Solvent Process for Efficient Light-Emitting Diodes.

Metal halide perovskites have been focused as a candidate applied as a promising luminescent material for next-generation high-quality lighting and high-definition display. However, as perovskite films formed, high density of defects would be produced in solution processing inevitably, leading to low exciton recombination efficiency in light-emitting diodes (LEDs). Herein, a facile and novel self-passivation strategy to inhibit defect formation in perovskite films for constructing high-performance LEDs is developed.

Rapid Depolymerization of Decrystallized Cellulose to Soluble Products via Ethanolysis under Mild Conditions.

Efficient cellulose depolymerization is a major bottleneck for economical production of second-generation biofuels. In this work, crystalline cellulose was subjected to sequential ball milling and ethanolysis as a mild and selective depolymerization approach. Ball milling and ethanolysis resulted in 38±1 % cellulose conversion, with 24 % ethyl-glucopyranoside as the main identified and quantified product and negligible side reaction of the ethanol solvent to form diethyl ether.

Multinuclear solid-state NMR of complex nitrogen-rich polymeric microcapsules: Weight fractions, spectral editing, component mixing, and persistent radicals.

The molecular structure of a crosslinked nitrogen-rich resin made from melamine, urea, and aldehydes, and of microcapsules made from the reactive resin with multiple polymeric components in aqueous dispersion, has been analyzed by C, C{H}, H-C, H, C{N}, and N solid-state NMR without isotopic enrichment. Quantitative C NMR spectra of the microcapsules and three precursor materials enable determination of the fractions of different components. Spectral editing of non-protonated carbons by recoupled dipolar dephasing, of CH by dipolar DEPT, and of C-N by C{N} SPIDER resolves peak overlap and helps with peak assignment.

Phase transition of spiropyrans: impact of isomerization dynamics at high temperatures.

Isomerization behaviors of spiropyran derivatives in neat condensed phase were studied to understand their unusual phase transitions including cold-crystallization after extreme supercooling down to -50 °C. Compounds with different functional groups were compared, and the equilibrium between isomers at high temperatures was found to determine phase transitions.

Chain Trajectory, Chain Packing, and Molecular Dynamics of Semicrystalline Polymers as Studied by Solid-State NMR.

Chain-level structure of semicrystalline polymers in melt- and solution-grown crystals has been debated over the past half century. Recently, C⁻C double quantum (DQ) Nuclear Magnetic Resonance (NMR) spectroscopy has been successfully applied to investigate chain-folding (CF) structure and packing structure of C enriched polymers after solution and melt crystallization. We review recent NMR studies for (i) packing structure, (ii) chain trajectory, (iii) conformation of the folded chains, (iv) nucleation mechanisms, (v) deformation mechanism, and (vi) molecular dynamics of semicrystalline polymers.

Synthesis of stable and phase-adjustable CsPbBr@CsPbBr nanocrystals novel anion-cation reactions.

All-inorganic cesium lead halide perovskites have emerged as promising semiconductor materials due to their preeminent performance in lighting, display, light detecting, and laser fields. However, the applications of lead halide perovskites are limited by the dissatisfactory stability owing to their fragile ionic crystal characteristics and highly dynamic surface-coordinated states. The diphase structure passivation possessing the same chemical constituents (such as passivating CsPbBr with CsPbBr) has been proven to be an effective way to improve the stabilities and simultaneously maintain the highly efficient luminescence properties.

Stoichiometry and Packing Structure of Poly(lactic acid) Stereocomplex as Revealed by Solid-State NMR and C Isotope Labeling.

Poly(l-lactic acid) (L)/poly(d-lactic acid) (D) blends form a stereocomplex (SC) at a mixing ratio of 7/3-3/7. The stoichiometry and packing structure of L/D in the SC are controversial topics because the SC is semicrystalline and because the enantiomeric pair has the same chemical structure. In this study, both the stoichiometry and packing structure of 33% C CH-labeled () L/nonlabeled D blends at mixing ratios of 7/3-3/7 were investigated by using solid-state (SS) NMR.

Chain Trajectory of Semicrystalline Polymers As Revealed by Solid-State NMR Spectroscopy.

Over the last half century, a chain-folding structure of semicrystalline polymers has been debated in polymer science. Recently, C-C double quantum (DQ) NMR spectroscopy combined with C selective isotope labeling has been developed to investigate re-entrance sites of the folded chains, mean values of adjacent re-entry number ⟨⟩ and fraction ⟨⟩ of semicrystalline polymers. This viewpoint highlights the versatile approaches of using solid-state (ss) NMR and isotope labeling for revealing (i) chain trajectory in melt- and solution-grown crystals, (ii) conformation of the folded chains in single crystals, (iii) self-folding in the early stage of crystallization, and (iv) unfolding of the folded chains under stretching.

Unfolding of Polypropylene under Uniaxial Stretching.

Despite numerous investigations on polymer processing, understanding the deformation mechanisms of semicrystalline polymer under uniaxial stretching is still challenging. In this work, C-C Double Quantum (DQ) NMR was applied to trace the structural evolution of C-labeled polypropylene (PP) chains inside the crystallites stretched to an engineering strain () of 21 at 100 °C. DQ NMR based on spatial proximity of C labeled nuclei proved conformational changes from the folded chains to the locally extended chains induced by stretching.

Folding of Polymer Chains in the Early Stage of Crystallization.

Understanding the structure formation of an ordered domain in the early stage of crystallization is one of the long-standing issues in polymer science. In this study, we investigate the chain trajectory of polypropylene (PP) formed via rapid and deep quenching, using solid-state NMR spectroscopy. Comparisons of experimental and simulated C-C double quantum (DQ) buildup curves demonstrated that individual PP chains adopt adjacent re-entry sequences with an average folding number ⟨⟩ = 3-4 in the mesomorphic form, assuming an adjacent re-entry fraction ⟨⟩ of 100%.

Three-Dimensional Conformation of Folded Polymers in Single Crystals.

The chain-folding mechanism and structure of semicrystalline polymers have long been controversial. Solid-state NMR was applied to determine the chain trajectory of (13)C CH3-labeled isotactic poly(1-butene) (iPB1) in form III chiral single crystals blended with nonlabeled iPB1 crystallized in dilute solutions under low supercooling. An advanced (13)C-(13)C double-quantum NMR technique probing the spatial proximity pattern of labeled (13)C nuclei revealed that the chains adopt a three-dimensional (3D) conformation in single crystals.

Determination of Local Packing Structure of Mesomorphic Form of Isotactic Polypropylene by Solid-State NMR.

Understanding the local packing structures of a disordered mesomorphic phase is a challenging issue in polymer characterization. In this work, C-C through-space interactions, as well as a molecular dynamics analysis based on the reorientation of chemical shift anisotropy (CSA), were proposed for the evaluation of the local packing structure of the mesomorphic form of isotactic polypropylene (PP). C-C double quantum (DQ) buildup curves of C 15% CH selectively labeled PP and spin-dynamics simulations demonstrated that the local packing structures in the mesomorphic form were very similar to the packing in the β phase.