Constraining Carbon Nanothread Structures by Experimental and Calculated Nuclear Magnetic Resonance Spectra.

A one-dimensional (1D) sp3 carbon nanomaterial with high lateral packing order, known as carbon nanothreads, has recently been synthesized by slowly compressing and decompressing crystalline solid benzene at high pressure. The atomic structure of an individual nanothread has not yet been determined experimentally. We have calculated the 13C nuclear magnetic resonance (NMR) chemical shifts, chemical shielding tensors, and anisotropies of several axially ordered and disordered partially saturated and fully saturated nanothreads within density functional theory and systematically compared the results with experimental solid-state NMR data to assist in identifying the structures of the synthesized nanothreads. In the fully saturated threads, every carbon atom in each progenitor benzene molecule has bonded to a neighboring molecule (i.e., 6 bonds per molecule, a so-called "degree-6" nanothread), while the partially saturated threads examined retain a single double bond per benzene ring ("degree-4"). The most-parsimonious theoretical fit to the experimental 1D solid-state NMR spectrum, constrained by the measured chemical shift anisotropies and key features of two-dimensional NMR spectra, suggests a certain combination of degree-4 and degree-6 nanothreads as plausible components of this 1D sp3 carbon nanomaterial, with intriguing hints of a [4 + 2] cycloaddition pathway toward nanothread formation from benzene columns in the progenitor molecular crystal, based on the presence of nanothreads IV-7, IV-8, and square polymer in the minimal fit.

In situ vibrational spectroscopy of adsorbed nitrogen in porous carbon materials.

This study uses in situ vibrational spectroscopy to probe nitrogen adsorption to porous carbon materials, including single-wall carbon nanotubes and Maxsorb super-activated carbon, demonstrating how the nitrogen Raman stretch mode is perturbed by adsorption. In all porous carbon samples upon N2 physisorption in the mesopore filling regime, the N2 Raman mode downshifts by ∼2 cm-1, a downshift comparable to liquid N2. The relative intensity of this mode increases as pressure is increased to saturation, and trends in the relative intensity parallel the volumetric gas adsorption isotherm. This mode with ∼2 cm-1 downshift is thus attributed to perturbations arising due to N2-N2 interactions in a condensed film. The mode is also observed for the activated carbon at 298 K, and the relative intensity once again parallels the gas adsorption isotherm. For select samples, a mode with a stronger downshift (>4 cm-1) is observed, and the stronger downshift is attributed to stronger N2-carbon surface interactions. Simulations for a N2 surface film support peak assignments. These results suggest that N2 vibrational spectroscopy could provide an indication of the presence or absence of porosity for very small quantities of samples.

Mechanochemical Synthesis of Carbon Nanothread Single Crystals.

Synthesis of well-ordered reduced dimensional carbon solids with extended bonding remains a challenge. For example, few single-crystal organic monomers react under topochemical control to produce single-crystal extended solids. We report a mechanochemical synthesis in which slow compression at room temperature under uniaxial stress can convert polycrystalline or single-crystal benzene monomer into single-crystalline packings of carbon nanothreads, a one-dimensional sp3 carbon nanomaterial. The long-range order over hundreds of microns of these crystals allows them to readily exfoliate into fibers. The mechanochemical reaction produces macroscopic single crystals despite large dimensional changes caused by the formation of multiple strong, covalent C-C bonds to each monomer and a lack of reactant single-crystal order. Therefore, it appears not to follow a topochemical pathway, but rather one guided by uniaxial stress, to which the nanothreads consistently align. Slow-compression room-temperature synthesis may allow diverse molecular monomers to form single-crystalline packings of polymers, threads, and higher dimensional carbon networks.

Benzene-derived carbon nanothreads.

Low-dimensional carbon nanomaterials such as fullerenes, nanotubes, graphene and diamondoids have extraordinary physical and chemical properties. Compression-induced polymerization of aromatic molecules could provide a viable synthetic route to ordered carbon nanomaterials, but despite almost a century of study this approach has produced only amorphous products. Here we report recovery to ambient pressure of macroscopic quantities of a crystalline one- dimensional sp(3) carbon nanomaterial formed by high-pressure solid-state reaction of benzene. X-ray and neutron diffraction, Raman spectroscopy, solid-state NMR, transmission electron microscopy and first-principles calculations reveal close- packed bundles of subnanometre-diameter sp(3)-bonded carbon threads capped with hydrogen, crystalline in two dimensions and short-range ordered in the third. These nanothreads promise extraordinary properties such as strength and stiffness higher than that of sp(2) carbon nanotubes or conventional high-strength polymers. They may be the first member of a new class of ordered sp(3) nanomaterials synthesized by kinetic control of high-pressure solid-state reactions.

Systematic Enumeration of sp(3) Nanothreads.

Slow decompression of crystalline benzene in large-volume high-pressure cells has recently achieved synthesis of a novel one-dimensional allotrope of sp(3) carbon in which stacked columns of benzene molecules rehybridize into an ordered crystal of nanothreads. The progenitor benzene molecules function as six-valent one-dimensional superatoms with multiple binding sites. Here we enumerate their hexavalent bonding geometries, recognizing that the repeat unit of interatomic connectivity ("topological unit cell") need not coincide with the crystallographic unit cell, and identify the most energetically favorable cases. A topological unit cell of one or two benzene rings with at least two bonds interconnecting each adjacent pair of rings, accommodates 50 topologically distinct nanothreads, 15 of which are within 80 meV/carbon atom of the most stable member. Optimization of aperiodic helicity reveals the most stable structures to be chiral. We generalize Euler's rules for ring counting to cover this new form of very thin one-dimensional carbon, calculated their physical properties, and propose a naming convention that can be generalized to handle nanothreads formed from other progenitor molecules.

Linearly Polymerized Benzene Arrays As Intermediates, Tracing Pathways to Carbon Nanothreads.

How might fully saturated benzene polymers of composition [(CH)6]n form under high pressure? In the first approach to answering this question, we examine the stepwise increase in saturation of a one-dimensional stack of benzene molecules by enumerating the partially saturated polymer intermediates, subject to constraints of unit cell size and energy. Defining the number of four-coordinate carbon atoms per benzene formula unit as the degree of saturation, a set of isomers for degree-two and degree-four polymers can be generated by either thinking of the propagation of partially saturated building blocks or by considering a sequence of cycloadditions. There is also one 4 + 2 reaction sequence that jumps directly from a benzene stack to a degree-four polymer. The set of degree-two polymers provides several useful signposts toward achieving full saturation: chiral versus achiral building blocks, certain forms of conformational freedom, and also dead ends to further saturation. These insights allow us to generate a larger set of degree-four polymers and enumerate the many pathways that lead from benzene stacks to completely saturated carbon nanothreads.

Theory of Borazine-Derived Nanothreads: Enumeration, Reaction Pathways, and Piezoelectricity.

Nanothreads are one-dimensional macromolecules formed by pressure-induced polymerization along stacks of multiply unsaturated (or highly strained) molecules such as benzene (or cubane). Borazine is isoelectronic to benzene yet with substantial bond polarity, thus motivating a theoretical examination of borazine-derived nanothreads with degrees of saturation of 2, 4, and 6 (defined as the number of four-coordinated boron and nitrogen atoms per borazine formula unit). The energy increases upon going from molecular borazine to degree-2 borazine-derived threads and then decreases for degree-4 and degree-6 nanothreads as more σ bonds are formed. With the constraint of no more than two borazine formula units within the repeat unit of the framework's bonding topology, there are only 13 fully saturated (i.e., degree-6) borazine-derived nanothreads that avoid energetically costly homopolar bonds (as compared to more than 50 such candidates for benzene-derived threads). Only two of these are more stable than borazine. Hypothetical pathways from molecular borazine to these two degree-6 borazine-derived nanothreads are discussed. This relative paucity of outcomes may assist in kinetic control of reaction products. Beyond the high mechanical strength also predicted for carbon-based threads, properties such as piezoelectricity and flexoelectricity may be accessible to the polar lattice of borazine-derived nanothreads, with intriguing prospects for expression in these extremely thin yet rigid objects.

Alectinib and lorlatinib function by modulating EMT-related proteins and MMPs in NSCLC metastasis.

Most advanced non-small cell lung cancer (NSCLC) patients are accompanied by brain metastasis which is the major cause of increased mortality. The fusion rearrangement of anaplastic lymphoma kinase (ALK) gene is an important feature of brain metastasis in lung cancer. The novel ALK inhibitors alectinib and lorlatinib are shown to be effective against NSCLC brain metastasis, while their underlying mechanism of action is unclear. Epithelial-mesenchymal transition (EMT) proteins and matrix metalloproteinases (MMPs) play important roles in brain metastasis by regulating the blood-brain barrier (BBB). To reveal the molecular function of alectinib and lorlatinib, we explored their effects on the cellular levels of EMT markers: VIM and FN1 and the matrix metalloproteinases MMP-9 and MMP-7. The mRNA and protein levels of VIM, FN1, MMP-9, and MMP-7 were elevated in H3122 cells. However, upon alectinib and lorlatinib treatment, the levels were significantly reduced. Similar results were obtained when these experiments were performed either in a dose-dependent or time-dependent manner. Furthermore, alectinib and lorlatinib also inhibited the cell viability and migration of H3122 cells. Interestingly, in comparison to individual drugs, the combination of alectinib and lorlatinib was found to be substantially more effective. Overall, these results suggest that alectinib and lorlatinib possibly function through the downregulation of MMPs and EMT in NSCLC metastasis.

Transcription Factors Leading to High Expression of Neuropeptide L1CAM in Brain Metastases from Lung Adenocarcinoma and Clinical Prognostic Analysis.

BACKGROUND: There is a lack of understanding of the development of metastasis in lung adenocarcinoma (LUAD). This study is aimed at exploring the upstream regulatory transcription factors of L1 cell adhesion molecule (L1CAM) and to construct a prognostic model to predict the risk of brain metastasis in LUAD. METHODS: Differences in gene expression between LUAD and brain metastatic LUAD were analyzed using the Wilcoxon rank-sum test. The GRNdb (http://www.grndb.com) was used to reveal the upstream regulatory transcription factors of L1CAM in LUAD. Single-cell expression profile data (GSE131907) were obtained from the transcriptome data of 10 metastatic brain tissue samples. LUAD prognostic nomogram prediction models were constructed based on the identified significant transcription factors and L1CAM. RESULTS: Survival analysis suggested that high L1CAM expression was negatively significantly associated with overall survival, disease-specific survival, and prognosis in the progression-free interval (p < 0.05). The box plot indicates that high expression of L1CAM was associated with distant metastases in LUAD, while ROC curves suggested that high expression of L1CAM was associated with poor prognosis. FOSL2, HOXA9, IRF4, IKZF1, STAT1, FLI1, ETS1, E2F7, and ADARB1 are potential upstream transcriptional regulators of L1CAM. Single-cell data analysis revealed that the expression of L1CAM was found significantly and positively correlated with the expression of ETS1, FOSL2, and STAT1 in brain metastases. L1CAM, ETS1, FOSL2, and STAT1 were used to construct the LUAD prognostic nomogram prediction model, and the ROC curves suggest that the constructed nomogram possesses good predictive power. CONCLUSION: By bioinformatics methods, ETS1, FOSL2, and STAT1 were identified as potential transcriptional regulators of L1CAM in this study. This will help to facilitate the early identification of patients at high risk of metastasis.

Anomalous Stability of Two-Dimensional Ice Confined in Hydrophobic Nanopores.

The freezing of water mostly proceeds via heterogeneous ice nucleation, a process in which an effective nucleation medium not only expedites ice crystallization but also may effectively direct the polymorph selection of ice. Here, we show that water confined within a hydrophobic slit nanopore exhibits a freezing behavior strongly distinguished from its bulk counterpart. Such a difference is reflected by a strong, non-monotonic pore-size dependence of freezing temperature but, more surprisingly, by an unexpected stacking ordering of crystallized two-dimensional ice containing just a few ice layers. In particular, confined trilayer ice is found to exclusively crystallize into a well-ordered, hexagonal stacking sequence despite the fact that nanopore exerts no explicit constraint on stacking order. The absence of cubic stacking sequence is found to be originated from the intrinsically lower thermodynamic stability of cubic ice over hexagonal ice at the interface, which contrasts sharply the nearly degenerated stability of bulk hexagonal and cubic ices. Detailed examination clearly reveals that the divergence is attributed to the inherent difference between the two ice polymorphs in their surface phonon modes, which is further found to generically occur at both hydrophobic and hydrophilic surfaces.

Anisotropic Singlet Fission in Single Crystalline Hexacene.

Singlet fission is known to improve solar energy utilization by circumventing the Shockley-Queisser limit. The two essential steps of singlet fission are the formation of a correlated triplet pair and its subsequent quantum decoherence. However, the mechanisms of the triplet pair formation and decoherence still remain elusive. Here we examined both essential steps in single crystalline hexacene and discovered remarkable anisotropy of the overall singlet fission rate along different crystal axes. Since the triplet pair formation emerges on the same timescale along both crystal axes, the quantum decoherence is likely responsible for the directional anisotropy. The distinct quantum decoherence rates are ascribed to the notable difference on their associated energy loss according to the Redfield quantum dissipation theory. Our hybrid experimental/theoretical framework will not only further our understanding of singlet fission, but also shed light on the systematic design of new materials for the third-generation solar cells.

Revised definition of predicted left ventricular mass using ambulatory blood pressure in healthy Korean adults.

BACKGROUND: Left ventricular hypertrophy is influenced by both hemodynamic and non-hemodynamic factors. Ambulatory blood pressure is correlated with left ventricular hypertrophy. We established the influences of hemodynamic and non-hemodynamic factors, including ambulatory blood pressure, on variation in left ventricular mass in healthy Korean adults. METHOD: We included 172 subjects (male = 71, female = 101), with normal body mass index and blood pressure, in an analysis of data from the Yangpyung and Yeoju cohort studies and a tertiary cardiovascular center. Left ventricular mass was calculated using the equation: [1.04 × (IVSd + LVDd + PWTd) 3-(LDVs3)] × 0.8 + 0.6. Stroke volume was calculated (mL/beat) using Teichholz's formula. Stroke work (SW in gram-meters/beat [g-m/beat]) was computed as ambulatory systolic BP × stroke volume × 0.0144. RESULTS: Stroke work was the most important determinant associated with left ventricular mass (adjusted R2 = 0.442, p < 0.001), independent of height2.7 and sex. In a regression model including stroke work, height,2.7 and sex, the left ventricular mass was predicted by the equation: 43.11 + 0.61 × SW (g-m/beat) + 9.21 × height2.7-13.99 × sex (male = 1, female = 2) (constant = 43.11 ± 25.88, adjusted R2 = 0.532, p < 0.001). CONCLUSION: We examined ambulatory blood pressure, as in previous studies, and identified stroke work, height2.7, and sex as important determinants of left ventricular mass in Korean adults of normal weight and normal blood pressure. Ambulatory blood pressure is superior to clinical blood pressure for determining stroke work and predicted left ventricular mass.

Relationship between nocturnal blood pressure and 24-h urinary sodium excretion in a rural population in Korea.

BACKGROUND: The relationship between sodium intake and blood pressure (BP) is affected by many factors such as absolute level of sodium intake, salt sensitivity, and the accuracy or the timing of the BP measurement. There is no epidemiologic study using both ambulatory BP monitoring (ABPM) and 24-h urine sample in a middle-aged general population. METHODS: In the rural area, Yeojoo County, Gyunggi Province in South Korea, 218 subjects with age between 30 and 59 years old were measured with ABPM and 24-h urine sample. ABPM device was TM2430, and the 24-h urine sample was collected using the aliquot cup. Metabolic syndrome (MetS) score was calculated by the sum of the number of abnormal criteria other than BP. RESULTS: For both ABPM and 24-h urine sample, 148 subject data was acceptable for the analysis by the creatinine equation and/or the completeness of collection. Age was 47.4 ± 8.3 years (range 30 to 59 years), and female was 85 (57.4%). In multiple linear regression analysis, sodium intake was not an independent factor for casual BPs and daytime BPs whereas sodium intake was an independent factor for nighttime systolic BP (ß = 1.625, p = 0.0026) and nighttime diastolic BP (ß = 1.066, p = 0.0017). When compared to the lowest quartiles of sodium intake, daytime diastolic BP and nighttime BPs were in the higher three quartile groups. CONCLUSIONS: Sodium intake was associated not with casual BPs and daytime BPs but with increased nighttime BPs in the middle-aged general population in Korea.