Polymer mechanochemistry has traditionally been employed to study the effects of mechanical force on chemical bonds within a polymer backbone or to generate force-responsive materials. It is ...under-exploited for the scalable synthesis of wholly new materials by chemically transforming the polymers, especially products inaccessible by other means. Here we utilize polymer mechanochemistry to synthesize a fluorinated polyacetylene, a long-sought-after air-stable polyacetylene that has eluded synthesis by conventional means. We construct the monomer in four chemical steps on gram scale, which involves a rapid incorporation of fluorine atoms in an exotic photochemical cascade whose mechanism and exquisite stereoselectivity were informed by computation. After polymerization, force activation by ultrasonication produces a gold-coloured, semiconducting fluoropolymer. This work demonstrates that polymer mechanochemistry is a valuable synthetic tool for accessing materials on a preparative scale.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Paramagnetic Fe(II) and Co(II) complexes are utilized as the first transition metal examples of 1H NMR shift agents (paraSHIFT) for thermometry applications using Magnetic Resonance Spectroscopy ...(MRS). The coordinating ligands consist of TACN (1,4,7-triazacyclononane) and CYCLEN (1,4,7,10-tetraazacyclododecane) azamacrocycles appended with 6-methyl-2-picolyl groups, denoted as MPT and TMPC, respectively. 1H NMR spectra of the MPT- and TMPC-based Fe(II) and Co(II) complexes demonstrate narrow and highly shifted resonances that are dispersed as broadly as 440 ppm. The six-coordinate complex cations, M(MPT)2+ and M(TMPC)2+, vary from distorted octahedral to distorted trigonal prismatic geometries, respectively, and also demonstrate that 6-methyl-2-picolyl pendents control the rigidity of these complexes. Analyses of the 1H NMR chemical shifts, integrated intensities, line widths, the distances obtained from X-ray diffraction measurements, and longitudinal relaxation time (T 1) values allow for the partial assignment of proton resonances of the M(MPT)2+ complexes. Nine and six equivalent methyl protons of M(MPT)2+ and M(TMPC)2+, respectively, produce 3-fold higher 1H NMR intensities compared to other paramagnetically shifted proton resonances. Among all four complexes, the methyl proton resonances of Fe(TMPC)2+ and Co(TMPC)2+ at −49.3 ppm and −113.7 ppm (37 °C) demonstrate the greatest temperature dependent coefficients (CT) of 0.23 ppm/°C and 0.52 ppm/°C, respectively. The methyl groups of these two complexes both produce normalized values of |CT|/fwhm = 0.30 °C–1, where fwhm is full width at half-maximum (Hz) of proton resonances. The T 1 values of the highly shifted methyl protons are in the range of 0.37–2.4 ms, allowing rapid acquisition of spectroscopic data. These complexes are kinetically inert over a wide range of pH values (5.6–8.6), as well as in the presence of serum albumin and biologically relevant cations and anions. The combination of large hyperfine shifts, large temperature sensitivity, increased signal-to-noise ratio, and short T 1 values suggests that these complexes, in particular the TMPC-based complexes, show promise as paraSHIFT agents for thermometry.
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Herein we report the synthesis and characterization of light responsive metal organic framework (MOF) single crystals containing the photochromic diarylethene ...1,2-bis(2,5-dimethyl-thien-3-yl)perfluorocyclopentene. Polarized light microscopy on single crystals indicates that the photochrome is preferentially aligned along the c-axis of the host.
Covalent organic frameworks (COFs) have emerged as versatile, functional materials comprised of low-cost molecular building blocks. The permanent porosity, long-range order, and high surface area of ...3D-COFs permit co-crystallization with other materials driven by supramolecular interactions. We designed a new subphthalocyanine-based 3D covalent organic framework (NEUCOF1) capable of forming cocrystals with fullerene (C60) via periodic ball-and-socket binding motifs. The high cocrystalline surface area and long-range order of NEUCOF1 eliminate the typical surface area vs long-range order trade-off in organic photovoltaics (OPVs). We used plane-wave density functional theory (PBE) to optimize NEUCOF1 and NEUCOF1–C60 co-crystals and determine their electronic band structures. Molecular dynamics (MD) simulations showed that dispersive interactions promote co-crystallinity in NEUCOF1–C60 and are stable up to 350 K. The band structures at 0 and 350 K suggest that there is a driving force of 0.27 eV for exciton charge transfer to the pocket-bound fullerenes. Charge separation could then occur at the COF-C60 D–A interface, followed by the transfer of the free electron to the nanowire of C60 acceptors with a driving force of 0.20 eV.
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The synthesis and characterization of novel photochromic diarylethene-based linkers for use in metal–organic frameworks is described including crystal structure analysis of nearly all reaction ...intermediates. The bis-carboxylated dithien-3-ylphenanthrenes can be prepared under relatively mild conditions in high yield and were subsequently used to create a photoresponsive metal–organic framework, UBMOF-1. While the photochromism of the ligand TPDC in solution is fully reversible, the cycloreversion reaction is suppressed when this linker is incorporated into the crystalline framework of UBMOF-1.
Hexafluorobenzene and many of its derivatives exhibit a chemoselective photochemical isomerization, resulting in highly strained, Dewar-type bicyclohexenes. While the changes in absorption and ...emission associated with benzene hexafluorination have been attributed to the so-called “perfluoro effect”, the resulting electronic structure and photochemical reactivity of hexafluorobenzene is still unclear. We now use a combination of ultrafast time-resolved spectroscopy, multiconfigurational computations, and non-adiabatic dynamics simulations to develop a holistic description of the absorption, emission, and photochemical dynamics of the 4π-electrocyclic ring-closing of hexafluorobenzene and the fluorination effect along the reaction coordinate. Our calculations suggest that the electron-withdrawing fluorine substituents induce a vibronic coupling between the lowest-energy 1B2u (ππ*) and 1E1g (πσ*) excited states by selectively stabilizing the σ-type states. The vibronic coupling occurs along vibrational modes of e2u symmetry which distorts the excited-state minimum geometry resulting in the experimentally broad, featureless absorption bands, and a ∼100 nm Stokes shift in fluorescencein stark contrast to benzene. Finally, the vibronic coupling is shown to simultaneously destabilize the reaction pathway toward hexafluoro-benzvalene and promote molecular vibrations along the 4π ring-closing pathway, resulting in the chemoselectivity for hexafluoro-Dewar-benzene.
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Background
The current technique for locating nonpalpable breast lesions is wire localization (WL). Radioactive seed localization and intraoperative ultrasound were developed to improve difficulties ...with WL. The SAVI SCOUT surgical guidance system was developed to improve these methods. The SCOUT system is a non-radioactive, FDA-cleared medical device that uses electromagnetic wave technology to provide real-time guidance during excisional breast procedures.
Methods
Consenting patients underwent localization and excision using an implantable electromagnetic wave reflective device (reflector) and a detector handpiece with a console. Using image guidance, the reflector was placed up to 7 days before the surgical procedure. The primary end points of the study were successful reflector placement, localization, and retrieval. The secondary end points were percentage of clear margins, reexcision rates, days of placement before excision, and physician comparison with WL.
Results
This study analyzed 50 patients. The reflectors were placed under mammographic guidance (
n
= 18, 36 %) or ultrasound guidance (
n
= 32, 64 %). Of the 50 patients, 10 (20 %) underwent excisional biopsy and 40 (80 %) had a lumpectomy. The lesion and reflector were successfully removed in all 50 patients, and no adverse events occurred. Of the 41 patients who had in situ and/or invasive carcinoma identified, 38 (93 %) had clear margins and 3 (7 %) were recommended for reexcision.
Conclusions
These data suggest that the SCOUT system is safe and effective for guiding the excision of nonpalpable breast lesions and a viable alternative to standard localization options. A larger prospective, multi-institution trial of SCOUT currently is underway to validate these findings.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The solution chemistry and solid state structures of the Co(II), Fe(II), and Ni(II) complexes of N,N′-bis(imidazole-2-ylmethyl)-4,10-diaza-15-crown-5 (HINO) are reported. The Co(II) and Ni(II) ...complexes of HINO are the first examples of paraCEST agents (paramagnetic chemical exchange saturation transfer) that feature exchangeable imidazole NH protons. The crystal structures of Co(HINO)CoCl4·H2O and Fe(HINO)(CF3SO3)2 have the metal ions coordinated to four nitrogen and three oxygen donor atoms of the macrocyclic ligand in a distorted pentagonal bipyramidal geometry. In Ni(HINO)(CF3SO3)2, the nickel ion is bound to only two of the three ether oxygens and three nitrogens to produce a complex with a distorted octahedral geometry. The 1H NMR spectra of the three paramagnetic complexes show resonances characteristic of effective C 2 symmetry in solution. CEST peaks attributed to the imidazole NH proton of the pendent group are observed at 32 and 55 ppm away from bulk water for Co(HINO)2+ and Ni(HINO)2+, respectively, on a 11.7 or 9.4 T NMR spectrometer. For both complexes, an optimal CEST effect was observed at pH 7.2, and the rate constant for proton exchange under these conditions was 1.0 × 103 s–1. Fe(HINO)2+ did not produce a CEST peak due to oxidation of the complex in water at neutral pH. The CEST peak of Co(HINO)2+ or Ni(HINO)2+ is observed in the presence of human serum albumin (HSA). These complexes show enhanced kinetic inertness toward dissociation in acid or in the presence of HSA in comparison to analogous complexes with amide pendent groups.
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The Engage Study is a longitudinal biobehavioral cohort study of gay, bisexual and other men who have sex with men (GBM) in Toronto, Montreal, and Vancouver. Baseline data (2,449 participants) were ...collected from February 2017 - August 2019 using respondent-driven sampling (RDS). Recruitment in Montreal required fewer seeds, had a much shorter recruitment period, and recruited the largest sample.
To better understand why RDS recruitment was more successful in Montreal compared to other sites, we conducted an analysis to examine RDS recruitment characteristics for GBM in each of the three study sites, explore demographic characteristics and measures of homophily, that is, the tendency of individuals to recruit other study participants who are like themselves, and compared motivations for study participation.
Montreal had the greatest proportion of participants over the age of 45 (29.1% in Montreal, 24.6% in Vancouver, and 21.0% in Toronto) and the highest homophily for this age group, but homophily was high across the three cities. Montreal also reported the lowest percentage of participants with an annual income greater or equal to $60,000 (7.9% in Montreal, 13.1% in Vancouver and 10.6% in Toronto), but homophily was similar across all three cities. The majority of participants indicated interest in sexual health and HIV as the main reason for participating (36.1% in Montreal, 34.7% in Vancouver, and 29.8% in Toronto). Financial interest as the main reason for participation was low (12.7% in Montreal, 10.6% in Vancouver, and 5.7% in Toronto).
Taken together, although we found some differences in study demographic characteristics and homophily scores, we were unable to fully explain the different recruitment success based on the data available. Our study underlines the fact that success of RDS implementation may vary by unknown factors, and that researchers should be proactive and flexible to account for variability.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Storing solar energy is a vital component of using renewable energy sources to meet the growing demands of the global energy economy. Molecular solar thermal (MOST) energy storage is a promising ...means to store solar energy with on-demand energy release. The light-induced isomerization reaction of norbornadiene (NBD) to quadricyclane (QC) is of great interest because of the generally high energy storage density (0.97 MJ kg–1) and long thermal reversion lifetime (t 1/2,300K = 8346 years). However, the mechanistic details of the ultrafast excited-state 2 + 2-cycloaddition are largely unknown due to the limitations of experimental techniques in resolving accurate excited-state molecular structures. We now present a full computational study on the excited-state deactivation mechanism of NBD and its dimethyl dicyano derivative (DMDCNBD) in the gas phase. Our multiconfigurational calculations and nonadiabatic molecular dynamics simulations have enumerated the possible pathways with 557 S2 trajectories of NBD for 500 fs and 492 S1 trajectories of DMDCNBD for 800 fs. The simulations predicted the S2 and S1 lifetimes of NBD (62 and 221 fs, respectively) and the S1 lifetime of DMDCNBD (190 fs). The predicted quantum yields of QC and DCQC are 10 and 43%, respectively. Our simulations also show the mechanisms of forming other possible reaction products and their quantum yields.
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