A detailed investigation of the photophysical parameters and photochemical reactivity of meso-methyl BODIPY photoremovable protecting groups was accomplished through systematic variation of the ...leaving group (LG) and core substituents as well as substitutions at boron. Efficiencies of the LG release were evaluated using both steady-state and transient absorption spectroscopies as well as computational analyses to identify the optimal structural features. We find that the quantum yields for photorelease with this photocage are highly sensitive to substituent effects. In particular, we find that the quantum yields of photorelease are improved with derivatives with higher intersystem crossing quantum yields, which can be promoted by core heavy atoms. Moreover, release quantum yields are dramatically improved by boron alkylation, whereas alkylation in the meso-methyl position has no effect. Better LGs are released considerably more efficiently than poorer LGs. We find that these substituent effects are additive, for example, a 2,6-diiodo-B-dimethyl BODIPY photocage features quantum yields of 28% for the mediocre LG acetate and a 95% quantum yield of release for chloride. The high chemical and quantum yields combined with the outstanding absorption properties of BODIPY dyes lead to photocages with uncaging cross sections over 10 000 M–1 cm–1, values that surpass cross sections of related photocages absorbing visible light. These new photocages, which absorb strongly near the second harmonic of an Nd:YAG laser (532 nm), hold promise for manipulating and interrogating biological and material systems with the high spatiotemporal control provided by pulsed laser irradiation, while avoiding the phototoxicity problems encountered with many UV-absorbing photocages. More generally, the insights gained from this structure–reactivity relationship may aid in the development of new highly efficient photoreactions.
Photocages are light-sensitive chemical protecting groups that provide external control over when, where, and how much of a biological substrate is activated in cells using targeted light ...irradiation. Regrettably, most popular photocages (e.g., o-nitrobenzyl groups) absorb cell-damaging ultraviolet wavelengths. A challenge with achieving longer wavelength bond-breaking photochemistry is that long-wavelength-absorbing chromophores have shorter excited-state lifetimes and diminished excited-state energies. However, here we report the synthesis of a family of BODIPY-derived photocages with tunable absorptions across the visible/near-infrared that release chemical cargo under irradiation. Derivatives with appended styryl groups feature absorptions above 700 nm, yielding photocages cleaved with the highest known wavelengths of light via a direct single-photon-release mechanism. Photorelease with red light is demonstrated in living HeLa cells, Drosophila S2 cells, and bovine GM07373 cells upon ∼5 min irradiation. No cytotoxicity is observed at 20 μM photocage concentration using the trypan blue exclusion assay. Improved B-alkylated derivatives feature improved quantum efficiencies of photorelease ∼20-fold larger, on par with the popular o-nitrobenzyl photocages (εΦ = 50–100 M–1 cm–1), but absorbing red/near-IR light in the biological window instead of UV light.
This is a comparative study in search for common patterns in the relaxation dynamics of amorphous materials in the approach of a liquid-to-solid transition from the liquid side. Observations with two ...representative materials provide guidance for the study. The first material, a concentrated colloidal suspension, represents the glass transition. The second material is a cross-linking polymer far above its glass transition; it represents gelation. The entire study is founded in Boltzmann’s constitutive equation of linear viscoelasticity; the stress is caused by a wide range of relaxation modes where, as argued here, fast modes dominate gelation and slow modes dominate the glass transition. For both classes of amorphous materials, the relaxation time spectrum broadens and adopts powerlaw format, but the powerlaw exponent is positive for the glass transition and negative for gelation, i.e. the relaxation patterns of gelling fluids and glass formers are inverse near the transition. Several examples are shown for each class of materials in order to test the proposed transition behavior for glasses (colloidal and molecular) on the one side and chemical/physical gels on the other. Among several results, this experimental study provides a decisive criterion that distinguishes the glass transition from gelation. It also shows a relation between the zero shear viscosity and the diverging longest relaxation time for both materials.
Difunctionalization reactions of C-C σ-bonds have the potential to streamline access to molecules that would otherwise be difficult to prepare. However, the development of such reactions is ...challenging because C-C σ-bonds are typically unreactive. Exploiting the high ring-strain energy of polycyclic carbocycles is a common strategy to weaken and facilitate the reaction of C-C σ-bonds, but there are limited examples of highly strained C-C σ-bonds being used in difunctionalization reactions. We demonstrate that highly strained bicyclo1.1.0butyl boronate complexes (strain energy ca. 65 kcal/mol), which were prepared by reacting boronic esters with bicyclo1.1.0butyl lithium, react with electrophiles to achieve the diastereoselective difunctionalization of the strained central C-C σ-bond of the bicyclo1.1.0butyl unit. The reaction shows broad substrate scope, with a range of different electrophiles and boronic esters being successfully employed to form a diverse set of 1,1,3-trisubstituted cyclobutanes (>50 examples) with high diastereoselectivity. The high diastereoselectivity observed has been rationalized based on a combination of experimental data and DFT calculations, which suggests that separate concerted and stepwise reaction mechanisms are operating, depending upon the migrating substituent and electrophile used.
Zeolites play a crucial part in acid-base heterogeneous catalysis. Fundamental insight into their internal architecture is of great importance for understanding their structure-function ...relationships. Here, we report on a new approach correlating confocal fluorescence microscopy with focused ion beam-electron backscatter diffraction, transmission electron microscopy lamelling and diffraction, atomic force microscopy and X-ray photoelectron spectroscopy to study a wide range of coffin-shaped MFI-type zeolite crystals differing in their morphology and chemical composition. This powerful combination demonstrates a unified view on the morphology-dependent MFI-type intergrowth structures and provides evidence for the presence and nature of internal and outer-surface barriers for molecular diffusion. It has been found that internal-surface barriers originate not only from a 90 degrees mismatch in structure and pore alignment but also from small angle differences of 0.5 degrees-2 degrees for particular crystal morphologies. Furthermore, outer-surface barriers seem to be composed of a silicalite outer crust with a thickness varying from 10 to 200 nm.
Bacteria have the potential to translocate between sites in the human body, but the dynamics and consequences of within-host bacterial migration remain poorly understood. Here we investigate the link ...between gut and lung Pseudomonas aeruginosa populations in an intensively sampled ICU patient using a combination of genomics, isolate phenotyping, host immunity profiling, and clinical data. Crucially, we show that lung colonization in the ICU was driven by the translocation of P. aeruginosa from the gut. Meropenem treatment for a suspected urinary tract infection selected for elevated resistance in both the gut and lung. However, resistance was driven by parallel evolution in the gut and lung coupled with organ specific selective pressures, and translocation had only a minor impact on AMR. These findings suggest that reducing intestinal colonization of Pseudomonas may be an effective way to prevent lung infections in critically ill patients.
The effect of internal mammary and medial supraclavicular lymph-node irradiation (regional nodal irradiation) added to whole-breast or thoracic-wall irradiation after surgery on survival among women ...with early-stage breast cancer is unknown.
We randomly assigned women who had a centrally or medially located primary tumor, irrespective of axillary involvement, or an externally located tumor with axillary involvement to undergo either whole-breast or thoracic-wall irradiation in addition to regional nodal irradiation (nodal-irradiation group) or whole-breast or thoracic-wall irradiation alone (control group). The primary end point was overall survival. Secondary end points were the rates of disease-free survival, survival free from distant disease, and death from breast cancer.
Between 1996 and 2004, a total of 4004 patients underwent randomization. The majority of patients (76.1%) underwent breast-conserving surgery. After mastectomy, 73.4% of the patients in both groups underwent chest-wall irradiation. Nearly all patients with node-positive disease (99.0%) and 66.3% of patients with node-negative disease received adjuvant systemic treatment. At a median follow-up of 10.9 years, 811 patients had died. At 10 years, overall survival was 82.3% in the nodal-irradiation group and 80.7% in the control group (hazard ratio for death with nodal irradiation, 0.87; 95% confidence interval CI, 0.76 to 1.00; P=0.06). The rate of disease-free survival was 72.1% in the nodal-irradiation group and 69.1% in the control group (hazard ratio for disease progression or death, 0.89; 95% CI, 0.80 to 1.00; P=0.04), the rate of distant disease-free survival was 78.0% versus 75.0% (hazard ratio, 0.86; 95% CI, 0.76 to 0.98; P=0.02), and breast-cancer mortality was 12.5% versus 14.4% (hazard ratio, 0.82; 95% CI, 0.70 to 0.97; P=0.02). Acute side effects of regional nodal irradiation were modest.
In patients with early-stage breast cancer, irradiation of the regional nodes had a marginal effect on overall survival. Disease-free survival and distant disease-free survival were improved, and breast-cancer mortality was reduced. (Funded by Fonds Cancer; ClinicalTrials.gov number, NCT00002851.).
meso-methyl BODIPY photocages have recently emerged as an exciting new class of photoremovable protecting groups (PPGs) that release leaving groups upon absorption of visible to near-infrared light. ...In this Perspective, we summarize the development of these PPGs and highlight their critical photochemical properties and applications. We discuss the absorption properties of the BODIPY PPGs, structure–photoreactivity studies, insights into the photoreaction mechanism, the scope of functional groups that can be caged, the chemical synthesis of these structures, and how substituents can alter the water solubility of the PPG and direct the PPG into specific subcellular compartments. Applications that exploit the unique optical and photochemical properties of BODIPY PPGs are also discussed, from wavelength-selective photoactivation to biological studies to photoresponsive organic materials and photomedicine.
Microglia, the resident myeloid cells of the central nervous system, play important roles in life-long brain maintenance and in pathology. Despite their importance, their regulatory dynamics during ...brain development have not been fully elucidated. Using genome-wide chromatin and expression profiling coupled with single-cell transcriptomic analysis throughout development, we found that microglia undergo three temporal stages of development in synchrony with the brain--early, pre-, and adult microglia--which are under distinct regulatory circuits. Knockout of the gene encoding the adult microglia transcription factor MAFB and environmental perturbations, such as those affecting the microbiome or prenatal immune activation, led to disruption of developmental genes and immune response pathways. Together, our work identifies a stepwise microglia developmental program integrating immune response pathways that may be associated with several neurodevelopmental disorders.
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