Variations on the Bergman Cyclization Theme: Electrocyclizations of Ionic Penta-, Hepta-, and Octadiynes.

The Bergman cyclization of ()-hexa-3-ene-1,5-diyne to form the aromatic diradical -benzyne has garnered attention as a potential antitumor agent due to its relatively low cyclization barrier and the stability of the resulting diradical. Here, we present a theoretical investigation of several ionic extensions of the fundamental Bergman cyclization: electrocyclizations of the penta-1,4-diyne anion, hepta-1,6-diyne cation, and octa-1,7-diyne dication, leveraging the spin-flip formulation of the equation-of-motion coupled cluster theory with single and double substitutions (EOM-SF-CCSD). Though the penta-1,4-diyne anion exhibits a large cyclization barrier of +66 kcal mol, cyclization of both the hepta-1,6-diyne cation and octa-1,7-diyne dication along a previously unreported triplet pathway requires relatively low energy.

Single-molecule super-resolution light-sheet microscopy.

Single-molecule super-resolution imaging is a new promising tool for investigation of sub-cellular structures. Concurrently, light-sheet microscopy, also known as selective plane illumination microscopy (SPIM), has gained rapid favor with the imaging community in developmental biology due to its fast speed, high contrast, deep penetration, and low phototoxicity. While nearly a dozen reviews thoroughly describe the development of light-sheet microscopy and its technological breakthroughs with a main focus on improving the 3D imaging speed of fish embryos, central nervous system, and other tissues, few have addressed the potential of combining light-sheet microscopy and localization-based super-resolution imaging to achieve sub-diffraction-limited resolution.

Non-invasive monitoring of cell metabolism and lipid production in 3D engineered human adipose tissues using label-free multiphoton microscopy.

Non-linear optical microscopy methods can characterize over time multiple functional properties of engineered tissues during development. Here, we demonstrate how the combined use of third-harmonic generation (THG) and two-photon excited fluorescence (2PEF) imaging can provide direct quantitative biomarkers of adipogenic stem cell differentiation and metabolic state, respectively. Specifically, we imaged over nine weeks silk scaffolds embedded with human mesenchymal stem cells and exposed to either propagation (PM) or adipogenic differentiation media (AM).

Multicolor two-photon tissue imaging by wavelength mixing.

We achieve simultaneous two-photon excitation of three chromophores with distinct absorption spectra using synchronized pulses from a femtosecond laser and an optical parametric oscillator. The two beams generate separate multiphoton processes, and their spatiotemporal overlap provides an additional two-photon excitation route, with submicrometer overlay of the color channels. We report volume and live multicolor imaging of 'Brainbow'-labeled tissues as well as simultaneous three-color fluorescence and third-harmonic imaging of fly embryos.

Molecular orientation in dry and hydrated cellulose fibers: a coherent anti-Stokes Raman scattering microscopy study.

Coherent anti-Stokes Raman scattering (CARS) microscopy is combined with spontaneous Raman scattering microspectroscopy and second harmonic generation (SHG) microscopy to interrogate the molecular alignment in dry and hydrated cellulose fibers. Two types of cellulose were investigated: natural cellulose I in cotton fibers and regenerated cellulose II in rayon fibers. On the basis of the orientation of the methylene symmetric stretching vibration, the molecular alignment of cellulose microfibrils is found to be conserved on the micrometer scale.

Quantitative detection of chemical compounds in human hair with coherent anti-Stokes Raman scattering microscopy.

Coherent anti-Stokes Raman scattering (CARS) microscopy is used to determine the distribution and concentration of selected compounds in intact human hair. By generating images based on ratiometric CARS contrast, quantitative concentration maps of both water and externally applied d-glycine are produced in the cortex of human hair fibers. Both water and d-glycine are found to homogeneously distribute throughout the cortical regions of the hair.

Characterization of microstructures fabricated by two-photon polymerization using coherent anti-stokes Raman scattering microscopy.

We demonstrate the possibility to image microstructures fabricated by two-photon polymerization (TPP) using coherent anti-Stokes Raman scattering (CARS) microscopy. The imaging contrast based on chemical selectivity attained by CARS microscopy is used to gather qualitative information on TPP. Upon the basis of detailed knowledge of the characteristic signatures of the photoresist Raman spectrum, quantitative relationships between laser writing conditions and polymer cross-linking are demonstrated.

Following dimethyl sulfoxide skin optical clearing dynamics with quantitative nonlinear multimodal microscopy.

Second-harmonic generation (SHG) imaging is combined with coherent anti-Stokes Raman scattering (CARS) microscopy to follow the process of optical clearing in human skin ex vivo using dimethyl sulfoxide (DMSO) as the optical clearing agent. SHG imaging revealed that DMSO introduces morphological changes to the collagen I matrix. By carefully measuring the dynamic tissue attenuation of the coherent nonlinear signal, using CARS reference signals during the clearing process, it is found that DMSO reduces the overall SHG response from dermal collagen.