Soft fluorescent nanomaterials have attracted recent attention as imaging agents for biological applications, because they provide the advantages of good biocompatibility, high brightness, and easy ...biofunctionalization. Here, we provide a survey of recent developments in fluorescent soft nano-sized biological imaging agents. Various soft fluorescent nanoparticles (NPs) (including dye-doped polymer NPs, semiconducting polymer NPs, small-molecule organic NPs, nanogels, micelles, vesicles, and biomaterial-based NPs) are summarized from the perspectives of preparation methods, structure, optical properties, and surface functionalization. Based on both optical and functional properties of the nano-sized imaging agents, their applications are then reviewed in terms of
in vitro
imaging,
in vivo
imaging, and cellular-process imaging, by means of specific or nonspecific targeting.
Various soft fluorescent nanomaterials based on organic chromophores are highly competent nano-probes for
in vitro
and
in vivo
imaging.
Enthalpies of nine TiO2 polymorphs under different pressures are presented to study the relative stability of the TiO2 polymorphs. It is important to include the dispersion correction for van der ...Waals interaction and the Hubbard U term for the Ti 3d orbital in the DFT-GGA calculation to correctly reproduce the relative stability of rutile, brookite, and anatase. Band structures for the TiO2 polymorphs are calculated by density functional theory with generalized gradient approximation, and the band energies at high symmetry k-points are corrected using the GW method to accurately determine the band gap. The differences between direct band gap energies and indirect band gap energies are very small for rutile and columbite-structured TiO2, indicating a quasi-direct band gap character. For optical response calculations, two-particle effects have been included by solving the Bethe–Salpeter equation for Coulomb correlated electron–hole pairs. TiO2 with baddeleyite, pyrite, and fluorite structures has optical transitions in the violet light region.
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We present a first-principles study of effects of small biaxial strain (varepsilon < or = 5%) and perpendicular electric field (E-field) on the electronic and phonon properties of low-buckled ...silicene and germanene. With an increase of the biaxial strain, the conduction bands at the high-symmetric Gamma and M points of the first Brillouin zone shift significantly towards the Fermi level in both silicene and germanene. In contrast, the E-field changes the band dispersions near the Gamma and open a small band gap at the K point in silicene. We found that the field-induced gap opening in silicene could be enhanced by a compressive strain while mitigated by a tensile strain. This result highlights the tunability of the electronic structure of silicene by combining mechanical strain and electric field.
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Previous calculations of the dielectric and optical properties of 2D materials often overlooked or circumvented the influence of vacuum spacing introduced in periodic calculations, which gave rise to ...mispredictions of the intrinsic properties of 2D materials or merely qualitative results. We first elucidated the relationship between the vacuum spacing and the dielectric and optical properties of 2D materials in periodic calculations, and then formulated an effective method to accurately predict the dielectric and optical properties of 2D materials by restoring the intrinsic dielectric functions of 2D materials independent of the additional vacuum spacing. As examples, the intrinsic dielectric and optical properties of ultrathin hexagonal boron nitride (h-BN) and molybdenum sulphide (MoS
2
) from a monolayer to a pentalayer, including dielectric functions, optical absorption coefficients, refraction indexes, reflectivities, extinction coefficients, and energy loss functions, have been calculated by our method. Our calculations reveal that the out-of-plane optical dielectric constants, static refraction indexes, and static reflectivities of 2D h-BN and MoS
2
increase as the number of layers increases, while the in-plane counterparts remain unchanged. The excitonic frequency-dependent optical properties of h-BN and MoS
2
from a monolayer to bulk are also calculated by solving the Bethe-Salpeter equation and they show strong anisotropy. The present method shows better agreement with the experimental results compared to previous calculations and demonstrates enormous potential to investigate the dielectric and optical properties of other 2D materials extensively and quantitatively.
A highly feasible method to restore the intrinsic optical properties of 2D materials in supercell calculations was formulated and applied.
Recently, a great deal of interest has been developed to isolate and investigate novel bioactive components with health benefit effects from natural resources. The dried root of Astragalus ...membranaceus, one of the most popular health-promoting herbal medicines, has been used historically as an immunomodulating agent for the treatment of common cold, diarrhea, fatigue and anorexia for more than 2000 years. Modern phytochemistry and pharmacological experiments have proved that polysaccharide is one of the major active ingredients in the root of A. membranaceus with various important bioactivities, such as immunomodulation, antioxidant, antitumor, anti-diabetes, antiviral, hepatoprotection, anti-inflammation, anti-atherosclerosis, hematopoiesis and neuroprotection. The aim of the present review is to summarize previous and current references and give a comprehensive summary regarding the structural features and biological activities of A. membranaceus polysaccharides in order to provide new insight for further development of these macromolecules.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A novel dielectric material of monolayer 1T-HfO2 has been investigated using first-principles calculations. The stability of 1T-HfO2 has been proved by both phonon dispersions and ab initio molecular ...dynamics calculations, although its 2H structural counterpart is dynamically unstable. 1T-HfO2 monolayer can be cleaved from the (111) facet of cubic HfO2. It is found that 1T-HfO2 has a large band gap of 6.73 eV, exceeding the band gaps of h-BN (5.97 eV) and bulk HfO2 (5.7 eV). From the microscopic perspective of dielectric polarization, we provide an explanation for the dependence of the dielectric constant directly calculated from the supercell of a two-dimensional (2D) system on the variable vacuum spacing, and we thus obtain a rational method for accurately evaluating the dielectric constants of 2D materials based on the calculated value obtained from a supercell to meet periodic conditions. Our derivation can be verified by the data fitting of a series of calculations with different vacuum spacings. The static dielectric constants of 1T-HfO2 along the in-plane and out-of-plane directions are 27.35 and 4.80, respectively, higher than those of monolayer h-BN. The large band gap and high dielectric constant make 1T-HfO2 a promising candidate as a dielectric layer in 2D field-effect transistors and heterojunctions.
Ab initio calculations based on density functional theory are performed to study the stability of newly proposed C3N4 forms. Heptazine-based g-C3N4 was found to be energetically favored relative to ...other phases. The quasiparticle band energies of different C3N4 phases are calculated using the GW method. Among the seven phases of C3N4 studied, only the pseudocubic phase and g-h-triazine phase have direct band gaps, and all of the other phases have indirect band gaps. The band gap of α-C3N4, β-C3N4, cubic-C3N4, pseudocubic-C3N4, g-h-triazine, g-o-triazine and g-h-heptazine is 5.49 eV, 4.85 eV, 4.30 eV, 4.13 eV, 2.97 eV, 0.93 eV and 2.88 eV, respectively. From the viewpoint of band gap energies, both the g-h-heptazine and the g-h-triazine phases can be used as suitable photocatalysts for hydrogen production using water.
► Band gap characters of seven C3N4 polymorphs investigated by GW method. ► g-h-triazine phase of graphitic C3N4 has a direct band gap of 2.97 eV. ► g-h-heptazine phase of graphitic C3N4 has an indirect band gap of 2.88 eV. ► g-o-triazine phase of graphitic C3N4 has an indirect band gap of 0.93 eV.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Recently, isolation and investigation of novel ingredients with biological activities and health benefit effects from natural resources have attracted a great deal of attention. The fruit of Lycium ...barbarum L., a well-known Chinese herbal medicine as well as valuable nourishing tonic, has been used historically as antipyretic, anti-inflammation and anti-senile agent for thousands of years. Modern pharmacological experiments have proved that polysaccharide is one of the major ingredients responsible for those biological activities in L. barbarum. It has been demonstrated that L. barbarum polysaccharides had various important biological activities, such as antioxidant, immunomodulation, antitumor, neuroprotection, radioprotection, anti-diabetes, hepatoprotection, anti-osteoporosis and antifatigue. The purpose of the present review is to summarize previous and current references regarding biological activities as well as potential health benefits of L. barbarum polysaccharides.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Geometry optimizations are performed for three polytypes of h-BN using density functional theory with dispersion correction for the van der Walls interaction. Quasiparticle band structure ...calculations are carried out to solve the controversy on band gap type of h-BN. Band energies are corrected by GW method. The h-BN with Bk structure has an indirect band gap of 5.840eV. Two kinds of h-BN polytypes are shown to be mechanically stable and have quasi-direct band gap type.
► Structures of hexagonal boron nitride polytypes are studied by dispersion-corrected DFT. ► Band gap characters of hexagonal boron nitride are predicted by GW method. ► Hexagonal boron nitride polytype with quasi-direct band gap type is probably exists. ► GW band-gap energies are used to interpret recently reported experimental results.
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