Probing the periphery of dendrimers by heterogeneous electron transfer

The accessibility of the electroactive periphery was studied and compared for dendrimers and linear analogs by heterogeneous electron transfer using microelectrodes.     

Electronic structure and bonding studies on triple-decker sandwich complexes with a P6 middle ring

DFT and hybrid HF-DFT studies of structure and bonding of CpMP6MCp triple-decker sandwich complexes, ranging from 18-28 valence electrons (VE) with M=Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, show that the middle P6 ring complexes adopt symmetric planar (28 valence electron count [VEC]), asymmetric planar (26 VEC), and puckered (24 VEC) geometries. According to the mno Rule, 50 skeletal electrons are needed for these triple-decker cluster frameworks. For 28 VEC, this corresponds to 10 electrons more than the 50 electrons of the mno Rule if all VE of the metal are included. These additional electrons control the distortion of a P6 middle ring and other finer structural details. Completely filled 2a* and 2b* orbitals in 28 VE complexes lead to a planar symmetrical P6 middle ring, while the occupancy in either 2a* or 2b* alone explains the in-plane distortions (asymmetric) in 26 VE complexes. In comparison with 28 VE complexes, the puckering of P6 middle ring in 24 VE complexes is due to the greater stabilization of 5a and the extra stabilization of the +4 oxidation state of Ti. The quintet state of 22 VE complexes is planar as 2a* and 2b* are half filled. Similar geometrical and bonding patterns of CpScP6ScCp and C2P3H2ScC3P3H3ScC2P3H2 support the carbon-phosphorus analogy further. The 18 VE systems, CpScC3B3H6ScCp+ and CpScP3B3H3ScCp+, have the 50 skeletal electrons as stipulated by the mno Rule. Corresponding anions have 52 skeletal electrons (20 VE); the middle rings here are distorted in the plane.     

Retracted: Synthesis,Molecular Properties,and Biological Evaluation of Hybrid 1,2,3‐Triazolylpolyaza Heterocyclic Compounds

In this research article, a highly efficient, cost‐effective synthesis of various hybrid molecules possessing 1,2,3‐triazolyltetrazoles and evaluation of their biological activity have been addressed. The structure elucidation of these new library hybrid molecules has been carried out by IR, ¹H NMR, ¹³C NMR, and mass spectral analysis. The compounds have been screened for their anticancer activity against human colon cancer cell line Colo‐205 and human lung cancer cell line HOP‐205, and the results attest that most of the compounds have shown very good therapeutic nature. In particular, compounds 3d , 3j , 6a , and 6e were more cytotoxic than Adriamycin against all tested human cancer cell lines with 68%, 101.8%, 94%, and 104.5% growth, respectively. In the present investigation, a series of 3a – j and 6a – h were subjected to molecular properties prediction, drug likeness by Molinspiration, and toxicity risks by Molsoft software programs. All the 18 analogues were chosen on the basis of Lipinski “Rule of five” for the synthesis, screening their antibacterial and anticancer as oral bioavailable drugs/leads.     

Fire response of polyamide 6 with layered and fibrillar nanofillers

To improve the fire retardancy performance of polyamide 6 (PA 6), layered silicates are used in combination with multi-walled carbon nanotubes (CNTs) to address the issue of packing density and uniformity of the protective inorganic barrier formed at the burning surface of the nanocomposites during combustion. Benzimidazolium is used to modify the silicate layers instead of conventional alkyl ammonium surfactants to tackle the issue of thermal stability. However, the poor dispersion of the modified layered silicates in PA 6 has a significant negative effect on the fire performance of the materials and offsets the positive effect of CNTs. Also, the results point to the apparent contradictions with different fire exposure tests; that is, significant reductions in heat release and mass loss rates in the cone calorimetry test do not imply a higher rating in the UL 94 vertical burning test.     

Shedding Light on the Extinction‐Enhancement Duality in Gold Nanostar‐Enhanced Raman Spectroscopy

Surface‐enhanced Raman spectroscopy (SERS) has evolved from an esoteric physical phenomenon to a robust and effective analytical method recently. The need of addressing both the field enhancement and the extinction of nanoparticle suspensions, however, has been underappreciated despite its substantive impact on the sensing performance. A systematic experimental investigation of SERS enhancement and attenuation is performed in suspensions of gold nanostars, which exhibit a markedly different behavior in relation to conventional nanoparticles. The relationship is elucidated between the SERS enhancement and the localized surface plasmon resonance band, and the effect of the concentration of the gold nanostars on the signal propagation is investigated. It is shown that an optimal concentration of gold nanostars exists to maximize the enhancement factor (EF), and the maximum EF occurs when the LSPR band is blue‐shifted from the excitation wavelength rather than at the on‐resonance position.     

Synthesis and characterization of Y2Ti2O7 and ErxY2−xTi2O7 nanofibers

Journal of Sol-Gel Science and Technology - 1-D nanostructures are deemed to be important building blocks for future optical and optoelectronic nanodevices. We have used electrospinning methods to...     

Silica‐supported Perchloric Acid Catalyzed One‐pot Synthesis of 1,4‐Dihydropyridines

An environmentally friendly and highly efficient procedure for the preparation of 1,4‐dihydropyridines by the reaction between α,β‐unsaturated aldehydes, aromatic amines and β‐keto esters in the presence of silica supported perchloric acid is described.     

Near-infrared Fluorescence Spectroscopy Detects Alzheimer's Disease In Vitro

The purpose of this study was to investigate whether near-infrared (NIR) fluorescence spectroscopy could be used to detect Alzheimer's disease (AD) by brain tissue autofluorescence. Unfixed temporal cortex specimens from AD cases and age-matched, non-AD controls were frozen at autopsy and then thawed just prior to spectral measurement. Spectra of intrinsic tissue fluorescence induced by 647 nm light were recorded from 650 to 850 nm. We used principal component analysis of the tissue spectra from 17 AD cases and 5 non-AD control cases in a calibration study to establish a diagnostic algorithm. Retrospectively applied to the calibration set, the algorithm correctly classified 23 of 24 specimens. In a prospective study of 19 specimens from 5 AD brains and 2 non-AD control brains, 3 of the 4 control specimens and all AD specimens were correctly diagnosed. Both the excitation light used and the measured brain tissue autofluorescence are at NIR wavelengths that can propagate through skull and overlying tissue. Therefore, our results demonstrate an optical spectroscopic technique that carries direct molecular level information about disease. This is the first step toward a clinical tool that has the potential to be applied to the noninvasive diagnosis of AD in living patients.     

Dual‐Sensitized Luminescent Europium(ΙΙΙ) and Terbium(ΙΙΙ) Complexes as Bioimaging and Light‐Responsive Therapeutic Agents

Dual‐photosensitized stable Eu^ΙΙΙ and Tb^ΙΙΙ complexes, namely [Eu(dpq)(tfnb)₃] ( 1 ) and [Tb(dpq)(tfnb)₃] ( 2 ), in which dpq=dipyrido[3,2‐d:2′,3′‐f]quinoxaline and Htfnb=4,4,4‐trifluoro‐1‐(2‐napthyl)‐1,3‐butanedione, were designed as bioimaging and light‐responsive therapeutic agents. Their X‐ray structures, photophysical properties, biological interactions, photoinduced DNA damage, photocytotoxicity, and cellular uptake properties were studied. Discrete mononuclear complexes adopt an eight‐coordinated {LnN₂O₆} distorted square antiprism geometry with bidentate N,N‐donor dpq and O,O‐donor tfnb ligands. The designed probes have the advantage of dual‐sensitizing antennae (dpq, Htfnb) to modulate their desirable optical properties for cellular imaging and light‐responsive intracellular damage. The remarkable photostability, absence of inner‐sphere water (q<1), and longer excited‐state lifetimes of the complexes make them suitable as cellular‐imaging probes. The dpq ³T state is well located energetically to allow efficient energy transfer (ET) to the emissive ⁵D₀ and ⁵D₄ states of Eu^ΙΙΙ and Tb^ΙΙΙ. This leads to higher quantum yields (φ=0.15–0.20) in aqueous media and makes these compounds suitable cellular‐imaging probes. The complexes display significant binding ability toward DNA and bovine serum albumin (K≈10⁵ m ^?1). They effectively cleave supercoiled DNA to its nicked circular form at λ=365 nm through photoredox pathways. The cellular internalization studies showed cytosolic and nuclear localization. The remarkable photocytotoxicity of these probes offers a strategy towards developing photoresponsive Ln^ΙΙΙ probes as cellular‐imaging and phototherapeutic agents.     

Energy and charge transfer dynamics in fully decorated benzyl ether dendrimers and their disubstituted analogues

We examine the photophysics of a series of molecules consisting of a benzthiadiazole core surrounded by a network of benzyl ether arms terminated by aminopyrene chromophores, which function as both energy and electron donors. Three classes of molecules are studied: dendrimers whose peripheries are fully decorated with aminopyrene donors (F), disubstituted dendrimers whose peripheries contain only two donors (D), and linear analogues in which a pair of benzyl ether arms link two donors to the central core (L). The electronic energy transfer (EET) and charge transfer (CT) rates are determined by fluorescence lifetime measurements on the energy donors and electron acceptors, respectively. In all three types of molecules, the EET time scales as the square root of the generation number G, consistent with the flexible nature of the benzyl ether framework. Transient anisotropy measurements confirm that donor-donor energy hopping does not play a major role in determining the EET times. The CT dynamics occur on the nanosecond time scale and lead to stretched exponential decays, probably due to conformational disorder. Measurements at 100 degrees C confirm that conformational fluctuations play a role in the CT dynamics. The average CT time increases with G in the L and D molecules but decreases for the F dendrimers. This divergent behavior as G increases is attributed to the competing effects of larger donor-acceptor distances (which lengthen the CT time) versus a larger number of donors (which shorten the average CT time). This work illustrates two important points about light-harvesting and charge-separation dendrimers. First, the use of a flexible dendrimer framework can lead to a more favorable scaling of the EET time (and thus the light-harvesting efficiency) with dendrimer size, relative to what would be expected for a fully extended dendrimer. Second, fully decorated dendrimers can compensate for the distance-dependent slowdown in CT rate as G increases by providing additional pathways for the CT reaction to occur.