April 22, 2013
How do substituents affect isophorone luminogens emission? Luminogens with efficient solid-state emission have high-tech applications such as fluorescence imaging and light-emitting devices. A research team at Anhui University (Hefei, China) led by H. Zhou created a series of isophorone derivatives (1–4, Figure 1) that luminesce intensely in the solid state. They then studied how the substituents affect the luminogens’ photophysical behavior.
When the isophorone substituent varies from imidazole (1) to pyrazole (2), triazole (3), and carbazole (4), the luminogen’s light-emitting properties (e.g., color, lifetime, and quantum yield) change because of variations in electronic structure and molecular packing. The luminogen molecules do not emit in the solution state, but their solid aggregates emit efficiently—yet another example of aggregation-induced emission (AIE).
Figure 2 shows fluorescence images of 1–4 in powder form, at 5 × 10–5 M concentration in neat EtOH solution (“0%”), and at the same concentration in EtOH–H2O (5:95 v/v) suspension (“95%”) when the molecules are excited with a 365-nm light source.
The aggregated solids are clearly more fluorescent than the solutions; and the fluorescence color depends on the isophorone substituent. The authors believe that the AIE effect is the result of restricted intramolecular rotation imposed by aggregate formation. (J. Org. Chem. 2013, 78, 3222–3234; Ben Zhong Tang)
Prevent hangovers with enzyme nanocomplexes. The activity and functionality of enzymes rely largely on their environment. In certain cases, multiple enzymes are spatially colocalized to enhance reactivity and specificity. By mimicking this pattern, which is found widely in biological systems, L. Shi, W. Chen, C. Ji, Y. Lu, and coauthors at Nankai University (Tianjin, China); the University of California, Los Angeles; the University of Southern California (Los Angeles); Shanghai Jiao Tong University; and the Beijing Institute of Biotechnology designed nanocomplexes with conjugated enzymes encapsulated in polymeric “nanocontainers”. The constructs can perform several synergistic or complementary enzymatic functions.
For example, the triple-enzyme nanocomplex n(HRP-GOx-Inv) can be assembled through a DNA complex that contains inhibitors for three enzymes: horseradish peroxidase (HRP), glucose oxidase (GOx), and invertase (Inv). The assembled enzyme group is polymerized in situ, which encapsulates the enzymes in a permeable shell. The inhibitor DNA strand is then removed
The authors show that n(HRP-GOx-Inv) and n(HRP-GOx), a similar nanocomplex, have 24- and 34-fold greater o-dianisidine oxidation rates, respectively, than native enzyme mixtures. The nanocomplexes also appear to be more robust; 70% of their activity is retained after incubation at 65 °C for 1 h. In contrast, the native enzyme mixtures lose >98% of their activity under the same conditions.
The authors also prepared the nanocomplex n(AOx-Cat), which contains alcohol oxidase (AOx) and catalase (Cat). Cat removes the toxic H2O2 generated from AOx-catalyzed oxidation. They tested n(AOx-Cat) as a prophylactic and antidote; in both cases, n(AOx-Cat) significantly lowered the concentration of blood alcohol in mice. The authors expect that incorporating aldehyde oxidase (ADOx) into n(AOx-Cat) will improve the efficiency of the nanocomplex. These findings may lead to ways to prevent or cure alcohol hangovers. (Nat. Nanotechnol. 2013, 8, 187–192; Xin Su)
Unravel nanoparticle self-assembly by using in situ transmission electron microscopy (TEM). Using in situ liquid TEM, Y. Liu and fellow researchers at Argonne National Laboratory (IL) explored the self-organization of negatively charged citrate ions with positively charged cetyltrimethylammonium (CTA)–gold nanoparticles (AuNPs) when they are exposed to electron beams (e-beams) in water. Time-lapse TEM images of AuNPs coated with CTA showed that they assemble into 1-D nanostructures when e-beam illumination is greater than a threshold value. Negatively charged Au NPs did not organize regardless of e-beam strength.
The authors believe that e-beam exposure influences the hydrated charge state and leads to reduced surface charge repulsion that allows the positively charged nanoparticles to self-assemble. Particle tracking with this technique displays local phenomena that occur during the assembly process.
The authors also explain the role of e-beam intensity in the occurrence and rate of AuNP self-organization. In mixtures of dissimilar CTA–AuNP sizes (20 and 45 nm), 1-D assembly occurs only between nanoparticles of same size because of voltage gradients, liquid cell–height separation, and variations in the surface charge layer. (J. Am. Chem. Soc. 2013, 135, 3764–3767; LaShanda Korley)
D. Libman and L. Huang* at Hofstra University (Hempstead, NY) reviewed several chemistry-related apps for smartphones. They selected and tested a dozen free or inexpensive (
The authors also discuss using several apps for teaching and learning chemistry; they focused on apps for molecule viewing, study guides and references, structure drawing, the periodic table, and utilities (e.g., calculating). They conclude that these inexpensive apps attract students, help them solve problems, and increase chemistry learning as a complement to traditional books and courses. (J. Chem. Educ. 2013, 90, 320–325; José C. Barros)
How stable are Togni’s reagents? Togni’s reagents, 1,3-dihydro-3,3-dimethyl-1-trifluoromethyl-1,2-benzodioxole (reagent I) and 1-trifluoromethyl-1,2-benzodoxol-3(1H)-one (reagent II), are versatile electrophilic trifluoromethylating compounds. N. Fiederling, J. Haller*, and H. Schramm at Novasep Synthesis (Leverkusen, Germany) report, however, that these compounds have explosive properties.
Reagent II, prepared by the authors, had a decomposition energy of 502 J/g, as measured by differential scanning calorimetry (DSC), but it was not shock- or friction-sensitive. Another sample, however, had a low impact sensitivity of 20 J, similar to that of TNT.
A purchased sample of reagent I had an even higher decomposition energy, 790 J/g. The energy was almost twice this value—1403 J/g—when measured in a glass vial, and its decomposition onset temperature was 135 °C. Presumably, there are interactions between the glass and fluoride released by reagent I.
The authors conclude that “these compounds should only be handled with the appropriate knowledge and safety measures. [L]aboratory work should be done behind safety shields with small amounts, open flames and circumstances that can produce sparks have to be avoided, grinding should not be done with brute force, and soft and polished tools should be used for manipulations. During preparation and especially isolation of these compounds, caking should be avoided, and lumps should be dispersed early. It must be emphasized that impurities may influence the thermal and mechanical sensitiveness. The transport of explosive compounds requires the permission of competent authorities.” (Org. Process Res. Dev. 2013, 17, 318–319; Will Watson)
Palladium nanoparticles catalyze the aerobic oxidation of hydrocarbons and alcohols. The selective aerobic oxidation of hydrocarbons and alcohols is used more and more frequently to produce fine chemicals such as aldehydes, ketones, acids, and esters. The catalytic efficiency of traditional methods, however, is not satisfactory. Y. Wang and co-workers at Zhejiang University (Hangzhou, China) prepared a series of palladium-based catalysts in the form of palladium-loaded, nitrogen-doped carbon materials that exhibit extraordinary catalytic activity for the aerobic oxidation of hydrocarbons and alcohols.
The authors first prepared nanostructured carbon materials (e.g., C-GluA-550) from D-glucose by using the borax-mediated hydrothermal carbonization method in the presence of nitrogen-containing additives. (In the materials’ nomenclature, the subscript denotes the additive and the number is the carbonization temperature.) The additives are stable structures that contain pyridinic, pyrrolic, or quaternary nitrogen atoms; the materials feature a hierarchical porous network with a Brunauer–Emmett–Teller surface area of 424 m2/g. Palladium nanoparticles were then deposited ultrasonically onto C-GluA-550.
The aerobic oxidation of indane in the presence of 0.5% Pd@C-GluA-550 at 120 °C reached a turnover frequency (TOF) of 863 h–1 with 30.4%conversion. Similarly, high TOFs were obtained with excellent selectivity in aerobic oxidations of benzyl alcohol (14,802 h–1) and 1-phenylethanol (13,181 h–1).
Under an oxygen atmosphere, the catalytic capability of Pd@C-GluA-550 was much higher than catalysts such as Au/TiO2 and Au/CeO2. 2-Octanol was selectively oxidized to 2-octanone with a TOF of 86 h–1, whereas traditional AuPd/TiO2 catalyst was inactive under the same conditions. Pd@C-GluA-550 catalysts can be recycled via centrifugation with negligible palladium loss. (Nat. Commun. 2013, 4, No. 1593; Xin Su)