Increase In Optical Activity Research Articles

Processable Circularly Polarized Luminescence for the Synthesis of Chiral Plasmonic Nanoparticles

AbstractCircularly polarized light is previously shown as a chiral bias to enable the synthesis of chiral plasmonic nanomaterials through light‐matter interactions. The traditional approach for circularly polarized light generation relies on a “top‐down” approach by removing undesired light polarization through optics, which suffers from energy loss and compatibility issues. An alternative approach is to develop chiral phosphors that emit efficient circularly polarized luminescence (CPL). However, most materials fail to produce processable CPL with both high quantum yield and dissymmetry factors, let alone the synthesis of chiral nanomaterials. Herein, a liquid‐crystal‐templated framework is developed to assemble halide perovskite nanocrystals, CsPbX3 (X = Cl, Br, I), and achieved efficient CPL with the record‐high figure of merit (FM) for three primary colors (Red, Green, Blue). The fidelity of the CPL is further demonstrated in the synthesis of chiral gold nanoparticles, where a five‐fold increase in optical activity is achieved.

Synthesis and Characterization of Polyvinyl Chloride Matrix Composites with Modified Scrap Iron for Advanced Electronic, Photonic, and Optical Systems.

In this study, Fe2O3 powder was synthesized using the co-precipitation method from scrap iron, which was then treated with varying concentrations of copper. Afterwards, the modified Fe2O3 was reinforced in the PVC matrix by using the solution-casting method to synthesize PVC composite films, which were subjected to a UV-visible spectrophotometer, a Fourier transform infrared spectrophotometer, an X-ray diffractometer, and a thermal gravimetric analyzer to evaluate the optical, chemical, structural, and thermal properties. FTIR analysis reveals the formation of the composite through vibrational bands pertaining to both components present, whereas no significant changes in the XRD patterns of PVC were observed after the doping of modified iron oxide, which reveals the compatibility of fillers with the PVC matrix. The optical properties of the copper-doped iron oxide-PVC composites, including absorbance, refractive index, urbach energy, and optical as well as electrical conductivity are measured, and show an increase in optical activity when compared to the pure PVC compound. Moreover, the increased thermal stability of the synthesized composite was also observed and compared with conventional compounds, which, in accordance with all the other mentioned properties, makes the copper-dopped iron oxide-PVC composite an effective material for electronic, photonic, and optical device applications.

Stereochemical language in supramolecular polymer chemistry: How we can do better

AbstractStereochemical nomenclature remains a point of attention; especially now different fields in chemistry become more and more entwined. The ubiquitously used terminology “amplification of chirality” is fundamentally incorrect, as chirality cannot be amplified. Instead, we now recommend “amplification of asymmetry” as an alternative in the field of (supramolecular) polymer chemistry. Amplification of asymmetry refers to the increase of the magnitude of the asymmetry in the enantiomeric composition either at the molecular or the supramolecular level, and covers observations of nonproportional increase in optical activity in helical (supramolecular) polymers and in high enantiomeric excesses found when nonlinear effects are operative in asymmetric catalysis.

Influence of Eu valence on the optical activity of BaTiO3 decorated with CaF2 synthesized by microwave-assisted hydrothermal method.

Inorganic hybrid materials have promising applications in absorbers and for the photon harvesting of solar irradiation, such as in DSSC photoanodes. Moreover, investigation of the interactions between the photoanode constituent materials is extremely important, since it is known that the properties of the materials are strongly dependent on the nucleation and growth process. Therefore, the purpose of this work was to synthesize a system consisting of a synergic combination of two inorganic hosts, BaTiO3 and CaF2, synthesized together through a microwave-assisted hydrothermal method, which allows single-phase materials to be obtained after short synthesis times and at low temperatures. The increase in optical activity was investigated after the insertion of Eu ions. From the structural results, it was possible to observe that the method used to obtain the system was efficient, even using temperatures as low as 140 °C and a reaction time of one minute. The optical properties (emission and excitation) were evaluated in the visible and VUV region from 2.5 to 10.5 eV. The XANES Eu Liii edge differences associated with the XEOL results indicate that the synthesis method incorporated Eu3+ in the hosts and the surface of the two compounds, BaTiO3 and CaF2. Therefore, the combination between the Eu3+ activators and the F centers of the host increased the range for photon harvesting, making these systems a promising material for future applications in photoanodes for DSSCs.

Monolayer Filaments versus Multilayer Stacking of Bent-Core Molecules.

Bent-core materials exhibiting lamellar crystals (B4 phase), when dissolved in organic solvents, formed gels with helical ribbons made of molecular monolayers and bilayers, whereas strongly deformed stacks of 5-6 layers were found in the bulk samples. The width and pitch of the helical filaments were governed by molecular length; they both increased with terminal-chain elongation. It was also found that bulk samples were optically active, in contrast to the corresponding gels, which lacked optical activity. The optical activity of samples originated from the internal structure of the crystal layers rather than from the helicity of the filaments. A theoretical model predicts a strong increase in optical activity as the number of layers in the stack increases and its saturation for few layers, thus explaining the smaller optical activity for gels than for bulk samples. A strong increase and redshift in fluorescence was detected in gels as compared to the sol state.

Monolayer Filaments versus Multilayer Stacking of Bent‐Core Molecules

AbstractBent‐core materials exhibiting lamellar crystals (B4 phase), when dissolved in organic solvents, formed gels with helical ribbons made of molecular monolayers and bilayers, whereas strongly deformed stacks of 5–6 layers were found in the bulk samples. The width and pitch of the helical filaments were governed by molecular length; they both increased with terminal‐chain elongation. It was also found that bulk samples were optically active, in contrast to the corresponding gels, which lacked optical activity. The optical activity of samples originated from the internal structure of the crystal layers rather than from the helicity of the filaments. A theoretical model predicts a strong increase in optical activity as the number of layers in the stack increases and its saturation for few layers, thus explaining the smaller optical activity for gels than for bulk samples. A strong increase and redshift in fluorescence was detected in gels as compared to the sol state.

Optical recording of spatiotemporal patterns of cardiorespiratory neuronal activity in the nucleus tractus solitarii network imaged in situ

The pattern and distribution of neuronal activity evoked by sensory input in the nucleus tractus solitarii (NTS) is not well understood. In the present study, we performed optical recordings (MiCAM02 system, Brain Vision Inc) in situ to investigate the spatiotemporal pattern of NTS neuronal activity in response to activation of cardiorespiratory inputs. The dorsal medullary surface was exposed and stained with the voltage-sensitive dye, Di-2-ANEPEQ, at the level of calamus scriptorius. Graded electrical stimulation of the central vagus nerve and the brachial plexus (1 ms pulse, 200 ms duration, 1–10 Hz) at low frequency (<5 Hz) evoked a fast (50–75 ms), transient increase in optical activity that adapted rapidly; whereas, high frequency stimulation (>5 Hz) produced a sustained elevation of fluorescence that recovered following termination of the stimulus. In contrast, activation of peripheral chemoreceptors (NaCN, 0.03%) evoked a prolonged (4–6s) increase in optical activity that was superimposed by phasic changes in fluorescence coupled to the respiratory cycle. Synaptic blockade virtually abolished stimulus evoked fluorescence suggesting that optical signals represented post-synaptic activity. These results suggest that optical imaging is capable of detecting differences in spatiotemporal patterns of neuronal activity in the NTS evoked by distinct populations of cardiorespiratory afferents. This work was funded by NIH HL059167.

The free space of sugars in plant tissues6

The total volume of the free space (FS) and the external film (EF) outside the cell wall of living plant materials was determined as partition volumes of sugars and dextran, respectively. Sugar uptake and kinetics of FS and EF saturation were recorded polarimetrically. The FS equilibrates within 20 s in suspension culture of Chenopodium album L. Here, the free apoplastic volume (FAV), i.e. the difference between sugar and dextran partition volumes, was determined by shortterm partitioning of fructose and dextran in samples containing the plant material and an optically compensated (non-rotating) solution of both components. The selective partitioning of the sugar with the FAV causes an increase in optical activity, which is dependent on the FAV. The FAV of a suspension cultured biomass was found to be correlated with the percentage volume of dead cells. The volume originating by plasmolysis between cell wall and plasma membrane was measured as an increase of the FAV. In seedling root segments of Zea mays L., the component of FS equilibrating within 1 min consisted of the EF and a portion of the FAV (probably dead cells at the surface). Saturation of the apoplast of the infiltrated root cortex with α-methylglucoside, a sugar not taken up by the cells, showed slow equilibration kinetics and was not complete within 30 min.

Near-UV circular dichroism of band 3. Evidence for intradomain conformational changes and interdomain interactions.

Near-UV circular dichroism (CD) was used to identify differences in the tertiary structure of human erythrocyte band 3, the chloride/bicarbonate exchange protein, consequent to covalent binding of anion transport inhibitors to the intramonomeric stilbenedisulfonate (ISD) site. Isolated intact band 3 and its membrane domain (B3MD) were compared. Spectral differences were observed which involved intradomain effects, in that they were seen both with intact band 3 and with B3MD, or interdomain effects, in that they were observed only for B3MD, but were inhibited when the cytoplasmic domain was attached. The intradomain effect involved a significant loss in optical activity in the Phe/Tyr region of the spectrum below 280 nm. It was seen only when the ISD site had stilbenedisulfonates bound covalently at pH 7.4. Raising the pH to 9.6 after adduct formation "normalized" this spectral change irreversibly. The interdomain effect was identified in the Trp spectral region at 292 nm. There was a significant increase in optical activity at 292 nm when bulky covalent ligands such as DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonate) were bound to B3MD, but not when the same ligands were bound to intact band 3. These latter results offer evidence that certain aspects of the conformational response of the integral domain are inhibited by the presence of an attached cytoplasmic domain. The potential significance of interdomain interactions to band 3 function is discussed briefly.

The kinetics of the reaction between trans- dichlorobis(1,2-diaminoethane)cobalt(III) perchlorate and monoamines in dimethylformamide—I. Spectrophotometric and spectropolarimetric measurements

The title reaction is first-order in both complex and amine concentrations and second order rate constants were obtained spectrophotometrically ( k 2 spectro) under pseudo- first-order conditions (excess amine). For amines of the type RCH 2NH 2, the rate is proportional to p K a , but steric factors are important. Thus, k 2 spectro values for n-, sec- and iso- butylamine (with approximately constant p K a ) are in the ratio 1 : 0.41 : 0.37, respectively, and likewise 1 : 0.46 : 0.33 for benzylamine, α-Me- and N-Me-, respectively. The spectrophotometric method essentially monitors the rate of loss of the trans-dichloro- by all paths and the rate of coordination of the monoamine was more securely measured by monitoring the rate of increase in optical activity ( k 2 CD) using chiral amines. Where comparable data are available, k 2 CD is usually less than k 2 spectro, and k 2 spectro data are probably composite quantities.

Solvent effect on the conformation of actinomycin D.

THERE have been several different approaches to the stereochemistry of the interaction of actinomycin and DNA, including studies of the interaction of DNA-like polynucleotides with actinomycin1,2, and of DNA with model compounds related to actinomycin3–5, using various experimental techniques. Reports on the optical rotatory-dispersion (ORD) and circular dichroism (CD) data for the actinomycin–DNA complex and for actinomycin alone6–9, as well as unpublished results from this laboratory, indicate that the rotational strength of the optically active transitions—which can be ascribed to the dimethylaminophenoxazone chromophore of actinomycin—in the visible region of the spectrum increases in the presence of DNA. The molecular mechanism of the interaction of actinomycin with DNA is still obscure, however, for the increase in optical activity could result from a change in the conformation of actinomycin in the presence of DNA and/or from the perturbing influence of the asymmetric environment (DNA) on the chromophore transitions of actinomycin.

Low temperature circular dichroism of poly (glycyl- l-prolyl- l-alanine)

The circular dichroism of poly(glycyl- l-prolyl- l-alanine) ‡ ‡ Abbreviation used in the text for this compound is (Gly-Pro-Ala) n. , a synthetic polytripeptide analogue of the non-polar regions of collagen, was investigated in ethylene glycol-water solution (2:1, v v ) over the temperature range of −112 °C to + 24 °C. Lowering of the temperature results in an increased optical activity of (Gly-Pro-Ala) n . At −112 dgC (Gly-Pro-Ala) n exhibits circular dichroism maxima and minima similar in position, but not as large as those observed for guinea pig skin collagen. A comparison of the low-temperature circular dichroism of (Gly-Pro-Ala) n with that of poly- l-proline II and collagen (in the same solvent and at the same temperature) indicates that the observed increase in optical activity of (Gly-Pro-Ala) n is not the result of temperature-dependent solvent effects. Thus the observed increase in optical activity of (Gly-Pro-Ala) n with decreasing temperature is the result of an increase in the amount of periodic structure present in the polymer. Although it is not possible to specify the structure formed in (Gly-Pro-Ala) n at low temperatures in solution, the far ultraviolet circular dichroism is consistent with the structure being a triple helix of the type present in collagen and suggested for (Gly-Pro-Ala) n in the solid state.