Chiral Filter Research Articles

Three-dimensional quantum Hall states as a chiral electromagnetic filter

Three-dimensional quantum Hall states as a chiral electromagnetic filter

Intense Circularly Polarized Fluorescence and Room-Temperature Phosphorescence in Carbon Dots/Chiral Helical Polymer Composite Films

Chiral carbon dots (C-dots) with a circularly polarized fluorescence (CPF) property have attracted tremendous attention due to their significant applications in chiral optoelectronics and theranostics. However, constructing circularly polarized room-temperature phosphorescent (CPRTP) C-dots remains a great challenge. Herein, a strategy is established to achieve efficient CPF and CPRTP emissions in C-dots/chiral helical polymer bilayer composite film. Taking advantage of the chiral filter effect of chiral helical polymer, intense CPF and CPRTP emissions with large dissymmetric factors up to 1.4 × 10-1 and 1.2 × 10-2 are respectively obtained, even though there is only a simple interface contact between the C-dots layer and the chiral helical polymer layer. More importantly, white-color CPF emission and multiple information display and encryption are further realized based on the prepared chiral luminescent composite films.

Racemic Monomer‐Based One‐Handed Helical Polymer Recognizes Enantiomers through Auto‐Evolution of Its Helical Handedness Excess

AbstractA racemic monomer‐based optically inactive polyacetylene folds into a one‐handed helix assisted by a nonracemic alcohol, which can separate various enantiomers as a chiral stationary phase in chromatography. The chiral‐resolving power is virtually identical to that of the enantiopure monomer‐based one‐handed helical polyacetylene. Because of its unique static memory of the induced helicity, the original racemic polyacetylene expresses an auto‐evolution of its helical handedness over time, and at the same time, chirality of the nonracemic alcohol is discriminated accompanied by successive enhancement of its optical purity enantioselectively adsorbed on the helical polyacetylene owing to the chiral filter effect as directly monitored by NMR, which contributes to further enhancing the helix‐sense‐excess of the helical polyacetylene.

Nuclear axial currents from scale-chiral effective field theory**Supported by National Science Foundation of China (NSFC) (11475071, 11547308) and the Seeds Funding of Jilin University

By incorporating hidden scale symmetry and hidden local symmetry in the nuclear effective field theory, combined with the double soft-pion theorem, we predict that the Gamow-Teller operator coming from the space component of the axial current should remain unaffected by the QCD vacuum change caused by the baryonic density, whereas the first forbidden beta transition operator coming from the time component should be strongly enhanced. While the latter has been confirmed for some time, the former was given support by a powerful recent ab initio quantum Monte Carlo calculation for light nuclei, which also confirmed the old “chiral filter hypothesis.” Formulated in terms of the Fermi-liquid fixed point structure of strong-coupled nuclear interactions, we offer an extremely simple resolution to the long-standing puzzle of the “quenched gA,” [], found in nuclear Gamow-Teller beta transitions, giant Gamow-Teller resonances, and double beta decays.

Chiral filtration-induced spin/valley polarization in silicene line defects

The spin/valley polarization in silicene with extended line defects is investigated according to the chiral filtration mechanism. It is shown that the inner-built quantum Hall pseudo-edge states with identical chirality can serve as a chiral filter with a weak magnetic field and that the transmission process is restrained/strengthened for chiral states with reversed/identical chirality. With two parallel line defects, which act as natural chiral filtration, the filter effect is greatly enhanced, and 100% spin/valley polarization can be achieved.

Preparation of filter paper with chiral separation function by oxidation and Schiff-base reaction

Paper chromatography (PC) is a highly flexible, fast, and efficient separation method. In this study, a chromatographic paper with a chiral separation function was investigated and a paper chromatographic method for chiral separation was developed. Single-factor experiments and orthogonal tests were used to determine the optimal oxidation conditions for filter paper. The optimal conditions were that sodium periodate 4% (mass percentage), pH 2 buffer solution, reaction temperature 45℃, and reaction time 4 h. Under the optimal conditions, the aldehyde group content of a dialdehyde-based filter paper was 57.93% (amount of substance percentage). A paper-based chiral separation material was synthesized by a microwave-assisted Schiff-base reaction of the oxidized filter paper with L-glutamic acid. The developing solvent for separating racemic tartaric acid using this chiral filter paper consisted of 100 mL of n-butanol, 50 mL of 50%(v/v) acetic acid, and 0.1000 g of bromophenol blue. The rate of flow (Rf) values of L-tartaric acid and D-tartaric acid were 0.52 and 0.40, respectively. This method does not require large-scale equipment to perform the chiral separation and it is therefore suitable for general teaching, research, and industrial applications.

Modification of cellulose acetates for preparing chiral sorbents

Modifi cation of cellulose acetates via sorption-desorption of vapors of mesogenic solvents in which the polymer forms a lyotropic liquid crystal phase and of mixtures of these solvents with water leads to the formation of a new chiral structure of the polymeric sample. This is manifested in a signifi cant change in the value and even sign of the specifi c optical rotation of the polysaccharide system. The sorbents based on cellulose acetates that have been modifi ed by such treatment exhibit specifi c affi nity for defi nite optical antipodes. When a racemic mixture of L- and D-isomers of amino acids is passed through this sorbent, it acts as a chiral fi lter owing to "steric recognition" of one of the enantiomers, so that the fi ltrate contains an optically pure product (isomer). The revealed effects served as a basis for the development of a new procedure for preparation of optically pure stereoisomers of chiral products.

Circular differential scattering of polarized light by a chiral random medium

Differential scattering of left- and right-handed circularly polarized waves is a general property of scattering media lacking space-inversion symmetry. We show in this paper that this scattering difference has remarkable properties in the case of an almost transparent chiral random medium. By tuning the refractive indices of the materials composing the medium, this scattering difference can be varied and even inverted. Within the limit of a dense scattering material, the difference of scattering cross sections between polarizations of opposite handedness can be largely adjusted. These properties are illustrated by measurement of the difference between the transmission of right- and left-handed polarized waves through a chiral Christiansen filter.

Enantioselective Adsorption of Chiral Amines on an Induced Helical Poly(bis(4-carboxyphenoxy)phosphazene): Chiral Filter Effect

Optically inactive poly((bis(4-carboxyphenoxy)phosphazene) (poly-1) showed a large optical rotation upon complexation with optically active (R)- or (S)-1-phenylethylamine (2) in DMSO after annealing the complex solution at 65 °C for ca. 2 h and maintained its optical activity in the presence of an equimolar amount of the opposite-handed 2. The detailed analysis of the enantiomeric excess of 2 adsorbed on the poly-1 revealed that the helical poly-1 induced by (R)- or (S)-2 most likely acts as a “chiral filter” to exclude one enantiomer from racemic 2, resulting in the retention of its induced helical structure.

Polarization-dependent filters based on chiral photonic structures with defects

A one-dimensional photonic device to perform optical multiple-wavelength filtering for light of a particular circular polarization state is presented and modelled. It is shown that the transmission spectrum of a stacked structure consisting of two cholesteric films with the same pitch gradient in the helix can be tailored by incorporating the defects of pitch jump and phase jump in the middle of the structure. The introduction of the defects results in the exhibition of multiple-band-pass characteristics inside the photonic band gap when incident circularly polarized light has the same handedness as the cholesterics. Some critical parameters are analysed: the thickness of the double-composite film, co-polarized/cross-polarized transmittance and reflectance, and the twist angle. For light of specified circular polarization, the shift of the filter in transmitted wavelength can be tuned linearly by adjusting the amount of the phase jump. The proposed chiral filter may be useful for multichannel lightwave systems. Some rules for the practical implementation of a filter with polarization sensitivity are given.

Stereoisomer Composition of the Chiral UV Filter 4-Methylbenzylidene Camphor in Environmental Samples

4-Methylbenzylidene camphor (4-MBC) is an important organic UV filter used in many personal care products such as sunscreens and cosmetics. After use, 4-MBC may enter the aquatic environment due to its release from skin during recreational activities (swimming, bathing) and from personal hygiene measures (washing, laundering of cloths) via wastewater treatment plants (WWTPs). In fact, 4-MBC has been detected in wastewater, in surface waters, and even in fish. 4-MBC can exist as distinct cis-(Z)- and trans-(E)-isomers, both of which are chiral. Despite the fact that stereoisomers often show a different biological behavior, the stereochemistry of 4-MBC has hardly ever been considered in environmental or biological studies. In this study, enantioselective gas chromatography-mass spectrometry (GC-MS) was used to determine the stereoisomer composition of 4-MBC. For stereoisomer assignment, the pure enantiomers of (E)-4-MBC were synthesized from (+)- and (-)-camphor. The photochemical isomerization (sunlight) of these (E)-isomers to the corresponding (Z)-isomers eventually allowed the configurational assignment of all four stereoisomers of 4-MBC. In a technical material and in a major brand sun lotion, 4-MBC was shown to consist entirely (>99%) of (E)-isomers and to be racemic (R/S, 1.00 +/- 0.02). Wastewater showed the presence of both (E)- and (Z)-4-MBC with a clear excess of (E)-isomers (E > Z). Untreated wastewater showed a nearly racemic composition (R/S= 0.95-1.09), suggesting that most if not all commercial 4-MBC is racemic. Treated wastewater indicated some excess of (R)- or (S)-stereoisomers (R/S, 0.89-1.17), likely as a result of some enantioselective (bio)degradation in WWTPs. Residues of 4-MBC in lakes and in a river with inputs from WWTPs and/or recreational activities consisted mainly of (E)-4-MBC and, with exception of one lake (Greifensee), showed a small enantiomer excess (R/S, 1.04-1.16). In Greifensee, 4-MBC showed a higher enantiomer excess (R/S, 1.70-1.83), probably as a result of more extensive biotic degradation in this lake. The analysis of 4-MBC in a small number of fish from these lakes indicated residues with nearly racemic compositions or a moderate enantiomer excess (R/S, approximately 1.0-1.2) in roach (Rutilus rutilus), whereas in perch (Perca fluviatilis) a much higher enantiomer excess (R/S, approximately 5) was observed. The data indicate that the stereoisomer composition of 4-MBC in environmental samples is not only a function of initial product composition but is also modified by enantioselective processes in lakes and biota (fish).

Multilayered chiral filter response at oblique incidence

AbstractThe response of multilayered chiral filters is investigated at oblique incidence. It is found that there is a slight degradation with respect to the same filter operating at normal incidence. A possible application is proposed for this device: a reflector or a subreflector fed at two different frequencies by two feeds situated on each side of a multilayered chiral filter functioning as a frequency‐selective surface. The response of this device is well behaved, and is similar for TE and TM modes. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 192–195, 2001.

Multi-Layered Chiral Filters

ABSTRACT The use of multi-layered chiral structures as filters in the microwave frequency range is studied in this paper. These chiral devices can replace their dielectric counterparts when the synthesis of the latter has furnished values of refractive indices which are unavailable, and, in addition, they are able to rotate the plane of polarization of the transmitted wave by a given angle. These features are achieved due to the extra degree of freedom provided by the chirality admittance. The sensitivities of the two kinds of filters are calculated, analyzed and compared. The dependence of the permittivity of the medium on the chirality admittance is taken into account in order to evaluate its influence on the characteristics of the chiral filter and to compensate for it. Finally an accurate model which considers lossy frequency dependent parameters, is used to design a wide stop-band filter. The chiral filter is compared to a dielectric one: a large attenuation at the stop-band, a steep response at the cutoff frequency and a wide stop-band, are the three main advantages of the chiral filter over its dielectric counterpart.

Exchange currents from chiral Lagrangians.

Exchange currents in nuclei are derived from chiral Lagrangians, and a justification is offered for the ``chiral filter hypothesis'' which seems to be supported by all presently available experimental data.