Values Of Linear Dichroism Research Articles

Characterization of polarization properties of colorectal cancer using decomposition Mueller matrix method

Rectal cancer is the third most prevalent cancer diagnosed and is traditionally screened using colonoscopy. Meanwhile, polarization characteristic measurement has emerged as an attractive alternative in recent years owing to its deep analysis of the structure of samples and non-invasive nature. Accordingly, this study employed the Mueller matrix decomposition method to measure the effective optical parameters of 100 slices from 20 healthy rectal tissue samples and 100 slices from 20 cancerous rectal tissue samples. The mean values and expression levels of the linear birefringence, circular birefringence, linear dichroism, circular dichroism, and depolarization index properties of the samples were compared using t-tests and ANOVA tests. The experimental results showed that the linear birefringence, orientation angle of linear dichroism, and values of linear dichroism and circular dichroism showed significant differences between the different tissue types. Thus, these parameters may serve as useful biomarkers for the diagnosis of rectal cancer.

Terahertz dichroic device withy multi-functionality, multi-band operation and multi-dimensional tunability

Most existing dichroic metasurfaces have limitations such as single operating band, single functionality, fixed dichroic performance or only adjustable in a single dimension, as well as complex structure. Here, we propose a terahertz dichroic device based on patterned graphene layer and gold layer to address these limitations. By utilizing the anisotropy endowed by the patterned graphene layer and the gold layer, the proposed device can achieve both dual-band circular dichroism (CD) and linear dichroism (LD), with maximum CD values of 0.866 at 1.09 THz and −0.614 at 1.76 THz, and maximum LD values of 0.779 at 0.51 THz and −0.633 at 0.76 THz. Meanwhile, the dichroism of the device can be regulated through multiple dimensions, i.e., the rotation angle of the top patterned graphene layer, the Fermi level of graphene and the incident angle. The proposed dichroic device offers multi-functionality, multi-band operation and multi-dimensional adjustability with a relatively simple structure, and is expected to be widely used in the fields of terahertz imaging, polarization detection, optical sensing and biological spectroscopy.

Photoinduced tunable birefringence and dichroism in silver nanogratings

Silver nanogratings are anisotropic plasmonic nanostructures with potential application in optical components due to their large birefringence and dichroism. We induced linear birefringence and linear dichroism in subwavelength Ag-AgCl films by irradiating with a single low-power linearly polarized laser beam. The laser beam aligns silver nanoparticles in the direction of laser polarization and forms nanograting. We used Stokes parameters to determine linear birefringence and linear dichroism in silver aligned nanostructures. The values of linear dichroism and linear birefringence in silver nanogratings are controllable through manipulating the spatial period of nanogratings. The dispersion characteristic of dichroism and birefringence is also investigated.

Defining Cyclic-Acyclic Exciton Transition at the Single-Molecule Level: Size-Dependent Conformational Heterogeneity and Exciton Delocalization in Ethynylene-Bridged Cyclic Oligothiophenes.

Conformational disorder in π-conjugated cyclic systems plays a crucial role in controlling the extent of exciton delocalization in much the same way as that in linear counterparts. However, to date, there have been no detailed spectroscopic investigations on the nature of excitons in π-conjugated cyclic systems at the single-molecule level. Herein, we studied the effect of conformational disorder on the excitonic behaviors of cyclic oligothiophenes composed of 6, 8, 10, and 12 subunits (C-6T, C-8T, C-10T, and C-12T, respectively) by employing single-molecule fluorescence spectroscopy. We found that, due to the cyclic symmetry constraint which suppresses S1-S0 transition, small and rigid C-6T and C-8T exhibit extremely long fluorescence lifetimes, while short lifetimes typical of linear systems are dominant in large, flexible C-10T and C-12T. Two-dimensional correlation maps between fluorescence lifetimes and spectral positions show that, by torsional defects created through continued photoexcitation, fully delocalized cyclic excitons shrink to form acyclic excitons in the case of C-10T, while localized acyclic excitons from initial states are maintained in the case of C-12T. The distribution of linear dichroism values from C-6T to C-10T gradually broadens but narrows in C-12T, suggesting a cyclic-to-acyclic transition in excitonic nature between C-10T and C-12T.

The Hoechst 33258 Covalent Dimer Covers a Total Turn of the Double-stranded DNA

With the goal to design ligands recognizing extended regions on dsDNA, a covalent dimer of the fluorescent dye Hoechst 33258 [bis-HT(NMe)] composed of two dye molecules linked via the phenol oxygen atoms with a (CH2)3-N+H(CH3)-(CH2)3 fragment was constructed using computer modeling and then synthesized. Its interactions with the double-stranded DNA (dsDNA) were studied by fluorescent and UV-Vis spectroscopy and circular (CD) and linear dichroism (LD). Based on variations in the affinity to the dsDNA, it was shown that complexes of three types are formed. The first type complexes result from binding of a bis- HT(NMe) monomer in the open conformation; in this case the ligand covers the total dsDNA turn and is located in the minor groove according to the positive value of CD at 370 nm. In addition, the ability to form bis-HT(NMe)-bridges between two dsDNA molecules, i.e., each of the two bis-HT(NMe) ends binds to two different dsDNA molecules, was demonstrated for the first type complexes. Spectral characteristics (maximal absorption at 362 nm, positive sign, and maximal value of CD at 370 nm) of the first type complexes conform to those of the specific Hoechst 33258 complex with poly[d(A-T)] · poly[d(A-T]. The second type complexes correspond to the bis-HT(NMe) sandwich (as an inter- or intramolecular) binding to dsDNA with stoichiometry ≥ 5 bp. Thereby, a negative LD at 360 nm and the location of bis- HT(NMe) sandwiches in the minor groove of B form dsDNA seems contradictory. Spectral characteristics (maximal positive CD at 345 nm, a dramatic decrease in fluorescence intensity and the shift of its maximum to 490 nm) of these complexes favor a suggestion that this binding correlates to the formation of nonspecific dimeric Hoechst 33258 complex with dsDNA. The third type complexes are characterized by stoichiometry of one bis-HT(NMe) molecule per ≈ 2 bp and the tendency to zero of LD values at 270 and 360 nm. We assume that in these complexes bis-HT(NMe) sandwich dimers are formed on dsDNA. The complexes of this type conform to the aggregation type complex of Hoechst 33258 with dsDNA. The ability of bis-HT(NMe) to cover the whole dsDNA turn or form bridges with two dsDNA upon the formation of the first type complexes essentially distinguishes it from Hoechst 33258, which can only occupy 5 bp and does not form such bridges. This specific property of bis-HT(NMe) may support new biological activities.

Torsion induced circular dichroism in hexagonal CdS

The influence of the torsion on the absorption properties of hexagonal CdS has been studied in our experiments. The undeformed CdS does not possess circular dichroism (CD) but it manifests linear dichroism (LD). An appearance of CD and a change of LD can be observed in the torsion deformed CdS crystals. The mentioned absorption phenomena occur in the vicinity of the isotropic point (i.p.), the crossing point of the curves of the refractive indicesn 0(λ) andn e (λ). The sign of CD is connected with the direction of the torsional momentM. The magnitude ofM influences the shape of CD spectra as well as the values of LD. The appearance of CD and the change of LD are explained by the torsion induced gyrotropy in the CdS crystals, i.e. by the created chirality in the hexagonal CdS.

Gaussian decomposition of absorption and linear dichroism spectra of outer antenna complexes of photosystem II.

Room temperature and 10 K absorption and linear dichroism spectra of the chlorophyll-protein complexes comprising the outer antenna of PSII (LHCII, CP29, CP26, CP24) have been analyzed in terms of a linear combination of asymmetric Gaussian bands. The results demonstrate the following: (a) The absorption and linear dichroism spectra of each sample can be described by nearly the same set of Gaussian bands at room temperature and 10 K. (b) The relative distributions of the transition moments of the major red-absorbing spectral forms seem to be similar in all four outer antenna chlorophyll-protein complexes at room temperature, with the 684-nm band being oriented closest to the particle plane at room temperature and the 677- and 669-nm bands being tilted at progressively greater angles out of the particle plane. The shorter wavelength transitions seem to be oriented close to the magic angle, but interpretation is complicated in this spectral region due to the low linear dichroism values and by overlap with vibrational bands. (c) The 684-nm band, detected in room temperature absorption and linear dichroism spectra of all complexes, vanishes at 10 K.

DNA-hydrolyzing autoantibodies.

Catalysis by antibodies could be a frequent phenomenon if the immune system generates a sufficiently diverse number of antibody-active sites, some of which may possess catalytic activity. A catalytic antibody can be expected to do more damage than one that simply binds antigen. The best biochemical marker of systemic lupus erythematosus (SLE) is presence of autoantibodies to DNA. In the present article, we describe the DNA-hydrolyzing activity of DNA-binding autoantibodies purified from SLE patients. The substrates employed were supercoiled plasmid, radiolabeled plasmid fragments, and oligonucleotides. Hydrolysis of DNA by the antibodies was indicated by the appearance of fragments visualized by ethidium bromide staining of agarose gels or autoradiography of polyacrylamide gels. Changes in linear dichroism values were also indicative of DNA hydrolysis. The antibody activity was purified by protein A-sepharose chromatography, high-performance liquid chromatography gel filtration, and DNA-affinity chromatography. Scrupulous control studies were done to demonstrate that DNA-hydrolyzing activity really belongs to the antibodies. Purified Fab fragments showed hydrolyzing activity, whereas the Fc fragment was inactive. The specificity of DNA cleavage was investigated, and the rate parameters of hydrolysis by antibodies and conventional nucleases were compared.

Orientation and assignment of the four cytochrome hemes in Rhodopseudomonas viridis reaction centers

Low temperature absorption and linear dichroism measurements on oriented reaction centers of Rhodopseudomonas viridis at different redox potentials allow the α-bands of the four hemes to be spectrally resolved. The high-potential heme C556 presents an α-band split into two components absorbing at 555 and 551 nm. The corresponding linear dichroism spectrum shows two transitions of opposite sign and equal amplitudes. Comparison of our experimental results with the linear dichroism values calculated from the atomic coordinates leads us to assign unambiguously the high-potential C556 cytochrome with heme 2, the third heme away from the primary donor. Taken together with other available spectroscopic observations, this result implies the following sequence for the redox centers in Rhodopseudomonas viridis: C554 C556 C552 C559 P.

Optical anisotropy of chromatin. Flow linear dichroism and electric dichroism studies.

The optical anisotropy of chromatin with different length of the linker DNA isolated from a variety of sources (Frend erythroleukemia cells, calf thymus, hen erythrocytes and sea urchin sperm) has been studied in a large range of mono- and bivalent cations concentrations by the use of flow linear dichroism (LD) and electric dichroism. We have found that all chromatins studied displayed negative LD values in the range of 0.25 mM EDTA - 2 mM NaCl and close positive values in the range of 2-100 mM NaCl. Mg2+ cations, in contrast to Na+ cations, induce optically isotropic chromatin fibers. All chromatin samples exhibit positive form effect amounting to 5-10% of LD amplitude observed at 260 nm. This form effect is determined by the anisotropic scattering of polarized light by single chromatin fibers. The conformational transition at 2 mM NaCl leads to the distortion of chromatin filament structure. The reversibility of this distortion depends on the length of the linker DNA - for chromatins with the linker DNA of 10-30 b.p. it is parially reversible, while for preparations with longer linker DNA it is irreversible. Relatively low electric field does not affect chromatin structure, while higher electric field (more than 7 kV/cm) distorts the structure of chromatin. Presented results explain the contradictory data obtained by electrooptical and hydrooptical methods.