STUDIES ON HUMAN LENSES: II. DISTRIBUTION AND SOLUBILITY OF FLUORESCENT PIGMENTS IN CATARACTOUS AND NON-CATARACTOUS LENSES OF INDIAN ORIGIN

Abstract— Fluorometric studies of cataractous and non-cataractous human lenses were carried out to study the emission characteristics and the distribution and solubility of lenticular pigments. Most of the detected fluorophores were well distributed over the cortical and nuclear portion of the lens. The decrease in solubility of proteins with aging and cataract formation is concomitant with increasing photolysis of tryptophan. However, this is likely a phenomenon independent of the photochemical transformations of the lens proteins. The number of emitting species in the diseased lenses are higher than in the normal mature lenses. A species emitting around 375 or 388 nm is of particular interest (λ_cx, 330 nm) in that the emission characteristics of this fluorophore resemble kynurenic acid which has a high photosensitizing efficiency. The concentration of fluorescent pigments in the lenses of Indian origin is significantly high. The intense pigmentation could be attributed largely to the formation of photoproducts in the absence of normal endogenous antioxidant accumulation that is dependent on nutrition standard. If, indeed, any of these fluorescent pigments, because of their photosensitizing ability, are responsible for lenticular opacity, it is not the abundance of sunlight alone but also malnutrition that could account for the high incidence of cataract in India.     

Microwave spectrum of 1,2,4-trifluorobenzene

The microwave spectrum of 1,2,4-trifluorobenzene has been observed in the range 12.5–18.0 GHz and 21.5–25.3 GHz at dry-ice temperature and assigned up to angular momentum state J = 39. The ground state rotational constants and the five quartic centrifugal distortion constants thus obtained are (in MHz): à = 3084.0037 ± 0.0108, B? = 1278.3614 ± 0.0062, C? = 903.6989 ± 0.0108, d_j = ( ?4.599 ± 0.621) · 10^?4, d_jk = (5.9757 ± 1.1586) · 10^?3, d_k = (11.4923 ± 2.0886) · 10^?3, d_wj = (4.0 ± 1.0) · 10^?7, d_wk=(?5.8± 1.1) · 10^?6.The small value of Δ = 0.029 (amu Ų) shows that the molecule is planar and an r₀ - structure using a regular hexagonal benzene ring with the bond lengths C-C = 1.397 Å, C-H = 1.084 Å and C-F = 1.312 Å, reproduces the rotational constants.     

Module structure of interphotoreceptor retinoid-binding protein (IRBP) may provide bases for its complex role in the visual cycle – <Emphasis Type="Italic">structure/function study of Xenopus IRBP</Emphasis>

Background  

Interphotoreceptor retinoid-binding protein's (IRBP) remarkable module structure may be critical to its role in mediating the transport of all-trans and 11-cis retinol, and 11-cis retinal between rods, cones, RPE and Müller cells during the visual cycle. We isolated cDNAs for Xenopus IRBP, and expressed and purified its individual modules, module combinations, and the full-length polypeptide. Binding of all-trans retinol, 11-cis retinal and 9-(9-anthroyloxy) stearic acid were characterized by fluorescence spectroscopy monitoring ligand-fluorescence enhancement, quenching of endogenous protein fluorescence, and energy transfer. Finally, the X-ray crystal structure of module-2 was used to predict the location of the ligand-binding sites, and compare their structures among modules using homology modeling.     

Comparison of analytical techniques for purity evaluation of single-walled carbon nanotubes

We compare popular analytical techniques, including scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and Raman and near-infrared (NIR) spectroscopy, for the evaluation of the purity of bulk quantities of single-walled carbon nanotubes (SWNTs). Despite their importance as imaging techniques, SEM and TEM are not capable of quantitatively evaluating the purity of typical inhomogeneous bulk SWNT samples because the image frame visualizes less than 1 pg of SWNT material; furthermore, there is no published algorithm to convert such images into numerical data. The TGA technique is capable of measuring the amount of metal catalyst in an SWNT sample, but does not provide an unambiguous separation between the content of SWNTs and carbonaceous impurities. We discuss the utilization of solution-phase near-infrared spectroscopy and solution-phase Raman spectroscopy to quantitatively compare arbitrary samples of bulk SWNT materials of different purities. The primary goal of this paper is to provide the chemical community with a realistic evaluation of current analytical tools for the purity evaluation of a bulk sample of SWNTs. The secondary goal is to draw attention to the growing crisis in the SWNT industry as a result of the lack of quality control and the misleading advertising by suppliers of this material.     

Solution NMR studies of supramolecular complexes of [60]- and [70]fullerenes with mono O-substituted calix[6]arene

Supramolecular complexation of [60]- and [70]fullerenes with 37-allyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert butyl)calix[6]arene (I) has been studied in CCl(4) medium by NMR spectrometric method. All of the complexes are found to be stable with 1:1 stoichiometry. Formation constants (K) of the above supramolecular complexes have been determined from systematic variation of NMR chemical shifts of specific protons of I in the presence of [60]- and [70]fullerenes. Trends in the K value suggest that [70]fullerene binds more strongly with I relative to [60]fullerene. Both PM3 and ab initio calculations reveal that the intermolecular interaction in the [70]fullerene/I complex proceeds through quite deep energy minima.     

Solution of coupled differential equations of soliton theory

We present the complete set of solutions of the coupled differential equations of the form ()²=(), ² =(). Equations of this form appear in several physical situations.     

A Comparative study of p-Em and C12-Em interactions at 4·5 GeV/c per nucleon

In this paper we present a comparative study of inelastic interactions of C¹²-Em and p-Em at 4·5 GeV/c per nucleon. The multiplicity distributions and their correlations have been studied. The results show a strong correlation of n _s onn _h in the case of C¹²-Em but not in the case of p-Em. It is also shown that the n _s increases with the increase of the projectile mass. The angular distribution of the target fragments in C¹²-Em shows a massive forward collimation. Comparison is also made in the pseudorapidity distribution of both C¹²-Em and p-Em, the result shows many interesting features.     

Recent advances and perspectives on the synthesis and C–H bond functionalization of quinoxalin-2(1H)-one

Abstract

Over the past few decades, quinoxalin-2(1H)-one derivatives are serving as active components in diverse families of drugs such as antimicrobial, anticancer, antithrombotic agents and protein kinase inhibitor. Previously, significant attention has been marked for its synthesis and recent years have also observed an upsurge in the modification of this scaffold as well as its functionalization. This review (2008–2020) focused on selective C–H bond functionalization namely arylation, amination, acylation, amidation, alkylation, benzylation, alkoxycarbonylation, cyanoalkylation and phosphorylation etc. at C-3 position of quinoxalin-2(1H)-one. Additionally, alternative complimentary route (radical cyclization protocol) for its synthesis part is well elaborated herein. We also briefly summarized the mechanistic pathway of the C–H bond functionalization approach.     

New syntheses of the C,D-ring pyrromethenones of phytochrome and phycocyanin

Pyrromethenone 7, the C,D-ring segment of phytochrome (Pr, 4), has been prepared in an efficient fashion employing three new strategies. Each of these has potential advantages for the synthesis of labeled material. Our first approach is related to the Gossauer synthesis, with the difference that strong alkali is avoided in the condensation of the C- and D-ring components 8 and 17. The key silyloxypyrrole 17 was readily prepared on multigram scales beginning with inexpensive butyrolactone (10). A second synthesis began with 2-acetylbutyrolactone (41). The key steps involved conversion of 41 to the Z-enoltriflate 42, followed by Pd(0)-catalyzed coupling with trimethylsilylacetylene, p-chlorophenylselenide ring opening, and finally, amidation to afford the ring-D synthon 45 having the proper geometry and oxidation state for conversion to 7. Sonogashira coupling of 45 with the iodopyrrole 22, followed by oxidative elimination, and F(-)-induced 5-exo-dig cyclization of the resultant pyrroloalkyne 47, then completed the synthesis. In similar fashion, we have also prepared pyrromethenone 6, the C,D-ring segment of phycocyanin (2).