Modulation of the optical properties of chiral porphyrin dimers by introducing bridged chiral amide-bonds

2020 ◽  
Vol 25 (01) ◽  
pp. 37-46
Author(s):  
Mingfeng Qin ◽  
Zhen Zhang ◽  
Weihua Zhu ◽  
John Mack ◽  
Rodah C. Soy ◽  
...  
Keyword(s):  
Optical Properties ◽  
Amino Acid ◽  
Electronic Structures ◽  
Anion Radical ◽  
Cd Spectra ◽  
Radical Species ◽  
Amide Bonds ◽  
Band Region ◽  
Porphyrin Dimers

The d/l-enantiomers of a series of three Zn(II)tetraarylporphyrin dimers were synthesized and isolated by incorporating a bridging amide-bonded xanthene moiety at the para-position of one of the meso-aryl rings. The electronic structures and optical properties were modulated by incorporating chiral amino acid moieties into the amide-bonding moieties of the xanthene bridge that contain methyl, tolyl and 2-methylindole substituents. A cofacial dimer was formed in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) resulting in a significant red shift of the B band, due to a relative destabilization of the HOMO, which has large MO coefficients on the pyrrole nitrogens. The sign sequences observed in the B band region of the CD spectra due to the presence of the chiral amino acid moieties were modified due to this change in geometry. Significant CD intensity is also observed in the B band region of the CD spectra of anion radical species during in situ spectroelectrochemical measurements.

Series of sequential polypeptides containing lysine or arginine: Preparation and characterization

1988 ◽  
Vol 53 (1) ◽  
pp. 145-156 ◽  
Author(s):  
Jana Pírková ◽  
Svetlana Churkina ◽  
Vladimír Gut ◽  
Ivo Frič ◽  
Karel Bláha
Keyword(s):  
Molecular Weight ◽  
Amino Acid ◽  
Peptide Synthesis ◽  
Average Molecular Weight ◽  
Basic Amino Acid ◽  
Cd Spectra ◽  
Active Esters ◽  
Marked Tendency

The sequential polypeptides (Lys-Ala)n, (Lys-Ala-Ala)n, (Lys-Ala-Ala-Ala)n, (Lys-Leu-Ala)n, (Lys-Leu-Ala-Ala)n, (Lys-Leu-Ala-Ala-Ala)n, (Lys-Ala-Leu)n, (Lys-Ala-Leu-Ala)n, (Orn-Leu-Ala)n,(Arg-Ala-Ala)n, (Arg-Leu-Ala)n, (Arg-Leu-Ala-Ala)n, (Arg-Ala-Leu)n, and (Arg-Ala-Leu-Ala)n were synthesized by polymerization of active esters (1-succinimidyl or pentafluorophenyl) of the corresponding Nα-deblocked monomers. The monomers were prepared using the usual methods of peptide synthesis in solution. Upon dialysis, the average molecular weight of the polymer was 6 000-9 000 as determined by sedimentation in ultracentrifuge. Polypeptides, containing leucine in addition to the basic amino acid, showed a marked tendency to aggregation. CD spectra of the products were measured for characterization.

Synthesis and conformation of sequential basic polypeptides with branched and linear side chains

1985 ◽  
Vol 50 (12) ◽  
pp. 2925-2936 ◽  
Author(s):  
Štěpánka Štokrová ◽  
Jan Pospíšek ◽  
Jaroslav Šponar ◽  
Karel Bláha
Keyword(s):  
Amino Acid ◽  
Salt Concentration ◽  
Salt Solution ◽  
Theoretical Work ◽  
Side Chain ◽  
Amino Acid Residues ◽  
Cd Spectra ◽  
Low Salt ◽  
Conformational Freedom ◽  
Basic Polypeptides

Polypeptides (Lys-X-Ala)n and (Lys-X-Gly)n in which X represents residues of isoleucine and norleucine, respectively, and polypeptide (Tle-Lys-Ala)n, were synthesized via polymerization of 1-hydroxysuccinimidyl esters of the appropriate tripeptides to complete previously studied series. Circular dichroism (CD) spectra of the respective polymers were measured as a function of pH and salt concentration of the medium. The results were correlated with those obtained previously with the same series containing different amino acid residues at the X-position. The helix forming ability of the polypeptides (Lys-X-Ala)n with linear X side chain was found to be independent of the length. In the series (Lys-X-Gly)n the unordered conformation was the most probable one except (Lys-Ile-Gly)n. This polymer assumed the β conformation even in low salt solution at neutral pH. An agreement with some theoretical work concerned with the restriction of conformational freedom of amino acid residue branching at Cβ atom with our experimental results is evident.

scholarly journals B0AT1 amino acid transporter complexed with SARS-CoV-2 receptor ACE2 forms a heterodimer functional unit: in situ conformation using radiation inactivation analysis

Function ◽  
2021 ◽  
Author(s):  
Bruce R Stevens ◽  
J Clive Ellory ◽  
Robert L Preston
Keyword(s):  
Amino Acid ◽  
Membrane Trafficking ◽  
Functional Unit ◽  
Membrane Vesicles ◽  
High Energy ◽  
Amino Acid Transporter ◽  
Neutral Amino Acid ◽  
Transport Activity ◽  
Acid Transporter

Abstract The SARS-CoV-2 receptor, Angiotensin Converting Enzyme-2 (ACE2), is expressed at levels of greatest magnitude in the small intestine as compared to all other human tissues. Enterocyte ACE2 is co-expressed as the apical membrane trafficking partner obligatory for expression and activity of the B0AT1 sodium-dependent neutral amino acid transporter. These components are assembled as an [ACE2: B0AT1]2 dimer-of-heterodimers quaternary complex that putatively steers SARS-CoV-2 tropism in the gastrointestinal (GI) tract. GI clinical symptomology is reported in about half of COVID-19 patients, and can be accompanied by gut shedding of virion particles. We hypothesized that within this 4-mer structural complex, each [ACE2: B0AT1] heterodimer pair constitutes a physiological “functional unit.” This was confirmed experimentally by employing purified lyophilized enterocyte brush border membrane vesicles that were exposed to increasing doses of high-energy electron radiation from a 16 MeV linear accelerator. Based on established target theory, the results indicated the presence of Na+-dependent neutral amino acid influx transport activity functional unit with target size mw = 183.7 ± 16.8 kDa in situ in intact apical membranes. Each thermodynamically stabilized [ACE2: B0AT1] heterodimer functional unit manifests the transport activity within the whole ∼345 kDa [ACE2: B0AT1]2 dimer-of-heterodimers quaternary structural complex. The results are consistent with our prior molecular docking modeling and gut-lung axis approaches to understanding COVID-19. These findings advance the understanding of the physiology of B0AT1 interaction with ACE2 in the gut, and thereby potentially contribute to translational developments designed to treat or mitigate COVID-19 variant outbreaks and/or GI symptom persistence in long-haul Post-Acute Sequelae of SARS-CoV-2 (PASC).

scholarly journals Comparative Study on Electronic Structure and Optical Properties of α-Fe2O3, Ag/α-Fe2O3 and S/α-Fe2O3

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 424
Author(s):  
Cuihua Zhao ◽  
Baishi Li ◽  
Xi Zhou ◽  
Jianhua Chen ◽  
Hongqun Tang
Keyword(s):  
Optical Properties ◽  
Optical Absorption ◽  
Electronic Structures ◽  
Density Functional ◽  
Peak Strength ◽  
Visible Range ◽  
High Symmetry ◽  
Functional Theory ◽  
Optical Absorption Peak ◽  
Calculation Results

The electronic structures and optical properties of pure, Ag-doped and S-doped α-Fe2O3 were studied using density functional theory (DFT). The calculation results show that the structure of α-Fe2O3 crystal changes after Ag and S doping, which leads to the different points of the high symmetry of Ag-doped and S-doped α-Fe2O3 with that of pure α-Fe2O3 in the energy band, as well as different Brillouin paths. In addition, the band gap of α-Fe2O3 becomes smaller after Ag and S doping, and the optical absorption peak shifts slightly toward the short wavelength, with the increased peak strength of S/α-Fe2O3 and the decreased peak strength of Ag/α-Fe2O3. However, the optical absorption in the visible range is enhanced after Ag and S doping compared with that of pure α-Fe2O3 when the wavelength is greater than 380 nm, and the optical absorption of S-doped α-Fe2O3 is stronger than that of Ag-doped α-Fe2O3.

scholarly journals A Study of Catechin Photostability Using Photolytic Processing

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 293
Author(s):  
Jeu-Ming P. Yuann ◽  
Shwu-Yuan Lee ◽  
Meei-Ju Yang ◽  
Shiuh-Tsuen Huang ◽  
Chien-Wei Cheng ◽  
...  
Keyword(s):  
Ascorbic Acid ◽  
Superoxide Anion ◽  
Anion Radical ◽  
Alkaline Solutions ◽  
Light Illumination ◽  
Drug Resistant ◽  
Alkaline Ph ◽  
Radical Species ◽  
Alkaline Conditions ◽  
Photolytic Reaction

Catechin exhibits numerous physiological characteristics. In this study, we determined the photosensitivity of catechin to various lights under alkaline conditions, and the mechanisms by which catechin generates free radical species and polymerizes via a photoreaction. In addition to this, the application of catechin photolysis was investigated. A solution of catechin is transparent, but turns yellowish under blue light illumination (BLI) in neutral or weak alkaline solutions. When catechin is subjected to BLI, a dimeric catechin (proanthocyanidin) and a superoxide anion radical (O2•−) are generated in a photolytic reaction. When ascorbic acid or gallic acid is added to catechin and the mixture is subjected to BLI at alkaline pH, fewer catechin dimers and less O2•− are produced, because both acids inhibit the photosensitive oxidation of catechin. When AlCl3 is added to catechin and the mixture is subjected to BLI at pH 8, a photolytic reaction is suppressed by AlCl3, and AlCl3 acts as a catalyst for the disconnection of proanthocyanidin during photolysis. Under alkaline conditions, catechin generates O2•− via photosensitive oxidation, which suppresses the growth of Acinetobacter baumannii (A. baumannii) by at least 4 logs, and deactivates its multi-drug-resistant strain. This study shows that catechin photolysis is a process of oxidation, and that it can be safely applied as a tool for environmental applications.

Electronic Structures of Crystalline and Aqueous Solutions of LiBr, NaBr, KBr, and KBrO3:  In Situ Br L-Edge Near-edge X-ray Absorption Fine Structure

2003 ◽  
Vol 107 (46) ◽  
pp. 12562-12565 ◽  
Author(s):  
Shuji Matsuo ◽  
Ponnusamy Nachimuthu ◽  
Dennis W. Lindle ◽  
Hisanobu Wakita ◽  
Rupert C. C. Perera
Keyword(s):  
Fine Structure ◽  
Aqueous Solutions ◽  
Electronic Structures ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption

scholarly journals Evaluating model parameterizations of submicron aerosol scattering and absorption with in situ data from ARCTAS 2008

2016 ◽  
Vol 16 (14) ◽  
pp. 9435-9455 ◽  
Author(s):  
Matthew J. Alvarado ◽  
Chantelle R. Lonsdale ◽  
Helen L. Macintyre ◽  
Huisheng Bian ◽  
Mian Chin ◽  
...  
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Aerosol Size Distribution ◽  
Visible Radiation ◽  
Submicron Aerosol ◽  
In Situ Data ◽  
Aerosol Absorption ◽  
Aerosol Scattering ◽  
The Impact

Abstract. Accurate modeling of the scattering and absorption of ultraviolet and visible radiation by aerosols is essential for accurate simulations of atmospheric chemistry and climate. Closure studies using in situ measurements of aerosol scattering and absorption can be used to evaluate and improve models of aerosol optical properties without interference from model errors in aerosol emissions, transport, chemistry, or deposition rates. Here we evaluate the ability of four externally mixed, fixed size distribution parameterizations used in global models to simulate submicron aerosol scattering and absorption at three wavelengths using in situ data gathered during the 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign. The four models are the NASA Global Modeling Initiative (GMI) Combo model, GEOS-Chem v9-02, the baseline configuration of a version of GEOS-Chem with online radiative transfer calculations (called GC-RT), and the Optical Properties of Aerosol and Clouds (OPAC v3.1) package. We also use the ARCTAS data to perform the first evaluation of the ability of the Aerosol Simulation Program (ASP v2.1) to simulate submicron aerosol scattering and absorption when in situ data on the aerosol size distribution are used, and examine the impact of different mixing rules for black carbon (BC) on the results. We find that the GMI model tends to overestimate submicron scattering and absorption at shorter wavelengths by 10–23 %, and that GMI has smaller absolute mean biases for submicron absorption than OPAC v3.1, GEOS-Chem v9-02, or GC-RT. However, the changes to the density and refractive index of BC in GC-RT improve the simulation of submicron aerosol absorption at all wavelengths relative to GEOS-Chem v9-02. Adding a variable size distribution, as in ASP v2.1, improves model performance for scattering but not for absorption, likely due to the assumption in ASP v2.1 that BC is present at a constant mass fraction throughout the aerosol size distribution. Using a core-shell mixing rule in ASP overestimates aerosol absorption, especially for the fresh biomass burning aerosol measured in ARCTAS-B, suggesting the need for modeling the time-varying mixing states of aerosols in future versions of ASP.

A facile one pot route for the synthesis of imide tethered peptidomimetics

2016 ◽  
Vol 14 (2) ◽  
pp. 556-563 ◽  
Author(s):  
Veladi Panduranga ◽  
Girish Prabhu ◽  
Roopesh Kumar ◽  
Basavaprabhu Basavaprabhu ◽  
Vommina V. Sureshbabu
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Efficient Method ◽  
One Pot ◽  
Protected Amino Acid

A simple and efficient method for the synthesis of N,N’-orthogonally protected imide tethered peptidomimetics is presented. The imide peptidomimetics were synthesized by coupling the in situ generated selenocarboxylate of Nα-protected amino acids with Nα-protected amino acid azides in good yields.

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