An official website of the United States government
Abstract The type II polyproline helix (PPII) is a fundamental secondary structure of proteins, important in globular proteins, in intrinsically disordered proteins, and at protein‐protein interfaces. PPII is stabilized in part byn→π* interactions between consecutive carbonyls, via electron delocalization between an electron‐donor carbonyl lone pair (n) and an electron‐acceptor carbonyl (π*) on the subsequent residue. We previously demonstrated that changes to the electronic properties of the acyl donor can predictably modulate the strength ofn→π* interactions, with data from model compounds, in solution in chloroform, in the solid state, and computationally. Herein, we examined whether the electronic properties of acyl capping groups could modulate the stability of PPII in peptides in water. InX−PPGY‐NH2peptides (X=10 acyl capping groups), the effect of acyl group identity on PPII was quantified by circular dichroism and NMR spectroscopy. Electron‐rich acyl groups promoted PPII relative to the standard acetyl (Ac−) group, with the pivaloyl andiso‐butyryl groups most significantly increasing PPII. In contrast, acyl derivatives with electron‐withdrawing substituents and the formyl group relatively disfavored PPII. Similar results, though lesser in magnitude, were also observed inX−APPGY‐NH2peptides, indicating that the capping group can impact PPII conformation at both proline and non‐proline residues. The pivaloyl group was particularly favorable in promoting PPII. The effects of acyl capping groups were further analyzed inX–DfpPGY‐NH2andX−ADfpPGY‐NH2peptides, Dfp=4,4‐difluoroproline. Data on these peptides indicated that acyl groups induced order Piv‐ > Ac‐ > For‐. These results suggest that greater consideration should be given to the identity of acyl capping groups in inducing structure in peptides.
more »
« less
Photoinduced modification of optical properties of ferroelectric PZT thin films
Abstract This study investigates ultrafast photoinduced changes in optical properties of ferroelectrics (PZT) on femtosecond to nanosecond timescales, using broadband transient reflectivity studies. Surprisingly, spectral features were observed below the bandgap, which could not be attributed to ground state bleaching, excited state absorption, and/or stimulated emission. A model based on probe energy independent changes in refractive index and extinction coefficient showed good agreement with experimental results. Three relaxation processes were phenomenologically considered for the temporal evolution. Laser-induced heating was ruled out as the cause of short timescale behavior and photorefractive effect was suggested as a potential mechanism for changes in the optical properties. Graphical abstract
more »
« less
- Award ID(s):
- 1902652
- PAR ID:
- 10470733
- Publisher / Repository:
- Cambridge University Press (CUP)
- Date Published:
- Journal Name:
- MRS Communications
- Volume:
- 14
- Issue:
- 1
- ISSN:
- 2159-6867
- Format(s):
- Medium: X Size: p. 17-25
- Size(s):
- p. 17-25
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract This article describes the development of novel, hydrolytically stable cardiotonic steroid analogs featuring a 3β‐amine moiety instead of the commonly found 3β‐carbohydrates such as oleandrose. To establish the desired 3β‐configuration stereoselectively, a new method based on chiral phosphoric acid‐controlled diastereoselective reductive amination with Hantzsch esters was developed. This method utilizes readily available unsubstituted (S)‐BINOL‐based hydrogen phosphate as the catalyst, enabling the synthesis of 13 different 5β‐androsterone and digitoxigenin analogs with up to 36:1 β:α diastereoselectivity. Additionally, this strategy was applied to generate two novel oleandrigenin analogs15aand15gin 3 steps from readily available gitoxigenin. The synthetic analogs were subjected to the NCI‐60 human tumor cell lines screen, and several different digitoxigenin derivatives with tumor cell growth inhibitory power in submicromolar range were identified. The subsequent in vitro evaluation of digitoxigenin and oleandrin derivatives13a,13g,15a, and15gdemonstrated that these four analogs reduced steady‐state ATP1A1 levels in T98G cells in the 12–96 nM range. Interestingly, only the oleandrin analog15glowered also steady‐state levels of the cellular prion protein (PrPC), the main therapeutic target for the treatment of prion diseases.more » « less
-
Abstract Accurately mapping changes in cellular membrane potential across large groups of neurons is crucial for understanding the organization and maintenance of neural circuits. Measuring cellular voltage changes by optical means allows greater spatial resolution than traditional electrophysiology methods and is adaptable to high‐throughput imaging experiments. VoltageFluors, a class of voltage‐sensitive dyes, have recently been used to optically study the spontaneous activity of many neurons simultaneously in dissociated culture. VoltageFluors are particularly useful for experiments investigating differences in excitability and connectivity between neurons at different stages of development and in different disease models. The protocols in this article describe general procedures for preparing dissociated cultures, imaging spontaneous activity in dissociated cultures with VoltageFluors, and analyzing optical spontaneous activity data. © 2021 Wiley Periodicals LLC. This article was corrected on 20 July 2022. See the end of the full text for details. Basic Protocol 1: Preparation of dissociated rat hippocampal or cortical cultures Alternate Protocol: Preparation of microisland dissociated cultures Basic Protocol 2: Imaging of spontaneous activity in dissociated cultures using voltage‐sensitive dyes Basic Protocol 3: Analysis of spontaneous activity imaging datamore » « less
-
Abstract This study introduces a benzodithiophene‐S,S‐tetraoxide (BDTT) monomer as an acceptor and 3,4‐ethylenedioxythiophene flanked thiophene (TEDOT2) and terthiophene (T3) as donor molecules for polymer formation. The synthesis of thepoly(TEDOT2‐BDTT)andpoly(T3‐BDTT)copolymers was performed via a single‐step monomer radical formation that is typically associated with electropolymerization methods. The electropolymerization is controlled by using a suitable monomer stoichiometric ratio that enables the deposition of copolymer thin films on the working electrode. Resultant copolymers were investigated by electrochemical analysis and their electronic properties are discussed in detail. A low average electron transport resistance of 16.5 Ω was found forpoly(TEDOT2‐BDTT), indicating excellent conductive behavior. Solid‐state absorbance and emission studies of the copolymers show visible to near‐infrared spectral activity. Results support an effective strategy towards highly efficient electronically conducting polymers (ECPs) based on a unique BDTT monomer.more » « less
-
Abstract Understanding dynamic processes in battery materials under real-time conditions is critical for advancing electrochemical storage technologies. Here, we develop anoperandooptical technique to probe changes in the wide-field reflectance of vanadium oxide cathodes during cycling in aqueous Zn-ion batteries by using a budget-friendly experimental setup and lab-made Python code. The results indicate that brightness of the vanadium oxide was dramatically changed with intercalation process at certain states-of-(dis)charge. Our methodology correlates wide-field reflectance changes with electrochemical behavior, enablingoperandomonitoring of the materials' evolution in aqueous battery systems. Graphical abstractmore » « less
