Cis Conformation Research Articles

Shape-Persistent Liquid Crystal Elastomers with Cis-Stable Crosslinkers Containing Ortho-Methyl-Substituted Azobenzene

Shape-persistent cis-isomer-stable azobenzene-functionalized liquid crystal elastomers (azo-LCEs) were prepared using an azobenzene crosslinker with two methyl substitutions at the ortho positions of azobenzene [4,4′-di(4-(acrylolylhexyloxy) benzoyloxy)-2,6-dimethylazobenzene (DADO)] via thiol–acrylate Michael addition photopolymerization. Ultraviolet–visible (UV–vis) and nuclear magnetic resonance (NMR) spectroscopies revealed that the methyl substituents on DADO rocked its cis conformation under UV irradiation and significantly delayed the visible (laser)-light-induced cis-to-trans isomerization. Raman spectroscopy and small-/wide-angle X-ray scattering analyses indicated that the cis-isomers in DADO-linkage-containing monodomain azo-LCE (azo-MLCEDADO) were not readily converted to the trans conformation under visible (laser)-light irradiation but transformed easily upon mechanical drawing. The azo-MLCEDADO film exhibited a low-plateau modulus and high elongation because of the weak intermolecular interactions caused by its bulky methyl substituents, leading to considerable UV-irradiation-induced contraction (up to 50%) and suspended weight-induced recovery to its original length. These cis-stable azo-MLCEDADO films can be used in shape-persistent actuators in soft robotics, haptics, and biomedical device fabrication.

Tetrazo[1,2-b]indazoles: Straightforward Access to Nitrogen-Rich Polyaromatics from s-Tetrazines.

The straightforward access to a new class of aza-polyaromatics is reported. Starting from readily available fluorinated s-tetrazine, a cyclization process with azide leads to the formation of an unprecedented tetrazo[1,2-b]indazole or a bis-tetrazo[1,2-b]indazole (cis and trans conformers). Based on the new nitrogen core, further N-directed palladium-catalyzed ortho-C-H bond functionalization allows the introduction of halides or acetates. The physicochemical properties of these compounds were studied by a joint experimental/theoretical approach. The tetrazo[1,2-b]indazoles display solid-state π-stacking, low reduction potential, absorption in the visible range up to the near-infrared, and intense fluorescence, depending on the molecular structure.

Structure, Vibrational Spectra, and Cryogenic MatrixPhotochemistry of 6-Bromopyridine-2-carbaldehyde: From the Single Molecule of the Compound to the Neat Crystalline Material

6-Bromopyridine-2-carbaldehyde (abbreviated as BPCA) is used both as a building block in supramolecular chemistry and as a ligand for transition metal catalysts and luminescent complexes. In this study, the structure and vibrational spectra of BPCA were investigated in both the room temperature neat crystalline phase and for the compound isolated in cryogenic Ar, Kr and Xe matrices. The experimental studies were complemented by quantum chemical DFT(B3LYP)/6-311++G(d,p) calculations. For the crystalline compound, infrared and Raman spectra were obtained and interpreted. Comparison of the obtained infrared spectrum of the crystal with those obtained for the isolated molecules of BPCA in the studied cryomatrices helped to conclude that the intermolecular interactions in the crystal do not significantly perturb the intramolecular vibrational potential. Structural analysis further supports the existence of weak coupling between the intermolecular interactions and the structure of the constituting molecular units in crystalline state. The intermolecular interactions in the BPCA crystal were also evaluated by means of Hirshfeld analysis, which revealed that the most important interactions are weak and of the H…N, H…O, H…H, H…Br and Br…Br types. The conformer of BPCA present in the crystal was found to correspond to the most stable form of the isolated molecule (trans), which bears stabilizing C-H…O=C and C(=O)H…N interactions. This conformer was shown to be the single conformer present in the as-deposited cryogenic matrices prepared from the room temperature gaseous compound. Broadband UV irradiation of matrix-isolated BPCA (λ ≥ 235 nm) resulted in the conversion of the trans conformer into the higher-energy cis conformer, where repulsive C-H…H-C(=O) and C=OLP…LPN (where LP designates a lone electron pair) interactions are present, and decarbonylation of the compound with formation of 2-bromopyridine (plus CO). The decarbonylation reaction was found to be more efficient in the more polarizable Xe matrix, indicating stabilization of the radicals initially formed upon breaking of the C-C(HO) and C-H (aldehyde) bonds in this medium, and testifying the occurrence of the decarbonylation reaction with involvement of radical species. TD-DFT calculations were used to access the nature of the excited states associated with the observed UV-induced reactions. As a whole, this study provides fundamental data to understand the physicochemical behavior of the compound, bridging the properties of the isolated molecule to those of the neat crystalline com-pound. Such information is of fundamental importance for the understanding of the role of BPCA in supramolecular chemistry and to potentiate its applications in synthesis and as a ligand for transition metal catalysts and luminescent complexes.

Proline isomerization compensates for the effect of phosphorylation in conformations of the disordered RNA polymerase II CTD.

RNA Polymerase II transcribes mRNA. The largest subunit of this complex contains a C-terminal domain (CTD) that is an intrinsically disordered protein with a repetitive amino acid heptad sequence making the domain very difficult to study. Kinases and Phosphatases regulate CTD through post-translational modifications. Small angle x-ray scattering data shows very little change in CTD compaction with phosphorylation, despite the repulsion between the negatively charged phosphate groups. Data also shows an increase in Pro6 isomerization when Ser5 is phosphorylated. Prior work shows that a variation of the consensus sequence where Ser7 is replaced with Asn increases the population of the proline cis conformation. We use Gaussian accelerated molecular dynamics simulations to determine how the CTD domain conformation and dynamics are impacted by phosphorylation. Simulations were run on a 21-residue construct consisting of three heptads, with the middle heptad containing Asn7. Results show that due to proline isomerization, the domain can move reversibly between a compact and extended structure. The phosphorylated CTD domain samples more prolines in cis, which compensates for the effect of phosphorylation, resulting in a similar radius of gyration to the unphosphorylated domain. Future work includes running simulations with the consensus sequence for all three heptads of our construct to determine why having asparagine in position 7 increases Pro6 isomerization compared to serine.

Polyadenine complexed to polyglutamine suggests the peptide backbone has a cis conformation

The polyadenine (poly(A)) tail of mRNA is a homopolymer and as such is a potential H-bonding partner for other cellular homopolymers. The secondary structure of proteins and peptides employs the polar groups of the homopolymer backbone to bind with themselves or other polymers to respectively form an alpha helix or a beta sheet. These same backbone polar groups appear to be suitably positioned to bind with poly(A) but only when the backbone has rotated to the all-cis conformation. However the all-cis conformation of peptides or proteins is rarely encountered and so they would seem to be unlikely binding partners. Here we show that a homopolymer of glutamine (poly(Q)) may be an exception to this rarity because its default conformation seems to be all-cis. We found that exposure of poly(A) to increasing amounts of poly(Q) causes a progressive loss of soluble poly(A) migrating on gel electrophoresis, indicating binding between the two polymers. Stereochemical modelling of the likely complex has suggested the particular polar groups that are responsible for binding of the two polymers, along with an explanation for the all-cis conformation of poly(Q).

Formation of α,β-Unsaturated Imines in Apolar Aprotic Solvent: Effect of Hidden Acid Catalysts Analyzed by Theoretical Calculations

A theoretical investigation of the 1,2-additon and 1,4-addition reactions of benzylamine to crotonaldehyde in toluene solution is reported in this study, including the effect of trace amounts of acetic acid (AcOH) and methanesulfonic acid (CH3SO2OH). We have determined the reaction free energy profile and performed a detailed microkinetic analysis. Our results point out that this reaction system needs catalysis to take place and it was found that CH3SO2OH is a powerful catalyst, outperforming AcOH in lowering the free energy barrier for the 1,2-addition reaction, which leads to the formation of a,b-unsaturated imine. On the other hand, the 1,4-addition reaction has the direct nucleophilic attack of benzylamine to the b-carbon of s-cis conformation of crotonaldehyde as the rate-determining step, corresponding to slow kinetics. Our results suggest that the experimentally observed formation of the imine can be explained by the presence of hidden acid catalysts present in the reaction medium.

Mechanistic insights into the nickel-dependent allosteric response of the Helicobacter pylori NikR transcription factor

In Helicobacter pylori, the nickel-responsive NikR transcription factor plays a key role in regulating intracellular nickel concentrations, which is an essential process for survival of this pathogen in the acidic human stomach. Nickel binding to H.pylori NikR (HpNikR) allosterically activates DNA binding to target promoters encoding genes involved in nickel homeostasis and acid adaptation, to either activate or repress their transcription. We previously showed that HpNikR adopts an equilibrium between an open conformation and DNA-binding competent cis and trans states. Nickel binding slows down conformational exchange between these states and shifts the equilibrium toward the binding-competent states. The protein then becomes stabilized in a cis conformation upon binding the ureA promoter. Here, we investigate how nickel binding creates this response and how it is transmitted to the DNA-binding domains. Through mutagenesis, DNA-binding studies, and computational methods, the allosteric response to nickel was found to be propagated from the nickel-binding sites to the DNA-binding domains via the β-sheets of the metal-binding domain and a network of residues at the inter-domain interface. Our computational results suggest that nickel binding increases protein rigidity to slow down the conformational exchange. A thymine base in the ureA promoter sequence, known to be critical for high affinity DNA binding by HpNikR, was also found to be important for the allosteric response, while a modified version of this promoter further highlighted the importance of the DNA sequence in modulating the response. Collectively, our results provide insights into regulation of a key protein for H.pylori survival.

The Essential Role of Prolines and Their Conformation in Allosteric Regulation of Kaiso Zinc Finger DNA-Binding Activity by the Adjacent C-Terminal Loop

Kaiso is a methyl-DNA-binding protein containing three C2H2 zinc fingers with a C-terminal extension that participates in DNA binding. The linker between the last zinc finger and the DNA-binding portion of the extension contains two prolines that are highly conserved in vertebrates and in cognate ZBTB4 and ZBTB38 proteins. Prolines provide chain rigidity and can exist in cis and trans conformations that can be switched by proline isomerases, affecting protein function. We found that substitution of the conserved proline P588, but not of P577, to alanine, negatively affected KaisoDNA-binding according to molecular dynamics simulation and in vitro DNA-binding assays. Molecular dynamics simulations of the Kaiso DNA-binding domain with P588 either substituted to alanine or switched to the cis-conformation revealed similar alterations in the H-bonding network and uncovered allosteric effects leading to structural rearrangements in the entire domain that resulted in the weakening of DNA-binding affinity. The substitution of proline with a large hydrophobic residue led to the same negative effects despite its ability to partially rescue the intrinsic DNA-binding activity of the C-terminal loop. Thus, the presence of the C-terminal extension and cis-conformation of proline residues are essential for efficient Kaiso-DNA binding, which likely involves intramolecular tension squeezing the DNA chain.

Agnathia-Otocephaly Complex Due to a De Novo Deletion in the OTX2 Gene

Agnathia-otocephaly complex (AOC) is a rare and usually lethal malformation typically characterized by hypoplasia or the absence of the mandible, ventromedial and caudal displacement of the ears with or without the fusion of the ears, a small oral aperture with or without a tongue hypoplasia. Its incidence is reported as 1 in 70,000 births and its etiology has been attributed to both genetic and teratogenic causes. AOC is characterized by a wide severity clinical spectrum even when occurring within the same family, ranging from a mild mandibular defect to an extreme facial aberration incompatible with life. Most AOC cases are due to a de novo sporadic mutation. Given the genetic heterogeneity, many genes have been reported to be implicated in this disease but to date, the link to only two genes has been confirmed in the development of this complex: the orthodenticle homeobox 2 (OTX2) gene and the paired related homeobox 1 (PRRX1) gene. In this article, we report a case of a fetus with severe AOC, diagnosed in routine ultrasound scan in the first trimester of pregnancy. The genetic analysis showed a novel 10 bp deletion mutation c.766_775delTTGGGTTTTA in the OTX2 gene, which has never been reported before, together with a missense variant c.778T>C in cis conformation.

Infrared Spectra and Phototransformations of meta-Fluorophenol Isolated in Argon and Nitrogen Matrices

Monomers of meta-fluorophenol (mFP) were trapped from the gas phase into cryogenic argon and nitrogen matrices. The estimated relative energies of the two conformers are very close, and in the gas phase they have nearly equal populations. Due to the similarity of their structures (they only differ in the orientation of the OH group), the two conformers have also similar predicted vibrational signatures, which makes the vibrational characterization of the individual rotamers challenging. In the present work, it has been established that in an argon matrix only the most stable trans conformer of mFP exists (the OH group pointing away from the fluorine atom). On the other hand, the IR spectrum of mFP in a nitrogen matrix testifies to the simultaneous presence in this matrix of both the trans conformer and of the higher-energy cis conformer (the OH group pointing toward the fluorine atom), which is stabilized by interaction with the matrix gas host. We found that the exposition of the cryogenic N2 matrix to the Globar source of the infrared spectrometer affects the conformational populations. By collecting experimental spectra, either in the full mid-infrared range or only in the range below 2200 cm-1, we were able to reliably distinguish two sets of experimental bands originating from individual conformers. A comparison of the two sets of experimental bands with computed infrared spectra of the conformers allowed, for the first time, the unequivocal vibrational identification of each of them. The joint implementation of computational vibrational spectroscopy and matrix-isolation infrared spectroscopy proved to be a very accurate method of structural analysis. Some mechanistic insights into conformational isomerism (the quantum tunneling of hydrogen atom and vibrationally-induced conformational transformations) have been addressed. Finally, we also subjected matrix-isolated mFP to irradiations with UV light, and the phototransformations observed in these experiments are also described.

Cover Feature: Light‐Responsive Oligothiophenes Incorporating Photochromic Torsional Switches (Chem. Eur. J. 65/2022)

A novel class of light-responsive π-conjugated compounds incorporates photochromic torsional switches (PTS). These compounds are able to tune the planarization of their π-conjugated backbone, and thus their optical and electronic properties, by using light as an external stimulus. The PTS unit is based on a bithiophene fragment linked to a photochromic azobenzene moiety. When this PTS-containing oligothiophene is not exposed to light, the azobenzene moiety assumes its extended trans conformation, which forces the oligothiophene backbone to twist out of coplanarity. Exposure to UV light results in isomerization to the cis conformation, which allows the bithiophene fragment to assume a planar, π-conjugated conformation. More information can be found in the Research Article by D. Fazzi, E. Orentas, G. Sforazzini, and co-workers (DOI: 10.1002/chem.202202698).

High-Performance Ionanofluids from Subzipped Carbon Nanotube Networks

Investments in the transfer and storage of thermal energy along with renewable energy sources strengthen health and economic infrastructure. These factors intensify energy diversification and the more rapid post-COVID recovery of economies. Ionanofluids (INFs) composed of long multiwalled carbon nanotubes (MWCNTs) rich in sp2-hybridized atoms and ionic liquids (ILs) display excellent thermal conductivity enhancement with respect to the pure IL, high thermal stability, and attractive rheology. However, the influence of the morphology, physicochemistry of nanoparticles and the IL-nanostructure interactions on the mechanism of heat transfer and rheological properties of INFs remain unidentified. Here, we show that intertube nanolayer coalescence, supported by 1D geometry assembly, leads to the subzipping of MWCNT bundles and formation of thermal bridges toward 3D networks in the whole INF volume. We identified stable networks of straight and bent MWCNTs separated by a layer of ions at the junctions. We found that the interactions between the ultrasonication-induced breaking nanotubes and the cations were covalent in nature. Furthermore, we found that the ionic layer imposed by close MWCNT surfaces favored enrichment of the cis conformer of the bis(trifluoromethylsulfonyl)imide anion. Our results demonstrate how the molecular perfection of the MWCNT structure with its supramolecular arrangement affects the extraordinary thermal conductivity enhancement of INFs. Thus, we gave the realistic description of the interactions at the IL-CNT interface with its (super)structure and chemistry as well as the molecular structure of the continuous phase. We anticipate our results to be a starting point for more complex studies on the supramolecular zipping mechanism. For example, ionically functionalized MWCNTs toward polyionic systems─of projected and controlled nanolayers─could enable the design of even more efficient heat-transfer fluids and miniaturization of flexible electronics.

Conformational fidelity and hydrogen bond associability of L-histidine with sulfamate anion studied through XRD, quantum chemical, spectroscopic and molecular docking simulation as a cdk-4 inhibitor against retinoblastoma

L-histidinium sulfamate, (C6H10N3O2)+.SO3NH2−,crystallizes in the orthorhombic space group, P212121, with four molecules per unit cell. The asymmetric part of unit cell comprises a diprotonated monovalent histidinium cation and a sulfamate anion. The amino nitrogen of the cation is deviated from the carboxylate group plane. The backbone conformations are observed to be cis and trans conformations. The side chain conformations are witnessed to be gauche I / gauche II / gauche I rotomers. The conformations of the cation are dominated by the three dimensional intermolecular hydrogen bonding network in the crystal packing. The classical hydrogen bonds are observed in the crystalline landscapes categorically cation-cation, anion-anion and cation-anion interactions leading to chain C(4), C(5) and C(7) motifs and ring R33(10), R33(14), R33(21) and R55(30) motifs. The molecular structure, FT-IR, FT-Raman, Frontier Molecular Orbitals (FMO), Natural Bond Orbital (NBO) analysis Mulliken charge analysis, Electrostatic potential analysis (ESP), Non-Linear Optical (NLO) properties of L-histidinium sulfamate have been evaluated using the (DFT) calculations with B3LYP/6‒311++G (d, p) basis set. TD-DFT in gas phase with the same basis set was used to analyze electronic parameters such as excitation energy, wavelength, band gap, and oscillator strength from the theoretical UV–Visible spectrum. The Fukui function was also used to investigate the molecule's local reactivity. The contribution of distinct interactions within the molecule and the strength of molecular packing in the compound have been evaluated through Hirshfeld surface (HS) analysis .Retinoblastoma is the most well-known pediatric malignant development of the eye. The protein cyclin dependent kinase (Cdk) plays a role in the phosphorylation process; its inhibition triggers the retinoblastoma protein's suppressor function, which stops tumor development. Molecular docking simulation has been performed through PyRx software and the new single crystal L-histidinium sulfamate showed effective binding to the Cdk-4 protein with the binding score of -6.7 Kcal/mol and pharmacokinetic studies showed a good safety profile of L-histidinium sulfamate.

Expression of Mutant Glycine Receptors in Xenopus Oocytes Using Canonical and Non-Canonical Amino Acids Reveals Distinct Roles of Conserved Proline Residues.

Pentameric ligand-gated ion channels (pLGIC) play important roles in fast neuronal signal transmission. Functional receptors are pentamers, with each subunit having an extracellular domain (ECD), a transmembrane domain (TMD) and an intracellular domain. The binding of the agonist to the ECD induces a structural change that is transduced to the TMD to open the channel. Molecular details of this process are emerging, but a comprehensive understanding is still lacking. Proline (Pro) is one amino acid that has attracted much interest; its unusual features generate bends in loops and kinks and bulges in helices, which can be essential for function in some pLGICs. Here, we explore the roles of four conserved Pros in the glycine receptor (GlyR), creating substitutions with canonical and noncanonical amino acids, characterizing them using two electrode voltage clamp electrophysiology in Xenopus oocytes, and interpreting changes in receptor parameters using structural data from the open and closed states of the receptor. The data reveal that for efficient function, the Pro in the α1β1 loop is needed to create a turn and to be the correct size and shape to interact with nearby residues; the peptide bond of the Pro in the Cys-loop requires the cis conformation; and the Pros in loop A and M1 allow efficient function because of their reduced hydrogen bonding capacity. These data are broadly consistent with data from other pLGICs, and therefore likely represent the important features of these Pros in all members of the family.

Conformational Properties of Aromatic Amides Bearing Imidazole Ring and Acid-Induced Trans–Cis Amide Switching

Aromatic amides bearing secondary amide bond exist in trans conformation both in the crystal and in solution, whereas the conformation of the N-methylated derivatives is cis in the crystal and predominantly cis in various solvents. The cis conformational preference of N-alkylated benzanilide provides access to aromatic foldamers such as oligo(N-alkyl-p-benzamide)s, which adopt dynamic helical structures. Here, the conformational properties of imidazole-substituted amide in the crystal and in solution were examined. Imidazole-substituted amides 2a and 4a existed mainly in the cis conformation in solution. The ratio of the cis conformer of N-methyl-N-(1-methyl-1H-imidazol-4-yl)benzamide (4a) was smaller than that of N,1-dimethyl-N-phenyl-1H-imidazole-2-carboxamide (2a) or N-methylbenzanilide, but the introduction of a substituent strongly affected the conformer ratio. Compounds 6a and 7a bearing an electron-withdrawing group on the imidazole ring existed predominantly in trans form. On the other hand, the introduction of an electron-withdrawing group on the phenyl ring or a bulky substituent on the amide nitrogen of 4a increased the ratio of cis conformer. Further, the major conformer of N-alkylated N-imidazolylamides was switched from cis to trans by the addition of acid. These results suggest that imidazole-substituted amides might be applicable as conformational switches in aromatic foldamers to enable environment-dependent structural change.

Active immunotherapy against pathogenic Cis pT231-tau suppresses neurodegeneration in traumatic brain injury mouse models

Traumatic brain injury (TBI), characterized by acute neurological impairment, is associated with a higher incidence of neurodegenerative diseases, particularly chronic traumatic encephalopathy (CTE), Alzheimer's disease (AD), and Parkinson's disease (PD), whose hallmarks include hyperphosphorylated tau protein. Recently, phosphorylated tau at Thr231 has been shown to exist in two distinct cis and trans conformations. Moreover, targeted elimination of cis P-tau by passive immunotherapy with an appropriate mAb that efficiently suppresses tau-mediated neurodegeneration in severe TBI mouse models has proven to be a useful tool to characterize the neurotoxic role of cis P-tau as an early driver of the tauopathy process after TBI. Here, we investigated whether active immunotherapy can develop sufficient neutralizing antibodies to specifically target and eliminate cis P-tau in the brain of TBI mouse models. First, we explored the therapeutic efficacy of two different vaccines. C57BL/6 J mice were immunized with either cis or trans P-tau conformational peptides plus adjuvant. After rmTBI in mice, we found that cis peptide administration developed a specific Ab that precisely targeted and neutralized cis P-tau, inhibited the development of neuropathology and brain dysfunction, and restored various structural and functional sequelae associated with TBI in chronic phases. In contrast, trans P-tau peptide application not only lacked neuroprotective properties, but also contributed to a number of neuropathological features, including progressive TBI-induced neuroinflammation, widespread tau-mediated neurodegeneration, worsening functional deficits, and brain atrophy. Taken together, our results suggest that active immunotherapy strategies against pathogenic cis P-tau can halt the process of tauopathy and would have profound clinical implications.

The adsorption and electropolymerization of terthiophene on Au(1 1 1) electrode – Probed by in situ STM

• In situ STM imaging terthiophene molecule adsorbed on an ordered Au(1 1 1) electrode in sulfuric and perchloric acid. • Dominant effect of potential control on the adsorption and oxidation of terthiophene admolecule. • Terthiophene admolecules accompanied by bisulfate anions to form highly ordered adlattices. • Revelation of adsorption configuration and spatial arrangement of TT on Au(1 1 1) electrode. • STM visualization of oligothiophenes produced by anodization. In situ scanning tunneling microscopy (STM) was used to examine terthiophene (TT) adsorbed on an ordered Au(1 1 1) electrode in 0.1 M H 2 SO 4 and HClO 4 , as a model system to gain a fundamental understanding of the effects of potential control on the coadsorption of anion and the oxidation of a thiophene - bearing entity. TT was irreversibly adsorbed onto an Au(1 1 1) bead crystal from a dosing solution made of ethanol at room temperature. The cyclic voltammogram (CV) recorded with this sample in 0.1 M H 2 SO 4 showed a series of well-defined peaks, resulting from the restructuring of the TT adlayer, coupled with anion coadsorption and the phase transition of the Au(1 1 1) electrode. In contrast, the CV obtained in 0.1 M HClO 4 was mostly featureless before TT admolecules were irreversibly oxidized at E > 0.7 V (vs Ag/AgCl). TT molecule was adsorbed most horizontally on Au(1 1 1) electrode in H 2 SO 4 , but displaced by bisulfate anion at positive potential. Anodization of this TT/Au(1 1 1) electrode triggered the oxidation and subsequent coupling of TT monomers to yield oligothiophenes, whose internal structures and dimensions were revealed by STM in pH1 and 5 sulfate media. The as – produced oligothiophenes appeared as winding ribbons spanning ∼ 200 and ∼ 40 Å in pH 5 and 1 sulfate media. Their internal structures, particularly the trans and cis conformations of neighboring thiophenes units, were visualized by molecular resolution STM.

Central condensed ring changes for manipulating the self-assembly and photophysical behaviors of cyanostilbene-based hexacatenars

Two series of condensed ring hexacatenars consisting of a central naphthalene/anthracene and two cyanostilbene units as the π-conjugated rigid core were reported. The thermodynamics behaviors and liquid crystalline structures of these mesogens were investigated by the combination of POM, DSC and XRD. It is indicated that only higher naphthalene-based homologues exhibit hexagonal columnar phases, the other lower naphthalene-based homologues and all the anthracene-based homologues are non-mesogens. The results demonstrated that the steric effect provided by the larger central aromatic group hinders the ordered molecular stacking. The temperature-dependent fluorescence demonstrated that the fluorescence stability of these hexacatenars increased from central phenyl via naphthyl to anthryl due to the increased degree of molecular distortions induced by the central larger aromatic group. The solvatochromism and AIEE behaviors were also studied by UV–vis absorption, fluorescence emission and density functional theory (DFT) demonstrating that the anthracene-based compounds exhibit more distinct solvatochromism, higher fluorescence quantum yield than those of naphthalene-based compounds and more distinct ICT effect, and both series of compounds exhibited strong fluorescence in both solutions and aggregated state due to ICT effect and the long π-conjugated aromatic core with twisted conformations. Additionally, photoisomerization behaviors demonstrated both cis and trans conformations showed high stability in condensed and solution states.

Total synthesis of a reversed cyclopurpuracin using a combination of solid and solution phase methods

AbstractCyclopurpuracin is a cyclooctapeptide isolated from the methanol extract of Annona purpurea seeds with the following sequence cyclo‐Gly‐Phe‐Ile‐Gly‐Ser‐Pro‐Val‐Pro residue. In this study, a reversed cyclopurpuracin, namely cyclo‐Pro‐Val‐Pro‐Ser‐Gly‐Ile‐Phe‐Gly, was successfully synthesized using a combination of solid and solution phase synthesis methods. The precursor was head‐to‐tail cyclized using 1.25 mM in DCM with 3 eq. HBTU and 1% v/v DIPEA. The final product was obtained (3.8 mg) with an overall yield of 7.4%. The synthetic products were characterized by HR‐ToF‐MS, 1H‐NMR, 13C‐NMR, and 2D NMR, showing different NMR profiles. The presence of the conformation was confirmed by providing additional signals in the 1H NMR and 13C NMR spectrum and the correlation peaks shown by 2D NMR. The presence of the cis conformer in conformer B was proven by the chemical shifts of Ser6 Cβ, Pro7 Cβ, and Pro8 Cβ in conformer B, which were more upfield than the conformer A chemical shifts, and the presence of NOE correlation between Hα/Hα of Val7 and Pro8. The NMR of the reversed cyclopurpuracin revealed the presence of two conformers, conformer A (cyclo‐[trans‐Pro‐Val‐trans‐Pro‐Ser‐Gly‐Ile‐Phe‐Gly]) and conformer B (cyclo‐[cis‐Pro‐Val‐trans‐Pro‐Ser‐Gly‐Ile‐Phe‐Gly]). The presence of dual conformers has not been observed in the NMR spectra of natural cyclopurpuracin.

Comprehensive Quantum Chemical Characterization of the Astrochemically Relevant HCnH Chain Family: An Attempt to Aid Astronomical Observations

AbstractIn this paper, the results of a comprehensive theoretical investigation of neutral HCnH0 and charged HCnH± chains are reported using state‐of‐the‐art compound model chemistries (W1BD, G4, CBS‐QB3, CBS‐APNO, CBS‐4M) and single point methods (including “gold standard” CCSD(T)). The properties envisaged include electronic and chemical bonding structure data, enthalpies of formation, adiabatic and vertical ionization (IP), and electron attachment (EA) energies, gas phase acidities, C−H bond strengths, and chain “deprotecting” (HCnH → H + Cn + H) energies. The best theoretical estimates based on composite models reported here for the various properties investigated agree with the available experimental data and are better than all previous theoretical estimates. To exemplify, for the enthalpies of formation, the G4 composite model achieves a RSMD (root square mean deviation) of 0.28 kcal mol−1 and a MUD (maximum unsigned deviation) of 0.45 kcal mol−1. Most importantly from the astrochemical perspective, it is predicted that the stable HCnH− anions with are nonlinear. Having sufficiently large dipole moments, the anion HCnH− cis conformers are potential candidates for detection in space via rovibrational spectroscopy.