Left-handed Helical Structure Research Articles

Crystal structure and Hirshfeld surface analysis of 1,2-bis-(2',6'-diisoprop-oxy-[2,3'-bipyridin]-6-yl)benzene.

The title mol-ecule, C38H42N4O4, displays a helical structure induced by the combination of the C-C-C-C torsion angle [-10.8 (2)°] between two 2,3'-bipyridyl units attached to the 1,2-positions of the central benzene ring and consecutive connections between five aromatic rings through the meta- and ortho-positions. Intra-molecular C-H⋯π inter-actions between an H atom of a pyridine ring and the centroid of a another pyridine ring contributes to the stabilization of the helical structure. In the crystal, weak C-H⋯π inter-actions link the title mol-ecules into a two-dimensional supra-molecular network extending parallel to the ac plane, in which the mol-ecules with right- and left-handed helical structures are alternately arranged. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the mol-ecular packing is dominated by van der Waals inter-actions between neighbouring H atoms, as well as by C-H⋯π inter-actions. One isopropoxyl group is disordered over two sets of sites [occupancy ratio 0.715 (5):0.285 (5)].

Comprehensive analysis of damage associated SNPs of MMP9 gene: A computational approach

Extracellular matrix is a dynamic meshwork of macromolecules that plays an important role in biological processes such as tissue remodeling and various developmental processes. Collagen is the chief component of ECM. Upon hydrolysis, it forms an irreversible left-handed helical structure which is further hydrolyzed by a specialized group of MMP family i.e. Gelatinases (MMP2 and MMP9). Present study was carried to figure out deleterious SNPs associated with MMP9 gene. Our results showed that two nsSNP (rs8125581 and rs41529445) that are present in catalytic domain are highly conserved and affect the protein structure and function.7 SNPs located in UTRs were found to alter miRNA seed region 13 SNPs of splice site were predicted to affect splice signals thereby affecting the post translational expression of MMP9. Most of the SNPs are still uncharacterized thereby present study provides a direction that can help to validate the relation between the altered expressions and functions of MMP9 protein in terms of disease susceptibility.

BioEssays 4∕2018

BioEssaysVolume 40, Issue 4 1870041 Cover PictureFree Access BioEssays 4∕2018 First published: 30 March 2018 https://doi.org/10.1002/bies.201870041AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract In article number 1700213, Popp et al. discuss the impact of technological advances in structural biology on uncovering the architectures of previously intractable protein systems, with a focus on biological filaments. The cover shows two examples of recent filament structures determined by cryoEM. The 3.6 Å double-stranded right-handed actin helical structure (shades of green) is shown juxtaposed with the 4.3 Å double-stranded left-handed helical ParM structure (pink and claret) (pdb accession numbers 5JLF (Actin) and 5AEY (ParM)). Volume40, Issue4April 20181870041 RelatedInformation

Modifying oligoalanine conformation by replacement of amide to ester linkage.

Oligo(lactic acid) is an ester-analogue of short oligoalanine sequence and adopts a rigid left-handed helical structure. In this study, oligo(lactic acid) was incorporated into oligoalanine sequences and their conformations were studied by vibrational circular dichroism and electronic circular dichroism spectroscopy. The results suggested that oligo(lactic acid) moiety in these sequences maintains a left-handed helix and increases the conformational propensity of the oligoalanine moiety to form a left-handed polyproline type II-like helix. The importance of the chirality of oligo(lactic acid) moiety for the oligoalanine conformation was also studied. The results obtained in this study should be useful in developing ester-containing oligopeptides that function better than normal peptides.

Self-assembly of near-unity helical Ce1−xMxO2 (x = 0.1, M = Ni and Bi) solid solutions with tunable optical activity

Ce1−xMxO2 solid solutions show tunable optical activity throughout the whole UV–visible range ascribed to electronic exciton coupling between left-handed helical structures.

The Composition of the Mobile Phase Affects the Dynamic Chiral Recognition of Drug Molecules by the Chiral Stationary Phase.

More than half of all pharmaceuticals are chiral compounds. Although the enantiomers of chiral compounds have the same chemical structure, they can exhibit marked differences in physiological activity; therefore, it is important to remove the undesirable enantiomer. Chromatographic separation of chiral enantiomers is one of the best available methods to get enantio-pure substances, but the optimization of the experimental conditions can be very time-consuming. One of the most widely used chiral stationary phases, amylose tris(3,5-dimethylphenyl carbamate) (ADMPC), has been extensively investigated using both experimental and computational methods; however, the dynamic nature of the interaction between enantiomers and ADMPC, as well as the solvent effects on the ADMPC-enantiomer interaction, are currently absent from models of the chiral recognition mechanism. Here we use QM/MM and molecular dynamics (MD) simulations to model the enantiomers of flavanone on ADMPC in either methanol or heptane/2-propanol (IPA) (90/10) to elucidate the chiral recognition mechanism from a new dynamic perspective. In atomistic MD simulations, the 12-mer model of ADMPC is found to hold the 4/3 left-handed helical structure in both methanol and heptane/IPA (90/10); however, the ADMPC polymer is found to have a more extended average structure in heptane/IPA (90/10) than in methanol. This results from the differences in the distribution of solvent molecules close to the backbone of ADMPC leads to changes in the distribution of the (φ, ψ) dihedral angles of the glycoside bond (between adjacent monomers) that define the structure of the polymer. Our simulations have shown that the lifetime of hydrogen bonds formed between ADMPC and flavanone enantiomers in the MD simulations are able to reproduce the elution order observed in experiments for both the methanol and the heptane/IPA solvent systems. Furthermore, the ratios of hydrogen-bonding-lifetime-related properties also capture the solvent effects, in that heptane/IPA (90/10) is found to make the separation between the two enantiomers of flavanone less effective than methanol, which agrees with the experimental separation factors of 0.9 versus 0.4 for R/S, respectively.

Counteranion Driven Homochiral Assembly of a Cationic C3-Symmetric Gelator through Ion-Pair Assisted Hydrogen Bond.

The helical handedness in achiral self-assemblies is mostly complex due to spontaneous symmetry breaking or kinetically controlled random assembly formation. Here an attempt has been made to address this issue through chiral anion exchange. A new class of cationic achiral C3-symmetric gelator devoid of any conventional gelation assisting functional units is found to form both right- and left-handed helical structures. A chiral counteranion exchange-assisted approach is successfully introduced to control the chirality sign and thereby to obtain preferred homochiral assemblies. Formation of anion-assisted chiral assembly was confirmed by circular dichroism (CD) spectroscopy, microscopic images, and crystal structure. The X-ray crystal structure reveals the construction of helical assemblies with opposite handedness for (+)- and (-)-chiral anion reformed gelators. The appropriate counteranion driven ion-pair-assisted hydrogen-bonding interactions are found responsible for the helical bias control in this C3-symmetric gelator.

Redox-Triggered Helicity Inversion in Chiral Cobalt Complexes in Combination with H(+) and NO3(-) Stimuli.

Three chiral ligands with variable denticity, H2L2-H2L4, conjugated by N,N'-ethylenebis[N-methyl-(S)-alanine] and an ortho-heterosubstituted aromatic amine, were newly synthesized as analogues of previously reported H2L1. Four contracted-Λoxo cobalt(III) complexes [Co(L)](+) with left-handed helical structure of Λ4Δ2 configuration were prepared by one-electron oxidation of the corresponding contracted-Λred cobalt(II) complexes [Co(L)], which were generated from chiral ligands and Co(ClO4)2·6H2O or Co(CF3SO3)2·5.2H2O in the presence of an organic base. Although the prepared cobalt(III) complexes were very inert and kinetically stable against protonation and NO3(-) complexation, cobalt(III) reduction in the presence of CF3SO3H and/or Bu4NNO3 allowed immediate changing of their three-dimensional structures from the contracted-Λoxo form to the extended-Λ [Co(H2L)Y2](n+) (Y = solvent and/or anion, n = 0-2) form with left-handed helicity or to the extended-Δ [Co(H2L)(NO3)](+) form with right-handed helicity via N- to O-amide coordination switching. Both extended forms were contracted to the original Λoxo form by oxidation of the cobalt(II) center in the presence of an organic base. Thus, redox reactions triggered dynamic helicity inversion of the chiral cobalt complexes, via multiple molecular motions consisting of relaxation/compression, extension/contraction, and helicity inversion motions in combination with deprotonation/protonation of amide linkages and NO3(-) anion complexation.

Structural Studies on Porphyrin-PNA Conjugates in Parallel PNA:PNA Duplexes: Effect of Stacking Interactions on Helicity.

Parallel PNA:PNA duplexes were synthesized and conjugated with meso-tris(pyridyl)phenylporphyrin carboxylic acid at the N-terminus. The introduction of one porphyrin unit was shown to affect slightly the stability of the PNA:PNA parallel duplex, whereas the presence of two porphyrin units at the same end resulted in a dramatic increase of the melting temperature, accompanied by hysteresis between melting and cooling curves. The circular dichroism (CD) profile of the Soret band and fluorescence quenching strongly support the occurrence of a face-to-face interaction between the two porphyrin units. Introduction of a L-lysine residue at the C-terminal of one strand of the parallel duplex induced a left-handed helical structure in the PNA:PNA duplex if the latter contains only one or no porphyrin moiety. The left-handed helicity was revealed by nucleobase CD profile at 240-280 nm and by the induced-CD observed in the presence of the DiSC2 (5) cyanine dye at ~500-550 nm. Surprisingly, the presence of two porphyrin units led to the disappearance of the nucleobase CD signal and the absence of CD exciton coupling within the Soret band region. In addition, a dramatic decrease of induced CD of DiSC2 (5) was observed. These results are in agreement with a model where the porphyrin-porphyrin interactions cause partial loss of chirality of the PNA:PNA parallel duplex, forcing it to adopt a ladder-like conformation.

Photoinduced polymer-stabilised chiral nematic liquid crystal films reflecting both right- and left-circularly polarised light

A phototunable polymer-stabilised liquid crystal film reflecting both right- and left-circularly polarised light has been successfully fabricated by a washout/refill method. The film was obtained by prefabricating the polymer network with a left-handed helical structure and then refilling a light-driven chiral nematic liquid crystal with a right-handed helical structure into the network. Interestingly, the reflection wavelength and the reflectivity properties can be precisely tuned by UV-light irradiation. A hyper-reflective notch, the reflectivity of which approaches 100%, was achieved in a layer when the pitch lengths of the two opposite helical structures are almost the same. Moreover, their original state can be properly returned by visible-light irradiation.

FIRST HIGH-RESOLUTION SPECTROSCOPIC OBSERVATIONS OF AN ERUPTING PROMINENCE WITHIN A CORONAL MASS EJECTION BY THEINTERFACE REGION IMAGING SPECTROGRAPH(IRIS)

Spectroscopic observations of prominence eruptions associated with coronal mass ejections (CMEs), although relatively rare, can provide valuable plasma and 3D geometry diagnostics. We report the first observations by the Interface Region Imaging Spectrograph (IRIS) mission of a spectacular fast CME/prominence eruption associated with an equivalent X1.6 flare on 2014 May 9. The maximum plane-of-sky and Doppler velocities of the eruption are 1200 and 460 km/s, respectively. There are two eruption components separated by ~200 km/s in Doppler velocity: a primary, bright component and a secondary, faint component, suggesting a hollow, rather than solid, cone-shaped distribution of material. The eruption involves a left-handed helical structure undergoing counter-clockwise (viewed top-down) unwinding motion. There is a temporal evolution from upward eruption to downward fallback with less-than-free-fall speeds and decreasing nonthermal line widths. We find a wide range of Mg II k/h line intensity ratios (less than ~2 expected for optically-thin thermal emission): the lowest ever-reported median value of 1.17 found in the fallback material and a comparably high value of 1.63 in nearby coronal rain and intermediate values of 1.53 and 1.41 in the two eruption components. The fallback material exhibits a strong ($> 5 \sigma$) linear correlation between the k/h ratio and the Doppler velocity as well as the line intensity. We demonstrate that Doppler dimming of scattered chromospheric emission by the erupted material can potentially explain such characteristics.

Metal–Organic Framework InH(d-C10H14O4)2 for Improved Enantioseparations on a Chiral Cyclodextrin Stationary Phase in GC

The chiral MOF InH(d-C10H14O4)2 has a left-handed helical structure and adopts a diamond network. In this work, three capillary columns (A, B, and C) containing InH(d-C10H14O4)2, peramylated β-cyclodextrin and sodium chloride, and InH(d-C10H14O4)2 and peramylated β-cyclodextrin have been prepared and their respective enantioseparation abilities have been investigated. The polarity of the MOF is moderate, whereas peramylated β-cyclodextrin provides a stationary phase of low polarity. The numbers of theoretical plates (plate m−1) of the three columns have been measured with n-dodecane at 120 °C, which followed an increasing order of A (2,973) < B (3,563) < C (3,665). 1-Phenylethanol, dihydrocarvyl acetate, citronellal, leucine, methyl l-β-hydroxyisobutyrate, limonene, and menthol were separated with different resolutions on columns A, B, and C. The relative standard deviations (RSDs) in the run-to-run and column-to-column retention times were 0.50 and 2.50 %, respectively. The test results indicated that the incorporated InH(d-C10H14O4)2 enhanced the separations of racemates on a peramylated β-cyclodextrin stationary phase, resulting in high column efficiency and good reproducibility in gas chromatography.

Photo-Thermal Modulation of Cholesteric Liquid Crystals with a Dual Circularly Polarized Light Reflection Band

In this study, we developed a cholesteric liquid crystal (Ch-LCs) composite with a dual (both right- and left-) circularly polarized light reflection band by utilizing a polymer template method, where a glassy Ch-LCs oligomer (GCLCO) with left-handed helical structure containing azobenzene dopant (AD) was infiltrated into the polymer template with right-handed helical structure. Photo-optical, thermal as well as glass-forming properties of the Ch-LCs film with a dual circularly polarized light reflection band were investigated, trans–cis (E–Z) photoisomerization of the AD in the GCLCO induced pitch length shortenings in response to the formation of the Z isomers by 365 nm ultraviolet (UV) irradiation, resulting that the reflection band of left-handed circularly polarized component of light in the Ch-LCs composite after UV irradiation exhibited a blue shift. What is more, the changed reflected color could be fixed in Ch glassy solid by rapid cooling from their Ch temperatures to below glass transition temperature (Tg), in which the photo and thermal isomerization of the AD could not influence the Ch pitch any longer and the color was stably stored. This technique has great applications such as tunable lasers, optical sensors, and security technology.

Evidence for a dispersion relation of optical modes in the cuticle of the scarab beetle Cotinis mutabilis

Variable angle Mueller matrix spectroscopic ellipsometry is used to study the properties of light reflected from the exoskeleton (cuticle) of the scarab beetle Cotinis mutabilis. For unpolarized incident light, the ellipticity and degree of polarization of the reflected light reveal a left-handed helical structure in the beetle cuticle. Analysis of the spectral position of the maxima and minima in the interference oscillations of the Mueller-matrix elements provides evidence for a dispersion relation similar to that of optical modes in chiral nematic liquid crystals calculated within a two-wave approximation. Additionally, a structural model for the cuticle of C. mutabilis is derived from the properties of the optical modes for non-attenuated propagation or selective reflection.

Enantioselective synthesis of a chiral coordination polymer with circularly polarized visible laser.

Circular dichroism is known to be the feature of a chiral agent which has inspired scientist to study the interesting phenomena of circularly polarized light (CPL) modulated molecular chirality. Although several organic molecules or assemblies have been found to be CPL-responsive, the influence of CPL on the assembly of chiral coordination compounds remains unknown. Herein, a chiral coordination polymer, which is constructed from achiral agents, was used to study the CPL-induced enantioselective synthesis. By irradiation with either left-handed or right-handed CPL during the reaction and crystallization, enantiomeric excesses of the crystalline product were obtained. Left-handed CPL resulted in crystals with a left-handed helical structure, and right-handed CPL led to crystals with a right-handed helical structure. It is exciting that the absolute asymmetric synthesis of a chiral coordination polymer could be enantioselective when using CPL, and provides a strategy for the control of the chirality of chiral coordination polymers.

In Depth Study on Solution-State Structure of Poly(lactic acid) by Vibrational Circular Dichroism

Polyesters are biodegradable analogues of polypeptides, but their biochemical applications have been hampered by the lack of a method to analyze polyester conformation in a solution state. We have demonstrated that vibrational circular dichroism (VCD) spectroscopy can conveniently and accurately elucidate the conformation of polyesters through the studies on poly(l-lactic acid) (PLLA), PLLA-amylose complex, and oligo(l-lactic acid). The analysis of VCD exciton couplet of these molecules has clarified the stable left-handed helical structure of PLLA, while density functional theory calculations of oligo(l-lactic acid) have revealed its detailed structural nature.

Helical DNA origami tubular structures with various sizes and arrangements.

We developed a novel method to design various helical tubular structures using the DNA origami method. The size-controlled tubular structures which have 192, 256, and 320 base pairs for one turn of the tube were designed and prepared. We observed the formation of the expected short tubes and unexpected long ones. Detailed analyses of the surface patterns of the tubes showed that the short tubes had mainly a left-handed helical structure. The long tubes mainly formed a right-handed helical structure and extended to the directions of the double helical axes as structural isomers of the short tubes. The folding pathways of the tubes were estimated by analyzing the proportions of short and long tubes obtained at different annealing conditions. Depending on the number of base pairs involved in one turn of the tube, the population of left-/right-handed and short/long tubes changed. The bending stress caused by the stiffness of the bundled double helices and the non-natural helical pitch determine the structural variety of the tubes.

Handedness preference and switching of peptide helices. Part I: Helices based on protein amino acids.

In this article, we review the relevant results obtained during almost 60 years of research on a specific aspect of stereochemistry, namely handedness preference and switches between right-handed and left-handed helical peptide structures generated by protein amino acids or appropriately designed, side-chain modified analogs. In particular, we present and discuss here experimental and theoretical data on three categories of those screw-sense issues: (i) right-handed/left-handed α-helix transitions underwent by peptides rich in Asp, specific Asp β-esters, and Asn; (ii) comparison of the preferred conformations adopted by helical host-guest peptide series, each characterized by an amino acid residue (e.g. Ile or its diastereomer aIle) endowed with two chiral centers in its chemical structure; and (iii) right-handed (type I)/left-handed (type II) poly-(Pro)n helix transitions monitored for peptides rich in Pro itself or its analogs with a pyrrolidine ring substitution, particularly at the biologically important position 4. The unique modular and chiral properties of peptides, combined with their relatively easy synthesis, the chance to shape them into the desired conformation, and the enormous chemical diversity of their coded and non-coded α-amino acid building blocks, offer a huge opportunity to structural chemists for applications to bioscience and nanoscience problems.

Solvent-induced two Cu(II) complexes with 4-acyl pyrazolone derivative: From discrete structure to 1D helical chain

Two new copper(II) complexes [Cu2L2(CH3OH)]·CH3OH (1) and [CuL]n (2) (H2L=N-(1-phenyl-3-methyl-4-benzal-pyrazolone-5)-salicylidene hydrazide) with different structures have been synthesized by the reactions of copper acetate with the 4-acyl pyrazolone derivative H2L in MeOH or EtOH solvent, respectively. The X-ray diffraction analyses revealed that 1 displays a dinuclear structure which is further linked by weak coordination interactions and hydrogen bonds to generate an infinite 1D chain. Complex 2 exhibits 1D left-handed and right-handed helical chains structure in a 1:1 ratio along the c axis, and the 1D chains with the same handedness were linked by hydrogen bonds to form a racemic two-fold interpenetrated 3D framework. The results demonstrated that the solvents with different coordination abilities have significant effect on the structure of the complexes. On the other hand, the ligands H2L adopt tridentate chelating mode and tetradentate chelating-bridging mode to coordinate with Cu(II) ions in 1 and 2, which attested that the flexible 4-acyl pyrazolone Schiff base derivative can adopt different coordination modes to form complexes with varied structures. The variable temperature magnetic investigation indicates that 2 exhibits typical antiferromagnetic behavior.

Complementary Induction of Right- and Left-Handed Helical Structures by the Positioning of Chiral Groups on the Monomer Units: Introduction of (-)-Menthol as Side Chains of Poly(quinoxaline-2,3-diyl)s.

Poly(quinoxaline-2,3-diyl) bearing menthyloxymethyl side chains derived from (-)-menthol at the 6- and 7-positions of the quinoxaline ring showed a single, right-handed helical structure in chloroform. Upon introduction of the same (-)-menthol-derived side chains into the 5- and 8-positions, a single, left-handed helical structure was formed in chloroform. The former poly(quinoxaline-2,3-diyl)s showed solvent-dependent inversion of the helical sense in 1,1,2-trichloroethane to form a left-handed helical structure with high screw sense purity. Copolymers bearing both menthyloxymethyl and o-(diphenylphosphino)phenyl groups in their side chains served as highly enantioselective chiral ligands in the palladium-catalyzed hydrosilylation of styrene.