Structure In Chloroform Research Articles

DBU-catalyzed synthesis of unsymmetrical cross-conjugated 2-arylidene-5-((dimethylamino)methylene)cyclopentanones

A simple and efficient method for the synthesis of a new type of unsymmetrical cross-conjugated system based on 2-arylidene-5-((dimethylamino)methylene)cyclopentanone by reaction of 2-arylidenecyclopentanones with dimethylformamide dimethyl acetal catalyzed by DBU was discovered. The preparation of target compounds on a gram-scale is considered. The fluorescent properties of the synthesized systems are considered depending on the structure ofchloroform.

Unveiling the Molecular Structure of Antimalarial Drugs Chloroquine and Hydroxychloroquine in Solution through Analysis of 1H NMR Chemical Shifts

Chloroquine (CQ) and hydroxychloroquine (HCQ) have been standard antimalarial drugs since the early 1950s, and very recently, the possibility of their use for the treatment of COVID-19 patients has been considered. To understand the drug mode of action at the submicroscopic level (atoms and molecules), molecular modeling studies with the aid of computational chemistry methods have been of great help. A fundamental step in such theoretical investigations is the knowledge of the predominant drug molecular structure in solution, which is the real environment for the interaction with biological targets. Our strategy to access this valuable information is to perform density functional theory (DFT) calculations of 1H NMR chemical shifts for several plausible molecular conformers and then find the best match with experimental NMR profile in solution (since it is extremely sensitive to conformational changes). Through this procedure, after optimizing 30 trial distinct molecular structures (ωB97x-D/6-31G(d,p)-PCM level of calculation), which may be considered representative conformations, we concluded that the global minimum (named M24), stabilized by an intramolecular N-H hydrogen bond, is not likely to be observed in water, chloroform, and dimethyl sulfoxide (DMSO) solution. Among fully optimized conformations (named M1 to M30, and MD1 and MD2), we found M12 (having no intramolecular H-bond) as the most probable structure of CQ and HCQ in water solution, which is a good approximate starting geometry in drug-receptor interaction simulations. On the other hand, the preferred CQ and HCQ structure in chloroform (and CQ in DMSO-d6) solution was assigned as M8, showing the solvent effects on conformational preferences. We believe that the analysis of 1H NMR data in solution can establish the connection between the macro level (experimental) and the sub-micro level (theoretical), which is not so apparent to us and appears to be more appropriate than the thermodynamic stability criterion in conformational analysis studies.

Cover Feature: Conformational Preferences of Cyclopentane‐Based Oligo‐δ‐peptides in the Gas Phase and in Solution (ChemPlusChem 4/2021)

The Cover Feature shows the conformational preferences of oligomers of δ-amino acid (δAc5a) with a cyclopentyl constraint in the Cβ−Cγ bond of the backbone investigated by using DFT methods in the gas phase and in solution. In particular, the hexameric Ac-(δAc5a)6-NHMe preferentially adopted the mixed H16/14 helical structure in chloroform and the H14 helical structure in water. Pyrrolidine-substituted analogues also adopted helical structures. More information can be found in the Full Paper by H. S. Park and Y. K. Kang.

Structural Polymorphism of Resorcinarene Assemblies

In 1997, a study based on X-ray crystallography revealed that resorcinarenes adopt a hexameric capsule-like structure. The function of resorcinarenes has been discussed on the basis of this structure; however, our recent study showed that the hexamer may be only one of resorcinarenes' polymorphic members. Here, we present the solvent dependence of the aggregation number of C-undecylresorcinarene in water-saturated toluene and chloroform using small-angle neutron and X-ray scattering and analytical ultracentrifugation measurements. We found that a new octamer was formed in toluene where the eight resorcinarene units were placed at the vertices of a regular cube; this contrasts to the previous structure in chloroform, namely, a hexamer with the six resorcinarenes located at the vertices of a regular octahedron that has a cavity inside where chloroform molecules are pooled.

Effect of the α-substituted chiral side chain on the helical conformation of N-substituted poly(p-benzamide)

The effect of the side chain chiral center position on the secondary structure of oligomers and polymers of N-substituted 4-aminobenzoic acid was studied. Monomer 1 was prepared from l-alanine methyl ester hydrochloride in seven steps. The poly(p-benzamide) having an α-substituted side chain at the nitrogen atom (α-Me-PA) was obtained from the polymerization of 1 with triethylsilane, CsF, and 18-crown-6 in THF. The circular dichroism (CD) studies in solution demonstrated that α-Me-PA adopted a right-handed helical conformation in protic polar solvents, such as water and methanol, and a random structure in chloroform, indicating that solvophobic interactions played an important role in the helical folding of α-Me-PA. The tetramer of (S)-4-(sec-butylamino)benzoic acid was synthesized as a model compound of α-Me-PA. The single crystal X-ray analysis of the tetramer revealed that the right- and left-handed helical molecules existed in a one-to-one ratio in the crystal, and that the screw pitch of the right-handed helix was shorter than the left-handed helix.

Observation of Intermolecular Hydrogen Bonding Interactions in Biosynthesized and Biodegradable Poly [(R)-3-hydroxybutyrate- co-(R)-3-hydroxyhexanoate] in Chloroform and 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP).

In this work, we describe polymer-solvent interactions in biosynthesized and biodegradable poly[(R)-3-hydroxybutyrate- co-(R)-3-hydroxyhexanoate] (PHBHx) and the atactic homopolymer, poly(3-hydroxybutyrate) (a-PHB), which were studied both as neat polymers and in solutions of chloroform and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). Specifically, infrared frequency shifts of the carbonyl band were observed in semi-crystalline PHBHx, but not in a-PHB, because it cannot form the helical conformation required for crystallization. The carbonyl band of PHBHx exhibited the high frequency associated with amorphous structure in chloroform and the lower frequency traditionally attributed to the helical crystalline structure in HFIP. The same results were obtained for a-PHB, demonstrating that the helical structure is not required for a lower frequency carbonyl-stretching mode. It is proposed that the band shift is due to hydrogen bonding between the carbonyl and hydroxyl hydrogen in HFIP. Therefore, the carbonyl frequency observed upon crystallization is most likely due to hydrogen bonding between the carbonyl and methyl hydrogen of the neighboring polymer chain in the crystal lattice as previously suggested.

Self-assembled organic nanostructures and nonlinear optical properties of heteroleptic corrole–phthalocyanine europium triple-decker complexes

Two heteroleptic corrole–phthalocyanine europium triple-decker complexes were fabricated into organic nanostructures by the standard phase-transfer method. The investigated compounds are represented by Eu2(Pc)2[Cor(ClPh)3] (1) and Eu2[Pc(OC8H17)8]2[Cor(ClPh)3] (2), where Pc represents the dianion of phthalocyanine and Cor(ClPh)3 the trianion of 5,10,15-tri(4-chlorophenyl)corrole. Both compounds 1 and 2 show typical electronic absorption spectra for a non-aggregated molecular structure in chloroform or toluene. However, in methanol compound 1 self-assembled into belt-like nanostructures while compound 2, which possesses long OC8H17 alkoxy side chains, self-assembled into large scale sheet-like nanostructures. The third-order nonlinear optical properties of both triple-decker compounds were also investigated in toluene by the Z-scan technique and characterized as showing nonlinear reverse saturation absorption and self-defocusing behavior. A third-order nonlinear optical susceptibility, χ(3), of 3.18 × 10−10 and 3.35 × 10−10 esu was obtained for 1 and 2, respectively, thus indicating the potential application of these compounds in the field of optical devices.

Poly(p‐benzamide) having isopropyl‐substituted chiral tri(ethylene glycol) side Chain: Synthesis and helical conformation

ABSTRACTIsopropyl‐substituted tri(ethylene glycol) is used as a chiral side chain of N‐substituted poly(p‐benzamide) in order to increase the difference of stability between the right‐ and left‐handed helical structures of the polymer. The target polymer is synthesized by the chain‐growth condensation polymerization of the corresponding monomer with an initiator using lithium 1,1,1,3,3,3‐hexamethyldisilazide as a base. A circular dichroism (CD) study of the polymer reveals that the CD signal is due to an excess of a thermodynamically controlled right‐handed helical structure of the polymer, and that the replacement of the methyl group with a bulkier isopropyl group at the side chain of poly(p‐benzamide) increases the abundance of right‐handed helical structure in chloroform. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1623–1628

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.

Helical folding of poly(naphthalenecarboxamide) in apolar solvent

Helical folding of poly(naphthalenecarboxamide)s with aliphatic side chains in hydrophobic solvents is investigated. The CD spectra of the polyamide showed a predominant left-handed helical structure in chloroform, THF, and cyclohexane. Furthermore, the sergeants and soldiers experiment in cyclohexane showed a clear chiral amplification. These results indicate that the helical structure was stabilized by an intramolecualr self-association based on the solvophobic effect, and that there is cooperativity between the monomer units constituting the helical structure.

Testing Computational Models of Hyperpolarizability in a Merocyanine Dye Using Spectroscopic and DFT Methods

The structural and electronic properties of a highly solvatochromic merocyanine dye, 2-(3-cyano-5,5-dimethyl-4-(3-(1-octadecylpyridin-4(1H)-ylidene)prop-1-enyl)furan-2(5H)-ylidene)malononitrile (pyr3pi), have been investigated using UV-vis, NMR, hyper-Rayleigh scattering, and Raman spectroscopies and further interpreted using computational chemistry. Spectroscopic data indicate that pyr3pi exists in its zwitterionic form even in low polarity solvents with electronic absorption spectra showing a hypsochromic shift with an increase in solvent polarity and NMR experiments indicating an increasingly zwitterionic structure in chloroform as the temperature is lowered. Raman spectra in increasingly polar solvents show small variations of the structure that are consistent with a change toward a structure with more zwitterionic character. However, comparison of the calculated and experimental vibrational energies and intensities and comparison of NMR coupling constants with calculated bond order indicate that calculations underestimate the amount of charge separation seen in low polarity solvents. Although for this system density functional theory (DFT) calculations and the two-state model qualitatively reproduce negative solvatochromism, they fail to reproduce the trends in hyperpolarizability seen experimentally. This is attributed to solvent field DFT calculations underestimating the degree of charge separation in reaction fields representing low polarity solvents.

Novel linear fluoro-silicon-containing pentablock copolymers: synthesis and their properties as coating materials

A series of linear fluorosilicone pentablock copolymers consisting of poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA) and poly(dodecafluoroheptyl methacrylate) (PDFHM), named as PDMS-b-(PMMA-b-PDFHM)2, have been synthesized by ATRP and their thermal properties, self-assembly behavior in different solutions and surface features of films have been systematically investigated. TGA measurements reflect that the thermal stability of PDMS-b-(PMMA-b-PDFHM)2 is enhanced by the middle-block PDMS. TEM observation and DLS analysis reveal that PDMS-b-(PMMA-b-PDFHM)2 is able to self-assemble into unimers in both chloroform and dioxane solutions, and spherical micelles with a core–corona structure in chloroform, oblate spheroidal micelles with a multilayer core–corona structure in dioxane. The diameters of micelles in the dioxane solution are larger, while the concentrations of unimers in the chloroform solution are higher. SCA, QCM-D and XPS measurements have confirmed that the unimers play a dominant role in governing the surface properties of PDMS-b-(PMMA-b-PDFHM)2 films. In the case of PDMS-b-(PMMA-b-PDFHM)2 with a PMMA/PDMS weight ratio of 10 : 1 and 20%wt of DFHM content, the film cast from chloroform solution has a lower surface free energy of 16.8 mN m−1, lower adsorbed amounts of 8.6 × 104 ng cm−2 for water and 6.6 × 104 ng cm−2 for hexadecane, and higher surface stability. Such excellent thermal and surface properties demonstrate that this novel pentablock copolymer PDMS-b-(PMMA-b-PDFHM)2 is a promising candidate as a coating material.

Influence of Solvent on the Dispersion of Single-Walled Carbon Nanotubes in Polymer Matrix and the Photovoltaic Performance

Solvent effects on the bulk heterojunction of poly(3-hexylthiophene) (P3HT) and single-walled carbon nanotubes (SWNTs) have been studied. Not only the morphology of P3HT but also the SWNT dispersion in P3HT matrix show strong dependence on the solvents. Atomic force microscopy images suggest that P3HT forms poor crystal structure in chloroform but better in solvents that have relatively high boiling points such as chlorobenzene, toluene, and o-xylene. However, the results of quench rate of photoluminescence and the exciton lifetime decay rate in SWNT/P3HT indicate that a good SWNT dispersion can only be obtained in chloroform and chlorobenzene cases. This suggests that more effective interfaces can be formed when these two solvents are used and thus leads to enhanced charge separation rate, which eventually will benefit the photovoltaic performance. Our photovoltaic demonstration further confirms the idea and suggests that using chlorobenzene for preparation of SWNT/P3HT photovoltaic devices will give more promising results.

Unambiguous Assignment of Vibrational Spectra of Cyclosporins A and H

Vibrational infrared and circular dichroism spectra of two cyclosporins A and H are predicted by density functional theory calculations using the nuclear magnetic resonance proposed structure in chloroform. Spectral signatures in the important amide II, I, and A regions are identified for typical peptide secondary structures including type II' beta-turn, antiparallel beta-sheet, inverse gamma-turn, N-methylated peptide bond, and side-chain H-bond. Our theoretical spectra agree very well with available experimental data in nonpolar media and unambiguously clarify their controversial vibrational assignment. The new insights into the spectral signatures of secondary structures can be very useful for peptide conformation analysis in general.

Marked Effect of Aromatic Solvent on Unfolding Rate of Helical Ethynylhelicene Oligomer

Optically active acyclic ethynylhelicene oligomers were synthesized in high yields by a two-directional method involving Sonogashira coupling and deprotection. Their CD spectra in chloroform exhibited large differences between the oligomers with less than seven helicenes and their higher homologues, which indicated the formation of helical structures for the latter and random coil structures for the former. The helical heptamer gradually unfolded to a random coil structure in chloroform at room temperature. The unfolding rate was examined by CD in several aromatic solvents as well, and the rate constant k was found to be highly dependent on the type of aromatic substituent: k differed by seven orders of magnitude between iodobenzene and trifluoromethylbenzene. Several features of the rates are notable: The reaction rates in halobenzenes were in the order of iodobenzene > bromobenzene > chlorobenzene > benzene > fluorobenzene > m-difluorobenzene, those in alkylbenzenes were styrene > phenylacetylene > ethylbenzene > toluene > benzene, and those in heteroatom-substituted arenes were thioanisole > benzonitrile > anisole > ethyl benzoate > benzene > trifluoromethylbenzene. The log k values exhibited good correlation with the absolute hardness, eta, of the arenes, and higher unfolding rates were observed in the soft arenes. Vapor pressure osmometry studies indicated that the helical structure of the heptamer is dimeric in benzene, fluorobenzene, and trifluoromethylbenzene, while the random coil structure of the heptamer is monomeric in chloroform and toluene. When a chloroform solution of the random coil structure was concentrated to a small volume, the helical structure could be regenerated.

Field effect transistors based on poly(3-hexylthiophene) at different length scales

In this paper we report on thin film transistors based on drop casting solutions ofregioregular poly(3-hexylthiophene) (P3HT) over prefabricated gold electrodes. Thispolymer is known to self-organize into a lamellar structure in chloroform resulting in highfield-effect mobilities. We studied the dependency of the charge carrier mobility ofdevices prepared from solution in chloroform with electrode spacings ranging from5 µm to 20 nm. It was found that the overall trend was that the mobility decreased as theelectrode spacing was made smaller, indicating that the transport properties on closelyspaced electrodes were dominated by the contacts. Applying an ac voltage duringthe preparation of such films resulted in lower mobilities. However, P3HT inp-xylene forms fibres, which were aligned between the electrodes byapplying an ac field. Films of aligned fibres with mobilities as high as0.04 cm2 V−1 s−1 were prepared.

Molecular dynamics simulations of peptides containing an unnatural amino acid: dimerization, folding, and protein binding.

We have performed molecular dynamics (MD) simulations to study the dimerization, folding, and binding to a protein of peptides containing an unnatural amino acid. NMR studies have shown that the substitution of one residue in a tripeptide beta-strand by the unnatural amino acid Hao (5-HO2CCONH-2-MeO-C6H3-CO-NHNH2) modifies the conformational flexibility of the beta-strand and the hydrogen-bonding properties of its two edges: The number of hydrogen-bond donors and acceptors increases at one edge, whereas at the other, they are sterically hindered. In simulations in chloroform, the Hao-containing peptide 9 (i-PrCO-Phe-Hao-Val-NHBu) forms a beta-sheet-like hydrogen-bonded dimer, in good agreement with the available experimental data. Addition of methanol to the solution induces instability of this beta-sheet, as confirmed by the experiments. MD simulations also reproduce the folding of the synthetic peptide 1a (i-PrCO-Hao-Ut-Phe-Ile-Leu-NHMe) into a beta-hairpin-like structure in chloroform. Finally, the Hao-containing peptide, Ac-Ala-Hao-Ala-NHMe, is shown to form a stable complex with the Ras analogue, Rap1 A, in water at room temperature. Together with the available experimental data, these simulation studies indicate that Hao-containing peptides may serve as inhibitors of beta-sheet interactions between proteins.

Structure of azo dye organotin(IV) compounds containing a C,N‐chelating ligand

AbstractTwo complexes derived from simple azo dyes (methyl orange and para‐methyl red) and the [(2‐dimethylaminomethyl)phenyl](diphenyl)tin(IV) moiety have been prepared and their NMR, MS, IR, Raman and UV–VIS spectra were measured and X‐ray structures determined. Both compounds reveal the same structure in chloroform and in the solid state. The central tin atoms exist in a slightly distorted trans‐trigonal bipyramidal geometry. Copyright © 2003 John Wiley & Sons, Ltd.

Physical Chemistry of the Lowest Excited Singlet State of trans-Stilbene in Solution as Studied by Time-Resolved Raman Spectroscopy

Abstract Structure and dynamics of the lowest excited singlet state of trans-stilbene (the S1 state of tSB) in solution are discussed with an emphasis placed on the elucidation of the mechanism of the trans–cis photoisomerization. Structure of S1 tSB in solution is first discussed based on the time-resolved Raman spectral data and their isotope substitution effects. Original data for an asymmetrically deuteriated tSB, tSB-d5, are presented to confirm the ethylene-like structure of the central C–C linkage of S1 tSB. Next, the time-, temperature-, and solvent-dependent band shape changes of the olefinic C=C stretch band are discussed in terms of the solvent induced dynamic polarization. It is shown that the dynamic polarization model accounts very well, not only for the observed band shape changes, but also for their relevance to the isomerization mechanism. A new microscopic view on the photoisomerization of tSB is thus presented. Picosecond energy dissipation process of S1 tSB is then discussed in relation to the microscopic solvation structure in chloroform. Finally, the mechanism of a new bimolecular reaction between S1 tSB and carbon tetrachloride is discussed on the basis of the diffusion-controlled reaction model.

Quantitative analysis of the kinetic constant of the reaction of N,N'-propylenedinicotinamide with the hydroxyl radical using dimethyl sulfoxide and deduction of its structure in chloroform.

N,N'-Propylenedinicotinamide (Nicaraven) is presently being developed for the treatment of cerebral stroke including subarachnoid hemorrhage. This drug is promising because some data suggest it to have an ability to scavenge the hydroxyl radical under physiological conditions in vivo, while it also has a high permeability through the blood brain barrier. Using the kinetic constant of the reaction between the hydroxyl radical and dimethyl sulfoxide, the formula derived by Babbs and Griffin (Free Rad. Biol. Med., 6 1989) was applied to obtain the kinetic constant of Nicaraven with the hydroxyl radical using a dimethyl sulfoxide-xanthine oxidase-hypoxanthine-Fe system, and this yielded the kinetic constant 3.4x10(9) M(-1) s(-1) (1 M=1 mol dm(-3)) for Nicaraven. Structurally related compounds were also investigated. The amide group of Nicaraven was thus found to play an important part in the reaction with the hydroxyl radical. Methanesulfinic acid, which was obtained from the reaction between dimethyl sulfoxide and the hydroxyl radical, was found to be stable under this adopted experimental condition and therefore was used to quantify the kinetic constant of Nicaraven. The structure of Nicaraven has also been investigated in CDCl3 using IR spectra, computer calculations and 1H-NMR analysis, and Nicaraven was thus shown to have an intramolecular hydrogen bond which forms a 7-membered ring that resembles a part of the 1H-1,4-benzodiazepines. This structure may play an important role in the penetration through the blood brain barrier.