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Lactic and malic acids are key substances in a number of biochemical processes in living cells and are also utilized in industry. Vibrational spectroscopy represents an efficient and sensitive way to study their structure and interactions. Since water is the natural environment, proper understanding of their molecular dynamics in aqueous solutions is of critical importance. To this end, we employed Raman spectroscopy and Raman optical activity (ROA) to study the conformation of l-lactic and l-malic acids in water (while varying pH, temperature, and concentration), with special emphasis on their double hydrogen bonding dimerization propensity. Raman and ROA experimental data were supported by extensive theoretical calculations of the vibrational properties and by additional experiments (IR absorption, vibrational circular dichroism, and NMR). Conformational behavior of the acids in water was described by molecular dynamics simulations. Reliability of the results was verified by calculating the vibrational properties of populated conformers and by comparing thus obtained spectral features with the experimental data. Calculations estimated the incidence of H-bonded dimers in water to be low in lactic acid and comparable to monomers in malic acid. The "hybrid" approach presented here reveals limitations of relying on the experimental spectra alone to study dimer formation.

Hexamethoxycalix[6]arene 3 forms a directional pseudorotaxane complex with the chiral axle (S)-(α-methyl-benzyl)benzylammonium 2+. Between the two (endo-chiral)-2+@3 and (exo-chiral)-2+@3 pseudorotaxane stereoisomers, the former is preferentially formed. This result confirms the validity of the “endo-α-methyl-benzyl rule”, previously reported by us. DFT calculations suggest that C-H … π interactions between the methyl group of 2+ and the calixarene aromatic rings, determine the stereoselectivity of the threading process toward the “endo-α-methyl-benzyl preference”. An amplification of optical rotation is observed upon formation of the pseudorotaxane complex (endo-chiral)-2+@3 with respect to free axle 2+. Thus, the specifical rotation of the 1:1 mixture of chiral 2+·B(ArF)4− salt and achiral 3 was augmented upon formation of the pseudorotaxane and DFT calculations were used to rationalize this result.

A family of inherently chiral electroactive selectors based on the 2,2’‐biindole atropisomeric scaffold, of easy synthesis and modulable functional properties, is studied in cascade in two enantioselection contexts. They are at first investigated as probes in enantioselective HPLC, studying molecular structure and temperature effects, and achieving very efficient semipreparative enantioseparation. The enantiomers thus obtained, of remarkable chiroptical features (optical rotation as well as circular dichroism), are successfully applied as selectors in chiral voltammetry in different media for discrimination of the enantiomers of chiral electroactive probes, either by conversion into enantiopure electroactive electrode surfaces by electrooligomerization on glassy carbon substrate (the two monomers with shorter alkyl chains), or as chiral additive in achiral ionic liquid (the monomer with longest alkyl chains). Discrimination is conveniently and reproducibly achieved in terms of significant potential differences for the two enantiomers, specularly inverting either probe or selector configuration. In one case successful discrimination is also observed with the two probe enantiomers concurrently present, either as racemate or with enantiomeric excesses, neatly accounted for by the peak current ratios., A series of inherently chiral electroactive selectors based on the 2,2’‐biindole atropisomeric scaffold is studied in two enantiodiscrimination contests: as probes in enantioselective HPLC and as selectors in chiral voltammetry for successful discrimination of the enantiomers of chiral electroactive probes, either by conversion into enantiopure electroactive electrode surfaces or as chiral additive in achiral ionic liquid.

Four new α-pyrone derivatives, named germicidins P-S (1-4) along with nine known analogues (5-13) were discovered from the sponge-associated Streptomyces sp. 18A01 guided by Global Natural Products Social (GNPS) molecular networking, the LC-DAD-MS profile, and hexokinase II (HK2) inhibitory activity. The structures of 1-13 were elucidated by analysis of their HRMS, optical rotation, and NMR spectroscopic data. The absolute configurations of germicidin P (1) and germicidin Q (2) were determined on the basis of comparisons of experimental and theoretically calculated ECD spectra. Bioactivities of the isolated compounds were assayed against human HK2. The bioassay results showed that compounds 1-4 and 11-13 exhibited significant inhibitory activities against HK2, with IC50 values ranging from 5.1 to 11.0 μM. A molecular docking simulation demonstrated that these germicidins were docked in the inner active site tunnel of HK2. Interestingly, the amino residue Arg91 has a better binding affinity and efficacy than the amino residue Asn89 in the process of HK2 binding to the ligands, resulting in better hexokinase inhibitory activity. This result provided a valuable perspective for better understanding their HK2 inhibition activity.

Since the discovery of left-handed G-quadruplex (L-G4) structure formed by natural DNA, there has been a growing interest in its potential functions. This study utilised it to catalyse enantioselective Diels-Alder reactions, considering its different optical rotation compared to an ordinary G4. It was determined that when L-G4 was used with a combination of copper(II) ions, there was a good enantioselectivity (−52% ee) without further addition of ligands. When further consideration was given by adding G4 ligands, G4 was further stabilised, even obtaining a better enantioselectivity (up to −80% ee). Moreover, when using ligands that have regulatory effects on G4, the ee value can be adjusted. In this work, a minimal left-handed G4 was reported. A follow-up study was also conducted, which recovers that the minimal left-handed G4 remains its catalytic effect and enantioselectivity, but is not so effective as the former case. This indicates that a complete G4 structure is relatively conducive to chiral catalysis.

A mathematical model for determining the sucrose concentration in honey, based on the optical rotation of the plane of polarization in solutions, is described. The dependencies of the dispersion of the specific rotation in the main polysaccharides (sucrose, glucose and fructose) included in honey are obtained. A working hypothesis is put forward and experimentally tested to determine the angle of rotation of the plane of polarization of light passed through a cuvette with honey as an algebraic sum of the rotation angles for light that passed through individual components of honey. A prototype of a device for express analysis of honey has been developed and manufactured to determine the excess of sucrose concentration over its value in natural honey.

Raman optical activity (ROA) spectral features reliably indicate the structure of peptides and proteins, but the signal is often weak. However, we observed significantly enhanced low-frequency bands for α-helical poly-L-alanine (PLA) in solution. The biggest ROA signal at ∼100 cm−1 is about 10 times stronger than higher-frequency bands described previously, which facilitates the detection. The low-frequency bands of PLA were compared to those of α-helical proteins. For PLA, density functional simulations well reproduced the experimental spectra and revealed that about 12 alanine residues within two turns of the α-helix generate the strong ROA band. Averaging based on molecular dynamics (MD) provided an even more realistic spectrum compared to the static model. The low-frequency bands could be largely related to a collective motion of the α-helical backbone, partially modulated by the solvent. Helical and intermolecular vibrational coordinates have been introduced and the helical unwinding modes were assigned to the strongest ROA signal at 101–128 cm−1. Further analysis indicated that the helically arranged amide and methyl groups are important for the strong chiral signal of PLA, while the local chiral centers CαH contribute in a minor way only. The strong low-frequency ROA can thus provide precious information about the motions of the peptide backbone and facilitate future protein studies.

The first convergent total synthesis for the proposed structures of microcyclamides MZ602 (1) and MZ568 (2) has been accomplished in 11 linear steps with 12.5 and 16.8% overall yield, respectively. Key features of the syntheses include a one-pot cascade reaction to construct core Boc-l-Ile-Thz-OAllyl fragment 5, and a removable pseudoproline (ΨMe,Me pro) inducer assisted cyclization of thiazole-containing all-l linear peptides. The spectral data (1H NMR, 13C NMR, and HRMS) of synthetic MZ602 (1) were quite similar to those of the proposed natural microcyclamide MZ602, except to an opposite sign of the optical rotation value. Surprisingly, the synthetic MZ568 (2) presented large discrepancies in characteristic spectral data from those of the reported natural product, although the absolute configuration of key intermediate 36 was unambiguously determined by single-crystal X-ray analysis in our work. These findings revealed that the proposed structures of natural microcyclamides MZ602 and MZ568 required revision.

In this work, we present two compact basis sets optimized for the calculation of specific rotation: augD-3-21G and augT3-3-21G. They are obtained by combining the standard 3-21G basis set with the diffuse functions of aug-cc-pVDZ and aug-cc-pVTZ, respectively, followed by a reoptimization of the exponents of the diffuse functions. The exponent optimization is based on minimization of the root-mean-square relative error (RMSE) of the specific rotation computed at 589.3 nm (the sodium D line, [α]

Hemslecin C, a compound with a novel skeleton, is synthesized by refluxing hemslecin A with KOH in alcohol. Hemslecin C was structurally characterized by specific optical rotation measurement, high-resolution mass spectroscopy, and nuclear magnetic resonance spectroscopic analysis. In addition, the molecular structure of hemslecin C was unambiguously determined by X-ray single-crystal determination. We found that its structure was different from that reported in the literature. The acetyl group of hemslecin A is transferred to the carbonyl α carbon of the side chain and is attacked by the 22-hydroxyl group to give a hemi-acetal that is dehydrated to give hemslecin C. The anticancer activity of this new skeleton is determined by sulforhodamine B assay method, and demonstrates excellent activity, thus providing a new framework for the development of anticancer drugs.

The stereoselective transformation of chiral UV-transparent amines and alcohols to phthalimides has proved to be a simple and efficient method to enhance the chiroptical response of these substrates allowing their reliable absolute configuration determination by computational analysis of ECD spectra. Such a transformation also leads to a significant reduction in the molecular conformational flexibility thus simplifying the conformational analysis required by the computational treatment. The method described herein thus allows the absolute configuration assignment to these challenging substrates to be much easier and reliable.

Synthesis of tetra-armed cyclens (2a-2e), with substituted styrylmethyl groups as side-arms, and their Ag+ complexes is reported. The Ag+ complex with a tetra styrylmethyl-armed cyclen (2a) incorporates alkyl nitriles in a pseudo-cavity formed by the four styrylmethyl side-arms. This prompted us to apply this system to the determination of the absolute configurations of chiral nitriles with low [α]D and low circular dichroism (CD) intensity. In the CD spectra of the 2a/Ag+ complex, (S)- and (R)-G1 did not show a specific Cotton effect, while when chiral nitriles were added to the 2a/Ag+ complex, drastic spectral changes were observed. The (S)-G1@2a/Ag+ system exhibited first a negative and then a positive Cotton effect, whereas the (R)-G1@2a/Ag+ system showed the mirror image of the Cotton effect of (S)-G1@2a/Ag+. We have, therefore, demonstrated a new technique for determining the absolute configurations of weak optical rotation molecules using the Ag+ complex with 2a.

Sugars are crucial components in biosystems and industrial applications. In aqueous environments, the natural state of short saccharides or charged glycosaminoglycans is floating and wiggling in solution. Therefore, tools to characterize their structure in a native aqueous environment are crucial but not always available. Here, we show that a combination of Raman/ROA and, on occasions, NMR experiments with Molecular Dynamics (MD) and Quantum Mechanics (QM) is a viable method to gain insights into structural features of sugars in solutions. Combining these methods provides information about accessible ring puckering conformers and their proportions. It also provides information about the conformation of the linkage between the sugar monomers, i.e., glycosidic bonds, allowing for identifying significantly accessible conformers and their relative abundance. For mixtures of sugar moieties, this method enables the deconvolution of the Raman/ROA spectra to find the actual amounts of its molecular constituents, serving as an effective analytical technique. For example, it allows calculating anomeric ratios for reducing sugars and analyzing more complex sugar mixtures to elucidate their real content. Altogether, we show that combining Raman/ROA spectroscopies with simulations is a versatile method applicable to saccharides. It allows for accessing many features with precision comparable to other methods routinely used for this task, making it a viable alternative. Furthermore, we prove that the proposed technique can scale up by studying the complicated raffinose trisaccharide, and therefore, we expect its wide adoption to characterize sugar structural features in solution., Author summary Saccharides are an essential part of many biosystems. Not only their identification but also their structural characterization is crucial to understanding their role. For example, animal cells possess a surrounding aqueous layer rich in sugars. Although its sugar content is known, the structures formed by these sugars in such a flexible and mobile environment are lesser understood. A trustworthy characterization of their atomistic structure will foster our knowledge and contribute to drug development. This characterization is also crucial in developing accurate computer models needed to study such environments. Unfortunately, many available structure characterization techniques are inadequate when applied to flexible molecules such as saccharides. Therefore, new methods are welcomed. We use molecular dynamics simulations and quantum chemical calculations to extract structural data of sugars in solution when compared against experimental Raman/ROA/NMR spectra. This combination of techniques allows interpreting aforementioned spectra to extract structural features of saccharides. We get, for example, the molecular structure of sugar rings (puckering confirmation) or the preferred orientation of bonds connecting two sugar units (glycosidic bonds). We can determine the presence of different sugar moieties in solutions and their proportions. Overall, this technique should contribute to the understanding of sugars in their native aqueous environment.

The absolute configuration of chiral 2-aryl and 2-aryloxy propionic acids, which are among the most common chiral environmental pollutants, has been readily and reliably established by either electronic circular dichroism spectroscopy or optical rotation measurements employing suitably designed 4,4′-disubstituted biphenyl probes. In fact, the 4,4′-biphenyl substitution gives rise to a red shift of the diagnostic electronic circular dichroism signal of the biphenyl A band employed for the configuration assignment, removing its overlap with other interfering dichroic bands and allowing its clear sign identification. The largest A band red shift, and thus the most reliable results, are obtained by employing as a probe the 4,4′-dinitro substituted biphenylazepine 3c. The method was applied to the absolute configuration assignment of 2-arylpropionic acids ibuprofen (1a), naproxen (1b), ketoprofen (1c) and flurbiprofen (1d), as well as to the 2-aryloxypropionic acids 2-phenoxypropionic acid (2a) and 2-naphthoxypropionic acid (2b). This approach, allowing us to reveal the sample’s absolute configuration by simple optical rotation measurements, is potentially applicable to online analyses of both the enantiomeric composition and absolute configuration of these chiral pollutants.

This study investigates the significantly different luminescent and chiroptical properties of tetracycline (TC) when coordinated to Eu(III). The approach involves understanding the 1) speciation of TC and 2) conformation and species formed between Eu(III) and TC in a ratio of 1 : 1 in a dimethylformamide (DMF) solution and as a function of the pH value. By identifying the conformational changes of the various 1 : 1 Eu(III) : TC species, the results from this study explain information on the local microenvironment about the Eu(III) metal center. In particular, 5 D0 ←7 F0 Eu(III) laser excitation spectroscopy was employed to distinguish the different types of species found in solution in order to understand the interaction between Eu(III) and TC. On the other hand, circularly polarized luminescence (CPL) spectroscopy was used to understand the structural changes within the 1 : 1 Eu(III) : TC complex that could be related to the chirality of the Eu(III)-containing species. The CPL spectrum serves as a "fingerprint" to indicate the conformational changes within the 1 : 1 Eu(III) : TC complex as a result of the chiroptical signal arising from the various Eu(III) : TC species.

The aim of this study was to explore whether rotational three-dimensional (3D) visualization of optical coherence tomography angiography (OCTA) volume data may yield valuable information regarding diabetic retinal microaneurysm (MA) characteristics. In this retrospective, observational study, we collected data from 20 patients (20 eyes) with diabetic retinopathy. Subjects were imaged with the SS-OCTA system (PLEX Elite 9000, Carl Zeiss Meditec Inc., Dublin, CA, USA). The OCTA volume data were processed with a volume projection removal algorithm and then exported to imageJ in order to obtain a 3D visualization of the analyzed MAs. The rotational three-dimensional OCTA images were qualitatively and quantitatively investigated. A total of 52 MAs were included in the analysis. On rotational 3D OCTA images, the number of vessels associated with each MA varied between 1 and 4, and most MAs (59.6%) were associated with 2 vessels. Moreover, in 20 MAs (38.4%) these vessels seem to originate from the SCP, while 26 MAs (50.0%) had associated vessels originating from the DVC, and 6 MAs had associated vessels arising from both the SCP and DVC (11.6%). Most MAs (31/52) had a ‘saccular’ shape. The number of retinal layers occupied by each MA ranged between 1 and 3 and the inner nuclear layer was the retinal layer most frequently occupied by MAs. In conclusion, this study used an algorithm to obtain rotational three-dimensional visualization of retinal MAs. The MAs’ architecture is complex and 3D visualization may clarify the true vascular origin of these lesions, which is often mistaken using en face OCTA images.

Phosphorylation of glucose is the prime step in sugar metabolism and energy storage. Two key glucose phosphates are involved, that is, glucose 6-phosphate (G6P) and α-glucose 1-phosphate (αG1P). The chiral conformation of glucose, G6P, and αG1P plays an essential role in enzyme-mediated conversions. However, few techniques were able to give a direct view of the conformational changes from glucose to G6P and αG1P. Here, Raman optical activity (ROA) was used to elucidate the stereochemical evolution of glucose upon phosphorylation. ROA was found to be extremely sensitive to different phosphorylation sites. A characteristic ROA marker of (+)980 cm-1, originated from the phosphate group symmetric stretching vibration, is observed for αG1P with phosphorylation at chiral C1, while no corresponding ROA signal for G6P with phosphorylation at achiral C6 is observed. Phosphorylation-induced gauch-gauch (gg)/gauch-trans (gt) rotamer distribution changes can be sensitively probed by the sign of the ROA band around 1460 cm-1. A positive ROA band at 1465 cm-1 of glucose corresponds to a higher gt ratio, while a negative band at 1455 cm-1 of G6P suggests a dominant gg population, and the disappearance of this ROA band for αG1P indicates a nearly balanced gg/gt distribution. Meanwhile, the phosphorylation at C6 and C1 could cause dramatic reduction of the conformational flexibility of the adjacent C4-OH and C2-OH, respectively. These stereochemical changes revealed by ROA spectra offer a structural basis on the understanding of sugar phosphorylation from the perspective of chirality.

Induced circular dichroism (ICD) of polyoxomolybdates and polyoxotungstates was realized in three kinds of natural polysaccharide hydrogels possessing hierarchical chirality. Interestingly, the extrinsic chiral factors were dominant in ionic κ/ι-carrageenan hybrids, while the ICD of clusters was dominantly influenced by the intrinsic alternating bond length (ABL) distortions of polyoxometalates in agarose hybrid. The optical activity of the POMs shows sensitive response to multiple stimuli, such as temperature, K+ salts, UV irradiation and redox agents.

A collaborative program to discover new specialized metabolites from aquatic environments of Iceland led to the deconvolution of tetrahydroisoquinoline amide E/Z rotamers [(E/Z)-N-acetyl-MY336-a; 1] and conformers produced by a Streptomyces sp. All structures were elucidated by NMR and MS analysis, and interpretation of electronic circular dichroism (ECD) data. ECD and optical rotation (OR) simulations permitted the unequivocal assignment of the absolute configuration of compound 1 and provided an important example of delineating the spectroscopic contributions of equilibrating rotamers and boat/chair conformers of a common natural product scaffold.

Precise optical rotation measurements play an important role in the analysis of chiral molecules in various fields, especially in biological chemistry and pharmacology. In this paper, we demonstrate a new variant of continuous-wave cavity-enhanced polarimetry for detecting the optical activity of two enantiomers of a chiral molecule at 730 nm. It is based on a signal-reversing technique for which the chiral specific rotation is directly determined by the cavity ring-down signal from two counter-propagating beams in a bow-tie cavity. In particular, we ensure reproducible excitation of both modes by broadening the linewidth of a diode laser source by application of a radio frequency perturbation to its injection current. The performance of the polarimeter is demonstrated for the specific rotation of (+)- and (−)-α-pinene in different environments, including the pure vapor, open air, and the liquid phase; the detection precision ranges between 10–5 and 10–4 degrees per cavity pass depending on the environment. The apparatus is a robust and practical tool for quantifying chirality and can be developed for the entire visible and near-infrared spectral regions.

Thirteen pairs of I3P enantiomers were screened using nine polysaccharide chiral stationary phases and three different mobile phases. The purification strategy for 13 pairs of I3P enantiomers were designed and optimized considering enantiomeric purity and enrichment of isomers. Out of 13 I3P derivatives which were screened using supercritical fluid chromatography, 10 derivatives displayed excellent baseline separation using a Lux Cellulose—4 column and their resolution from higher to lower order of I3P-11, 13, 4, 12, 2, 1, 9, 3, 7 and 8 derivatives whereas in case of Lux Cellulose—2 column, the moderate separation was achieved as compared to Cellulose—4 in the order I3P-5, 6 and 10 derivatives. Excellent enantiomeric separations and retentions for all 13 I3P enantiomer derivatives were obtained in Cellulose—4 and Cellulose—2 columns in presences of methanol as organic modifier without any additives except in the case of I3P 12 enantiomer. The absolute stereochemical assignment of the purified isomers was determined through an optical rotation study. Among the series of I3P derivatives, I3P-5 showed potent antioxidant activity against catalase with an IC50 value of 13.78 μM. Further molecular docking, MM/GBSA and molecular dynamics studies revealed that the I3P-5 derivatives effectively bind to catalase with a docking score of −5.41 kcal/mol. Which validated chiral docking and indicated great potential for enantiomeric separation in drug discovery and present studies (R)—enantiomer preferentially depicts good binding capacity with catalase.

A chiral sensor with optical rotation detection based on weak measurement for the kinetic study of sucrose hydrolysis is presented. Based on the polarization modulation to the pre-selection state, the optical rotation of chiral sample was accurately determined through the central wavelength shift of the output spectrum. With this approach, the concentration response curves of sucrose and its hydrolysis products, i.e., fructose and glucose, were experimentally obtained for the hydrolysis analysis. By collecting the output spectrum with a frequency of 100 Hz and fitting the central wavelength shift synchronously during the measurement, the sucrose hydrolysis process was monitored in real time. Different hydrolysis conditions with varied concentration of invertase enzyme and citrate were implemented in this work. As a consequence, the real-time hydrolysis curves of the hydrolysis process with distinct velocities was achieved and analyzed. Such a kinetic monitoring about sucrose hydrolysis with optical rotation detection technology played a critical role in the researches involving sucrose, and also revealed the great potential of weak measurement in intersections, such as food safety inspection and chemical analysis.

We present time-dependent density functional theory (TDDFT) calculations of the electronic optical rotation (ORP) for seven oxirane and two aziridine derivatives in the gas phase and in solution and compare the results with the available experimental values. For seven of the studied molecules it is the first time that their optical rotation was studied theoretically and we have therefore investigated the influence of several settings in the TDDFT calculations on the results. This includes the choice of the one-electron basis set, the exchange-correlation functional or the particular polarizable continuum model (PCM). We can confirm that polarized quadruple zeta basis sets augmented with diffuse functions are necessary for converged results and find that the aug-pc-3 basis set is a viable alternative to the frequently employed aug-cc-pVQZ basis set. Based on our study, we cannot recommend the generalized gradient functional KT3 for calculations of the ORP in these compounds, whereas the hybrid functional PBE0 gives results quite similar to the long-range correct CAM−B3LYP functional. Finally, we observe large differences in the solvent effects predicted by the integral equation formalism of PCM and the SMD variant of PCM. For the majority of solute/solvent combinations in this study, we find that the SMD model in combination with the PBE0 functional and the aug-pc-3 basis set gives the best agreement with the experimental values., P.F.P. acknowledges financial support from CONICET and UNNE (PI: 15/F002 Res. 1017/15 C.S.). S.P.A.S. thanks the TWAS Visiting Expert Programme (F.R. 3240301376) and the Abdus Salam International Centre for Theoretical Physics (VS-536) for supporting his visits to Department of Physics, Northeastern University, Corrientes, Argentina. MBF was funded by UBACYT 20020170100456BA, from Universidad de Buenos Aires; PIP 11220130100377, from CONICET.

Two new phomaligols, deketo-phomaligol A (1) and phomaligol E (2), together with six known compounds (3&ndash, 8) were isolated from the culture broth of the marine-derived fungus Aspergillus flocculosus. Compound 1 was first isolated as a phomaligol derivative possessing a five-membered ring. The structures and absolute configurations of the new phomaligols were determined by detailed analyses of mass spectrometry (MS), nuclear magnetic resonance (NMR) data, optical rotation values and electronic circular dichroism (ECD). In addition, the absolute configurations of the known compounds 3 and 4 were confirmed by chemical oxidation and comparison of optical rotation values. Isolated compounds at a concentration of 100 &mu, M were screened for inhibition of nitric oxide (NO) production in lipopolysaccharide (LPS)-induced BV-2 microglial cells. Among the compounds, 4 showed moderate anti-neuroinflammatory effects with an IC50 value of 56.6 &mu, M by suppressing the production of pro-inflammatory mediators in activated microglial cells without cytotoxicity.

International audience; Enantiopure tris-helicenic chiral-at-iridium complexes have been prepared, constituting the first examples of organometallic metal-tris-helicenes. They have the mer- or fac-Ir(CC:)(3) form, where (CC:) is an N-heterocyclic carbene ligand N-substituted with a hexahelicene. Their triskelion geometry and stereochemistry have been thoroughly studied and assigned by NMR in combination with quantum-chemical modelling and by comparison with the X-ray structure of analogues. Thanks to their Ir(iii)-based multihelicenic architecture, the complexes display strong electronic circular dichroism and optical rotation along with long-lived yellow phosphorescence, involving circularly polarized emission with g(lum) factors around 10(-3).

Optical rotatory dispersion (ORD) is a beautiful analytical technique for the study of chiral molecules and polymers. In this study, ORD was applied successfully to follow the degree of polycondensation of l-(+)-lactic acid toward the formation of poly(lactic acid) oligomers (PLAO) and high molecular weight poly(L-lactic acid) (PLLA) in a simple esterification reaction equipment. PLLA is a biodegradable polymer obtainable from renewable raw materials. The racemization of the intrinsically isotactic PLLA through thermal treatment can be easily followed through the use of ORD spectroscopy. Organic or molecular electronics is a hot topic dealing with the combination of &pi, conjugated organic compounds and polymers with specific properties (e.g., chirality) which can be exploited to construct optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) high efficiency cells, switchable chirality devices, organic field-effect transistors (OFETs), and so on. ORD spectroscopy was applied to study either the gigantic optical rotation of PLLA films, as well as to detect successfully the excitonic coupling, occurring in thin solid PLLA green film loaded with a combination of two dyes: SY96 (a pyrazolone dye) and PB16 (the metal-free phthalocyanine pigment). The latter compound PLLA loaded with SY96 and PB16 shows a really gigantic optical activity in addition to typical ORD signal due to exciton coupling and may be considered as a simple and easily accessible model composite of a chiral polymer matrix combined with &pi, conjugated dyes for molecular electronics studies.

Helical frontier molecular orbitals (MOs) appear in disubstituted allenes and even-n cumulenes. Chiral molecules are optically active, but while these molecules are single-handed chiral, π-orbitals of both helicities are present. Here we computationally examine whether the optical activity of chiral cumulenes is controlled by the axial chirality or the helicity of the electronic structure. We exploit hyperconjugation with alkyl, silaalkyl, and germaalkyl substituents to adjust the MO helicity without altering the axial chirality. For the same axial chirality, we observe an inversion of the helical MOs contribution to the electronic transitions and a change of sign in the electronic circular dichroism and optical rotation dispersion spectra. While the magnitude of the chiroptical response also increases, it is similar to that of chiral cumulenes without helical π-orbitals. Overall, Helical π-orbitals correlate with the big chiroptical response in cumulenes, but are not a prerequisite for it.

BackgroundOfloxacin is an important drug with anti-bacterial effects, and (–)-ofloxacin has been shown to have better anti-bacterial activity than racemic ofloxacin. But chiral resolution of compounds is a major challenge worldwide. Many methods do not show high specificity to target molecules, causing errors in the separation of these pharmaceutical molecules, thus affecting the purity of drugs.MethodThe paper mainly research on a method for quick resolution of ofloxacin using chiral magnetic surface molecular imprinting polymers (chiral MMIP). Fe3O4 magnetic nanoparticles coated with silica is acted as the substrate. Chiral reagent is N-octyl-D-glucosamine as monomer, with ofloxacin as the template molecules to prepare magnetic surface molecularly imprinted polymer. The chiral polymer can be combined with (+)-ofloxacin, eventually (-)-ofloxacin was isolated. ResultsFinally by using extermal magnetic field and transmission electron microscopy (TEM), the character of magnetic surface molecularly imprinted polymer is tested, and The product was tested by ultraviolet spectrum and optical rotation tests and was confirmed to be (-)-ofloxacin. ConclusionA simple, rapid, and cost-effective method for separating chiral compounds was established.

The effect of ultrasound was studied on the flavonoid rutin to understand its hydrolysis to aglycones, antioxidant capacity and optical rotation. The total phenolic content increased >56% at 3.6–36 kJ/cm3, indicating production of phenolic compounds. In the water media, at 27 kJ/cm3 and 47 °C, the total flavonoid content increased from control 0.26 ± 0.01 to 0.45 ± 0.02 mg catechin equivalent/mg rutin hydrate. Quercetin yield in citric acid media increased with change in energy density from 0.34 ± 0.09% at 0.1 kJ/cm3 (68 °C) to 2.23 ± 0.04% at 7.0 kJ/cm3 (86 °C). A plummeting effect was only observed in water media after 27 kJ/cm3 by FRAP (47 °C) and DPPH (86 °C) antioxidant activities, indicating that the presence of solutes (citric acid and NaCl) after 27 kJ/cm3 reduced degradation of flavonoids. Furthermore, ultrasonication increased levorotatory rutin enantiomers, that can be used to further modify physico-chemical properties of other food components.

International audience; By attaching pyridine groups to a diaza[6]helicene, a helical, bis-ditopic, bis-N N-coordinating ligand can be accessed. Dinuclear rhenium complexes featuring this bridging ligand, of the form [{Re(CO) Cl} (N N-N N)], have been prepared and resolved to give enantiopure complexes. These complexes are phosphorescent in solution at room temperature under one- and two-photon excitation. Their experimental chiroptical properties (optical rotation, electronic circular dichroism and circularly polarized emission) have been measured. They show, for instance, emission dissymmetry factors of c.a. ±3x10 . Quantum-chemical calculations indicate the importance of stereochemistry on the optical activity, pointing towards further design improvements in such types of complexes.

Artemisinin and two of its derivatives, dihydroartemisinin and artesunate, which are front line drugs against malaria, were investigated using Raman optical activity (ROA) and vibrational circular dichroism (VCD) experiments, both supported by density functional theory (DFT) level calculations. The experimental techniques combined with DFT calculations could show that dihydroartemisinin was present as an epimeric mixture in solution. In addition, an approximation of the epimeric ratio could be extracted which was in agreement with the ratio obtained by(1)H-NMR spectroscopy. The current study also demonstrates that both ROA and VCD are able to assign the correct absolute configuration (AC) of artemisinin and artesunate out of all their possible diastereomers without any explicit knowledge on their correct stereochemistry and accentuates the synergetic effect between ROA and VCD in AC determination.

We show that the polycondensation of chiral sol-gel precursors can be efficiently followed up by optical rotation measurements. Three silanes were studied, namely, the hexaethoxysilane derivatives of l-threonine, l-isoleucine, and dimethyl-l-tartrate. Two main sol-gel polycondensation mechanisms were identified, namely, linear kinetics product growth and second-order cluster–cluster growth. Dynamic light scattering measurements are used to support the proposed mechanisms.

Optically pure dicyano oxa[7]helicenes and helicene-like molecules have been prepared and investigated for their optical behavior. The isomers of the intermediate 4,4'-biphen-anthrene-3,3'-diol were resolved by physically separating their 1-menthyl carbonate derivatives. In this work a mild method was developed to cleave ArOMe in presence of a cyano group. The optical rotation of atropisomeric diol, helicenes-like compounds and the oxa[7]helicenes was observed to be in increasing order, while the molecules also showed good response to circularly polarized luminescence.

We present the first detailed experimental study of discrete wavelength resolved specific optical rotations (SORs) of chiral molecules embedded in achiral micelles. Eight different chiral compounds embedded in SDS and TX100 micelles have been used to analyze their SORs in comparison to those obtained for the same chiral molecules in achiral solvents. An important observation made is that the SORs of hydrophobic chiral molecules, α-pinene and 2-carene, in hydrophobic achiral solvents (dodecane, heptane and CCl4) are greater than those of same chiral molecules embedded in hydrophobic core of SDS micelles. This difference is envisioned to be due to the differences in microenvironments provided by achiral SDS micelle and organic solvents. The ratio of SOR for a chiral molecule in CCl4 solvent and achiral micelles is found to reflect the locus of solubilization of chiral molecule in achiral micelle. The locus of solubilization of chiral molecules in TX100 micelles has been independently verified using 1H NMR studies. The emerging general observations are: (a) when chiral molecule is located deep inside the hydrophobic core of the micelle, SOR in micelle is smaller than that in CCl4. (b) When chiral molecule is located at the interface of hydrophobic and hydrophilic regions of the micelle, SOR in micelle is slightly greater than, or equal to, that in CCl4. While quantum chemical (QC) calculations to explain these observations in micelles need significantly larger computational time line, the prospect for such calculations has been verified by undertaking QC predictions of SOR for a representative chiral molecule, fenchone, in water (with 4 A solvation sphere), and comparing the predicted results with the corresponding experimental observations in water. The predictions and observations are found to be in good agreement. The present results are expected to provide impetus for understanding the microenvironment that influences most of the spectroscopic observations.

Helicene ligands possess a unique helicoidal π-conjugated framework providing high optical rotation values. This has stimulated a growing interest in helicene derivatives as building blocks, which has triggered the development of simple strategies to tune their properties. In this context, we evaluated the formation of cation-π complexes derived from [6]- and [7]helicene, involving Sn2+ , Cd2+ , and In+ in addition of Ag+ , which appears as a plausible modification of such helicoidal structure. The nature of the cation-π interaction in the studied helicene complexes exhibits a covalent character, accounting for ligand π-donation to 5 s and 5p empty orbitals of the involved cations. Furthermore, the evaluation of their optical activity exhibits notorious modification patterns in the circular dichroism spectrum, suggesting that the modifications of the optical activity are dependent on the nature of the cation and its related charge state. Thus, the plausible formation of new cation-π complexes derived from helicene ligands, as discussed here, may lead to the characterization of novel species expanding the chemistry of helicene metal complexes to even to larger helicene units. We believe that the present study may open new avenues in the formation of cation-π helicene complexes.

To understand or identify whether a dimer forms or not derived from a chiral compound via H-bonds in solution is critically important. In our previous study, sotolon 1 has two methyl groups, it can form dimers in solution, but maple furanone 2 , derived from 1 , has one ethyl group and one methyl group, it cannot form dimer. This could be checked by using chiroptical spectroscopies of optical rotation (OR), electronic circular dichroism (ECD) and vibrational circular dichroism (VCD). In this study, four methods was used for the chiral α-hydroxyl ketones and esters ( 3 – 8 ). B3LYP and MPW1PM91 methods with four sets were used to calculate OR, ECD and VCD. The theoretical results exhibited that VCD method could provide more details and promises to ultimately distinguish between the presence of monomer or dimer in solution.

Menthol has been widely used in pharmaceuticals, food industry, oral health care products, cosmetic industry, and tobacco products, and its HPLC chiral separation has been less reported till now. Herein, a simple and direct method has been developed for separation of menthol by normal-phase HPLC coupled with refractive index detector and/or optical rotation detector, in which special sample pretreatment and derivatization were not required. The effects of chiral stationary phases, alcoholic modifiers, column temperature, and injection amount were studied in detail. The amylose tris(3,5-dimethylphenylcarbamate)-coated chiral stationary phase showed the best separation performance for menthol with the resolution of 2.84. Through the optical rotation detector, (+)-menthol was first eluted on the amylose-based chiral stationary phase in the hexane-2-propanol mixture, but later eluted on the cellulose-derived chiral stationary phases in the same mobile phase. In addition, retention and resolution of menthol displayed an upward trend along with the content of 2-propanol and column temperature reduction. Chiral separation of menthol could be attributed to an enthalpically driven process, since ΔΔH (− 3.04 kJ mol− 1) and ΔΔS* (− 8.57 J mol− 1 K− 1) for two enantiomers were negative in the experimental temperature range. Moreover, the limits of detection and quantitation for the menthol enantiomers with the refractive index detector were similar to the optical rotation detector. These results would provide useful information for direct resolution for chiral compounds without typical chromophoric groups.

A series of indolocarbazole-pyridine (IP) hybrid foldamers containing chiral residues at multiple different positions were prepared to reveal the matched and mismatched phenomena of local stereocenters on the induction of helical bias. These foldamers adopted stable helical conformations, thus affording well-resolved separate sets of 1H NMR signals for right- (P) and left-handed (M) helices in water saturated organic solvents such as toluene and dichloromethane. The ratios of P- and M-helices were determined by integrating the 1H NMR signals, in combination with the molar circular dichroism (Δe) and optical rotation ([α]D) values. The degree of helical bias was larger in the IP foldamer bearing chiral residues at the termini relative to those at the pyridine side chains, but the preferred helix orientation was opposite to each other. Foldamers 5(SS)t(SSS)py and 6(RR)t(SSS)py with chiral residues at five different positions demonstrated the matched and mismatched phenomena of local stereocenters in 6(RR)t(...

The experimental assignment of absolute configurations of chiral compounds is generally expensive and time consuming. Theoretical prediction of optical rotations can greatly assist in this endeavor. Herein a chemoinformatics exploration is reported to automatically distribute ionic liquids (IL) in a counterpropagation neural network incorporating a Kohonen layer for processing descriptors of cations, and five output layers to store optical rotations of ILs with five different anions. Cations were represented by chiral descriptors based on parities of the chiral centers assigned according to several steric and physicochemical atomic properties of the ligands. A data set with 106 chiral ionic liquids and their enantiomers was used covering a range of specific optical rotation between −147.3° and +147.3°. The obtained maps reveal relationships between the molecular structure of cations, the anions, and the optical rotation. The correct assignment of the sign of the specific optical rotations was achieved for 20 of the 22 pairs of enantiomers in an independent test set. CPG NNs estimated the value of the specific rotation with a RMS error of 22°, but more accurate predictions were obtained with a random forest that yielded a RMS error of 11°.

The recent synthesized helical tetraphenylethylene (TPE) exhibits broad application prospects such as display, catalysis, and medical imaging. A full understanding of the intricate relation between structure and property is rather important to structural design and performance improvement. Here, we employed density functional theory (DFT) and time-dependent DFT to calculate their ground- and excited-state structures, electron transition properties, optical rotation (OR), and second-order nonlinear optical (NLO) properties. For compound 1, the simulated UV–vis/CD spectra and calculated OR value are in reasonable agreement with the experimental ones, allowing us to reliably assign the electron transition and determine the absolute configuration. Intriguingly, TPE derivatives are excellent candidates for the second-order NLO materials in view of the large first hyperpolarizability values and intrinsic asymmetric structures. The intramolecular charge transfer cooperativity for this kind of compound was achiev...

Herein, we report the formation of a highly luminescent, pH-sensitive, thermoreversible nanoaggregate in pure aqueous medium through the self-agglomeration of carbazole-based amphiphiles. The self-assembly process restricted the intramolecular motion of the molecules and induced a change in its emission signal from blue to cyan, owing to an aggregation-induced emission (AIE) effect. A similar type of ratiometric response was also observed in the presence of human serum albumin (HSA). However, in this case, the molecular motion of the flexible fluorescent probe was restricted by its embedded microenvironment, owing to a motion-induced change in emission (MICE) effect, not by aggregation. Moreover, the probe showed quite high selectivity for HSA over other serum albumin proteins. Our carbazole-based fluorescent probes are a unique example of the ratiometric sensing of HSA through the sole involvement of reversible noncovalent interactions. Considering the important of HSA in clinical diagnosis, a wide range of biological fluids, such as human urine, saliva, and plasma, were screened to analyze their HSA content. In addition, this system was also employed for the detection of trypsin at subnanomolar concentrations through the digestion of HSA.

Successive reaction of long chain w-1, w-2, w-4 and w-5 hydroxycarboxylic acids 1a-1e with a cyanuric chloride (CC) and triethylamine afforded the corresponding racemic lactones 2a-2e in high yields. Optically pure R lactones 4a-4e were synthesized stereoselectively by porcine pancreas lipase-catalysed resolution of racemic 2a-2e. The resolution conditions were investigated, determined and optical rotations were measured. The mentioned chiral lactones were synthesized by this method for the first time. The obtained racemic and chiral lactones were analysed by NMR, IR, Mass, optical rotation and C,H analysis.

Drude's equation, a classical equation, can be used to express the properties of optic polarization. In the paper, an optimized two-term Drude's equation is introduced for expressing the specific rotation. The optical rotation angle for each wavelength is measured by a charge-coupled device. In order to verify the precision and versatility of the equation, we compare the obtained specific rotation with published analysis at a wavelength of 589.3 nm. Moreover, the two-term Drude's equation is translated into calculate the approximatively individual concentration of the molecules in aqueous solution. The calculation is based on the linear functional relation and fitting parameters of total rotation without knowing the ranges of concentrations and setting constraints. The viability and flexibility of this method demonstrate the potential applications in optics.

The first experimental application of enantioselective Raman spectroscopy (esR) is demonstrated using the example of the chiral alcohol 2-butanol. Samples of the neat enantiomers and the racemic mixture were analyzed in a self-built Raman set-up. The Raman spectrum allows the discrimination of the chemical species. It is shown that the optical rotation of a Raman peak with a small depolarization ratio can be measured. In addition, without any sample modification, e.g. chiral solvent, the enantiomers are distinguishable at a suitable half-wave retarder angle detecting only the vertically polarized component of the Raman signal.

Littordial F ( 1 ), a novel meroterpenoid with an unique 6/8/9/4-tetracyclic nucleus, was isolated from the leaves of Psidium littorale . The structure of 1 was established by spectroscopic data, and its absolute configuration was confirmed by computational 13 C NMR and optical rotation data. Compound 1 exhibited potential cytotoxic activities on A549, B16, and HepG-2 cell lines. A plausible biosynthetic pathway for littordial F was proposed.

Diaportheone A (1), a chromone natural product was previously isolated from the endophytic fungi Diaporthe sp. P 133. Its structure was established by spectroscopic methods, however, its absolute configuration remained undefined. This study dealt on the total synthesis of diaportheone A (1) utilizing the cyclization and in situ thermal syn-elimination of a β-ketosulfoxide. The C-1R absolute configuration of the natural product was established by X-ray crystallography of the synthetic diaportheone A (1) (>99% ee) and comparison with the optical rotation.

Achiral poly(diphenylacetylene)s (PDPAs: pMe3, pEt3, piPr3, pMe2O1, pMe2OD1, and mMe3) with different alkyl side chains at the para or meta position of the side phenyl ring were prepared to examine achiral-to-chiral transformations upon thermal annealing in a chiral solvent. All the para-substituted PDPAs showed significant circular dichroism (CD) enhancement upon annealing, whereas the meta-substituted polymer, mMe3, was inert to the same treatment. To investigate the kinetics, the asymmetric conformational change was monitored by observing the changes in the magnitude of circular polarization (gCD) or optical rotation. PDPAs with bulkier, round-shaped side groups (pEt3 and piPr3) had greater gCD values at equilibrium than pMe3 with a smaller side group. Moreover, the activation energy for the forward reaction (Eaf) was lower in the bulkier polymers than in pMe3 owing to enhanced miscibility with the chiral solvent. Similarly, the long alkyl chains of pMe2O1 and pMe2OD1 acted as internal plasticizers to ...

The utilization of chiroplasmonic effects provides unique feasibility in the fields of enantioselective detection and recognition. In this work, the chiroplasmonic fiber probes were created through the coupling of a highly optically active dielectric medium with intrinsically non-chiral plasmon-active nanostructures. The specifically designed enantiomers of helicenes with a huge optical rotation were selectively immobilized to thin gold and silver layers deposited on an optical fiber core. The chirality transfer from helicene enantiomers to closed plasmon active noble metals films results in excitation of chiral plasmon waves with opposite rotation on gold or silver surfaces. The created chiroplasmon-active optical fiber probes were used for environmental chirality monitoring and found to be sensitive to the presence of left- or right-handed molecules (glucose enantiomers) or biomolecules conformation (β-Lactoglobulin) in surrounding solutions. Control experiments confirmed that observed chirality-related plasmon band shift can be attributed to the interaction of chiral plasmon waves with the external environment, but not to the immobilization of probing molecules on the fiber surface. Created structures allow us to simultaneously estimate the presence of optically active molecules, with both, point or conformation chirality, and provides the ability to studying chiral macromolecular structure of proteins.

We present precise optical rotation measurements of gaseous chiral samples using near-IR continuous-wave cavity-enhanced polarimetry. Optical rotation is determined by comparing cavity ring-down signals for two counter-propagating beams of orthogonal polarisation which are subject to polarisation rotation by the presence of both an optically active sample and a magneto-optic crystal. A broadband RF noise source applied to the laser drive current is used to tune the laser linewidth and optimise the polarimeter, and this noise-induced laser linewidth is quantified using self-heterodyne beat-note detection. We demonstrate the optical rotation measurement of gas phase samples of enantiomers of α-pinene and limonene with an optimum detection precision of 10 µdeg per cavity pass and an uncertainty in the specific rotation of ∼0.1 deg dm−1 (g/ml)−1 and determine the specific rotation parameters at 730 nm, for (+)- and (−)-α-pinene to be 32.10 ± 0.13 and −32.21 ± 0.11 deg dm−1 (g/ml)−1, respectively. Measurements of both a pure R-(+)-limonene sample and a non-racemic mixture of limonene of unknown enantiomeric excess are also presented, illustrating the utility of the technique.

By using amino acids as anions, ten chiral ionic liquids (CILs) composed of tetrabutylammonium or cholinium as cations were synthesized by neutralization reactions and further characterized by assessing their optical rotation, thermophysical properties (melting and decomposition temperatures, density, viscosity and refractive index) and ecotoxicity against the marine bacterium Aliivibrio fischeri. The CILs are shown to display, in general, high thermal stability (> 439 K) and low to moderate toxicities (86-217 mg·L−1). It was found that the cation plays an important role in the density and viscosity of the CILs. Additionally, the effect of CILs optical configuration on these properties was evaluated by comparing the tetrabutylammonium D/L-phenylalaninate ([N4444][D/L-Phe]) and cholinium D/L-phenylalaninate ([N1112(OH)][D/L-Phe]) pairs. Finally, the CILs potential to form aqueous biphasic systems with sodium sulfate, citrate buffer and phosphate buffer was assessed and the ternary phase diagrams were determined. These allowed to infer the impact of the CILs’ cation, anion, and salt on the aqueous biphasic system formation. It was shown that the cation has a more pronounced impact on the aqueous biphasic system formation than the anion. Cholinium-based CILs failed to form aqueous biphasic systems with sodium sulfate under the tested conditions, contrary to the more hydrophobic tetrabutylammonium-based CILs. The ability of the tested salt and buffers to induce liquid-liquid demixing shows that citrate buffer and sodium sulfate represent the weakest and the strongest salting-out agents, respectively.