Perfect appearance match between self-luminous and surface colors can be performed with isomeric spectra

Surface color results from a reflected light bounced off a material, such as a paper. By contrast, self-luminous color results directly from an emitting light, such as a Liquid Crystal (LC) display. These are completely different mechanisms, and thus, surface color and self-luminous color cannot be matched even though both have identical tristimulus values. In fact, previous research has reported that metameric color matching fails among diverse media. However, the reason for this failure remains unclear. In the present study, we created isomeric color-matching pairs between self-luminous and surface colors by modulating the spectral distribution of the light for surface colors. Then, we experimentally verified whether such color matching can be performed. The results show that isomeric color matching between self-luminous and surface colors can be performed for all participants. However, metameric color matching fails for most participants, indicating that differences in the spectral distributions rather than the different color-generating mechanisms themselves are the reason for the color matching failure between different devices. We experimentally demonstrated that there is no essential problem in cross-media color matching by generating isomeric pairs. Our results can be considered to be of great significance not only for color science, but also for the color industry.

A novel method to distinguish β-methylphenylethylamines from isomeric α-methylphenylethylamines by liquid chromatography coupled to electrospray ionization mass spectrometry

Purpose Various phenylethylamines have been detected lately in dietary or sports supplements. N-Methyl-2-phenylpropan-1-amine (phenpromethamine) and 2-phenylpropan-1-amine (β-methylphenylethylamine, BMPEA) are known to produce mass spectra almost identical to those produced by methamphetamine (MA) and amphetamine (AP), respectively, when analyzed by liquid chromatography/mass spectrometry (LC/MS). They may interfere with the analysis of MA and AP. The aims of the present study were to determine whether some substances other than phenpromethamine and BMPEA give mass spectra similar to those given by MA or AP and to develop an analytical method of distinguishing phenpromethamine from MA and BMPEA from AP by derivatization. Methods Twenty isomers of MA or AP were selected to be analyzed using LC/MS. Six reagents were examined for derivatization of MA, AP, phenpromethamine, and BMPEA. Three mass spectrometers from two manufacturers were evaluated for their ability to reproduce the data. Results All isomers except phenpromethamine and BMPEA were shown to be distinguishable from MA and AP by their mass spectra. For the discrimination of isomeric pairs, derivatization using N-succinimidyl-4-nitrophenylacetate was found to be the best for tandem mass spectrometry and that using 4-nitrobenzoyl chloride was the best for in-source collision-induced dissociation. One or more ions from each pair of isomers gave adequate difference in their relative intensities according to the World Anti-Doping Agency criteria. Conclusions The newly developed method was proved to be usable for discriminating among those phenylethylamines.

Simultaneous determination of various platycosides in Four Platycodon grandiflorum cultivars by UPLC-QTOF/MS

In Platycodi Radix (root of Platycodon grandiflorum), there are a number of platycosides that consist of a pentacyclic triterpenoid aglycone and two sugar moieties. Due to the pharmacological activities of platycosides, it is critical to assess their contents in PR, and develop an effective method to profile various platycosides is required. In this study, an analytical method based on ultra performance liquid chromatography coupled with quadrupole time-of-flight/mass spectrometry (UPLC-QTOF/MS) with an in-house library was developed and applied to profile various platycosides from four different Platycodi Radix cultivars. As a result, platycosides, including six isomeric pairs, were successfully analyzed in the PRs. In the principal component analysis, several platycosides were represented as main variables to differentiate the four Platycodi Radix cultivars. Their different levels of platycosides were also represented by relative quantification. Finally, this study indicated the proposed method based on the UPLC-QTOF/MS can be an effective tool for identifying the detail characterization of various platycosides in the Platycodi Radix.

Nitrile-Halogen Interactions in Some Bridge-Flipped Isomeric Benzylideneanilines

We designate as "bridge-flipped isomers" those pairs of molecules that differ only in the orientation of a bridge of atoms linking two major molecular fragments: in benzylideneanilines, Ar-CH=N-Ar' vs. Ar-N=CH-Ar'; in phenylhydrazones, Ar-NH-N=CH-Ar' vs. Ar-CH=N-NH-Ar' (Ar = aryl). We use them as a context in which to evaluate the roles of molecular conformation, hydrogen bonding, space-filling requirements, and supramolecular synthons in establishing crystalline isomorphism or non-isomorphism. To examine nitrile-halogen and halogen-halogen interactions in solid isomeric benzylideneanilines, we have determined the structures of 2-cyanobenzylidene-2'-iodoaniline (I), 2-iodobenzylidene-2'-cyanoaniline (II), 2-cyanobenzylidene-2'-bromoaniline (III), 2-cyanobenzylidene-2'-chloroaniline (IV), and 2-chlorobenzylidene-2'-cyanoaniline (V) by single-crystal X-ray diffraction. I/II and IV/V are bridge-flipped isomeric pairs. I, III, and IV are isomorphous; the I/II and IV/V pairs are not. In I, III, and IV, translationally related molecules are linked into chains by C≡N···X contacts; no close X···X contacts occur. Although C≡N···X contacts between translationally related molecules define chains in II similar to those in I, III, and IV, and although II likewise lacks close X···X contacts, the molecular packing arrangements differ (monoclinic for I, III, and IV vs. triclinic for II). V in contrast assumes an orthorhombic structure from which the C≡N···X interaction is absent and which is isomorphous with 2-chlorobenzylidene-2'-chloroaniline (VI), the nitrile group of V exchanged for the aniline-side chlorine of VI, that chlorine atom in VI not involved in a close intermolecular Cl···Cl contact. Although neither C≡N···X nor X···X contacts result in isomorphous bridge-flipped isomers in the cases of I/II and IV/V, the C≡N···X contacts apparently play a major structure-defining role and supersede any potential X···X contacts in I-IV.

Comparison of different theory models and basis sets for the calculation of FbC-M10Iso-Bn geometry and geometries of chlorin-imide and chlorin-isoimide isomeric pairs

Various density functional theory (DFT) methods with different basis sets to predict the molecular geometry of FbC-M10Iso-Bn macrocycle, a chlorin-isoimide, are compared in this study. DFT methods, including M06-2X, B3LYP, LSDA, B3PW91, PBEPBE, and BPV86, are examined. Different basis sets, such as 6-31G*, 6-31+G (d, p), 6-311+G (d, p), 6-311++G (d, p), cc-PVDZ, cc-PVTZ, and cc-PVQZ are also considered. The examined hybrid DFT methods are in agreement with the geometry of X-ray crystallography available for comparison. B3LYP/cc-PVDZ level is particularly consistent with available X-ray crystallography in terms of predicting the geometries of FbC-M10Iso-Bn. Geometries of chlorin-imide and chlorin-isoimide isomeric pairs are described through B3LYP/cc-PVDZ method. The bond lengths of chlorin-isoimide, specifically C13–C14, C14–C15, and C2–C3, increase as bond overlap index decreases because of charge transfer. β-β bond lengths (C2–C3 bond lengths) with a three-substituent benzylcarbamoyl group also increase as bond overlap index decreases compared with other molecules. The bond lengths of chlorin-imide are smaller than those of chlorin-isoimide. Angles with β-β bond lengths, specifically C2–C3–C4 in ring A, also decrease with a three-substituent benzylcarbamoyl group; however, the angles in C1–C2–C3 increase. Potential energy on the surfaces of the chlorin-imide and chlorin-isoimide isomeric pairs is optimized by calculating the total and relative energies at B3LYP/cc-PVDZ level. Results indicate that chlorin-imides are more stable than chlorin-isoimides. Normal-coordinate structural decomposition shows that chlorin-imides exhibit greater deformation than chlorin-isoimides except for FbC-M10Iso-Ph.

Competing intermolecular interactions in some `bridge-flipped' isomeric phenylhydrazones

To examine the roles of competing intermolecular interactions in differentiating the molecular packing arrangements of some isomeric phenylhydrazones from each other, the crystal structures of five nitrile–halogen substituted phenylhydrazones and two nitro–halogen substituted phenylhydrazones have been determined and are described here: (E)-4-cyanobenzaldehyde 4-chlorophenylhydrazone, C14H10ClN3, (Ia); (E)-4-cyanobenzaldehyde 4-bromophenylhydrazone, C14H10BrN3, (Ib); (E)-4-cyanobenzaldehyde 4-iodophenylhydrazone, C14H10IN3, (Ic); (E)-4-bromobenzaldehyde 4-cyanophenylhydrazone, C14H10BrN3, (IIb); (E)-4-iodobenzaldehyde 4-cyanophenylhydrazone, C14H10IN3, (IIc); (E)-4-chlorobenzaldehyde 4-nitrophenylhydrazone, C13H10ClN3O2, (III); and (E)-4-nitrobenzaldehyde 4-chlorophenylhydrazone, C13H10ClN3O2, (IV). Both (Ia) and (Ib) are disordered (less than 7% of the molecules have the minor orientation in each structure). Pairs (Ia)/(Ib) and (IIb)/(IIc), related by a halogen exchange, are isomorphous, but none of the `bridge-flipped' isomeric pairs,viz.(Ib)/(IIb), (Ic)/(IIc) or (III)/(IV), is isomorphous. In the nitrile–halogen structures (Ia)–(Ic) and (IIb)–(IIc), only the bridge N—H group and not the bridge C—H group acts as a hydrogen-bond donor to the nitrile group, but in the nitro–halogen structures (III) (withZ′ = 2) and (IV), both the bridge N—H group and the bridge C—H group interact with the nitro group as hydrogen-bond donors, albeitviadifferent motifs. The occurrence here of the bridge C—H contact with a hydrogen-bond acceptor suggests the possibility that other pairs of `bridge-flipped' isomeric phenylhydrazones may prove to be isomorphous, regardless of the change from isomer to isomer in the position of the N—H group within the bridge.

Do corresponding coupling constants in hydrogen-bonded homo- and hetero-chiral dimers differ?

Ab initio equation-of-motion coupled cluster singles and doubles (EOM–CCSD) calculations have been carried out to evaluate spin–spin coupling constants in six pairs of homo- and hetero-chiral dimers: (HOOH)2, (H2NNH2)2, (FOOH)2, (FHNNH2)2, (HOOOH)2, and (FOOOH)2. Corresponding spin–spin coupling constants in these isomeric pairs of C2 and Ci symmetry may differ, but these differences are small and may not be detectable experimentally. For the complexes with O1–H···O and O1–H···F hydrogen bonds, 1J(O1–H) has a larger absolute value in the C2 isomer. For the same set of complexes, 1J(O1–O2) has a larger absolute value in the Ci isomer. No distinguishable patterns could be discerned in the remaining spin–spin coupling constants in the C2 and Ci isomers of these complexes, nor in complexes with N–H···N hydrogen bonds.