The carbon-13 NMR spectrum of dimethoxybilirubin dimethyl ester

The ¹³C NMR spectrum of dimethoxybilirubin dimethyl ester (1) is reported. Methoxyvinylneoxanthobilirubinic acid methyl ester, a compound containing one endo-vinylpyrromethene unit, was prepared and used in the assignment of the spectrum of 1.     

Syntheses of Bile Pigments. Part 16. Synthesis of a vinyl-substituted 2,3-Dihydrobilinedione: Possible role of this new class of bile pigments in phycobilin biosynthesis

The total synthesis of racemic cis-2,3,18¹, 18², -tetrahydroprotobiliverdin IXα dimethyl ester ( 19b ), which is identical with the dimethyl ester of rac- 4 , is described (Scheme 2). Under virtually neutral conditions, in solution, this bile pigment isomerized within a few min to racemic Z-phycocyanobilin dimethyl ester (rac- 5b ). Likewise, acid-catalyzed allyl rearrangement of 3-vinyl-substituted cis- and trans-2,3-dihydrodipyrrin-1(10H)-ones 11c and 13c , respectively, yielded the corresponding ethylidene derivatives. In this case, however, the E-isomer was formed stereo selectively from both substrates. The above results prove that, if protobiliverdin IXα ( 2 ) is transformed enzymatically to its 2,3,18¹, 18²-tetrahydro derivative, the latter would isomerize spontaneously to phycocyanobi-lin. The biosynthesis of bacteriochlorophyll a and b from a common precursor bearing a vinyl group at C(8)may be straightforwardly explained in the same way.     

Reaction of poly(vinyl alcohol) with superoxide anion

Reaction of pol(vinyl alcohol) (PVA) with superoxide anion was carried out in a dimethyl sulfoxide solution at 40°C under nitrogen and changes in the yield of recovered polymer, molecular weight, and chemical structure were examined. Appreciable decreases in the yield of recovered polymer and molecular weight were observed during the reaction, which indicated that a main chain scission of the polymer had occurred. Residual acetyl groups identified by the absorption peaks at ca. 1720 and 1250 cm^?1 in infrared (IR) spectra were removed rapidly and β-diketone groups identified by the peaks at ca. 1640 and 1560 cm^?1 in IR spectra and at ca. 255 nm in ultraviolet (UV) spectra were formed during the reaction. Formation of carboxylate groups was also assumed. The reaction mechanism was discussed on the basis of the results obtained.     

<Superscript>13</Superscript>C-labeled bilirubin: synthesis of 3<Superscript>1</Superscript>(3<Superscript>2</Superscript>),17<Superscript>1</Superscript>(17<Superscript>2</Superscript>)-di-[<Superscript>13</Superscript>C]-mesobilirubin-XIIIα

Abstract  The title compound, labeled with ¹³C in the ethyl groups was synthesized from K¹³CN and low-molecular-weight components. The synthetic relay compound was 3¹(3²)[¹³C]-xanthobilirubinic acid methyl ester in a synthetic route that leads to a label in the ethyl β-substituent of a dipyrrinone model for bilirubin. This labeled dipyrrinone was oxidatively coupled to the dimethyl ester of mesobiliverdin-XIIIα, thereby providing a route to a ¹³C-labeled mesobiliverdin and mesobilirubin, with one carbon of each ethyl being 98% ¹³C-enriched. Graphical Abstract        

Crystal Effects on Mesobilirubin: A Combined NMR Spectroscopic and Density Functional Theory Study

We report solid‐state NMR investigations of crystal effects in powdered mesobilirubin‐IXα, an open‐chain tetrapyrrole that is structurally related to bilirubin‐IXα but hydrogenated at the 3‐ and 18‐vinyl groups. ¹³C and ¹⁵N cross‐polarization magic‐angle spinning (CP/MAS) NMR experiments were performed on the compound at natural abundance. To facilitate the spectral analysis, density functional calculations were carried out at the B3LYP/6‐311G(d,p) level of theory, using an enneameric cluster to simulate the solid. The ¹H, ¹³C and ¹⁵N chemical shift data calculated for the enneamer are in a good agreement with those observed in the experimental spectra, and the relative order of the calculated resonances was thus used to confirm the tentative assignments obtained mainly from the heteronuclear correlation spectra. The observed signal splittings of a small subset of the ¹³C resonances in the peripheral regions of the two terminal rings provide evidence for microcrystalline heterogeneity of the powdered compound.     

A new tigliane-type diterpene ester from <Emphasis Type="Italic">Wikstroemia scytophylla</Emphasis>

A new tigliane-type diterpene ester, wiksphyllamin B (1), and one known compound, 12-O-benzoylphorbol 13-octanoate (2), were isolated from the stems of Wikstroemia scytophylla Diels. Their structures were identified using spectroscopic methods. The incorrect assignment of ¹³C NMR data of compound 2 in the literature was revised according to the 2D NMR spectra.     

One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers

N‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from ¹H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were r_V = 0.09, r_M = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The ¹³C{¹H} and ¹H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the ¹³C and ¹H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional ¹³C‐¹H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional ¹H‐¹H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002     

One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers

N‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from ¹H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were r_V = 0.09, r_M = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The ¹³C{¹H} and ¹H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the ¹³C and ¹H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional ¹³C‐¹H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional ¹H‐¹H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002     

The assignment of the 1H and the 13C NMR chemical shifts of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam

The assignment of the signals in the ¹³C and ¹H NMR spectra of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam is difficult for the signal pairs C-2 and C-4, C-1 and C-3, (C-1)? H, (C-2)? CH₃ and (C-4)? CH₃. The ¹³C NMR spectrum recorded under gated decoupling conditions provide long-range couplings which make possible an unambiguous assignment of the ¹³C NMR signal pairs. Application of the ¹H CW off-resonance decoupling technique in recording the ¹³C NMR spectra enables the assignment information from the ¹³C NMR spectrum to be transferred to the ¹H NMR spectrum.     

Solid‐state cross‐polarization magic angle spinning 13C and 15N NMR characterization of Sepia melanin,Sepia melanin free acid and Human hair melanin in comparison with several model compounds

This paper presents the high‐resolution ¹³C and ¹⁵N cross‐polarization magic angle spinning (CP/MAS) NMR spectra of three natural melanin solids: Sepia officinalis melanin, Sepia officinalis melanin free acid (MFA) and Human hair melanin. The functional group characterization of Human hair melanin by NMR is the first to date and the ¹³C CP/MAS NMR spectra reported here show improved resolution of chemically inequivalent sites. The observed spectral regions of the solid melanin samples can be assigned to the postulated structural unit of the polymer chain of Sepia MFA derived from solution‐state NMR studies. To assist in the assignment of functional groups in the spectra, the solid‐state CP/MAS NMR spectra are compared with high‐resolution ¹³C and ¹⁵N CP/MAS spectra of four model compounds, L ‐dopa, dopamine, 2‐methoxycarbonyl‐3‐ethoxycarbonyl‐4‐methylpyrrole and ethyl 5,6‐dimethoxyindole‐2‐carboxylate. To aid further in the assignment of protonated and non‐protonated carbon atoms, CP contact time dependence and non‐quaternary carbon suppression (NQS) experiments were performed on the melanin samples. The ¹⁵N CP/MAS spectra of the melanin samples confirm the presence of indole and pyrrole units in the melanin polymer chain. The NMR peaks observed in all of the melanin samples are relatively broad, presumably owing to the presence of free radicals. Electron spin resonance (ESR) data shows that all three melanin samples contain localized free radicals (g = 2.007), with the Sepia melanin containing a 10‐fold higher free radical density than Human hair melanin. Copyright © 2003 John Wiley & Sons, Ltd.     

The effects of overall composition and monomer sequence distribution on the infrared carbonyl stretching frequencies of ethylene–vinylacetate and styrene–vinylacetate copolymers

The vinyl acetate centered triad fractions of some free radically prepared ethylene–vinyl acetate and styrene–vinyl acetate copolymers have been determined from the patterns of vinyl acetate methine carbon peaks in their ¹³C nuclear magnetic resonance (NMR) spectra. The positions and shapes of the carbonyl bands in the infrared (IR) absorption spectra of the copolymers recorded in chloroform are shown to depend on the compositions of the copolymers and on the proportions of the various vinyl acetate centered triads. Infrared absorption measurements may thus be used in part to characterize the monomer sequence distributions of these copolymers.     

1H and 13C NMR spectra of cyclic trimers,tetramers and pentamers derived from p-substituted phenylacetylenes

The ¹H and ¹³C spectra of p-substituted 1,3,5-triarylbenzenes, 7- and p-substituted 1,3,9-triaryl-9-methyl-fluorenes and 2-, 10- and p-substituted 6,12,13a-triaryl-12-methylbenzo(6,7)cycloheptadieno[1,2,3-jk]fluorenes have been examined. p-Substituents were methoxy, methyl and fluorine groups. The ¹H spectra were recorded at 300 MHz and permitted assignments for the aromatic protons by selective proton decouplings. Partial assignment of the carbon atoms in the ¹³C spectra was also possible.     

13C n.m.r. spectroscopy: Comparison of the spectra of some dimeric Catharanthus alkaloids and their derivatives

The ¹³C n.m.r. spectra of some dimeric Catharanthus alkaloids are reported and assigned. Methods devised to aid in the assignment of resonances in complex molecules are described. The ¹³C n.m.r. spectra of several derivatives of vinblastine are discussed.     

Raman,infrared and NMR spectra and structure of divinylmethylborane

The Rarnan spectra of gaseous, liquid and solid divinylmethylborane have been recorded from 20–3500 cm^?1 and the IR spectra of gaseous and solid divinylmethylborane recorded over the range 30–3500 cm^?1. A variable temperature study of the Raman spectrum of the liquid phase has been carried out. A complete vibrational assignment is presented. In the solid phase the molecule appears to have a planar heavy atom skeleton (C_s symmetry). From analysis of the spectra of the fluid phases, the presence of a second isomer, in which one or both of the vinyl groups are twisted slightly out of the BC₃ plane (C₁ symmetry), is proposed. Variable temperature ¹³C NMR studies have been carried out. A comparison of the ¹³C chemical shift of C_β of the vinyl group with the corresponding value in other vinylboranes indicates that relatively little delocalization of the π-electron density occurs in this molecule. Low temperature (?115°C) ¹³C NMR data are consistent with a low barrier to rotation about the boron-vinyl carbon bond.     

Statistical Approach for the Determination of the Stereoregularity of Optically Active Propylene–CO Copolymers

A two‐parameter statistic model was applied to analyze the NMR spectra of a series of stereoregular propylene–CO copolymers synthesized by catalytic polymerization in the presence of various transition‐metal complexes containing chiral ligands. The concentration of the different pentads, estimated to be recognizable in the spectra, was determined. A tentative assignment of the nature of the different peaks composing the signal of the C?O group in the ¹³C‐NMR spectra is proposed.     

A study of the properties and13C NMR spectra of pinifolic acid and its derivatives

The properties and¹³C NMR spectra of pinifolic acid (13S-labd-8,17-ene-15,18-dioic acid), its monomethyl ester, its dimethyl ester, its dicyclohexylammonium salt, dihydropinifolic acid, 18-hydroxy-13S-labd-8(17)-en-15-oic acid, the cyclohexylammonium salt of the monomethyl ester, the bis(diethylammonium) salt, pinifodiol (13S-labd-8(17)-ene-15,18-diol), the acetate of 18-hydroxy-13S-labd-8(17)-en-15-oic acid, and the diacetate of pinifodiol have been studied.     

Das tautomere Gleichgewicht des Bilirubins Kurze Mitteilung

The equilibrium between lactam and lactim forms of bilirubin was studied by means of optical pK-measurements of model compounds of the arylmethylidenepyrrolinone and pyrromethenone series as well as bilirubin, bilirubin dimethyl ester and dimethoxybilirubin dimethyl ester. The lactam form of bilirubin was found to be more stable by a factor of at least 10⁴ compared with the lactim form. Therefore the latter is not responsible for the spectroscopic anomalies of bilirubin.     

Application of two-dimensional NMR spectroscopy to the complete analysis of the 1H and 13C NMR spectra of d-biotin in aqueous solution

The ¹H and ¹³C NMR spectra of d-biotin were observed at 400 and 100 MHz, respectively. Various types of two-dimensional NMR spectroscopy were performed to assign the spectra. The previous assignment of ¹³C NMR spectrum of d-biotin reported by Bradbury and Johnson was modified, and the dihedral angles between the C? H bonds of the ring were determined. The populations of the conformers produced by internal rotation around the C-2? C-δ bond were estimated.     

Crystal Structure and Conformation of a Bilirubin Ester

Summary. Crystal structures determined for three bilirubin analogs with gem-dimethyl groups at C(10) are reported, including the first X-ray structure of a bilirubin dimethyl ester. Conformation-determining torsion angles and key hydrogen bond distances and angles were compared to those from molecular dynamics calculations. Like other rubins, the component dipyrrinones of the three compounds were found to adopt the syn conformation, with Z-configuration double bonds at C(4) and C(15) and bis-lactam tautomeric structures of the end rings. No large differences in bond lengths and bond angles at C(10) were found, and the crystal structures of the two 10,10-dimethyl rubin acids showed considerable similarity to that of bilirubin: both pigments adopt a folded, intramolecularly hydrogen bonded ridge-tile conformation stabilized by six hydrogen bonds, with an interplanar angle in ridge-tile of 98° and 86°. In contrast, the dimethyl ester is intermolecularly hydrogen bonded in the crystal. Each molecule of the ester has its two syn-Z-dipyrrinones rotated into a conformation syn to the gem-dimethyl group, whereas in the acids they are anti.     

Propylene sorption and coordinative interactions for poly(N‐vinyl pyrrolidone‐co‐vinyl acetate)/silver salt complex membranes

When poly(N‐vinyl pyrrolidone‐co‐vinyl acetate) (PVP‐co‐PVAc) containing amide and ester groups were complexed with silver salts to form silver polymer electrolyte membranes, their separation performance of propylene/propane mixtures showed the high selectivity of propylene over propane of 55 and the high mixed gas permeance of 12 GPU (1 GPU = 1.0 × 10^?6 cm³(STP) cm^?2 s^?1 cmHg^?1). The separation performance strongly depends on the composition of the copolymer: the higher concentration of PVP in the copolymer, the better separation performance was achieved. These results suggest that the amide group is more effective in facilitated propylene transport than the ester group, primarily due to the stronger interaction of the silver ions with the amide than the ester oxygens, as demonstrated by FT‐IR and FT‐Raman spectroscopies. In‐situ FT‐IR spectra upon propylene sorption also demonstrate that the interaction strength of the silver ions with the ligands is arranged: amide > C?C > ester. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2263–2269, 2007