13C NMR spectral assignment of ribonuclease S-peptide. Some new structural information about its low-temperature folding

The ¹³C NMR spectrum of S-peptide (Ribonuclease 19 residue N-terminal fragment) (pH 5.4, 32°C, 12 mM in D₂O has been assigned with a basis on characteristic values for ¹³C signals of amino acids included in short peptides, SFOR multiplicities, ¹J_CH reduced values and spectral pH variations. The shift vs. temperature changes have been followed in the range 0°C–50°C and the corresponding curves analyzed by using the ΔH° and ΔS° values for the helix-coil transition obtained from ¹H NMR spectra. Values for chemical shifts in the coil and in the helix have been obtained in this way. Transition shifts are largest for CO and C_α resonances in the fragment 3–13, confirming that isolated S-peptide folds in a manner closely ressembling the native structure.     

Hydroquinone Decorated with Alkyne,Quaternary Ammonium,and Hydrophobic Motifs to Mitigate Corrosion of X-60 Mild Steel in 15 wt.% HCl

1-(6-Bromohexyloxy)-4-propargyloxybenzene upon quaternization with 3-dimethylamino-1-propanol and N,N-dimethyldodecylamine produced two new inhibitor molecules: N-[6-(4-Propargyloxyphenoxy)hexyl]-N,N-dimethyl-N-(3-hydroxypropyl)ammonium bromide (PHAB) and N-[6-(4-Propargyloxyphenoxy)hexyl]-N,N-dimethyl-N-dodecylammonium bromide (PDAB), respectively, in excellent yields. The inhibitor molecules were characterized by elemental analysis, Fourier transform infrared spectroscopy, ¹H NMR, and ¹³C NMR spectroscopy. The inhibitors were evaluated for X-60 mild steel corrosion in 15 wt.% HCl using different electrochemical and gravimetric techniques. The potentiodynamic polarization confirms both the inhibitors as mixed-type corrosion inhibitors. A low concentration (15 ppm) of PDAB has demonstrated excellent corrosion inhibition efficiencies of 97%, 98%, and 86% at 25 °C, 50 °C, and 70 °C, respectively, for 24 h exposure time. SEM and EDX spectra reveal that the adsorptions of corrosion inhibitors on X-60 mild steel create a protective film that serves as a barrier to mitigate the corrosion process. The X-ray photoelectron spectroscopy confirmed the chemical interaction between the corrosion inhibitors and mild steel, which was predicted by the Langmuir adsorption model. Assembly of inhibitive motifs of the alkyne, π-electron-rich aromatic, quaternary ammonium and C₁₂ alkyl chain hydrophobe in PDAB has augmented its inhibiting action.     

13C NMR spectra of benzofuroxan and related compounds

The ¹³C n.m.r. spectrum of benzofuroxan at ?15°C is assigned on the basis of selective decoupling experiments and by comparison with the ¹³C chemical shifts of model compounds. The ¹³C spectra were also measured in trifluoroacetic acid as a solvent. From the temperature dependence of the ¹³C spectrum of benzofuroxan in CDCl₃, a barrier of 14·0 ± 0·2 kcal mol^?1 is obtained for the degenerate tautomerism in this compound.     

Synthesis and Characterization of (βDiketonate)(7-norbornadienyl acetate)Copper(l) Complexes,Single-Crystal Structure of (hfac)Cu(7-AcO-NBD)

Copper(I) complexes of general formula (β-diketonate)Cu(7-AcO-NBD), where 7-AcO-NBD = 7-norbornadienyl acetate and β-diketonate = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate (1), 1,1,1-trifluoro-2,4-pentanedionate (2), 2,4-pentanedionate (3), 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate (4), 4,4,4-trifluoro-1-phenyl-1,3-butanedionate (5), were prepared from reactions of CuCl with Na(β-diketonate) in the presence of 7-AcO-NBD. AH compounds were characterized by elemental analyses, ¹H, ¹³C, ¹⁹F NMR and IR spectra. Single-crystal strucutre of compound 1 was determined by X-ray diffraction analysis that showed a mononuclear copper species with coordination of a chelating β-diketonate ligand through two oxygen atoms and the 7-AcO-NBD through its C? C double bond and an oxygen atom in the solid state. For compound 1, the crystal data are: triclinic, space group $ {\rm P}\bar 1 $, a= 5.4519(14) Å, b= 11.852(3) Å, c= 13.304(3) Å, α = 74.721(20)° β = 80.220(20)°, γ= 76.848(19)°, Z = 2, R_F = 0.060 and R_w = 0.064. Hot-wall chemical vapor deposition experiments revealed that compound 1 is suitable as a precursor for deposition of copper films in the temperature range 170–260 °C.     

Influence of chemical exchange on the temperature dependence of Eu(fod)3-induced shifts

Temperature dependences of the paramagnetic shifts induced by Eu(fod)₃ in ¹H NMR spectra of ethylene oxide in carbon disulphide solution are obtained in the temperature range from +40 to ? 100°C at 100 MHz and from +30 to ?60°C at 60 MHz. The influence of chemical exchange leads to a decrease of the observed paramagnetic shifts with decreasing temperature. It is shown that a modified Swift and Connick equation can be used to describe the observed dependences. Upper limits of the mean lifetimes of the Eu(fod)₃-ethylene oxide adduct are τ_p < 1·7 × 10^?8 s at 14 °C and τ_p < 1 × 10^?8 s at 20 °C, respectively. The corresponding activation energy is equal to V_a = 13·7 kcal/mol.     

Steroids of the spirostand and furostan series from plants of the genusAllium. II. The structure of alliospiroside B fromAllium cepa

A new steroid glycoside — alliospiroside B (I) — has been isolated from the collective fruit ofAllium cepa L. On the basis of chemical transformations and with the aid of physicochemical measurements it has been established that compound (I) has the structure of (25S)spirost-5-ene-1β,3β-diol 1-O-[O-α-L-rhamnopyranosyl-(1 → 2)-β-D-galactopyranoside. Compound (I) C₃₉H₆₂O₃, mp 200–202°C (from ethanol). [α] _D ²⁰ ?110.9±2° (c 1.01; pyridine) was obtained by extracting the collective fruit ofA. cepa with ethanol folowed by the column chromatographic separation of the combined glycosides on silica gel. The acid hydrolysis of (I) gave (25S)-ruscogenin (II), C₂₇H₄₂O₄, mp 189–191°C, [α] _D ²³ ?104.1±2° (c 0.98; pyridine). The¹H and¹³C NMR spectra are given for both compounds and the IR spectrum for compound (I).     

Solid‐state CP/MAS 13C NMR studies on conformational polymorphism in sertraline hydrochloride,an antidepressant drug

The C(2) isotropic chemical shift values in solid‐state CP/MAS ¹³C NMR spectra of conformational polymorphs Form I (δ 28.5) and III (δ 22.9) of (1S,4S)‐sertraline HCl ( 1 ) were correlated with a γ‐gauche effect resulting from the respective 162.6° antiperiplanar and 68.8° (+)‐synclinal C(2)? C(1)? N? CH₃ torsion angles as measured by X‐ray crystallography. The similarity of the solution‐state C(2) chemical shifts in CD₂Cl₂ (δ 22.8) and DMSO‐d₆ (δ 23.4) with that for Form III (and other polymorphs having C(2)? C(1)? N? CH₃ (+)‐synclinal angles) strongly suggests that a conformational bias about the C(1)? N bond exists for 1 in both solvents. This conclusion is supported by density functional theory B3LYP/6‐31G(d)‐calculated relative energies of C(1)? N rotameric models: (kcal) 0.00 [73.8 °C(2)? C(1)? N? CH₃ torsion angle], 0.88 (168.7°), and 2.40 (?63.4°). A Boltzmann distribution of these conformations at 25 °C is estimated to be respectively (%) 80.3, 18.3, and 1.4. Copyright © 2002 John Wiley & Sons, Ltd.     

Crystal structure of 2-(6-chloro-4-P-tolylamino)pyrido[3,2-d]pyrimidin-1-ium-1-yl)acetate oxonium bromide

The crystals of 2-(6-chloro-4-(p-tolylamino)pyrido[3,2-d]pyrimidin-1-ium-1-yl)acetate (zwitterionic form) oxonium bromide, C₁₆H₁₃ClN₄O₂·Br⁻·H₃O⁺ (I) were prepared and studied by single-crystal X-ray diffraction method. The compound crystallizes in the triclinic space group P-1 with a = 8.3121(8) ?, b = 9.3885(8) ?, c = 13.2903(12)?, α = 106.788(2)°, β = 95.204(3)°, γ = 110.871(2)°, V = 905.81(14) ?³, Z = 2; final R = 0.053, wR2 = 0.150. It is interesting that methylene C in the BrCH₂COOH molecule binds to the N1 of the pyrimidine ring. In the crystal studied, two neighboring organic molecules are connected by hydrogen bonds through carboxylate oxygen, oxonium and bromide ions to form a dimer.     

Structure of lilidine

The new alkaloid lilidine, isolated for the first time from the epigeal part ofLilium martagon has been studied by special methods. It has the composition B₅H₆NO₂, mp 118–110°C, [α]_D-26.3°. The¹H and¹³C NMR spectra were studied in detail. The values of the direct and long-range spin-spin coupling constants between the¹³C carbon nuclei and the¹H nuclei of the alkaloid molecule were measured with the aid of¹³C-[{su1}H] selective heteronuclear double resonance. The structure of 5-hydroxy-3-methyl-3-pyrrolin-2-one is suggested for lilidine.     

Methylmercuric halide-halide complexation in ethanol solution

The formation constants for CH₃HgCl₂^? at 26°C (0.31 l/mole), and for CH₃HgBr₂^? at 26°C (0.94 l/mole) and at 60°C (0.70 l/mole) in ethanol solution have been determined from the variation of Hg NMR chemical shift (by INDOR) with composition of methylmercuric halide-lithium halide solutions. These data have been employed in a reexamination of the “one-anion” and “two-anion” catalysed reactions of mercuric bromide with alkylmercuric bromides.     

Reaction of cyclooctatetraene dianion with halosilanes: Preparation of 3,4-(tetramethyldisiloxy)-1,3,5-cyclooctatriene and 5,8-bis(trimethylsilyl)-1,3,6-cyclooctatriene

The dipotassium salt of cyclooctatetraene dianion, COT^2?, reacts at ?35° with dimethyldichlorosilane, followed by aqueous workup, to give C₈H₈[Si(CH₃)₂]₂O (I) in 4.4% yield. On the basis of spectroscopic (IR, mass, ¹H and ¹³C NMR spectra) and chemical data, compound 1 is formulated as 3,4-(tetramethyldisiloxy)-l,3,5-cyclooctatriene. Reaction of COT^2? with trimethylchlorosilane yields the compound C₈H₈[Si(CH₃)₃]₂ in 50% yield, which is shown to be 5,8-bis(trimethylsilyl)-1,3,6-cyclooctatriene.     

A direct carbon-13 and nitrogen-15 nmr study of europium(iii)-isothiocyanate complex formation in aqueous solvent mixtures

A continuation of the contact ion-pairing studies of the trivalent lanthanides by direct, low-temperature, multinuclear magnetic resonance techniques has been completed for the europium(III)-isothiocyanate system. In water-acetone-Freon-22 solvent mixtures, ligand exchange is sufficiently slow at — 100°C to - 125°C to permit the observation of¹³C and¹⁵N NMR signals for Eu³⁺-NCS^- contact ion-pair complexes. With each nuclide, signals for four complexes are observed, displaced approximately 250 ppm upfield from free anion in the^13C spectra, and 2,500 ppm upfield from bulk NCS^- in the¹⁵N spectra. The concentration dependence of the signal areas is consistent with the formation of Eu(NCS)²⁺ through Eu(NCS) ₄ ^1- , with water molecules completing the solvation shell. In the¹⁵N NMR spectra, the large chemical shifts identified the nitrogen atom as the NCS^- binding site. Also, the observation of two¹⁵N NMR signals for isomers of Eu(NCS) ₂ ¹⁺ was possible in several spectra. In methanol, a medium of higher dielectric constant, complex formation was diminished, with signal area integrations confirming the dominance of Eu(NCS) ₁ ²⁺ . A comparative binding study of Cl^- and NCS^- also was made by³⁵C1 NMR chemical shift and linewidth measurements in water-methanol mixtures. The much stronger coordinating ability of NCS^- was evident in these experiments, but there is a strong possibility of Eu³⁺-Cl^- ion-pairing in the absence of this anion.     

Deprotection‐free preparation of propargyl ether‐containing phosphinated benzoxazine and the structure–property relationship of the resulting thermosets

Generally, protection and deprotection procedures of amino groups are required in preparing propargyl ether‐containing benzoxazines. In this study, we report a facile, deprotection‐free preparation of a propargyl ether‐containing phosphinated benzoxazine (2) from the nucleophilic substitution of a phenolic OH‐containing phosphinated benzoxazine (1) and propargyl bromide in the catalysis of potassium carbonate. The structure of (2) was characterized and confirmed by a high‐resolution mass spectrum, ¹H, ¹³C, ¹H‐¹H, ¹H‐¹³C nuclear magnetic resonance (NMR) spectra, and X‐ray single crystal diffractogram. infrared (IR) and differential scanning calorimetry were used to monitor the ring‐opening of benzoxazine and crosslinking of propargyl ether. The microstructure and the structure–property relationship of the resulting homopolymers and copolymers are discussed. The T_g of homopolymer of (2) is 208 °C by dynamic mechanical analysis, the coefficient of thermal expansion is 43 ppm/°C, and T_d 5% (N₂) is 393 °C, respectively, which are higher than those of the homopolymer of (1) . Similar trends were observed in the copolymerization system. The results demonstrate the beneficial effect of crosslinking afforded by the propargyl ether group is higher than that by the phenolic OH group. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Insect pheromones and their analogs

A four-stage asymmetric synthesis of (+)-disparlure [(7R,8S)-(+)-cis-methyl-7,8-epoxyoctadecane (V)] has been effected from 8-methylnon-2Z-en-l-ol (I), obtained by the carboalumination of acetylene with tris(5-methylhexyl)aluminum using the Sharpless reaction. The asymmetric epoxidation of (I), (Ar, mol. sieve A, (+)-DET, (iOPr)₄Ti, t-BuOOH, ?15°C, 20 h; H₂O, 1 h, NaOH, ?7°C, 30 min) gave 8-methyl-2S,3R-epoxynonan-l-ol (II), which was oxidized (kieselguhr-CrO₃-Py, 0°C, 2 h; 25°C, 2 h) to 8-methyl-2S,3R-epoxynonan-l-al (III). The coupling of (III) with n-C₈H₁₇CH=PPh₃ (?78°C, 1 h; 25°C, 15 h) gave 2-methyl-7R,8S-epoxyoctadec-9Z-ene (IV), the hydrogenation (H₂/5% Pd-C, 25°C, 5 days) of which led to (V) in admixture with an isomerization product. Compound (V) was isolated by HPLC. Substance, yield, [α] _D ²⁵ : (II), 73, ?2.75°; (III), 80, [80.8°; (IV), 50, +37.25°; (V), 50, +0.8°. The IR and PMR spectra of (II–IV), the¹³C NMR spectra of (II) and (III), and the mass spectrum of (IV) are given.     

Palladium(0) and platinum(0) complexes of p,p′-diisopropyldibenzylideneacetone and their NMR spectra

The zerovalent diisopropyldibenzylideneacetone (dipdba, p-i-PrC₆H₄CHCHCOCHCH-p-i-PrC₆H₄) complexes M₂(dipdba)₃ (III, M = Pd; IV, M = Pt) have been prepared and their NMR spectra studied in solution. The ¹H and ¹³C NMR spectra of III and IV show complex patterns which are consistent with the complexes having very asymmetric structures in solution. The metal atoms are π-bonded to the olefins and the frameworks are stereochemically rigid over the temperature range ?90°C to +60°C on the NMR time scale. The ¹H spectra show the aryl groups to be rotating at +25°C but to be frozen out on the NMR time scale at low temperatures.     

Synthesis, spectroscopic, and thermal studies of some Hg(II) and Cd(II) coordination compounds of N,N-bis[(E)-3-(phenylprop)-2-enylidene]propanediamine

Some new coordination compounds of cadmium(II) and mercury(II) with N,N-bis[(E)-3-(phenylprop)-2-enylidene]propanediamine (L) as a new bidentate Schiff base ligand with general formula MLX₂ (X = Cl^?, Br^?, I^?, SCN^?, and N₃ ^?) have been prepared. They were characterized by elemental analysis, FT-infrared (FT-IR) and Ultraviolet–Visible spectra, ¹H- and ¹³C-NMR spectra. The reasonable shifts of FT-IR and NMR spectral signals of the complexes with respect to the free ligand confirm well coordination of ligand and anions(X-) in inner sphere coordination mode. The thermal behavior of the complexes from room temperature to 800 °C shows weight loss by decomposition of the anions and ligand segments in the subsequent steps. The results showed that cadmium complexes have no water molecules (neither as lattice nor as coordinated water) and are decomposed in two temperature steps except about cadmium thiocyanate complex that is decomposed in three steps. Final residual contents of cadmium complexes are suggested to be cadmium oxide or sulfide. Mercury complexes were decomposed in three to four temperature steps. Mercury bromide and azide complexes leave out a little amount of mercury oxide in final, while mercury chloride, iodide, and thiocyanate complexes were found to be completely decomposed without any residual matter.     

Novel Copolymers of Styrene. 6. Some Oxy Ring-Disubstituted Butyl 2-Cyano-3-Phenyl-2-Propenoates

Novel trisubstituted ethylenes, oxy ring-disubstituted butyl 2-cyano-3-phenyl-2-propenoates, RPhCH=C(CN)CO₂C₄H₉ (where R is 4-methoxy-2-methyl, 4-methoxy-3-methyl, 3-ethoxy-4-methoxy, 4-ethoxy-3-methoxy, 3,4-dibenzyloxy, 2-benzyloxy-3-methoxy, and 3-benzyloxy-4-methoxy) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and butyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C-NMR.

Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200-500°C range with residue (2-17 % wt.), which then decomposed in the 500-800°C range.     

Preparation,X-ray crystal structure and 13C- and 1H-NMR study of 1-methyl-2-(N-methyl-N-phenylglycyl)-3-(N-methylanilino)indole

Reaction of N-methylaniline with 40% glyoxal yields 1-methyl-2-(N-methyl-N-phenylglycyl)-3-(N-methylanilino)indole ( 1a ) as the main product together with 1-methyl-3-(N-methylanilino)indole ( 1b ). The reaction appears to be general for aromatic secondary amines since N-ethylaniline and N-phenylbenzylamine yield the corresponding indoles. The structure of 1a has been verified by single crystal X-ray diffraction. Compound 1a (C₂₅H₂₅N₃O) crystallized in the triclinic space group Pl? with cell dimensions a = 10.085(3)Å, b = 10.371(3)Å, c = 11.908(5)Å, α = 74.2(3)°, β = 74.7(3)° and γ = 60.7(2)° with Z = 2. The complete ¹H and ¹³C nmr assignment of indoles 1a and 1b was achieved from two-dimensional HETCOR and COSY spectra with the aid of homonuclear and heteronuclear double resonance experiments.     

Novel copolymers of styrene. 8. Phenoxy ring-substituted butyl 2-cyano-3-phenyl-2-propenoates

Novel trisubstituted ethylenes, phenoxy ring-substituted butyl 2-cyano-3-phenyl-2-propenoates, RPhCH = C(CN)CO₂C₄H₉ (where R is 2-(4-chlorophenoxy), 3-(4-chlorophenoxy), 4-(3-chlorophenoxy), 4-(4-chlorophenoxy), 4-(4-fluorophenoxy), 2-(3-methoxyphenoxy), 2-(4-methoxyphenoxy), 3-(4-methoxyphenoxy), 4-(4-methoxyphenoxy), 3-(4-methylphenoxy) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and butyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C-NMR. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200-500°C range with residue (3.1-6.5% wt), which then decomposed in the 500-800°C range.     

1H NMR parameters of the N-terminal 13-residue C-peptide of ribonuclease in aqueous solution

The ¹H NMR chemical shifts and the spin-spin coupling constants of the non-exchangeable protons of the N-terminal 13-residue C-peptide of ribonuclease A, obtained by cleavage of the enzyme with cyanogen bromide, have been measured in a 5 mM solution in D₂O (pH 3.0, 24°C) at 360 MHz. The titration parameters for end groups (Lys-1 and homo-Ser-13) and side chains (Lys-1, Glu-2, Lys-7, Glu-9 and His-12) have been determined. The chemical shifts, their temperature coefficients and the vicinal coupling constants, ³J(HNCH-α), for the exchangeable NH protons have been measured in a 5 mM solution in D₂O/H₂O (1:9 v/v) at pH 3.0. An assignment of observed signals to individual residue protons based on characteristic shifts, standard double resonance experiments, spectral simulations and titration shifts is proposed. All experimental evidence indicates that under the conditions studied the C-peptide is in a random coil form.