CH2 Protons Research Articles

1H NMR study of the hetero‐association of unsaturated alcohols with pyridine

The 1H NMR titration method is used to investigate the association of some unsaturated alcohols with pyridine in benzene. The association constant for allyl alcohol (2‐propen‐1‐ol) is slightly higher than for alkanols, but putting one methylene group between the OH and vinyl group completely eliminates this enhancement. In alkynols both the OH and ≡CH protons associate with pyridine. Here, the effects of chain‐lengthening on the association constant are irregular. Values for alkynols and some alcohols with hetero‐atom substituents are lower than expected on the basis of a Taft polar constant (σ*) correlation of alkanol association constants and of a correlation with the pKa’s of the corresponding carboxylic acids. It is suggested that stabilization of the ground state by OH/π interactions is responsible for these low association constants. Small increases in the NMR shifts of the OH protons in the 3‐carbon and 4‐carbon alkenols and alkynols can also be attributed to OH/π interactions, but the 5‐carbon analogues have shifts as low as alkanols. Copyright © 2011 John Wiley & Sons, Ltd.

Structural Investigation of Rimantadine Inhibition of the AM2-BM2 Chimera Channel of Influenza Viruses

The M2 channel of influenza A is a target of the adamantane family antiviral drugs. Two different drug-binding sites have been reported: one inside the pore, and the other is a lipid-facing pocket. A previous study showed that a chimera of M2 variants from influenza A and B that contains only the pore-binding site is sensitive to amantadine inhibition, suggesting that the primary site of inhibition is inside the pore. To obtain atomic details of channel-drug interaction, we determined the structures of the chimeric channel with and without rimantadine. Inside the channel and near the N-terminal end, methyl groups of Val27 and Ala30 from four subunits form a hydrophobic pocket around the adamantane, and the drug amino group appears to be in polar contact with the backbone oxygen of Ala30. The structures also reveal differences between the drug-bound and -unbound states of the channel that can explain drug resistance.

C–H⋯O/N hydrogen bonded complexes of FKrCCH are stronger than FCCH complexes: Effect of rare gas insertion

C–H⋯O/N hydrogen bonding ability of rare gas inserted molecules was explored by investigating complexes of FKrCCH with series of the colloquial acceptor molecules using high level of ab-initio calculations. Structure, energetics, shifts in the C–H stretching frequencies as well as topological study of electron density provided unequivocal evidence for the formation of C–H⋯O/N hydrogen bonded complexes. Further, the strength of the hydrogen bonding in complexes of rare gas inserted molecule FKrCCH is found to be enhanced than the parent molecule FCCH which can be attributed to the increased acidity of the CH proton due to insertion of the Kr atom.

Selective J‐resolved‐HMQC‐1 and ‐2, new methods for measuring proton–proton coupling constants in strongly coupled spin systems

Efficient pulse sequences for measuring (1)H-(1)H coupling constants (JHH) in strongly coupled spin systems, named selective J-resolved-HMQC-1 and -2, have been developed. In the strongly coupled spin systems such as -CH2-CHA(OH)-CHB(OH)-CH2-, measurements of (3)JHAHB are generally difficult owing to the complicated splitting caused by the adjacent CH2 protons. For easier and accurate measurements of (3)JHAHB in such a spin system, a selective excitation pulse is incorporated into the J-resolved HMQC pulse sequence. In the proposed methods, only two strongly coupled protons, HA and HB which are excited by a selective pulse, are observed as J-resolved HMQC signals. The cross peaks of HA and HB appear as doublets owing to (3)JHAHB along the F1 dimension in the selective J-resolved HMQC-1 and -2 experiments. The efficiency of the proposed pulse sequences has been demonstrated in application to the stereochemical studies of the complicated natural product, monazomycin.

Probing Intermolecular Crystal Packing in γ-Indomethacin by High-Resolution 1H Solid-State NMR Spectroscopy

An NMR crystallography approach that combines experimental solid-state magic-angle-spinning (MAS) NMR with calculation is applied to the γ polymorph of the pharmaceutical molecule, indomethacin. First-principles calculations (GIPAW) for the full crystal structure and an isolated molecule show changes in the 1H chemical shift for specific aliphatic and aromatic protons of over −1 ppm that are due to intermolecular CH-π interactions. For the OH proton, 1H double-quantum (DQ) CRAMPS (combined rotation and multiple-pulse spectroscopy) spectra reveal intermolecular H–H proximities to the OH proton of the carboxylic acid dimer as well as to specific aromatic CH protons. The enhanced resolution in 1H DQ–13C spectra, recorded at 850 MHz, enables separate 1H DQ build-up curves (as a function of the DQ recoupling time) to be extracted for the aromatic CH protons. Supported by eight-spin density-matrix simulations, it is shown how the relative maximum intensities and rates of build-up provide quantitative insight in...

Manganese Alkane Complexes: An IR and NMR Spectroscopic Investigation

Manganese propane and manganese butane complexes derived from CpMn(CO)(3) were generated photochemically at 130-136 K with the alkane as solvent and characterized by FTIR spectroscopy and by (1)H NMR spectroscopy with in situ laser photolysis. Time-resolved IR spectroscopic measurements were performed at room temperature with the same laser wavelength. The ν(CO) bands in the IR spectra of the photoproducts in propane are shifted to low frequency with respect to CpMn(CO)(3), consistent with formation of CpMn(CO)(2)(propane). The (1)H NMR spectra conform to the criteria for alkane complexes: a high-field resonance for the η(2)-CH protons that shifts substantially on partial deuteration of the alkane and exhibits a coupling constant J(C-H) on (13)C-labeling of ca. 120 Hz. The NMR spectrum of each system exhibits two diagnostic product resonances in the high-field region for the η(2)-CH protons, corresponding to CpMn(CO)(2)(η(2)-C1-H-alkane) and CpMn(CO)(2)(η(2)-C2-H-alkane) isomers. Partial deuteration of the alkane at C1 results in characteristic strong isotopic perturbation of equilibrium of the η(2)-CH resonance of CpMn(CO)(2)(η(2)-C1-H-alkane). With propane-(13)C(1), the η(2)-CH resonance of CpMn(CO)(2)(η(2)-C1-H-alkane) isomer exhibits (13)C satellites with J(C-H) = 119 Hz. The corresponding resonance of CpMn(CO)(2)(η(2)-C2-H-alkane) is identified by use of propane-2,2-d(2). The lifetimes of the (η(2)-C1-H-alkane) isomers of the manganese complexes were determined by NMR spectroscopy as 22 ± 2 min at 134 K (propane) and 5.5 min at 136 K (butane). The corresponding spectra and lifetimes of the CpRe(CO)(2)(alkane) complexes were measured for reference (CpRe(CO)(2)(propane) lifetime ca. 60 min at 161 K; CpRe(CO)(2)(butane) 13 min at 171 K). The lifetimes determined by IR spectroscopy were similar to those determined by NMR spectroscopy, thereby supporting the assignments. These measurements extend the range of alkane complexes characterized by NMR spectroscopy from rhenium and rhodium derivatives to include less stable manganese derivatives.

Synthesis and Antimicrobial Evaluation of Some New Tetrahydropyrimidine Derivatives

The utility of 1,2,3,4-tetrahydropyrimidine-5-carboxylate (1a,b), and 1,2-dihydropyrimidine-5-carboxylate (2) in the synthesis of some new functionalized pyrimidine derivatives such as 6-(2-(dimethylamino)vinyl)-1,2,3,4tetrahydropyrimidine, 6-(1-cyano-2-(phenylamino)-2-thioxoethyl)-1,2,3,4-tetrahydropyrimidine and 4,6-distyryl-1,2-dihydropyrimidine derivatives is reported. Antimicrobial evaluation of some selected examples from the synthesized products was carried out and showed promising results. Pyrimidine derivatives are reported to possess antibacterial, antifungal anticancer, antiinflammatory, and cardioprotective effects. In addition, certain pyrimidine derivatives are known to display antimalarial, antifilarial and antileshmainal activities. Also, pyrimidine nucleus is considered as one of the most important classes of chemotherapeutic drugs. Many pyrimidine derivatives are used for thyroid drugs and leukemia. In view of the these results and as an extension of our recent work concerned with the synthesis of heterocycles of interested biological activity we decided to synthesize some new pyrimidine derivatives starting from the readily obtainable 1,2,3,4-tetrahydropyrimidine-5-carboxylate derivatives 1a, 1b, and dihydropyrimidine 2 as highly versatile and useful building blocks for the synthesis of a wide variety of pyrimidine derivatives and to test their antimicrobial activity. 1,2,3,4-Tetrahydropyrimidine 1a was found to react readily with dimethylformamide dimethyl acetal (DMF-DMA) to produce ethyl 6-(2-(dimethylamino)vinyl)-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine5-carboxylate (3) (Scheme 1). The IR spectrum of the product 3 showed absorption bands at, 1624, 1701, 3117, 3244 cm due to two carbonyl groups, and two imino functions, respectively. Its H NMR spectrum showed a triplet signal at  1.11 (J = 6.9 Hz) due to CH3 protons, singlet signal at  2.85, characteristics for two methyl protons, a quartet signal at  3.96 (J = 6.9 Hz) due to CH2 protons, a doublet signal at  5.17 (J = 3.6 Hz) due to CH proton, two doublets at  6.18 and  7.48 (J = 14.1 Hz) due to two olefinic protons, and two D2O-exchangeable signals at  7.52 and 8.61 corresponding to two NH protons, in addition to an aromatic multiplet in the region  7.22-7.29. The value of the coupling constant for the ethylenic protons indicates that the pyrimidine 3 exists exclusively in the E-configuration.

Nitro-substituted 3,3′-bis(indolyl)methane derivatives as anion receptors: Electron-withdrawing effect and tunability of anion binding properties

A series of nitro-substituted 3,3′-bis-indolyl phenylmethane derivatives were synthesized and their anion binding properties were investigated in detail. The introduction of the electron-withdrawing nitro group into indole unit and/or meso-phenyl ring, which leads to the increased acidity of indole NH and meso-position CH proton, has a positive effect on anion binding. The nitro-substituted bis(indolyl)methane receptors exhibited selective colorimetric sensing of F − anion, as revealed by the notable color and spectral changes, rationally due to the deprotonation of the indole NH of the receptor. Meanwhile, the additive introduction of the nitro substituents on the meso-phenyl ring of bis(indolyl)methane can lead to the deprotonation of the meso-position CH and further induce an irreversible oxidation process obtaining bis(indolyl)methene product in the F − anion sensing system.

Synthesis of 3,5-dichlorocyclopentane-1,2,4-trione

In continuation of our studies on the synthesis and properties of chlorinated cyclopentenones derived from hexachlorocyclopentadiene [1, 2], in the present communication we describe the synthesis of 3,5-dichlorocyclopentane-1,2,4-trione (Ia) as a new derivative of cyclopentane-1,2,4-trione (IIa). Although parent completely enolized trione IIa has long been known [3–5], published data on its reactions are relatively poor. Known examples include only some simplest transformations of trione IIa, such as reactions with amines, diazomethane, methanol under acidic conditions, and dimethyl sulfoxide [6], as well as prostaglandin syntheses starting from substituted cyclopentanetriones [7, 8]. According to [4, 5], cyclopentanetrione IIa can exist as enol tautomers IIb and IIc (Scheme 1). taking into account additional activation of the CH protons by chlorine atoms; furthermore, compound Ib should be more acidic than IIb (pKa 3.0) [5]. The spectral parameters of compound Ia suggest that it exists as only one of the two possible enol tautomers, namely enol Ib (Scheme 2). Therefore, trione IIa was also assumed to have enol structure IIb, and this structure was confirmed by comparison of the spectral data for its methylation product, 2,4-dichloro-5-methoxycyclopent-4-ene-1,3-dione (V) with those for structurally related compounds [1]. ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 12, pp. 1885–1887. © Pleiades Publishing, Ltd., 2010. Original Russian Text © N.A. Ivanova, K.S. Kislitsina, M.S. Miftakhov, 2010, published in Zhurnal Organicheskoi Khimii, 2010, Vol. 46, No. 12, pp. 1870–1872.

Measurement of N‐acetylaspartylglutamate in the human frontal brain by 1H‐MRS at 7 T

N-Acetylaspartylglutamate in human brain has been measured with difference editing at 7 T. The CH(2) proton resonances (∼ 2.5 ppm) of the aspartyl groups of N-acetylaspartylglutamate and N-acetylaspartate were difference edited (MEGA) using 20-msec gaussian radiofrequency pulses for selective 180 ° rotations of the coupling partners at 4.61 and 4.38 ppm, respectively. The echo time of the editing sequence, 108 msec, was obtained in phantom tests. Single-voxel localized in vivo measurements were conducted in the medial prefrontal and right frontal cortices of five healthy volunteers. The gray and white matter fractions within the voxels were obtained from T(1)-weighted image segmentation. Using linear regression of the metabolite concentration vs. fractional white matter contents within the voxels, the N-acetylaspartylglutamate-to-N-acetylaspartate concentration ratios in gray and white matter were estimated to be 0.13 and 0.28 by difference editing (95% confidence intervals 0.07-0.19 and 0.22-0.34), respectively, assuming identical relaxation effects between the metabolites.

Long-Range Migration of a Water Molecule To Catalyze a Tautomerization in Photoionization of the Hydrated Formamide Cluster

The dynamics on the vacuum-ultraviolet one-photon ionization of a formamide-water cluster is investigated by a combination of theoretical reaction-path search and infrared spectroscopic methods. A keto-enol tautomerization of the formamide moiety occurs after photoionization by a catalytic action of the water molecule accompanied with its long-distance migration; the water molecule in the cluster migrates almost one turn around the formamide moiety. During the migration, the water molecule abstracts the proton of CH in the formamide moiety and carries it to the O atom side in the carbonyl group through a "catch and release"-type catalytic action.

ChemInform Abstract: Reactivity of 3-Alkyl-4-arylazomethylene-3,4-dihydro-1,2,3-benzotriazines in Protic Solvents: 1,4-Addition Reactions and Dimroth Rearrangement.

3-Alkyl-4-arylazomethylene-3,4-dihydro-1,2,3-benzotriazines 5a and 5b undergo facile 1,4-addition of methanol or ethanol to afford stable crystalline hydrazones, 6 and 8 which have been characterised by spectroscopic analysis. In particular, the nmr spectrum of 8 shows novel features due to the diastereotopic nature of the CH2 protons in the two O-ethyl groups. Compound 5b shows a property unique to the compounds in this series; refluxing this arylazomethylenetriazine in ethanol affords a rearranged product, characterised as the 1-aryl-2-cinnolinylhydrazine (9). The formation of 9 is rationalised as a ring opening-ring closure process analogous to the Dimroth rearrangement. The cinnoline 9 displays some novel chemistry arising from the facility of the arylhydrazino substituent to react with acid to give a fragmentation product, 3-methylindazole (7).

N-2,4-dichlorobenzoyl phosphoric triamides: Synthesis, spectroscopic and X-ray crystallography studies

New phosphoric triamides 1–9 were synthesized by the reaction of N-2,4-dichlorobenzoyl phosphoramidic dichloride with various cyclic aliphatic amines and the products were characterized by 1H, 13C, 31P NMR, IR spectroscopy and elemental analysis. Surprisingly, the 1H NMR spectrum of 2 indicated long range 6 J (P, H) coupling constant = 1.3, 1.4 Hz and those of molecules 3, 4, 6–8 display long-range 4 J (H, H) coupling constants (1.8–1.9 Hz) for the coupling of aromatic protons in 2,4-dichlorophenyl rings. 1H NMR spectra indicated 3 J (PNCH) for enantiotopic and diastereotopic benzylic CH2 protons in compounds 7 and 8. The spectroscopic data of newly synthesized compounds were compared with those related N-benzoyl derivatives. The structures of compounds 5, 8 and 10 (2,4-Cl2-C6H3C(O)NHP(O)[NCH2CH(CH3)2]2) have been determined by X-ray crystallography. The structures form centrosymmetric dimers through intermolecular strong -P=O…H-N-hydrogen bonds. The dimers connect to each other via rather strong and weak C-H…O plus weak C-H…Cl H-bonds to produce a 1-D network for 5 while 3-D polymeric chains for 8 and 10.

ChemInform Abstract: A Novel DAST-Induced Debenzylative Cycloetherization in D-1,2-O-Isopropylidene-3,4,5-tri-O-benzyl-myo-inositol.

Diethylaminosulfur trifluoride (DAST) has been used extensively for the introduction of fluorine into various types of organic compounds via reactions with alcohols, aldehydes, ketones, and sulfoxides. In particular, DAST has been found to be an excellent reagent for converting ROH to RF. The DAST reaction with alcohols usually occurs with inversion of configuration, although retention of configuration is sometimes observed when the assumed SN2 process is highly unfavorable for steric reasons or a neighboring group participation is available. While conducting synthetic studies toward various ringfluorinated inositol derivatives by employing DAST, we have observed a novel debenzylation with concomitant ring closure, which is the subject of the present report. When D1,2-O-isopropylidene-3,4,5-tri-O-benzyl-myo-inositol (3), prepared from D-1-O-acetyl-3,4,5-tri-O-benzyl-myo-inositol (1) in two steps as shown in Scheme 1, was treated with DAST (3.7 mol. equiv.) in dichloromethane at -78 C to room temperature for 1 hr, an unexpected compound was obtained in 94% yield. The compound contained no fluorine at all, but still retained the isopropylidene and two benzyl groups. The structure was assigned as 4 on the basis of spectral analyses. H nmr of 4 showed the isopropylidene methyl groups at δ 1.30 and 1.49 as singlets, the aromatic protons at δ 7.28-7.38, four benzylic protons at δ 4.43-4.57 as multiplets, and six ring protons at δ 3.39 (d, J = 1.7 Hz, H-4), 3.93 (br. d, J = 5.2 Hz, H-5), 4.28 (d, J = 5.7 Hz, H-2), 4.39 (br. s, H-1), 4.44 (d, J = 5.8 Hz, H-6), and 4.77 (d, J = 5.7 Hz, H3). The ring proton signals were assigned on the basis of HH COSY, and the ring carbon signals on the basis of Heteronuclear Multiple Quantum Correlation, which clearly showed two sets of benzylic CH2 protons as well. In order to confirm the structural assignment of 4, the experiment was repeated with racemic samples of DL-1,2-Oisopropylidene-3,4,5-tri-O-benzyl-myo-inositol, which was readily derived from myo-inositol by the known procedures. When the racemic 3 was treated with DAST under the same conditions, the racemic form of the same cyclic ether was obtained. The product was hydrolyzed with 80% aq. AcOH to give a crystalline diol 6, whose structure was determined by X-ray diffraction (Figure 1), thus proving the proposed structure of 4 beyond any doubt. Details of the X-ray data collection and structural refinement are presented in Table 1. A possible mechanistic process for the ether formation is shown in Scheme 1. Treatment of 3 with DAST is expected to give an intermediate 5. The decomposition of the σ-sulfurane species can generate an incipient cationic species, which is evidently trapped by a conformationally available benzyl ether to give the product 4. Participation of the benzyl ether to a neighboring cationic site is precedented in the reported transformation of benzyloxy-alcohols to tetrahydrofurans under the Mitsunobu conditions.

The First Examples of a Crown Ether Intramolecularly Encapsulating Mono- and Diorganotin Dications: Synthesis and Structures of [PhSnCH2([16]crown-5)][ClO4]2and [HOSnCH2([16]crown-5)][Y]2(Y=ClO4, CF3SO3)

The reaction of silver perchlorate with [PhI(2)SnCH(2)([16]crown-5)] (1) and [I(3)SnCH(2)([16]crown-5)] (2) gave the organotin(IV)-substituted crown ether complexes [PhSnCH(2)([16]crown-5)][ClO(4)](2) (3) and [HOSnCH(2)([16]crown-5)][Y](2) (4: Y=ClO(4), 5: Y=CF(3)SO(3)), respectively. All compounds have been isolated as air-stable materials and characterised by (1)H, (13)C, (119)Sn and (119)Sn MAS (5) NMR spectroscopy, ESIMS spectrometry, elemental analysis and by single-crystal X-ray diffraction analysis. The molecular structures of 3-5 show that the tin(IV) cation fits perfectly into the crown ether cavity and is coordinated by the five oxygen atoms of the ring to give a pentagonal bipyramidal configuration about the central metal cation. Notably, compounds 4 and 5 contain the first monomeric monoorganotin dication. Moreover, there are (3)J((1)H,(119)Sn) coupling constants to the CH(2)CH proton of 377 (3) and 470 Hz (4, 5) that are, to the best of our knowledge, the biggest such couplings ever reported.

TH‐D‐201C‐10: Improved Quantification of the CH2/CH3 Ratio of Lipids: Illustration in Vivo on Tibial Bone Marrow at 3 T

Purpose: To improve the accuracy of lipid CH2/CH3 ratios determined by proton magnetic resonance spectroscopy (MRS) by minimizing J‐coupling modulations of the CH3 lipid peak. Method and Materials: Experiments were conducted in vivo on the tibial bone marrow lipids of four volunteers at 3 T. A regular PRESS (Point RESolved Spectroscopy) sequence was used to estimate the T2 (transverse relaxation) of the CH2 protons by acquiring spectra at five echo times (TEs) and plotting the areas as a function of TE. The curve was fitted to the function Moexp(−TE/T2) where M0 is proportional to the CH2 proton concentration. The CH3 response to a regular PRESS sequence is modulated due to J‐coupling interactions and does not decay monotonically. To determine Mo of the CH3 protons a narrow‐bandwidth PRESS sequence was designed that rewinds the J‐coupling evolution of the CH3 protons in the voxel of interest and spectra were acquired with the same five TEs. The CH2/CH3 ratio was calculated by dividing the CH2 Mo by that determined for CH3 and the result was multiplied by 1.5 to compensate for the different proton multiplicities. Results: The mean T2 of the CH2 protons was estimated to be ≈ 88 ms. Applying the narrow‐bandwidth PRESS sequence minimized CH3 signal variations due to J‐coupling and resulted in a decay curve that could be described by a monoexponential T2 decay function. The mean T2 for the CH3 protons was ≈ 133 ms. A mean ratio of 12:1 was calculated for the CH2:CH3 ratio of the tibial bone marrow lipids of all volunteers. Conclusion: The presented PRESS sequence enables the T2 of the CH3 lipid protons to be measured with more accuracy than would be determined by using short‐TEs thereby allowing a more accurate measure of the CH2/CH3 lipid composition ratio to be determined.

T2 determination of the J‐coupled methyl protons of lipids: In vivo ilustration with tibial bone marrow at 3 T

To demonstrate how J-coupling modulations of the CH(3) lipid resonance can be minimized enabling a representative T(2) to be measured. Experiments were conducted on canola oil and in vivo on tibial bone marrow of four volunteers at 3 T. The T(2) of the CH(2) protons was measured with a standard point resolved spectroscopy (PRESS) sequence, whereas the T(2) of the CH(3) protons was determined with a PRESS sequence composed of narrow bandwidth refocusing pulses designed to exploit the chemical shift displacement effect and rewind the J-coupling evolution of the CH(3) protons in the desired voxel. Spectra were acquired at five echo times. The narrow bandwidth PRESS sequence rewound the J-evolution of the CH(3) protons resulting in a T(2) curve that was well described by a monoexponential function. The mean T(2) of the bone marrow CH(3) protons was calculated to be 132.6 msec. The mean T(2) of the bone marrow CH(2) protons was estimated with a regular PRESS sequence to be 88.0 msec. The mean CH(2):CH(3) tibial bone marrow composition was estimated to be 12.0:1. The presented technique permits the T(2) of the methyl protons of lipids to be determined with more accuracy by minimizing contributions from J-coupling.

Anion binding studies of tris(2-aminoethyl)amine based amide receptors with nitro functionalized aryl substitutions: A positional isomeric effect

Syntheses and crystal structures of tren-based amide, L 1 , N, N′,N″-tris[(2-amino-ethyl)-4-nitro-benzamide] and L 2 , N, N′, N″-tris[(2-amino-ethyl)-2-nitro-benzamide] are reported and compared with previously published tripodal amide receptor L 3 , N, N′, N″-tris[(2-amino-ethyl)-3-nitro-benzamide]. The crystallographic results show intramolecular and intermolecular hydrogen-bonding interactions between two arms of the tripodal receptor and two other adjacent molecules in cases of L 1 and L 2 whereas in addition to the above interactions an aromatic π ···π stacking among tripodal arms is also observed in L 3 . Receptors L 1 , L 2 and L 3 having electron withdrawing – NO 2 substituted ( para, ortho and meta, respectively) phenyl moieties are explored toward their solution state anion binding properties and selectivity studies. The substantial changes in chemical shifts are observed for the amide protons (–N H) and aromatic protons (–C H) with F − and Cl − in cases of L 1 and L 3 , and only with F − for L 2 , indicating the participation of –NH and –CH protons in the solution state binding events. Binding constants for the above cases are calculated by 1H NMR titration upon monitoring the –NH signal. Receptor L 2 shows exclusive selectivity toward F − in dimethyl sulfoxide (DMSO). The structural aspects of binding I −, ClO 4 − and SiF 6 2− with the monoprotonated L 1 , L 1 H +·I −·DMF ( 1), L 1 H +·ClO 4 −·DMF ( 2) and L 1 H +·0.5SiF 6 2−·H 2O ( 3), respectively are examined crystallographically. Anion binding with multiple receptor units is observed via amide N–H···anion as well as aryl C–H···anion hydrogen-bonding interactions in all the complexes as observed in cases of previously reported crystal structures of anionic complexes of protonated L 3 . The aryl group having nitro functionality that contributes to solution state anion binding with the neutral receptor and solid state coordination in complexes 1– 3 through CH···anion interactions is noteworthy.

An NMR structural study of nickel-substituted rubredoxin

The Ni(II) and Zn(II) derivatives of Desulfovibrio vulgaris rubredoxin (DvRd) have been studied by NMR spectroscopy to probe the structure at the metal centre. The beta CH(2) proton pairs from the cysteines that bind the Ni(II) atom have been identified using 1D nuclear Overhauser enhancement (NOE) difference spectra and sequence specifically assigned via NOE correlations to neighbouring protons and by comparison with the published X-ray crystal structure of a Ni(II) derivative of Clostridium pasteurianum rubredoxin. The solution structures of DvRd(Zn) and DvRd(Ni) have been determined and the paramagnetic form refined using pseudocontact shifts. The determination of the magnetic susceptibility anisotropy tensor allowed the contact and pseudocontact contributions to the observed chemical shifts to be obtained. Analysis of the pseudocontact and contact chemical shifts of the cysteine H beta protons and backbone protons close to the metal centre allowed conclusions to be drawn as to the geometry and hydrogen-bonding pattern at the metal binding site. The importance of NH-S hydrogen bonds at the metal centre for the delocalization of electron spin density is confirmed for rubredoxins and can be extrapolated to metal centres in Cu proteins: amicyanin, plastocyanin, stellacyanin, azurin and pseudoazurin.

A Dual‐Response [2]Rotaxane Based on a 1,2,3‐Triazole Ring as a Novel Recognition Station

Two novel multilevel switchable [2]rotaxanes containing an ammonium and a triazole station have been constructed by a Cu(I)-catalyzed azide-alkyne cycloaddition reaction. The macrocycle of [2]rotaxane containing a C6-chain bridge between the two hydrogen bonding stations exhibits high selectivity for the ammonium cation in the protonated form. Interestingly, the macrocycle is able to interact with the two recognition stations when the bridge between them is shortened. Upon deprotonation of both [2]rotaxanes, the macrocycle moves towards the triazole recognition site due to the hydrogen-bond interaction between the triazole nitrogen atoms and the amide groups in the macrocycle. Upon addition of chloride anion, the conformation of [2]rotaxane is changed because of the cooperative recognition of the chloride anion by a favorable hydrogen-bond donor from both the macrocycle isophthalamide and thread triazole CH proton.