Different hydrogen-bonding patterns in two [Zn(ENTPP)] complexes with water or methanol as ligands

We have synthesized zinc complexes of H₂ENTPP (5-(8-ethoxycarbonyl-1-naphthyl)-10,15,20-triphenyl porphyrin) as a model to study hydrogen-bonding interactions. When water or methanol is a ligand, crystals of [Zn(ENTPP)(CH₃OH)] or [Zn(ENTPP)(H₂O)]?·?C₆H₅CH₃ were obtained. In both structures, the ligand has hydrogen-bonding interactions, but in different patterns. In [Zn(ENTPP)(CH₃OH)], the methanol oxygen and carboxylate oxygen in the naphthyl group form an intermolecular hydrogen bond. In [Zn(ENTPP)(H₂O)]?·?C₆H₅CH₃, there are two independent molecules A and B. In molecule B, there is an intramolecular hydrogen bond between the water oxygen and the carboxylate oxygen, while in molecule A, besides the intramolecular hydrogen bond, there is an intermolecular hydrogen bond between the water oxygen and the carboxylate oxygen. ¹H NMR spectra suggest the binding of methanol or water to zinc are equilibrium processes in solution. Equilibrium constant has been determined by UV-Vis measurements, and it suggests the binding affinity of zinc to methanol has been moderately increased.     

Synthesis, Characterization and Weak Intramolecular Interactions of Porphyrins Bearing Nucleobases

5,10, 15-Triphenyl-20-{2- [α- (adenine-9 ) acetylamino]} phenyl porphyrin ( 1 ), 5,10, 15-triphenyl-20-{2-[α-(cytosine-1)acetylamino]} phenyl porphyrin (2), 5, 10, 15-triphenyl-20-{4-[α-(cytosine-1)ethoxy]} phenyl porphyrin (3) and their zinc complexes Zn-1, Zn-2 and Zn-3 have been prepared and characterized by ^1H NMR spectra, elemental analyses, electronic absorption spectra and mass spectra (FAB). Intramolecular π-π interactions and intramolecular metal-~ interaction for 1, 2, Zn-1,and Zn-2 have been investigated by several methods. ^1H NMR studies demonstrate that the porphyrin π-system in 1 and 2 is parallel to the adenine and the cytosine aromatic ring, respectively. The electronic absorption spectral properties of free porphyrin derivatives and their zinc complexes have been compared with those of H2TPP and ZnTPP. The results show that the UV-vis spectra of 1 and 2 are the same as that of H2TPP,whereas the spectra of their zinc complexes show 7 nm red shifts of the Soret bands compared to that of ZnTPP. The emission spectra of Zn-1 and Zn-2 are independent of excitation wavelength. From combination of the evidence of absorption and emission spectra it is suggested the existence of intramolecular metal-π interaction in Zn-1 and Zn-2. The results of conformational analysis agreed quite nicely with that of experiments, thus it was further to validate the experimental conclusions.     

Hydrogen bonding-driven elastic bis(zinc)porphyrin receptors for neutral and cationic electron-deficient guests with a sandwich-styled complexing pattern

This Letter reports the design and synthesis of a new type of hydrogen bonding-mediated foldamer-derived tweezer receptors that are incorporated with two peripheral (zinc)porphyrin units. Due to the existence of four intramolecular hydrogen bonds, the (zinc)porphyrin units are forced to approach and stack with each other. ¹H NMR and fluorescent studies revealed that the new receptors could form 1:1 complexes with planar electron-deficient molecules such as naphthalene and benzene diimides and paraquat through a unique sandwich-styled binding pattern. The association constants of the new complexes have been evaluated by the ¹H NMR or fluorescent titration methods.     

Highly Soluble Porphyrin (TPP)-Perylene Diimide (PDI) Dyad and Triad:Synthesis and Spectroscopic Studies

Novel porphyrin‐perylene diimide dyad (TPP‐PDI) and porphyrin‐perylene diimide‐porphyrin triad (TPP‐PDI‐TPP) were synthesized and characterized. Their structure and properties were studied by UV, FL, ¹H NMR, MS, elemental analysis, etc. The variation of fluorescence feature and UV spectra of TPP‐PDI‐TPP triad were investigated at different concentration of CF₃COOH in THF. The incorporation of CF₃COOH leads to the closure of the efficient charge transfer decay. After protonation of porphyrin units, the fluorescence intensity of TPP‐PDI‐TPP triad increased greatly. The fluorescence intensity of TPP‐PDI‐TPP triad restored after addition of triethylamine into the solution. Thus, TPP‐PDI‐TPP triad was a proton‐type fluorescence switch based on acid‐base control. Moreover, different from porphyrin‐perylene type molecular switches reported before, this TPP‐PDI‐TPP triad has wonderful solubility in organic solvents.     

Synthesis and Characterization of a Novel Phenol‐tailed Porphyrin Ligand and Its Iron(III) Complex

The phenol‐tailed porphyrin ligand, H₃L was synthesized as a model compound for catalases. H₃L and its corresponding iron complex [Fe(L)] were synthesized by using the precursor, 5‐(8‐ethoxycarbonyl‐1‐naphthyl)‐10, 15, 20‐triphenyl porphyrin (ENTPP). They were characterized by ¹H NMR spectroscopy, mass spectrometry, X‐ray crystallography, and cyclic voltammetry. All the results have confirmed that the phenol group is covalently attached to the porphyrin. In the iron complex, phenolate oxygen is coordinated to iron(III) as the fifth ligand, leading to the five‐coordinate high‐spin iron(III) species.     

Hydrogen bonding-mediated foldamer-bridged zinc porphyrin-C60 dyads: ideal face-to-face orientation and tunable donor-acceptor interacion

Four porphyrin-bridge-C₆₀ dyads have been synthesized by covalently linking the chromophores at the opposite ends of a hydrogen bonded arylamide-derived foldamer bridge. For comparison, four C₆₀-free porphyrin derivatives of the same frameworks have also been prepared. The fully hydrogen bonded bridges enable the appended porphyrin and C₆₀ moieties to contact in a face-to-face manner. ¹H NMR, UV-vis and fluorescent investigations in chloroform indicate that such a structural matching remarkably facilitates the intramolecular energy and electron transfer and charge separation between the two chromophores and also retards the recombination of the charge-separated state. Removing one hydrogen bond considerably reduces the energy and electron transfer. Further removing another one leads to no important interaction between the chromophores to occur.     

Synthesis of imidazole‐containing conjugated polymers bearing phenol unit as side group and excited state intramolecular proton transfer‐mediated fluorescence

Dibromobenzimidazole and dibromoimidazole bearing hydroxyl group‐protected phenol unit ( 1 and 2 ) were prepared and they showed an intramolecular hydrogen bonding between ether oxygen and amino proton of imidazole. The palladium‐catalyzed Suzuki coupling polymerization of 1 and 2 with benzene bis(boronic acid) derivatives gave soluble polymers ( 3 and 4 ), where the molecular weights were limited probably due to the coordination ability of imidazole to palladium metal. The phenol hydroxyl groups were subsequently deprotected using BBr₃ to obtain 3 ′ and 4 ′. From the ¹H NMR spectra, the complete conversion to the hydroxyl group and the formation of another type of intramolecular hydrogen bonding between hydroxyl proton and imine nitrogen were confirmed. In the UV and PL spectra of 3 ′ and 4 ′, the excited state intramolecular proton transfer (ESIPT) occurred to shift the emission spectra toward lower energy region compared to 3 and 4 . Especially, the PL spectrum of 3 ′ demonstrated large stokes shift (145 nm) in THF solution. The ESIPT‐mediated fluorescence was influenced by the addition of methanol and trifluoroacetic acid, which inhibited the formation of intramolecular hydrogen bonding. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4822–4829, 2009     

Metal complexes of a phenol-tailed porphyrin with different hydrogen bonds

Hydrogen bonds are very common and important interactions in biological systems, they are used to control the microenvironment around metal centers. It is a challenge to develop appropriate models for studying hydrogen bonds. We have synthesized two metal complexes of the phenol-tailed porphyrin, [Zn(HL)] and [Fe(HL)(C₆H₄(OH)(O))]. X-ray crystallography reveals that the porphyrin functions as a dianion HL^2? and the phenol OH is involved in hydrogen bonds in both structures. In [Zn(HL)], an intramolecular hydrogen bond is formed between the carbonyl oxygen and OH. In [Fe(HL)(C₆H₄(OH)(O))], the unligated O(5) of the ligand is involved in two hydrogen bonds, as a hydrogen bond donor and a hydrogen bond acceptor. The overall electronic effect on the ligand could be very small, with negligible impact on the structure and the spin state of iron(III). The structural differences caused by the hydrogen bonds are also discussed.     

Foldamer-based pyridine-fullerene tweezer receptors for enhanced binding of zinc porphyrin

This paper reports the design and synthesis of a new series of hydrogen bonding-mediated foldamer-derived tweezer receptors that are used for efficient complexation of zinc porphyrin guest. One end of the rigidified aromatic amide backbone is incorporated with one fullerene unit, while another end is connected to one pyridine or imidazole unit. The ¹H NMR, UV-vis, and fluorescent investigations in chloroform revealed that, due to the intramolecular hydrogen bonding-driven preorganized folded conformation, the fullerene and pyridine units of the receptors are located with suitable spatial separation and consequently able to co-complex zinc porphyrin with remarkably increased stability. In contrast, the imidazole-incorporated receptor displays a weakened binding affinity possibly due to structural mismatching and large steric hindrance. The association constants of the complexes of the new receptors with zinc porphyrin have been determined.     

Regioselective Long‐Range Proton Transfer in New Rifamycin Antibiotics: A Process in which Crown Ethers Act as Stronger Brønsted Bases than Amines

Water‐mediated proton transfer in six new derivatives of 3‐formylrifamycin SV that contain crown, aza‐crown, and benzo‐crown ether rings were investigated by FTIR and NMR spectroscopy. ¹H–¹H COSY couplings provide evidence for the formation of zwitterionic structures of the aza‐crown and crown ether derivatives of rifamycin, in which a proton from one of the phenolic groups is transferred to tertiary and secondary nitrogen atoms. The increased intensity of the continuous absorption in the mid‐infrared region together with the NMR data indicate proton transfer from the phenol group of the rifamycin core to the cavity of the benzo‐crown ether ring. This proton transfer is achieved by formation of hydronium (H₃O⁺) or Zundel ions (H₅O₂⁺), which form intermolecular hydrogen bonds with the oxygen atoms of the crown ether. DFT calculations are in agreement with the spectroscopic data and allow visualization of the structures of all new rifamycin derivatives, characterized by different intramolecular protonation sites.     

Synthesis and properties of ms- and β-substituted Pt(II) and Pt(IV) tetraphenylporphyrinates

The interaction of 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetra-(4-chlorophenyl)porphyrin, 2-bromo-5,10,15,20-tetraphenylporphyrin, and 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin with platinum(II) chloride in boiling phenol has been studied. The corresponding platinum(II) porphyrinates have been synthesized; their subsequent treatment with bromine in chloroform resulted in platinum(IV) porphyrinates. The Pt(II) and Pt(IV)(Br)₂ porphyrinates have been identified by elemental analysis, electron absorption, IR, and ¹H NMR spectroscopy.     

基于酰腙和酚羟基的阴离子受体的合成及其在含水介质中的阴离子比色识别性能

设计合成了一系列基于羟基和氨基的酰腙类受体分子.利用紫外-可见吸收光谱及1HNMR考察了其与F-,Cl-,Br-,I-,CH3COO-,H2PO4?,HSO4?,ClO?4等阴离子的作用.结果表明,该类受体分子在DMSO溶液中能较好地比色识别F-,CH3COO-,H2PO4?,其中受体2在含水介质中[V(DMSO)∶V(H2O)=7∶3]能选择性比色识别CH3COO-.1HNMR滴定实验研究了受体分子与阴离子之间的作用,结果表明受体分子与阴离子之间以氢键作用方式相结合.     

Bis(5‐tert‐butyl‐2‐hydroxy‐3‐methylbenzyl)(6‐hydroxyhexyl)ammonium chloride monohydrate,an anion receptor complex

In the title compound, C₃₀H₄₈NO₃⁺·Cl⁻·H₂O, the cation acts with a water molecule as a chloride ion receptor. The chloride ion forms three strong intramolecular hydrogen bonds. The water molecule forms both an intramolecular bridge between one phenol H atom and the chloride ion, and an intermolecular link to the aliphatic alcohol O atom. Weak intermolecular C—H...Cl and C—H ...O hydrogen bonds provide additional packing interactions.     

Proton-driven conformational change in a 2-aryl-p-carborane constrained by an intramolecular C-H?O hydrogen bond

2-(2-Hydroxyphenyl)-p-carborane forms an intramolecular hydrogen bonding based on the results of X-ray, IR, and ¹H NMR studies. The hydrogen bonding is released by the addition of acid in solution. Density functional theory (DFT) calculations on the phenol, phenolate and protonated phenol structures indicated two stable conformational state, hydrogen bonding form for phenol and phenolate, and dihydrogen bonding form for protonated phenol.     

Light-Modulated Self-Blockage of a Urea Binding Site in a Stiff-Stilbene Based Anion Receptor

Anion binding to a receptor based on stiff-stilbene, which is equipped with a urea hydrogen bond donating group and a phosphate or phosphinate hydrogen bond accepting group, can be controlled by light. In one photoaddressable state (E isomer) the urea binding site is available for binding, while in the other (Z isomer) it is blocked because of an intramolecular interaction with its hydrogen bond accepting motif. This intramolecular interaction is supported by DFT calculations and ¹H NMR titrations reveal a significantly lower anion binding strength for the state in which anion binding is blocked. Furthermore, the molecular switching process has been studied in detail by UV/Vis and NMR spectroscopy. The presented approach opens up new opportunities toward the development of photoresponsive anion receptors.     

Organotin mefenamic complexes—preparations,spectroscopic studies and crystal structure of a triphenyltin ester of mefenamic acid: novel anti‐tuberculosis agents

The triphenyltin adduct of mefenamic acid, [SnPh₃L] ( 1 ), the monophenyltin complex [PhSnOL] _n ( 2 ), and the dibutyltin complex [SnBu₂L₂] (3), where HL is 2‐[bis(2,3‐dimethylphenyl)amino]benzoic acid (mefenamic acid), have been prepared and structurally characterized by means of vibrational, ¹H and ¹³C NMR spectroscopies. The crystal structure of 1 has been determined by X‐ray crystallography. X‐ray analysis revealed a pseudo‐pentacoordinated structure containing Ph₃Sn coordinated to the carboxylato group. The structural distortion is a displacement from the tetrahedron toward the trigonal bipyramid. Significant C? H–π interactions and intramolecular hydrogen bonds stabilize the structure 1. The polar imino hydrogen atom participates in intramolecular hydrogen bonds. Complex 1 is self‐assembled via C? H–π and stacking interactions. Vibrational and NMR data are discussed in terms of the crystal structure and the proposed structures for 1–3. Compounds 1 and 3 were tested for antimycobacterial activity against Mycobacterium tuberculosis H37Rv. Copyright © 2002 John Wiley & Sons, Ltd.     

4-{[(1E)-(2-Hydroxyphenyl)methyl­idene]amino}-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-one

In the title compound, C₁₈H₁₇N₃O₂, a strong intramolecular O—H⃛N hydrogen bond [N⃛O 2.607 (3), O—H 0.97 (3) and H⃛N 1.71 (3) Å, and O—H⃛N 153 (2)°] was observed, which leads to a unique phenol–imine tautomerism in the solid state. The C=N imine bond distance and the C—N—C bond angle [1.287 (2) Å and 121.7 (1)°, respectively] indicate the existence of this phenol–imine tautomer. In solution, the phenol–imine tautomer of the title free Schiff base ligand is dominant in both polar and non-polar solvents, as supported by ¹H NMR and UV–visible spectroscopic data.     

Spectroscopic studies of water-soluble superstructured iron(III) porphyrin. Interaction with the bovine serum albumin protein

Abstract

Acid-base equilibrium of the “one-face”-hindered sulfonated porphyrin, α5,15-[2,2′(dodecamethyleneoxy),(5-sulfonato)diphenyl]-10,20-bis(2-hydroxy,5-sulfonatophenyl)porphyrinato iron(III), has been studied by paramagnetic ¹H NMR. The isotropically shifted signals change in a fast exchange regime on the NMR time-scale. ¹H longitudinal relaxation times and temperature dependence of the chemical shifts were measured and analyzed. The electronic structure of hydroxo specie is characteristic of a six- or five-coordinate high-spin iron(III) porphyrin with an S = 5/2 ground state. The ¹H NMR titration allowed determination of the acidity constant, pK_a 6.2 (0.1 M KNO₃, 25 °C). In addition, we also report the interaction between the monohydroxo iron(III) porphyrin and the bovine serum albumin protein. From a ¹H NMR titration, we have determined the affinity apparent constant, log K_ap 3.2 (pH 7, KNO₃ 0.1 M, 25 °C). The formation of superstructured iron porphyrin-albumin protein adduct was confirmed by electronic absorption spectroscopy and electron paramagnetic resonance.     

Protonation of Tetrapropoxy-4-tert-butylcalix[4]arene: NMR Study of Interaction and Probable Structures of the Product

Using ¹H and ¹³C NMR spectroscopy, the interaction of tetrapropoxy-p-tert-butyl-calix[4]arene (1) with H₃O⁺ ions produced by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and traces of water was studied in nitrobenzene-d ₅. It was shown that 1 readily forms an equimolecular complex with H₃O⁺. The equilibrium constant K of its formation is 2.6 at 296 K. Exchange between bound and free 1 is fast even under mild excess of HDCC, the correlation time τ_ex being about 0.13 ms. NMR shows that H₃O⁺ is bound to the aryl-oxygen atoms and this binding forces the calixarene cup to adopt a more open and symmetrical conformation. This conclusion is in full accord with high precision quantum DFT calculations which find one structure of the complex corresponding to a global energy minimum, in which the H₃O⁺ ion is bound to three of the oxygen atoms by strong hydrogen bonds and to the remaining oxygen by two weaker hydrogen bonds. The calixarene part is forced into a C₄ symmetrical opened form.

When stored for weeks, the complex gradually transforms into other forms, most probably its hydrates, according to spectral evidence and DFT calculations.     

Naryl-substituted anthranilamides with intramolecular hydrogen bonds

Hydrogen bonding interaction as one type of non-covalent force has proven itself to be highly efficient for constructing structurally unique artificial secondary structures. Here, the structure of N_aryl-substituted anthranilamide in solution is demonstrated by various NMR technique, the intramolecular hydrogen bonds between amide attached to arylamine of the same ring is proposed, which is supported by its crystal structure in the solid phase. The substituent on the nitrogen atom of arylamine plays an important role in forming the presence of intramolecular hydrogen bonds. The chemical shift of the N_aryl-H downfield changes obviously, due to the formation of intramolecular hydrogen bonds and the deshielding effect of oxygen, and the neighboring C–H is activated and shows downfield protonic signal too. The presence of intramolecular hydrogen bonds probably provides the explanation for the transformation from N_aryl-substituted anthranilamide to imine, which could be converted into 2-aryl quinazolinone finally.