Cation-induced Dimerization Research Articles

Cation-Induced Dimerization of Crown-Substituted Gallium Phthalocyanine by Complexing with Alkali Metals: The Crucial Role of a Central Metal.

The single-crystal X-ray diffraction characterization of cation-induced supramolecular assembly of the gallium(III) tetra(15-crown-5)phthalocyaninate [(HO)Ga(15C5)4Pc] (1Ga) is reported. The structures of two crystalline dimers, {[(1Ga)2Rb4]4+(iNic-)4}·10CDCl3 and {[(2Ga)2Rb4]4+(OH-)2(Piv-)2}·16CDCl3 (2Ga-[(Piv)Ga(15C5)4Pc]), as well as UV-vis and NMR studies of the soluble supramolecular dimers formed by 1Ga and K+, Rb+, and Cs+ salts are provided. In contrast to the previously reported aluminum complex where the Al-O-Al bond was formed, no μ-oxo bridge was observed between the gallium atoms in the supramolecular dimers under similar conditions, despite the fact that aluminum and gallium belong to the same group of the periodic table. The detailed investigation of the cation-induced dimers of 1Ga confirms the uniformity of their structure for all large alkali cations, where two molecules of crown-substituted gallium phthalocyaninate are 4-fold bound by K+, Rb+, or Cs+. The gallium(III) coordination sphere is labile, and the nature of the solvent during supramolecular dimerization has an effect on the axial ligand exchange: Piv- in nonpolar CHCl3 replaces the initial OH- in 1Ga, while such a process is not observed in CHCl3/CH3OH media.

Cation-Induced Dimerization of Heteroleptic Crown-Substituted Trisphthalocyaninates as Revealed by X-ray Diffraction and NMR Spectroscopy.

We report comprehensive X-ray diffraction and NMR studies of potassium-induced dimerization of heteroleptic triple-decker crown-phthalocyaninates [(15C5)4Pc]M(Pc)M(Pc) (1M, M = Y and Tb). Characterization of the crystalline dimer 2(1Y)·4KBPh4·12CH3CN·10CHCl3 gave the first structural evidence of the formation of a six-decker structure with four rare earth metal ions perfectly aligned near the symmetry axis. NMR studies of soluble supramolecular dimers 2(1M)·4KOAc provided a spectral-structural model that allowed us to assign the NMR spectra of related complexes with paramagnetic lanthanides and to further evaluate their structure and long-range interaction between the Ln(III) centers in multinuclear tetrapyrrolic complexes. The obtained results are promising for elaboration of new supramolecular magnetic materials.

Specific Features of Cation-Induced Aggregation of Tetracrown-Substituted Aluminum(III) Phthalocyaninates

The cation-induced dimerization of tetra-(15-crown-5)-substituted Al(III) phthalocyaninate with Na+, K+ and Rb+ salts in solution has been studied by 1H NMR. It has been demonstrated that two types of supramolecular dimers coexist in solutions, which is consistent with the existence of both the monomeric and oxygen-bridged dimeric forms of the initial Al(III) complex. With the use of mass spectrometry (MALDI-TOF and HR-ESI), it has been shown that Al(III) monophthalocyaninate [(OH)AlR4Pc] forms supramolecular dimers {[M4(XAlR4Pc)2]4+(X−)4}, whereas Al(III) μ-oxodiphthalocyaninate [(AlR4Pc)2(μ-O)] forms oxygen-bridged supramolecular dimers {[M4(XAlR4Pc)2(μ-O)]2+(X−)2}.

Spectrophotometric study of the cation-induced dimerization of heteroleptic terbium(III) tetra-15-crown-5-bisphthalocyaninate

We proposed a new approach to the synthesis of heteroleptic crown-substituted terbium(III) bisphthalocyaninate, [(15C5)4Pc]Tb(Pc) (1) based on the reaction of unsubstituted lanthanum bisphthalocyaninate (La(Pc)2) with tetra-15-crown-5-phthalocyanine (H2[(15C5)4Pc]) and terbium(III) acetate in a mixture of octanol and chloronaphthalene in the presence of 1,8-diazabicyclo[ 5.4.0]undec-7-ene as an organic base. For the first time, we carried out a comparative spectrophotometric titration of compound 1 with MBPh4 solutions (M = K, Rb, Cs) and demonstrated the formation of isostructural cofacial supramolecular dimers. Spectral-structural correlations were developed for evaluation of the distances between phthalocyanine ligands in new supramolecular assemblies, which can be used for the development of polynuclear suprasingle-molecule magnetic materials.

Understanding proton capture and cation-induced dimerization of [Ag29(BDT)12]3- clusters by ion mobility mass spectrometry.

Proton transfer reactions have been a topic of fundamental interest in several areas of chemistry and biology. However, such reactivity has not been explored in detail for nanoscale materials. In this article, we present a unique reaction of an atomically precise monolayer-protected silver nanocluster, [Ag29(BDT)12]3-, with a proton (H+). Under controlled conditions, the strong proton affinity facilitated a complete conversion of the cluster to its protonated form, [Ag29(BDT)12H]2-. Moreover, binding of alkali metal ions (Li+, Na+, K+, Rb+ and Cs+) induced specific structural changes and also favored dimerization of the cluster. In this case, the cations acted as a bridge between the two clusters and the degree of dimerization was specific to the size of the cations. The conformational changes and separation of the alkali-metal ion bound dimers from their respective monomers have been investigated by ion mobility mass spectrometry (IM MS) and tandem mass spectrometric studies. Density functional theory (DFT) calculations have been used to determine the possible structures of the monomers and the dimers. Similar reactivity of the cluster can also be extended to other metal ions. While the present study helps to expand the ion-chemistry of atomically precise clusters, gas-phase basicity of the molecule can be explored in further detail and this can find applications in the areas of sensing and materials in general.

Cation-Induced Dimerization of Crown-Substituted Phthalocyanines by Complexation with Rubidium Nicotinate As Revealed by X-ray Structural Data.

The supramolecular dimeric complex [(μ-oxo)bis(tetra-15-crown-5-phthalocyaninato)(nicotinato)aluminum(III)]tetra(rubidium) bis(nicotinate) was prepared by addition of an excess of a methanol solution of rubidium nicotinate to a chloroform solution of the aluminum crown-phthalocyaninate, [(HO)Al(15C5)4Pc]. A single-crystal X-ray diffraction study of {[Rb4(NicAl(15C5)4Pc)2(μ-O)]2+(Nic-)2}·2.36HNic·11H2O demonstrated that two molecules of the aluminum crown-phthalocyaninate nicotinate are connected through an Al-O-Al bridge supported by sandwiching of crown ether moieties by Rb+ cations.

Synthesis, spectral properties, cation-induced dimerization and photochemical stability of tetra-(15-crown-5)-phthalocyaninato indium(III)

The novel 2,3,9,10,16,17,23,24-tetra-(15-crown-5)phthalocyaninato indium(III) hydroxide [(15 C 5)4 Pc ] In ( OH )(I) was obtained by direct interaction of tetra-(15-crown-5)-phthalocyanine with indium acetylacetonate with 90% yield. The set of UV-vis, 1 H NMR and MALDI-TOF spectroscopy data allowed the unambiguous interpretation of complex structure. It was shown that the developed synthetic approach can be also used for synthesis of indium(III) 2,3,9,10,16,17,23,24-octabutoxyphthalocyanine [( BuO )8 Pc ] In ( OH )(II). Photophysical characteristics (fluorescence and singlet oxygen quantum yields) of I were established. The photochemical stability of I was compared with tetra-(15-crown-5)-phthalocyanine H 2[(15 C 5)4 Pc ] and aluminum(III) complex [(15 C 5)4 Pc ] Al ( OH ). It was found that cation-induced formation of cofacial dimers [2I × 4MX] ( M = K +, Rb +, X = CO 32-, OPic -, OPiv -, SO 42-, ClO 4-, Br -) resulted in significant enhancement of complex photostability.

Synthesis, characterization and cation-induced dimerization of new aza-crown ether-appended metalloporphyrins

New metalloporphyrins bearing one or two aryl-aza-crown ether moieties at meso-positions have been synthesized using a palladium catalyzed amination reaction and fully characterized by spectral techniques. X-Ray structural data have been presented for the zinc and copper complexes of mono-substituted aza-crown ether appended metalloporphyrins. UV-Vis and (1)H NMR spectroscopic studies showed that addition of K(+) cations to a solution of monomeric aza-crowned porphyrins in CHCl(3)/MeOH led to cation-induced dimerization of these porphyrins, whereas addition of Na(+) cations yielded a monomeric complex. Axial coordination of the exobidentate ligand (DABCO) to zinc complexes of aza-crowned porphyrins and following binding metal ions led to formation of sandwich complexes with high stability constants.

Cation-Induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates

Cation-induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates (Ni(II)TCP, Pd(II)TCP, and Pt(II)TCP) on treatment with potassium thiocyanate in a chloroform-methanol solution has been studied by electronic absorption spectroscopy. The formation of [{MTCP}2(K+)4](SCN−)4 in solution induces a hypsochromic shift of the Soret band and a bathochromic shift of the β-band with respect to their positions in the spectrum of MTCP. The equilibrium constants (K) for the 2MTCP + 4K+ = [{MTCP}2(K+)4] processes at 20°C are determined to be as follows: log KNi(II)TCP = 27.31 ± 1.67, logKPd(II)TCP = 27.16 ± 1.43, and logKPt(II)TCP = 26.15 ± 1.56.

Dimerization of human immunodeficiency virus (type 1) RNA: stimulation by cations and possible mechanism.

The retroviral genome consists of two identical RNA molecules joined close to their 5' ends by the dimer linkage structure. Recent findings indicated that retroviral RNA dimerization and encapsidation are probably related events during virion assembly. We studied the cation-induced dimerization of HIV-1 RNA and results indicate that all in vitro generated HIV-1 RNAs containing a 100 nucleotide domain downstream from the 5' splice site are able to dimerize. RNA dimerization depends on the concentration of RNA, mono- and multivalent cations, the size of the monovalent cation, temperature, and pH. Up to 75% of HIV-1 RNA is dimeric in the presence of spermidine. HIV-1 RNA dimer is fairly resistant to denaturing agents and unaffected by intercalating drugs. Antisense HIV-1 RNA does not dimerize but heterodimers can be formed between HIV-1 RNA and either MoMuLV or RSV RNA. Therefore retroviral RNA dimerization probably does not simply proceed through mechanisms involving Watson-Crick base-pairing. Neither adenine and cytosine protonation, nor quartets containing only guanines appear to determine the stability of the HIV-1 RNA dimer, while quartets involving both adenine(s) and guanine(s) could account for our results. A consensus sequence PuGGAPuA found in the putative dimerization-encapsidation region of all retroviral genomes examined may participate in the dimerization process.

Short and long-range forces involved in cation-induced aggregation of chromaffin granule membranes

The kinetics and equilibria of cation-induced aggregation of chromaffin granule (CG) membranes are analyzed. The following mechanistic observations are made 1. (1) Cation-induced dimerization of CG membranes is brought about by reducing the membrane surface potential and hence by reducing the electrostatic repulsion between membranes. This can be accomplished by either monovalent or divalent cations. 2. (2) The dimerization reaction is nearly diffusion-controlled. The activation energy of the process is low. 3. (3) The kinetics are analyzed in terms of an “encounter complex” model formulated for comparison with the delay times involved in Ca 2+ -triggered exocytotic release. The half time for aggregation of vesicles with distances of separation between 26 Å and 126 .Å is calculated to be on the order of 3 msec. 4. (4) The role of van der Waals attraction, electrostatic repulsion and dipolar repulsion is considered. Calculations show that dipolar repulsion of phosphatidyl choline polar head groups should outweigh van der Waals attraction for short distances of separation. 5. (5) Phospholipid vesicles prepared from CG membrane lipids also show cation-induced aggregation. However, the behavior is qualitatively and quantitatively dissimilar to that of the CG membrane. The rates of aggregation are two orders of magnitude slower. This is shown to be due to a negative entropy of activation resulting from the necessity of matching the surfaces of the vesicles. Vesicle approaches involving high energies (enthalpies) of activation are excluded.