Dinuclear calcium complex with weakly NH...O hydrogen-bonded sulfonate ligands

The novel intramolecularly NH...O hydrogen-bonded Ca(II)-aryl sulfonate complex, [Ca2(SO3-2-t-BuCONHC6H4)2(H2O)4]n(2-t-BuCONHC6H4SO3)2n (1), sulfonate anion, (HNEt3)(SO3-2-t-BuCONHC6H4) (2a), (PPh4)(SO3-2-t-BuCONHC6H4) (2b), (n-Bu4N)(SO3-2-t-BuCONHC6H4) (2c), and sulfonic acid, 2-t-BuCONHC6H4SO3H (3), were synthesized. The structures of 1, 2a, and 2b depict the presence of the formation of NH...O hydrogen bonds between the amide NH and S-O oxygen for a series of compounds as determined by IR and 1H NMR analyses both in the solid state and in the solution state. Thus, the NH...O hydrogen bonds with neutral amide groups are available for investigation of the electronic state of the O- anion. The combined data from the IR and 1H NMR spectra indicate that the sulfonic acid, sulfonate anion, and Ca(II) complex have a substantially weak intramolecular NH...O hydrogen bond between the SO3 oxygen and amide NH. In the detailed comparison with the intense NH...O hydrogen bonds for the carboxylate, weak NH...O hydrogen bonds for sulfonate is due to the strong conjugation of the SO3- group with the lower nucleophilicity.     

[Ru(phen)2(H2biim)](PF6)2配合物与阴离子的选择性作用

研究了[Ru(phen)₂(H₂biim)](PF₆)₂(1)与各种阴离子之间的选择性作用, 发现配合物1与Cl^-, Br^-, I^-, NO₃^-, HSO₄^-和H₂PO₄^-阴离子之间存在氢键作用. OAc^-阴离子与配合物1作用, 由于强的氢键作用使H₂biim上的一个H转移到OAc^-上, 使配合物1脱去一个质子, 形成{[Ru(phen)₂(H₂biim)](OAc)}结合体, 溶液颜色由黄色变为橙棕色. 由于F^-能形成非常稳定的HF₂^-, 配合物1逐步脱去2个质子, 溶液颜色由黄色变为紫色, 因此可作为裸眼检测阴离子的识别剂.     

{AsW9O33}-{Mo3S4} based polyoxometalates including a metal-metal bond with Pd or Ni. Synthesis, structure and studies in solution

Heterometallic cuboidal clusters [Mo(3)S(4)M(H(2)O)(9)Cl](3+) M = Pd or Ni react with the trivacant [AsW(9)O(33)](9-) anion to give tetramodular complexes [(H(2)AsW(9)O(33))(4){Mo(3)S(4)M(H(2)O)(5)}(2)](20-) (M = Pd for anion 2 and M = Ni for anion 3) in good yield. Both anions crystallized as single crystals of potassium salts to give K-2 and K-3 salts which have been characterized structurally by X-ray diffraction. Both compounds are isomorphous and the anions 2 and 3 are described as two dimeric moeties, associated by internal hydrogen bonds, electrostatic interactions involving four outer potassium ion and coordination bonds within a central {M(2)S(2)} unit containing a M-M metallic bond. Studies in solution reveal that the dimeric association is maintained in solution in the 2 × 10(-4)-2 × 10(-3) mol L(-1) range. Conversely, in the presence of exogeneous ligands, such as iodide or pyridine the UV-vis data are consistent with the dissociation of the anion 2 into monomer through a Pd-L coordination bond (L = I(-) or Py). Furthermore, (183)W NMR spectrum of 2 shows that molecular structure of 2 is retained in solution. Elemental analysis and IR are also supplied. Electrochemical behavior of 2 and 3 are given and compared with the Pd or Ni free parent anion. The CVs are dominated mainly by irreversible reduction or oxidation processes, where the peak potentials appear dependent upon the ionic charge of the complex. However, the CV of the Pd-containing anion (2) is consistent with the deposition of Pd metal at the electrode, which gives rise to an oxidation process into palladium oxide.     

Moderate and advanced intramolecular proton transfer in urea-anion hydrogen-bonded complexes

The study of the interactions of the three urea-based receptors AH, BH(+) and CH(2+) with a variety of anions, in MeCN, has made it possible to verify the current view that hydrogen bonding is frozen proton transfer from the donor (the urea N-H fragment in this case) to the acceptor (the anion X(-)). The poorly acidic, neutral receptor AH establishes two equivalent hydrogen bonds N-H···X(-), with all anions, including CH(3)COO(-) and F(-), in which moderate proton transfer from N-H to the anion takes place. The strongly acidic, dicationic receptor CH(2+) forms, with most anions, complexes in which two inequivalent hydrogen bonds are present: one involving moderate proton transfer (N-H···X(-)) and one in which advanced proton transfer has taken place, described as N(-)···H-X. The degree of proton advancement is directly related to the basic tendencies of the anion. The cationic receptor BH(+) of intermediate acidic properties only forms complexes with two inequivalent hydrogen bonds (moderate+advanced proton transfer) with CH(3)COO(-) and F(-), and complexes with two equivalent hydrogen bonds (moderate proton transfer) with all the other anions. Moreover, [B···HF] and [C···HF](+), on addition of a second F(-) ion, lose the bound HF molecule to give HF(2)(-). Release of CH(3)COOH, with the formation of [CH(3)COOH···CH(3)COO](-), also takes place with the [B···CH(3)COOH] complex in the presence of a large excess of anion.     

Hydrogen bond and residence dynamics of ion-water and water-water pairs in supercritical aqueous ionic solutions: dependence on ion size and density

We have carried out a series of molecular dynamics simulations to investigate the hydrogen bond and residence dynamics of X(-)-water (X=F, Cl, and I) and pairs in aqueous solutions at a temperature of 673 K. The calculations are done at six different water densities ranging from 1.0 to 0.15 g cm(-3). The hydrogen bonds are defined by using a set of configurational criteria with respect to the anion(oxygen)-oxygen and anion(oxygen)-hydrogen distances and the anion(oxygen)-oxygen-hydrogen angle for an anion(water)-water pair. The F(-)-water hydrogen bonds are found to have a longer lifetime than all other hydrogen bonds considered in the present study. The lifetime of Cl(-)-water hydrogen bonds is shorter than that of F(-)-water hydrogen bonds but longer than the lifetime of water-water hydrogen bonds. The lifetimes of I(-)-water and water-water hydrogen bonds are found to be very similar. Generally, the lifetimes of both anion-water and water-water hydrogen bonds are found to be significantly shorter than those found under ambient conditions. In addition to hydrogen bond lifetimes, we have also calculated the residence times and the orientational relaxation times of water molecules in ion(water) hydration shells and have discussed the correlations of these dynamical quantities with the observed dynamics of anion(water)-water hydrogen bonds as functions of the ion size and density of the supercritical solutions.     

Reductive PET cycloreversion of oxetanes: singlet multiplicity, regioselectivity, and detection of olefin radical anion

Cycloreversion of 2-(p-cyanophenyl)-4-methyl-3-phenyloxetane (1) is achieved using 1-methoxynaphthalene (2) as electron-transfer photosensitizer. The experimental results are consistent with the reaction taking place from the singlet excited state of the sensitizer. Ring splitting of the radical anion 1*- occurs with cleavage of O-C2 and C3-C4 bonds, leading to products (acetaldehyde and p-cyanostilbene) different from the reagents used in the Paterno-Büchi synthesis of 1. The olefin radical anion involved in the electron-transfer process has been detected by means of laser flash photolysis.     

The OH-anion acting as an acid

In the crystalline state, the OH- anion is shown to be capable of acting as a base or as an acid with respect to waters of crystallization to which it is linked by hydrogen bonds. We examined the OH- anion in three crystalline samples and studied its behavior using quantum mechanics. Four quantum mechanical approximations were employed (HF, B3LYP, SVWN, and MP2) to obtain the relative stability of isomers of the H3O2- molecule in the three crystals considered. In one crystal state (LICQIX), the H3O2- anion corresponds to a geometry in which OH- acts as an acid, but not so as a free molecule. The free anion H3O2- has two qualitatively different structures. In one structure, the hydrogen bond is long, while in the other structure, the hydrogen bond is shorter and the hydrogen atom lies at an equal distance between donor and acceptor oxygen atoms.     

Contribution of the intramolecular hydrogen bond to the shift of the pKa value and the oxidation potential of phenols and phenolate anions

Intramolecularly OHO[double bond, length as m-dash]C hydrogen bonded phenols, 2-HO-C6H2-3,5-(t-Bu)2-CONH-t-Bu (1-OH), 2-HO-C6H2-5-t-Bu-1,3-(CONH-t-Bu)2 (2-OH) and 2-HO-C6H2-3,5-(t-Bu)2-NHCO-t-Bu (4-OH), were synthesized and their phenolate anions were prepared as tetraethylammonium salts (-1O-(NEt4+), 2-O-(NEt4+) and 4-O-(NEt4+)) with intramolecular NHO(oxyanion) hydrogen bonds. 4-HO-C(6)H(2)-3,5-t-Bu(2)-CONH-t-Bu (3-OH) and its phenolate anion, 3-O-(NEt4+), were synthesized as non-hydrogen bonded references. The presence of intramolecular hydrogen bonds was established through the crystallographic analysis and/or (1)H NMR spectroscopic results. Intramolecular NHO(phenol) hydrogen bonds shift the pK(a) of the phenol to a more acidic value. The results of cyclic voltammetry show that the intramolecular OH...O=C hydrogen bond negatively shifts the oxidation potential of the phenol. In contrast, the intramolecular NHO(oxyanion) hydrogen bond positively shifts the oxidation potential of the phenolate anion, preventing oxidation. These contributions of the hydrogen bond to the pKa value and the oxidation potentials probably play an important role in the formation of a tyrosyl radical in photosystem II.     

Interaction of hydroxyapatite with sodium chondroitin sulfate and calcium chondroitin sulfate in an aqueous phase

The suspension pH at a given concentration of hydroxyapatite (HAP) decreased with the concentration of calcium chondroitin-6-sulfate (CaChs), whereas it increased with the concentration of sodium chondroitin-6-sulfate (Na2Chs). The former effect is due to the increase in the concentration of H+ by ion exchange between H+ on the surface of HAP and Ca2+ of CaChs, and the latter is due to the protonation of phosphate ion (Pi) released from the surface of HAP. The absorbed amount of chondroitin-6-sulfate anion (Chs) by HAP was higher with CaChs than with Na2Chs over the concentration range examined. The equilibrium concentration of Pi decreased with increasing concentration of added CaChs because the concentration of free Ca2+, which dissociates from CaChs, regulates the free concentration of Pi through the restriction of the solubility product of HAP (Ksp). In contrast, that in the presence of Na2Chs increased with increasing concentration of added Na2Chs owing to the anion exchange between Chs and Pi of the HAP surface. The total concentration of Ca2+, which was released from HAP into the solution phase, increased after passing through a minimum with increasing concentration of added Na2Chs. That is, the concentration of Ca2+ free from Chs decreased with an increase in the concentration of released Pi owing to the restriction of the solubility product, whereas that of Ca2+ bound by Chs increased with increasing concentration of added Na2Chs through the ion exchange of Na+ with Ca2+. It was confirmed by the dialysis method that the value of Ksp was almost constant around 10, although HAP dissolves incongruently in the presence of Na2Chs.     

Metallosupramolecular chemistry with bis(benzene-o-dithiolato) ligands

The bis(benzene-o-dithiol) ligands H(4)-1, H(4)-2, and H(4)-3 react with [Ti(OC(2)H(5))(4)] to give dinuclear triple-stranded helicates [Ti(2)L(3)](4)(-) (L = 1(4)(-), 2(4)(-), 3(4)(-)). NMR spectroscopic investigations revealed that the complex anions possess C(3) symmetry in solution. A crystal structure analysis for (PNP)(4)[Ti(2)(2)(3)] ((PNP)(4)[14]) confirmed the C(3) symmetry for the complex anion in the solid state. The complex anion in Li(PNP)(3)[Ti(2)(1)(3)] (Li(PNP)(3)[13]) does not exhibit C(3) symmetry in the solid state due to the formation of polymeric chains of lithium bridged complex anions. Complexes [13](4)(-) and [14](4)(-) were obtained as racemic mixtures of the Delta,Delta and Lambda,Lambda isomers. In contrast to that, complex (PNP)(4)[Ti(2)(3)(3)] ((PNP)(4)[15]) with the enantiomerically pure chiral ligand 3(4)(-) shows a strong Cotton effect in the CD spectrum, indicating that the chirality of the ligands leads to the formation of chiral metal centers. The o-phenylene diamine bridged bis(benzene-o-dithiol) ligand H(4)-4 reacts with Ti(4+) to give the dinuclear double-stranded complex Li(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] containing two bridging methoxy ligands between the metal centers. The crystal structure analysis and the (1)H NMR spectrum of (Ph(4)As)(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] ((Ph(4)As)(2)[(16]) reveal C(2) symmetry for the anion [Ti(2)(4)(2)(mu-OCH(3))(2)](2)(-). For a comparative study the dicatechol ligand H(4)-5, containing the same o-phenylene diamine bridging group as the bis(benzene-o-dithiol) ligands H(4)-4, was prepared and reacted with [TiO(acac)(2)] to give the dinuclear complex anion [Ti(2)(5)(2)(mu-OCH(3))(2)](2)(-). The molecular structure of (PNP)(2)[Ti(2)(5)(2)(mu-OCH(3))(2)] ((PNP)(2)[17]) contains a complex anion which is similar to [16](2)(-), with the exception that strong N-H...O hydrogen bonds are formed in complex anion [17](2)(-), while N-H...S hydrogen bonds are absent in complex anion [16](2)(-).     

Photophysical, electrochemical and anion sensing properties of Ru(II) bipyridine complexes with 2,2'-biimidazole-like ligand

A new anion sensor [Ru(bpy)(2)(DMBbimH(2))](PF(6))(2) (3) (bpy is 2, 2'-bipyridine and DMBbimH(2) is 7,7'-dimethyl-2,2'-bibenzimidazole) has been developed. Its photophysical, electrochemical and anion sensing properties are compared with two previously investigated systems, [Ru(bpy)(2)(BiimH(2))](PF(6))(2) (1) and [Ru(bpy)(2)(BbimH(2))](PF(6))(2) (2) (BiimH(2) is 2,2'-biimidazole and BbimH(2) is 2,2'-bibenzimidazole). The high acidity of the N-H fragments in these complexes make them easy to be deprotonated by strong basic anions such as F(-) and OAc(-), and they form N-H···X hydrogen bonds with weak basic anions like Cl(-), Br(-), I(-), NO(3)(-), and HSO(4)(-). Complex 3 displays strong hydrogen bonding with these 5 weak basic anions, with binding constants between 17,000 and 21,000, which are larger than those observed in complex 1, with binding constants between 3300 and 5700, and in complex 2, which shows no hydrogen bonding toward Cl(-), Br(-), I(-), and NO(3)(-), and forms considerable hydrogen bonds with HSO(4)(-) with a binding constant of 11,209. These hydrogen bonding behaviours give different NMR, emission and electrochemical responses. The different anion binding affinity of these complexes may be mainly attributed to their different pK(a1) values, 7.2 for 1, 5.7 for 2, and 6.2 for 3. The additional methyl groups at the 7 and 7' positions of complex 3 may also play an important role in the enhancement of anion binding strength.     

Structures and energetics of hydrated oxygen anion clusters

Hydration of the atomic oxygen radical anion is studied with computational electronic structure methods, considering (O(-))(H(2)O)(n) clusters and related proton-transferred (OH(-))(OH)(H(2)O)(n)(-)(1) clusters having n = 1-5. A total of 67 distinct local-minimum structures having various interesting hydrogen bonding motifs are obtained and analyzed. On the basis of the most stable form of each type, (O(-))(H(2)O)(n)) clusters are energetically favored, although for n > or = 3, there is considerable overlap in energy between other members of the (O(-))(H(2)O)(n) family and various members of the (OH(-))(OH)(H(2)O)(n)(-)(1) family. In the lower-energy (O(-))(H(2)O)(n) clusters, the hydrogen bonding arrangement about the oxygen anion center tends to be planar, leaving the oxygen anion p-like orbital containing the unpaired electron uninvolved in hydrogen bonding with any water molecule. In (OH(-))(OH)(H(2)O)(n)(-)(1) clusters, on the other hand, nonplanar arrangements are the rule about the anionic oxygen center that accepts hydrogen bonds. No instances are found of OH(-) acting as a hydrogen bond donor. Those OH bonds that form hydrogen bonds to an anionic O(-) or OH(-) center are significantly stretched from their equilibrium value in isolated water or hydroxyl. A quantitative inverse correlation is established for all hydrogen bonds between the amount of the OH bond stretch and the distance to the other oxygen involved in the hydrogen bond.     

Gas-phase carbene radical anions: new mechanistic insights

The gas-phase reactivity of the CHCl*- anion has been investigated with a series of halomethanes (CCl4, CHCl3, CH2Cl2, and CH3Cl) using a FA-SIFT instrument. Results show that this anion primarily reacts via substitution and by proton transfer. In addition, the reactions of CHCl*- with CHCl3 and CH2Cl2 form minor amounts of Cl2*- and Cl-. The isotopic distribution of these two products is consistent with an insertion-elimination mechanism, where the anion inserts into a C-Cl bond to form an unstable intermediate, which eliminates either Cl2*- or Cl- and Cl*. Neutral and cationic carbenes are known to insert into single bonds; however, this is the first observation of such reactivity for carbene anions.     

Ruthenium(II) 2,2'-bibenzimidazole complex as a second-sphere receptor for anions interaction and colorimeter

A ruthenium(II) complex [Ru(bpy) 2(H 2bbim)](PF 6) 2 ( 1) as anions receptor has been exploited, where Ru(II)-bpy moiety acts as a chromophore and the H 2bbim ligand as an anion binding site. A systematic study suggests that 1 interacts with the Cl (-), Br (-), I (-), NO 3 (-), HSO 4 (-), and H 2PO 4 (-) anions via the formation of hydrogen bonds. Whereas 1 undergoes a stepwise process with the addition of F (-) and OAc (-) anions: formation of the monodeprotonated complex [Ru(bpy) 2(Hbbim)] with a low anion concentration, followed by the double-deprotonated complex [Ru(bpy) 2(bbim)], in the presence of a high anion concentration. These stepwise processes concomitant with the changes of vivid colors from yellow to orange brown and then to violet can be used for probing the F (-) and OAc (-) anions by naked eye. The deprotonation processes are not only determined by the basicity of the anion but also related to the strength of hydrogen bonding, as well as the stability of the formed compounds. Moreover, a double-deprotonated complex [Ru(bpy) 2(bbim)].CH 3OH.H 2O ( 3) has been synthesized, and the structural changes induced by the deprotonation has also been investigated. In addition, complexes [Ru(bpy) 2(Hbbim)] 2(HOAc) 3Cl 2.12H 2O ( 2), [Ru(bpy) 2(Hbbim)](HCCl 3CO 2)(CCl 3CO 2).2H 2O ( 4), and [Ru(bpy) 2(H 2bbim)](CF 3CO 2) 2.4H 2O ( 5) have been synthesized to observe the second sphere coordination between the Ru(II)-H 2bbim moiety and carboxylate groups via hydrogen bonds in the solid state.     

Conformational analysis of 3-(trimethylsilyl)propionic acid by NMR spectroscopy: an unusual expression of the beta-silyl effect

The rotational freedom of the carbon-carbon single bonds of 1,2-disubstituted ethanes affords the possibility of these compounds existing as a rapidly interconverting mixture of conformers in solution. The conformational preferences of one such compound, 3-(trimethylsilyl)propionic acid, and its anion were studied in water, dimethyl sulfoxide, methanol, ethanol, isopropyl alcohol, tert-butyl alcohol, tetrahydrofuran, and toluene with 1H NMR spectroscopy. The conformational preferences were determined from the vicinal proton-proton coupling constants between the hydrogen nuclei of the CH(2)CH(2) group with the aid of the Altona equations to derive the equilibrium anti and gauche percentages of rotamers from the averaged NMR-time scale couplings. Conformational analyses of 4,4-dimethylpentanoic acid and its anion as well as 2-(trimethylsilyl)ethanesulfonate anion were also conducted to compare the relative structural influences on the conformational preferences of silicon and carbon.     

Synthesis and characterization of the face-sharing bioctahedral [Mo2O6F3]3- anion

The face-sharing bioctahedral molybdenum(VI) oxide fluoride anion [Mo2O6F3]3- has been isolated in the new compound [Cu(3-apy)4]3(Mo2O6F3)2 (3-apy = 3-aminopyridine) and has been characterized by experimental and computational techniques. Single-crystal X-ray diffraction studies show that the structure of the [Mo2O6F3]3- anion resembles two distorted face-sharing octahedra, each with three short terminal metal-ligand bonds and three long metal-ligand-metal bridging interactions. Aspects of the electronic structure, as well as geometric comparisons of the bond lengths and angles in [Mo2O6F3]3- with those in the similarly distorted [MoO3F3]3- anion, suggest that the six terminal ligand positions of the confacial bioctahedra are occupied exclusively by oxide ligands and that the three bridging sites are occupied by fluorides. Crystal data for [Cu(3-apy)4]3(Mo2O6F3)2: trigonal space group R3 (No. 148) with hexagonal axes of a = 13.881(1) A and c = 31.783(3) A (Z = 3).     

Study on Infrared Spectra and Chemical Bonding of the Cluster Anion ［Cl_2FeS_2MoS_2Cu（PPh_3）_2］~－

ＳｔｕｄｙｏｎＩｎｆｒａｒｅｄＳｐｅｃｔｒａａｎｄＣｈｅｍｉｃａｌＢｏｎｄｉｎｇｏｆｔｈｅＣｌｕｓｔｅｒＡｎｉｏｎ［Ｃｌ_２ＦｅＳ_２ＭｏＳ_２Ｃｕ（ＰＰｈ_３）_２］~－ＫｏｎｇＸｉａｎ－Ｌｉｎｇ；ＣｈｅｎＺｈｉ－Ｄａ；ＳｈｅｎｇＴｉａｎ－Ｌｕ；ＷｕＸｉ...     

A variety of spin-crossover behaviors depending on the counter anion: two-dimensional complexes constructed by NH...Cl- hydrogen bonds, [FeIIH3LMe]Cl.X (X = PF6 -, AsF6 -, SbF6 -, CF3SO3 -; H3L(Me) = Tris[2-{[(2-methylimidazol-4-yl)methylidene]amino}ethyl]amine)

A family of spin-crossover (SC) complexes, [Fe(II)H(3)L(Me)]Cl.X (X(-) = PF(6) (-), AsF(6) (-), SbF(6) (-), CF(3)SO(3) (-)), 1-4, has been synthesized, in which H(3)L(Me) denotes the hexadentate N(6) tripod-like ligand tris[2-{[(2-methylimidazol-4-yl)methylidene]amino}ethyl]amine, containing three imidazole groups, with a view to establishing the effect of the counter anion on the SC behavior. These complexes have been found to crystallize in the same monoclinic crystal system with similar cell dimensions. The general crystal structure consists of a two-dimensional (2D) extended network constructed by NH...Cl- hydrogen bonds between Cl- and the imidazole NH groups of three neighboring [Fe(II)H(3)L(Me)]2+ ions, while the anion X exists as an isolated counter anion and occupies the space between the 2D sheets. Magnetic susceptibilities and M?ssbauer spectra have revealed a variety of SC behaviors depending on the counter anion, including a one-step HS<==>(HS + LS)/2 (1, X = PF(6) (-)), a two-step HS<==>(HS + LS)/2<==>LS with a slow thermal relaxation (2, X = AsF(6) (-)), a gradual one-step HS<==>LS (3, X = SbF(6) (-)), and a steep one-step HS<==>LS with hysteresis (4, X = CF(3)SO(3) (-)). The complexes assume the space group P2(1)/n in the HS state, P2(1) in the HS + LS state, and P2(1)/n in the LS state. The Fe-N bond lengths and the N-Fe-N bond angles are indicative of the HS, HS + LS, and LS states. The molecular volumes, V, of the counter anions have been evaluated by quantum-chemical calculations as follows: 53.4 A(3) (BF(4) (-)), 54.4 A(3) (ClO(4) (-)), 73.0 A(3) (PF(6) (-)), 78.5 A(3) (AsF(6) (-)), 88.7 A(3) (SbF(6) (-)), and 86.9 A(3) (CF(3)SO(3) (-)). The size and shape of the counter anion affects the flexible 2D network structure constructed by the hydrogen bonds, leading to modifications of the SC behavior. These estimated relative sizes of the counter anions correlate well with the observed SC behaviors.     

Elucidation of adsorption mechanism of bone-staining agent alizarin red S on hydroxyapatite by FT-IR microspectroscopy

To elucidate adsorption mechanism of alizarin red S (ARS), which is often used for staining bones in histology, adsorption of ARS on hydroxyapatite, Ca10(PO4)6(OH)2 (HAP), was investigated by a batch method, compared with alizarin, phenols, and benzenesulfonates. We found that ionized 1-, 2-OH groups (1-, 2-O(-)) of ARS can be electrostatically bound to Ca2+ on HAP, but that the 3-SO3(-) group of ARS hardly participates in adsorption on HAP. ARS-adsorbed HAP (ARS-HAP) in dark reddish violet was also prepared and analyzed by FT-IR microspectroscopy to gain structural information on bonding between ARS and HAP. The obtained spectrum, which was converted to difference spectra, indicated a single band of nu(C=O) at 1627 cm(-1) and two types of symmetric C=O stretching bands of nu(s)(C=O) + nu(C=C) at 1345 cm(-1) and nu(s)(C=O) + delta(O-C=C) at 1272 cm(-1). These bands imply the existence of a salt form in ARS-HAP via 1-, 2-OH groups of ARS. As a result of the existence of a chelate form in ARS-HAP via 1-OH and 9-C=O groups of ARS, two bands of nu(C=C) + nu(C=O) at 1572 cm(-1) and nu(C=O) + nu(C=C) at 1537 cm(-1) were also observed. In addition, ARS was almost desorbed from colored ARS-HAP at 50 degrees C by using neutral phosphate buffer to recover slightly pale pinkish HAP, or De-ARS-HAP. The desorbed ARS belongs to ARS previously adsorbed on HAP by salt formation, while the remaining color on De-ARS-HAP indicates ARS still adsorbed on HAP by chelate formation. Consequently, we elucidated two adsorption mechanisms of ARS on HAP: The major adsorption is salt formation made up with 1-, 2-O(-) of ARS and Ca2+ on HAP, and the minor adsorption is chelate formation made up with 1-O(-) and 9-C=O of ARS and Ca2+ on HAP.     

Dimers of heptapnictide anions: As14 4- and P14 4- in the crystal structures of [Rb(18-crown-6)]4As14.6NH3 and [Li(NH3)4]4P14.NH3

Compounds [Rb(18-crown-6)]4As14.6NH3 (1) and [Li(NH3)4]4P14.NH3 (2) were prepared by the reaction of Rb4As6 with SbPh3 and 18-crown-6 and by the reduction of white phosphorus with elemental lithium in liquid ammonia, respectively. Both were characterized by low-temperature single-crystal X-ray structure analysis. They were found to contain the Ci symmetrical Pn14(4-) anion (Pn = P, As), which consists of two nortricyclane-like Pn7-cages connected by a single bond. Molecular complexes of [Rb(18-crown-6)(NH3)]2[Rb(18-crown-6)]2As14 are formed in 1, which are connected to fanfold sheets via N-H...O bonds. The anion is isolated in 2, and N-H...N bonds result in the formation of {[Li(NH3)4](mu-NH3)2[Li(NH3)4]}2+ cationic complexes.