Oxygen Promoted On-Surface Synthesis of Polyboroxine Molecules.

We present our findings on the on-surface synthesis of polyboroxine molecules derived from boroxine molecules precursors. This process is promoted by oxygen species present on the Au(111) surface: oxygen atoms facilitate the detachment of naphthalene units of trinaphthyl-boroxine molecules and bridge two unsaturated boroxine centers to form a boroxine-O-boroxine chemical motif. X-ray spectroscopic characterization shows that, as the synthesis process proceeds, it progressively tunes the electronic properties of the interface, thus providing a promising route to control the electron level alignment. .

[Gd(HB-DO3A)]: Equilibrium, Dissociation Kinetic and Structural Differences in a Simple Homolog of [Gd(HP-DO3A)] (Prohance®).

[Gd(HP-DO3A)] (gadoteridol) as an active compound of ProHance® is a widely employed contrast agent in clinical MRI scans in the last 30 years. Recent concerns about the long-term retention of gadolinium-based contrast agents (GBCAs) led to a deeper investigation of the structural features underlying the integrity of the paramagnetic metal complex. Several human and nonclinical studies have noted marked differences among the macrocyclic GBCAs, with the least retention of Gd traces and most rapid elimination consistently being reported for [Gd(HP-DO3A)]. It was deemed of interest to assess how minor structural/electronic changes associated to the ligand structure may affect basic properties of the metal complex with several [Gd(HP-DO3A)] analogues synthesized and characterized in the last years. We recently reported that the closest homolog of [Gd(HP-DO3A)], i. e.: [Gd(HB-DO3A)], in which a (±)-2-hydroxy-1-propyl pendant arm is replaced by a (±)-2-hydroxy-1-butyl moiety, showed a significantly different retention behaviour in the model interaction with collagen, despite the apparently very minor structural difference. In this paper we report a comprehensive study of the structural, thermodynamic, kinetic and relaxation properties of [Gd(HB-DO3A)], compared to the parent [Gd(HP-DO3A)] and to other closely related macrocyclic GBCAs to assess whether very minor structural changes can modulate the physico-chemical properties of Gd3+ complexes.

Modulating the Shape of Short Metal-Mediated Heteroleptic Tapes of Porphyrins.

In view of developing artificial light-responsive complex systems, the preparation of discrete and robust heteroleptic assemblies of different chromophores in precisely defined positions is of great value since they would allow to investigate directional processes unavailable in symmetrical architectures. Here we describe the preparation, through a modular stepwise approach, and characterization of four novel and robust metal-mediated heteroleptic 4+3 porphyrin tapes, labeled D4 -T4 -D4 , D3 -T4 -D3 , D4 -T3 -D4 , and D3 -T3 -D3 , where a central meso-tetrapyridylporphyrin (either 3'-TPyP=T3 or 4'-TPyP=T4 ) is connected to two equal cis-dipyridylporphyrins (either 3'cisDPyMP=D3 or 4'cisDPyMP=D4 ) through four {t,c,c-RuCl2 (CO)2 } fragments. Whereas D4 -T4 -D4 is flat, the tapes containing at least one 3'PyP, i. e. D3 -T4 -D3 , D4 -T3 -D4 , and D3 -T3 -D3 , have unprecedented - and well defined - 3D geometries, and each exists in solution as a pair of stereoisomers in slow conformational equilibrium. The X-ray molecular structures of two such conformers, the C-shaped (D3 -T4 -D3 )C and the z-shaped (D4 -T3 -D4 )z , were determined and are fully consistent with the solution NMR findings.

Computational NEXAFS Characterization of Molecular Model Systems for 2D Boroxine Frameworks.

The electronic properties of 2D boroxine networks are computationally investigated by simulating the NEXAFS spectra of a series of molecular models, with or without morphologic defects, with respect to the ideal honeycomb structure. The models represent portions of an irregular 2D boroxine framework obtained experimentally, as supported by the Au(111) surface. The B K-edge NEXAFS spectra are calculated within the transition potential (TP) approximation (DFT-TP). The role of the Au(111) supporting surface on the spectral features has also been investigated by comparing the calculated spectra of a defect-rich model in its free-standing and supported form. The calculated NEXAFS spectra differ from the experimental ones, as the position of the main resonance does not match in the two cases. This finding could suggest the presence of a strong interaction of the 2D boroxine network with the Au substrate, which is not captured in the model calculations. However, good agreement between measured and calculated B K-edge NEXAFS spectra is obtained for a model system, namely, trihydroxy boroxine, in which the B atoms are less screened by the valence electrons compared to the B-B linked boroxine network models considered here. These results suggest catalytic activity in the gold substrate in promoting a weakening or even the breaking of the B-B bond, which is not revealed by calculations.

A Flexible Synthetic Strategy for the Preparation of Heteroleptic Metallacycles of Porphyrins.

We present a stepwise synthetic strategy for the preparation of the unprecedented heteroleptic 2+2 neutral metallacycle [{t,c,c-RuCl2(CO)2}2(4'cisDPyP)(3'cisDPyP)] (5), in which two different 5,10-meso-dipyridylporphyrins, 4'cisDPyP [i.e., 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin] and 3'cisDPyP [i.e., 5,10-bis(3'-pyridyl)-15,20-diphenylporphyrin], are joined through equal 90°-angular Ru(II) connectors. The synthesis of 5 was accomplished through the preparation of a reactive ditopic intermediate in which one of the two pyridylporphyrins is linked to two neutral ruthenium fragments, each having one residual readily available coordination site (a dmso-O). Thus, compound 5 was obtained under mild conditions through two complementary routes: either by treatment of [{t,c,c-RuCl2(CO)2(dmso-O)}2(4'cisDPyP)] (3) with 1 equiv of 3'cisDPyP or, alternatively, by treatment of [{t,c,c-RuCl2(CO)2(dmso-O)}2(3'cisDPyP)] (4) with 1 equiv of 4'cisDPyP. Heteroleptic metallacycle 5 was isolated in pure form in acceptable yield and fully characterized. Spectroscopic data and a molecular model show that 5 has an L-shaped geometry, with the two porphyrins almost orthogonal to one another. The modular approach that we established is highly flexible and opens the way to several possible exciting developments.

cis-Locked Ru(II)-DMSO Precursors for the Microwave-Assisted Synthesis of Bis-Heteroleptic Polypyridyl Compounds.

We describe a synthetic strategy for the preparation of bis-heteroleptic polypyridyl Ru(II) complexes of the type [Ru(L1)2(L2)]2+ (L1 and L2 = diimine ligands) from well-defined Ru(II) precursors. For this purpose, a series of six neutral, anionic, and cationic cis-locked Ru(II)-DMSO complexes (2-7) of the general formula [Y] fac-[RuX(DMSO-S)3(O-O)]n (where O-O is a symmetrical chelating anion: oxalate (ox), malonate (mal), acetylacetonate (acac); X = DMSO-O or Cl-; n = -1/0/+1 depending on the nature and charge of X and O-O; when present, Y = K+ or PF6-) were efficiently prepared from the well-known cis-[RuCl2(DMSO)4] (1). When treated with diimine chelating ligands (L1 = bpy, phen, dpphen), the compounds 2-7 afforded the target [Ru(L1)2(O-O)]0/+ complex together with the undesired (and unexpected) [Ru(L1)3]2+ species. Nevertheless, we found that the formation of [Ru(L1)3]2+can be minimized by carefully adjusting the reaction conditions: in particular, high selectivity toward [Ru(L1)2(O-O)]0/+ and almost complete conversion of the precursor was obtained within minutes, also on a 100-200 mg scale, when the reactions were performed in absolute ethanol at 150 °C in a microwave reactor. Depending on the nature of L1 and concentration, with the oxalate and malonate precursors, the neutral product [Ru(L1)2(O-O)] can precipitate spontaneously from the final mixture, in pure form and acceptable-to-good yields. When spontaneous precipitation of the disubstituted product does not occur, purification from [Ru(L1)3]2+ can be rather easily accomplished by column chromatography or solvent extraction. By comparison, under the same conditions, compound 1 is much less selective, thus demonstrating that locking the geometry of the precursor through the introduction of O-O in the coordination sphere of Ru is a valid strategic approach. By virtue of its proton-sensitive nature, facile and quantitative replacement of O-O in [Ru(L1)2(O-O)]0/+ by L2, selectively affording [Ru(L1)2(L2)]2+, was accomplished in refluxing ethanol in the presence of a slight excess of trifluoroacetic acid or HPF6.

Ruthenium(II) 1,4,7-trithiacyclononane complexes of curcumin and bisdemethoxycurcumin: Synthesis, characterization, and biological activity.

Two cationic ruthenium(II) 1,4,7-trithiacyclononane ([9]aneS3) complexes of curcumin (curcH) and bisdemethoxycurcumin (bdcurcH), namely [Ru(curc)(dmso-S)([9]aneS3)]Cl (1) and [Ru(bdcurc)(dmso-S)([9]aneS3)]Cl (2) were prepared from the [RuCl2(dmso-S)([9]-aneS3)] precursor and structurally characterized, both in solution and in the solid state by X-ray crystallography. The corresponding PTA complexes [Ru(curc)(PTA)([9]aneS3)]Cl (3) and [Ru(bdcurc)(PTA)([9]aneS3)]Cl (4) have been also synthesized and characterized (PTA = 1,3,5-triaza-7-phosphaadamantane). Bioinorganic studies relying on mass spectrometry were performed on complexes 1-4 to assess their interactions with the model protein lysozyme. Overall, a rather limited reactivity with lysozyme was highlighted accompanied by a modest cytotoxic potency against three representative cancer cell lines. The moderate pharmacological activity is likely connected to the relatively high stability of these complexes.

Orthogonal Coordination Chemistry of PTA toward Ru(II) and Zn(II) (PTA = 1,3,5-Triaza-7-phosphaadamantane) for the Construction of 1D and 2D Metal-Mediated Porphyrin Networks.

This work demonstrates that PTA (1,3,5-triaza-7-phosphaadamantane) behaves as an orthogonal ligand between Ru(II) and Zn(II), since it selectively binds through the P atom to ruthenium and through one or more of the N atoms to zinc. This property of PTA was exploited for preparing the two monomeric porphyrin adducts with axially bound PTA, [Ru(TPP)(PTA-κP)2] (1, TPP = meso-tetraphenylporphyrin) and [Zn(TPP)(PTA-κN)] (3). Next, we prepared a number of heterobimetallic Ru/Zn porphyrin polymeric networks-and two discrete molecular systems-mediated by P,N-bridging PTA in which either both metals reside inside a porphyrin core, or one metal belongs to a porphyrin, either Ru(TPP) or Zn(TPP), and the other to a complex or salt of the complementary metal (i.e., cis,cis,trans-[RuCl2(CO)2(PTA-κP)2] (5), trans-[RuCl2(PTA-κP)4] (7), Zn(CH3COO)2, and ZnCl2). The molecular compounds 1, 3, trans-[{RuCl2(PTA-κ2P,N)4}{Zn(TPP)}4] (8), and [{Ru(TPP)(PTA-κP)(PTA-κ2P,N)}{ZnCl2(OH2)}] (11), as well as the polymeric species [{Ru(TPP)(PTA-κ2P,N)2}{Zn(TPP)}]∞ (4), cis,cis,trans-[{RuCl2(CO)2(PTA-κ2P,N)2}{Zn(TPP)}]∞ (6), trans-[{RuCl2(PTA-κ2P,N)4}{Zn(TPP)}2]∞ (9), and [{Ru(TPP)(PTA-κ3P,2N)2}{Zn9(CH3COO)16(CH3OH)2(OH)2}]∞ (10), were structurally characterized by single crystal X-ray diffraction. Compounds 4, 6, 9, and 10 are the first examples of solid-state porphyrin networks mediated by PTA. In 4, 6, 8, 9, and 11 the bridging PTA has the κ2P,N binding mode, whereas in the 2D polymeric layers of 10 it has the triple-bridging mode κ3P,2N. The large number of compounds with the six-coordinate Zn(TPP) (the three polymeric networks of 4, 6 and 9, out of five compounds) strongly suggests that the stereoelectronic features of PTA are particularly well-suited for this relatively rare type of coordination. Interestingly, the similar 1D polymeric chains 4 and 6 have different shapes (zigzag in 4 vs "Greek frame" in 6) because the {trans-Ru(PTA-κ2P,N)2} fragment bridges two Zn(TPP) units with anti geometry in 4 and with syn geometry in 6. Orthogonal "Greek frame" 1D chains make the polymeric network of 9. Having firmly established the binding preferences of PTA toward Ru(II) and Zn(II), we are confident that in the future a variety of Ru/Zn solid-state networks can be produced by changing the nature of the partners. In particular, there are several inert Ru(II) compounds that feature two or more P-bonded PTA ligands that might be exploited as connectors of well-defined geometry for the rational design of solid-state networks with Zn-porphyrins (or other Zn compounds).

Investigating the reactivity of neutral water-soluble Ru(ii)-PTA carbonyls towards the model imine ligands pyridine and 2,2'-bipyridine.

As a continuation of our strategy for preparing new Ru(ii) precursors to be exploited as building blocks in the construction of metal-mediated supramolecular assemblies with improved solubility in water, here we describe the reactivity of selected neutral Ru(ii)-PTA carbonyls (PTA = 1,3,5-triaza-7-phosphaadamantane) towards the model imine ligands pyridine (py) and 2,2'-bipyridine (bpy) and the preparation and characterization of several neutral and cationic water-soluble derivatives: trans,trans,trans-[RuCl2(CO)(py)(PTA)2] (7), cis,cis,trans-[RuCl2(CO)2(py)(PTA)] (9), cis,trans-[Ru(bpy)Cl(CO)(PTA)2]Cl (10), mer-[Ru(bpy)(CO)(PTA)3](Cl)2 (12), cis,trans-[Ru(bpy)(CO)2Cl(PTA)]Cl (13), cis,trans-[Ru(bpy)(CO)2(PTA)2](NO3)2 (14NO3). In addition, we found that light-induced isomerization in some bpy compounds could be induced. The following species, either side-products isolated in low yield or compounds obtained exclusively in solution, were also unambiguously identified: cis,cis,trans-[RuCl2(CO)(py)(PTA)2] (8), trans-[RuCl2(bpy)(CO)(PTA)] (11), cis,cis-[Ru(bpy)Cl(CO)(PTA)2]Cl (15) and cis,cis-[Ru(bpy)(CO)2Cl(PTA)]Cl (16). The X-ray structures of 7, 11·H2O, and 12·7H2O are also reported. All compounds are new and - with few exceptions - show a good solubility in water.

Rare Example of Stereoisomeric 2 + 2 Metallacycles of Porphyrins Featuring Chiral-at-Metal Octahedral Ruthenium Corners.

In this paper, we describe three new stereoisomers of the already known 2 + 2 metallacycle of porphyrins [ trans, cis, cis-RuCl2(CO)2(4' cisDPyP)]2 (2, 4' cisDPyP = 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin), namely [{ trans,cis,cis-RuCl2(CO)2}(4' cisDPyP)2{ cis,cis,cis-RuCl2(CO)2}] (14) and [ cis,cis,cis-RuCl2(CO)2(4' cisDPyP)]2 (15), in which the chiral { cis,cis,cis-RuCl2(CO)2} fragment has either a C or A handedness. The least abundant 15 exists as a mixture of two stereoisomers defined as alternate (15alt, both porphyrins are trans to a Cl and a CO) and pairwise (15pw, one porphyrin is trans to two chlorides and the other to two carbonyls), each one as a statistical mixture of meso ( AC) and racemic ( AA and CC) diastereomers. Remarkably, both 14 and 15 are-to the best of our knowledge-unprecedented examples of 2D metallacycles with octahedral chiral-at-metal connectors, and 14 is the first example of a 2 + 2 molecular square with stereoisomeric Ru(II) corners. Whereas 2 is selectively obtained by treatment of trans,cis,cis-RuCl2(CO)2(dmso-O)2 (1) with 4' cisDPyP, 14 and 15 were obtained, together with 2 (major product), using stereoisomers of 1, either cis,cis,trans-RuCl2(CO)2(dmso-S)2 (5) or cis,cis,cis-RuCl2(CO)2(dmso)2 (6), as precursors. From a general point of view, this work demonstrates that-even for the smallest 2 + 2 metallacycle and using a symmetric organic linker-several stereoisomers can be generated when using octahedral metal connectors of the type {MA2B2} that are not stereochemically rigid. As a proof-of-concept, it also opens the way to new-even though challenging-opportunities: unprecedented and yet unexplored chiral metallosupramolecular assemblies can be obtained and eventually exploited (e.g., for supramolecular catalysis) by using stereogenic octahedral metal connectors amenable to become chiral centers.

Ru(ii)-Peptide bioconjugates with the cppH linker (cppH = 2-(2'-pyridyl)pyrimidine-4-carboxylic acid): synthesis, structural characterization, and different stereochemical features between organic and aqueous solvents.

Three new Ru(ii) bioconjugates with the C-terminal hexapeptide sequence of neurotensin, RRPYIL, namely trans,cis-RuCl2(CO)2(cppH-RRPYIL-κNp) (7), [Ru([9]aneS3)(cppH-RRPYIL-κNp)(PTA)](Cl)2 (8), and [Ru([9]aneS3)Cl(cppH-RRPYIL-κNp)]Cl (11), where cppH is the asymmetric linker 2-(2'-pyridyl)pyrimidine-4-carboxylic acid, were prepared in pure form and structurally characterized in solution. The cppH linker is capable of forming stereoisomers (i.e. linkage isomers), depending on whether the nitrogen atom ortho (No) or para (Np) to the carboxylate on C4 in the pyrimidine ring binds the metal ion. Thus, one of the aims of this work was to obtain pairs of stereoisomeric conjugates and investigate their biological (anticancer, antibacterial) activity. A thorough NMR characterization clearly indicated that in all cases exclusively Np conjugates were obtained in pure form. In addition, the NMR studies showed that, whereas in DMSO-d6 each conjugate exists as a single species, in D2O two (7) or even three if not four (8 and 11) very similar stable species form (each one corresponding to an individual compound). Similar results were observed for the cppH-RRPYIL ligand alone. Overall, the NMR findings are consistent with the occurrence of a strong intramolecular stacking interaction between the phenol ring of tyrosine and the pyridyl ring of cppH. Such stacking interactions between aromatic rings are expected to be stronger in water. This interaction leads to two stereoisomeric species in the free cppH-RRPYIL ligand and in the bioconjugate 7, and is somehow modulated by the less symmetrical Ru coordination environments in 8 and 11, affording three to four very similar species.

Water-Soluble Ruthenium(II) Carbonyls with 1,3,5-Triaza-7-phosphoadamantane.

As a continuation of our strategy for preparing new Ru(II) precursors with improved water solubility through the introduction of highly water-soluble 1,3,5-triaza-7-phosphoadamantane (PTA) supporting ligands in the coordination sphere, in this work, we address the largely unexplored preparation of Ru(II)-PTA carbonyls. Two complementary synthetic approaches were used: (1) the treatment of a series of neutral Ru(II)-CO-dmso compounds of general formula RuCl2(CO) n(dmso)4- n ( n = 1-3, 1-5) with PTA; (2) the reaction of Ru(II)-PTA complexes with CO. Through the first approach, we obtained and fully characterized seven novel neutral compounds bearing from one to three PTA ligands per Ru atom, namely, the four monocarbonyls, cis, cis, trans-RuCl2(CO)(dmso-S)(PTA)2 (6), trans-RuCl2(CO)(PTA)3 (7), cis, mer-RuCl2(CO)(PTA)3 (8), and trans, trans, trans-RuCl2(CO)(OH2)(PTA)2 (10), and the three dicarbonyls, trans, trans, trans-RuCl2(CO)2(PTA)2 (11), [RuCl2(CO)2(PTA)]2 (12), and cis, cis, trans-RuCl2(CO)2(PTA)2 (13). The less stable, and thus more elusive, species fac-RuCl2(CO)(PTA)3 (9) and cis, cis, cis-RuCl2(CO)2(PTA)2 (14) were also unambiguously identified but could not be obtained in pure form and fully characterized. The complementary synthetic approach, that involved the treatment of the trans- and cis-RuCl2(PTA)4 (15, 16) isomers with CO, afforded only one new Ru(II)-PTA carbonyl, the cationic species cis-[RuCl(CO)(PTA)4]Cl (17). In general, the choice of the solvent was very relevant for obtaining the products with high yield and purity. We were unable to isolate Ru(II)-PTA compounds with more than two carbonyls. The thermodynamically preferred species have CO trans to Cl and two mutually trans PTAs, and only in the dinuclear compound 12 there is a single PTA per Ru atom. Compounds 7 and 17 feature the unprecedented trans-{Ru(CO)(PTA)} fragment. The X-ray structures of cis, cis, cis-RuCl2(CO)2(dmso)2 (3), 6-8, 10, 11, 13, and 17 are also reported. All compounds are new, are air-stable, and show a good solubility in water ( S from 10 to 165 g·L-1) and, most often, also in chloroform.

Electronic properties of the boroxine-gold interface: evidence of ultra-fast charge delocalization.

We performed a combined experimental and theoretical study of the assembly of phenylboronic acid on the Au(111) surface, which is found to lead to the formation of triphenylboroxines by spontaneous condensation of trimers of molecules. The interface between the boroxine group and the gold surface has been characterized in terms of its electronic properties, revealing the existence of an ultra-fast charge delocalization channel in the proximity of the oxygen atoms of the heterocyclic group. More specifically, the DFT calculations show the presence of an unoccupied electronic state localized on both the oxygen atoms of the adsorbed triphenylboroxine and the gold atoms of the topmost layer. By means of resonant Auger electron spectroscopy, we demonstrate that this interface state represents an ultra-fast charge delocalization channel. Boroxine groups are among the most widely adopted building blocks in the synthesis of covalent organic frameworks on surfaces. Our findings indicate that such systems, typically employed as templates for the growth of organic films, can also act as active interlayers that provide an efficient electronic transport channel bridging the inorganic substrate and organic overlayer.

(15)N NMR spectroscopy unambiguously establishes the coordination mode of the diimine linker 2-(2'-pyridyl)pyrimidine-4-carboxylic acid (cppH) in Ru(ii) complexes.

We investigated the reactivity of three Ru(ii) precursors -trans,cis,cis-[RuCl2(CO)2(dmso-O)2], cis,fac-[RuCl2(dmso-O)(dmso-S)3], and trans-[RuCl2(dmso-S)4] - towards the diimine linker 2-(2'-pyridyl)pyrimidine-4-carboxylic acid (cppH) or its parent compound 4-methyl-2-(2'-pyridyl)pyrimidine ligand (mpp), in which a methyl group replaces the carboxylic group on the pyrimidine ring. In principle, both cppH and mpp can originate linkage isomers, depending on how the pyrimidine ring binds to ruthenium through the nitrogen atom ortho (N(o)) or para (N(p)) to the group in position 4. The principal aim of this work was to establish a spectroscopic fingerprint for distinguishing the coordination mode of cppH/mpp also in the absence of an X-ray structural characterization. By virtue of the new complexes described here, together with the others previously reported by us, we successfully recorded {(1)H,(15)N}-HMBC NMR spectra at natural abundance of the (15)N isotope on a consistent number of fully characterized Ru(ii)-cppH/mpp compounds, most of them being stereoisomers and/or linkage isomers. Thus, we found that (15)N NMR chemical shifts unambiguously establish the binding mode of cppH and mpp - either through N(o) or N(p)- and can be conveniently applied also in the absence of the X-ray structure. In fact, coordination of cppH to Ru(ii) induces a marked upfield shift for the resonance of the N atoms directly bound to the metal, with coordination induced shifts (CIS) ranging from ca.-45 to -75 ppm, depending on the complex, whereas the unbound N atom resonates at a frequency similar to that of the free ligand. Similar results were found for the complexes of mpp. This work confirmed our previous finding that cppH has no binding preference, whereas mpp binds exclusively through N(p). Interestingly, the two cppH linkage isomers trans,cis-[RuCl2(CO)2(cppH-κN(p))] (5) and trans,cis-[RuCl2(CO)2(cppH-κN(o))] (6) were easily obtained in pure form by exploiting their different solubility properties.

New cationic and neutral Ru(II)- and Os(II)-dmso carbonyl compounds.

The preparation and structural characterization of three cationic Ru(II)-dmso carbonyls and of four neutral mono- and dicarbonyl Os(II)-dmso derivatives is reported. The two monocarbonyl species fac-[Ru(CO)(dmso-O)3(dmso-S)2][PF6]2 (11) and cis,cis,cis-[RuCl(CO)(dmso-O)2(dmso-S)2][PF6] (12) were obtained from the neutral monocarbonyl precursor cis,trans,cis-[RuCl2(CO)(dmso-O)(dmso-S)2] (3) upon stepwise replacement of the chlorides with dmso, that binds in each case through the oxygen atom. The dicarbonyl cationic complex cis,cis,trans-[Ru(CO)2(dmso-O)2(dmso-S)Cl][PF6] (13) was instead obtained upon treatment of the neutral tricarbonyl precursor fac-[RuCl2(CO)3(dmso-O)] (8) with AgPF6 in the presence of DMSO: replacement of a Cl(-) with a dmso-O implied also the substitution of one CO ligand by another dmso (that binds through S trans to Cl). The Os(II) carbonyls trans,trans,trans-[OsCl2(CO)(dmso-O)(dmso-S)2] (17), trans,cis,cis-[OsCl2(CO)2(dmso-O)2] (18), cis,mer-[OsCl2(CO)(dmso-S)3] (19), and cis,trans,cis-[OsCl2(CO)(dmso-O)(dmso-S)2] (20) were obtained by treatment of the Os(II)-dmso precursors trans-[OsCl2(dmso-S)4] (14) and cis,fac-[OsCl2(dmso-O)(dmso-S)3] (15) with CO. Each one of them is structurally similar to an already known Ru(II) analog, even though--in agreement with the expected greater inertness of Os(II)--more forcing reaction conditions were required for their preparation. Interestingly, compound 20 could not be isolated in pure form, but only as a 1:1 cocrystallized mixture with its precursor 15. The dmso ligand is always bound through the oxygen atom when trans to CO. We are confident that the new Ru(II)- and Os(II)-dmso carbonyl species described here represent a contribution to expand the pool of complexes bearing some easily replaceable dmso ligands to be used as well-behaved precursors in inorganic synthesis.

Determination of patulin in apple juice: comparative evaluation of four analytical methods.

The performance of 4 purification methods for the analysis of patulin in apple juice was evaluated by high-performance liquid chromatography (HPLC). Samples were spiked with patulin at 10, 20, 50, 100, and 150 ppb (ng/mL) and extracted by one of 4 methods (3 solid-phase extraction and one liquid-liquid extraction), and then analyzed by HPLC-UV under the same isocratic conditions. The methods were validated for recovery, linearity, and precision at high and low concentrations. Recoveries were all >70% for spiking range 10-150 ppb. The relative standard deviation for repeatability was found to meet European Union Directive requirements. In addition, all the methods showed baseline separation from hydroxymethylfurfural.

Interaction of hydrogen with cerium oxide surfaces: a quantum mechanical computational study.

The interaction of the (110) and (111) surfaces of ceria (CeO(2)) with atomic hydrogen is studied with ab initio calculations based on density functional theory. A Hubbard U term added to the standard density functional allows to accurately describe the electronic structure of the two surfaces. The minimum energy configuration for the adsorbed H on each of the two surfaces is obtained. An O-H-O bridge is formed on the (110) surface, whereas an axial tricoordinated OH group results on the (111) surface. For both surfaces, the adsorption of an H atom is accompanied by the reduction of a single Ce ion (which is one of the nearest neighbors of the adsorbed atom) and by a substantial outward protrusion of the O atom(s) directly bound to H. The adsorption of atomic H on the (110) and (111) surfaces is energetically favored by -150.8 and -128.3 kJ/mol, respectively, with respect to free molecular H(2). The calculated frequencies for the OH stretching vibrational mode are 3100 cm(-1) for the (110) surface and 3627 cm(-1) for the (111) surface. The latter value is in excellent agreement with experimental data reported in the literature.

Electronic and atomistic structures of clean and reduced ceria surfaces.

The atomistic and electronic structures of oxygen vacancies on the (111) and (110) surfaces of ceria are studied by means of periodic density functional calculations. The removal of a neutral surface oxygen atom leaves back two excess electrons that are shown to localize on two cerium ions neighboring the defect. The resulting change of valency of these Ce ions (Ce4+ --> Ce3+) originates from populating tightly bound Ce 4f states and is modeled by adding a Hubbard U term to the traditional energy functionals. The calculated atomistic and electronic structures of the defect-free and reduced surfaces are shown to agree with spectroscopic and microscopic measurements. The preferential defect segregation and the different chemical reactivity of the (111) and (110) surfaces are discussed in terms of energetics and features in the electronic structure.