Anzhela Galstyan

Periodic Mesoporous Organosilica-Based Nanocomposite Hydrogels as Three-Dimensional Scaffolds**

a class offunctional organic–inorganic hybrid silica particles on thenanometer-scale, are a new alternative material as porousmaterials for new NC hydrogel formation owing to its uniqueproperties,forexample,highorderedmesopores,highspecificsurface area, narrow pore-size distributions, and easy surfacefunctionalization.

Electrostatics Plus O–π Interactions Rather Than “Directed” Hydrogen Bonding Keep SO42− in a Triangular Pt3Pd3–Tris(2,2′‐bipyrazine) Host

Sulfate binding to host molecules in the solvent water represents a major challenge due to its strongly negative hydration energy of DGh 1100 kJ mol . The predominant strategy for capturing SO4 2 by synthetic hosts is therefore to take advantage of “directed” hydrogen bonds. After all, nature does the same in the sulfate-binding protein. The moderate basicity of SO4 2 (pKa of HSO4 is ca. 2) is of advantage in this respect and the propensity of SO4 2 to engage in multiple hydrogen-bonding interactions with its neighbors (e.g. up to 12 hydrogen bonds) have led to numerous approaches to construct sulfate receptors on this basis. Interest in sulfate-selective complexation comes, among others, from the need to remove the corrosion-inducing SO4 2 from nuclear waste. The use of sulfate as a templating agent in supramolecular chemistry relies on very similar principles as does the generation of receptors. A positive charge on the synthetic receptor, as achieved by protonation of receptor atoms, or metal coordination, can markedly improve SO4 2 binding. In fact, remarkably high association constants between 10 and 10 in water have been reported by us for flat, triangular, and square metal complexes containing three and four trans-{(NH3)2Pt } entities. Here we report on a rare case of sulfate encapsulation in the hydrophobic cavity of a triangular, vase-shaped host cation in water. The host is built up of three cis-{(NH3)2Pt } and three {(en)Pd} units (en=ethylenediamine) as well as three bridging 2,2’-bipyrazine (bpz) ligands. The host cis[{(NH3)2Pt(N4,N4’-bpz-N1,N1’)Pd(en)}3] 12+ (1) is an analogue of the complex containing {(en)Pt} instead of cis{(NH3)2Pt }, [{(en)Pt(N4,N4’-bpz-N1,N1’)Pd(en)}3] 12+ (2), which we have previously reported on. 11] A unique feature of the solid-state structure of [2]ACHTUNGTRENNUNG(NO3)4ACHTUNGTRENNUNG(PF6)8 was the capture of two different anions in the hydrophobic cavity of the vase, with the NO3 covering the floor of vase, and a PF6 anion sitting on top of it. Solution studies in D2O with the pure nitrate salt [2]ACHTUNGTRENNUNG[NO3]12 and alkali salts with different anions revealed moderately strong binding of SO4 2 (Kass = 256 57 m ), in contrast to weaker binding of the tetrahedral anions ClO4 and BF4 . Attempts to crystallize 2 as its SO4 2 salt and to understand the special behavior of sulfate binding to 2 had failed. With 1, obtained upon reaction of cis-[(NH3)2Pt ACHTUNGTRENNUNG(H2O)2]SO4 with bpz and [(en)PdACHTUNGTRENNUNG(H2O)2]SO4, and analyzing as [1] ACHTUNGTRENNUNG(SO4)6 · 24.5 H2O crystallization was now successful. The X-ray crystal structure of this compound reveals that one of the six SO4 2 ions is encapsulated in the vase, together with a water molecule (Figure 1). The sulfate anion in 2 is disordered over two positions, occupying two of the interior corners of the triangular vase. On both corners, an oxygen atom (O41/O51) from each disordered moiety is anchored to the electron-deficient region localized between the two upright pyrazine rings, thus stabilizing both sulfate positions. This feature was not previously observed with sulfate ions, but is more common with perchlorate. Anion–p interactions involving sulfate are scarce. The third corner of the vase is occupied by a water molecule (O1w) which, again, displays lone pair–p interactions. The lone electron pairs of O1w point towards the centroids of the rings in an evident tetrahedral disposition (O–centroids distance: 2.96 , 3.01 , angle: 108.58), as O41 and O51 do in the case of the sulfate anion. There is hydrogen bonding between the protons of the water molecule and the trapped disordered SO4 2 (O1w···O44/O53, ca 2.53 ), yet no hydrogen bonding between the cationic vase and the encapsulated guests. Distances between the oxygen atoms of SO4 2 and the closest H3 atoms (not C3!), are between 2.5 and 3.0 , yet the C-H3-O ACHTUNGTRENNUNG(SO3) angles are unfavorable for hydrogen bond formation. Within the crystal, pairs of centrosymmetrically arranged cations 1 are oriented in such a way as to produce a Ptcapped block consisting of twelve metal ions, six bpz ligands, [a] A. Galstyan, Dr. P. J. Sanz Miguel, Prof. Dr. B. Lippert Fakult t Chemie, Technische Universit t Dortmund 44221 Dortmund (Germany) Fax: (+49) 231-755-3797 E-mail : pablo.sanz@tu-dortmund.de bernhard.lippert@tu-dortmund.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000500.

Silicon(IV) Phthalocyanine-Decorated Cyclodextrin Vesicles as a Self-Assembled Phototherapeutic Agent against MRSA.

The host-guest complexation of a tailored Si(IV) phthalocyanine with supramolecular β-cyclodextrin vesicles (CDV) was studied, revealing a reduced aggregation of the photoactive center upon binding to the CDV, even in aqueous environments. For this purpose, a photosensitizing unit axially decorated with one adamantyl group and one pyridinium moiety on the other side was obtained by two successive click reactions on a bis-azido-functionalized derivative of Si(IV) phthalocyanine. To evaluate its potential as a photosensitizer against antibiotic-resistant bacteria, comparative studies of the photophysical properties including absorption and emission spectroscopy, lifetimes as well as fluorescence and singlet oxygen quantum yields were determined for the Si(IV) phthalocyanine alone and upon self-assembly on the CDV surface. In vitro phototoxicity against the methicillin-resistant Staphylococcus aureus (MRSA) USA300 was evaluated, showing an almost complete inactivation.

Sterically Hindered Luminescent PtII–Phosphite Complexes for Electroluminescent Devices

Pt(II) complexes with one bulky, sterically demanding, tertiary phosphite ancillary ligand and a coordinating chromophore are herein presented. The phosphite ligand, tris(2,4-di-tert-butylphenyl) acts as a bidentate ligand coordinating the platinum ion through the central phosphorus atom and a cyclometalating carbon atom of one of the substituents. The two free phenoxy moieties lie above and below the coordination plane, leading to steric hindrance that avoids aggregation and provides solubility in organic solvents. The other two coordination sites on the central metal ion are occupied by a chromophoric ligand, which is responsible for the energy of the luminescent excited state. This separation of functions, on the two coordinated ligands, allows the use of a wider range of luminophores with good luminescent properties, maintaining the control of the intermolecular interactions with the non-chromophoric ligand. Based on this approach we were able to achieve a bright deep blue emission (λ=444 nm, Φem =0.38) from a complex with a tailored ligand, which was then used for the fabrication of an electroluminescent device. In addition commercially available luminophores were also employed to synthesize green emitters.

Preparation of Dithienylphospholes by 1,1‐Carboboration

In this study the scope of the 1,1-carboboration reaction was extended to the preparation of mixed heterole-based conjugated π-systems. Two arylbis(alkynyl)phosphane starting materials 2 were synthesized bearing two thiophene isomers at the alkyne units and the bulky tipp-substituent (tipp=2,4,6-triisopropylphenyl) at the phosphorous atom. The bis(thienylethynyl)phosphanes 2 were converted into the corresponding 2,5-thienyl-substituted 3-borylphospholes 4 in a double 1,1-carboboration reaction sequence employing the strongly electrophilic B(C6 F5 )3 reagent under mild reaction conditions. Subsequent Suzuki-Miyaura type cross-coupling yielded the corresponding 3-phenylphospholes 7 in a one-pot procedure from phosphanes 2 in high yields. Phospholes 7 were converted into the respective phosphole oxides 8. A photophysical characterization of derivatives 7 and 8 was carried out. The results presented here demonstrate the suitability of the 1,1-carboboration reaction for the preparation of phosphole-/thiophene-based, light-emitting systems.

Boronic Acid Functionalized Photosensitizers: A Strategy To Target the Surface of Bacteria and Implement Active Agents in Polymer Coatings

Advanced methods for preventing and controlling hospital-acquired infections via eradication of free-floating bacteria and bacterial biofilms are of great interest. In this regard, the attractiveness of unconventional treatment modalities such as antimicrobial photodynamic therapy (aPDT) continues to grow. This study investigated a new and innovative strategy for targeting polysaccharides found on the bacterial cell envelope and the biofilm matrix using the boronic acid functionalized and highly effective photosensitizer (PS) silicon(IV) phthalocyanine. This strategy has been found to be successful in treating planktonic cultures and biofilms of Gram-negative E. coli. An additional advantage of boronic acid functionality is a possibility to anchor the tailor made PS to poly(vinyl alcohol) and to fabricate a self-disinfecting coating.

Striking an access to the bacteria via (reversible) control of lipophilicity

The development of antimicrobial photodynamic therapy (aPDT) is highly dependent on the development of suitable photosensitizers (PSs); ideally, affinity of a PS towards bacterial cells should be much higher than that towards mammalian cells. A cationic charge on a PS may lead to its selective binding to bacteria mediated through electrostatic interaction; however, the photodynamic outcome is highly dependent on the lipophilicity of the PS. Herein, we report the aPDT effect of silicon(IV) phthalocyanine derivatives bearing four positive charges and methyl, phenyl, or naphthyl substituents at the periphery of the macrocycle. We show that through modulation of lipophilicity, it is possible to find a therapeutic window in which bacteria, but not mammalian cells, are effectively killed. The photobiological activity of these PSs was significantly lower when they were deployed as host-guest complexes with cucurbit[7]uril (CB[7]). CB[7] blocks the hydrophobic part of the PS and reduces its lipophilicity, indicating that a hydrophobic interaction with the outer membrane of bacterial cells is essential for aPDT activity. The efficacies of the obtained PSs have been evaluated by using different uropathogenic E. coli isolates and human kidney epithelial carcinoma cells.

AquaGroupAcidity in Complexes of theType trans-[Pt(NH3 )2(L)(H2O)]2+ (with L = Substituted Pyridines). Linear, yetWeak Dependence of pKa of the Aqua Ligand from L Basicity

The pKa of the aqua ligand in complexes of the type trans-[Pt(NH3)2(L)(H2O)]n+ depends on the nature of the ligand trans to H2O, as expected. With L = NH3 or NH2R and n = 2, the pKa is around 6.0 - 6.4.With L = N-heterocyclic ligands generally higher acidities of the aqua ligands are observed, with pKa values being in the range of 4.7 - 5.4. These values are between those for L = H2O, n = 2 (4.4) and L = Cl−, n = 1 (5.7). For differently substituted pyridine ligands L a linear relationship exists between the pKa of the H2O ligand and the basicity of the heterocyclic ligand L, which is relatively weak, however Graphical Abstract AquaGroupAcidity in Complexes of theType trans-[Pt(NH3 )2(L)(H2O)]2+ (with L = Substituted Pyridines). Linear, yetWeak Dependence of pKa of the Aqua Ligand from L Basicity

Breaching the wall: morphological control of efficacy of phthalocyanine-based photoantimicrobials

An efficient treatment of infections using antimicrobial photodynamic therapy (aPDT) anticipates that uptake of photosensitizer (PS) by bacterial cells is very fast and effective. In this work, the design, synthesis, characterization, and photodynamic activity of amphiphilic, water-soluble zinc(ii)phthalocyanine (Zn(ii)Pc) molecules bearing none, three or six thiophenyl moieties are described. We show that PSs that contain no or flexible substituents on non-peripheral positions can photoinactivate microbes at very low loading concentrations and low light doses. In contrast, a PS derivative that contains non-flexible substituents is rendered less effective, despite an increased generation of cytotoxic singlet oxygen, higher lipophilicity and a lower tendency to aggregate. Our unexpected finding emphasizes the role of the morphology of PSs in bacterial cell-molecule interactions and suggests another relevant and hitherto disregarded characteristic to improve PS design.

Oxygen-Insensitive Aggregates of Pt(II) Complexes as Phosphorescent Labels of Proteins with Luminescence Lifetime-Based Readouts

The synthesis and photophysical properties of a tailored Pt(II) complex are presented. The phosphorescence of its monomeric species in homogeneous solutions is quenched by interaction with the solvent and therefore absent even upon deoxygenation. However, aggregation-induced shielding from the environment and suppression of rotovibrational degrees of freedom trigger a phosphorescence turn-on that is not suppressed by molecular oxygen, despite possessing an excited-state lifetime ranging in the microsecond scale. Thus, the photoinduced production of reactive oxygen species is avoided by the suppression of diffusion-controlled Dexter-type energy transfer to triplet molecular oxygen. These aggregates emit with the characteristic green luminescence profile of monomeric complexes, indicating that Pt-Pt or excimeric interactions are negligible. Herein, we show that these aggregates can be used to label a model biomolecule (bovine serum albumin) with a microsecond-range luminescence. The protein stabilizes the aggregates, acting as a carrier in aqueous environments. Despite spectral overlaps, the green phosphorescence can be separated by time-gated detection from the dominant autofluorescence of the protein arising from a covalently bound green fluorophore that emits in the nanosecond range. Interestingly, the aggregates also acted as energy donors able to sensitize the emission of a fraction of the fluorophores bound to the protein. This resulted in a microsecond-range luminescence of the fluorescent acceptors and a shortening of the excited-state lifetime of the phosphorescent aggregates. The process that can be traced by a 1000-fold increase in the acceptors lifetime mirrors the donors triplet character. The implications for phosphorescence lifetime imaging are discussed.