BOPHY-Fullerene C60 Dyad as a Photosensitizer for Antimicrobial Photodynamic Therapy

A novel BOPHY–fullerene C₆₀ dyad ( BP-C₆₀ ) was designed as a heavy-atom-free photosensitizer (PS) with potential uses in photodynamic treatment and reactive oxygen species (ROS)-mediated applications. BP-C₆₀ consists of a BOPHY fluorophore covalently attached to a C₆₀ moiety through a pyrrolidine ring. The BOPHY core works as a visible-light-harvesting antenna, while the fullerene C₆₀ subunit elicits the photodynamic action. This fluorophore–fullerene cycloadduct, obtained by a straightforward synthetic route, was fully characterized and compared with its individual counterparts. The restricted rotation around the single bond connecting the BOPHY and pyrrolidine moieties led to the formation of two atropisomers. Spectroscopic, electrochemical, and computational studies disclose an efficient photoinduced energy/electron transfer process from BOPHY to fullerene C₆₀. Photodynamic studies indicate that BP-C₆₀ produces ROS by both photomechanisms (type I and type II). Moreover, the dyad exhibits higher ROS production efficiency than its individual constitutional components. Preliminary screening of photodynamic inactivation on bacteria models (Staphylococcus aureus and Escherichia coli) demonstrated the ability of this dyad to be used as a heavy-atom-free PS. To the best of our knowledge, this is the first time that not only a BOPHY–fullerene C₆₀ dyad is reported, but also that a BOPHY derivative is applied to photoinactivate microorganisms. This study lays the foundations for the development of new BOPHY-based PSs with plausible applications in the medical field.     

Photodynamic Action Mechanism Mediated by Zinc(II) 2,9,16,23‐Tetrakis[4‐(N‐methylpyridyloxy)]phthalocyanine in Candida albicans Cells

The photoreaction type I/type II pathways mediated by zinc(II) 2,9,16,23‐tetrakis[4‐(N‐methylpyridyloxy)]phthalocyanine (ZnPPc⁴⁺) was studied in Candida albicans cells. This photosensitizer was strongly bound to C. albicans cells at short times. After 30 min irradiation, 5 μM ZnPPc⁴⁺ produced ~5 log decrease in cell viability. Different probes were used to detect reactive oxygen species (ROS) in cell suspensions (~10⁶ CFU mL^?1). Singlet molecular oxygen, O₂(¹Δ_g), was observed by the reaction with 9,10‐dimethylanthracene (DMA) and tetrasodium 2,2‐(anthracene‐9,10‐diyl)bis(methylmalonate) (ABMM), whereas the nitro blue tetrazolium (NBT) method was used to sense superoxide anion radical (). Moreover, the effects produced by an anoxic atmosphere and cell suspensions in D₂O, as well as the addition of sodium azide and mannitol as ROS trapping were evaluated in the PDI of C. albicans. These investigation indicates that O₂(¹Δ_g) is generated in the cells, although a minor extension other radical species can also be involved in the PDI of C. albicans mediated by ZnPPc⁴⁺.     

Thermal analysis to assess pozzolanic activity of calcined kaolinitic clays

The use of calcined clays as partial replacement of cement is encouraged since it promotes the reduction of the green-house gas emission and the energy requirement of cement-based material, maintaining or enhancing the mechanical properties and the durable performance of these materials. In this paper, the use of thermal methods—DTA/TG and calorimetry—to select and to evaluate two kaolinitic clays for their use as pozzolanic materials was explored. The content and crystallinity of kaolinite in clays can be determined by DTA/TG analysis, and this technique is also suitable to select the calcination temperature for complete kaolinite dehydroxylation. Calorimetric analysis on blended cements (30 % by mass of replacement) can differentiate the reactivity of calcined kaolinitic clays. Results show that more reactive calcined kaolinitic clay develops the second and third peaks earlier than those of PC with great intensity and high acceleration. The reactivity of calcined clays is associated to raw materials containing kaolinite with high structural disorder that determines calcined clays with large specific surface area, high grindability, and small mean particles size (d ₅₀) for the same grinding objective. Finally, the DTA/TG analysis can determine the type and the amount of hydrated phases obtained at different ages to evaluate the pozzolanic reaction of calcined clay in accordance with the standardized pozzolanic activity index.     

The Douglas-Kroll-Heß Method: Convergence and Block-Diagonalization of Dirac Operators

We show that the Douglas-Kroll block-diagonalization method for the Dirac operator with Coulomb potential is convergent in norm resolvent sense for coupling constant γ less than γ_c = 0.37758 which corresponds to atomic number 51. Moreover, we give an explicit expression for the corresponding block-diagonalized Dirac operator. Communicated by Vincent Rivasseau submitted 26/02/05, accepted 12/04/05     

On the Eigenfunctions of No-Pair Operators in Classical Magnetic Fields

We consider a relativistic no-pair model of a hydrogenic atom in a classical, exterior magnetic field. First, we prove that the corresponding Hamiltonian is semi-bounded below, for all coupling constants less than or equal to the critical one known for the Brown-Ravenhall model, i.e., for vanishing magnetic fields. We give conditions ensuring that its essential spectrum equals [1,∞) and that there exist infinitely many eigenvalues below 1. (The rest energy of the electron is 1 in our units.) Assuming that the magnetic vector potential is smooth and that all its partial derivatives increase subexponentially, we finally show that an eigenfunction corresponding to an eigenvalue λ < 1 is smooth away from the nucleus and that its partial derivatives of any order decay pointwise exponentially with any rate a < ?{1-l²}a < \sqrt{1-\lambda^2}, for l ? [0, 1)\lambda \in [0, 1), and a < 1, for λ < 0.     

Line transversals to blown up closed balls

The number ?? _d (k) is defined as the minimum ???>?0 such that the following holds: For any finite family ${\mathcal {F}=\{B_1,B_2, \ldots , B_n\}}$ of closed balls in ${{\mathbb{R}}^d}$ such that every k elements of ${\mathcal {F}}$ have a common line transversal, the elements of the blown up family ${\lambda\mathcal {F}=\{\lambda B_1,\lambda B_2, \ldots , \lambda B_n\}}$ have a common line transversal. In this paper we show that ${\lambda_d(d+1)\leq4, \lambda_2(4)\leq 2\sqrt 2}$ and ??₂(3)?<?2.88.     

Collisional enhancement of the I(52P12) emission at 1.3μm by parent molecules CF3I,C2F5I,i-C3F7I and n-C3F7I

The magnetic dipole transition I(5²P_{$\text{1}\text{2}$}-5²P_{$\text{3}\text{2}$}) at 1.3152 μm is shown to be enhanced by collisions of the metastable iodine atoms with the parent RI molecules CF₃I, C₂F₅I, i-C₃F₇I and n-C₃F₇I. The enhancing mechanism is exciplex emission of the RI·I(5²P_{$\text{1}\text{2}$}) molecule at 1.3 μm, with different rates for each iodide. The influence of this effect on the measurement of the quantum yields to I(5²P_{$\text{1}\text{2}$}) and of the respective reaction rates by infrared fluorescence is discussed.     

Spectral properties and reactivity of the binuclear complex ion μ-(p-benzoquinonediimine)bis[pentacyanoferrate(II)]

Summary A sodium salt containing the binuclear complex anion -(p-benzoquinonediimine) bis(pentacyanoferrate(II)], [(NC)₅FeHNC₆H₄NHFe(CN)₅]^6- [first described by Herington⁽³⁾) has been isolated as a solid from an oxygenated solution ofp-phenylenediamine and sodium amminepentacyanoferrate(II) in a 12 molar ratio. The i.r. and u.v.-vis. spectra point to a quinonediimine structure for the bridging ligand. In aqueous solution this ion dissociates into aquopentacyanoferrate(II) andp-benzoquinonediiminepentacyanoferrate(II), with k_obs=1.1×10^–2s^–1. The formation of the mononuclear pentacyanoferrate(II) complex of protonatedp-benzoquinonediimine is favoured at pH8. The pK_a value for the coordinated diimine isca. two orders of magnitude higher than that for the free ligand, thus indicating thatp-benzoquinonediimine is stabilized by coordination to the [Fe(CN)₅]^3- moiety, though to a lesser extent than in rutheniumammine analogues.Presented in part at the VIth Argentine Congress on Physical Chemistry, held at Termas de Río Hondo, Santiago del Estero, R. Argentina, April 1989.