Free Meso Research Articles

Stepwise Oxidative C-C Coupling and/or C-N Fusion of Zn(II) meso-Pyridin-2-ylthio-porphyrins.

The synthesis and characterization of zinc(II) meso-pyridin-2-ylthio-porphyrins are presented in this manuscript. The (electro)chemical oxidation of [5-(pyridin-2-ylthio)-10,20-bis(p-tolyl)-15-phenylporphyrinato] zinc(II) or [5,15-bis(pyridin-2-ylthio)-10,20-bis(p-tolyl)porphyrinato] zinc(II) leads to the formation of one or two C-N bond(s) by intramolecular nucleophilic attack of the peripheral thiopyridinyl fragment(s) on the neighboring β-pyrrolic position(s) (C-N fusion reaction). In addition, the chemical oxidation of [5-(pyridin-2-ylthio)-10,20-bis(p-tolyl)porphyrinato] zinc(II), i.e., bearing one free meso position, mainly affords the meso,meso-dimer. Further stepwise electrochemical oxidation selectively produces the mono and bis C-N fused meso,meso-dimer. The resulting pyridinium derivatives exhibit important changes in their physicochemical properties (NMR, UV-vis, CV) as compared to their initial unfused precursors. Also, the X-ray crystallographic structures of three unfused monomers, one unfused meso,meso-dimer, and two C-N fused monomers are presented.

Metal Complexes of Singly, Doubly and Triply Linked Porphyrins and Corroles: An Insight into the Physicochemical Properties.

Metal complexes of multi‐porphyrins and multi‐corroles are unique systems that display a host of extremely interesting properties. Availability of free meso and β positions allow formation of different types of directly linked bis‐porphyrins giving rise to intriguing optical and electronic properties. While the fields of metalloporphyrin and corroles monomer have seen exponential growth in the last decades, the chemistry of metal complexes of bis‐porphyrins and bis‐corroles remain rather underexplored. Therefore, the impact of covalent linkages on the optical, electronic, (spectro)electrochemical, magnetic and electrocatalytic activities of metal complexes of bis‐porphyrins and ‐corroles has been summarized in this review article. This article shows that despite the (still) somewhat difficult synthetic access to these molecules, their extremely exciting properties do make a strong case for pursuing research on these classes of compounds.

ON DIFFUSE INSTABILITY OF ORTHOTROPIC VISCOPLASTIC PLATES

Elastic strain is covered by the effective medium homogenization method inside a representative volume element (RVE). It has an incremental quasi rate-independent (QRI) form obtained by the endochronic concept of thermodynamic time. The rate dependence takes place by means of stress rate dependent value of the initial yield stress. Free meso rotations and constrained micro rotations within a representative volume element (RVE) are assumed. A comparison between QRI and J2 diffuse instability equations is presented for orthotropic materials. A new QRI nonlinear evolution equation for orthotropic materials is derived by tensor function representation with Spencer-Boehler structural tensors.

Synthesis and characterization of novel 5-monocarbohydrate-10,20-bis-aryl-porphyrins

The synthesis of derivatives bearing glucose or galactose units linked by an acrylate spacer to one free meso position of a bis-aryl-porphyrin macrocycle was developed and characterized by standard spectroscopic techniques. The new mono-substituted gluco- and galacto-porphyrin derivatives 5–8 present an alternative to the widespread tetra-aryl porphyrin functionalization. Singlet oxygen studies showed a comparable singlet oxygen production with TPP. Furthermore, the less bulky architectures here synthesized present an opportunity to enhance the PDT and PDI capabilities of glycoporphyrins with a simple synthetic modification at one of the meso positions.

Diffuse instability of anisotropic inelastic plates by J2 and QRI models

Elastic strain is covered by the effective medium homogenization method inside a representative volume element (RVE). Evolution equation formed by tensor representation is derived from very simple micro-evolution equation. It has an incremental quasi rate-independent (QRI) form obtained by the endochronic concept of thermodynamic time. The rate dependence takes place by means of stress rate dependent value of the initial yield stress. Free meso rotations and constrained micro rotations within a representative volume element (RVE) are assumed. The theory is applied to metal forming of orthotropic austenitic steel plates. A comparison between QRI and J2 diffuse instability equations is presented for transversely isotropic as well as for orthotropic materials.

A BODIPY-based turn-on fluorescent probe for the selective detection of hydrogen sulfide in solution and in cells

A new turn-on fluorescent probe, incorporating 7-nitrobenzoxadiazole (NBD) ether group into a BODIPY molecule, was synthesized and studied for the detection of H2S and biothiols in aqueous solution and in living cells. The design was based on thiol-induced thiolysis of the NBD ether bond and followed by the cleavage and the release of free meso-(4-hydroxybenzyl)-substituted BODIPY fluorophore. The BODIPY-based probe displayed highly sensitive and selective fluorescence enhancement respond to H2S over competing biothiols such as cysteine (Cys) and glutathione (GSH), mainly due to the weak reactivity of biothiols toward the probe. There was a good linearity between the fluorescence intensity and the concentrations of H2S in the range of 1–200µM with a detection limit of 2.6µM. The proposed reaction mechanism was confirmed by mass spectrometry and optical spectroscopy, and the mechanism of turn-on fluorescent response was further determinated by the density functional theory (DFT) calculations using Gaussian 03 program. Moreover, the probe was successfully applied for the fluorescence imaging of H2S in HeLa cells under physiological conditions (pH 7.4).

Electrochemistry as an attractive and effective tool for the synthesis and immobilization of porphyrins on an electrode surface.

Magnesium(II) 10-phenyl-5,15-p-ditolylporphyrin is easily and cleanly transformed by electrolysis. A nitro group is first introduced at the free meso position by anodic substitution. Hydrogenation into the amine is then carried out electrocatalytically under ambient conditions with water as a hydrogen supplier. The synthesized porphyrin under the nickel(II) form can be covalently grafted onto a platinum electrode by electrochemical reduction of the diazonium cation, generated in situ by a reaction of the nickel(II) aminoporphyrin with sodium nitrite and trifluoroacetic acid. The electrosynthesized thin film gives an electrochemical response typical of a porphyrin material. Films grown under our conditions have a maximum surface coverage of approximately 5×10(-10) mol cm(-2). The modified electrode exhibits a reproducible electrochemical behavior and a good level of stability over potential cycling and exposition to air.

El colon Ilio-Pélvico en los peruanos II Parte: Relaciones, longitud y dolicosigmoides

Hemos visto la diversidad de posiciones en que se puede hallar el colon sigmoideo. Algunos autores atribuyen esta particularidad a la existencia de su meso libre, que le permite amplia movilidad, debido a que la inserción parietal del meso es más corta que la visceral. Al mismo tiempo esta excesiva movilidad ocasionaría reducción de su amplitud y cierto grado de esclerosis. que puede llegar desde el adosamiento de sus dos raíces a toda la altura del meso, debido a inflamadones e infecciones de vecindad, propagadas por vía linfótico ( 152) para unos; para otros como resultado de crisis sub-oclusivas iterativas del período de estado del dolicocolon que pueden determinar compresiones de los vasos a nivel de las acodaduras. En principio, la anatomía macroscópica nos enseña, que la fascia de adosamiento que fija las porciones del colon descendente y del colon ílícco no existe en el sicrnoides, ya que justamente esta porción móvil comienza en el punto en donde termina aquella. Sin embargo, este proceso de coalescencia está sujeto, según los autores clásicos, a numerosas variaciones: pudiendo llegar al borde interno del psoas ilíaco o un poco más arriba, cerca de la cresta ilíaca, siendo en este último caso más amplia el asa sigmoidea; otras veces 6.] adosamiento falta en la parte posterior, quedando un meso de 1 a 2 cms. en la última porción del colon lumbo-ilíaco y en otros casos es tan irregular, que ofrece sólo algunos centímetros sin adosamiento, constituyendo las fositas paracólicas, verdaderos fondos de saco retrocólicos, en donde falta la soldadura ( 150) (438).

Porphyrin Dimers and Arrays

AbstractCurrent applications of porphyrins in medicine and optics, such as photodynamic therapy or nonlinear absorbers, increasingly require the use of far‐red absorbing dyes. Modifications of the porphyrin structure to accommodate these conditions can be achieved by extending the conjugation of the porphyrin π‐system, which causes a bathochromic shift in the absorption spectrum. Thus, conjugated porphyrin oligomers have found widespread use. However, past synthetic strategies have mainly targeted symmetric porphyrin dimers, trimers, and oligomers, which limit the practical use of such chromophores. Here, a series of symmetric and unsymmetric dimeric and trimeric porphyrin systems, which are connected by conjugated linkers, namely alkyne and phenylacetylene, were synthesized by palladium‐catalyzed C–C coupling reactions. Adopting two approaches, firstly, a series of new unsymmetric dimers was synthesized by the incorporation of all substituents on the monomeric components prior to coupling. The second was the synthesis of new symmetric dimers and trimers with free meso positions enabling further chemistry to be carried out. The majority of these conjugated arrays exhibited a bathochromic shift in their UV/Vis absorption, in particular the alkyne‐linked arrays showed absorption greater than 720 nm. The mass spectra of phenylacetylene‐ and diphenylbutadiene‐linked zinc arrays exhibited detachment of zinc from the porphyrin core. These unusual results are both linker and metal dependent, usually only seen for more labile metals.

A Stable Radical Species from Facile Oxygenation of meso‐Free 5,10,20,25‐Tetrakis(pentafluorophenyl)‐Substituted [26]Hexaphyrin(1.1.1.1.1.1)

A stable radical: The title compound 1 has been synthesized as the first example of a meso-free variant and characterized as a strongly aromatic macrocycle with a spectacles-like planar conformation. The incorporation of free meso positions is promising for the exploration of novel structural and electronic properties.

Peripherally-metallated porphyrins: meso-η1-porphyrinyl-platinum(II) complexes of 5,15-diaryl- and 5,10,15-triarylporphyrins

Attempted metathesis reactions of peripherally-metallated meso-η1-porphyrinylplatinum(II) complexes such as trans-[ PtBr ( NiDPP )( PPh 3)2]( H 2 DPP = 5,15- diphenylporphyrin ) with organolithium reagents fail due to competitive addition at the porphyrin ring carbon opposite to the metal substituent. This reaction can be prevented by using 5,10,15-triarylporphyrins, e.g. 5,10,15-triphenylporphyrin ( H 2 TrPP ) and 5-phenyl-10,20-bis(3′,5′-di-t-butylphenyl)porphyrin ( H 2 DAPP ) as substrates. These triarylporphyrins are readily prepared using the method of Senge and co-workers by addition of phenyllithium to the appropriate 5,15-diarylporphyrins, followed by aqueous protolysis and oxidation. They are convenient, soluble building blocks for selective substitutions and subsequent transformations at the remaining free meso carbon. The sequence of bromination, optional central metallation and oxidative addition of Pt (0) tris(phosphine) complexes generates the organoplatinum porphyrins in high overall yields. The bromo ligand on the Pt (II) centre can be substituted by alkynyl nucleophiles, including 5-ethynyl NiDPP , to form the first examples of meso-η1-porphyrinylplatinum(II) complexes with a second Pt - C bond. The range of porphyrinylplatinum(II) bis(tertiary phosphine) complexes was extended to the triethylphosphine analogues, by oxidative addition of H 2 TrPPBr to Pt ( PEt 3)3, and the initially-formed cis adduct is only slowly thermally transformed to trans-[ PtBr ( H 2 TrPP )( PEt 3)2]16. The molecular structures of NiDAPP 9b, trans-[ Pt ( NiDPP )( C 2 NiDPP )( PPh 3)2]14 and 16 were determined by X-ray crystallography.

Electrolysis of V(IV) and free meso -tetraphenyl porphyrin in two immiscible liquids

The electrochemical decomposition of free and vanadyl tetraphenyl porphyrin in xylene solutions, and in the presence of water, using K2SO4 as electrolyte, was studied. Electrolysis of the two-phase system was carried out at constant current density and potential. It was observed that the electrochemical decomposition of the porphyrins, using a two-phase liquid system, is possible. An inexpensive organic solvent (xylene instead of THF, acetonitrile, methylene chloride etc.) can be very effectively used in such a system. The decomposition occurs through an oxidation process, with the subsequent formation of cationic and dicationic radicals, and a final breakdown of the macrocycle.

Mechanistic studies on the nucleophilic reaction of porphyrins with organolithium reagents.

Porphyrins react readily with organolithium reagents under substitution of free meso positions. As this method has proven to be very versatile for the preparation of a wide range of meso substituted porphyrins, a mechanistic study of the reaction was undertaken using 5,15-diaryl- and dialkyl substituted porphyrins, 2,3,7,8,12,13,17,18-octaethylporphyrin, and the respective nickel(II) complexes. A combination of deuteration experiments, electronic absorption spectroscopy of the reactive intermediates, trapping of intermediates with organic electrophiles, and reaction at different pH values showed significant differences in the reaction pathways of free base porphyrins and metalloporphyrins. In both cases the reaction proceeds initially under formation of phlorin like intermediates which are stable in water. For the Ni(II)phlorins a mesomeric carbanionic form with a highly distorted structure exists that can react as a nucleophile with electrophiles such as RI, H+, or D+. In the latter case a protonation-deprotonation equilibrium involving porphodimethen intermediates has to be assumed. Free base phlorins do not react as nucleophiles but can undergo H/D exchange reactions in strongly acidic media.

2,3,7,8,12,13,17,18‐Octamethoxyporphyrin

An eightfold donor-substituted porphyrin with free meso positions 1 has been obtained for the first time. In the solid state one of the two methoxy groups on each pyrrole ring lies almost parallel to the porphyrin plane, thus allowing conjugation with the π-electron system of the macrocycle. Further evidence is provided by the spectroscopic properties of 1, which deviate significantly from those of the related octaalkylporphyrins.

Porphyrins. 22. Synthesis of porphyrins with two cyclopentane rings

The Vilsmeier formylation of meso-methylporphyrins and a porphyrin with a cyclopentane ring was investigated. A meso substituent increases the ability of free meso positions to undergo electrophilic substitution reactions. Schiff bases of meso-formylporphyrins were subjected to thermolysis, and a porphyrin with two cyclopentane rings was synthesized for the first time.