ABSTRACT
Guanidinium is a versatile functional group with unique properties. In biological systems, hydrogen-bonding and electrostatic interactions involving the arginine side chains of proteins are critical to stabilise complexes between proteins and nucleic acids, carbohydrates or other proteins. Leading examples of artificial receptors for carboxylates, phosphates and other oxoanions, such as sulfate or nitrate are highlighted in this tutorial review, addressed to readers interested in biology, chemistry and supramolecular chemistry.
Subject(s)
Carboxylic Acids/chemistry , Guanidine/chemistry , Receptors, Cell Surface/chemistry , Anions , Binding Sites , DNA/chemistry , DNA/metabolism , Models, Molecular , Proteins/chemistry , Proteins/metabolismABSTRACT
Supramolecular dendrimers resulting from the dimerization of fullerene-functionalized dendrons through a quadruple hydrogen-bonding motif were prepared. The synthetic strategy is based on the esterification of a tert-butoxycarbonyl (Boc)-protected 2-ureido-4-[1H]pyrimidinone precursor possessing an alcohol function with fullerodendrons bearing a carboxylic acid unit at the focal point. Subsequent acidic treatment to cleave the protecting group and reaction of the resulting amine with octylisocyanate affords the targeted compounds. As demonstrated by the results of MALDI-TOF mass spectrometry and 1H NMR spectroscopy, both of the 2-ureido-4-[1H]pyrimidinone derivatives form self-assembled dimers spontaneously through hydrogen-bonding interactions, thus leading to supramolecular structures containing two or ten fullerene moieties.
Subject(s)
Fullerenes/chemistry , Macromolecular Substances/chemical synthesis , Hydrogen Bonding , Macromolecular Substances/chemistry , Magnetic Resonance Spectroscopy/methods , Magnetic Resonance Spectroscopy/standards , Molecular Structure , Reference Standards , StereoisomerismABSTRACT
The preorganization of bifunctional 2-ureido-4-pyrimidinones mediated by either 1,3-substituted adamantane or meta-substituted phenylene ring linkers leads to the preferred formation of stable pentameric (1)(5) and hexameric (2)(6) assemblies, respectively. Despite the high binding constant of the 2-ureido-4-pyrimidinone dimers and the highly preorganized structure of the monomer, the predominant formation of cycles (1)(5) and (2)(6) in solution occurs only within a specific concentration range.
ABSTRACT
Novel thermodynamically stable supramolecular donor-acceptor dyads have been synthesized. In particular, we assembled successfully C(60), as an electron acceptor, with the strong electron donor TTF through a complementary guanidinium-carboxylate ion pair. Two strong and well-oriented hydrogen bonds, in combination with ionic interactions, ensure the formation of stable donor-acceptor dyads. The molecular architecture has been fine-tuned by using chemical spacers of different lengths (i.e., phenyl versus biphenyl) and functional groups (i.e., ester versus amide), thus providing meaningful incentives to differentiate between through-bond and through-space electron-transfer scenarios. In electrochemical studies, both the donor and acceptor character of the TTF and C(60) units, respectively, have been clearly identified. Steady-state and time-resolved emission studies, however, show a solvent-dependent fluorescence quenching in C(60)*TTF dyads as well as the formation of the C(60)(*)(-)*TTF(*)(+) radical ion pairs, for which we determined lifetimes that are in the range of hundred of nanoseconds to microseconds. The complex network that connects C(60) with TTF in the dyads and the flexible nature of the spacer result in through-space electron-transfer processes. This first example of electron transfer in C(60)-based dyads, connected by strong hydrogen bonds, demonstrates that this approach can add outstanding benefits to the construction of artificial photosynthetic systems that bear a closer resemblance to the natural one.
ABSTRACT
A novel class of macrobicyclic receptors for carbohydrate recognition based on upper rim, peptide-bridged calix[4]arenes has been designed and synthesized. Receptor 12, in which a charged phosphate group cooperates with peptide hydrogen-bonding donor and acceptor groups in the binding process, is the most efficient and selective in the complexation of simple carbohydrate derivatives. The selectivity observed is toward beta-glucoside 13a, which is better bound (DeltaG degrees = 19.6 kJ mol(-)(1)) compared to the corresponding alpha anomer 13b (DeltaG degrees = 17.0 kJ mol(-)(1)) and to the beta-galactoside 13c (DeltaG degrees = 17.7 kJ mol(-)(1)) in CDCl(3). A substantial drop in the stability constant is observed by esterification of the phosphate group in the host 12 or by alkylation of the OH groups in the 2 and 3 positions in the beta-glucoside and beta-galactoside derivatives. On the basis of a careful analysis of the (1)H NMR data available, a binding mode of the beta-octylglucoside 13a to receptor 12 is proposed.
Subject(s)
Carbohydrates/chemistry , Peptides/chemistry , Phosphates/chemistry , Polycyclic Compounds/chemistry , Calixarenes , Carbohydrate Sequence , Chromatography, Thin Layer , Indicators and Reagents , Magnetic Resonance SpectroscopyABSTRACT
Presentamos los resultados de un estudio cromosómico realizado a 61 personas con retinitis pigmentosa (RP), pertenecientes a 49 familias colombianas. La población estudiada estuvo conformada por pacientes diagnosticados con retinitis pigmentosa, en sus diversas formas genéticas: autosómica recesiva, autosómica dominante, Ligada a X, RP aislada y RP sindromal. De los 61 pacientes examinados, 36 (59,02 por ciento) presentaban un complemento cromosómico normal, 6 (9.84 por ciento) un complemento cromosómico anormal y 19 (31.15 por ciento) fragilidad cromosómica, para un total de 25 individuos (40.98 por ciento) con alguna alteración en su cariotipo. Las anormalidades fueron: traslocaciones cromosómicas en dos individuos (6.9 por ciento), tetraploidia mosaico en uno (3.45 por ciento), trisomia universal 47 XXY en uno (3.45 por ciento), trisomia mosaico 46 XX/47XXX en uno (3.45 por ciento) y monosomia mosaico del cromosoma 22 46 XX/45XX-22 en otro (3.45 por ciento). En cuanto a las fragilidades, se detectó fragilidad de algún autosoma en 16 individuos (84.2 por ciento), fragilidad del cromosoma X en 3 (15.8 por ciento), y en la madre de uno de los pacientes del estudio. Es importante hacer énfasis en lo relativo a estos hallazgos, ya que no se tienen aún cifras establecidas del porcentaje de personas normales que pueden presentar fragilidad en autosomas, por lo que, en el presente estudio no podemos dar conclusiones definitivas al respecto, ni lanzar hipótesis sobre el significado de su presencia en estos pacientes. Por lo tanto, en el análisis de resultados sólo consideramos importante resaltar el hallazgo de las otras anomalías cromosómicas, tales como traslocaciones, tetraploidias, trisomias o monosomias. Estos resultados demuestran la importancia del estudio genético y cromosómico en todo paciente con diagnóstico de retinitis pigmentosa
Subject(s)
Congenital Abnormalities , Retinitis PigmentosaABSTRACT
La endoftalmitis y la coroidorretínitis endógena son complicaciones poco frecuentes de la sepsis por gramnegativos y por Candida albicans, pero debido a su agresividad pueden llevar incluso a la ceguera. Mediante este estudio descriptivo, se analizaron las manifestaciones oculares en 38 pacientes con diagnóstico clínico de sepsis, en la Unidad de Cuidados Intensivos del Hospital Universitario de San Ignacio. Se definieron tres grupos de manifestaciones oculares: coroidorretinitis por Candida; endoftalmitis por candida, y lesiones inespecíficas, según los criterios establecidos por Donahue y colaboradores. Teniendo en cuenta la totalidad de la muestra, en 10 pacientes se encontraron hallazgos positivos, que indicaban compromiso coroidorretiniano por sepsis y hallazgos inespecíficos para coroidorretinitis por Candida. Se presentaron como factores de riesgo cirugía mayor, catéteres endovenosos, ventilación mecánica, antibiotícoterapia y administración de alimentación parenteral. De acuerdo a los resultados se concluye que la valoración oftalmológica de los pacientes con sepsis, permite orientar el diagnóstico etiológico y realizar una temprana intervención terapéutica
Subject(s)
Retinal Diseases , Candida albicans , Choroid Diseases , Gram-Negative BacteriaABSTRACT
Os autores discutem a clínica, a epidemiologia, a histopatologia, a etiologia e o tratamento do pilomatricoma, inclusive em sua forma maligna
