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Red Hair Benzothiazines and Benzothiazoles: Mutation-Inspired Chemistry in the Quest for Functionality
No full textA review. Nature provides a primary source of leads for the design of π-conjugated org. chromophores and other functional mol. systems useful for mol. recognition, light harvesting, photoconversion, and other technol. applications. In this Account, we draw attention to a unique group of naturally occurring heterocyclic compds., the 2H-1,4-benzothiazines and related benzothiazole derivs. Derived from tyrosine and cysteine, these mols. arise from a mutation-induced deviation of the melanin pathway to provide the core structure of the red human hair pigments pheomelanins. Since the elucidation of the biosynthetic pathway of pheomelanins in the 1960s, researchers have focused on 1,4-benzothiazines and red hair pigments. Not only do these mols. have interesting photochem. and mol. recognition properties, they also have compelling biomedical significance. Numerous studies have linked higher levels of pheomelanins and mutations in the pathways that produce these pigments in individuals with red hair and fair skin with an increased sensitivity to UV light and a higher susceptibility to melanoma and other skin cancers. Prompted by new data about the structure and photochem. of the bibenzothiazine system, this Account highlights the chem. of benzothiazines in red-haired individuals as a novel source of inspiration in the quest for innovative scaffolds and biomimetic functional systems. Model studies have gradually shed light on a no. of remarkable phys. and chem. properties of benzothiazine-based systems. Bibenzothiazine is a robust visible chromophore that combines photochromism and acidichromism. Benzothiazine-based polymers (synthetic pheomelanins) show remarkable photochem., paramagnetic, and redox cycling properties. Biomimetic or synthetic manipulations of the benzothiazine systems, through decarboxylation pathways controlled by metal ions or unusually facile ring-contraction processes, can produce a diverse set of mol. scaffolds
Optimizing the Relaxivity of MRI Probes at High Magnetic Field Strengths With Binuclear GdIII Complexes
Get PDFThe key criteria to optimize the relaxivity of a Gd(III) contrast agent at high fields (defined as the region ≥ 1.5 T) can be summarized as follows: (i) the occurrence of a rotational correlation time τR in the range of ca. 0.2–0.5 ns; (ii) the rate of water exchange is not critical, but a τM < 100 ns is preferred; (iii) a relevant contribution from water molecules in the second sphere of hydration. In addition, the use of macrocycle-based systems ensures the formation of thermodynamically and kinetically stable Gd(III) complexes. Binuclear Gd(III) complexes could potentially meet these requirements. Their efficiency depends primarily on the degree of flexibility of the linker connecting the two monomeric units, the absence of local motions and the presence of contribution from the second sphere water molecules. With the aim to maximize relaxivity (per Gd) over a wide range of magnetic field strengths, two binuclear Gd(III) chelates derived from the well-known macrocyclic systems DOTA-monopropionamide and HPDO3A (Gd2L1 and Gd2L2, respectively) were synthesized through a multistep synthesis. Chemical Exchange Saturation Transfer (CEST) experiments carried out on Eu2L2 at different pH showed the occurrence of a CEST effect at acidic pH that disappears at neutral pH, associated with the deprotonation of the hydroxyl groups. Then, a complete 1H and 17O NMR relaxometric study was carried out in order to evaluate the parameters that govern the relaxivity associated with these complexes. The relaxivities of Gd2L1 and Gd2L2 (20 MHz, 298 K) are 8.7 and 9.5 mM−1 s−1, respectively, +77% and +106% higher than the relaxivity values of the corresponding mononuclear GdDOTAMAP-En and GdHPDO3A complexes. A significant contribution of second sphere water molecules was accounted for the strong relaxivity enhancement of Gd2L2. MR phantom images of the dinuclear complexes compared to GdHPDO3A, recorded at 7 T, confirmed the superiority of Gd2L2. Finally, ab initio (DFT) calculations were performed to obtain information about the solution structure of the dinuclear complexes
Macrocyclic trinuclear gadolinium(iii) complexes: the influence of the linker flexibility on the relaxometric properties
No full textMultimeric systems assembled by linking GdIII complexes to a central scaffold can be Magnetic
Resonance Imaging (MRI) contrast agents of improved efficiency at high magnetic fields. Two novel
mononuclear GdDO3A-derivatives (DO3A = 1,4,7,10-tetraazacyclododecane-N,N0 ,N00-triacetic acid)
featuring a flexible (hexanoic acid, GdL1) or rigid (methyl benzoic acid, GdL2) pendant arm were
synthesized and conjugated to a central 1,4,7-triazacyclononane unit through amide coupling to form
two novel trinuclear systems. A variable temperature and frequency 1H and 17O NMR relaxometric study
on the mononuclear complexes indicated that GdL2 exhibits two water molecules in the inner
coordination sphere, as does the parent [Gd(DO3A)(H2O)2] complex (q = 2). However, the flexibility of
the alkyl chain of GdL1 allows its folding and coordination to the Gd3+ ion with displacement of one
water molecule (q = 1) around neutral pH. In Gd3L4, the linker rigidity results in a compact and rather
rigid trinuclear system from the point of view of rotational dynamics, with each GdIII center having q =
2. This favors a considerable degree of coupling between local and overall tumbling motions and hence
high relaxivity values (r1 = 13.8 mM-1 s-1; 60 MHz and 298 K). On the other hand, the flexibility of the
alkyl chain significantly affects the properties of Gd3L3. The relaxation data suggest the easy folding of
one of the chelates with coordination of Gd by an amide group of the central macrocyclic unit (q = 1).
The other two complexes (q = 2) exhibit a high degree of rotational mobility around the linker that
results in a significant limit on the relaxivity (r1 = 9.8 mM-1 s-1; 60 MHz and 298 K)
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Trichocyanines: A Red-Hair-Inspired Modular Platform for Dye-Based One-Time-Pad Molecular Cryptography
No full textCurrent molecular cryptography (MoCryp) systems are almost exclusively based on DNA chemistry and reports of cryptography technologies based on other less complex chemical systems are lacking. We describe herein, as proof of concept, the prototype of the first asymmetric MoCryp system, based on an 8-compound set of a novel bioinspired class of cyanine-type dyes called trichocyanines. These novel acidichromic cyanine-type dyes inspired by red hair pigments were synthesized and characterized with the aid of density functional theory (DFT) calculations. Trichocyanines consist of a modular scaffold easily accessible via an expedient condensation of 3-phenyl- or 3-methyl-2H-1,4-benzothiazines with N-dimethyl- or o-methoxyhydroxy-substituted benzaldehyde or cinnamaldehyde derivatives. The eight representative members synthesized herein can be classified as belonging to two three-state systems tunable through four different control points. This versatile dye platform can generate an expandable palette of colors and appears to be specifically suited to implement an unprecedented single-use asymmetric molecular cryptography system. With this system, we intend to pioneer the translation of digital public-key cryptography into a chemical-coding one-time-pad-like system
Red-Hair-Inspired Chromogenic System Based on a Proton-Switched Dehydrogenative Free-Radical Coupling
No full textIn the presence of micromolar peroxides or biometals (Fe(III)???, Cu(II)???, V(V) salts)???, and following a strong acid input, the stable 3-???phenyl-???2H-???1,???4-???benzothiazine is efficiently converted to a green-???blue ??2,???2'-???bi(2H-???1,???4-???benzothiazine) chromophore via dehydrogenative coupling of a 1,???4-???benzothiazinyl radical. The new system is of potential practical interest for colorimetric peroxide and redox biometal detection
Glycosylated eumelanin building blocks by thioglycosylation of 5,6-diacetoxyindole with an expedient selenium-based dynamic-mixture methodology
No full textA series of 3-thioglycosylated 5,6-diacetoxyindole derivatives, which are important tools for eumelanin research and application, were prepared through a practical and efficient approach exploiting a dynamic mixture of thioglycoside agents. The strategy is feasible for installing both mono- and disaccharide units and relies on the facile in situ conversion of glycosyl disulfides into the corresponding, more reactive, phenylselenenyl sulfides in the presence of diphenyl diselenide, N-bromosuccinimide (NBS) and tetrabutylammonium bromide (TBAB)
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Modifying LnHPDO3A Chelates for Improved T 1 and CEST MRI Applications
No full textThe new ligand HPDO3MA [(R,R,R,R)-10-(2-hydroxypropyl)-a,a’,a’’-trimethyl-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid] was designed to combine and optimize the chemical properties of the macrocyclic ligands HPDO3A and DOTMA. The presence of the methyl groups on the acetic pendant arms of HPDO3A is expected to rigidify the structure of the ligand and favor an increase of the kinetic inertness of the Ln complexes. 1H NMR spectra of Eu(HPDO3MA) displayed the presence of two pairs of diastereoisomers: SAP (square antiprismatic) and TSAP (twisted square
antiprismatic) isomers (56 and 44%, respectively). In addition, 1H and 17O relaxometric NMR studies of Gd(HPDO3MA) showed approximately a 10% increase in relaxivity and a faster water exchange rate with respect to Gd(HPDO3A). Moreover, a detailed chemical exchange saturation transfer (CEST) characterization of Yb(HPDO3MA) displayed a sensitivity about two times larger than that of Yb(HPDO3A) both in phantom and in cell labeling experiments. Finally, the kinetic inertness of Yb(HPDO3MA) was measured to be twice as high as that of Yb(HPDO3A), with a dissociation half-life at physiological pH of about 2500 years
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