Cemental tear is defined as cementum fragment completely or partially detached from the root surface, and it has been associated with localized rapid periodontal breakdown. Although history of trauma ...and/or attrition may be risk factors, the etiopathology of cemental tear remains unknown. This case series aims to discuss the clinical, radiographic and histopathologic features of cemental tears to aid clinicians in making differential diagnosis. Three teeth from three patients presenting a periradicular lesion underwent an exploratory surgery to determine the cause and provide treatment. Soft and hard tissue biopsies were obtained from each lesion and forwarded for histopathologic evaluation. Two patients received a guided tissue regeneration (GTR) procedure, which allowed the tooth to be retained. One patient received an extraction with simultaneous guided bone regeneration (GBR) due to a hopeless prognosis of the tooth. The results after histopathologic evaluation yielded a final diagnosis of cemental tear for all three patients. Cemental tears may be overlooked, and therefore, they should be included in the differential diagnosis of periapical periodontitis, endodontic‐periodontal lesion and vertical root fracture (VRF).
We describe two routes for the synthesis of a trisubstituted 1,2,5-hexahydro-3-oxo-1H-1,4-diazepine ring (DAP), a novel, conformationally constrained, seven-membered dipeptidomimetic ring system. The ...linear precursor for the model DAPs, targeted for conformational analysis studies, was obtained by reductive alkylation of tert-butyl alaninate or phenylalaninate by N-Boc-α-amino-γ-oxo-N,N-dimethylbutyramide. Acetylation of the newly formed secondary amine followed by acidolytic deprotection of the amino and carboxyl terminal protecting groups and subsequent diphenylphosphorazidate-mediated ring formation yielded the blocked model DAPs. The synthesis of the DAP synthon started with 1-tert-butyl hydrogen N-(benzyloxycarbonyl)aspartate. The aldehyde obtained from the β-carboxyl was used to reductively alkylate benzyl phenylalaninate, generating a secondary amine. Hydrogenolytic deprotection of the end-groups yielded the linear precursor which was cyclized via lactam formation mediated by 1-hydroxy-7-azabenzotriazolyl-N,N,N‘,N‘-tetramethyluronium hexafluorophosphate. This route yielded the reversibly protected hexahydro-1H-3-oxo-2(S)-benzyl-5(S)-(tert-butyloxycarbonyl)-1,4-diazepine. This synthon unit can be subsequently elaborated by substituting the functional groups (secondary amine and carboxyl). Therefore, the DAPs may serve as novel molecular scaffolds to reproduce a biologically relevant topology or as a dipeptido-conformation-mimetic that can be incorporated into bioactive peptides. In addition, these synthetic routes will allow the introduction of different chiralities at positions 2 and 5 as well as the diversification of the side chains at position 2. Furthermore, the synthetic routes described here can be easily modified to obtain larger ring systems with variable degrees of conformational flexibility.
The conformation of a novel 1,2,5-trisubstituted hexahydro-3-oxo-1H-1,4-diazepine system (DAP) has been investigated by proton and carbon NMR and refined with computer simulations. Four N ...1-acetyl-5-(N,N-dimethylamino)carbonyl DAP analogues, differing in the chirality and substituents at C2, have been studied: 2-benzyl-(2S,5S)-DAP (SS -F), 2-benzyl-(2R,5S)-DAP (RS-F), 2-methyl-(2S,5S)-DAP (SS-A), and 2-methyl-(2R,5S)-DAP (RS-A). The NMR spectra for each of the four analogues showed the presence of two configurational isomers slowly interconverting on the NMR time scale; the site of the cis/trans isomerization was identified as the N1-acetyl peptidic bond. The experimental restraints from NMR data consisted of a limited number of interproton distances and well-determined coupling constants; their utilization in distance geometry and distance and angle driven dynamics calculations produced high-resolution structures for three of the analogues. The C2 chirality (R or S) in the seven-membered ring determines the topological projection of the acetyl group with respect to the plane of the ring. The nature of the C2 substituent has only a small effect on the conformation of the ring and overall orientation of the N1 and C5 substituents. No significant structural differences result from the cis or trans configuration at the N1-acetyl peptidic bond. The results presented here indicate that DAP is a useful dipeptidomimetic with structural characteristics distinct from those of the widely used benzodiazepine.
SummaryThe conformational features of a novel, dipeptide-based molecular scaffold are described. Four model systems of a trisubstituted 1,4-diazepine-3-one system, varying in the chirality and amino ...acid within the ring system, have been investigated by high-resolution NMR and metric-matrix distance geometry calculations. Because of the small number of protons within the scaffold, nuclear Overhauser effects provide only limited conformational information. Instead, extensive use of scalar1H−H1 and1H−13C coupling constants was utilized in the refinement. The resulting conformations of the model systems provide insigh into the expected topological orientation of the amino acids or chemical functionalities and attached to the seven-membered ring system, the first step of the utilization of this scaffold in the rational design of peptidomimetics.
The time dependence of slow electroluminescence has been used as an experimental probe for studying the physical characteristics of the recombination region in anthracene. Under conditions where two ...injecting contacts are used, and neither carrier is trapped to a large extent, the recombination zone is found to occupy approximately 0.3 of the crystal volume for current densities of 10
−5
-10
−8
amps cm
−2
. When forced hole injection is used, the recombination volume at low currents decreases, particularly at low temperatures. This decrease in recombination volume is discussed in terms of carrier trapping and filament formation.
Observations of the transient behaviour of electroluminescence in sublimation flakes have shown that quenching of the delayed electro-luminescence component by the carriers themselves becomes ...important at high currents. The results show quenching is of the same order as observed for carrier quenching of optically produced triplet excitons. No quenching was observed in thick crystals though carrier densities of the same order are present. This is presumably due to the difference in recombination zone width which may be larger in these thick crystals.
