Speciation, Luminescence, and Alkaline Fluorescence Quenching of 4-(2-methylbutyl)aminodipicolinic acid (H2MEBADPA)

4-(2-Methylbutyl)aminodipicolinic acid (H2MEBADPA) has been synthesized and fully characterized in terms of aqueous phase protonation constants (pKa\u27s) and photophysical measurements. The pKa\u27s were determined by spectrophotometric titrations, utilizing a fully sealed titration system. Photophysical measurements consisted of room temperature fluorescence and frozen solution phosphorescence as well as quantum yield determinations at various pH, which showed that only fully deprotonated MEBADPA2– is appreciably emissive. The fluorescence of MEBADPA2– has been determined to be quenched by hydroxide and methoxide anions, most likely through base-catalyzed excited-state tautomerism or proton transfer. This quenching phenomenon has been quantitatively explored through steady-state and time-resolved fluorescence measurements. Utilizing the determined pKas and quenching constants, the fluorescent intensity of MEBADPA2– has been successfully modeled as a function of pH

Scaling the state: Egypt in the third millennium BC

Discussions of the early Egyptian state suffer from a weak consideration of scale. Egyptian archaeologists derive their arguments primarily from evidence of court cemeteries, elite tombs, and monuments of royal display. The material informs the analysis of kingship, early writing, and administration but it remains obscure how the core of the early Pharaonic state was embedded in the territory it claimed to administer. This paper suggests that the relationship between centre and hinterland is key for scaling the Egyptian state of the Old Kingdom (ca. 2,700-2,200 BC). Initially, central administration imagines Egypt using models at variance with provincial practice. The end of the Old Kingdom demarcates not the collapse, but the beginning of a large-scale state characterized by the coalescence of central and local models

Conformation-Dependent Photophysics of Bifunctional Hydrogen Bond Donor/Acceptor Molecules

A series of heteroazaaromatic molecules possessing both a hydrogen bond donor and acceptor groups linked by a single bond was studied using electronic absorption and fluorescence techniques, combined with quantum--chemical calculations. Fluorescence lifetimes and quantum yields strongly depend on the solvent. Double exponential decays are observed in alcohols. This was interpreted in terms of alcohol-induced syn-anti rotamerization in the ground electronic state. The driving force for the conformational change is provided by two factors: (a) solvent polarity increase; (b) the formation of two separate hydrogen bonds in the anti species. In the syn structure, formation of cyclic hydrogen bonds leads to rapid depopulation of the lowest excited singlet state via two competing mechanisms: proton transfer and enhanced internal conversion. The experimental results are rationalized by calculations which include specific and nonspecific solvent effects

Conformation-Dependent Photophysics of Bifunctional Hydrogen Bond Donor/Acceptor Molecules

A series of heteroazaaromatic molecules possessing both a hydrogen bond donor and acceptor groups linked by a single bond was studied using electronic absorption and fluorescence techniques, combined with quantum--chemical calculations. Fluorescence lifetimes and quantum yields strongly depend on the solvent. Double exponential decays are observed in alcohols. This was interpreted in terms of alcohol-induced syn-anti rotamerization in the ground electronic state. The driving force for the conformational change is provided by two factors: (a) solvent polarity increase; (b) the formation of two separate hydrogen bonds in the anti species. In the syn structure, formation of cyclic hydrogen bonds leads to rapid depopulation of the lowest excited singlet state via two competing mechanisms: proton transfer and enhanced internal conversion. The experimental results are rationalized by calculations which include specific and nonspecific solvent effects