Quantum-chemical and correlation study of deprotonation and complexation of 1-amino-4-hydroxyanthraquinone

Existing views on the deprotonation and complexation of 1-amino-4-hydroxyanthraquinone are wrong. This compound, its anions, and complexes with metals are not individual substances, but they form a dynamic equilibrium mixture of keto-enol (keto-oxide) and amino-imine tautomers. Different samples of the same compound differ by the tautomeric composition, the respective information is contained in their electron absorption spectra. In weak alkaline solutions the deprotonation occurs exclusively at the hydroxy group. Most typical structure of 1-amino-4-hydroxyanthraquinone anions is 1,10-quinoid, its metal complexes have 9,10-and 1,10-quinoid structures. The ground states of molecules are more responsible for the tautomeric transformations than the excited states. Quantum-chemical calculations of tautomeric anthraquinones by semiempirical PPP methods are more reliable than modern ab initio calculations.     

Tautomeric composition as a compound characteristic

Russian Journal of General Chemistry -     

Inversionless Amplification in a Three-Level System Driven by a Single Field

The three-level system subjected to electromagnetic fields is investigated. It is shown that when one of two fields is strong (the pumping field), the system can amplify the second (probe) field even if no population inversion is created, but some phase relations are satisfied. The conditions necessary for inversionless amplification to take place are discussed. The connection between this effect and stimulated Raman emission is shown. Numerical simulations for each one of the discussed cases were performed.     

Tautomerism of metal complexes with carminic acid

The diversity of the absorption spectra of complexes with carminic acid was shown to be due to the shift of tautomeric equilibria that takes place upon the change in the medium pH, the nature of the metal, and the composition of the complex. A classification of known carminic acid complexes based on the results of correlation analysis of the positions of experimental π _l ,π* absorption bands with those calculated by PPP quantum chemical methods is proposed.     

Blood oxygen level-dependent and perfusion magnetic resonance imaging: detecting differences in oxygen bioavailability and blood flow in transplanted kidneys

Functional magnetic resonance imaging (fMRI) is a powerful tool for examining kidney function, including organ blood flow and oxygen bioavailability. We have used contrast enhanced perfusion and blood oxygen level-dependent (BOLD) MRI to assess kidney transplants with normal function, acute tubular necrosis (ATN) and acute rejection. BOLD and MR-perfusion imaging were performed on 17 subjects with recently transplanted kidneys. There was a significant difference between medullary R2? values in the group with acute rejection (R2?=16.2/s) compared to allografts with ATN (R2?=19.8/s; P=.047) and normal-functioning allografts (R2?=24.3/s;P=.0003). There was a significant difference between medullary perfusion measurements in the group with acute rejection (124.4±41.1 ml/100 g per minute) compared to those in patients with ATN (246.9±123.5 ml/100 g per minute; P=.02) and normal-functioning allografts (220.8±95.8 ml/100 g per minute; P=.02). This study highlights the utility of combining perfusion and BOLD MRI to assess renal function. We have demonstrated a decrease in medullary R2? (decrease deoxyhemoglobin) on BOLD MRI and a decrease in medullary blood flow by MR perfusion imaging in those allografts with acute rejection, which indicates an increase in medullary oxygen bioavailability in allografts with rejection, despite a decrease in blood flow.     

Tautomerism of metal complexes with quinalizarin

The formation of complexes with quinalizarin was found to occur through the peri-hydroxycarbonyl groups with participation of tautomers and conformers. The diversity of the electronic absorption spectra of quinalizarin complexes is explained not only by the ligand ionization degree but also by the shifts in the tautomeric and conformer equilibria. The classification of the known quinalizarin complexes is suggested on the basis of spectrophotometric data and quantum-chemical calculations of the π _l ,π^*-band position by the Pariser-Parr-Pople method.     

Tautomerism of anthraquinones: IX. Protonated 1,5- and 1,8-dihydroxyanthraquinones

Fine structure of π_l,π* absorption of mono- and dications derived from 1,5- and 1,8-dihydroxyanthraquinones originates from their existence as dynamic equilibrium mixtures of isomers differing by position of the positive charge, double bond distribution, and number of intramolecular hydrogen bonds. Protonation is accompanied by displacement of isomeric equilibria. Isomeric transformations of protonated dihydroxyanthraquinones involve mainly excited states of their molecules.     

Group-metric multiuser decoding

We propose the new group metric (GM) soft-decision decoder for convolutionally coded synchronous multiple-access channels. The GM decoder exploits the independently operating encoders of the multiuser channel by making decoding decisions for a subset of the users, but incorporating all the multiuser information in its metrics. For a single user, this decoder will have a reduced complexity that is exponential in the sum of encoder memory and the number of users. The soft-decision maximum-likelihood (ML) joint decoder is well known. This optimal decoder suffers from a high complexity requirement that is exponential in the product of encoder memory and the number of users. The size of the decoded subset is a design parameter which allows a tradeoff between complexity and performance. The performance of the GM decoder, once properly characterized, can be analyzed using standard techniques. In addition, a new analysis technique is presented which considers decomposable sequences for the fading channel. With this analysis, we have a new tool for bounding error probabilities for multiuser decoders. Applying this technique to the GM decoder, we can directly identify sequences that are decomposable some fraction of the time, and obtain a new upper bound. Further, this improved bound can be expressed in closed form. Numerical results show that the actual performance gap between the GM and ML decoders can be quite small