Biomedical subjects

Agnieszka Sawicka

Publications and source records attributed to Agnieszka Sawicka.

4 recordsLinked to original sources

PubMed2005

Inverse potassium hydride: a theoretical study.

Results of an experimental study on the unusual "inverse" charge state (H(+)Na(-)) in salts where the H(+) ion is sequestered, combined with our earlier theoretical calculations on an unsequestered model compound (Me(3)N-H(+)...Na(-)), prompted us to further investigate such systems. In particular, we examined Et(3)N-H(+)...K(-) because considerations of the proton affinity of the amine and of the metal-hydride bond strength suggested that this ion-pair complex might be more stable to proton abstraction than was Me(3)N-H(+)...Na(-). In the present work, the ground-state potential energy surface of the Et(3)N-H(+)...K(-) ion pair was examined using second-order Møller-Plesset perturbation theory and 6-311++G basis sets. We found Et(3)N-H(+)...K(-) to be metastable to dissociation with a barrier of 8 kcal mol(-1) (computed at the CCSD(T) level of theory). This barrier indeed is substantially larger than that found earlier for (Me(3)N-H(+)...Na(-)) and suggests that unsequestered inverse-charged H(+)M(-) ion-pair salts may offer a reasonable route to creating high-energy materials if a means for synthesizing them in the laboratory can be designed.

Journal Article↗

PubMed2005

Coulomb-assisted dissociative electron attachment: application to a model peptide.

The fragmentation of positively charged gas-phase samples of peptides is used to infer the primary structure of such molecules. In electron capture dissociation (ECD) experiments, very low-energy electrons attach to the sample and rupture bonds to effect the fragmentation. It turns out that ECD fragmentation tends to produce cleavage of very specific types of bonds. In earlier works by this group, it has been suggested that the presence of positive charges produces stabilizing Coulomb potentials that allow low-energy electrons to exothermically attach to sigma orbitals of certain bonds and thus to cleave those bonds. In the present effort, the stabilizing effects of Coulomb potentials due to proximal positive charges are examined for a small model peptide molecule that contains a wide range of bond types. Direct attachment of an electron to the sigma orbitals of eight different bonds as well as indirect sigma bond cleavage, in which an electron first binds to a carbonyl C=O pi orbital, are examined using ab initio methods. It is found that direct attachment to and subsequent cleavage of any of the eight sigma bonds is not likely except for highly positively charged samples. It is also found that attachment to a C=O pi orbital followed by cleavage of the nitrogen-to-alpha-carbon bond is the most likely outcome. Interestingly, this bond cleavage is the one that is seen most commonly in ECD experiments. So, the results presented here seem to offer good insight into one aspect of the ECD process, and they provide a means by which one can estimate (on the basis of a simple Coulomb energy formula) which bonds may be susceptible to cleavage by low-energy electron attachment.

Alanine↗

PubMed2005

[Nephrology of love].

The article presents different aspects of the connection between human heart and kidneys. This connection is evident in the symbolism of the Old Testament of the Bible, organ donation as the manifestation of the love of our neighbor, endocrinological and sexual dysfunction, and finally in searching for biological determinants of finer feelings. In the Old Testament tradition kidneys were thought to be human spirit's dwelling. Moreover, the simultaneous studying of kidneys and heart meant profound understanding of the matter. Nowadays, it is also possible to find the Biblical love of our neighbor, for instance among kidney donors. What is more, every nephrologist should treat his patients with love and dedication, which makes it easier for him to understand their problems, especially these concerning sexual dysfunction. Sexual dysfunction occurs among men and women equally and specialists, apart from using many different methods, have to deal with the consequences of renal failure mainly by means of transplantation.

Bible↗

PubMed2003

Inverse sodium hydride: a theoretical study.

A recent experimental investigation in which a salt containing the unusual charge distribution H(+) and Na(-) was synthesized and characterized prompted us to undertake an ab initio theoretical investigation. In the salt synthesized, the H(+) is bound to the nitrogen center of an amine and the Na(-) alkalide is "blocked" from approaching the protonated amine site by steric constraints of a cage structure. Although one expects that the Na(-) would deprotonate an unprotected R(3)N-H(+) cation, we decided to further explore this issue. Using extended atomic orbital basis sets and Møller-Plesset and coupled-cluster treatments of electron correlation, we examined the relative stabilities of the prototype (Me)(3)N + NaH, (Me)(3)N + Na(+) + H(-), (Me)(3)N-H(+) + Na(-), and (Me)(3)N-Na(+) + H(-) as well as the ion pair complexes (Me)(3)N-H(+).Na(-) and (Me)(3)N-Na(+).H(-). The primary focus of this effort was to determine whether the high-energy (Me)(3)N-H(+).Na(-) ion pair, which is the analogue of what the earlier workers termed "inverse sodium hydride", might be stable with respect to proton abstraction under any reasonable solvation conditions (which we treated within the polarized continuum model). Indeed, we find that such ion pairs are metastable (i.e., locally geometrically stable with a barrier to dissociation) for solvents having dielectric constants below approximately 2 but spontaneously decompose into their constituent ions for solvents with higher dielectric constants. We suggest that amines with large proton affinities and/or metals with weaker MH bond strengths should be explored experimentally.

Journal Article↗