PubMed Health⌕ Search

Biomedical subjects

D K Kondepudi

Publications and source records attributed to D K Kondepudi.

9 recordsLinked to original sources
PubMed2001

Chiral asymmetry in spiral galaxies?

Spiral galaxies are chiral entities when coupled with the direction of their recession velocity. As viewed from the Earth, the S-shaped and Z-shaped spiral galaxies are two chiral forms. What is the nature of chiral symmetry in spiral galaxies? In the Carnegie Atlas of Galaxies that lists photographs of a total of 1,168 galaxies, we found 540 galaxies, classified as normal or barred spirals, that are clearly identifiable as S- or Z- type. The recession velocities for 538 of these galaxies could be obtained from this atlas and other sources. A statistical analysis of this sample reveals no overall asymmetry but there is a significant asymmetry in certain subclasses: dominance of S-type galaxies in the Sb class of normal spiral galaxies and a dominance of Z-type in the SBb class of barred spiral galaxies. Both S- and Z-type galaxies seem to have similar velocity distribution, indicating no spatial segregation of the two chiral forms.

Journal Article↗
PubMed2001

Conditions for chiral asymmetry generation in the preparation of the chiral octahedral cobalt complex.

We have reported that the random chiral asymmetry generation, which is a spontaneous preferential generation of one enantiomer, was observed in the synthesis of a chiral octahedral cobalt complex, cis-[CoBr(NH(3))(en)(2)]Br(2). In this article, we review our studies to explain in this system the autocatalytic growth of small enantiomeric excess that arises due to statistical fluctuations. One important experimental finding was that the rate of chiral autocatalysis increased with increasing the degree of supersaturation. Furthermore, our numerical simulation indicates that even small inhomogeneities in the reaction system may play a significant role because their effect is amplified by the autocatalytic reaction under appropriate conditions. In a small volume, fluctuations in concentration can grow if the autocatalytic growth overcomes the diffusional loss of the excess concentration from this volume. This may makes the enantiomeric excess of the chiral complex randomly fluctuate from run to run.

Journal Article↗
PubMed2001

Chiral autocatalysis, spontaneous symmetry breaking, and stochastic behavior.

During the past decade, chirally autocatalytic systems that exhibit unusual and interesting phenomena, such as spontaneous chiral symmetry breaking and stochastic behavior, have been identified. In this Account we outline the context in which chiral autocatalysis is of interest, summarize recent advances, and discuss our current understanding of the underlying kinetics and mechanisms. In addition, we note some fundamental aspects of amplification of enantiomeric excess and sensitivity of symmetry breaking transitions to asymmetric factors.

Biopolymers↗
PubMed1996

Homochirality as the signature of life: the SETH Cigar.

A characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. It is therefore suggested that a search for extra-terrestrial life can be approached as a Search for Extra-Terrestrial Homochirality (SETH). A novel miniaturized space polarimeter, called the SETH Cigar, is described which could he used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. It is believed that homochirality will be found in the subsurface layers on Mars as a relic of extinct life.

Astronomy↗
PubMed1992

Gravity detection through bifurcation.

Bifurcation is a phenomenon in which a physical system is forced to make a choice between one of the several possible states to which it can evolve. In this process the system can become extremely sensitive to very small influences--smaller than the size of the fluctuations--that favor one of the states. A general theory of this sensitivity and a simple model for gravity detection is presented. The difference between systems in thermodynamic equilibrium and those that are far from equilibrium is also discussed.

Animals↗
PubMed1991

Detection of gravity through nonequilibrium mechanisms.

Using the principles of physics, could we set a fundamental lower limit for the size of a cell that can respond to gravity? Pollard (1965) tried to obtain such a limit assuming a gravity sensing mechanism that could be described as a system in thermodynamic equilibrium. In this chapter, a dynamic gravity sensing mechanism that is not in thermodynamic equilibrium is considered. It is shown that under some conditions nonequilibrium systems can be more sensitive than equilibrium systems. The dynamic mechanism described here is able to respond to gravity by virtue of its ability to perform a process similar to "signal averaging" used in electronic detection of weak signals. Through this process, a system is able to respond to a small systematic force embedded in a larger but randomly fluctuating force.

Cell Movement↗
PubMed1982

Possible effects of 10(11) Hz radiation on the oxygen affinity of hemoglobin.

When oxygen binds to one of the subunits of hemoglobin, the oxygen affinity of the other subunits is enhanced. This cooperative interaction of the subunits is initiated by the movement of the heme plane toward the proximal side when oxygen binds to the heme. This motion is transmitted to the surface of the globin through a "reaction channel" consisting of a group of atoms whose motion is well correlated. Considering the detailed geometry and X-ray diffraction data of the mean square displacement of the atoms surrounding the heme, a simple model for the heme plane oscillations is developed. Using this model, the natural frequency of oscillations is shown to be approximately 5 X 10(11) Hz. This result, along with the recent experimental data on the kinetics of the conformational changes of the heme, points to the possibility of radiation influencing the oxygen affinity of hemoglobin. If such an effect exists, it is likely that the oxygen affinity will be enhanced by the radiation.

Heme↗
PubMed1978

Field-induced instabilities in two-component systems: the cell-free glycolytic system.

The effects of weak static electric field on a cell-free glycolytic system, which is known to exhibit oscillatory behavior, have been studied using an allosteric model (due to Goldbeter and Lefever). Linear stability analysis is used to determine the change in the nature of stability and the consequent appearance of dissipative structures, due to the electric field. The results show that for this system all the necessary conditions for a field induced instability are satisfied. An order of magnitude calculation of the field strength shows that field strength in the range 10-100 V/cm is required to produce observable change in the system's behavior.

Cell-Free System↗