Physical world and mathematics

Pentosidine

Pentosidine is a fluorescent advanced glycation end product that cross-links arginine and lysine residues in proteins through a pentose-derived ring, accumulating in aging, diabetes, and uremia.

Pentostatin, also known as 2'-deoxycoformycin, is a nucleoside antibiotic isolated in 1974 from Streptomyces antibioticus that potently inhibits adenosine deaminase and is used to treat hairy cell leukemia, marketed as Nipent.

Pentti Eskola

Pentti Eskola (1883–1964) was a Finnish geologist and petrologist, professor at the University of Helsinki, who originated the metamorphic facies concept and won the Wollaston Medal.

Pentylenetetrazole

Pentylenetetrazole, also known as pentetrazol and formerly sold as Metrazol, is a GABA A receptor antagonist used in laboratory animals to induce seizures for epilepsy research and drug screening.

PEP-II

PEP-II was a two-ring, asymmetric electron–positron B factory at SLAC's Stanford Linear Accelerator Center that delivered collisions to the BaBar detector from 1999 to 2008.

Pepstatin

Pepstatin, also called pepstatin A, is a pentapeptide natural product from the bacterium Streptomyces testaceus, discovered in 1970, that potently inhibits aspartic proteases including pepsin and cathepsin D.

Peptide amphiphiles

Peptide amphiphiles are molecules with a hydrophobic alkyl tail and a hydrophilic peptide head that self-assemble in water into nanofibers, used as scaffolds for tissue regeneration and drug delivery.

Peptide bond

The peptide bond, or peptide linkage, is the amide covalent bond linking amino acids into polypeptide chains, formed by loss of a water molecule and made rigid and planar by resonance.

Peptide C–H functionalization

Peptide C–H functionalization directly converts carbon–hydrogen bonds within amino acid residues of a peptide into carbon–carbon or carbon–heteroatom bonds, bypassing prefunctionalized groups and enabling late-stage modification such as macrocyclization and stapling of peptide therapeutics.

Peptide macrocyclization

Peptide macrocyclization is the chemical, enzymatic, or supramolecular ring-closing of a linear peptide into a macrocycle of 12 or more atoms, improving stability and binding.

Peptide nanofibers

Peptide nanofibers are filaments with nanometer-scale diameters formed when short peptide molecules self-assemble in water, and they are engineered as biomaterials for drug delivery, vaccine carriers, and tissue repair.

Peptide receptor radionuclide therapy

Peptide receptor radionuclide therapy, or PRRT therapy, is a targeted radiopharmaceutical treatment in which lutetium-177 dotatate binds somatostatin receptors on neuroendocrine tumors and delivers beta radiation, approved in the US in 2018.

Peptide synthesis

Peptide synthesis is the laboratory construction of short amino acid chains, most commonly by solid-phase peptide synthesis on a polymer resin, a method introduced by R. B. Merrifield in 1963.

Peptide YY

Peptide YY (PYY) is a 36-amino-acid gut hormone released after meals; its circulating fragment PYY3-36 reduces appetite and food intake, and it was studied as an anti-obesity drug.

Peptoids

Peptoids are synthetic peptidomimetics, oligomers of N-substituted glycine whose side chains attach to the backbone nitrogen; they were developed at Chiron Corporation in the early 1990s.

Oct 10, 2026

Per Bak

Per Bak (1947–2002) was a Danish theoretical physicist who proposed self-organized criticality with Chao Tang and Kurt Wiesenfeld at Brookhaven in 1987, later professor at the Niels Bohr Institute.

Per E. M. Siegbahn

Per E. M. Siegbahn, born 1945 in Stockholm, is a Swedish theoretical chemist at Stockholm University who introduced the CASSCF method and models metalloenzyme mechanisms, including nitrogenase.

Per Geijer

Per Geijer was a Swedish geologist specializing in ore geology, professor at the Royal Institute of Technology and head of the Geological Survey of Sweden.

Oct 10, 2026

Per Lindström

Per Lindström, known as Pelle Lindström, was a Swedish logician at the University of Gothenburg who proved Lindström's theorem in 1969 and introduced Lindström quantifiers in 1966.

Per Linse

Per Linse was a physical chemist at Lund University, PhD in 1984, who pioneered Monte Carlo simulation of charged colloids and polyelectrolytes and developed the MOLSIM simulation software used worldwide.

Oct 10, 2026

Per Martin-Löf

Per Martin-Löf (born 1942) is a Swedish logician and mathematician who held a chair at Stockholm University, known for his 1966 definition of random sequences and intuitionistic type theory, which influences proof assistants like Agda.

Per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS), often called forever chemicals, are persistent fluorinated chemicals used since the 1940s in nonstick coatings and firefighting foam, and now regulated in drinking water.

Per-Tau Shell

The Per-Tau Shell is a near-spherical cavity in the local interstellar medium, about 500 light-years wide, surrounding and connecting the Perseus and Taurus molecular clouds, revealed by 3D dust mapping in 2021.

Peracetic acid

Peracetic acid, also called peroxyacetic acid, is an organic peroxide used as a sterilant, disinfectant, and bleaching agent, best known for sterilizing heat-sensitive medical instruments and disinfecting wastewater as a chlorine alternative.

Percent composition

Percent composition is the percentage by mass of each element in a chemical compound, calculated from masses or a formula and used to find empirical formulas.

Percent sign

The percent sign (%) is a symbol indicating a number or ratio as a fraction of 100. It evolved from an Italian scribal abbreviation of "per cento" around 1425.

Percentage

A percentage, from the Latin per centum, expresses a number as a fraction of 100; 100% equals the whole, and percentages let proportions from different totals be compared.

Percentage point

A percentage point (pp or p.p.) is the unit used for the arithmetic difference between two percentages; a rate moving from 10% to 9% has fallen 1 point, but 10%.

Percentile

A percentile, also known as a centile, is a value below which a given percentage of ordered data falls; coined by Francis Galton in 1885, percentiles are widely used in child growth charts and educational testing.