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Molecular Weight

The mass of one mole of a compound, in grams per mole — what converts a mass concentration into a molar one.

Molecular weight is the mass of one mole of a substance, in grams per mole. It is the sum of the atomic weights of every atom in the molecular formula, so formula and mass are not independent facts — one determines the other.

That relationship is a usable check. A formula containing an atom the stated mass does not account for is an error, not a rounding difference. This catalog shipped exactly that: GHK-Cu was published with a copper-containing formula against the copper-free mass of 340.9, roughly 63 g/mol light. Every molecular weight published here is now recomputed from its own formula before it goes live.

Quoted values are average molecular weights, calculated from standard atomic weights, for the neutral free base unless the product is explicitly a salt or a metal complex. Mass spectrometry may report a monoisotopic mass instead, which is a different and slightly smaller number for the same molecule.

Topic: Fundamentals

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Guides that cover this

Charged Aerosol and ELSD Detection for Peptides Without a Chromophore

Nebulisation-based detectors answer a physical question rather than an optical one: how much non-volatile mass reached the detector. What that buys when a sequence has no tryptophan or tyrosine, why the response is a power law, how far mobile-phase composition moves it and what inverse-gradient compensation corrects, and the precise claim a relative mass percent from CAD or ELSD will and will not support.

Cyclic Peptide Passive Permeability and Molecular Chameleonicity

Permeability in this class tracks how many backbone donors are still exposed at the membrane rather than how many the molecule owns, though no single count settles it. The size and polarity boundaries, the intramolecular hydrogen bonding that shields donors in a low dielectric, how the two conformations are demonstrated by NMR in polar and apolar solvent, N-methylation as the designed alternative, and why PAMPA and cell monolayers disagree.

Stability Study Design: Bracketing, Matrixing and Extrapolation

Long-term, intermediate and accelerated arms answer different questions. What bracketing assumes about monotonicity and matrixing costs in power to detect a slope difference, how the shape of the degradation curve decides where pull points can be removed, and why an activation energy that changes with the condition means a 40 °C ranking is not a 5 °C ranking.

Regioselective Disulfide Formation in Bridged Peptides

Oxidation does not know which cysteines you meant to join. When a single thermodynamic fold makes random oxidation legitimate, when orthogonal protection is the only honest route, and how concentration, redox buffer and oxidant choice decide which isomer you get.

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