804:
394:, that is, the mass of the molecule containing only the most common isotope of each element. This also differs subtly from the molecular mass in that the choice of isotopes is defined and thus is a single specific molecular mass of the many possibilities. The masses used to compute the monoisotopic molecular mass are found on a table of isotopic masses and are not found on a typical periodic table. The average molecular mass is often used for larger molecules since molecules with many atoms are unlikely to be composed exclusively of the most abundant isotope of each element. A theoretical average molecular mass can be calculated using the
448:) of macromolecules depends on volumetric proportion of the dispersed particles in a particular solvent. Specifically, the hydrodynamic size as related to molecular mass depends on a conversion factor, describing the shape of a particular molecule. This allows the apparent molecular mass to be described from a range of techniques sensitive to hydrodynamic effects, including
105:
The terms "molecular mass", "molecular weight", and "molar mass" may be used interchangeably in less formal contexts where unit- and quantity-correctness is not needed. The molecular mass is more commonly used when referring to the mass of a single or specific well-defined molecule and less commonly
407:
Mass photometry (MP) is a rapid, in-solution, label-free method of obtaining the molecular mass of proteins, lipids, sugars & nucleic acids at the single-molecule level. The technique is based on interferometric scattered light microscopy. Contrast from scattered light by a single binding event
398:
found on a typical periodic table, since there is likely to be a statistical distribution of atoms representing the isotopes throughout the molecule. The average molecular mass of a sample, however, usually differs substantially from this since a single sample average is not the same as the average
110:
quantities expressed in daltons (Da) were by definition numerically equivalent to molar mass expressed in the units g/mol and were thus strictly numerically interchangeable. After the 2019 revision, this relationship is only nearly equivalent, although the difference is negligible for all practical
101:
is most authoritatively synonymous with relative molecular mass; however, in common practice, use of this terminology is highly variable. When the molecular weight is given with the unit Da, it is frequently as a weighted average similar to the molar mass but with different units. In molecular
606:
IUPAC. Compendium of
Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. ISBN 0-9678550-9-8.
366:
are observed as distinct molecules, with molecular masses of approximately 16.031 Da and 17.035 Da, respectively. The intensity of the mass-spectrometry peaks is proportional to the isotopic abundances in the molecular species. C H
408:
at the interface between the protein solution and glass slide is detected and is linearly proportional to the mass of the molecule. This technique is also capable of measuring sample homogeneity, detecting protein
472:
can then be used to approximate molecular mass using a series of macromolecule-specific standards. As this requires calibration, it's frequently described as a "relative" molecular mass determination method.
94:), and the molecular mass the mass of one specific particle or molecule. The molar mass is usually the more appropriate quantity when dealing with macroscopic (weigh-able) quantities of a substance.
102:
biology, the mass of macromolecules is referred to as their molecular weight and is expressed in kDa, although the numerical value is often approximate and representative of an average.
424:) and protein interactions such as protein-protein interactions. Mass photometry can measure molecular mass to an accurate degree over a wide range of molecular masses (40kDa – 5MDa).
524:
354:
The uncertainty in molecular mass reflects variance (error) in measurement not the natural variance in isotopic abundances across the globe. In high-resolution
118:
of elements in the molecule. The molecular masses of macromolecules, such as proteins, can also be determined by mass spectrometry; however, methods based on
656:
Sonn-Segev, A., Belacic, K., Bodrug, T. et al. Quantifying the heterogeneity of macromolecular machines by mass photometry. Nat Commun 11, 1772 (2020).
493:
detectors. Molecular masses determined by this method do not require calibration, hence the term "absolute". The only external measurement required is
162:
has a molar mass of 18.0153(3) g/mol, but individual water molecules have molecular masses which range between 18.010 564 6863(15) Da (H
668:
Soltermman et al. Quantifying protein-protein interactions by molecular counting using mass photometry. Angew. Chem Int Ed, 2020, 59(27), 10774-10779
718:"Accurate Molecular Weight Determination of Small Molecules via DOSY-NMR by Using External Calibration Curves with Normalized Diffusion Coefficients"
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465:
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have almost identical numerical values as relative atomic and molecular masses. For example, the molar mass and molecular mass of
717:
49:(Da) is often used. Different molecules of the same compound may have different molecular masses because they contain different
457:
453:
490:
687:
Johnson Jr., C. S. (1999). "Diffusion ordered nuclear magnetic resonance spectroscopy: principles and applications".
794:
782:
433:
114:
The molecular mass of small to medium size molecules, measured by mass spectrometry, can be used to determine the
824:
481:
It is also possible to determine absolute molecular mass directly from light scattering, traditionally using the
449:
529:
677:
Paul, Hiemenz C., and Lodge P. Timothy. Polymer
Chemistry. Second ed. Boca Raton: CRC P, 2007. 336, 338–339.
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Young et al. (2018). Quantitative imaging of single biological macromolecules. Science 360, 423-427. DOI:
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A Free
Android application for molecular and reciprocal weight calculation of any chemical formula
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197:(u) is still used in common practice. Relative atomic and molecular masses as defined are
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In mass spectrometry, the molecular mass of a small molecule is usually reported as the
808:
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702:
829:
818:
587:(9th ed.), International Bureau of Weights and Measures, Dec 2022, p. 145,
554:
432:
To a first approximation, the basis for determination of molecular mass according to
198:
193:
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106:
than molecular weight when referring to a weighted average of a sample. Prior to the
46:
68:
The molecular mass and relative molecular mass are distinct from but related to the
515:
17:
539:
206:
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of the element in a given sample (usually assumed to be "normal"). For example,
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for calculation of molecular weights, reaction coefficients and stoichiometry.
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143:
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74:. The molar mass is defined as the mass of a given substance divided by the
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and relative molecular masses (molecular weights) are calculated from the
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188:
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497:, which describes the change in refractive index with concentration.
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and light-scattering are also used to determine molecular mass when
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79:
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of many particles or molecules (potentially containing different
625:
202:
412:
state, characterisation of complex macromolecular assemblies (
622:"Atomic Weights and Isotopic Compositions for All Elements"
792:
183:
Atomic and molecular masses are usually reported in
154:. The standard atomic weight takes into account the
690:
Progress in
Nuclear Magnetic Resonance Spectroscopy
371:can also be observed with molecular mass of 17 Da.
485:. This can be accomplished either via classical
187:, which is defined in terms of the mass of the
525:Dumas method of molecular weight determination
126:or mass spectrometric data are not available.
8:
399:of many geographically distributed samples.
658:https://doi.org/10.1038/s41467-020-15642-w
219:
217:, are calculated respectively as follows:
747:
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134:Molecular masses are calculated from the
780:Stoichiometry Add-In for Microsoft Excel
460:when the eluent is an organic solvent),
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646:https://doi.org/10.1126/science.aar5839
571:
466:nuclear magnetic resonance spectroscopy
61:ratio of the mass of a molecule to the
86:(g/mol). That makes the molar mass an
171:O) and 22.027 7364(9) Da (H
7:
53:of an element. The derived quantity
27:Mass of a given molecule in daltons
25:
581:The International System of Units
201:. Molar masses when expressed in
191:C (carbon-12). However, the name
802:
716:Neufeld, R.; Stalke, D. (2015).
609:https://doi.org/10.1351/goldbook
65:(which is equal to one dalton).
305:Total molecular mass (Da or u)
241:or molecular weight (unitless)
213:, whose molecular formula is CH
142:present in the molecule, while
1:
703:10.1016/S0079-6565(99)00003-5
491:multi-angle light scattering
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495:refractive index increment
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239:Total molar mass (g/mol)
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38:) is the mass of a given
464:, and diffusion ordered
194:unified atomic mass unit
550:Molar mass distribution
487:static light scattering
477:Static light scattering
396:standard atomic weights
358:the mass isotopomers CH
148:standard atomic weights
108:2019 revision of the SI
76:amount of the substance
55:relative molecular mass
535:Standard atomic weight
520:ebullioscopic constant
434:Mark–Houwink relations
299:Nuclide mass (Da or u)
233:Standard atomic weight
78:, and is expressed in
530:François-Marie Raoult
468:(DOSY). The apparent
436:is the fact that the
156:isotopic distribution
428:Hydrodynamic methods
289:Molecular mass of CH
63:atomic mass constant
545:Absolute molar mass
511:cryoscopic constant
438:intrinsic viscosity
785:2011-05-11 at the
739:10.1039/C5SC00670H
97:The definition of
594:978-92-822-2272-0
470:hydrodynamic size
392:monoisotopic mass
386:Mass spectrometry
380:Mass spectrometry
356:mass spectrometry
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18:Molecular weights
16:(Redirected from
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540:Mass number
483:Zimm method
446:suspensions
130:Calculation
116:composition
819:Categories
726:Chem. Sci.
631:2007-10-14
566:References
462:viscometry
111:purposes.
71:molar mass
507:Cryoscopy
442:solutions
414:ribosomes
120:viscosity
783:Archived
758:29142693
560:SDS-PAGE
501:See also
348:16.0313
327:1.007825
319:12.0000
150:of each
138:of each
92:isotopes
59:unitless
51:isotopes
40:molecule
809:Physics
749:5656982
489:or via
333:4.0313
313:12.0000
284:16.043
255:12.011
211:methane
189:isotope
185:daltons
152:element
140:nuclide
88:average
57:is the
795:Portal
756:
746:
591:
362:and CH
302:Number
269:4.032
249:12.011
236:Number
47:dalton
42:. The
721:(PDF)
585:(PDF)
418:GroEL
263:1.008
160:water
80:grams
830:Mass
754:PMID
626:NIST
589:ISBN
518:and
509:and
444:(or
180:O).
82:per
44:unit
30:The
744:PMC
734:doi
699:doi
458:GPC
454:SEC
450:DLS
440:of
422:AAV
207:mol
84:mol
821::
752:.
742:.
723:.
695:34
693:.
624:.
452:,
420:,
416:,
338:CH
274:CH
797::
760:.
736::
730:6
705:.
701::
634:.
611:.
369:3
367:H
364:4
360:4
340:4
330:4
324:H
316:1
310:C
291:4
276:4
266:4
260:H
252:1
246:C
225:4
215:4
205:/
203:g
176:2
167:2
36:m
34:(
20:)
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