i “het Udaafde

git.

(Goutridution Ne. 2261 from the Gates and Crellin leberaterios ef
Gheaistry, Califeemia Institute ef Technology, Pasadena, California )

 

Sillinen Leeture, Tale University, Osteder 15, 197

ly
isms Carl Pomling

Prefeseer ef Chenistry
Galiferaia Institute of Technelegy

the hundved years cf existence of the Sheffield Sclentifia
Seheol of Tale University have witnessed the transition of chenistry
from an essentially empirical and deseriptive selence to a largely
exact and theeretionl ons. One hundred years age the properties of
many chemical substances hai boon investigated, the difference between
clenents and cempomés had been recegnized, analytics) chentstry hai
boon doveleped te guch om extent as te be a reliable toel, many nethods
ef synthecie of inorganic ani organic substances had been discovered,
emi the foundations had been laid fer an extensive chemical industry.

However, at that time, in 1647, the correct atomic weights of the

elements had not yet been generally accepted, 20 that the formula of
water was still written ae WD by many chenists. ‘The idea of valenes
had net yet been fermiated--tt was not witil five years later that
“2

the statement was firet mate (by 3. Frankland in Ingland) that atoze
have a definite asbining pewer, which determines the formelas of com
pounds. The first structural formulas for molequles were not draw
‘antil 1858, when Archibald 5. Couper introduced the idea of the valence
bond; in the deme year August Kekule, in Germany, showed thet carbon
ie quadrivalent. During the next half ountury, developed very rapidly,
to become the great science--and powerful art--that it now is.

Here in Yow Haven, where Josiah Villard Gibds was ders, studied,
worked, and died, I oan iitustrate the progress of chemical sclence
during the past 100 years Beet by discussing chemical thernmedynanias,
the field of science that, in the werds of Wilhelm Ostwald, was
founded by Gibbs. In 1647 J. Willard Odds wae a dey ofght:yeape:024.
the first law of thermedynemics--the law ef conservation ef energy--
had not yet been accepted by physicists, although Joule had recently
make his determination ef the nechanical equivalent of heat. It was
not wmtil « year later, in 1848, thet Berman Heluholts recognised Gi
the importance of Joule's werk and fellewed ite implications through
various problems in chemistry, physics, and viclegy. The second law
ef thermodyaanies hat been formulated by S. Carnet, in 1824, but it was
mot until 1852 that Lerd Kelvin and Clausive combined 1¢ with the firet
law to produce the present science of thermedynanias, in ite application
to physical phenemema. ‘then in the period between 1573 and 1575
Willard Gibbs published his great papers dealing with the application of
thermodynamics to chenieal phenomena. Gibbs’ werk put the sciences of
“+

chemical thermedynanice in nearly its final fern; only one nore great
discovery remained to ve made--that of the third law of thernedynanios,
Wy W . Serast at the beginning of the twentieth santury.

let “oe eentrast the knowledge about a chemical reaction avail-
able in 1847 with that in 1947. In 1847 0 reantion invelving the con-
version of certain reachant gubstances inte certain products, such as
mitregen and hydregen inte ammonia, eould be disauseed only to the extent
that direst experinental iafernation obtained Ww edserving the reaction
itecl? vas at hand. Only if the reactants had actually been observed te
combine te fom the produsts cwuld it be sald to be 2 possible chenical
veection. ‘the aneunt ef heat evolved or absorbed during the reaction
woald have been known anly if the reaction had actually taken place,
and the heat evelution or abverption had been ensured. ‘the question of
increasing the yield of the preduct could not heave beem diseussed at all--
there was no knowledge as to whether increasing the temperature, inoreasing
the pressure, or making other changes in the sytem would increase or de
crease the enount of predust obtained. In 1947 1¢ ie possible, fren
knowledge of the thernofynemic properties of the reactant qubstances and
the products, to preduct, for a reaction that has never been observed te
coeur, nostéf its important charscteristice--the anount of heat that
would be evelved or absorbed vhen the reaction takes place, and the ex-
tent pear would take place, in ite dependence on temperature, preesure,
consemtrations of the reactants, amd other factors. ‘there still remains,
however, one nost important question to which s definite anewer cannot
in general be given. This is the question as to the rate at which the
Yeaction will take place under given circunstances. We are not yet able
oho

te make predictions about this rate of reaction, exeept for certain
eimple eyetens. the field ef chenical eheructynamion io in nearly ite
final state of developments the field of eheutenl kinsties ie just
Deginning to be develeped.

Guenieal thermcdynesies, like nearly every ether field of
cheniatry, has doen influensed ty the great progress that has taken
place in extending our knovledge of atonie and molecular structure during
the past fow decaies. the electron iteelf was discovered in 1897, and the
atenic moleus in 2911; sinee then a penetrating oni detalbed understanding
ef the electrents and atomic strusture of matter hes been obtained, and
cheaiete are nev able to talk about the atosic anf electronic architecture
ef molecules and erystals almost as @afidently as architects can talk
avout the structural elenenbe of skyscrapers and bridges. Wy the methods
ef spectroscepy, x-ray Giffrantion, and electron diffrastion detathed. -
interatomic distances have been deternined fer thousands of substances.
The magnitudes of the forces sperating Between the atoms have alse been
deteruined experimentally for very many molecules and oryetals. Farther
(nformation about the nature of substances has been sbtained by the
application of many different techziques of modern physies--the study of
the diamagnetic, paransgnetic, and ferromagnetic properties ef the substances,
their electrical preperites, the spectroscopy mot only of the Visible,
infrered, x-ray, and ultraviolet regions but even, in recent years, of the
wicrowave and long wave radio regions of the spectrum. the structural
knowledge obtained in this way about molecules permits the calculation
of thernedynsmio properties for many substances.

& signifieant start has already been unde on the task of
formulating a complete aystem of chemical shermedynemias of pure substances.
Tails task invelves the Getermination for cach substance at one tenperature
of i satnaipy, Pelativa te the elements that oompese it. It is further
neceseary to deternine the entropy ef the substance at ome teuperature,
whieh can be dene Wy any ome of thres methods, the measurement of a
chemical equilitriws imvelving the substance andpther substances of knova
thermodynamic properties, the seasurement of the heat capacity down te
very low temperatures and the application ef the third law of thermogy-
manica, or the caleulation of the entrepy from etructural data obtained
W spectroscopic and diffraction methods. Kuowledge of the heat capacity
of the substance ever a wide range of temperatures, sdtained either by
direst experiment or by calenlation fren knowa strustural preperties, then
permite the extension of the tables of thermedynanic propertics over this
femperatare range. ue may well expect that at some time in the distant
future there will be available extensive tables ef the enthalpy, entropy,
and free energy of thousands of substances over wide ranges of conditions.
There would then still remain, however, the problem of the thermodynamic
properties of solutions, for wich no euch sinaple and inclusive set ef
data could be formalated.

It is interesting te note that, in a practical sense, the third
lew of thermodynamies differs from the fires and secon’ lave, in that it
gannot be applied completely independently of structural considerations.
In general, thermodynamic deductions are expected to be independent of any
structural considerations, amd to be reliable, provided only that true

thermodynamic equilibrium has been appreoximted or achieved in the
experinent.  Lavestignutions carried ent during the past twenty-five years,
eepecially by Professor Villian F. Gisigig, have shown, hevever, that the
applications of the third lew of therncdpnanics te the caloulation of

 

entropy values fer crysteiiine gadstaness by atamurements of heat capacity
made to lew temperatures are often in practios net reliable, unless some
structural information about the residual entropy in the crystals at the
Loweet temperatures at which sengurmentes are made is available. ‘Thus simple
sabetances wach as hydrogen, earbon monoxide, mitrous oxide, aad aitroges
dioxide have residual eatropies of signifieant amount, caused hy such
etvuctaral features an a randommess of orientation of molecules in the
orpetal lattices. It any be said, with justice, that the experinonts have
not yet Deen carried cut ta sufficieatly low tonperntures, er—thet—wut--
fictontiy—cev-tempevatures, of that sufficient time han sot teen allowed
for the oryetale to achieve a atate of truce thermodynamics equilibrium;
nevertheless, the practical problem still existe--the reliable application
of the third law of tharnedynanics requires a penetrating understanding
of the structure of the crystalline substance under investigation.

fhe resent decadee have seen an sxtraordinary developaent of the
art of oryogenics, the production of low temperatures The pioneer work of
Dewar was extended by Kandorlingh Onnes, whose feat of reaching s teaper-
ture ae low as 0.71° K. ewemed for many yeare te be incapable of signifi-
gant betterment. Then, in 1924, Willian fF. aqua “auggeatod atKi fate
practice the astounding new method of ceoling by demagnetization, with which
he and other investigators have been able to reach temperatures as low os
about 0.001° EK.
Although the production of lew tenperatures sight well be
eonsiderved to de a part of the science of physics, the fact that this
final great achievenent of reaching the temperature of @.001° K. was
nade by a professor of chemistry, using a method iavented by hineolf, has
led me to include mention of it in my talk thie evening. The work done
ty Profeseor Glanque illustrates the fact that the borderline between
chenietry and physics ie a d4iffieult one to define, as ie alse the
Porderline between chemistry and biology. ‘The logarithmic dependence of
eortain thermodynanie quantities on temperature is, of course, responsible
for the great diffieulty found in decreasing the temperature by successive
factors of ten, and leads to the theeren of the imposeiblity of reaching
the adsolute sere itself. It has recently been pointed out to me by
Profeceor Trans simex! at Oxford, hovever, that we should not teal that
shore ie an interesting portion of mature to which access is denied te
wen, namely, the pertion of nature that deals with the properties of satter
at temperatures lover than thoee that can ever be achieved in the laboratory.
Professor Simon pointed out that the only low temperature range that is
inaccessible te man is that in which nc interesting phenomena cocur, be-~
eause if any phenemena were to cecur, they themselves could be used as the
method of achieving the lew temperature.

let us now return te the basis of chenistry--the atoms of the
ehenical elenen6s. ‘The last hundred yeags have seen the systematisation —
of the elements through the periodic system of Mendeleyey, the assignment
of precise atomic weights to most of the known elements, the Aiscovery of
the elements predicted by the unfilled sequences in Hondeleyev'a table,

as well as the unanticipated series of noble gnees, and finally, in recent
aGo

years, the development of modern aleheny, the conversion cf one clement
into another, and the artificial production of acw elamente. I need do
no more than to refer to Professor Lawrence's lecture this afternoon, in
woich he has des@ribed the development of this mont exciting firld of
e¢lunce. How that four tranguraniwa elements heve been reported, nep-
tundum, pluteniua, awericiun, and curiua, we may lock forward wlth confi~
dence to the announcement thet st111 more new alements have been mada, and
that pragtical methods of wamufsctuce fa lerge quantities ef the uost rare
of the lighter elements have also bean developed. Ye may well expect
that im the future world mmelear chemistry will be found of the greatest
value in many vaya, not only dy tho production of now eleuents and SF tne
uge of radioactive elenanis aa iracers, but also op tne pratypeten of new
Chanical reactions thrcugh the use of bombardment with high anergy par
vicleae

Tnorgmmlc chemistry hes been making steady progresas The ine
organic chawist of today has a great advantage ever his fellow of praced-
ing generetions, in that he hag a thorough understanding of the molecular
asiructurs of most of the substances with which he is working, and of the
relation betwoon the phyeleal ani chemical properties of the substances
wad their structurdse 4n iilustration of the usefulnuss of sbruciural
imorludge provided by the recent develogasnt of wabsiances that are
alailar to organic compousis, wat with silicon atams, which fora the same “
tatranedral bonds as carbo:n, in place ef sase or all of the carbon atoms.
She fivet substance of thie mature #as made helf a cenbury agoe It had

not Deen foun! poseible to make in lerge quantities the gubstanes dianend
which is a very useful material because it is the hardest of all knows
wabetances. However, it was found possible to make a new substance, with
the same tetrahedral structure as diamond, but with half of the carbon
atoms replaced by silicon atone-—the substance ogyborundua, which has
now £67 many years found extencive use as an abrasive. Then it was found
that other compounds of silicon could be made, the silicones, which have,
in place of lomg chains of carben atone, chains of silicon atems (usually
with oxygen atoms interspersed, in a sort of ether linkage), with methyl

3

groups or other side chaing attached, The silicones have many very use-
fal properties. They can be used as insulating lacquers, permitting
electrical motore to be wuilt for eperation at much higher temperatures
than with orgafie insulators; eilicone rubber can he made, eepecially for
use at higher temperatures than ‘vithatood by ordinary natural rubber or
ayathetic rubber; some of the silicone oils have a very valuable property,
that of changing their viseoesity only a small amount with change in tenpere-
ture--a property that seems to be due te the tendeney ef the molecules to
e011 into a roughhy spherical shape at low temperatures, and hence to roll
over one another relatively easily, whereas at higher temperatures, at
which the molecules uneoil, they become entangled with one another, and
thus overcome in large part the normal tendency of a liquid te show a
pronounced decrease in viscosity with increase in temperature.

The chemistry of fluorine has made great progress in recent
years. The valuable properties of new compounds of fluorine depend on the
wolatility of fluorine compounds and the low chemical reactivity ef the

Oarbon-fluorine bond. Useful fluorine compounds include the freons, such
=10-

oe GPg0ig, whieh are used us the fluid im refrigerating machines and as
nen-toxie solvents for ineseticides ond ether selutes, and the flucrine-
eurbden high polymers, such as the extremely unreactive pheaphie that is
fegued by the polymerisation ef tetvaflucrecthylene.

Am interesting recent development in inorganic chemistry ie
that of new teehaiques for growing large eryetale fer special purposes.
During the wer it was found possible te grew large oryetals weighing many
pounds, of wach gudstanees as ethylenediannontun tartrate, valuable be~
enue of their pleseslectrie properties, which find use in radar and other
fields ef modern physies. In Germany an interesting technique ef growing
large eryetale of synthetic mien we developed, whieh depends for its
waeoess on the erientation of the growing cryetal in a atrong magnetic

The art of organic chenistry and the saienee of organic chenl stry
have moved along steadily hand in band. Organic cheniste develep a feal-~
fag for the chenieal properties of the many substances G1th vaich they
werk which gees far deyend the ayatenatised theoretical knowledge that
they ean express; wut the theory of organic chenietey has nevertheless
now developed to such a state that the science ie ne longer a uysterious
one, purely an art whose praction depends on the application of empiriesa)
rules. It is now possible fer the organic chentst to mee hie kncwledge
of molecular structure to predict, with sene confidence, that certain

 

eould be carried out te produce preduets with certain desired
propertics, One most intesesting application #f this new method =

organic chemist$y has been to the manufacture of high polymere, uch as

the new fibrous and plastic eubstances, which were synthesised {1 con sng Atinte-
“ll-
ef predictions of their properties male upon the besia of considerations
of molecular structure,

The methods used by the organic chemists besane more powerful
trom decade to deande. He now has at hand techniques of very high pree-
ware hydrogenation, the use of catalysts specific to certain reactions,
powerful techniques of separation wach aq chromatographic analyals and
molequiar digtillation, and new physicel methods for structural studies
gugh ag Meray diffraction and spectroscopy. A vary interesting exammle of
the interrelation between organic chemistry and ether fields was provided
@uring the war by the concerted attack on the problem of the structure of
pentotliin’ The organic chenists who were working on the problem: found
it impossible to determine the correct structure by the conventional
methods, dbecmise the molecule hag some structural characteristics that
have not appeared before in any mown substances, and 1¢ remained for
physical chemists and physiciets, using the techniques of x-ray diffrace
tion and infradped spectroscopy, to determine the structure for them.

It is the field of chesistry in relation to biology and medicine
in which most striking progress has been made in recent decades, and which
offers the most promise for the future. Biologists now are becoming chem-
ists - they isolate vitamins, hormones, enaymes, acetyl choline in nervous
procesaes, histamine in anaShylaxis and alliargic responses, plant growth
factors, wold healing qubstances, flewering substances, substances to
held the fruit on the trees and to ripen the frait after 4% hae left the
trees. Wo longer is it possible for a chamist to achieve a fealing of
superiority to the biolegist simply by quoting yin complex chemical far«
malas ~ nor, indeed, for the physicist to overcome the chemist by quoting
eome complex mathematics.
~12-

And in medicine, as in biology, a new future 1s drawing near ~ a
future of great progress through ever closer cooperation with the baaie
sclences, There has indeed been great progress in medicine during the past
century. In forty years the mesn expectancy of life has increased from 49
to 65 years. The childhood diseases - diphtheria, scarlet fever, whooping
cough - have decreased to 10 percent of their mortality in a quarter of a
century. Other infectious diseases are in the main well under control, by
vaccines, seruma, the sulfa drugs, and now penicillin. Shakespeare nentioned

"the rotten diseases of the south, the guta~griping, ruptures, catarrhs,

Loads ofgravel if the back, lethargies, cold palsies, raw eyes,

dirt-rotten livers, wheezing lungs, bladders full of imposthume,

aciaticas, lime-kiins 1! the valm, incurable bone-ache,

and the rivelled fee-simple of the totter."
Moat of these diseases are no longer important - there are now no serious
cases, so far as I know, of rivelied fee-simple of the tetter, but "incurable
bone~ache,*® under which we wight include arthritia, is s very serious dia-
ease, of which little control has been obtained. There are still virus
diseases that are very troublesome - poliomyelitis, influenag, the common
cold. Then there remains the problem of the degenerative disenses - cancer,
heart disease, cerebral disease, nephritis - which, as control of other
diseases is obtained, are becoming increasingly important. To attack these

great sedical problems new basic knowledge is ueeded, about the netre of

cella and of physiological processes, and about the chemotherapeutic action,

ag well ss the norsal physiclogical action, of chemical subetances.
oli.

The grextest problem that remains to be solved ta that of the
structural bagle of the vhysfologienl activity of chemical subs tances.
“hen once this problen hag bean solved, and when it hes hecome posstble
to Cetermine im ‘etall the molecular structure of the vectors of (i sense
aul of the Goastituants of the celia of the human body, we shall be able
to deve up the speeifications of the specific theranautic agent to >rotect
the body against « specific danger, and then to proceed to amthesize the
agent agoording te the apeetfications. So far we have only the hint that
chemotherapeutic agents may act through competition with essential meta~
bolites, as in the competition, vointed out by Yoo's and vildes? of the
walfe drugs witht pertnobonsote acid.

I Delieve that thie predlem, that of the nature of the competition
of two substances cremuebly for specific combination with soma part of a
living oell, is very closely relnted to the @tneral problem of the nature
of the foreas that leads to the striking specificity of properties show
by many bielegical substences, sepecially the native vroteing and polysac~
charides. I believe that these forces are aleo operative in the phenomenon
of self-daplication shown by viruses, genes, and othar biclogiocal entities,
ami which will be diegussed by Dr. Stanley and Professor Beadle in their
lectures tomorrow. I nyeelf have been especially interested in the spe-
cific forces operating between an antibody molecule and the molecules of
antigens or haytens with which 1t has the power of specific conbination.
iy interest in this prodlem was developed ever ten yeara ago in conver-
sations mn ty. Karl Lawisteiner and the work that. my collaborators and
T have dene has Consieted largely in the extension and refinement of

investigations initiated by Dr. Law evetner &
aie

Permit me to rewier briefly the basic phenosena of inmmochend stry,
When = foreign material of lexge moleculer veight - x Brotein or poly sace
charide, either pure or pert of the structure of an animal or plant cell -
ia injected into an anivel, wach ss a rebbit, the enimel fn the course of
& few days may develop in ite blood and within ite cellsy eubstances,
celled antibetics, that have the power of evegific Combination with the
injected material, the antigen. Thug rhen 2 perticular animal or plant
protein ie ingested dato o rabbit, the rebbit develope in ite blood anti-
bodies thet are enpable of senbining with thet protein, but not, or at any
rate only very exceptionsily, capable of combining with any of the tense of
thonemads of other vroteins that exist in nature, Yer example, an antiserum
made by injeating hemoglobin obtained from one animal inte a rabbit is able
$0 combine with thet form of hemoglobin, but net with hemoglobin obtained
from the rei celle of other animals, except those of Wary closely related
wpecies. The act of combinstion of entibody and ite honelogous antigen may
be shown by several different phenomena, such ca the agglutination of sells,
in the caes of a cellular antigen, the formation of a precipitate on mixing
& eolution of antigen and «tq homologous antibody, the allergte response
of @ sensitised animal on receiving a subsequent injeetion of the antigen,
ami the lysis or other changed behavior of cells to which antibody has
attached {teelr,

The phenomena of ismunochand stry raise two @reat questions, ‘ths
first fs that as to the nature of the forces between antibddy and ans igen,
which leads to the power of seleetive combination of antibody and the
hanolegeus antigen and the rejection ef other molecules, except those
aloe
wary sleesly related to the homologue antigane. ‘The second pobvle is
What of the mechanion of the manufsoture of the antibody, and of ita
enicwsent with this power of specific combination. The great vergntility
of the living organiens in their preductien of specific antibodisa was
shown by the early work of Landsteiner with artificiak conjugated orcteing
ae cntigens! landgteiner found that it was possible to causes an animal to
wake antibodies with the power of specifica casbination with varique chem
ical gabstances of known structure. He achieved this by attaching these
Ghamical substances to a protein molecule, which was then injeatad nee a
rabbit. The rabbit, wader the influence of the injooted protein, produced
on antigerun santaining antibodies cavable in general of aombining with the
partiouler protein that waa used in making the artificial conjugated oro~
tein, and also capable of caubining with the atiached chemical substances.
Yor example, an antiserwa prepared by coupling diazotised promi nobensene~
arsonic acid with ovalbwain was found to form a precipitate strongly with
this partioular asoprotein, and alee to precipitate, in omaller amounts,
evalowein iteslf and aleo any ssoprovein made by coupling diasotised
peaminobensencarsomic acid with snother arotein, such as sheep serua al~
Wado. che precipitation by the antiserun of saan an agoprotein, in which
the protein part is completely different from that of the dmmunising aco-
protein, is evideues thimt somo of the mtibodies in the antiserum have a
specific combining power with the bensenearsomic acid grow, Landeteiner
ami his collaboratora were able in this way 40 prepare antisera coutaining
antibodies with the power of speciyvic combination with scores of different’
Ghewical wibstences, many ef which could hardly be consiaered to have any
 

~16-

metural relation to the injected aniusal. these rewulés showed that the
verambility of the living argenies in antibody production ig very great,
emi made it probable that the antibody precursor was to be concidered as
4 phoetac material, able to be infiuences by the injected antigen in guch
a way as to cbiain directly from the antigen itself the property that
deade to the power‘ot specific combination with it.

lanGigteiner and hie collaborators also discovered and utilized
an important phenomenon, that of hapten tahtvition™ They foumd that, for
exemple, when denseneargonic acid itwelf is sided to an antiserum made by
injegting an asgprotein containing the prasobenzeneargonic acid group no
precipitas
of the bensenearsonic acid, ithe bengenearsoenio acid in thus shown to have

oceura, although » precipitate would ba corme: in the absence

  
 

 

the power of combining with antibody howologeus to thie haptente grouping,
to form a soluble complex. Information about the strength of the combine-
tica of the hapten and of the antibody can be obtaiued by seeing what con-
centration of hapten is necesuery to prevent the precipitation of the
antiverus with « hapten-hemologous asoprotein. lLamisteiner and his colla-
boratora in this way obtained a great amount of qualitative information
abait the combining powers cf various cheuical substances with antibodies
homclegous to haptenic groupe of known structure. ‘They found, for example,
that mot only bensenearsonic acid but also various subetituted bensenear~
gonic acide have the power of combining with anti~p-asobensenearsonia acid
serma and that the strength of the combination depends won the nature of
the group substituted in the benzene ring and on the position in which it
| as substituted. Tims in general a group edbstituted in the para position

 

between the benzenearsonic acid and the antibody, because on addition of an

is formed. Nevertheless, it can be deduced that combination hes occurred
azoprotein containing the peazobenzenearsonic acid group no precipitate
@l?-

in Densenenrsonic acid increnses the combining power with anti~p-ascbensane-~
arewnic acid serum, wherene the substitution of a growp in the ertho of mata
position decreases the combining power with thee antibodies.

My callaboraters (Prefeesar Dan H. Campbell, David Preseaan, Garol
Tkeca, Migs Tkawa, David He Brown, John - Maynard, Allan Ls Orossherg.
Senley MW. Swingle, John H. Bryden, Leland H. Fence, ond Frank Lanni) and I
have continued and extended this work, primarily ty developing and using
quantitative methods, permitting the determination of approximate values
for the equilibrium comatant of the reaction of coubination of hepten and
antivody” Ve have aleo made use of a simplification in the experimants, in-
volving the elimination of one protain from the precipttation test. Inae
mach ae the structure of no protein ip as yet yadinown, o precipitation
reaction involving :wo proteins, the antibody and the aseprotein, ts an
eupecially couplicated reaction to study, and the poratbility of obtaining
information about the antibody wight well become greater {f the other pro~
tein could be climinated. Jlandeteiner and van der Scheer obserred that
@ertain simple substances that they had prepered for use as hapten inhibi-
tors theaselves gave a presipitate with the hapten-hosclogous anti sarania
These wibstances were dyes obtained by coupling ¢we or more heptente groupes
together ~ an example would be resorcinol with two or three agobensensar~
#onic acid groups atieoned to it. Many of cur hapten-tmhibition ex:eriments
have boom carried oat with use of precipitating polyhectemtic antigens of this
type, the syetem under stady then containing only one substance of unimow
atructure, the antibody itself.
Navel

a

Land steiuer's results could ba interpreted Un terms of our modern
imowledge of aimale col molecular structure fo sormit + defintta conclusion
to be rasened razarding tha naturs of the epesific fordas betwaan antibody
and antiges, and tho atoucture o° antibody soleouls, and thia omeilusion
ung Dean strengthened by the adittional inforsuation civen by tha excerlaente
Saat ny collsbecesters and T have oerried ous in Pmaadante The conglusion
4a that toe specificity of et rection of antibody and homologous antigen
tegalés from « detailed complewonteriness in structure, ag waa first sug
gaetad by Yaurewkts and 2eeini and by Jerom® Alexander Ba later anohesi sed
by Stuart ctadde The complanentariness in structure suet be mich sa $5
permit a large portion of she swrrsece of the satigen to be brought into

justapesition with a corresponding portion of the surface of the antibody

' molecules the wank forces thet opgrats between any ston or small atanic

grap and aijecent stesy would then eome into play betwoen each surface
stem of the antigen and the tmmediately adjacent stous of the antibody;
these wask forces, integrated over the Juxtsyose’ surfaces, vould produce
a regultant force etrong s.ough to lead to the formation of an effective
bond. Inagumch “2 moet of the weak forces operating between ston snd

1 molecules fall off very shearvly with incressing digtancs, an effea-
tive bond would be forme: only if the two melecules ware in contact with
one another, thai is, if the surfaces of the stoma of antigen end sntibody
wore to be mo mare than « vary few Ingstroms apart. ‘The specificity of the
bomi formed in this way would result from the detefled complementariness
nob only in general surface configuration but alse ix the vositions of the
groups capable of forming hydrogen bonds and in the cositiong of the vesitive
~15-
and negative electrical charges. It can readily be seen that this mech-
anion does provide the pessibility of very great specificity. ‘thas a
eandining region with area of perhaps 200 square Raget rons, representing
a murface of about fifty atone, cold be prevented frem approaching to
Gontact with the complementary region on the autibody simply by replacing s
mathyl group, say, on the antigen warface, by a phenyl group, which would
extend about 3 2. above the former surface, and would hence hold the anti-
vedy 3 & farther away from the antigen, thas reducing the farces of
attraction to such an extent as no longer to permit them to result in a
significant bond.

The approximation of the antibody to the haptenie group af the
imemunising antigen mast be very close. A striking bit of evidence, from
aning the great snount that exists, is that of the cross reactivity of two
Closely related haptenic groups, the m-aminobensolc acid group and the
Yaghlaro~ j-eminobensoic acidyeerum precipitates readily both with the

mMme-
( napt en-honel ogvas asoprotein and with an asoprotein containing the ano~

 

bensoic acid group, Om the ether hand, the anti-p-ascbensoic acid serum
precipitates readily an asepratein containing the Brascbensoic acid group,
but does not form a precipitate with an asoprotein containing the 4—chiaro-
j-asobensoic acid group. The explanation that we propose of this eross
reactivity between one antiserum and the substituted asoprotein but not
between the other antiserum and the different asoprotein is that the

 

phenasenon depends upon the fact that the chlorine aten te much larger
than the hydrogen atom that it replaces, the van der Yaals radius of

| shlarine being about 1.8 R, and that of wyrdrogen only about 1,2 % Tf it
group, which differs from the first only in having » chlorine atom *Y

 

place of the hydrogen atom. lLandsteiner and his collaborators found
that anti-t-chloro-3-aminobenzoic acid Cc

 

 
AN

-2-
is aswamed that the combining region of an antibody fits tightly about
she haptenie group of the fmmunising antigen, the anti-i-chlare-j-aso-~
pensolo acid antibodies would contain in the appropriate place a onvity
fate which a ghlorina atom could fit, aleng with the rest ef the haptenic
grow. This cavity, with radive 1.8 2, would be large enough to accept
easily « hydrogen ates in the unsubstituted asoprotein, and the replace-
ment of chlorine ty hydrogen would have no effect other than to decrease
alightly the force of attraction between the haptenic aroap and the enti-
body, as a rewult of the sualler wan der Waale attraction of a hydrogen
atow and of a chlorine atom for qurrounding atoms. On the other hand,
the cavity in the anti-~p-asobensoio acid antibody is required only to be
lange enough to receive a hydrogen atos with van der Yaale radius 1.2 %
There might well then be a considerable amount of a steria strain if the
Hechlero- j~asebensoic acid haptenic group were to be forced into this
cavity in the antibody, ani the steric strain might be great enough to
decrease the combining power to such an extent that no precipitate would
be observed hy the investigators.

Thie experimental result indicates that the fit of antibody to
antigen is, in some cases at least, «a very close one, 90 that a difference
in atomic radius of 0.6 2. ts efgnificant. Our quantitative investigations
in Pasadena provided a large amount of evidence mubstantiating this canelu-
sion. (ne extensive eerias of investigations was made of the combination of
autigera homologous to the o-bensenearsonic acid haptenic group, the m-
agcbensenear sonic acid group, and the zraucbensenearsonic acid group. It
was found that in each case the substituted bensenearsonic acids with the
~~

mibetitwent fn the same position as the age eroup of the imumising aso-
protein cambine more strongly with the antibody then those with the mb-
stituent group in a different position, and the @uGlusion wag reached fron
the values of the hapten imbibition constant that the surface configuration
of the combining regious of the antibody molecules approximates that of the
haptenic group to within closer than 1 2, 4 sistler conelusion has alec
been veadhed ty a study of the effect of electrical charge. The ratio of
inhibiting powers of two similar haptens, one containing a positively
charged group, the trimethylemmonius fen group, and the other the uncharged
group with the anme sise and shape, the tertiary butyl] group, with anti-
soru sade by injeeting rabbite with sheep serum with attached Prascbensene~-
trimethylamcnium ion groups, could be interpreted to chow that the positive
Gharge of the charged haptenie group interagts with « negative charge in
the antibody 7 X. away. Inaswach as the positive charge in the phenyltri-
methylacsoniua ion may be considered to be at the center of the nitrogen
atom, and the radius ef thie ion (the distance from the center of the nitro~
gen atom to the surface of the methyl groups) is 305 2, amt that alse the
minimum distance of approach of a negative charge to the surface of the
antibody may be taken as the radius of an oxygen atom, 1.4 %, the minim
@istance ef approach of a positive Gharge in the hapten and a negative
charge in the antibody is calgulated to be 4.9% the fact that the value
ealoulated from the hapten-imhibition date is only 21 %. greater than
this again indicates that in general there is a very great complementariness
in structure and cleseness of f1t of antibody and antigen.

Tt is my epinion thet the genoral problem of the nature of specific
biological forces has thus been solved, and that with the extension of our
knowledge of detailed satanic structure of proteins and ether biclogical
-22-
mibstances we may hope that this under standing of—the-nature-ef—specitsa

 

eheiegionl-ferews Gill permit a more effective attack on may of the
probleme of biology and medicine.

I should like now to discuaes a closely related question - that of
the mature of ensymes and of entalystes in general. In order to function,
the living cell carries out many specific chemical reactions that do not
take place when the reactants are simply mixed with ome ancther. ‘these
reactions oceur in nature because there are present molecules of a specific
catalyst, the enzyme appropriate to the reaction. I believe that on enayme
has a structure clesely similar to thet found for mtibodies, but with one
important difference, namely, that the surface configuration of the enzyme
is not 20 closely complementary to fin specific substrate as is that of an
aatibedy to its homologous antigen, Dut is instead complementary to an
wasteable molecule with only transient existence - namely, the "activated
complex" for the resetion that is catalysed by the ensyme. ‘The mode of
agiion of an ensyme would then be the following: the enayme would show
wewriieby a swall power of attraction for the gqubetrate molecule or mole~
cules, which would become attached to it in its active surface region.

Tais substrate moleoule, or these molecules, would then be strained by the
forces of attraction for the enusyme, which would tend to deform it into the
configuration of the activated complex, far which the power of attraction
vy the enayme is the greatest. ‘the activated complex would then, wader

the influence of ordinary thermal agitation, oither reasmme the cenfigura-
tion corresponding to the reactants, or assume the configuration correapond-
ing to the products. The assumption made above that the enayme has a
-23-
oonfiguration complementary to the activated complex, and sceordingly
hag the strongest power of attraction for the activated complex, means
that the activation energy far the reaction 1s less in the presence of
the enayme than in its absence, and accordingly that the reaction would
ve speeded up by the onayme, My colleague Professor Garl Niemann aad I
ara carrying out experiments on inhibition of muyme activity designed to
test thie postulate, hy the search for inhibitors that have a greater
power of combination with the enayme than have the substrate molecules
thenselveas This method of attack should, indeed, provide ue with infor-
mation about the nature of the active region of the ansyme, namely, that it
is complementary to the configuration of the strong inhibitors.

Thie picture of the nature of enzymes may wall make ua optimistic
about the future of chemothorapeutias, for 1+ predicta that for every enayne,
ami in pertieuler for the enzymes that are ossential for basterial growth,
dt would be possible to find an inhibiting molecule which is mora closely
complementary in structure to the en-yue than is the qubstBate itself, and
which would accordingly be an effective inhibitor. The pioture even presents
ue with ideas as to the nature of substances which would be effective inhi-
bitors - namely, thet they should closely resemble the activated complex,
intermediate in configuration between the reactants and the products of the
catalysed reaction. A possible praatical application of thie concept ta
that to penicillin and ite destruction by the enayme penicillinase. Some
of the organioms that resist the bacteriostatic action of penicillin aay
achieve their reelatance through the mamafacture of penicillinase, which
destrays the penicillin as it approaches the organism If 4¢ ware poseible
oie
$e aynthesise or to obtain by the degradation of penicillin itself a
Wehatance with molecular configuration such that it would combine with
peniclilinase mere strongly than does penicillin, and thus would inhibit
the action of the pentcillinase, this specific inkibiter might be injected
{or even taken by mouth) along with the penicillin, which might thigs in
thie way increase its basteriostatic action.

Va have far less evidence bearing in a detailed way on the vroblen
af the prosess of formation of complex biological molecules than on the
predlem of the nature of specific biological forces. Beverthaless, a
reasonable proposal can be uade as to the process of formation of these
moleaules, on the basie of the information available on the nature of the
forces themeelves, and the aseaaption that the known laws of molecular
phyeice are applicable to biological systems. I shall iliuctrate this
proposal hy discussing a possible mechanien ef formation of gvecific anti~

*

bodias.

= mh i a ee etl tee

* maPwulings J. Amer. Chem. Sees, 62, 2683 (1940).

The problem that we poss ig the following: how is it possible for
m call to mamfacture an antibedy molecule with the power of specific aaa-
bination with an arbitrarily chosen antigen? It might be that the differ-
ence in structure of the antibody molecule and a normal molecule of Y=
globulin er an antibody molecule homologous to another antigen would result
from a difference in the ordering of the amino-acid reaidues in the poly-

ty ib
peptide chains, aa was suggested by Breini and Haurowlts and by Muda. **

eee ee ee a em ete

»

. ¥. Breinl and 7. Haurowits, 2. physiol. chem, 192, 45 (1930); & Mudd,
de Treranel., 235 423 (1932).
25
However, « simpler aswueption is that all antibody molecules produced ty
the seme protective mechani in the cell contain the same polypeptide
thains ac the normal globulin and differ fran normal glebulin and each
other only in the configuration of the ghain, that 10, in the way the
Genin 49 celled in the meleeule. It is mush easier to devies a mechanion
for causing the polypeptide chain to asame the decired ons of the alter-
native configurations than to devise s medhanies for predacing great vari-
ations in the ordering of the acine-neid residues. Moreover, the mumber
of configurations acsensible to a pelypeptide chain containing 9 thousand
oy more amine~nedd residues Le so great an to provide an explanation of the
ability of the animal te form antibodies capable of specific combination
with a vary greet meiber of 4ifferent antigens. Let us asmens that a
pertion of a polypeptide ahein, one end, say, vhich would be involved in
the formation of a combining region ef the antibody, is of such a anture
that it is able to coil inte agy one of « large wanber of alternative
configurations, all of which have wery nearly the same energetic atability,
so that the choice smong them may be determined by relatively «aall changes
in the envirenment, tending to stabilise one or another of the configura-
tions. In the absence of an antigen the polypeptide chain would fold into
the configuration that happens to be the most stable in the environment in
the cell, and would produce a molecule of normal Y-glebulin. In the
presence of the antigen, however, the felding of the polypeptide chain
would take place in a way determined to some extent by the internotion af
the chain with the atoms in the surface of the entigen molecule. This
imberaction would find expression in the formation of that configuration
~26-
or those configurations of the polypeptide ¢hain that permit the aystem as
a@ whole to have the greatest stability. The grentest stability remlts,
of course, from the formation of the strongest bond between the folded poly~
peptide chain and the antigen molecule, Agcardingly, we hava in this simple
mechaniga, involving the folding of a polypeptide chain into 4 structure
whose nature ie determined in considerable part by the presence of on
antigen in the immediate neighborhood, »® straightforward way of producing
an sntibody molecule with the power of specific cogbinction with the v:ar~
ticular antigen pres@at, resulting from a complementariness in structure
that ia aut ontically aceumed by the polypeptide chain that constitutes the
combining region of the antibody molecule,

It is clear that the sane mechanien, whereby one molecule present
in the cell may influence the structure of another molecule that 12 being
formed, may be invoked as an explanation of both hetero-gatalytic and auto~
eatalyiic activities of biologice] molecules in general. A gene my heave
tho power of cruging the synthesis of a certain protein molecule cnpable
of acting as an snsyne Gatalyaing a particular chemicnl régtion through
its possession of a structure essentially complementary to thet of the
ective region of the enxyme molemmle, and which can act as a template in
the production of that ensyme molecule. ‘She power of self-dupliertion of
the gone might well have « similar explanation ~ in case th&®~ the gene
happens to be complementary to iiself, than 1+ could serve directly ar
the patiern for fteelf; ar it might produce the same result, the marru-
fagbure of replicas of itself, by working through an intermediate camle-

mentary to liself, “hich then serves ag the pattern for the new gene,
-2]=

aanplementary to the intermediate and identical with the eriginal gene. How-
ever, relisble information about the detailed asture of these fundemental mo-
lecular procesees in biolegical systems must await further experimental Gtady.

So far I have been discussing the lunst interesting agpects of the
develagmenta of chomigtry in the futures These least interesting aspects
ara those thes can be predicted, thai can be foreseen on the basis of our
presant knowledge. “hey consist primwily of the regults of application
¢ that have alyveady been madae The great

 
 

 

the present world ~ are the discoveries thas will in fact be made as goon
ac tae idea underlying them take shape in the mind of some inmginative
aGientist. “ho ise there among us who ten years ago would have predicted

taai sus fheld of qmuclear strucsure and abasic energy would develap in the
now
way that it nas? “no can ,say what thu great discoveries of the aext ten

yeera will ber

I heave talked abeuti pepe for the future - Ow che discoveries thet
yor
we cnn Soresse may not all be obviously beneficial. Let me say, with Falt

“J know I wa restless and make obhexn 50,
I knor thet my works sre full of danzar, full of death,

Yor I confront peace, security, amd all the settled laws,
to unsettle themes s.«

{the threat of what is call'd hell ie little or
nothing to me,

Aud the lure of what ia onll'd heeven fie little or nothing
to me}

Dear cameradol I confess TI have wreed you ovard vith me,
asxl #411 urge you, without the least ides what is
we deatination,

Ge whether we shall be victorious, or utterly quaell'd and

baodanntad. #
-2t

Seience cannot be stepped. Man will gather knowledge no matter what the
consequences ~ and we canact predict whiai they will be. Seience will ge
on ~ whether we are pessimistic, or, opbimistio, as I em: I imow that
qareat, interesting, and valuable discoveries can be and will be made, of
the gort that I have just described - but I aleo know that still more
interesting Giscoveries will be made that I have not the imagination to
degerite ~ and I an awaiting them, full ef curiosity and entiusiaa.
REFERENCES FOR “CHEMICAL ACHIEVEMENT, AND HOPS
FOR THE FUP," BY LIWGS PAULI, SILLIMAN LECTURE

ioge le WeF. Giauque, d. dm, Gree S0Ce, a, 1964 (1927).
7 2 ¥F. Simon, personal communication, 1947.
3

Sth line

2 Jo BeQ» Roghew, "An Introduction to the Chenistry of
after “at- Silicones,* John Wiley and Sens, ine. , Kew Tork, 1946.
tached"

wu Me Biosynthesis of Penictliins, Editorial Beard of the
Lith line Memegragh on Penicillin, Science, 306. 503 (1987).
after *pyoni-
sillia®

3 5. BD. Woods and P, Fildes, Quen. tat. , 59. 433 (1940).
10th line .

1 G. Ie Pauling. J. due Ghem. S00. 2 BZ (1940); Chem
nak. $0 lest me. ere és 100s (1946). Se
tine » after

15 Te EK Yamdstoiner, "The Specificity of Serclegical Reastions, *
6th line Q.G. Thoms, Springfield, Mlineis, 1936; revised edition,
after Harvard University Proes, Cambridge, Massachusetta, 195.
*antigens"

ub S- K Jandstetner ani J. ven der Scheer, Prot. Soa. Hxpe
Sth line Biel. Med., 29, TH] (1932).
after "ty
hobitdiont

a7 3- The Serological Properties of Simple Substances. 1. Pre-
0th line Gipitation Reactions between Antibodies and Substances Gan-

after taining Iwo or Mere Maptenic Groups, ly Pauling, 3B. Preas-

“ant Loedy* man, D, Oe dey; ie: nd Ke Tmen, J. don. Chom,
foes, 3 T%.the Rffoate of Changed Ganditions

Mapteus en oar ty Pending Ranch ions of

haptenic @imple Substances, Pauling, By Presse, DH.
Campbell, and G. Ixeda, ibid, Oi, 3003 (1942); IT%. ‘the
Gemposition ef Precipitates of Ansibedies and Polyhaptonie
Simple Substances; the Valence of Antibodies, L, Pauling,
B. Froscusn, and 6. Deedm, ibid, @, 3010 (1942); IV.
Mapten Inhibition ef Precipitation ef Antibodies ani Poly-
haptenic Simple Sabstances, D. Preseaan, Tol. frown, and
we Pooling, fbid, OF, 3015 (19K2).

x &
“16 Line (See above)
Ghenical Achievement, ete. «2 lame Pauling

gun ane
9th Line
10th Line
hah Line

from bottan
efter "sien."

9; 10. ‘The Serological Properties of Simple Substances. Y,

ond dutiscrun Remoloceus to the 2 Glace
phenylareonic Acid Group ant Ite bition ty Bapteas,
DB Presenmn, 3.%, Maynard, Ady Gros » and Tey Prol-
aipitatian ef a Mixture "we Specifies Antisera ly a
Dihaptenic Substance Gontaining the twe Gerr

Weptenic Groups} Evidence = the a. s theay

the Prosipitation of Polyhapteniec Huple vianel

serels cal Précipitati De PFreesnm,
Gempbell, ibid, * 530 30 Cl h)s ViteA Qua
staaive Thesry of, the bition of Baptens of the

Preeipitatian of ja dntioora with Antigens,
and Goupariven with Experimental Results for
heptenia Bimple Substances and for Asoproteina,
= ¢ De Presasen, and Ak. Grossberg, ibid, §
is) YX1E. The Reactions of Antiserus
tems te the p~Asobensoic Acid Grow, Dh. Presanm,
gle, Avln Grossberg, and le Pauling, ibid,
& TR Cgs).

& Bretal and ¥. Becrowits, % rhysiel. Chem,
Ws (1930). 1a,
a. Aexendep, #. Proteplaas, wy 296 (1932).

f% Madd, 3. Teemnel., Bis kay (1932).

Wi. The Serological Properties of Simple Substanceae IX.

Mepten Inhibition of Precipitation of Antisera Hendle-
to the S-> Yr, and p-Anophenylarecnic Acid Grows,
Pauling and &, Presesta, #. de Chem. Soo., 67, 1003
C985); XE. the Reactions of Antisera Momolacous te Var-
saya il gk oe abe Ss
e dai cap with ens,
B. Pressman, A.B. Pardee, ani In Pauling, {hid, 1902
te X¥Z. The Reactions of Antiserum Rasologums te
trimethylaameniva Group, D. Presmrn,
gborg, eH. Pence, and %. Feuling, ibid,
250 tine) }s XITE. the Reactions of Antiseras
2 the aT ae Yon Group, D. Pressman, her
den, i Ie Pauling, ana, te appear im ae 41 1