Molecular Nano Dynamics

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MOLECULAR RECOGNITION OF TRANS-CHIRAL SCHIFF BASE METAL COMPLEXES

FOR INDUCED CD

Takashiro Akitsu1 and Chigusa Kominato1

1Department of Chemistry, Faculty of Science, Tokyo University of Science, Tokyo, apan

INTRODUCTIONSchiff !ase is one of the most popular ligands in the field of coordination chemistry "1#$%& Conventionally,

transition metal comple'es having Schiff !ase ligands have !een investigated a!out stereochemistry and

corresponding electronic properties mainly& For e'ample, solution paramagnetism of (i)**+ comple'es,

structural phase transition of Cu)**+ comple'es, chiral catalysts, and some types of molecule#!ased

magnets and other interesting facts a!out correlation !eteen structures and properties are knon and

these facts are cooperative effect involving intermolecular interactions and molecular recognition&

-ecause of developing importance as functional chiral materials, many researchers have investigated

crystal structures )including thermally#induced structural phase transition and polymorphism !y solvents+

of trans#type chiral Schiff !ase metal comple'es and e'tract important features of chiral molecular

recognition in the solid states&

As mentioned in A!stract section, e have tested o!servation of some novel phenomena associated ith

chirality or CD spectroscopy !ased on intermolecular interactions& *nduced CD on various nano#scaled)inorganic+ materials from chiral Schiff !ase metal comple'es is one of them and not only electronic and

magnetic dipole moments !ut also molecular recognition !eteen chiral compounds and nano#scaled

materials are important factors for these phenomena "., /%& For e'ample, e have o!served induced CD

peaks from chiral Schiff !ase (i)**+ comple'es at d#d region for achiral or chiral Schiff !ase Cu)**+comple'es )ithout e'changing ligands+ "0%, at d#d and CT regions for Cu)**+#coordinated

metallodendrimers )A2A2+, and surface plasmon region for Cu#clusters prepared in A2A2 !y

irradiation of U3 light for the first time " 4, 15%& *n this ay, e have also reported on induced CD peaks

of metal comple'es )!oth achiral and chiral ones+, organometallics )ferrocene+ " 11%, metallodendrimers,

metal nano#clusters, and nano#particles "4, 15% of metal#semiconductors "16%& Additionally, e have

successfully o!served si7e#dependence of avelengths of induced CD peaks from chiral Schiff !ase

8n)**+ comple'es involving a7o#groups at surface plasmon region on colloidal gold particles "19%&

As for the induced CD !eteen chiral Schiff !ase (i)**+ or 8n)**+ comple'es and Cu#clusters prepared inA2A2, e have also investigated the role of chiral ligands for molecular recognition& For e'ample,

naphtylgroups are appropriate for induced CD, hile more fle'i!le groups are not " 1:% )Figure 1+&

Therefore, several e'amples indicated that supramolecular or molecular recognition must !e a key reason

for specific intermolecular interactions& *n this revie article, e have summari7ed several e'amples of

crystal structures and optimi7ed structures )as a model of them in solutions+ of trans#type chiral Schiff

!ase (i)**+, Cu)**+, and 8n)**+ comple'es& *n order to derive important steric factors for molecular recognition, e ill point out characteristic features of molecular shapes or their conformational changes

in silico&

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Figure.1: ;'amples of suita!le "left% and unsuita!le "center% ligands for induced CD !ased on

e'periments "4,15, 1:%& "<ight%*mportant )!old circles+ and unimportant )!roken circle+ moieties of

ligands for induced CD&

COMPUTATION

According to a CCDC data!ase "1$%, e selected some crystal structures of trans#type Schiff !ase metalcomple'es& As modeling conformational changes in solutions, e o!tain optimi7ed structures and their

heat of formation !y using 226& =e ill search appropriate features of molecular shapesfor induced CD&

RESULTS AND DISCUSSION

16 e'amples of trans#type Schiff !ase comple'es investigated are mentioned !elo, molecular structures

"top%, crystal structures "middle%, and optimi7ed structures "!ottom% as space#filling models ith

comments&













Figure.2: CCDC 2*2T>S51 "1.%&The compound has a formula C9:?$6Cu(:>:6@, 6)(>9

#+& (ovel feature

mentioned is that attaching dialkylaminomethyl arms to commercial phenolic o'ime copper e'tractants

yields reagents hich transport !ase metal salt vary efficiently !y forming neutral 11 or 16 comple'esith 7itterionic forms of the ligands& Apparently conformational changes ere from a sBuare planar

geometry to an um!rella form and tist form )a!out :$ degree+&





Figure.3: CCDC MAHEA "1/%&The compound has a formula C95?60Cu(6>6& (ovel feature mentioned

is that it adopts a stepped conformation and displays a sBuare#planar trans#"Cu(6>6% coordination

geometry& The asymmetric unit contains to independent half molecules and each Cu atom is located on

acenter of symmetry&





Figure.!: CCDC MA"NI# "10%&The compound has a formula C9:?9.Cu(6>:& (ovel feature mentioned is

that compressed tetrahedral coordination geometry ith an (R,R)#a!solute configuration& These

comple'es differ from one another ith respect to the 1#phenylethylamine moieties, the direction of the

!en7ene rings !eing inside and outside of the molecules& Apparently conformational changes ere froman um!rella and tist )a!out :$ degree+ form to same and tist )a!out 45 degree+ form& The e'tended

conformation of the phenethylimine pendant groups results in crystal packing formed !y eakly

aggregated planar molecules& Apparently conformational changes ere from a relatively flat step form to

a significantly sharp step form&





Figure.$: CCDC MI%GIM "14%&The compound has a formula C95?6:Cu(6>:& (ovel feature mentioned is

that the coordination geometry around the copper atom in the comple' is intermediate !eteen sBuare#

planar and tetrahedral ith to salicylaldimine ligands in trans arrangement& The molecular chains are

linked via additional C#?⋅⋅⋅⋅> hydrogen !onds to form a three#dimensional supramolecular netork&

Apparently conformational changes ere from a moderately um!rella and slightly tist form to a tist

)a!out 45 degree+ form&





Figure.&: CCDC IBHBCU'1 "65%&The compound has a formulaC9:?9:Cl6Cu(6>6& (ovel feature

mentioned is that the iso!utyl comple' e'ists in to distinct crystalline forms, green and red& The green

isomerhas the iso!utyl groups pointing to the same side of the appro'imate "Cu> 6 (6% plane& The red

isomer of the iso!utyl comple' contains to crystallographically independent molecules having the

iso!utyl groups& Apparently conformational changes as from a step form to an um!rella and tist )a!out

45 degree+ form&





Figure.(: CCDC DPESCU11 "61%&The compound has a formula C95?60Cu(6>6& (ovel feature mentioned

is that copper)**+ comple'es of three chiral enantiomeric pairs of o#hydro'y Schiff !ases derived from

)<+#)@+#1#phenylethylamineandor )S+#)#+#1#phenylethylamine, ere prepared and characteri7ed&The

geometry around the metal atom is distorted sBuare planar& Apparently conformational change as from a

tist )a!out :$ degree+ form to a tist )a!out 45 degree+ form&





Figure.): CCDC MSACOP12 "66%&The compound has a formula C1.?1.Cu(6>6& (ovel feature

mentioned is that a dimeric molecule in hich monomeric halves is oined !y to Cu#> !ondsto

complete a sBuare#pyramidal configuration a!out each copper atom& Distortions in the molecule are

evidentlydue to the close approach of non#!onding regions& *t is no seen that this compound displays

three different coordination arrangements in its three polymorphic forms& Apparently conformational

change as from a step form to an um!rella and tist )a!out :$ degree+ form&





Figure.*: CCDC MA"CU+ "69%&The compound has a formula C66?6:Cl:Cu(6>6& (ovel feature

mentioned is that it has a compressed tetrahedral trans#"Cu(6>6% coordination environment ith an

um!rella conformation of the overall molecule&The a!solute configuration is found to !e (S,S) for thecrystale'amined&2olecular recognition for the chiral molecules could not !e carried out using hydrogen

!onding !ecause of no possi!le hydrogen !onding sites in the crystal packing& Apparently conformational

change as from an um!rella and tist form to a tist )a!out :$ degree+ form&





Figure.1': CCDC ,UPBIH "6:%&The compound has a formula C95?96Cu(6>6& (ovel feature mentioned

is that correlation !eteen the !ulkiness of the imine nitrogensu!stituent, deformation of the copper

coordination sphere is important and t-u group in the N #t-u derivative prevents such dynamic action& *n

the crystal, this N #t-u comple' changes upon DFT geometry optimi7ation to a more

tetrahedralconfiguration& Apparently conformational change as from an um!rella and slightly tistsform to an um!rella and tist )a!out 45 degree+ form&





Figure.11: CCDC ,UPBON "6:%&The compound has a formula C6.?6:Cu(6>6& (ovel feature mentioned

is that the coordination sphere of the (#ethyl derivative has a flat#tetrahedral geometry& The(ECuE(and

>ECuE> angles and the dihedral angle !eteenthe planes (ECuE> and (ECuE>in the solid state found

!y #ray diffraction in this study are affected !y crystalpacking forces according to these DFT

calculations& Apparently conformational change as from a flat and sBuare planar form to an um!rella

and 3#shaped form drastically&





Figure.12: CCDC UBLA" "69%&The compound has a formula C..?00-r 6Cu9 (.>6& (ovel feature

mentioned is that it appears that pro!lematic deprotonation of the phenol to give a chelating or !ridging





ligand is the primary reason for the o!served insta!ility !ased on the sta!ility of related copper (?CEaryl

o'ide compounds )including mi'ed valence Cu)*+Cu)**+ centers Cu)*+ sites in ligands+ Apparently

conformational change as from a step and slightly tist form to an um!rella and tist )a!out 45 degree+

form&

Figure.13: CCDC METSU% "6:%&The compound has a formula C 95?6. (:>.8n& (ovel feature mentioned

is that it crystalli7es in the noncentrosymmetric space groups& The geometry around the 8n)**+

metalcenter is pseudo#tetrahedral ith to o'ygen and to nitrogen atoms from the ligands and has the G





a!soluteconfiguration& Apparently conformational change as slight, namely it remained a tist )a!out

45 degree+ from&

*n principle, induced CD is caused !y non#contact interactions !eteen )electric+ dipole moments of

chiral additives and achiral materials& -ecause it is an electromagnetic phenomenon essentially, contact

intermolecular interactions, in other ords molecular recognition, may not !e an important factor for it&?oever, the e'perimental facts that only comple'es ith specific ligands or metal ions )hich determine

their coordination geometries+ suggested that induced CD appears under appropriate steric )as ell asstereochemical+ conditions for metal comple'es& >ne of the important factors of steric factors for metal

comple'es may !e distance !eteen )electric+ dipole moments at the surface achiral materials hich keep

their shapes rigidly& The reason for this assumption is that !oth metallodendrimers metal and

nanoparticles have appro'imately spherical shapes essentially even surrounded in softmaters&

As for !iomolecules such as proteins, hoever, CD spectra are used for monitoring folding or unfolding

of peptide chains after !inding small molecules of metal comple'es "6$%& This different phenomenon is

not classified into the induced CD mentioned in this article& -y including small molecules into proteins

ith eakly supramolecular forces, molecules of proteins change their molecular conformation, hich

attri!uted to shift of strong HIHJ !ands of C> moieties electronic or CD spectra& This docking

mechanism is directly molecular recognition accompanying ith conformational changes of proteins as

ell as small molecules, hich is also confirmed !y Buenching of fluorescence intensity due to energy

transfer&*n contrast, non#contact interactions of )electric+ dipole moments for CD spectra have complicated

pro!lems& >ur preliminary results of CD spectra of chiral Schiff !ase metal comple'es in viscous

solutions dissolved a certain protein e'hi!ited concentration dependence of so#called artifact peaks of

solid#state CD spectra "6.%& The artifact CD peaks are attri!uted to anisotropic molecular orientation andremoved in matri' environment hich permits molecular rotation isotropically accompanying ith

)magnetic+ dipole moments of chiral molecules "6/%& Therefore,not only CD spectra of chiral molecules in

anisotropically oriented matri' such as !iomolecules !ut also induced CD !ands involving softmaters is

still an open Buestion&

CONCLUSION

As summari7ed in Figure 1"right%, according to chemical structures, 8n)**+ center and naphtylgroups are

suita!le factors for induced CD, hile 9,$#dichlorosalycilaldehyde moieties are not regardless of commonfactors& revious study "11% revealed that in optimi7ed structure, naphtylgroups act as largely spread

planar parts outside of a molecular face, hich plays an important role in induced CD for this case& *n the

present study, compounds having identical features ere also investigated in vie of optimi7ed structures&

According to not only9,$#dichlorosalycilaldehyde moieties )*-?-CU51 and2ACU=+ !ut also tert#-u#

groups )2*2T>S51 and LU-MA+, ;t># groups )2A(*3+, and (>6# groups )2;TSU8+ gave

significantly large steric hindrance resulting in steric repulsion !eteen ligands& ?oever, specificgeometry could not !e induced !y !ulky groups& Nenerally, 8n)**+ comple'es afford a tetrahedral

coordination geometry, hich prevents from forming flatten planar molecular shapes in vie of ligands&

Therefore, these to factors may not !e definitive factors solely& >n the other hand, !esides in amine

parts )Figure 1+, naphtylgroups in aldehyde parts )KU-*? andKU->(+ are also keeping appropriateconditions, namely largely spread planar parts outside of a molecular face& As far as in the sense of

molecular recognition, it has advantage for penetrating into inside of dendrimer as ell as contacting tothe surface of metal nano#particles& Further e'perimental andor theoretical investigation including

electric factors ill !e necessary to understand deeply&

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0& T& Akitsu, (& Uchida, L& Aritake, & Lamaguchi, )655, 6550*nduced d#d -ands in CD Spectra due

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Application for Structural ;stimation& Trend& inorg& chem& 15:1:4

4& T& Akitsu, & Lamaguchi, (& Uchida, Aritake, L)6554The Studies of Conditions for *nducing

Chirality to Cu)**+ Comple'es !y Chiral 8n)**+ and (i)**+ Comple'es ith Schiff -ase& <es& lett&

mater& sci& :0:1/6&

15& T& Akitsu, & Lamaguchi, L& Aritake, T& ?iratsuka, ()651& Uchida, ()6515>!servation of enhanced CD !ands of metal comple'es, metallodendrimers, and metal clusters !y chiral Schiff

!ase metal comple'es& *nt& & curr& chem& 11.

11& T& Akitsu, ()651& Uchida, ()6515*nduced d#d !ands in CD spectra of solution of chiral Schiff

!ase nickel)**+ comple' and ferrocene& Asian chem&lett& 1:616016& L& Aritake, T& (akayama, ?& (ishi7uru, T Akitsu, )6511>!servation of induced CD on CdSenano#

particles from chiral Schiff !ase (i)**+, Cu)**+, 8n)**+ comple'es& *norg& chem& commun&

1::69:6$

19& (& Kimura, ?& (ishi7uru, T& Akitsu, unpu!lished results&

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for induced CD !ands to metallodendrimers& *nt& & curr& chem& 61.$1/6

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=hite, 6550Transport of metal salts !y 7itterionic ligandsO simple !ut highlyefficient

salicylaldo'imee'tractants&Chem&commun& :5:4:5$1

1/& T& Akitsu, L& ;inaga, )655, (#6 #phenylethyl#salicydenaminato#k& (& -is, *& >+copper, 655:-is)(#

6#phenylethyl#salicydenaminato#k6(,>+copper)**+& Acta& crystallogr& ;.5m1$$$#m1$$/&

10& T& Akitsu, L& ;inaga, )655, <+#9 $ #dichloro& -is"#(#)1#phenyl#ethyl+salicylideneaminato#k, (&>%copper, *& , 655:-is")<+#9,$#dichloro#(#)1#phenyl#ethyl+salicylideneaminato#k6(,>%copper)**+

and!is")<+#9#etho'y#(#)1#phenylethyl+salicylideneaminato#k6(,>%copper)**+& Acta& crystallogr&

;.5m.:5#m.:6&

14& S& -aneree, A& K& 2ukheree, *& -aneree, <& M& De (eumann, M& Mouer, 655$Synthesis,spectroscopic studies and a!#initio structuredetermination from #ray poder diffraction of!is#

)(#9acetophenylsalicylaldiminato+copper)**+&Cryst&res&technol& :01$#:061&65& & C& Chia, D& & Frey!erg, N& 2& 2ockler, ;& Sinn, 14//Synthesis and roperties of-is" (#<# )$#

chloro# a#phenyl# 6#hydro'y!en7ylidene+ aminatolcopper )11+ Comple'esand Crystal and

2olecular Structures of the Derivatives ith < m-utyl and < *so!utyl )To Structural

*somers+&*norg&chem&1.6$:6.:

61& & 2& Fernande7#N, C& Aus!un#3aldes, Toscano& <& A& Non7ale7#Nuerrero, 655/Characteri7ation

and Crystal Structure of some Schiff -ase Copper)**+Comple'es derived from ;nantiomeric airs

of Chiral Amines& 8&anorg&allg&chem&.9916$116$.



66& D& ?all, S& 3& Sheat, T& =aters, T()14.0The Colour *somerism and Structure of Some Copper

Co#ordinationCompounds& art 31&l The Crystal Structure of the gama#Form of -is#)(#

methyfsalicylaldiminato+copper)**+& & chem&soc&A :.5:.9

69& T& Akitsu, L& ;inaga, 655:-is")S+#(#)6#!utyl+#9$dichlorosalicylideneaminato#k6(,>%copper)**+&

Acta& crystallogr& ;.5m1.5$#m1.5/&6:& 2& 3illagran, F& Caruso, 2& <ossi, & ?& 8agal, & Costamagna, 6515Su!stituent ;ffects on

Structural, ;lectronic, and <edo' roperties of-is)(#alkyl#6 #o'y#1#naphthaldiminato+copper)**+Comple'es <evisited#*neBuivalence in Solid# and Solution#State Structures !y

;lectronicSpectroscopy and #ray Diffraction ;'plained !y DFT& ;ur& &inorg&chem& 19/9#1905&

6$& A& Simonovic, A& C& =hitood, =& Clegg, <& =& ?arrington, 2& -& ?ursthouse, M& 2ale, <& ;&

Douthaite, 6554Synthesis of Copper)*+ Comple'es of (#?eterocyclic Car!ene#

heno'yimineamine Migands Structures of 2ononuclear Copper)**+, 2i'ed#3alenceCopper)*+

)**+, and Copper)**+ Cluster Comple'es& ;ur&&inorg&chem& 1/0.1/4$

6.& C& ;vans, D& Muneau, 6556(e Schiff !ase 7inc)**+ comple'es e'hi!iting second

harmonicgeneration&& chem&soc&,daltontrans& 090.

6/& A& <ay, -& K& Seth, U& al, S& -asu, 6516(ickel)**+#Schiff !ase comple' recogni7ing domain ** of

!ovine and human serum al!umin Spectroscopic and docking studies& spectrochimicaacta A&

461.:1/:

60& T& ?ayashi, T& Akitsu, Unpu!lished results )P;nvironmental effect on CD spectra of chiral Schiff !ase 9d#:f comple'esQpresented in the :5th *nternational Conference on Coordination Chemistry,

6516Spain+&

64& L& >kamoto, K& (idaira, T& Akitsu, 6511;nvironmental Dependence of Artifact CD eaks of

Chiral Schiff -ase 9d#:f Comple'es inSoftmater 22A 2atri'& *nt&&mol& sci& 16.4...4/4

CITATION

Takashiro Akitsu and Chigusa Kominato )6519+& 2olecular <ecognition of Trans#Chiral Schiff -ase

2etal Comple'es for *nduced CD, An *ntegrated 3ie of the 2olecular <ecognition and To'inology #

From Analytical rocedures to -iomedical Applications, Dr& Nandhi <adis#-aptista );d&+, *S-( 4/0#

4$9#$1#11$1#1, *nTech, D>* 15&$//6$666.&

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