Indi~ln JOllrnal of Chemistry Vol. 42A, February 2003. pp. 227-239

Advances in Contemporary Research

Saccharide complexes of lanthanides

Chebrolu P Rao* & T Mohan Das

Bioinorganic Laboratory. Dcpartment of Chcmistry. Indian Institute of Technology Bombay. Powai. Mumbai 400076. India.

Received 30 May 2002; revised 12 Decelllber 2002

The main focus of this revicw article is to bring out different aspects of interactions of saccharides with lanthanide ions. V:lrious charactcristic propcrties of lanthanidc-saccharide complcxes have been compared appropriately with those of the transition mctal ones.

Dr C P R:lo received his doctoral degrcc on "Biophysical and bioinorganic aspects of peptides" from IISc. Bangalore. He moved over to Harvard University and worked with Prof. R.H . Holm at MIT. USA, on bioinorganic chemistry relevant to metal­thiolates. He worked for another two years at MIT with Prof. S .l . Lippard and carried out

st udi~s on organometallic chemistry of carbonyl coupling. He is curren tly Professor in the Department of Chemistry, liT Bombay. His rcsearch interests involve bioinorganic chemistry of s:lccharides, calixarcnes and othcr -OH containing molecules, as well as biomimetic chcmistry of mctalloproteins and I11ctallocnzy meso

Dr. T Mohan Das got his Ph.D. degree on "Synthesis and char:lcterization of sacch:lride deriv:ltives including N-glycosides and their metal ion complcxes" from lIT. Bombay. At present. he is working as a post doctoral fellow under the guidance of Prof. Der-Hang Chin , National Chung-Hsing University, Taiwan on chemical modifications of

chron10phore of the antitumor antibiotic neocarzinostatin and its effect in the regulation of the chromoprotein.

Introduction Saccharides are widely distributed on earth in many

different forms . These are present in various natural substances and hence belong to an important class of molecules found in hiological systems where saccharide units are integrated in variety of ways both in the small as well as in the large molecules. These are involved in various processes t

, such as, storage, transport and transmission of genetic information, enzymatic reactions2

, and regulation of the metabolism3

. Saccharides and their derivatives are considered to be important not only due to their

E-nwil: cprao@chcm.iitb.ac.in

natural occurrence, but also due to their hydroxy-rich periphery, coordinating ability , homo-chirality , stereo specificity, weak immunogenicity and low toxicit/. In spite of the considerable knowledge gathered regarding the metal ion - saccharide interactions in the literature, several questions pertinent to this were unanswered and this includes, binding preferences, structural and stereo-chemical features and stabilities of the species formed. This review article discusses some important aspects of metal ion complexes of saccharides in general and lanthanide metal Ion complexes in particular.

Interaction of metal ions with saccharides Complexing abilities of different saccharides are

primarily dependantS on two of its important properties, viz., conformation and stereo-chemistry. On the basis of the conformational analysis, it was

. proposed that the polyols possessing axial-equatorial­axial (ax-eej-ax) orientation or 1,3,5-triaxial arrangement (a.x-ox-ax) of the hydroxyl groups provide better coordinating geometry to bind to the metal ions (Fig. I a) . Among the furanose and pyranose forms, the pyranose form can bind metal ions using its cis- as well as tralls- diol arrangements , whereas the furanose form can bind only in its cis-diol arrangement (Fig. I b). In the open chain form , saccharides tend to bind to the metal ions with a preference of tlzreo > erytlzro in diols, and threo-threo > tlzreo-erythro > erythro-erythro in triols (Fig. I c). In addition to the conformational and stereo-chemical aspects of the saccharides, the size of the metal ion also plays an important role6 in effective complexation with saccharides and this happens with the metal ions having radius of 1.00-1.1 I A.. The

22R INDIAN J CHEM .. SEC. A, FEBRUARY 2003

M (C) (d)

H~OH HyOH

R (f)

.. M, HO' ... " OH

t;} (b)

H HO pH

" . (e)M

HO~H HyOH

R (9)

Fi~. I-Favnr'lblc metal inn hinding modes by saccharides: (a), Lis OX-e(I-OX: (b). 1.3.5 tri a.HIX-{{X: (e) .. pyranose - 'cis': (d) , pyranose - ' IroIlS' : (e). furanose; (1),lilreo: (g), erwilro - torms.

general trend in the stability of the complexes was found to be, M+ < M2+ < MJ+. The complexation is further effective with harder metal ions due to the hard nature of the -OH groups, as governed by the HSAB principles,

[n 1825, the first crystalline adduct of n-glucose (D­(rlu) with NaCI was reported7. After a gap of one and ~ half century, in 1971, Angyal and Davies8 reported metal ion interactions with neutral saccharide molecules and thereby. opened new vistas of research with advanced perspecti ves. Later, studies on the interaction of saccharide molecules with alkali and alkaline earth metal ions were reported by research

. 'l 1(J .. R' h· II-I} B . d groups 01 Angyal' and TaJmlr- la I , ugg an coworkers 14· 18 reported the crystal structure of a Ca(II)-carbohydrate complex. Till late 1980's, the work of metal-saccharide interactions were mostly confined to the alkali and alkaline earth metal ions, and the isolated solid products were all found to be "adducts" or "addition compounds", where the sacch:lride -OH groups were bound to the metal ions through ion-dipole interactions and not through the de-protonatcd hydroxyl groups to result in covalently bound alkoxo-complexes, Therefore, the interaction

. . h h 'd I'J .20 d thel' I' of metal Ions Wit sacc an es an derivatives21 is considered to be a promising field in the general area of bioinorganic chemistry22 and hence the literature concerned with alkali and alkaline earth metal ions is being reviewed periodically"J·28,

Among various main group elements, borate complexes2'J.}(J were the most studied based on

solution conductivity and (I H, I3C and liB) NMR spectral studies, where some of the complexes of polycils were found to be stabilized by intramolecular hydrogen bonds}l. [n case of ua(II[) and In(lll), formation of variable compositions were reported with D-glucaric acid. Formation of di fferent types of Pb(I1) complexes were also reportedJ2 ill acidic and basic media with D-gluconic acid. Saccharides and its derivatives ~ere used for the synthesis of adducts and

, ,} 14 .15 Pb( I I ).16 . .18 complexes of Ga(III) .. .. , In(III), , AS(I1I)J9, Te(III) 40-42, and 1(111)43.44.

[n the past, studies of the interaction of saccharides with transition metal ions were not given much importance in the literature and those few studies reported were mainly based on the solution work. The tirst structurally characterized complex of a reducing sugar was the complex of the ~-lyxofuranose with molybdate where the xylose was isomerized to Iyxose by molybdate interaction and in the structure the pentose sugar provides an 0 4 core for binding4

).

Recently Klufers el al.4(1 reported the metal ion

complex of Pd(l!) with D-glu which was charact.erized. structurally, Over the past one decade, studies of transition metal ion interaction with saccharides received prominence. In this regard, our group contributed extensively to the synthesis, isolation, characterisation and solution stability studies of transition metal ions, including those of the d.ivalent (Mn Co Ni Cu Zn)47-5J, trivalent (Cr, Fe)54.61 and

, , , , (- 1

tetravalent (V)62, as well as hexavalent (Mo) 1 •• Our effort in this direction was extended to the bio­interaction studies of V02+-, Cr(JII)- and Fe(lII)-

. . I 59.64·(,6 RN' complexes, that Includes , DNA c eavage , ase inhibition,65 protein synthesis in rabit reticulocyte lysate66

, Fe(Jll) transport through rat intestines, ill vivo metallothionein induction49, lipid peroxidation and cell toxicity and influence on ha'emutological parameters. We have also reported ill vitro reducing abilities of V(V), Cr(l[1) and Mo(VI) towards

I I 5('.67"6') Th I ' saccharides and related mo ecu es, aug 1 a large amount of work is known ' in literature, the interaction of rare earth metal"ions with the hydroxyl containirig molecules were not explored much . Thus, the present review focuses mainly on the contribution made by our research group towards the 'understanding of coordination chemistry of n\rc eart h­sacchal~ide complexes. ' Further, correlations among the data were drawn in case of lanthanide metal ion complexes as well as in case of transition metal ion complexes.

RAOe! at.: SACCHARIDE COMPLEXES OF LANTHANIDES 229

Origin and scope It is evident from the literature that the coordination

chemistry of lanthanides progressed enormously, where the ligands employed range from simple

I· I I' 70-71 B 'd h acyc IC to comp ex macrocyc IC ones . . est es t e spectral and the structural characterisation of certain complexes, their chemical, photochemical and biological activities have also been addressed in the literature 74-7(,. As far as studies on saccharides as ligands are concerned, those with the lanthanides are extended only to a few solution interactions and these were monitored by NMR techniques77

-79

. Studies in the literature are also concerned with the ability. of lanthanide-saccharide complexes to act as probes in magnetic resonance imaging technique in aqueous solutions. Complexes formed between Eu(lII), Ce(llI) or U02

2+ and saccharide-acids are reported in the

I· 80-84 Th b' I' f' h Iterature . . e sta t tty constants 0 t ese complexes at low and high pH values have also been determined. Thus the saccharide interactions with

~HO ',.---0

H' 1 9 Hp , OH t/' OH

(a)

HO OH ~~To~

Hq.jO~OH 1

(e)

H9---\-.----~ --'" ~ '!HO T' 'OH

..----OH OH (e) .

HO •

~OH HO OH

\/ (g)

HO--+

.Lrt:q HO~OH

, 'OH (bl

• OS Ho~.l\/'oH

3[21' . OH OH

(d)

• OH

HO~-5'-1°\ 'OH 3r2~ OH

(f)

• • 0 H~~OH

, OH

(h)

HO~ \ OH . ~ 0 HO+--"'C,r."'0H • l' -0 / ______ ---- / 1 H\ r. ~O ,. OH H9-".·

(i) /

H~~S 0 • HO •. ~O~_o

HO- ,. O. 1 OH ~ OH HO- ,

1 OH

(j)

Fig. 2- Schemalic slructures of Ihe aldohexoses: (al, D-glll: (b), D-gal: (c), I)-man: aldoketoses: (d), D-fru: (el, D-sor; aldopenlos<!s : (f), I)-am; (g), I)-rih; (h), D-xyl ; and disccharides: (i), o-mal; U). 0-

lac used for synlhesising lanlhanide complexes. Arrows at ditTerenl groups indicale the hinding mode.

lanthanide metal ions were not well recognized in the literature. In view of this, our group has recently taken up a systematic study and contributed to the development of lanthanide-saccharide chemistry which is the primary focus of this article.

Complexes of mono- and di-saccharides (Fig. 2) of lanthanide ions, such as, La(lIl) (j\ Ce(lIl) (j'), Pr(III) (f2), Nd(lII) (j3), Sm(lll) (j\ Eu(II1) (j())and Dy(IlI) (j'» have been synthesized and characterized by a variety of analytical, spectral and magnetic techniques.

Lanthanide-saccharide complexes The complexes synthesized in this connection were

shown in Fig.3, in the form of histogram. These were generally prepared85 by reacting the hydrated metal halides with the di - or tetra - sodium salt of mono- or di - saccharides in 1:3 or 1:2 metal ion to ligand ratio in MeOH to result in the products in 40-75% yield. However, the Ce(llf) complexes were synthesized under an atmosphere of argon to prevent aerial oxidation. The complexes were generally found to be hygroscopic and resulted in brownish pasty material when kept exposed to air for 3-4 days, but can ,be kept unaltered for long periods when stored under dry conditions. The lanthanide complexes were found to be less hygroscopic than the corresponding ones of the transition metal ions. The complexes are soluble in water, but insoluble in any common orgalllc solvent.

Analytical studies All the lanthanide-saccharide complexes yielded

satisfactory results based on elemental analysis and the corresponding compositions were established as given in Table 1.

9 1 8 ' 7 ] 6 5 4 3 2 1 0

La Ce Pr Nd Sm Eu Oy

I I

Fig. 3--Hislogram showing the saccharide complexes of different lanthanides: filled portion indicate mono-saccharide complexes and unfilled indicate di-saccharide complexes.

230 INDIAN J CHEM .. SEC. A. FEBRUARY 2003

Table l-Col11position of lanthanide-saccharide complexes fitted with the forl11ula. in case of l11ono-saccharides. Na,,[M(SacMOH). (H"O)u].(CH, OH)c' (CH,COCH,lr.(H"O )g : and in case of di-saccharide

cOl11plexes. N a,,[ M (Sac )h(OH ),.(H ~O)ul.(CH:lOH )c. (CH, COC H:l ),.(1-1 20\

Metal ion a b c d e " '" Monosaccharide cOl11plexes Ce(lII ) 3 3 I 1-4 La(lIl ) 2 0 2 D-2 0-2 D-I Pre III ) :1 3 0 0 0-1 D-I 1-2 NeI(lll ) 3 3 () 0 0- 1 0-1 1-3 SI11(III) 3 3 0-1 1 D-2 0 D-J Eu(lIl) 2-3 2-3 0-2 0-1 D- I 0 o-s Dy(lll ) 2-3 2-3 D-2 D-I 0-2 D O-S

Di saccharide cOl11plexes Ce(lIl ) I La(lIl ) 1 I Pr(llI ) 3 2 0 Nd(lIl ) 3 2 0 5111(111) 3 2 0 Eu (llI l 2 2 0 Dy(1I1) 2 2 0

# . Is a dlllllcicar cOl11pl ex.

Lanthanide-saccharide complexes were generally observed to be anionic with Na+ as counter cation. When the measured aqueous molar conductivity (ohm- t mol-I em-I) was plotted against the total number of ions present in each of these complexes the plot exhibits a near linear correlation as shown in Fig. 4. The observed high saccharide-to-lanthanide ratios compared to the transition metal ion complexes is attributable to the greater affinity of saccharide ligands (oxa-donors) towards lanthanide ions, and also the high ionic potential and the ability to accommodate higher coordination numbers by these Ions.

Thermal studies of these complexes showed the presence of solvent molecules, such as, acetone and or methanol along with varying number of water molecules(») (0 to 5) . Loss of solvent molecule and degradation of the saccharide moiety were observed in 3-7 steps and total weight loss is in the range 40 to 851"/0 . The initial weight loss is an endothermic process, observed in the temperature range, 50-150°C, corresponding to the loss of solvent molecules . Above this temperature exothermic processes were observed due to loss of CO2, H20, and CO. End product of thermal studies was found 8

() to be oxide of lanthanide of the formula Ln20 ).

FTI R spectra The FTIR spectra of the complexes exhibited

broad .. bands characteristic of metal-bound saccharide

2 2 0 0

0 0

0- I 2 I 0 0 D D

195

t .... 1 , , I , , , , '

0 0 0 0

0

" I I I , , , , , , , I ... .!

0-1 0 2 2

0-3 0-2 2-5

b

:1 , , , , , , I , I , I , , C

~ ; a 45,+---~,~--~--~,----,---~,'----~

2 3 4 No. of ions in solution

Fig. 4--Plot of nUl11ber of ions vs. l110lar conductivity of lanthanide - saccharide cOl11plexes: Among the 60 coillplexes. 12 are l11ono-Jnionic (a, two ions). R are eli-anionic (b, three ions) and 40 are tri-anionic (c. four ions).

. . so 87 0 h hid t· . I mOietIes ' . n t e ot er Ian , spectra 0 simp e metal ion adducts generally give sharp signalss.,j . The position, shape and width of the band observed in the range 3350-34()0 cm·1 indicates the presence or ~ater molecule and secondary interactions of saccharides through its free hydroxyl groups. Band observed in the range, 2850-2950 em-I is indicative of C-H stretching vibrations in all these complexes. Though a one-lo-one assignment was n()t possible. the bands appeared in the region, 1600-1650, ' 1350-1450 and 1000-1100 cm- I were assignable to bH-O-I-j, Vc.c and Ve-

0, and VO-C-H and VC.C-H, respectively . Thus the FTIR

RAOel al.: SACCHARIDE COMPLEXES OF LANTHANIDES 231

studies have demonstrated the binding of saccharide unit to the metal ion, thereby exhibiting the complex formation.

NMR spectra Resonances anslng from different saccharide

protons overlap to result in broad bands with multiplet

(0)

c.L I ,..\L.ooo III.L Jw, i

....,.., 90 80 70 60

rd)

.Ii tJ JjJ 9080 70 GO

Fig. S--' :lC NMR spectra of (a) , Ce(lll)-Il-fru; (b), Pr(lIl) ·D-ara; (c) , Nd(IIl)-Il-gal and (d), Sm( IlI)-D-lac.

structures, and thereby individual resonances could

not be resol ved and identified. However, the overall 8 range corresponding to the skeletal protons of the saccharide molecule was found to be shifted down field upon coordination to the metal ion. Instead , 13C NMR spectrum was found to be quite useful in structure elucidation of the complex. Representative DC NMR spectra are shown in Fig. 5. The anomeric form and the saccharide conformations were identifiable from the 13C NMR spectra. Based on the

shift observed in the 8 of the corresponding carbon

(~8 = coordination induced shift, CIS = 8c(lIllP1cx -

81igulld), it is possible to identify whether the saccharide is binding in the de-protonated form (Sac-O-) or in the protonated form (-OH) or not bound at all. Thus the preferential interaction of one oxo group of the saccharide over the other could be identified from the magnitude of down-field shift suffered by the corresponding carbon signal. While large ~8 (CIS) values were assigned to saccharide-O- bound to metal

ion, the smaller ~8 values are assigned to saccharide­OH binding, indicating the difference in the binding strength of these two types . Based on CIS of the lanthanide complexes, it has been possible to identify that the aldohexoses chelate through 0-3 and 0-4 and provides additional coordination through OH-6; ketohexoses chelate through 0-4 and 0-5, with an additional coordination through OH-3; and aldopentoses interact only through 0-2, 0-3 and 0-4, among which 0-2 and 0-3 are predicted to be involved in chelation , and the 0-4 interacts weakly . Mode of saccharide binding to the metal ions is shown in Fig. 2 . Among 60 lanthanide saccharide complexes, 55 exhibited chelation through 03-04 and only four used 02-03 as listed in Table 2. Thus in almost all the complexes 03 is exclusively involved in the coordination to metal ion in its deprotonated

form (as C3-0T). Thus the combination of 03 with 02 or 04 in chelation is explainable based on the

TJble 2-l3i nding patlern of the de-proto naled -OH groups of saccharides to lanthnnide metal ions in different lanthan ide complexes

Chelatiiln patle rn

02·m 03-04 or 03'-04'*

04-05

Details Jbout the complexes

Pr(lll )-D-rib. Pr(III)- I) -xy l, Sm(III)-o -rib, Sm(lll)- 0 -xy l All mono and di-saccharide complexes of Ce(lll) (except Il-sor); La(1I1), Pr(lll ) (except I)-rib, D-xyl ); Sm(llI) (except I)-rib, o-xyl) ; Nd(III); Eu(lll), Dy(lll) Ce(1I 1)- D-sor

*Indicates that the chelation is through reducing part of the disaccharide

Total ilumber of complexes

4 55

232 [NOlAN J CHEM., SEC. A, FEBRUARY 20m

(i)

OH

O~<I O •• OH

O~/ ... ~ o:......ce..., HO. /Jb 0 0

HO~~6H OH

o

O~HO 0

~ O •• OH

o :' OH ~~OH2

o / OH

OH,

(iii)

(ii)

Fig. f>.-Proposed structurcs ofCe(III)·complexes: (i), D-rib; (ii), f)-glu: (iii), f)-la c.

orientation of the corresponding -OH groups on going from one type of saccharide to another (Fig. 2).

Based on the I.1C NMR spectral studies, it has also been possible to derive that the saccharide exists primarily in the pyranose form in at least 54 compounds and in furanose form in the remaining 6. This could be attributed to metal ion induced conformational change in the saccharide molecule. It has been shown in the literatl1re

Bg that when the metal

ion complex of monosaccharide is in the arabinopyranose conformation , the corresponding interaction is site specific, involving the C-30H and C-40H groups. Similar interactions were observed in case of lanthanide metal ion complexes of aldohexoses. It is also worth noting that the affinity of lectins (which has an arabinopyranose moiety) toward~ saccharides is sensitive to the orientations of the OH groups present at C-3 and C-4. Complexes form ed from disaccharides act as tridentate with additional interactions being present through -OH groups. For example, while J)· maltose (D-mal) can act

as 0-3'-0-4'-0-3 chelate, D-lactose (D-lac) can act as

0-3'-0-4'-0-2 chelate. Thus the saccharide moieties in different metal ion complexes showed not only the binding 01'0-, but also the binding of OH. Representative example of Ce(III )-mono and di­saccharide complexes are shown in Fig. 6.

24 24

22 '1- :JP2 22 ' = 2G9I2_ 20 - 'Po 20

-2G512

18 18 _ 2G

712 - '0, 16 16 4H '1.'2-

4F912 -14 14 - 4S

712

12 12 4S9I2-

10 - 4S

3t2 10 _ lG.

8 'F, _ 8

6 JH2= 3F) 6 _41 ,5'2

4 - JH15 4 - 41

1312

2 - 41 '112 2

0 - ' 1-1, 419/2

(a) (b)

Fig. 7-Electronic ene rgy levels Dr lanthanidc doped ions: (a), Pr(llI ) and (b), Nd(llI) . Possible e lectronic transitions arc shown by arrows.

Electronic spectra The electronic transitions in lanthanide complexes

are expected to show sharp signals as the perturbation caused due to the external ligand field is minimum in case of the deep-seated Iorbitals. When a lanthan ide ion is doped in some host latt ice a large number of

very sharp }'-7I transitions (1'1)1.112 = 0.05 to 0 .2 nl1l ) occur due to the existence of a number of microstates arising from a given I" configurationS'), but when the ion is in solution in the presence of some ligand, the number of observed transitions will be less because of the merging of some of the sharper signals to result in a broad one with larger bandwidth. Thus the band widths in lanthanide-saccharide complexes are generally broad by a factor of 100 when compared to that in the doped ions. This could be atrributed to the excitation of j'-electron to any of the higher orbital {(n+2)s, (n+2)p, (n+ I )d) or may also be due to the charge transfer transitions from Sac-O--7M(III ) ~II . Energy level diagram of the Pr(lll) and Nd(lII) are shown in Fig. 7. Thus, the solution absorpti on spectral bands of the complexes were broad. While Pr(lll) , Sm(III), and Eu(IIJ) have all their transitions belo w 600 nm, Nd(III) and Dy(lII) exhibit some transitions even above 750 nm. Representative spectra of La(lll) _. saccharide complexes are shown in Fig. ~.

Similarities in the spectral features have also been observed among the lanthanide-saccharide complexes. For example, Sm(lI/)-complexes show similar features as that observed in case of Pr(III ) and Nd(IlI)-complexcs. Absorption band positions obtained in the case of Nd(lll)-complexes have close

RAOel (I/.: SACCHARIDE COMPLEXES OF LANTHANIDES 233

0.250 0.250 iii

0.200 0.200 .. u c .8 0.15 0.150 ... 0

~ 0.100 OlOO ~

0.050 0.05

0.000 0.000 300 400 300 400

Wavelength (nm)

Fig. X--Aqucous solution absorption spectra of La(lI!) complexes: (i). La(lll)--I>-glu ; (ii). La(lIlj-I>-l'ru: (iii). La(lll)-I>-gal: (iv). La(III )­I)·man; (v), La(lll)- I>-sor. ; (vi ). La(lll)-I>-ara; (vii). La(III)-H-rib; (viii ), La(lll)-I>-xyl ; (ix). La(III )-I>-mal and (x). La(III)·I>-lac.

Table }-Absorption spectral data of the lanthanide complexes in aqueous solution

Metal ion No off Absorption wavelength (nm)* Molar absorptivity (Ur'cm- ' ) Possible transitions electrons

La(lIl) ° 255-270,327-330,350-375 1000· 2360, 210-870, 120-690 LMCT

Ce(lIl ) 1 257-274, 324-332, 364-368 1940-5490. 1290-7760,950-2340 LMCT

Pr(llI) 2 269-273, 329-344, 442-446, 1885-6470, 1570-5986, 3-6, 6-12, LMCT; JH4 .... ' D~ ; J H4 ~ \: JH4 465-468,478-483,585-590 7-14, 19-26 .... Jp ,; JH4 --7 Jpz

Nd(lIl) 3 268-276, 305-327, 505-512, 1500-3754, 1640-5000, 12-34 .. 18- LMCT; 41 w2 .... ~H1I 2 ; 41'1 /2 .... ~H W2 : 518-522, 570-573. 735-745, 53,32-73,29-71. 14-90, 12·32 4"Jl2 ~ 4S1l2 : 41w2 .... 2r'Jl2: 41 w2 .... 789-795, 860-865 cGO/2 ; 41'Jl2 .... 2GW2 : 4Iw2 ~ 4G " /2

Sm(lIl) 5 270-274. 309-321. 331-342, 1053-1495. 1389-1144, 1059- LMCT: (' HV2 .... 4 F J/2 : 6 H '/2 .... 411:112 : 400-405,462-465 , 474-478 IS70, 28-76, 6-26, 6-22 ('HO/2 .... ('PV2; 6H o/2 .... 4PW2

Eu(lll ) 6 192- 199, 356-378, 393-396, 3050-3960,880-1422,18-63, 6-12 LMCT: 7Fo - 7 7F2 : 7Fo .... °DJ :

523-529 Fo .... 7F ,

Dy(lll) 9 276-279. 302-303. 349-359, 1720-3407, 1540-3303, 1390· LMCT; 6 H,)n .... 41'0 /2; ('H"12 .... 449-452, 471-474, 756-758, 3368. 1424, 17-223,8-14.14-36 4F<J/2: 6 H 'V2 .... ('F,I2. 7/ 2; 6H I.V2 .... 805-g07

* Over differelll saccharide complexes of same metal ion.

relevance with the features obtained in case of porphyrinato doubie decker complexes lli

. UV region spectra of the complexes show bands around 260, 335 , 370 nm which are characteristic of Sac­oxo-7M(III) charge transfer transitions. Except in case of LaOII) and Ce(I1I) complexes, all others show bands in the visible region arising from /-7{ transitions and the corresponding data including molar absorptivities is given in Table 3. Diffuse rellectance spectra of the solid lanthanide-saccharide complexes showed broad bands at the same position as that observed in solution . Thus the study indicates the retainment of the solid-state structure upon dissolution.

6Fv2

Circular dichroism Circular dichroism spectra of all the complexes in

aqueous solution exhibited bands in the range, 215-400 nm. Though the Cotton effect is not very prominent in most of the disaccharide complexes, [he sign of the CD curve was found to be similar to that of the mono-saccharide complexes. The spectral results indicate similarities in the configuration around the metal center in all these complexes . Some general features observed are as follows: among the aldohexoses, complexes of O-galaclose (I)-gal) showed opposite sign compared to the complexes ,of o-glu and O-man, whereas, the complexes ofKcto­hexose have shown CD band with same sign . But in

234 IND!AN J CHEM .. SEC. A. FEBRUARY 2003

Tahle 4--M,lgnl!lic momenl <I,lla for lanthani<l l! . saccharide complexes.

Ml!lal ion No or/, /lJ (caicul,lled)* /lJ (observed) ei<.:c lrons (13M) (BM)** *

IA III) () () 0 Ce( lIl) I 2.54 2.05-2.n2 1'1'( III ) 2 3.5X 3.30-3.95 Nd( lIl ) :I 3.62 3.40-:1.10 Snl ( lll) 5 O.X4 ( 1.5-1.6)* * l .m- I.X3 ElI( III) 6 00.4-3.6)** 3.00-3 .63 Dy(lIl) 9 10.63 9.9X-10.93

*C lIcli lalcdllsing Ihe express ion gIJ(J+ I) II I~ 13M where J is for Ihe grou nd stale level and g = 1+111(1+ I )+S(S+ 1)-L(L+ I ) 1121(1+ I)} I I~

**/ll.+s = 1 L(L+ I )+4S(S+ I) II "ri. ***OVCl' differenl saccharide complexes of the sa me metal ion

case of aldo-pentose complexes, D-xylose (D-xyl) showed opposite sign of CD spectra compared to those of D-arabinose (D-ara) and D-ribose (D-rib). It implies that when the orientation of the saccharide in the coordination sphere is different , thi s leads to a difference in the sign of CD spectra. In case of disaccharide complexes, D-mal and D-Iac showed the same sign of curves as that of D-glu and D-gal respectively, suggesting that the disaccharides retain the configuration of their non-reducing part in the complexes. Thus, the spectral analysis of these complexes very well indicated difference in the orientation of a particular saccharide moiety in the corresponding metal ion complex.

Magnetic studies Room temperature magnetic susceptibility

mcasurcment of the solid products of lanthanide saccharide complexes exhibited different )..le!! values. The observed and the calculated )..lell values of lanthanide complexes are given in Table 4. Ce(lI[) and S m(lll) complexes showed )..lcil values in the rangc 2.05-2.62 and 1.03-1.83 BM respectively, whereas, Pr(lIl) and Nd(lIl) complexes showed 3.30-3.95 BM. The magnetic moment was calculated for Ce(lIl) ion using appropriate )..lJ expression. The variation observed between the experimental and the calculated )..len values in case of Ce(llI) complexes is attributed to the presence of a mixture of compounds in different oxidation states. Whereas in the case of Sm(I [[ )-complexes, the )..lell observed are in accordance with those reported in the literatureY2

·9'.

Thus, the study revealed that the oxidation state of the

metal ion in all the complexes is +3 . Comparison of [he calculated )..len with that of the observed shows good agreement except in case of Sm(III) and Eu(II[) complexes that may be due to the smaller energy gap present between the di fferent energy levels, and as a result the first, second and third exc ited energy levels getting more populated.

Data correlations and proposed structures Spectral techniques, such us, FT[R and absorption

spectra have demonstrated the direct binding of the saccharide moieties with M(\II) lanthanide ions . Both the LMCT and the f-~/ transitions were characteristic of the complexes formed. The CD spectra demonstrated the dissymmetry present around the metal ion center in the field of saccharide moieties. On the other hand, the thermal degradation experiments (TGA and DTA) revealed the presence of H20 and/or solvent molecules and the total loss of organic moiety present in the complexes . These studies also elicited the fragmentati on pattern .

However, the 13C NMR studies delineated the binding of specific oxo (-0-) and/or hydroxy (-OH) groups to the metal center. Such N M R based assignment took advantage of the magnitude of coordination induced shift, CIS (ilO) in various carbon centers and also that of the orientation of the adjacent hydroxyl groups present in the corresponding saccharide moiety, whether such -OH groups are capable of forming a chelate or not. [I' the single 4/ electron ofCe(lll) were to be shifted to Sd. one would expect concomitant changes in the absorption spectra and also in the magnetic susceptibility measurements. Though the )..l'o'al was found to be higher than the spin­only value, it is certainly lower than the expected value of 2.49 BM, which includes the total contribution of spin-orbit coupling. [I' the d-character was to be considered, a lowering of spin-orbit coupling is expected.

The molar conductance values for mono-saccharide complexes are observed in the range 160-200 ol1m- l mol- 1 cm~, whereas those of the disaccharide complexes are in the range of 50-90 ohm - Imol - Icm~. The conductance data suggests a I: I, 1:2 and 1:3 electrolyte behavior in different complexes and the data correlates fairly linear with the number of ions present in the complex as shown in the Fig. 4. Thus the data supports the presence of a tri-negati ve complex anion of the formula [M(D-Sachf- for mono-saccharides and a mono-anionic core of the

RAOel 01.: SACCHARIDE COMPLEXES OF LANTHANIDES 235

(i)

~OHOH

o ... '. 0

OH '. I o '. ./ 011;>

........ La'

~/'\' Of-!"'~O OH2

HO,,<~OH o

(ii)

~~~o 0- ' .. :/

OH' ~>~a~ OH,

o I OH

OH,

(iii )

Fig. 9---l'ropns~d , trllctures of La(III) complexes: (i), I)·glu ; (ii), I)·man ; (iii), 1)·lac.

formula [M(I>-di-Sac)(OH)(H20hr for disaccharides. Eiemental analysis data agrees well with our proposed composition of the complexes. Proposed structures of some representative mono- and di-saccharide complexes of La(III) are shown in Fig. 9 .

In case of the rare earth metal-saccharide complexes the coordination numbers are generally seven (Sm(lll), Eu(II I) ancl Dy(JII)), eight (La(II I), Sm(lll), Eu(III) and Dy(III)) and nine (Ce(lIl), PrOIl), Nd(lll) and a few Sm(ll!), Eu(lll) and Dy(lII) complexes) with the geometry proposed being pentagonal bipyramidal , bi-capped octahedron or bi­capped trigonal prism, and tri-capped trigonal prism, respecti vel y.

Presence of nine coordination in Pr(III)- and Nd(lll)-complex is supported by single crystal XRD studies of the corresponding D-rib complex')4, as shown in Fig . 10. Out of the nine ligations, eight were through oxygen atoms (three from n-rib and five from water molecules) and ninth one was through chloride. The saccharide provides an ax-eq-ax orientation and retains its chair conformation, in the complex. Similar structural characteristics were observed in case of Nd(III)-n-galactitol complexes'!5. Both the complexes exhibited extensive hydrogen bond interactions using

-OH, H~O alld CI- groups. It has been noted in recent literature that Eu(I1I) binds with two molecules of

rig . IO-- Crystal structure of I'r(l I1)-I)·rib.'i I leO COlllplex (fmm ref. 04)

O~OHqH CH OHIH '. 0 , '. I C CH,oHIH

o '/ ~O

o-=?~o~----r~

~OfOH

HO· ·. H

', 6 0

',,\ / __ OH

~Srn

~" '\ ""

. • 0 'OH HO HO'" OH

CH,OHIH

o

HO 0 - /. ' "

~/., OH/H,O

o ," . 0_ ,' .

, .,0

(I) (ii )

OdJ-:-:~ o " 0 .. 0

O~\ -"' // /Sm .... .... ~S\~" O~/ /~ \''. ' OH

2 0 \"0

, OH

ci 0

OH oJo (Iii)

Fig, II-Proposed structures of SIll(III) coillplex~s: (i), I)-glu, 1)­

gla and I)-ara; (ii ), I)-rib and I)-xyl: ( iii), I)-lac,

cyclohexanetriol as tridentate along with one or two chelating nitrates and water molecules to crystallize predominantly to give a nine- coordinated, tri-capped trigonai prismatic complex %. Representati ve examples of mono- and di-saccharide complexes of Sm(lIl), and Eu(lll) and Dy(lIl) are shown in Figs II and 12 respectively'l7. It has been found in the literature that mono-saccharides act as tri-dentate and di-saccharides act as tetra- or penta-dentate li-gands in the complexes of lanthanide ions , however, these act

INDIAN J CHEM .. SEC. A, FEBRUARY 2003

O(OH eto

, ~

~'~ o ... , '

, 0 OH .... I OH

o o

o~ \..:

O~ 0"

O~\'S: " 0, 0

.. /' , , ' . ' M' .

... /\ ~ 6---. /OH o>r/ ... -/ -.... M

/I' , -M 0-· "-

~'\ OH/H,Q : 0

H~'~:~"&b OH/H,Q

~~OH :' 0 0

t' .. , '

O~ HO HO OH o

o

(i) (Ii)

HO

OH 0 o (iii)

o

Fig . 12- Proposed structures 01' M(lII) 1M = Eu and Dyl complexes: (i), f)-gill: (ii), n-ara, n-ribose and IJ-xy!: (iii), IJ·lac.

~0"f0H

HO .... H " 0 0

\\/ ____ -----OH

"~?~~:/-\ HO ~(

HO

(i) (i i)

Fig. I3--Proposed structures of M(lII ) fM=Pr and Ndl complexes: (i), D-rib: (ii ), n-ma!.

as bi- or tri-dentate ones in case of transition metal . I 4S'IX· IOI Ion comp exes" .

Structurally similar PrOli)-n-rib and Nd(lll) complexes show tridentate mode of binding as shown . F' 10' f' I I I 1)4 'IS H . 111 tg. In case a : comp ex " . owever, In our stuciies ll

)2 while the mono-saccharides exhibited complexes with 1:3 ratio, those of di-saccharides exhibited I: I complex as shown in Fig. 13.

Conclusions Saccharides are building blocks of a number of

biological molecules, including small and large ones. These systems drew the attention of scientists, with diverse interests , from all over the world. By their c1iCmical nature, these can act as potential molecules for interacting with metal ions , Though this review

addresses various aspects related to the metal ion­saccharide interactions especially of lanthanide ones, the coordination chemistry of saccharides is still found to be in its infancy stage. Based on several spectral and analytical techniques, structure and binding aspects of lanthanide-saccharide complexes were established. Primary aim of this article is to highlight the synthesis and characterization of saccharide complexes of trivalent lanthanide ions. The lanthanide-saccharide complexes have shown structural diversity among them as given in this review (Figs 6, 9, /1-13), Molecular composition (in terms of ratio), coordination number, presence of solvent molecules, and conformation of the saccharide moiety are described based on different spectral and analytical techniques,

RAOe! al.: SACCHARIDE COMPLEXES OF LANTHANIDES 237

Recent developments and future projections

Presence of saccharide moieties in biological systems provide impetus for the growth of the field of metal ion - saccharide interactions. Recent trends in this ficld include the development of synthetic methodologies followed by characterization. In this context, the recent literature deals with the synthesis, isolation, characterization and bio-interaction studies of a number of transition metal ions with simple saccharides and their derivatives. Biointeraction

d· h DNA I 5964-66 RN stu les, suc as, c eavage', ase inhibition65

, protein synthesis in rabit reticulocyte lysate65

, Fe(lIl) transport, ill vivo metallothionein induction49

, lipid peroxidation and cell toxicity were performed and putative biointeractions of transition metal - saccharide complexes is reported. Studies reveal that these complexes have some biological significance and promise to be potentially useful in medicine and even in clinical trails . In spite of all these developmcnts it is still correct in saying that the studies of metal ion - saccharide interactions is largely unexplored.

Due to the fact that the saccharides undergo easy isomerisation and conformational changes, its complexation with metal ion results in the formation of mixture of products, hence researchers are reluctant to take up this particular field of research . During the past several year researchers are putti ng constant efforts to develop methodologies to crystallize metal ion-saccharide complexes. Attempts to circumvent this resulted in the development of protecting group,

h . d N I I ' . 101-1 10 anc onng group an -g ycosy atlOn strategies . ". The results were encouraging with the report of a number of crystallized metal ion-complexes of protected saccharides in the recent literaturellJ-116 and our group is contributing substantially to the synthesis, characterization and solution behavior of saccharides and its derivatives including N-glycosyl

. 117-120 d' I . I 121-1 2(, amlllcs an Its meta Ion comp exes · . .

Acknowledgement CPR acknowledges the financial support from the

Council of Scientific and Industrial Research, and the Department of Science and Technology, New Delhi. CPR acknowledges the contributions made by his former student, Dr. A. Mukhopadhyay, and his collaborator, Prof. E. Kolehmainen from the University of Jyvaskyla, Finland.

References I Kenncdy J F & White C A in 13io(l{:til'e car/}()hydm!es ill

chelllis!ry. hiochelllistrv ({nd hiolog\'; (John Wiley and Sons: Ncw York ) 19X3.

2 Noltmann E A. £I1ZYllles. 3 ( 1970) 271. 3 Root R L. Durrwachlcr J R & Wong C H. J Alii ehelll Soc.

107 (1985) 2997. 4 Montrcuil J. Pitre appl Chelll. 56 ( 1984) X59. 5 Angyal S J. Chell! Soc Rev. 9 (1980) 415. 6 Mills J A. Bioc/,elll Biop/r.vs Res COIII/IIII1I. 0 ( 1961) 418. 7 Callolld F. J Ph({rlll. II (1825) 562. 8 Angyal S J & Davies K P. J c/,elll Soc. Chelll COIII IIIllIl .

( 1971) 500. 9 Angyal S J. Pure app/ Chelll . 35 ( 1973) 13 1. 10 AngyaISJ.AustJChelll.25(1972) 1957. II Tajmir-Riahi H A . Car/;ohydr Res. 122 ( 19X3) 241. 12 Tajmir-Riahi H A, Car/;ohydr Res. 125 (1984) 13. 13 Tajmir-Riahi H A. Car/;ohydrRes. 127 ( 1984) I. 14 Cook w J & Bligg C E. J Alii chelll Soc . 95 ( 1973) 0442. 15 Cook W J & l3ugg C E, AC/a Crystallogr. 1329 (1973) 907. 16 Brown E A & Bugg C E. Ac!a CI)'swllogr. 1336 ( 1980)

2597. 17 Einspahr H & 1311gg C E. Ac/a Crvswllogr. 1337 ( 198 1)

1044. 18 Einspahr H & Bligg C E in Me!a/ i(JIl.I· ill bio!ogiw/ systellls.

edited by H. Sigel . 17 (19X4) 51. 19 Bock K & Pederson C. Adv Car/}()hydr Chelll Bioclrelll . 41

(1983) 27. 20 Bock K & Pederson C. Ad" Car/;ohydr Cirelli Bioc/U'III. 42

(1984) 193. 2 1 Bandwar R P & Rao C P. Cltrr Sci (!ndia). 72 (1997) 7XX

and references 19-3X therein. 22 Sawyer D T . CIrelli Rev. 64 ( 1964) 633. 23 Rendleman J A Jr. Ad" Car/;ohydr ChI'lli Bioc/,elll. 21

(1966) 209. 24 Rendleman J A Jr. Ad" Corhohydr Chelll Biochl'lII, 117

(1973) 106. 25 Angyal S J. Chelll Soc Rev. 9 (1980) 415. 26 Angyal S J. Adv Corbohydr Chelll Biochelll. 47 (1989) I . 27 Montgomery R, Adv Chelll Ser. 117 ( 1973) 197. 28 Haines A H, Adv Corho/ryrir Chelll Biochelll. 33 (1976) II . 29 Kennedy G R & How M J. Carhohvdr Res. 2!i (1973) 13. 30 Bell C F, Beauchamb R D & Shor E L. Car/;lIhydr Res. 147

(1986) 191. 31 Paal T, AC/a Chilll Acad Sci Hllllg. 95 (1977) 371. 32 Vesala A. L1nnbcrg H. Kippi R & Arpalahti J. Cor/Jolrydr

Re.l'.102(1982)312. 33 Csikkelnc S A, Ac/a Phorm Hllllg. 6 1 (1991) 253. 34 Gonalez-Velasco J. Ayllon S & Sancho J, J illorg IIl1d

Chelll. 41 (1979) 1075. 35 Pene E & Macarov ici C G. Rev ROlllII ChillI. 16 (1971)

1749. 36 Ekstrom L G & 01 in A. Ac/a Chilll Scam!. SCI' A 31 ( 1977)

S38. 37 Coccooli F & Vicedomini M . J il/org lWei Chelll. 40 (197X)

2103. 38 Coccooli F & Viccdomini M . .I illorg l/lld Cirelli. 40 (1978)

2106. 39 Mikan A & Banusek M. Collec! Czech ChI'lli COIIIIl/IIII. 45

(1980) 2645.

..

238 INDIAN J CHEM .. SEC. A. FEBRUARY 2003

40

41

42

43

44

45

46 47 48

49

50 51

52 53

54

55 56 57

58

59

00

01

Elli son H R. Edwards J 0 & Healy EA. JAm chem Soc. 84 (1902) I H20.

Ellison H R. Edwards J 0 & Nyberg L. J Alii chelll Soc. 84 (1962) IH24 .

Popicl W J & Rustom M S. J illorg IIlIeI ClIem. 40 (1978) 921. Angyal S J. Greevcs 0 & Picklcs V A. Car/Johydr Res. 35 ( 1973) 105. Popiel W J & Rustom M S. Carhohydr Res. 56 (1977) 4071. Taylor G E & Waters J M. Tetrahedroll Lell. 22 ( 198 1) 1277 . Klufers P & Kuntc T. Allgew Chemlll! Ed. 40 (2001) 4211. Kaiwar S P & Rao C P. Car/Johydr Res. 237 (1992) 203. Srcedhara A. Raghavan M S S & Rao C P. Car/Johydr Res. 264 ( 1994) 203. Bandwar R P. G iralt M. Hidalgo J & Rao C P. Carbohydr Res. 284 (1996) 73. Bandwar R P & Rao C P. Car/)ohydr Res. 287 (1996) 157. Banelwar R p. Sastry M O. Kadall1 R M & Rao C P. Carbohydr Res. 297 ( 1997) 333. Bandwar R P & Rao C P. Carhohydr Res, 297 (1997) 341. Band war R P. Flora S J S & Rao C p. Biollleta{s. 10 ( 1997) 337. Ran C P. Geetha K & Bandwar R P. Bioorgallic & Medicillal Chemislly Lell. 2 (1992) 997. Rao C P & Kaiwar S P. CariJohydr Res. 237 ( 1992) 195. Rao C P & Kaiwar S P. CariJoiJydr Res. 244 (1993) 15. Ran C p. Gcetha K & Raghavan M S S. Biomelals, 7 ( 1994) 25. Kaiwar S P. Bandwar R p. Raghavan M S S & Rao C p , Proc II/d Acad Sci (Chelll Sci), 106 ( 1994) 743. Kaiwar S P. Raghavan M S S & Rao C p, J Chem Soc Dullol/ Tral/s. (1995) 1509. Geetha K, Raghavan M S S. Kulshreshtha S K, Sasikala R & Rao C P. Carhohydr Res. 271 (1995) 163. Rao C P, Geetha K, Raghava n M S S. Srecdhara A, Tokunaga K, Yamaguchi T. Jadhav V, Ganesh K N, Kri shnamoo rthy T, Rall1aiah K V A & I3hattacharyya R K, II/org Chim Acta. 297 (2000) 373.

02 Rao C P & Kaiwar S P. II/org Chilli Acw. 180 (1991) 11 . 03 Mukhopadhyay A, Karkamkar A. Kolehmainen E & Ran C

P. Car/)ohydr Res. 311 (1998) 147. 04 Sreedhara A, Susa N, Patwardhan A & Rao C P, Biochelll

Biophys Res COI/IIIIUlI. 224 (1996) 115. 65 Sreedhara A, Rao C P & Rao B J. Carbohydr Res. 289

(1990)39. 06 Kaiwar S p, Sreedhara A. Raghavan M S S. Rao C P.

Jaelhav V & Ganesh K N, Polyhedroll. 15 (1990) 765.

67 Bandwar R P & Rao C P. Car/)ohwlr Res, 277 (1995) 197. 08 Kaiwar S P & Rao C p. Chelll-Biollllt. 95 ( 1995) 89.

09 Kaiwar S p. Raghavan M S S & Rao C p, Carhohydr Res. 250 (1994) 29.

70 Schaverien J . Adv Org(ll1OIIIet Chem, 36 (1994) 283. 71 Edelman F T & Gun ' ko Y K. Coord Chelll Rev, 165 (1997)

163. 72 Clark 0 L. Gordon J C. Scott B L & Watk in J C.

Polyhedroll , 18 ( 1999) 3723.

73 Ephritikhine M. Chem Rev. 97 (1997) 2193. 74 Petricek S, Dell1sar A & Golic L. Polyhedron. 17 (1998)

529.

75 Kenellakopulos S, Maier R, Marques N, Ocmatns A l' & Rebizant J. Polyhedrol/ , 18 (1999) 263.

76 Tsubouchi A & Bruice T C. J Alii Chelll Soc. I 17 ( 1995 ) 7399.

77 Tagle P G & Yatsimirsky A K, J ChI'lli Soc Daltoll TrailS , (1998) 2957.

78 Mao G, Zhang H J. Ni J Z . Wang S B & Mark T C W. PolyhedHIIl . 17 ( 1998) 3999.

79 Anthonscn T, Larscn B & Smidsrod O. Acta Chel1l S("{/I/(I. 26 (1972) 2988.

80 Kvam B J, Grasdalen H. Smidsrod 0 & Anthonscn T. Acta Chell! Scw/{I, B 40 (1986) 735.

81 Panda C & Patnajk R K. J Illdiall Chel1l Soc. 53 ( 1976) 1079.

82 Panda C & Patnajk R K. J Illdilill Chelll Soc. 56 ( 1979) 133. 83 Kharitonov Yu & Alikhanova Z M. R{/diokhilllivil. 6 (1%4)

702. 84 Geraldes C F G C. Castro M M C A. Saraiva M E,

Aureliano M & Oias 13 A. J Coord Chelll. 17 (198H) 205. 85 Mukhopadhyay A, Kolehmaincn E & Rao C P. Car/whydr

Res, 324 (2000) 3~. 80 Chu Y, Gao Y C. Scott B L & Watkin J C. Pol.l'hedroll . 18

(1999) 1389. 87 Attain W J, Mol S'nte,. 22 (1990) 385. 88 Goldstein J, Hollcnnan C E & Smith E E. Biochelllistrv. 4

(1965) 876. 89 Dickc G H, in Spectra 111,,1 ellerg), lel'e/s of" /"lire ('o r/It iOlls

ill cry.I·Ials , ed ited by H M Crosswhite & Crossw hi te. (John­Willey & Sons, New York). 1968.

90 Duttn R L & ShYJllal S in Elelllellts oIII/{{glle!ochel1lislrv, Esat-Wcst (lnel), 1992.

91 Spyroulias G A. Raptapoulou C P. Montauzon D. Mari A. Poilblanc R. Tcrzis A & Coutsolelos A G. Illorg Cit 1'111. 38 ( 1999) 1683 .

92 Chen H & Archer R D, Illorg Cite/II, 33 (1994) 5195. 93 Spyrolias GA. Coutsolelos A G, Ruptapoulou C P & Tcrzis

A, Illorg Chelll , 34 ( 1995) 2476. 94 Yang L. Zhao Y. Xu Y. Jin X. Weng S, Tian W, Wu J & Xu

G, C{/rbohvdr Res. 334 (2001) 91. 95 Yang L. Zhao Y. Tian W. Jin X, Weng S & Wu J.

Carbohydr Res, 330 (2001) 125. 96 Hu sson P. Delnngle p. Pecaut J & Voettro P J A. In org

01'111 ,38 ( 1999) 2012. 97 Mukhopadhyay A. Kol ehillainen E & Rao C P. Illdiall J

Oelll , 40A (2001) 1045. 98 Tsukagoshi K & Shinkai S, J org Cllelll. 56 ( /991 ) 40X9. 99 Andries M L D & Perez S. Carbohvdr Res, 124 (1983) 324. 100 Lenkinski R E & Ruben J, J Alii cltelll Soc, 98 ( 1976) 3089. 101 Angyal S J & Greeves D. A list J Chelll , 29 ( 1976) 1223. 102 Mukhopadhyay A, Kolehmaincn E & Ran C P. Car/)ohvdr

Res. 328 (2000) 103. 103 Bjorndal H. Hellerquist C G. Lindberg B & Svensson S.

Allgew Che/II lilt Ed Ellgl, 9 (1976) 610. 104 Bieckel C A A V, Westcrdrin P & Van-BooJll J.H.

Tetrahedron/ell. 22 (1981) 2819. 105 Waber W p, Silicoll reagellts Jill" orgallic sYllthesis:

(Springer- Verlag; Berlin), 1983. 106 Nagel Y & Beck W Z. NatllrjofSch. B 40 ( 1985) 1 I R I. 107 Pill T & Beck W Z , Natllr!nrsch , B 48 (1993) 1461. 108 Babu T V R & Ayers T A. Tetrahedroll Lell. 3:'i (1994)

4295.

RAOel af.: SACCHARIDE COMPLEXES OF LANTHANIDES 239

109 Zholl Y. Wagner B. Polborn K. Sunkel K & Beck W Z. Natllr:f(m·ch. B 49 (1994) 1193.

110 TSlibomlira T. Yano S. Kobayashi K. Sakurai T & Yoshikawa S. J Chelll Soc Chelll COIIIIIIIlII . (1986) 459.

III KlIdllk-Jawnrska. J Trails Met Chelll (LOI/{/Oll). 19 (1994) 296.

11 2 Bochkov. Zaikov G E. Chelllistry of rhe glycoside bOlld .IiJl"ll/lIlirlll (II/{/ cleavage. Pergamon Press-Oxford. 1979.

11 3 Rajak K K. Rath S p. Mandai S & Chakravorty A. /l1org Chelll. 38 ( 1999) 3238.

114 Piralili U. Williams D N. Floriani C. Gervasio G & Viterbo D. J chelll Soc Chelll CO/III1lUIl. (1994) 1409.

1 15 Tanase T. Y suda Y, Onaka T & Yano S, J chem Soc Du/toll Tmlls. (1998) 345.

116 Yano S. 1nolle S, Yasuda Y. Tanase T, Mikata Y. Kakuchi T. Tsobllmura T, Yamasaki M. Kinoshita T & Doe M, J ChclII Soc Oil/fOil TrelliS . (1999) 1851.

I 17 Raj sekhar G. Rao C p. Saarcnkcto P K. Kalemainen E & Rissancn K. CariJohvdr Res. 337 (2002) 187.

118 Sah A K. Rao C p" Saarenkelo P K & Rissanen K. CariJoiJydr Res. 337 (2002) 79.

119 Das T M, Kolehmainen E & Rao C p, CuriJohytir Res, 334 (2001) 261.

120 Sah A K. Raa C P. Saarenketa P K & Kolemainen E. CariJohytir Res. 335 (200 I) 33.

121 Das T M. Raa C P & Kolemainen E. Car/Johytir Res, 335 (200 I ) 151.

"22 Sah A K. Rao C P. Saarenketa P K & Rissanen K. Chem Lett. (200 I ) 1296.

123 Sah A K. Rao C P, Wegelills E K. Kolemainen E & Rissanen K. CariJohydr Res. 336 (2001) 249.

124 Das T M. Raa C P, Kolehmainen E, Kadam R M & Sastry M D, Car/Johydr Res. 337 (2002) 289.

125 Sah A K. Rao C P. Saarenketo P K. Wegelius E K. Kolemainen E & Rissanen K. Ellr J il10rg Chelll, (2001) 2773.

126 Sah A K. Raa C P. Saarenketo P K. Wegelius E K. Rissanen K & Kolemainen E. J chem Soc Dillfoll TrailS. (2000) 3681.