investigation on the interactions between diperoxovanadate and substituted phenanthroline

Spectrochimica Acta Part A 64 (2006) 255–263

Investigation on the interactions between diperoxovanadateand substituted phenanthroline

Ting Huang a, Shuhui Cai a,∗, Xianyong Yu a, Zhong Chen a,b,∗a Departments of Physics and Chemistry, State Key Laboratory of Physical Chemistry of Solid Surface, Xiamen University,

Xiamen, Fujian 361005, People’s Republic of Chinab State Key Laboratory of Structural Chemistry, Fuzhou 350002, People’s Republic of China

Received 19 May 2005; accepted 4 July 2005

Abstract

Detailed investigations were carried out to explore the interaction systems of NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline andNH4VO3/H2O2/5-methyl-1,10-phenanthroline in aqueous solution under physiological conditions by NMR spectroscopy, such as 1D 1H,13C, 51V variable temperature, and 2D COSY, NOESY, HETCOR, COLOC techniques as well as density functional calculations. New species[OV(O ) (5,6-dimethyl-1,10-phenanthroline)]− and [OV(O ) (5-methyl-1,10-phenanthroline)]− including isomers were formed in a bidentatecoTro1©

K

1

teoodedcodfc

1d

2 2 2 2

oordination fashion which were stable under the experimental conditions. The solution structures of these new species were proposed basedn the direct NMR experimental information and confirmed by the theoretical calculations. All the 1H and 13C NMR peaks were assigned.he calculated 1H and 13C chemical shifts on the whole are in fair agreement with the experimental values. The methyl groups on the aromatic

ing of the three new complexes were found to have a steric hindrance effect on the coordination process. Experimental results show that therder of coordination capability of phenanthroline and its derivants was: 1,10-phenanthroline > 5-methyl-1,10-phenanthroline > 5,6-dimethyl-,10-phenanthroline.

2005 Elsevier B.V. All rights reserved.

eywords: Diperoxovanadate; Interactions; NMR; Substituted phenanthroline

. Introduction

Peroxovanadate complexes are receiving renewed atten-ion recently for their biological relevance involving insulinnhancement, anti-tumor activities, and functional modelsf haloperoxidase enzymes and for their application asxidants in different catalytic processes [1–9]. Among theiverse influences of peroxovanadate complexes, insulinnhancing effects have greatly increased interests in vana-ium coordination chemistry [10,11]. The coordinationhemistry of vanadium has great versatility for adjustmentf pharmacological characteristics [12]. Decomposition ofiperoxovanadate in aqueous solution is a limiting factoror potential pharmaceutical use [13]. Peroxovanadateomplexes of heteroligands revealed a range of stabilities

∗ Corresponding authors. Tel.: +86 592 2181712; fax: +86 592 2189426.E-mail address: [email protected] (Z. Chen).

toward decomposition in aqueous solution, depending onthe nature of the heteroligands [14]. The most stable diper-oxovanadate complexes are those of Mn[VO(O2)2(L-L′)]n−(where M = NH4

+, K+, Na+; n = 1, 2, 3; L, L′ = ligand).Potassium biperoxo(1,10-phenanthroline) oxovanadate(V)trihydrate [abbr. bpV(phen)] is one of the most stableperoxovanadate complexes with two nitrogen atoms enteringthe coordination sphere of vanadium [15]. Recently, wehave reported some diperoxovanadate complexes formedin the interaction systems of NH4VO3/H2O2/L (L = organicligands) [16–20]. In this paper, we reported three new stablediperoxovanadate complexes formed through the interactionsystems of NH4VO3/H2O2/L with L = 5,6-dimethyl-1,10-phenanthroline and 5-methyl-1,10-phenanthroline inaqueous solution under physiological conditions. The vana-dium atoms of the new complexes were bidentate coordinatedby two nitrogen atoms. For the system of NH4VO3/H2O2/5-methyl-1,10-phenanthroline, two diperoxovanadate isomers

386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2005.07.016

256 T. Huang et al. / Spectrochimica Acta Part A 64 (2006) 255–263

were observed. 1D and 2D NMR techniques were combinedto investigate the chemistry of the interaction systems. Thedirect experimental information on the solution structuresof new species were obtained, and all the 1H and 13C NMRpeaks of the peroxovanadate(V) complexes were assigned.Density functional calculations were performed to verify thestructural proposes and 1H and 13C spectral assignments.

2. Experimental and theoretical

2.1. Materials and preparation

The compounds NH4VO3, H2O2, D2O, NaCl, 1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, and5-methyl-1,10-phenanthroline were analytic grade reagents.To form the ternary system of NH4VO3/H2O2/ligand(ligand = 1,10-phenanthroline; 5,6-dimethyl-1,10-phenan-throline; 5-methyl-1,10-phenanthroline), NH4VO3 andH2O2 were first mixed in D2O to produce the species[OV(O2)2(D2O)]−/[OV(O2)2(H2O)]−, then the ligand wasadded to the solution. The ionic medium, 0.15 mol/L NaCl inD2O solution at 25 ◦C, was chosen to represent physiologicalconditions in all NMR experiments except for the variabletemperature 51V NMR experiments.

2

s1

satwuit

2

tifeeVL6wfriaF

were used [26,27]. Based on the optimized geometries, the1H and 13C NMR chemical shifts were computed usinggauge-independent atomic orbital (GIAO) method at theB3LYP level of theory. The solvation effects of the chem-ical shieldings were further considered using polarizablecontinuum models (PCM [28,29]) at each optimized gasphase geometries. All calculations were carried out withthe Gaussian 98 program suite [30]. Vibrational frequencieswere calculated to ensure that each minimum is a true localminimum (only real frequencies).

3. Results and discussion

3.1. Interaction system of NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline

3.1.1. 51V NMRThe mixture of NH4VO3 and H2O2 with 1:5 molar

ratio (0.2 mol/L vanadate concentration) had a strong51V peak locating at −692 ppm, which was assignedto [OV(O2)2(D2O)]−/[OV(O2)2(H2O)]− according tothe previous reports [31–33]. When 5,6-dimethyl-1,10-phenanthroline was added to the mixture, a new 51V NMRsingle peak appeared at about −746 ppm. Its intensityi11maapis

Fd(ts1

.2. NMR spectroscopy

All NMR spectra were recorded on a Varian Unity plus 500pectrometer operating at 500.4 MHz for 1H, 125.7 MHz for3C, and 131.4 MHz for 51V. The solvent for 1H, 13C, and 51Vpectra was D2O. DSS [3-(trimethylsilyl)-propanesulfoniccid sodium salt] was used as an internal reference forhe 1H and 13C chemical shifts. The 51V chemical shiftsere measured relative to the external standard VOCl3 withpfield shifts considered negative. Signal-to-noise ratios weremproved by a line-broadening factor of 10 Hz in the Fourierransformation of all 51V spectra.

.3. Computational method

The geometries of [OV(O2)2(5,6-methyl-1,10-phenan-hroline)]− and [OV(O2)2(5-methyl-1,10-phenanthroline)]−somers were optimized using the B3LYP hybrid densityunctional, which includes a mixture of Hartree–Fockxchange with Beck88 exchange functional under gen-ralized gradient approximation plus a mixture ofosko–Wilk–Nusair local correlation functional andee–Yang–Parr nonlocal correlation functional [21–23]. The-31G* basis set [24] developed by Pople and co-workersas used for the metal center, where the single f polarization

unction was changed to two sets based on the even scalingule suggested by Frisch et al. [25], i.e., the single exponentn the f function was replaced by two exponents, one twices large and one half as large as the original exponent.or O, N, C, and H, the standard 6-31G(2d,2p) basis sets

ncreased with the increasing quantity of 5,6-dimethyl-,10-phenanthroline (from 0.50 to 0.75, 1.0, and finally.25 equivalents) before reaching a maximum. In theeantime, the peak locating at −692 ppm became smaller

nd smaller, as shown in Fig. 1. The new peak wasssigned to a new species [OV(O2)2(5,6-dimethyl-1,10-henanthroline)]−. Since 5,6-dimethyl-1,10-phenanthrolines a bidentate ligand, we tentatively assumed that the newpecies was seven-coordinated like [OV(O2)2(bibyridine)]−

ig. 1. 51V spectra of the interaction system of NH4VO3/H2O2/5,6-imethyl-1,10-phenanthroline in aqueous solution with different molar ratios1:5:n) and 0.2 mol/L the total concentration of vanadate species. From (a)o (d), n = 0.50, 0.75, 1.0, and 1.25 equivalents, respectively. The chemicalhifts of [OV(O2)2(H2O)]−/[OV(O2)2(D2O)]− and [OV(O2)2 (5,6-methyl-,10-phenanthroline)]− are located at −692 and −746 ppm, respectively.

T. Huang et al. / Spectrochimica Acta Part A 64 (2006) 255–263 257

Fig. 2. Structure sketches of [OV(O2)2(5,6-methyl-1,10-phenanthroline)]− (a), isomer A [OV(O2)2(5-methyl-1,10-phenanthroline)]− (b), and isomer B[OV(O2)2(5-methyl-1,10-phenanthroline)]− (c).

[34], as shown in Fig. 2(a). When the equivalent of 5,6-dimethyl-1,10-phenanthroline reached 1.25, almost all[OV(O2)2(D2O)]−/[OV(O2)2(H2O)]− was converted intothe new species.

Variable temperature 51V NMR experiments were car-ried out to study the influence of temperature on the equi-librium of the reaction system. The 51V NMR spectra ofthe interaction system of NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline with 1:5:1 molar ratio (0.2 mol/L vanadateconcentration) in the temperature range of 20–60 ◦C areshown in Fig. 3. Experimental results showed that: (1) thechemical shifts of all peaks moved toward downfield whenthe temperature increased and the trend was reversed whenthe temperature decreased; (2) all the vanadium species werestable in the experimental temperature range.

In order to study stability of the newly-formed speciesin solution, 51V NMR spectra of the interaction system ofNH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline with dif-ferent molar ratios were recorded every 12 h at 25 ◦C. It wasfound that the newly-formed species were stable during theexperimental period (about a week). This implied that thespectra obtained without detectable changes in long timemeasurement, such as 13C NMR spectra were creditable.

3.1.2. 1H and 13C NMR spectra1 13

o1tCa

was used instead of NH4VO3/H2O2 to produce[OV(O2)2(D2O)]−/[OV(O2)2(H2O)]− in the NOESYexperiment. The COLOC spectrum is shown in Fig. 4.

For the interaction system of NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline with 1:5:1 molar ratio, both1H and 13C NMR spectra had only one group of peaks,suggesting that 5,6-dimethyl-1,10-phenanthroline had almostcoordinated to the central vanadium atom. When the molarratio of the interaction system increased to 1:5:1.25, another

Foaia

The H and C NMR spectra of the interaction systemf NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline with:5:1 and 1:5:1.25 molar ratios (0.2 mol/L vanadate concen-ration) were recorded. 2D COSY, NOESY, HETCOR, andOLOC techniques were used to assign all the signals. Tovoid the release of oxygen, K3[OV(O2)2(C2O4)]·H2O

ig. 3. Variable temperature 51V NMR spectra of the interaction systemsf NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline with 1:5:1 molar rationd 0.2 mol/L the total concentration of vanadate species from 20 to 60 ◦Cn the increase of 10 ◦C (from bottom to top, the temperature increased first,nd then decreased.).


Fig. 4. COLOC spectrum of the interaction system of NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline with 1:5:1 molar ratio and 0.2 mol/L the totalconcentration of vanadate species.

group of peaks appeared. This group was assigned to thefree ligand. The assignments of all spectral data are listedin Table 1 (δH

exp and δCexp for 1H and 13C chemical shifts,

respectively. See Fig. 2(a) for atom numbering). Obviousdifferences were observed in the 1H and 13C NMR spectrabetween the free ligand and coordinated one. Some valuableinformations about the geometrical arrangement of the newcomplex in aqueous solution can then be deduced from the

data. First of all, the 13C NMR spectra of the interaction sys-tem with 1:5:1 molar ratio had 14 resonances, which weretwice as many as those of the free ligand. This result indi-cated that the equivalence of carbon atoms existing in the freeorganic ligand was not survived after coordination reaction.Secondly, compared to the free ligand, the chemical shifts ofC-2 and C-4b atoms which were closed to the N-1 atom onthe coordinated ligand were obviously downfield. The varia-tions of the chemical shifts of C-9 and C-6b which were closeto N-10 atom were smaller than those of C-2 and C-4b. Sincethe nitrogen atom in the equatorial position was much closerto the peroxo ligand, the chemical shifts of the proton and car-bon atoms adjacent to it were usually more downfield thanthose in the apical position owing to being more deshielded[34,35]. Based on this fact, we deduced that N-1 atom wason the equatorial position.

3.2. Interaction system of NH4VO3/H2O2/5-methyl-1,10-phenanthroline

3.2.1. 51V NMRAs mentioned above, the strong 51V peak locating at

−692 ppm in the mixture of NH4VO3 and H2O2 with1:5 molar ratio (0.2 mol/L vanadate concentration) wasassigned to [OV(O2)2(D2O)]−/[OV(O2)2(H2O)]−. When 5-mnt

Table 1Assignments of 1H and 13C NMR spectra of the interaction system of NH4VO3/H2

δHexp(ppm) δH

cal δHdiff δH

cal,s δHdiff,s

[OV(O2)2{5,6-dimethyl-1,10-phen}]−9.59 (d, J = 3.8 Hz, H-2) 11.42 1.83 10.64 1.058.26 (d, J = 3.8 Hz, H-9) 9.29 1.03 9.01 0.758.05 (d, J = 8.0 Hz, H-7) 7.51 −0.54 8.61 0.567.97 (d, J = 8.0 Hz, H-4) 8.22 0.25 9.05 1.087.66 (m, H-3) 7.47 −0.19 8.32 0.667.48 (m, H-8) 6.82 −0.66 7.80 0.321.64 (s, H-6 methyl) 2.45 0.81 2.73 1.09

1.32 (s, H-5 methyl) 2.56 1.23 2.82 1.49

51.181.211.00

1.39

S ve to TMS (δTMS = 0). The experimental values were obtained from the interactions H H C C

3

,6-dimethyl-1,10-phen8.32 (d, J = 3.5 Hz, H-2, H-9) 9.43 1.13 9.507.61 (d, J = 7.5 Hz, H-4, H-7) 8.39 0.78 8.827.13 (m, H-3, H-8) 7.63 0.50 8.13

1.40 (s, H-5,6 methyl) 2.69 1.29 2.79

ee text for the details of the symbols used. All the chemical shifts are relati
ystem of NH4VO3/H2O2/5,6-dimethyl-1,10-phen with 1:5:1.25 molar ratio. The c1.64, 192.5, and 192.9 ppm, respectively. For symmetric equivalent atoms, the val
ethyl-1,10-phenanthroline was added to the mixture, aew single peak appeared at about −746 ppm (The spec-rum is not shown for briefness). Its intensity increased

O2/5,6-dimethyl-1,10-phenanthroline (ppm)

δCexp(ppm) δC

cal δCdiff δC

cal,s δCdiff,s

152.4 (C-2) 148.4 −4.0 148.9 −3.5144.4 (C-9) 138.6 −5.8 140.5 −3.9142.4 (C-4b) 145.2 2.8 142.8 0.4139.0 (C-6b) 141.1 2.1 138.2 −0.8136.2 (C-4) 126.1 −10.1 133.4 −2.8133.3 (C-7) 120.6 −12.7 129.6 −3.7130.3 (C-5) 121.6 −8.7 128.3 −2.0

129.0 (C-6) 125.7 −3.3 130.1 1.1128.8 (C-4a) 125.1 −3.7 128.4 −0.4128.0 (C-6a) 125.0 2.0 127.1 4.1124.2 (C-3) 115.5 −8.7 121.4 −2.8124.1 (C-8) 116.5 −7.6 121.5 −2.613.2 (C-6 methyl) 16.8 3.6 17.3 4.113.0 (C-5 methyl) 16.7 3.7 17.3 4.3

146.3 (C-2, C-9) 145.7 −0.6 146.2 −0.1136.2 (C-4b, C-6b) 145.8 9.6 144.7 8.5133.4 (C-4, C-7) 128.2 −5.2 131.4 −2.0

129.0 (C-4a, C-6a) 127.8 −1.2 129.0 0.0127.2 (C-5, C-6) 128.1 0.9 130.1 2.9123.0 (C-3, C-8) 119.5 −3.5 121.8 −1.213.1 (C-5,6 methyl) 17.4 4.3 17.7 4.6

alculated chemical shieldings σcal, σcal,s, σcal, and σcal,s of TMS are 31.65,ues were averaged.


with the increasing quantity of 5-methyl-1,10-phenanthroline(from 0.25 to 0.50, 0.75, 1.0, and finally 2.0 equiv-alents) before reaching a maximum. In the meantime,the intensity of the peaks locating at −692 ppm grad-ually decreased. The new peak was assigned to a newspecies [OV(O2)2(5-methyl-1,10-phenanthroline)]−. Whenthe equivalent of 5-methyl-1,10-phenanthroline reaches2.0, all the [OV(O2)2(D2O)]−/[OV(O2)2(H2O)]− was con-verted into the new species [OV(O2)2(5-methyl-1,10-phenanthroline)]−. Considering the unsymmetry of 5-methyl-1,10-phenanthroline and the steric hindrance causedby methyl, we tentatively put forward that two isomerswere formed and isomer A was the preferential confor-mation, as shown in Fig. 2(b) and (c). As only one peakappeared in the 51V spectra, the 51V chemical shifts of thetwo isomers should be very close to each other. This wasconfirmed in the following studies. Similar to the systemof NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline, vari-able temperature 51V NMR experiments were carried outto study the influence of temperature on the equilibrium ofNH4VO3/H2O2/5-methyl-1,10-phenanthroline system with1:5:1 molar ratio (0.2 mol/L vanadate concentration) in thetemperature range of 20–60 ◦C. Same conclusions can bedrawn. It is worth noting that, the peaks of the two isomersA and B which were overlapped at the room temperaturebecame divided with the increasing temperature. This maybpf

3

t1t1

aa[odafaaa

Cu1bTiTwt

Fig. 5. 13C spectrum of the aqueous solution of NH4VO3/H2O2/5-methyl-1,10-phenanthroline with 1:5:2 molar ratio and 0.2 mol/L the total concen-tration of vanadate species. 2 and 9 refer to C-2 and C-9 of the isomer A; 2′and 9′ refer to C-2 and C-9 of the isomer B; 2′′ and 9′′ refer to C-2 and C-9of the free ligand.

1H–1H COSY. In the NOESY spectrum, it had a cross-peakat 2.10 ppm which was assigned to the preferential resonanceof the methyl group. Since H-4 was closed to the methylgroup in space, the result indicated that the peak at 8.29 ppmbelonging to the preferential confirmation should be assignedto H-4. The spectra analysis thus confirmed that the isomerA was the preferential configuration. The exact assignmentsof all spectral data are listed in Table 2.

3.3. Theoretical study on the reaction products

The optimized structures of [OV(O2)2(5,6-dimethyl-1,10-phenanthroline)]− and two [OV(O2)2(5-methyl-1,10-phenanthroline)]− isomers are quite similar disregardingthe methyl (see Fig. 2 for sketch structures). All of themare seven-coordinated, coincident with our deduction fromexperimental observations. The whole structure of the threecomplexes is almost Cs symmetric with the phenanthrolinering locating in the mirror plane. The five oxygen and twonitrogen atoms coordinating to the V atom form a distortedpentagonal bipyramid. The bond lengths of the N atom inequatorial plane and the V atom are between 2.23 and 2.24 A,and the bond lengths of the N atom locating on the oppositesite of vanadyl oxygen atom and the V atom are between 2.42and 2.43 A. The V O bond length is 1.61 A, and the V ObNtvtid

tapclw

sita

δ

e due to the decrease of the half-height-width of the twoeaks and the different effect of temperature on the shieldedactor of V atom in different species.

.2.2. 1H and 13C NMR spectraThe 1H and 13C NMR spectra of the interaction sys-

em of NH4VO3/H2O2/5-methyl-1,10-phenanthroline with:5:1 and 1:5:2 molar ratios (0.2 mol/L vanadate concentra-ion) were recorded. When the molar ratio was 1:5:1, bothH and 13C NMR spectra had two groups of peaks withn integration area ratio of 1:1.4. Considering that almostll of the 5-methyl-1,10-phenanthroline had converted intoOV(O2)2(5-methyl-1,10-phenanthroline)]−, the two groupsf signals were assigned to the newly-formed species withifferent kinds of coordination mode. The results were ingreement with our previous supposition that isomers wereormed during the process. When the molar ratio of the inter-ction system increased to 1:5:2, another group of peaksppeared both in 1H and 13C NMR spectra. This group wasssigned to the free ligand. The 13C spectrum is shown Fig. 5.

In order to assign the 1H and 13C NMR spectra, 2DOSY, NOESY, HETCOR, and COLOC techniques weresed. Similar to the case of NH4VO3/H2O2/5,6-dimethyl-,10-phenanthroline system, NH4VO3/H2O2 was replacedy K3[OV(O2)2(C2O4)]·H2O in the NOESY experiment.he NOESY spectrum was especially useful for determin-

ng the spatial configuration of the newly-formed isomers.he preferential resonance at 8.29 ppm in the 1H spectrumas assigned to the H atom locating at the apical posi-

ion of the aromatic ring (either H-4 or H-7) according to

ond lengths are 1.89 A for the two oxygen atoms close to theatoms and 1.87 A for the remained two oxygen atoms. All

hese data are within the range of reported ones for diperoxo-anadate complexes [11,14,34]. The isomer A was calculatedo be 0.25 kcal/mol more stable than the isomer B, which isn excellent agreement with experimental observations (pre-icted ratio, 1.6:1; found, 1.4:1).

The ab initio and density functional computation of spec-roscopic parameters has been used for a long time toid/support the interpretation of experimental data. In thisaper, 1H and 13C chemical shifts were calculated. Thealculated isotropic chemical shifts relative to TMS wereisted in Tables 1 and 2 (because the experimental resultsere reported relative to TMS). δH

cal (δCcal) and δH

cal,s (δCcal,s)

tand for the calculated 1H (13C) chemical shifts exclud-ng and including solvation effects, respectively. The devia-ions between theoretical and experimental values are defineds δH

diff = δHcal − δH

exp (δCdiff = δC

cal − δCexp) and δH

diff,s = δHcal,s −

Hexp(δC

diff,s = δCcal,s − δC

exp).


Table 2Assignments of 1H and 13C NMR spectra of the interaction system of NH4VO3/H2O2/5-methyl-1,10-phenanthroline (ppm)

δHexp(ppm) δH

cal δHdiff δH

cal,s δHdiff,s δC

exp(ppm) δCcal δC

diff δCcal,s δC

diff,s

[OV(O2)2{5-methyl-1,10-phen}]− isomer A9.59 (d, J = 4.0 Hz, H-9) 11.35 1.76 10.59 1.00 155.2 (C-9) 148.3 −6.9 149.0 −6.28.44 (d, J = 3.5 Hz, H-2) 9.31 0.87 9.09 0.65 147.9 (C-2) 139.0 −8.9 141.3 −6.68.07 (d, J = 8.0 Hz, H-4) 7.45 −0.62 8.60 0.53 145.0 (C-6b) 145.4 0.4 142.8 −2.27.76 (d, J = 8.0 Hz, H-7) 7.89 0.13 8.88 1.12 142.6 (C-4b) 142.1 −0.5 139.2 −3.47.68 (m, H-8) 7.44 −0.24 8.27 0.59 141.3 (C-7) 128.4 −12.9 135.6 −5.77.61 (m, H-3) 6.83 −0.78 7.84 0.23 136.1 (C-4) 120.2 −15.9 129.5 −6.66.53 (s, H-6) 7.18 0.65 8.12 1.59 135.3 (C-5) 128.0 −7.3 133.2 −2.1

1.84 (s, H-methyl) 2.40 0.56 2.71 0.87 131.0 (C-6a) 124.2 −6.8 127.5 −3.5130.4 (C-4a) 124.4 −6.0 126.4 −4.0126.9 (C-8) 115.9 −11.0 121.8 −5.1126.6 (C-3) 116.4 −10.2 121.4 −5.2126.2 (C-6) 119.3 −6.9 123.6 −2.619.6 (C-methyl) 21.1 1.5 21.0 1.4

[OV(O2)2{5-methyl-1,10-phen}]− isomer B9.68 (d, J = 3.5 Hz, H-2) 11.49 1.81 10.71 1.03 155.8 (C-2) 148.8 −7.0 149.6 −6.28.37 (d, J = 3.0 Hz, H-9) 9.28 0.91 8.98 0.61 147.4 (C-9) 138.5 −8.9 140.5 −6.97.97 (d, J = 8.0 Hz, H-4) 8.17 0.20 9.04 1.07 145.9 (C-4b) 145.8 −0.1 143.6 −2.37.88 (d, J = 7.0 Hz, H-7) 7.25 −0.63 8.45 0.57 141.9 (C-6b) 141.7 −0.2 138.6 −3.37.70 (m, H-3) 7.51 −0.19 8.36 0.66 138.9 (C-4) 125.8 −13.1 133.4 −5.57.53 (m, H-8) 6.79 −0.74 7.77 0.24 138.4 (C-7) 123.0 −15.4 131.7 −6.76.77 (s, H-6) 7.20 0.43 8.07 1.30 134.6 (C-5) 124.0 −10.6 131.5 −3.1


5-methyl-1,10-phen8.55 (d, J = 2.0 Hz, H-2) 9.51 0.96 9.57 1.02 150.6 (C-2) 146.1 −4.5 146.7 −3.98.51 (d, J = 2.0 Hz, H-9) 9.44 0.93 9.50 0.99 150.2 (C-9) 146.0 −4.2 146.5 −3.77.43 (d, J = 8.0 Hz, H-4) 8.35 0.92 8.78 1.35 144.3 (C-6b) 146.2 1.9 145.0 0.77.28 (d, J = 7.5 Hz, H-7) 8.05 0.77 8.60 1.32 144.2 (C-4b) 146.6 2.4 145.6 1.47.18 (m, H-3) 7.66 0.48 8.16 0.98 138.0 (C-7) 130.8 −7.2 133.9 −4.17.15 (m, H-8) 7.60 0.45 8.09 0.94 136.5 (C-5) 130.6 −5.9 132.7 −3.86.18 (s, H-6) 7.61 1.43 8.07 1.89 135.0 (C-4) 127.9 −7.1 131.1 −3.9


Same notation as Table 1. The molar ratio of the interaction NH4VO3/H2O2/5-methyl-1,10-phen system is 1:5:2.

First consider the 1H chemical shifts. It can be seen thatall of the δH

cal values for free ligands are overestimated, whilefor coordinated ligands, some of the δH

cal values are overesti-mated and some are underestimated. The largest deviationis about 1.8 ppm at H-2 of [OV(O2)2(5,6-dimethyl-1,10-phenanthroline)]− and H-2 (isomer B) and H-9 (isomer A)of [OV(O2)2(5-methyl-1,10-phenanthroline)]−. All of theatoms (H-2 or H-9) locate in the similar positions (next tothe N atom in equatorial plane and close to the oxo atom)and have the greatest changes in the chemical shifts dueto coordination. Taking the solvation effects into account,the calculated values are all overestimated. They all moveto downfield except for the H-2 and H-9 in the coordinated

ligands, indicating the different solvation effects. Althoughsome of the absolute δH

diff,s values are larger than the abso-lute δH

diff values, the δHdiff,s values are more convergent than

δHdiff and the variation trends of δH

cal,s become closer to theexperimental ones (see Fig. 6(a) for an example).

The relationships between the theoretical and experimen-tal chemical shifts can be seen from the linear fitting of thetwo sets of theoretical values to the experimental values. Thelinear regression equations can be expressed as

δHcal = 0.95 δH

exp + 0.88, (1)

δHcal,s = 0.94 δH

exp + 1.37. (2)


Fig. 6. Illustration of experimental and calculated chemical shifts of isomerA: (a) 1H NMR; (b) 13C NMR.

The correlation coefficients for Eqs. (1) and (2) are 0.96 and0.99, respectively. The correlation coefficient can be taken asan index to characterize the quality of the calculated results.The near unity value indicates good correlativity between thetheoretical and experimental results. Obviously, inclusion ofsolvation effects improves this correlativity. The closer tounity the slope of the fitting line is, the better the parallelrelationship is between the fitting and experimental lines, i.e.,the more similar the variation trend is between the fittingshieldings and the experimental measurements. In this study,the slopes of the two fitting lines are close to each other.

Now we turn to the 13C chemical shifts. It can be seen thatmost of the δC

cal values are underestimated. The largest devi-ations occur at C-7 and C-4 of coordinated ligands, whichare para to the coordinated N atoms. Taking the solvationeffects into account, the calculated values all move to down-field except for the C-6b and C-4b. Most of the absolute δC

diff,s

values are smaller than the absolute δCdiff values. The largest

deviation after PCM correction decreases to about one halfof the deviation before PCM correction, and the δC

cal,s val-

ues are more convergent than δCcal. These indicate the better

agreement of δCcal,s with the experimental measurements (see

Fig. 6(b) for example).The relationships between the theoretical and experimen-

tal chemical shifts can be seen from the linear fitting of thet

linear regression equations can be expressed as

δCcal = 0.94 δC

exp + 3.09, (3)

δCcal,s = 0.95 δC

exp + 4.03. (4)

The correlation coefficients for Eqs. (3) and (4) are 0.99and 1.00, respectively. Similar to 1H NMR calculations,inclusion of solvation effects improves the correlativity andthe slopes of the two fitting lines are close to each other.

The deviation of the theoretical results from the experi-mental ones may be due to the solvation effects, the diver-gence of the optimized structures from the real ones, etc.It is well known that the generalized gradient approxima-tion (GGA) tends to overestimate the average bond lengths[36]. The systematic error in bond lengths will have a strongimpact on the computed chemical shieldings. Furthermore,as we have shown, the chemical shifts were calculated basedon the minimum energy structures of species computed in thegas phase, while the experimental NMR spectra are recordedin solution. Solvation may not only influence the geometrystructure, but also alter the polarization or electronic chargedistribution of the species, especially when the species is notneutral, thus causes the variation of chemical shifts in dif-ferent mediums. For example, our experimental results showthat the changes of 1H and 13C chemical shifts of the free5-methyl-1,10-phenanthroline can reach 0.66 and 11.9 ppm,rppppAdmtIeanewc

3i

aNVre(([r
wo sets of theoretical values to the experimental values. The
espectively from H2O to the NH4VO3/H2O2/5-methyl-1,10-henanthroline system with 1:5:2 molar ratio. To predict thehysical and chemical behavior of molecules in condensedhases accurately, many subtle effects induced by the com-lex chemical environment must be taken into consideration.lthough many models (e.g. PCM) have been proposed toescribe the solvation effects, they are still rather approxi-ate and only take some effects into account. For example,

he influences of pH and hydrogen bond are often ignored.n addition, as an aliphatic compound, TMS is quite differ-nt from the aromatic substituted phenanthroline. There aredditional influences from metallic vanadium on the coordi-ated substituted phenanthroline. Therefore, the systematicrror introduced by the computational approach may not beell cancelled out when the chemical shielding values were

onverted to chemical shifts.

.4. Comparison of 51V NMR spectra of differentnteraction systems

By comparing the 51V NMR spectra of the inter-ction systems of NH4VO3/H2O2/1,10-phenanthroline,H4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline, and NH4O3/H2O2/5-methyl-1,10-phenanthroline with 1:5:1 molar

atio, further information could be obtained. When 1.0quivalent 1,10-phenanthroline was add to the [OV(O2)2D2O)]−/[OV(O2)2(H2O)]− solution, almost all [OV(O2)2D2O)]−/[OV(O2)2(H2O)]− converted into the speciesOV(O2)2(1,10-phenanthroline)]− with an integration areaatio of 0.01:1. Comparing to the cases of NH4VO3/H2O2/


Fig. 7. The possible interaction mode of the interaction system of NH4VO3/H2O2/5-methyl-1,10-phenanthroline.

5-methyl-1,10-phenanthroline (0.02:1) and NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline (0.1:1), we suggestthat the methyl group at the aromatic ring has steric hindranceeffect on the coordination process. The coordination abilityof the three ligands was: 1,10-phenanthroline > 5-methyl-1,10-phenanthroline > 5,6-dimethyl-1,10-phenanthroline.

3.5. Interaction modes of different interaction systems

After analyzing and comparing the 1H and 13C NMRspectra of the interaction systems of NH4VO3/H2O2/5,6-dimethyl-1,10-phenanthroline and NH4VO3/H2O2/5-me-thyl-1,10-phenanthroline in aqueous solution under thephysiological conditions, we figured out the most possiblereaction modes of the interaction systems as follows (seeFig. 7): (1) the ligand attacked the V atom from the oppositesite of the terminal oxygen of [OV(O2)2(D2O)]− formingtransition states TS1 and TS2 (for the coordination of5,6-dimethyl-1,10-phenanthroline, TS1 and TS2 werethe same). (2) Accompanied by the leaving of water, thenitrogen atom in the apical position turned to the equatorialposition, meanwhile, the second nitrogen atom entered thecoordination sphere of the apical position and formed thesecond V N bond. The formation of isomers was due to thevarious positioning of the two different dentation sites of theligand, e.g. the two nitrogen atoms (as shown in Fig. 2).

4

HHcSl[vi

rings had steric hindrance effect on the coordination process.The coordination ways and solution structures of the newspecies were analyzed based on the spectral data andtheoretical calculations. Experiments on the biologicalactivity and recrystallization of the newly-formed speciesare being performed.

Acknowledgments

This work was supported by Key Project of Health andScience and Technology of Xiamen, United Project of Healthand Education of Fujian. NCET and EYTP of Ministry ofEducation of China.

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