Molecular Modeling Studies of the Structural, Electronic, and UVAbsorption Properties of Benzophenone DerivativesBianca A. M. Correa, Arlan S. Goncalves,† Alessandra M. T. de Souza, Caroline A. Freitas,Lucio M. Cabral,‡ Magaly G. Albuquerque,⊥ Helena C. Castro,# Elisabete P. dos Santos,§
and Carlos R. Rodrigues*
CCS, Faculty of Pharmacy, ModMolQSAR, Federal University of Rio de Janeiro (UFRJ), 21941-590 Rio de Janeiro, RJ, Brazil
*S Supporting Information
ABSTRACT: Benzophenone derivatives (BZP), an important classof organic UV filters, are widely used in sunscreen products due totheir ability to absorb in the UVA and UVB ranges. The structural,electronic, and spectral properties of BZP derivatives have beenstudied by density functional theory (DFT) and time-dependentDFT (TD-DFT) methods. DFT/B3LYP with the 6-31G(d) basis setis an accurate method for optimizing the geometry of BZPs. Theabsorption maxima obtained from the TD-DFT calculations in avacuum were in agreement with the experimental absorption bandsand showed that the main electronic transitions in the UVA/UVBrange present π → π* character, the major transition being HOMO→ LUMO. The oscillator strength seems to increase in the presence of disubstitution at the para position. For proticsubstituents, the position appears to be related to the absorption band. Absorption in the UVB range occurs in the presence ofpara substitution, whereas ortho substitution leads to absorption in the UVA spectral region. The obtained results provide somefeatures for BZP derivatives that can be useful for customizing absorption properties (wavelengths and intensities) and designingnew BZP derivatives as sunscreens.
1. INTRODUCTION
The electromagnetic spectrum emitted by the sun includesultraviolet (UV) radiation that is comprosed of UVA, UVB, andUVC radiation.1 The human body is constantly exposed to theUVB (∼290−320 nm) and UVA (320−400 nm) wave-lengths.2,3 The UVB wavelengths less than 295 nm and theUVC radiation are filtered by the stratospheric ozone layer.4
Acute and chronic exposure to solar UV radiation causes skindamage, including erythema (sunburn), cutaneous photoaging,immune suppression, and an increased risk of skin cancer.Organic UV filters are the most common active constituents insunscreen products used for attenuating skin photodamage.1,4,5
Organic filters absorb UV radiation by exciting an electron fromits ground state into an excited state due to the presence of asystem with certain unsaturated groups (π orbitals) and atomswith unpaired electrons (n orbitals). Some saturated groupsthat bond to this system also contribute to UV absorption.Benzophenone derivatives (BZP), an important class of
organic UV filters, are widely used in sunscreen products due totheir ability to absorb in the UVA and UVB ranges. BZPs (i.e.,diphenylketones) usually show n → π* and π → π* transitions,resulting in two peaks in the UV range, one in the UVA rangeand another in the UVB range.6 Some peaks in the UV regionhave also been attributed to the intramolecular charge-transfertransition involving the carbonyl and hydroxyl groups of certainhydroxyBZPs (o-hydroxybenzophenones).6,7
Some BZPs have been approved by regulatory agencies inmany countries for use in sunscreens, including 2-hydroxy-4-methoxybenzophenone (oxybenzone or benzophenone-3;BZP-3), 2,2-hydroxy-4-methoxybenzophenone (dioxybenzoneor BZP-8), 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid(sulisobenzone or BZP-4), and diethylamino hydroxybenzoylhexyl benzoate (DHHB).7,8 BZP-3 is one of the most widelyused UV filters in commercial sunscreens due to its ability toabsorb in the UVB and UVA regions of the electromagneticspectrum, although it has poor UVA efficiency.7,8 DHHB is anew UV filter with good photostability and a UVA absorptionspectrum peak at 354 nm.8
Molecular modeling is an important and useful tool thatallows a better understanding of spectral behavior.7,9 It helps toestablish the structure−property relationships9 and also enablesthe screening of compounds that have the ability to absorbradiation in the desired range.7,9,10 Furthermore, it allows forthe prediction and interpretation of the excited-state propertiesof different types of molecules.9−14
Density functional theory (DFT) is a quantum mechanicalmethod that can provide an accurate description of thestructure, energy, and molecular properties of the ground state.By extending the efficiency of the DFT calculations to excited
Received: June 21, 2012Revised: August 29, 2012Published: August 30, 2012
states, the time-dependent density functional theory (TD-DFT) allows good agreement between calculated andexperimental spectra.9,15−17
This investigation focuses on BZP derivatives and presentsmolecular modeling studies of the structural, electronic, and UVspectral properties of BZP derivatives that have been approvedor that have substituents similar to those that have beenapproved by regulatory agencies. To reach these goals, in thepresent work, we performed quantum mechanical calculationsof the ground and excited states of BZP derivatives using theDFT and TD-DFT15,16 methods. In the first step, themethodology to be used for the geometry optimizations wasset up by comparing the geometric parameters of the calculatedstructure and crystal data from the Cambridge StructuralDatabase (CSD).18 In the second step, the electronic and UVspectral properties were calculated. To evaluate the predictivecapacity (i.e., accuracy) of the method, some of the results werecompared with experimental data. Lastly, the results wereanalyzed, and the structure−property relationships of BZPderivatives were established to obtain data that may be usefulfor customizing the absorption properties (wavelengths andintensities) and designing new BZP derivatives as sunscreens.
2. METHODOLOGY
2.1. Theoretical Calculations. Molecular structures werebuilt, and the geometries were optimized using the Spartan’10program (Wavefunction Inc., Irvine, California, U.S.A.).Preliminary calculations with semiempirical RM1 and PM6,ab initio HF, and DFT with the hybrid functional B3LYP(Becke’s hybrid exchange functional B319 with the Lee−Yang−Parr correlation functional LYP20,21) using different basis setswere performed on BZP-3 to establish the methodology to beused to optimize the geometry of the compounds.The optimized structures have been statistically analyzed
using the crystal data from BZP derivatives available in CSD,and all results are reported in the Supporting Information.Subsequently, Cartesian coordinates based on the bond
lengths and angles of the optimized structures of BZPderivatives were used as inputs for theoretical studies ofabsorption spectra by means of TD-DFT15,16,22 at the samelevel of theory as B3LYP/6-31G(d) in vacuum using theGAMESS US23,24 program. The lowest 10 singlet−singletexcitations have been computed with their respective wave-lengths, transition energies, main transition configurations, andoscillator strengths.2.2. Experimental Section. Absorbance spectra of BZP-3
were analyzed at room temperature (297 K) on a UV/visspectrophotometer (JASCO V-630). The data were correctedfor solvent background by the instrument’s calibration using thesolvent as a blank. The spectrum in the range of 270−400 nmwas measured in a solution (20 μg/mL) of BZP-3 (Aldrich,98% pure) that was prepared in a dichloromethane solvent(Sigma-Aldrich, ≥99.8% pure).
3. RESULTS AND DISCUSSION
3.1. Ground-State Geometry Optimization. The opti-mized and experimental (available X-ray crystal structure25)geometric parameters of BZP-3 are reported in the SupportingInformation. The optimized geometries are local minimum-energy structures obtained by semiempirical RM1 and PM6, abinitio HF, and DFT/B3LYP methods in the ground state.
The semiempirical and ab initio methods underestimate theOC(2) bond length. Larger OC(2) bond length variationswere observed between experimental25 and HF/6-31G(d) orHF/6-31G(d,p) results (Δrmax = 0.043 Å for both).There is an intramolecular hydrogen bond between the
hydroxyl group and the carboxyl oxygen that influences theOC(2) bond length. The smaller the hydrogen bond length,the longer the OC(2) length.26 The semiempirical and abinitio methods showed smaller OC(2) and longer O−H···OC(2) bond lengths than those obtained by exper-imental and DFT/B3LYP methods.The bond lengths calculated using the DFT/B3LYP method
with 6-31G(d), 6-31G(d,p), and 6-31+G(d) basis sets are inagreement with the experimental results25 (Δrmax < 0.02 Å).The difference value percentages (DVPs) between thecalculated parameters by the DFT/B3LYP method with the6-31G(d), 6-31G(d,p), and 6-31+G(d) basis sets andexperimental data25 are shown in the Supporting Information.It can be observed that all of the DVP values are less than 2.0%.Considering the valuable accuracy and computational speed9 ofthe most parsimonious basis set, the DFT/B3LYP/6-31G(d)method was chosen for the following calculations.Additionally, other optimized structures of BZPs have been
compared to X-ray crystal structures available in theCSD,25,27−35 and all DVP values are less than or close to2.0% (see the Supporting Information). The structuralparameters calculated with the DFT/B3LYP/6-31G(d) methodand those that were obtained experimentally are reported withthe respective DVP values in the Supporting Information.
3.2. Electronic and UV Absorption Properties of BZPs.3.2.1. Methodology Validation. To determine the ability topredict UVA/UVB absorption spectra, TD-DFT calculations invacuum were performed on the selected optimized geometry ofBZP-3 at the same level of theory as that used for theoptimization, and the results were compared with anexperimental absorption spectrum measured in a dichloro-methane solution (20 μg/mL of BZP-3) (Figure 1). For clarity,
the maximum absorbance was normalized according to themaximum intensity of each spectrum. The experimentalabsorption bands measured at 287 and 325 nm were computedat 285 and 326 nm in a vacuum. Therefore, the absorptionmaxima computed in a vacuum are in agreement with theexperimental absorption bands.
Figure 1. Comparison of the BZP-3 experimental UV absorption(dichloromethane) and the theoretical UV absorption maxima(vacuum, TD-DFT/B3LYP/6-31G(d) method). The normalizationof the absorbance was performed according to the maximum intensityof each spectrum.
The Journal of Physical Chemistry A Article
dx.doi.org/10.1021/jp306130y | J. Phys. Chem. A 2012, 116, 10927−1093310928
Previous studies indicated that the absorption spectra ofBZP-3 are not strongly affected by the presence of the solvent.7
However, other BZPs show solvatochromic shifts in differentsolvents.6,7 Although solvatochromic effects in the spectralproperties are important to quantitative simulations, calcu-lations of absorption spectra with molecules in vacuum canprovide qualitative trends.9
3.2.2. Structure−Property Relationships. In an effort todetermine the structure−property relationships, the TDDFT/B3LYP/6-31G(d) calculations of the absorption spectra in avacuum were carried out using the optimized geometry of BZPderivatives that have been approved or with substituents similarto those that have been approved by regulatory agencies. Themost relevant wavelengths (λ > 280 nm), the energy oftransition and the oscillator strengths ( f > 0.1) calculated fromthe absorption spectra, and their main transition configurationsare listed in Table 1.To confirm the accuracy of the TD-DFT calculations in a
vacuum, experimental UV absorption spectra available inprevious reports were used.6,7 The experimental UV absorptionspectra are in agreement with the TD-DFT calculationsperformed on the isolated BZP derivatives (R2 = 0.9912)(Figure 2). The nonsubstituted BZP shows an experimentalband at 257 nm in water.6 This band was calculated in avacuum at 261 nm. The 2,2′-hydroxy-4-methoxybenzophenoneexperimental absorption bands measured at 299 and 355 nm intoluene7 were computed at 296 and 356 nm in a vacuum. Thecompound 4-hydroxybenzophenone shows an experimentalband at 285 nm in diethyl ether6 and a theoretical absorptionmaximum in a vacuum at 283 nm. The experimental absorptionmaxima measured at 261 and 337 nm in ethanol6 werecalculated in a vacuum at 268 and 340 nm for 2-hydroxybenzophenone. The 2,4-hydroxybenzophenone exper-imental UV absorptions at 281 and 324 nm in cyclohexane6
were calculated at 281 and 323 nm in a vacuum.a. Oxygenated BZP Derivatives. A general analysis of
hydroxybenzophenone absorption shows that these derivativesexhibit at least one peak in the UVA or UVB range, while 2,4-OHBZP, 2,4,4′-OHBZP, and 2,2′,4,4′-OHBZP show maximumwavelengths in both spectra regions. Considering the nature ofthe molecular orbitals involved in the transitions, all derivativesshowed absorptions maximum peaks assigned to a π → π*character (Figure 3).For monohydroxybenzophenones (2-OHBZP and 4-
OHBZP), the lower-energy transition is predominantlyHOMO → LUMO (Table 1) and shifts with changes in thehydroxyl group position (Figure 3). This transition correspondsto 340 nm ( f = 0.104) for 2-OHBZP and 283 nm ( f = 0.280)for 4-OHBZP. Considering the molecular orbital distributionfor both derivatives, the HOMO is mainly localized in thesubstituted ring A (Figure 3). Furthermore, the orbitaltransition of 2-OHBZP is accompanied by a change in theelectron density on the hydroxyl and carbonyl oxygensattributed to an excited-state proton transfer (ESPT), asalready reported in previous studies.6,7
Addition of another hydroxyl substituent at the orthoposition led to some red shifting in the UVA energy transitions,340 to 364 nm (2-OH/2,2′-OH) and 283 to 323 nm (4-OH/2,4′-OH), with the same HOMO → LUMO transitionaccompanied by a change in the electron density on thehydroxyl and carbonyl groups assigned to a proton transfer inthe excitation process. We can infer that the proximity of thehydroxyl and carbonyl groups promotes lower-energy tran-
sitions. With the addition of an extra hydroxyl group at the paraposition, the 4,4′-OHBZP derivative showed larger oscillatorstrength than the monosubstituted derivative (Table 1). In thismolecule, the transition is predominantly HOMO−1 →
Table 1. Transitions (nm/eV), Oscillator Strength ( f) ( f >0.1), and Composition in Terms of the MOs Calculated forthe BZPs
Subst-BZPλ/nm eV MO f
2-OH 340 3.651 HOMO → LUMO: 0.92 0.1044-OH 283 4.375 HOMO → LUMO: 0.78 0.2802,2′−OH 364 3.409 HOMO → LUMO: 0.94 0.1812,4-OH 281 4.407 HOMO−3 → LUMO:
dx.doi.org/10.1021/jp306130y | J. Phys. Chem. A 2012, 116, 10927−1093310929
LUMO, where HOMO−1 is localized in both ring moieties,most likely due to the presence of hydroxyl substituents (Figure3). This disubstitution at the para position leads to high-intensity absorption in the UVB region in comparison withmonosubstitution at this position.
Ortho and para hydroxylation of BZP (2,4,4′-OHBZP and2,2′,4,4′-OHBZP) led to a broad absorption spectrum (Table1). However, these compounds can be absorbed throughhuman skin after dermal application and are able to mimic thebiological activities of hormones, showing estrogenic orantiandrogenic activity.36−38 The endocrine-disrupting actionsof BZPs may pose a risk to humans and wildlife, a nondesirablefeature for sunscreen products.36
Substitution of a methoxy at the ortho position (2-MeOBZP) led to an absorption peak at 266 nm, which is outof the desirable range. In contrast, substitution of a methoxy atthe para position (4-MeOBZP) resulted in an absorptionmaximum in the UVB range at 291 nm with a transitionassigned to HOMO → LUMO, as seen for 4-OHBZP. Thiselectronic transition involves the substituted ring A, itssubstituent, and the carbonyl group (Table 1 and Figure 3).Surprisingly, the addition of an extra methoxy at the paraposition of ring B (4,4′-MeOBZP) led to a slight blue shift inthe UVB region, with an already expected increase of oscillatorstrength (Table 1).The presence of a hydroxyl substituent at the ortho position
led to an extra absorption in the UVA region of 4-MeOBZP (2-
Figure 2. Comparison between the theoretical and experimentalwavelengths (nm) of the absorption maxima.
Figure 3. Frontier molecular orbitals of oxygenated BZP derivatives.
The Journal of Physical Chemistry A Article
dx.doi.org/10.1021/jp306130y | J. Phys. Chem. A 2012, 116, 10927−1093310930
OH-4-MeOBZP, 2,2′-OH-4-MeOBZP) and 4,4′-MeOBZP(2,2′-OH-4,4′-MeOBZP), categorizing these derivatives asbroad-spectrum organic filters. However, studies showed thatthese para methoxylated derivatives can also be absorbedthrough the skin and undergo biotransformation by demethy-lation, leading to metabolites with estrogenic activity.36,37,39 Inall cases, it can be seen that the occupied orbital contribution(HOMO and HOMO−1) for UVA and UVB absorption ispredominantly related to the methoxy and its substituted ring(Figure 3).Ethoxybenzophenones showed the same pattern as the
previous derivatives. Substitution at the ortho position, as withthe methoxy group, did not result in absorption within thedesirable spectral range. Para substitution seems to be related toUVB absorption as well as the hydroxylation of the 4-EtOBZPderivative (2-OH-4-EtOBZP), which broadened the absorptionspectrum, but with a lower oscillator strength (Table 1).Considering all of the oxygen-substituted BZP derivatives,
4,4′-EtOBZP exhibits the largest oscillator strength ( f = 0.511),with λmax computed at 294 nm and a HOMO−1 → LUMOtransition involving the electron density on the oxygen of theethoxy group and both substituted rings (Table 1 and Figure3).b. Aminobenzophenones. Similar transition energies and
oscillation strengths for the amino and hydroxyl-substitutedBZPs were expected due to their electronic resemblances(Table 1).We may infer that the presence of OH and NH at the ortho
position is accompanied by a change in the electron density onthe OH/NH and carbonyl oxygen, which supports an ESPTand keto−enol/amino−imino tautomerism. Comparison be-tween OH/NH and O-alkyl/N-dialkyl substituents at the orthoposition confirms that the low energy necessary for absorptionin the UVA region is related to this proton transfer. The λmax
computed for 2-N(Me)2BZP and 2-N(Et)2BZP are out of thedesired range (lower than 260 nm). The same was observed foralkoxy groups at the ortho position, as already reported in thepresent study.In the case of the para amino-substituted BZPs, the
disubstitution increases the oscillator strength similarly tohydroxyl-substituted BZPs (Table 1). Furthermore, orthohydroxylation also broadened the absorption spectrum, withthe λmax computed at 297 and 310 nm assigned to HOMO−1→ LUMO and HOMO → LUMO transitions, respectively.Differing from the oxygen-substituted BZPs, hydroxylation of
4-NH2BZP at the ortho position (2-OH-4-NH2BZP) did notinduce an absorption peak in the UVA range, leading only to anextra absorption in the UVB range (Table 1). Theseabsorptions showed the coefficient of distribution of theoccupied orbitals, HOMO and HOMO−1, mainly localized inthe substituted A ring and its substituents due to their inductiveeffect (Figure 3).The presence of alkylamino substituents (-N(Me)2 and
-N(Et)2) at the para position led to a red shift from 311 nm for4-N(Et)2BZP to 330 nm for 4,4′-N(Et)2BZP, and a smaller redshift was observed from 323 nm for 4-N(Me)2 to 334 nm for4,4′-N(Me)2BZP.The electronic transitions of these derivativesinvolve a HOMO → LUMO transition within the substitutedring and its substituents (Figure 4).Similarly to 4-NH2BZP, hydroxylation of alkylamino
derivatives, 2-OH-4-N(Me)2BZP and 2-OH-4-N(Et)2BZP, didnot induced a broad absorption spectrum and only led to a red-shifted absorption spectrum. Due to this substitution, 2-OH-4-N(Me)2BZP presented a red shift from the UVB to the UVAregion (311/322 nm), showing a strong resonance effectrelated to the hydroxyl substituent.All diethylaminobenzophenone derivatives exhibit a single
peak in the UVA region with a HOMO → LUMO transition
Figure 4. Frontier molecular orbitals of aminobenzophenones.
The Journal of Physical Chemistry A Article
dx.doi.org/10.1021/jp306130y | J. Phys. Chem. A 2012, 116, 10927−1093310931
involving the substituted rings. Interestingly, 4,4′-N(Et)2BZPshowed the highest oscillator strength of all of the BZPderivatives studied.c. Other BZP Derivatives. The λmax values computed for 2-
COOH-, 2-COOMe-, and 2-COOEt-substituted BZPs are outof the desired range, exhibiting maximum absorptions lowerthan 280 nm.
4. CONCLUSION
Here, we report on our studies of the structural, electronic, andspectral properties of BZP derivatives with different sub-stituents and ring positions as UV absorbers. The DFT/B3LYPwith the 6-31G(d) basis set proved to be an accurate methodfor optimization of the geometry of the BZPs. Using TD-DFT,we reproduced the experimental UV absorption wavelengths ofa set of BZP derivatives and combined the data to establishtheir structure−property relationships. After validation of thecomputational methodology using experimental data fromBZP-3, we performed geometry optimizations and calculationsof the UV absorption spectra of BZP derivatives. Our resultsshowed that the main electronic transitions in the UVA/UVBrange present π → π* character, with HOMO → LUMO beingthe major transition. The occupied orbital involved in thetransition (HOMO, HOMO−1, HOMO−2, and/or HOMO−3) is normally distributed over the substituted ring, includingthe electron-donating substituent.The oscillator strength, which is related to the strength of the
transition, seems to increase in the presence of disubstitution atthe para position, with the exception of 4,4′-MeOBZP. Thehighest oscillator strength, f = 0.712, occurs for 4,4′-N(Et2)BZP. In contrast, it seems that substitution at theortho position is directly related to a lower oscillator strengthand absorption in the UVA region. We can infer that thepresence of protic substituents at this position decreases theenergy necessary for the electronic transition because proximityto the BZP carbonyl results in tautomerism.Finally, the position of protic substituents on the BZP moiety
appears to be related to the absorption peak; absorption in theUVB range occurs in the presence of para substitution, whereasortho substitution leads to absorption in the UVA spectralregion.Overall, our TD-DFT calculation results revealed some
features of BZP derivatives that may be useful in furtherinvestigations of safer organic UV filters with broad absorptionspectra.
■ ASSOCIATED CONTENT
*S Supporting InformationDifference value percentages (DVPs) between the calculated(DFT) and experimental geometries of BZP-3; list of the CSDrefcodes and references for the statistically analyzed benzophe-none derivatives; geometric parameters and H-bond length ofBZP-3 calculated using different methods and demonstratedexperimentally; and structural parameters of benzophenonederivatives calculated with DFT/B3LYP/6-31G(d) and dem-onstrated experimentally. This material is available free ofcharge via the Internet at http://pubs.acs.org.
Present Addresses†Chemistry Department, Federal Institute of Education,Science and Technology (IFES), Guarapari, ES 29215-090,Brazil.‡CCS, Faculty of Pharmacy, LabTIF, Federal University of Riode Janeiro (UFRJ), 21941-590 Rio de Janeiro, RJ, Brazil§CCS, Faculty of Pharmacy, LADEG, Federal University of Riode Janeiro (UFRJ), 21941-590 Rio de Janeiro, RJ, Brazil.⊥IQ-CCMN, Department of Organic Chemistry, LabMMol,Federal University of Rio de Janeiro (UFRJ), 21949-900 Rio deJaneiro, RJ, Brazil.#Institute of Biology, LABioMol, Fluminense Federal Uni-versity, 24001-970 Niteroi, RJ, Brazil.
NotesThe authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This study was supported by Coordenacao de Aperfeicoamentode Pessoal de Nivel Superior (CAPES), Rede Nanobiotec-Brasil, Conselho Nacional de Desenvolvimento Cientifico eTecnologico (CNPq), and Fundacao de Amparo a Pesquisa doEstado do Rio de Janeiro (FAPERJ).
■ REFERENCES(1) Stechschulte, S. A.; Kirsner, R. S.; Federman, D. G. Postgrad. Med.2011, 123, 160−167.(2) Velasco, M. V. R.; Balogh, T. S.; Pedriali, C. A.; Sarruf, F. D.;Pinto, C. A. S. O.; Kaneko, T., M.; Baby, A. R. Rev. Cienc. Farm. BasicaApl. 2011, 32, 27−34.(3) Wang, S. Q.; Balagula, Y.; Osterwalder, U. Dermatol. Ther. 2010,23, 31−47.(4) Antony, R, Y. Prog. Biophys. Mol. Biol. 2006, 92, 80−85.(5) Gilaberte, Y.; Gonzalez, S. Actas Dermo-Sifiliogr. 2010, 101, 659−672.(6) Dilling, W. L.T. J. Org. Chem. 1966, 31, 1045−1050.(7) Baughman, B. M.; Stennett, E.; Lipner, R. E.; Rudawsky, A. C.;Schmidtke, S. J. J. Phys. Chem. A 2009, 113, 8011−8019.(8) Tuchinda, C.; Lim, H. W.; Osterwalder, U.; Rougier, A. Dermatol.Clinics 2006, 24, 105−117.(9) Jacquemin, D.; Perpete, E. A.; Ciofini, I.; Adamo, C. Acc. Chem.Res. 2009, 42, 326−334.(10) Walters, C.; Keeney, A.; Wigal, C. T.; Johnston, C. R.;Cornelius, R. D. J. Chem. Educ. 1997, 74, 99−101.(11) Amat, A.; Clementi, C.; De Angelis, F.; Sgamellotti, A.; Fantacci,S. J. Phys. Chem. A 2009, 113, 15118−15126.(12) Promkatkaew, M.; Suramitr, S.; Karpkird, T. M.; Namuangruk,S.; Ehara, M.; Hannongbua, S. J. Chem. Phys. 2009, 131, 224306.(13) Improta, R.; Santoro, F. J. Phys. Chem. A 2005, 109, 10058−10067.(14) Barone, V.; Polimeno, A. Chem. Soc. Rev. 2007, 36, 1724−1731.(15) Runge, E.; Gross, E. K. U. Phys. Rev. Lett. 1984, 52, 997−1000.(16) Gross, E. K. U.; Kohn, W. Adv. Quantum Chem 1990, 21, 255−291.(17) Bamgbelu, A.; Wang, J.; Leszczynski, J. J. Phys. Chem. A 2010,114, 3551−3555.(18) Allen, F. Acta Crystallogr., Sect. B 2002, 58, 380−388.(19) Becke, A. D. Density functional thermochemistry. III. The roleof exact exchange. J. Chem. Phys. 1993, 98, 5648−5652.(20) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett.1989, 157, 200−206.(21) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789.(22) Kutzke, H.; Klapper, H.; Hammond, R. B.; Roberts, K. J. ActaCrystallogr., Sect. B 2000, 56, 486−496.(23) Liebich, B. W.; Parthe, E Acta Crystallogr., Sect. B 1974, 30,2522−2524.
The Journal of Physical Chemistry A Article
dx.doi.org/10.1021/jp306130y | J. Phys. Chem. A 2012, 116, 10927−1093310932
(24) Saraswat, K.; Prasad, R. N.; Ratnani, R.; Drake, J. E.;Hursthouse, M. B.; Light, M. E. Inorg. Chim. Acta 2006, 359, 1291−1295.(25) Kooijman, H.; ten Cate, M. G. J.; van Leeuwen, F. W. B.; Crego-Calama, M.; Reinhoudt, D. N.; Spek, A. L. Private Communication,2005.(26) Liebich, B. Acta Crystallogr., Sect. B 1979, 35, 1186−1190.(27) Ferguson, G.; Glidewell, C. Acta Crystallogr., Sect. B 1996, 52,3057.(28) Schlemper, E. Acta Crystallogr., Sect. B 1982, 38, 554−559.(29) Van der Velden, G. P. M.; Noordik, J. H. J. Chem. Cryst 1980,10, 83−92.(30) Guo, S.; Su, G.; Pan, F.; He, Y. Acta Crystallogr., Sect. C 1992,48, 576−578.(31) Kus, P.; Jones, P. G. Pol. J. Chem. 2000, 74, 965−977.(32) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem. Phys.1998, 109, 8218−8224.(33) Lasinski, M. E.; Romero, N. A.; Yau, A. D.; Kedziora, G.;Blaudeau, J.-P.; Brown, S. T. IEEE Conference Proceedings, DoDHPCMP Users Group Conference, 2008; pp 437−441.(34) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.;Gordon, M. S.; Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.;Su, S. J.; et al. J. Comput. Chem. 1993, 14, 1347−1363.(35) Cox, P. J.; Kechagias, D.; Kelly, O. Acta Crystallogr., Sect. B 2008,64, 206−216.(36) Suzuki, T.; Kitamura, S.; Khota, R.; Sugihara, K.; Fujimoto, N.;Ohta, S. Toxicol. Appl. Pharmacol. 2005, 203, 9−17.(37) Molina-Molina, J.-M.; Escande, A.; Pillon, A.; Gomez, E.;Pakdel, F.; Cavailles, V.; Olea, N.; Aït-Aïssa, S.; Balaguer, P. Toxicol.Appl. Pharmacol. 2008, 232, 384−395.(38) Okereke, C. S.; Barat, S. A.; Abdel-Rahman, M. S. Toxicol. Lett.1995, 80, 61−67.(39) Jeon, H. K.; Sarma, S. N.; Kim, Y. J.; Ryu, J. C. Toxicology 2008,248, 89−95.
The Journal of Physical Chemistry A Article
dx.doi.org/10.1021/jp306130y | J. Phys. Chem. A 2012, 116, 10927−1093310933
![Index [ ] a Absorption, 2/939 – atomic absorption spectrometry (AAS), 2/853 ... – spectrum of ninhydrin and its reaction products, 2/571 – UV absorption, 1/259](https://static.documents.pub/doc/80x56/5aa197827f8b9ada698bd252/index-a-absorption-2939-atomic-absorption-spectrometry-aas-2853-.jpg)
