J . Phys. Chem. 1988, 92, 4556-4558
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Fourfer Transform Infrared Spectroscopy Study of Hydrogen-Bonded Complexes Involving Hydroxylic Derivatives and N , N ,1,g-Tetramethylguanine J. De Taeye, J. Parmentier, and Th. Zeegers-Huyskens* Department of Chemistry, University of Leuven, Celestijnenlaan 200F, 8-3030 Heuerlee, Belgium (Received: December 28, 1987)
The interaction between water and phenols and N,N,1,9-tetramethylguanine(TMG) has been investigated by FT-IR spectroscopy. The thermodynamic data for complex formation have been determined in 1,2-dichloroethane. The analysis of the spectra in the vOH and vC4 region strongly suggests that the interaction occurs at the O6 and N7 atoms of TMG. This result is compared with ab initio calculations on the conformation of the guanine-water dimer.
Introduction Despite their biological interest, very few qualitative results concerning the interaction between nucleic acid bases and model proton donors are available in the literature. This is ascribable to the very poor solubility of the bases in nonpolar solvents, and this difficulty can be overcome by N-methylation of the molecules. In recent works, the complexing ability of 1,3-dimethyIuracil (DMU), N,N,3-trimethylcytosine (TMC)’ and N,N,9-trimethyladenine (TMA)2 toward hydroxylic derivatives has been investigated by infrared and Isnitrogen N M R spectroscopy. The present paper is concerned with the interaction between proton donors and N , N ,1,9-tetramethylguanine (TMG) in 1,2-di0
TABLE I: Thermodynamic Data for Complexes between Proton Donors and TMG PgaK, K323K, -AHo, -Bo, J proton donors dm3 mol-’ dm3 mol-’ kJ mol-I mol-I K-I water 4.2’ c c c
19.2b phenol 4-bromophenol 45.9 3-bromophenol 71.2 3,4-dichlorophenol 136 3,5-dichlorophenol 241 3,4,5-trichlorophenoI 446
11.7 24.2 33.7 54.4 83.2 131
15.8 20.5 24 29.3 34.1 39.2
28.5 31.7 45 51.6 68.6 80.9
‘Standard deviation f20%. bStandard deviation *5%. CTooweak to be determined with precision. atives and a least-mean-squares treatment yields the following equations: log PssK = 7.47
- 0.62 pKa ( r = 0.999)
(1)
log K323K= 5.80 - 0.47 pKa ( r = 0.999)
(2)
TMG
-AHo = 123 - 10.9 pKa ( r = 0.999)
(3)
chloroethane. The thermodynamic parameters of complex formation are reported, and the hydrogen-bonding site in this polyfunctional base is investigated by FT-IR spectroscopy.
In previous works on the interaction between nucleic acid bases and the same hydroxylic proton donors, the following equations have been obtained:
Experimental Section The formation constants have been computed from the absorbance of the vOH stretching vibration; the methods used for the determination of the thermodynamic data have been described in previous and the spectra have been recorded with a Perkin-Elmer 580B spectrophotometer. The interaction site has been investigated by FT-IR spectrometry, and the spectra have been recorded with a FT-IR Bruker 88 spectrophotometer. The spectra have been studied in 1,2-dichloroethane as a solvent. To avoid overlapping with the vCH bands of this solvent, we studied the vOH absorption of the phenol complexes extending to 3000 cm-’ in tetrachloroethylene. TMG has been synthesized according to a method described in the l i t e r a t ~ r e . ~
for the DMU complexes]
Results and Discussion Thermodynamic Data. Table I lists the values of the formation constants ( K ) measured at 298 and 323 K along with the values of the enthalpies (-AHo) and entropies (-ASo)of complex formation. These data have been obtained in 1,2-dichloroethane. The logarithms of the equilibrium constants and the enthalpies of formation are linearly related to the pKa of the phenol deriv( 1 ) Kasende, 0.;Zeegers-Huyskens, Th. J . Phys. Chem. 1984,88,2636. (2) Toppet, S.; De Taeye, J.; Zeegers-Huyskens, Th., submitted for publication i n Phys. Chem; (3) De Taeye, J.; Zeegers-Huyskens, Th. J . Pharm. Sci. 1985, 74, 660. (4) Golovchinskava, E. S.; Ovacharova, I. M.; Cherkasova, A. A. Zh. Obsch. Khim. 1960,-30,3332.
>.
log
PssK = 4.06 - 0.30 pK,
(4)
for the T M C complexes’ log
PssK = 8.96 - 0.69 pKa
(5)
for the TMA complexes2 = 5.30 log P98K
- 0.42 pK,
(6)
Comparison of eq 1,4, 5, and 6 shows that larger intercepts are generally associated with larger slopes and that, whatever the phenol derivative, the strength of the interaction is ordered according to T M C > TMG > TMA > DMU It is interesting to compare these results with those obtained by high-resolution ‘H N M R spectroscopy for the binding of carboxylic acids to partially methylated nucleic bases;5 in this case, the strength of interaction decreases in the order N,N,9-trimethylguanine > 1-cyclohexylcytosine > 9-ethyladenine > 1cyclohexyluracil. These complexes are stabilized by cyclic structures where the N H group(s) can act as proton donor. In the complex between NJV”9-trimethylguanine and butyric acid, the cyclic conformation involves the N , H and Cs=O bonds of the base and the C = O and OH functions of the acid. In this case, ( 5 ) Lancelot, G. J . Am. Chem. Soc. 1977, 99, 7037.
0022-365418812092-4556$01.50/00 1988 American Chemical Society
The Journal of Physical Chemistry, Vol. 92, No. 15, 1988 4557
FT-IR Study of Hydrogen-Bonded Complexes
RFR=JDET343
1760
1740
1720
1700
1680
1660
1640
1620
I0
WRVENUMBERS C H - 1
Figure 3. FT-IR spectra (1760-1600 cm-I) of (A) TMG (0.03 M) in 1.2-dichloroethaneand (B) TMG (0.03 M) and 3,4-dichlorophenol (0.03 M) in 1,2-dichloroethaneand (C) difference spectrum of B and A.
t II
t YRVENUMBERS C M - I
Figure 2.
FT-IRspectrum (3700-3000 cm-’) of a solution containing
4-bromophenol (0.005 M) and TMG (0.005 M) is tetrachloroethylene. the formation constant determined in CDC13is much higher (660 dm3 mol-’). Interaction Site. Figure 1 reproduces the FT-IR spectrum of the complex between water and TMG in the vOH stretching region. The free water bands are observed at 3670 and 3585 cm-’ (spectrum A), and in the presence of T M G two broad bands are observed at 3450 and 3375 cm-’ (spectrum B); this region does not contain any absorption of the base, and the two broad bands are assigned to the complex. The weaker absorption at 3220 cm-l originates from the 280H vibration. By comparison with literature data on water complexes,6~’the band a t 3450 cm-’ is assigned to water bonded to the C=O group of TMG and the absorption observed a t 3375 cm-’ to water bonded to a nitrogen atom. Figure 2 shows the FT-IR spectrum of the complex between 4-bromophenol and TMG. Besides the free vOH absorption at 3600 cm-’, two complex bands are observed at 3320 and 3180 cm-I. These bands can be. assigned to OH--O=C and OH-N hydrogen bonds by comparison with literature data.E This interpretation ~
~~~
(6) Paul, S. 0.;Ford, T. A. J . Chem. Soc., Faraday Trans. 2 1981, 77, 33.
Kasende, 0.;Zeegers-Huyskens, Th. Spectrosc. Lett. 1980, 13, 493. (8) Jmten, M. D.; Schaad, L. J. Hydrogen Bonding, Marcel Dekker: New (7)
York, 1974.
is strengthened by the analysis of the FT-IR spectrum in the vM region. As shown by Figure 3, the free -v absorption of TMG is observed at 1691 cm-’ (spectrum A). In the presence of 3,4dichlorophenol, the intensity of this band decreases and a new absorption at 1672 cm-I is observed. A shoulder to the highfrequency side of the free band can also be noticed (spectrum B). The difference spectrum (C) clearly shows an absorption at 1705 cm-’. The bands at 1705 and 1672 cm-’ can be assigned to complexes formed on a nitrogen atom and the C=O function, respectively. Similar frequency shifts on the high- and low-frequency side of the vC+ band have indeed been observed in polyfunctional bases having carbonyl and nitrogen atoms as potential sites for hydrogen-bond f~rmation.’~Metalation and protonation at the N7site of the guanine ring also shifts the -v band toward higher frequencies by about 10 cm-’.I4 TMG has mainly two nitrogen atoms available for hydrogenbond formation: the N 3 and N7atoms. The FT-IR spectra show that the vibrations having a high “pyrimidine” character (at 1548, 1207, 1143, and 718 cm-l)+l3 are not perturbed by complex formation. The vibrations having a high “imidazole” character at 1533, 1379, and 958 cm-’ are shifted by 2 cm-I. This suggests that complex formation occurs at the N7atom. This agrees with the lower ionization potential of the N7 atom (1 1.2 eV) as compared with that of the N3 atom (1 1.6 eV).I5 Further, previous works have shown that the hydrogen-bonding site is mainly determined by the accessibility of the lone pair of the base and by the a-charge density at the interaction center.* In TMG, the accessibility of the lone pair of the N7 atom is much higher than that of the N3atom. No a b initio calculations are available for this base, but in g ~ a n i n e ’ ~and . ’ ~ 9-methylguanineI8 the a-charge density at the N7 atom is slightly higher than that at the N3atom. It is interesting to compare our results with the structure of the complex guanine-water predicted by a b initio calculations. The calculations of Pullman19have shown that the largest sta(9) Delabar, J. M.; Majoube, M. Spectrochim. Acta 1978, M A , 129. (101 Maioube. M. J. Mol. Struct. 1984. 114. 403. (1 l j Nisbmura, Y.; Tsuboi, M.; Kato, S.fMorokuma,K. Bull. Chem. Soc. Jpn. 1985, 58, 638. (12) Latajka, Z.; Person, W. B.; Morokuma, K. J . Mol. Struct. 1986, 135, 253. _. .
(13) Kasende, 0.;Vanderheyden, E.; Zeegers-Huyskens, Th. J. Heterocycl. Chem. 1985, 22, 1647. (14) Jaymir, H. A.; Theophanides, T. Can. J . Chem. 1984,62, 266. (15) Pullman, A.; Rossi, M. Biochim. Biophys. Acta 1964, 88, 211. (16) Pullman, A.; Kochanski, Z.; Gilbert, M.; Denis, A. Theor. Chim. Acta 1968, 10, 231. (1 7) Renugopalakrishnan, V.; Lakhminarayanan, A. V.; Sasisekharan, V. Biopolymers 1971, 10, 1159. (18) Jordan, F. J . Am. Chem. SOC.1974, 96, 5911.
J . Phys. Chem. 1988, 92, 4558-4565
4558
bilization energy (1 1 kcal mol-') is obtained for an in-plane bridging configuration where the water molecule is a double proton donor at N7and O6(I). The calculations of Del Bene,zohowever,
I
I1
I11
have shown that the most stable complex is a wobble'dimer in the N I H and O6region with a stabilization energy of -10.7 kcal mol-', the configuration at N7 and O6having an energy of only -6.8 kcal mol-'. The structure of Pullman is difficult to prove by infrared spectroscopy. The wavenumbers of the uoHcomplex bands are typical for OH-O=C and OH-N hydrogen bonds. Owing to (19) Port, G. N. J.; Pullman, A. FEBS Lett. 1973, 31, 70. (20) Del Bene, J. E. J . Mol. Srrucz. 1984, 108, 179.
the cooperative effect operating in a hydrogen bond, the frequencies of the two voHbands should be somewhat higher (lower shifts) when water acts as a double-proton donor.21 It can also be anticipated that the two complex bands should have about the same intensity. It appears from Figure 1 that the intensity of the high-frequency band is higher than the second one. As a consequence, a mixture of complexes having the structure I1 and 111, with a greater participation of 11, seems more likely in solution. With the phenol derivatives, however, the concentration of complexes having structure I11 seems to be higher, and this is suggested by the higher intensity of the second complex band (Figure 2). The complexes between TMG and the proton donors studied in this work are characterized by normal OH-.O and OH-aN hydrogen bonds. With stronger acid (HCl, HBr), guanine is protonated at the N7 atom.22 Registry No. TMG, 93739-36-7; H20, 7732-18-5;4-bromophenol, 106-41-2; 3,4-dichlorophenol, 95-77-2; phenol, 108-95-2;3-bromophenol, 591-20-8; 3,5-dichlorophenol,5 19-35-5;3,4,5-trichloropheno1,60919-8. (21) Huyskens, P. L. J. Am. Chem. SOC.1977, 99, 2578. (22) Sobell, H. M.;Tomita, K.I. Acta Crystallogr. 1964, 17, 126.
Solld-State Electron Beam Chemistry of Mlxtures of Diazoketones in Phenolic Resins: AZ Reslsts J. Pacansky* and R. J. Waltman IBM Research, Almaden Research Center, San Jose, California 951 20-6099 (Received: July 20, 1987; In Final Form: December 9, 1987)
Equimolar mixtures of a 2-diazo-1-naphthaquinoneand a phenolic resin are exposed to a 25-kV electron beam and UV light. The mechanism for the photochemistry is explained on the basis of the well-known Wolff rearrangement. The electron beam exposure, however, does not appear to p r d via the Wolff rearrangement but instead invokes reactions of a carbene with the phenolic resin. The carbene, formed by loss of N2from the diazoketone, forms chemical products with the resin which are soluble in base. In essence, this explains the functioningof a large class of electron beam resists consistingof diazoketone/resin mixtures. Electron beam exposures are also performed on mixtures of 2-diazo-1-naphthaquinone in m-cresol or in benzene; the results of these experiments suggest that a major product of the electron beam induced chemistry is a substituted naphthol.
Introduction Since the pioneering work by Siis' formulations consisting of diazoketones in phenolic resins have been widely used by the electronics industry to produce microlithographic patterns. These materials, commonly called resists, are formulated by incorporation of a diazoketone, structurally similar to 1, in a phenolic resin like 2 (see Figure 1). The function of the diazoketone is twofold: first it acts as a solvent inhibitor by reducing the solubility of the resin toward an aqueous, inorganic base developer, like KOH; second, it serves as a photoactive compound which upon absorption of radiation converts to a base soluble material. The latter function was investigated in detail3 where it was shown that 1, when exposed to UV light, converts to a ketene intermediate 4, which, in the presence of moisture, reacts with water to form the carboxylic acid 3 (see Figure 2). Since the latter species is soluble in the basic developer this led to the reasonable conclusion that the photochemical formation of the carboxylic acid was the mechanism responsible for the positive working nature of the resist; i.e., areas exposed to light are rendered more soluble than the nonexposed areas. These observations are summarized in Figure 2. (1) SUs, 0.Justus Liebigs Ann. Chem. 1944, 556, 65. (2) Elliot, D. J. Integrated Circuit Fubrication; McGray-Hill: New York, 1982. (3) Pacansky, J.; Lyerla, J. R. IBM J . Res. Deu. 1979, 23, 42.
0022-365418812092-4558$01.50/0
The fact that the particular ketene intermediate 4 did not react with the acidic -OH groups of the resin 2, when exposures were carried out in air (at least to the detectability of infrared measurements), was quite unexpected. In order to explore an explanation for this observation, experiments were conducted under conditions of high vacuum; these experiments not only showed that the ester 5 of the carboxylic acid 3 was formed but also revealed that the reaction proceeded through a ketene intermediatea4 In effect, after the ketene is formed it may partition itself along two reaction paths, depending on rates, i.e., with the -OH groups of water or the resin. The fact that the rate for the ketene-water reaction is much faster than the rate for the ketene-resin led to the conclusion that the solid state may have hindered the latter reaction; the ketene-resin reaction requires a significant amount of molecular movement, and the solid state may constrain this motion to decrease its rate. On the other hand, permeation of the atmosphere into the polymeric resist or water hydrogen bonded to the phenolic OH groups of the hydroscopic resin, cannot be excluded as major factors which facilitate the ketene-water reaction. Formulations based on mixtures of diazoketones and phenolic resins are not only used as positive photoresists but are also used as positive electron beam resists where now the electron beam (4) Pacansky, J.; Johnson, D. J. Electrochem. SOC.1977, 124, 862.
0 1988 American Chemical Society
