Browsing by Author "Hsu, HS"

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New imidazoles as probes of the active site topology and potent inhibitors of beta-glucosidase
(1998-03-01)
Li, YK
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Hsu, HS
;
Chang, LF
;
Chen, G
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應用化學系
Series of 4-arylimidazoles, omega-N-acylhistamines and 4-(omega-phenylalkyl) imidazoles were synthesized in order to probe the active site topology of sweet almond beta-glucosidase. These imidazole derivatives were shown to be very powerful competitive inhibitors. Among the 20 tested compounds, omega-N-benzoylhistamine and 4-(3'-phenylpropyl)imidazole are the most potent inhibitors of the enzyme, with pH-independent K-i values of 0.06 and 0.07 mu M, respectively, The inhibition of 4-(omega-phenylalkyl)imidazoles exhibited an interesting trend as to K-i values: 4-phenylimidazole (6.6 mu M)>4-benzylimidazole (1.4 mu M)>4-(2'-phenylethyl)imidazole (0.82 mu M)>4-(3'-phenylpropyl)imidazole (0.07 mu M)<4-(4'-phenylbutyl)imidazole (0.13 mu M)<4-(5'-phenylpentyl)imidazole (0.3 mu M), This revealed that the imidazole and aryl binding sites (which result from favorable interactions within the corresponding glycone and aglycone binding subsites) are separated by the optimal distance equivalent to the length of a -CH2-CH2-CH2-group, Substitutions of the phenyl moieties of 4-phenylimidazole and 4-benzoylhistamine result in weaker inhibition, These classes of imidazoles are particularly powerful inhibitors of sweet almond beta-glucosidase.
The design of CMOS continuous-time VHF current and voltage-mode lowpass filters with Q-enhancement circuits
(1996-05-01)
Wu, CY
;
Hsu, HS
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
In this paper, very high frequency (VHF) current and voltage biquadratic lowpass filters implemented directly by the linear wideband finite-gain current and voltage amplifiers, respectively, are proposed and analyzed. A new Q-enhancement circuit which consists of a finite-gain wideband tunable voltage amplifier and a Miller capacitor is also proposed. It can increase the maximum-gain frequency f(M) and enhance the maximum-gain quality factor Q(M) of the VHF lowpass filters. Experimental results have successfully verified the capability of the proposed new filter implementation method in realizing both VHF current and voltage lowpass filters with maximum-gain frequency f(M) tunable in the range of 148 MHz to 92 MHz. It is also shown from experimental results that the VHF current lowpass biquad with the Q-enhancement circuit has the maximum-gain frequency f(M) near 185 MHz and the maximum-gain quality factor Q(M) up to 18.5. A fourth-order Chebyshev current lowpass filter with the cut-off frequency of 190 MHz has been successfully designed by using the current biquads with Q-enhancement circuits.