A little algebra gives K=(b/T)^(1/a).
Using nlinfit:
T=[200 600 1000 1400];
K=[1 0.4 0.3 0.25];
Kfit = @(B,T) (B(2)./T).^(1./B(1)); % Model
B = nlinfit(T, K, Kfit, rand(2,1));
Tv = linspace(min(T), max(T));
figure(1)
plot(T,K,'*')
hold on
plot(Tv, Kfit(B,Tv), '-r')
hold off
grid
giving a=1.3 and b=199.
