Make a vector equal to another by filling 'NaN' without interpolation

I have a time stamp as follow.

Now I have another two column vector.

ab =

 243.0300    0.5814
 243.0717    0.6405
 243.1134    0.6000
 243.1550    0.5848
 243.1967    0.5869

First column is 'Time2' and second column is 'Conc'.

 Time2 = ab(:,1);
 Conc  = ab(:,2);

Now I want to match 'Conc' based on 'Time2' with 'Time' but only filling with 'NaN'. Also 'Time2' is not exactly as 'Time'. I can use something like following

Conc_interpolated = interp1(Time2,Conc,Time)

but it does an interpolation with artificial data. I only want to match vector length by filling with 'NaN' in 'Conc' not with interpolated data.Any recommendations? Thanks

Solution

My understanding is a little different, it doesn't add to Time but rather assigns each Conc to the nearst Time based on it's Time2:

 ind = zeros(size(ab,1),1); %//preallocate memory
 for ii = 1:size(ab,1)
    [~, ind(ii)] = min(abs(ab(ii,1)-Time)); %//Based on this FEX entry: http://www.mathworks.com/matlabcentral/fileexchange/30029-findnearest-algorithm/content/findNearest.m
 end

 Time(:,2) = NaN; %// Prefill with NaN
 Time(ind, 2) = ab(:,2)

This results in:

Time =

   243.00000         NaN
   243.00690         NaN
   243.01390         NaN
   243.02080         NaN
   243.02780     0.58140
   243.03470         NaN
   243.04170         NaN
   243.04860         NaN
   243.05560         NaN
   243.06250         NaN
   243.06940     0.64050
   243.07640         NaN
   243.08330         NaN
   243.09030         NaN
   243.09720         NaN
   243.10420         NaN
   243.11110     0.60000
   243.11810         NaN
   243.12500         NaN
   243.13190         NaN
   243.13890         NaN
   243.14580         NaN
   243.15280     0.58480
   243.15970         NaN
   243.16670         NaN
   243.17360         NaN
   243.18060         NaN
   243.18750         NaN
   243.19440     0.58690

for your example inputs