google.maps.event.addListener(map, 'zoom_changed', function() {
    setTimeout(moveMap, 10);
    });

    function moveMap() {
            map.panBy(300, 0);
    }

var map, // Your map object
    mapWidth = $('#map').css('width'); // Width of map container
    nCentre,
    cCentre,
    visibleWidth = 200; // Visible area in PX you want map to be centered in

// Make sure width is an Int
mapWidth = parseInt(mapWidth.replace(/px$/, ''), 10);

// Get the center of viewable area
cCentre = visibleWidth / 2;

// Create the new position variable
nCentre = cCentre - (mapWidth / 2);

// Pan the map to the centre of the visible area
if (nCentre !== 0) {
    map.panBy(nCentre, 0);
}